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NOVEMBER 16 - 18, 2005 |
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Princeton University Graduate Student Seminar |
Topic: |
Szemeredi's Regularity Lemma |
Presenter: |
Po-Shen Loh, Princeton University |
Date: |
Wednesday, November 16, 2005, Time: 12:30 p.m., Location: Fine Hall 224 |
Abstract: |
A famous result of Roth states that for any fixed density $\delta > 0$, for sufficiently large $n$ every $S \subset \{1, 2, \ldots, n\}$ with $|S| \geq \delta n$ contains a 3-term arithmetic progression. While this theorem may seem to have little to do with graph theory, it turns out to have an elegant proof via Szemer\'{e}di's Regularity Lemma---a powerful tool in extremal combinatorics! The Lemma states (roughly speaking) that very large graphs exhibit characteristics found in random graphs, for which many results are known. In this talk, we will introduce the Regularity Lemma, catch a glimpse of the main ideas of its proof, and use it to prove Roth's Theorem. No prior knowledge of graph theory or combinatorics will be required. |
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Statistical Mechanics Seminar |
Topic: |
The Bose Gas, Part I |
Presenter: |
Jakob Yngvason, University of Vienna |
Date: |
Wednesday, November 16, 2005, Time: 2:00 p.m., Location: Jadwin 343 |
Abstract: |
This will be the first of several lectures on the theory of the Bose gas and its various properties at or near absolute zero temperature. |
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Department Colloquium |
Topic: |
Higher Teichmuller theory |
Presenter: |
A. Goncharov, Brown University |
Date: |
Wednesday, November 16, 2005, Time: 4:30 p.m., Location: Fine Hall 314 |
Abstract: |
Let S be a topological surface. The classical Teichmuller space parametrises complex structures on S. Thanks to the Poincare uniformization theorem, it can be viewed (barring few trivial cases) as the moduli space of faithful discrete representations of the fundamental group of S to PGL(2, R).
We develope a more explicit approach to the classical
Teichmuller-Thurston theory. It allows us to show that a big part of this theory admits a generalization where PGL(2, R) is replaced by any semi-simple real split Lie group G with trivial center, e.g. PGL(n, R).
We define the higher Teichmuller space and show that it parametrises faithful discrete representations of the fundamental group of S to G. We find a collection of explicit parametrizations of this space. Using them we define its quantum version, and construct an infinite dimensional unitary representation of the mapping class group of S. This is a joint work with V. Fock |
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Topology Seminar |
Topic: |
Knot Floer homology and doubling |
Presenter: |
Matthew Hedden, Princeton University |
Date: |
Thursday, November 17, 2005, Time: 4:30 p.m., Location: Fine Hall 314 |
Abstract: |
I will discuss the behavior of the knot invariants introduced by Ozsvath and Szabo, and independently by Rasmussen, under certain cases of the satellite operation. The cases I'll discuss will be cabling and Whitehead doubling. I will present formulae for the invariants of a Whitehead doubled or cabled knot in terms of the invariants of the knot you start with. Time permitting, I might say a few words about how one may be able to tie these resultes together using a Floer homology theory for links. |
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Geometric Analysis Seminar |
Topic: |
The complex Monge-Ampere equation and pluripotential theory |
Presenter: |
Slawomir Kolodziej, Jagiellonian University, Poland |
Date: |
Friday, November 18, 2005, Time: 3:00 p.m., Location: Fine Hall 314 |
Abstract: |
Recently the domain of the complex Monge-Ampere operator has been characterized. There are some new existence and stability results for the solutions of the Monge-Ampere equation in hyperconvex domains. Applying the methods of pluripotential theory the Monge-Ampere equation is also studied on compact Kahler manifolds which leads to various generalizations of the Calabi-Yau thaorem. The talk will survey those new developments and discuss open questions. |
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NOVEMBER 21 - 25, 2005 |
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PACM Colloquium |
Topic: |
Seismic tomography: some mathematical aspects |
Presenter: |
Guust Nolet, Geosciences, Princeton University |
Date: |
Monday, November 21, 2005, Time: 4:00 p.m., Location: Fine Hall 214 |
Abstract: |
"Seismic tomography" is the term geophysicists use for a collection of methods to use seismic waves to image the interior of the Earth, much like in a CAT scan. Tomographic imaging has led to important discoveries, such as the observation that ocean floor subducts to the bottom of the Earth's mantle and - more recently - that plumes of hot material rise up from the lower mantle.
In its simplest form, the approximations of geometrical optics are applied to high frequency seismic waves. These waves then follow raypaths and the most useful observable is a travel time along the ray: T = \int ds / v(r). In a typical interpretation, \mathcal O (10^6) data with a signal-to-noise ratio of order 1 are inverted for \mathcal O (10^4-10^5) parameters. The mathematical challenge is mostly that of an adequate regularization of the problem that minimizes artifacts. More accurate travel time measurements can be obtained using cross-correlation on digital seismograms with sensitivity to lower frequency. For such waves a first order perturbation theory is needed to include the effects of wave diffraction around small anomalies. The travel time becomes then frequency dependent, and T is given by a volume integral, with an increase by several orders of magnitude in the numerical effort. Finally, for the lowest frequency waves we use the whole waveform as data. These waveforms can be modeled by summation of normal modes, but the problem is inherently nonlinear and again a ray approximation is needed to render the inverse problem feasible. The challenge is to relax this constraint and take effects of diffraction into account. We shall speculate about the possible role of wavelets in meeting these challenges. |
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Algebraic Geometry Seminar |
Topic: |
Holonomy groups of stable vector bundles |
Presenter: |
János Kollár, Princeton University |
Date: |
Tuesday, November 22, 2005, Time: 4:30 p.m., Location: Fine Hall 322 |
Abstract: |
In analogy with the holonomy groups in differential geometry, we define the notion of holonomy groups for a stable vector bundle. Then we illustrate the principle that either the holonomy is large or there is a clear geometric reason why it should be small. Joint work with Balaji and Larsen. |
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Mathematical Physics Seminar |
Topic: |
Commutation of SLEs |
Presenter: |
Julien Dubedat, Courant Institute |
Date: |
Tuesday, November 22, 2005, Time: 4:30 p.m., Location: Jadwin 343 |
Abstract: |
Schramm-Loewner Evolutions (SLEs) have proved a powerful tool for describing, in the scaling limit, a conformally invariant simple curve. In several instances, such as: percolation, Potts model clusters, and the uniform spanning tree, the curves are initially defined in a discrete setting. We will discuss questions pertaining to the joint law of these curves in the scaling limit. |
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Special Topology Seminar *** Note special date |
Topic: |
TBA |
Presenter: |
Ilya Kapovich, University of Illinois (Urbana/Champaign) |
Date: |
Tuesday, November 22, 2005, Time: 4:30 p.m., Location: Fine Hall 314 |
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Statistical Mechanics Seminar |
Topic: |
Ultraviolet stability and multiscale analysis |
Presenter: |
Giovanni Gallavotti, University of Rome |
Date: |
Wednesday, November 23, 2005, Time: 2:00 p.m., Location: Jadwin 343 |
Abstract: |
An exposition of the key ideas and methods used to establish the lower bound on the ground state energy in two and three dimensional scalar quantum field theories. |
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Discrete Mathematics Seminar |
Topic: |
A book about tic-tac-toe like games |
Presenter: |
Jozsef Beck, Rutgers University |
Date: |
Wednesday, November 23, 2005, Time: 2:15 p.m., Location: Fine Hall 224 |
Abstract: |
See http://www.math.princeton.edu/~bsudakov/beck2005-2006.pdf |
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NOVEMBER 28 - DECEMBER 2, 2005 |
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PACM Colloquium |
Topic: |
Thermally-driven rare events and large deviation theory |
Presenter: |
Maria Reznikoff, Mathematics, Princeton University |
Date: |
Monday, November 28, 2005, Time: 4:00 p.m., Location: Fine Hall 214 |
Abstract: |
Thermal or stochastic effects are prevalent in physical, chemical, and biological systems. Particularly in small systems, noise can overpower the deterministic dynamics and lead to "rare events", events which would never be seen in the absence of noise. One example is the thermally-driven switching of the magnetization in small memory elements. Wentzell-Freidlin large deviation theory is a mathematical tool for studying rare events. It estimates their probability and also the "most likely switching pathway," which is the pathway in phase space by which rare events are most likely to occur. We explain how large deviation theory and concepts from stochastic resonance may be applied to analyze thermally-activated magnetization reversal in the context of the spatially uniform Landau-Lifschitz-Gilbert equations. The time-scales of the experiment are critical. One surprising and physically relevant result is that in multiple-pulse experiments, nonconvential "short-time switching pathways" can dominate. The effect is dramatic: the usual pathway (connected with the Arrhenius-law) underestimates the probability of switching by an exponential factor.
An advantage of the method via large deviation theory is that it generalizes to systems with spatial variation. To discuss the complications and richness that emerge when spatial variation is taken into account, we consider the (simpler) Allen-Cahn equation. In this context, the rare event of interest is phase transformation from u = -1 to u = +1, and the most likely switching pathway is a pathway through function space. A natural reduced problem emerges in the "sharp-interface limit." We give a brief overview of some results (rigorous in d = 1, heuristic in d > 1.)
The first part of the talk is joint work with Bob Kohn and Eric Vanden-Eijnden. The second part includes work that is also joint with Felix Otto and Yoshihiro Tonegawa. |
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Joint Princeton University and Institute for Advanced Study Number Theory Seminar *** Please note special day and time |
Topic: |
Serre's modularity conjecture |
Presenter: |
Chandrashekhar Khare, University of Utah |
Date: |
Monday, November 28, 2005, Time: 4:30 p.m., Location: Fine 314 |
Abstract: |
The title refers to a conjecture that Serre made in the early 1970's, that has proved to be very influential. I will sketch the main ideas of the proof of the level 1 case of Serre's conjecture. If time permits, I will indicate how these ideas can be extended to prove almost all of Serre's conjecture. The latter is joint work with J-P. Wintenberger. |
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Mathematical Physics Seminar |
Topic: |
Isoperimetric inequalities for eigenvalues of the Laplacian in the hyperbolic space H_n |
Presenter: |
Rafael Benguria, Universidad Catolica Santiago, Chile |
Date: |
Tuesday, November 29, 2005, Time: 4:30 p.m., Location: Jadwin 343 |
Abstract: |
I will review several isoperimetric inequalities for eigenvalues of the laplacian on bounded, smooth domains of $H_n$ with Dirichlet boundary conditions. In particular, I will present our recent proof of an isoperimetric inequality for the second Dirichlet eigenvalue. This is joint work with Helmut Linde. |
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Algebraic Geometry Seminar |
Topic: |
A_6 is of general type |
Presenter: |
David Lehavi |
Date: |
Tuesday, November 29, 2005, Time: 4:30 p.m., Location: Fine Hall 322 |
Abstract: |
This is a joint work with S. Grushevsky. We construct new effective geometric divisors on the moduli spaces A_g of principally polarized complex abelian varieties. For g >= 5 we obtain a divisor of slope smaller than the currently known minimum. This in particular allows us to prove that A_g is of general type for g >= 6, thus settling the case of the Kodaira dimension of A_6 - since the 1980s the only dimension for which it has been unknown. |
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Operations Research and Financial Engineering Seminar |
Topic: |
TBA |
Presenter: |
Tom Salisbury, York University |
Date: |
Tuesday, November 29, 2005, Time: 4:30 p.m., Location: Room E-219, Engineering Quad |
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Princeton University Graduate Student Seminar |
Topic: |
The Face Numbers of a Simple Convex Polytope |
Presenter: |
Balin Fleming, Princeton University |
Date: |
Wednesday, November 30, 2005, Time: 12:30 p.m., Location: Fine Hall 224 |
Abstract: |
A polytope $K$ is the convex hull of a finite collection of points in $R^n$. Let $f_i$ be the number of i-dimensional faces of $K$. We ask: what vectors $(f_0, ..., f_{n-1})$ arise as the face numbers of some $n$-dimensional $K$? For simplicial polytopes McMullen proposed a conjecture. This was proved by Billera and Lee (sufficiency) and Stanley (necessity). Stanley's proof uses deep results in algebraic geometry by tying the $f_i$ to the cohomology of an associated toric variety, but later McMullen gave another, more combinatorial proof. We'll discuss a variation on McMullen's argument, by passing from K to its normal fan, combinatorially constructing the cohomology as the ring of continuous conewise polynomial functions, and investigating the structure of this ring. |
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Discrete Mathematics Seminar |
Topic: |
What is known about Frieman's theorem? |
Presenter: |
Ben Green, Clay Institute, University of Bristol and MIT |
Date: |
Wednesday, November 30, 2005, Time: 2:15 p.m., Location: Fine Hall 224 |
Abstract: |
See http://www.math.princeton.edu/~bsudakov/green2005-2006.pdf |
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Department Colloquium |
Topic: |
TBA |
Presenter: |
Yum-Tong Siu, Harvard University |
Date: |
Wednesday, November 30, 2005, Time: 4:30 p.m., Location: Fine Hall 314 |
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Operations Research and Financial Engineering Seminar |
Topic: |
Prospect Eleven: The making, testing, and running of Princeton's entry in the 2005 Darpa Grand Challenge |
Presenter: |
Alain L. Kornhauser and Members of the Prospect Eleven Team |
Date: |
Wednesday, November 30, 2005, Time: 4:30 p.m., Location: Friend Bowl 008 |
Abstract: |
The DARPA Grand Challenge last October 8 was a field test intended to accelerate research and development in autonomous ground vehicles. Prospect Eleven was an "extreme" entry in that it was completely designed, built/modified and tested by a dedicated core of Princeton undergraduates and was only one of two entries that relied on stereo vision. Prospect Eleven performed flawlessly for the first ten miles before succumbing to a software bug. Unsatisfied, part of the team returned to the desert during Fall Break. After changing one line of code, Prospect Eleven autonomously completed what remained of the 132 mile course as well as the more difficult 143 mile 2004 course. The talk will focus on Prospect Eleven's fundamental design concepts, experiences and lessons learned. |
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Operations Research and Financial Engineering Seminar |
Topic: |
Comprehensive Robust Optimization |
Presenter: |
Aharon Ben-Tal, Minerva Optimization Center, Department of Industrial Engineering, Technion University |
Date: |
Thursday, December 1, 2005, Time: 4:30 p.m., Location: Room E-219, Engineering Quad |
Abstract: |
We propose a new methodology for handling optimization problems under uncertainty. Whereas in the standard Robust Optimization (RO) paradigm one seeks decisions ensuring a required performance for all realizations of the data belonging to a given bounded uncertainty set, in the new Comprehensive Robust Optimization (CRO) paradigm one requires also a controlled deterioration in the performance for data outside the uncertainty set. The CRO methodology opens up new possibilities to solve efficiently multi-stage finite horizon uncertain optimization problems, in particular to analyze and synthesize linear controllers for discrete time dynamical systems. |
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Geometric Analysis Seminar |
Topic: |
Quasilinear and Hessian equations with nonlinear source terms |
Presenter: |
Igor Verbitsky, University of Missouri-Columbia |
Date: |
Friday, December 2, 2005, Time: 3:00 p.m., Location: Fine Hall 314 |
Abstract: |
We will give a characterization of removable singularities and present a solution to the existence problem for a class of quasilinear and fully nonlinear PDE with nonlinear source terms. Model problems involve the p-Laplacian or k-Hessian operators. Solutions, possibly singular, are understood in the renormalized (entropy) or viscosity sense. Sharp global and local estimates, and Liouville theorems will be discussed. Our approach is based on sharp forms of Harnack's inequality, nonlinear potential theory, and harmonic analysis methods. This work is joint with Nguyen Cong Phuc. |
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DECEMBER 5 - 9, 2005 |
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PACM Colloquium |
Topic: |
The Boosting Approach to Machine Learning |
Presenter: |
Robert Schapire, Computer Science, Princeton University |
Date: |
Monday, December 5, 2005, Time: 4:00 p.m., Location: Fine Hall 214 |
Abstract: |
Machine learning studies the design of computer algorithms that automatically make predictions about the unknown based on past observations. Often, the goal is to learn to categorize objects into one of a relatively small set of classes. Boosting, one method for solving such learning problems, is a general technique for producing a very accurate classification rule by combining rough and moderately inaccurate "rules of thumb." While rooted in a theoretical framework of machine learning, boosting has been found to perform quite well empirically. After introducing the boosting algorithm AdaBoost, I will explain the underlying theory of boosting, including our explanation of why boosting often does not suffer from overfitting. I also will touch on some of the other theoretical perspectives on boosting, and describe some recent applications and extensions. |
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Algebraic Geometry Seminar |
Topic: |
TBA |
Presenter: |
R. Guralnick, University of Southern California |
Date: |
Tuesday, December 6, 2005, Time: 4:30 p.m., Location: Fine Hall 322 |
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Operations Research and Financial Engineering Seminar |
Topic: |
Consistent prices and face-lifting pricing under transaction costs |
Presenter: |
Paolo Guasoni, Boston University |
Date: |
Tuesday, December 6, 2005, Time: 4:30 p.m., Location: Room E-219, Engineering Quad |
Abstract: |
Consistent Price Systems (CPS) are the counterparts of martingale measures for models with transaction costs, as they guarantee the absence of arbitrage, and allow to characterize superreplication prices of contingent claims. Unfortunately, and especially for non semimartingale models, the explicit calculation of CPS may not be easy.
We first establish the existence of CPS for price processes endowed with their natural filtration from a condition on their topological support, which can often be easily verified. In particular, we see that any two nonatomic continuous processes with full support have the same set of consistent price systems.
We then exploit this result to characterize the superreplication prices of a class of contingent claims as the backward recursive concave envelope (face-lifting) of their payoff. For European calls and puts, we obtain a very simple proof that their prices are trivial.
(Joint work with W. Schachermayer) |
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Princeton University Graduate Student Seminar |
Topic: |
The Prime Number Theorem on the Nose |
Presenter: |
Alex Kontorovich, Columbia University |
Date: |
Wednesday, December 7, 2005, Time: 12:30 p.m., Location: Fine Hall 224 |
Abstract: |
When Gauss was a little boy, he did many wonderful things. One of them was conjecture the asymptotic formula for the number of primes less than some fixed bound, which of course implies an asymptotic formula for the size of the n-th prime. About a century later, his conjecture was answered affirmatively and is now known as the Prime Number Theorem. We will describe (read: handwave) a recent result on how many primes are exactly equal to their average value (we call these "primes on the nose"). No prior knowledge is assumed. |
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Discrete Mathematics Seminar |
Topic: |
TBA |
Presenter: |
Mario Szegedy, Rutgers University |
Date: |
Wednesday, December 7, 2005, Time: 2:15 p.m., Location: Fine Hall 224 |
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Geometric Analysis Seminar |
Topic: |
TBA |
Presenter: |
Pierre Albin, MIT |
Date: |
Friday, December 9, 2005, Time: 3:00 p.m., Location: Fine Hall 314 |
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Special Topology & Geometry Meeting in Honor of Wu-chung Hsiang |
Presenters: |
Tobias Colding, MIT and NYU
Michael Hopkins, Harvard University
Dennis Sullivan, Suny at Stony Brook
Zoltan Szabo, Princeton University |
Date:
Location: |
Saturday, December 10, 2005
A01 McDonnell Hall, Princeton University |
See http://www.math.princeton.edu/HsiangTopologyDay/ for more information. |
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DECEMBER 12 - DECEMBER 16, 2005 |
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PACM Colloquium |
Topic: |
Turbulence and Large-scale Geophysical Circulations |
Presenter: |
Geoff Vallis, Geosciences/Atmospheric & Oceanic Sciences, Princeton University |
Date: |
Monday, December 12, 2005, Time: 4:00 p.m., Location: Fine Hall 214 |
Abstract: |
The large-scale circulation is not only affected but is essentially effected by turbulent flows. This turbulence is not the small-scale turbulence that is (unfortunately) sometimes connoted by the word turbulence, but is turbulence up to the scale of the large-scale flow itself. This is largely two-dimensional, so-called geostrophic turbulence. We will discuss what is known and what is unknown about such flow, the problems of both simulating it and of understanding it, and whether these two are the same. |
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Discrete Mathematics Seminar |
Topic: |
TBA |
Presenter: |
Prasad Tetali, Georgia Tech |
Date: |
Wednesday, December 14, 2005, Time: 2:15 p.m., Location: Fine Hall 224 |
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