

MARCH 2009 


Department Colloqium 
Topic: 
Quantum Unique Ergodicity and Number Theory 
Presenter: 
K. Soundararajan, Stanford 
Date: 
Wednesday, March 11, 2009, Time: 4:30 p.m., Location: Fine Hall 314 
Abstract: 
A fundamental problem in the area of quantum chaos is to understand the distribution of high eigenvalue eigenfunctions of the Laplacian on certain Riemannian manifolds. A particular case which is of interest to number theorists concerns hyperbolic manifolds arising as a quotient of the upper halfplane by a discrete ``arithmetic" subgroup of SL_2(R) (for example, SL_2(Z), and in this case the corresponding eigenfunctions are called Maass cusp forms). In this case, Rudnick and Sarnak have conjectured that the high energy eigenfunctions become equidistributed. I will discuss some recent progress which has led to a resolution of this conjecture, and also on a holomorphic analog for classical modular forms. 


Graduate Student Seminar 
Topic: 
Morse theory 
Presenter: 
Michael McBreen, Princeton University 
Date: 
Thursday, March 12, 2009, Time: 12:30 p.m., Location: Fine Hall 314 
Abstract: 
Morse theory gives the cell structure of a manifold in terms of the critical points of a 'random' realvalued function on this manifold. Besides being clever and pleasing to the eye, it has given us Bott periodicity, counts of geodesics, periodic orbits of dynamical systems, Heegard Floer homology, the foundations of Mirror Symmetry and many many more riches. I will explain the construction in detail, then sketch the applications. 


Ergodic Theory and Statistical Mechanics Seminar 
Topic: 
Random walks with memory and statistical mechanics 
Presenter: 
Thomas Spencer, Institute for Advanced Study 
Date: 
Thursday, March 12, 2009, Time: 2:00 p.m., Location: Fine Hall 401 
Abstract: 
This talk will review some results and conjectures about history dependent random walks. For example, edge reinforced random walk (ERRW) is a random walk which prefers to visit edges it has visited in the past. Diaconis showed that ERRW can be expressed as a random walk in a random environment. This environment is highly correlated and is described in terms of statistical mechanics. Phase transitions for closely related models are believed to occur in three dimensions. One phase corresponds to diffusion and the other phase to localization. This talk is based work of Merkl and Rolles on ERRW and my recent preprint with Disertori and Zirnbauer on a hyperbolic sigma model. 


Discrete Mathematics Seminar 
Topic: 
Inverse LittlewoodOfford theory, Smooth Analysis and the Circular Law 
Presenter: 
Van Vu, Rutgers University 
Date: 
Thursday, March 12, 2009, Time: 2:15 p.m., Location: Fine Hall 224 
Abstract: 
A corner stone of the theory of random matrices is Wigner's semicircle law, obtained in the 1950s, which asserts that (after a proper normalization) the limiting distribution of the spectra of a random hermitian matrix with iid (upper diagonal) entries follows the semicircle law. The nonhermitian case is the famous Circular Law Conjecture, which asserts that (after a proper normalization) the limiting distribution of the spectra of a random matrix with iid entries is uniform in the unit circle.
Despite several important partial results (GinibreMehta, Girko, Bai, Edelman, GotzeTykhomirov, PanZhu etc) the conjecture remained open for more than 50 years. Last year, T. Tao and I confirmed the conjecture in full generality. I am going to give an overview of this proof, which relies on rather surprising connections between various fields: combinatorics, probability, number theory and theoretical computer science. In particular, ideas from ADDITIVE COMBINATORICS play crucial roles. 


Number Theory Seminar 
Topic: 
The RudnickSarnak Conjectures 
Presenter: 
Roman Holowinsky, University of Toronto 
Date: 
Thursday, March 12, 2009, Time: 4:30 p.m., Location: IAS S101 
Abstract: 
We'll discuss the quantum unique ergodicity conjecture of Rudnick and Sarnak and its holomorphic analogue. Highlighting the key ideas in recent joint with with K. Soundararajan, we'll demonstrate how one may use number theoretic techniques to solve this problem. 


Topology Seminar 
Topic: 
Congruence subgroup problem for mapping class groups 
Presenter: 
Ben McReynolds, University of Chicago 
Date: 
Thursday, March 12, 2009, Time: 4:30 p.m., Location: Fine Hall 314 
Abstract: 
I will discuss the congruence subgroup problem for mapping class groups, a problem that generalizes the classical one for arithmetic groups. I will discuss an unpublished proof by W. Thurston for an affirmative answer to this problem for genus zero mapping class groups. Time permitting, I will discuss the current state of this problem. 


Applied Mathematics Seminar 
Topic: 
Parallelintime algorithms and longtime integration 
Presenter: 
Claude Le Bris, University of Minnesota 
Date: 
Friday, March 13, 2009, Time: 1:00 p.m., Location: Fine Hall 224 
Abstract: 
We investigate some issues related to the integration of Hamiltonian systems when using integrators that are parallel in time (the socalled class of parareal integrators, introduced by JL Lions, Y. Maday and G. Turinici in C. R. Acad. Sci., Paris, Sér. I, Math. 332, No.7, 661668 (2001)). We show that, when appropriately adjusted, this original class of integrators enjoy excellent properties of conservation over long times. We present some elements of numerical analysis that explain the numerical observations. We also present a possible symmetrized version of such algorithms, with similar, agreeable properties. This is joint work with Yvon Maday (University Paris 6) and Frederic Legoll (Ecole des Ponts). 


Differential Geometry and Geometric Analysis Seminar 
Topic: 
The EinsteinWeyl Equations, Scattering Maps, and Holomorphic Disks 
Presenter: 
Claude LeBrun, SUNY Stony Brook 
Date: 
Friday, March 13, 2009, Time: 3:00 p.m., Location: Fine Hall 314 
Abstract: 
This talk will show that conformally compact, globally hyperbolic, Lorentzian EinsteinWeyl 3manifolds are in natural onetoone correspondence with orientationreversing diffeomorphisms of the 2sphere. The proof hinges on a holomorphicdisk analog of Hitchin's minitwistor correspondence. 


Number Theory Seminar 
Topic: 
padically completed cohomology and the padic Langlands program 
Presenter: 
Matthew Emerton, Northwestern University 
Date: 
Thursday, March 19, 2009, Time: 4:30 p.m., Location: IAS S101 
Abstract: 
Speaking at a general level, a major goal of the padic Langlands program (from a global, rather than local, perspective) is to find a padic generalization of the notion of automorphic eigenform, the hope being that every padic global Galois representation will correspond to such an object. (Recall that only those Galois representations that are motivic, i.e. that come from geometry, are expected to correspond to classical automorphic eigenforms).
In certain contexts (namely, when one has Shimura varieties at hand), one can begin with a geometric definition of automorphic forms, and generalize it to obtain a geometric definition of padic automorphic forms. However, in the nonShimura variety context, such an approach is not available. Furthermore, this approach is somewhat remote from the representationtheoretic point of view on automorphic forms, which plays such an important role in the classical Langlands program.
In this talk I will explain a different, and very general, approach to the problem of padic interpolation, via the theory of padically completed cohomology. This approach has close ties to the padic and mod p representation theory of padic groups, and to noncommutative Iwasawa theory.
After introducing the basic objects (namely, the padically completed cohomology spaces attached to a given reductive group), I will explain several key conjectures that we expect to hold, including the conjectural relationship to Galois deformation spaces. Although these conjectures seem out of reach at present in general, some progress has been made towards them in particular cases. I will describe some of this progress, and along the way will introduce some of the tools that we have developed for studying padically completed cohomology, the most important of these being the Poincare duality spectral sequence.
This is joint work with Frank Calegari. 


Analysis Seminar 
Topic: 
TBA 
Presenter: 
Robert Strain, Princeton University 
Date: 
Monday, March 23, 2009, Time: 4:00 p.m., Location: Fine Hall 110 


PACM Colloquium 
Topic: 
The Empirical Mode Decomposition: the method, its progress, and open questions 
Presenter: 
Zhaohua Wu, Department of Meteorology & Center for OceanAtmospheric Prediction Studies, Florida State University 
Date: 
Monday, March 23, 2009, Time: 4:00 p.m., Location: Fine Hall 214 
Abstract: 
The Empirical Mode Decomposition (EMD) was an empirical onedimensional data decomposition method invented by Dr. Norden Huang about ten years ago and has been used with great success in many fields of science and engineering. In this talk, I will introduce, from the perspective of a physical scientist, the thinking behind and the algorithm of EMD; and its most recent developments, especially the Ensemble EMD (EEMD), a noiseassisted data analysis method, and the multidimensional EMD based on EEMD. I will also outline some open questions that we currently do not have answers, or even clues to the answers, such as how to optimize EMD algorithm, what is the mathematical nature of EMD. To a significant degree, this is a talk intended for obtaining helps from mathematicians. 


Analysis Seminar *** Rescheduled from March 2, 2009  Please note special time 
Topic: 
On the evolution of solutions to a manybody Schrödinger equation 
Presenter: 
Matei Machedon, University of Maryland 
Date: 
Monday, March 23, 2009, Time: 5:00 p.m., Location: Fine Hall 110 
Abstract: 
In part I, I will describe background material and a new proof for the uniqueness of solutions to the GrossPitaevskii hierarchy. This is joint work with S. Klainerman and is a simplification, based on spacetime estimates, of an older proof of Erdös, Schlein and Yau.
In Part II (joint work with M. Grillakis and D. Margetis) I will discuss a new, highly nonlinear but explicit NLS in two space variables, whose solutions, if they exist, provide a second order correction to the usual tensor product approximation, which works in the Fock space norm. This is inspired by recent work of Rodnianski and Schlein, as well as older work of Wu. 


Algebraic Geometry Seminar 
Topic: 
TBA 
Presenter: 
Junecue Suh, MIT 
Date: 
Tuesday, March 24, 2009, Time: 4:30 p.m., Location: Fine Hall 322 


Mathematical Physics Seminar 
Topic: 
TBA 
Presenter: 
Cedric Villani, ENS Lyon and IAS 
Date: 
Tuesday, March 24, 2009, Time: 4:30 p.m., Location: Jadwin 343 


Department Colloqium 
Topic: 
TBA 
Presenter: 
Cedric Villani, ENS Lyon and IAS 
Date: 
Wednesday, March 25, 2009, Time: 4:30 p.m., Location: Fine Hall 314 


Graduate Student Seminar 
Topic: 
Sumproduct estimates via combinatorial geometry 
Presenter: 
PoShen Loh, Princeton University and UCLA 
Date: 
Thursday, March 26, 2009, Time: 12:30 p.m., Location: Fine Hall 314 
Abstract: 
Every twodimensional drawing of any graph with V vertices and E ≥ 4V edges necessarily has at least E3/V2 pairs of crossing edges. Also, for every set A of real numbers, one of A+A (the set of all pairwise sums of elements of A) or A·A (the set of all pairwise products) has size at least A5/4. What could these two theorems possibly have in common, besides the fact that Endre Szemerédi coauthored both? Surprisingly, quite a lot. We will see the proof of the first result, followed by a series of fascinating consequences which culminate in the second result. Of course, the Probablistic Method will make a crucial appearance. 


Ergodic Theory and Statistical Mechanics Seminar 
Topic: 
TBA 
Presenter: 
Manfred Denker, Penn State University 
Date: 
Thursday, March 26, 2009, Time: 2:00 p.m., Location: Fine Hall 401 


Discrete Mathematics Seminar 
Topic: 
Avoiding small subgraphs in Achlioptas processes 
Presenter: 
PoShen Loh, Princeton University and UCLA 
Date: 
Thursday, March 26, 2009, Time: 2:15 p.m., Location: Fine Hall 224 
Abstract: 
Consider the following random process. At each round, one is presented with two random edges from the edge set of the complete graph on n vertices, and is asked to choose one of them. The selected edges are collected into a graph, which thus grows at the rate of one edge per round. This is known in the literature as an Achlioptas process, and has been studied by many researchers, mainly in the context of delaying or accelerating the appearance of the giant component.
In our work, we investigate the classical small subgraph problem for Achlioptas processes. That is, given a fixed graph H, we study whether there is a deterministic online algorithm that substantially delays or accelerates a typical appearance of H, compared to its threshold of appearance in the random graph G(n,M). It is easy to see that one cannot accelerate the appearance of any fixed graph by more than a factor of 2, so we concentrate on the task of avoiding H. We determine thresholds for the avoidance of all cycles C_t, cliques K_t, and complete bipartite graphs K_{t,t}.
Joint work with Michael Krivelevich and Benny Sudakov. 


Topology Seminar 
Topic: 
Recurrence of random paths and counting closed geodesics in strata 
Presenter: 
Maryam Mirzakhani, Princeton University 
Date: 
Thursday, March 26, 2009, Time: 4:30 p.m., Location: Fine Hall 314 
Abstract: 
We discuss the problem of counting closed geodesics in a stratum of the moduli space of Abelian(quadratic) differentials. This is joint work with Alex Eskin and Kasra Rafi. 


Analysis Seminar 
Topic: 
TBA 
Presenter: 
Cedric Villani, Ecole Normale Supérieure de Lyon 
Date: 
Monday, March 30, 2009, Time: 4:00 p.m., Location: Fine Hall 110 


PACM Colloquium 
Topic: 
On the interplay between coding theory and compressed sensing 
Presenter: 
Olgica Milenkovic, Electrical & Computer Engrg, University of Illinois  UrbanaChampaign 
Date: 
Monday, March 30, 2009, Time: 4:00 p.m., Location: Fine Hall 214 
Abstract: 
Compressed sensing (CS) is a signal processing technique that allows for accurate, polynomial time recovery of sparse datavectors based on a small number of linear measurements. In its most basic form, robust CS can be viewed as a specialized errorcontrol coding scheme in which the data alphabet does not necessarily have the structure of a finite field and where the notion of a “paritycheck” is replaced by a more general functionality. It is therefore possible to combine and extend classical CS and codingtheoretic paradigms in terms of introducing new minimum distance, reconstructions complexity, and quantization precision constraints. In this setting, we derive fundamental lower and upper bounds on the achievable compression rate for such constrained compressed sensing (CCS) schemes, and also demonstrate that sparse reconstruction in the presence of noise can be performed via lowcomplexity correlationmaximization algorithms that operate based on belief propagation iterations. Our problem analysis is motivated by a myriad of applications ranging from compressed sensing microarray designs, reliabilityreordering decoding of linear blockcodes, identification in multiuser communication systems, and fault tolerant computing. This is a joint work with Wei Dai and Vin Pham Hoa from the ECE Department at UIUC. 


Algebraic Geometry Seminar 
Topic: 
TBA 
Presenter: 
Nicolas Templier, IAS 
Date: 
Tuesday, March 31, 2009, Time: 4:30 p.m., Location: Fine Hall 322 


Mathematical Physics Seminar 
Topic: 
UC Berkeley 
Presenter: 
Detlev Buchholz , Univ of Goettingen 
Date: 
Tuesday, March 31, 2009, Time: 4:30 p.m., Location: Jadwin 343 
Abstract: 
Recently, Grosse and Lechner introduced a deformation procedure for noninteracting quantum field theories, giving rise to interesting examples of theories with nontrivial scattering matrix in any number of spacetime dimensions. In this talk we outline an extension of this procedure to the general framework of quantum field theory by introducing the concept of "warped" convolutions of operator functions. These convolutions have some intriguing properties which permit the deformation of arbitrary nets of algebras based on wedgeshaped regions of Minkowski space to nets which still satisfy Einstein's principles of relativistic covariance and causality. The deformed nets still admit a scattering theory and give rise to a deformed scattering matrix. 


APRIL 2009 


Department Colloqium 
Topic: 
On a conjecture of De Giorgi 
Presenter: 
Ovidiu Savin, Columbia 
Date: 
Wednesday, April 1, 2009, Time: 4:30 p.m., Location: Fine Hall 314 
Abstract: 
In 1978 De Giorgi made a conjecture about the symmetry of global solutions to a certain semilinear elliptic equation. He stated that monotone, bounded solutions of $$ \triangle u=u^3u$$ in $\mathbb{R}^n$ are one dimensional (i.e. the level sets of $u$ are hyperplanes) at least in dimension $n \le 8$. This problem is in fact closely related to the theory of minimal surfaces and it is sometimes referred to as "the $\varepsilon$ version of the Bernstein problem for mininimal graphs". In my talk I will explain this relation and I will give an idea about the proof of this conjecture for $n \le 8$. We mention that recently Del Pino, Kowalzyk and Wei provided a counterexample in dimension $n \ge 9$. 


Ergodic Theory and Statistical Mechanics Seminar 
Topic: 
Large deviations of the current and phase transitions 
Presenter: 
Thierry Bodineau, IAS 
Date: 
Thursday, April 2, 2009, Time: 2:00 p.m., Location: Fine Hall 401 
Abstract: 
Using the framework of the hydrodynamic limits, we will discuss the large deviations of a particle current through a diffusive system. The deviations can lead to dynamical phase transitions. In the case of asymmetric dynamics we will explain how the large deviation functional of the current provides a physical interpretation to the nonentropic solutions of Burgers equation. 


Topology Seminar 
Topic: 
Bordered Floer homology: bimodules and computations 
Presenter: 
Robert Lipshitz, Columbia University 
Date: 
Thursday, April 2, 2009, Time: 4:30 p.m., Location: Fine Hall 314 
Abstract: 
We will review the structure of bordered Floer homology, including how it depends on the parametrization of the boundary. We will then discuss how to compute it, and consequently another algorithm for computing HFhat. This is work in progress with Peter Ozsvath and Dylan Thurston. 


Discrete Mathematics Seminar ***Please note special day 
Topic: 
TBA 
Presenter: 
Jeff Kahn, Rutgers University 
Date: 
Friday, April 3, 2009, Time: 2:15 p.m., Location: Fine Hall 224 


Analysis Seminar 
Topic: 
TBA 
Presenter: 
Alexei Poltoratski, Texas A&M University 
Date: 
Monday, April 6, 2009, Time: 4:00 p.m., Location: Fine Hall 110 


PACM Colloquium 
Topic: 
TBA 
Presenter: 
Shannon Hughes, PACM, Princeton University 
Date: 
Monday, April 6, 2009, Time: 4:00 p.m., Location: Fine Hall 214 


Algebraic Geometry Seminar 
Topic: 
TBA 
Presenter: 
Jarod Alper, Columbia University 
Date: 
Tuesday, April 7, 2009, Time: 4:30 p.m., Location: Fine Hall 322 


Department Colloqium 
Topic: 
TBA 
Presenter: 
Igor Rodnianski, Princeton University 
Date: 
Wednesday, April 8, 2009, Time: 4:30 p.m., Location: Fine Hall 314 


Ergodic Theory and Statistical Mechanics Seminar 
Topic: 
TBA. 
Presenter: 
Corinna Ulcigrai, University of Bristol 
Date: 
Thursday, April 9, 2009, Time: 2:00 p.m., Location: Fine Hall 401 


Discrete Mathematics Seminar 
Topic: 
TBA 
Presenter: 
William Cook, Georgia Tech. 
Date: 
Thursday, April 9, 2009, Time: 2:15 p.m., Location: Fine Hall 224 


Analysis Seminar 
Topic: 
TBA 
Presenter: 
Camillo De Lellis, Universitaet Zuerich 
Date: 
Monday, April 13, 2009, Time: 4:00 p.m., Location: Fine Hall 110 


Analysis Seminar ***Please note special time 
Topic: 
New results for reactiondiffusion equations arising from reversible chemistry 
Presenter: 
Laurent Desvillettes, ENS Cachan 
Date: 
Monday, April 13, 2009, Time: 5:00 p.m., Location: Fine Hall 110 
Abstract: 
Entropy/entropy dissipation methods have been used with success lately in the study of the large time behavior of kinetic equations, nonlinear diffusions, etc., and have led to the development of the concept of hypocoercivity. They are also very useful in the context of reactiondiffusion equations (especially when they are derived from reversible chemistry), where they lead to new results of convergence to equilibrium as well as new results of existence of weak and strongs solutions. We shall detail some of those results, together with their links with recent works on coagulationfragmentation models, and the use of results of regularity for singular parabolic problems. 


Algebraic Geometry Seminar 
Topic: 
TBA 
Presenter: 
Brian Osserman, UC Davis 
Date: 
Tuesday, April 14, 2009, Time: 4:30 p.m., Location: Fine Hall 322 


Mathematical Physics Seminar 
Topic: 
An Asymptotic Expansion for the Dimer Lambda_d 
Presenter: 
Paul Federbush, University of Michigan 
Date: 
Tuesday, April 14, 2009, Time: 4:30 p.m., Location: Jadwin 343 
Abstract: 
The dimer problem is to count the number of ways a ddimensional "chessboard" can be completely covered by nonoverlapping dimers (dominoes), each dimer covering two nearest neighbor boxes. The number is ~exp(Lambda_d*V) as the volume V goes to infinity. It has been long known Lambda_d ~ (1/2)ln(d) +(1/2)(ln(2)1) We derive an asymptotic expansion whose first few terms are Lambda_d ~ (1/2)ln(d) +(1/2)(ln(2)1) +(1/8)(1/d) + (5/96)(1/d2) + (5/64)(1/d3) The last term here was calculated by computer, and we conjecture the next term will never be explicitly computed ( just by reason of required computer time ). The expansion is not yet rigorously established. 


Department Colloqium 
Topic: 
TBA 
Presenter: 
Giovanni Forni, University of Maryland 
Date: 
Wednesday, April 15, 2009, Time: 4:30 p.m., Location: Fine Hall 314 


Ergodic Theory and Statistical Mechanics Seminar 
Topic: 
TBA. 
Presenter: 
Giovanni Forni, University of Maryland 
Date: 
Thursday, April 16, 2009, Time: 2:00 p.m., Location: Fine Hall 401 


Discrete Mathematics Seminar 
Topic: 
Geometric selection theorems 
Presenter: 
Boris Bukh, Princeton University and UCLA 
Date: 
Thursday, April 16, 2009, Time: 2:15 p.m., Location: Fine Hall 224 
Abstract: 
In combinatorial geometry one frequently wants to select a point or a set of points that meets many simplices of a given family. The two examples are choosing a point in many simplices spanned by points of some P in R^d, and choosing a small set of points which meets the convex hull of every large subset of P (the weak epsilonnet problem). I will present a new class of constructions that yield the first nontrivial lower bound on the weak epsilonnet problem, and improve the best bounds for several other selection problems. Joint work with Jiří Matoušek and Gabriel Nivasch. 


Topology Seminar 
Topic: 
TBA 
Presenter: 
Zoltan Szabo, Princeton University 
Date: 
Thursday, April 16, 2009, Time: 4:30 p.m., Location: Fine Hall 314 


Analysis Seminar 
Topic: 
TBA 
Presenter: 
Diogo Arsenio, Courant Institute 
Date: 
Monday, April 20, 2009, Time: 4:00 p.m., Location: Fine Hall 110 


PACM Colloquium 
Topic: 
TBA 
Presenter: 
Jennifer Chayes, Microsoft Corporation 
Date: 
Monday, April 20, 2009, Time: 4:00 p.m., Location: Fine Hall 214 


Algebraic Geometry Seminar 
Topic: 
Automorphisms mapping a point into a subvariety 
Presenter: 
Bjorn Poonen, MIT 
Date: 
Tuesday, April 21, 2009, Time: 4:30 p.m., Location: Fine Hall 322 
Abstract: 
Given a variety X, a point x in X, and a subvariety Z of X, is there an automorphism of X mapping x into Z? We prove that this problem is undecidable. 


Department Colloqium 
Topic: 
TBA 
Presenter: 
J. M. Bismut 
Date: 
Wednesday, April 22, 2009, Time: 4:30 p.m., Location: Fine Hall 314 


Ergodic Theory and Statistical Mechanics Seminar 
Topic: 
TBA 
Presenter: 
Michael Hochman, Princeton University 
Date: 
Thursday, April 23, 2009, Time: 2:00 p.m., Location: Fine Hall 401 


Discrete Mathematics Seminar 
Topic: 
TBA 
Presenter: 
Maria Chudnovsky, Columbia University 
Date: 
Thursday, April 23, 2009, Time: 2:15 p.m., Location: Fine Hall 224 


Topology Seminar 
Topic: 
TBA 
Presenter: 
Kekiko Kawamuro, IAS 
Date: 
Thursday, April 23, 2009, Time: 4:30 p.m., Location: Fine Hall 314 


Analysis Seminar 
Topic: 
Stefan Problem with Surface Tension 
Presenter: 
Yan Guo, Brown University 
Date: 
Monday, April 27, 2009, Time: 4:00 p.m., Location: Fine Hall 110 


PACM Colloquium 
Topic: 
Stateoftheart Computer Simulations of Supernova Explosions 
Presenter: 
Adam Burrows, Astrophysics, Princeton University 
Date: 
Monday, April 27, 2009, Time: 4:00 p.m., Location: Fine Hall 214 
Abstract: 
To simulate supernova explosions, one must solve simultaneously the nonlinear, coupled partial differential equations of radiation hydrodynamics. What's more, due to a variety of instabilities and asymmetries, this must eventually be accomplished in 3D. The current stateoftheart is 2D, plus rotation and magnetic fields (assuming axisymmetry). Nevertheless, with the current suite of codes, we have been able to explore the evolution of the highdensity, hightemperature, highspeed environment at the core of a massive star at death. It is in this core that the supernova explosion is launched. However, the complexity of the problem has to date obscured the essential physics and mechanisms of the phenomenon, making it indeed one of the "Grand Challenges" of 21st century astrophysics. Requiring forefront numerical algorithms and massive computational resources, the resolution of this puzzle awaits the advent of peta and exascale architectures and the software to efficiently use them. In this talk, I will review the current state of the science and simulations as we plan for the fully 3D, multiphysics capabilities that promise credibly to crack open this obdurate astrophysical nut. 


Algebraic Geometry Seminar 
Topic: 
TBA 
Presenter: 
Chad Schoen, Duke University 
Date: 
Tuesday, April 28, 2009, Time: 4:30 p.m., Location: Fine Hall 322 


Mathematical Physics Seminar 
Topic: 
TBA 
Presenter: 
Mihai Stoiciu, Williams College 
Date: 
Tuesday, April 28, 2009, Time: 4:30 p.m., Location: Jadwin 343 


Ergodic Theory and Statistical Mechanics Seminar 
Topic: 
LeeYang zeros for the Diamond Hierarchical Lattice and 2D rational dynamics 
Presenter: 
Mikhail Lyubich, State University of New York at Stony Brook 
Date: 
Thursday, April 30, 2009, Time: 2:00 p.m., Location: Fine Hall 401 
Abstract: 
In a classical work of 1950's, Lee and Yang proved that zeros of the partition functions of the Ising models on graphs always lie on the unit circle. Distribution of these zeros is physically important as it controls phase transitions in the model. We study this distribution for a special ``Diamond Hierarchical Lattice". In this case, it can be described in terms of the dynamics of an explicit rational map in two variables. We prove partial hyperbolicity of this map on an invariant cylinder, and derive from it that the LeeYang zeros are organized asymptotically in a transverse measure for the central foliation. From the global complex point of view, the zero distributions get interpreted as slices of the Green (1,1)current on the projective space. It is a joint work with Pavel Bleher and Roland Roeder. 


MAY 2009 


Ergodic Theory and Statistical Mechanics Seminar 
Topic: 
TBA 
Presenter: 
Ilya Vinogradov and Francesco Cellarosi, Princeton University 
Date: 
Thursday, May 7, 2009, Time: 2:00 p.m., Location: Fine Hall 401 



