Web: http://www.ima.umn.edu | Email: ima-staff@ima.umn.edu | Telephone: (612) 624-6066 | Fax: (612) 626-7370
This month's talks available at http://www.ima.umn.edu/newsletters

IMA Newsletter #344

June 2005

2004-2005 Program

Mathematics of Materials and Macromolecules

See http://www.ima.umn.edu/matter for a full description of the 2004-2005 program on
Mathematics of Materials and Macromolecules: Multiple Scales, Disorder, and Singularities
and http://www.ima.umn.edu/schedule for schedule updates.

News and Notes

New Participating Corporation: Medtronic

Medtronic has joined the IMA as a Participating Corporation. Suping Lyu will serve as Medtronics's representative on the IMA Industrial Advisory Board.
IMA Events

IMA Annual Program Year Workshop

Effective Theories for Materials and Macromolecules

June 8-11, 2005

Organizers: Richard D. James (University of Minnesota), Robert V. Kohn (New York University), Claude Le Bris (CERMICS), Mitchell Luskin (University of Minnesota)

http://www.ima.umn.edu/matter/spring/theories.html

This informal workshop will explore new methods, challenges, and opportunities in the development and analysis of effective theories that reduce the degrees of freedom and bridge time and space scales in physics, chemistry, and biology.

Topics to be covered in lectures, discussion, and poster sessions include pattern formation, coarse-graining in statistical physics, epitaxial growth, atomic to continuum models, and complex fluids.

PI Summer Graduate Program

Stochastic Partial Differential Equations & Environmental & Geophysical Modeling

June 13 - July 1, 2005

The University of Wyoming, Laramie, will host the IMA summer graduate program in mathematics. The program consists of five lecture series:
  • Stochastic Navier Stokes Equations on Riemannian Manifolds and Stochastic Partial Differential Equations with Nonlinear Constraints, Zdzislaw Brzezniak (University of Hull)
  • White Noise Theory and Malliavin Calculus for Lévy Processes and Applications to SPDEs and Finance, Bernt Øksendal (University of Oslo)
  • Stochastic Hyperbolic Equations and Random Wave Propagation, Pao-Liu Chow (Wayne State University)
  • Statistical Theory of Turbulence and Modeling of Vortex Dynamics, Franco Flandoli (University of Dini)
  • Stochastic Partial Differential Equations: Theory & Applications, Jerzy Zabczyk (Polish Academy of Sciences)

The PI summer graduate program, which is open only to graduate students from IMA Participating Institutions, is currently full.

2005 Summer Program: Wireless Communication

June 22 - July 1, 2005

Organizers: Prathima Agrawal (Auburn University), Matthew Andrews (Lucent Technologies), Philip Fleming (Motorola, Inc.), George Yin (Wayne State University), Lisa Zhang (Lucent Technologies)

http://www.ima.umn.edu/wireless/

The 2005 Summer program has been organized to meet the challenges posed by the rapid growth in the demand for multimedia wireless services such as voice, data, web-browsing, video, and e-commerce in mobile telephony. Mathematical methods have had a major impact on communication theory. Stochastic calculus, stochastic approximation, and stochastic control theory have been used in hybrid communication network models, asynchronous communication networks, CDMA systems, heavy traffic formulation, fluid models, etc., in an essential way. Wireless networks has recently stimulated further developments in the aforementioned areas, and more research is needed.

The aim of the program is to bring together some of the leading researchers to present state-of-the-art results as well as to identify open problems and future directions. One feature of the program is that it will focus on the deeper issue of studying the interplay of the physical, link, and network layers in wireless networks. It will emphasize therefore involve stochastic calculus, information theory, signal processing, optimization, and control theory. Our objective is to facilitate the communications between academia and the industry, and to bridge the mathematical sciences, engineering, and operations research communities.

The program will consist of a 3-day tutorial, which precedes a 5-day workshop. The tutorial is aimed especially at young researchers new to this area, will provide background knowledge for the workshop, and entry to this active research area. Topics of the workshop include: control and optimization approach to wireless networks, network planning and optimization, air interface scheduling, multihop networks, coding theory for high-speed data over wireless, performance measurement of wireless data networks, information theory of multiple antennas, wireless channel prediction.

Schedule

Wednesday, June 1

11:15a-12:15pFrom discrete to continuum systems: Crystallization in two dimensionsFlorian Theil
University of Warwick
Lind Hall 409 MS

Wednesday, June 8

All DayChair: Mitchell LuskinEE/CS 3-180 W6.8-11.05
8:30a-9:15aCoffee and RegistrationEE/CS 3-176 W6.8-11.05
9:15a-9:30aWelcome and IntroductionDouglas N. Arnold
University of Minnesota
EE/CS 3-180 W6.8-11.05
9:30a-10:30aEstimating systematic errors: sloppy modelsJames P. Sethna
Cornell University
EE/CS 3-180 W6.8-11.05
10:30a-11:30aCoffeeEE/CS 3-176 W6.8-11.05
11:00a-12:00pInserting computational chemistry in materials science: a guided tourClaude Le Bris
CERMICS
EE/CS 3-180 W6.8-11.05
12:00p-2:30pLunch Break W6.8-11.05
2:30p-3:30pBoundary conditions for molecular dynamicsXiantao Li
University of Minnesota
EE/CS 3-180 W6.8-11.05
3:45p-4:45pIMA Tea and more (with POSTER SESSION)Lind Hall 400 W6.8-11.05
A mechanical model of the teleost fin raySilas Alben
New York University - Courant Institute
Higher order gradient continuum description of atomistic models for crystalline solids Marcel Arndt
University of Bonn
A stochastic immersed boundary method for biological fluid dynamics at microscopic length scales Paul Atzberger
Rensselaer Polytechnic Institute
A nonlinear membrane model by means of Young measuresMarian Bocea
University of Utah
Microtwists & NanodefectsAntonio Di Carlo
Universita` degli Studi Roma Tre
A direct approach to numerical homogenization in finite elasticityAntoine Gloria
CERMICS - ENPC
On the use of topological indices in quantitative structure-property relationships for macromolecules Kevin W. Mclaughlin
University of Wisconsin - River Falls
General nonlinear hydrodynamic description of non-Newtonian fluidsHarald Pleiner
Max Planck Institute for Polymer Research
Slip boundary condition for the moving contact line in immiscible two-phase flowsTiezheng Qian
Hong Kong University of Science and Technology
Anchoring distortions coupled with plane Couette and Poiseuille flows of nematic polymersHong Zhou
Naval Postgraduate School
Non-affine deformations of networks of semi-flexible polymersErik van der Giessen
University of Groningen

Thursday, June 9

All DayChair: Robert V. KohnEE/CS 3-180 W6.8-11.05
9:00a-9:30aCoffeeEE/CS 3-176 W6.8-11.05
9:30a-10:30aThermodynamic framework for systematic coarse-graining of atomistic models for fluidsHans Christian Oettinger
ETHZ
EE/CS 3-180 W6.8-11.05
10:30a-11:30aCoffeeEE/CS 3-176 W6.8-11.05
11:00a-12:00pA paradigm of kinetic theories for suspensions and nematic polymersQi Wang
Florida State University
EE/CS 3-180 W6.8-11.05
12:00p-2:30pLunch Break W6.8-11.05
2:30p-3:30pSystematic coarse-graining and concurrent multiresolution simulation of molecular liquidsCameron F. Abrams
Drexel University
EE/CS 3-180 W6.8-11.05
3:30p-3:45pCoffee W6.8-11.05
3:45p-4:45pDislocation field theory in 2D: formulation and validationErik van der Giessen
University of Groningen
EE/CS 3-180 W6.8-11.05

Friday, June 10

All DayChair: Richard D. JamesEE/CS 3-180 W6.8-11.05
9:00a-9:30aCoffeeEE/CS 3-176 W6.8-11.05
9:30a-10:30aContinuum approach to crystal surface morphology evolutionDionisios Margetis
Massachusetts Institute of Technology
EE/CS 3-180 W6.8-11.05
10:30a-11:00aCoffeeEE/CS 3-176 W6.8-11.05
11:00a-12:00pSelf-assembly and shape transitions of epitaxial nanowires and strained monolayer islandsVivek Shenoy
Brown University
EE/CS 3-180 W6.8-11.05
12:00p-2:30pLunch Break W6.8-11.05
2:30p-3:30pComputations of strained heteroepitaxy in 3 dimensions using kinetic Monte CarloPeter Smereka
University of Michigan
EE/CS 3-180 W6.8-11.05
3:30p-3:45pCoffeeEE/CS 3-176 W6.8-11.05
3:45p-4:45pThe effect of screening and correlations in Ostwald ripeningBarbara Niethammer
Humboldt Universität zu Berlin
EE/CS 3-180 W6.8-11.05

Saturday, June 11

All DayChair: Claude Le BrisEE/CS 3-180 W6.8-11.05
9:00a-9:30aCoffeeEE/CS 3-176 W6.8-11.05
9:30a-10:30aSlip boundary condition for the moving contact line in immiscible two-phase flowsTiezheng Qian
Hong Kong University of Science and Technology
EE/CS 3-180 W6.8-11.05
10:30a-11:00aCoffeeEE/CS 3-176 W6.8-11.05
11:00a-12:00pMultiscale modeling of contact line dynamics Weiqing Ren
Princeton University
EE/CS 3-180 W6.8-11.05
12:00p-2:30pLunch Break W6.8-11.05
2:30p-3:30pSimple lattice systems with complex macroscopic descriptionAndrea Braides
II Universita degli studi di Rome (Tor Vergata)
EE/CS 3-180 W6.8-11.05

Wednesday, June 22

<
1:00p-1:15pWelcomeDouglas N. Arnold
University of Minnesota
Philip Fleming
Motorola, Inc.
EE/CS 3-180 SP6.22-7.1.05
1:15p-1:45pOverviewPhilip Fleming
Motorola, Inc.
EE/CS 3-180 SP6.22-7.1.05
1:45p-2:00pBreakEE/CS 3-176 SP6.22-7.1.05
2:00p-3:00pEntropy, inference, and channel capacitySean P. Meyn
University of Illinois - Urbana-Champaign
EE/CS 3-180 SP6.22-7.1.05
3:00p-3:30pBreakEE/CS 3-176 SP6.22-7.1.05
3:30p-4:30pSystem analysis of wireless packet networks carrying voice over IP Philip Fleming
Motorola, Inc.
EE/CS 3-180 SP6.22-7.1.05
4:30p-5:00pBreakEE/CS 3-176 SP6.22-7.1.05
5:00p-6:00pScheduling and resource management in 3G, Wimax and all-IP wireless networksThierry Klein
Lucent Technologies
EE/CS 3-180 SP6.22-7.1.05
7:00p-8:00pDinnerLocation: TBA SP6.22-7.1.05

Thursday, June 23

<
8:30a-9:00acoffee and rollsEE/CS 3-176 SP6.22-7.1.05
9:00a-10:30aCapacity, architecture, and protocols for ad hoc wireless networks P. R. Kumar
University of Illinois - Urbana-Champaign
EE/CS 3-180 SP6.22-7.1.05
10:30a-11:00aBreakEE/CS 3-180 SP6.22-7.1.05
11:00a-12:30pCapacity, architecture, and protocols for ad hoc wireless networks P. R. Kumar
University of Illinois - Urbana-Champaign
EE/CS 3-180 SP6.22-7.1.05
12:30p-2:00p Lunch SP6.22-7.1.05
2:00p-3:00pEntropy, inference, and channel capacitySean P. Meyn
University of Illinois - Urbana-Champaign
EE/CS 3-180 SP6.22-7.1.05
3:00p-3:30pBreakEE/CS 3-176 SP6.22-7.1.05
3:30p-4:30pScheduling and resource management in 3G, Wimax and all-IP wireless networksThierry Klein
Lucent Technologies
EE/CS 3-180 SP6.22-7.1.05
5:00p-6:00pReceptionEE/CS 3-176 SP6.22-7.1.05

Friday, June 24

8:00a-8:30a coffee and rollsEE/CS 3-176 SP6.22-7.1.05
8:30a-10:00aSystem analysis of wireless packet networks carrying voice over IP Philip Fleming
Motorola, Inc.
EE/CS 3-180 SP6.22-7.1.05
10:00a-10:30aBreakEE/CS 3-176 SP6.22-7.1.05
10:30a-11:30aEntropy, inference, and channel capacitySean P. Meyn
University of Illinois - Urbana-Champaign
EE/CS 3-180 SP6.22-7.1.05
11:30a-1:00pLunch SP6.22-7.1.05
1:00p-2:30pScheduling and resource management in 3G, Wimax and all-IP wireless networks Thierry Klein
Lucent Technologies
EE/CS 3-180 SP6.22-7.1.05
2:30p-3:00pWrap-upDouglas N. Arnold
University of Minnesota
Philip Fleming
Motorola, Inc.
EE/CS 3-180 SP6.22-7.1.05

Monday, June 27

8:30a-9:15aCoffeeEE/CS 3-176 SP6.22-7.1.05
9:15a-9:30aOpening:Douglas N. Arnold
University of Minnesota
EE/CS 3-180 SP6.22-7.1.05
9:30a-10:30aCross layer optimization in wireless networksFrancois Baccelli
Ecole Normale Superieure
EE/CS 3-180 SP6.22-7.1.05
10:30a-11:00aCoffeeEE/CS 3-176 SP6.22-7.1.05
11:00a-12:00pFlow-level performance in wireless data networks Sem C. Borst
Lucent Technologies - Bell Laboratories
EE/CS 3-180 SP6.22-7.1.05
12:00p-2:00pLunch SP6.22-7.1.05
2:00p-3:00pCharacterization and computation of optimal distributions for channel coding Sean P. Meyn
University of Illinois - Urbana-Champaign
SP6.22-7.1.05
3:00p-3:15pCoffeeEE/CS 3-176 SP6.22-7.1.05
3:15p-4:15pScheduling high speed data in (adversarial) wireless networks Matthew Andrews
Lucent Technologies
EE/CS 3-180 SP6.22-7.1.05
4:15p-4:45pSecond ChancesEE/CS 3-180 SP6.22-7.1.05
5:00p-6:30pReception and Poster SessionLind Hall 400 SP6.22-7.1.05
High SNR analysis of MIMO broadcast channelsNihar Jindal
University of Minnesota
Cooperation vs. compression for sensor networksChulhan Lee
University of Texas - Austin
Effective capacity approach to providing statistical quality-of-service guarantees in wireless networksDapeng Wu
University of Florida

Tuesday, June 28

9:00a-9:30aCoffeeEE/CS 3-176 SP6.22-7.1.05
9:30a-10:30aSelforganizing control of network structure in wireless communicationMartin Greiner
Siemens
EE/CS 3-180 SP6.22-7.1.05
10:30a-11:00aCoffeeEE/CS 3-176 SP6.22-7.1.05
11:00a-12:00pControl of multi-node mobile Communications networks with time varying channels via stability methods Harold J. Kushner
Brown University
EE/CS 3-180 SP6.22-7.1.05
12:00p-2:00pLunch SP6.22-7.1.05
2:00p-3:00pAn optimization model of protocol stack and hetergeneous protocols Steven Low
California Institute of Technology
EE/CS 3-180 SP6.22-7.1.05
3:00p-3:15pCoffeeEE/CS 3-176 SP6.22-7.1.05
3:15p-4:15pCross-layer control in wireless networks with QoS constraints Eytan Modiano
Massachusetts Institute of Technology
EE/CS 3-180 SP6.22-7.1.05
4:15p-4:45pSecond ChancesEE/CS 3-180 SP6.22-7.1.05

Wednesday, June 29

9:00a-9:30a CoffeeEE/CS 3-176 SP6.22-7.1.05
9:30a-10:30aSpectrum Sharing GamesRandall A. Berry
Northwestern University
EE/CS 3-180 SP6.22-7.1.05
10:30a-11:00aCoffeeEE/CS 3-176 SP6.22-7.1.05
11:00a-12:00pStructural results in cross layer optimization of wireless networks Vikram Krishnamurthy
University of British Columbia
EE/CS 3-180 SP6.22-7.1.05
12:00p-1:30p Lunch SP6.22-7.1.05
1:30p-2:30pConvergence and optimality of channel aware scheduling and resource allocation algorithms Rajeev Agrawal
Motorola, Inc.
EE/CS 3-180 SP6.22-7.1.05
2:30p-3:30pTBAKenneth L. Clarkson
Bell Laboratories
EE/CS 3-180 SP6.22-7.1.05
3:30p-4:00pCoffeeEE/CS 3-176 SP6.22-7.1.05
4:00p-5:00pCross-layer design for wireless networks Ness Shroff
Purdue University
EE/CS 3-180 SP6.22-7.1.05
5:00p-5:30pSecond ChancesEE/CS 3-180 SP6.22-7.1.05

Thursday, June 30

9:00a-9:30aCoffeeEE/CS 3-176 SP6.22-7.1.05
9:30a-10:30aSome Information theory and codes for half-duplex relaysGerhard Kramer
Lucent Technologies
EE/CS 3-180 SP6.22-7.1.05
10:30a-11:00a CoffeeEE/CS 3-176 SP6.22-7.1.05
11:00a-12:00pTBAColin D. Frank
Motorola, Inc.
EE/CS 3-180 SP6.22-7.1.05
12:00p-1:30pLunch SP6.22-7.1.05
1:30p-2:30pOverlay networks for wireless ad hoc networks Christian Scheideler
Johns Hopkins University
EE/CS 3-180 SP6.22-7.1.05
2:30p-3:30pDistributed canonical correlation and distortion-rate analyses for centralized compression-estimation using wireless sensor networksGeorgios Giannakis
University of Minnesota
EE/CS 3-180 SP6.22-7.1.05
3:30p-4:00pCoffeeEE/CS 3-176 SP6.22-7.1.05
4:00p-5:00pHeavy traffic models and control of wireless systems Robert Buche
North Carolina State University
EE/CS 3-180 SP6.22-7.1.05
5:00p-5:30pSecond ChancesEE/CS 3-180 SP6.22-7.1.05
6:00p-8:00pDinner SP6.22-7.1.05

Friday, July 1

8:30a-9:00aCoffeeEE/CS 3-176 SP6.22-7.1.05
9:00a-10:00aMathematical problems in ad hoc wireless networks Wing Shing Wong
Chinese University of Hong Kong
EE/CS 3-180 SP6.22-7.1.05
10:00a-10:15aCoffeeEE/CS 3-176 SP6.22-7.1.05
10:15a-11:15aOptimization of IEEE 802.11 DCF based on Bayesian estimation of the number of competing terminals Xiaodong Wang
Columbia University
EE/CS 3-180 SP6.22-7.1.05
11:15a-12:15pEnergy efficiency in multiple-access wireless networks: Nash equilibria in power control games Vincent Poor
Princeton University
EE/CS 3-180 SP6.22-7.1.05
12:15p-12:45pSecond Chances and Concluding RemarksEE/CS 3-180 SP6.22-7.1.05
Abstracts
Cameron F. Abrams (Drexel University) Systematic coarse-graining and concurrent multiresolution simulation of molecular liquids
Abstract: Systematic coarse-graining is a class of techniques in which judicious approximations are invoked to coarsen a system of many degrees of freedom onto one with relatively fewer in a statistical mechanically consistent way. Collective variables are chosen and the resulting potentials of mean force at a given thermodynamic state are derived from the atomic level potential energy hypersurface. These techniques are briefly reviewed in their connection with the molecular simulation of specific synthetic polymers. Further developments incorporating on-the-fly coarse-graining into concurrent multiresolution simulations of simple molecular liquids are also discussed.
Rajeev Agrawal (Motorola, Inc.) Convergence and optimality of channel aware scheduling and resource allocation algorithms
Abstract: With an abstraction of serving rate-adaptive sources on a broadcast-type wireless channel as a utility maximization problem, it is shown how one can design many intuitive online scheduling policies based upon the feedback that one obtains at the scheduler. Using a stochastic approximation argument it is then shown that the constructed algorithms converge to optimal solutions of the utility maximization problem over different sets which critically depend on the quality of the feedback information. We then apply the theory developed above to the downlink in a CDMA based wireless network. In terms of operational variables the problem is to select a subset of the users for transmission at each transmission oppurtunity and for each of the users selected, to choose the modulation and coding scheme, transmission power, and number of codes used. We refer to this combination as the physical layer operating point (PLOP). Each PLOP consumes different amounts of code and power resources. Thus, the task is to pick the ``optimal'' PLOP taking into account both system-wide and individual user resource constraints that can arise in a practical system. Using an information theoretic model for the achievable rate per code results in a tractable convex optimization problem. By exploiting the structure of this problem, we give algorithms for finding the optimal solution with geometric convergence. We also use insights obtained from the optimal solution to construct low complexity near optimal algorithms that are easily implementable. Numerical results comparing these algorithms are also given.
Silas Alben (New York University - Courant Institute) A mechanical model of the teleost fin ray
Abstract: This work considers the mechanics of fish swimming. In collaboration with the Lauder lab at Harvard, we are studying the structure of fish fin rays. Approximately half of all fish species utilize the same basic structure--body segments linked by a collagen network--to transduce fin ray shape and motion from a given input force. We present a simple coupled elastica model which uses only geometry and a single elastic constant to obtain the scalings of forces and displacements.
Matthew Andrews (Lucent Technologies) Scheduling high speed data in (adversarial) wireless networks
Abstract: Wireless networks for transmitting high speed data are becoming increasingly common. Such networks lead to new and interesting scheduling problems, in large part because the quality of a wireless channel constantly changes over time. It is important to schedule in an opportunistic fashion, i.e. we want to transmit data between two users during the times when the associated wireless channel has good quality. A number of models have been proposed for studying such systems. These differ according to the assumptions made on the arrival process, the assumptions made on the channel conditions, and the metrics that are to be optimized. In this talk we shall survey some of these models and present contrasting scheduling results that arise in each model. We shall concentrate on the case in which the channel conditions are governed by an adversary and present limits on the optimum fairness and quality-of-service that can be achieved in the resulting adversarial environment.
Marcel Arndt (University of Bonn) Higher order gradient continuum description of atomistic models for crystalline solids
Abstract: We propose an upscaling scheme for the passage from atomistic to continuum mechanical models for crystalline solids. It is based on an expansion of the deformation function up to a given order and leads to a continuum mechanical model which involves higher order gradients. The resulting model is an approximation of the atomistic system for a fixed and finite number of atoms within the quasi-continuum regime. The higher order terms allow the description of the microscopic material properties to a higher extent than commonly used continuum mechanical models. In particular, the discreteness effects of the underlying atomistic model are captured. Our upscaling technique is compared to other upscaling schemes and analyzed with respect to well-posedness and the asymptotic scale behavior. The qualitative properties of our technique are numerically studied for the model problem of a one-dimensional atomic chain. The approach is then applied to the physically more relevant three-dimensional example of a silicon crystal. The resulting approximation properties are studied.
Paul Atzberger (Rensselaer Polytechnic Institute) A stochastic immersed boundary method for biological fluid dynamics at microscopic length scales
Abstract: With advances in cell and molecular biology there is an increasing interest in modeling microscopic systems at a coarse level where methods such as molecular dynamics become infeasible as a consequence of the wide range of active length and time scales. An alternative approach is to use a continuum description where neglected degrees of freedom of the system are accounted for by an effective model either through averaging or an appropriate stochastic model. In this poster an extension of the immersed boundary method [1] is presented for this purpose which includes appropriate stochastic forcing to model thermal fluctuations of the fluid and immersed structures. A stochastic numerical method is presented which deals with stiffness in the system by carefully handling statistical contributions of the dynamics of the fluid and immersed structures over long time steps. A number of physical checks are presented for the method which show for example that immersed particles diffuse with the appropriate scaling in the physical parameters and have the correct equilibrium statistics. The method is also demonstrated to reproduce well-known hydrodynamic effects such as the 3/2 decay in the tail of the velocity autocorelation function of a Brownian particle. In conclusion, numerical results are presented for specific applications to polymers and membranes. [1] Peskin, C.S (2002), The immersed boundary method, Acta Numerica, 11, pp. 1-39.
Randall A Berry (Northwestern University) Spectrum Sharing Games
Abstract: In wireless networks a key consideration is how to mitigate interference among multiple users in a given spectrum band. This is especially true in unlicensed or open bands, where users may be deployed without any centralized frequency planning or control. In this talk, we describe some simple mathematical models for sharing a given spectrum band. We discuss both a case where a spectrum manager controls access and a case where there is no manager and users implement a distributed algorithm to manage access. In the first case, we describe an auction mechanisms where the users bid for spectrum access. We model this auction as a game and characterize the equilibrium. In the second case, we discuss a distributed algorithm, in which users announce "price" signals which indicate the cost of interference to them. We relate this algorithm to a "fictitious" game, which in certain cases is supermodular. This relation is used to characterize the algorithms convergence. Extensions to multi-channel networks will also be discussed, where users can allocate their power over multiple frequency bands, as in a OFDM system.
Marian Bocea (University of Utah) A nonlinear membrane model by means of Young measures
Abstract: The integral representation of a relaxed functional arising in the derivation of a nonlinear membrane model is obtained in terms of a special class of Young measures generated by sequences of scaled gradients. Algebraic and analytical conditions on parametrized probability measures both necessary and sufficient to guarantee that they belong to this class are identified, in the spirit of Kinderlehrer and Pedregal's characterization of gradient Young measures. Joint work with Irene Fonseca.
Sem C. Borst (Lucent Technologies - Bell Laboratories) Flow-level performance in wireless data networks
Abstract: Channel-aware scheduling strategies provide an effective mechanism for improving throughput performance in wireless data networks by exploiting channel fluctuations. In the talk, we focus on the flow-level performance of channel-aware scheduling algorithms in a dynamic setting with random finite-size data transfers. We show that in certain cases the flow-level performance may be evaluated by means of a multi-class Processor-Sharing model where the total service rate varies with the total number of users. In addition, we present simple necessary conditions for flow-level stability in the presence of channel variations, and establish that these are also sufficient for a broad class of utility-based scheduling strategies and arbitrary rate statistics. Time permitting, we conclude with a discussion of capacity issues and flow-level performance in wireless networks with multiple interacting base stations.
Andrea Braides (II Università degli studi di Rome (Tor Vergata)) Simple lattice systems with complex macroscopic description
Abstract: I will present a homogenized description of the simplest lattice systems, where the lattice energy depends on a variable that possesses only two states (without loss of generality we may take these two values as +1 and -1). The overall behavior of the system, as the number of nodes increases can be described, upon scaling, by a continuum expansion. in terms of Gamma-convergence. In the limit energies we may recognize bulk terms, interfacial energies, anti-phase boundaries and microscopical oscillations, depending on the lattice parameters and shape. Some comments on the random case will also be given.
Robert Buche (North Carolina State University) Heavy traffic models and control of wireless systems
Abstract: Heavy traffic methods are useful for wireline queueing analysis and show promise for wireless systems. The main difference compared to the wireline setting is the randomly-varying environment in which wireless systems operate. In the heavy traffic analysis, typically a Brownian driven stochastic differential equation with reflection (SDER) models the queueing dynamics. We will discuss these models and the associated stochastic control problem along with some numerical simulation results. Recently, the importance of modeling long range dependence in wireless systems has been shown. We will give some initial comments on extending the analysis to this case where the SDER is driven by a more general Levy process.
Antonio Di Carlo (Università degli Studi Roma Tre) Microtwists & Nanodefects
Abstract: Abstract: Prototype nanoelectromechanical devices incorporating individual multiwall carbon nanotubes as torsion bars or rotary bearings have been fabricated and tested by various groups. Typical length scales are: 1 micron for the overall span, 25 nm for the diameter, 0.5 nm for the interwall gap. The experimental evidence collected so far is puzzling, pointing out a need for a better understanding of the interwall mechanical coupling mechanisms. We speculate that the basic mechanism behind progressive interwall coupling is the formation of bridging defects, that is, covalent links between adjacent walls, triggered by inward migration of chromium atoms (which are evaporated onto the outer wall of the nanotube when fabricating the device).
Philip Fleming (Motorola, Inc.) System analysis of wireless packet networks carrying voice over IP
Abstract: Joint work with Amitava Ghosh and Ivan Vukovic. This tutorial will cover the system architecture, protocol design and performance characteristics of voice and other quasi-real-time applications such as push-to-talk over wireless packet networks. We address features of the bearer path such as voice coding and IP header compression as well as control plane characteristics such as call set-up and hand-off latency. We will give an overview of the next generation wireless wide area network technologies, HRPD (EV-DO), HSUPA/HSDPA and 802.16e and present analysis and simulation of system behavior for each under moderate and heavy loading conditions using both real- and non-real-time traffic and mixtures. Packet scheduling and media access control will also be discussed in some detail. Toward the end of the tutorial we will discuss open research areas.
Georgios Giannakis (University of Minnesota) Distributed canonical correlation and distortion-rate analyses for centralized compression-estimation using wireless sensor networks
Abstract: Wireless sensor networks deployed to perform surveillance and monitoring tasks have to operate under stringent energy and bandwidth limitations. These motivate well distributed compression and estimation scenarios based on reduced dimensionality sensor observations which may have to be severely quantized before transmission to a fusion center. We will show how distributed correlation analysis can be used to compress observations and explore the fundamental performance limits dictated by distortion-rate analysis in this decentralized estimation setup. We will further present interesting tradeoffs that emerge even in distributed mean-location estimation based on severely quantized observations along with their fundamental error-variance limits. Estimators utilizing either independent or colored binary data will be developed and analyzed. Corroborating simulations will provide comparisons with the clairvoyant estimators based on unquantized sensor observations, and include a motivating application with a sensor net employed for habitat monitoring. In the poster session we will also discuss dynamical systems and present (extended) Kalman Filtering ideas based on single-bit observations.
Brief Bio: G. B. Giannakis received his B.Sc. in 1981 from the Ntl. Tech. Univ. of Athens, Greece and his M.Sc. and Ph.D. in Electrical Engineering in 1983 and 1986 from the Univ. of Southern California. Since 1999 he has been a professor with the Department of Electrical and Computer Engineering at the University of Minnesota, where he now holds an Endowed ADC Chair in Wireless Telecommunications. His general interests span the areas of communications and signal processing, estimation and detection theory -- subjects on which he has published more than 200 journal papers, 350 conference papers, and two edited books. Current research focuses on complex-field and space-time coding, multicarrier, ultra-wide band wireless communication systems, cross-layer designs and wireless sensor networks. He is the (co-) recipient of six best paper awards from the IEEE Signal Processing (SP) and Communications Societies (1992, 1998, 2000, 2001, 2003, 2004) and also received the SP Society's Technical Achievement Award in 2000. He is an IEEE Fellow since 1997 and has served the IEEE in various editorial and organizational posts.
Antoine Gloria (CERMICS - ENPC) A direct approach to numerical homogenization in finite elasticity
Abstract: We present a direct approach to tackle the numerical simulation of a homogenized problem in nonlinear elasticity at finite strain. We provide an approximation result for this problem and derive an error estimate in the particular case of convex energy densities. We have implemented this approach in a nonlinear elasticity solver and performed several numerical tests on idealized rubber foams.
Martin Greiner (Siemens) Selforganizing control of network structure in wireless communication
Abstract: Wireless multihop ad hoc communication networks represent an infrastructure-less peer-to-peer generalization of todays cellular networks. Since a central control authority is missing, the complex network has to selforganize itself for various operating tasks. Key is the design of simple, yet robust distributive control rules, which allow the overall network to perform well. Two examples from topology control are given. The first one addresses the connectivity issue, where a selforganizing rule is presented and shown to lead to strong network connectivity almost surely. A generic packet-traffic analysis is used in the second example to first develop a phenomenological description of the end-to-end throughput capacity for fixed network structures and then to sketch further steps towards a selforganizing rule for obtaining throughput-optimized network structures.
Nihar Jindal (University of Minnesota) High SNR analysis of MIMO broadcast channels
Abstract: The behavior of the multiple antenna broadcast channel at high SNR is investigated. The sum rate capacity (achievable by dirty paper coding), the sum rate achievable using transmitter beamforming, and an upper bound to the sum rate capacity are studied. Though these three terms are equivalent in the sense of the multiplexing gain, i.e. in terms of first order growth, there is an absolute difference between the corresponding rates. These difference terms are calculated and simple and intuitive geometrical interpretations are given.
Gerhard Kramer (Lucent Technologies) Some Information theory and codes for half-duplex relays
Abstract: A relay channel has a source terminal transmitting a message to a destination terminal with the help of one or more relays. We review a selection of the existing information theory for such channels, with emphasis on half-duplex models. We further consider aspects of code and receiver design, including phase and symbol synchronization.
Vikram Krishnamurthy (University of British Columbia) Structural results in cross layer optimization of wireless networks
Abstract: In the first part of the talk, we consider the interaction between the physical and link layers for single user systems. By using a Lagriangian approach to constrained Markov decision processes and stochastic dominance results, we examine the structural effects of buffer size, fading channel dynamics and traffic dynamics on system throughput. Also a channel aware ARQ protocol is proposed that uses a partially observed Markov deicision process to optimize the tradeoff between latency and throughput. In the second part of the talk, we consider cross layer admission control and vertical handoff between WLAN and CDMA networks for multiuser systems. We present gradient learning based stochastic approximation algorithms to optimize the resulting constrained Markov decision process.
P. R. Kumar (University of Illinois - Urbana-Champaign) Capacity, architecture, and protocols for ad hoc wireless networks
Abstract: Topics This tutorial is motivated by two considerations. (i) There has been some progress in recent years in developing a quantitative framework for wireless networks. (ii) The research community is entering a phase of designing several second generation protocols for wireless networks which aim to not only improve performance, but also to address unmet needs. Our goal in this tutorial is twofold: (i) We will provide a clear presentation of the key ideas underlying this emerging theory of wireless networks. The goal is to make the theory accessible to all researchers in the area, to understand the questions addressed, the questions unaddressed, the methods used, and address its shortcomings, as well as its results, i.e., basically to understand it. (ii) We will provide some candidate second generation protocol designs. In particular we will stress the importance of paying attention to the architecture of the implementation. We will also address some issues related to the emerging topic of cross-layer design. We will also stress the importance of implementing designs.
Harold J. Kushner (Brown University) Control of multi-node mobile Communications networks with time varying channels via stability methods
Abstract: Consider a communications network consisting of mobiles, each of which can be scheduled to serve as a receiver and/or transmitter. Data from many external sources arrives at the various mobiles in some random way. Each mobile can serve as a node in the possibly multihop path from source to destination. At each mobile the data is queued according to the source-destination pair until transmitted. Time is divided into small scheduling intervals. The connecting channels are randomly varying due to the motion of the mobiles and consequent scattering. At the beginning of the intervals, the channels are estimated via pilot signals and this information is used for scheduling. The issues are the allocation of transmission power and/or time and bandwidth to the various queues at the various mobiles in a queue and channel-state dependent way to assure stability and good operation. Lost packets might or might not have to be retransmitted. The decisions are made at the beginning of the scheduling intervals. In a recent work, stochastic stability methods were used to develop scheduling policies for the simple system where there is a single transmitter communicating with many mobiles. The resulting controls were readily implementable and allowed a range of tradeoffs between current rates and queue lengths, under very weak conditions. Here the basic methods and results are extended to the network case. The choice of Liapunov function allows a choice of the effective performance criteria. All essential factors are incorporated into a "mean rate" function, so that the results cover many different systems. Because of the non-Markovian nature of the problem, we use the perturbed Stochastic Liapunov function method, which is designed for such problems.
Claude Le Bris (CERMICS) Inserting computational chemistry in materials science: a guided tour
Abstract: We will introduce the audience to the basic modelling in computational quantum chemistry. We will overview the mathematical and numerical aspects, pointing out some recent works. A special emphasis will be laid upon the approaches used for large size systems, and, beyond, the different methods coupling quantum chemistry models and models of materials science.
Chulhan Lee (University of Texas - Austin) Cooperation vs. compression for sensor networks
Abstract: In a sensor network, nodes share information about their observations, and the amount of shared information can often be substantial. This paper compares two different strategies that exploit this redundant information - compression and cooperation. It finds compression to be the winning strategy when energy savings is the most important objective, but finds cooperation to be the throughput maximizing strategy. A weighted optimization problem is formulated to obtain intermediate schemes that allow a critical level of cooperation in the system, thereafter compressing all other redundant information.
Xiantao Li (University of Minnesota) Boundary conditions for molecular dynamics
Abstract: At the atomic scale, crystalline solids can be modelled by Molecular dynamics (MD), which provides a very useful tool to study crystal structure and defect dynamics. MD simulations can be conducted either in isolation, with some experimental loading condition applied to its boundary, or they can be coupled with a continuum model replacing all the atoms outside of the atomistic region. In both cases, a key issue is to eliminate the reflection of phonons at the boundary or the continuum/atomistic interface. In this talk, I will present a variational formulation for constructing boundary conditions that suppress phonon reflections. Local boundary conditions, which are practical for computational purpose, are obtained from this formulation. A few examples, including 1D chain, 2D triangular lattice, 3D BCC lattice and Graphene (complex lattice) will be given. Finally we apply these boundary conditions to fracture simulations. This is joint work with Weinan E (Princeton).
Steven Low (California Institute of Technology) An optimization model of protocol stack and hetergeneous protocols
Abstract: Can we integrate the various protocol layers into a single coherent theory by regarding them as carrying out an asynchronous distributed primal-dual computation over the network to implicitly solve a global optimization problem? Different layers iterate on different subsets of the decision variables using local information to achieve individual optimalities, but taken together, these local algorithms attempt to achieve a global objective. Such a theory will expose the interconnection between protocol layers and can be used to study rigorously the performance tradeoff in protocol layering as different ways to distribute a centralized computation. We describe some preliminary work on cross layer interactions involving HTTP, TCP, IP, MAC, and scheduling. All of these instances can be integrated within a utility maximization model. We present equilibrium and stability properties of networks shared by TCP sources that react to different pricing signals where the current utlity maximization model breaks down.
Dionisios Margetis (Massachusetts Institute of Technology) Continuum approach to crystal surface morphology evolution
Abstract: The design of small devices with novel properties relies on the synthesis and stability of nanoscale surface structures. At temperatures below roughening crystal surfaces have flat, macroscopic regions known as "facets'' and evolve via the motion of interacting atomic steps. This talk describes macroscopic evolution laws on the basis of the microscopic step motion. First, continuum evolution equations in (2+1) dimensions are derived from kinetic considerations; the surface height profile outside facets satisfies a nonlinear PDE that accounts for mass fluxes parallel and transverse to steps via an appropriate tensor mobility. Second, the PDE is tested through comparisons of analytical predictions with experimental results and numerical simulations that follow the motion of individual steps. The challenging problem of suitable boundary conditions at the boundaries of facets is discussed.
Kevin W. Mclaughlin (University of Wisconsin - River Falls) On the use of topological indices in quantitative structure-property relationships for macromolecules
Abstract: Chemical graph theory has been extensively applied to predicting the physical properties of small molecules through quantitative-structure property relationships (QSPR). This has been accomplished by demonstrating strong correlations between physical properties and one or more topological indices. Extending the application of topological indices to macromolecules can lead to potential problems for such models. Using the Hosoya index, we illustrate both the problems associated with degeneracy of a topological index as molecular size and complexity increases, and what limits should be placed on the development of such models.
Sean P. Meyn (University of Illinois - Urbana-Champaign) Characterization and computation of optimal distributions for channel coding
Abstract: This presentation concerns the structure of optimal codes for stochastic channel models. An investigation of an associated dual convex program reveals that the optimal distribution in channel coding is typically discrete. Based on this observation we construct a new class of algorithms is introduced, based on the cutting-plane method, to generate discrete distributions that are optimal within a prescribed class. This lecture builds upon a tutorial lecture to be presented by Meyn prior to the workshop at IMA.
Eytan Modiano (Massachusetts Institute of Technology) Cross-layer control in wireless networks with QoS constraints
Abstract: In this talk we will describe algorithms for resource allocation in wireless networks that attempt to optimize network performance across multiple layers of the protocol stack. In the first part of the talk we will consider the joint problem of flow control, routing, and scheduling in a wireless network subject to Quality of Service requirements. In particular, we will describe a dynamic control strategy that maximizes the sum utility in the network; and can be used to achieve a wide range of fairness objectives. In the second part, we consider a wireless transmitter whose data rate can be controlled by varying the transmission power. For such a system we will describe optimal transmission policies that satisfy delay constraints and also minimize the total transmission energy expenditure.
Barbara Niethammer (Humboldt Universität zu Berlin) The effect of screening and correlations in Ostwald ripening
Abstract: The classical theory by Lifshitz, Slyozov and Wagner describes diffusion limited coarsening of particles in the limit of vanishing volume fraction. Due to several shortcomingis of the LSW theory first order corrections in terms of the volume fraction should be taken into account. We discuss a new method to effeciently identify first-order corrections in a statistically homogeneous system. The key idea is to relate the full system of particles to systems where a finite number of particles has been removed. This method allows to decouple screening and correlation effects and allows to effiently evaluate conditional expected values of the particle growth rates.
Hans Christian Oettinger (ETHZ) Thermodynamic framework for systematic coarse-graining of atomistic models for fluids
Abstract: For this talk, I distinguish between two fundamentally different simulation approaches in materials science, "brute-force simulations" and "thermodynamically guided simulations." Brute-force simulations can be thought of as computer experiments mimicking the physical situation of interest directly on a computer; thermodynamically guided simulations rely on a nonequilibrium statistical ensemble containing the variables of some coarse-grained description of the system of interest. The availability of an appropriate coarse-grained level of description is thus crucial for thermodynamically guided simulations and should be considered as a reasonable price to pay for bridging widely separated time scales (and deeper understanding). The above remarks are elaborated in the context of molecular dynamics simulations of Lennard Jones fluids and of polymer melts. It is shown how simulations based on nonequilibrium ensembles can help to bridge the wide range of time scales from monomer motions to polymer processing. The importance of coarse-grained models for specifying an ensemble and for identifying suitable quantities of interest is illustrated.
Harald Pleiner (Max Planck Institute for Polymer Research) General nonlinear hydrodynamic description of non-Newtonian fluids
Abstract: We review conventional constitutive equations for non-Newtonian fluids from a hydrodynamic point of view. Using general thermodynamic and symmetry arguments and applying valid physical principles we describe viscoelasticity by setting up nonlinear dynamic equations either for a relaxing (Eulerian) strain tensor or for a transient orientational order parameter tensor. This covers the usual non-Newtonian effects, like shear thinning, strain hardening, stress overshoot, normal stress differences and non exponential stress relaxation. In both cases an effective dynamic equation for the stress tensor can be derived in terms of a power series and compared with conventional non-Newtonian rheological models. It is more general in structure than those, comprises most, restricts some, and discards a few of them. In addition, we generalize this approach into a 2-fluid description for multi-component fluids, which is appropriate, when the relative velocity of the different components is relaxing slowly. Special emphasis is laid on nonlinearities involving velocities that are governed by symmetry and other general invariance principles. It is shown that the proper velocities, with which the dynamic quantities are transported and convected, cannot be chosen at will, since there are subtle relations among them. Within allowed combinations the convective velocities are generally material dependent and not fixed by general principles. The so-called stress division problem, i.e. how the total stress is distributed between the different components, is shown to depend partially on the choice of the convected velocities, but is otherwise also material dependent. A set of reasonably simplified equations is given for viscoelastic fluids, polymeric gels, and ferrofluids focusing on an effective concentration dynamics that may be used for comparison with experiments.
Vincent Poor (Princeton University) Energy efficiency in multiple-access wireless networks: Nash equilibria in power control games
Abstract: The energy efficiency (measured in bits-per-Joule) of multiple-access wireless data networks is considered via the behavior of Nash equilibria in non-cooperative power control games. Particular issues considered include the effects of multiuser detection and multiple antennas on energy efficiency, energy efficient carrier loading in multi-carrier CDMA systems, and the effects of delay constraints on energy efficiency. Some open problems of interest are also discussed.
Tiezheng Qian (Hong Kong University of Science and Technology) Slip boundary condition for the moving contact line in immiscible two-phase flows
Abstract: From extensive molecular dynamics simulations on immiscible two-phase flows, we find the relative slipping between the fluids and the solid wall everywhere to follow the generalized Navier boundary condition, in which the amount of slipping is proportional to the sum of tangential viscous stress and the uncompensated Young stress. The latter arises from the deviation of the fluid-fluid interface from its static configuration. We give a continuum formulation of the immiscible flow hydrodynamics, comprising the generalized Navier boundary condition, the Navier-Stokes equation, and the Cahn-Hilliard interfacial free energy. Our hydrodynamic model yields interfacial and velocity profiles matching those from the molecular dynamics simulations at the molecular-scale vicinity of the contact line.
Weiqing Ren (Princeton University) Multiscale modeling of contact line dynamics
Abstract: The moving contact line (MCL) problem is analyzed using the multiscale methods developed recently by Ren and E. It is well-known that the no-slip boundary condition results in a non-integrable singularity in the stress at the contact line. Numerous empirical slip models have been proposed to remove the stress singularity. For the multiscale method, we solve the Navier-Stokes (NS) equations for the macro-scale flow field, and calculate the needed boundary condition, e.g., the shear stress, at the contact line region based on molecular dynamics (MD). In the talk, we will discuss the details of the multiscale method, the validation study, and the results on large scale contact line problem.
Christian Scheideler (Johns Hopkins University) Overlay networks for wireless ad hoc networks
Abstract: In this talk I will give an overview of various techniques to organize Wireless nodes in an overlay network with near-optimal communication Paths between any pair of nodes. Many of these overlay network constructions are based on the theory of graph spanners. Spanners first appeared in computational geometry, were then discovered as an interesting tool for approximating NP-hard problems, and have recently also attracted a lot of attention in the context of routing and topology control in wireless ad hoc networks. After introducing the concept of graph spanners and giving several Examples relevant for wireless ad hoc networks, I will discuss various distributed, self-stabilizing protocols for maintaining a spanner among the wireless nodes, using a very simple wireless communication model just to provide a proof of concept. Afterwards, I will also discuss a much more realistic wireless communication model that has just recently been published, and I will demonstrate how to design a self-stabilizing overlay network protocol within that model.
James P. Sethna (Cornell University) Estimating systematic errors: sloppy models
Abstract: Joint work with Søren Fredericksen, Karsten W. Jacobsen, and Kevin S. Brown Science is filled with multiparameter models that must be fit to observations. An ecosystem has many interacting species, a cell has interacting proteins and genes, and a material has many atoms whose forces are governed by quantum-mechanical electronic calculations. A key question for these models is when we can trust their predictions: usually only wisdom and experience can judge for which problems a given model will likely be reliable. One source of unreliability in these models is that they are sloppy: the parameters are ill-determined by the data, with enormous ranges giving roughly equivalent fits. These parameters giving roughly equivalent fits, however, do not yield the same predictions! By using an ensemble of good parameter sets, we have been able to produce `sloppy model' estimates of the errors in one particular system: the interatomic potential for the element Molybdenum. Our error estimates capture most of the systematic error in this system, for three different forms of the interatomic potential.
Vivek Shenoy (Brown University) Self-assembly and shape transitions of epitaxial nanowires and strained monolayer islands
Abstract: Several interesting shape transitions have been recently observed during the growth of submonolayer islands on lattice-mismatched substrates. These shapes, which allow relaxation of mismatch strain, include nanowires that are elongated along certain crystallographic directions with widths in the single-digit nanometer range, shapes that show concave boundaries in equilibrium and formation of highly ramified or branched structures during growth. In this talk, I will present a sharp interface model and a phasefield model to study the shapes (kinetic and equilibrium) of individual islands and stability and coarsening kinetics of monolayer island arrays. Our model includes the kinetics of adatom diffusion on the terraces and island edges, attachment kinetics to islands, substrate-mediated elastic interactions between the islands and anisotropies associated with the creation of island edges. Particular emphasis will be given to selfassembled growth of regular arrays of epitaxial nanowires that have potential applications as non-lithographically fabricated interconnects.
Ness Shroff (Purdue University) Cross-layer design for wireless networks
Abstract: Joint work with Xiaojun Lin. In this talk we develop an optimal cross-layer solution for rate control in multihop wireless networks. In particular, we study the impact on the performance of cross-layer rate control if the network control and information from the lower layers is imperfect, a practical reality in communication networks. We establish desirable results on the performance bounds of cross-layered rate control under an imperfect platfrom. Our cross-layered approach provides provably better performance bounds when compared with a layered approach (that does not design rate control and scheduling together). The insights drawn from our analyses also enable us to design a fully distributed cross-layered rate control and scheduling algorithm under a restrictive interference model.
Peter Smereka (University of Michigan) Computations of strained heteroepitaxy in 3 dimensions using kinetic Monte Carlo
Abstract: The growth of strained heteroepitaxial films in 3 dimensions using a Solid-on-Solid model is discussed. Elastic effects are included by using a ball and spring model. The system is evolved in time using a kinetic Monte Carlo method. Discrete models of this form naturally include nanoscale effects, such as nucleation, which are difficult to incorporate in continuum models. On the other hand, it is more computationally intensive to use these discrete models simulate film growth on experimentally relevant length scales. This talk will discuss some of the computational challenges and approaches we have developed for simulation of heteroepitaxy. In addition, some preliminary results of film growth will be presented which shows that when the elastic effects are small the film grows in a layer-by-layer fashion. However, when the elastic effects become strong we observe mound formation (self-assembled quantum dots).
Florian Theil (University of Warwick) From discrete to continuum systems: Crystallization in two dimensions
Abstract: While the analysis of contiuum models of spatially extended systems is a well studied mathematical discipline, much less is know about the relation between discrete systems and their continuum limits. I will highlight some of the challenges which arise when passing from discrete to continuum scales and give an overview of recent mathematical developments. A fundamental challenge in this area is the crystallization problem where one attempts to characterize the asymptotic behavior of the ground state of N particles that interact via Lennard-Jones type potentials with each other. I will report on new mathematical results which partically solve this problem.
Qi Wang (Florida State University) A paradigm of kinetic theories for suspensions and nematic polymers
Abstract: In this talk, I will present a systematic approach to the development of kinetic theories for suspensions and nematic polymers ranging from rigid bodies to deformable ones. The theories account for the molecular configuration of the suspensions and polymers. For example, the kinetic theory for biaxial liquid crystal polymers account for the broken symmetry at the molecular level in the transport equation for the number density function as well as the mesoscopic stress tensor calculation. We will discuss the connection with the existing kinetic theories and give some examples in simple flows.
Xiaodong Wang (Columbia University) Optimization of IEEE 802.11 DCF based on Bayesian estimation of the number of competing terminals
Abstract: The performance of the Distributed Coordination Function (DCF) of the IEEE 802.11 protocol has been shown to heavily depend on the number of terminals accessing the distributed medium. The DCF uses a carrier sense multiple access scheme with collision avoidance (CSMA/CA) where the backoff parameters are fixed and determined by the standard. While those parameters were chosen to provide a good protocol performance under light loads, they fail to provide an optimum utilization of the channel in many scenarios. In particular, under heavy load scenarios, the utilization of the medium can drop tenfold. Most of the optimization mechanisms proposed in the literature are based on adapting the DCF backoff parameters to the estimate of the number of competing terminals in the network. However, existing estimation algorithms are either inaccurate or too complex. In this paper we propose an enhanced version of the IEEE 802.11 DCF that employs an adaptive estimator of the number of competing terminals based on sequential Monte Carlo methods. The algorithm uses a Bayesian approach, optimizing the backoff parameters of the DCF based on the predictive distribution of the number of competing terminals. We show that our algorithm is simple yet highly accurate even at small time scales. We implement our proposed new DCF in the ns-2 simulator and show that it outperforms existing methods. We also show that its accuracy can be used to improve the results of the protocol even when the nodes are not in saturation mode. Moreover, we show that there exists a Nash equilibrium strategy that prevents rogue nodes from changing their parameters for their own benefits, making the algorithm applicable in a complete distributed fashion without having to modify the standard or the existing base stations.
Wing Shing Wong (Chinese University of Hong Kong) Mathematical problems in ad hoc wireless networks
Abstract: In this talk, we discuss selected problems arising from ad hoc wireless networks, problems such as the fairness in routing and distributed state estimation. We show how these problems lead naturally to concepts such as generalized Perron-Frobenius eigenvectors, von Neumann equilibrium, and low data rate distributed controller, as well as to Baynesian decision function and stochastic approximation.
Dapeng Wu (University of Florida) Effective capacity approach to providing statistical quality-of-service guarantees in wireless networks
Abstract: The next-generation wireless networks are targeted at supporting various applications such as voice, data, and multimedia with diverse quality of service (QoS) requirements. To provide explicit QoS guarantees such as a data rate, delay bound, and delay-bound violation probability triplet, it is necessary to analyze a QoS provisioning system in terms of these QoS measures. This task requires characterization of the service (channel modeling), and queueing analysis of the system. However, the existing channel models such as finite-state Markov chain models, do not explicitly characterize a wireless channel in terms of these QoS measures. This leads to high complexity in characterizing the relation between the control parameters of QoS provisioning and the calculated QoS measures. Recognizing that the above difficulty is the lack of a channel model that can easily relate the control parameters of a QoS provisioning system to the QoS measures, we propose and develop a link-layer channel model termed the effective capacity (EC) model. The EC model captures the effect of channel fading on the queueing behavior of the link, using a computationally simple yet accurate model, and thus, is a critical tool for designing efficient QoS provisioning mechanisms. Such an approach to channel modeling and QoS provisioning, is called effective capacity approach. In this poster, I will present our effective capacity approach to channel modeling.
Hong Zhou (Naval Postgraduate School) Anchoring distortions coupled with plane Couette and Poiseuille flows of nematic polymers
Abstract: The aim of this work is to model and simulate Processing-induced heterogeneity in rigid, rod-like nematic polymers In viscous solvents. We employ a mesoscopic orientation tensor model due to Doi, Marrucci and Greco which extends the small molecule, liquid crystal theory of Leslie-Frank to nematic polymers. We focus simulations in the regime of weak flow and strong distortional elasticity to expose the effects due to wall anchoring conflicts. A remarkably simple diagnostic emerges in this physical parameter regimes, in which salient morphology features are controlled by the amplitude and sign of the difference in plate anchoring angles of the director field at the two plates.
Erik van der Giessen (University of Groningen ) Dislocation field theory in 2D: formulation and validation
Abstract: Plastic deformation of crystalline metals at the scale of micrometers and smaller is often size dependent, particularly in the presence of strain gradients. Standard local theories are not able to capture these size effects because they lack a material length scale. Therefore, numerous nonlocal models have been proposed during the last decade, the majority of which are phenomenological strain-gradient theories. An alternative description will be presented here, which is termed Dislocation Field Theory (DFT). It is based on a rigorous statistical averaging of the dislocation motion of edge dislocations gliding on a single slip system. The resulting field equations are then coupled to a crystal plasticity model using Orowan's relation. The resulting DFT is subsequently generalized to multipe slip, albeit in two dimensions. The main characteristic that distinguishes DFT from other plastic strain-gradient theories is that the material length scale --the average dislocation spacing-- is not a material constant but evolves with deformation. It will be shown how the few material parameters in DFT are fitted to discrete dislocation results for one particular problem, and how the subsequent predictions of the theory for other problems compares with discrete dislocation simulations. The problems addressed include shearing of a model composite; constrained shear; bending; and stress relaxation in a thin film.
Visitors in Residence
Cameron F. Abrams Drexel University 6/7/2005 - 6/11/2005
Prathima Agrawal Auburn University 6/26/2005 - 6/30/2005
Rajeev Agrawal Motorola, Inc. 6/26/2005 - 7/1/2005
In Soo Ahn Bradley University 6/21/2005 - 7/1/2005
Silas Alben Harvard University 6/7/2005 - 6/12/2005
Jeffrey G. Andrews University of Texas - Austin 6/21/2005 - 7/1/2005
Matthew Andrews Lucent Technologies 6/26/2005 - 7/1/2005
Marcel Arndt University of Bonn 6/7/2005 - 6/12/2005
Douglas N. Arnold University of Minnesota 7/15/2001 - 8/31/2006
Donald G. Aronson University of Minnesota 9/1/2002 - 8/31/2005
Festus Asemota University of Benin 6/20/2005 - 7/3/2005
Alexei Ashikhmin Lucent Technologies - Bell Laboratories 6/26/2005 - 7/1/2005
Paul Atzberger Rensselaer Polytechnic Institute 6/8/2005 - 6/11/2005
Gerard Awanou University of Minnesota 9/2/2003 - 8/31/2005
Francois Baccelli Ecole Normale Superieure 6/26/2005 - 7/1/2005
Yuliy Baryshnikov Bell Laboratories 6/8/2005 - 6/11/2005
James Berger Duke University 6/16/2005 - 6/18/2005
Randall A. Berry Northwestern University 6/26/2005 - 7/1/2005
Marian Bocea University of Utah 6/7/2005 - 6/11/2005
Sem C. Borst Lucent Technologies - Bell Laboratories 6/26/2005 - 7/1/2005
Nigel Boston University of Wisconsin 6/26/2005 - 7/1/2005
Andrea Braides II Università degli studi di Rome (Tor Vergata) 6/1/2005 - 6/15/2005
Robert Buche North Carolina State University 6/21/2005 - 7/1/2005
Maria-Carme Calderer University of Minnesota 9/1/2004 - 6/30/2005
Eric Cances CERMICS 6/8/2005 - 6/12/2005
Pedro Ponte Castaneda Ecole Polytechnique 6/7/2005 - 6/11/2005
Dov Chelst DeVry University 6/21/2005 - 7/3/2005
Qianyong Chen University of Minnesota 9/1/2004 - 8/31/2006
Rong-Rong Chen University of Utah 6/21/2005 - 6/29/2005
Ae-Gyeong Cheong Clemson University 5/13/2005 - 6/13/2005
Kenneth L. Clarkson Bell Laboratories 6/26/2005 - 7/1/2005
Cristina Comaniciu Stevens Institute of Technology 6/26/2005 - 7/1/2005
Brian Conrey American Institute of Mathematics 6/16/2005 - 6/18/2005
Antonio DeSimone SISSA-Italy 3/10/2005 - 7/15/2005
Antonio Di Carlo Università degli Studi Roma Tre 4/10/2005 - 6/12/2005
Brian DiDonna University of Minnesota 9/1/2004 - 8/31/2006
Nicolas P. Dirr Max Planck Institute for Math in the Sciences 6/6/2005 - 6/12/2005
Georg Dolzmann University of Maryland 5/31/2005 - 6/3/2005
Tyrone Duncan University of Kansas 6/26/2005 - 7/1/2005
Kossi Delali Edoh Elizabeth City State University 6/21/2005 - 7/1/2005
Martin Eiger Telcordia Technologies 6/26/2005 - 7/1/2005
David Eisenbud Mathematical Sciences Research Institute 6/16/2005 - 6/18/2005
Ryan S. Elliott University of Michigan 1/1/2005 - 6/30/2005
Guler Ergun University of Bath-UK 6/7/2005 - 6/12/2005
Dean Evasius National Science Foundation 6/17/2005 - 6/19/2005
Ali Eydgahi Unversity of Maryland Eastern Shore 6/21/2005 - 7/2/2005
Philip Fleming Motorola, Inc. 6/22/2005 - 6/24/2005
Colin D. Frank Motorola, Inc. 6/26/2005 - 7/1/2005
Avner Friedman Ohio State University 6/16/2005 - 6/19/2005
Gero Friesecke University of Warwick 6/4/2005 - 6/11/2005
Tim Garoni University of Minnesota 8/25/2003 - 8/31/2005
Adriana Garroni Università di Roma La Sapienza 6/1/2005 - 6/15/2005
Eugene C. Gartland Jr. Kent State University 1/10/2005 - 6/30/2005
Georgios Giannakis University of Minnesota 6/21/2005 - 7/1/2005
Antoine Gloria CERMICS - ENPC 5/25/2005 - 6/12/2005
Mark Green California State University - Los Angeles 6/16/2005 - 6/18/2005
Martin Greiner Siemens 6/25/2005 - 7/2/2005
Phillip A. Griffiths Institute for Advanced Study 6/17/2005 - 6/18/2005
Colette Guillope University of Paris XII 6/6/2005 - 6/14/2005
Robert Gulliver University of Minnesota 9/1/2004 - 6/30/2005
Katherine Guo Bell Laboratories 6/26/2005 - 7/3/2005
Rohit Gupta University of Minnesota 6/22/2005 - 7/1/2005
Chuan-Hsiang Han University of Minnesota 9/1/2004 - 8/31/2005
Nidhi Hegde France Telecom 6/21/2005 - 7/1/2005
John Hobby Bell Laboratories 6/26/2005 - 7/1/2005
Michael L. Honig Northwestern University 6/26/2005 - 7/1/2005
Qun Huo North Dakota State University 6/7/2005 - 6/11/2005
Syed Ali Jafar University of California - Irvine 6/22/2005 - 7/1/2005
Richard D. James University of Minnesota 9/1/2004 - 6/30/2005
Arulsaravana Jeyaraj University of California - Irvine 6/21/2005 - 7/1/2005
Chuanyi Ji Georgia Institute of Technology 6/22/2005 - 7/1/2005
Shi Jin University of Wisconsin 1/4/2005 - 6/30/2005
Yasong Jin University of Kansas 6/21/2005 - 7/2/2005
Nihar Jindal University of Minnesota 6/22/2005 - 7/2/2005
Sookyung Joo University of Minnesota 9/1/2004 - 8/31/2006
Vladimir Kamotski University of Bath-UK 5/24/2005 - 6/14/2005
Chiu Yen Kao University of Minnesota 9/1/2004 - 8/31/2006
Sang Wu Kim Iowa State University 6/22/2005 - 6/25/2005
Robert V. Kohn New York University 6/6/2005 - 6/10/2005
Soumitri Kolavennu Honeywell 6/26/2005 - 7/1/2005
Richard Kollar University of Minnesota 9/1/2004 - 8/31/2005
Gerhard Kramer Lucent Technologies 6/26/2005 - 7/1/2005
Vikram Krishnamurthy University of British Columbia 6/26/2005 - 7/1/2005
Komandur R. Krishnan Telcordia Technologies 6/27/2005 - 7/1/2005
P. R. Kumar University of Illinois - Urbana-Champaign 6/21/2005 - 7/1/2005
Matthias Kurzke University of Minnesota 9/1/2004 - 8/31/2006
Harold J. Kushner Brown University 6/26/2005 - 7/1/2005
Batool Labibi K. N. Toose University of Technology 6/21/2005 - 7/2/2005
Christopher J. Larsen Worcester Polytechnic Institute 6/7/2005 - 6/12/2005
Claude Le Bris CERMICS 6/1/2005 - 6/17/2005
Chulhan Lee University of Texas - Austin 6/22/2005 - 7/2/2005
Sungyun Lee Korea Advanced Institute of Science & Technology 6/7/2005 - 6/11/2005
Frederic Legoll University of Minnesota 9/3/2004 - 8/31/2006
Debra Lewis University of Minnesota 7/15/2004 - 8/31/2006
Xiantao Li University of Minnesota 8/3/2004 - 8/31/2005
Chun Liu Pennsylvania State University 9/1/2004 - 6/30/2005
Hailiang Liu Iowa State University 1/1/2005 - 6/30/2005
Xin Liu University of California - Davis 6/22/2005 - 7/1/2005
Yuanjin Liu Wayne State University 6/21/2005 - 7/2/2005
Deborah F. Lockhart National Science Foundation 6/17/2005 - 6/19/2005
David Love Purdue University 6/25/2005 - 7/1/2005
Steven Low California Institute of Technology 6/26/2005 - 7/1/2005
Tom Luo University of Minnesota 6/26/2005 - 7/1/2005
Mitchell Luskin University of Minnesota 9/1/2004 - 6/30/2005
Dionisios Margetis Massachusetts Institute of Technology 6/7/2005 - 6/12/2005
Karsten Matthies Freie University Berlin 5/1/2005 - 6/15/2005
David Mclaughlin New York University 6/16/2005 - 6/18/2005
Kevin W. Mclaughlin University of Wisconsin - River Falls 6/7/2005 - 6/11/2005
Sean P. Meyn University of Illinois - Urbana-Champaign 6/21/2005 - 6/29/2005
Wei Mo Iowa State University 6/21/2005 - 7/1/2005
Eytan Modiano Massachusetts Institute of Technology 6/26/2005 - 7/1/2005
Bagisa Mukherjee Penn State Worthington Scranton 5/8/2005 - 6/9/2005
Arnie Neidhardt Telcordia Technologies 6/21/2005 - 7/1/2005
Mahdi Nezafat University of Minnesota 6/22/2005 - 7/1/2005
Barbara Niethammer Humboldt Universität zu Berlin 6/2/2005 - 6/11/2005
Hans Christian Oettinger ETHZ 6/7/2005 - 6/11/2005
Miao-Jung Yvonne Ou University of Central Florida 6/7/2005 - 6/12/2005
Peter Philip University of Minnesota 8/22/2004 - 8/31/2006
Harald Pleiner Max Planck Institute for Polymer Research 5/10/2005 - 6/18/2005
Vincent Poor Princeton University 6/21/2005 - 7/1/2005
Lea Popovic University of Minnesota 9/2/2003 - 8/31/2005
Alexandre Proutiere France Telecom 6/21/2005 - 7/2/2005
Tiezheng Qian Hong Kong University of Science and Technology 6/7/2005 - 6/12/2005
Leela Rakesh CMU 6/7/2005 - 6/12/2005
Weiqing Ren Princeton University 6/7/2005 - 6/12/2005
William Rundell National Science Foundation 6/16/2005 - 6/18/2005
Rolf Ryham Pennsylvania State University 9/1/2004 - 6/30/2005
Tathagata Samanta Florida Institute of Technology 6/21/2005 - 7/2/2005
Vittorio Sansalone Italian Agency for New Technologies, Energy and the Environment 5/25/2005 - 6/12/2005
Chekad Sarami Fayetteville State University 6/21/2005 - 7/1/2005
Arnd Scheel University of Minnesota 7/15/2004 - 8/31/2006
Christian Scheideler Johns Hopkins University 6/26/2005 - 7/2/2005
George R Sell University of Minnesota 9/1/2004 - 6/30/2005
James P. Sethna Cornell University 5/30/2005 - 6/12/2005
Vivek Shenoy Brown University 6/8/2005 - 6/11/2005
Tien-Tsan Shieh Indiana University 9/1/2004 - 6/30/2005
Shagi-Di Shih University of Wyoming 5/1/2005 - 7/2/2005
Ness Shroff Purdue University 6/26/2005 - 7/1/2005
Rahul Sinha Illinois Institute of Technology 6/21/2005 - 7/1/2005
Ioana Sirbu Western Illinois University 6/7/2005 - 6/12/2005
Peter Smereka University of Michigan 5/30/2005 - 6/12/2005
Valery P. Smyshlyaev University of Bath-UK 4/10/2005 - 6/16/2005
Qingshuo Song Wayne State University 6/22/2005 - 7/1/2005
Kevin William Sowerby University of Auckland 6/21/2005 - 7/2/2005
Daniel Spirn University of Minnesota 9/1/2004 - 6/30/2005
Peter J. Sternberg Indiana University 8/15/2004 - 6/15/2005
Vladimir Sverak University of Minnesota 9/1/2004 - 6/30/2005
Jun Tan Motorola, Inc. 6/22/2005 - 7/1/2005
Choon Yik Tang Honeywell 6/26/2005 - 7/1/2005
Alain B. Tchagang University of Minnesota 6/22/2005 - 7/1/2005
Luciano Teresi Università degli Studi Roma Tre 4/10/2005 - 6/12/2005
Florian Theil University of Warwick 4/4/2005 - 6/11/2005
Lev Truskinovsky Ecole Polytechnique, Palaiseau 6/1/2005 - 6/11/2005
Igor Tsukerman University of Akron 6/7/2005 - 6/11/2005
Gabriel Turinici CERMICS 5/22/2005 - 6/10/2005
Eric van den Berg Telcordia Technologies 6/26/2005 - 7/1/2005
Erik van der Giessen University of Groningen 6/7/2005 - 6/10/2005
Sriram Vishwanath University of Texas - Austin 6/21/2005 - 7/1/2005
Pascal Olivier Vontobel ETH - Zurich 6/21/2005 - 7/2/2005
Fan Wang Motorola, Inc. 6/21/2005 - 7/1/2005
Qi Wang Florida State University 6/8/2005 - 6/12/2005
Xiaodong Wang Columbia University 6/26/2005 - 7/1/2005
Zhengdao Wang Iowa State University 6/22/2005 - 7/1/2005
Wing Shing Wong Chinese University of Hong Kong 6/26/2005 - 7/1/2005
Doug Wright University of Minnesota 2/15/2005 - 8/31/2005
Dapeng Wu University of Florida 6/27/2005 - 7/2/2005
Baisheng Yan Michigan State University 9/1/2004 - 6/15/2005
Gregory E. Yawson Lawrence Technological University 6/7/2005 - 6/11/2005
Yunjung Yi Honeywell 6/26/2005 - 7/1/2005
George Yin Wayne State University 6/21/2005 - 7/1/2005
Aaron Nung Kwan Yip Purdue University 1/16/2005 - 6/30/2005
Emmanuel Yomba University of Ngaoundéré 10/6/2004 - 8/31/2005
Hossein Zare University of Minnesota 6/22/2005 - 7/1/2005
Ofer Zeitouni University of Minnesota 6/26/2005 - 7/1/2005
Junshan Zhang Arizona State University 6/21/2005 - 6/25/2005
Lisa Zhang Lucent Technologies 6/22/2005 - 6/24/2005
Qian Zhang University of Wisconsin - Madison 6/21/2005 - 7/2/2005
Qing Zhang University of Georgia 6/26/2005 - 7/2/2005
Hong Zhou Naval Postgraduate School 6/8/2005 - 6/11/2005
Johannes Zimmer Max-Planck-Institute for Math in the Sciences 5/29/2005 - 6/12/2005
Legend: Postdoc or Industrial Postdoc Long-term Visitor

Participating Institutions: Carnegie Mellon University, Consiglio Nazionale delle Ricerche (CNR), Georgia Institute of Technology, Indiana University, Iowa State University, Kent State University, Lawrence Livermore National Laboratories, Los Alamos National Laboratory, Michigan State University, Mississippi State University, Northern Illinois University, Ohio State University, Pennsylvania State University, Purdue University, Rice University, Sandia National Laboratories, Seoul National University (BK21), Seoul National University (SRCCS), Texas A & M University, University of Chicago, University of Cincinnati, University of Delaware, University of Houston, University of Illinois - Urbana-Champaign, University of Iowa, University of Kentucky, University of Maryland, University of Michigan, University of Minnesota, University of Notre Dame, University of Pittsburgh, University of Texas - Austin, University of Wisconsin, University of Wyoming, Wayne State University
Participating Corporations: 3M, Boeing, Corning, ExxonMobil, Ford Motor Company, General Electric, General Motors, Honeywell, IBM Corporation, Johnson & Johnson, Lockheed Martin, Lucent Technologies, Medtronic, Inc., Motorola, Schlumberger-Doll Research, Siemens, Telcordia Technologies