abstract booklet - university of michigan

Abstract Booklet

8th Annual Engineering Graduate

Symposium

Friday, November 15, 2013

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College of Engineering, University of Michigan, Ann Arbor

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Table of Contents Message from the Chairs

Committee and Volunteers

Sponsors

Abstracts

Aerospace Engineering: Flight Dynamics and Controls Aerospace Engineering: Fluid Dynamics, Thermal Sciences and Combustion

Atmospheric, Oceanic, and Space Sciences: Atmospheric and Climate Sciences

Atmospheric, Oceanic, and Space Sciences: Space and Planetary Sciences

Biomedical Engineering

Chemical Engineering: Sustainable Energy

Chemical Engineering: Nanotechnology and Microfabricated Systems

Civil and Environmental Engineering: Infrastructure Error! Bookmark not defined. Civil and Environmental Engineering: Environment and Water Resources

Computer Science and Software Design Electrical Engineering: Applied Electromagnetics and Plasma Science

Electrical Engineering: Integrated Circuits, VLSI, MEMS, and Microsystems

Electrical Engineering: Optics, Photonics, and Solid State Devices

Electrical Engineering Systems: Systems Engineering and Communication

Electrical Engineering Systems: Control Systems, Power and Energy

Electrical Engineering Systems: Signal and Image Processing, Computer Vision

Industrial and Operations Engineering: Operations Research

Industrial and Operations Engineering: Ergonomics

Mechanical Engineering: Design and Manufacturing Mechanical Engineering: Automotive Engineering and Transportation

Mechanical Engineering: Mechanics of Materials and Structures

Material Science and Engineering: Materials for Energy Conversion and Storage

Material Science and Engineering: Synthesis and Application of Organic and Bio Materials

Nuclear Engineering and Radiological Sciences: Fission Systems and Radiation

Measurements/Imaging Richard and Eleanor Towner Award

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From the Chairs

We, on the behalf of the planning committee, would like to welcome you to the 8th

edition of the annual

Engineering Graduate Symposium (EGS ’13), which is a premier event for graduate students in the College

of Engineering (CoE). This event is aimed at establishing collaboration and communication from different

disciplines, as well as facilitating interactions between current graduate students, prospective students,

faculty members and corporate sponsors.

This year’s symposium is focused on fostering enterprenurial thinking among the graduate students and a

lecture titled “Arbor Networks Ph.D Research Impact Lecture” will be the keynote. This lecture is based on

an award given to an alum that has made significant discovery or innovation translating into an industry or

company, based on their dissertation. The research poster presentation by the current graduate students

is the central theme of the event.

EGS ‘13 has received about 300 submissions this year, which is a new record for this event. The planning

committee comprises of sub-committees and representatives from all departments / tracks in the CoE,

who review the submissions in their respective areas of expertise. This enables graduate students to share

their research and accomplishments as well as review the research currently being conducted by their

peers. In addition to the technical program, the symposium hosts special sessions and tours for

prospective graduate students invited from top schools nationwide, introducing them to the broad

research portfolio of the College of Engineering.

We look forward to meeting you and welcoming you on November 15, 2013.

Best regards,

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Riddhiman Bhattacharya & Deepak Singh

Symposium Co-Chairs

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Committee and Volunteers

Mike Nazareth Director for Graduate Recruitment

Tiffany Porties Assistant Director for Graduate Education Programs

Andria Rose Coordinator for Graduate Education Programs

Shira Washington Coordinator for Graduate Education Programs

EGS Planning Committee

Riddhiman Bhattacharya MS&E EGS Planning Committee Co-Chair

Deepak Singh AOSS EGS Planning Committee Co-Chair

Brandan Walters BME Editorial Chair

Kendra Keady NERS Logistics Chair

Abhinav Dasari Aero Publicity Chair

Alex Emly MS&E Sponsor Recruiter

Jacob Davidson Aero Website, Aero Track Chair

Aravind Venkitasubramony AOSS AOSS Track Chair

Barry Belmont BME BME Track Chair

Ran Gao CEE CEE Track Chair

Anh Ta ChE ChE Track Chair

Cheng Zhang EE EE Track Chair

Parinaz Naghizadeh Ardabili EE:Sys EE:Systems Track Chair

Greggory Schell IOE IOE Track Chair

Nakul Shah IS+D IS+D Track Chair

Joshua Padeti ME ME Track Chair

Sung Joo Kim MS&E MS&E Track Chair

Bruce Pierson NERS NERS Track Chair

Austin Allen Aero Editorial Committee

Janakiraman Balachandran ME Sponsorship Committee

Huai-Ning Chang BME Logistics Committee

Adam Mendrela EE EE Committee

Samanthule Nola Macro Logistics Committee

Rahul Singh BME Logistics Team

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Eric Yu EE EE Committee

Prospective Committee

Aramis Alvarez EE

Sarah Paleg ChE

David Burdette Aero

Minnae Chabwera Aero

Liz Cloos EE

Michelle Gonzalez Melendez

ChE

Juan Lopez MS&E

Elizabeth Mamantov CSE

Jose Mesa NAME

Irving Olmedo CSE

Christina Reynolds CEE

Megan Szakasits ChE

Andre Thompson MS&E

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Sponsors

We would also like to thank:

Are You a Human Benzinga

In2being Logic Solutions

ProSource International, LCC Quantum Signal

SRS Technologies, LLC

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Abstracts

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Aerospace Engineering: Flight Dynamics, Controls & Optimization Session Chair: Jacob Davidson

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Nonlinear optimal control of a rotary inverted pendulum Ambarish Desai1, Dr. Noboru Sakamoto2 1 Department of Aerospace Engineering, University of Michigan, Ann Arbor, USA

2 Department of Aerospace Engineering, Nagoya University, Nagoya, Japan

In this work, we have addressed the problem of swing up and stabilization of a rotary inverted pendulum. The motivation was to derive a single feedback control law for both the swing up and stabilization unlike most of past work which use different feedback control laws for these two operations. The problem is formulated as an optimal control problem and solved using stable manifold approach which has been proposed to solve the Hamilton-Jacobi equation. The problem is solved by extending the domain of solutions to include the pending position. After a finite number of iterations, an optimal feedback control law for a reduced system is obtained. The closed loop system dynamics with this controller is then verified using simulations. We acknowledge the contribution of Kazuo Ishikawa and Kyosuke Yamaguchi and the staff of the JUACEP at Nagoya University in completion of this work. This work was done as a part of the graduate research exchange program at Nagoya University under the ambit of JUACEP in collaboration with IPE at University of Michigan, Ann Arbor, supported and funded by Nagoya University, Japan.

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Large-Scale Multidisciplinary Optimization of a Small Satellite's Design and Operation

John T. Hwang1, Dae Young Lee1, James W. Cutler1, Joaquim R. R. A. Martins1 1 Department of Aerospace Engineering, University of Michigan

Gradient-based multidisciplinary optimization is applied to a small satellite. This problem involves large numbers of design variables, state variables, and disciplines, necessitating the use of a gradient-based optimizer, adjoint-based coupled derivative computation, a new multidisciplinary optimization framework, and the multidisciplinary feasible architecture. The modeled disciplines are orbit dynamics, attitude dynamics, cell illumination, temperature, solar power, energy storage, and communication. Many of these contain discontinuities and non-smooth regions that are addressed to enable numerically exact derivative computation for all modeled variables. The design problem’s wide-ranging time scales, spanning 30 seconds to 1 year, are captured through a combination of multi-point optimization and the use of a small time step in the analyses. Optimizations involving over 25,000 design variables and 2.2 million unknowns require 100 hours to converge nearly 5 and 3 orders of magnitude in feasibility and optimality, respectively. Results show that geometric design variables yield a 40% improvement in the total data downloaded, which is the objective function, and operational design variables yield another 40% improvement. This work was partially supported by NASA through award No. NNX11AI19A — Technical Monitor: Justin S. Gray. The authors thank Daniel Meinzer, who developed the OpenGL-based exposed area model, Alyssa Francken, who developed the transmitter gain model, and John Springmann for providing his knowledge of small satellites.

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X-HALE: Flight Testing and Development of an Unmanned Aeroelastic Test Vehicle

Jessica R. Jones1, Carlos E.S. Cesnik1 1 Department of Aerospace Engineering, University of Michigan

An experimental, remotely-piloted aircraft has been designed and fabricated at University of Michigan that is aeroelastically representative of very flexible aircraft. Known as X-HALE, this Experimental High-Altitude Long-Endurance aircraft exhibits geometrically nonlinear behavior and displays specific, well-characterized aeroelastic traits. This unique test-bed aircraft is used to study the coupling between the elastic and rigid-body modes that are typical of very flexible aircraft and gather aeroelastic data to validate existing and future aeroelastic codes. This poster presents the preliminary data from the initial flight tests of the lightly instrumented X-HALE Risk Reduction Vehicle that confirm the airframe’s expected aeroelastic characteristics. This data is also compared with simulations of the X-HALE generated using the University of Michigan Nonlinear Aeroelastic Simulation Toolbox. These flight tests also provided data used to inform the re-design of the fully-instrumented X-HALE platform which will be used in future flight tests to provide high quality data to support validation of coupled, nonlinear aeroelastic/flight dynamic codes. This work has been supported by the Air Force Research Lab, The Boeing Company, and the National Science Foundation.

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Model predictive control of spacecraft maneuvers using the IPA-SQP approach Hyeongjun Park1, Ilya Kolmanovsky1, and Jing Sun2

1 Department of Aerospace Engineering, University of Michigan

2 Department of Naval Architecture and Marine Engineering, Department of Electrical Engineering and

Computer Science, University of Michigan

A Model Predictive Controller (MPC) based on the Integrated Perturbation Analysis and Sequential Quadratic Programming (IPA-SQP) is designed and analyzed for spacecraft relative motion maneuvering. We treat the spacecraft relative motion control problems as a nonlinear MPC problem and solve it using the IPA-SQP. The IPA-SQP combines the solutions derived using the Perturbation Analysis (PA) and Sequential Quadratic Programming (SQP). It obtains the solution to MPC problem using neighboring optimal control theory for constrained discrete-time systems and then corrects the result using an SQP update. The combination of PA and SQP improves computational efficiency as shown in our previous work. In this work, we apply the IPA-SQP MPC to spacecraft relative motion control problems with thrust magnitude constraints. To evaluate the effectiveness of the IPA-SQP approach, the simulation results of the IPA-SQP MPC are compared with the results of the linear quadratic MPC. The fuel consumption is also evaluated for both approaches. In addition, we present the simulation results of the IPA-SQP algorithm handling a nonlinear thrust magnitude constraint.

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RANS-based High Fidelity Aerodynamic Shape Optimization Peter Zhoujie Lyu1, Joaquim R.R.A. Martins1

1 Aerospace Engineering, University of Michigan

A series of aerodynamic shape optimization for an 800-passenger blended-wing-body aircraft is performed using Reynolds-averaged Navier--Stokes equations. A gradient-based optimization algorithm and a parallel structured multiblock RANS solver with a Spalart--Allmaras turbulence model are used. The derivatives are computed using a discrete adjoint method considering both frozen-turbulence and full-turbulence assumptions. A total of 274 shape and planform design variables are optimized. The objective function is the drag coefficient at nominal cruise condition. Lift, trim and center plane bending moment are constrained. Control surfaces at the rear centerbody are used to trim the aircraft via a nested free-form deformation volume approach. The optimized design is trimmed and stable in both on- and off-design conditions. The drag coefficient of the optimized design is reduced by 37 counts. Trim and bending moment constraints are satisfied. The addition of planform design variables provide an additional 2 drag count reduction. This work was funded by Michigan/AFRL/Boeing Collaborative Center in Aeronautical Sciences (MAB-CCAS). The computations were performed on Flux HPC at the University of Michigan CAEN Advanced Computing Center, and Stampede HPC of the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number OCI-1053575.

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Aerospace Engineering: Fluid Dynamics, Thermal Sciences and Combustion

Session Chair: Jacob Davidson

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Chemical Kinetic Modeling for the Oxidation of Branched

AlkanesShao Teng Chong1 1 Department of Mechanical Engineering, University of Michigan, Ann Arbor

The rising cost of petroleum and environmental concerns have stimulated efforts to

advance the production of renewable biomass fuels as potential alternatives to D2 Diesel.

In order to better understand the combustion process of these novel biosynthetic fuels,

the chemical characterization of lightly branched alkanes which appear in high

concentrations in the renewable fuels is required. In the present study, a detailed

chemical kinetic model for 2,5-Dimethylhexane was developed over the temperature

range of 550 - 1500 K, pressures from 0.01 – 10 atm, and equivalence ratios from 0.5 – 1

with Argon or Helium as the diluent. Quantum chemistry ab initio/DFT methods were used

to calculate the bond dissociation energies and generate the potential energy surface.

RRKM/Master Equation simulations were performed to compute pressure and

temperature dependent rate constants for the first oxidation reactions. The proposed rate

constants were based on a previously presented model for 2-methylalkane by Sarathy et

al. 2011. The updated model was validated against new and existing experimental data

from pulsed-photolysis and shock tube experiments. Sensitivity analysis identified the

most important reactions for 2,5-dimethylhexane ignition which is then further refined by

using the solution mapping fractional factorial design method. The proposed model shows

good agreement with all the data obtained from the experimental conditions.

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An optimal HDG-DPG method for advection-diffusion Johann P.S. Dahm1, Steven M. Kast1, Krzysztof J. Fidkowski1 1 Department of Aerospace Engineering, University of Michigan

We present a new version of the hybrid discontinuous Galerkin (HDG) finite-element method that displays optimal convergence in chosen outputs of interest. HDG methods are a new, efficient approach to numerically solving fluid problems. However, on their own, they don't achieve optimal stability or output accuracy. To make HDG optimal, we introduce ideas from discontinous Petrov-Galerkin (DPG) methods, which are provably optimal in the above respects. We apply our new HDG-DPG method to the advection-diffusion equation and show that it is both more efficient and accurate than standard finite-element methods. This work is funded by the National Science Foundation (NSF) and the Department of Defense (DoD) through NSF-GRFP and NDSEG fellowships.

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Dynamics of Laser-Induced Cavitation Bubbles Joel Hartenberger1, Steve Ceccio1,2 1 Deptartment of Naval Architecture and Marine Engineering, University of Michigan Ann Arbor

2 Department of Mechanical Engineering, University of Michigan Ann Arbor

The collapse of cavitation bubbles damages pumps, propellers, and spillways resulting in reduced performance and costly repairs. Numerous studies of the dynamics of bubble collapse suggest that this cavitation erosion is primarily the result of a high velocity re-entrant jet which forms in the later stages of collapse. However, recent findings suggest that the shockwave emitted at collapse may also be a significant source of damage. In the work presented here, a pulsed Nd:YAG laser was used to produce single cavitation bubbles in a quiescent flow near solid boundaries and video of the consequent bubble growth and collapse was recorded using a high-speed camera. Simultaneously, a needle hydrophone recorded the impulse generated during bubble collapse. The needle probe was used to spatially and temporally resolve the pressures of the impulses created by both the re-entrant jet and shockwave at collapse. The authors thank the Office of Naval Research (ONR) for funding this work and Prof. Eric Johnsen and Renaud Gaudron for their insights into single cavitation bubble collapse.

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A study of the entrainment and mixing of co- and counter-flowing gas in confined turbulent jets used for industrial combustion

I. S. Lee1 and A. Atreya1 1 Department of Mechanical Engineering, University of Michigan at Ann Arbor

Confined reacting turbulent jets are widely used in industrial furnaces. The flame pattern and emissions of confined turbulent jet flames are influenced by the jet interaction and mixing. This paper presents the results of an experimental and numerical investigation of mixing and entrainment characteristics in a confined, non-reacting turbulent jet. This is a basic first step toward understanding the confined reacting jets. The experiments were designed to simulate exhaust flow from co- or counter-flowing 1 to 10 MMBtu industrial-scale burners. NO was used as a tracer gas to determine mixing and entrainment. The apparatus consists of: (i) a 20 inch inner diameter, 6ft long cylindrical vertical duct that carries 328.15 K (slightly hot) air at co- or counter-flow velocities ranging from 0.61 to 3.12 m/s, (ii) and an ambient temperature high velocity air jet containing NO as a tracer gas which is discharged by a ¼ inch nozzle in the center of the vertical duct. Radial profile measurements of stream wise velocity, composition, and temperature are made along the length of the jet to determine the extent of entrainment and the dilution of the jet fluid as a function of the co- or counter-flow velocities, as well as,jet flow velocities. Numerical calculations using FLUENT are conducted to determine the details of the flow field. These calculations essentially confirm the experimental results and provide a picture of the flow field. These results provide fundamental information on entrainment and flow characteristics of confined jets used in industry.

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Nanoparticle growth mechanisms in flames Jeffrey Lowe1, Paolo Elvati2, and Angela Violi1,2,3,4,5 1 Department of Chemical Engineering, University of Michigan

2 Department of Mechanical Engineering, University of Michigan

3 Department of Biomedical Engineering, University of Michigan

4 Department of

Macromolecular Science, University of Michigan

5 Department of Applied Physics, University of Michigan

The widespread emission of carbonaceous nanoparticles (CNPs) from combustion engines poses a significant health risk to humans; therefore, CNP formation has been studied by the combustion community in great detail. The community has deduced that CNP formation consists of a number of steps involving both chemical and physical growth mechanisms. However, the particle nucleation step, or the transition from gas-phase particles to solid-phase particles, is not well understood. Our work aims at developing a more complete picture of the particle nucleation process by studying a possible mechanism: the dimerization of aliphatic-substituted polycyclic aromatic hydrocarbons (PAHs). Specifically, we have quantified the effect of geometry on the free energy stability of dimerized compounds of PAHs with saturated and unsaturated chains. We employed molecular dynamics techniques coupled with the well-tempered metadynamics algorithm to measure the free energy surfaces (FESs) of dimerization between compounds of interest. We found that molecules with saturated chains display an increase in stability with an increase in the number of substituted chains whereas molecules with unsaturated chains have stabilities relatively unaffected by the number of chains. Further, we determined that monomer structure affects the shape of the FES of substituted PAHs. Some substituted PAHs displayed broader minima on their FESs, showcasing the remarkable stability of a range of dimer configurations for those PAHs. These results demonstrate the feasibility of the dimerization of aliphatic-substituted PAHs as a particle nucleation model and add another level of theory to the development of a predictive code to model CNP formation. This research was funded by the Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences under Contract No. DE-SC0002619

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High-pressure low-temperature ignition behavior of syngas mixtures A.B. Mansfield1, M.S. Wooldridge2 1 Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109

2 Department of Aerospace Engineering, University of Michigan, Ann Arbor, MI 48109

Ignition properties of simulated syngas mixtures were systematically investigated at high-pressure low-temperature conditions relevant to gas turbine combustor operation using the University of Michigan Rapid Compression Facility. Pressure time-history measurements and high-speed imaging of the ignition process were used to determine auto-ignition delay times and observe ignition behaviors. The simulated syngas mixtures were composed of H2 and CO with a molar ratio of 0.7, for equivalence ratios (φ) of 0.1 and 0.5, near air dilution, with N2 as the primary diluent gas. The pressures and temperatures after compression ranged from 3 – 15 atm and 870 – 1150 K. Inhomogeneous ignition behaviors were evident for all mixtures at some thermodynamic conditions, characterized by localized flame-like structures. Analysis of the behavior revealed a strong dependence of the ignition behavior on the dominant H2/O2 chemistry, suggesting that thermal sensitivity of the auto-ignition delay time is an important factor in the occurrence of inhomogeneous ignition. The proposition, calculation, and comparison of a criterion for thermal sensitivity revealed critical values of 0.7 ms/K for φ = 0.1 and 0.04 ms/K for φ = 0.5; where any region (i.e. state and mixture conditions) with a sensitivity value in excess of this critical limit exhibited inhomogeneous ignition phenomena and any region with a lower value exhibited only homogeneous ignition. The thermal sensitivity metric and the ignition behavior maps created in the present work provide important tools for understanding and validating ignition chemistry and behaviors as well as powerful tools for the design of combustion devices using syngas fuels. The authors acknowledge the generous support of the U.S. Department of Energy via the National Energy Technology Laboratory, Award Number DE-FE0007465 and the Department of Mechanical Engineering at the University of Michigan.

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Modeling Ramjet Engine Transient Behavior: A Quasi 1D Approach Christopher Marley1, James Driscoll1 1 Department of Aerospace Engineering, University of Michigan

The transient behavior of a ramjet engine is investigated. The engine comprises of a

converging-diverging inlet with a normal shock in the diverging section, a combustor and

a propulsive nozzle. The assumption of quasi-steady flow, which can be valid for

simulating turbojet engines, is of particular interest in this study. The model is based on

the unsteady quasi-one-dimensional Euler equations with a thermally perfect gas; the

combustor is modeled as a heat addition source term in the energy equation. A throttling

maneuver is simulated and the thrust response is compared to the response from a

similarly modeled turbojet engine. The dynamic response of a gas-turbine engine is

dominated by the relatively slow shaft dynamics and hence the flow can be accurately

modeling as quasi-steady. As expected, the results of this study indicate that the quasi-

steady assumption is not valid for modeling the transient performance of a ramjet. This

unsteady quasi-one-dimensional ramjet model has important implications in

understanding the highly transient phenomenon of engine unstart. A transient reduced

order model is obtained by applying proper orthogonal decomposition to the quasi-one-

dimensional model. This reduced order model can be used in stability analysis of the

engine inlet shock and for controller design to avoid engine unstart.

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Stability of a Hanging Pendant Drop Parameshwaran Pasupathy1, Behrouz Shiari2 1 Department of Aerospace Engineering, University of Michigan

2 National Nanotechnology Infrastructure Network, Electrical Engineering and Computer Science

Department, University of Michigan

The Hanging Drop Method has various applications in life sciences research such as anti-cancer drug sensitivity testing. It provides for high throughput capabilities and offers several advantages over conventional spheroid cell culture methods. In the paper, the Finite Element Method is used to study a pendant drop (hanging drop) hanging under gravity. The formation of a hanging drop in a micro-fluidic channel and its stability is investigated by simulating the problem as a two phase flow. The level set method available in the micro-fluidics module in COMSOL is used for the analysis. Parametric studies have been carried out to evaluate the size and stability of the drop with respect to varying channel geometry, contact angle and boundary conditions. It is observed that volume of the droplet increases with height until a maximum value is reached and the droplet remains stable as long as its volume increases with height. In addition, 3D simulations of a hanging drop are performed to study the stability of the drop in a rectangular channel. Support from the NNIN computation program (NNIN/C) at Michigan is gratefully acknowledged.

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Cavitation rheology in finite volume limits: Using bubbles to measure the elasticity of small volumes of viscoelastic biomaterials Leonid Pavlovsky1, Mahesh Ganesan1, John G. Younger2, and Michael J. Solomon1 1 Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109

2 Department of Emergency Medicine, University of Michigan, Ann Arbor, MI 48109

We evaluate the application of cavitation rheology to characterize the elasticity of biological soft matter that may be confined to volumes as small as 1 µL. Cavitation rheology, a technique developed by Zimberlin et. al (Soft Matter, 3(6), 765-767, 2007), is a simple, rapid method to characterize the mechanical properties of materials that can be approximated as linearly elastic by creating a bubble, or cavity, in a relatively small volume of the material. This technique relates the critical pressure necessary to form the cavity to the material elasticity in a limit where the bubble size is small relative to size of the specimen. For characterization of small volumes of biological soft matter, such as surface adherent bacterial biofilms, this method must be extended to accommodate situations in which the cavitation volume is finite relative to the specimen volume. We therefore investigated the underlying principles of cavitation rheology. From basic elasticity theory, we mathematically related the critical pressure to the sample elasticity for finite sample volumes and evaluated the results by numerical simulation. We use semi-dilute solutions of polyethylene oxide (PEO) to test the performance of cavitation rheology in the limit of small volumes and applied the method to evaluate the elasticity of Staphylococcus epidermidis biofilms. This work was funded, in part, by the NSF CDI Program and NIGMS.

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Simulations of Shockwave Propagation in Viscoelastic Media

Mauro Rodriguez1, Eric Johnsen1

1 Department of Mechanical Engineering, University of Michigan at Ann-Arbor

Understanding the mechanics of shock waves emitted by cavitation bubbles and

propagating through viscoelastic media is important to various naval and medical

applications, particularly in the context of cavitation damage. In such problems, the

constitutive models describing the material are non-trivial, and include effects such as

nonlinear elasticity, history and viscosity. Thus, the influence of the shock on the material

and the response of the material to the shock are generally unknown. A novel numerical

approach is proposed for simulating shock and acoustic-wave propagation in a Zener-like

viscoelastic medium. The method is based on a high-order accurate weighted essentially

non-oscillatory (WENO) scheme for shock capturing and introduces evolution equations

for the stresses. The HLLC Riemann solver is used for upwinding, with a reconstruction of

the primitive variables. The performance and accuracy of the numerical approach is

presented for several one- and two-dimensional problems, including acoustic wave

propagation and the Sod shock tube problem for various combinations of elasticities,

viscosities and relaxation times. This work is supported by ONR grant N00014-12-1-0751.

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A Computationally Efficient Thermodynamic Model of Boosted HCCI Combustion for Engine Systems Analysis Prasad S. Shingne1, Janardhan Kodavasal2, Dennis N. Assanis3 and Jason B. Martz1

1 Walter E Lay Automotive Laboratory, University of Michigan, Ann Arbor, MI, USA

2 Argonne National Laboratory, Lemont, IL, USA

3 Stony Brook University, Stony Brook, NY, USA

As the global energy crisis worsens and the effects of climate change become dire there is pressing need for more efficient transportation. Homogeneous Charge Compression Ignition (HCCI) has been a topic of widespread research due to its potential of reducing in cylinder NOx and particulate emissions while maintaining high thermal efficiencies. Typically a large number of experiments are required in order to define engine systems and strategies suitable for a new combustion mode such as HCCI. This poster presents a model for boosted HCCI combustion for use in thermodynamic engine cycle simulations. The model consists of two parts; an ignition model which predicts the location of ignition and burn model which predicts the rate of combustion. Ignition model uses an auto-ignition integral (AI) with an ignition delay term that is provided with the temperature of the adiabatic core, computed thermodynamically at each time step. The adiabatic core model has been validated against motored as well as reacting CFD simulations; predicted

adiabatic core temperatures are within 1% of the peak charge temperature at TDC from motored CFD simulations. The burn profile is modeled as a Wiebe curve fit with experimental data collected over a wide range of engine operating conditions, with the locations of ignition, 10% and 75% mass fraction of fuel burned (MFB). The 10% and 75% MFB locations are correlated as a function of the location of auto-ignition and the conditions at intake valve closing (IVC). The combustion model is implemented into GT-Power and validated against experimental HCCI. This material is based upon work supported by the Department of Energy [National Energy Technology Laboratory] under Award Number(s) DE-EE0003533. This work is performed as a part of the ACCESS project consortium (Robert Bosch LLC, AVL Inc., Emitec Inc., Stanford University, and University of Michigan) under the direction of PI Hakan Yilmaz and Co-PI Oliver Miersch-Wiemers, Robert Bosch LLC. The authors also acknowledge Jeff Sterniak from Robert Bosch LLC for providing experimental data for the burn rate model and many useful discussions.

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An Extreme Learning Machine Approach to Predicting Near Chaotic HCCI Combustion Phasing in Real-Time Adam Vaughan1 1 Department of Mechanical Engineering, University of Michigan

Homogeneous Charge Compression Ignition (HCCI) is an advanced low temperature combustion strategy that can simultaneously improve engine fuel efficiency and dramatically lower smog precursor production (i.e. NOx). Unfortunately, broad usage of gasoline HCCI is hampered by combustion instabilities and a limited operation envelope. Difficulties also include highly non-linear chemistry, almost chaotic period doubling bifurcation(s), turbulent mixing, model parameters that can drift day-to-day, combustion deposits, and mixture state information that is typically not available cycle-to-cycle, especially during transients. As an alternative to traditional physics based, control-oriented models that often struggle with the aforementioned processes, this work proposes an online adaptive machine learning approach that is specifically aimed at enabling cycle-to-cycle predictions at the HCCI stability limit on a multi-cylinder engine. This fully causal method is shown to account for 79% of the cycle-to-cycle combustion phasing variance across a wide variety of random transient and steady-state conditions, right up to complete engine misfire. The hope is that this new modeling framework will enable a new class of cycle-to-cycle predictive control strategies that extend HCCI’s constrained load envelope. To this end, ongoing experimental work is being done to explore predictive control using this new approach and custom developed electronic hardware for the low-cost Raspberry Pi platform. The author thanks his co-advisors Dr. Stanislav V. Bohac and Prof. Claus Borgnakke for their support, Dr. Vijay Janakiraman for providing the raw data analyzed in this work, and Jeff Sterniak for both his test cell and project support. This material is based upon work supported by the Department of Energy [National Energy Technology Laboratory] under Award Number(s) DE-EE0003533. This work is performed as a part of the ACCESS project consortium (Robert Bosch LLC, AVL Inc., Emitec Inc., Stanford University, University of Michigan) under the direction of PI Hakan Yilmaz and Co-PI Oliver Miersch-Wiemers, Robert Bosch LLC.

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Atmospheric, Oceanic, and Space Sciences: Atmospheric & Climate Sciences Session Chair: Aravind Venkitasubramony

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Synoptic and local controls on precipitation patterns in the Great Lakes region Alexander M. Bryan1, Guiling Wang2, Derek Posselt1, Allison L Steiner1 1 Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan

2 Department of Civil and Environmental Engineering, University of Connecticut

Using the Regional Climate Model coupled with the Community Land Model (RegCM-CLM), we examine the role of synoptic versus local processes on precipitation processes in the Great Lakes Region. Synoptic processes are examined through the selection of varying lateral boundary conditions, and local processes are examined through the land and lake feedbacks. Both can affect the magnitude and distribution of precipitation, and the Great Lakes region is one that is particularly sensitive to both forces. First, we consider the individual effects of climate and land use change by simulating present-day (1980–2004) and future (2041–2065) precipitation under changing climate and land use independently. To assess the large-scale influences of synoptic meteorology on precipitation patterns, we then compare two present-day simulations driven by two contrasting global circulation models: the Earth-System component of the Hadley Centre Global Environment Model version 2 (HadGEM2-ES) and the Geophysical Fluid Dynamics Laboratory Earth System Model version 2 with GFDL’s Modular Ocean Model version 4.1 (GFDL-ESM2M). For the local influences on precipitation, we investigate deficiencies in latent heat release and examine the sensitivity of precipitation to terrestrial evapotranspiration. While large-scale boundary conditions can influence the simulation of precipitation in the region, the local feedbacks also play an important role and suggest the need for improved parameterizations of surface layer processes controlling fluxes across the surface boundary condition. Funding for this work was provided by the National Science Foundation under Grant No. 1039043.

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Spectral Dependence of the Response Time of Sea State to Local Wind Forcing David D. Chen1, Scott Gleason2, Chris Ruf1, Mounir Adjrad3 1Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI, USA

2Department of Electrical and Computer Engineering, Concordia University, Montreal, Québec, Canada

3Department of Electronic and Electrical Engineering, University College London, London, UK

Measurements of wind near the surface of the ocean are essential to the determination of momentum and energy fluxes at the air/sea interface and to the forecasting of weather phenomena such as hurricanes. Bistatic remote sensing using L-band GPS signals has been proposed as an alternative to the conventional microwave radiometers and monostatic radar scatterometers for spaceborne ocean surface windspeed measurements. L-band waves can easily penetrate precipitation, and the cost and accommodation requirements of GPS receivers are significantly lower than their radiometer and scatterometer counterparts. However, L-band scattered signals are sensitive to waves with longer wavelengths than those sensed by conventional radiometers and scatterometers, which typically operate at higher frequencies. It is known that longer surface waves take more time to respond to surface winds, propagate further before decaying, and are generally less directly coupled to the local wind field. These factors could affect the ability of scattered GPS L-band signals to retrieve local wind fields. In this work, we attempt to quantify the relationship between the longwave spectrum and local winds by examining windspeed and surface slope measurements by buoys. Specifically, by applying a lag-correlator, it is observed that the average lag time decreases monotonically as the ocean surface wavelength decreases. It is found that 1 hour serves as a conservative upper bound on the average response time of L-band waves to local wind forcing. This work is funded by a NASA Earth and Space Science Fellowship (NESSF).

40

Sensitivities of AGCM-Simulated Tropical Cyclones to Varying Initial Conditions Fei He1, Derek J. Posselt1, Naveen N. Narisetty2, Colin M. Zarzycki1, and Vijayan N. Nair2 1 Department of Atmospheric, Oceanic and Space Science, University of Michigan

2 Department of Statistics, University of Michigan

This study examines how the development of Tropical Cyclones (TCs) is represented in Atmospheric General circulation Models (AGCMs) and assesses the impact of changes in initial conditions on modeled TCs. The National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM) has been used to simulate the development of idealized TCs over 10 days. A Latin Hypercube Sampling (LHS) method is used to generate two 300-member space-filling ensembles of simulations with grid

resolution of 1 ´1 and 0.5 ´0.5 , respectively. Composite analysis is first used to analyze

the ensemble results, then, the Expanded Multivariate Adaptive Regression Splines (EMARS) method is implemented to characterize various TC response functions. Both 0.5 and 1.0 degree simulations produce a wide range of TC intensities ranging from tropical depression to category 5 on the Saffir-Simpson scale. On average, storms in the higher resolution simulations are stronger than those produced by the coarser-resolution model. Specifically, it is found that (1) the intensity, track, cloud, precipitation and radiative fields of simulated TCs are highly sensitive to changes in the initial vortex characteristics and surrounding environment; (2) nonlinear interaction between the initial conditions is crucial to the distribution of clouds, precipitation, and radiation of simulated TCs; (3) favorable

initial conditions are able to produce intense and destructive TCs even in 1 ´1 resolution global climate models.

41

The role of pollution state on urban heat islands in the Midwestern United

States

Stacey Kawecki1,Allison Steiner1, David Stensrud2,Larissa Reames3,Geoffrey Henebry4

1 Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan

2 NOAA/National Severe Storms Laboratory

3 School of Meteorology, University of Oklahoma

4 Geospatial Sciences Center of Excellence, South Dakota State University

Concentrations of anthropogenic greenhouse gases and other pollutants are magnified in

urban areas and likely affect urban heat islands (UHIs). UHIs are defined by temperatures

in the urban core that are warmer relative to nearby rural areas. These warmer

temperatures alter atmospheric stability, cloud and precipitation formation, and increase

photochemical smog production. However, the air quality-UHI link remains unquantified.

Here we assess the chemical contribution of pollution state to the UHI. We focus on small

to medium-sized (population ranging from 300,000 to 1.2 million) cities in the Great

Plains, a region known for its springtime extreme weather and good to moderate air

quality. We investigate the urban pollution state using satellite and ground-based

observations for aerosol optical depth (AOD), nitrogen dioxide (NO2: an important

anthropogenic precursor for ozone formation), and ozone (O3: a greenhouse gas). To

isolate the chemical effects of urban pollution on the UHI, we simulate an isolated

supercell thunderstorm crossing the Oklahoma City urban area using the WRF-Chem

model. One simulation includes the physical effects of the UHI over Oklahoma City during

a severe convective event. The second simulation further incorporates the radiative

effects of short-lived climate forcing agents such as aerosols and tropospheric ozone and

its precursors to determine the chemical contribution to the UHI. Through these

simulations with and without atmospheric chemistry, we assess the chemical contribution

to the UHI and the formation and sustenance of this severe weather event.

42

Numerical modeling of the energy balance and the englacial temperature of Greenland Ice Sheet Xiaojian Liu1, Jeremy N. Bassis1


The surface mass and energy balance of ice sheets links the response of ice sheets to atmospheric forcing. Historically, ice sheet model have relied on empirical parameterizations of these surface processes. More recently, global and regional climate models (e.g., RACKMO, MAR) have begun to incorporate sophisticated surface process models in an attempt to simulate ice sheet mass balance using a more physically based modeling approach. In this study we explore the limits of simple downscaling techniques to obtain the appropriate atmospheric forcing for surface energy balance models from global reanalysis products and evaluate the partition of uncertainties associated with downscaling and with various albedo, turbulent energy transfer and densification parameterizations. To accomplish this we have developed a simple physically based numerical model of the coupled radiation, snow and ice system has been developed. The model is a one-dimensional multi-layer snow and ice model that accounts for both the surface energy balance and subsurface heating to evaluate the energy and mass balance in the upper part of Greenland Ice Sheet and calculates the surface energy balance, temperature and density evolution in the uppermost part of ice. It is run over the full annual cycle, simulating melting, temperature and density profiles throughout the seasons. We assess uncertainty in the forcing by driving the model using downscaled ECMWF ERA-Interim reanalysis data and comparing this with forcing derived from in situ AWS stations from Greenland AWS data and performs sensitivity studies for the albedo, turbulent fluxes and densification.

43

Is the earth flat or only the models are telling so Yue Ma1, Jeremy Bassis2 1 Department of Physics, University of Michigan

2 Department of Atmospheric, Oceanic and Space Sciences, University of Michigan

At this moment, most models are using polar stereographic projection to treat ice sheets on a flat earth. Under the current conditions where most ice sheets are relatively small in size, the approximation provides acceptable results. However, as the size of ice sheet increases, the difference introduced by the assumption of a flat earth would become obvious. We address this point by starting from the known Vialov profile and solving the ice thickness equations in spherical coordinates without having to compromise the simplicity of solutions. The difference between results on a flat and a round earth is noticeable when the size of the ice sheet is comparable to the radius of the earth (~7 km) or in other words big enough to cover a quarter of earth's surface. On the other hand, the higher creep exponent n, the less discrepancy between ice sheets on a flat and a round earth.

44

Design, Modeling, and In-situ Verification of WiBAR as Snowpack/Lake Ice Thickness Sensor Hamid Nejati1, Sing Y. E. Wong1, Roger D. De Roo2, Lin van Nieuwstadt2, Kamal Sarabandi1, and Anthony W. England1,2 1 Departament of Electrical Engineering and Computer Science, University of Michigan


Wideband autocorrelation radiometer (WiBAR) enables us to measure the physical characteristics of layered media. Due to multiple reflections occurring within the layered media, the autocorrelation response of the received signal demonstrates distinct peaks corresponding to the travel times of subsequent reflections. Since the Fourier transform of the autocorrelation response gives the power spectral data, monitoring the received power spectral data enables the extraction of physical characteristics of the layered media. We have successfully implemented WiBAR in the frequency range of 7− 10GHz by connecting a high gain pyramidal horn antenna to a wideband amplifier chain. The output is then monitored using a handheld spectrum analyzer. The sensitivity of the implemented WiBAR is tuned by setting the resolution and video bandwidths of the spectrum analyzer. WiBAR adopts a different calibration procedure from typical radiometers, since the absolute temperature measurement is not required in WiBAR. We have gathered the H-polarized far field measurements of snow covered terrains/ lake ice using our implemented WiBAR over some locations in Ann Arbor and Houghton, MI. The estimation of the snow thickness requires a good approximation of snow dielectric constant. We have used the refractive index mixing formula using the ice density of the snow that we have measured in site. The reconstructed estimated snow thicknesses are in good agreement with in-situ measurements. The accuracy of our device in measuring snow/ice thicknesses are within 1cm.

45

Comparison of a Moist Idealized Test Case and Aquaplanet Simulations in an Atmospheric General Circulation Model Diana Thatcher1 and Christiane Jablonowski1 1 Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan

The vast array of dynamical and physical processes within atmospheric general circulation models (GCMs) makes it difficult to correctly isolate sources of model errors. Simplified test cases are important in testing the accuracy of individual model components, such as the fluid flow component in the dynamical core. Typically, dynamical cores are coupled to complex subgrid-scale physical parameterization packages, and nonlinear interactions between various components of the model mask the causes and effects of atmospheric phenomena. Idealized tests are a computationally efficient method for analyzing the underlying numerical techniques of dynamical cores. The proposed test case is based on the widely-used test for dry dynamical cores by Held and Suarez, which replaces the full physical parameterization package with temperature relaxation and damping of low-level winds on an idealized planet. The impact of moisture, a crucial physics-dynamics coupling process, is missing from this test. Here we present an idealized test case of intermediate complexity with moisture feedbacks. It uses simplified physical processes to model large-scale condensation, boundary layer turbulence, and surface fluxes of horizontal momentum, latent heat, and sensible heat between the atmosphere and an ocean-covered planet. We apply this test to the Spectral Element (SE) dynamical core within the NSF/DoE Community Atmosphere Model (CAM) version 5.3 and compare the results to aqua-planet experiments with complex physical parameterizations. The moist idealized test case successfully reproduces many features of the general circulation seen in the aqua-planet simulations, such as the Hadley cell, precipitation patterns, and atmospheric waves.

46

Atmospheric, Oceanic, and Space Sciences: Atmospheric & Climate Sciences Session Chair: Aravind Venkitasubramony

47

Statistical Storm-Time Examination of MLT Dependent Plasmapause Location Derived from IMAGE EUV R. M. Katus1, D. L. Gallagher2, M. W. Liemohn1, and J. Goldstein3

1 Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI, United

States. 2 Marshall Space Flight Center (MSFC), NASA, Huntsville, AL, United States.

3 Southwest Research Institute (SwRI), San Antonio, TX, United States.

The location of the outer edge of the plasmaphere (the plasmapause) as a function of geomagnetic storm-time is investigated statistically in terms of the solar wind driver. Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) Extreme Ultraviolet (EUV) data is used in an automated plasmapause extraction. The extraction technique searches a set range of possible plasmasphere densities for a maximum gradient. The MLT dependent plasmapause results are then compared to manual extractions. The plasmapause results are then examined along a normalized epoch storm timeline to determine the average plasmapause Lshell as a function of MLT and storm time. The smoothness of the plasmapause is inspected to describe the spatial scale of the electric field. The results are then investigated in terms of the solar wind driver and the storm intensity.

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Automated tracking of changes to terminus position of Greenland’s marine outlet glaciers Fiona Seifert 1, Charles Galey2, Jeremy Bassis1 1 Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI, United

States. 2 Mission Systems Concepts, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA,

United States.

Mass loss from the Greenland ice Sheet is primarily through the dynamic changes of its marine terminating outlet glaciers. Understanding the behavior of these glaciers is therefore key to understanding how much the ice sheet will contribute to sea level in the next century. Glacier behavior is, however, complex, with wide disparities in behavior even between glaciers that occupy adjacent fjords. Deciphering the multitude of factors that control glacier behavior requires a comprehensive dataset of near daily changes in terminus position for a large set of glaciers over many years. The creation of this dataset has been difficult due to the time required to process the changes manually. Evolution in computational methods allows the creation of an automated algorithm, using a combination of filtering techniques and edge detection, which ingests MODIS imagery and tracks changes to (i) the terminus position and (ii) the areal extent of mélange downstream of the terminus. We tested the algorithm on several well-studied glaciers including Jakobshavn, Helheim, and Kangerdlugssuaq. Comparison with manually identified terminus positions proved the algorithm accurate to within +/- 2 pixels (500 m). The validated model was then applied to a larger set of Greenland’s marine terminating outlet glaciers. We use this higher temporal resolution dataset to determine statistical patterns to the calving events and ask whether these patterns are linked to mélange extent, fjord geometry, and any seasonal component affecting the regularity of the events.

49

Examination of Nonlinearities in the Van Allen Probes Data During Geomagnetic Storms Lois Keller Smith1, Michael Liemohn1 1 Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan

In the recently released Van Allen Probes data, signatures indicating geomagnetic activity were examined closely. In particular, we chose several different storms throughout 2012-2013 where a large ionized oxygen flux was seen in conjunction with a significant drop in the disturbed storm time (DST) index. For these storms, the electric and magnetic fields in a Cartesian coordinate system were analyzed for coupled nonlinearities. Preliminary results show that during storm time, the magnetic field in the z direction will drop dramatically, sometimes reversing direction in extreme situations. The results of this work give a clearer picture of the behavior of the inner magnetosphere during storm times.

50

Coronal sources, elemental fractionation, and release mechanisms of heavy ion dropouts in the solar wind Micah J. Weberg1, Thomas H. Zurbuchen1, and Susan T. Lepri1 1 Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan

The elemental abundances of heavy ions (m > He) in the solar wind provide information concerning physical processes occurring in the corona. Additionally, the charge state distributions of these heavy ions are sensitive to the temperature profiles of their respective source regions in the corona. Both the abundances and charge states become set within a few solar radii and propagate unchanged throughout the heliosphere, regardless of turbulence, propagation effects, and local heating. Therefore, heavy ions yield in-situ evidence of an environment inaccessible to spacecraft and traditionally only observed via spectroscopy. Heavy ion dropouts are a relatively new class of solar wind events. Their origins lie in large, closed coronal loops where processes such as gravitational settling dominate and can cause a mass-dependent fractionation pattern. In this study we consider and attempt to answer three fundamental questions concerning heavy ion dropouts: (1) Where are the source loops located in the large scale corona? (2) How does the interplay between coronal processes influence the end elemental abundances?, and (3) What are the most probable release mechanisms?. We begin by analyzing the temporal and spatial variability of heavy ion dropouts and their correlation with heliospheric plasma and magnetic structures. Next we investigate the ordering of the elements inside dropouts with respect to mass, charge state, and First Ionization Potential. Finally, we consider the prevailing solar wind theories and the processes they posit that may be responsible for the release of coronal plasma into interplanetary space.

51

Searching for Separatrix-Web Signatures in the Solar Wind A. Young1, M. Stakhiv1, T. Zurbuchen1, J. Linker2, S. Antiochos3


2 Predictive Science, Inc.

3 Goddard Space Flight Center, NASA

There are two types of solar wind emanating from the sun. The fast wind has speeds of 600-800 km/s and is known to originate from coronal holes. The slow wind ranges from 450-600 km/s and has a higher average charge-state composition. This suggests its source exists in the corona where temperatures are known to be 1.0 million degrees. This is supported by spectroscopic measurements of the corona showing elemental abundances matching those found in slow solar wind. It is unknown how the slow wind escapes from a region where the dominant magnetic field is closed rather than open to the solar wind. The separatrix-web (S-Web) theory proposes that a web of interface regions, existing along the boundaries of coronal holes, is continuously undergoing magnetic reconnection. This would allow closed magnetic field to become open and release hot plasma into the heliosphere. These interface regions, where reconnection is highly likely, can be found by looking for where neighboring field lines diverge quickly. This divergent property is quantized by the “squashing factor” (Q). Values of Q have been calculated from magneto-hydrodynamic simulations of the heliosphere, where observed photospheric magnetic field maps were used as an initial condition. By taking the values of Q calculated in these simulations and comparing to in-situ data such as speed, elemental charge-state, and compositional charge-state, we should be able to detect signatures of the S-Web in the solar wind measured at Earth. The authors acknowledge Ben Lynch and Justin Edmondson for their collaboration.

52

Biomedical Engineering Session Chair: Barry Belmont

53

Development of Acid-Sensitive Micelles for Targeted Delivery of Chemotherapeutic Agents to Cancer Lesions in Bone Omer Aydin1, Yasemin Yuksel Durmaz1, Mohamed E. H. ElSayed1 1 Department of Biomedical Engineering, University of Michigan

Prostate cancer (PC) is the 2nd leading cause of cancer related deaths in U.S. men. Metastasized PC to other organs (e.g. bone) has posed a significant challenge because of the inability to deliver therapeutic concentrations of anticancer drugs (e.g. cabazitaxel; CTX) to PC lesions in bone. Further, systemic administration of chemotherapeutic agents has been associated with major side effects (e.g. neutropenia, renal cytotoxicity, and peripheral edema). To address current therapeutic limitations, we have developed a new tri-block copolymer composed of a hydrophilic polyethylene glycol (PEG) block, a central polyacrylic acid (PAA) block, and hydrophobic polymethylmethacrylate (PMMA) block sequentially linked via “click” coupling. This tri-block copolymer self-assembles in aqueous solutions forming nano-sized non-shell cross-linked micelles (NSCL, 25.2 ± 2.1 nm). To increase the stability of micelles in aqueous environments, we introduced glutaraldehyde as a cross-linker that is able to react with NH2 functional groups of the functionalized PAA block of the copolymer forming acid-labile hydrazone linkages (SCL Micelles, 28.2± 3.1nm). Further, we encapsulated model drug Nile Red (NR) and CTX, achieving 80% and 55% encapsulation efficiency rates and 8% and 10% loading ratios, respectively. Meanwhile, we investigated the release profiles of NR and CTX from NSCL and SCL micelles at pH 7.4 and 5.0. The model drugs are significantly arrested in SCL micelles at pH 7.4 with minimal burst release, while they are gradually released in acidic pH, as compared to NSCL and SCL micelles at pH 5.0. Current investigation focuses on anti-cancer activity of the particles on PC cell lines. These results indicate pH-sensitive, CTX-loaded SCL micelles can potentially achieve tunable CTX release in tumor lesion, which can selectively kill tumor cells while limiting systemic side effects. Acknowledgement: The Univeristy of Michigan Prostate Specialized Programs of Research Excellence (SPORE), Republic of Turkey the Ministry of National Education (1416), Sanofi-Aventis.

54

Home away from home: recreating the metabolic and proliferative microenvironment of disseminated tumor cells within a 3D bone marrow niche. Stephen P. Cavnar1, Brendan Leung1, Sasha Cai Lesher-Perez1, Rahul Iyengar1, Kathryn E. Luker2, Shuichi Takayama1,3, and Gary D. Luker1,2,4 1 Department of Biomedical Engineering, University of Michigan

2 Center for Molecular Imaging, Department of Radiology, University of Michigan Medical School

3 Department of Macromolecular Sciences, University of Michigan

4 Department of Microbiology and Immunology, University of Michigan Medical School

Identifying and therapeutically targeting disseminated tumor cells is a major hurdle in limiting disease recurrence and improving survival of cancer patients. Chemotherapeutic drugs often target rapidly dividing and metabolically active cancer cells, which is effective in debulking the primary tumor. However, disseminated tumor cells, particularly those that reach the bone marrow, often become dormant with limited/no proliferation, resist many chemotherapies, and potentially seed disease recurrence years later. We use a 3D tissue model of the bone marrow niche to study how the bone marrow stroma confers drug resistance and cancer dormancy. Using this system we evaluate the chemotherapeutic sensitivity of multiple breast cancer cell lines within 2D and 3D bone marrow niche co-cultures. We corroborate 3D drug sensitivities using autofluorescence redox imaging, fluorescent cell cycle indicators, and bioluminescence imaging, which measure the metabolic status, cell cycle, and cancer burden in the bone marrow niche, respectively. Using this system we expect to recreate long-term drug resistance and disease relapse, to screen therapeutic candidates specific to dormant cancer cells, and to optimize dosing as to limit toxicities to normal bone marrow cells. S.P.C. was funded on the Proteome Informatics of Cancer Training Program #T32 CA140044 and the National Science Foundation Graduate Research Fellowship Program. The project was also funded by the Provocative Questions Grant #R01 CA170198-01.

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Chronically-stable recording neural microprobes with deployed electrodes and vertical stiffeners Daniel Egert1 and Khalil Najafi1

1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI

Motor neuroprosthetics aid the paralyzed to regain independence by controlling artificial limbs with signals recorded from the brain. Clinical pilot studies on these devices are presently being employed. A key requirement for control of motor neuroprosthetics is the ability to record brain activity of awake, freely behaving hosts accurately enough to distinguish action potentials of single neuron. To date, only neural probes implanted into the brain can provide the required specificity. However, the high spatial resolution of these neural probes comes at the cost of a high degree of invasiveness; the host immune response inhibits recording over a patient’s lifetime. This project pursues two technologies to mitigate the immune response to implanted neural probes and its impact on their performance. The developed neural probes consist of silicon or Parylene formed into millimeter-long, needle-like shanks hosting multiple microelectrodes. Following the first technology, individual electrodes are placed at the end of very fine and flexible needle extensions, supported by the shank. Before implantation the needles are locked into a protected position close to the shank using biodissolvable glue. After implantation they deploy away from the shank into healthy tissue, where they act like satellites, floating almost freely inside the brain tissue. This is expected to greatly extend their working life. A second technique uses Parylene, a flexible and biocompatible polymer. It allows improving the insertion of Parylene probe shanks by formation of sharp tips and mechanical robustness enhancement without significantly increasing its size. This work was funded, in part, by the DARPA Hybrid Insect MEMS program under grant # N66001-07-1-2006. Portions of this work were performed in the University of Michigan’s Lurie Nanofabrication Facility.

56

Probing the associative interactions of biofilm extracellular polymers Mahesh Ganesan1, Prannda Sharma2, John G. Younger2 and Michael J. Solomon1 1 Department of Chemical Engineering, University of Michigan, Ann Arbor, USA

2 Department of Emergency Medicine, University of Michigan, Ann Arbor, USA

Biofilms are surface adherent microbial aggregates enclosed within an extracellular (EPS) matrix consisting of polysaccharides, proteins and eDNA. Bacterial biofilms have been frequent causes of bloodstream related nosocomial infections. A commonly isolated pathogen related to these infections is the bacteria Staphylococcus epidermidis. A vital polymer in the S. epidermidis EPS is the polysaccharide intercellular adhesin (PIA). PIA is crucial for the biofilm lifecycle in protecting the bacteria against blood shear forces and antibiotics. However, knowledge of the synergistic role of PIA with extracellular proteins and eDNA towards the microstructure of the biofilm matrix is still minimal. It is important to study the interaction of PIA with these macromolecules to understand the construction of the biofilm EPS and thus its role as a protective barrier. We view the biofilm as a composite soft matter constituting of associating polymers. Using techniques based on static and dynamic light scattering, and gel electrophoresis, we show that PIA forms complexes with both DNA and proteins at concentrations relevant in situ. We also establish that eDNA binds with a class of histone like DNA binding matrix proteins. This implies that, all the major extracellular macromolecules exist in a state of intra and inter-molecular associations that hold the EPS together. This knowledge, aids in the theoretical re-construction of the extracellular hydrogel to study its responses towards a variety of external stimuli. This would help in advancing our understanding on the rudimentary protective role of the EPS in a biofilm and thus support better treatment methods. We thank NIH and NSF for their financial support

57

Superior glenoid labrum pathomechanics Eunjoo Hwang1,2, James Carpenter3, Richard Hughes3,4, Mark Palmer1,2 1 Department of Biomedical Engineering, University of Michigan

2 School of Kinesiology, University of Michigan

3 Department of Orthopaedic Surgery, University of Michigan

4 Department of Industrial and Operations Engineering, University of Michigan

The purpose was to understand the effects of superior humeral head translation and load of the long head of biceps on the pathomechanics of the superior glenoid labrum by predicting labral strain. Using MicroCT cadaver images, a finite element model of the glenohumeral joint consisting of humerus, glenoid bone, cartilages, labrum and the long head of biceps tendon was generated. A 50N compression and 0N, 22N, 55N, or 88N of biceps tension were applied. The humeral head was superiorly translated from 0mm to 5mm at 1mm increments. The highest labral strain occurred at the interface with the glenoid cartilage and bone beneath the origin of the biceps tendon. The maximum strain is lower than the reported failure strain. Labral strain was significantly affected by biceps tension, translation of the humeral head, and location along the superior labrum (P ≤ 0.002). A linear regression model demonstrated that these parameters account for approximately 74% of the strain predicted by the model. This supports the mechanistic hypothesis that superior labral lesions may occur as a result of superior migration of the humeral head. However, repetitive microtrauma rather than a single loading event may be necessary to cause a mid-substance failure of the labrum. This work was funded by an internal grant from the Valassis Endowed Research Fund and the Department of Orthopaedic Surgery.

58

Decoding finger information from macaque motor cortex Z. T. Irwin1, K. E. Schroeder1, D. E. Thompson1, A. J. Sachs6, P. G. Patil2, 3, 1, C. A. Chestek1 1 Department of Biomedical Engineering, University of Michigan,

2 Department of Neurosurgery, University of Michigan,

3 Department of Anesthesiology, University of Michigan,

4 Department of Electrical Engineering and Computer Science, University of Michigan,

5 Department of Neuroscience, University of Michigan,

6 Department of Neurosurgery, University of Ottawa

Intracortical brain-machine interfaces (BMIs) could one day restore normal function to people with motor disabilities. In general, BMI research has focused on upper-arm movement, as opposed to the fine motor skills needed to naturally grasp and manipulate objects. In order to investigate the possibilities for decoding finger information from neuronal activity, we implanted a rhesus macaque with two 96-channel Utah arrays in the hand area of motor cortex. We recorded spikes while inducing somatosensory responses by brushing the monkey’s fingertips. Using two seconds of neural data, we were able to classify the brushed finger (out of 5) with 68.3% correct using a Naïve Bayes classifier on the lateral array, compared to chance at 20%. When restricted to classification of thumb, index, and little fingers, the same algorithm performed at 91.7% correct on the lateral array, compared to chance at 33.3%.The monkey was also trained to hit virtual targets on a computer screen by performing a four-finger bend (as measured by a bend sensor attached to the index finger). A Naïve Bayes classifier decoded flexion versus extension at 94.4% correct and movement versus rest at 100% correct for the lateral array (chance at 50% for both).These results demonstrate that sufficient hand and finger information may be present in motor cortex within the recording scope of a standard microelectrode array to decode both motor behavior and sensory stimulus. These signals could be used in the future to give motor BMIs the fine motor skills needed to produce dexterous hand movements. Funding: Taubman Medical Institute (P. G. Patil)

59

Pilot in-vivo study of chronically implanted Bi-directional Optrodes in rat cerebral cortex

K. Kampasi1, B.L. McLaughlin2, G.E. Perlin2, J. LeBlanc2, C. Segura2, and D. Kipke1 1 University Biomedical Engineering, University of Michigan, Ann Arbor, MI 48105 USA

2 Charles Stark Draper Laboratory, Cambridge, MA 02139 USA

Many recent advances in Neural Engineering are focusing on investigating the cause of chronic failure of neural microelectrodes. This demands significant attention towards understanding the impact of tissue immune response on long-term performance of neural implants. Different tissue monitoring techniques like In-vivo Imaging and Tissue Immunohistology, have been employed over past years to assess the dynamic nature of tissue response. Unfortunately, these techniques are either retrospective, cumbersome or suffer from sensitivity limitations at deeper brain areas. Bi-directional Optrodes propose a novel approach to obtain real time histological assessment of neural tissue interface failure at any cortical depth with constant sensitivity. This pilot study presents first in-vivo analysis of Optrode’s spectroscopic measurement data and provides a critical analysis of device performance. While a significant change in tissue optical properties was observed post implantation period, more follow-up work is needed to better understand tissue spectral characteristics and their direct dependence on tissue response.

This material is based upon the work supported by DARPA-RENET under award number N66001-11-1-4191. Animal procedures were administered through the University of Michigan Institutional Animal Care and Use Committee (IACUC) and the USAMRMC Animal Care and Use Review office (ACURO) protocol 08227. The authors gratefully acknowledge staff at ULAM Pathology Department (University of Michigan) and Microscopy and Imaging Lab (University of Michigan) for their technical assistance. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of DARPA.

60

Multicompartmental nanocarriers for Medical Applications Asish C Misra1, Tae-Hong Park2, Srijanani Bhaskar3, Amanda Stacer4, Nicholas Clay2, Randy P. Carney5, Francesco Stellacci5, Gary Luker4, Joerg Lahann1,2,3


2 Department of Chemical Engineering, University of Michigan

3 Department of Macromolecular Science & Engineering, University of Michigan

4 Medical School, University of Michigan

5 Department of Materials Science & Engineering, École Polytechnique Fédérale de Lausanne

There is great potential for polymer micro- and nanocarriers in biomedical applications such as tissue engineering or drug delivery. However, while such technologies are hypothesized in some case to increase efficacy and potency of small molecule drugs this goal has not been realized. There are many barriers to effective therapy caused by both physiological and pathophysiological processes. Therefore, multifunctional carriers capable of addressing multiple challenges are required for effective therapy. Electrohydrodynamic co-jetting is a technique that may allow for the manufacturing of such particles. Here we propose to develop several particle systems using the co-jetting technique to address the challenge of developing carriers that can cope with these barriers to effective therapy. This work was funded in part by the Department of Defense.

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Kinesin motion in the presence of obstacles on microtubules Woochul Nam1, Bogdan I. Epurenau1 1 University Mechanical Engineering, University of Michigan

Kinesin molecules walk by moving their heads to binding site on microtubules. This walk involves 16 nm advances of each kinesin head, realized by a conformational change in the structure and by diffusion. Most previous studies focus on movement on microtubules which have almost every binding site accessible. However, obstacles such as other molecular motors or different proteins can occupy binding sites in front of a kinesin. This study focuses on predicting the effects of obstacles on the dynamics of kinesin. First, a novel quantitative model is developed to capture the diffusion of kinesin heads in the absence of obstacles. To obtain probabilities of a head to bind at different neighboring sites, this model considers the combined effects of the head geometry on the extension of neck linkers, the interaction of the head and microtubules, and the dynamic behavior of the coiled-coil structure of kinesin neck. The model reveals that the unwinding of the neck and the binding of the head with tilted configuration are required to obtain the comparable probability of side walk of kinesin as was measured in previous experiments. Then, the motion of kinesin in the presence of obstacles is studied by using this model. The results of previous experiments with obstacles suggest that the unbinding rate of kinesin increases in the presence of interference with obstacles. Thus, this effect is also incorporated in the model. The effects of the size and number of obstacles on the velocity and run length of single kinesins are predicted.

62

Signal Magnitude, Reliability, and Validity of Regenerative Peripheral Nerve Interface Device Function during Movement Andrej Nedic1, D Ursu2, JD Moon3, CA Hassett3, RB Gillespie2, NB Langhals1,3, PS Cederna1,3 MG Urbanchek3 1 Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI

2 Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI

3 Department of Plastic Surgery, University of Michigan, Ann Arbor, MI

Regenerative Peripheral Nerve Interface (RPNI) devices successfully transduce peripheral nerve action potentials to electrical signals suitable for prosthesis control. Voltage changes are the controlling mechanism and can be observed during electromyography (EMG). However, RPNI device signaling has not been characterized during voluntary movements. Our purpose was to: a) characterize active RPNI signal strength compared to background activity and b) define the reliability and validity of RPNI signal function during purposeful movements. Three groups of rats were trained to walk on a treadmill: Control (n=3), RPNI (n=3), 100% Denervated (n=3). Bipolar electrodes were implanted onto the soleus muscles in each group. While walking on a treadmill, rats were videographed and raw EMG signals were simultaneously recorded. Rectified EMG was integrated (iEMG) and then normalized (NiEMG) to time for each gait phase: stance, swing, and sit (nonactive). Fidelity of RPNI activity (stance) to background signaling (sit) was 5.6 to 1, double the Control signal fidelity. Significant differences between stance and swing NiEMG activity were confirmed for the Control and RPNI groups. As expected, stance and swing EMG signals were not different for the Denervated group. Correlations between iEMG and stance time for the Control (r=0.74) and RPNI (r=0.76) indicate good RPNI signal reliability. These data comparing gait cycle to EMG activation accuracy between Control, RPNI, and Denervated groups validated RPNI signaling as purposeful peripheral nerve activity appropriate for meaningful control of prostheses (Chi Square; p<0.05). This work was sponsored by DARPA MTO through Grant N66001-11-C-4190.

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Carbon fiber array insertion assisted by controlled application and removal of polyethylene glycol. Paras R. Patel1, Huanan Zhang2, Takashi D. Y. Kozai3, Nicholas A. Kotov2, Daryl R. Kipke1, Cynthia A. Chestek1 1 Department of Biomedical Engineering, University of Michigan


3 Department of Bioengineering, University of Pittsburgh

In both human clinical applications and neuroscience studies, such as neural plasticity, penetrating electrodes serve as a primary front end interface. In either field, the successful implementation of neural probes that can function for long durations will require recording arrays with high channel counts that simultaneously cause minimal damage to the surrounding brain region and provide high quality neural signals. Recent advances in this field have led to ultrasmall devices (<10µm) manufactured using carbon fibers insulated with a highly conformal, yet thin, insulating layer of parylene (Kozai et al., 2012). Owing to their small size, these probes have been shown, through histology, to cause a minimal immune response and require no assistance in penetrating the brain at short lengths. However, longer carbon fibers (>1mm), can be difficult to insert as they are prone to bending or buckling which necessitates the use of forceps or other tools that can in turn damage or break the probes. To this end we have developed a method to aid the insertion of longer fibers by temporarily encapsulating them in a polyethylene glycol (PEG) block, leaving only a small portion of the fiber exposed that can easily penetrate the brain. By further dissolving away the PEG in a controlled manner, our group has been able to reach insertion depths of 2.5mm. This method has been tested with a 16 channel carbon fiber array, yielding high quality recordings from distinct neuronal populations. This work was financially supported by an NIH Challenge Grant in Health and Science Research from the National Institute of Neurological Disorders and Stroke (NINDS, 1RC1NS068396-0110) and the Center for Neural Communication Technology, a P41 Resource Center funded by the National Institute of Biomedical Imaging and Bioengineering (NIBIB, P41 EB002030) and the National Institutes of Health (NIH). This material is also based upon work partially supported by the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (DE-SC0000957).

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Orthogonal Decoration of Patchy Particles and Their Applicationsin Drug Delivery Sahar Rahmani1, Sampa Saha2, Tae-Hong Park2, Asish Misra1,3, Acacia Dishman4, and Joerg Lahann1,2,5,6

1 Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109

2 Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109

3 Medical School, University of Michigan, Ann Arbor, MI 48109

4 Department of Biophysics, University of Michigan, Ann Arbor, MI 48109

5 Department of Material Science & Engineering, University of Michigan, Ann Arbor, MI 48109

6 Department of Macromolecular Science & Engineering, University of Michigan, Ann Arbor, MI 48109

Drug delivery is a rapidly growing field with numerous novel discoveries in the last few years. These discoveries have tried to address some of the major challenges in this field, which include the delivery of multiple drugs with distinct pharmacokinetics, sustained release over a set period of time, the fabrication of nanoparticles, the inclusion of imaging agents, and the surface modification of such particles for the incorporation of targeted and stealth moieties. Through electrohydrodynamic co-jetting, our group has been able to fabricate multi-compartmental, biodegradable particles that can be used for predictable, controlled, and distinct delivery of multiple therapeutics. In such cases, each compartment can be loaded with a different drug and/or polymer with varying degradation kinetics and release profiles. Additionally, each compartment can be selectively surface modified to include targeting and stealth moieties, thereby increasing uptake to the desired tissue and minimizing systemic side effects. Adjusting the size of the particles can enhance this level of tissue specificity. Through the use of different solvents and additives, we have been able to show the capability of fabricating particles that range in

size from nanoparticles (50-80 nm in diameter) to hundreds of microns (200-400 μm). Tuning the size of the nanocarriers enables us to exploit different processes in the body, for example the EPR (Enhanced Permeation and Retention) effect or size-dependent phagocytosis by the RES (Reticulo-Endothelial System). Together, such characteristics make our anisotropic carriers the optimal theranostic vehicles. We would like to acknowledgement our funding sources the American Cancer Institute, National Institute of Health, and the Department of Defense.

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Mobile, passive monitoring of breath sounds for management of asthma Bharath Balaji Sathiyamoorthy1, Matt Christensen2, Evan Leitner2, Ben Levy3, Dr. Thomas Sisson4, Dr. David T. Burke5 1 Department of Biomedical Engineering, University of Michigan

2 Medical School, University of Michigan 3 Department of Computer Science and Engineering, University of Michigan

4 Department of pulmonary and critical care, University of Michigan Hospital

5 Department of Genetics, University of Michigan

Asthma is an obstructive lung disease which is difficult to manage as the symptoms vary frequently. According to AAFA, 44,000 Americans have an asthma attack every day and these attacks can be mild, moderate or severe. It is essential to monitor the developments and improvements in asthmatic care of the patients through the assessment of pulmonary function on daily basis. We have designed and developed a home-centric asthma monitoring system using wireless and smart mobile technologies at low cost with high precision of data available both to the patient and the physician, engaging the patient providing its sustainability. In this, we acquired the tracheal sound signals through a specially designed hardware attached to the patient in the form of a band in the neck, positioned at the suprasternal notch, where the signal-to-noise ratio was at its best. The signals acquired were recorded via Bluetooth on the patient’s iOS device through the app developed by us and they were visualized after decibel filtering in real-time. The recorded signals would then be sent to cloud services with HIPPA compliance and these signals would be analysed by LabVIEW software running continuously on a protected server. LabVIEW processes all the requests from the patient using its in-built restful webservices and its algorithms. The responses to the requests will be available on the cloud as well as directly on our patient’s iOS app. The data available on the cloud can be accessed both by the patient as well as the physician. Acknowledgements: This project was funded by an educational grant from the Verizon Foundation. Thanks goes out to the Department of Pulmonary and Critical care for coordinating this interdisciplinary project with special thanks to Donna Johns. Dr. David Burke and Dr. Thomas Sisson have been critical to the project's progress and they have been excellent mentors.

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Somatosensory responses in finger area of macaque motor cortex

KE Schroeder1, Z Irwin1, DE Thompson1, AJ Sachs6, PG Patil2,3,1, CA Chestek1,4,5


2 Department of Neurosurgery, University of Michigan

3 Department of Anesthesiology, University of Michigan

4 Department of Electrical Engineering and Computer Science, University of Michigan

5 Department of Neuroscience, University of Michigan

6 Department of Neurosurgery, University of Ottawa, ON, Canada

Recent work in intracortical Brain-Machine Interfaces (BMIs) has stressed the need for sensory feedback to improve the performance of neuroprosthetics, leading to renewed interest in the amount and nature of sensory information encoded in primary motor cortex (M1). Previous single unit studies in monkeys showed M1 is responsive to tactile stimulation, as well as passive and active movement of the limbs. Recent work in this area has focused on proprioception, but we are interested in how somatosensation of the hand and fingers is represented in M1. We recorded threshold crossings (<-4.5 RMS, 97 trials) from macaque M1 while gently brushing individual finger pads by hand at about 2 Hz. Surprisingly, the majority of channels showed a significant change in firing rate during brushing when compared to a rest condition, and 48 of 96 channels showed significant differences in firing rate between individual fingers (p<.05). Power spectral density analysis on spike trains of exemplary trials showed a peak at about 2 Hz, the frequency of stimulation, suggesting that some cells in M1 perform rate coding of somatosensory inputs. We also created a map of tuning curves for all channels in the array based on the physical location of electrodes. No somatotopic organization of finger preference was obvious across cortex; however, for any given channel, preference did vary linearly across the hand. Understanding M1 function with and without sensory inputs to the skin (and potentially directly to the cortex via optogenetic stimulation) will inform better sensory feedback to clinical prosthetic devices. This work was supported by the Taubman Medical Institute and the University of Michigan Department of Biomedical Engineering.

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Interaction of atmospheric pressure DBDs with liquid covered tissues Wei Tian1 and Mark Kushner2 1 Department. of Nuclear Engineering& Radiological Science, University of Michigan

2 Department of Electrical Engineering & Computer Science, University of Michigan

Atmospheric pressure dielectric barrier discharges in contact with liquid are of interest in the context of tissue treatment in plasma medicine, from sterilization to wound healing, because the tissues are often covered by a thin layer of liquid. This liquid is dominantly water with dissolved gases and proteins. The liquid evaporates water into and humidifying the adjacent gas. This liquid layer processes the plasma produced radicals and ions prior to their reaching the tissue. In this paper, we report on a computational investigation of the interaction of DBDs contacting a thin liquid layer covering tissue. These simulations were performed using nonPDPSIM, a 2-dimensional model in which Poisson’s equation, electron temperature equation and transport equations for charged and neutral species are solved. The liquid layer, typically hundreds of microns thick, is water containing dissolved. The discharges are operated at -15 kV with multiple pulses at 100 Hz followed by a 1 s afterglow. Reactive oxygen and nitrogen species (RONS) produced in the gas phase intersect the water vapor saturated air above the liquid and then solvate when reaching the liquid. The photoionization and photodissociation of water by the plasma produced UV/VUV radiation play a significant role in the radical production. In liquids without RH, O2- dominates the negative ions while hydronium (H3O+) dominates the positive ions. The hydronium concentration determines the pH value of the liquid. [1] G. V. Buxton, C. L. Greenstock, W. P. Helman, and A. B. Ross, J. Phys. Chem. Ref. Data. 17, 513 (1988). * Work was supported by the DOE Office of Fusion Energy Science and the National Science Foundation.

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Quantifying nanomaterial partitioning into the cell membrane: A connection to effective gene delivery? Sriram Vaidyanathan 1, Bradford G.Orr 2, Mark M. Banaszak Holl 1,3

1 Department of Biomedical Engineering, University of Michigan, Ann Arbor 48109

2 Department of Physics, University of Michigan, Ann Arbor 48109

3 Department of Chemistry, University of Michigan, Ann Arbor 48109

The delivery of biomolecules such as nucleic acids and proteins to tissue for therapeutic applications is an area of active research. Surfactants, cationic polymers (e.g poly(ethyleneimine)) and cationic lipids (e.g DOTAP) are used in the formulation of such therapeutics. We have investigated the effect of various surfactants, polymers, cationic lipids and polymer-DNA polyplexes on the membrane conductivity of HEK293A and HeLa cells using an automated whole cell patch clamp technique that can measure membrane currents from 320 cells simultaneously. We have observed that the exposure of cells to surfactants and polymers results in increased membrane permeability which is not reversible for over 15 minutes. A 10 s exposure the fluorescent surfactant-like molecule Octadecyl rhodamine B is sufficient to both increase membrane conductivity and fluorescently tag the cell membrane. We have further used whole cell patch clamp to determine the amount of surfactants partitioned in the cell membrane. This method is also being used to quantify the amount of polymers and polyplexes complexes partitioned into the membrane. It is known from literature that dyes used to stain the cell membrane are distributed to the internal organelles. Future work will be focused on determining the role of this membrane intercalated material in drug and gene delivery. We thank BME departmental fellowship, Rackham research grant and NIH EB005028.

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Live-Cell Subcellular Study of Force-Mediated Focal Adhesion Morphogenesis Using Elastomeric Micropost Force Sensors

Shinuo Weng1, Yue Shao1, Weiqiang Chen1, and Jianping Fu1,2 1 Department of Mechanical Engineering , University

2 Department of Biomedical Engineering, University

External mechanical stretch/strain plays an important role in regulating cellular processes including signal transduction, gene expression, growth, and survival. Mechanical stimuli applied to the cells are predominantly detected at focal adhesions (FAs), the adhesion structure containing structural and singling molecules. The co-localization of mechanical and biochemical functions at FAs has suggested its functional role in transducing mechanical forces on FAs into appropriate biochemical responses. However, the correlation and cooperation between cytoskeleton (CSK) force and FAs in response to the external stretch/strain is largely unclear due to the limitation of the current methods for correlating CSK Force with FAs. In this research, we used a novel cell stretching device that allows for real-time measurement of mechanical stimuli and CSK forces, and constrains the recruitment of FAs only on each force sensors. We applied 8% equibiaxial stretching to REF-52 cells stably expressing YFP-Paxillin (gift from Dr. A. Bershadsky), and time-lapse fluorescent images of YFP-Paxillin and micropost tops were taken before and after stretch. Images were analyzed using customized Matlab code to determine CSK force and FAs on each adhesive sites. We observed a strong correlation between CSK force and FAs before and after stretch. Acute increase of CSK force and FA recruitment within 1min after stretch was independent of the initial CSK force, the initial FAs, and the position of the adhesion sites inside the cell body. In the long term, spatiotemporal evolution of subcellular distribution of CSK force and FAs were coordinated and compensated to reestablish the tensional homeostasis.

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Chemical Engineering: Sustainable Energy Session Chair: Anh Ta

71

Transition-Metal Carbide and Nitride Supercapacitor materials

Olabode T Ajenifujah1, Abdoulaye Djire1, Alice E. S. Sleightholme1, Paul Rasmussen1, 2, Levi T Thompson1,2

1 Department of Chemical Engineering

2 Hydrogen Energy Technology Laboratory

University of Michigan, Ann Arbor, MI

Supercapacitors are energy-storage devices just like batteries, but they possess high power density, long cycle life and moderate energy density. They fill the gap between conventional capacitors and batteries in respect to their power and energy density. Their commercial applications include use in hybrid commercial vehicles for load-leveling during start-up, acceleration and regenerative braking, memory back-up in electronic device, and uninterruptible power supplies. However, their moderate energy densities and high cost limit their application in a number of areas. Carbon based materials are currently used commercially as supercapacitor electroactive material, which are unsustainable and costly. In our approach to these challenges, we explore the use of early transition-metal carbide and nitride as the electroactive materials for these devices, which are cheap, have high electronic conductivity, and can be synthesized with high surface area. This poster describes the synthesis of novel low-cost, high-surface-area transition-metal carbides and nitrides via temperature program reaction and their characterization as electroactive materials. Among many early transition-carbide and nitride materials, we currently focused our attention on Titanium Nitride(TiN), Niobium Nitride(NbN) and Tungsten carbide(βWC1-X). The characterization of these materials were done physically using X-ray diffraction(XRD) to determine the phase purity, Brunauer-Emmett-Teller(BET) to determine the pore size distribution and the surface area of these materials. Then, we characterized the materials using electrochemical techniques such as Open circuit potential (OCP), to determine the voltage at which the current is zero (equilibrium potential), cyclic voltammetry (CV); we applied voltage and get current output. Using the CV curve, we determined the capacitance of the material, and understand the chemistry and the two possible charge storage mechanisms (puesdocapacitance and double layer) that may be occurring on these materials. Varying the scan rate of the CV experiment, we were able to determine the contribution of each storage mechanism to the total capacitance, which we found interesting and important toward understanding how these materials store charges. The authors acknowledge financial support from the Automotive Research Center, Army Tank Command and Army Research Office.

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Liquid Phase Carbon Dioxide Hydrogenation to Methanol over Molybdenum Carbide Based Catalysts

Yuan Chen1, Levi T. Thompson1,2 1 Department of Chemical Engineering, University of Michigan, Ann Arbor

2 Hydrogen Energy Technology Laboratory, Energy Institute, University of Michigan, Ann Arbor

Carbon dioxide is generated during the combustion of fossil fuels and has been linked to global climate change. CO2 could also be used as a source of carbon for the synthesis of fuels and commodity chemicals. This project explores the possibility of hydrogenating CO2 to methanol, an attractive first product, commonly used as a fuel or chemical precursor.

This presentation will describe a low temperature route to produce methanol from CO2 in the liquid phase. A possible pathway to produce methanol under these conditions is via a three-step tandem reaction: i) hydrogenation of CO2 to formic acid; ii) esterification of formic acid to alkyl formate; iii) hydrogenolysis of alkyl formate to methanol. Effective homogeneous catalysts exist for the first two steps; however, catalysts for the rate-determining step, the third step, are needed. We observed that molybdenum carbide (Mo2C) based materials are highly active for formate hydrogenolysis. The selectivity to methanol was enhanced, when nanoscale particles of Cu and/or Pd, the species that are active for methanol synthesis, were deposited onto high surface area Mo2C. The results indicate the viability of employing metal supported Mo2C in the tandem conversion of CO2 to methanol. This work is supported by the NSF under the CCI Center for Enabling New Technologies through Catalysis (CENTC) Phase II Renewal, CHE-1205189.

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Effects of Surface Oxygen on Charge Storage in Transition- Metal Carbide and Nitride Supercapacitor Materials Abdoulaye Djire1, Olabode T Ajenifujah1, Alice E. S. Sleightholme1, Aniruddha Deb2, Paul Rasmussen1,3, James Penner-Hahn2, Levi T Thompson*1,3


2 Department of Chemistry

3 Hydrogen Energy Technology Laboratory

University of Michigan, Ann Arbor, MI 48109-2130

Supercapacitors are a relatively new type of energy-storage device that provide high power densities, long cycle life and moderate energy densities. They fill the gap between conventional capacitors and batteries. These devices can replace batteries in a number of applications (e.g. electronic devices, military platforms) or can complement batteries in hybrid systems to extend the lifetime of a battery pack. One of the emerging applications of supercapacitors is in storing the intermittent energy available from renewable sources including solar and wind. These devices could facilitate the introduction of renewable electricity into the grid. The energy stored in supercapacitors is a function of the capacitance and voltage. In order to increase the energy density of supercapacitors to meet the current Department of Energy target of 15 Wh/kg, one would need to significantly increase the capacitance and/or the operating voltage. The materials used currently in commercial supercapacitors are based on carbon which is unsustainable and costly. Over the past few years, significant emphasis has been placed on finding low-cost, better performing materials for supercapacitor applications. This poster describes the use of low-cost, high-surface-area transition-metal carbides and nitrides as electroactive materials for supercapacitor applications. These materials possess very high capacitances over a wide voltage window. Recently, we observed that pretreatment of the surface significantly improved the capacitances of all of the materials from 43% for VN to a 79% increase for Mo2C. The use of this pretreatment technique is of interest in the design of higher-energy-density carbide and nitride-based supercapacitor electrode materials. The authors acknowledge financial support from the Automotive Research Center, Army Tank Command and Army Research Office.

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Electrolyte Strategies for Magnesium-Oxygen Batteries James Saraidaridis1, Gulin Vardar2, Alice Sleightholme1, Don Siegel3,4, Charles Monroe1 1 Department of Chemical Engineering, University of Michigan

2 Department of Materials Science, University of Michigan



Electric vehicles (EVs) employing state-of-the-art Li-ion battery packs are too expensive and provide insufficient range to compete with internal combustion engine vehicles (ICEVs) in mass markets. Although Li-ion technology will likely progress enough to allow mass competition between EVs and ICEVs in the car sector, the chemistry lacks the energy density to compete in larger vehicle sectors like small and large trucks. Magnesium-oxygen chemistries have theoretical energy densities an order of magnitude larger than Li-ion. Magnesium is readily abundant, inexpensive and stable during electrochemical deposition or dissolution. However, developing a rechargeable Mg-O2 battery requires overcoming magnesium’s tendency to passivate and also preferentially forming reversible discharge products. Herein we describe our progress in developing Mg-O2 batteries. Thank you to Denso International America for financially supporting this project, to Lucas Griffith in the Monroe Laboratory, and Professor Bartlett and Emily Nelson from Department of Chemistry at the University of Michigan for their synthetic facilities and expertise.

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Chemical Engineering: Nanotechnology and Microfabricated Systems Session Chair: Anh Ta

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Entropically Patchy Particles and their Emergent Valence N Khalid Ahmed1, Greg van Anders1, Daphne Klotsa1, Ross Smith2, Michael Engel1 and Sharon C. Glotzer1,2 1 Department of Chemical Engineering, University of Michigan, Ann Arbor

2 Department of Material Science and Engineering, University of Michigan, Ann Arbor

The self assembly of target crystal structures has been shown to be possible by selectively introducing specific chemical patches and surface patterns on particles that use enthalpy to align themselves anisotropically, resulting in the formation of a crystal lattice. Recent computer simulations and experiments additionally have shown that entropy can also be used to order hard anisotropic particles into complex crystals, liquid crystals and even quasicrystals. The emergence of directional entropic forces (DEFs) has been proposed for the ordering of non-spherical particles. We compute these forces for particles of different shapes and show that they are at least several kT at the onset of ordering, comparable to forces contributing to assembly in nano colloidal systems such as traditional depletion interactions and van der Waals forces amongst others. Thus we propose a new rubric for the design of nano and colloidal building blocks, by systematically modifying particle shape and inducing emergent forces that drive monodisperse systems of hard particles to self-assemble various target crystals structures using entropy alone. We successfully self-assemble interesting crystal structures in this manner. These design schemes are generalized into anisotropy dimensions, similar to those exploited for enthalpically patchy particles. This material is based upon work supported by, or in part by, the U.S. Army Research Office under Grant Award No. W911NF-10-1-0518, the DOD/ASD(R&E) under Award No. N00244-09-1-0062 and the James S. McDonnell Foundation 21st Century Science Research Award for Studying Complex Systems.

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Anomalous Dispersions of Hedgehog Particles Joong Hwan Bahng1, Bongjun Yeom2, Yi Chun Wang1, Siu On Tung4, Nicholas Kotov1, 2, 3,

4, * 1 Department of Biomedical Engineering, University of Michigan, 3074 H.H. Dow Building, 2300 Hayward

Street, Ann Arbor, MI 48109, USA 2

Department of Chemical Engineering, University of Michigan, 3074 H.H. Dow Building, 2300 Hayward Street, Ann Arbor, MI 48109, USA 3 Department of Material Science & Engineering, University of Michigan, 3074 H.H. Dow Building, 2300

Hayward Street, Ann Arbor, MI 48109, USA 4 Macromolecular Science and Engineering Program, University of Michigan, 3062C H.H. Dow Building,

2300 Hayward Street, Ann Arbor, MI 48109, USA

Aqueous dispersion of hydrophobic colloids is a procedural requirement in current technological demands ranging from drug delivery to environmental remedy. Despite undoubted success, the prevalence of chemical masking of the hydrophobic surfaces with surfactants and amphiphilic polymers limit versatilities and untapped potential of particle technologies due to toxicity and cost. In this letter, we demonstrate a novel route to dispersion of hydrophobic colloids by topological modification to sculpture pronounced nano-asperities at the interface. Methodological motivation stems from Cassie-Baxter wetting and we hypothesized that air entrapment amidst the nano-asperities exert significant repulsive potential that overrides decreased hydrophobic attractive potential due to substantial reduction in the fractional hydrophobic surface. We have constructed hydrophobic Hedgehog particles, reflective of its morphology, by either or both hydrothermal sonochemcial growth of ZnO nano-spikes on a polystyrene spherical core. Their hydrophobic equivalents are modeled by silanation of surface corrugations. We will confirm our hypothesis by providing experimental observation of aqueous dispersion and evidences of air-entrapment in the interstitial voids between nano-spikes. In addition, we will demonstrate density manipulation to enable free aqueous suspensions facilitated by the air-entrapment. Lastly, we will illuminate dispersion mechanism via evaluation of total interaction potential between the hydrophobic Hedgehog particles. Acknowledgement: This work is funded by ARO/MURI. We thank Doty Sorensen of MIL for help with TEM and Jiyoung Kim for the help with CdTe synthesis

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Towards Advanced Manufacturing of Hierarchical Carbon Nanotube Structures

Mostafa Bedewy1, and A. John Hart1,2 1 Department of Mechanical Engineering, University of Michigan

2 Department of Mechanical Engineering, Massachusetts Institute of Technology

The unique properties of organized carbon nanotubes (CNTs) highlight their potential for integration in high-performance structural composites, electrical interconnects, thermal interfaces, and filtration membranes. However, materials and devices that are based on hierarchical CNT ensembles require CNTs that are monodisperse, well aligned, and densely packed. Hence, precise control of the morphology of as-grown CNT structures is needed. In my Ph.D. research, I have created and validated tailored synthesis methods, characterization techniques, and mathematical models that enable the production of highly uniform CNT “forests”. Since a large number of CNTs grow simultaneously in a typical chemical vapor deposition (CVD) process (typically 109 CNTs/cm2), understanding the collective chemical and mechanical effects of growth is key. We have developed a comprehensive non-destructive methodology for studying CNT population growth dynamics by combining high-resolution spatial mapping of synchrotron X-ray scattering and mass attenuation, with real-time forest height kinetics (laser-triangulation measurements). By interrogating millions of CNTs concurrently, the CNT diameter distribution, quantified alignment and density are obtained. Inferring mass kinetics of CNT subpopulations, also reveals the size-dependent activation-deactivation competition during the successive growth stages. Further, we demonstrate that mechanical coupling among neighboring CNTs is not only responsible for the self-organization into the aligned morphology, but is also an important limiting mechanism. Finally, we show that the synergetic chemical coupling between CNT microstructures can be exploited to design uniform CNT micropillar arrays. We thank E. Meshot, and B. Farmer for collaborative contributions. This work was funded, each in part, by DOE (DE-SC0004927), ONR (N000141010556), and NSF (CMMI-0800213).

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Patterned nanocomposite sensing skins for distributed strain sensing Andrew Burton1, Jerome Lynch1,2 1 Department of Civil and Environmental Engineering, University of Michigan


Advanced performance requirements of modern structural systems are driving technology development for monitoring structural performance. Paramount to these efforts are multifunctional materials that produce an electrical response, or signal, when acted on by a mechanical stimulus, such as strain. Carbon nanotube (CNT)-polymer thin films have shown exceptional promise as one such material that can be nanoengineered into a multifunctional skin for structural sensing. However, a layer-by-layer deposition process used in creating these skins has previously limited the control and precision in sensing skin fabrication. The scalability and utility of CNT-polymer sensing skins for sensing distributed strain could be greatly enhanced with the ability to patterning precise sensor geometries as this would allow for efficient spatial damage detection, increased CNT film sensor scalability, and component-specific design of structural sensors. Here, processes common to microelectromechanical systems (MEMS) are used to fabricate CNT-polymer skins with various geometries and subsequently characterize the potential of such patterning in the context of structural sensing. This is achieved as a carbon nanotube-polymer composite thin film is deposited on a glass substrate using a layer-by-layer fabrication process then and patterned through an optical lithography lift-off process. The pattern fabricated consists of five linear sensing elements of varying width, as linear patterns are generally characteristic of strain sensors. The mechanical responses of varying skin geometries are investigated by bonding sensors to structural test specimens and then deforming these specimens in a load frame. Pattern fabrication quality is characterized with optical and scanning electron microscopy.

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Self-assembly of colloidal shape alloys Eric S. Harper1, Ryan Marson1, Joshua Anderson2, Sharon Glotzer1,2 1 Department of Materials Science and Engineering, University of Michigan


Self-assembly of nanoparticles and colloids holds great promise to create useful new materials. Nearly ubiquitous in nature, self-assembly is a powerful tool for organizing matter, observed in everything from the formation of virus capsids and protein folding to the bubbles on top of a glass of beer. Scientists and engineers in a wide variety of disciplines hope to better understand how different particles self-assemble to facilitate the engineering of desired assemblies of materials. While the use of DNA tethers, chemical functionalization, and even magnets have been shown to effectively direct self-assembly, the effect of particle shape on self-assembly has received surprisingly little attention. Nature makes extensive use of shape-based complementary interactions, such as the “lock and key” mechanism of enzymes and protein recognition at the surface of a cell. We investigate a class of complementary “shape alloys” that can be used to stabilize desired phases. These complementary particles fit together in a manner similar to that of puzzle pieces. We begin with a two dimensional system of squares, which assemble into a square lattice. When split into equal area rectangles and right isosceles triangles, the rectangles assemble into an ordered lattice while the triangles do not. These were compared with rectangles and triangles that have been “cut” so as to complement each other. We see evidence that this shape complementarity promotes the desired assembly, even in a system which otherwise would not assemble e.g. the right isosceles triangles. This material is based upon work supported by the National Science Foundation Open Data IGERT DGE 0903629, the U.S. Army Research Office under Grant Award No. W911NF-10-1-0518, and the DOD/ASD(R&E) under Award No. N00244-09-1-0062.

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Heat Dissipation in Atomic-Scale Junctions Woochul Lee1, †, Kyeongtae Kim1, †, Wonho Jeong1, Linda Angela Zotti2, Fabian Pauly3, Juan Carlos Cuevas2, Pramod Reddy1, 4 1 Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA

2 Departamento de Física Teórica de la Materia Condensada and Condensed Matter Physics Center

(IFIMAC), Universidad Autónoma de Madrid, Madrid 28049, Spain 3 Department of Physics, University of Konstanz, D-78457 Konstanz, Germany

4 Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, 48109, USA

†These authors contributed equally to this work.

Heat dissipation is ubiquitous in nanoscale circuits and devices, yet it remains largely unexplored. Here, we report heat dissipation studies in atomic and single-molecule junctions using custom-fabricated scanning probes with integrated nanoscale thermocouples. Heat dissipation in the electrodes of molecular junctions, whose transmission characteristics are strongly dependent on energy, is asymmetric—that is, unequal between electrodes—and also dependent on both the bias polarity and the identity of the majority charge carriers (electrons versus holes). In contrast, atomic junctions whose transmission characteristics show weak energy dependence do not exhibit appreciable asymmetry. These studies unambiguously relate the electronic transmission of nanoscale junctions to their heat dissipation properties proving a central prediction of Landauer theory that has remained untested despite its relevance to a range of nanoscale systems. Reference Woochul Lee, Kyeongtae Kim, Wonho Jeong, Linda Angela Zotti, Fabian Pauly, Juan Carlos Cuevas, and Pramod Reddy, “Heat dissipation in atomic-scale junctions”, Nature, 498, 209 (2013)

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Plasma-Assisted Nanoprinting for Manufacturing Large Arrays of MoS2-Based Functional Devices Hongsuk Nam1, Sungjin Wi1, Hossein Rokni1, Mikai Chen1, Greg Priessnitz1, Wei Lu1, and Xiaogan Liang1 1 Department of Mechanical Engineering, University of Michigan

Molybdenum disulfide (MoS2), widely used as a lubricant material, recently attracts a great deal of attention because of its attractive electronic, optoelectronic, and mechanical properties. Especially, monolayer and few-layer MoS2 films have a large direct bandgap that is suitable for semiconductor-related applications such as thin-film transistors, chemical sensors, and light emission devices. Such atomically layered films also exhibit a high mechanical flexibility and can be used for making flexible electronic products with high performance. The current methods for producing few-layer MoS2 flakes include scotch tape exfoliation, chemical vapor deposition, and laser-thinning process etc. These methods still suffer from specific disadvantages and cannot create ordered, pristine MoS2 device arrays over large areas that are required for large-area applications. Therefore, novel low-cost, upscalable nanofabrication methods are needed for addressing such manufacturing-related issues and enabling the future scale-up applications of MoS2 in electronics and optoelectronics. In this work, we systematically studied transfer-printing approaches for creating orderly arranged MoS2 micro- and nanostructures over large (cm2-scale) areas and demonstrated working field-effect transistors (FETs) made from printed MoS2 flakes with excellent transistor performance. This research also identified the key processing conditions affecting the printing uniformity over large areas, morphologies of printed MoS2 structures, and ultimate transport properties of MoS2-based FETs. Our work demonstrated the printing of high-quality, well-defined MoS2 flakes over large areas and working MoS2 FETs with excellent performance. The fundamental knowledge achieved in this work could also be used for optimizing the printing-based manufacturing routes for producing other atomically layered materials and functional devices. Acknowledgement: NSF Grant #CMMI-1232883, NSF Grant #ECCS-1307740

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Computational study of entropically driven crystal nucleation Sam Nola1, Richmond Newman2, Sharon Glotzer1,2 1 Department of Macromolecular Engineering, University of Michigan


Through simulations and theory we are studying the self-assembly dynamics of hard polyhedra systems that form rotator crystal phases in simulation. The transition path for the crystallization of hard sphere systems is known to be a nucleation and growth process resulting in FCC crystals. The polyhedra systems considered here also exhibit nucleation and growth kinetics, but have significant differences in the observed homogeneous nucleation rates and critical packing fractions. Formation of crystal nuclei in these systems, including sphere systems, is a rare event: The formation of a stable nuclei occurs on a timescale much smaller than the time between events. This makes sampling and studying these events challenging. We employ several statistical and free energy based methods to sample nucleation events in order to identify the critical nuclei and understand transition paths.

84

Fabrication of a Wire Grid Polarizer by the Angled-evaporation Method Showing an Increased Viewing Angle

Young Jae Shin1, Yi-Kuei Wu2, Kyu-Tae Lee2, Jong G. Ok3, and L. Jay Guo1,2,3 1 Department of Macromolecular Sciences and Engineering, University of Michigan



A wire grid polarizer (WGP) was fabricated by using a simplified approach with a combination of nanoimprint lithography (NIL) and angled metal deposition. The period of the imprinted polymer nanograting used in this study was 180 nm. The WGP was formed by 2 consecutive angled aluminum evaporation processes essentially halving the period for the aluminum (Al) nanograting. The fabricated WGP showed good optical properties for polarized light. More importantly, because of the slight reduction of the period of the nanograting as compared with our previous results, the viewing angle, which is one of the most important characters in display equipment, was extended greatly. Encapsulation of the WGP using poly(methyl methacrylate) was conducted for practical application of the WGP. The thickness of the coating was controlled to be less than 1 µm to prevent the degradation of the optical properties of the WGP.

85

Nanograting–Mediated Growth of Bismuth Selenide Topological Insulator Nanoribbons

Sungjin Wi1, Eljon Elezi1, Amy Liu1, Vishva Ray2, Kai Sun3, and Xiaogan Liang *1 1 Department of Mechanical Engineering,

2 Lurie Nanofabrication Facility, Department of Electrical Engineering and Computer Science,

3 Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109

Topological Insulators (TIs) are a group of emerging materials that exhibit unusual electronic properties. The ballistic transport of carriers via these conductive surface states can be topologically protected against the scattering by nonmagnetic defects. Therefore, TIs could be implemented to make low-dissipation electronic channels for applications in spintronics, thermoelectrics, and magnetoelectronics. However, additional research is needed to significantly improve the yield of sub-100 nm wide TNRs and also obtain a high uniformity of the ribbon widths. In this work, we present a nanostructure-mediated growth process specifically for producing bismuth selenide (Bi2Se3) TNRs with a high yield. In this process, TI nanostructures are grown on nanograting templates by using NP-catalyzed VLS mechanism. In comparison with the growth processes on flat and randomly rough substrates, such a nanograting-mediated growth process produces TNRs with a higher yield (~15,000/mm2), a narrower average ribbon width (wavg < 60 nm), and a higher uniformity in width (σ < 30 nm); effectively suppresses the formation of other unwanted morphologies; and also results in the axial growth of nanoribbons along specific in-plane directions relative to pre-structured gratings. The TEM characterization shows that the produced nanoribbons are single crystals with atomically smooth edges. Finally, Aharonov–Borm (AB) oscillations in the magnetoresistance were observed and clearly demonstrated the coherent transport of electrons through topological surface states of Bi2Se3 nanoribbons. This work could serve as an important foundation for nanomanufacturing topological insulator nanoribbons with controllable feature size, large-area uniformity and ordering suitable for future applications in low-dissipation nanoelectronics and magnetoelectronic sensors.

86

Chiral Transmission to Self-Assembling Nanostructures from Circularly

Polarized Light

Jihyeon Yeom1, Bongjun Yeom2, Sung Jin Chang3, Wei-Shun Chang4, Gongpu Zhao5, Peijun Zhang5, Stephan Link4, Nicholas A. Kotov1,2* 1Department of Macromolecular Science and Engineering, University of Michigan, Ann Arbor, MI 48109,

USA 2 Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109, USA

3 Division of Material Sciences, Korea Basic Science Institute, Daejeon, 305-333, Republic of Korea,

4 Department of Electrical and Computer Engineering, Rice University, Houston TX 77005, USA

5 University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA

*To whom correspondence should be addressed. E-mail: [email protected] (N.A.K.)

Regarding life’s distinctive selectivity of chiral molecular species, and various chirooptical properties of chiral materials, synthesizing chiral nanostructures have attracted strong scientific interest. However, control over enantiomeric preference for artificial inorganic nanomaterials has limited to templating method using biological compounds. Here we show that circularly polarized light can drive the self-assembly of cadmium telluride nanoparticles (CdTe NPs) into nanoribbons controlling helical directions by transcription of chiral information from the light to NPs. Different helical directions of laser induce different light adsorption of CdTe NPs which lead to greater reactivity of a selective chirality. This simple method for chiral nanoribbons can open the door to understanding life’s homochirality and chiroptical devices. Key words: chirality, self-assembly, circularly polarized light, nanoribbon, chirooptical

87

Civil Engineering: Infrastructure Session Chair: Ran Gao

88

Capturing Spatial and Temporal Variations in Non-Uniform Thermal Loads on Structural Elements Paul A. Beata1, Dr. Ann E. Jeffers1 1 Department of Civil and Environmental Engineering, University of Michigan

In a typical analysis of a structure exposed to fire, the scenario is idealized as a compartment fire model and the heating is represented by a uniform gas temperature. However, local fires present a more complicated thermal load that cannot be fully captured by a compartment fire model. The proposed method for handling non-uniform thermal loads is a finite-element approach based on energy equivalence. First, a computational fluid dynamics (CFD) model representing the fire scenario was used to measure the thermal loads as they vary across the surface of a structural element. Using these measurements in conjunction with a temporal sub-cycling algorithm that was developed in a previous study, the thermal loads on the surface of the element were specified as input to the finite element heat transfer analysis. The non-uniform surface fluxes from the CFD simulation are represented in the finite element heat transfer model using numerical techniques such as time-average subcycling and spatial homogenization to provide an energy-equivalent boundary condition in the heat transfer model. Results from a preliminary study involving a plate exposed to a local fire show that the new analysis technique is efficient beyond the CFD simulation phase; the heat transfer analysis is accurate without adding substantial simulation time.

89

Performance Evaluation of Existing Highway Bridges under Combined Hazard of Seismic and Corrosion

Xiaohu Fan1 and Jason McCormick1 1 Department of Civil and Environmental Engineering, University of Michigan

Given the increasing awareness of seismic hazard in the Central and Eastern United States (CEUS), the seismic performance of the area’s highway bridge infrastructure is gaining more concern in both public and academic communities. Particularly, a majority of the bridges, constructed based on outdated design codes with little seismic consideration, are approaching their design service life, which have sustained corrosion in steel components such as steel bearings to various levels. According to the 2013 ASCE report card, many bridges of the CEUS will need major rehabilitation due to deficiency and deterioration. Thus, it is vital to identify the structural components in these bridges requiring the most urgent retrofit and upgrade. In this poster, one of the critical components, steel bearings that are representative of those found in the CEUS and have been experimentally investigated in a previous study regarding their seismic response at various levels of corrosion, is emphasized in the performance evaluation of an older highway bridge under moderate seismic loading. Constitutive models that are correlated with corrosion levels are established for the first time for a suite of steel bearings considered in the mentioned experimental study. A full bridge model is also created for a typical four span continuous highway bridge considering a variety of nonlinearities. This study will fully explore the combined effect of corrosion and seismic on the performance of older highway bridges regarding bearing displacements, pier wall plasticity development, and deck-abutment impact to assist the search for sustainable and viable retrofit strategies.

90

Structural reliability evaluation under fire

Qianru Guo1 and Ann E. Jeffers1

1 Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor

The current fire resistance design methodology in the United States is based on prescriptive requirements for fire resistance rating of isolated structural elements without considering the structural system performance and the actual fire scenario. In order to change this situation and also to give engineers more flexibility on fire resistance design, the professional society is trying to move from the prescriptive design to the performance-based design. As an important component of performance-based design, an efficient reliability-based design methodology is urgently needed to ensure adequate reliability in the face of uncertainty. This poster shows a framework that is able to simulate structural response in fire and to evaluate the failure probability of structure subjected to fire. The compartment fire model, the thermal heat transfer model, and the structural model are coupled together to predict the actual gas temperatures, structural element temperatures, and structural responses during a fire. Both analytical reliability methods, namely the First-Order Reliability Method (FORM) and Second-Order Reliability Method (SORM), and Monte Carlo Simulation (MCS) are applied to quantify the structural reliability of the multi-physical and highly nonlinear system. An application involving a protected steel column exposed to natural fire is presented in this poster. The FORM is recommended for the rapid estimation of the reliability of structures threatened by fire based on its comparison with MCS on the accuracy and the efficiency.

91

Damage Detection in Metallic Elements using a Point-based Thermal Measurement Strategy Nephi R. Johnson1, Jerome P. Lynch1, 2, Ann E. Jeffers1

1 Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI


Early detection of damage in metallic structures (e.g., bridges, ships, aircraft) is crucial to the success of structural health monitoring (SHM). Often times, visual inspection or single point surface mounted sensors are not enough to detect some forms of damage with adequate time to perform preventative maintenance on the structure. Non-destructive methods using thermal imaging have been developed to monitor the state of a structure in two and three dimensions. These techniques use an infrared (IR) camera to track the heat conduction through the material, which has been heated by either a laser or a lamp. While these methods have proven to be effective techniques in the lab or during short-term field deployments, they are expensive and generally not feasible for long-term permanent applications. This poster presents a method of thermography-based damage detection that employs an economic sensor setup that is feasible for permanent deployment in operational structures. The setup includes resistive heating elements and an array of IC temperature sensors mounted to the boundary of 2 aluminum plate specimens (1 undamaged, 1 damaged). As the heat is conducted from the resistor through the metal, sensors measure the time variance in temperature rise at the sensor locations. This data can then be used in an inverse manner using a high-fidelity finite element model (FEM) to solve for imperfections in the metal that cause delays in heat conduction. Correlations between the finite element and the temperature sensor system are analyzed as well as damage detection results of the inverse problem solver. The authors would like to gratefully acknowledge the generous support offered by the U.S. Department of Commerce, National Institute of Standards and Technology (NIST) Technology Innovation Program (TIP) under Cooperative Agreement Number 70NANB9H9008. Additional support was provided by the National Science Foundation through Grant Number 0846256.

92

Development of ECC Slurry for Levee Cut-off Wall Applications Lena M. Soler Ayoroa1, Victor C. Li1 1 Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI

Earthen levees are used as the primary flood protection system in many U.S. river cities, and their structural stability is maintained by the use of slurry cut-off walls. However, due to the slurry material’s brittle nature (generally a mixture of cement, soil and bentonite) and lack of steel reinforcement, its performance in seismically active regions is often questioned. Engineered Cementitious Composites (ECC) are ultra-ductile cement based composites, which have been successfully employed in a variety of structures for enhancing durability and structural performance under seismic loads. The present study focuses on evaluating various ECC mixtures for their applicability in cut-off walls in terms of cost, greenness, workability, strength, and ductility. Although ECC has proven to be exceedingly better than other cementitious based materials due to its ductile ability, the high cost of the polyvinyl alcohol (PVA) fibers typically used in ECC mixtures prohibits the use of these composites for slurry wall applications. Hence for this study, high-tenacity polypropeleyne (HTPP) fibers will be evaluated as a possible replacement for PVA fibers since they reduce both cost and environmental impact of the mixtures. Furthermore, greenness and ductility were further improved by increasing the fly ash content. Results show that mixtures with high fly ash (HFA) content and HTPP fibers meet slurry requirements in terms of cost, workability, permeability, and compressive performance. In addition, HFA-ECC with HTPP fibers exceed the current slurry cut-off walls in terms of mechanical properties such as tensile strength and strain, and other properties such as permeability which makes ECC slurry a viable and desirable replacement for current cut-off walls. Acknowledgements Support from the University of Michigan is gratefully acknowledged. The project is funded by the National Science Foundation (NSF). The authors would also like to recognize the support given by Lafarge (cement), Headwaters (fly ash), WR Grace (HRWRA), Brasit (HTPP fibers), and Poraver® (Poraver®).

93

Impact of Dissolved Oxygen and Microbial Populations on Pharmaceutical Biotransformations in Wastewater Lauren B. Stadler1, Lijuan Su2, Diana S. Aga2, and Nancy G. Love1 1 Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI

2 Department of Chemistry, University at Buffalo, State University of New York, Buffalo, NY

Thousands of pharmaceuticals are excreted by humans in intact and metabolized forms, reaching wastewater treatment plants (WWTPs) before entering our waterways. WWTPs represent the entry point for the environmental proliferation of pharmaceuticals. Yet they are also the last line of defense against this chemical pollution. Our limited understanding of pharmaceutical transformation pathways prevents us from aligning the design and operation of WWTPs to reduce pharmaceutical exposure and associated risk in receiving environments In addition, as the industry moves toward implementing technologies in the name of sustainability, such as low dissolved oxygen (DO) treatment, it must recognize the consequences that these systems have on other treatment objectives that impact the environment and public health.

The objective of this study is to evaluate how low DO treatment affects the profile of pharmaceuticals in effluents and to understand which microbial populations are responsible for pharmaceutical biotransformation. This is achieved by measuring biotransformation rates of six commonly used pharmaceuticals in batch experiments using cultures of heterotrophs and ammonia oxidizers enriched under different DO conditions. Pharmaceutical quantification is performed using liquid chromatography and mass spectrometry. Initial results show that certain pharmaceuticals such as 17α-ethinylestradiol (EE2), a drug commonly used for birth control, is biotransformed much faster by ammonia oxidizers than heterotrophs and occurs faster in high DO than low DO conditions. These results will further our understanding of the fate of pharmaceuticals during wastewater treatment will improve our ability to design WWTPs to achieve multiple goals (i.e. reduce energy demands and achieve pharmaceutical inactivation).

94

Time-Dependent Behavior of Sand Zhijie Wang1 1 Department of Civil and Environmental Engineering, Uniersity of Michigan

Time-dependent increase in small strain stiffness of sand under sustained load has been reported by some researchers, but the mechanisms causing this behavior are not well understood. The hypothesis in this research considers delayed fracturing of micro-morphological features on grain surfaces at inter-granular contacts as a key mechanism contributing to time-dependent behavior of sand at the macroscopic scale. Experimental work has been carried out at both the microscopic (a single contact) and the macroscopic (sand specimen) scales. Time-dependent behavior of a single contact was investigated using custom-designed device, which allows one to measure a time-dependent response of a contact once it had been loaded. A modified consolidometer was then used to investigate the response of a large assembly of grains (sand specimen) to sustained load. The inaccuracies of measurements of the radial stress in the consolidometer were overcome through a fluid-calibration process. Both dry and water-saturated specimens have been tested. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the surface of the grains where the key process contributing to aging is believed to take place. The results were found to be very sensitive to temperature and vibrations, and the experiments have been performed in an

environmental chamber with constant temperature of 20C (and constant relative humidity of 20%). Preliminary results will be presented. These results have been found consistent with the proposed hypothesis.

95

Incorporation of Innovative Materials in Seismic Hollow Structural Section Connections Dan Wei1, Matthew Fadden2, Jason McCormick, Ph.D.1 1 Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI,48105

2 Department of Civil Engineering, University of Louisiana at Lafayette, Lafayette, LA, 70504

Hollow structural sections (HSS) are currently underutilized in steel moment frame system. In order to evaluate cyclic behavior and design details of HSS to HSS connection in seismic moment frame systems, cyclic quasi-static tests of four different detailing connections are conducted. The behavior of reinforced connections can limit the location of inelasticity to beam and panel zone region which is more desirable than unreinforced ones. However, based on these test results, the behavior during cyclic loading can be affected by local buckling and the damage associated with the inelastic behavior. The voids of structural members provide an often underutilized location for the application of non-traditional materials. One means of mitigating local buckling and providing supplemental energy dissipation capacity is through the use of non-traditional materials for passive control applications. The high damping properties polymer foams, metal foams and rubber materials provide a unique means of adding energy dissipation capacity to the plastic hinge region of a member with minimal increase in weight. To determine the properties and energy dissipation capacity of the selected fill materials, future work will focus on cyclic material characterization studies under loadings and loading rates expected during an earthquake. The results are used to evaluate the ability of the passive control systems to control the behavior of structures during a seismic event.

96

Ductile spray-applied fire-resistive material for enhanced fire safety of steel structures

Qian Zhang1, Victor Li1 1 Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor

Spray-applied fire-resistive material (SFRM) is one of the most widely used passive fire protection material in North America. However, SFRM is inherently brittle and tends to dislodge or delaminate under extreme loading conditions (earthquakes or impacts) and even under normal service conditions such as wind induced building movement. Such loss of fire protection material puts the steel structure in great danger under fire loading, especially under multi hazards (post-earthquake or post-impact fires). As an alternative to conventional brittle cementitious material, engineered cementitious composites (ECC) is a family of high performance fiber reinforced cementitious composites. ECC typically exhibits strain hardening behavior with very high tensile ductility (3-5%) under static and high rate loading. In this paper, a new spray-applied fire-resistive material that combines the desirable thermal insulation property, ease of construction (facilitated by sprayability), lightweightness of SFRM and the enhanced ductility of ECC is developed as an alternative material to current SFRM. The newly developed spray-applied fire-resistive ECC (SFR-ECC) exhibits density as low as 550 kg/m3 yet with tensile strength up to 1MPa and tensile strain capacity greater than 2%, significantly higher than those of conventional SFRM with tensile strength of less than 0.1MPa and no inelastic tensile strain. The thermal conductivity of SFR-ECC is measured in accordance with ASTM E2584 and is shown to be comparable to conventional SFRM within the same density range. SFR-ECC with enhanced mechanical performance is expected to improve the overall fire safety of steel structure under both service and extreme loads. The authors wish to express their gratitude and sincere appreciation to 3M, Lafarge, WR Grace, Dayton and Brasilit for material supply for this research project.

97

Frost heave and thaw settlement of ground surface above an oil pipeline Yao Zhang1

1 Department of Civil and Environmental Engineering, University of Michigan

Freezing and Thawing of frost-susceptible soils often causes substantial damage to infrastructure. A pipeline system could be vulnerable to such issue since the medium transported may have below-freezing temperature and the surrounding soil is above freezing, or vice-versa. Such examples may include chilled gas pipelines going through normal temperature soils or warm oil pipelines buried in permafrost region. Accounting for frost heave and thaw settlement is important in transportation infrastructure, and of particular concern are the regions in soils where thermal front (freezing and thawing) may propagate into the soil at different rates, leading to differential heave or settlement. A Thermal-hydro-mechanical (THM) model will be introduced including basic partial differential equations (PDEs) for conservation of energy, conservation of mass and mechanical equilibrium, to describe the multi-physical feature of soils under freezing and thawing. The constitutive relationship in the model is elastic-plastic and on the basis of critical state framework with consideration of freezing effect. Frost heave and thaw settlement induced by a chilled gas pipeline as well as seasonal temperature change will be simulated using this model, and the potential damage to the pipeline will be analyzed. This work was funded, in part, by the Army Research Office, grant No. W911NF-08-1-0376.

98

Computer Science Session Chairs: Cheng Zhang and Parinaz Naghizadeh Ardabili

99

Robust Image Denoising with Multi-Column Deep Neural Networks

Forest Agostinelli1, Honglak Lee1, Michael Anderson1 1 Department of

Computer Science, University of Michigan

Stacked sparse denoising auto-encoders (SSDAs) have recently been shown to be successful at removing noise from corrupted images. However, like most denoising techniques, the SSDA is not robust to variation in noise types beyond what it has seen during training. We present the multi-column stacked sparse denoising autoencoder, a novel technique of combining multiple SSDAs into a multi-column SSDA (MC-SSDA) by combining the outputs of each SSDA. We eliminate the need to determine the type of noise, let alone its statistics, at test time. We show that good denoising performance can be achieved with a single system on a variety of different noise types, including ones not seen in the training set. Additionally, we experimentally demonstrate the efficacy of MC-SSDA denoising by achieving MNIST digit error rates on denoised images at close to that of the uncorrupted images.

100

The Moo and Cement Shoes: A Real-World Application of Sensor Swarms Miran Alhaideri1, Michael Rushanan2, Denis Foo Kune1, Kevin Fu1 1 Department of Computer Science and Engineering, University of Michigan

2 Department of Computer Science and Engineering, Johns Hopkins University

Passively-powered computational RFIDs (CRFID) have dispelled the assumption that only simple computations are possible under harvested RF-power. This lass of RFIDs feature reprogrammable microcontrollers, electronic sensors and actuators, and nonvolatile memory. Most importantly, the sensors and actuators provide the foundation for a not-too-distant paradigm shift toward the integration of cyber-physical worlds. A classical approach in civil engineering is to address the structural integrity of an infrastructure retroactively. This process often requires human intervention, introducing non-negligible error, and is restricted to a limited set of data points subject to interpolation. In an attempt to gauge the gap between research and industry, we immersed devices built on our research platform in a real-world application. We embedded 19 epoxied CRFIDs, Moo Platform 1.1 [4], inside the concrete walls of a residential basement. Each Moo was placed inside a concrete-filled cinderblock at parallel diagonals, along three distinct heights. Afterwards, we immediately began sampling from the Moo's external temperature and accelerometer sensors. The temperature sensor was used to capture the concrete curing process, while the three-dimensional accelerometer was used to measure structural changes in the position of the wall over time. This work was supported in part by the TerraSwarm Research Center and the Center for Future Architectures Research (C-FAR).

101

X-ray: Automating Root-cause Diagnosis of Performance Anomalies in Production Software

Mona Attariyan1, Michael Chow2, Jason Flinn2

1 Google Inc.

2 Department of Computer Science & Engineering, University of Michigan

Troubleshooting the performance of production software is challenging. Most existing tools, such as profiling, tracing, and logging systems, reveal what events occurred during performance anomalies. However, users of such tools must infer why these events occurred; e.g., that their execution was due to a root cause such as a specific input request or configuration setting. Such inference often requires source code and detailed application knowledge that is beyond system administrators and end users. We introduce performance summarization, a technique for automatically diagnosing the root causes of performance problems. Performance summarization instruments binaries as applications execute. It first attributes performance costs to each basic block. It then uses dynamic information flow tracking to estimate the likelihood that a block was executed due to each potential root cause. Finally, it summarizes the overall cost of each potential root cause by summing the per-block cost multiplied by the cause-specific likelihood over all basic blocks. Performance summarization can also be performed differentially to explain performance differences between two similar activities. X-ray is a tool that implements performance summarization. Our results show that X-ray accurately diagnoses 17 performance issues in Apache, lighttpd, Postfix, and PostgreSQL, while adding 2.3% average runtime overhead.

102

Low-Power, Real-Time Gaze Tracking Russ Bielawski1, Prabal Dutta1 1 Department of Electrical Engineering and Computer Science, University of Michigan

It has long been said that they eye is the window to the soul. However, until now, this all-important visual context information has been absent from the personal computing infrastructure. With advances in low-power CMOS imaging technology and wireless radios, continuous, low-power eye tracking is an idea whose time has come. The SensEye wireless gaze detection prototype represents the first step in augmenting the computational ecosystem with real-time gaze information. This visual context has board applications in transportation and medicine as well as in more long-term ideas such as augmented reality. SensEye is a low-power, lightweight system for tracking a person’s gaze fixation in real time. Our wireless eyeglasses weigh only slightly more than a heavy pair of spectacles and are capable of six hours of continuous operation. This work is supported by the National Science Foundation, NSF Grant 1239341, in collaboration with Deepak Ganesan, Benjamin Marlin, Marco Duarte, Christopher Salthouse, Addison Mayberry, Boyan Lu, Pan Hu, Hamid Dadkhahi, Venkatesh Murthy, Pengyu Zhang and Jeremy Gummeson at the University of Massachusetts.

103

When to attack? Android UI state inference as an attack building block

Qi Alfred Chen1, Zhiyun Qian2, Zhuoqing Morley Mao1 1 University of Michigan, Ann Arbor

2 NEC Labs America, Inc.

Recently many studies have pointed out that on mobile platforms such as Android, a malicious app running in the background can hijack TCP connections, infer web pages and keystrokes, etc., endangering security and privacy of mobile users. However, these attacks usually only work during certain operation of the victim app, e.g. keystroke inference for user input related operations. Thus, not knowing when to attack makes such attacks infeasible in practice (due to success rate, overhead and stealthiness concerns). In this work, we solve this problem by introducing User Interface (UI) state inference as a building block for these attacks: an unprivileged background app with minimal privileges is able to peek into another application's UI and track its states closely in real time, thus allowing attacker to choose the best attack moment. The underlying problem is that the design and implementation of Android UI framework has interesting and unexpected interactions with publicly accessible side channels. Since there is no obvious vulnerability in either design or implementation, it is non-trivial to eliminate the problem. Our evaluation shows that the accuracy of UI state inference is 80-90% for the first candidate UI state on popular apps such as WebMD, Chase Bank, etc., and over 95% for top three candidates. Furthermore, through case studies, we have designed and implemented fully several interesting new attacks based on UI state inference, including capturing sensitive pictures (e.g. checks for banking app) at the background, and monitoring private information of the user (e.g., medical conditions in health app).

104

Senbazuru: A Prototype Spreadsheet Database Management System Zhe Chen1, Michael Cafarella1, Jun Chen1, Daniel Prevo1, Junfeng Zhuang1

1 Department of Computer Science & Engineering, University of Michigan

Spreadsheets have become a critical data management tool, but they lack explicit relational metadata, making it difficult to join or integrate data across multiple spreadsheets. Because spreadsheet data are widely available on a huge range of topics, a tool that allows easy spreadsheet integration would be hugely beneficial for a variety of users. We demonstrate that Senbazuru, a prototype spreadsheet database management system (SSDBMS), is able to extract relational information from spreadsheets. By doing so, it opens up opportunities for integration among spreadsheets and with other relational sources. Senbazuru allows users to search for relevant spreadsheets in a large corpus, probabilistically constructs a relational version of the data, and offers several relational operations over the resulting extracted data (including joins to other spreadsheet data). Our demonstration is available on two clients: a JavaScript-rich Web site and a touch interface on the iPad. During the demo, Senbazuru will allow VLDB participants to search spreadsheets, extract relational data from them, and apply relational operators such as select and join.

105

Anception: Hybrid Virtualization for Smartphone Applications Earlence Fernandes1, Alexander Crowell1, Ajit Aluri1, Atul Prakash1

1 Department of Computer Science and Engineering, University of Michigan, Ann Arbor

The improved performance and functionality of smartphones in recent years has transformed them into mobile extensions of desktops and laptops. But with this new versatility also comes the security threats that plague other computer systems. Methods for allowing trusted and untrusted desktop applications to securely share the same environment have been well researched, producing approaches that use system call redirection and virtualization, among other methods. However, that research often does not carry over neatly to the mobile environment, where resource constraints are a limiting factor and the user interface paradigm is fundamentally different. This paper proposes a new security mechanism called hybrid virtualization that combines elements of traditional full-system virtualization with selective system call redirection. Hybrid Virtualization provides high-performance isolation while largely preserving the original user interface in terms of receiving notifications from apps in multiple trust domains and being able to interact with them with low latency. We describe our implementation of \emphAnception, which realizes hybrid virtualization in the Android environment with only minimal modifications to the Linux kernel. Our security evaluation based on reported vulnerabilities from the past 4 years shows that Anception provides comparable security to full-system virtualization. Anception incurs only a 1.2% overhead on the SunSpider application benchmark and up to 3.88% overhead on 2D and 3D graphics benchmarks.

106

Emotion Classification via Utterance-Level Dynamics: A Pattern-Based Approach to Characterizing Affective Expressions Yelin Kim1 and Emily Mower Provost1 1 Departament of Electrical Engineering and Computer Science, University of Michigan Ann Arbor

Human emotion changes continuously and sequentially. This results in dynamics intrinsic to affective communication. One of the goals of automatic emotion recognition research is to computationally represent and analyze these dynamic patterns. In this work, we focus on the global utterance-level dynamics. We are motivated by the hypothesis that global dynamics have emotion-specific variations that can be used to differentiate between emotion classes. Consequently, classification systems that focus on these patterns will be able to make accurate emotional assessments. We quantitatively represent emotion flow within an utterance by estimating short-time affective characteristics. We compare time-series estimates of these characteristics using Dynamic Time Warping, a time-series similarity measure. We demonstrate that this similarity can effectively recognize the affective label of the utterance. The similarity-based pattern modeling outperforms both a feature-based baseline and static modeling. It also provides insight into typical high-level patterns of emotion. We visualize these dynamic patterns and the similarities between the patterns to gain insight into the nature of emotion expression.

107

Putting the IT in QuIT Smoking Noah Klugman1, Prabal Dutta1 1 Departament of Electrical Engineering and Computer Science, University of Michigan

Cigarette smoking is responsible for millions of deaths, despite valiant individual efforts to quit. In response to these failures, new programs have been proposed that would offer incentives to smokers to quit. Unfortunately, the programs suffer from dependence on unreliable, self-reported data to determine a participant’s compliance [Abroms11]. We claim that information technology can offer a better compliance mechanism. Because cigarette smoke contains carbon monoxide (CO), the absence of CO from a program participant’s breath offers reliable evidence of compliance with an intervention program. We propose a CO monitor that pairs with a smartphone to measure an individual’s breath CO concentration. Our CO monitor communicates wirelessly with a smartphone using the Bluetooth Low Energy protocol. An IOS app stores the data locally, displays CO concentration to the user, and delivers the data to the cloud for analysis and compliance verification. Our prototype offers comparable accuracy to existing monitors while greatly improving usability and user satisfaction. [Abroms11] Abroms et al., iPhone apps for smoking cessation: A content analysis. 2011.

108

Using N-gram and Word Network Features for Native Language Identification

Shibamouli Lahiri1, Rada Mihalcea2

1 Computer Science and Engineering, University of North Texas

2 Computer Science and Engineering, University of Michigan

Native Language Identification is an interesting and challenging problem in natural

language processing, where the goal is to identify an author's native language (L1) from

his/her writings in a second language (L2), usually English. The task is conventionally

framed as a multi-class classification problem, where training documents are in L2, and

the class labels are different authors' L1s. In our study, we experimented with two sets of

features - a traditional feature set comprising the raw frequency, normalized frequency,

and binary presence/absence indicator of the most frequent character, word, and part-of-

speech n-grams (n = 1, 2, 3), and a new feature set comprising centrality measures of

most frequent words in the documents' word co-occurrence networks. Among traditional

features, we observed that word unigrams with punctuations were the best performers on

the training dataset released by the Educational Testing Service (ETS), under ten-fold

cross-validation. On the same training corpus, our new feature set involving centrality

measures on word networks showed promising performance. Degree and neighborhood

size (of order one) were the best-performing centrality measures, whereas function words

like ''a'', ''however'', and ''the'' were found to be among the most discriminatory words. We

performed an extensive array of experiments with several different classifiers, and

Support Vector Machines (SVM) emerged as the best classifier under most settings.

109

Emotion Recognition from Spontaneous Speech using Hidden Markov Models with Deep Belief Networks Duc Le1, Emily Mower Provost1 1 Departament of Electrical Engineering and Computer Science, University of Michigan

Research in emotion recognition seeks to develop insights into the temporal properties of emotion. However, automatic emotion recognition from spontaneous speech is challenging due to non-ideal recording conditions and highly ambiguous ground truth labels. Further, emotion recognition systems typically work with noisy high-dimensional data, rendering it difficult to find representative features and train an effective classifier. We tackle this problem by using Deep Belief Networks, which can model complex and non-linear high-level relationships between low-level features. We propose and evaluate a suite of hybrid classifiers based on Hidden Markov Models and Deep Belief Networks. We achieve state-of-the-art results on FAU Aibo, a benchmark dataset in emotion recognition. Our work provides insights into important similarities and differences between speech and emotion.

110

AMC: Verifying User Interface Properties for Vehicular Applications

Kyungmin Lee1, Jason Flinn1, T.J. Giuli2, Brian Noble1, Christopher Peplin2 1 Computer Science and Engineering, University of Michigan

2 Ford Motor Company

Vehicular environments require continuous awareness of the road ahead. It is critical that mobile applications used in such environments (e.g., GPS route planners and location-based search) do not distract drivers from the primary task of operating the vehicle. Fortunately, a large body of research on vehicular interfaces provides best practices that mobile application developers can follow. However, when we studied the most popular vehicular applications in the Android marketplace, no application followed these guidelines. In fact, vehicular applications were not substantially better at meeting best practice guidelines than non-vehicular applications. To remedy this problem, we have developed a tool called AMC that uses model checking to automatically explore the graphical user interface (GUI) of Android applications and detect violations of vehicular design guidelines. AMC is designed to give developers early feedback on their application GUI and reduce the amount of time required by a human expert to assess an application's suitability for vehicular usage. We have evaluated AMC by comparing the violations that it reports with those reported by an industry expert for 12 applications. AMC generated a definitive assessment for 85\% of the guidelines checked; for these cases, it had no false positives and a false negative rate of under 2%. For the remaining 15% of cases, AMC reduced the number of application screens that required manual verification by 95%.

111

Robot Navigation in Dynamic and Uncertain Environments via Hierarchical and Integrated Motion Planning and Control

Jong Jin Park1 and Benjamin Kuipers2 1 Department of Mechanical Engineering, University of Michigan

2 Computer Science and Engineering, University of Michigan

The ability to navigate intelligently and effectively in dynamic and uncertain environments is crucial for any autonomous mobile agent to survive, to interact with the world, and to achieve its goals. For this, we have proposed the model predictive equilibrium point control (MPEPC) framework, applicable for navigation to a target pose in space [2], and also for person pacing and following for human-robot companionship [3]. The algorithm builds upon a smooth control law which enables the robot to reach any pose in space gracefully [1], which shapes and defines a continuous space of realizable actions for the mobile robot. The controller puts useful constrains on some of the degrees of freedom of the robot so that the resulting trajectories of the robot are smooth and comfortable, and also provide a low-dimensional parametric representation of the remaining degrees of freedom, which in turn defines the search space of the trajectory planner. The trajectory planner lets the robot navigate by selecting and executing the best local trajectory at each planning cycle, where each trajectory hypothesis is tested for the expected utility to find the locally optimal solution, fully considering probability of collision, cost of action and progress toward achieving the agent's goal, either a fixed pose in space or a moving target about a person. With our low-dimensional representation of the trajectory space and integrated planning and control architecture, the typical optimization cycle takes <200ms on a physical robot. Acknowledgement: Research of the Intelligent Robotics lab is supported in part by grants from the National Science Foundation (CPS-0931474 and IIS-1111494), and from the TEMA-Toyota Technical Center. References: [1] J. Park and B. Kuipers, “A Smooth Control Law for Graceful Motion of Differential Wheeled Mobile Robots in 2D

Environment”, Proceedings of IEEE International Conference on Robotics and Automation (ICRA), 2011.

[2] J. Park, C. Johnson and B. Kuipers, "Robot Navigation with Model Predictive Equilibrium Point Control",

Proceedings of IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2012

[3] J. Park and B. Kuipers, "Autonomous Person Pacing and Following with Model Predictive Equilibrium Point

Control", Proceedings of IEEE International Conference on Robotics and Automation (ICRA), 2013

112

A multimodal dataset for deception detection Veronica Perez-Rosas1, Rada Mihalcea2, Mihai Burzo2. 1 Computer Science and Engineering. University of North Texas

2 Computer Science and Engineering. University of Michigan

The automatic identification of deceptive behavior in human responses is a desirable capability of applications in human-computer interaction. Most of the previous work presented in this area has focused on individually analyzing specific components of human deceptive responses, such as spoken or written language, visual behaviors, or physiological responses. More recently, in an effort to improve the understanding of deceit, multimodal approaches have been explored. In these studies, one important requirement is the availability of deception datasets, which to date are scarce. Motivated by the lack of multimodal resources for the task of deception detection, we introduce a new multimodal dataset. We elicit subject’s deceptive responses by using three deceit scenarios in which participants express deceptive and truthful statements about different topics. The data is collected in a multimodal setting where we acquire video, audio, thermal, and physiological recordings of the participants. After presenting a detailed description of the experimental protocol and the data acquisition process, we present a set of descriptive statistics. Furthermore, we discuss directions for future research that might benefit from using this data set.

113

TARDIS: Secure Time Keeping For Embedded Devices Without Clocks Amir Rahmati1, Mastooreh Salajegheh2, Dan Holcomb3, Jacob Sorber4, Wayne P. Burleson2, Kevin Fu1 1Computer Science and Engineering, University of Michigan

2CS, University of Massachusetts Amherst

3Electrical Engineering and Computer Science, University of California Berkeley

4CS, Dartmouth Collage

Lack of a locally trustworthy clock makes security protocols challenging to implement on batteryless embedded devices such as contact smartcards, contactless smartcards, and RFID tags. A device that knows how much time has elapsed between queries from an untrusted reader could better protect against attacks that depend on the existence of a rate-unlimited encryption oracle. The TARDIS (Time and Remanence Decay in SRAM) helps locally maintain a sense of time elapsed without power and without special-purpose hardware. The TARDIS software computes the expiration state of a timer by analyzing the decay of existing on-chip SRAM. The TARDIS enables coarse-grained, hourglass-like timers such that cryptographic software can more deliberately decide how to throttle its response rate. Our experiments demonstrate that the TARDIS can measure time ranging from seconds to several hours depending on hardware parameters. Key challenges to implementing a practical TARDIS include compensating for temperature and handling variation across hardware. Our contributions are (1) the algorithmic building blocks for computing elapsed time from SRAM decay; (2) characterizing TARDIS behavior under different temperatures, capacitors, SRAM sizes, and chips; and (3) proof-of-concept implementations that use the TARDIS to enable privacy-preserving RFID tags, to deter double swiping of contactless credit cards, and to increase the difficulty of brute-force attacks against e-passports.113113113

114

AppProfiler: A Flexible Method of Exposing Privacy-Related Behavior in Android Applications to End Users Sanae Rosen1, Zhiyun Qian1, Z. Morley Mao1

1Computer Science and Engineering, University of Michigan

Although Android's permission system is intended to allow users to make informed decisions about their privacy, it is often ineffective at conveying meaningful, useful information on how a user's privacy might be impacted by using an application. We present an alternate approach to providing users the knowledge needed to make informed decisions about the applications they install. First, we create a knowledge base of mappings between API calls and fine-grained privacy-related behaviors. We then use this knowledge base to produce, through static analysis, high-level behavior profiles of application behavior. We have analyzed almost 80,000 applications to date and have made the resulting behavior profiles available both through an Android application and online. Nearly 1500 users have used this application to date. Based on 2782 pieces of application-specific feedback, we analyze users' opinions about how applications affect their privacy and demonstrate that these profiles have had a substantial impact on their understanding of those applications. We also show the benefit of these profiles in understanding large-scale trends in how applications behave and the implications for user privacy.

115

Organizational Design Principles and Techniques for Decision-Theoretic Agents

Jason Sleight1, Edmund Durfee1 1Computer Science and Engineering, University of Michigan

Recent research has shown how an organization can influence a decision-theoretic agent by replacing one or more of its model components (transition/reward functions, action/state spaces, etc.), and how each of these influences impacts the agent's decision-making performance. This work delves more precisely into exactly which parts of an agent's model should be organizationally influenced, and asserts a broader principle for delineating what aspects of an agent's behavior an organization should be sanctioned to influence. We present a formal framework for specifying factored organizational influences and incorporating them into agents' decision models, and empirically demonstrate that organizational specifications based on our proposed principle outperform the alternatives. We further describe an algorithm for automating the organizational-design process that is inspired by this principle, and demonstrate empirically that its organizational designs are both intuitively sensible and also find and exploit domain structure that our hand-generated designs miss. This work was supported by NSF grant IIS-0964512.

116

Electrical Engineering: Applied Electromagnetics and Plasma Science

Session Chairs: Cheng Zhang and Parinaz Naghizadeh Ardabili

117

Investigating the Potential of Miniature Electrodynamic Tethers to Enhance Capabilities of Ultra-small Sensor Spacecrafts Iverson C. Bell, III1 1 Department of Electrical Engineering, University of Michigan

The success of nanospacecraft (1–10 kg) and the evolution of the millimeter-scale wireless sensor network concept have generated interest in small, sub-kilogram scale, “smartphone”-sized spacecraft, either as stand-alone satellites or as elements in a maneuverable fleet. These satellites are in the picosatellite (100 g–1 kg) and femtosatellite (<100 g) mass categories. The need for propellantless propulsion is evident: not only would formation flying of a fleet require the maneuverability of each satellite, but flat pico- and femtosat wafers also can have an inherently short orbital life in low Earth orbit (LEO) due to atmospheric drag, ranging from a few weeks to a few hours. In this paper, we present the results of trade studies that investigate the feasibility of using short (few meters), semi-rigid electrodynamic tethers (EDTs) for pico- and femtosat propulsion. The results reveal that an insulated tether, only a few meters long, can provide milligram-to-gram-level satellites with complete drag cancellation and even the ability to change orbit. Our goal in this paper is also to improve our understanding of the spacecraft’s interaction with the ionosphere by conducting ground-based plasma experiments that capture critical characteristics of the LEO environment. By further investigating plasma contactors in the system concept, we aim to better understand the feasibility of the dual ultra-small satellite–EDT propulsion concept. The authors acknowledgement support from AFOSR grant FA9550-09-1-0646, the National Science Foundation Graduate Student Research Fellowship under Grant No. DGE 1256260, and the Michigan Space Grant Consortium.

118

Ultra-Wide-Band Slot Antenna with Uni-axial Dielectric Superstrate

Hatim Bukhari1 and Kamal Sarabandi1

1 The Radiation Laboratory, Electrical Engineering and Computer Science Department, University of

Michigan, Ann Arbor, MI

Slot antennas constitute one of the most popular planar low-profile antennas which are easy to fabricate, have high radiation efficiencies, are easy to integrate with the RF frontend, and are low-cost. Their radiation pattern and bandwidth are similar to dipole antennas and thus number of modifications are required to achieve ultra-wideband performance and for radar applications to make the antenna radiation pattern directional. In this paper, a new technique in designing a slot antenna with 60% fractional bandwidth and directional radiation pattern is presented. In order to further improve the bandwidth, reduce the size, and achieve directional radiation pattern, the use of a stepped index superstrates with tapered dielectric constants, from dense to sparse, is proposed. The electromagnetic waves behavior can be controlled by adding different materials with different permittivities which allows better matching of the waves in the superstrate to the surrounding medium. Adding superstrate with equivalent dielectric constant of periodic media create a dielectric resonance mode near to the other resonance of the slot antenna itself. Proper feeding can also create a fictitious short along the slot antenna. The superstrate has the effect of reducing the slot dimension for given resonance and therefore, the slot radiates effectively toward the superstrate and reduces the backward radiation. The stepped index allows a better matching to free-space. The width and length of the slot antenna and the thicknesses of each periodic layer of the superstrate are optimized to achieve the required operating bandwidth.

119

Tailoring the phase and power flow of electromagnetic fields Gurkan Gok1, Anthony Grbic1


A method for arbitrarily controlling the phase progression and power flow of electromagnetic fields within a region of space is introduced. Specifically, we describe how a 2D inhomogeneous, anisotropic medium can be designed that supports desired spatial distributions of the wave vector and Poynting vector direction. Plane-wave relations in anisotropic media are used in conjunction with an impedance matching process to find the required material parameters. The developed formulation allows one to independently tailor the phase and amplitude of a field profile. In the presentation, the use of the proposed method in transformation of the cylindrical source radiation into desired amplitude and phase profiles are shown. In addition, design of a wide-band antenna beam-former generating a collimated beam from a cylindrical source is outlined. Implementation of the beam-former using tensor transmission-line metamaterials and simulation results are presented. This work was supported by a NSF Faculty Early Career Development Award (ECCS-0747623) and the Presidential Early Career Award for Scientists and Engineers (PECASE) grant (FA9550-09-1-0696).

120

Dielectric Characterization of Thin Materials at 240 GHz Amr Ibrahim1, Kamal Sarabandi2 1 Departament of Electrical Engineering and Computer Science, University of Michigan 1 Departament of Electrical Engineering and Computer Science, University of Michigan

The increasing demand on higher data rates in modern communication systems has pushed the operating carrier frequencies to the millimeter wave (MMW) regime. Also MMW and sub-MMW frequencies are being considered for small short range radars envisioned for autonomous robotic applications. In order to develop a robust communication or radar system, the surrounding multi-path channel and the radar clutter environment needs to be accurately modeled. For doing so, the electromagnetic properties (complex permittivity, magnetic permeability, electric conductivity…) of different materials found in the physical transmission medium are required. The characterization of different thin materials at millimeter-wave frequency, 240 GHz, is presented in this abstract. This includes vegetation leaves as well as different types of fabrics. The complex permittivity retrieval algorithm is based on fitting the measured transmission coefficient at different incident angles to the corresponding analytical transmission coefficient of a simple dielectric slab. The extracted dielectric permittivity values for the fabrics are compared with the corresponding values measured at low microwave frequency (~1 GHz), using a standard material analyzer, where they are found to be nearly the same. For the leaf measurements, it is found that a simple dielectric mixing formula can be used to predict the value of dielectric permittivity.

121

Micromachined Frequency Beam Scanning Patch Array Antenna at J-Band Armin Jam1, Mehrnoosh Vahidpour1, Jack East1, and Kamal Sarabandi1


This paper presents the design, fabrication and characterization of a frequency beam scanning array antenna operating from 230 GHz to 245 GHz. The array is designed using hollow rectangular waveguides with slot cuts placed on the H-plane of the waveguide wall. The slots in turn excite a linear patch array above it. The progressive phase shift between the slots is facilitated by meandered waveguide lines supporting TE10 mode. By changing the frequency, the propagation constant of the waveguide changes, which in turn will change the excitation phase of each slot and hence the beam is steered. This one-dimensional array forms a narrow beam width in the plane of slots while generating a wide beam in a plane perpendicular to that. In order to confine the beam in the elevation direction, the antenna aperture is widened by using slot-coupled patch arrays. This two-dimensional structure provides a two-dimensional confined beam. The patches are positioned on top of the slots separated by a dielectric substrate. The center patch is fed by the slot on the bottom layer of the substrate, while the rest are series-fed through the center one. One method to fabricate the antenna is the micromachining technique where the waveguide trenches are etched in silicon and then covered with gold. Next the slots are fabricated on a wafer and bonded to the other wafer to form the one-dimensional array. Finally, the patches are fabricated on a membrane which is then attached to the one dimensional array to form the complete antenna. This project is funded by Army Research Lab (ARL).The authors would like to thank M. Moallem and the staff at the Lurie Nanofabrication Facility (LNF), University of Michigan, Ann Arbor for their thoughtful comments and suggestions.

122

An Optically Transparent Two-Element Wideband Array Antenna with Unidirectional and Tilted Beam for Ground Vehicles M. Kashanianfard1, K. Sarabandi1

1 Departament of Electrical Engineering and Computer Science Department, University of Michigan

Wireless communication between vehicles is affected by some of the adverse effects of the communication channel such as multi-path fading, attenuation, non-line-of-sight, etc. To mitigate some of these effects, operation at lower frequencies (UHF and VHF) is often preferred for ad hoc communication networks. One drawback of operating at these frequencies for mobile platforms is the size of the antenna. In addition, for situations where different channels or space diversity are needed, the close proximity of many such antennas results in co-site interference and other undesired issues. Embedding the antenna in the windows of the vehicle eliminates the mentioned problems but imposes additional requirements such as optical transparency and unidirectionality (radiation inside the cabin is unwanted). To compensate for the tilt angle of the windshield, a two element phased array can be used. In this paper, a planar two element array antenna is designed to be embedded in the described window. A rigorous numerical optimization of the design parameters is performed and transmission line based matching circuits are designed to enhance the impedance matching and produce the required phase shift between the array elements. A number of balun designs are used and their effect on the radiation pattern and input impedance of the antenna is studied. The optical transparency of the antenna is improved by replacing the bow-tie antenna elements with a wire mesh of the same shape.

123

Large Signal Modeling of Intrinsically Switchable Ferroelectric FBARs and Its Application to Linearity Analysis of BST FBAR Filters Seungku Lee1, Victor Lee1, Seyit Sis1, and Amir Mortazawi1

1 Departament of Electrical Engineering and Computer Science, University of Michigan

This presentation presents the large signal modeling procedure of intrinsically switchable ferroelectric thin film bulk acoustic resonators (FBARs) as well as its application to FBAR filter linearity analysis. There has been a growing interest in ferroelectric FBARs due to their electric field dependent permittivity and electric field induced piezoelectricity. Ferroelectric barium strontium titanate (BaxSr(1-x)TiO3, BST) FBARs are intrinsically switchable, namely they have resonances that switch on with the application of a dc bias voltage. In this presentation, the large signal performance and nonlinear behavior of ferroelectric BST FBARs are investigated. Measurement results show that the device nonlinearity can be reduced by applying higher dc bias voltages. Moreover, a large signal model that accurately describes the dc bias voltage as well as RF power dependent performance of BST FBARs is developed. Large signal simulation results obtained from this model at different bias voltages and RF power levels show good agreement with the measurement results. Then, BST FBAR filters composed of two series FBARs and one shunt FBAR are designed, fabricated, and measured. IIP3 of more than 26 dBm for a 1.6-GHz filter with insertion loss of 4.1 dB is obtained. A linearity improvement technique for BST FBAR filters is also demonstrated through simulation using a nonlinear BST FBAR model.

124

Beam Shaping with Metamaterial Huygens’ Surfaces Carl Pfeiffer1, Anthony Grbic1


Metamaterials have demonstrated the ability to manipulate electromagnetic waves with unprecedented control. However, their notable thickness often leads to significant loss and fabrication challenges. This has motivated the development of metasurfaces: the two dimensional analog of metamaterials. Here, a new type of metasurface, referred to as a metamaterial Huygens’ surface, is introduced. Metamaterial Huygens’ surfaces are capable of arbitrarily manipulating electromagnetic wavefronts without reflection. These surfaces will likely find a wide range of beam shaping applications including: single-surface lenses, polarization controlling devices, stealth technologies, and perfect absorbers. A proof of concept Huygens’ surface was designed that refracts a normally incident plane wave to an angle of 45o from normal. The electric response is realized with loaded strips and the magnetic response is realized with split-ring-resonators. This structure was fabricated by stacking 58 identically patterned printed-circuit-boards, and measured with a near field scanning system. The half-powered bandwidth and peak efficiency were measured to be 24.2% and 86% respectively, which closely agreed with simulations. This work was supported by a US Air Force grant (FA4600-06-D003) and the National Science Foundation Materials Research Science and Engineering Center program DMR 1120923 (Center for Photonics and Multiscale Nanomaterials at the University of Michigan).

125

Simulation of Micro-Plasma Based Pressure Sensors* J. C. Wang1, Z. Xiong1, C. Eun1, X. Luo1, Y. Gianchandani1, and M. J. Kushner1

1 Departament of Electrical Engineering and Computer Science Department, University of Michigan, Ann Arbor, USA

Pressure sensors having dimensions of a few mm are used for automotive, biomedical and industrial applications based on piezoresistive and capacitive methods. Recently, a microplasma-based sensor has been developed for pressure measurements in harsh environments. In these sensors, a microplasma is sustained between an anode and two competing cathodes in a sealed chamber with a diaphragm mounted on one cathode. The external pressure deforms the diaphragm which then redistributes the current collected by the cathodes. Pressure is then measured based on the relative difference in currents. In this presentation, we will discuss the properties of microplasma-based pressure sensors using results from a two-dimensional simulation. The model, nonPDPSIM, solves Poisson’s equation and transport equations for charge species and electron energy equation for electron temperature. Radiation transport is addressed using a Green’s function approach. The microplasma is sustained between an anode (A) biased with hundreds of volts and two grounded cathodes (K1, K2) in a sealed chamber filled with 1 atm of Ar. The reference cathode (K1) is located adjacent to the anode (A) while the sensing cathode (K2) is mounted on the diaphragm separated by a gap of 10 μm. We find that a highly conductive plasma is first generated between AK2, and then repetitive ionization waves propagate along AK1. The current on K1 and K2 varies with inter-electrode spacing (AK2) which is changed by deflection of the diaphragm due to the external pressure. The current distribution can also be optimized by adjusting the impedance connected to electrodes. *Work was supported by the Advanced Energy Consortium.

126

Super-miniaturized Borehole Antenna Design and Radio-wave Estimation of Sub-surface Hydraulic Fractures at MF Band Jiangfeng Wu1, Kamal Sarabandi1


In this paper we present a medium frequency (MF) band helical dipole antenna for borehole application. The proposed antenna is loaded with a ferrite-bundle and is

optimized to achieve an ultra-compact size to fit within a volume of λ0/1337 × λ0/1337 ×

λ0/80 while maintaining a relatively high efficiency of about 20%. To feed the antenna from the center using an external source, the effect of a metallic cylinder placed in the center is also examined. The feeding network is designed to match the antenna input impedance with the frequency tunability. Based on the proposed antenna, a radio-wave technique for detecting and measuring the extent of hydraulic fractures in subsurface rock layers using MF band is developed. Compared with conventional high frequency mapping system, the penetrating distance has increased by one to two orders of magnitude due to the low propagation loss at MF band frequencies. The method is based on transmission measurements among elements of vertical synthetic arrays in the boreholes. The array patterns are optimized to minimize the direct-link from the transmitter antenna to receiver antenna. Post-processing maps the conductivity contrast in the target area with a good resolution.

127

Electrical Engineering: Integrated Circuits VLSI, MEMS, & Microsystems

Session Chairs: Cheng Zhang and Parinaz Naghizadeh Ardabili

128

HEMT-Based Read-out of a AlGaN/GaN Thickness-mode Resonators Azadeh Ansari1, Mina Rais-Zadeh1 1 Departament of Electrical Engineering and Computer Science, University of Michigan

AlGaN/GaN high electron mobility transistors (HEMTs) have been widely used in broad-band power amplifiers in base station applications due to high electron mobility in the two-dimensional electron gas (2DEG) channel and high saturation velocity. The high electron concentration of nitride HEMTs is induced by piezoelectric and spontaneous polarization of the strained AlGaN layer. Thus, Nitride HEMTs are very sensitive to mechanical pressure, which changes the piezoelectric polarization-induced surface and interface charges. In this work, the HEMT drain current is modulated with the strain induced in the 2DEG channel through a Schottky back gate contact. This work combines the benefits of piezoelectric actuation with HEMT-based sensing. Authors would like to thank staff at LNF for their help with fabrication and NSF for funding the project.

129

Fused Silica Platform for Inertial MEMS Devices Zongliang Cao1, Yi Yuan1, Guohong He1, Rebecca L. Peterson1, and Khalil Najafi1 1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI

This project aims to create an extremely compact platform for MEMS based inertial sensors. Such compact systems are ideally suited to mobile applications as well as navigational guidance where space is limited. In particular, we aim to build a high performance timing and inertial measurement unit (TIMU) with size comparable to an apple seed. Our TIMU consists of three single-axis accelerometers and three single-axis gyroscopes and a clock. Miniaturization is achieved via vertical integration of the devices and packing within the same framework. Fused silica, a non-traditional bulk material for MEMS, serves as both the structural material for the devices as well as packaging. This was enabled by newly developed silica etching capabilities here at the University of Michigan. It is expected that superior resonant devices of higher Q-factor can be built on fused silica due to its much lower material losses, enhancing device performance. In addition, its thermally and electrically isolating nature makes it ideal for packaging and low-power ovenization while also allowing for lower noise feedthroughs. To date, we have demonstrated seven working devices in a package smaller than 13 mm3 with 60 electrical feedthroughs. Challenges that remain are improving device sensitivity, vacuum packaging, and reducing mechanical coupling between devices.

This work is supported by DARPA TIMU award #N66001-11-C-4170. Portions of this work were performed in the University of Michigan’s Lurie Nanofabrication Facility

130

A 5.9-μm Pixel-Pitch, 336×256 Pixels 3-D Camera with Background Light Suppression over 100klx

Jihyun Cho1, Seokjun Park1, Euisik Yoon1

1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI, USA

Real-time depth profiling or imaging now became an essential part in human-computer interaction (HCI) and security systems. In these applications, the three dimensional (3-D) profile provides secure and stable information compared to conventional 2-D intensity images because 3-D information is independent of illumination conditions. Time-of-flight (TOF) is the most popular solution to realize the depth sensors due to its fast acquisition speed and sufficient resolution of centimeter range. However, TOF measurement relies on active illumination; thus, any extraneous light disturbs the measurement. For example, the sensor cannot produce any useful information when saturated by strong background light (BGL). For this reason, most TOF sensors are only used for indoor applications. To overcome this problem, some TOF sensors implemented the BGL suppression function by employing dedicated pixel-level circuitry at the cost of large pixel size, which makes it difficult to extend the array size for high resolution imaging. In this poster, a 3-D camera with column-level BGL suppression scheme is presented for high resolution outdoor applications. The sensor achieved over 100klx BGL suppression with the smallest pixel size of 5.9-μm among all reported TOF sensors. Though the array size in the prototype chip is QVGA, it can be easily extended to a larger array thanks to the smallest pixel. The array can also be dynamically reconfigured by binning and superresolution techniques, providing spatial and/or temporal resolution controllability. This, in turn, enables an adaptable imaging for the optimal performance in various conditions by compromising the spatial resolution, frame-rate, and BGL suppression performance. Acknowledgements This research was supported by Samsung Advanced Institute of Technology in South Korea.

131

Resonant Infrared Detector Arrays Vikrant J. Gokhale1 and Mina Rais-Zadeh1

1Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor

This work presents design, fabrication and measured results demonstrating the use of gallium nitride (GaN) based micromechanical (MEMS) resonator arrays as uncooled, high-sensitivity, fast response, low-noise infrared (IR) detectors. The resonator arrays batch fabricated using single crystal GaN-on-SOI, and commonly used MEMS process technology. Incident IR radiation is absorbed in a thin film silicon nitride absorber layer that is deposited in top of the mechanical resonators, causing a proportionate increase in the temperature of the device. This increased temperature changes the resonance frequency of the resonators. The mechanism of sensing is this change in frequency in proportion to the incident IR radiation. MEMS resonators can potentially provide highly-accurate and sensitive measurements even for low levels of incident radiation. Interfering effects such as changes in pressure or ambient temperature can be eliminated by comparing the sensor response to that of a reference resonator that is uncoated with silicon nitride, but identical in all other aspects to the sense resonator. Each array of sensors can have one such reference. The small format resonator array prototypes are characterized for their RF and thermal performance and exhibit a radiant responsivity of 1.68%/W, thermal time constant on the order of 556 µs and an average IR responsivity of -1.5 % when compared to a reference resonator, for a 100 mK radiation-induced temperature rise. The current results show promise for optimized designs that can compare with state of the art uncooled IR detectors.

This research was supported in part by the National Science Foundation and the Army Research Laboratory through participation in the MAST CTA.

132

A Reconfigurable Characterization, Control, and Compensation System for MEMS Rate and Rate-Integrating Gyroscopes Jeffrey Gregory1, Christopher Boyd2, Jong-Kwan Woo3, Khalil Najafi4 1 Departament of Electrical Engineering , University of Michigan – Ann Arbor

Inertial sensors are valuable in many applications including automotive, consumer electronics, robotics, vehicle navigation systems, and distributed environmental monitoring systems. MEMS gyroscopes and accelerometers offer the advantages of low power operation, small size, and reduced cost through batch fabrication. However, MEMS devices require a readout interface and control system in order to achieve high performance operation as sensors. Among these sensors, a gyroscope can be operated in a mode-matched rate-mode for increased sensitivity or rate-integrating mode for greatly increased dynamic range and bandwidth, however controlling this as a sensor is challenging. This work focuses on developing a software/hardware co-design to assist in the characterization, control, and compensation of MEMS gyroscopes. The platform was built using FPGA based hardware and open source software at a cost of less than $1000. When operated in the rate mode the system provides amplitude, rate, and quadrature closed loop feedback which improves the noise and stability performance over 400% compared to open loop operation. The system can also operate in rate integrating mode and has the advantage of continuous gyroscope operation, unlike previous systems where operation time is limited by ring down time. The next phase of this project will examine the effectiveness of multiple DSP-based control schemes for inertial sensors and implement an optimized control system on an ASIC. Our ultimate goal is to achieve a navigation-grade inertial microsystem which only occupies an area of 10mm3. The authors thank Mr. Robert Gordenker for testing support.

133

A Microdischarge-Based Monolithic Pressure Sensor Xin Luo1, Christine Eun2, Jun-Chieh Wang2, Zhongmin Xiong2, Mark Kushner2, Yogesh B. Gianchandani1, 2 1Mechanical Engineering, University of Michigan, Ann Arbor

2Electrical Engineering and Computer Science, University of Michigan, Ann Arbor

This work describes the investigation of a microdischarge-based approach for sensing the diaphragm deflection in a monolithically fabricated pressure sensor. Microdischarge-based transduction is advantageous for harsh environments, such as those encountered in oil exploration and production, because of its immunity to temperature and inherently large signals. The device consists of a deflecting Si diaphragm with a sensing cathode and a glass substrate with an anode and a reference cathode. The total exterior volume of the device is 0.05 mm3; typical electrode size and separations are 35 µm and 10 µm. Pulsed microdischarges are initiated in a sealed chamber formed between Si and glass chips and filled with Ar gas. External pressure deflects the Si diaphragm and changes the interelectrode spacing, thereby redistributing the current between the anode and two competing cathodes. The differential current, expressed as (I1-I2)/(I1+I2), is indicative of the diaphragm deflection which is determined by the external pressure. A 6-mask microfabrication process is investigated for device fabrication. Electrode connections to the interior of the chamber are provided by laser drilling and copper electroplating through high aspect ratio glass vias. The Si and glass substrates are bonded by Au-In eutectic. The re-distribution of plasma current between competing cathodes, as a consequence of diaphragm deflection over a range of pressure (0–40 MPa), was experimentally demonstrated.

134

A Pulsed High-Voltage Generator Utilizing a Monolithic PZT Element and Evaluation of Nonlinear Piezoelectric Behavior in Transient Mode Xin Luo1, Yogesh B. Gianchandani1, 2 1 Mechanical Engineering, University of Michigan, Ann Arbor

2 Electrical Engineering and Computer Science, University of Michigan, Ann Arbor

This work presents a monolithic pulsed high-voltage (HV) generator utilizing a single piezoelectric element (PZT51 disk, 5 mm in diameter and 740 µm thick) with electrodes series-connected via a flexible polyimide cable. The design, fabrication, assembly, and testing of the HV generator are described. In response to transient mechanical load, the HV generator is evaluated within the stress range from 1 MPa to 5 MPa, and the corresponding peak output voltages vary from 100 V to 900 V. Performance comparison between single-electrode pair HV generator without electrodes series-connection and three-electrode pair device indicates that series-connected electrodes on a monolithic PZT element greatly boost the output voltage under the same mechanical load conditions. In further tests, the generated high-voltage pulses exceed 1.35 kV and are successfully used to initiate microdischarges on monolithically patterned electrodes across a 75 µm air gap. The measured capacitance of the test HV generator is 25 pF and the calculated charge delivered to the terminal electrodes in each discharge is 34 nC. The nonlinear piezoelectric property of the PZT51 in transient mode is studied. We experimentally obtain a linear increase of the effective piezoelectric coefficient as the applied pressure increases within the range from 1 MPa to 5 MPa.

135

A Vibration Harvesting System for Bridge Health Monitoring Applications James McCullagh1 and Khalil Najafi1

1 Department of Electrical and Computer Engineering, University of Michigan, Ann Arbor, MI

Energy harvested from vibrations on a bridge can be used to power bridge health monitoring sensors. Sensing a bridge’s structural integrity at hard to reach positions will be made easier if energy can be harvested to power these sensors, eliminating the need for expensive and inconvenient wired power or battery replacement. This abstract presents a system comprising of electronics and an electromagnetic energy harvester used for harvesting the low-frequency, low amplitude, and non-periodic vibrations present on bridges. The energy harvester in this system is the Parametric Frequency Increased Generator (PFIG). The PFIG, designed at Michigan, uses a non-resonant architecture that up-converts the low frequency bridge vibrations found on bridges to higher frequencies. Multiple passive and active circuit designs have been built to boost, rectify, and store the PFIG’s output. A passive circuit design uses the PFIG’s two outputs that are fed into two transformers. The transformer outputs are fed into two cascaded three-stage Cockcroft multipliers. This design has been used in short-term and long-term testing on the New Carquinez bridge in CA. Best results showed that an average of 5 µW was harvested over a period of 120 seconds by the PFIG. The electronics could regularly charge a 10 µF storage capacitor to between 1 V and 2 V. Long-term tests have shown that the system has remained operational for 13 months demonstrating its robustness. A full-wave IC-based active diode charge pump capable of sub-threshold start-up and high efficiency harvesting with ~16× boosting has recently been designed for this system. This work was funded, in part, by National Institute of Standards and Technology (NIST) Technology Innovation Program (TIP) under Cooperative Agreement Number 70NANB9H9008

136

High-Q 3–D Resonators Fabricated with a Novel Blowtorching Molding Technique Tal Nagourney1, Jae Yoong Cho1, Khalil Najafi1 1 Departament of Electrical Engineering and Computer Science, University of Michigan

A novel method of producing high-Q three-dimensional resonators with a computerized blowtorch is introduced. A 100 µm-thick chip of fused silica is placed over a graphite mold, quickly heated to its softening point (~1585 °C), and pulled into the mold with vacuum. Fused silica has been selected in this case for its isotropic structure and high quality factor, but this technique can be applied to any material with a softening temperature within the ~2500 °C range of the propane-oxygen torch. Major advantages of this technique over traditional micromachining include the ability to make devices with a large height/width ratio, fast fabrication time (several seconds for feature definition), and low operating cost. This project focuses on the definition of hemispherical and half-toroid (birdbath) shapes, with potential application for a rate-integrating gyroscope. Using this technique, birdbath resonators with a resonant frequency of ~10 kHz and quality factor of 249k have been fabricated.

137

79.5pJ/pixel Bio-Inspired Time-Stamp Based Optic Flow Sensor for Micro Air Vehicles Seokjun Park1, Jaehyuk Choi1, Jihyun Cho1 and Euisik Yoon1

1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor,MI, USA

A vision-based autonomous navigation utilizing optic flow as front-end information is a promising approach for micro-air-vehicle (MAV) applications, not only because the power source of the MAV system is extremely limited, but also because its application is indispensable where GPS signal does not reach. Conventional optic flow algorithms, such as Lucas-and-Kanade, require huge amount of calculation; therefore, they require substantial digital hardware (CPU and/or FPGA) on a system. As an alternative approach, bio-inspired elementary motion detector (EMD) based algorithms (or neuromorphic algorithms) are studied and implemented in a form of analog VLSI circuits for autonomous navigation. However, pure analog signal processing is easily susceptible to temperature and process variations to provide a stable optic flow. Also, the analog processing should be implemented in pixel-level circuits; as a result, it is difficult to either scale the pixel size. In this paper, we report a bio-inspired analog/digital mixed-mode optic flow sensor. This sensor employs a time-stamp-based optic flow algorithm, which is modified from the EMD algorithm to give an optimum partitioning of hardware blocks in analog and digital domains. Temporal filtering is remained in a pixel-level analog processing unit. Feature detection and time-stamp latching blocks are implemented using digital circuits in column parallel. Finally, time-stamp information is decoded into velocity from simple arithmetic circuits, thus significantly reducing core digital processing power consumption. The sensor estimates 1-D optic flow from the integrated mixed-mode algorithm core and 2-D optic flow with an external time-stamp processing. The sensor provides 1-D 8-b optic flows at 79.5pJ/pixel. Acknowledgments This research was supported by the U.S. Army Research Laboratory under contract W911NF and prepared through collaborative participation in the Microelectronics Center of Micro Autonomous Systems and Technology (MAST) Collaborative Technology Alliance (CTA).

138

Piezoelectrically Transduced Fused Silica Higher-order Lamè Mode Resonators Adam Peczalski1, Zhengzheng Wu1, Vikram Thakar2, and Mina Rais-Zadeh1,2

1 Department of Electrical Engineering and Computer Science, University of Michigan - Ann Arbor

2 Department of Mechanical Engineering, University of Michigan - Ann Arbor

This paper reports a micro-machined piezoelectric MEMS resonator for use in timing devices. Microelectromechanical system (MEMS) resonators seek to replace current quartz-based timing references by offering a cheap, batch produced, small form factor alternative with equivalent or better performance. Fused silica was chosen as the resonating material for its strong thermal and mechanical characteristics, which include low acoustic loss, thermal conductivity, and coefficient of thermal expansion. An additional benefit of fused silica is its low thermoelastic damping (TED) at low MHz frequencies, where silicon devices can show significant loss. The resonating mode was chosen as a Lamè mode for its low anchor loss and TED, providing a high performance resonator. Higher-order Lamè modes were chosen in order to decrease motional impedance, increase power handling, and decrease squeeze-film damping, all of which are required to realize a high performance timing reference. This work shows fabricated resonators in both the second- and third-order Lamè modes. The second-order mode shows a center frequency at 8 MHz with a loaded Q of 17,400 (unload 18,100) and a motional impedance of 2.475 kΩ, while the third-order mode shows a center frequency at 12 MHz with a loaded Q of 17,300 (unloaded 18,400) and a motional impedance of 1.604

kΩ. The maximum measured f·Q product of these resonators is 2.071011, which is a 3x improvement over previously published fused silica devices. Future work will focus on improving device Q and further investigating designs for higher-order modes. This work was funded by DARPA under the Timing and Inertial Measurement Unit (TIMU) program.

139

iGC1: An integrated fluidic system for gas chromatography including Knudsen pump, preconcentrator, column, and detector, micro-fabricated by a three-mask process Yutao Qin1, Yogesh B. Gianchandani1

1 Departament of Electrical Engineering and Computer Science, University of Michigan

Abstract: This work reports an integrated micro gas chromatography (μGC) system, which contains four components: a Knudsen pump (KP), a preconcentrator-focuser (PCF), a separation column and a gas detector. All the four components are fabricated from glass wafers using a three-mask process with minimal post-processing. In a stackable architecture, the components are finally assembled into a 4-cm3 system. The Knudsen pump operates based on the thermal transpiration in nanoporous mixed-cellulose-ester membranes, and produces a measured 0.4 sccm air flow with 1 W power. The preconcentrator absorbs vapor analytes and produces a <2 sec injection peak. The column separates the analytes with an efficiency of ≈2600 plates/m. The gas detector creates microdischarges with emission spectra, which indicate the quantities of analytes eluting the column. The stacked system demonstrates the successful separation and detection of an alkane mixture in the range of C5-C8 in <60 sec. Acknowledgements: The study was supported in part by the Microsystems Technology Office of the Defense Advanced Research Projects Agency High-Vacuum Program (DARPA Contract #W31P4Q-09-1-0011). Facilities used for this research included the Lurie Nanofabrication Facility (LNF) operated by the Solid-State Electronics Laboratory (SSEL) and the University of Michigan. The authors thank Prof. Ken Wise and Mr. Robert Gordenker for providing access to test facilities, Mr. Seungdo An for wafer metallization, and Dr. Naveen Gupta, Dr. Jing Liu, Mr. Xin Luo, Prof. Katsuo Kurabayashi, and Prof. Xudong Fan for discussions.

140

Micro-Hydraulic Structure for High Performance Biomimetic Air Flow Sensor Arrays Mahdi M. Sadeghi1, Khalil Najafi1


We introduce a novel micro-hydraulic structure to significantly improve performance of many MEMS devices. The micro-hydraulic system in conjunction with application-specific appendages can realize high-performance sensors and actuators. For instance, biomimetic hair-like structures can provide airflow sensing with high accuracy and high resolution. Moreover, hairs with small footprints enable array fabrication to provide redundancy, fault tolerance and directional sensitivity. In previous works, the high accuracy is achieved at the expense of dynamic range. Using a micro-hydraulic structure we fabricated and tested a new type of low-power, accurate and robust flow sensor in which a hair-like appendage is used to translate flow into hydraulic pressure. This pressure is sensed with an integrated capacitor within the micro-hydraulic system by which the sensitivity is amplified. The airflow sensor can detect flow speeds ranging from about 2 mm.s-1 to over 15 m.s-1 with a resolution of 1.7 mm.s-1. This corresponds to about 78.9 dB of range to minimum detection ratio, which is the highest range over resolution ratio to our best of knowledge. An array of sensors can realize 2D directional sensing with 13° angular resolution.

The micro-hydraulic structure can be used as a platform to realize many cross-disciplinary high-performance devices. We have used this platform to make tactile sensors resembling human skin that are highly needed in humanoid robotics. Additionally, these structures have been tested in actuation mode to form micro-valves for micro-fluidic circuitry. The significant impact of this work is its advancement and applicability to other important research and commercial applications. This work is funded, in part, by MAST Program of the Army Research Lab under Award Number W911NF-08-2-0004.

141

Miniature Wireless Magnetoelastic Resonant Motor with Frequency Selectable Bi-directional Rotation Jun Tang1, Scott R. Green1, Yogesh B. Gianchandani1

1 Center for Wireless Integrated MicroSensing and Systems (WIMS2), University of Michigan

This work presents the analysis, fabrication, and experimental results of wirelessly actuated, chip-scale rotary motors. Two designs are described. Design M is actuated by a ø8 mm magnetoelastic stator lithographically micromachined from Metglas™ 2826MB-bulk-foil with 25 µm thick. It operates at a resonant frequency of 11.35 kHz while a 3 Oe DC and a 2 Oe-amplitude AC magnetic field are applied. The measured rotation speed, start torque, calculated driving step size, and payload are 44 rpm, 2 nN•m, ≈23 milli-degree and 9 mg, respectively. Design S uses a stator that is a sandwich of Si (ø8 mm diameter and 65 µm thick) and magnetoelastic foil (ø8 mm diameter and 25 µm thick) to tailor the stiffness. The typical resonant frequency of clockwise (CW) mode and counterclockwise (CCW) mode are 6.1 kHz and 7.9 kHz, respectively. The CCW mode provides a rotation rate of about 100 rpm, start torque of 30 nN•m, driving step size of 74 milli-degree, while a 8 Oe DC and a 6 Oe-amplitude AC magnetic field are applied. Bi-directional rotation is realized by switching the applied frequency, thereby exciting the stator in a slightly different mode shape. Design S shows at least 100 mg payload capability.

142

Technology for Fabricating Dense 3-D Microstructure Arrays for Biomimetic Hair-Like Sensors

Yemin Tang1, Rebecca L. Peterson1, and Khalil Najafi1

1 Departament of Electrical Engineering , University of Michigan, Ann Arbor

The project focuses on design, fabrication and simulation of highly-dense arrays of 3-D high-aspect ratio MEMS structures that can imitate biological hairs. Hair has many unique properties including high aspect ratios, local neural processing, robustness, and multiplicity of functions. A key feature of our arrays is the tall, 3-D structure which allows for spatially efficient integration of traditional MEMS resonators which use a large mass to bend a much smaller spring. The sensors can be combined in series or in parallel and can include local signal processing using underlying CMOS circuitry. We implement 2-axis capacitive acceleration sensor arrays. Each sensor consists of a proof mass atop a narrow post. The post acts as mechanical spring and the mass is surrounded by four walls for capacitive sensing of deflection. The sensor is fabricated using a silicon-on-glass (SOG) process. DRIE is used to define the small capacitive gaps while simultaneously etching more deeply to separate neighboring sensors. The device is modeled in COMSOL to maximize sensitivity within the available process windows. Based on these simulations, the mass height is fixed at 400 µm and the average gap is ~6 µm. The gap can be further reduced by refilling it. After DRIE the Si wafer is bonded to a glass wafer which has been prepared with recesses and metal electrodes. By taking advantage of high aspect ratio DRIE and SOG process, we have fabricated a new class of highly dense 3-D MEMS sensor arrays which offer improvements in performance, robustness, and multi-sensor functionality.

143

Optimization of support tether geometry to achieve low anchor loss in Lamé mode resonators Vikram Thakar1 and Mina Rais-Zadeh1,2 1 Department of Mechanical Engineering, University of Michigan, Ann Arbor

2 Department of Electrical Engineering, University of Michigan, Ann Arbor

The quality factor (Q) of micromachined resonators in the sub-GHz regime is most often limited by anchor loss (design dependent) rather than the fundamental material dissipation limits1. In this work we study the fundamental cause of anchor dissipation in Lamé- or wineglass-mode resonators and show that by optimizing the resonator tether geometry, low anchor losses can be achieved2, making it possible to reach the intrinsic f×Q limit of the resonator.

In order to support the Lamé-mode resonance, the tethers are required to undergo forced flexural vibrations. As a consequence the anchor loss in such resonators is strongly dictated by the resonance frequency of the tether and for tether geometries having resonances far from the Lamé-mode frequency, the device shows a much higher anchor Q. To verify this hypothesis, finite element analysis of the structures is performed using COMSOL using the Perfectly Matched Layer (PML) approach 3 . For experimental characterization, devices are fabricated on a low-resistivity SOI substrate with 1 μm actuation gaps. Both the simulation and measurement results are found to corroborate the presented hypothesis. Using such an optimization technique, a high-Q Lamé-mode resonator operating in its fundamental mode at 41.5 MHz is demonstrated with a Q of 296,000 (in vacuum, at room temperature, and 300 V bias). The f×Q of the resonator is 1.23×1013, which is close to the fundamental limit for silicon1.

This work is supported by NASA under the Chip-Scale Precision Timing Unit project. The authors acknowledge A. Peczalski and Z. Wu for useful discussions and staff at the LNF for their help with the device fabrication.

1 R. Tabrizian, M. Rais-Zadeh and F. Ayazi, Transducers, 2009.

2 L Khine and M. Palaniapan, J. Micromech. Microeng., vol. 19, pp. 015017, 2009.

3 D. Bindel and S. Govindjee, Int. J Numer. Meth. Eng., vol. 64, pp. 789-818, 2005.

144

Environmentally stable piezoelectric-on-silica MEMS oscillator Zhengzheng Wu1, and M. Rais-Zadeh1,2 1 Departament of Electrical Engineering Department, University 2 Mechanical Engineering Department, University

Microelectromechanical (MEMS) resonators and oscillator have shown great potential in realizing miniaturized and integrated timing references. In this work, a high performance MEMS clock reference is implemented for a chip-scale timing and inertia measurement unit. For the first time, we have demonstrated a low phase-noise MEMS oscillator based on a fused silica micro-mechanical resonator. The resonator is implemented using a piezoelectric-on-silica structure, achieving high quality factor (Q ~15,860) and low

motional impedance (Rm ~360Ω) at 5 MHz. By interfacing the resonator to a CMOS

amplifier, an oscillator phase noise of -138 dBc/Hz at 1 kHz and -155 dBc/Hz at far-from-carrier has been achieved. Vibration tests on the oscillator indicate a low acceleration sensitivity of less than 4 ppb/g. The noise performance of this oscillator is among the best between all reported MEMS oscillators. As an ultra-stable master clock, temperature stability of the oscillator is improved by combining both passive and active compensation techniques. A two-resonator temperature sensing and compensation scheme based on phase-lock technique has been designed. Low power and low noise CMOS integrated circuit design has been investigated in order to realize temperature sensing and the thermal control algorithms. Such active temperature compensation scheme is expected to reduce environment-induced drifts of the MEMS clock and other sensors on the platform by orders of magnitude. Therefore, the compensation can push the miniaturized silica MEMS sensor fusion platform to various demanding and emerging applications, such as inertia navigation.

145

Design, and fabrication of high aspect ratio MEMS meandering springs

Chuming Zhao1, Katherine Knisely+1, Karl Grosh1* 1 Department of Mechanical Engineering, University of Michigan, Ann Arbor

*[email protected]

Flexible meandering structures are often introduced in microelectrical-mechanical systems (MEMS) to increase mechanical compliance in prescribed directions of motion. In order to tune the device performance, an understanding of the stiffness of the spring structure is essential. Many variables in the microfabrication process can affect the meander compliance including choice of photoresist, exposure and development time, sidewall profile and undercut of photoresist. In this study, we present a finite element analysis (FEA) model, using COMSOL, which we use to optimize a high aspect ratio meander spring that has high lateral compliance and sufficient stiffness in orthogonal directions to resist motion under gravity, for instance. The spring is designed to be with width from 10um to 20um, height from 20um to 40um, amplitude from 50um to 100um, and length from 250um to 350um. A non-dimensional variable is introduced to study the effect of those geometric parameters. Different shapes of meanders are also studied. Selected designs are then fabricated in the Lurie Nanofabrication Facility (LNF) using lithography and gold electroplating. Gold is chosen as the material of the meanders for its high malleability and ductility. Trenches with height to width aspect ratio of 4:1 are achieved by using photoresist KMPR 1025 as the mold for electroplating. As high aspect ratio electroplating has a number of challenges, we discuss typical failures and potential issues of the fabrication process. The geometry of the FEA model is modified to fit the actual meanders in order to get a more accurate result.

146

Electrical Engineering: Optics, Photonics, and Solid-State Devices Session Chairs: Cheng Zhang and Parinaz Naghizadeh Ardabili

147

Vertical Ge/Si Nanowire Heterojunction Devices Lin Chen, Wayne Fung, and Wei Lu 1 Departament of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor

Different vertical nanowire heterojunction devices were fabricated and tested based on single Ge nanowire grown epitaxially at low temperature on (111) Si substrate. Vapor-Liquid-Solid growth and our transfer-free process resulted in a sharp and clean Si/Ge interface. The nearly-ideal Si/Ge heterojunction has a well-controlled, abrupt doping profile which was verified through material analysis and electrical characterization. In the nSi/pGe heterojunction diode, an ideality factor of 1.16, sub-picoampere reverse saturation current and rectifying ratio of 106 were obtained; while the n+Si/p+Ge structure leads to Esaki tunnel diodes with high peak tunneling current of 4.57 kA/cm2 and negative differential resistance at room temperature. The large valence band discontinuity between Ge and Si in the nanowire heterojunction was further verified in the p+Si/pGe structure, which showed a rectifying behavior instead of an Ohmic contact and raised an important issue in making Ohmic contacts to heterogeneously integrated materials. All measurement data can be well explained and fitted by theoretical models with known material parameters, suggesting that the Si/Ge nanowire system offers a very clean heterojunction interface with low defect density and holds great potential as a platform for future high density, high performance electronics. The authors acknowledge partial support of this work by the National Science Foundation (ECS-0601478 and ECCS-1202126). This work used the Lurie Nanofabrication Facility (LNF) at UM, a member of the National Nanotechnology Infrastructure Network (NNIN) funded by the NSF.

148

Stable few-layer MoS2 rectifying diodes formed by plasma-assisted doping Mikai Chen1, Hongsuk Nam1, Sungjin Wi1, Xiaogan Liang1 1 Mechanical Engineering, University of Michigan

Molybdenum disulfide (MoS2) and other two-dimensional layered transition metal dichalcogenides recently attracted a great deal of interest because of their excellent electronic, optoelectronic, and mechanical properties. To explore new mechanical/chemical mechanisms and process for tailoring the band structures of 2D LTMD micro-/nanostructures to achieve desirable characteristics for device applications in various fields, my first step is to develop upscalable techniques for realizing controlled doping and creating p-n junctions in MoS2 and other 2D semiconductors, which are demanded for making LTMD-based complementary electronic circuits and optoelectronic devices. To meet this milestone, I developed and studied a new doping method for creating stable p-n junctions in MoS2 using the selected-area plasma treatment of few-layer MoS2 flakes. Such plasma-doped diodes exhibit high forward/reverse current ratios and a superior long-term stability at room temperature. Furthermore, the transport and X-ray photoelectron spectroscopic characterizations of MoS2 transistors treated with different plasmas systematically confirm that the rectifying characteristics of plasma-created MoS2 diodes are attributed to plasma-induced p-doping and p-n junctions in MoS2. This method is anticipated to play an important role in the development of MoS2-based nanoelectronic devices. In addition, the presented plasma-assisted doping process has been demonstrated to be able to produce MoS2-based ambipolar and p-type transistors that have not been achieved by other groups. Acknowledgment. This work is supported by NSF grant CMMI-1232883 and ECCS-1307744. The authors would like to thank the staff of Electron Microbeam Analysis Laboratory for providing the support of XPS characterization; the staff of Lurie Nanofabrication Facility for providing the support of device fabrication.

149

Random Telegraph Noise and Resistance Switching Analysis of Oxide Based Resistive Memory Shinhyun Choi1, Yuchao Yang1, and Wei Lu1

1 Departament of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor

Resistive random access memory (RRAM) devices (sometimes termed “memristors”) are widely believed to be a promising candidate for future memory and logic applications. Although excellent performance has been reported, the nature of resistance switching is still under extensive debate. We perform systematic investigation of the resistance switching mechanism in a TaOx based RRAM through detailed noise analysis, and show the resistance switching from high-resistance to low-resistance is accompanied by the accumulation of oxygen-vacancies. Specifically, pronounced random-telegraph noise (RTN) with values up to 25% was observed in the device high-resistance state (HRS) but not in the low-resistance state (LRS). Through time-domain and temperature dependent analysis, we show the RTN effect shares the same origin as the resistive switching effects, and both can be traced to the (re)distribution of oxygen vacancies (VOs). From noise and transport analysis we further obtained the density of states and average distance of the VOs at different resistance states, and developed a unified model to explain the conduction in both the HRS and the LRS and account for the resistance switching effects in these devices. The authors thank J.H. Lee, L. Chen and P. Sheridan for useful discussions. This work was supported in part by the National Science Foundation (NSF) CAREER award (ECCS-0954621), and by the AFOSR through MURI grant FA9550-12-1-0038 and grant FA9550-12-1-0441. S.H. Choi is supported in part by Samsung Scholarship. This work used the Lurie Nanofabrication Facility at the University of Michigan, a member of the National Nanotechnology Infrastructure Network (NNIN) funded by NSF.

150

Radiative Decay Rate Enhancement of InGaN Site-Controlled Quantum Dots in a Silver Cavity Brandon Demory1, Tyler Hill2, Chu-Hsiang Teng1, Lei Zhang2, Hui Deng2, and Pei-Cheng Ku1 1 Department of Electrical Engineering and Computer Science, The University of Michigan, Ann Arbor, MI

2 Department of Physics, The University of Michigan, Ann Arbor, MI

InGaN quantum dots show single photon emission potential at higher temperatures, but the long radiative lifetimes on the order of tens of nanoseconds limit the potential applications. One way to address the long lifetimes is to increase the local density of states near the quantum dot. Coupling an emitter to a cavity alters its decay rate by the Purcell Factor and changes the density of states of the system. The Purcell factor for a metallic cavity depends on the dipole orientation, metal film thickness, and the spacing between the metal film and the emitter. By adjusting these parameters, we can change the magnitude of the decay rate enhancement and the ratio of the radiative enhancement to non-radiative enhancement. Simultaneously, due to the shape of our InGaN quantum dot pillar structure, the silver cavity’s resonance wavelength is highly tunable by adjusting the same film thickness parameters. Previously, we have shown Radiative decay rate enhancement and Photoluminescence Intensity enhancement using a silver cavity with a Quantum efficiency of 60% at the resonance wavelength of 430nm. In this work, we demonstrate that with an optimized cavity structure we can achieve Radiative decay rate enhancements of ~80x with a Quantum efficiency of 75% at the resonance wavelength of 460nm. This work is funded, in part, by the National Science Foundation

151

Electrically driven polarized single photon emission from InGaN quantum dot in a single GaN nanowire

Saniya Deshpande1, Junseok Heo1, Ayan Das1 and Pallab Bhattacharya1


48109-2122, USA

In a classical light source, such as a laser, the photon number follows a Poissonian distribution. For quantum information processing and metrology applications, a non-classical emitter of single photons is required. A single quantum dot (QD) is an ideal source of single photons and such single photon sources in the visible spectral range have been demonstrated with III-nitride and II-VI based single quantum dots. It has been suggested that short wavelength blue single photon emitters would be useful for free space quantum cryptography, with the availability of high speed single photon detectors in this spectral region. Here, we demonstrate blue single photon emission with electrical injection from an In0.25Ga0.75N quantum dot in a single nanowire. The emitted single photons are linearly polarized along the c-axis of the nanowire with a degree of linear polarization of ~70%.

152

Selection rule-based transmission filtering of a single-layer dielectric grating

Justin M. Foley1, Steve M. Young1, and Jamie D. Phillips1,2

1 Applied Physics Program, University of Michigan

2 Electrical Engineering and Computer Science Department, University of Michigan

Spectral manipulation is ubiquitous in today’s society where personal electronics including cell phones, tablets, computers, and cameras require the ability to focus light onto a CCD, reflect light back to a viewer’s eyes and filter light to provide red, green and blue pixels. Optical components used in these applications generally consist of metallic mirrors, glass lenses and absorption-based filters, which are ill-suited for many applications since ordinary glass is not transparent across all wavelengths, dyes are not always opaque, and metallic mirrors can absorb heavily upon transmission. Thermal imaging, in particular, is extensively used in surveillance, remote sensing, and spectroscopy where many conventional optical materials and components cannot function properly. Developing reliable and low-cost components to work in this spectral range would enable the next generation of thermal imaging systems, including hyperspectral capabilities where the electromagnetic spectrum is generated for each pixel within a viewing plane.

We report our progress on narrowband transmission filters based on lossless dielectric gratings that show potential to enhance thermal imaging capabilities. The optimized suspended silicon gratings exhibit greater than 90% reflectance between 8 and 14 µm at normal incidence with resonant transmission peaks developing away from normal incidence. We use finite element analysis to model the spectral response, which agrees well with the experimental results. Using modal analysis that permits complex propagation constants, we show the resonant phenomenon is a consequence of interference between wave-guided modes within the grating that can be understood using a simple slab waveguide model.

153

Stochastic memristive devices for computing and neuromorphic applications Siddharth Gaba1, Patrick Sheridan1, Jiantao Zhou+1, Shinhyun Choi1 and Wei Lu1

1 Departament of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor.

Nanoscale resistive switching devices (memristive devices or memristors) have been studied for a number of applications ranging from non-volatile memory, logic to neuromorphic systems. However a major challenge is to address the potentially large variations in space and time in these nanoscale devices. Here we show that in metal-filament based memristive devices the switching can be fully stochastic. While individual switching events are random, the distribution and probability of switching can be well predicted and controlled. Rather than trying to force high switching probabilities using excess voltage or time, the inherent stochastic nature of resistive switching allows these binary devices to be used as building blocks for novel error-tolerant computing schemes such as stochastic computing and provides the needed “analog” feature for neuromorphic applications. To verify such potential, we demonstrated memristor-based stochastic bitstreams in both time and space domains, and show that an array of binary memristors can act as a multi-level “analog” device for neuromorphic applications. The authors thank Dr. Zhengya Zhang, Phil Knag and Lin Chen for useful discussions. This work was supported in part by the AFOSR through MURI grant FA9550-12-1-0038 and by the National Science Foundation (NSF) through grant CCF-1217972. This work used the Lurie Nanofabrication Facility at the University of Michigan, a member of the National Nanotechnology Infrastructure Network (NNIN) funded by NSF.

154

Three-Dimensional Vertical Dual-Layer Oxide Memristive Devices Siddharth Gaba1, Chao Du1 and Wei Lu1 1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor.

The exponential growth in the semiconductor industry in the past a few decades has been largely driven by device scaling following Moore’s law. However, as the transistor size reaches sub-10 nm regime, continued scaling faces a number of fundamental and technical challenges. In addition to the lateral scaling based on continued shrinkage of the device size, vertical scaling that aims at enhancing the device performance or functionality through expansion in the vertical direction is now being widely researched for future memory and logic applications. In particular, resistive memories (RRAMs) based on two-terminal resistive switching devices have attracted broad attention due to their compatibility with vertical scaling In this poster, we fabricate and show that vertical, 3D dual layer resistive switching devices based on WOx exhibit well-defined analog memristive behavior. The device characteristics in the dual layer stack are closely matched and exhibit excellent incremental potentiation and depression characteristics with no degradation up to ten thousand cycles. The demonstration of vertical, multi-layer memristive devices fabricated in CMOS friendly fashion makes them well suited for analog memory or large-scale neuromorphic computing applications. The authors thank L. Chen, P. Sheridan and Dr. Y. Yang for useful discussions. This work was supported in part by the Air Force Office of Scientific Research (AFOSR) through MURI grant FA9550-12-1-0038. This work used the Lurie Nanofabrication Facility at the University of Michigan, a member of the National Nanotechnology Infrastructure Network (NNIN) funded by the NSF.

155

Molybdenum as a contact material for solution-processed zinc tin oxide thin film transistors Wenbing Hu1 and Rebecca L. Peterson1


Solution-processed zinc tin oxide (ZTO), as an indium-free transparent amorphous oxide semiconductor, is an inexpensive, non-toxic candidate for future printed electronics. For high-speed, high-current, short-channel thin film transistors (TFTs), the source and drain contact resistance must be minimal and stable. Here we show that Mo is a superior contact material for solution-processed ZTO TFTs. The gate electrode and dielectric are formed by p+-Si thermal SiO2. ZTO was deposited by spin-coating [1] and patterned by wet etch. ITO, Mo or Au/Ti source/drain electrodes were deposited and patterned by lift-off. The TFT channel length varies from 3 µm to 400 µm. Transmission line measurements are used to extract contact resistance properties. The width-normalized contact resistance of Mo/ZTO, Au/Ti/ZTO and ITO/ZTO, is 8.7Ω•cm, 90.7Ω•cm and 163.4Ω•cm respectively, comparable to or smaller than previously reported metal-ZTO contacts [2-4]. The small Mo/ZTO contact resistance results in a higher effective mobility of ~5.9 cm2/(V•s) for narrow channel devices. The results show that Mo can be used as a contact material for sub-micron TFTs. This project is funded by National Science Foundation ECCS Award #1032538. Portions of this work were performed in the Lurie Nanofabrication Facility, a site of the National Nanotechnology Infrastructure Network, which is funded in part by NSF. References: [1] Hu, et al., J. Mater. Res. 27 (2012) 2286. [2] Jackson, et al., Appl. Phys. Lett. 87 (2005) 193503. [3] Yang, et al., Appl. Phys. Lett. 98 (2011) 122110. [4] Avis, et al., J. Mater. Chem. 22 (2012) 17415.

156

High speed high sensitivity carbon-nanomaterial based chemical and biological sensors Girish Kulkarni1 and Zhaohui Zhong1

1 Department of Electrical Engineering and Computer Science, University of Michigan Ann Arbor

Nanosensors based on the unique electronic properties of 1-D and 2-D nanomaterials have the potential to revolutionize the field of rapid on-site chemical and biological detection. Most of the current nanoelectronic chemical and biological sensors rely ubiquitously on the detection of electrochemical potential or conductance change associated with the adsorbed charges on the surface. However, such charge-based direct-current (DC) detection has many limitations. For example, DC chemical sensors suffer from extremely slow sensing response and recovery (~10-100s of seconds), which arises from the slow dynamics of interface trapped charges. In biological sensors, direct-current detection fails in physiologically relevant background concentrations (~100mM), where the sensitivity of devices suffers from Debye screening effect due to mobile ions present in the solution. Here, we report a radically new sensing mechanism for chemical and biological detection wherein we operate carbon nanomaterial based field-effect-transistors as high-frequency mixers and measure the adsorbed molecules’ dipole moment rather the associated charge. We demonstrate for the first time, high speed (~0.1 s) and extremely high sensitivity (< 1ppb detection limit) detection of chemical vapors on a pristine graphene device without any surface functionalization. To demonstrate the universality of our technique, we use a carbon-nanotube based high-frequency mixer platform and detect streptavidin-biotin binding in 100mM background salt solutions, an environment where conventional charge-based techniques fail. These results not only open the door for a novel frequency-mixing based nanoelectronic sensing methodology, but can also lead to rapid and highly sensitive nanosensors ideally suited for real time on-site chemical/biological analysis. Acknowledgement: The work is supported by the National Science Foundation Scalable Nano-manufacturing Program (DMR-1120187). This work used the Lurie Nanofabrication Facility at University of Michigan, a member of the National Nanotechnology Infrastructure Network funded by the National Science Foundation.

157

Non-Destructive Wafer Recycling for Low-Cost Thin-Film Flexible Optoelectronics Kyusang Lee1, Jeramy D. Zimmerman1, Tyler W. Hughes2, and Stephen R. Forrest 1,2,3

1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor,

2

Department of Physics, University of Michigan, Ann Arbor 3 Department of Material Science and Engineering,

University of Michigan, Ann Arbor

Compound semiconductors are the basis for many of the highest performance optical and electronic devices in use today. Their widespread commercial application has, however, been limited due to the high cost of substrates. Device costs can, therefore, be significantly reduced if the substrate can be reused in a simple, totally non-destructive and rapid process. Here, we demonstrate a method that allows for the indefinite reuse and recycling of wafers, employing a combination of epitaxial “protection layers”, plasma cleaning techniques that return the wafers to their original, pristine and epi-ready condition following epitaxial layer removal and adhesive-free bonding to a secondary plastic substrate. We demonstrate the generality of this process by fabricating high performance GaAs-based photovoltaic cells, light emitting diodes, and metal-semiconductor field effect transistors that are transferred, without loss of performance, onto flexible and lightweight plastic substrates, and then the parent wafer is recycled for subsequent growth of additional device layers. Our process leads to a transformative change in, device cost, arising from the inevitable consumption of the wafer that accompanies conventional epitaxial liftoff followed by chemo-mechanical polishing. The authors thank Jaesang Lee and Xiao Liu for assistance with LEDs measurements, and the Army Research Laboratory MAST program and Global Photonic Energy Corp. for partial financial support of this work. .

158

Angle-insensitive color filters employing highly absorbing materials Kyu-Tae Lee1, Sungyong Seo1, Jae Yong Lee1, and L. Jay Guo1 1 Department of Electrical Engineering and Computer Science, The University of Michigan.

Color filters have played a crucial role as a key element for a wide variety of applications such as liquid crystal display, light emitting diodes, and complementary metal-oxide-semiconductor (CMOS) image sensors. Traditional color filters utilize organic dyes that are susceptible to surrounding environment, for example, longstanding UV illumination and high temperature resulting in a degradation of performance over time. Additionally, the size of the dye-based filters cannot be scaled down to the order of several hundred nanometers, mainly due to the small absorption of the color pigment. Owing to higher durability to both heat and constant UV radiation exposure, color filters, which rely on photonic subwavelength gratings based on guided-mode resonance, and plasmonic nanostructures, have recently been under intensive investigation to overcome the aforementioned problems. However, most plasmonic and photonic based color filters suffer from a resonance shift which occurs when light is incident upon the device at different angles of incidence. This resonance shift results in an undesirable color change, dramatically limiting the use of this type of filter today. Therefore, there is a strong need to improve the angular dependence property of color filters. Here, we demonstrate the color filters with wide viewing angles up to 70 degrees based on a strong resonance behavior in a lossy material. The underlying physics behind improved angular dependence of proposed filters is investigated by numerical calculation and experiment.

159

Observation of an unexpected ultrafast photo-Dember field in graphene

Chang-Hua Liu1, You-Chia Chang2, Ted Norris1.2 and Zhaohui Zhong1 1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109

2 Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, MI 48109

The photo-Dember effect arises from the asymmetric diffusivity of ultrafast photoexcited electrons and holes, which create a spatial charge distribution and transient dipole radiation. Conventionally, this effect was exhibited strongly in bulk semiconductors with the large asymmetry of electron-hole mobility, such as GaAs or InAs. In contrast, the photo-dember effect was principally considered negligible in graphene due to its similar electron and hole mobilities.. Here, we utilize photocurrent spectroscopy and observe the formation of intense photo-Dember field when exciting graphen-metal interface with femtosecond laser. Scanning photocurrent measurements reveal the polarity of photocurrent is determined by device mobility. Furthermore, ultrafast pump probe measurements indicate the magnitude of photocurrent is related to hot carrier cooling rate. Our simulations suggest intense field originates from graphene truly 2D nature combined with its low electronic specific heat. Taken together, our results indicate ultrafast photoresponse in graphene could be strongly correlated with its electrical properties, atomic structure as well as light-graphene interaction. This observations are both of fundamental interest and relevant for applications in future graphne-based terahertz emitters.

This work was supported by the National Science Foundation Center for Photonic and Multiscale Nanomaterials (DMR 1120923), and by NSF CAREER Award (ECCS-1254468). Devices were fabricated in the Lurie Nanofabrication Facility at University of Michigan, a member of the NSF National Nanotechnology Infrastructure Network.

160

Scattering nanostructures for angle selective light management in semitransparent photovoltaics Brian Roberts1, Qi Chen1, and P.-C. Ku1 1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor

Semitransparent photovoltaics (PVs) have the potential to enable widespread light harvesting when integrated with buildings and windows, though their conversion efficiency is limited by an intrinsic tradeoff between absorption and transparency. To address this drawback, we propose an angle selective PV window system which transmits normally incident light for visibility while selectively absorbing light at an elevated angle (including direct sunlight). This functionality can be realized by exploiting the optical backscattering properties of high aspect ratio nanostructures. Two nanostructured systems of interest are studied and described. Metal nanorods can be engineered to selectively backscatter angled light via their localized surface plasmon resonance, though they are difficult to fabricate and introduce optical losses to the system. Dielectric nanopores, such as those of self-assembled anodized aluminum oxide (AAO) films, can also enable angle selective light management via coherent scattering processes, including scattering to extreme near-horizontal angles and guided modes in accompanying PV films. Research supported as part of the Center for Solar and Thermal Energy Conversion (CSTEC), an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under Award # DE-SC0000957

161

Machine learning with memristive devices

Patrick Sheridan1, Wen Ma1, Chao Du1, Wei Lu1


Machine learning can improve the efficiency and accuracy of data analysis from a variety of sources, such as email spam filter and facial recognition technologies. While these learning algorithms can be implemented with traditional CMOS transistors, implementing them with novel nanoelectronic devices can save significant amounts of time, space, and energy. Further, the unique dynamics afforded by these devices mimic neuron behavior found in real biological systems. This work presents the simulation of machine learning tasks implemented with nanoelectronic resistive switching (memristive) device networks. Memristive device dynamics were modeled after tungsten oxide (WOx) devices, which were characterized using a set of diverse inputs. Spike-timing-dependent plasticity, a phenomenon observed in multiple brain regions, was employed to train the weights of neural network while conserving energy. The development of receptive fields, or input pattern selective neuron activation, in an unsupervised learning algorithm was demonstrated with potential uses in pattern recognition and image compression. Further, the study of nanoeletronic networks can provide insights into how neurons are able to collectively compute complex functions and can improve machine learning development and application. We would like thank DARPA for funding this research.

162

Polarization-controlled Single Photon Emission from Site-controlled InGaN Quantum Dots Chu-Hsiang Teng1, Lei Zhang2, Tyler Hill2, Brandon Demory1, Hui Deng2, Pei-Cheng Ku1 1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor

2 Department of Physics, University of Michigan, Ann Arbor

Single photon emission and potential single photon emitters have been studied extensively in the past decades because they are critical for quantum information technologies. Moreover, a lot of applications require linearly polarized single photon emission. In this work, we present a polarization control scheme of single photon emission from InGaN quantum dots (QDs) based on manipulating the QD geometry. The polarization control was achieved by engineering asymmetric strain relaxation and valence band mixing. Simulation was performed to investigate the strain and electronic structures and revealed that III-nitride QDs provide better polarization properties than other III-V QDs. Experimentally, InGaN QDs were fabricated by top-down approach. The shape, size, and position were determined by E-beam lithography. Micro-photoluminescence measurements were carried out and revealed linearly polarized emission and controlled polarization properties from InGaN QDs. More importantly, single photon emission with designated polarization properties was demonstrated experimentally for the first time.

163

Heterojunction n-ZnSe/p-ZnTe Solar Cells Alan S. Teran1, Chihyu Chen2, Jamie D. Phillips1, 2 1 Department of Electrical Engineering and Computer Science, The University of Michigan, Ann Arbor, MI

2 Department of Applied Physics, The University of Michigan, Ann Arbor, MI

Heterojunctions based on II-VI materials can be used to increase the efficiency of multi-junction solar cells, and may also offer the opportunity to realize next generation approaches such as the intermediate-band solar cell (IBSC) based on highly-mismatched alloys or quantum dots. One material of particular interest is ZnTe:O, where IB solar energy conversion has been demonstrated. Efficient doping in many II-VI materials, however, is often a major obstacle to achieving high-quality junction diodes. ZnTe is no exception, where efficient p-type doping is possible, but n-type doping is difficult to obtain. In this work, studies of n-ZnSe/p-ZnTe heterojunction solar cells grown by molecular beam epitaxy on GaAs and GaSb substrates will be reported. Dark current-voltage (I-V) measurements show improved reverse saturation current and ideality factor for the solar cells grown on GaSb. These improvements agree with I-V measurements done under illumination where short-circuit current (JSC,GaSb = 2.13 mA/cm2, JSC,GaAs = 0.53 mA/cm2), open-circuit voltage (VOC,GaSb = 0.84 V, VOC,GaAs = 0.54 V), and fill-factor (FFGaSb = 0.43, FFGaAs = 0.37) are improved for the solar cells grown on GaSb. Temperature dependent I-V (T-I-V) measurements allow us to identify and understand the nature of the limiting features of our solar cells, demonstrating a strong linear dependence of Voc on temperature with the solar cells grown on GaSb having larger activation energy (EA,GaSb = 1.55 eV, EA,GaAs = 1.44 eV). The design and future directions for ZnSe/ZnTe heterojunction solar cells will be presented, including the application of these heterojunctions to ZnTe:O IBSCs. This work was jointly funded by the National Science Foundation Materials World Network DMR-1006154 and the bilateral US-Spain Research Programme with Contract C11.0910B.01.

164

Dispersion Engineering for Vertical Microcavities using Sub-wavelength Gratings Zhaorong Wang1, Bo Zhang2, Hui Deng2 1 Department of Electrical Engineering and Computer Science Department, University of Michigan

2 Department of Physics, University of Michigan

Energy dispersion is a fundamental property of a confined system. It defines the distinct features of different dimensionalities—the density of states (DOS), effective mass, phase and group velocity of the eigen-modes. Dispersion engineering of the photonic modes has been implemented via metamaterial and photonic crystals to enable novel optical functionalities. However all existing methods have their limitations of either loss or evanescent nature. Here we show the possibility of engineering cavity dispersion using a high-index-contrast subwavelength grating (SWG) as the top mirror of a conventional DBR cavity. The phase responses of the SWG is investigated in a revealing way, which helps us to both understand the physical origins and guide dispersion engineering via the resonance phase condition. Our results imply many applications under the research area of cavity-quantum electrodynamics (CQED), particularly in polariton research and devices. Thanks NSF and AFOSR for funding. Thanks Pavel Kwiecien for rcwa-1d code.

165

Ultra-high efficiency small molecule photovoltaic cell with a fullerene-based electron filtering buffer

Xin Xiao1, Kevin J. Bergemann2, Jeramy D. Zimmerman1, Kyusang Lee1, Stephen R. Forrest1,2,3 1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI

2 Department of Physics, University of Michigan, Ann Arbor, MI

3 Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI

Small molecule organic photovoltaic (OPV) cells have attracted intense interest owing to

their high purity, ease of processing, and minimal batch-to-batch variation in device

performance. The power conversion efficiency (PCE), however, has not attained values of

interest for commercial use. Recently, we have developed an efficiency planar-mixed

heterojunction (PM-HJ) based on tetraphenyldibenzoperiflanthene (DBP) and C70. The

optimal cell has achieved a PCE of 6.4 ± 0.3% under 1 sun illumination. However, the fill

factor (FF) is relatively low, which limits the device performance. Here, we employ a

fullerene-based mixed buffer in PM-HJ cell, acting as an electron filter buffer, which can

spatially separate excitons and electrons and, therefore, reduce both bimolecular

recombination and exciton-polaron quenching. FF is significantly increased from 56 ± 1 %

to 66 ± 1 %. The optimal DBP:C70 cell with the electron filter buffer results in PCE = 8.1 ±

0.4% under 1 sun illumination, which is the highest reported efficiency for OPV cells

grown by vacuum thermal evaporation. Moreover, we incorporate DBP:C70 cells into a

tandem cell. Previous tandem cells demonstrated in our lab suffered from a low FF

characteristic of the SubPc:C70 graded HJ as a back subcell. By replacing the previous

back subcell with a DBP:C70 PM-HJ cell, along with a solvent-annealed blended

squaraine bilayer cell as a front subcell, the tandem achieves PCE = 8.3 ± 0.4 % under 1

sun illumination, which is, to our knowledge, the highest reported efficiency for small

molecule tandem cells in the literature.

This work was funded, in part, by the Center for Solar and Thermal Energy Conversion at the University of Michigan, the SunShot NextGenII Program of the Department of Energy, Global Photonic Energy Corp.

166

The Simulation on Pit-Defect in Stressed AlGaN/GaN High Electron Mobility Transistors by Nanostructure Evolution Jung Hsiang Yang1

1 Department of Electrical Engineering and Computer Science, University of Michigan-Ann Arbor

AlGaN/GaN high electron mobility transistors (HEMTs) has widely been designed to the high-frequency and high-power application for many years. However, when the device is operated at high voltage, an unpreventable electrical degradation is induced. The detailed studies about reliability issue are still required and the length of pit-defect is one of critical indicators to examine the performance of device. In this project, 2-D finite element method (FEM) is implemented to understand the growth of pit-defect near the gate contact edges by nanostructure evolution. The COMSOL with MATLAB software package is completely exploited in the overall study and the evolution model considers the interface migration, atom diffusion and the electric field from the applying voltage. The important dimensional parameters like gate length (Lg) and distance from gate contact to drain contact (Sgd) are carefully studied. There are three findings from the simulating results. First, the pit-depth growths in the source-side and drain-side have stronger linear relationship with the drain voltages. This confirms that the electrical degradation can possibly be more serious if the higher drain voltage applied under OFF-state. Second, the depths of pit-defect in both sides are inversely proportional to the Sgd. Moreover, a significant pit-defect growth when the Sgd decrease from 1 µm to 0.5 µm. Finally, the degree of pit-defect growth in the device becomes much larger with the decrease of gate length. It can be explained that the smaller gate length can dominate the pit-defect growth even though there is a long enough Sgd.

167

Electrical Engineering: Systems Engineering and Communication Session Chairs: Cheng Zhang and Parinaz Naghizadeh Ardabili

168

Polar Codes Achieve the Shannon Capacity and Rate- Distortion Function Aria Ghasemian1, Sahebi1, and S. Sandeep Pradhan1

1 Department of Electrical Engineering and Computer Sceince, University of Michigan

Polar codes were originally proposed by Arikan for discrete memory-less channels (DMCs) with binary input alphabets. Polar codes over binary-input channels are linear codes capable of achieving the “symmetric capacity” of channels and are constructed

based on the Kronecker power of the matrix

. It was later shown that Polar

codes can achieve the symmetric capacity of arbitrary DMCs. These codes are the first known class of codes achieving the symmetric capacity of channels with an explicit construction. The symmetric capacity of a channel is defined as the mutual information between the channel input and the channel output when the input distribution is confined to be uniform. The symmetric capacity coincides with the true (Shannon) capacity only for a small fraction of channels called symmetric channels and in general it can be very small compared to the true capacity of the channel. In this paper, we show that Polar codes can achieve the Shannon capacity of (binary or non-binary) DMCs. We show that using two polar codes, one contained in another, in the form of a “nested’ code, the input distribution of the channel can be “shaped” to any arbitrary distribution. The novelty of the approach is to break the (non-symmetric) channel coding problem into two simpler problems: A source coding problem with a symmetric source and a channel coding problem with a symmetric channel. We also show that Polar codes can achieve the true (Shannon) rate-distortion function for the source coding problem as opposed to the “symmetric rate-distortion” function available in the literature.

169

Group Learning and Opinion Diffusion in a Broadcast Network

Yang Liu1, Mingyan Liu1 1 Department of Electrical Engineering and Computer Science: Systems, University of Michigan, Ann Arbor

We analyze the following group learning problem in the context of opinion diffusion: Consider a network with $M$ users, each facing $N$ options. In a discrete time setting, at each time step, each user chooses $K$ out of the $N$ options, and receive randomly generated rewards, whose statistics depend on the options chosen as well as the user itself, and are unknown to the users. Each user aims to maximize their expected total rewards over a certain time horizon through an online learning process, i.e., a sequence of exploration (sampling the return of each option) and exploitation (selecting empirically good options) steps. Within this context we consider two group learning scenarios, (1) users with uniform preferences and (2) users with diverse preferences, and examine how a user should construct its learning process to best extract information from other's decisions and experiences so as to maximize its own reward. Performance is measured in \em weak regret, the difference between the user's total reward and the reward from a user-specific best single-action policy (i.e., always selecting the set of options generating the highest mean rewards for this user). Within each scenario we also consider two cases: (i) when users exchange full information, meaning they share the actual rewards they obtained from their choices, and (ii) when users exchange limited information, e.g., only their choices but not rewards obtained from these choices. This work is partially supported by the NSF under grants CIF-0910765 and CNS 1217689.

170

Closing the Price of Anarchy Gap in the Interdependent Security Game Parinaz Naghizadeh1 and Mingyan Liu1

1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor

The security of an interconnected system depends on the collective effort of all users in security technologies. As a result, investment in security by strategic users has been typically modeled as a public good problem, known as an Interdependent Security (IDS) game. The equilibria for such games are often inefficient, as selfish users free-ride on positive externalities of others’ contributions. In this paper, we present a mechanism that can implement the socially optimal equilibrium in an IDS game through a message exchange process, in which users submit proposals about the security investment and tax profiles of one another. This mechanism is different from existing solutions in that (1) it results in socially optimal levels of investment, closing the Price of Anarchy gap in the IDS game, (2) it is applicable to a general model of user interdependencies, (3) it does not need to monitor or audit users, record their incidents, or dictate their investments. We further consider the issue of individual rationality, often a trivial condition to satisfy in many resource allocation problems, and argue that with positive externality, the incentive to stay out and free-ride on others’ investment makes it harder to design an individually rational mechanism.

171

A Decentralized Routing Problem in a Simple Queueing System Yi Ouyang1, Demosthenis Teneketzis1 1 Department of Electrical Engineering and Computer Science, University of Michigan

The following routing problem in a queueing system with non-classical information structure is investigated in discrete time. A service system consists of two service stations and two controllers; one controller is affiliated with each station. Each station has an infinite size buffer. The service stations provide the same service with identical Bernoulli(μ) service time distributions and identical holding costs. Customers requiring service arrive at one of the service stations. The processes describing the two arrival streams are independent Bernoulli(λ).At any time, a controller can route one of the waiting customers in its own service station to the other service station. Each controller knows perfectly the workload in its own station. Furthermore, it observes perfectly the arrival stream to its own station as well as the arrivals due to customers routed from the other service station. The structure of the controllers' routing strategies that minimize the total expected holding cost is determined. Under certain conditions on the initial workload at each station, the controllers' optimal routing strategies are explicitly determined.

172

Computing sum of sources over an arbitrary multiple access channel Arun Padakandla1, Sandeep Pradhan1 1 Department of Electrical Engineering and Computer Science, University of Michigan

The problem of computing sum of sources over a multiple access channel (MAC) is considered. Building on the technique of linear computation coding (LCC) proposed by Nazer and Gastpar [2007], we employ the ensemble of nested coset codes to derive a new set of sufficient conditions for computing the sum of sources over an arbitrary MAC. The optimality of nested coset codes [Padakandla, Pradhan 2011] enables this technique outperform LCC even for linear MAC with a structural match. Examples of non-additive MAC for which the technique proposed herein outperforms separation and systematic based computation are also presented. Finally, this technique is enhanced by incorporating separation based strategy, leading to a new set of sufficient conditions for computing the sum over a MAC. This work was supported by NSF grant CCF-1111061.

173

PHY layer strategies based on algebraic codes for multiplexing information over broadcast networks Arun Padakandla1, Sandeep Pradhan1 1 Department of Electrical Engineering and Computer Science, University of Michigan

We present an achievable rate region for the general three user discrete memoryless broadcast channel, based on nested coset codes. We characterize 3-to-1 discrete broadcast channels, a class of broadcast channels for which the best known coding technique, which is obtained by a natural generalization of that proposed by Marton for the general two user discrete broadcast channel, is strictly sub-optimal. In particular, we identify a novel 3-to-1 discrete broadcast channel for which Marton's coding is analytically proved to be strictly suboptimal. We present achievable rate regions for the general 3-to-1 discrete broadcast channels, based on nested coset codes, that strictly enlarge Marton's rate region for the aforementioned channel. We generalize this to present achievable rate region for the general three user discrete broadcast channel. Combining together Marton's coding and that proposed herein, we propose the best known coding technique, for a general three user discrete broadcast channel. This work was supported by NSF grants CCF-0915619 and CCF-1116021

174

Symmetric Nash Equilibrium in Secondary Spectrum Market Shang-Pin Sheng1, Mingyan Liu1


We consider a secondary spectrum market where multiple primary license holders (sellers) seek to sell excess bandwidth to secondary users (potential) buyers. The channels are considered to be heterogeneous while the buyers are assumed to be identical. We compute the sellers' pricing strategy in the symmetric Nash equilibrium and show that the pricing decreases when channel quality increases.

175

Distributed Source Coding in Absence of Common Components

Farhad Shirani1


We introduce a coding scheme for the distributed source coding problem using two layers of codes. The first layer code is of constant finite block-length while the second layer code has block-length approaching infinity. We give a general achievable rate-distortion region for this scheme. It is shown that the scheme achieves the common component rate-distortion region in the case when the sources have a common component, while if the common component is replaced with highly correlated functions of the two inputs; it improves upon existing achievable bounds. We argue that it is beneficial to have the initial finite-length code to capture the high correlation between components of the two sources. We show that as the block-length of the first layer code is increased, the transmission rate required in the scheme decreases, reaches its minimum at some finite value and then increases. This phenomenon is not typically seen in traditional schemes used in multi-terminal source coding.

176

Generalised Proportional Allocation Mechanism Design for Multi-rate Multicast Service on the Internet Abhinav Sinha1, Achilleas Anastasopoulos1

1 Department of Electrical Engineering: Systems, University of Michigan

In multicast transmission on the Internet, agents are divided into multicast groups based on the content they demand. In addition, when multi-rate transmission is used, each user in the same multicast group may request different quality of service for the same content. With multi-rate multicast transmission, each link on the network carries only the highest quality content of each multicast group passing through this link, thus resulting in substantial resource savings compared to unicast transmission. In this paper two mechanisms are constructed that fully implement social welfare maximizing allocation in Nash equilibria for the case of multi-rate multicast service under the assumption of strategic agents for whom utilities are private information. The first applies to a Weak Budget Balance setting while the second applies to a Strong Budget Balance setting. The emphasis of this work is on full implementation, which means that all pure strategy Nash equilibria of the induced game result in the optimal allocations of the centralized allocation problem. The mechanism, which is constructed in a quasi-systematic way starting from the dual of the centralized problem, has a number of additional useful properties. Specifically, the proposed mechanism results in feasible allocation (in fact in Pareto optimal allocation) even off equilibrium. Finally, handling the Strong Budget Balance setting is shown as a simple extension to the mechanism for Weak Budget Balance.

177

Real-time Posterior Matching Scheme for Multiple Access Channels with Complete Feedback over DMC

Jui Wu1, Achilleas Anastasopoulos1 1 Department of Electrical Engineering: Systems, University of Michigan

An achievable rate region of the communication systems over a special class of multiple access channels (MACs) with two transmitters and one receiver with complete feedback was proposed by Cover and Leung and proved to be the capacity region by Willems. Inspired by the block-wise transmission scheme in their work, a sequential transmission scheme could be found. For analysis, first we view the communication system as an equivalent controlling system operating in discrete time which has sequential encoding and decoding strategies. With two-stage simplification, another equivalent system is derived with states which are the posterior distributions. Furthermore, from the converse part of the proof of the capacity region, a set of necessary conditions for variables in the system, such as independence between the current state and previous states, is derived. Based on the derived conditions and the simplified system, a communication system composed of a sequential posterior matching scheme is established.

178

Electrical Engineering: Control Systems, Power and Energy Session Chairs: Cheng Zhang and Parinaz Naghizadeh Ardabili

179

Robust Iterative Learning for High Precision Control through L1 Adaptive Feedback Berk Altın1, Kira Barton2 1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor

2 Department of Mechanical Engineering, University of Michigan, Ann Arbor

We introduce a modified robust iterative learning control (ILC) framework with L1 adaptive feedback for single-input single-output (SISO) linear time invariant (LTI) systems with iteration varying constant parametric uncertainties. We use the adaptive loop to compensate for nonrepetitive effects (exogenous disturbances and/or uncertainties) and ensure that the plant, as seen from the ILC input, is sufficiently close to its nominal value for performance improvement through learning. We reformulate the L1 controller to accommodate the feedforward input, which results in an adaptation that considers changes in the system trajectory due to learning. We present a rigorous stability analysis, and evaluate performance and trade-offs via simulation. Our findings indicate that the augmentation of the L1 controller with the feedforward input results in an overall controller that focuses on minimizing the reference tracking error. The design trade-off thus simplifies to the performance-robustness trade-off that can be seen in the respective domains of both controllers. This work was supported by startup funds from the University of Michigan.

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Control Signal Impact on HVAC Demand Response Efficiency Ian Beil1, Ian Hiskens1, Scott Backhaus2 1 Department of Electrical Engineering and Computer Science, University of Michigan

2 Condensed Matter and Magnetic Science, Los Alamos National Laboratory

Building heating, ventilation, and air conditioning (HVAC) represents a sizable portion of electrical grid loading. Reducing or offsetting HVAC power through demand response (DR) has been proposed as a way to alleviate power system stress while avoiding installation of peak generation. In this research, a commercial HVAC building has been equipped for DR control through global thermostat resets. A series of experiments was run to determine the additional energy needed to provide DR services and, by comparing this behavior to baseline performance, calculate a measure of efficiency. Results suggest that tuning of the HVAC system parameters and the types of control input applied have a significant impact on DR performance.

181

Monjolo: An Energy-Harvesting Energy Meter Architecture

Samuel DeBruin1, Bradford Campbell1, Prabal Dutta1


Conventional AC power meters perform at least two distinct functions: power conversion, to supply the meter itself, and energy metering, to measure the load consumption. This paper presents Monjolo, a new energy-metering architecture that combines these two functions to yield a new design point in the metering space. The key insight underlying this work is that the output of a current transformer – nominally used to measure a load current – can be harvested and used to intermittently power a wireless sensor node. The hypothesis is that the node’s activation frequency increases monotonically with the primary load’s draw, making it possible to estimate load power from the interval between activations, assuming the node consumes a fixed energy quanta during each activation. This paper explores this thesis by designing, implementing, and evaluating the Monojolo metering architecture. The results demonstrate that it is possible to build a meter that draws zero-power under zero-load conditions, offers high accuracy for near-unity power factor loads, works with non-unity power factor loads in combination with a whole-house meter, wirelessly reports readings to a data aggregator, is resilient to communication failures, and is parsimonious with the radio channel, even under heavy loads. Monjolo eliminates the high-voltage AC-DC power supply and AC metering circuitry present in earlier designs, enabling a smaller, simpler, safer, and lower-cost design point that supports novel deployment scenarios like non-intrusive circuit-level metering.

182

Energy Positioning: Economics and Control: Optimal Power Flow with Storage and Renewable Generation

Jennifer K. Felder1, Ian A. Hiskens2 1 Department of Electrical Engineering and Computer Science: Systems, University of Michigan


Solution algorithms for the optimal power flow (OPF) problem are well established for traditional electricity networks. However, there is an increasing need for integrating renewable sources and energy storage into electricity networks. These newer devices have physical properties that require modification of traditional OPF algorithms. In particular, energy storage devices introduce temporal coupling over the optimization horizon. This paper explores two algorithms that expand traditional OPF methods to incorporate energy storage devices and wind generation. The first method is based on a traditional LP-AC OPF method, while the second is a quadratic program with DC power flow constraints. The algorithms are demonstrated using several test cases that are based on a modified RTS-96 system. The performance of the two algorithms is compared in terms of convergence properties and quality/optimality of their respective solutions.

183

Mitigating Power Fluctuations in Electrical Ship Propulsion Using Model Predictive Control with Hybrid Energy Storage System Jun Hou1, Jing Sun1, 2, Heath Hofmann1 1 Department of Electrical Engineering and Computer Science, University of Michigan

2 Department of Naval Architecture and Marine Engineering, University of Michigan

Shipboard electric propulsion systems experience large power and torque fluctuations on their drive shaft due to propeller rotational motions and waves. This paper explores new solutions to address the fluctuations by integrating a hybrid energy storage system (HESS) and exploring coordinated power management. A propeller and ship dynamic model, which captures the underlying physical behavior, is established to support the control development and system optimization. Given the fact that both high and low frequency contents exist in the power fluctuations, a combination of battery pack and ultracapacitor bank is proposed, coordinated control is developed, and performance is evaluated in different sea conditions. Simulation results show that the proposed HESS with predictive model reference control provides substantial benefits in terms of reducing fluctuation and sustaining self-operation, compared to other solutions that involve batteries or ultracapacitors alone. Moreover, our analysis shows that the benefits of HESS are achievable only through both effective power management and device coordination.

Acknowledgement of the U.S. Office of Naval Research (ONR) and the Naval

Engineering Education Center (NEEC)

184

Hybrid dynamic modeling of legged robots with a spinal joint Mohammad Khodabakhsh1 1 Bio-Inspired Robotics Laboratory, Ecole Polytechnique Federale De Lausanne

Legged systems such as quadrupedal mammals are adept at moving on rough terrain, unreachable by wheeled vehicles. Many researchers have investigated the effect of morphology on the locomotive performance of legged robot in attempt to replicate animal ability [1, 2]. Consideration of various morphological properties such as actuation mechanisms, geometric specifications, and mass distribution allowed for improved locomotor performance. Since performing experiments on robotic platforms is costly and time-consuming, developing a mathematical model can be helpful. In this poster, we present a hybrid dynamic model for quadruped robots. Extending previous models, we include a rotational spinal joint and two point masses in each leg (lower and upper) connected by a prismatic actuator. Legs connect to trunk via a spring-damper. Elaborating the mass distribution of the legs allowed for a more realistic model of the collision effects at touchdown compared with the commonly used Spring Loaded Inverted Pendulum (SLIP) model. Implementing our model may allow for improved estimates of morphological parameters for the legged robots to be obtained. Funded by the European Union 231688 program. This work was performed during an internship in EPFL, Switzerland, summer 2011.

185

A Hybrid System Provides a Robust Alternative to a Linear Regulator

Matthew D. Kvalheim1, Shai Revzen1


"Multiple contact" animal gaits, in which multiple legs touch down nearly simultaneously, can be modeled by ordinary differential equations with periodic solutions and vector fields which are smooth except for discontinuities at states representing touch down -- they are "hybrid systems". The stability of such systems can be studied by considering the stability their Poincaré maps. We analyze a class of these hybrid systems in comparison to linear continuous systems with identical Poincaré maps. We compare the robustness to time-varying actuator disturbances of both the hybrid and linear systems through their effect on the Poincaré maps and present the two-dimensional case. Let p denote the fixed point of the Poincaré map corresponding to the unperturbed linear and hybrid systems, and let hn and cn denote the output of the nth iteration of the Poincaré map for the hybrid and linear systems, respectively. We show that as n approaches infinity, the Euclidean distance d(hn, p) is immune to suitably bounded actuator disturbances, whereas the Euclidean distance d(cn, p) depends linearly on actuator disturbances. We conclude that as a hybrid controller, this system is fundamentally more robust than a comparable linear regulator. This may help explain the widespread appearance of multiple contact gaits in many terrestrial animal species.

186

Grazing Concepts for Reachability Analysis of Uncertain Power Systems Maxim Markov1, Ian A. Hiskens1 1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI

The dynamic behaviour of power systems is affected by many parameters that cannot be easily quantified. Load model parameters provide an important example. When major disturbances occur, more often than not the match between the measured and simulated responses is substandard, with load models being a major contributing factor. Likewise, as renewable generation grows, its inherent variability will challenge the usefulness of traditional approaches to dynamic security assessment that currently rely almost exclusively on forward simulation. We will describe an innovative suite of numerical continuation algorithms for analysis and design of power systems with slow and fast timescales, coupled components, and with state resets and switches typical of models of power systems. These algorithms provide understanding of changes in the observed dynamics as system parameters change, and hence can be used for assessing the impact of parameter uncertainty. In order to scale the continuation methods to high-dimensional hybrid systems with competing timescales, new trajectory-discretization algorithms based on asynchronous collocation methods and associated mesh-adaptation strategies have been developed. The above techniques form the basis for reachability analysis that can be used to assess the vulnerability of power systems to undesirable outcomes. This reachability assessment uses the fact that trajectories which graze the boundary of an undesirable region of state-space demarcate acceptable from unacceptable behaviour. Such grazing trajectories can be incorporated into the collocation methods via a boundary-value formulation. Multi-dimensional covering algorithms can then be applied to obtain bifurcation diagrams that establish boundaries, in parameter space, between safe and unsafe operation.

187

Reactive Power Limitation due to Wind-Farm Collector Networks Jonathon A. Martin1, Ian A. Hiskens1

1 Department of

Electrical Engineering and Computer Science, University of Michigan

Type-3 and Type-4 wind turbines are capable of contributing to the reactive power required by wind-farms for supporting grid voltages. However, characterizing the maximum reactive power capability of a wind-farm by summing the individual generator ratings does not account for the effect of voltage variations over the radial collector network and can significantly overestimate the total reactive power production capacity. This paper uses a continuation process to show that maximum reactive power production can be achieved by sending a common control signal to all turbines. The outcome of the continuation process is explored using an interior-point optimization algorithm. Analysis suggests that global optimality is achieved. Several examples demonstrate how generator voltage limits can significantly curtail the reactive power output requested by the control strategy. This improved characterization of wind-farm reactive power production will enable better design and operation of wind-farm reactive power resources, reducing the need for additional shunt capacitors and Statcoms.

188

Transmission Constrained Economic Dispatch: A Public Goods Approach

Erik Miehling and Demosthenis Teneketzis1 1 Department of Electrical Engineering and Computer Science, University of Michigan

This report offers a solution to the transmission constrained economic dispatch (TCED) problem when the agents’ utilities are their private information, agents are non-strategic, and losses are taken into account using a modified DC power flow method. The modified DC power flow allows us to solve for the system operating point more accurately than with the standard DC power flow method. We approach the problem by treating the system as a public goods network. We first formulate the centralized information problem with losses; we approximate the total system losses by a strictly convex quadratic function of the vector of power injections at all nodes in the network; we distribute the losses among the generators in the system using participation factors. The centralized information problem is, in general, non-convex. We proceed to solve this non-convex problem as follows. We decompose it into a sequence of linearized subproblems each of which is convex; the solution of each subproblem in this sequence is the linearization point of the next subproblem in the sequence. The solutions of this sequence of subproblems converge to the optimal solution of the original centralized non-convex problem. For each convex subproblem in the above sequence we propose an externality algorithm which satisfies the TCED problem’s informational constraints and converges to the optimal solution of the subproblem. We thus obtain a nested iterative method/algorithm which satisfies the TCED problem’s informational constraints and converges to the optimal allocation of the original non-convex centralized TCED problem.

189

Nonlinear Internal Model Controller Design for Wastegate Control of a Turbocharged Gasoline Engine Zeng Qiu1, Jing Sun2, Mrdjan Jankovic3, Mario Santillo3 1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor

2 Department of Naval Architecture and Marine Engineering, University of Michigan, Ann Arbor

3 Ford Motor Company

This work investigates the design of nonlinear internal model control (IMC) for wastegate control of a turbocharged gasoline engine. We extend the inverse-based IMC design for linear time-invariant (LTI) systems to nonlinear systems. A fourth-order nonlinear model which sufficiently describes the dynamic behavior of the turbocharged engine is implemented to serve as the model in the IMC structure. To leverage the available tools for LTI IMC deign, we have explored the quasi linear parameter varying (quasi-LPV) model. IMC design through transfer function inverse of the quasi-LPV model is ruled out due to parameter variability. A new approach for nonlinear inverse, referred to as the structured quasi-LPV model inverse, is developed and validated. The controller based on this nonlinear inverse is then designed to achieve boost pressure tracking. Finally, simulations on a validated high fidelity model are carried out to show the feasibility of the IMC. Its closed-loop performance and robustness are compared with a well-tuned PI controller with extensive feed-forward and anti-windup built in. I would like to acknowledge Ford Motor Company for their sponsorship. I wish to show appreciation to Prof. Jing Sun for her patient guidance and instructions, and to Mrdjan Jankovic and Mario Santillo for their valuable and constructive suggestions.

190

Resilient Monitoring System for Boiler/Turbine Plant M. T. Ravichandran1, S. M. Meerkov1 and H. E. Garcia2 1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109,

USA 2 Idaho National Laboratory, P. O. Box 1625, Idaho Falls, ID 83415-3675, USA

Resilient monitoring systems are sensor networks that degrade gracefully under malicious attacks on their sensors, which cause them to project misleading information. The goal of this work is to design, analyze, and evaluate the performance of a resilient monitoring system intended to monitor the condition (normal or anomalous) of a boiler/turbine (B/T) plant. A main feature of the system considered here is that process variables that characterize the B/T plant are not independent, which leads to the possibility of inferring the state of one variable using measurements of the other. A four-layer monitoring system architecture is developed, which consists of data quality assessment, process variable assessment, plant condition assessment, and sensor network adaptation layers. The measure of resiliency of the monitoring system is quantified using Kullback-Leibler divergence and is shown, using simulations, to be sufficiently high in several attack scenarios. W.-C Lin of Idaho National Laboratory is acknowledged for his participation in this research. Support for this research has been provided by the U.S. Department of Energy under DOE Contract DE-AC07-05ID14517 and performed as part of the Instrumentation, Control, and Intelligent Systems (ICIS) initiative at the Idaho National Laboratory.

191

A Robust Adaptive Controller for Surface-Mount Permanent Magnet Machines David M. Reed1, Jing Sun2, and Heath Hofmann1 1 Department of Electrical Engineering and Computer Science, University of Michigan

2 Department of Naval Architecture and Marine Engineering, University of Michigan

High torque density and the potential for high efficiency have made Surface-Mount Permanent Magnet machines an attractive option for many high-performance drive applications. However, parameter variations due to temperature changes, skin effect, and magnetic saturation, can detune the transient characteristics of the drive, and cause large mismatches in torque regulation. The approach presented in this paper utilizes a combination of adaptively tuned feedforward and feedback-decoupling terms, in addition to standard proportional feedback for added robustness. The resulting controller achieves consistent transient response characteristics with zero steady-state error over a wide range of operating points, without the use of integral control. The adaptive law is derived using Lyapunov's stability theorem, and a robust switching σ-modification is used to prevent parameter drifting due to the presence of unmodeled disturbances. Additionally, overactuation is exploited to allow the use of persistently exciting inputs without compromising the control objective (torque regulation). The performance of resulting robust adaptive torque regulator is analyzed and tested numerically in Simulink. Experimental results confirm the performance of the proposed adaptive controller. This work was supported by funding from the U.S. Office of Naval Research (ONR) and the Naval Engineering Education Center (NEEC).

192

Mitigating the Impact of Wind Power Variability on Sub-transmission Networks

Sina Sadeghi Baghsorkhi1 and Ian Hiskens1

1 Department of Electrical Engineering and Computer Sciences, University of Michigan

Wind power variability, in weak grids, can significantly alter the voltage profile and flow patterns across the network. Due to high sensitivity of voltage magnitudes to wind injection, distribution (<40kV) and sub-transmission (40-120kV) network operators are requiring the voltage at the point of interconnection of the wind farm to be “strictly” regulated. The introduction of large sizes of local reactive compensation (for voltage regulation) is starting to interfere with the key voltage regulator of distribution and sub-transmission networks, the on-load tap changing transformer (OLTC). We have investigated this interaction and proposed a coordinated voltage control scheme that minimizes the tap-changing operations of OLTC transformers induced by variation in wind generation. This method, by reducing the tap operations extends the lifetime of these critical and costly components of the power system while facilitating larger penetration levels of wind power.

193

Optimized Energy Harvesting Methods and Power Electronics for Variable Capacitive Devices Aaron Stein1 and Heath Hofmann1 1 Department of Electrical Engineering: Systems, University of Michigan

The utility of wireless sensor nodes can be extended by harvesting ambient energy to power them. Variable capacitive energy harvesters are typically micro-electromechanical systems (MEMs). In order to effectively harvest energy from these devices, highly-efficient power electronic circuitry is extremely important and can be the difference between generating or losing energy during the harvesting cycle. Two basic methods of harvesting energy from these devices are known: Constant Voltage and Constant Charge. However, other harvesting cycles have been developed which combine the properties of the basic methods: the Passive Method and the Constant Charge with a Parallel Capacitor Method. All four methods have been reported; however, the literature is lacking a formal comparison of these methods. This paper evaluates these four methods while considering circuit efficiency as a parameter. By including efficiency as a parameter new fundamental properties can be derived: a threshold efficiency for energy harvesting, analytical solutions for optimal operating conditions, and a more realistic comparison of the four methods at nominal operating conditions. These properties demonstrate the advantage of using the passive method and lead to a proposed design which implements two DC-DC converters to operate the variable capacitive device at its optimal operating conditions.

194

Optimal Energy Procurement from a Strategic Seller with Renewable Generation Hamidreza Tavafoghi1, Demosthenis Teneketzis 1 1 Department of Electrical Engineering and Computer Science, University of Michigan

We consider a mechanism/contract design problem for energy procurement, when there is one buyer and one seller. We assume that the buyer has all the bargaining power and therefore is the mechanism designer. The seller has the ability to generate power from a conventional plant and a non-conventional plant (renewable). The generation from the non-conventional plant is not deterministic, it depends on a random variable W (e.g. weather), which is realized at the time of production, and the seller's technology, which is her private information. There is a cost of energy produced from the conventional plant; this cost depends on the seller's technology, which is her private information. The seller's expected utility is given by the payment she receives from the buyer for the energy delivered minus the expected cost of energy production. The buyer's utility is given by his benefit from the energy he receives minus the payment he makes to the seller. This utility is the buyer's private information. The objective is to design a mechanism/contract that maximizes the buyer's expected utility, and guarantees the voluntary participation of the seller. We prove that the solution to the problem is a menu of contracts from which the seller chooses one based on her technologies.

195

Ensuring Privacy in Location-Based Services: An Approach Based on Opacity Enforcement Yi-Chin Wu1, Karhik Abinav2, Stéphane Lafortune1 1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor

2 Department of Computer Science and Engineering, Indian Institute of Technology, Madras

Opacity is an information-flow property that characterizes whether the secret of the system can be inferred by an observer. In this work, we study the location privacy in Location-Based Services (LBS) as the notion of opacity in Discrete Event Systems. We show that privacy can be enhanced using the framework of opacity insertion enforcement mechanism that we proposed in our prior work. Non-deterministic finite state automata are used to capture the mobility model of LBS users. Using the opacity verification techniques, we show how LBS server can infer the accurate location of the user by tracking queries that contain only generalized spatial information. To enhance location privacy, we deploy i-enforcing insertion functions that insert fictitious queries to the user’s original query sequences. With the i-enforceability property, the insertion functions provably generate convincing fictitious queries such that modified queries are always consistent with the mobility model and thus LBS server can never know for sure the user’s accurate location. Finally, to minimize the overhead from fictitious queries, we design an optimal insertion function that introduces the minimum average number of fictitious queries. This work was partially supported by the NSF Expeditions in Computing project ExCAPE: Expeditions in Computer Augmented Program Engineering (grant CCF- 1138860).

196

A General Approach for Synthesis of Supervisors for Partially-Observed Discrete-Event Systems

Xiang Yin1, Stéphane Lafortune1 1 Department of Electrical Engineering and Computer Science, University of Michigan

We revisit the synthesis of supervisors for partially-observed discrete-event systems from a new angle, based on the construction of a new structure called the All Inclusive Controller (or AIC). We consider control problems for safety specifications, where the legal language is a prefix-closed sublanguage of the system language. We define the AIC as a transition system that embeds all safe supervisors and thus all controllable and observable sublanguages of the legal language. The structure of the AIC is that of a bipartite graph, reminiscent of a game between the supervisor and the system, with (i) control states, where all safe control decisions are enumerated, and (ii) system states, where all feasible observable system events are executed. The states of the AIC are information states, i.e., subsets of system states. We present an algorithm for the construction of the AIC. This algorithm exploits the pre-computation of the so-called extended specification, which makes the safety of a control state a function of the current information state alone, thereby allowing for on-the-fly construction of the AIC, if so desired. We discuss the properties of the AIC. We also describe how the AIC can be used for synthesis of supervisors that posses desired maximality and/or optimality properties. This work was partially supported by the NSF Expeditions in Computing project ExCAPE: Expeditions in Computer Augmented Program Engineering (grant CCF-1138860).

197

Finite-Element-Based Computationally-Efficient Electric Machine Model Suitable for Integration in Vehicle Design Optimization Kan Zhou1, Andrej Ivanco2, Zoran Filipi2, Heath Hofmann1 1 Department of Electrical Engineering and Computer Science, University of Michigan

2 Department of Automotive Engineering, Clemson University

Electric machines and their corresponding power electronic circuitry are not only a key component of electric/hybrid electric vehicle powertrains, but also play important roles in traditional vehicles as generators to provide on/off-board power generation. It is therefore important that vehicle-system-level design and control engineers have access to accurate computationally-efficient, physics-based modeling tools of the electromagnetic behavior of electric machines. The ability to quickly generate and simulate electric machine designs is crucial for vehicle-level design and optimization. For example, efficiency maps of an electric machine design are a useful tool for vehicle system designers. In this paper, electric machine design scaling techniques are proposed to easily and flexibly generate new machine designs. The efficiency maps of the scaled designs are then calculated based on a “base design” database generated by 2D magneto-static finite element analysis (FEA), without the necessity of re-solving computationally-intensive FEA for each scaled designs. Results show that the proposed techniques can be extremely useful for vehicle powertrain-level or system-level design and optimization. With these techniques, powertrain or system designers can easily and quickly adjust the characteristics and the performance of the machine in ways that are favorable to the overall vehicle performance. *This work is supported by the Automotive Research Center (ARC), a U.S. Army Center of Excellence for Modeling and Simulation of Ground Vehicles led by the University of Michigan. This work has been submitted to the 2014 Twenty-Ninth Annual IEEE Applied Power Electronics Conference and Exposition (APEC).

198

Electrical Engineering: Signal and Image Processing Session Chairs: Cheng Zhang and Parinaz Naghizadeh Ardabili

199

Accelerated MRI Field Map Estimation Michael J. Allison1, Jeffrey A. Fessler1


In magnetic resonance imaging (MRI), inhomogeneity in the main magnetic field can cause artifacts. However, these artifacts can be corrected with accurate estimates of the field inhomogeneity. The majority of field inhomogeneity estimators use multiple scans with varying echo times to avoid phase wrapping in the estimate. One such method [1], uses a penalized-likelihood approach consisting of a sinusoidal data-fit term and a quadratic regularizer that promotes smoothness in the estimate. This method is highly accurate and robust to phase wrapping, but its current minimization strategy is computationally expensive. In this work, we develop methods to accelerate the computation of this estimator. We begin by extending the separable quadratic surrogate (SQS) minimization method in [1] to define a set of quadratic surrogate functions for the penalized-likelihood cost function. We then consider two minimization frameworks where we can use these functions: Huber's algorithm for quadratic surrogates [2] and a non-linear conjugate gradient (NCG) method. For the case of Huber's algorithm for quadratic surrogates, the minimization strategy requires iteratively solving a linear system of equations based on our quadratic surrogate functions. For the case of the NCG method, we use our quadratic surrogate functions for both preconditioning the problem as well as for a monotonic line search strategy [3]. Numerical experiments on a simulated dataset found that all of the minimization methods converged to similar estimates with our new methods doing so approximately 20 times faster than the existing SQS method. This work was funded, in part, by NSERC and NIH-CA87634. [1] A. Funai et al., IEEE-TMI, 27(10), 2008. [2] P. Huber, Robust Statistics, pp. 184-5,

1981. [3] J. A. Fessler et al., IEEE-TMI, 8(5), 1999.The

200

Performance of Regularized Canonical Correlation Analysis (RCCA) Nicholas Asendorf1, Raj Rao Nadakuditi1 1 Department of Electrical and Computer Engineering, University of Michigan

Multi-modal data fusion is a challenging but common problem arising in fields such as economics, statistical signal processing, medical imaging, and machine learning. In such applications, we have access to multiple datasets that use different data modalities to describe different system features. Canonical correlation analysis (CCA) is a multidimensional data fusion algorithm used to extract correlated features from exactly two datasets. CCA uses the SVD of the empirical covariance matrices to find a linear transformation for each dataset such that the transformed datasets are maximally correlated. However, when the number of observations is less than the combined dimension of the datasets, CCA deterministically returns a perfect correlation between the datasets. In an effort to overcome this undesired property of CCA, a regularized version (RCCA) is regularly employed in the sample starved regime. In this work, we explore the performance of RCCA. We first use random matrix theory to theoretically predict the distribution of the RCCA correlations when the data matrices are purely noise. We then compare the performance of CCA and RCCA when used to detect the presence of a correlated signal in noisy datasets. This analysis shows that RCCA provides little improvement in detection performance and is especially sensitive to the choice in regularization parameter. Motivated by insights from random matrix theory, we provide an informative CCA (ICCA) algorithm that, unlike CCA and RCCA, is able to reliably detect correlated signals in the sample starved regime. Work partially supported by the US Army Research Office (ARO) under grant W911NF-11-1-0391.

201

Deep Community Detection using Local Fiedler Vector Centrality Pin-Yu Chen1 and Alfred O. Hero1

1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor

In this poster, a new centrality called local Fiedler vector centrality (LFVC) is proposed to analyze the connectivity structure of a graph. It is associated with the sensitivity of algebraic connectivity to node or edge removals and features distributed computations via the associated graph Laplacian matrix. LFVC can be related to a monotonic submodular set function that guarantees that greedy node or edge removals come within a factor 1-1/e of the optimal non-greedy batch removal strategy. Due to the close relationship between graph topology and community structure, we use the proposed centrality measure to detect deep and overlapping communities on various real-world social network datasets. Compared with conventional community detection method, the results offer new insights on community detection by discovering new significant communities and key members in the network. Notably, LFVC is also shown to greatly outperform other well-known node centralities for revealing communities embedded in a graph.

202

Improving Isotropy and Uniformity of Spatial Resolution and Noise Characteristics for low-dose 3D Axial X-ray CT Jang Hwan Cho1, Jeffrey A. Fessler1 1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI

Improved noise and spatial resolution properties are one of the potential advantages of statistical image reconstruction methods over conventional filtered back-projection (FBP) reconstruction. Regularized image reconstruction methods, such as penalized weighted least squares (PWLS) method or a penalized likelihood (PL) method, provide noise control by integrating a roughness penalty into the cost function. Although statistical weighting and system models are responsible for improving image quality, their interaction with a conventional quadratic roughness penalty results in images as anisotropic and nonuniform spatial resolution and noise. Due to the large number of voxels in the image volume, regularization design methods based on discrete Fourier transforms would require prohibitive computational cost. In this study, we propose two quadratic regularization design methods for 3D axial X-ray computed tomography (CT) that aim to improve isotropy and uniformity of resolution and noise, respectively. In addition, the developed method is not limited to improving isotropy and uniformity, but can be used for promoting other user-defined characteristics. Simulations and a phantom experiment show that the proposed methods lead to more uniform and isotropic spatial resolution and noise characteristics in 3D axial CT with modest computational cost.

203

Spatio-Temporal Analysis of Gaussian WSS Processes via Complex Correlation and Partial Correlation Screening With Applications to Financial Data Hamed Firouzi1, Dennis Wei1, Alfred Hero1 1 Department of Electrical Engineering: Systems, University of Michigan

We propose a framework for spatio-temporal correlation analysis of jointly Gaussian Wide Sense Stationary (WSS) multivariate time series. The goal is to identify the hub time series, i.e., the ones that are highly correlated with a number of other time series. When the dimension of the multivariate time series and the number of time samples are relatively large, direct correlation analysis in the time domain could be computationally intractable. As an alternative, we apply the Discrete Fourier Transform to the time series and perform correlation analysis in the frequency domain. We extend the previous theory of hub screening to the complex domain to accommodate complex-valued Fourier transforms. The theory allows p-values to be assigned to time series for being a hub under the null hypothesis that the time series are independent of each other. It also specifies thresholds for which thresholded sample (partial) correlation matrices can be used to identify hubs. We then use an independence property of Gaussian WSS time series in the frequency domain to perform multiple inference for detecting hub time series. Experimental results on both synthetic data and real financial data illustrate the accuracy of our theoretical results and the usefulness of the proposed framework. The research in this paper was supported in part by AFOSR grant FA955013-1- 0043.

204

Kronecker Sum Decompositions of Spatio-Temporal Data Kristjan Greenewald1, Theodoros Tsiligkaridis1, Alfred O. Hero III1 1 Department of Electrical Engineering and Computer Science, University of Michigan

In this paper we consider the use of the space vs. time Kronecker product decomposition in the estimation of covariance matrices for spatio-temporal data. This decomposition imposes lower dimensional structure on the estimated covariance matrix, thus reducing the number of samples required for estimation. To allow a smooth tradeoff between the reduction in the number of parameters (to reduce estimation variance) and the accuracy of the covariance approximation (affecting estimation bias), we introduce a diagonally loaded modification of the sum-of-kronecker products representation (Tsiligkaridis et al. 2013). We derive an asymptotic Cramer-Rao bound (CRB) on the minimum attainable mean squared predictor coefficient estimation error for unbiased estimators of Kronecker structured covariance matrices. We illustrate the accuracy of the diagonally loaded Kronecker sum decomposition by applying it to video data of human activity. This research was partially supported by ARO under grant W911NF-11-1-0391 and AFRL under grant FA8650-07-D-1220-0006.

205

An Iterative, Backscatter-Analysis Based Algorithm For Increasing Transmission Through Highly-Backscattering Random Media Using Phase-modulated Wavefronts

Curtis Jin1, Raj Rao Nadakuditi1, Eric Michielssen1, and Stephen Rand1

1 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48104

Materials such as turbid water, white pain and egg shells are opaque because it is impossible for light to pass straight through them. In such media, the randomly arranged particles cause light to scatter in random directions, thereby frustrating its passage. As the thickness of a slab of highly scattering random medium increases, this effect becomes more pronounced, and less and less light is transmitted through. Surprisingly, it turns out that there are a few highly transmitting wavefronts that achieve perfect transmission through such media. We describe new, physically-realizable algorithms that rapidly construct these wavefronts using backscatter-analysis only and describe phase-only modulated variants of these algorithms that enable their implementation in optical experiments using phase-only spatial light modulators. This work was supported by an NSF-CCF award.

206

Fast ordered subsets optimization algorithms using momentum for statistical X-ray CT image reconstruction Donghwan Kim1, Sathish Ramani2, and Jeffrey A. Fessler1 1 Department of Electrical Engineering and Computer Science, University of Michigan

2 CT Systems and Applications Laboratory, GE Global Research Center

X-ray computed tomography (CT) has been criticized for its radiation exposure to the patients, and the CT industry and researchers have responded by developing a reduced-dose CT machine with sophisticated statistical image reconstruction algorithms to deal with the noisier measurement data. Statistical image reconstruction provides good images from low-dose scans, but requires very long computation time for minimizing an X-ray CT statistical cost function. Therefore, our goal is to develop fast optimization algorithms for statistical X-ray CT problems. Ordered subsets (OS) methods are widely used in tomography problems including CT, accelerating the convergence by the number of subsets ‘M’ in early iterations, by using only a subset of a measurement data per iteration for computational efficiency. Here, we further accelerate OS algorithms by introducing a momentum approach that dramatically speeds up the convergence rate. We particularly combine the OS algorithm with Nesterov’s momentum algorithms, leading to a promising ‘M2’ times acceleration in early iterations. However, we have observed unstable behavior of the algorithm in some cases, and we propose to adapt diminishing step sizes to stabilize the algorithm while preserving the fast convergence rate. A real 3D helical CT scan is used to examine the acceleration of the proposed algorithms. This work was supported in part by GE Healthcare, the National Institutes of Health under Grant R01-HL-098686, and equipment donations form Intel.

207

Regularized Image Reconstruction for Parallel MRI using ADMM

Mai Le1, Sathish Ramani2, Jeffrey A. Fessler1 1 Department of Electrical Engineering and Computer Science, University of Michigan

2 GE Global Research Center

To reduce motion blur, decrease operation costs, and improve spatial and temporal

resolution, a number of methods to accelerate MRI have been proposed. Sensitivity

Encoded (SENSE) MRI is a method of receiving spatially encoded signals simultaneously

on multiple receive coils, and Compressed Sensing inspired undersampling techniques

have also been proposed to reduce acquisition time. Both SENSE and random

undersampling require spatial regularization for good image quality, but sparsity-based

regularization involves computationally costly nonlinear optimization. Variable splitting

algorithms seek to minimize computation time by decoupling a single, costly nonlinear

optimization into several smaller problems of less computational complexity. In particular,

the AL-P2 method in [1] demonstrated very fast convergence speeds, but did not satisfy

known sufficient conditions for convergence. Here, we present variable splitting

algorithms that satisfy the conditions for the Alternating Direction Method of Multipliers

(ADMM) and subsequently convergence. In particular one proposed method exploits the

structure of 1st-order finite difference regularizers to apply fast tridiagonal matrix

inversions in the inner variable updates. Preliminary results indicate that the image quality

of the new algorithm, ADMM AL-P2 is comparable to that of other variable splitting

methods. Further experiments will compare the speed of ADMM AL-P2 and AL-P2, and

further analysis will characterize the behavior as a function of several algorithmic

parameters.

1. S. Ramani and J.A. Fessler. Parallel MR image reconstruction using augmented

Lagrangian methods, IEEE Trans. Med. Imag., 30(3):694-706, March 2011

208

Sparse positive-definite FIR filter design with Schatten p-norm optimality Madison G McGaffin1, Jeffrey A Fessler1 1 Department of Electrical Engineering:Systems, University of Michigan

Many models in signal processing can be usefully approximated with circulant operators. Because circulant matrices are diagonalized by the discrete Fourier transform, the inverses of these circulant approximations are easy to compute. These model inverses are particularly useful in preconditioner design for gradient-based optimization, where an efficient approximation to the inverse of the cost function Hessian is used to determine a good search direction. Traditional convergence theory requires that these preconditioners be positive-definite to ensure convergence, which is simple to enforce on a dense circulant matrix. The traditional approach to applying these operators is a pair of fast Fourier transforms and a few scalar operations. In some applications, even the conventionally "fast" FFT is unacceptably slow. The FFT is also not ideally suited for modern highly parallel architectures like the GPU, which favor highly localized memory accesses. In these cases, a few-tap finite impulse response (FIR) filter implemented with convolution is considerably more efficient. In this work we consider the problem of designing an FIR filter with few taps that "best" approximates (in a Schatten p-norm sense) a given dense circulant matrix, while also remaining positive definite. We propose an iterative algorithm to solve this design problem and demonstrate the effectiveness of our FIR filter-based preconditioners on a challenging denoising problem. Supported in part by NIH grant R01 HL 098686 and a hardware donation by Intel.

209

Distributed Learning of Gaussian Graphical Models via Marginal Likelihoods Zhaoshi Meng1, Dennis Wei1, Ami Wiesel2 and Alfred O. Hero III1 1 Department of Electrical Engineering and Computer Science, University of Michigan

2 School of Computer Science and Engineering, The Hebrew University of Jerusalem

We consider distributed estimation of the inverse covariance matrix, also called the concentration or precision matrix, in Gaussian graphical models. Traditional centralized estimation often requires inverse of full covariance matrix through expensive global inference, which can be computationally intensive in large distributed networks. In this work, we propose a general framework for distributed estimation based on a maximum marginal likelihood (MML) approach. Each node independently computes a local estimate by maximizing a marginal likelihood defined with respect to data collected from its local neighborhood. Due to the non-convexity of the MML problem, we introduce and solve a convex relaxation. The local estimates are then combined into a global estimate without the need for iterative message-passing between neighborhoods. We analyze the behavior of the proposed estimator in the classical asymptotic regime, and also derive its rate of convergence to the true parameters in the high-dimensional scaling regime. We show that under certain assumptions the error due to our computational relaxation is only a lower-order term compared with the intrinsic statistical estimation error. Numerical experiments validate our theoretical findings and demonstrate the improved performance of the two-hop version of the proposed estimator, which almost closes the gap to the centralized maximum likelihood estimator at a reduced computational cost. This research was supported in part by ARO grant W911NF-11-1-0391 and ISF 786/11.

210

OptShrink: An optimal algorithm for estimating a low-rank matrix buried in noise Brian Moore1 and Rajesh Rao Nadakuditi1 1 Department of Electrical Engineering and Computer Science, University of Michigan

We propose a novel spectral algorithm for estimating a low-rank matrix buried in noise. Our approach is motivated by recent results in random matrix theory on the eigenvalues of low-rank perturbations of large random matrices. Specifically, we leverage this theory to design an optimal data-driven shrinkage function to apply to the eigenvalue spectrum of the observed data. We show that the resulting algorithm is asymptotically optimal and, in particular, strictly outperforms the ubiquitous principal component analysis (PCA) estimator and its so-called robust generalizations. OptShrink is optimal for a large class of noise models, including the standard setting of independent and identically distributed (i.i.d.) Gaussian noise. Our analysis provides first-principles justification for the use of non-convex shrinkage functions in spectral optimization. We also show that our algorithm asymptotically solves a certain matrix optimization problem with non-convex regularizer. OptShrink has no tuning parameters, so it can be safely integrated into any system that requires low-rank matrix estimation. We validate our theoretical results with numerical simulations and motivate future research on some related open problems. This work was supported by an ONR Young Investigator Award N000141110660, an AFOSR Young Investigator Award FA9550-12-1-0266, a NSF award CCF-1116115 and an ARO MURI grant W911NF-11-1-0391.

211

Optimal fusion of multiple, noisy adjacency matrices for improving community detection Himanshu Nayar1, Raj Rao Nadakuditi1 1 Department of Electrical Engineering and Computer Science Department, University of Michigan, Ann

Arbor

We consider the problem of extracting common community structure from multiple noisy adjacency multiple matrices. We derive an asymptotic expression for the optimal linear combining coefficients that leverages analytical insights from Random Matrix Theory to improve the probability of correct detection. We validate our results using simulations and show that the fusion techniques developed can identify community structure even when community structure cannot be reliably identified from any of the individual adjacency matrices.

212

Energy Efficient Source Localization on a Manhattan Grid Wireless Sensor Network Matthew A. Prelee1 and David L. Neuhoff1

1 Department of Electrical Engineering and Computer Science Department, University of Michigan

In the area of wireless sensor networks, several decentralized algorithms have been developed to solve the problem of locating a source that emits acoustic or electromagnetic waves, based solely on received signal strength. There are many motivations for implementing decentralized algorithms, including the fact that they reduce the number of transmissions between sensors, thereby prolonging sensor battery life. Whereas most such algorithms are designed for arbitrary sensor placements, including random placements, this work focuses specifically on applications that allow an a priori choice of sensor placement. In particular, to ensure small communications cost, it is proposed to place sensors uniformly along evenly spaced rows and columns, i.e., a Manhattan grid. The Midpoint Algorithm is proposed for such a placement, which is a simple noniterative decentralized algorithm. This work demonstrates that Manhattan grid networks offer an improved accuracy vs. energy tradeoff over randomly distributed networks. Results also show that the proposed Midpoint Algorithm offers a gain in energy savings over the recent POCS algorithm. This work was supported by NSF grant CCF 0830438.

213

Rapid Prediction of Image Noise Variance for 3DCT with Arbitrary Trajectories Stephen M. Schmitt1, Jeffrey A. Fessler1


Fast variance prediction for iteratively reconstructed helical CT images is useful for analysis of resulting images and potentially for dynamic dose adjustment during a scan. Previous methods require impractical computation times to generate an approximate map of the image variance; other methods are able to approximate variance quickly but only for specific CT geometries. We present an approximation to the local frequency response of projection and back-projection for third-generation CT geometries. We also present an application of this frequency response to predict the variance of iteratively reconstructed helical CT images. Compared to the empirical variance derived from multiple simulated reconstruction realizations, our method is accurate in most of an image to within 15% while being computable for over 2000 voxels per second. This work was supported in part by NIH grant R01 HL-098686.

214

The Performance of MUSIC-based DOA in White Noise with Missing Data Raj Tejas Suryaprakash1 and Raj Rao Nadakuditi1


Multiple Signal Classification (MUSIC) is a widely used algorithm for estimating the direction of arrival (DOA) of signals impinging on a sensor array. We analyze the performance of MUSIC-like algorithms in the large array setting, where we have relatively few signal-plus-white-noise snapshots, and where only a random, sample-independent fraction of the data is observed. Using recent results from random matrix theory, we obtain a closed-form, minimal stochastic representation for the DOA estimation error, that captures how the performance depends on the number of sensors, number of snapshots, Signal-to-Noise ratio (SNR) and the probability of observing an entry of the data matrix. This minimal representation facilitates accurate computation of the DOA mean squared error (MSE) and other desired statistics. Our analysis brings into sharp focus the presence of a phase transition that separates a regime where MUSIC-based algorithms accurately localize a source, from a regime where the source is present but the algorithms fail. The critical phase transition threshold depends on the number of sensors, the number of samples and the probability of observing an entry of the data matrix in a simple manner that we make explicit. We validate our asymptotic theoretical predictions with simulations.

215

Real-time Visual Scene Understanding for an Indoor Navigating Agent Grace Tsai1, Benjamin Kuipers2

1 Department of Electrical Engineering: Systems, University of Michigan

2 Department of Computer Science and Engineering, University of Michigan

How can an indoor navigating agent with vision sensor learn about its local environment? In this work, we present the Planar Semantic Model (PSM), a semantic geometric representation for the local 3D indoor environment. The PSM is a coarse-grained description of the indoor environment in terms of meaningful planes (the ground plane and the walls), instead of a low-level fine-grained representation like a point cloud. The PSM is capable of representing partial knowledge of the local environment so that unknown areas can be incrementally built as observations become available. We demonstrate an on-line method that efficiently constructs the PSM of the local environment from a monocular camera, in real-time, without the need for prior training data or the Manhattan-world assumption. Our method generates and evaluates a set of qualitatively distinct PSM hypotheses and refines the parameters within each hypothesis quantitatively. Our method is a continual, incremental process that transforms current PSM hypotheses into children hypotheses describing the same environment in more detail. This work has taken place in the Intelligent Robotics Lab in the Computer Science and Engineering Division of the University of Michigan. Research of the Intelligent Robotics lab is supported by grants from the National Science Foundation.

216

Learning To Classify With Possible Sensor Failures Tianpei Xie1, Nasser Nasrabadi2, Alfred O. Hero III1 1 Department of Electrical Engineering, systems, University of Michigan, Ann Arbor

2 US. Army Research Lab

Corruptions and sensor failure are inevitable in real signal processing systems and it is well-known that the max-margin classifier, such as Support Vector Machine (SVM) is sensitive to such anomalous events. In this project, we propose an efficient algorithm to train a robust max-margin classifier when the corrupted measurements are present in the training set. By incorporating a non-parametric prior based on the empirical distribution of the training data, the proposed Geometric-Entropy-Minimization regularized Maximum Entropy Discrimination (GEM-MED) method would perform classification and anomaly detection in a joint manner. We demonstrate that our method can yield improved performance over the conventional Ramp-loss-based classification methods in terms of both classification and detection accuracy in simulated data set and real footstep data set. Acknowledgement: the research in this paper was partially supported by ARO grant WA11NF-11-1-103A1

217

Study of complex bilevel image quality

Yuanhao Zhai1, Prof. David Neuhoff1 1Department of Electrical Engineering and Computer Science Department, University of Michigan

Bilevel images are images with only two intensity levels: black and white. Different from text, silhouettes and halftones, the bilevel image in which we are interested are complex “scenic images”, which contain natural scenes, e.g. landscapes and portraits. Several lossy coding algorithms have been developed to compress such images. Four of such are studied in this project. Traditionally, percentage error is used as a metric to quantify the fidelity of compressed bilevel images, which is equivalent to mean squared error (MSE) in the bilevel case. However, this metric is not always consistent with human perception. Some images with similar percentage error appear very different to viewers. To develop a better metric to quantify bilevel image fidelity, the first step is needed to collect human judgments about a series of bilevel images with different distortions.

This project includes two parts. The first part is a survey designed to collect human judgments about different distorted bilevel images. The database images are formed using all four existing compression methods with different compression qualities, together with three manually added distortions: random flip, erosion and dilation. The results provide the ground truth with which to compare different compression methods. The second part of this project is to developing an objective bilevel image quality metric, based on the ground truth obtained in part one. The new metric includes the features using the concepts of adjusted percentage error, connected component and binary gradient histogram and gives significantly better predictions of bilevel image quality than percentage error.

218

Industrial and Operations Engineering: Operations Research Session Chair: Greggory Schell

219

Mathematical Modeling of Pediatric Patients Jason S. Card, BSE1, Alison D. Cator, MD, PhD3, Amy M. Cohn, PhD1, 2, 4, Joseph R. East, BS1, Tara Lynn O’Gara, BSE1, Emily J. Burns1, Michelle L. Macy, MD, MS 3 1 Industrial & Operations Engineering, University of Michigan

2 School of Public Health, University of Michigan

3 Children’s Emergency Services, Department of Emergency Medicine, University of Michigan

4 Center for Healthcare Engineering and Patient Safety, University of Michigan

We use mathematical models and data analysis to observe how pediatric patients are treated and discharged in the emergency department and inpatient units. We study length-of-stay and other metrics for patients using different discharge methods. We compare the results and discuss the implications of the findings. Acknowledgements: This study was funded through support from the Center for Healthcare Research and Transformation (CHRT), the University of Michigan Center for Research on Learning and Teaching (CRLT), the Center for Healthcare Engineering and Patient Safety (CHEPS), and the Bonder Foundation.

220

Improving Quality of Service and Fairness in Stochastic Operating Room Planning Yan Deng1, Siqian Shen1, Brian Denton1 1 Department of Industrial and Operations Engineering, University of Michigan

Existing research on stochastic operating room (OR) planning rely on an expected-cost-based approach, which penalizes under-performance and minimizes the total expected cost. However, penalty costs are often difficult to estimate accurately. In this paper, we formulate the problem as chance-constrained programs, where waiting and overtime are limited by probabilities. Chance constraint provides a natural representation of Quality of Service parameters. It also promotes fairness by accounting for individual surgeries and ORs. We consider a set of surgeries with uncertain duration and a set of ORs with fixed length of opening time, we decide (i) which ORs to open, (ii) surgery-to-OR allocation and (iii) starting time of individual surgeries, to minimize OR opening cost. We formulate chance constraints to capture the on-time-start guarantees for individual surgeries and the on-time-closure target of the entire OR sector. We provide two alternative models where surgeries are scheduled in continuous time and discrete time blocks respectively. Via sampling, we reformulate chance constraints in each model as mixed-integer programming (MIP) constraints based on finite realizations of uncertain surgery duration. We also decompose the discrete-time MIP and develop cutting planes to improve the computational efficiency. We test randomly generated instances based on real data from a healthcare provider and develop insights of how our approaches improve the quality of service and fairness in stochastic OR planning.

221

Modeling the Underlying Dynamics of the Spread of Crime David McMillon1, Carl Simon2, Jeffrey Morenoff3 1 Applied & Interdisciplinary Mathematics, Industrial & Operations Engineering, University of Michigan

2 Mathematics & Public Policy, University of Michigan

3 Sociology, University of Michigan

The spread of crime is a complex, dynamic process that calls for a systems level approach. Here, we build and analyze a series of dynamical systems models of the spread of crime, imprisonment, and recidivism, using abstract transition parameters based on empirical research on criminological dynamics. To find general patterns among these parameters - patterns which are independent of the underlying particulars - we compute analytic expressions for the tipping points between high-crime and low-crime equilibria using Lyapunov functions. We examine, among other relationships, the effects of longer prison terms and of increased incarceration rates on the long-term prevalence of crime, with a follow-up analysis of the “Three-Strike Policy.”

222

When Is Bone Scan Needed For The Baseline Staging Of Newly Diagnosed

Prostate Cancer?

Selin Merdan1, David C. Miller2,3, MD, MPH, Christine Barnett1, MEng, James E.

Montie2,3, MD, Zaojun Ye2,3, MS, Susan Linsell3, MSHA, Brian T. Denton1, Ph.D. 1 Department of Industrial and Operations Engineering, University of Michigan, Ann Arbor, MI, 48109, USA

2 Department of Urology, University of Michigan, Ann Arbor, MI, 48109, USA

3 Michigan Urological Surgery Improvement Collaborative, Ann Arbor, MI, 48109, USA

Bone scans are often performed in the staging evaluation of patients with newly diagnosed prostate cancer (PCa). The most important aspect of staging is the detection of bone metastasis (BM). Considering that the skeleton is the most painful and debilitating site of metastasis from PCa, an accurate staging is of crucial importance for treatment choice as well as for patient diagnosis. Bone scan (BS) is the most widely accepted method for evaluating the entire skeleton for evidence of metastatic PCa; however it is also an expensive and time-consuming staging modality. Moreover, patients vary widely in risk of harboring BM at diagnosis. This may translate into a high number of patients for whom staging BS can be safely avoided with a significant reduction in financial burden on the healthcare system and reduced anxiety for patients. Recently, several international guidelines have been published addressing the need to reduce the unnecessary use of BS in low risk patients; however, no consensus currently exists regarding the use of imaging for evaluating primary PCa. This poster will present a study using statistical methods to evaluate the ability of clinical and pathological variables in predicting positive BS among a large sample of PCa patients from community and academic practices. We used the statistical model to identify subgroup of patients for whom staging BS could be safely eliminated due to low probability of BM. Furthermore, the performance characteristics of the published guidelines are evaluated in terms of sensitivity and specificity by adjusting for verification bias. This material is based in part upon work supported by the National Science Foundation (NSF) under Grant Number CMMI 0969885. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the NSF.

223

Using Stochastic Programming and Discrete Event Simulation to Improve Service Quality in an Outpatient Infusion Center Spyridon Potiris1, Autumn Heiney2, Jeremy Castaing1, Amy Cohn1, Brian Denton1, Christopher Friese2 1 Department of Industrial and Operations Engineering, University of Michigan

2 School of Nursing, University of Michigan

Background: Demand for outpatient chemotherapy delivery is rising, resulting in high patient volumes at infusion centers. Reduction in patient wait times can help address this challenge. Operations research techniques such as discrete event simulation and stochastic programming can inform more efficient patient scheduling. Methods: First, 60 hours of observation in the UMHS Comprehensive Cancer Center's outpatient infusion center contributed in mapping patient flow. Then, a computer simulation model was created to examine the effects on patient wait times and total hours of operation under different scheduling paradigms. 9 months of data from the electronic medical record and scheduling systems were used as input for the simulation model. To create different appointment schedules, both simple heuristics and a more complex stochastic programming model were developed. The aforementioned scheduling methods explicitly consider the variability in infusion times. Results: The baseline average patient wait time was 130.48 minutes (95% CI 122.38-138.68). Computer simulation results show that schedules generated by the stochastic programming model perform better than baseline and simple heuristics, reaching a 70% reduction in waiting times. Schedules that allocated patients with longer infusion times to earlier appointments resulted in both reduced average patient wait times and total hours of operation. Conclusions: Based on our results from the computer simulation model, scheduling patients with longer infusion times earlier in the day results in shorter patient waiting times and total length of day of operations. Next steps include development of a simple heuristic to support appointment scheduling that conforms to the optimal appointment schedule. Acknowledgements The Seth Bonder Foundation, the TDC Foundation, and Center for Healthcare Engineering and Patient Safety (CHEPS), University of Michigan

224

Scheduling Residents to Achieve Adequate Training on Procedures with Random Occurrences William Pozehl1, Ryan Chen1, Amy Cohn1, Mark Daskin1, Rishi Reddy2, Jake Seagull3 1 Department of Industrial and Operations Engineering, University of Michigan

2 Department of Surgery, University of Michigan Health System

3 Department of Medical Education, University of Michigan Medical School

Surgical residents must accrue a certain minimum number of case experiences on a variety of procedures (e.g., heart transplants) to receive certification. These residents work a rotating call schedule to cover unplanned, emergency cases that occur randomly. Due to the coupling of unplanned events with fixed schedules, not all residents will necessarily accrue enough case experiences even with a sufficient total number of cases. We analyze the current system to identify alternative methods by which residents can achieve certification more reliably. We develop a simulation model of this problem and outline alternative scheduling rules that increase the number of residents who can be certified in a graphical tool developed in Visual Basic. The simulation tool also has some degree of customizability; the user can stipulate such factors as: how to assign multiple procedures in one day, how the residents’ call schedule works, how seasonality affects procedure occurrences, etc. These statistics can be displayed for one repetition or can be aggregated over multiple repetitions. In addition, the simulation tool has a feature which calculates the probabilities of all residents receiving sufficient case experiences for certification as a function of the mean number of procedures performed per year. Our results demonstrate that the likelihood of certifying all residents training for heart and lung transplant certification in an average year at the University of Michigan Health System is exceedingly low. Medical personnel may use the tool to conceptually and visually understand the effects of randomness on the ability to train residents effectively. We would like to thank the Seth Bonder Foundation, The Doctors Company Foundation, and the Center for Healthcare Engineering and Patient Safety for funding this project.

225

Transmission Expansion Planning with Demand and Contingency Uncertainty and Transmission Switching as Recovery Action

Kathryn Schumacher1, Richard Li-Yang Chen2, Amy E.M. Cohn1 1 Department of Industrial and Operations Engineering, University of Michigan

2 Quantitative Modeling and Analysis, Sandia National Laboratories

One of the major challenges in deciding where to build new transmission lines is that there is uncertainty regarding future loads, levels of renewable penetration and equipment failures. We propose a robust optimization model whose transmission expansion solutions ensure that demand can be met over a wide range of conditions. Specifically, we require feasible operation for all loads and renewable generation levels within given ranges, and for all single transmission line failures. Furthermore, we consider transmission switching as an allowable recovery action. This relatively inexpensive method of redirecting power flows improves the network’s resiliency, but introduces computational challenges. We present a novel algorithm to solve this model. Computational results will be discussed.

226

Optimization Models for Differentiating Quality of Service Levels in Probabilistic Network Capacity Design Problems

Siqian Shen1, Zhihao Chen1 1 Department of Industrial and Operations Engineering, University of Michigan

This paper focuses on various forms of chance-constrained models for the probabilistic network design problem (PNDP), where given uncertain demand we aim to differentiate the quality of service (QoS) and measure the related network performance. The upper level problem of the PNDP designs continuous/discrete link capacities shared by multi-commodity flows, while the lower level problem ensures a certain level of demand satisfaction via recourse. The differentiated QoS adjusts the feasible region for given prioritized customers and/or commodities. We consider PNDP variants that have either fixed flows (formulated at the upper level) or recourse flows (at the lower level) according to different applications. We transform each probabilistic model as a mixed-integer program, and derive polynomial-time algorithms for special cases with single-row chance constraints. The paper formulates benchmark stochastic programming models by either enforcing to meet all demand or penalizing unmet demand via a linear cost function. We compare different models and approaches by testing randomly generated diverse networks and an instance given by the Sioux-Falls network. We analyze the numerical results to demonstrate the effectiveness of our models, and to derive managerial insights.

227

Using Monte Carlo Simulation to Conduct Sensitivity Analysis on Markov Chains Haipeng Wu1; Yuanhui Zhang2; Brian T. Denton1; James R. Wilson3


2 Graduate Program in Operations Research, North Carolina State University

3 Edward P. Fitts Department of Industrial and Systems Engineering, North Carolina State University

Markov chain (MC) models are commonly used in medical decision making. Since transition probabilities are usually estimated using sample data or conflicting subjective information, they are subject to uncertainty. However, methods for conducting sensitivity analysis on the transition probability matrix (TPM) of an MC have not been widely adopted. We describe two simulation-based methods for performing sensitivity analysis on MCs with uncertain TPMs. Given an initial estimate of the TPM, method 1 samples the TPM’s rows independently. Assuming no prior knowledge of the TPM’s distribution, method 1 samples the TPM uniformly in a user-specified uncertainty set whose reference point is the initial TPM estimate. Method 2 generates an initial sample from the estimated multi-normal distribution of the TPM’s maximum likelihood estimator; then taking that TPM as the uncertainty set’s reference point, we generate the final TPM uniformly in the uncertainty set by method 1. We use both methods for performance evaluation of published treatment guidelines for glycemic control of type 2 diabetes patients, where an MC models the natural variation in Glycosylated hemoglobin (HbA1c). We report the variation in expected quality-adjusted life span and medication cost due to uncertainty in the associated TPM. We also compare the computation times for methods 1 and 2. Acknowledgement: This material is based in part upon work supported by the National Science Foundation (NSF) under Grant Number CMMI 0969885. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the NSF.

228

Incorporating Functionality into Radiation Therapy Treatment Planning Optimization Victor Wu1, Marina Epelman1, Mary Feng2, Troy Long1, Martha Matuszak2, Edwin Romeijn1 1 Department of Industrial and Operations Engineering, University of Michigan

2 Radiation Oncology, University of Michigan Health System

Conventional Radiation Therapy Treatment Planning (RTTP) has the goals of (i) maximizing dose to eradicate the tumor and (ii) minimizing dose to preserve critical structures. Although post-treatment functionality of critical structures is a main clinical concern, current RTTP optimization models do not explicitly consider functionality. In liver cancer cases, dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) provides perfusion maps that have been shown to be a good indicator of tissue function both locally and globally [Cao 2013]. We propose a model that explicitly incorporates functionality metrics obtained from perfusion maps with the goal of redistributing dose through lower-functioning areas while achieving conventional treatment planning goals. We use liver cancer cases to compare treatment plans with and without using functionality information. Initial results indicate redistribution of dose while satisfying clinically used metrics. Future steps in model development include incorporating uncertainty of functionality information from image registration (“matching”) of DCE-MRI (for perfusion maps) with CT (for patient geometry maps). This project is funded by MCubed.

229

Industrial and Operations Engineering: Ergonomics Session Chair: Greggory Schell

230

Development of a Next-Gen Hand Model Rosemarie Figueroa1, Thomas Armstrong PhD 1, Mark Palmer PhD2 1 Department of Industrial and Operations Engineering, The University of Michigan

2 School of Kinesiology, The University of Michigan

Hands are the primary means by which we exercise control over objects in our environment. In industry, proper design of workspace and tools, considering hand properties and population variability, is necessary for proactive prevention of hand acute and chronic injuries. To fully understanding the relationship between exposure and development of work-related musculoskeletal disorders, objective measurements to quantify physical risk factors (e.g. human models) are needed. The main goal of this project is to collect new knowledge to develop a scalable 3D biomechanical hand model. This model could be used to determine required hand forces and postures so that risk factors can be identified and controlled. CT-Scans, of a hand in different poses (e.g. “FH-flat hand”, “LP-lateral pinch”) were used to create 3D quantitative images. Bones of FH and LP poses were used to estimate anatomical joint centers, bone distances and to create representative vectors of each bone. Spheres were fitted to proximal and distal ends of four phalanges. The center of these spheres corresponded to the joints instantaneous centers of rotation (COR). The distal COR was linked to the distal COR for the previous bone to create a representative finger vector. On average, representative vector length from “flat hand” and “lateral pinch” poses varies by 12% showing that movement changes the location of COR, and thus, having vector lengths that vary with hand posture is essential. To validate the segmentation process hand key dimensions such as hand length, index finger length, hand breath and index finger breath will be analyzed.

231

Vessel Diameter Mismatch in Microsurgical Free Flap Transfer and Methods for Rectification C. Green1, D. Yu1, R. Minter 2, A. Frischknecht3, S. Kasten2, T. Armstrong1 1 Center for Ergonomics, University of Michigan

2 Department of Surgery, University of Michigan

3 College of Human Medicine, Michigan State University

Microvascular anastomosis is an integral aspect of free flap transfer surgery. When a tumor is excised from a patient, the blood vessel network is also removed. To restore blood flow to the impacted area, a pedicle containing blood vessels may be extracted from another body region such as the anterolateral thigh. However, since the vessels being anastomosed generally serve different physiological purposes, the vessel diameters may significantly differ. If this diameter disparity is not surgically rectified, medical complications may arise. Numerous methods have been created to rectify the disparity, including altering anastomotic geometry, physically altering the vessels and introducing tools to alter vessel diameter. To determine if these methods were present and how they altered surgical patency at varying levels of vessel diameter mismatch, 68 free flap transfers performed on 63 patients at the University of Michigan were analyzed. This study determined that two of the three aforementioned methods were utilized. The anastomotic geometry was altered by creating an end-to-side anastomosis and a mechanical coupler was utilized to anastomose vessels. Vessel alteration methods such as oblique cutting and fish mouth incisions were not witnessed. No clear pattern emerged when the surgical patency rates for the observed techniques were compared against the level of diameter mismatch. For end-to-side anastomoses, at a mismatch less than double, the complication rate was 100%, however when the mismatch was more than double, the complication rate was 14.3%. These results may have occurred due to post-operative data collection timing or the relatively minor diameter disparities present. This work was financially supported, in part, through the Graduate Medical Education Innovations Program through the University of Michigan Health System.

232

How drivers react with their hands or feet in intersection crashes? Heejin Jeong1 and Paul Green1, 2 1 Department of Industrial and Operations Engineering, University of Michigan, Ann Arbor

2 Driver Interface Group, University of Michigan Transportation Research Institute

According to the National Motor Vehicle Crash Causation Survey report of 2008, 36% of roadway crashes occurred when turning or crossing at intersections. Given this frequency, driving behavior at particularly crash-prevalent intersections should be investigated, including: Straight Crossing Path (SCP, 30%), Left Turn Across-Path Lateral Direction (LTAP/LD, 28%), and LTAP-Opposite Direction (LTAP/OD, 20%) crashes. To understand how people drive in these situations, some 24 drivers drove through 70 intersections in a driving simulator, 10 of which involved conflicts. While driving, their steering wheel angle, accelerator position, and brake pedal position were recorded, as well as speed and lane position to determine how drivers reacted to each crash scenario. In SCP, RTIP, and LTIP scenarios, older subjects (over age 65) actively steered more often than young subjects (ages 18-30). In SCP scenarios, male drivers were more likely to use foot controls than female drivers. The next step in the analysis is to develop quantitative predictions of how drivers respond in each of the situations and then to develop predictions of how those responses will change when various types of warning systems to reduce those crashes are introduced. Those predictions will be validated in a follow-on experiment. This research was supported by a grant provided by the National Science Foundation.

233

Effects of Primary Flight Display Clutter: Evidence from Performance and Eye Tracking Measures Nadine Moacdieh1, Julie Prinet1, and Nadine Sarter1


There is an ever-growing increase in the amount of information needed and available to operators in complex environments. One example of this trend is modern primary flight displays (PFD), many of which now include weather, terrain, and navigation data. The addition of more information to already busy displays has raised concerns about display clutter. In this study, our goal was to investigate the performance and attentional costs associated with PFD clutter during a simulated flight and to determine to what extent pilots are aware of clutter and its effects. Low, medium, and high-clutter PFDs were developed, and pilots flew a simulated flight scenario containing periods of high and low workload using one of the three PFDs. Pilots were asked to detect different visual alerts and notifications that appeared on the PFD throughout the flight. Performance, eye tracking, and subjective measures were recorded. Clutter significantly increased the response time to alerts, and high workload resulted in more alerts being missed. The eye tracking data provided insight into pilots’ monitoring strategies and efficiency in the different clutter conditions. Spatial density and the number of transitions were found to be larger in the case of higher clutter, whereas the number of fixations on flight mode annunciators was higher in the low-clutter condition. Importantly, pilots rated clutter as being relatively low even in the high-clutter condition. In combination, these results suggest that pilots may benefit from real-time clutter detection and reduction techniques that are based on eye tracking metrics. This research was supported, in part, by a research grant from the Federal Aviation Administration (10-G-022; technical monitors: Dr. Tom McCloy and Colleen Donovan). We would also like to thank Joseph Phillips, Khevna Shah, Noah Klugman, Brian Anthony, and Michael Stengel.

234

Cross-modal matching: Towards the development of a novel technique Brandon Pitts1, Sara Lu1, and Nadine Sarter1 1 Department of Industrial and Operations Engineering, University of Michigan – Ann Arbor

Research in the area of multimodal displays and information processing has reported several benefits of distributing information across multiple sensory channels (vision, audition, and touch, in particular). However, with few exceptions, studies on multimodal information processing involve the potential risk of confounding modality with other factors, such as salience, because no cross-modal matching is being performed prior to experiments. To date, no agreed-upon cross-modal matching method has been developed. The goal of our research is to develop and compare the feasibility and validity of various approaches. In this poster session, we present the findings for one particular technique that employs cue adjustments and bidirectional matches. Six participants were asked to perform a series of 216 matching tasks for combinations of cues in vision, audition and touch. The results show that participants’ matches differed from one another, were inconsistent across trials, and were also a function of the intensity level of the initial cue. The findings from this research further highlight the need for careful matching of multimodal cues in research on multisensory information processing and will result in refinements of the proposed technique. The authors would like to acknowledge the National Science Foundation Graduate Research Fellowship Program (NSF GRFP), Noah Klugman, Christie Rockwell, and Katherine Lu for helping to conduct and support this research.

235

Technique variations among different surgeons and conditions: Using a hierarchical taxonomy to describe techniques that impact outcomes Denny Yu1, Adam Frischknecht2, Steven J. Kasten2, Rebecca Minter2, Thomas J. Armstrong1 1 Department of Industrial and Operations Engineering, University of Michigan, Ann Arbor, MI

2 Department of Surgery, University of Michigan, Ann Arbor, MI

Standardization of surgical procedures on best methods can improve patient outcomes and reduce the time and cost. A hierarchical taxonomy is proposed for describing the variability in surgical technique to identify best methods. Hierarchical task analysis (HTA) was performed on eight “microvascular anastomosis” cases. It was found that the analyses could be simplified by redefining subtasks and elements to only describe actions and adding attributes to describe the work object, method, tool, material, conditions, and ergonomics factors. The resulting taxonomy was used to describe 64 cases. Differences were found among cases for the frequency and duration of subtask, elements, attributes, and element sequences. Observed variations were used to formulate hypotheses about the relationship between different methods and outcomes that can be tested in future studies. The taxonomy can provide a framework to define best practices both within and across operations, and for teaching surgical trainees and assessing performance.

The authors would like to acknowledgement all the surgical team members that participated in this study. This work was financially supported, in part, by the Graduate Medical Education Innovations Program through the university health systems and by the National Science Foundation.

236

Materials Science and Engineering: Materials for Energy-Conversion and Storage

Session Chair: Sung Joo Kim

237

Synthesis and Characterization of Cu(4-x)Li(x)S2 (x = 1, 2, 3) Erica Chen1 and Pierre F. P. Poudeu1 1 Laboratory for Emerging Energy and Electronic Materials, Materials Science and Engineering Department

University of Michigan, Ann Arbor, 48109, USA

Li(4-x)Cu(x)S2 (x = 0, 1, 2) were synthesized using conventional solid-state reaction in a tube furnace, annealed mechanical alloying, and induction melting. The products of these reactions were structurally characterized using powder X-ray diffraction (XRD). Differential scanning calorimetry (DSC) was used to investigate possible phase transitions in the synthesized compounds between room temperature and 1000°C. Laser flash method was used to determine the thermal conductivity of the compounds. Lastly, cyclic voltammograms (CV) were obtained to locate the redox peaks in each composition (x-value). Capacities were also calculated based upon the CV data. This work has been supported by ACS-PRF Grant # 52761-ND 10. Special thanks to TimCal and Arkema for generously providing Super P 45 carbon black and HSV761A PVDF respectively. Thank you to Poudeu Lab members for helpful discussion and insight.

238

The effect of capping chemistry on GaSb Quantum Dot shape and

photoluminescence.

Matt DeJarld,1 M. Luengo-Kovac2, E. Smakman3, P. Koenraad,3 V. Shih2,

J.M.Millunchick1 1 Department of Materials Science, University of Michigan, Ann Arbor, MI.

2 Department of Physics, University of Michigan, Ann Arbor, MI.

3 Eindhoven University, Applied Physics, Netherlands

The formation of quantum dots by droplet epitaxy has been studied with consistent

success for the GaAs system, but the underlying mechanisms have not been confirmed

and the use of heavier group V elements as Sb is not well characterized. When capped

with GaAs, GaSb will disintegrate into clusters and islands of various sizes. This

phenomenon has been observed in cross sectional STM and can degrade device

performance in next generation devices by induce band broadening. An examination of

GaSb quantum dot evolution indicates that upon reaching the critical thickness, some of

the quantum dot can incorporate into the adjacent wetting layer upon dissolution. To

better understand quantum dot disintegration, GaSb quantum dots grown on GaAs were

capped with four different compounds, 50nm of GaAs, one monolayer of AlAs with 50nm

of GaAs, three monolayers of AlAs with 50nm of GaAs, and 20nm of Al0.5Ga0.5As. From

cross sectional STM data, the AlAs and Al0.5Ga0.5As capping layers significantly retained

the quantum dot shape, with only 20% of the dots being demolished with the Al0.5Ga0.5As

capping as opposed to 60% of the dots capped with just GaAs. Additionally, the PL peaks

for the quantum dots were significantly more pronounced in the Al0.5Ga0.5As and three

monolayer AlAs samples. However, the overall intensity decreases with more compact

dots, which may signify an increased density of defects.

This work was supported as part of the Center for Solar and Thermal Energy Conversion,

an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of

Science, Basic Energy Sciences under Award #DE-SC0000957.

239

A Model for Anodic Film Growth on Aluminum Coupling Bulk Transport and Interfacial Reactions

Stephen DeWitt1 and Katusyo Thornton1,2 1 Department of Applied Physics, University of Michigan – Ann Arbor

2 Department of Materials Science and Engineering, University of Michigan – Ann Arbor

Anodization is an electrochemical method to grow oxide films on metallic substrates that can either be nanostructured (e.g. nanoporous) or compact. Anodic films have a wide range of applications that include nano-templates, capacitors, solar cells, batteries, biomedical devices, sensors, and anti-corrosion finishes. However, the mechanisms underlying anodic growth are not fully understood. To provide improved understanding of these growth mechanisms, we present a new continuum model and one-dimensional simulations for anodic film growth incorporating high-field ionic conduction, Butler-Volmer reaction kinetics, and space charge within the film. We demonstrate that the simulated results reproduce experimental trends for the Al3+ ejection current, transient responses, and embedded surface charge in compact films as well as equilibrium pore-base thickness and growth velocity in nanoporous films. We also discuss the application of this model to multi-dimensional simulations of anodic nanopore growth and self-organization.

Support for this work was provided by the U.S. Department of Energy under contract numbers DE-AC05-06OR23100, DE-FOA-0000559, and DE-SC0000957.

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Design principle of molecular doping for enhanced thermoelectric efficiency G. H. Kim1, L. Shao1, K. Zhang1, and K. P. Pipe1,2 1 Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI


Organic semiconductors (OSCs) provide advantages over inorganic semiconductors (ISCs) such as low cost, mechanical flexibility, and large-area deposition. For thermoelectric applications, OSCs further offer low thermal conductivity. Carrier transport mechanisms in OSCs differ from those in ISCs, leading to different tradeoffs in Seebeck coefficient, electrical conductivity, and thermal conductivity (e.g., OSCs do not typically obey the Wiedemann–Franz law). Doping plays a critical role in optimizing the thermoelectric power factor (S2 ), since it dictates both free carrier concentration and carrier mobility (µ). For OSCs, which typically have low S2 , the presence of dopants can affect µ significantly by increasing the distance between weakly bonded molecules and thereby the length over which carriers must hop. Furthermore, weak bonding in OSCs leads to a small dopant ionization fraction (i.e., a small number of free carriers per dopant); achieving a given carrier concentration therefore requires a relatively large total dopant volume. We show that the volume associated with a large number of unionized dopants in an OSC exponentially decreases the hopping rate and consequently S2 . Therefore, reducing the number of unionized dopants is crucial to maximizing ZT in OSCs. We develop a model for thermoelectric transport parameters that includes the effects of dopant volume, and experimentally demonstrate the importance of reducing total dopant volume by dedoping non-ionized poly(styrenesulfonate) (PSS) dopants from poly(3,4-ethylenedioxythiophene) (PEDOT). We find that this dedoping causes all three parameters that compose ZT to vary in a manner so that ZT is increased, yielding ZT = 0.42 at room temperature.1 [1] G.-H. Kim, L. Shao, K. Zhang, and K. P. Pipe, Engineered doping of organic semiconductors for enhanced thermoelectric efficiency, Nature Mater. 12, 719 (2013).

241

Tailoring the morphology and performance of bulk heterojunction organic photovoltaics using conjugated copolymers Anton Li1, Jojo Amonoo2, Bingyuan Huang1, Ed Palermo3, Peter Goldberg3, Anne McNeil3, Peter Green1,2 1 Department of Materials Science & Engineering, University of Michigan, Ann Arbor, MI 48109

2 Department of Applied Physics Program, University of Michigan, Ann Arbor, MI 48109

3 Department of Chemistry, University of Michigan, Ann Arbor, MI 48109

Thin film organic photovoltaics hold great potential, but further progress largely hinges upon understanding nano-scale structure-property relationships, and being able to manipulate them through molecular design and materials processing. To this end, we have synthesized and characterized novel fully-conjugated copolymers and investigate ways to exploit their unique behavior to tailor the morphology and properties of solar cell devices. This study focuses on the effects of incorporating the random copolymer poly((3-hexylthiophene)-r-(3-((hexyloxyl)methyl)thiophene)) (P(3HT-r-3HOMT)) into a blend of P3HT homopolymer and indene-C60 bisadduct (ICBA). The structure and properties of the active layer thin film were characterized using UV-visible spectroscopy, conductive atomic force microscopy (c-AFM), and energy-filtered transmission electron microscopy (EFTEM). Along with bulk current-voltage device measurements, charge carrier dynamics were studied using photo-induced charge extraction with a linearly increasing voltage (photo-CELIV). Using this combination of techniques, was found adding a small fraction of P(3HT-r-3HOMT) to the baseline P3HT:ICBA blend generated an improved microphase-separated morphology, leading to reduced charge recombination and yielding a 20% improvement in device efficiency. Ongoing work on copolymers of other chemistries and architectures are uncovering different types of morphologies with correspondingly different device characteristics. These findings provide insights on designing polymers and processing protocols to produce devices with appropriate nanostructure and properties for optimal light harvesting and energy conversion. This work was funded as part of the Center for Thermal and Solar Energy Conversion, an Energy Frontiers Research Center supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award #DE-SC-0000957. We also thank Jonas Locke for his work on copolymer synthesis.

242

Tuning the HOMO-LUMO Gap in Conjugated Polymers for Organic Photovoltaics Applications based on First-Principles Calculations

Xiao Ma1, Hossein Hashemi1, Bong Gi Kim1, Jinsang Kim1, and John Kieffer1 1 Department of Materials Science and Engineering, University of Michigan, Ann Arbor

To tune the HOMO and LUMO energy levels via alternating donor-acceptor monomer units, we investigated a series of conjugated polymers (CP)s in which the electron withdrawing power of the acceptor group and the electron giving power of the donor group is varied, while maintaining the same conjugated chain conformation. We observed that the introduction of electron withdrawing groups lowers the LUMO level, while keeping the HOMO level almost unchanged. Conversely, inserting the electron donating groups raises the HOMO level while maintaining the LUMO level unchanged. According to these trends, designing a low band gap polymer requires strong donors and acceptors. Using first-principles calculations we investigated underlying reason. Charge localization on the electron-rich and electron-poor segments in CPs plays a key role. We identified strong correlations between the withdrawing strength of the acceptor group, the HOMO and LUMO levels, and the degree of orbital localization, which allows us to derive reliable design principles for CPs.

243

Incorporation Kinetics and Bi Surfactant Growth in Mixed Anion Compound Semiconductor Alloys Joanna M Millunchick1, Evan M Anderson1, Chris Pearson2, Wendy L. Sarney3, Stefan P. Svensson3

1 Department of Materials Science and Engineering, University of Michigan-Ann Arbor

2 Department of Computer Science, Engineering, and Physics, University of Michigan-Flint

3 Army Research Laboratory

We present a kinetic model predicting the behavior of anion incorporation in InAsSb. Included are the effects of As desorption, Sb segregation, and Sb displacement by As, which may be limited by the In flux if it is comparatively larger. The model captures experimental data over a range of growth conditions for the InAsSb system using activation energies for desorption and Sb segregation found in literature. The activation energy for Sb displacement is 1.22eV. This model is general and should be valid for other mixed anion systems, or, appropriately modified, mixed cation systems and mixed anion/cation systems such as AlInAsSb. Additional experiments have been performed using Bi as a surfactant, resulting in a decrease in Sb incorporation with increasing Bi flux and constant In, As, and Sb fluxes. JMM, EMA, and CP gratefully acknowledge Chakrapani Varanasi and the support of the Department of Defense, Army Research Office via the grant number W911NF-12-1-0338. We also acknowledge Adam Lundquist for acquiring XRD and AFM data.

244

Structure and Electrical Properties of Stoichiometric CuxAgySe2 Synthesized via Redox Solid State Phase Transformations

Alan Olvera1, Pierre Ferdinand Poudeu Poudeu1 1 Department of

Material Science & Engineering, University of Michigan

Silver chalcogenides have regained attention over the past decade because of their multiple temperature dependent structural phase transitions, which generally induce interesting changes in electronic transport properties. These structural transitions have been reported previously in the Cu2Se, Ag2Se, Ag2S, and Ag2SeS systems, where significant increase in the electrical conductivity and large decrease in the lattice thermal conductivity are generally observed due to the ‘liquid-like’ disordered state of the metal ions within the rigid lattice formed by the chalcogen atoms. Here we report a new approach for an energy efficient synthesis of novel stoichiometric ternary phases with

general formula CuxAgySe2 (1 x, y 3) in the Ag-Cu-Se system. The compounds Cu3AgSe2, CuAg3Se2, and Cu2Ag2Se2 were synthesized by solid-state transformation of CuSe2 via mechanical alloying using the corresponding amount of Cu and/or Ag metal powders. X-ray diffraction study on a single crystal of CuAg3Se2 at 100K revealed that the compound crystallizes in the monoclinic space group C2/m with lattice parameters a =

9.8720 Å, b = 18.0780 Å, c = 5.3091 Å, = 105.13, Z = 8 and adopts a new structure type. In the structure, two corrugated chains of corner-sharing [(Cu/Ag)Se4] tetrahedra further share corners to form a one-dimensional ribbon, which stitches adjacent layers of edge-sharing [AgSe6] octahedra and [AgSe8] bicapped trigonal prisms. The large void left by this packing arrangement is occupied by a linearly coordinated Cu atom. The thermal behavior of the Cu3AgSe2, CuAg3Se2, and Cu2Ag2Se2 phases and their potential as thermoelectric materials will be discussed.

245

Molecular Dynamics Study of Heat Transfer at CuPc-metal Interfaces

Chen Shao1, Yansha Jin1, Max Shtein1, Kevin Pipe2, and John Kieffer1 1 Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, USA

2 Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, USA

We use classical molecular dynamics (MD) simulations to carry out a systematic study of the nanoscale processes that govern the thermal boundary resistance at copper phthalocyanine (CuPc)/metal interfaces. Non-equilibrium MD simulations (NEMD) are performed on metal–CuPc–metal junctions to study thermal energy transport across the interfaces through the Müller-Plathe method. The interfacial bonding strength is controlled directly in the MD simulation by scaling the interaction parameters for the materials juxtaposed at the interface. The thermal boundary resistance is closely related to the interfacial bonding strength. By comparing the MD calculation results with the experimental measurements, the work of adhesion between CuPc and metal substrates is estimated to be 0.06 J/m2 for CuPc/Au, 0.04 J/m2 for CuPc/Ag, and 0.4 J/m2 for CuPc/Al interfaces. These findings confirm the experimental observation of very weak bonding between CuPc and Au or Ag and strong bonding at the CuPc/Al interface. Our study shows that the interfacial bonding strength is a very important factor in predicting thermal boundary resistance at CuPc/metal interface. Conversely, the acoustic impedance mismatch between the adjoining materials appears to be less important. To further investigate the mechanisms of interfacial heat transfer we carry out a detailed analysis of the momentum exchange across the interface, based on incoherent space-time correlation functions of the atomic motion and their spectral representations. Our results suggest that the anharmonic contributions to the phonon spectrum directly correlate with the thermal boundary resistance at the CuPc-metal interface.

246

Characterization of Magnesium Rare Earth Precipitates

Ellen Sitzmann1, John Allison1, Emmanuelle Marquis1 1 Department of

Materials Science and Engineering, University of Michigan

Magnesium is the lightest of all the commonly used structural metals today, with a density about two thirds that of aluminum and one fourth that of steels. Due to the significant weight savings, magnesium alloys have become of great interest to automotive industries. Although magnesium is an abundant material, the yield strength, creep-resistance, formability, and corrosion resistance of cost-effective magnesium alloys are insufficient for use in engineering applications. To increase the strength of magnesium alloys, solid-state precipitates are formed by an age hardening heat treatment. Typically, magnesium alloys that do not contain rare earth elements are relatively weak structural materials because the precipitates form parallel to the crystallographic basal planes. Mg alloyed with Nd, Y, and/or Gd, on the other hand, form precipitates on prismatic planes of the magnesium matrix phase, providing a more effective barrier to dislocation motion. However, rare earth elements tend to be expensive, motivating the design of alternative alloy compositions with comparable mechanical properties. The mechanisms of precipitation in Mg-RE alloys are not fully understood and the nature of the precipitate phases remains matter of debate. Therefore, the objective of this project is to first understand the thermodynamic and kinetic mechanisms that control the complex precipitation sequence in Mg-Nd, Mg-Nd-Y, and Mg-Nd-Zr alloys. The evolution of precipitates (nucleation, growth, and coarsening of each phase) is systematically characterized as a function of aging conditions using transmission electron microscopy and atom probe tomography. Acknowledgements: PRedictive Integrated Structural Materials Science (PRISMS) UM-DOE Software Innovation Center for Integrated Multi-Scale Modeling of Structural Metals Funding provided by DOE-BES contract DE-SC0008637.

247

Reversible Pt Nanoparticle Formation in Pt-doped BaCeO3 and Related Application S.Y. Zhang1, X.F. Du1, M. H. Fang1, M.B. Katz1, G. W. Graham1 and X.Q. Pan1 1 Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109, USA.

Engineered nanocomposites are of considerable interest for potential application in areas such as photonics, catalysts and thermoelectrics [1-3]. In this work, we report a reversible process of Pt nanoparticle formation in Pt-doped BaCeO3, a phenomenon that may be exploited to create and control engineered nanocomposites. Both ex-situ and in-situ reactions have been studied through scanning transmission electron microscope. An application of this phenomenon, to lower the thermal conductivity of oxide materials, whose potential in thermoelectrics has been inhibited by their relatively high thermal conductivities, is presented as an example. The thin films of BaCeO3 (BCO), doped with 5% Pt, were grown by pulsed laser deposition (PLD) on (001) MgO substrates. Pt dopants presumed to occupy B sites of the perovskite matrix in the as grown film. After 1 hour’s reduction at 800 °C in 10% H2 balanced with N2, Pt nanoparticles, were expelled from the perovskite lattice, appearing uniformly dispersed throughout the film, at grain boundaries, and on the free surface. The reduced film was then subjected to an oxidation treatment in dry air at 800 °C for one hour. Almost all the Pt particles, including those as large as 7-8 nm, disappeared, having completely dissolved back into the perovskite lattice, and the system itself has essentially returned to the initial, as-grown state. We next conducted a second reduction treatment on the oxidized film, again at 800 °C for 1 hour, and found that Pt particles were again expelled, but now exhibiting a more uniform size and spatial distribution. The authors gratefully acknowledge funding from Ford Motor Company under a University Research Proposal grant and the National Science Foundation under grants DMR-0723032 and CBET-115940

248

Materials Science and Engineering: Synthesis and Application of Organic and Bio Materials

Session Chair: Sung Joo Kim

249

Reduction of Voc loss in a polymer photovoltaic cell via interfacial molecular design: insertion of a molecular spacer David Bilby1, Jojo Amonoo2, Matthew E. Sykes1, Bradley Frieberg3, Bingyuan Huang1, Julian Hungerford4, Max Shtein1,3,4, Peter Green1,2,3,4, Jinsang Kim1,3,4,5 1 Materials Science and Engineering, University of Michigan


3 Macromolecular Science and Engineering, University of Michigan


5 Department of Chemistry, University of Michigan

Loss to the open circuit voltage (Voc) in organic photovoltaic cells is a critical bottleneck to achieving high power conversion efficiency. We demonstrate that the insertion of multilayers of a poly(phenylene ethynylene) spacer into the planar heterojunction between poly(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester incrementally escalates the Voc of a polymer solar cell from 0.43 V to 0.9 V. Through a combination of light intensity and temperature dependent measurements, we show that this control over the molecular structure local to the interface increases Voc by raising the polaron pair energy and by suppressing the dark-diode current. This work was supported as part of the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award Number DE-SC-0000957.

250

Design principles of conjugated polymers for realization of directed alignment Kyeongwoon Chung,1 Bong-Gi Kim,2 Eun Jeong Jeong,2 Jong Won Chung,4 Sungbaek Seo,1 Bonwon Koo,4 and Jinsang Kim1,2,3* 1 Macromolecular Science and Engineering,

2 Department of Material Science and Engineering,

3 Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109, USA.

4 Display Device Laboratory, Materials and Device Institute, Samsung Advanced Institute of Technology,

Samsung Electronics Company, Ltd., Youngin 446-712, Korea Conjugated polymers (CPs) having one-dimensional p-orbital overlap along their long rigid rod-like conjugated backbone exhibit anisotropy in their characteristics such as absorption, emission and charge mobility. Therefore, alignment of CPs is essential to fully realize their unique anisotropic properties in device applications. In this presentation, molecular design principles in order to achieve directed alignment of CPs will be systematically discussed: (1) chain planarization under a concentrated condition, and (2) bulky side chains on (3) tetrahedral out-of-plane bonding to regulate the mobility of the CP chains and their self-assembly. The aligned film of the designed lyotropic liquid crystalline CP exhibited a high dichroic ratio of 16.67 in emission, and well-defined lamellar-type molecular packing and alignment were confirmed by means of 2-D grazing incidence X-ray diffraction measurement. Moreover, the hole mobility along the alignment direction was measured as high as 0.86 cm2/V•s in thin film transistors, which is more than three orders of magnitude higher than that of the perpendicular to the alignment direction. This work is supported by the US Department of Energy (DOE), Office of Basic Energy Sciences, as part of the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center (DE-SC0000957).

251

5,6-Dihydroxyindole as Key Mussel-Mimicking Adhesive Molecular Structure in Biomimetic Thin Films Noah Gajda1 and Jinsang Kim1,2,3,4 1 Department of Materials Science and Engineering


3 Department of Biomedical Engineering

4 Department of Macromolecular Science and Engineering

University of Michigan, Ann Arbor, MI 48109-2130

Dopamine has become a molecule of great interest within the field of mussel-inspired adhesive materials because it self-deposits to form a hydrophilic thin film, polydopamine, on a wide variety of surfaces. Structural characterization of polydopamine has been difficult because of its high reactivity and insoluble nature. Previous efforts have proposed that dopamine undergoes an oxidative self-reaction to form the conjugated intermediate 5,6-dihydroxyindole (DHI) and then aggregates to form thin films onto substrates. While this structure has been clearly identified within polydopamine, we further explored the DHI intermediate to determine the link between its structure and the adhesive properties of the thin films. We found that catecholamine functionalities are enough for molecules to self-deposit onto surfaces but without the presence of a conjugated indole structure, the thin films did not have the same robust nature as polydopamine. Through the formation of DHI oligomers with extended conjugation, these molecules are able to self-assemble with extremely strong intermolecular forces that generate the versatile adhesive characteristics and insoluble nature of the film. We will continue to explore the properties of the mussel-mimicking structure DHI for the use in further biomimetic adhesive applications. Acknowledgement of funding agencies, and collaborators who are not co-authors.

252

Transparent Superomniphobic Surfaces Kevin Golovin1, Duck Hyun Lee1, Joseph Mabry2, Anish Tuteja1 1 Department of Materials Science and Engineering, University of Michigan

2 Air Force Research Laboratory, Edwards Air Force Base, CA

Superomniphobic surfaces display contact angles >150° with nearly all liquids. Such a surface has the potential to be self-cleaning, drag reducing, chemical shielding and stain repelling. Not only are these surfaces extremely rare, but the large majority are opaque. To extend the usefulness of liquid-repellant surfaces to applications such as windows, smartphone screens, LCDs or eyeglasses, the surfaces must be transparent. In this work, we design superomniphobic surfaces that are highly transparent while maintaining a contact angle hysteresis of <3° for all tested liquids. The surfaces are fabricated using a facile mold and spray technique that is easily scalable to large scale fabrication. The flow field formed during spray-coating allows for highly controllable particle deposition. Such control facilitates the design of textured surfaces that repel organic solvents, alcohols, oils, acids and aqueous media. Nearly all known liquids simply bead up and roll off the surfaces with little-to-no tilt angle. The surfaces fabricated in this work are the first to maintain a high degree of transparency while allowing low surface tension liquids like ethanol and hexadecane to roll off with a contact angle hysteresis of <3°.

253

Patterned Superomniphobic-Superomniphilic Surfaces: Templates for Site-Selective Self-Assembly Sai P.R. Kobaku1, Arun K. Kota2, Duck Hyun Lee2, Joseph M. Mabry3, and Anish Tuteja1,2*

1 Department of Macromolecular Science & Engineering, University of Michigan, Ann Arbor

2 Department of Materials Science & Engineering, University of Michigan, Ann Arbor

3Rocket Propulsion Divison, Air Force Research Laboratory

Superomniphobic surfaces display both superhydrophobicity (apparent contact angle, q *

> 150º and low contact angle hysteresis with water) and superoleophobicity (q * > 150º and low contact angle hysteresis with low surface tension liquids like oils and alcohols).

Superomniphilic surfaces display both superhydrophilicity and superoleophilicity i.e., q * ~ 0º with both water and low surface tension liquids. Patterned surfaces containing well defined domains that display both these extreme wetting properties have many potential applications in fog harvesting and liquid transport, microchannels and microreactors, enhanced condensation and boiling heat transfer, and the selective deposition of thin films. However, the majority of patterned surfaces developed thus far exhibit extreme wettability contrast only with high surface tension liquids such as water (surface tension,

= 72.1 mN m-1), thereby limiting the applications of such surfaces mostly to surfactant-

free aqueous systems. In this work, we have developed first-ever patterned superomniphobic-superomniphilic surfaces that exhibit stark contrast in wettability with a wide range of polar and non-polar liquids. Using such patterned surfaces, we demonstrate the site-selective self-assembly of both high as well as very low surface tension liquids upon dipping and spraying. We have also demonstrated that here developed patterned surfaces can be applied to enhance both condensation and boiling heat transfer with low surface tension liquids. Further, we have utilized these patterned surfaces for site-selective self-assembly of a wide variety of polymers films and microparticles in different shapes and sizes.

We thank Dr. Charles Y-C. Lee and the Air Force Office of Scientific Research (AFOSR) for financial support under grants FA9550-11-1-0017

glv

254

Room Temperature Phosphorescence of Metal-free Organic Materials

Dongwook Lee1, Onas Bolton2, Byoung Choul Kim1,4, Ji Ho Youk5, Shuichi Takayama1,4,6, and Jinsang Kim1,2,3,4,* 1 Macromolecular Science and Engineering,

2 Department of Materials Science and Engineering,

3 Department of Chemical Engineering, 2300 Hayward St., University of Michigan, Ann Arbor, MI 48109;

4 Department of Biomedical Engineering, 2200 Bonisteel Blvd., University of Michigan, Ann Arbor, MI 48109;

5 Department of Advanced Fiber Engineering, Division of Nano-Systems Engineering, Inha University,

Incheon, 402-751, Korea, 6 Division of Nano-Bio and Chemical Engineering WCU Project, UNIST, Ulsan, Korea

Phosphorescent materials have attracted much attention due to potential applications in solid-state lighting because they can provide three-fold higher internal quantum efficiency in electronic luminescence devices than fluorescent alternatives by harvesting triplet excitons through intersystem crossing. Many organometallic compounds are efficient phosphors since spin-orbit coupling is promoted by metals. While these materials exhibit high quantum efficiency they require rare and expensive elements such as platinum and iridium. Developing metal-free organic phosphorescent materials is promising but challenging because suppressing the vibration of triplets, one of the key processes to be phosphorescent, is not efficient without heavy metal atoms. While recent studies reveal that bright room temperature phosphorescence can be realized in purely organic crystalline materials through directed halogen bonding, these organic phosphors still have limitations to practical applications due to the stringent requirement of high quality crystal formation. In this presentation, we will report bright room temperature phosphorescence by embedding a purely organic phosphor into an amorphous glassy polymer matrix. Our study implies that the reduced beta (β)-relaxation of isotactic PMMA most efficiently suppresses the vibrational decay and allows the embedded organic phosphors to achieve a bright 7.5% phosphorescence quantum yield. We will also demonstrate a microfluidic device integrated with a novel temperature sensor based on the metal-free purely organic phosphors in the temperature-sensitive polymer matrix. This unique system has many advantages: (i) simple device structures without feeding additional temperature sensing agents, (ii) bright phosphorescence emission, (iii) a reversible thermal response, and (iv) tunable temperature sensing ranges by using different polymers.

255

Developments of Polydiacetylene Liposome Microarray toward Influenza A Virus Detection Sungbaek Seo1, Jiseok Lee1, Eun-Jin Choi5, Eun-ju Kim5, Jae Young Song5, Jinsang Kim1,2,3,4 1 Macromolecular Science and Engineering,

2 Department of Materials Science and Engineering,

3 Department of Chemical Engineering,

4 Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109,

5 Animal Plant and Fisheries Quarantine and Inspection Agency, 175 Anyangro, Manan-Gu, Anyangsi,

Gyeonggido, 430-757, Republic of Korea

We systematically studied the effect of the target size on the turn-on signaling of polydiacetylene (PDA) sensory systems for detection of biological molecules based on the intermolecular interactions between a probe molecule and its target. The interaction between the M1 peptide and the M1 antibody of influenza A virus was rationally devised into a PDA sensor design for direct and indirect detection of influenza A virus. By using the same pair but only switching their role as a probe or a target in the detection system, we could keep the same paring affinity and therefore unquestionably examine the target size effect. While the larger M1 antibodies produced red fluorescence emission upon binding with densely packed M1 peptides at the PDA liposome surface, the smaller M1 peptides could not generate any noticeable signal when they bound to tightly packed M1 antibodies. When the probe density at the PDA surface was low, we could not observe any sensory signal generation from the PDA microarray regardless of the role of M1 antibody and M1 peptide. These results clearly revealed that the PDA sensory signal is mainly from the steric repulsion between probe-target complexes not the strength of the probe-target binding force. Based on the finding, we developed PDA microarray for direct detection of influenza A virus. The PDA liposome microarrays having densely packed M1 antibody probes and co-assembled phospholipids allows turn-on sensory signal within 1 hour and comparable detection limit with conventional kits. The demonstrated target size effect can be readily applicable to various PDA-based biosensor design and developments.

256

Nanoparticle encapsulation in thin film micellar structures: A physical method for functional materials design

Junnan Zhao1 and Peter F. Green1* 1 Department of Materials Science and Engineering, University of Michigan, Ann Arbor

Thin films functional materials exhibit properties that render them viable for diverse applications from sensors to electronic devices. The properties of these materials can be tuned by controlling the spatial distribution of inorganic nanoparticles over various length scales. The major fabrication challenge is associated with understanding and controlling the factors, such as confinement and enthalpic and entropic interactions, which affect the organization of nanoparticles. In this work, we investigate the confinement of gold nanoparticles, onto which poly(2-vinylpyridine) (P2VP) are end-tethered, in supported thin film diblock copolymer polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP)/homopolymer PS blends. The thin film nanocomposites were prepared by spin-casting mixtures of nanoparticles, the copolymer chains and homopolymer chains onto a substrate. The samples were then annealed above the glass transition of the polymers, resulting in the formation of spherical micelles composed of inner cores of the P2VP segments and outer coronas of the PS blocks throughout the PS homopolymer host. All nanoparticles were encapsulated within micelle cores; on average each micelle contains one, or no, nanoparticle. The micelles exhibited a strong tendency to self-organize at interfaces when the PS homopolymer chain length is large compared to the PS corona chain length. In comparison to pure PS-b-P2VP/PS blends, the nanoparticle/PS-b-P2VP/PS blends contain a higher density of, on average, smaller micelles. This sample fabrication procedure is straightforward and compliments the current “toolbox” used to create functional materials from block copolymer/nanoparticle systems.

257

Mechanical Engineering: Design and Manufacturing Session Chair: Joshua Padeti

258

Optimal Data Assimilation and Utilization for Intelligent Traffic Management Kang-Ching Chu1, Kazuhiro Saitou1

1 Mechanical Engineering, University of Michigan

Traffic congestion in urban areas is posing many challenges, while utilizing high-quality traffic information from traffic flow model can be beneficial for congestion management. Because of the popularization of GPS equipment, travel data from individual vehicles (as known as probing data) became an attractive alternative to fix-location detectors as a data source for traffic status estimation. However, traffic engineers are still trying to develop an optimal strategy for traffic data collection and traffic information utilization. This research focuses on investigating the appropriate data assimilation technique for macroscopic traffic model using probing and fix-location data; formulating optimization problem for probe vehicle deployment by considering information quality and operation cost; and then developing traffic information distribution strategy with predicted traffic status. The first attempt used Newtonian relaxation method to incorporate probe data into a deterministic macroscopic traffic flow model. The preliminary result of probe vehicle deployment revealed the trade-off between the quality of traffic density estimation and probing cost using multi-objective genetic algorithm. The result suggested that probing strategy may be adaptive with traffic condition, since the decreasing probe data during congestion would only cause negligible degradation on the estimation performance. Filtering-based method for data assimilation with modified traffic flow model will be the next step. Future goal would be developing an adaptive traffic information utilization strategy using the prediction quality of traffic status under varied traffic condition. Furthermore, microscopic traffic simulation would be used to evaluate the benefit of individual driver and the efficiency of transportation system using proposed strategy.

259

Knowledge-based Trajectory Generation for Advanced Manufacturing Molong Duan1 1 Mechanical Engineering, University of Michigan, Ann Arbor

Advanced manufacturing machines (AMMs) are utilized in a family of manufacturing activities that, among others, make use of cutting edge materials and emerging capabilities enabled by the physical and biological sciences. AMMs have to maintain submicron tolerances during contouring and at the same time travel as fast as possible so as to increase productivity. Large portion of AMM’s motion error stems from the dynamic error due to the non-contact feature (e.g. laser micro machining and PCB manufacturing); therefore, motion generation (or trajectory generation) is often utilized to improve the motion quality of AMMs especially at sharp corners. The industrial look-ahead algorithms employ user defined parameters to slow down the process, which do not incorporate the knowledge of the system, controller limits accurately. Also, the procedure often leads to trial and error, and the possible conservative parameters sacrifice the velocity and thus reduce the productivity. Therefore, the objective of this research is to incorporate the machine dynamics of AMMs into motion generation so as to develop a comprehensive method for minimizing cycle time while ensuring that tolerance constraints are not violated. To be practical, the developed methods must be (1) computationally efficient and (2) robust to modeling errors. To achieve that goal, a two-stage architecture which consists of constrained trajectory optimization, parameterization, and inverse dynamics is established as a novel trajectory generation scheme, with which the corner velocity is significantly increased, also the contour error is maintained.

260

A simplistic model for quadrupedal walking and trotting

Zhenyu Gan1, C. David Remy2 1 Department of Mechanical Engineering

Traditionally, two different simplistic models have been used to describe the dynamics of human locomotion. A spring-mass model for running and an inverted pendulum model for walking. While the latter failed to explain the characteristic double hump in the vertical ground reaction forces of a walking motion found in nature, the spring-model can do so in a different oscillation mode. We developed a passive dynamic quadrupedal model that is able to produce walking and trotting with a single set of parameters. The model has an extended main body and four massless legs that, during swing, instantaneously go to a predefined angle of attack; similar to a bipedal SLIP model. Periodic motions of this model were identified in a MATLAB simulation framework for gait creation. An automated method to identify model parameters to optimally match the ground reaction forces of the model with experimental data has been developed. Our model is able to produce periodic walking and trotting gaits, that qualitatively exhibit the same ground reaction forces as seen in the data of a representative crossbred horse (as provided to us by the Veterinary Teaching Hospital Zurich). Through means of automated parameter adjustment, we are very closely matching trotting data in a quantitative fashion and currently investigating how to do so for a walking gait. Ideally we succeed in quantitatively matching ground reaction forces for both, trotting and walking gaits, thus creating a single model that explains the different dynamic behaviors of quadrupedal locomotion.

261

Estimation of Active Maintenance Opportunity Windows in Stochastic Production Lines Xi Gu1, Xiaoning Jin1, and Jun Ni1


Effective maintenance actions can preserve or improve system availability, product quality and plant cost-effectiveness in automated manufacturing systems. However, arbitrarily stopping machines for maintenance will occupy their production time and may introduce production losses to the system. There may exist hidden opportunities during production, such that specific machines can be actively shut down for maintenance without penalizing the system throughput. In this paper, such time intervals are defined as active maintenance opportunity windows (AMOWs). We develop a Bernoulli model to analytically estimate AMOWs in a stochastic two-machine-one-buffer line. A recursive procedure based on aggregation method is used to estimate the AMOWs in long lines. For balanced lines, a heuristic approach is proposed. The effectiveness of the methods has also been validated through numerical studies. This work is based upon work supported by the National Science Foundation under grant MES -0825789 “Short-Term Joint Maintenance and Production Decision Support Tool of Manufacturing Systems”.

262

Within-cycle monitoring and diagnosis of cyclic nonlinear profile signals Weihong (Grace) Guo1, Judy Jin1, S. Jack Hu2 1 Department of Industrial and Operations Engineering, The University of Michigan, Ann Arbor, MI

2 Department of Mechanical Engineering, The University of Michigan, Ann Arbor, MI

With the rapid development of online sensing technologies, many real-time signals of process information are readily available in manufacturing processes. Particularly, cyclic signals are collected from repeatable operations where each cycle represents the signal collected from one part produced. In order to fully utilize this information, there have been many studies on the monitoring of cyclic signals. However, existing research are limited to detecting process changes after a part is produced based on its complete cycle of signals. In practice, especially short-duration processes with critical part quality and high cost, between-cycle monitoring decisions are too late. It is more beneficial to detect the process changes before a part is produced so that corrective actions or process adjustments can be quickly triggered. This research develops a monitoring and diagnosis methodology based on an early portion of cyclic signals. The proposed method is capable of making within-cycle decisions and the results can be used for guiding real-time process adjustments for defect prevention. The work presented in this poster aims to determine the segmentation of the cyclic signal for early detections and to develop a within-cycle monitoring technique using wavelets, logistic regressions, and control charts. More specifically, we first determine a minimum signal segment which can make a reliable detection and also leave sufficient time till the end of the cycle for process adjustment to be effective. The changes in profiles are then characterized using wavelet coefficients. Logistic regression models and a control chart-based method are then developed to detect fault condition. Funding: The research is sponsored by the General Motors Collaborative Research Lab in Advanced Vehicle Manufacturing at the University of Michigan.

263

High-performance micromachining of glass using electrochemical discharge machining (ECDM) Baoyang Jiang1, Shuhuai Lan1, Jun Ni1


The demand of non-conductive material has grown rapidly with the broad application in optical, electrical, and mechanical systems. Glass is expansively employed due to the properties including optical transparency, high stiffness, and good chemical resistance. Typical engineering glass is non-conductive, brittle, and hard, making it difficult to machine. Conventional electrical discharge machining (EDM) or electrochemical machining (ECM) cannot be applied to glass because these machining processes require workpiece to be electrically conductive. Electrochemical discharge machining (ECDM), taking advantage of electrochemical discharge phenomenon, is a non-traditional micro-machining process for non-conductive materials. ECDM has been seen as a promising technology for precision micro-machining of glass. Features with high aspect ratio and complicated geometry can be created by ECDM. Machining quality and efficiency of conventional ECDM process is far from satisfactory. Surface quality and machinable depth is limited in many applications. ECDM process can be improved either by introducing innovative methods, or by refining current process with comprehensive process models. Both approaches are adopted in this research.

264

Low cost and Energy Efficient Vibration Reduction of Ultra-Precision Manufacturing Machines Jihyun Lee1, Chinedum Okwudire1

1 Mechanical Engineering, University of Michigan Ann Arbor

Due to increased global competition and concerns about the environment, today’s advanced manufacturing machines not only have to achieve high accuracy and speed but also low cost and energy consumption. Ultra-precision manufacturing (UPM) machines are designed to manufacture and measure parts with micron level features and nanometer level accuracy. Therefore, they play a central role in a variety of advanced manufacturing processes. Due to the stringent accuracy requirements on UPM machines, they need to be isolated from ground vibrations. Generally, passive isolators are often preferred over active isolators because they are cheaper and energy neutral. However, passively isolated UPM machines suffer from residual vibrations during the motion of the

machines’ axes which degrade their speed and accuracy. As a result, active isolators

are utilized in high end UPM machines to reduce residual vibrations but this leads to higher costs and energy consumption. It has however been observed that some machine design parameters (e.g. isolator/motor locations) have a significant impact on the performance of passively isolated UPM machines. For instance, prior results from my research have shown that unwanted vibrations can be significantly reduced simply by changing the isolator locations due to an interesting dynamic phenomenon known as mode coupling. My research seeks to understand how to optimally exploit mode coupling so that superior vibration reduction can be obtained using passive isolators. If successful, it will enable high end UPM machines to be designed with passive instead of active isolators thereby reducing cost and energy consumption while maintaining high performance.

265

Friction stir welding of dissimilar Al alloy to advanced high strength steel

Xun Liu1, Shuhuai Lan1, Jun Ni1

1 S.M. Wu Manufacturing Research Center, Department of Mechanical Engineering, University of Michigan,

Ann Arbor, MI 48109, USA

Sheets of aluminum alloy 6061-T6 and one type of Advanced High Strength Steel (AHSS), TRIP 780/800 have been successfully butt joined using Friction Stir Welding (FSW) technique. The maximum ultimate tensile strength of the joint can reach 85% of the base aluminum alloy. Effects of process parameters were investigated from aspects of microstructure evolution, mechanical welding forces and temperature distribution during the process. Intermetallic compound (IMC) layer of FeAl or Fe3Al with thickness of less than 1 micron is formed at the Al-Fe interface in the advancing side, which can actually contribute to the joint strength. Aluminum matrix in the weld nugget is enhanced by dispersed sheared-off steel fragments encompassed by a thin intermetallic layer or simply intermetallic particles. Welding speed has an insignificant effect on either temperature distribution or mechanical welding forces and accordingly the composition of the intermetallic layer. However, larger welding speed can effectively reduce the length of thermal history and the interlayer thickness. The relationship between the thickness of interlayer and welding speed depends on the type of intermetallic compound that is formed. Higher rotational speed and larger tool offset will increase the temperature distribution and reduce the required mechanical welding force in both lateral and axial directions. Besides, these two factors can affect the composition of the formed intermetallic compounds. Acknowledgements This work is supported by the CERC-CVC U.S.-China Program of Clean Vehicle.

266

Value of wind diversity for increased integration of wind power into the grid Josh Novacheck1, Jeremiah Johnson2 1

Department of Mechanical Engineering/School of Natural Resources and Environment, University of Michigan 2 Center for Sustainable Systems, School of Natural Resources and Environment, University of Michigan

Sudden variability in wind power output can cause wind to be an unreliable power source. The fast ramping up or down of its power output can have negative consequences for grid operations, including increased costs. One method to deal with ramp rate variability of wind farms is to develop wind farms that are subject to different wind patterns, essentially diversifying the wind power portfolio. If proper wind power portfolios are chosen, the cumulative power output of the portfolio will smooth out the variability of individual wind farms. Mean-Variance Portfolio optimization (MVP) is one technique that can be utilized to help determine optimal portfolios that are diverse and maximize power output. In one example, MVP is applied to investigate benefits of wind diversity in Minnesota. In this case, large ramping events, defined by the ramping up or down of wind power output by more than 5% of total capacity within ten minutes, are decreased from occurring 10% over the sample period to less than 2% of the time. Average forecasting errors also decrease from 14.2% to 7.8% using MVP. Using a zonal model of the US Eastern Interconnect, the benefits to the grid of using MVP to develop future wind power sites can be generalized beyond the simple Minnesota example. The benefits of adding diverse wind portfolios onto the grid can decrease the overall costs of wind power integration, allowing for increased wind power development. I would like to thank Maite Madrazo and Markus Walther, graduate students in the School of Natural Recourses and Environment, for their work to develop the Eastern Interconnect model.

267

A Near-Optimal Power Management Strategy for Rapid Component Sizing of Power Split Hybrid Vehicles with Multiple Operating Modes Xiaowu Zhang1 Huei Peng1, and Jing Sun2 1 Department of Mechanical Engineering, University of Michigan

2 Department of Naval Architecture & Marine Engineering, University of Michigan

In the design of hybrid vehicles, it is important to identify proper component sizes. When the design search space is large, exhaustive optimal strategies such as dynamic programming (DP) is too time-consuming to be used. Instead, a near-optimal method that is orders of magnitude faster than DP is needed. One such near-optimal method is developed and presented in this research. This method is applied to design the powertrain parameters of all power-split hybrid vehicles utilizing a single planetary gear (PG). There are 12 possible configurations, 6 input- and 6 output-split, and each configuration has up to 4 modes [1]. Based on the analysis of the efficiency of powertrain components of the four modes, and the “Power-weighted Efficiency” (PE) concept, we show that the computation time can be reduced by a factor of 10,000 compared with the dynamic-programming approach. The optimal design of each configuration is analyzed and presented.

[1] X. Zhang, C. Li, D. Kum, H. Peng, “Prius+ and Volt-: Configuration Analysis of Power-Split Hybrid Vehicles with a

Single Planetary Gear”, IEEE Transactions on Vehicular Technology, vol. 61, Issue 8, pp. 3544-3552, 2012.

268

Mechanical Engineering: Automotive Engineering & Transportation Session Chair: Joshua Padeti

269

Design of Next Generation Biofuels

Tyler Dillstrom1, Jason Lai1, Akbar Mohamad1, Paolo Elavti1, and Angela Violi1


Low temperature combustion is dominated by chemistry and transport propertied. The Violi group utilizes molecular scale simulations in tandem with quantum scale calculations to bridge the gap between biotechnology groups that engineer novel biofuels, and engine researchers. Out findings provide a necessary link between the molecular structure of fuels and their macro-scale performance in engines. Funding sources: NSF, AFORSR, DOE- CERC-CVC

270

“Wheels vs. Tracks” A Comparison Study for Small Unmanned Ground Vehicles from Power Consumption Perspective Tianyou Guo1, Huei Peng2 1 Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI

2 Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI

Small Unmanned Ground Vehicles (SUGVs) can perform many surveillance, scouting, detection and rescue missions and keep soldiers out of harms’ way in the battlefield. Usually SUGVs operate on various terrains (soft or hard, rough or flat). The issue of wheeled SUGVs vs. tracked SUGVs for off-road operations with regard to mobility and power consumption has been a subject of debate for a long period of time. This study that considers SUGVs at about 15kg aims at comparison of tracks vs. wheels that is focused on power consumption on soft soil. This study includes 3-D track-terrain interaction skid steering model and 5-D wheel-terrain interaction skid steering model to do the comparison. 5-D wheel-terrain interaction skid steering model is a new model that considers 3-dimensional contact surface with various sinkage of inner and outer wheels. Both models also include zero-radius turning maneuver which is widely used in skid steering SUGVs. Simulation compares torque and power consumption of each configuration and weight effect, slip ratio and drawbar pull are also studied. This work was funded by the Automotive Research Center (ARC), a U.S. Army center of excellence in modeling and simulation of ground vehicles at the University of Michigan.

271

Reaction Pathway and Elementary Ignition Behavior of Surrogates for JP-8 and Alternative JP-8 Fuels Dongil Kang1, Vickey Kaslaskar2, Jason Martz3, Angela Violi1,3 and André Boehman3


2 Energy and Mineral Engineering, Pennsylvania State University


The cetane number (CN) variation of jet fuels causes difficulty in military ground vehicles with

diesel/compression-ignition engines. Recently, computational fluid dynamic (CFD) modeling

studies from Dr.Violi’s research group at University of Michigan developed two accurate JP-8

surrogates (UM I, UM II), capturing the CN and property variations in the various types of jet fuels

that can be used in Army ground vehicles, but these surrogates are not validated on any practical

combustion platforms. Therefore, to provide validation experiments to compare elementary

ignition behavior, a modified Cooperative Fuel Research (CFR) engine was tested where various

equivalence ratios, compression ratios, and fuel and air intake temperature were employed,

focusing on the chemical portion of the ignition delay of the surrogate fuel formulations in

comparison with a practical JP-8 fuel (POSF-4658). Our group investigated the elementary

ignition behavior including the percentage of low temperature heat release the critical

compression ratio and the critical equivalence ratio of each surrogate single compound, the UM

surrogate JP-8 mixtures and the practical JP-8 fuel. Furthermore, condensed exhaust trapping

and subsequent detailed chemical analysis highlighted the reaction pathways for a particular

molecule. This study is intended to provide an intermediate step to validate simulations based on

the surrogate fuel representation of JP-8 and the kinetic model to describe its combustion,

contributing not only by supporting the ongoing work of Dr.Violi’s research group on surrogate

fuels development, but also by building a predictive engine simulation capability, resulting in the

development of robust and efficient vehicle powertrains fueled with JP-8.

Acknowledgement: “Automotive Research Center (ARC), a U.S. Army center of excellence in

modeling and simulation of ground vehicles”

272

Model Predictive Control based Vehicle Motion Control to Mitigate Secondary Crashes after a Minor First Impact Byung-joo Kim1, Huei Peng1 1 Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI

It has been shown that even a minor collision between vehicles can lead to devastating consequences if the driver fails to react properly. To reduce the severity of possible subsequent (secondary) crashes, this study considers both vehicle heading angle and lateral deviation from the original driving path. The research concept here is different from today’s electronic stability control (ESC) systems in the sense that the differential braking is activated even when the yaw rate and vehicle slip angle is very high, and the relative lateral and yaw positions with respect to the road are part of the control objective. As a control strategy to achieve the goal, the Linear Time Varying Model Predictive Control (LTV-MPC) method is used, with the key tire nonlinearities captured through linearization. We consider tire force constraints based on the combined-slip tire model and their dependence on vehicle motion. The computed high-level (virtual) control signals are realized through a control allocation problem, which uses a map between vehicle motion control commands and independent braking forces under feasible constraints. Numerical simulation and analysis results are presented to demonstrate the effectiveness of the control algorithm.

273

Maximum Load Limit of Boosted HCCI Combustion in a NVO Engine Stefan Klinkert1, George Lavoie1, Dennis Assanis2, Volker Sick1 1 Department of Mechanical Engineering, University of Michigan

2 Stonybrook University

Homogeneous charge compression ignition (HCCI) engines offer the potential to simultaneously achieve high efficiency and low emissions. Implementation and practical use of HCCI combustion, however, remain a challenge due to the limited operating range. Studies aiming at high load extension of HCCI to date have only been done on laboratory-type engines with conventional valvetrains and degrees of freedom over intake/ exhaust conditions that are not necessarily viable from a practical standpoint. This research work is unique in that a practical NVO engine was used to independently investigate the effects of intake boost pressure, charge composition, thermal/ compositional stratification (NVO) and exhaust-back pressure on burn duration and combustion phasing limits. To determine the potential benefit of conventional positive valve overlap (PVO) operation on the maximum load limit, experiments were supplemented by a parametric study using a 1-D engine simulation software. A parameter walk from a NVO to PVO engine showed that improved volumetric efficiency, due to enhanced breathing and a decrease in RGF content, and lower engine speed, allowing further combustion phasing retard, are key enablers that suggest PVO operation can be a useful pathway to achieving higher loads. The results of this research work have provided new insight into what limits maximum load of an HCCI engine and shown how the thermo-physical state of the mixture as well as operating conditions affect the maximum attainable load through its implications on combustion phasing limits.

274

Vehicle-Dynamics-Conscious Real-Time Hazard Avoidance in Autonomous Ground Vehicles Jiechao Liu1, Paramsothy Jayakumar2, James L. Overholt3, Jeffrey L. Stein1, Tulga Ersal1


2 U.S. Army RDECOM-TARDEC

3 Air Force Research Lab

Unmanned ground vehicles (UGVs) are gaining importance and finding increased utility in both military and commercial applications. Historically, UGVs have often been small and teleoperated but current interest is in much larger fully autonomous vehicles. Due to their size, higher operating speed and ability to navigate more complicated terrain, these larger size vehicles have significantly different dynamic and, therefore, require different approach to hazard avoidance algorithms. This work is focused on the development of a model predictive control (MPC) based hazard avoidance algorithm that is aware of the dynamic limitations of the vehicle and can thus push the vehicle to its limits to maximize its performance. To achieve this, a maximum steering angle that prevents tire lift-off is obtained from a vehicle model given the vehicle speed and terrain slope. The optimal steering sequence that avoids the obstacles and navigates the vehicle to the target is calculated within the safe steering range using another vehicle representation. The developed MPC based hazard avoidance algorithm is evaluated as a function of the incorporated model fidelity. Results indicate that mixed fidelity models can potentially be used to achieve good obstacle avoidance behavior while simultaneously reducing the computation required. In particular, a 14 degree of freedom (DoF) vehicle model with Pacejka Magic Formula tire model is used to establish the safe steering range and a 2 DoF vehicle model with linear tire model is used to find the optimal steering sequence along the prediction horizon. This work was supported by the Automotive Research Center (ARC), a U.S. Army Center of Excellence in Modeling and Simulation of Ground Vehicles, led by the University of Michigan and U.S. Army TARDEC.

275

Comparison of terramechanics modeling methods for simulating steady-state wheel-terrain interaction for small vehicles William Smith1, Daniel Melanz2, Carmine Senatore3, Karl Iagnemma3, and Huei Peng1 1Department of Mechanical Engineering, University of Michigan

2Department of Mechanical Engineering, University of Wisconsin

3Laboratory for Manufacturing and Productivity, Massachusetts Institute of Technology

A simulation study was conducted to evaluate three common terramechanics methods used for predicting single wheel performance of small vehicles on granular terrain. Small ground vehicles are used in areas where mission success is critical, such as planetary exploration and explosive disarmament. Modeling the interaction between wheel and soil using terramechanics can reduce the risk of immobilization due to insufficient thrust production and low propulsion efficiency through improved vehicle design and control. The Bekker method, the most common form of terramechanics modeling, assumes steady-state operation on smooth, flat ground. Small vehicles frequently operate under conditions that violate this assumption. More complex models are required to simulate multibody vehicle dynamics over rough terrain, such as the dynamic Bekker method and the discrete element method (DEM). Before these methods can be evaluated under dynamic conditions, they must first be tested in steady-state operation. Single wheel experiments were performed to evaluate wheel performance at various slip ratios on Mojave Martian Simulant. Similar tests were simulated using the three terramechanics modeling methods to evaluate the quantitative and qualitative accuracy of each method. Each method was tuned to match direct shear and pressure-sinkage soil tests using the same soil. The results show that DEM better predicts wheel performance at steady-state, though the computation penalty compared to Bekker-type methods is significant. DEM also captures some of the experimental time series behavior for drawbar pull and driving torque. This work was supported in part by a Science, Mathematics & Research for Transformation (SMART) Scholarship. The authors of this paper would like to acknowledge members of the US Army Tank Automotive Research Development and Engineering Center (TARDEC), especially Dr. Paramsothy Jayakumar, for their feedback and suggestions. We would also like to thank TARDEC for the use of their HPC cluster computer, which was used to conduct the majority of the DEM simulations.

276

Reducing Rollover Risk of a High Speed Mobile Manipulator Justin G. Storms1 and Dawn M. Tilbury1 1 Department of Mechanical Engineering, University of Michigan

Small-scale unmanned ground vehicles are prone to rollover when operated at high speed. Remote teleoperators are often forced to drive the robot slowly, with gradual turns to avoid rollover. This paper proposes to use a manipulator arm on the robot in a dynamic weight-shifting arrangement to reduce rollover risk. Compared to other methods for reducing rollover, this method does not require reducing speed or turning radius. Use of the manipulator arm for weight-shifting is presented, and a simple linear control law for the manipulator arm angle is proposed. A linear dynamic model is used to analyze the effect of the arm design (link length, mass, etc.) on the roll dynamics, and a more complex nonlinear simulation model is used to evaluate the roll reduction factor for a range of steering angles and velocities. In a simulation of the system for a nominal design using the same steering angle input, a roll reduction of 11% is shown. For the same radius turn a roll reduction of 24% occurs. Consequently, a 43% reduction in steering angle was used to achieve a similar turning radius when the dynamic weight-shifting is activated. By increasing the rollover stability region, this semi-autonomous behavior of roll reduction has the potential to increase the safe operating speed for mobile robots. This work was supported in part by a fellowship from the Department of Mechanical Engineering at the University of Michigan.

277

Mechanical Engineering: Mechanics of Materials & Structures Session Chair: Joshua Padeti

278

Effects of Microstructure on Very High Cycle Fatigue Behavior of Magnesium

Jacob Adams1, J. Wayne Jones1, John Allison1 1 Department of Materials Science and Engineering, University of Michigan

Magnesium alloys offer significant potential for structural applications because of their high specific strength. However, development of new magnesium alloys is hampered by incomplete understanding of the role of composition and microstructure on strengthening mechanisms and on fatigue behavior. The current work examines the initial results of research on the effects of microstructure on the Very High Cycle Fatigue (VHCF) behavior of a rare-earth magnesium alloy, WE43, and presents goals in the identification of critical fatigue mechanisms and phenomena necessary for the development of computational models as a step towards rapid material development. We gratefully acknowledge the U.S. Department of Energy for the funding of this project. We also thank Bruce Davis of Magnesium Elektron for providing the material for this research.

279

Force and Moment Generation of Fiber-reinforced Pneumatic Soft Actuators Joshua Bishop-Moser1 1 Department of Mechanical Engineering, University of Michigan

Soft actuators are found throughout nature from elephant trunks to round worms, demonstrating large specific forces without the need for sliding components. These actuators offer impact resilience, human-safe interaction, versatility of motion, and scalability in size. Biological structures often use a fiber-reinforcement around a fluid filled elastomeric enclosure, in which the elastomeric material will capture the distributed pressure and transfer it to the fibers, which will in turn direct the forces to the ends. We previously discovered an entire domain of fiber-reinforced elastomeric enclosures (FREEs), of which McKibben actuators are a small subset. The range of forces and moments possible with FREEs has not been previously investigated. 45 FREE actuators across the span of fiber angle configurations were fabricated and tested. The reaction force and moment of each actuator was determined across a gamut of pressures. Analytical models were generated using a variety of simplifying assumptions. These models were created to provide a closed form expression that models the force and moment data. The models were compared to the experimental values to determine their fit; this provides an understanding of which simplifying kinematic assumptions best represent the experimental results. Interpolated experimental results and the analytical models are all graphically represented for use as an intuitive design tool. The author would like to acknowledge the contribution of Prof. Girish Krishnan, Corey Bertch, Darlene Yao, and Prof. Sridhar Kota. This work was funded by the National Science Foundation.

280

Effects of Aluminum Content and Thickness on the Microstructure and Tensile Behavior of AM series Magnesium Alloys

Erin Deda1, John Allison1

1 Department of Materials Science & Engineering, University of Michigan

Magnesium alloys are of interest to the automotive industry for their weight reduction potential, due to their low density and good castability. Magnesium alloyed with aluminum and manganese is commonly used for high pressure die casting. The ductility is highly variable, and is dependent on location and local microstructural features. [1] This limits the ability to use these alloys in impact sensitive applications. Important microstructural features are porosity and secondary phase β-Mg17Al12, which have been predicted to limit ductility. [2] [3] Models have been developed to describe the impact of these microstructural features on the ductility, and the models that have been developed focus on the porosity of the castings. [4] High pressure die cast plates have been cast to assess the impact of plate thickness and aluminum content on the ductility and other tensile properties of Mg SVDC alloys. Microstructural features of the different alloys and thicknesses are characterized to be included in a weak link mechanical model for ductility. Primary features that are characterized are porosity, pore band structure, and distribution of β-Mg17Al12. Tensile properties are compared to literature models. This work was funded by the Department of Energy Vehicle Technologies Office under the Automotive LIghtweighting Materials Program managed by William Joost. The authors would like to thank Ford Motor Company for the assistance and advice from Mei Li, Jacob Zindel, Larry Godlewski, and Joy Forsmark, as well as Xin Sun at Pacific Northwest National Labs. The authors would like to acknowledge the help of Sunnie Han (UM) for her assistance with metallographic preparation. [1] G. Chadha, J. E. Allison, and J. W. Jones, “The Role of Microstructure on Ductility of Die-

Cast AM50 and AM60 Magnesium Alloys,” Metall. Mater. Trans. A, vol. 38, no. 2, pp. 286–297, Feb. 2007.

[2] C. D Lee, “Dependence of tensile properties of AM60 magnesium alloy on microporosity and grain size,” Mater. Sci. Eng. A, vol. 454–455, pp. 575–580, Apr. 2007.

[3] J. Song, S.-M. Xiong, M. Li, and J. Allison, “In situ observation of tensile deformation of high-pressure die-cast specimens of AM50 alloy,” Mater. Sci. Eng. A, vol. 520, no. 1–2, pp. 197–201, Sep. 2009.

[4] J. P. Weiler and J. T. Wood, “Modeling the tensile failure of cast magnesium alloys,” J. Alloys Compd., vol. 537, pp. 133–140, Oct. 2012.

281

Thermal Response of Laminates with Varying Fiber Orientation Adam Duran1, Nicholas Fasanella1 1 Department of Aerospace Engineering, University of Michigan

Hypersonic aircrafts are subject to severe aerodynamic heating which may cause thermal bucking. It is of great interest to investigate the material systems needed to maintain structural integrity under these extreme conditions. Composites allow for tailoring of material systems to attain the desired structural behavior. This characteristic may be exploited to obtain materials with enhanced resistance to buckling. We investigated the layering configuration of laminates which produced the highest resistance to thermal buckling given a specific thermal loading. We first investigated at symmetric, balanced, simply supported laminates. The fibers in each layer were restricted to be straight, and it was found that a 45° angle ply, [45/-45]s, allowed for the highest temperature, before buckling would occur. With modern manufacturing techniques, it is no longer necessary that the fiber paths be straight and so variable stiffness panels via curvilinear fibers were investigated. Here, fiber angles were varied along the length of the composite; therefore, the stiffness of the laminate was a function of position. Much like the straight fiber configuration, we sought the layup that would give the maximum temperature before buckling occurred. We found that the maximum buckling temperature could be improved by use of curvilinear fibers, a result contrary to examples in literature. The maximum buckling temperature is found to be at a configuration of T0=46° and T1=26°

282

An Atomistically-informed Energy Based Theory of Environmentally Assisted

Failure

Sriram Ganesan1, Veera Sundararaghavan1 1Department of Aerospace Engineering, University of Michigan-Ann Arbor, MI-48109, USA

For brittle fracture of crystalline solids capable of being plastically deformed, the critical energy

release rate defined as J = 2γ+γp (where, γ is the ideal work of fracture and γp is the plastic work)

is widely used as a macroscopic fracture criterion. The generally accepted notion that γp is a

material property, similar to γ, is called into question when considering embrittlement processes.

In this work, we study the critical energy release rate in embrittlement of Aluminum by Gallium

using first principles atomistic calculations and recent experiments to identify the parameters in a

power law relationship between γp, γ and 'stress intensity factor', k, γp= cka γb (where a,b and c

are material constants). Material constant a=2.002 was obtained for aluminum and is similar to

published results. The atomistic model and the simple power law form of γp give a good estimate

of the macroscopic brittle failure regime of the ductile material, and describe various aspects of

embrittlement such as fracture toughness, KIC and subcritical value of stress intensity, KIscc.

283

Novel Techniques for Studying the Role of Microstructural Variation on Very High Cycle Fatigue Crack Formation in Ti-6Al-2Sn-4Zr-2Mo Jason Geathers1, J. Wayne Jones2, Samantha Daly1,2 1 Department of Mechanical Engineering, University of Michigan

2 Department of Materials Science and Engineering, University of Michigan

Many aerospace components originally designed for 107 cycles are exceeding their expected lifetimes (107 < Nf < 109). Additionally, new components are being designed to operate in this very high cycle fatigue (VHCF) regime. Ultrasonic fatigue techniques at 20 kHz enable testing at 109 cycles to be achieved in hours, rather than days as required by a 40 Hz servo-hydraulic system. Although VHCF is characterized by nominally elastic strains, local cyclic plastic strain accumulation occurs on the microscale. Thus, fatigue damage mechanisms are much more sensitive to the microstructural landscape in this regime. New experimental methodologies that link local damage accumulation to microstructural variations are essential to the design and prediction of fatigue behavior for components in the gigacycle regime. The objective of this research is to understand the effect of microstructure variability and environment on fatigue crack nucleation and short crack propagation during VHCF. Ti-6Al-2Sn-4Zr-2Mo will be examined using a novel methodology that allows in-situ ultrasonic fatigue in an environmental scanning electron microscope (ESEM). Combined with advanced digital image correlation techniques, we can achieve full-field, quantitative, and in situ analysis of deformation mechanisms and damage accumulation at the microstructural length scale. We gratefully acknowledge the Air Force Office of Scientific Research, Structural Mechanics Program monitored by Dr. David Stargel, for funding the majority of this research, and the Rackham Merit Fellowship Program at the University of Michigan for providing the initial startup for this work. We would also like to thank Chris Torbet for equipment fabrication, and our AFRL collaborators, particularly Chris Szczepanski, for providing the material.

284

Deformation Mechanisms in Magnesium Alloy WE43 at the Microscale Alan Githens1, John Allison1, Samantha Daly2 1 Department of Materials Science and Engineering, University of Michigan

2 Department of

Mechanical Engineering, University of Michigan

A technique is currently being developed to better understand the phenomenology of ductility and fracture in magnesium alloy WE43 by determining possible failure mechanisms at the microstructural scale. Recently, digital image correlation has been combined with scanning electron microscopy in order to track, with high accuracy, strain on the microstructural level. The information gathered about intragranular strain inhomogeneities provides valuable information for computational crystal plasticity and continuum elasto-plasticity groups by providing experimental validation and experimental parameterization for their models. Chemistry has been developed to successfully deposit a fine speckle pattern required for digital image correlation at the microscale through a self-assembled arrangement of gold nanoparticles on the surface of magnesium. Depending on the size of the nanoparticles used, this speckle pattern may be applied for analysis at various length scales. Future work will track deformation under monotonic tension and compression of WE43 and assess the effect of slip, twinning, and micro-cracking on local strain. Funding is provided by DOE-BES contract DE-SC0008637.

285

Title: Non-diffusive Heterogeneous Phase Transformation on Shape Memory

Effect of Nitinol

Y. Gong1, S. Daly1 1 Department of Mechanical Engineering, The University of Michigan

The resultant full strain fields of non-diffusive solid phase transformation on shape

memory effect of Nitinol have been investigated. Phase transformation was induced by

uniaxial tension and temperature variation performed on an in-situ tensile stage mounted

in a scanning electron microscope. Scanning electron microscopy was used to capture

images of sample surface with micro scale speckle patterns upon every load or

temperature variation step. Digital image correlation (DIC) quantified evolution of small-

scale strain fields in order to match local strain to phase transformation and possible

detwinning modes of martensite variants. In situ observations of 50µm by 50µm field of

interest indicate prominent martensitic detwinning during uniaxial tension and martensite

to austenite phase transformation upon temperature increase. Plastic deformation

occurred post shape memory effect suggested by band like residual strain. The role of

microstructure and possible mechanism of detwinning of martensite and martensite to

austenite phase transformation will also be discussed.

286

Benchmarking the Accuracy of Inertial Measurement Units for Estimating Kinetic Energy Jessandra Hough1, Ryan S. McGinnis1, N.C. Perkins1 1 Department of Mechanical Engineering, University of Michigan

Newly developed miniature wireless inertial measurement units (IMUs) hold great promise for measuring and analyzing multibody system dynamics. This relatively inexpensive technology enables non-invasive motion tracking in broad applications, including human motion analysis. In this study, we point to the potential use of wireless IMUs for measuring the kinetic energy of human motion. Knowing the kinetic energy of the human body, and its decomposition into the kinetic energies of the major body segments, has tremendous value in a wide range of applications. Significant challenges thwart our ability to measure segmental kinetic energy in real (non-laboratory) environments. The aim of this research is to address these challenges by advancing the use of an array of miniaturized body-worn IMUs for estimating segmental kinetic energy. The study is conducted on a well-characterized mechanical system, a double pendulum, which also serves as an apt model for the lower or upper extremities. A two-node IMU array is used to measure the kinematics of each segment as input to computations of segmental kinetic energy. The segments are also instrumented with two high-precision optical encoders that provide the truth kinematic data for comparison. The segmental kinetic energies estimated using the IMU array remain within 1.1% and 2.8% of the kinetic energies estimated using the optical encoders for the top and bottom segments, respectively, for the freely decaying pendulum oscillations considered. These promising results point to the future development of body-worn IMU arrays for real-time estimates of segmental kinetic energy for health, sports, safety and military applications.

287

Quantitative Measures of Microstructural Phase Transformation in Nickel-Titanium Michael Kimiecik1, J. Wayne Jones1, Sam Daly1,2

1 Department of Materials Science and Engineering, University of Michigan


Martensitic transformation in superelastic Nickel-Titanium has been successfully quantified and analyzed at the microstructural length scale. A novel approach enables the determination of full-field, in situ surface displacements that are used as an indicator of the extent of microstructural martensitic transformation. The resulting high spatial-resolution displacement fields provide point-by-point information on the evolution of local deformation within individual grains as the macroscopic transformation front progresses, and enable analysis of the martensite phase fraction inside grains that results from interactions between the macroscopic front and microstructural features. The heterogeneous structure of the martensite band, including areas of elevated strain from plastic deformation and areas of low strain from retained austenite, will be given special attention. The high-spatial resolution strain data is related to the underlying crystallographic information, provided by Electron Backscatter Diffraction (EBSD), in order to quantify and elucidate microstructural effects on both small-scale and meso-scale phase transformation. Ultra high-resolution experiments focusing on individual microstructural elements, such as single grains, will also be discussed. The authors gratefully acknowledge the financial support of the US Department of Energy, Office of Basic Energy Sciences (contract No. DE-SC0003996 monitored by Dr. John Vetrano), who funded the in situ experiments and analysis detailed in this paper. The authors would like to acknowledge Mr. Adam Kammers for his development of the SEM-DIC methodology used in this work, and Mr. Jared Tracy for his experimental assistance.

288

Experiments and Inverse Analysis for Non-linear Viscoelastic (NLV) Properties Determination

Nhung Nguyen1, Alan Wineman1, Anthony Waas2 1 Department of Mechanical Engineering, University of Michigan


This work presents a methodology to extract NLV properties with applications to liquid-filled polymeric capsules and biological cells. Being used widely in the pharmaceutical industry, the performance of polymeric capsules is highly dependent on their mechanical properties, which govern the deformation during interactions inside the body. Thus, understanding the capsule’s mechanical behavior could be used in improving the product’s efficiency like predicting the bursting time for drug release. For this purpose, the mechanical responses of fluid-filled polymeric capsules are investigated using tests in which they are compressed between two flat, rigid, parallel plates. The bottom one is a transparent prism allowing the measurement of contact area during the compression process. The force-displacement-time response and contact area are used for the property extraction. The test is simulated using finite element (FE) in which the capsule material is modeled by a NLV constitutive relationship as suggested by the experimental data. An inverse analysis based on surrogate modeling and a Kriging estimator is also employed to automatically and efficiently determine NLV parameters for the capsule wall. This approach is also applied to biological cells in which experimental data is obtained utilizing atomic force microscopy. Cells are indented by spherical probes and force-time responses are recorded. The indentation experiment is also simulated using FE and the same inverse technique is applied to extract cell’s NLV properties. Such properties could be used to give more insight into the design of synthetic cells or investigating the possibility of using mechanical properties as biomarkers for disease.

289

Modeling, Capacitive Sensing and Optimal Filtering Algorithm Design for High-Precision Actuation of a Rotary Micro-Stage Jinhong Qu1, Kenn Oldham1 1 Department of Mechanical Engineering, University of Michigan

The goal of this work is to control a magnetoelastic rotary stage fabricated by MEMS technology, which can provide continuous rotation under large payload. Target specifications are 1000 degree/s over arbitrary angles with a resolution less than ±10 milli-degree. The first step in controller design towards achieving this behavior is to develop a dynamic model of the magnetoelastic rotary stage motion. A differential capacitive sensor, with accurate detection of several fixed points, is then designed for the stage to capture the rotation that will eventually be used for feedback control. The dynamic model of the stage is modeled in two parts: a collision model and a transient model. An analytical solution has been found and validated by experiments. Meanwhile, a capacitive sensor, with a capacitive readout circuit to transfer the signal, has been designed to sense the motion of the stage using gold electrodes placed on the stage with a symmetric geometry. Motion at several fixed angles detected by the electrodes with less error than standard analog sensing, which should increase the accuracy of the entire motion detection scheme. The controller will be designed based on the behavior of the stage motion and capacitive sensor. Given the behavior of the system, a Kalman filter and a Kalman smoother will be re-designed to reduce the noise of the analog signal. Current challenges that need to be considered include state-dependent noise from sensor and off-axis stage wobble. This work is supported by DARPA. Other collaborators not listed as co-authors: Jun Tang, Scott Green, Yogesh Gianchandani, Becky Peterson, Biju Edamna, Bongsu Hahn, Khalil Najafi, Erkan Aktakka.

290

Design of Materials for Blast Resistant Armor Tanaz Rahimzadeh1, Ellen Arruda1,2,3, Michael Thouless1,4 1 Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI

2 Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI

3 Macromolecular Science and Engineering Program, University of Michigan, Ann Arbor, MI

4 Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI

In the current US military, the Advanced Combat Helmet (ACH) is one of the main pieces of equipment used for head protection against blast and ballistic loading. Considering the current ACH design, being near an explosion (blast) can still produce a range of injuries called Traumatic Brain Injury (TBI). TBI is generally considered as the signature injury of the current military conflicts involving costly and life-altering long-term effects. Hence, there is an urgent need to battle this problem first by gaining a better understanding of the mechanisms responsible for the blast-induced TBI and second by designing/developing more effective head protection systems. In the present work, blast-induced TBI were reviewed from biological point of view and linked to several influencing mechanical parameters. Then several alternatives for the mitigation of the defined influencing mechanical parameters were explored such as impedance mismatch, energy dissipation through plasticity in irreversible crushable foams and finally stress relaxation concept and frequency tuning in visco-elastic materials. Using a systematic design optimization methodology, some potential multilayered ACH designs were proposed and their TBI mitigation capabilities were investigated using Finite Element Analysis (FEA). This work was funded, in part, by ONR. .

291

Modeling Crack Propagation in Polycrystalline Alloys using Variational Multiscale Cohesive Method Shang Sun1, Veera Sundararaghavan2 1 Department of Naval Architecture and Marine Engineering, University of Michigan


Crack propagation in polycrystalline grains is analyzed using a novel multiscale polycrystalline model. This model combines reduced order descriptors of microstructures with explicit representation of polycrystals at critical areas (eg. crack tips). For the critical areas, refined meshes are employed to discretize each crystal. The crack propagation in the microstructure is calculated using the variational multiscale cohesive method which allows for arbitrary intergranular and transgranular crack paths. The computational load is reduced substantially by combining probabilistic representation of the macroscale problem with exact resolution of the crystals at the crack tips. Examples of intergranular failure and inter and transgranular failure problems are demonstrated, showing exceptional mesh convergence and efficiency of the numerical approach.

292

Recrystallization in Binary Alpha Titanium Alloys Anna Trump1, John Allison2 1 Department of

Materials Science and Engineering, University of Michigan

Recrystallization can have a significant impact on the mechanical properties of metals and development of recrystallization models is an important element for any Integrated Computational Materials Engineering (ICME) capability for wrought structural metals. Throughout the forging process, the material is deformed and reheated multiple times, therefore it is important to understand exactly when and how much recrystallization is occurring during the process. Determining a relationship between the process variables and the amount of recrystallization allows for the prediction of the resulting mechanical properties of the material. A first step for producing such a model is to develop a high quality, quantitative experimental understanding which in turn requires development of accurate and efficient way to quantify recrystallization. This poster compares various methods for quantifying the percent of recrystallization in a binary alpha titanium alloy. These methods include hardness testing, optical microscopy and electron backscatter diffraction (EBSD). The fractional softening method relates changes in the hardness of a material to the amount of recrystallization. Recrystallization decreases the amount of dislocations in the material and therefore decreases the hardness. The optical point count method uses optical microscopy to visually determine what regions of the material are recrystallized. Grain orientation spread is an EBSD method that measures the local misorientation within each grain. A deformed grain will have a higher local misorientation than a recrystallized grain because of dislocations which induce lattice rotations. The advantages and disadvantages of each method are discussed. The authors acknowledge support of Office of Naval Research under Grant N00014-12-1-0013.

293

Progressive damage and failure analysis for 3D woven composites subjected to flexural loading Dianyun Zhang1, Anthony M. Waas1, and Chian-Fong Yen2 1 Department of Aerospace Engineering, University of Michgian

2 Army Research Laboratory

Textile composites are increasingly attractive for industrial applications. A 3D hybrid textile composite has been recently manufactured by weaving three different fibers (carbon, glass, and Kevlar) into a single dry preform, which is subsequently impregnated and cured using a Vacuum Assist Resin Transfer Molding (VARTM) process to form a solid panel. Previous studies in 3D textile composites have shown that this type of material has improved mechanical performance and increased resistance to delamination. A new computational multi-scaling approach is proposed to study the flexural response of a quasi-statically loaded 3D textile composite. For the experimental work, three-point bend tests were performed on a hydraulically activated machine at a loading rate of 1mm/min. The experimental observations suggest that the geometrical characteristics of the textile reinforcement play a key role on the mechanical response and progressive failure mechanism of this type of material. A computational model that reflects the detail of textile architecture and incorporates a damage constitutive law has been used to successfully capture the experimental results. The model has been implemented using a new multi-scaling approach in which the unit cell computations, carried out in closed form, are based on extreme values (as opposed to average values) to drive damage and failure. The resulting computational scheme is shown to be very fast and results in a high-fidelity and efficient computational model for assessing structural integrity and damage tolerance of textile fiber composites. The authors are grateful for the financial support from Army Research Laboratory.

294

Nuclear Engineering and Radiological Sciences Session Chair: Bruce Pierson

295

Coupling of 1D System Code to 3D Computational Fluid Dynamics Code

Timothy P. Grunloh1, Victor E. Petrov1, Annalisa Manera1

1 Nuclear Engineering and Radiological Sciences, University of Michigan

In order to properly simulate and, by extension, understand the behavior of a nuclear

power plant (NPP), a large number of physical phenomena with widely varying degrees of

complexity must be appropriately modeled. Hydrodynamically, the examples of simple

pipe flow and 3D mixing in the lower plenum juxtaposed represent the range of

complexity present in a NPP simulation. A similarly wide range of tools exists to cope with

these issues. Computational Fluid Dynamics (CFD) codes such as STAR-CCM+ excel at

the 3D simulation of fluid flows in complex geometries whereas system codes such as

TRACE excel at quickly simulating less complex flows found in NPPs.

It is the goal of this project to unite these two codes, exploiting their respective

advantages to accurately and efficiently simulate important physical phenomena. This

work has developed a coupling infrastructure that facilitates several types of interfaces on

simple geometries as a demonstration of principle, laying the groundwork for extension to

more complex and useful coupling configurations. The two primary philosophies of

coupling (separate and overlapping domains) are examined in this context, with emphasis

currently on explicit temporal discretization. Multiple scenarios, transient and steady state,

have been simulated. The results of this work show that coupling between the codes is

possible and provide a route through which more useful, and complex, coupled

simulations will be realized.

This work has been funded in part by a Nuclear Engineering University Programs (NEUP)

fellowship and by NRC-HQ-12-G-04-0083 grant.

296

First Efforts of Hybrid Monte Carlo Method in 2D Neutron Transport Changyuan Liu1, Prof. Edwards Larsen1

1 Nuclear Engineering and Radiological Science, University of Michigan

The Monte Carlo Method in neutron transport had a long history dated back to the first application of Digital Computer and the first simulation of extracting atomic powers. However with more demanding of the accuracy of atomic powered reactor simulation, problems with random fluctuation nature of the solution from Monte Carlo became intolerable. Later in 1990, the Coarse Mesh Finite Feedback (CMFD) method originally developed for the deterministic methods had been migrated and adapted to accelerate and reduce the noise levels in Monte Carlo Solver; nevertheless the results were not satisfactory as the reactor designer zoomed in details of the reactor. Nowadays the rapid growth of computation power makes a greater demand of a better. As a result, in the past decade, Professor Larsen had developed several so-called Hybrid Monte Carlo Methods, namely, which combine the deterministic and Monte Carlo together. As previous efforts of Dr. Yang and Wolters had shown, advantageous progresses could be made in one dimensional model problems. In this article, the author had developed a better method and took the first endeavors into the two dimensional problems, where only CMFD accelerations exist. Those new methods are called the Generalized Coarse Method Finite Difference Methods (GCMFD). We will show that with these new methods built on a triangular mesh will further reduce random fluctuation than CMFD. Moreover the efforts will demonstrate the application of a more advanced data structure for 2D geometry, borrowing ideas from CAD software, which will be promising for the future neutrontransport software development.

297

Characterization of Detection Limits Using Mock Waste Matrices in a 3He

Passive Drum Counter for Plutonium Waste Verification

Marc Gerrit Paff1,2, Bent Pedersen2, Jean-Michel Crochemore2, V. Canadell Bofarull3

1 Department of Nuclear Engineering and Radiologial Sciences, University of Michigan

2Nuclear Security Unit, Institute of Transuranium Elements, Joint Research Centre Ispra, European

Commission, Ispra, Italy 3

Nuclear Safeguards-Unit E1, Directorate General Energy, European Commission, Luxembourg,

Luxemburg

Waste streams from the fuel cycle or research facilities may contain measurable

quantities of plutonium that must be accounted for under international safeguards

agreements. Inspectors must perform measurements to verify operator declared

plutonium masses within waste matrices potentially containing sub-gram quantities of

plutonium. Neutron coincidence measurements are a standard tool to measure 240Pu

content due to its high spontaneous fission rate. Given prior knowledge of isotopics, total

plutonium mass can be estimated. For such measurements, the European Commission's

Joint Research Centre (JRC) maintains, tests and upgrades a 3He drum monitor for

deployment to European nuclear facilities at the request of EURATOM. This drum monitor

consists of 148 standard 3He tubes in a 4pi geometry for passive neutron coincidence

measurements using a shift register and standard INCC software. The neutron drum

monitor is designed and optimized to handle standard 55 gallon conditioned waste drums

of low plutonium content. This nondestructive measurement tool recently underwent

extensive electronic and structural refurbishments. Before redeployment, the passive

neutron detection system must undergo an extensive measurement campaign to

ascertain its limits of detection of plutonium in a variety of waste matrices. For this

purpose, mock waste matrices were produced. These consist of concrete filled standard

waste drums. A number of cavities at different distances from the drum center allow for a

variety of source locations to be tested. Plutonium metal and oxide samples ranging from

milligram to gram quantities were measured during this campaign.

“This research was performed under appointment to the Nuclear Nonproliferation

International Safeguards Fellowship Program sponsored by the National Nuclear Security

Administration’s Next Generation Safeguards Initiative (NGSI).”

298

A Quantitative Comparison of Analog and Digital Pulse-Shape-

Discrimination Systems for Organic Scintillators

Charles S. Sosa1, Marek Flaska1, and Sara A. Pozzi1

1 Department of Nuclear Engineering and Radiologial Sciences, University of Michigan

Organic scintillators require accurate discrimination of neutrons and gamma rays when

used in mixed neutron/gamma-ray radiation fields. Pulse-shape-discrimination (PSD)

systems are used in synergy with organic scintillators to identify the radiation type. This

paper compares PSD performance of a digital, charge-integration PSD system (based on

a CAEN V1720 waveform digitizer) against a state-of-the-art, analog, zero-crossing PSD

system (Mesytec MPD-4). The optimization of the MPD-4 analog PSD system was

successfully completed and verified using figure of merit (FOM) comparison studies for

different combinations of settings, to produce the best possible particle discrimination.

The MPD-4 was then compared against a state-of-the-art digital-PSD system using FOM

studies. The same equipment and sources were maintained for all measurements.

Measurements were performed using an organic liquid scintillator (EJ-309) coupled with a

photo-multiplier tube (ETL-9821B). A Cf-252 spontaneous-fission source was used to

provide neutrons and gamma rays for the measurements. From the FOM results, it was

determined that the performance of the digital-PSD system is slightly better than that of

the analog-PSD system. Future work will include various detector gains to potentially

further improve the PSD performance of the MPD-4.

299

Axial Solvers for the 2D/1D Implementation in MPACT

Shane Stimpson1, Benjamin Collins1, and Thomas Downar1

1 Department of Nuclear Engineering and Radiological Sciences, University of Michigan

The Michigan PArallel Characteristics-based Transport code (MPACT) has been developed to simulate light water reactor (LWR) cores, providing sub-pin-level flux distributions. One of the methods available is based on the 2D/1D method, which solves the 3D neutron transport equation by coupling 2D-radial and 1D-axial transport sweepers, usually wrapped by a three-dimensional coarse mesh finite difference (CMFD) accelerator. This scheme is successful because most of the heterogeneity in reactors usually exists radially, which is handled with 2D-MOC that uses an explicit geometric representation. Axially, however, there is less heterogeneity and a homogenized geometry can generally be used. Up to this point, 2D/1D development in MPACT has been limited to using finite difference axially, in which case there are no axial transport sweepers, but where the 3D-CMFD accelerator acts as the axial solver. To capture a more accurate representation of the axial flux profile, higher-fidelity methods are necessary. This work explores incorporating several different axial sweeper options, including both diffusion- and transport-based sweepers, most of which use higher-order expansions of the source and flux to allow for larger axial mesh. These axial solvers lighten the computation burden of requiring a large number of radial sweepers (as is the case when using finite difference) while providing higher fidelity axial solutions.

300

High-fidelity simulations of CRUD deposition on PWR fuel rods using neutronics, CFD, and coolant chemistry Daniel Walter 1, Victor Petrov1, Brian Kendrick 2, Annalisa Manera 1

1 Department of Nuclear Engineering and Radiological Sciences, University of Michigan

2 Theoretical Division, Los Alamos National Laboratory

The development of computational tools to predict CRUD deposition on commercial nuclear pressurized water reactor (PWRs) fuel rods within the DOE CASL project is ongoing. CRUD causes two primary operating issues: CRUD induced power shift (CIPS), and CRUD induced localized corrosion (CILC). The coupling of three physics, including neutronics, thermal-hydraulics, and coolant chemistry is necessary to accurately predict CRUD deposition and boron hideout. Several simulations have been performed including a single pin cell, a 4x4 sub-assembly, and a 5x5 sub-assembly. Due to the fidelity of the thermal-hydraulic characteristics that must be captured, computational fluid dynamics (CFD) is a requirement. However, the computational cost of CFD is very high and thus the current simulation effort is on small sub-assemblies. In this work, the most recent simulations and sensitivity studies will be discussed, which includes a 5x5 sub-assembly simulation using coupled CFD and coolant chemistry with STAR-CCM+ and MAMBA, respectively. Additionally, in this work it is shown that the azimuthal variation of the power distribution within a fuel rod may not significantly impact the locations of “hot spots”, or regions of highest temperature. In reality, the thermal-hydraulics, specifically the turbulent flow induced by spacer grid mixing vanes, more significantly controls the locations of the hot spots. Time stepping studies (frequency of data updates) on the feedback between CFD and coolant chemistry codes was also investigated. It was shown that, in general, coarse ~50 day time steps are sufficient to accurately predict CRUD and boron mass, as long as the precipitation of boron is not occurring. This work was funded, in part, by the Consortium for Advanced Simulation of Light Water Reactors (CASL).

301

Richard and Eleanor Towner Award for Outstanding Ph.D. Research Competition

302

Enhancing Vision via Stochastic Computing

Armin Alaghi1 and John P. Hayes1

1 Department of Computer Science and Engineering, University of Michigan

Vision chips, i.e., chips that have image sensors integrated with an image processing circuit, have several interesting applications such as human vision restoration and millimeter-scale stand-alone sensors. The area/power constraints associated with these applications are so demanding that make conventional digital design approaches unattractive or sometimes impossible, especially for real-time image processing. We show that stochastic computing is a solution to this problem. Stochastic computing is an unconventional technique which processes data in the form of bit-streams that denote probabilities. It can implement complex operations by means of simple logic circuits. We demonstrate that the simplicity of stochastic circuits, allows massively parallel processing of images in real-time. We also show that stochastic circuits are very noise tolerant, a property that is becoming ever important as the electronic technology advances.

303

Integrated Microfluidic Platform for Immunophenotyping of Subpopulations of Immune Cells Weiqiang Chen1, Nien-Tsu Huang1, Timothy T. Cornell2, Thomas P. Shanley2, Katsue Kurabayshi1,3, Jianping Fu1,4 1 Department of Mechanical Engineering,

2 Department of Pediatrics and Communicable Diseases,

3 Department of Electrical Engineering and Computer Science,

4 Department of Biomedical Engineering, University of Michigan, Ann Arbor

An accurate measurement of the immune status in patients with immune system disorders is critical in evaluating the stage of diseases and tailoring drug treatments. The functional cellular immunity test is a promising method to establish the diagnosis of immune dysfunctions. The conventional functional cellular immunity test involves measurements of the capacity of peripheral blood mononuclear cells to produce pro-inflammatory cytokines when stimulated ex vivo. However, this “bulk” assay measures the overall reactivity of a population of lymphocytes and monocytes, making it difficult to pinpoint the phenotype or real identity of the reactive immune cells involved. In this research, we developed an integrated microfluidic immunophenotyping assay (MIPA) platform that can perform efficient isolation, enrichment, and enumeration of peripheral blood mononuclear cells (PBMCs) as well as subpopulations of immune cells from minute quantities of human blood samples, and simultaneously perform quantitative measurements of multiple inflammatory cytokines secreted from these isolated immune cells using a no-wash, homogeneous chemiluminescence ("AlphaLISA") assay.

304

High Efficiency Single Cell Capture Chip by Using Herringbone Vortices for Small Sample Analysis Yu-Heng Cheng1, Yu-Chih Chen1, Patrick Ingram2 and Euisik Yoon1,2 1Dept. of Electrical Eng. and Computer Science, University of Michigan, Ann Arbor, MI, USA

2Dept. of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA

In this work, we report a high efficiency single cell capture scheme utilizing herringbone vortices for small assay samples incorporating only tens of cells. Single cell analysis has become increasingly important in cancer biology where rare sub-populations have been shown to have a large clinical impact. Cancer stem cells, for instance, have a strong potential for self-renewal and metastasis, driving disease progression. Circulating tumor cells (CTCs) can be found in patient blood and present an opportunity for cancer prognosis. However, due to the scarcity of such populations, only small numbers can be acquired for analysis. Thus, it is important to increase the capture efficiency of single cell platforms. In this design, we used herringbone vortices to induce hydrodynamic cell focusing to significantly enhance the capture efficiency. Three different designs were tested: no herringbone, cell focusing herringbone, and cell diverting herringbone. The cell focusing herringbone showed 70% cell capture efficiency, which is twice of the efficiency of no herringbone design. In addition, cell trajectories are also tracked in three designs. It shows that, due to the nature of the laminar flow, in the microwell without herringbone structures, the cell trajectories diverges when the cross-section of microfluidic channel is abruptly enlarged inside the microwell, limiting the capture efficiency. On the other hand, the turbulence generated by cell focusing herringbone can guide the cells back to the center to facilitate cell capture. It demonstrated the feasibility of herringbone cell-focusing capture scheme for analysis of small samples that contain tens of cells.

http://www.eecs.umich.edu/

305

Supervisory Control for Collision Avoidance in Vehicular Networks with Imperfect Measurements Eric Dallal1, Alessandro Colombo2, Domitilla Del Vecchio3, Stéphane Lafortune1 1 Department of Electrical and Computer Engineering, University of Michigan

2 Department of Mechanical Engineering, Politecnico di Milano

3 Department of Mechanical Engineering, Massachusetts Institute of Technology

We consider the problem of collision avoidance at road intersections in vehicular networks in the presence of uncontrolled vehicles, a disturbance, and measurement uncertainty. Our goal is to construct a supervisor of the continuous time system that is safe (i.e., avoids collisions), nonblocking (i.e., all vehicles eventually cross the intersection), and maximally permissive with respect to the discretization, despite the presence of a disturbance and of measurement uncertainty. We proceed in four steps: defining a discrete event system (DES) abstraction of the continuous time system, using uncontrollable events to model the uncontrolled vehicles and the disturbance; translating safety and non-blocking requirements to the DES level; solving at the DES level; and translating the resulting supervisor back from the DES level to the continuous level. We give sufficient conditions for this procedure to maintain the safety, non-blocking and maximal permissive properties as the supervisor is translated back from the DES level to the continuous level. Prior work on this problem based on similar abstractions assumes perfect measurement of position. Our method for handling measurement uncertainty is to introduce measurement events into the DES abstraction and then to compute the observer of the DES abstraction and the supremal controllable solution of the DES supervisory control problem. Research supported in part by NSF grant CNS-0930081.

306

Surface Dynamics of Miscible Polymer Blends Bradley Frieberg1, Jenny Kim2, Suresh Narayanan3, Peter F. Green1,2,4 1 Department of Macromolecular Science & Engineering, University of Michigan, Ann Arbor, MI

2 Department of Macromolecular Science & Engineering, University of Michigan, Ann Arbor, MI

3 Advanced Photon Source, Argonne National Laboratory, Argonne, IL

4 Department of Chemical Engineering, University of Michigan, Ann Arbor, MI

In the case of thin polymer films, the interactions between the polymer and an interface can have strong influences on the physical properties, including surface induced structure and dynamics which can differ significantly from the bulk material. In thin film polymer-polymer mixtures the component with the lower surface tension will preferentially segregate to the free surface to form a wetting layer. Due to this effect, the free surface of a polymer film can have a different composition than the average in the bulk material giving it significantly different properties. With the use of X-ray photon correlation spectroscopy (XPCS) we show that the dynamics of poly(vinyl methyl ether) (PVME) chains at the free surface of polystyrene (PS)/PVME thin film mixtures is 2 orders of magnitude faster than the PVME chains in the bulk. Furthermore, the thickness of the wetting layer and consequently the viscosity is demonstrated to be significantly influenced by the overall film thickness. Such enhancements in the surface dynamics manifest from the differences between the local compositions of the blend near the free surface and the bulk. Support from the Department of Energy, Office of Science, Basic Energy Sciences, Synthesis and Processing Program, DOE no. DE-FG02-07ER46412 is gratefully acknowledged. Use of the Advanced Photon Source was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

307

Using laser accelerated electrons for femtosecond electron diffraction application Zhaohan He1, Benoît Beaurepaire2, Victor Malka2, Jérôme Faure2, John Nees1, Bixue Hou1, Karl Krushelnick1 and Alexander G. R. Thomas1 1Center for Ultrafast Optical Science, University of Michigan Ann Arbor, Michigan, USA

2Laboratoire d’Optique Appliquée, ENSTA-CNRS-Ecole Polytechnique, Palaiseau, France

The development of tools to take ultrafast snapshots (at femtosecond time scale) of matter at the atomic scale has been a significant endeavor in the scientific community for understanding fundamental processes in biology, chemistry, material science and solid-state physics. Much progress has been made thanks to advances in ultrafast laser technology and the advent of X-ray free-electron laser light sources. Using electrons as probe is a cost-effective alternative to X-ray with unique advantages, such as the larger cross section for elastic interaction with matter, less radiation damage to samples and the possible higher spatial resolution due to the shorter wavelength of electron. However, achieving a time resolution better than 100 fs remains a great challenge for conventional photocathode based femtosecond electron source due to problems such as rf jitter and space charge effect. We develop a novel electron source based on laser-plasma wakefield accelerator using a high-repetition-rate femtosecond laser system. The inherent short bunch duration and perfect synchronization with the optical pump makes this source a promising candidate for ultrafast electron diffraction (UED) applications. We will present single-shot electron diffraction result from a crystalline gold foil in a proof-of-principle experiment to demonstrate the sufficient beam charge and quality. Simulations show that the accelerated electrons are energy chirped in time, which enables electron bunch compression for UED or utilizing the momentum-time correlation by streaking techniques for time-resolved experiments.

308

Engineering the elasticity of soft colloidal materials through surface modification and shape anisotropy Lilian C. Hsiao1, Richmond S. Newman1, Kathryn A. Whitaker2, Eric M. Furst2, Sharon C. Glotzer1, Michael J. Solomon1 1 Department of Chemical Engineering, University of Michigan, Ann Arbor MI

2 Department of Chemical Engineering, University of Delaware, Newark DE

Designing complex fluids has always involved the arduous manipulation of system-specific parameters. Recently, we developed a general correlation to predict the flow behavior of a range of soft matter based on their microstructure. By applying the framework of structural rigidity at the macroscale (bridges, buildings, domes) to the microscale, we are able to explain the nonlinear elasticity of colloids flowing at high rates that are typical of industrial processing. In particular, we find that we can design colloidal gels with better mechanical properties and stability without resorting to a greater quantity of materials, simply by incorporating particles with different shapes, sizes, and roughness. Biphasic particles with metallic facets have also been proposed to provide extraordinary structural strength due to their interaction anisotropy. We test these ideas by synthesizing monophasic and biphasic colloids of controlled roughness in various ellipsoidal shapes, dispersing the particles in refractive-index matched solvents, and inducing self-assembly and gelation with a measurable and tunable depletion attraction. To quantify their flow properties, rheological measurements are carried out in conjunction with microscopy experiments. Consider this scenario: a pharmaceutical product encapsulated in a viscoelastic gel is transported from a factory to a hospital, but the formulation phase separates after a bumpy ride in a truck, rendering the drug useless. Our work shows that this type of problem can be mitigated by applying the principle of structural rigidity to material design; for example, engineers can incorporate smaller ellipsoidal particles to increase yield stress without a significant increase in the production cost.

309

A reduced-order model of Titanium alloy for the control of microstructure-sensitive material properties Abhishek Kumar1, Veera Sundararaghavan1

1 Department of Aerospace, University of Michigan Ann Arbor

A crystal-plasticity based constitutive model for the large deformation of polycrystalline materials with hexagonal crystal structure deforming by mechanism of slip only(no twinning) is developed. To account for the infinite degrees of freedom of microstructural features, a model reduction on the micro-scale is introduced. Reduced-order models are developed to model the evolution of microstructure described by an orientation distribution function using a infinite element discretization of the orientation space. Novel design problems are introduced for the control of microstructure based on realistic polycrystalline plasticity. Specifically, a gradient based optimization framework is introduced using a multi-length scale continuum sensitivity method(CSM). The model reduction is extended to the sensitivity analysis and is a key element for the success of computational design of deformation processes. Numerical examples that highlight the benefits of the continuum sensitivity method and model reduction are presented.

310

Smart membranes for energy-efficient separation of liquid mixtures

Gibum Kwon1, Arun K. Kota1, Joseph M. Mabry2, and Anish Tuteja1,3# 1 Department of Materials Science and Engineering, University of Michigan

2 Rocket Propulsion Division, Air Force Research Laboratory, Edwards Air Force Base

3 Macromolecular Science and Engineering, University of Michigan

In this work, we have developed the next generation of smart membranes that can separate virtually all types of liquid mixtures using gravity alone. These counter-intuitive, liquid-responsive, smart membranes were designed by systematically tailoring the surface chemistry and the surface texture. The developed membranes can separate a range of different immiscible liquid mixtures, including all types of oil-water mixtures, with greater than 99.9% separation efficiency, using gravity alone. We also demonstrated continuous separation of oil-water emulsions for over 100 hours without a decrease in flux. Further, we developed a technique that combines liquid-liquid extraction and our smart membranes to separate numerous miscible liquid mixtures. We have utilized this technique for separating a wide variety of commercially relevant mixtures, including for the removal of sulfur compounds from both gasoline and diesel to less than 1 part per million. We also demonstrated the separation of alcohol-oil azeotropes and recovery of highly pure oils using this technique. Since the separation uses only gravity, it is an extremely energy-efficient and cost-effective methodology. We also developed another smart separation methodology that uses an electric field as a trigger to separate oil-water mixtures, on-demand. We anticipate that our smart membranes and separation methodology will have a wide range of commercial applications including clean up of marine oil-spills, wastewater treatment, separation of numerous commercially relevant oil-water emulsions, biofuel separation and recovery of oils, plastics recycling and fuel purification.

311

Improved Embryo Developmental Competence from Reduced Osmotic Stress by Gradual Shrinkage Rate Vitrification David Lai1,2, Jun Ding2,3, George W. Smith4, Gary D. Smith2,3, Shuichi Takayama1,2, … 1 Department of Biomedical Engineering, University of Michigan

2 Reproductive Sciences Program, University of Michigan

3 Department of Obstetrics and Gynecology, University of Michigan

4 Department of Physiology, Michigan State University

Treatment for cancer involves non-target specific radio- and chemotherapy that leave female patients with high risk of permanent infertility. With increasing cancer survival rates, oncofertility preservation has become a significant quality of life issue for young cancer survivors. Vitrification has become the preferred method for preservation of human oocytes due to higher survival rates and time efficiency. Current osmotic stress theories deal only with cryosurvival (percentage of cell death) and minimum cell volume, however the preservation of oocytes and zygotes necessitates the additional consideration of cell health and developmental competence. A major cause of sub-lethal osmotic stress is by high cell shrinkage rates for oocytes and zygotes. The new mechanism for osmotic stress was first derived mathematically using Kedem-Katchalsky equations and validated using a microfluidic device that enables a more gradual shrinkage rate not possible with manual cryoprotectant exchange. Importantly, the cell loading/withdrawal port allowed for 100% recovery of cells (n=474) from the device in a manner that enabled actual vitrification after the cryoprotectant agent exchange. Bovine oocytes vitrified with lower osmotic stress had 24.8% higher lipid retention than oocytes vitrified by manual pipetting (n=17, n=18). Murine zygotes vitrified with lower osmotic stress also have superior embryo developmental competence with more blastomeres (98±3 blastomeres, n=46) after 96h embryo culture compared to manual pipetting controls (89±3 blastomeres, n=35). We thank NIH GM 096040 for funding support.

312

Compressive Sensing Methods for Reducing Resource Requirements in Wireless Bridge Monitoring Systems: Validation on the Telegraph Road Bridge

Sean M. O’Connor1 and Jerome P. Lynch1

1 Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI

Wireless monitoring systems represent a cost-effective alternative to traditional tethered monitoring systems for monitoring the performance and health of bridges. While great advances have recently been made in wireless sensing technology, wireless sensors still suffer from two major limitations: limited communication bandwidth and a dependence on batteries. Data compression is one potential solution for reducing the amount of data required for communication in wireless sensor networks. By compressing data, the communication requirements of a wireless sensor can be lowered leading to improved communications and lower power requirements. A new approach to compression called compressive sensing offers even greater benefit by reducing the amount of sensor data required for sampling. Specifically, sub-Nyquist asynchronous sampling can be used to reduce the amount of data collected before transforming the data to a sparse representation with near perfect reconstruction potential. In this study, a compressive sensing framework is implemented within a wireless sensor network deployed to monitor the response of operational bridge structures. The paper reports on the implementation of the proposed compressive sensing-based wireless monitoring system on the Telegraph Road Bridge located in Monroe, MI. Field implementations of compressive sensing schemes in wireless SHM systems have been challenging due to the lack of commercially available sensing units capable of sampling methods (e.g., random) consistent with the compressive sensing framework, often moving evaluation of compressive sensing techniques to simulation and post-processing. The research presented here describes actual implementation of a random sampling scheme to the Narada wireless sensing unit. Sub-sampled data is communicated to the wireless monitoring system base station where a matching pursuit approach is employed to reconstruct the original bridge signal for subsequent data analysis. The study reports on the reduction in communication requirements for the wireless monitoring system in addition to the amount of energy saved through compression.

313

The Influence of Moisture and Gravity Wave Drag Parameterizations in Idealized Simulations of the Quasi-Biennial Oscillation Weiye Yao1, Christiane Jablonowski1 1 Department of Atmospheric Oceanic and Space Sciences, University of Michigan

The Quasi-Biennial Oscillation (QBO) can be characterized as a downward propagating wind regime that periodically changes the equatorial zonal wind from westerlies to easterlies in the tropical stratosphere. The QBO is mainly generated and influenced by vertically propagating gravity waves. The main difficulty in simulating the QBO with General Circulation Models (GCM) is the representations of subgrid-scale processes, including moist processes, which act as wave triggers and thereby impact the wave-mean flow interactions. In this work, idealized simulations of the QBO with simple gravity wave drag is investigated, and the influence of moisture on the QBO-like simulations is analyzed. In particular, the QBO-like oscillations are simulated with version 5 of the Community Atmosphere Model (CAM 5) which has been developed at the National Center for Atmospheric Research (NCAR). The QBO-like phenomenon is modeled with the spectral transform semi-Lagrangian (SLD) dynamical core, which is driven by a Newtonian temperature relaxation and Rayleigh damping. In addition, the Lindzen (1981) gravity wave drag scheme can be activated to parameterize the unresolved effects of small-scale gravity waves. By adding gravity wave drag, the QBO signal is strengthened. However, the period and amplitude of the QBO signal is highly related to the tuning parameter of the gravity wave drag. In the simulations with moisture, a simplified physics package is used to represent sub-grid scale processes, including the surface fluxes of moisture, sensible heat and momentum, large-scale condensation and convection parameterization. Wave-mean flow analysis is utilized to shed light on the QBO driving mechanisms.

abstract booklet - university of michigan

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