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IMA Newsletter #385

November 2008

2008-2009 Program

Mathematics and Chemistry

See http://www.ima.umn.edu/2008-2009 for a full description of the 2008-2009 program on Mathematics and Chemistry.

News and Notes

2005 New Directions Short Course instructor Alexei Kitaev of Caltech named MacArthur fellow

The half-million-dollar award, often referred to as the "genius award," is an unrestricted fellowships given to talented individuals who have shown extraordinary originality and dedication in their creative pursuits and a marked capacity for self-direction.



IMA Events

IMA Workshop

Scientific Challenges in Solar Energy Conversion and Storage

November 1, 2008

Organizers: Eray S. Aydil (University of Minnesota Twin Cities), Weinan E (Princeton University)

IMA Tutorial

Physics and mathematics of multiscale modeling for chemistry and materials

November 2, 2008

Speakers: Burkhard Dünweg (Max-Planck Institut für Polymerforschung), Weinan E (Princeton University), Richard D. James (University of Minnesota Twin Cities)

IMA Annual Program Year Workshop

Development and Analysis of Multiscale Methods

November 3-7, 2008

Organizers: Frank L. H. Brown (University of California), Anne M. Chaka (National Institute of Standards and Technology), Gero Friesecke (Technical University of Munich ), Kurt Kremer (Max-Planck Institut für Polymerforschung), Yousef Saad (University of Minnesota Twin Cities)

IMA Workshop

Mixed-Integer Nonlinear Optimization: Algorithmic Advances and Applications

November 17-21, 2008

Organizers: Jon Lee (IBM Thomas J. Watson Research Center), Sven Leyffer (Argonne National Laboratory)
Schedule

Saturday, November 1

8:00am-8:45amBreakfast and registrationEE/CS 3-176 SW11.1.08
8:45am-9:00amWelcome (Fadil Santosa and NSF officer)Fadil Santosa (University of Minnesota)EE/CS 3-180 SW11.1.08
9:00am-9:30amChallenges in efficient and inexpensive solar-to-electric energy conversion Eray S. Aydil (University of Minnesota)EE/CS 3-180 SW11.1.08
9:30am-10:30amMultiple exciton generation in semiconductor quantum dots and novel molecules: Applications to third generation solar photon conversionArthur J. Nozik (Department of Energy)EE/CS 3-180 SW11.1.08
10:30am-11:00amBreak and discussionEE/CS 3-176 SW11.1.08
11:00am-12:00pmQuantum dots and dye-sensitized semiconductors for solar energy conversion: time-domain ab initio studies of the photoinduced dynamicsOleg Prezhdo (University of Washington)EE/CS 3-180 SW11.1.08
12:00pm-12:30pmEngineering morphology in small molecule organic photovoltaic cells for efficient exciton diffusion and dissociationRussell J. Holmes (University of Minnesota)EE/CS 3-180 SW11.1.08
12:30pm-1:30pmLunch and discussionEE/CS 3-180 SW11.1.08
1:30pm-2:30pmExciton dissociation in solar cellsXiaoyang Zhu (University of Minnesota)EE/CS 3-180 SW11.1.08
2:30pm-3:00pmFunctionalized quantum dots and conjugated polymers for light harvesting applications: Theoretical insightsSergei Tretiak (Los Alamos National Laboratory)EE/CS 3-180 SW11.1.08
3:00pm-3:30pmBreak and discussionEE/CS 3-176 SW11.1.08
3:30pm-4:00pmComputational aspects of solid state transportChristian Ringhofer (Arizona State University)EE/CS 3-180 SW11.1.08
4:00pm-4:30pmReceiver technology for today and tomorrowAlex Marker (Schott North America, Inc.)EE/CS 3-180 SW11.1.08
4:30pm-5:00pmEnvironment-assisted quantum transport in photosynthetic complexes: Learning from nature for potential organic photovoltaic applications.Alán Aspuru-Guzik (Harvard University)EE/CS 3-180 SW11.1.08
5:00pm-5:30pmCHE-DMR-DMS solar energy initiativeHenry A. Warchall (National Science Foundation)EE/CS 3-180 SW11.1.08

Sunday, November 2

8:15am-8:45amCoffee and registrationEE/CS 3-176 T11.2.08
8:45am-9:00amWelcomeFadil Santosa (University of Minnesota)EE/CS 3-180 T11.2.08
9:00am-10:30amA mathematical perspective on the structure of matterRichard D. James (University of Minnesota)EE/CS 3-180 T11.2.08
10:30am-10:45amGroup photo
10:30am-11:00amBreakEE/CS 3-176 T11.2.08
10:45am-11:15amBreakEE/CS 3-176
11:00am-12:30pmBasic concepts of polymer physics and their numerical study Burkhard Dünweg (Max-Planck Institut für Polymerforschung)EE/CS 3-180 T11.2.08
12:30pm-2:00pmLunch T11.2.08
2:00pm-3:30pmCapturing the macroscopic behavior of complex systems using multiscale methodsWeinan E (Princeton University)EE/CS 3-180 T11.2.08
3:30pm-4:00pmDiscussionEE/CS 3-180 T11.2.08

Sunday, November 2

8:15am-8:45amCoffee and registrationEE/CS 3-176 T11.2.08
8:45am-9:00amWelcomeFadil Santosa (University of Minnesota)EE/CS 3-180 T11.2.08
9:00am-10:30amA mathematical perspective on the structure of matterRichard D. James (University of Minnesota)EE/CS 3-180 T11.2.08
10:30am-10:45amGroup photo
10:30am-11:00amBreakEE/CS 3-176 T11.2.08
10:45am-11:15amBreakEE/CS 3-176
11:00am-12:30pmBasic concepts of polymer physics and their numerical study Burkhard Dünweg (Max-Planck Institut für Polymerforschung)EE/CS 3-180 T11.2.08
12:30pm-2:00pmLunch T11.2.08
2:00pm-3:30pmCapturing the macroscopic behavior of complex systems using multiscale methodsWeinan E (Princeton University)EE/CS 3-180 T11.2.08
3:30pm-4:00pmDiscussionEE/CS 3-180 T11.2.08

Monday, November 3

All DayMultiscale modeling in soft and biological matter, I
Session Chair: Frank L. H. Brown (University of California)
W11.3-7.08
8:15am-9:00amRegistration and coffeeEE/CS 3-176 W11.3-7.08
9:00am-9:15amWelcome to the IMAFadil Santosa (University of Minnesota)EE/CS 3-180 W11.3-7.08
9:15am-10:00amMultiscale structural mechanics of viruses: Stretching the limits of continuum modeling William S. Klug (University of California, Los Angeles)EE/CS 3-180 W11.3-7.08
10:00am-10:30amCoffeeEE/CS 3-176 W11.3-7.08
10:30am-11:15amCoarse-graining of cholesterol containing lipid bilayers Mikko Karttunen (University of Western Ontario)EE/CS 3-180 W11.3-7.08
11:15am-12:00pmCoarse-grained simulation studies of mesoscopic membrane phenomena Markus Deserno (Carnegie Mellon University)EE/CS 3-180 W11.3-7.08
12:00pm-2:00pmLunch W11.3-7.08
2:00pm-2:45pmSoft coarse-grained models for multicomponent polymer melts: free energy and single-chain dynamicsMarcus Müller (Georg-August-Universität zu Göttingen)EE/CS 3-180 W11.3-7.08
2:45pm-3:30pmSimple models for biomembrane structure and dynamics Frank L. H. Brown (University of California, Santa Barbara)EE/CS 3-180 W11.3-7.08
3:30pm-3:45pmGroup Photo W11.3-7.08
3:45pm-4:15pmCoffeeEE/CS 3-176 W11.3-7.08
4:15pm-4:45pmSecond chancesEE/CS 3-180 W11.3-7.08
5:00pm-6:30pmReception and Poster Session
Poster submissions welcome from all participants
Lind Hall 400 W11.3-7.08
Ligand access/escape from protein cavities: A computational study of the insulin-phenol complexCameron F. Abrams (Drexel University)
Charge transport in discotic liquid crystals: a multiscale computer simulation studyDenis Andrienko (Max-Planck Institut für Polymerforschung)
Parallel multiscale simulation for crack propagationOlivier Coulaud (Institut National de Recherche en Informatique Automatique (INRIA))
A criterion to estimate the quality of the Mapping Scheme in Coarse-graining approaches Luigi Delle Site (Max-Planck Institut für Polymerforschung)
Realistic multiscale modeling of spatiotemporal behavior in surface reactions: Equation-free "heterogeneous coupled lattice-gas" (HCLG) simulationsJames W. Evans (Iowa State University)
Multiscale modeling of polystyrene in different environments Roland Faller (University of California, Davis)
Multiscale modeling of structure and phase behavior in heterogeneous lipid bilayers Roland Faller (University of California, Davis)
From atomistic to mesoscale systems without fitting: A coarse grained model for polystyrene Dominik Fritz (Max Planck Institute for Polymer Research)
From quantum to classical molecular dynamics Johannes Giannoulis (Technical University of Munich )
Comparative study of water: Atomistic vs. coarse-grainedChristoph Junghans (Max-Planck Institut für Polymerforschung)
Techniques for coarse-grained modeling and mechanics of viral capsidsWilliam S. Klug (University of California, Los Angeles)
Effective dynamics using conditional expectations Frédéric Legoll (École Nationale des Ponts-et-Chaussées)
Force matching versus structural coarse-graining Alexander Lukyanov (Max-Planck Institut für Polymerforschung)
A new procedure to building stabilized explicit Runge-Kutta methods for large systems of ODEsJesús Martín-Vaquero (University of Salamanca)
Quantifying chain reptation in entangled polymers by mapping atomistic simulation results onto the tube modelVlasis George Mavrantzas (University of Patras)
All-atom multiscale computational modeling of bionanosystem dynamicsStephen D Pankavich (Indiana University)
Adaptive resolution simulation of model mixturesSimon Poblete (Max Planck Institute for Polymer Research)
Charge transport in polypyrrole: the role of morphology Victor Rühle (Max Planck Institute for Polymer Research)
Spatial bounds on the effective complex permittivity for time-harmonic waves in random mediaLyubima B. Simeonova (University of Utah)
General purpose molecular dynamics on graphic processing units (GPUs) Alex Travesset (Iowa State University)
Mesoscopic model for the fluctuating hydrodynamics of binary and ternary mixtures Erkan Tüzel (University of Minnesota)
A bloch band base level set method in the semi-classical limit of the Schroedinger EquationZhongming Wang (University of California, San Diego)

Tuesday, November 4

All DayMolecular dynamics
Session Chair: Anne M. Chaka (National Institute of Standards and Technology)
W11.3-7.08
8:30am-9:15amCoffeeEE/CS 3-176 W11.3-7.08
9:15am-10:00amCoarse-grained and multiscale models of bulk liquids and macromoleculesTeresa Head-Gordon (University of California, Berkeley)EE/CS 3-180 W11.3-7.08
10:00am-10:30amCoffeeEE/CS 3-176 W11.3-7.08
10:30am-11:15amUnderstanding effective molecular dynamics on timescales beyond possible simulation timescalesChristof Schütte (Freie Universität Berlin)EE/CS 3-180 W11.3-7.08
11:15am-12:00pmLattice Boltzmann simulations of soft-matter systems Burkhard Dünweg (Max-Planck Institut für Polymerforschung)EE/CS 3-180 W11.3-7.08
12:00pm-2:00pmLunch W11.3-7.08
2:00pm-2:45pmMultiscale modeling and simulation of soft matter materialsPaul J. Atzberger (University of California, Santa Barbara)EE/CS 3-180 W11.3-7.08
2:45pm-3:30pmSoft potentials for coarse grained modelingIgnacio Pagonabarraga Mora (University of Barcelona)EE/CS 3-180 W11.3-7.08
3:30pm-4:00pmCoffeeEE/CS 3-176 W11.3-7.08
4:00pm-4:30pmSecond chancesEE/CS 3-180 W11.3-7.08

Wednesday, November 5

All DayMathematical aspects of scale-bridging
Session Chair: Gero Friesecke (Technische Universität München)
W11.3-7.08
8:30am-9:15amCoffeeEE/CS 3-176 W11.3-7.08
9:15am-10:00amSome representative issues in multiscale modelingWeinan E (Princeton University)EE/CS 3-180 W11.3-7.08
10:00am-10:30amCoffeeEE/CS 3-176 W11.3-7.08
10:30am-11:15amA general strategy for the design of seamless multiscale methodsEric Vanden-Eijnden (New York University)EE/CS 3-180 W11.3-7.08
11:15am-12:00pmPredictive and efficient quasicontinuum methodsMitchell Luskin (University of Minnesota)EE/CS 3-180 W11.3-7.08
12:00pm-2:00pmIMA Special Lunch W11.3-7.08
2:00pm-2:45pmVariational coarse-graining of lattice systems Andrea Braides (Seconda Università di Roma "Tor Vergata")EE/CS 3-180 W11.3-7.08
2:45pm-3:30pmPositive temperature coarse-graining of one-dimensional systemsClaude Le Bris (CERMICS)EE/CS 3-180 W11.3-7.08
3:30pm-4:00pmCoffeeEE/CS 3-176 W11.3-7.08
4:00pm-4:30pmSecond chancesEE/CS 3-180 W11.3-7.08

Thursday, November 6

All DayMultiscale modeling in soft and biological matter, II
Session Chair: Kurt Kremer (Max-Planck Institut für Polymerforschung)
W11.3-7.08
8:15am-8:45amCoffeeEE/CS 3-176 W11.3-7.08
8:45am-9:30amA rigorous multiscale bridge connecting atomistic and coarse-grained models William G. Noid (Pennsylvania State University)EE/CS 3-180 W11.3-7.08
9:30am-9:45amGrab a cup of coffee then proceed immediately to 331 Smith Hall for the 9:45am Moscowitz LectureEE/CS 3-176 W11.3-7.08
9:45am-10:45amMichael Frisch Moscowitz Lecture (Chemistry Department)
author of the widely used Gaussian computer program (for electronic structure calculations (including some multiscale algorithms) and the President of Gaussian, Inc.]
331 Smith Hall W11.3-7.08
11:00am-11:45amMolecular dynamics in mesoscopic solventsRaymond Kapral (University of Toronto)EE/CS 3-180 W11.3-7.08
11:15am-12:15pm Francisco Sayas Gonzalez, University of Zaragoza, Spain
TBA
Vincent Hall 570 AMS
11:45am-12:30pmUnveiling conformational changes of biological molecules using multiscale modeling and multiresolution experimentsFlorence Tama (University of Arizona)EE/CS 3-180 W11.3-7.08
12:30pm-2:00pmLunch W11.3-7.08
2:00pm-2:45pmMulti-scale modeling of DNAWilma K. Olson (Rutgers University)EE/CS 3-180 W11.3-7.08
2:45pm-3:30pmMapping particle based simulations to mesoscopic models Mark O. Robbins (Johns Hopkins University)EE/CS 3-180 W11.3-7.08
3:30pm-4:00pmCoffeeEE/CS 3-176 W11.3-7.08
4:00pm-4:45pmDevelopment of dynamic density functional theories of multiphase dense polymeric systemsToshihiro Kawakatsu (Tohoku University)EE/CS 3-180 W11.3-7.08
4:45pm-5:15pmSecond chancesEE/CS 3-180 W11.3-7.08
7:00pm-8:30pmWorkshop DinnerPagoda Restaurant
1417 4th St. SE
Minneapolis, MN
612-378-4710
W11.3-7.08

Friday, November 7

All DayAlgorithmic aspects of scale-bridging
Session Chair: Yousef Saad (University of Minnesota)
W11.3-7.08
8:30am-9:15amCoffeeEE/CS 3-176 W11.3-7.08
9:15am-10:00amThe adaptive resolution simulation scheme (AdResS): Basic principles and applications Luigi Delle Site (Max-Planck Institut für Polymerforschung)EE/CS 3-180 W11.3-7.08
10:00am-10:30amCoffeeEE/CS 3-176 W11.3-7.08
10:30am-11:15amAtomistic, mesoscopic and continuum hydrodynamics: coupling liquid models with different resolutionRafael Delgado-Buscalioni (Autonomous University of Madrid)EE/CS 3-180 W11.3-7.08
11:15am-12:00pmFinding effective equations for heterogeneous multiscale methods Bjorn Engquist (University of Texas)EE/CS 3-180 W11.3-7.08
12:00pm-12:30pmSecond chances and closing remarkEE/CS 3-180 W11.3-7.08

Monday, November 10

10:45am-11:15amCoffee breakLind Hall 400
2:30pm-3:30pmMath 8994: Topics in classical and quantum mechanics
Electronic structure calculations and molecular simulation: A mathematical initiation
Eric Cances (CERMICS)
Claude Le Bris (CERMICS)
Lind Hall 305

Tuesday, November 11

10:45am-11:15amCoffee breakLind Hall 400
11:15am-12:15pmA theory of fracture based upon extension of continuum mechanics to the nanoscaleTsvetanka Sendova (University of Minnesota)Lind Hall 305 PS
12:15pm-1:30pmpostdoc lunch meetingLind Hall 409

Wednesday, November 12

10:45am-11:15amCoffee breakLind Hall 400
2:30pm-3:30pmMath 8994: Topics in classical and quantum mechanics
Electronic structure calculations and molecular simulation: A mathematical initiation
Eric Cances (CERMICS)
Claude Le Bris (CERMICS)
Lind Hall 305
4:00pm-5:00pmFermi contact interactions evaluated from hidden relations in the Schrödinger equationDaniel M. Chipman (University of Notre Dame)Lind Hall 305 SMC

Thursday, November 13

10:45am-11:15amCoffee breakLind Hall 400
11:15am-12:15pmTBAEric Cances (CERMICS)Vincent Hall 570 AMS
4:00pm-5:00pmReading group for Professor Ridgway Scott's book "Digital Biology"Ridgway Scott (University of Chicago)Lind Hall 401

Friday, November 14

10:45am-11:15amCoffee breakLind Hall 400
1:25pm-2:25pmImage registration with applications in medical imaging towards drug discovery and developmentBelma Dogdas (Merck & Co., Inc.)Vincent Hall 570 IPS

Monday, November 17

8:00am-8:45amRegistration and coffeeEE/CS 3-176 SW11.17-21.08
8:45am-9:00amWelcome to the IMAFadil Santosa (University of Minnesota)EE/CS 3-180 SW11.17-21.08
9:00am-10:00amBuilding an effective solver for convex mixed integer nonlinear programsJeff Linderoth (University of Wisconsin)EE/CS 3-180 SW11.17-21.08
10:00am-10:30amCoffeeEE/CS 3-176 SW11.17-21.08
10:30am-11:15amBranching strategies and heurisitcs in a branch-and-bound for convex MINLPs Pierre Bonami (Centre National de la Recherche Scientifique (CNRS))EE/CS 3-180 SW11.17-21.08
11:15am-12:00pmBranching rules in branch-and-bound algorithms for nonconvex mixed-integer nonlinear programmingPietro Belotti (Lehigh University)EE/CS 3-180 SW11.17-21.08
12:00pm-2:00pmLunch SW11.17-21.08
2:00pm-2:45pmFast infeasibility detection in nonlinear optimizationJorge Nocedal (Northwestern University)EE/CS 3-180 SW11.17-21.08
2:30pm-3:30pmMath 8994: Topics in classical and quantum mechanics
Electronic structure calculations and molecular simulation: A mathematical initiation
Eric Cances (CERMICS)
Claude Le Bris (CERMICS)
Lind Hall 305
2:45pm-3:30pmUsing interior-point methods within MINLPHande Yurttan Benson (Drexel University)EE/CS 3-180 SW11.17-21.08
3:30pm-3:45pmGroup Photo SW11.17-21.08
3:45pm-4:15pmCoffeeEE/CS 3-176 SW11.17-21.08
4:15pm-5:15pmDiscussionSven Leyffer (Argonne National Laboratory)EE/CS 3-180 SW11.17-21.08

Tuesday, November 18

8:30am-9:00amCoffeeEE/CS 3-176 SW11.17-21.08
9:00am-10:00amCopositive programs and combinatorial optimizationFranz Rendl (Universität Klagenfurt)EE/CS 3-180 SW11.17-21.08
10:00am-10:30amCoffeeEE/CS 3-176 SW11.17-21.08
10:30am-11:15amThe difference between 5x5 doubly nonnegative and completely positive matrices Kurt M. Anstreicher (University of Iowa)EE/CS 3-180 SW11.17-21.08
11:15am-12:00pmConvex relaxations of non-convex MIQCPAnureet Saxena (Axioma Inc.)EE/CS 3-180 SW11.17-21.08
12:00pm-2:00pmLunch SW11.17-21.08
2:00pm-2:45pmA branch-and-refine method for nonconvex mixed integer optimization Annick Sartenaer (Facultés Universitaires Notre Dame de la Paix (Namur))EE/CS 3-180 SW11.17-21.08
2:45pm-3:30pmReformulations in mathematical programming: SymmetryLeo Liberti (École Polytechnique)EE/CS 3-180 SW11.17-21.08
3:30pm-4:00pmCoffeeEE/CS 3-176 SW11.17-21.08
4:00pm-5:00pmDiscussionFrancois Margot (Carnegie Mellon University)EE/CS 3-180 SW11.17-21.08
5:00pm-6:30pmPoster Session and Reception: 5:00-6:30
Poster submissions welcome from all participants
Lind Hall 400 SW11.17-21.08
Water network design by MINLPClaudia D'Ambrosio (Università di Bologna)
HIPO: A non-linear mixed integer constrained optimization algorithm for treatment planning in brachytherapy Andreas G. Karabis (PI Medical Ltd)
Variable neighbourhood search for MINLPsGiacomo Nannicini (École Polytechnique)
Direct numerical methods for mixed-integer optimal control problemsSebastian Sager (Ruprecht-Karls-Universität Heidelberg)
Convex relaxations of non-convex MIQCPAnureet Saxena (Axioma Inc.)
Some challenging mixed integer nonlinear optimization problems Tamás Terlaky (Lehigh University)
Exact algorithms for the quadratic linear ordering problemAngelika Wiegele (Universität Klagenfurt)

Wednesday, November 19

8:30am-9:00amCoffeeEE/CS 3-176 SW11.17-21.08
9:00am-10:00amWhat's new in SQP methods?Philip E. Gill (University of California, San Diego)EE/CS 3-180 SW11.17-21.08
10:00am-10:30amCoffeeEE/CS 3-176 SW11.17-21.08
10:30am-11:15amGlobal optimization of MINLP problems containing signomial functionsTapio Westerlund (Åbo Akademi (Finland-Swedish University of Åbo))EE/CS 3-180 SW11.17-21.08
11:15am-12:00pmA local relaxation approach for the siting of electrical substationsUday V. Shanbhag (University of Illinois at Urbana-Champaign)EE/CS 3-180 SW11.17-21.08
12:00pm-2:00pmLunch SW11.17-21.08
2:00pm-2:45pmA comparative study of linear and semidefinite branch-and-cut methods for solving the minimum graph bisection problemChristoph Helmberg (Technische Universität Chemnitz-Zwickau)EE/CS 3-180 SW11.17-21.08
2:30pm-3:30pmMath 8994: Topics in classical and quantum mechanics
Electronic structure calculations and molecular simulation: A mathematical initiation
Eric Cances (CERMICS)
Claude Le Bris (CERMICS)
Lind Hall 305
2:45pm-3:10pmPreprocessing techniques for discrete optimization problemsTodd S. Munson (Argonne National Laboratory)EE/CS 3-180 SW11.17-21.08
3:10pm-3:35pmUsing expression graphs in optimization algorithmsDavid M. Gay (Sandia National Laboratories)EE/CS 3-180 SW11.17-21.08
3:35pm-4:05pmCoffeeEE/CS 3-176 SW11.17-21.08
4:05pm-5:05pmDiscussionTamás Terlaky (Lehigh University)EE/CS 3-180 SW11.17-21.08

Thursday, November 20

8:30am-9:00amCoffeeEE/CS 3-176 SW11.17-21.08
9:00am-10:00amNonlinear discrete optimization IRobert Weismantel (Otto-von-Guericke-Universität Magdeburg)EE/CS 3-180 SW11.17-21.08
10:00am-10:30amCoffeeEE/CS 3-176 SW11.17-21.08
10:30am-11:15amNonlinear discrete optimization IIShmuel Onn (Technion-Israel Institute of Technology)EE/CS 3-180 SW11.17-21.08
11:15am-12:15pmTBACarlos J. Garcia-Cervera (University of California, Santa Barbara)Vincent Hall 570 AMS
11:15am-12:00pmOn the foundations of the theory of non-Linear and multi-objective integer optimizationJesus Antonio De Loera (University of California, Davis)EE/CS 3-180 SW11.17-21.08
12:00pm-2:00pmLunch SW11.17-21.08
2:00pm-2:25pmParallelization issues for MINLP Part IWilliam E. Hart (Sandia National Laboratories)EE/CS 3-180 SW11.17-21.08
2:25pm-2:50pmParallelization issues for MINLP Part IICynthia A. Phillips (Sandia National Laboratories)EE/CS 3-180 SW11.17-21.08
2:50pm-3:35pmMINLP application for optimizing sourcing decisions in a distressed supplier environment Erica Zimmer Klampfl (Ford)EE/CS 3-180 SW11.17-21.08
3:35pm-4:05pmCoffeeEE/CS 3-176 SW11.17-21.08
4:05pm-5:05pmDiscussionJon Lee (IBM)EE/CS 3-180 SW11.17-21.08
6:30pm-8:30pmWorkshop dinner at Pagoda RestaurantPagoda Restaurant
1417 4th St. SE
Minneapolis, MN
612-378-4710
SW11.17-21.08

Friday, November 21

8:30am-9:00amCoffeeEE/CS 3-176 SW11.17-21.08
9:00am-10:00amGeneralized disjunctive programming: A framework for formulation and alternative algorithms for MINLP optimization Ignacio Grossmann (Carnegie Mellon University)EE/CS 3-180 SW11.17-21.08
10:00am-10:30amCoffeeEE/CS 3-176 SW11.17-21.08
10:30am-11:15amMixed integer second order cone programmingSarah Drewes (TU Darmstadt)EE/CS 3-180 SW11.17-21.08
11:15am-12:00pmSolving nonconvex MINLP by quadratic approximation Stefan Vigerske (Humboldt-Universität)EE/CS 3-180 SW11.17-21.08
12:00pm-2:00pmLunch SW11.17-21.08
2:00pm-2:45pmNonlinear optimization via summation and integrationMatthias Koeppe (University of California, Davis)EE/CS 3-180 SW11.17-21.08
2:45pm-3:30pmTBAPablo A. Parrilo (Massachusetts Institute of Technology)EE/CS 3-180 SW11.17-21.08
3:30pm-4:00pmCoffeeEE/CS 3-176 SW11.17-21.08
4:00pm-5:00pmDiscussionTapio Westerlund (Åbo Akademi (Finland-Swedish University of Åbo))EE/CS 3-180 SW11.17-21.08
5:00pm-5:05pmClosing remarkJon Lee (IBM)
Sven Leyffer (Argonne National Laboratory)
EE/CS 3-180 SW11.17-21.08

Monday, November 24

10:45am-11:15amCoffee breakLind Hall 400
2:30pm-3:30pmMath 8994: Topics in classical and quantum mechanics
Electronic structure calculations and molecular simulation: A mathematical initiation
Eric Cances (CERMICS)
Claude Le Bris (CERMICS)
Lind Hall 305

Tuesday, November 25

10:45am-11:15amCoffee breakLind Hall 400
3:00pm-4:00pmReading group for Professor Ridgway Scott's book "Digital Biology"Ridgway Scott (University of Chicago)Lind Hall 401

Wednesday, November 26

10:45am-11:15amCoffee breakLind Hall 400
2:30pm-3:30pmMath 8994: Topics in classical and quantum mechanics
Electronic structure calculations and molecular simulation: A mathematical initiation
Eric Cances (CERMICS)
Claude Le Bris (CERMICS)
Lind Hall 305

Thursday, November 27

All DayThanksgiving holiday. The IMA is closed.

Friday, November 28

All DayFloating holiday. The IMA is closed.
Abstracts
Discussion
Abstract: No Abstract
Cameron F. Abrams (Drexel University) Ligand access/escape from protein cavities: A computational study of the insulin-phenol complex
Abstract: We apply random acceleration molecular dynamics (RAMD) simulation to identify potential escape routes of phenol from hydrophobic cavities in the hexameric insulin-phenol complex. We find three major pathways which provide new insights into (un)binding mechanisms for phenol. We identify several residues directly participating in escape events that serve to resolve ambiguities from recent NMR experiments. Reaction coordinates (RC) for dissociation of phenol are developed based on these exit pathways. Potentials of mean force (PMFs) along the RC for each pathway are resolved using multiple independent steered molecular dynamics (SMD) simulations with second order cumulant expansion of Jarzynski's equality. Our results for ΔF agree reasonably well within the range of known experimental and previous simulation magnitudes of this quantity. Based on structural analysis and energetic barriers for each pathway, we suggest a plausible preferred mechanism of phenolic exchange that differs from previous mechanisms. Several weakly-bound metastable states are also observed for the first time in the phenol dissociation reaction.
Denis Andrienko (Max-Planck Institut für Polymerforschung) Charge transport in discotic liquid crystals: a multiscale computer simulation study
Abstract: Charge mobilities of several derivatives of discotic liquid crystals have been determined by combining three methods into one scheme: (i) quantum chemical methods for the calculation of molecular electronic structures and reorganization energies (ii) molecular dynamics for simulation of the relative positions and orientations of molecules in a columnar mesophase, and (iii) kinetic Monte Carlo simulations and Master Equation approach to simulate charge transport. We reproduce the trends and magnitudes of mobilities as measured by pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) and connect mobility directly to the microscopic morphology of the columns. Our study also shows that it is possible to understand and reproduce experimental charge transport parameters, and, in some cases, accurately predict them.
Kurt M. Anstreicher (University of Iowa) The difference between 5x5 doubly nonnegative and completely positive matrices
Abstract: The convex cone of n×n completely positive (CPP) matrices and its dual cone of copositive matrices arise in several areas of applied mathematics, including optimization. Every CPP matrix is doubly nonnegative (DNN), i.e., positive semidefinite and component-wise nonnegative. Moreover for n less than 5, every DNN matrix is CPP. We investigate the difference between 5×5 DNN and CPP matrices. We give a precise characterization of how a 5×5 DNN matrix that is not CPP differs from a DNN matrix, and use this characterization to show how to separate an extreme DNN matrix that is not CPP from the cone of CPP matrices. Joint work with Sam Burer and Mirjam Duer.
Alán Aspuru-Guzik (Harvard University) Environment-assisted quantum transport in photosynthetic complexes: Learning from nature for potential organic photovoltaic applications.
Abstract: Transport phenomena at the nanoscale are of interest due to the presence of both quantum and classical behavior. In this work, we demonstrate that quantum transport efficiency can be enhanced by a dynamical interplay of the system Hamiltonian with the pure dephasing dynamics induced by a fluctuating environment. This is in contrast to fully coherent hopping that leads to localization in disordered systems, and to highly incoherent transfer that is eventually suppressed by the quantum Zeno effect. We study these phenomena in the Fenna-Matthews-Olson protein complex as a prototype for larger photosynthetic energy transfer systems. We also show that disordered binary tree structures exhibit enhanced transport in the presence of dephasing. This phenomena could in principle be applied for the development of materials with improved exciton transport properties. Our group is beginning work in this direction. If time is available, I will describe our distributed computing effort for finding novel candidates for organic photovoltaic devices by the harnessing volunteer CPU time.
Paul J. Atzberger (University of California, Santa Barbara) Multiscale modeling and simulation of soft matter materials
Abstract: We shall discuss a multiscale modeling and simulation formalism for soft matter materials taking into account hydrodynamic interactions and thermal fluctuations. A specific motivation is the study of lipid bilayer membranes and polymer fluids taking into account microstructure degrees of freedom. The approach is based on the immersed boundary method, where hydrodynamic interactions of the composite system are handled by an approximate treatment of the fluid-structure stresses. The microstructures (lipid molecules / polymers) are represented by Lagrangian degrees of freedom which are coupled to an Eulerian representation of the fluid, treated at the level of continuum mechanics. Thermal fluctuations are incorporated in the formalism by an appropriate stochastic forcing of the fluid-structure equations in accordance with the principles of statistical mechanics. The theoretical formalism presents a number of numerical challenges for temporal integration and spatial resolution which we shall address. This includes a time integrator for the stiff stochastic dynamics and methods to handle adaptive spatial discretizations of the underlying stochastic partial differential equations. We shall discuss specific applications of the approach, including the study of lipid flow in bilayer membranes, the shear viscosity of polymer fluids, and the diffusivity of particles in complex fluids.
Eray S. Aydil (University of Minnesota) Challenges in efficient and inexpensive solar-to-electric energy conversion
Abstract: Efficient solar-to-electric energy conversion with inexpensive solar cells and materials is one of the most important challenges we face in the 21st century. Crystalline silicon solar cells based on the conventional p-n junction dominate the solar cell market and are commercially available in modules with 15-20% efficiencies. However, they are still too expensive to manufacture which limits their potential for replacing energy from burning fossil fuels. This established technology faces the challenge of discovering innovative methods for making crystalline silicon at lower cost. Thin film solar cells based on various semiconductors such as copper indium gallium selenide (CIGS), cadmium telluride and amorphous silicon reduce the solar cell cost by reducing the amount of photovoltaic material and the amount of energy required to produce the solar cell. However, either their efficiencies are low compared to crystalline silicon or they are difficult to manufacture on large scale. In addition, last decade has produced a number of new ideas and solar cell designs based on inorganic quantum dots and on organic thin films. These ideas are now at the beginning stages of their technological evolution curves and face challenges ranging from establishing fundamental understanding of their operation principles to improving their efficiencies to levels competitive with silicon solar cells. Regardless of the solar cell technology, a number of different challenges must be surpassed to make electricity from solar energy conversion competitive with electricity obtained from burning fossil fuels. This talk will attempt to set the stage for the workshop by providing an overview of various approaches to solar-to-electric energy conversion and by summarizing the scientific challenges that must be addressed to advance the state of the art in photovoltaics.
Pietro Belotti (Lehigh University) Branching rules in branch-and-bound algorithms for nonconvex mixed-integer nonlinear programming
Abstract: For the general class of MINLP problems where relaxing the integrality on integer variables yields a nonconvex problem, a commonly used solution method is Branch-and-Bound (BB). Two crucial components of a BB algorithm are: a convex relaxation, often an LP relaxation, to obtain lower bounds; and branching rules for partitioning the solution set. We present an extension to nonconvex MINLP of a branching technique that proved successful for Mixed-Integer Linear Programming, namely reliability branching. Branching rules can be applied on both integer and continuous variables in nonconvex MINLPs, and the choice of the branching variable depends on both the MINLP problem and its linear relaxation. We discuss in detail the choice of both the branching variable and the branching point, i.e. the value of that variable where branching is done. We present some computational results and compare reliability branching with another branching technique for nonconvex MINLPs, Violation Transfer, on a set of publicly available instances.
Hande Yurttan Benson (Drexel University) Using interior-point methods within MINLP
Abstract: While implementations of infeasible interior-point methods remain the state-of-the-art in nonlinear programming, there are serious limitations in their use within the framework of MINLP due to lack of warm-start and infeasibility detection capabilities. We present a primal-dual penalty approach that allows interior-point methods to have such capabilities, and remains flexible enough to accommodate changing bounds, additional constraints, and additional variables in the nonlinear subproblems.
Pierre Bonami (Centre National de la Recherche Scientifique (CNRS)) Branching strategies and heurisitcs in a branch-and-bound for convex MINLPs
Abstract: Different variants of the branch-and-bound algorithm exist for solving exactly convex MINLPs. These variants differ mainly in the relaxation solved at the nodes of the tree. There are mainly two variants: one that solves a nonlinear programming relaxation at each node and one that solves a linear programming relaxation. In recent year the linear programming based branch-and-bounds have shown to be more effective on large sets of problems. In this talk, we study techniques to make the nonlinear programming based branch-and-bound more competitive. In particular, we study branching strategies and heuristics. The techniques have been implemented in the open-source solver Bonmin We present computational results to assess the effectiveness of the proposed strategies and compare the resulting algorithm with a linear programming (outer approximation based) branch-and-cut. This talk is based on joint works with Joao Goncalves, Jon Lee and Andreas Waechter.
Andrea Braides (Seconda Università di Roma "Tor Vergata") Variational coarse-graining of lattice systems
Abstract: Asymptotic variational methods are aimed at describing the overall properties of an increasingly complicated system by computing an effective limit energy where some parameters are averaged out or greatly simplified. Such methods include Gamma-convergence and variational expansions. An extremely interesting field of application is that of discrete (lattice) systems, where the determination of the relevant parameters in the limit theory is part of the problem. I will present an overview of the Gamma-convergence methods and a few examples that range from nonlinear discrete homogenization to expansions in fracture mechanics to size effects in thin films to variational percolation problems.
Frank L. H. Brown (University of California, Santa Barbara) Simple models for biomembrane structure and dynamics
Abstract: Simulation of biomembranes over length and time scales relevant to cellular biology is not currently feasible with Molecular Dynamics including full atomic detail. Barring an unforeseen revolution in the computer industry, this situation will not change for many decades. We present two coarse grained simulation models for biomembranes that treat water implicitly (i.e. no water molecules appear in our simulations. The hydrophobic effect, hydrodynamics and related properties are approximately included without simulation of solvent). These models enable the study of systems and phenomena previously intractable to simulation.
Eric Cances (CERMICS), Claude Le Bris (CERMICS) Math 8994: Topics in classical and quantum mechanics
Electronic structure calculations and molecular simulation: A mathematical initiation
Abstract: Meeting time: Mondays and Wednesdays 2:30 ‐ 3:30 pm Room 305 Lind Hall. The course will present the basics of the quantum theory commonly used in computational chemistry for electronic structure calculations, and the basics of molecular dynamics simulations. The perspective is definitely mathematical. After the presentation of the models, the mathematical properties will be examined. The state of the art of the mathematical knowledge will be mentioned. Numerical analysis and scientific computing questions will also be thoroughly investigated. The course is intended for students and researchers with a solid mathematical background in mathematical analysis and numerical analysis. Familiarity with the models in molecular simulation in the broad sense is not needed. The purpose of the course to introduce the audience to the field. This is a 1‐3 credit course offered through the School of Mathematics. Non‐student participants are welcome to audit without registering. Note that no particular knowledge of quantum mechanics or classical mechanics will be necessary: the basic elements will be presented. For additional information and course registration, please contact: Markus Keel (keel@math.umn.edu).
Daniel M. Chipman (University of Notre Dame) Fermi contact interactions evaluated from hidden relations in the Schrödinger equation
Abstract: Fermi contact interactions between electrons and nuclei govern important properties such as the hyperfine coupling constants observed in Electron Spin Resonance Spectroscopy and the spin-spin coupling constants observed in Nuclear Magnetic Resonance Spectroscopy. But approximate wavefunctions of the kinds commonly used for molecules are generally optimized through some kind of overall energy criterion, and so may have significant errors for the electron density at position of a nucleus where the Fermi contact interaction occurs. It will be shown how hidden relations that are implicit in the Schrödinger equation allow the Fermi contact interactions to be reexpressed in terms of more global properties of the electron density. For exact wavefunctions the hidden relations would give the same results as would direct pointwise evaluation of the electron density, but for approximate wavefunctions the results may differ and in fact provide improved accuracy. The relevant equations will be derived, and numerical examples will be given that demonstrate the point. An extension to higher order will also be developed for the well-known Kato cusp condition that constrains the behavior of the wavefunction
Olivier Coulaud (Institut National de Recherche en Informatique Automatique (INRIA)) Parallel multiscale simulation for crack propagation
Abstract: Concurrent multiscale methods are a powerful tool to solve with a low computational cost the local phenomena that occur at a small scale (atomic for example). Such methods are commonly used to study for example crack propagation, dislocations or nanoindentations. Even for small domain sizes, like the volume of a hundred nanometer cube, 3D atomistic simulations can lead to several hundred of millions atoms, and high performance parallel computation is naturally required. These simulations couple different parallel codes such as molecular dynamic code and elasticity code. The performance of the coupled code depends on how the data are well distributed on the processors. Here we focus on the parallel aspects of the Bridging Method introduced by T. Belytschko and Xiao [1]. This method assumes that an atomistic model and a continuum model are coupled through an overlap zone. We present our parallel multiscale environment called LibMultiscale [2], which is based on a coupling involving a legacy parallel code for molecular dynamics (Lammps) and a parallel finite element code for continuum mechanics (LibMesh). Data redistribution and atom migration issues are discussed. Moreover 2D and 3D waves propagation simulations and a 2D penny shape crack propagation simulation are shown. References: [1] Coupling Methods for continuum model with molecular model. T. Belytschko, S.P. Xio. International Journal for Multiscale Computational Engineering, 11 (2003). [2] LibMultiscale: http://libmultiscale.gforge.inria.fr/
Claudia D'Ambrosio (Università di Bologna) Water network design by MINLP
Abstract: The optimal design of a Water Distribution Network (WDN) is a real-world optimization problem known and studied since the seventies. Several approaches has been proposed, for example, heuristics, metaheuristics, Mixed Integer Linear Programming models and global optimization methods. Despite this interest, it is still an open problem, since it is very hard to find good solutions for even medium sized instances. In this work we propose a non-convex Mixed Integer Non-Linear Programming (MINLP) model that accurately approximates the WDN problem, and we solve it with an ad-hoc modified branch-and-bound for MINLPs. This was possible thanks to the use of the open-source MINLP solver Bonmin. Computational results are presented on literature instances and new instances based on data of medium-sized Italian cities. Even for the bigger instances, we are able to find good feasible solutions. This is a joint work with C. Bragalli, J. Lee, A. Lodi and P. Toth.
Jesus Antonio De Loera (University of California, Davis) On the foundations of the theory of non-Linear and multi-objective integer optimization
Abstract: In recent years algebraic geometry, number theory, and commutative algebra have shown their potential to solve challenging problems in discrete optimization. This talk hopes to show algebraic tools can be used to prove strong computational complexity results in optimization problems with non-linear or multi-objective objective functions and linear constraints. This is talk is partly based on joint work with M. Koeppe and R. Hemmecke.
Rafael Delgado-Buscalioni (Autonomous University of Madrid) Atomistic, mesoscopic and continuum hydrodynamics: coupling liquid models with different resolution
Abstract: The final goal of multiscale methods based on domain decomposition, is to retain full atomistic detail only where needed (within a region of interest), while using a coarse-grained model to introduce the essential information about the surroundings dynamics. Importantly, the atomistic region becomes an open sub-system which exchanges mass, momentum and energy with the exterior. The hydrodynamics of flux exchange can be solved using an hybrid molecular-continuum description (hybrid MD) [1,2]. However, molecule exchange across the hybrid interface becomes a complicated task as one deals with more complicated molecules, essentially owing to larger steric hindrance. A way to solve this bottleneck is to combine hybrid MD with adaptive coarse-graining. The set-up is like the layers of an onion [3]: the atomistic model lies at the core, surrounded by a thermodynamically compatible coarse-grained model, which interfaces with a continuum description of the liquid (maybe also including hydrodynamic fluctuations). Finally, open boundary conditions for the continuum description [4] allow evacuation of (shear, heat or sound) waves out of the whole system, and let it behave in a grand-canonical way, in contact with the prescribed outer thermodynamic state. [1] G. De Fabritiis, R. Delgado-Buscalioni and P. Coveney, Phys. Rev. Lett.97, 134501 (2006)
[2] R .Delgado-Buscalioni and G. De Fabritiis, Phys. Rev. E 76, 036709 (2007)
[3] R. Delgado-Buscalioni, K. Kremer and M. Praprotnik, J. Chem. Phys. 128, 114110 (2008)
[4] R. Delgado-Buscalioni, A. Dejoan, Phys. Rev. E, in press, (2008)
Luigi Delle Site (Max-Planck Institut für Polymerforschung) The adaptive resolution simulation scheme (AdResS): Basic principles and applications
Abstract: For the study of complex synthetic and biological molecular systems by computer simulations one is still restricted to simple model systems or to, by far too small, time scales. To overcome this problem multiscale techniques are being developed. However in almost all cases, the regions treated at different level of resolution are kept fixed and the free exchange of particles among these regions is not allowed. I here present a robust computational method and its basic theoretical framework for an efficient and flexible coupling of the different regimes. The key feature of the method is that it allows for a dynamical change of the number of molecular degrees of freedom during the course of the MD simulation by an on-the-fly switching between the atomistic and coarse-grained levels of detail. Thermodynamic equilibrium is preserved by interpreting the concept of changing resolution in terms of "geometrically induced phase transition." This leads to the introduction of a "latent heat" of switching and to the extension of the equipartition theorem to fractional (switching) degrees of freedom. The efficiency of the presented approach is illustrated in the application to several systems.
Luigi Delle Site (Max-Planck Institut für Polymerforschung) A criterion to estimate the quality of the Mapping Scheme in Coarse-graining approaches
Abstract: We propose a method to evaluate the approximation of separation of variables (ASV) in Molecular Dynamics (MD) and related fields. It is based on a point-by-point evaluation of the difference between the true potential and the corresponding potential where the separation of variables is applied. The major advantage of such an approach is the fact that it requires only the analytical form of the potential as provided in most of the MD codes. We provide an application of this criterion for alkane (aliphatic) chain and compare the efficiency for two different Mapping Schemes (MS).
Markus Deserno (Carnegie Mellon University) Coarse-grained simulation studies of mesoscopic membrane phenomena
Abstract: Lipid membranes exhibit a large spectrum of fascinating physical behavior, spanning many orders of magnitude both in length- and time scales. To cover this wide range, models of different resolution have been developed, from atomistically resolved lipid representations to triangulated fluid-elastic surfaces. In the intermediate regime of about 100 nanometer length scale and micro- to millisecond time scale mesoscopic coarse-grained models have recently covered much ground. They can approach phenomena in which cooperativity between several proteins are crucial, while still preserving the essence of many lipid degrees of freedom (area density, order, tilt, composition, etc.), whose coupling is deemed relevant in many biological situations, notably the "raft question". I will describe in more detail a particular solvent-free coarse-grained model recently developed by us and illustrate its applicability to a wide variety of phenomena, among them pore-formation by amphipathic peptides, protein aggregation on critically mixed bilayers, and membrane vesiculation driven by curvature-imprinting proteins.
Belma Dogdas (Merck & Co., Inc.) Image registration with applications in medical imaging towards drug discovery and development
Abstract: Imaging can be used to develop effective biomarkers to provide information on diseases and assessing therapeutic effects. In the past decade, several imaging modalities have been used for early detection of drug response. Although many imaging techniques are available to the medical community, no single method provides all the necessary information. For instance structural MR and CT imaging modalities provide anatomical information whereas PET and optical imaging can provide functional information. Often, it is useful to combine complementary information from different modalities, through a technique known as image registration. In addition, statistical characterization of morphological differences within and between groups or automated identification and labeling of specific anatomical structures with an atlas requires image registration. Therefore it is essential to understand image registration techniques to enable their effective use in imaging applications. In this talk, I will describe recent advances in image registration and provide examples of how it is being used in medical imaging towards drug discovery and development.
Sarah Drewes (TU Darmstadt) Mixed integer second order cone programming
Abstract: We present two algorithms to solve mixed integer second-order cone programming problems: a branch-and-cut method and an outer approximation based branch-and-bound approach. We use different techniques for the generation of linear and convex quadratic cuts and investigate their impact on the branch-and-cut procedure. The presented outer approximation based branch-and-bound algorithm is an extension of the well-known outer approximation based branch-and-bound approach for continuous differentiable problems to subdifferentiable constraint functions. Convergence can be guaranteed, since the subgradients, that satisfy the KKT conditions, can be identified using the dual solution of the occurring second order cone problems. Computational results for test problems and real world applications are given.
Burkhard Dünweg (Max-Planck Institut für Polymerforschung) Lattice Boltzmann simulations of soft-matter systems
Abstract: A brief introduction into the lattice Boltzmann method is given. For soft-matter applications, it is necessary to include thermal fluctuations by introducing stochastic collision rules. This can be done consistently based upon the concept of detailed balance. Brownian particles are coupled to the lattice Boltzmann solvent via a Stokes friction and interpolation. The Langevin equations of the overall system satisfy both momentum conservation and the fluctuation-dissipation theorem. The long-time mobility of the particles differs from the input Stokes value by a contribution from the surrounding flow. The usefulness of this method is demonstrated by examples from polymer physics (hydrodynamic screening of semidilute polymer solutions) and colloid physics (electrophoresis of charge-stabilized colloidal dispersions).
Burkhard Dünweg (Max-Planck Institut für Polymerforschung) Basic concepts of polymer physics and their numerical study
Abstract: Polymers are prototypical examples of soft-matter systems. The talk will first focus on equilibrium statistical mechanics, and introduce basic concepts like the random walk and the self-avoiding walk. This is complemented by a discussion of the notion of coarse-graining and scale invariance, which is at the basis of modeling polymers in terms of simple bead-spring models. The second part will then discuss the basics of polymer dynamics, in terms of the fundamental Rouse, Zimm, and reptation models. The third part is devoted to a brief overview over Monte Carlo and Molecular Dynamics models and simulation algorithms, which are directly based upon the insight into the essential physics. If time permits, a brief outlook on the physics of membranes will be added.
Weinan E (Princeton University) Some representative issues in multiscale modeling
Abstract: I will discuss the mathematical and numerical problems involved in coupling atomistic and continuum models as well as coupling electronic and atomistic models, with examples from materials and fluids.
Weinan E (Princeton University) Capturing the macroscopic behavior of complex systems using multiscale methods
Abstract: Joint work with Eric Vanden-Eijnden. In many problems of multiscale modeling, we are interested in capturing the macroscale behavior of the system with the help of some accurate microscale models, bypassing the need of using empirical macroscale models. This paper gives an overview of the recent efforts on establishing general strategies for designing such algorithms. After reviewing some important classical examples, the Car-Parrinello molecular dynamics, the quasicontinuum method for modeling the deformation of solids and the kinetic schemes for gas dynamics, we discuss three attempts that have been made for designing general strategies: Brandt's renormalization multi-grid method (RMG), the heterogeneous multiscale method (HMM) and the "equation-free" approach. We will discuss the relative merits and difficulties with each strategy and we will make an attempt to clarify their similarities and differences. We will then discuss a general strategy for developing seamless multiscale methods for this kind of problems. We will end with a discussion of the applications to free energy calculations and a summary of the challenges that remain in this area
Bjorn Engquist (University of Texas) Finding effective equations for heterogeneous multiscale methods
Abstract: An advantage with the framework of the heterogeneous multiscale method is that the full knowledge of an effective or macroscale equation is not required for the numerical approximation of a homogenized or averaged solution. A higher fidelity microscale model is used to supply the missing data. The efficiency is gained by only applying the microscale model in sub domains. The structure of the macroscale equation must however be known. Often it is well known from the setting of the original problem, but if it is not, new techniques are required to find the form of a relevant effective or macroscale equation.
James W. Evans (Iowa State University) Realistic multiscale modeling of spatiotemporal behavior in surface reactions: Equation-free "heterogeneous coupled lattice-gas" (HCLG) simulations
Abstract: A rich variety of spatiotemporal pattern formation and reaction front propagation has been observed in simple reactions on metal surfaces. Modeling has typically applied mean-field reaction-diffusion equations - ignoring the impact of reactant ordering or islanding on the reaction kinetics, and oversimplifying the treatment of surface diffusion in mixed reactant adlayers. In 1995, we introduced an equation-free HCLG simulation approach [Tammaro et al. J. Chem. Phys. 103 (1995) 10277] which performs parallel KMC simulations of an atomistic lattice-gas reaction model at spatial locations distributed across the surface, and suitably couples these to describe the effects of macroscopic surface diffusion. Recently, we have applied this approach to realistic models for CO-oxidation on Pd(100) and Rh(100) surfaces [Liu & Evans, Phys. Rev. B 70 (2004) 193408; Surf. Sci. - Ertl Nobel Issue 2008]. This requires a precise treatment of the collective and "tensorial" nature of the rapid diffusion of CO through a disordered environment of relatively immobile oxygen [Liu & Evans, J. Chem. Phys. 125 (2006) 054709].
Roland Faller (University of California, Davis) Multiscale modeling of polystyrene in different environments
Abstract: Polystyrene is a very abundant and industrially important polymer. We are modeling its dynamical behavior on multiple length scales and different environments. We start with pure PS where we develop a mesoscale polystyrene model based on atomistic simulations. The non-bonded effective potential is optimized against the atomistic simulation until the radial distribution function generated from the mesoscale model is consistent with the atomistic simulation. The mesoscale model allows understanding the polymer dynamics of long chains in reasonable computer time. Both models are investigated in the melt, the blend and in confined geometries. The dynamics of polystyrene melts are investigated at various chain lengths ranging from 15 to 240 monomers and the crossover to entangled dynamics is observed. As computer simulations cannot only address average properties of the system under study but also the distribution over any observable of interest we are study mixtures of polystyrene and polyisoprene by atomistic molecular dynamics and calculate correlation times for all segments in the system. We then identify fast and slow segments and can correlate the segment speed with the local neighborhood and obtain that fast segments have a surplus of the faster component in their neighborhood and vice versa. Finally we present a coarse grained model for the blend which is capable of showing phase separation.
Roland Faller (University of California, Davis) Multiscale modeling of structure and phase behavior in heterogeneous lipid bilayers
Abstract: The study of lipid structure and phase behavior at the nano scale length is of importance due to implications in understanding the role of the lipids in biochemical membrane processes. We performed a variety of simulations in homogeneous and heterogeneous membrane systems to elucidate such behaviors. Our simulations demonstrate that various coarse grained simulation models can predict different aspects of lipid phase separation and describe the change of the system under the influences of hydrophilic and hydrophobic support. The simulations are performed using models at different length scales ranging from the all atom scale to a scale where lipids are modeled by only three interaction sites. We are able to follow transformations, such as lipids phase transitions. These phase transitions are determined by analyzing parameters like area per lipid head group, the deuterium order parameter and dynamic properties. Phase diagrams of mixtures are reproduced consistent with experiments. We study the influence of a support on the systems on different length scales. We discuss the changes of the system phase behavior as well as differences between the two leaflets as induced by the support.
Dominik Fritz (Max Planck Institute for Polymer Research) From atomistic to mesoscale systems without fitting: A coarse grained model for polystyrene
Abstract: We present a coarse grained model for polystyrene, which is only based on properties of single chains and of systems consisting of two short oligomers. We do not need any fitting to atomistic melt simulations. The model keeps the information about the tacticity of the chains and reproduces the local distributions for bond length, angles and dihedral angles. Furthermore it is modeling statical properties of atomistic melts, e.g. radial distribution functions and internal distances.
David M. Gay (Sandia National Laboratories) Using expression graphs in optimization algorithms
Abstract: An expression graph, informally speaking, represents a function in a way that cam be manipulated to reveal various kinds of information about the function, such as its value or partial derivatives at specified arguments and bounds thereon in specified regions. (Various representations are possible, and all are equivalent in complexity, in that one can be converted to another in time linear in the expression's size.) For mathematical programming problems, including the mixed-integer nonlinear programming problems that are the subject of this workshop, there are various advantages to representing problems as collections of expression graphs. "Presolve" deductions (to be discussed in more detail by Todd Munson) can simplify the problem, e.g., by reducing the domains of some variables and proving that some inequality constraints are never or always active. To find global solutions, it is helpful sometimes to solve relaxed problems (e.g., allowing some "integer" variables to vary continuously or introducing convex or concave relaxations of some constraints or objectives), and to introduce "cuts" that exclude some relaxed variable values. There are various ways to compute bounds on an expression within a specified region or to compute relaxed expressions from expression graphs. This talk will sketch some of them. As new information becomes available in the course of a branch-and-bound (or -cut) algorithm, some expression-graph manipulations and presolve deductions can be revisited and tightened, so keeping expression graphs around during the solution process can be helpful. Algebraic problem representations are a convenient source of expression graphs. One of my reasons for interest in the AMPL modeling language is that it delivers expression graphs to solvers.
Johannes Giannoulis (Technical University of Munich ) From quantum to classical molecular dynamics
Abstract: We are interested in the rigorous justification of the passage from quantum to classical molecular dynamics in the heavy nuclei limit, i.e., when the mass ratio of elecronic to nucleonic mass tends to zero. For positive mass ratio the (non-relativistic) quantum dynamics is described by the time-dependent linear Schroedinger equation, where the potential U is the ground state Born-Oppenheimer potential energy surface obtained by minimization over electronic states. The classical dynamics is governed by the Liouville equation for an (appropriately defined) time-dependent Wigner measure W, obtained as the limit (for mass ratio tending to zero) of the Wigner functions corresponding to the wavefunctions solving the Schroedinger equation. Since the physically correct potential U possesses Coulomb singularities due to nuclei repulsion and can have kink type singularities if eigenvalue crossings are present, its level of smoothness is far lower than that required in previous rigorous approaches and renders the justification of the Liouville equation quite difficult. In the poster we present our results mainly concerning the case of potentials U with only Coulomb singularities and no crossings.
Philip E. Gill (University of California, San Diego) What's new in SQP methods?
Abstract: Sequential quadratic programming (SQP) methods a powerful and effective class of methods for a wide range of nonlinearly constrained optimization problems. Given the scope and utility of nonlinear optimization, it is not surprising that SQP methods are still a subject of active research. Recent developments in methods for mixed integer nonlinear programming and the minimization of functions subject to differential equation constraints has led to a heightened interest in methods that may be "hot started" from a good approximate solution. We discuss the role of SQP methods in this context, with particular reference to some recent enhancements to our large-scale SQP package SNOPT. We end with some discussion of the challenges associated with formulating algorithms that can exploit multicore and GPU-based computer architectures.
Ignacio Grossmann (Carnegie Mellon University) Generalized disjunctive programming: A framework for formulation and alternative algorithms for MINLP optimization
Abstract: Generalized disjunctive programming (GDP) is an extension of the disjunctive programming paradigm developed by Balas. The GDP formulation involves Boolean and continuous variables that are specified in algebraic constraints, disjunctions and logic propositions, which is an alternative representation to the traditional algebraic mixed integer programming (MIP) formulation. Our research on GDP problems has been motivated by its potential for improved modeling of MINLP optimization, and for the development of customized algorithms that exploit the underlying logical structure of the problem in both the linear and nonlinear cases. We first provide an overview of this work for the case of convex functions emphasizing the quality of continuous relaxations of alternative reformulations that include the big-M, the hull relaxation and the sequential intersection of disjunctions. We then review disjunctive branch and bound as well as logic-based decomposition methods that circumvent some of the limitations in traditional MINLP optimization. Finally, for the case when the GDP problem involves nonconvex functions, we propose a scheme for tightening the lower bounds for obtaining the global optimum using a combined disjunctive and spatial branch and bound search. We illustrate the application of the theoretical concepts and algorithms on a variety of engineering and OR problems.
William E. Hart (Sandia National Laboratories) Parallelization issues for MINLP Part I
Abstract: Sandia National Laboratories has invested considerable effort in massively parallel optimization tools. In this talk, we will summarize relevant experience from developing our parallel mixed-integer programming (MIP) solver PICO (Parallel Integer and Combinatorial Optimizer) and our parallel nonlinear solver GNLP. We will discuss parallel solution of mixed-integer nonlinear programs (MINLP). In particular, we will consider how the choice of parallel platform (tightly-coupled systems, cloud computing, grid computing, etc) can affect algorithmic decisions. We will highlight issues parallel solvers must face that serial solvers do not such as load balancing, ramp up, and termination and some issues that parallel solvers might do differently, such as decomposition. We expect some of our MIP/NLP experience to carry over, and some issues to be unique to, or uniquely difficult for, MINLP.
Teresa Head-Gordon (University of California, Berkeley) Coarse-grained and multiscale models of bulk liquids and macromolecules
Abstract: I will describe two coarse-grained models and a multiscale model relevant in the context of molecular or langevin dynamics of bulk liquids and macromolecules. We have recently achieved a fundamental result in deriving an analytical solution for computing the screened electrostatic interaction between arbitrary numbers of proteins of arbitrarily complex charge distributions, assuming they are well described by spherical low dielectric cavities in a higher dielectric salty medium [1]. Ultimately, smooth and systematic increase or decrease in spatial resolution back and forth between simple dielectric cavities and atomic level descriptions will be the centerpiece of a multiscale scheme [2]. I will also describe a coarse-grained model of water to investigate thermodynamic-dynamic relationships [3] as well as a coarse-grained protein model relevant for lengthscales and timescales relevant for disease aggregation [4, 5]. [1] I. Lotan & T. Head-Gordon (2006). An analytical electrostatic model for salt screened interactions between multiple proteins J. Comp. Theo. Chem. 2, 541-555. [2] E.-H. Yap & T.Head-Gordon (2008). In progress [3] M.E. Johnson and T. Head-Gordon (2008). Thermodynamic theories of liquid dynamics. submitted. [4] E.-H. Yap, N. Lux Fawzi & T. Head-Gordon (2008). A coarse-grained a-carbon protein model with anisotropic hydrogen-bonding. Proteins, Struct. Func.. Bioinf. 70, 626-638. [5] N. Lux Fawzi, E.-H. Yap, Y. Okabe, K. Kohlstedt, S. P. Brown & T. Head-Gordon (2008). Contrasting disease and non-disease protein aggregation. Acc. Chem. Research 41, 1037-1047.
Christoph Helmberg (Technische Universität Chemnitz-Zwickau) A comparative study of linear and semidefinite branch-and-cut methods for solving the minimum graph bisection problem
Abstract: Joint work with Michael Armbruster (TU Chemnitz), Marzena Fuegenschuh (TU Darmstadt), and Alexander Martin (TU Darmstadt). Semidefinite relaxations are known to deliver good approximations for combinatorial optimization problems like graph bisection. Using the spectral bundle method it is possible to exploit structural properties of the underlying problem and to apply, even to sparse large scale instances, cutting plane methods, probably the most successful technique in linear programming. We set up a common branch-and-cut framework for linear and semidefinite relaxations of the minimum graph bisection problem. It incorporates separation algorithms for valid inequalities presented in the recent study by Armbruster, Fuegenschuh, Helmberg, and Martin 2007 of the facial structure of the associated polytope. Extensive numerical experiments show that the semidefinite branch-and-cut approach outperforms the classical simplex approach on a clear majority of the sparse large scale test instances. On instances from compiler design the simplex approach is faster.
Russell J. Holmes (University of Minnesota) Engineering morphology in small molecule organic photovoltaic cells for efficient exciton diffusion and dissociation
Abstract: Organic materials are attractive for application in photovoltaic cells due to their compatibility with lightweight, flexible substrates, and high-throughput processing techniques. Optical absorption in these materials leads to the creation of a bound electron-hole pair known as an exciton. The exciton is mobile, and diffuses to a heterojunction where electron-hole dissociation and photocurrent generation may take place. In most organic materials, the exciton diffusion length is much shorter than the optical absorption length. This “exciton bottleneck” limits the active layer thickness and reduces the absorption efficiency of the cell. Routes around the bottleneck have centered on the use of mixed donor-acceptor morphologies to increase the area of the dissociating interface. While promising, these architectures are difficult to optimize, and can introduce resistance for the collection of photogenerated carriers. This talk will examine an alternate approach to overcome the exciton bottleneck, focusing on the use carefully controlled, graded morphologies in organic photovoltaics.
Richard D. James (University of Minnesota) A mathematical perspective on the structure of matter
Abstract: Beginning with some observations about the periodic and nonperiodic structures commonly adopted by elements in the periodic table, I will introduce a definition ("objective structures") of a mathematically small but physically well represented class of molecular structures. This definition will be seen to have an intimate relation to the invariance of the equations of quantum mechanics. The resulting framework can be used to design various multiscale methods, and gives a new perspective on some of the fundamental solutions in continuum mechanics for solids and fluids. Open mathematical problems will be highlighted.
Christoph Junghans (Max-Planck Institut für Polymerforschung) Comparative study of water: Atomistic vs. coarse-grained
Abstract: We employ the inverse Boltzmann method to coarse-grain three commonly used three site water models (TIP3P, SPC and SPC/E) where one molecule is replaced by one coarse-grained particle with two body interactions only. The shape of the coarse-grained potentials is dominated by the ratio two lengths, which can be rationalized by the geometric constraints of the water clusters. It is shown that for simple two body potentials either the radial distribution function or the geometrical packing can be optimized. In a similar way, as needed for multiscale methods, either the pressure or the compressibility can be fitted to the all atom liquid. In total, a speedup of a factor of about 50 in computation time can be reached by this coarse-gaining procedure.
Raymond Kapral (University of Toronto) Molecular dynamics in mesoscopic solvents
Abstract: Modeling the dynamics of complex molecular systems is difficult since physically relevant distance and time scales are often very long. Consequently, a variety of different coarse-grained molecular dynamics methods, which attempt to bridge gap between short and long scales, has been developed. The talk will focus one such method, multiparticle colision dynamics, for the computation of the mesoscopic dynamics of molecular systems. In particular, polymer and biopolymer dynamics in crowded molecular environments, such as those encountered in the interior of the cell, and the motion of self-propelled nanoparticles in solution will be considered. The mesoscopic simulations were carried out by combining a molecular dynamics description of the molecular with a coarse grained description of the solvent using multiparticle collision dynamics.
Andreas G. Karabis (PI Medical Ltd) HIPO: A non-linear mixed integer constrained optimization algorithm for treatment planning in brachytherapy
Abstract: Joint work with Stavroula Giannouli (Pi Medical) and Dimos Baltas (Klinikum Offenbach GmbH, Germany). HIPO (Hybrid Inverse Planning and Optimization) is a general, state-of-the-art treatment planning optimization tool with inverse planning capabilities for interstitial template based brachytherapy. HIPO was presented in 2005 and the first commercial release was launched in 2007. It is used in more than 30 clinics around the world. An improved version is presented here, able to take into account clinical recommendations as soft & hard constrains. During the template-based brachytherapy treatment procedure, a perforated template is fixed on patient’s body and needles are placed -through the holes- inside patient’s body, penetrating the tumour. Within the needles, an irradiating source is stepping. The total dose distribution in the tumour, the surrounding organs and tissue, is a function of the times (dwell times) that the source is spending at each position. The main purpose of planning is to irradiate the target while protecting the surrounding healthy tissues. The problem that the planer has to solve, is to define the optimal positions (binary variables) of a predefined number of catheters on the template, and then to optimize the dose distribution by adapting the dwell times (continuous variables). Typical numbers of template holes and required catheters can easily result to O(1012) possible combinations. This problem can be formulated as a mixed integer non-linear programming (MINLP) problem, where each combination requires the solution of a continuous nonlinear optimization problem. Furthermore, the clinical requirements that the planers are typically following (e.g. GEC-ESTRO recommendations) can be handled as soft or hard constrains. HIPO is giving a near optimal solution in relatively short time (typically 0.5-5min), convenient for real-time planning in the operation room. A hybrid algorithm, based on Simulated Annealing and a problem-specific, deterministic heuristic, is used for the binary optimization problem of catheter positioning. The problem-specific heuristic is incorporating expert knowledge. The continuous dose optimization for each set up of the catheters is solved by the standard LBFGS algorithm.
Mikko Karttunen (University of Western Ontario) Coarse-graining of cholesterol containing lipid bilayers
Abstract: I will discuss multiscale modeling of biological membranes. The approach is based on the so-called Inverse Monte Carlo (IMC) method and the Henderson theorem. The specific examples [1] will include single and multicomponent bilayers using different levels of coarse-graining, and the improvent of accuracy of the coarse-grained models by using a thermodynamic constraint. The motivation for including a constraint is that the basic IMC does not yield physically meaningful area compressibility or surface tension in coarse-grained bilayers. The results using cholesterol containing systems show formation of denser transient regions, resembling lipid rafts, which is in accord with observations from microscopic models. Finally, I will discuss some of the advantages and disadvantages of this approach. References: [1] T. Murtola, E. Falck, M. Patra, M. Karttunen, I. Vattulainen, J. Chem. Phys. 121:9156-9165
Toshihiro Kawakatsu (Tohoku University) Development of dynamic density functional theories of multiphase dense polymeric systems
Abstract: We present the results of our recent developments of multiscale modelling on dynamics of phase separation and phase transition in multiphase dense polymeric systems. Our modeling is based on density functional theories of polymeric systems, such as the self-consistent field (SCF) theory and the Ginzburg-Landau (GL) theory. We combine these theories with flow dynamics, diffusion dynamics, and the effects of external fields such as a flow field, electric field, and confinements.
Erica Zimmer Klampfl (Ford) MINLP application for optimizing sourcing decisions in a distressed supplier environment
Abstract: Ford was tasked with determining the best sourcing footprint for its $1.5 billion Automotive Components Holdings, LLC Interiors business. This extensive undertaking required a complete re-engineering of the supply footprint of 42 high-volume product lines over 26 major manufacturing processes and more than 50 potential supplier sites. We propose an approximation of the large-scale Mixed Integer Nonlinear Program (MINLP) that accurately accommodates the nonlinear nature of facility cost as a function of utilization and present an iterative Mixed Integer Program (MIP) approach to solve the underlying MINLP. We demonstrate that the resulting solution to the iterative algorithm provides an equivalent solution to the approximated MINLP. The recommendations from this work have been implemented in practice and have resulted in savings of approximately $40 million in upfront investment over the previously preferred alternative.
William S. Klug (University of California, Los Angeles) Multiscale structural mechanics of viruses: Stretching the limits of continuum modeling
Abstract: The last several years have seen a number of successful applications of continuum elasticity theory to the study of virus mechanics. Continuum modeling has been particularly effective in connection with atomic force microscopy nanoindentation experiment for understanding and predicting material properties of viral shells (capsids), and may hold promise for illuminating the physics of capsid assembly as well. I will consider the question of the limitations of continuum modeling of capsids, and discuss some examples of how conventional continuum theory is being extended or "stretched" to study multiscale features linked to the inherently discrete character of these molecular assemblies.
William S. Klug (University of California, Los Angeles) Techniques for coarse-grained modeling and mechanics of viral capsids
Abstract: As revealed by techniques of structural biology and single-molecule experimentation, the capsids of viruses are some of nature's best examples of highly symmetric multiscale self-assembled structures with impressive mechanical properties of strength and elasticity. We present a novel method for creating three-dimensional finite element meshes of viral capsids from both atomic data from PDB files and electron density data from EM files. The meshes capture heterogeneous geometric features and are used in conjunction with three-dimensional continuum elasticity to simulate nanoindentation experiments as performed using atomic force microscopy. Meshes and nanoindentation simulations are presented for several viruses: Hepatitis B, CCMV, HK97, and Phi 29.
Matthias Koeppe (University of California, Davis) Nonlinear optimization via summation and integration
Abstract: The classic idea to relate the maximum of a function over a discrete or continuous domain to certain sums or integrals has made its apppearance in a number of recent papers from the point of view of optimization (A.I. Barvinok, "Exponential integrals and sums over convex polyhedra", Funktsional. Anal. i Prilozhen. 26 (1992); J.B. Lasserre, "Generating functions and duality for integer programs", Discrete Optim. 1 (2004)). Efficient summation and integration procedures can give rise to efficient approximation algorithms for optimization problems. As an example, a fully polynomial-time approximation scheme for optimizing arbitrary polynomial functions over the integer points in polyhedra of arbitrary, fixed dimension has been obtained (work with J. A. De Loera, R. Hemmecke, R. Weismantel, Math. Oper. Res. 31 (2006)). In this talk I report on recent work (with V. Baldoni, N. Berline, J. A. De Loera, M. Vergne) to study the efficiency of integration procedures for polynomial functions in high dimension. The methods are related to Brion's formulas, Barvinok's exponential sums, and also to the polynomial Waring problem that asks to represent a polynomial as a sum of powers of few linear forms.
Claude Le Bris (CERMICS) Positive temperature coarse-graining of one-dimensional systems
Abstract: We present a possible approach for the computation of free energies and ensemble averages of one-dimensional coarse-grained models in materials science. The approach is based upon a thermodynamic limit process, and makes use of ergodic theorems and large deviations theory. In addition to providing a possible efficient computational strategy for ensemble averages, the approach allows for assessing the accuracy of approximations commonly used in practice. This is joint work with X. Blanc (University Paris 6), F. Legoll (ENPC-INRIA) and C. Patz (Weierstrass-Institut, Berlin), submitted to journal of nonlinear science, preprint available at http://hal.inria.fr/inria-00282107/en/.
Frédéric Legoll (École Nationale des Ponts-et-Chaussées) Effective dynamics using conditional expectations
Abstract: We consider a system described by its position Xt, that evolves according to the overdamped Langevin equation. At equilibrium, the statistics of X are given by the Boltzmann-Gibbs measure. Suppose that we are only interested in some given low-dimensional function ξ(X) of the complete variable (the so-called reaction coordinate). The statistics of ξ are completely determined by the free energy associated to this reaction coordinate. In this work, we try and design an effective dynamics on ξ, that is a low-dimensional dynamics which is a good approximation of ξ(Xt). Using conditional expectations, we build an original dynamics, and discuss how it is related to the free energy itself. Using an entropy-based approach, we are also able to derive error estimates. Numerical simulations will illustrate the accuracy of the proposed dynamics. Joint work with T. Lelievre (ENPC and INRIA).
Leo Liberti (École Polytechnique) Reformulations in mathematical programming: Symmetry
Abstract: If a mathematical program (be it linear or nonlinear) has many symmetric optima, solving it via Branch-and-Bound techniques often yields search trees of disproportionate sizes; thus, finding and exploiting symmetries is an important task. We propose a method for: (a) automatically finding the formulation group of any given Mixed-Integer Nonlinear Program, and (b) reformulating the problem so that it has fewer symmetric solutions. The reformulated problem can then be solved via standard Branch-and-Bound codes such as CPLEX (for linear programs) and Couenne (for nonlinear programs). Our computational results include formulation group tables for the MIPLib3, MIPLib2003, GlobalLib, MINLPLib and MacMINLP instance libraries, solution tables for some instances in the aforementioned libraries, and a theoretical and computational study of the symmetries of the Kissing Number Problem.
Jeff Linderoth (University of Wisconsin) Building an effective solver for convex mixed integer nonlinear programs
Abstract: The most effective solvers for mixed integer linear programs (MILP)s employ a variety of algorithmic refinements that have made previously intractable models routinely solvable. Solvers for Mixed Integer Nonlinear Programs (MINLP)s should be no different. In this talk, we will discuss the impact of applying advanced branching rules, primal heuristics, preprocessing, and cutting planes in algorithms to solve (convex) mixed integer nonlinear programs. Many of the ideas have been implemented in the solver FilMINT, and the talk contains computational results to demonstrate the improvements that can be obtained by applying traditional MILP techniques for MINLPs.
Alexander Lukyanov (Max-Planck Institut für Polymerforschung) Force matching versus structural coarse-graining
Abstract: Joint work with Victor Rühle and Denis Andrienko (Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany). We are working on a detailed comparison of two coarse-graining methods, force matching [1] and iterative inverse Boltzmann [2]. Force matching is generalized for coarse-graining of angle and dihedral potentials, in addition to standard bond stretching and non-bonded interactions. Some initial steps are made in order to develop solvent-free coarsegraining models for polymers in solutions for systems of a particular importance for organic electronics (soluble conjugated polymers). 1. S. Izvekov, G. Voth „Multiscale coarse graining of liquid-state systems“, J. Chem. Phys. 123, 134105 (2005) 2. W. Tschoep, K. Kremer, J. Batoulis, T. Buerger and O. Hahn, Acta Polym 49, 61 (1998)
Mitchell Luskin (University of Minnesota) Predictive and efficient quasicontinuum methods
Abstract: The development of predictive and efficient atomistic-to-continuum computational methods requires both an analysis of the error and efficiency of its many components (coupling method, model and mesh adaptivity, solution methods) as well as its integration into an efficient code capable of solving problems of technological interest. There are many choices available for the interaction between the representative atoms of the quasicontinuum method, especially between those in the atomistic and continuum regions, which has led to the development of a variety of quasicontinuum approximations. We will present criteria for determining a good choice of quasicontinuum approximation that considers trade-offs between accuracy and algorithmic efficiency. Our criteria are based on the effect of the coupling error on the goal of the computation, on the integration of the quasicontinuum approximation with model and mesh adaptivity, and on the development of efficient iterative solution methods. Joint Work with Marcel Arndt, Matthew Dobson, Ron Miller, Christoph Ortner, and Ellad Tadmor.
Alex Marker (Schott North America, Inc.) Receiver technology for today and tomorrow
Abstract: No Abstract
Jesús Martín-Vaquero (University of Salamanca) A new procedure to building stabilized explicit Runge-Kutta methods for large systems of ODEs
Abstract: Joint work with B. Janssen and B. Wade. Stabilized Runge-Kutta methods (or Chebyshev-Runge-Kutta methods) are explicit methods with extended stability domains, usually along the negative real axis. They are easy to use (they do not require algebra routines) and they are especially suited for MOL discretizations of two and three dimensional parabolic partial differential equations. However, existing codes have some difficulties in cases when the eigenvalues are very large. We have developed a new procedure to build this kind of algorithm and derive second-order methods with up to 320 stages, all with good stability properties. These methods are efficient numerical integrators of very large stiff ordinary differential equations. Applications to the numerical solution of reaction-diffusion problems will be presented.
Vlasis George Mavrantzas (University of Patras) Quantifying chain reptation in entangled polymers by mapping atomistic simulation results onto the tube model
Abstract: The topological state of entangled polymers has been analyzed recently in terms of primitive paths which allowed obtaining reliable predictions for the static (statistical) properties of the underlying entanglement network for many polymeric systems. Through a systematic methodology that first maps atomistic molecular dynamics trajectories onto time trajectories of primitive paths and then documents primitive path motion in terms of a one-dimensional curvilinear diffusion in a tube-like region around the coarse-grained chain contour, we further extend these static approaches by computing the most fundamental function of the reptation theory, namely the probability that a segment s of the primitive chain remains inside the initial tube after time t. Linear viscoelastic properties, such as the zero shear rate viscosity and the spectra of storage and loss moduli, obtained on the basis of the obtained curves, for three different polymer melts (polyethylene, cis-1,4-polybutadiene and trans-1,4-polybutadiene) agree remarkably well with experimental rheological data. The new methodology is general and can be routinely applied to analyze primitive path dynamics and chain reptation in atomistic trajectories (accumulated through computer simulations) of other model polymers or polymeric systems (e.g., bidisperse, branched, grafted, etc); it is thus believed to be particularly useful in future theoretical developments of more accurate tube theories for entangled systems.
Todd S. Munson (Argonne National Laboratory) Preprocessing techniques for discrete optimization problems
Abstract: Preprocessing technique simplify and strengthen a model prior to calculating a solution. A combination of rules exploiting the constraint set and primal-dual relationships are applied to fix variables, improve their bounds, and eliminate redundant expressions. In addition, some nonconvex constraints can be transformed into convex constraints. Exploiting discrete variables during preprocessing adds rules to identify and exploit special structures and strengthen the formulation prior to computing convex estimators and cuts, and exploring a branch-and-bound tree. In this talk, I will discusses a unified preprocessor for mixed integer mathematical programs with equilibrium constraints being developed for MINOTAUR.
Marcus Müller (Georg-August-Universität zu Göttingen) Soft coarse-grained models for multicomponent polymer melts: free energy and single-chain dynamics
Abstract: In soft, coarse-grained models for dense polymer liquids, harsh repulsive interactions (excluded volume) between segments are replaced by soft repulsive interactions, which are sufficient to suppress density fluctuations. These models allow to efficiently study polymer melts with an experimentally relevant invariant degree of polymerization by computer simulation. Two topics will be discussed: (i) The calculation of free energies in self-assembling systems will be illustrated by studying the interface free energy of two lamellar grains of a symmetric diblock copolymer melt with perpendicular orientation (T-junction). (ii) The softness of the segmental interactions in coarse-grained models does not guarantee non-crossability of the molecules during the course of their motion. The effect of these topological constraints, which lead to reptation dynamics in dense melts of long flexible molecules, can be mimicked by slip-links and application of slip-links to the single-chain dynamics in the disordered and lamellar phase will be discussed.
Giacomo Nannicini (École Polytechnique) Variable neighbourhood search for MINLPs
Abstract: In a recent work we presented a general-purpose heuristic for (nonconvex) MINLPs based on Variable Neighbourhood Search, Local Branching, Sequential Quadratic Programming and Branch-and-Bound, combining several commercial solvers together. That method, which we called RECIPE, turned out to be very effective on the majority of the test instances, finding solutions at least as good as the best known optima for 55% of the MINLPLib. We analyse the computational performance of RECIPE when relying on open-source solvers only. Moreover, we study the effect of iiteratively applying a bound tightening phase throughout the algorithm.
Jorge Nocedal (Northwestern University) Fast infeasibility detection in nonlinear optimization
Abstract: An important issue in branch and bound methods for mixed integer nonlinear programming is the fast detection of infeasibility. This topic has not received sufficient attention and the methods developed for nonlinear programming often required a large number of iterations before a declaration of infeasibility can be made. The focus of this talk is to address the need for optimization algorithms that can both efficiently solve feasible problems and rapidly detect when a given problem instance is infeasible. One way to address these concerns is to employ a switch in an algorithm to decide whether the current iteration should seek a solution of the nonlinear program or, in contrast, to solely minimize some measure of feasibility. A challenge with such an approach lies in the difficulty of designing effective criteria for determining when such a switch should be made. We propose an alternative approach involving a single optimization strategy, and show that it is effective for finding an optimal feasible solution (when one exists) or finding the minimizer of a feasibility measure (when no feasible point exists). Our algorithm is an active-set method that uses the penalty parameter to emphasize optimality over infeasibility detection, or vice versa. We establish superlinear convergence results and discuss numerical experiments that demonstrate the advantages of our approach.
William G. Noid (Pennsylvania State University) A rigorous multiscale bridge connecting atomistic and coarse-grained models
Abstract: Coarse-grained (CG) models provide a promising computational tool for investigating slow complex processes that cannot be adequately studied using more detailed models. However, unless the CG model is consistent with an accurate high-resolution model, the results of CG modeling may be misleading. The present talk describes a statistical mechanical framework that provides a rigorous “multiscale bridge” connecting models with different resolution. In particular, this framework provides a formal definition of consistency and a systematic computational methodology for constructing a coarse-grained (CG) model that is consistent with a particular atomistic model. The cornerstone of this approach is a variational principle for calculating a many-body potential of mean force, which is the appropriate potential for such a consistent CG model. The multiscale coarse-graining method employs this variational principle by numerically calculating the projection of the atomistic force field onto the subspace of CG force fields spanned by a given set of basis vectors. Because typical CG force field basis vectors correspond to correlated molecular interactions, these basis vectors are not orthogonal and, consequently, many-body correlation functions must be explicitly treated. The present talk describes this development, presents numerical applications for molecular systems, and demonstrates how this framework may be employed to develop transferable CG interaction potentials.
Arthur J. Nozik (Department of Energy) Multiple exciton generation in semiconductor quantum dots and novel molecules: Applications to third generation solar photon conversion
Abstract: In order to utilize solar power for the production of electricity and fuel on a massive scale, it will be necessary to develop solar photon conversion systems that have an appropriate combination of high efficiency (delivered watts/m2) and low capital cost ($/m2) to produce solar power that is competitive with coal. One potential, long-term approach to high efficiency is to utilize the unique properties of quantum dot nanostructures to control the relaxation dynamics of photogenerated carriers to produce either enhanced photocurrent through efficient photogenerated electron-hole pair multiplication or enhanced photopotential through hot electron transport and transfer processes. To achieve these desirable effects it is necessary to understand and control the dynamics of hot electron and hole relaxation, cooling, charge transport, and interfacial charge transfer of the photogenerated carriers with femtosecond (fs) to ns time resolution. At NREL, we have been studying these fundamental dynamics in various bulk and nanoscale semiconductors (quantum dots (QDs), quantum rods/wires, and quantum wells) for many years using fs transient absorption, photoluminescence, and THz spectroscopy. Recently, we predicted that the generation of more than one electron-hole pair (existing as excitons in QDs) per absorbed photon would be an efficient process in QDs . This prediction has been confirmed over the past several years in several classes of QDs. We have observed very efficient and ultrafast multiple exciton generation (MEG) from absorbed single high energy photons in Group IV-VI and recently in Si QDs. Efficient MEG has the potential to greatly enhance the conversion efficiency of solar cells that incorporate QDs for both solar.
Wilma K. Olson (Rutgers University) Multi-scale modeling of DNA
Abstract: Encoded in the strings of DNA bases that make up the genomes of living species are codes that regulate, control, and describe all sorts of biological processes. The underpinnings of these codes lie in the base sequence-dependent micromechanical properties of DNA, which determine the degree to which the long, threadlike molecule fluctuates and how it responds to the proteins that control its processing and govern its packaging. In order to understand the mechanisms by which DNA base sequence and tightly bound proteins control the biophysical properties of the long, threadlike molecule, we have developed a coarse-grained model, in which the DNA base pairs are treated as rigid bodies subject to realistic, knowledge-based energy constraints, and computational techniques to determine the minimum-energy configurations, intrinsic dynamics, and looping/cyclization propensities of these molecules. The presentation will highlight some of the unique, sequence-dependent spatial information that has been gleaned from analyses of the high-resolution structures of DNA and its complexes with other molecules and illustrate how this information can be used to gain new insights into sequence-dependent DNA polymeric behavior.
Shmuel Onn (Technion-Israel Institute of Technology) Nonlinear discrete optimization II
Abstract: We develop an algorithmic theory of nonlinear optimization over sets of integer points presented by inequalities or by oracles. Using a combination of geometric and algebraic methods, involving zonotopes, Graver bases, multivariate polynomials and Frobenius numbers, we provide polynomial-time algorithms for broad classes of nonlinear combinatorial optimization problems and integer programs in variable dimension. I will overview this work, joint with many colleagues over the last few years, and discuss some of its many applications in statistics and operations research, including privacy in statistical databases, experimental design, nonlinear transportation, multicommodity flows, error-correcting codes, matroids and general independence systems.
Ignacio Pagonabarraga Mora (University of Barcelona) Soft potentials for coarse grained modeling
Abstract: I will describe how to model the properties of non-ideal fluids using effective, soft, many body potentials. Although they are not derived from a microscopic systematic procedure, it is possible to understand their properties from a systematic saddle point expansion. Such an approach makes it possible to derive their equilibrium thermodynamic and structural features, opening the possibility to relate the effective parameters characterizing the soft potentials with their collective properties. I will also describe how such many body potentials can be used to analyze the properties of complex fluids out of equilibrium.
Stephen D Pankavich (Indiana University) All-atom multiscale computational modeling of bionanosystem dynamics
Abstract: The use of traditional techniques, such as Molecular Dynamics (MD), to model the long-time dynamics of bionanosystems (e.g., viruses, liposomes, or engineered nanocapsules for drug delivery) have proven infeasible, as the computational time required to obtain accurate results for the time scales of interest is on the order of many years. Using statistical mechanics, stochastic calculus, and techniques of multiscale analysis, we have recently designed (and are currently constructing) tools which greatly improve upon this problem by introducing and tracking slow variables that account for the large-scale behavior of the given system. The new VirusX simulator decreases computational time to the order of hours, rendering such simulations feasible for the first time. This is joint work with Peter Ortoleva and the Center for Cell and Virus Theory at Indiana University.
Cynthia A. Phillips (Sandia National Laboratories) Parallelization issues for MINLP Part II
Abstract: Sandia National Laboratories has invested considerable effort in massively parallel optimization tools. In this talk, we will summarize relevant experience from developing our parallel mixed-integer programming (MIP) solver PICO (Parallel Integer and Combinatorial Optimizer) and our parallel nonlinear solver GNLP. We will discuss parallel solution of mixed-integer nonlinear programs (MINLP). In particular, we will consider how the choice of parallel platform (tightly-coupled systems, cloud computing, grid computing, etc) can affect algorithmic decisions. We will highlight issues parallel solvers must face that serial solvers do not such as load balancing, ramp up, and termination and some issues that parallel solvers might do differently, such as decomposition. We expect some of our MIP/NLP experience to carry over, and some issues to be unique to, or uniquely difficult for, MINLP.
Simon Poblete (Max Planck Institute for Polymer Research) Adaptive resolution simulation of model mixtures
Abstract: We have systematically developed a set of coarse-grained potentials able to describe a system of spherical monomers solved in tetrahedral molecules. The potentials are able to reproduce the basic structure and thermodynamics of the original mixture over a wide range of concentrations, and have been successfully tested in the Adaptive Resolution Scheme (AdResS), showing a symmetric behavior between the explicit and coarse-grained descriptions.
Oleg Prezhdo (University of Washington) Quantum dots and dye-sensitized semiconductors for solar energy conversion: time-domain ab initio studies of the photoinduced dynamics
Abstract: Harvesting and applications of solar energy requires an understanding of the dynamical response of novel materials on the nanometer scale. We have developed state-of-the-art non-adiabatic molecular dynamics techniques and implemented them within time-dependent density functional theory in order to model the ultrafast photoinduced processes in these materials at the atomistic level, and in real time. The talk will focus on the photo-initiated charge transfer at the molecule-semiconductor interfaces and multiple excitons which can be generated in semiconductor quantum dots in competition with various relaxation processes.
Franz Rendl (Universität Klagenfurt) Copositive programs and combinatorial optimization
Abstract: It has recently been shown that linear programs over the cone of completely positive matrices give exact formulations for many NP-hard combinatorial optimization problems. This motivates the investigation of solution methods for such problems. In this talk I will present a heuristic algorithm for this problem, whos main effort in each iteration consists in solving a convex quadratic problem in sign constrained variables. The algorithm will be applied to random copositive programs as well as to the copositive formulation of some NP-hard graph optimization problems. (joint work with M. Bomze (Vienna) and F. Jarre (Duesseldorf))
Christian Ringhofer (Arizona State University) Computational aspects of solid state transport
Abstract: This talk will discuss various issues and approaches in the numerical simulation of carrier transport in solid state materials, relevant to the modeling of optical generation / recombination. We will discuss aspects of deterministic and Monte Carlo methods for the solid state Boltzmann transport equation as well as the inclusion of quantum effects in particle based transport simulators.
Mark O. Robbins (Johns Hopkins University) Mapping particle based simulations to mesoscopic models
Abstract: No Abstract
Victor Rühle (Max Planck Institute for Polymer Research) Charge transport in polypyrrole: the role of morphology
Abstract: A combination of methods is used to study charge transport in polypyrrole melts. First, the OPLS atomistic force field is refined using first-principles calculations. Amorphous and partially ordered melts are then generated with the help of this force-field. Finally, the charge mobility is calculated within the temperature activated hopping picture for charge transport [1]. [1] J. Kirkpatrick, V. Marcon, J. Nelson, K. Kremer, D. Andrienko, Phys. Rev. Lett. 98, 227402 (2007)
Sebastian Sager (Ruprecht-Karls-Universität Heidelberg) Direct numerical methods for mixed-integer optimal control problems
Abstract: Optimal control problems involving time-dependent decisions from a finite set have gained much interest lately, as they occur in practical applications with a high potential for optimization. Typical examples are the choice of gears in transport or separation processes involving valves to switch inflow/outflow locations between trays or columns. We present relaxation and convexification based rounding strategies for direct methods of optimal control such that the resulting trajectory fulfills constraints and reaches the objective function value of any (and in particular the optimal) relaxed solution up to a certain tolerance. We show that this tolerance depends on the control discretization grid, in other words, that the rounded solution will be arbitrarily close to the relaxed one, if only the underlying grid is chosen fine enough. This is even true for a finite number of switches, and holds for the linear as well as for the nonlinear case, involving path and control constraints. Examples will be supplied to illustrate the procedure.
Annick Sartenaer (Facultés Universitaires Notre Dame de la Paix (Namur)) A branch-and-refine method for nonconvex mixed integer optimization
Abstract: Joint work with Sven Leyffer (Argonne National Laboratory) and Emilie Wanufelle (University of Namur). Motivated by problems related to power systems analysis which give rise to nonconvex mixed integer nonlinear programming (MINLP) problems, we propose a global optimization method based on ideas and techniques that can be easily extended to handle a large class of nonconvex MINLPs. Our method decomposes the nonlinear functions appearing in the problem to solve into one- and two-dimensional components for which piecewise linear envelopes are constructed using ideas similar to special ordered sets. The resulting relaxations are then successively refined by branching on integer or continuous variables. We prove convergence to a global optimum within a desired accuracy under mild assumptions and present some preliminary numerical experience.
Anureet Saxena (Axioma Inc.) Convex relaxations of non-convex MIQCP
Abstract: Joint work with Pierre Bonami and Jon Lee. This talk addresses the problem of generating strong convex relaxations of Mixed Integer Quadratically Constrained Programming (MIQCP) problems. MIQCP problems are very difficult because they combine two kinds of non-convexities: integer variables and non-convex quadratic constraints. To produce strong relaxations of MIQCP problems, we use techniques from disjunctive programming and the lift-and-project methodology. In particular, we propose new methods for generating valid inequalities by using the equation Y = x xT. We use the concave constraint $0 succcurlyeq Y - x xT $ to derive disjunctions of two types. The first ones are directly derived from the eigenvectors of the matrix Y - x xT with positive eigenvalues, the second type of disjunctions are obtained by combining several eigenvectors in order to minimize the width of the disjunction. We also use the convex SDP constraint Y - x xT succcurlyeq 0 to derive convex quadratic cuts, and we combine both approaches in a cutting plane algorithm. We present computational results to illustrate our findings.
Anureet Saxena (Axioma Inc.) Convex relaxations of non-convex MIQCP
Abstract: same abstract as the 11/18 talk
Christof Schütte (Freie Universität Berlin) Understanding effective molecular dynamics on timescales beyond possible simulation timescales
Abstract: No Abstract
Tsvetanka Sendova (University of Minnesota) A theory of fracture based upon extension of continuum mechanics to the nanoscale
Abstract: I will present the analysis of several fracture models based on a new approach to modeling brittle fracture. Integral transform methods are used to reduce the problem to a Cauchy singular, linear integro-differential equation. We show that ascribing constant surface tension to the fracture surfaces and using the appropriate crack surface boundary condition, given by the jump momentum balance, leads to a sharp crack opening profile at the crack tip, in contrast to the classical theory of brittle fracture. However, such a model still predicts singular crack tip stress. For this reason we study a modified model, where the surface excess property is responsive to the curvature of the fracture surfaces. We show that curvature-dependent surface tension, together with boundary conditions in the form of the jump momentum balance, leads to bounded stresses and a cusp-like opening profile at the crack tip. Finally, I will discuss two possible fracture criteria, in the context of the new theory. The first one is an energy based fracture criterion. Due to the fact that the proposed modeling approach allows us to fully resolve the stress in a neighborhood of the crack tip, without the customary singularity, a second fracture criterion, based on crack tip stress, is possible.
Uday V. Shanbhag (University of Illinois at Urbana-Champaign) A local relaxation approach for the siting of electrical substations
Abstract: Joint work with Walter Murray (Stanford University). The siting and sizing of electrical substations on a rectangular electrical grid can be formulated as an integer programming problem with a quadratic objective and linear constraints. We propose a novel approach that is based on solving a sequence of local relaxations of the problem for a given number of substations. Two methods are discussed for determining a new location from the solution of the relaxed problem. Each leads to a sequence of strictly improving feasible integer solutions. The number of substations is then modified to seek a further reduction in cost. Lower bounds for the solution are also provided by solving a sequence of mixed-integer linear programs. Results are provided for a variety of uniform and Gaussian load distributions as well as some real examples from an electric utility. The results of GAMS/DICOPT, GAMS/SBB, GAMS/BARON and CPLEX applied to these problems are also reported. Our algorithm shows slow growth in computational effort with the number of integer variables.
Lyubima B. Simeonova (University of Utah) Spatial bounds on the effective complex permittivity for time-harmonic waves in random media
Abstract: When we consider wave propagation in random media in the case when the wave length is finite, scattering effects must be accounted for and the effective dielectric coefficient is no longer a constant, but a spatially dependent function. We obtain a bound on the spatial variations of the effective permittivity that depends on the maximum volume of the inhomogeneities and the contrast of the medium. A related optimization problem of maximizing the spatial average of the effective dielectric coefficient with respect to the spatial probability density function is presented. The dependence of the effective dielectric coefficient on the contrast of the medium is also investigated and an approximation formula is derived.
Florence Tama (University of Arizona) Unveiling conformational changes of biological molecules using multiscale modeling and multiresolution experiments
Abstract: Multipronged approaches have recently gained interest for tackling structural problems related to large biological complexes. Structural dynamical information is often obtained by low-resolution experimental techniques, such as Cryo Electron Microscopy (cryo-EM), Small Angle X-ray Scattering (SAXS) and Fluorescence Resonance Energy Transfer (FRET). Each of these techniques offers different advantages and meet with different pitfalls, artifacts and limitations. Therefore a more accurate description could be obtained if all pieces of experimental data were taken together to annotate conformational states. To achieve this goal we will present our current developments of multi-resolution/multi-scale computational tools to interpret conformational changes of biological molecules based on cryo-EM, SAXS or distance constraints. Normal Mode Analysis or Molecular Dynamics simulations are used to deform, in a physical manner, X-ray structures to fit low-resolution data. Using simulated data, we will show that such approaches are successful to predict structures in the range of 2~3 Å resolution.
Tamás Terlaky (Lehigh University) Some challenging mixed integer nonlinear optimization problems
Abstract: Nonlinear mixed integer optimization has numerous applications in engineering practice. We present two classes of MINLP problems that arise in engineering practice, but their solution to proven optimality in size relevant for practice is beyond the capacity of available MINLP solvers. Both of the following problem classes offer the possibility to generate test problem suites with increasing problem size. The first problem class is the optimization of the reloading of nuclear reactor core, where the physics of the problem is governed by PDE's, whose discretization combined with the reloading (assignment constraints) provide a large family of large scale MINP problems. The second class of problems arise from flood control, where safe dike heights need to be built at minimal cost while considering the expected risk of flooding.
Alex Travesset (Iowa State University) General purpose molecular dynamics on graphic processing units (GPUs)
Abstract: Molecular Dynamics (MD) on Graphic Processing Units (GPUs) provide spectacular advantages: an unexpensive GPU (less than 500$) provides the equivalent computer power of a 44 core cluster. This poster will introduce HOOMD, our new General purpose MD code, as well as describe the challenges involved in GPU programming. It will also show the very easy to use scripting system developed directed to the end user, so that it can make full use of HOOMD without having to learn about GPU programming. As it will become clear in the poster, HOOMD is particularly suited for coarse-grained MD.
Sergei Tretiak (Los Alamos National Laboratory) Functionalized quantum dots and conjugated polymers for light harvesting applications: Theoretical insights
Abstract: Using density functional theory (DFT) and time-dependent DFT quantum-chemical methodologies, we investigate interplay of electronic properties and conformational dynamics in several optically active materials. In quantum dots we explore the role of surface ligands on the electronic structure and observe strong surface-ligand interactions leading to formation of hybridized states and polarization effects. This opens new relaxation channels for high energy photoexcitations. Computations of Ru(II)-bipyridine attached to the semiconductor quantum dot systems demonstrate possibility of charge separation and energy transfer processes in the complex. In the amorphous clusters of conjugated polymers, we find that electron trap states are induced primarily by intra-molecular configuration disorder, while the hole trap states are generated primarily from inter-molecular electronic interactions. All these phenomena govern experimentally observed photoinduced dynamics and define technologically important properties of materials suitable for solar energy conversion.
Erkan Tüzel (University of Minnesota) Mesoscopic model for the fluctuating hydrodynamics of binary and ternary mixtures
Abstract: A recently introduced particle-based model for fluid dynamics with continuous velocities is generalized to model immiscible binary mixtures. Excluded volume interactions between the two components are modeled by stochastic multiparticle collisions which depend on the local velocities and densities. Momentum and energy are conserved locally, and entropically driven phase separation occurs for high collision rates. An explicit expression for the equation of state is derived, and the concentration dependence of the bulk free energy is shown to be the same as that of the Widom-Rowlinson model. Analytic results for the phase diagram are in excellent agreement with simulation data. Results for the line tension obtained from the analysis of the capillary wave spectrum of a droplet agree with measurements based on the Laplace's equation. The dispersion relation for the capillary waves is derived and compared with the numerical measurements of the time correlations of the radial fluctuations in the damped and over-damped limits. The introduction of "amphiphilic" dimers makes it possible to model the phase behavior of ternary surfactant mixtures.
Eric Vanden-Eijnden (New York University) A general strategy for the design of seamless multiscale methods
Abstract: I will present a new general framework for designing multiscale methods. Compared with previous work such as Brandt’s systematic up-scaling, the heterogeneous multiscale method and the “equation-free” approach, this new framework has the distinct feature that it does not require reinitializing the microscale model at each macro time step or each macro iteration step. In the new strategy, the macro- and micro-models evolve simultaneously using different time steps (and therefore different clocks), and they exchange data at every step. The micro-model uses its own appropriate time step. The macro-model runs at a slower pace than required by accuracy and stability considerations for the macroscale dynamics, in order for the micro-model to relax. I will discuss applications of the new seamless approach to a toy system used in climatic studies, to the modeling of complex fluids, and to free energy calculations in molecular dynamics. This is joint work with Weinan E and Weiqing Ren with applications performed in collaboration with Ibrahim Fatkullin and Luca Maragliano.
Stefan Vigerske (Humboldt-Universität) Solving nonconvex MINLP by quadratic approximation
Abstract: We present the extended Branch and Cut algorithm implemented in the software package LaGO for the solution of block-separable nonconvex mixed-integer nonlinear programs. The algorithm reformulates every function into a block-separable form and computes convex underestimators for each term separately. For that purpose, nonquadratic functions are first replaced by quadratic underestimators using a powerful heuristic. Nonconvex quadratic functions are then replaced by exakt convex underestimators. Finally, a linear outer approximation is constructed by linearization of the convex relaxation and the generation of mixed-integer rounding cuts and linearized interval gradient cuts. The efficiency of the method is improved by the application of a simple constraint propagation technique based on interval arithmetic.
Zhongming Wang (University of California, San Diego) A bloch band base level set method in the semi-classical limit of the Schroedinger Equation
Abstract: It is now known that one can use level set description to accurately capture multi-phases in computation of high frequency waves. In this paper, we develop a Bloch band based level set method for computing the semi-classical limit of Schrdinger equations in periodic media. For the underlying equation subject to a highly oscillatory initial data a hybrid of the WKB approximation and homogenization leads to the Bloch eigenvalue problem and an associated Hamilton-Jacobi system for the phase, with Hamiltonian being the Bloch eigenvalues. We evolve a level set description to capture multi-valued solutions to the band WKB system, and then evaluate total position density over a sample set of bands. A superposition of band densities is established over all bands and solution branches when away from caustic points. Numerical results with different number of bands are provided to demonstrate the good quality of the method.
Henry A. Warchall (National Science Foundation) CHE-DMR-DMS solar energy initiative
Abstract: No Abstract
Robert Weismantel (Otto-von-Guericke-Universität Magdeburg) Nonlinear discrete optimization I
Abstract: This talk is concerned with optimizing nonlinear functions over the lattice points in a polyhedral set. We present three families of polynomial time algorithms for special cases of the general problem. Each such algorithm makes use of combinatorial, geometric or algebraic properties of the underlying problem. The first problem deals with optimizing nonlinear functions over a matroid. (Joint work with Jon Lee and Shmuel Onn). The second class of problems concerns convex n-fold integer minimization problems. (Joint work with Raymond Hemmecke and Shmuel Onn). Our last family of problems is to maximize polynomials over the integer points in a polytope when the dimension is fixed. Under mild assumptions we present an FPTAS for performing this task. (Joint work with Jesus De Loera, Matthias Koeppe and Raymond Hemmecke).
Tapio Westerlund (Åbo Akademi (Finland-Swedish University of Åbo)) Global optimization of MINLP problems containing signomial functions
Abstract: Joint work with Andreas Lundell, Process Design and Systems Engineering, Åbo Akademi University Biskopsgatan 8, FIN-20500 Turku, Finland. Keywords: Transformation techniques; mixed integer nonlinear programming; signomial functions; global optimization. Abstract: In this presentation some transformation techniques are discussed. With the given techniques a class of non-convex MINLP problems, including signomial functions, can be solved to global optimality. The transformation techniques are based on single variable power and exponential transformations and the signomial functions can be converted into convex form, by the transformations. In addition, the original non-convex problem can be relaxed into convex form, if the transformations have certain properties and the inverse transformations are approximated by piecewise linear functions. The transformations are not unique and there exists degrees of freedom in selecting them. For determining an "optimal" set of transformations a mixed integer linear programming (MILP) problem can be formulated. The solution of the MILP problem can be used separately but acts, in our case, as a pre-processing step in the global optimization framework. Certain properties of the transformations can be emphasized in the initial MILP pre-processing step. For example, the total number of transformations needed can be minimized. The principles behind the transformation techniques are given and some numerical examples are used to illustrate the given techniques.
Angelika Wiegele (Universität Klagenfurt) Exact algorithms for the quadratic linear ordering problem
Abstract: The quadratic linear ordering problem naturally generalizes various optimization problems, such as bipartite crossing minimization or the betweenness problem, which includes linear arrangement. These problems have important applications in, e.g., automatic graph drawing and computational biology. We present a new polyhedral approach to the quadratic linear ordering problem that is based on a linearization of the quadratic objective function. Our main result is a reformulation of the 3-dicycle inequalities using quadratic terms, the resulting constraints are shown to be face-inducing for the polytope corresponding to the unconstrained quadratic problem. We exploit this result both within a branch-and-cut algorithm and within an SDP-based branch-and-bound algorithm. Experimental results for bipartite crossing minimization show that this approach clearly outperforms other methods. (Joint work with C. Buchheim and L. Zheng.)
Xiaoyang Zhu (University of Minnesota) Exciton dissociation in solar cells
Abstract: Excitons are bound electron-hole pairs, i.e., atomic-H like Bosonic quasiparticles, that determine many optical and optoelectronic properties of solid materials. Exciton formation and dissociation play decisive roles in next generation solar cells. In a conventional p-n junction solar cell, the built-in potential separates the photoexcited electron and hole. In contrast, separating the electron and the hole in an excitonic solar cell requires an energetic driving force at a donor/acceptor (D/A) materials interface. Here, photon absorption creates a localized Frenkel exciton or a delocalized Mott-Wannier exciton in the donor material. Such an exciton migrates to the D/A interface and decays into a charge transfer (CT) exciton: the Coulombically-bound electron and hole are located in spatially separate regions across the interface. Subsequent dissociation of the CT exciton leads to charge carriers and photocurrent. In this talk, I will present our understanding on the exciton dissociation problem from recent experiments and discuss challenges in theoretical/computation treatment of this problem. These challenges arise because one must simultaneous take into account translational symmetry of the donor and acceptor (when the donor and/or acceptor are crystalline materials) and the spatial correlation of the e-h pair.
Visitors in Residence
Cameron F. Abrams Drexel University 11/2/2008 - 11/7/2008
Rigoberto Advincula University of Houston 10/31/2008 - 11/2/2008
Alina Alexeenko Purdue University 10/31/2008 - 11/2/2008
Denis Andrienko Max-Planck Institut für Polymerforschung 11/1/2008 - 11/9/2008
Kurt M. Anstreicher University of Iowa 11/16/2008 - 11/21/2008
Donald G. Aronson University of Minnesota 9/1/2002 - 8/31/2009
Alán Aspuru-Guzik Harvard University 10/31/2008 - 11/2/2008
Paul J. Atzberger University of California, Santa Barbara 11/2/2008 - 11/7/2008
Eray S. Aydil University of Minnesota 11/1/2008 - 11/1/2008
Gregory L Baker Michigan State University 10/31/2008 - 11/2/2008
Amartya Sankar Banerjee University of Minnesota 11/2/2008 - 11/2/2008
Gang Bao Michigan State University 10/31/2008 - 11/2/2008
Pietro Belotti Lehigh University 11/16/2008 - 11/19/2008
Hande Yurttan Benson Drexel University 11/16/2008 - 11/21/2008
Dimitris Bertsimas Massachusetts Institute of Technology 11/18/2008 - 11/21/2008
Lorenz T. Biegler Carnegie Mellon University 11/20/2008 - 11/21/2008
Christian Bliek ILOG Corporation 11/15/2008 - 11/21/2008
Marian Bocea North Dakota State University 11/2/2008 - 11/8/2008
Pierre Bonami Centre National de la Recherche Scientifique (CNRS) 11/15/2008 - 11/22/2008
Nawaf Bou-Rabee California Institute of Technology 11/2/2008 - 11/7/2008
Bastiaan J. Braams Emory University 9/28/2008 - 11/8/2008
Andrea Braides Seconda Università di Roma "Tor Vergata" 11/1/2008 - 11/7/2008
James Joseph Brannick Pennsylvania State University 10/30/2008 - 11/2/2008
Frank L. H. Brown University of California, Santa Barbara 11/2/2008 - 11/7/2008
Peter Brune University of Chicago 9/8/2008 - 6/30/2009
Samuel Burer University of Iowa 11/18/2008 - 11/21/2008
Wei Cai University of North Carolina - Charlotte 10/31/2008 - 11/2/2008
Maria-Carme T. Calderer University of Minnesota 9/1/2008 - 6/30/2009
Hannah Callender University of Minnesota 9/1/2007 - 8/31/2009
Roberto Cammi Università di Parma 11/14/2008 - 12/20/2008
Stephen Campbell University of Minnesota 11/1/2008 - 11/1/2008
Eric Cances CERMICS 9/1/2008 - 12/23/2008
Xianjin Chen University of Minnesota 9/1/2008 - 8/31/2010
Daniel M. Chipman University of Notre Dame 9/14/2008 - 12/13/2008
Marco Cicalese Università di Napoli "Federico II" 11/1/2008 - 11/7/2008
Bernardo Cockburn University of Minnesota 11/1/2008 - 11/1/2008
Ludovica Cecilia Cotta-Ramusino University of Minnesota 10/1/2007 - 12/12/2008
Olivier Coulaud Institut National de Recherche en Informatique Automatique (INRIA) 11/1/2008 - 11/7/2008
Claudia D'Ambrosio Università di Bologna 11/15/2008 - 11/22/2008
Michel Jacques Daydé Institut National Polytechnique de Toulouse 11/15/2008 - 11/21/2008
Rafael Delgado-Buscalioni Autonomous University of Madrid 11/1/2008 - 11/8/2008
Luigi Delle Site Max-Planck Institut für Polymerforschung 11/1/2008 - 11/8/2008
Jesus Antonio De Loera University of California, Davis 11/16/2008 - 11/20/2008
Jeffrey Derby University of Minnesota 11/1/2008 - 11/1/2008
Markus Deserno Carnegie Mellon University 11/2/2008 - 11/7/2008
David C. Dobson University of Utah 10/31/2008 - 11/2/2008
Belma Dogdas Merck & Co., Inc. 11/13/2008 - 11/15/2008
Masao Doi University of Tokyo 11/2/2008 - 11/8/2008
Dan Dougherty North Carolina State University 10/31/2008 - 11/2/2008
Sarah Drewes TU Darmstadt 11/15/2008 - 11/21/2008
Qiang Du Pennsylvania State University 10/31/2008 - 11/5/2008
Olivier Dubois University of Minnesota 9/3/2007 - 8/31/2009
Burkhard Dünweg Max-Planck Institut für Polymerforschung 11/1/2008 - 11/8/2008
Phillip Duxbury Michigan State University 10/31/2008 - 11/2/2008
Weinan E Princeton University 10/31/2008 - 11/6/2008
Bob Eisenberg Rush University Medical Center 11/1/2008 - 11/8/2008
Bjorn Engquist University of Texas 11/6/2008 - 11/8/2008
Maria Esteban Université de Paris IX (Paris-Dauphine) 9/27/2008 - 11/15/2008
James W. Evans Iowa State University 11/2/2008 - 11/5/2008
Roland Faller University of California, Davis 11/2/2008 - 11/6/2008
Heather Lyn Finotti University of Tennessee 10/31/2008 - 11/2/2008
Daniel Flath Macalester College 8/27/2008 - 12/20/2008
Stephen Foster Mississippi State University 10/31/2008 - 11/2/2008
Christopher Fraser University of Chicago 8/27/2008 - 6/30/2009
Gero Friesecke Technical University of Munich 11/2/2008 - 11/7/2008
Dominik Fritz Max Planck Institute for Polymer Research 11/1/2008 - 11/9/2008
Kevin Furman Exxon Research and Engineering Company 11/19/2008 - 11/22/2008
Irene M. Gamba University of Texas 10/31/2008 - 11/2/2008
Weiguo Gao Fudan University 9/27/2008 - 12/13/2008
Carlos J. Garcia-Cervera University of California, Santa Barbara 9/2/2008 - 12/12/2008
David M. Gay Sandia National Laboratories 11/16/2008 - 11/21/2008
Johannes Giannoulis Technical University of Munich 11/2/2008 - 11/9/2008
Philip E. Gill University of California, San Diego 11/16/2008 - 11/19/2008
Guillermo Hugo Goldsztein Georgia Institute of Technology 10/31/2008 - 11/2/2008
Jay Gopalakrishnan University of Florida 9/1/2008 - 2/28/2009
Ignacio Grossmann Carnegie Mellon University 11/20/2008 - 11/21/2008
Oktay Gunluk IBM 11/16/2008 - 11/21/2008
Gloria Haro Ortega Universitat Politecnica de Catalunya 10/25/2008 - 11/1/2008
William E. Hart Sandia National Laboratories 11/16/2008 - 11/21/2008
Carsten Hartmann Freie Universität Berlin 11/2/2008 - 11/7/2008
Timothy F. Havel Massachusetts Institute of Technology 10/31/2008 - 12/12/2008
David Haws University of California, Davis 11/16/2008 - 11/21/2008
Teresa Head-Gordon University of California, Berkeley 11/2/2008 - 11/7/2008
Christoph Helmberg Technische Universität Chemnitz-Zwickau 11/15/2008 - 11/21/2008
William Henry Mississippi State University 10/31/2008 - 11/2/2008
Mark S. Herman University of Minnesota 9/1/2008 - 8/31/2010
Jan S. Hesthaven Brown University 10/31/2008 - 11/2/2008
Peter Hinow University of Minnesota 9/1/2007 - 8/31/2009
Russell J. Holmes University of Minnesota 11/1/2008 - 11/1/2008
Yunkyong Hyon University of Minnesota 9/1/2008 - 8/31/2010
Mark Iwen University of Minnesota 9/1/2008 - 8/31/2010
Alexander Izzo Bowling Green State University 9/1/2008 - 6/30/2009
Richard D. James University of Minnesota 11/1/2008 - 11/3/2008
Richard D. James University of Minnesota 11/2/2008 - 11/7/2008
Samson A. Jenekhe University of Washington 10/31/2008 - 11/2/2008
Robert L. Jernigan Iowa State University 11/5/2008 - 11/8/2008
Srividhya Jeyaraman University of Minnesota 9/1/2008 - 8/31/2010
Lijian Jiang University of Minnesota 9/1/2008 - 8/31/2010
Shi Jin University of Wisconsin 10/31/2008 - 11/1/2008
Sookyung Joo University of California, Santa Barbara 11/1/2008 - 11/22/2008
Terry Joyce 3M 11/1/2008 - 11/1/2008
Christoph Junghans Max-Planck Institut für Polymerforschung 11/1/2008 - 11/9/2008
Raymond Kapral University of Toronto 11/2/2008 - 11/6/2008
Andreas G. Karabis PI Medical Ltd 11/15/2008 - 11/22/2008
Mikko Karttunen University of Western Ontario 11/2/2008 - 11/7/2008
Markos A. Katsoulakis University of Massachusetts 10/31/2008 - 11/2/2008
Toshihiro Kawakatsu Tohoku University 11/2/2008 - 11/7/2008
Markus Keel University of Minnesota 7/21/2008 - 6/30/2009
Mustafa Rasim Kilinc University of Wisconsin 11/16/2008 - 11/21/2008
Yongho Kim University of Minnesota 11/1/2008 - 11/1/2008
Erica Zimmer Klampfl Ford 11/17/2008 - 11/21/2008
William S. Klug University of California, Los Angeles 11/2/2008 - 11/7/2008
Matthias Koeppe University of California, Davis 11/16/2008 - 11/21/2008
Robert V. Kohn New York University 10/31/2008 - 11/13/2008
Kurt Kremer Max-Planck Institut für Polymerforschung 11/2/2008 - 11/8/2008
Anna Krylov University of Southern California 9/25/2008 - 12/25/2008
Monica H. Lamm Iowa State University 11/2/2008 - 11/7/2008
Yueheng Lan University of California, Santa Barbara 11/2/2008 - 11/8/2008
Juan Latorre Freie Universität Berlin 11/2/2008 - 11/7/2008
Claude Le Bris CERMICS 9/11/2008 - 5/30/2009
Chiun-Chang Lee National Taiwan University 8/26/2008 - 7/31/2009
Hijin Lee Korea Advanced Institute of Science and Technology (KAIST) 11/1/2008 - 11/1/2008
Hijin Lee Korea Advanced Institute of Science and Technology (KAIST) 11/3/2008 - 11/7/2008
Jon Lee IBM 11/16/2008 - 11/22/2008
Long Lee University of Wyoming 10/31/2008 - 11/2/2008
Frédéric Legoll École Nationale des Ponts-et-Chaussées 11/1/2008 - 11/12/2008
Thomas Lehmann Universität Bayreuth 11/15/2008 - 11/22/2008
Sven Leyffer Argonne National Laboratory 11/16/2008 - 11/21/2008
Bo Li University of California, San Diego 11/3/2008 - 11/6/2008
Jichun Li University of Nevada 10/31/2008 - 11/2/2008
Tong Li University of Iowa 11/2/2008 - 12/10/2008
Yongfeng Li University of Minnesota 9/1/2008 - 8/31/2010
Leo Liberti École Polytechnique 11/15/2008 - 11/22/2008
Tai-Chia Lin National Taiwan University 8/23/2008 - 7/31/2009
Jeff Linderoth University of Wisconsin 11/16/2008 - 11/21/2008
Chun Liu University of Minnesota 9/1/2008 - 8/31/2010
Di Liu Michigan State University 10/31/2008 - 11/2/2008
Hailiang Liu Iowa State University 11/4/2008 - 11/7/2008
Jian-Guo Liu University of Maryland 10/31/2008 - 11/4/2008
Andrea Lodi Università di Bologna 11/16/2008 - 11/18/2008
Kevin Long Texas Tech University 10/31/2008 - 11/2/2008
Gang Lu California State University 10/31/2008 - 11/2/2008
James Luedtke University of Wisconsin 11/17/2008 - 11/21/2008
Mitchell Luskin University of Minnesota 9/1/2008 - 6/30/2009
Julien Mairal INRIA 10/26/2008 - 11/2/2008
Dionisios Margetis University of Maryland 11/3/2008 - 11/7/2008
Francois Margot Carnegie Mellon University 11/16/2008 - 11/21/2008
Susan Margulies Rice University 11/17/2008 - 11/22/2008
Alex Marker Schott North America, Inc. 10/31/2008 - 11/2/2008
Vasileios Maroulas University of Minnesota 9/1/2008 - 8/31/2010
Jesús Martín-Vaquero University of Salamanca 11/2/2008 - 11/7/2008
Vlasis George Mavrantzas University of Patras 11/2/2008 - 11/7/2008
James McCusker Michigan State University 10/31/2008 - 11/2/2008
Andrew James Miller Université de Bordeaux I 11/16/2008 - 11/23/2008
Kien Ming Ng National University of Singapore 11/16/2008 - 11/22/2008
John E. Mitchell Rensselaer Polytechnic Institute 11/16/2008 - 11/21/2008
Hans Mittelmann Arizona State University 11/16/2008 - 11/19/2008
Peter Monk University of Delaware 10/31/2008 - 11/1/2008
Susanna Monti Consiglio Nazionale delle Ricerche (CNR) 11/1/2008 - 11/9/2008
Marcus Müller Georg-August-Universität zu Göttingen 11/1/2008 - 11/6/2008
Todd S. Munson Argonne National Laboratory 11/16/2008 - 11/21/2008
Mahdi Namazifar University of Wisconsin 11/16/2008 - 11/21/2008
Giacomo Nannicini École Polytechnique 11/15/2008 - 11/22/2008
Zuhair Nashed University of Central Florida 10/31/2008 - 11/2/2008
Olalla Nieto Faza University of Minnesota 11/3/2008 - 11/7/2008
Jorge Nocedal Northwestern University 11/16/2008 - 11/21/2008
William G. Noid Pennsylvania State University 11/2/2008 - 11/6/2008
David Norris University of Minnesota 11/1/2008 - 11/1/2008
Arthur J. Nozik Department of Energy 10/31/2008 - 11/2/2008
Sang- Hyun Oh University of Minnesota 11/1/2008 - 11/1/2008
Isamu Ohnishi Hiroshima University 11/1/2008 - 1/17/2009
Wilma K. Olson Rutgers University 11/3/2008 - 11/7/2008
Shmuel Onn Technion-Israel Institute of Technology 11/16/2008 - 11/22/2008
Daniel Osei-Kuffuor University of Minnesota 11/2/2008 - 11/7/2008
Ignacio Pagonabarraga Mora University of Barcelona 11/2/2008 - 11/7/2008
Richa Pandey University of Minnesota 11/1/2008 - 11/1/2008
Stephen D Pankavich Indiana University 10/31/2008 - 11/7/2008
Pablo A. Parrilo Massachusetts Institute of Technology 11/16/2008 - 11/22/2008
Jaroslav Pekar Honeywell 11/15/2008 - 11/21/2008
Jiming Peng University of Illinois at Urbana-Champaign 11/16/2008 - 11/22/2008
Cynthia A. Phillips Sandia National Laboratories 11/16/2008 - 11/21/2008
Simon Poblete Max Planck Institute for Polymer Research 11/1/2008 - 11/9/2008
Cristina Popovici North Dakota State University 11/2/2008 - 11/8/2008
Matej Praprotnik Max Planck Institute for Polymer Research 10/8/2008 - 11/8/2008
Oleg Prezhdo University of Washington 10/31/2008 - 11/2/2008
Emil Prodan Yeshiva University 10/31/2008 - 11/2/2008
Keith Promislow Michigan State University 10/31/2008 - 11/6/2008
Kashif Rashid Schlumberger Cambridge Research Laboratories 11/16/2008 - 11/21/2008
Weiqing Ren New York University 11/4/2008 - 11/7/2008
Franz Rendl Universität Klagenfurt 11/15/2008 - 11/21/2008
Christian Ringhofer Arizona State University 10/31/2008 - 11/2/2008
Mark O. Robbins Johns Hopkins University 11/2/2008 - 11/6/2008
Kees Roos Technische Universiteit te Delft 11/17/2008 - 11/21/2008
Victor Rühle Max Planck Institute for Polymer Research 11/1/2008 - 11/9/2008
Yousef Saad University of Minnesota 11/3/2008 - 11/7/2008
Sebastian Sager Ruprecht-Karls-Universität Heidelberg 11/16/2008 - 11/23/2008
Fadil Santosa University of Minnesota 7/1/2008 - 6/30/2010
Annick Sartenaer Facultés Universitaires Notre Dame de la Paix (Namur) 11/15/2008 - 11/21/2008
Garikapati Narahari Sastry Indian Institute of Chemical Technology 11/2/2008 - 11/7/2008
Andreas Savin Université de Paris VI (Pierre et Marie Curie) 10/8/2008 - 11/6/2008
Anureet Saxena Axioma Inc. 11/17/2008 - 11/19/2008
Arnd Scheel University of Minnesota 9/1/2008 - 6/30/2009
Roman Schubert University of Bristol 10/5/2008 - 11/8/2008
Christof Schütte Freie Universität Berlin 11/1/2008 - 11/5/2008
Ridgway Scott University of Chicago 9/1/2008 - 6/30/2009
Tsvetanka Sendova University of Minnesota 9/1/2008 - 8/31/2010
Yuk Sham University of Minnesota 9/1/2008 - 6/30/2009
Uday V. Shanbhag University of Illinois at Urbana-Champaign 11/16/2008 - 11/19/2008
Stephen Shipman Louisiana State University 10/31/2008 - 11/2/2008
Chi-Wang Shu Brown University 10/31/2008 - 11/2/2008
Heinz Siedentop Ludwig-Maximilians-Universität München 9/22/2008 - 12/19/2008
Lyubima B. Simeonova University of Utah 11/2/2008 - 11/7/2008
Donald H. Singley 3M 11/1/2008 - 11/1/2008
Valery P. Smyshlyaev University of Bath 11/3/2008 - 11/8/2008
Andrew M. Stein University of Minnesota 9/1/2007 - 8/31/2009
John M. Stockie Simon Fraser University 11/2/2008 - 11/7/2008
Bo Su Iowa State University 11/2/2008 - 11/7/2008
Qiyu Sun University of Central Florida 10/31/2008 - 11/2/2008
Ellad B Tadmor University of Minnesota 11/2/2008 - 11/7/2008
Florence Tama University of Arizona 11/5/2008 - 11/7/2008
Molei Tao California Institute of Technology 11/1/2008 - 11/8/2008
P. Craig Taylor Colorado School of Mines 10/31/2008 - 11/1/2008
Tamás Terlaky Lehigh University 11/16/2008 - 11/21/2008
Brooke Timp University of Minnesota 11/1/2008 - 11/1/2008
William Tisdale University of Minnesota 11/1/2008 - 11/1/2008
Alex Travesset Iowa State University 11/2/2008 - 11/7/2008
Sergei Tretiak Los Alamos National Laboratory 10/31/2008 - 11/1/2008
Donald G. Truhlar University of Minnesota 9/1/2008 - 6/30/2009
Birkan Tunc Istanbul Technical University 10/25/2008 - 11/1/2008
Erkan Tüzel University of Minnesota 9/1/2007 - 8/31/2009
Steven M. Valone Los Alamos National Laboratory 9/8/2008 - 11/30/2008
Eric Vanden-Eijnden New York University 11/1/2008 - 11/7/2008
Jon Van Laarhoven University of Iowa 11/16/2008 - 11/22/2008
Mark van Schilfgaarde Arizona State University 10/31/2008 - 11/2/2008
Stefan Vigerske Humboldt-Universität 11/15/2008 - 11/21/2008
Tho T. Vu Top-Vu Technology, Inc 11/1/2008 - 11/1/2008
Bruce Wade University of Wisconsin 11/2/2008 - 11/8/2008
Andreas Waechter IBM 11/16/2008 - 11/22/2008
Brenton Walker Laborartory For Telecommunications Sciences 10/26/2008 - 11/1/2008
Richard A. Waltz University of Southern California 11/16/2008 - 11/21/2008
Hong Wang University of South Carolina 10/31/2008 - 11/2/2008
Lin-Wang Wang Lawrence Berkeley National Laboratory 10/31/2008 - 11/2/2008
Qi Wang University of South Carolina 10/31/2008 - 11/2/2008
Zhian Wang University of Minnesota 9/1/2007 - 8/31/2009
Zhongming Wang University of California, San Diego 11/2/2008 - 11/8/2008
Henry A. Warchall National Science Foundation 10/31/2008 - 11/2/2008
Robert Weismantel Otto-von-Guericke-Universität Magdeburg 11/16/2008 - 11/21/2008
Tapio Westerlund Åbo Akademi (Finland-Swedish University of Åbo) 11/15/2008 - 11/22/2008
Angelika Wiegele Universität Klagenfurt 11/15/2008 - 11/21/2008
Colin Wolden Colorado School of Mines 10/31/2008 - 11/2/2008
Dexuan Xie University of Wisconsin 9/4/2008 - 12/15/2008
Wei Xiong University of Minnesota 9/1/2008 - 8/31/2010
Jue Yan Iowa State University 10/31/2008 - 11/1/2008
Chao Yang Lawrence Berkeley National Laboratory 9/8/2008 - 11/8/2008
Fei Yang University of Minnesota 11/17/2008 - 11/21/2008
Xingzhou Yang Mississippi State University 10/31/2008 - 11/2/2008
Aaron Nung Kwan Yip Purdue University 11/1/2008 - 11/8/2008
Haijun Yu Purdue University 11/2/2008 - 11/8/2008
Jin Yu University of California, Berkeley 11/2/2008 - 11/7/2008
Luping Yu University of Chicago 10/31/2008 - 11/1/2008
Trihua Yu 3M 11/1/2008 - 11/1/2008
Hongchao Zhang Louisiana State University 11/16/2008 - 11/22/2008
Weigang Zhong University of Minnesota 9/1/2008 - 8/31/2010
Xiaoyang Zhu University of Minnesota 11/1/2008 - 11/1/2008
Yu Zhuang Texas Tech University 10/30/2008 - 11/2/2008
Legend: Postdoc or Industrial Postdoc Long-term Visitor

IMA Affiliates:
Arizona State University, Boeing, Corning, ExxonMobil, Ford, General Motors, Georgia Institute of Technology, Honeywell, IBM, Indiana University, Iowa State University, Kent State University, Lawrence Livermore National Laboratory, Lockheed Martin, Los Alamos National Laboratory, Medtronic, Michigan State University, Michigan Technological University, Microsoft Research, Mississippi State University, Motorola, Northern Illinois University, Ohio State University, Pennsylvania State University, Purdue University, Rice University, Rutgers University, Sandia National Laboratories, Schlumberger Cambridge Research Laboratories, Schlumberger-Doll, Seoul National University, Siemens, Telcordia, Texas A & M University, University of Central Florida, University of Chicago, University of Delaware, University of Houston, University of Illinois at 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 Tennessee, University of Wisconsin, University of Wyoming, US Air Force Research Laboratory, Wayne State University, Worcester Polytechnic Institute