Seminars and Colloquia Schedule

Large-Scale Inverse Problems in Imaging

Series
Applied and Computational Mathematics Seminar
Time
Monday, March 1, 2010 - 13:00 for 1 hour (actually 50 minutes)
Location
Skiles 255
Speaker
James G. Nagy – Mathematics and Computer Science, Emory University
Large-scale inverse problems arise in a variety of importantapplications in image processing, and efficient regularization methodsare needed to compute meaningful solutions. Much progress has beenmade in the field of large-scale inverse problems, but many challengesstill remain for future research. In this talk we describe threecommon mathematical models including a linear, a separable nonlinear,and a general nonlinear model. Techniques for regularization andlarge-scale implementations are considered, with particular focusgiven to algorithms and computations that can exploit structure in theproblem. Examples will illustrate the properties of these algorithms.

Two Weight inequalities for Hilbert Transform

Series
Analysis Working Seminar
Time
Monday, March 1, 2010 - 13:00 for 1 hour (actually 50 minutes)
Location
Skiles 269
Speaker
Michael Lacey – GT
We start the proof of arXiv:1001.4043, which characterizes the two weight inequality for the Hilbert transform. This session will be devoted to necessity of the Poisson A_2 condition and the Energy Condition. Joint work with Ignacio Uriate-Tuero, and Eric Sawyer.

Explicit points on the Legendre elliptic curve

Series
Algebra Seminar
Time
Monday, March 1, 2010 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 171
Speaker
Doug Ulmer – Georgia Tech
It turns out to be very easy to write down interesting points on the classical Legendre elliptic curve y^2=x(x-1)(x-t) and show that they generate a group of large rank. I'll give some basic background, explain the construction, and discuss related questions which would make good thesis projects (both MS and PhD).

How to Partition a Mixed Phase Space - with Applications to Atomic Physics

Series
Other Talks
Time
Monday, March 1, 2010 - 15:00 for 1 hour (actually 50 minutes)
Location
Howey N110
Speaker
Kevin Mitchell – University of California, Merced
Hamiltonian systems typically exhibit a mixture of chaos and regularity, complicating any scheme to partition phase space and extract a symbolic description of the dynamics. In particular, the dynamics in the vicinity of stable islands can exhibit extremely complicated topology. We present an approach to extracting symbolic dynamics in such systems using networks of nested heteroclinic tangles-- fundamental geometric objects that organize phase space transport. These tangles can be used to progressively approximate the behavior in the vicinity of stable island chains. The net result is a symbolic approximation to the dynamics, and an associated phase-space partition, that includes the influence of stable islands. The utility of this approach is illustrated by examining two applications in atomic physics -- the chaotic escape of ultracold atoms from an atomic trap and the chaotic ionization of atoms in external fields.

Two weight inequality for the Hilbert transform

Series
Research Horizons Seminar
Time
Tuesday, March 2, 2010 - 12:00 for 1 hour (actually 50 minutes)
Location
Skiles 255
Speaker
Michael Lacey – School of Math, Georgia Tech

Hosted by: Huy Huynh and Yao Li

The Hilbert transform is a foundational transform, with deep connections to electrical charge, and analyticity. The `two weight inequality for the Hilbert transform' concerns the most general setting in which the Hilbert transform admits a (weighted) L^2 inequality. We will give a couple of (surprising?) ways that this question arises. And we will indicate the surprise that is behind the recent description of all setting in which the two weight inequality holds.

Global solutions for the Navier-Stokes equations with some large initial data

Series
PDE Seminar
Time
Tuesday, March 2, 2010 - 15:05 for 1 hour (actually 50 minutes)
Location
Skiles 255
Speaker
Marius Paicu – Université Paris-Sud
We consider the three dimensional Navier-Stokes equations with a large initial data and we prove the existence of a global smooth solution. The main feature of the initial data is that it varies slowly in the vertical direction and has a norm which blows up as the small parameter goes to zero. Using the language of geometrical optics, this type of initial data can be seen as the ``ill prepared" case. Using analytical-type estimates and the special structure of the nonlinear term of the equation we obtain the existence of a global smooth solution generated by this large initial data. This talk is based on a work in collaboration with J.-Y. Chemin and I. Gallagher and on a joint work with Z. Zhang.

Two weight Inequality for Hilbert transform

Series
Analysis Working Seminar
Time
Wednesday, March 3, 2010 - 13:46 for 1 hour (actually 50 minutes)
Location
Skiles 269
Speaker
Michael Lacey – GT
We start the sufficiency proof of arXiv:1001.4043, which characterizes the two weight inequality for the Hilbert transform. This session will be devoted to the martingale methods employed. Joint work with Ignacio Uriate-Tuero, and Eric Sawyer.

For compactly supported measures, universality holds in measure

Series
Analysis Seminar
Time
Wednesday, March 3, 2010 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 269
Speaker
Doron Lubinsky – Georgia Tech
Let mu be a measure with compact support, with orthonormal polynomials {p_{n}} and associated reproducing kernels {K_{n}}. We show that bulk universality holds in measure in {x:mu'(x)>0}. The novelty is that there are no local or global conditions on the measure. Previous results have required regularity as a global condition, and a Szego condition as a local condition.As a consequence, for a subsequence of integers, universality holds for a.e. x. Under additional conditions on the measure, we show universality holds in an L_{p} sense for all finite p>0.

Inverse scattering and wave-equation tomography - Imaging Earth's deep interior

Series
School of Mathematics Colloquium
Time
Thursday, March 4, 2010 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 269
Speaker
Maarten V. de Hoop – Department of Mathematics, Purdue University
Much research in modern, quantitative seismology is motivated -- on the one hand -- by the need to understand subsurface structures and processes on a wide range of length scales, and -- on the other hand -- by the availability of ever growing volumes of high fidelity digital data from modern seismograph networks or multicomponent acquisition systems developed for hydro-carbon exploration, and access to increasingly powerful computational facilities. We discuss (elastic-wave) inverse scattering of reflection seismic data, wave-equation tomography, and their interconnection using techniques from microlocal analysis and applied harmonic analysis. We introduce a multi-scale approach and present a framework of partial reconstruction in connection with limited boundary acquisition geometry. The formation of caustics leads to one of the complications which will be discussed. We illustrate various aspects of this research program with examples from global seismology and mineral physics coupled to thermo-chemical convection.

Segmentation with hidden Markov model

Series
Stochastics Seminar
Time
Thursday, March 4, 2010 - 15:00 for 1 hour (actually 50 minutes)
Location
Skiles 269
Speaker
Dr Juri Lember – Tartu University, Estonia –
Abstract: We consider the hidden Markov model, where the dynamic of theprocess is modelled by a latent Markov chain Y and the observations X aresuch that: 1) given the realization of Y, the observations areindependent; 2) the distribution of the i-th observations (X_i) depends onthe i-th element of the Y (Y_i), only.The segmentation problem consists of estimating the underlying realization(path) of Y given the n observation. Usually the realization with maximumlikelihood, the so called Viterbi alignment is used. On the other hand, itis easy to see that the Viterbi alignment does not minimize the expectednumber of misclassification errors.We consider the segmentation problem in the framework of statisticallearning. This unified risk-based approach helps to analyse many existingalignments as well as defining many new ones. We also study theasymptotics of the risks and infinite alignments.

The geometry of dissipative evolution equation

Series
SIAM Student Seminar
Time
Friday, March 5, 2010 - 13:00 for 1 hour (actually 50 minutes)
Location
Skiles 255
Speaker
Yao Li – Georgia Tech
Last semester, I reviewed the relation between dynamical system, Fokker-Planck equation and thermodynamics (free energy and Gibbs distribution). This time let's go further. I will review the geometric properties of a kind of dissipative evolution equations. I will explain why this kind of evolutionary equations (Fokker-Planck equation, nonlinear Fokker-Planck equation, Porous medium equation) are the gradient flow of some energy function on a Riemannian manifold -- 2-Wasserstein metric space.

Introduction to the AJ Conjecture, Part II

Series
Geometry Topology Working Seminar
Time
Friday, March 5, 2010 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 269
Speaker
Anh Tran – Georgia Tech
I will explain another approach to the conjecture and in particular, study it for 2-bridge knots. I will give the proof of the conjecture for a very large class of 2-bridge knots which includes twist knots and many more (due to Le). Finally, I will mention a little bit about the weak version of the conjecture as well as some relating problems.

The Quasi-Randomness of Hypergraph Cut Properties

Series
Combinatorics Seminar
Time
Friday, March 5, 2010 - 15:00 for 1 hour (actually 50 minutes)
Location
Skiles 255
Speaker
Asaf Shapira – School of Mathematics, Georgia Tech
Let a_1,...,a_k satisfy a_1+...+a_k=1 and suppose a k-uniform hypergraph on n vertices satisfies the following property; in any partition of its vertices into k sets A_1,...,A_k of sizes a_1*n,...,a_k*n, the number of edges intersecting A_1,...,A_k is the number one would expect to find in a random k-uniform hypergraph. Can we then infer that H is quasi-random? We show that the answer is negative if and only if a_1=...=a_k=1/k. This resolves an open problem raised in 1991 by Chung and Graham [J. AMS '91]. While hypergraphs satisfying the property corresponding to a_1=...=a_k=1/k are not necessarily quasi-random, we manage to find a characterization of the hypergraphs satisfying this property. Somewhat surprisingly, it turns out that (essentially) there is a unique non quasi-random hypergraph satisfying this property. The proofs combine probabilistic and algebraic arguments with results from the theory of association schemes. Joint work with Raphy Yuster

Southeast SIAM Student Conference

Series
Other Talks
Time
Saturday, March 6, 2010 - 09:00 for 8 hours (full day)
Location
Skiles 269
Speaker
SIAM Student Conference – School of Mathematics, Georgia Tech
The SIAM Student Chapter at Georgia Tech will be hosting this conference. It is an extension of the ACES Workshop which has been held yearly by the universities of Auburn, Clemson, Emory, and South Carolina since 2006. As with the ACES Workshop, this conference is an opportunity for graduate students to present their research in applied mathematics and related fields as well as to meet with other graduate students from different universities and departments. See the conference site for more details.

Mathemagics - the art of mental calculation

Series
Other Talks
Time
Saturday, March 6, 2010 - 19:00 for 1 hour (actually 50 minutes)
Location
Instructional Center Room 103
Speaker
Art Benjamin – Harvey Mudd College
The speaker has combined his two loves to create a dynamic presentation called "Mathemagics," suitable for all audiences, where he demonstrates and explains his secrets for performing rapid mental calculations faster than a calculator. Reader's Digest calls him "America's Best Math Whiz". He has presented his high energy talk for thousands of groups throughout the world. This event is free but reservations are required. The signup form will be available before 5pm on February 25. See details about the speaker.