

FEBRUARY 2009 


Department Colloqium 
Topic: 
Large N limit of random matrices, free probability and the graded algebra of a planar algebra 
Presenter: 
Vaughan Jones, Berkeley 
Date: 
Wednesday, February 25, 2009, Time: 4:30 p.m., Location: Fine Hall 314 


Graduate Student Seminar 
Topic: 
Models and Fields: A delicate Passage to Characteristic p 
Presenter: 
Jacob Tsimerman, Princeton University 
Date: 
Thursday, February 26, 2009, Time: 12:30 p.m., Location: Fine Hall 314 
Abstract: 
If a polynomial map from $C^n$ to itself is injective, then it is also surjective. The first proof of this elegant result actually used a passage to characteristic p. I'll introduce the relevant notions from model theory and explain the proof, which will naturally yield the following much stronger result: Every statement in the first order logic of rings is true in the algebraic closure of $F_p$ for almost all p iff it is true in C. 


Discrete Mathematics Seminar 
Topic: 
Finding Lovasz's Needle in an Exponential Haystack 
Presenter: 
Joel Spencer, Courant Institute 
Date: 
Thursday, February 26, 2009, Time: 2:15 p.m., Location: Fine Hall 224 
Abstract: 
The Lovasz Local Lemma is a subtle and farreaching probability lemma. Roughly, given a large number of bad events which are "mostly" independent it sieves out an instance when none of the bad events occur. As an illustrative example, consider a huge family of 10element sets, where each set overlaps at most 100 others. We color randomly red and blue and for each set e there is a bad event that e is monochromatic. The conclusion is the existence of a coloring where none of the e are monochromatic. In theory. But if there are n sets a random coloring only has exponentially small chance of succeeding. Finding a polynomial time algorithmic implementation has proven elusive. There were some results of Jozsef Beck and Noga Alon in the early 1990s but they had limited application. Very recently Robin Moser (ETH) has made a breakthrough, giving an amazingly simple probabilistic algorithm to find the coloring and a not quite so simple proof that the algorithm indeed works.
We shall rephrase Moser's argument and give the entire argument. 


Ergodic Theory and Statistical Mechanics Seminar ***Please note special time 
Topic: 
Limit lognormal process, Selberg integral as Mellin transform, and intermittency differentiation. 
Presenter: 
Dmitry Ostrovsky 
Date: 
Thursday, February 26, 2009, Time: 4:00 p.m., Location: Fine Hall 401 
Abstract: 
The limit lognormal process is a multifractal stochastic process with the remarkable property that its positive integral moments are given by the celebrated Selberg integral. We will give an overview of the limit lognormal construction followed by a summary of our results on functional FeynmanKac equations and resulting intermittency expansions that govern its distribution. The talk will focus on the intermittency expansion for the Mellin transform. This expansion recovers Selberg’s formula for the positive integral moments and gives a novel product formula for the negative ones. By summing it in general using a moment constant method, we obtain an extension of Selberg’s finite product to the Mellin transform of a probability distribution in the form of an infinite product of ratios of gamma functions in the complex plane. This distribution is conjectured to be the limit lognormal distribution. 


Number Theory Seminar 
Topic: 
Bounding supnorms of cusp forms 
Presenter: 
V. Blomer, University of Toronto 
Date: 
Thursday, February 26, 2009, Time: 4:30 p.m., Location: IAS SH101 
Abstract: 
Given an L^2normalized cusp form f on a modular curve X_0(N), what can be said about pointwise bounds for f? For Hecke eigenforms, we will prove the first nontrivial bound in terms of the level N as well as hybrid bounds in terms of the level and the Laplacian eigenvalue. Similar techniques work for functions on other spaces, e.g. quotients of quaternion algebras. This is joint work with R. Holowinsky. 


Topology Seminar 
Topic: 
Topologically invariant Chern numbers of projective varieties 
Presenter: 
Dieter Kotschick, Munchen, IAS 
Date: 
Thursday, February 26, 2009, Time: 4:30 p.m., Location: Fine Hall 314 
Abstract: 
In 1954 Hirzebruch asked which linear combinations of Chern numbers are topological invariants of smooth complex projective varieties. Until recently, this problem was wide open, with few nontrivial results. We give a complete solution in arbitrary dimensions. An interesting feature of this solution is how it is derived from the well known case of complex dimension two, which at first sight looks rather special and exceptional. 


Differential Geometry and Geometric Analysis Seminar 
Topic: 
Ricci flow on ALE spaces 
Presenter: 
Xianzhe Dai, UCSB 
Date: 
Friday, February 27, 2009, Time: 3:00 p.m., Location: Fine Hall 314 


MARCH 2009 


Analysis Seminar 
Topic: 
On the evolution of solutions to a manybody Schrödinger equation 
Presenter: 
Matei Machedon, University of Maryland 
Date: 
Monday, March 2, 2009, Time: 4:00 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. 


PACM Colloquium 
Topic: 
Trouble with a chain of stochastic oscillators 
Presenter: 
Jonathan Mattingly, Duke University 
Date: 
Monday, March 2, 2009, Time: 4:00 p.m., Location: Fine Hall 214 
Abstract: 
I will discuss some recent (but modest) results showing the existence and slow mixing of a stationary chain of Hamiltonian oscillators subject to a heat bath. Such systems are used as simple models of heat conduction or energy transfer. Though the unlimite goal might be seen to under stand the "fourier" like law in this setting, I will be less ambitious. I will show that under some hypotheses, the chain posses a unique stationary state. Surprisingly, even these simple results require some delicate stochastic averaging. Furthermore, it is the existence of a stationary measure (not the uniquness) which is difficult. This is joint work with Martin Hairer . 


Ergodic Theory and Statistical Mechanics Seminar ***Please note special date 
Topic: 
What makes the ergodic theory of Markov chains in infinite dimensions different (and difficult) ? 
Presenter: 
Jonathan Mattingly, Duke University 
Date: 
Tuesday, March 3, 2009, Time: 2:00 p.m., Location: Fine Hall 401 
Abstract: 
I will discuss how Markov chains in infinite dimensions generically have typically have properties which make their ergodic theory difficult. Such properties are very pathological in finite dimensions, but in some sense generic in infinite dimensions. I will draw examples from stochastically forced PDEs and stochastic delay equations. We will see that in infinite dimensions, a typical system acts much more like an hypoelliptic diffusion then an elliptic one. I will also discuss the existence of spectral gaps as well as the uniqueness of invariant measures. If time permits I will discuss an extension of Hormander's "sum of squares theorem" to infinite dimensions. 


Algebraic Geometry Seminar 
Topic: 
Algebraic surfaces and hyperbolic geometry 
Presenter: 
Burt Totaro, Cambridge University 
Date: 
Tuesday, March 3, 2009, Time: 4:30 p.m., Location: Fine Hall 322 
Abstract: 
The intersection form on the group of line bundles on a complex algebraic surface always has signature (1,n) for some n. So the automorphism group of an algebraic surface always acts on hyperbolic nspace. For a class of surfaces including K3 surfaces and many rational surfaces, there is a close connection between the properties of the variety and the corresponding group acting on hyperbolic space. (In fancier terms: the MorrisonKawamata cone conjecture holds for klt CalabiYau pairs in dimension 2.) 


Mathematical Physics Seminar 
Topic: 
TBA 
Presenter: 
Yuval Peres, UC Berkeley 
Date: 
Tuesday, March 3, 2009, Time: 4:30 p.m., Location: Jadwin 343 


Department Colloqium 
Topic: 
Internal aggregation Models: From DiaconisFulton addition to a free boundary problem 
Presenter: 
Y. Peres, University of California, Berkeley 
Date: 
Wednesday, March 4, 2009, Time: 4:30 p.m., Location: Fine Hall 314 
Abstract: 
Start with n particles at each of k points in the ddimensional lattice, and let each particle perform simple random walk until it reaches an unoccupied site. The law of the resulting random set of occupied sites does not depend on the order in which the walks are performed, as shown by Diaconis and Fulton. We prove that if the distances between the starting points are suitably scaled, then the set of occupied sites has a deterministic scaling limit. In two dimensions, the boundary of the limiting shape is an algebraic curve of degree 2k. (For k = 1 it is a circle, as proved in 1992 by Lawler, Bramson and Griffeath.) The limiting shape can also be described in terms of a freeboundary problem for the Laplacian and quadrature identities for harmonic functions. I will describe applications to the abelian sandpile, and show simulations that suggest intriguing (yet unproved) connections with conformal mapping. Joint work with Lionel Levine. 


Ergodic Theory and Statistical Mechanics Seminar 
Topic: 
Hénon Renormalization 
Presenter: 
Marco Martens, State University of New York at Stony Brook 
Date: 
Thursday, March 5, 2009, Time: 2:00 p.m., Location: Fine Hall 401 
Abstract: 
The geometry of strongly dissipative infinite renormalizable Hénon maps of period doubling type is surprisingly different from its onedimensional counterpart. There are universal geometrical properties. However, the Cantor attractor is not geometrically rigid. Typically, it doesn't have bounded geometry. The average Jacobian is a topological invariant of the global attractor. Although the geometry of the Cantor attractor can be deformed by changing the average Jacobian, the geometry is universal in a distributional sense. 


Discrete Mathematics Seminar 
Topic: 
New bounds on the size of Kakeya sets in finite fields 
Presenter: 
Zeev Dvir, Institute for Advanced Study 
Date: 
Thursday, March 5, 2009, Time: 2:15 p.m., Location: Fine Hall 224 
Abstract: 
A Kakeya set is a set in (F_q)^n (the n dimensional vector space over a field of q elements) which contains a line in every direction. In this talk I will present a recent result which gives a lower bound of (q/2)^n on the size of such sets. This bound is tight to within a multiplicative factor of two from the known upper bounds. The proof extends the polynomial method used in [Dvir 08, Saraf Sudan 08] and uses polynomials of unbounded degree. If time allows I will also discuss the applications to the explicit construction of mergers that follow from our techniques.
Joint work with Kopparty, Saraf and Sudan (arxiv paper: "Extensions to the Method of Multiplicities, with applications to Kakeya Sets and Mergers"). 


Topology Seminar 
Topic: 
Subgroup classification in Out(F_n) 
Presenter: 
Lee Mosher, Rutgers, Newark 
Date: 
Thursday, March 5, 2009, Time: 4:30 p.m., Location: Fine Hall 314 
Abstract: 
We prove that for every subgroup G of Out(F_n), one of two alternatives holds: either there is a finite index subgroup H < G and a nontrivial proper free factor A of F_n such that each element of H fixes the conjugacy class of A; or there is an element g \in G such that no nontrivial power of g fixes the conjugacy class of any nontrivial proper free factor of F_n. This theorem is an analogue of Ivanov's classification of subgroups of surface mapping class groups. It has application to bounded 2nd cohomology of Out(F_n), by combining with results of BestvinaFeighn and of Hamenstadt. This work is joint with Michael Handel. 


Differential Geometry and Geometric Analysis Seminar 
Topic: 
TBA 
Presenter: 
Gabor Szekelyhidi, Columbia 
Date: 
Friday, March 6, 2009, Time: 3:00 p.m., Location: Fine Hall 314 


Analysis Seminar 
Topic: 
TBA 
Presenter: 
Mihai Tohaneanu, Berkeley 
Date: 
Monday, March 9, 2009, Time: 4:00 p.m., Location: Fine Hall 110 


PACM Colloquium 
Topic: 
Compressive Optical Imaging 
Presenter: 
Rebecca Willett, Electrical Engineering, Duke University 
Date: 
Monday, March 9, 2009, Time: 4:00 p.m., Location: Fine Hall 214 
Abstract: 
Recent work in the emerging field of compressed sensing indicates that, when feasible, judicious selection of the type of image transformation induced by imaging systems may dramatically improve our ability to perform reconstruction, even when the number of measurements is small relative to the size and resolution of the final image. The basic idea of compressed sensing is that when an image is very sparse (i.e. zerovalued at most locations) or highly compressible in some basis, relatively few incoherent observations suffice to reconstruct the most significant nonzero basis coefficients. These theoretical results have profound implications for the design of new imaging systems, particularly when physical and economical limitations require that these systems be as small, mechanically robust, and inexpensive as possible.
In this talk I will describe the primary theory underlying compressed sensing and discuss some of the key mathematical challenges associated with its application to practical imaging systems. In particular, I will explore several novel imaging system designs based on compressed sensing, including compressive coded aperture and hyperspectral imagers, and examine the interplay between compressed sensing theory and the practical physical constraints which must be considered to effectively exploit this theory. 


Algebraic Geometry Seminar 
Topic: 
Compactified Jacobians and Abel maps for singular curves 
Presenter: 
Eduardo Esteves, IMPA 
Date: 
Tuesday, March 10, 2009, Time: 4:30 p.m., Location: Fine Hall 322 
Abstract: 
We will discuss the problem of extending the construction of the classical Abel maps for smooth curves to the case of singular curves. The construction of degree1 Abel maps will be shown, together with an approach for constructing higher degree Abel maps. 


Department Colloqium 
Topic: 
TBA 
Presenter: 
K. Soundararajan, Stanford 
Date: 
Wednesday, March 11, 2009, Time: 4:30 p.m., Location: Fine Hall 314 


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. 


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. 


Differential Geometry and Geometric Analysis Seminar 
Topic: 
TBA 
Presenter: 
Claude LeBrun, SUNY Stony Brook 
Date: 
Friday, March 13, 2009, Time: 3:00 p.m., Location: Fine Hall 314 


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. 


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. 


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. 


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: 
TBA 
Presenter: 
Detlev Buchholz , Univ of Goettingen 
Date: 
Tuesday, March 31, 2009, Time: 4:30 p.m., Location: Jadwin 343 


APRIL 2009 


Department Colloqium 
Topic: 
TBA 
Presenter: 
O. Savin, Columbia 
Date: 
Wednesday, April 1, 2009, Time: 4:30 p.m., Location: Fine Hall 314 


Ergodic Theory and Statistical Mechanics Seminar 
Topic: 
TBA 
Presenter: 
Thierry Bodineau, Rutgers University 
Date: 
Thursday, April 2, 2009, Time: 2:00 p.m., Location: Fine Hall 401 


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 


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. 


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: 
TBA 
Presenter: 
Bjorn Poonen, MIT 
Date: 
Tuesday, April 21, 2009, Time: 4:30 p.m., Location: Fine Hall 322 


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 


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 


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


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 



