Seminars and Colloquia by Series

Circle Orders

Series
Research Horizons Seminar
Time
Wednesday, September 5, 2012 - 13:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
William Trotter – School of Mathematics, Georgia Tech
We survey research spanning more than 20 years on what starts out to be a very simple problem: Representing a poset as the inclusion order of circular disks in the plane. More generally, we can speak of spherical orders, i.e., posets which are inclusion orders of balls in R^d for some d. Surprising enough, there are finite posets which are not sphere orders. Quite recently, some elegant results have been obtained for circle orders, lending more interest to the many open problems that remain.

Sparse and low rank estimation problems

Series
Research Horizons Seminar
Time
Wednesday, April 18, 2012 - 12:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Vladimir Koltchinskii – Georgia Tech
Recently, there has been a lot of interest in estimation of sparse vectors in high-dimensional spaces and large low rank matrices based on a finite number of measurements of randomly picked linear functionals of these vectors/matrices. Such problems are very basic in several areas (high-dimensional statistics, compressed sensing, quantum state tomography, etc). The existing methods are based on fitting the vectors (or the matrices) to the data using least squares with carefully designed complexity penalties based on the $\ell_1$-norm in the case of vectors and on the nuclear norm in the case of matrices. Proving error bounds for such methods that hold with a guaranteed probability is based on several tools from high-dimensional probability that will be also discussed.

Elasto-Capillarity

Series
Research Horizons Seminar
Time
Wednesday, April 11, 2012 - 12:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
John McCuan – Georgia Tech
Classical mathematical capillarity theory has as its foundation variational methods introduced by Gauss. There was a heuristic explanation given earlier by Thomas Young, and his explanations did have quantitative scientific content. Due partially to their simplistic nature, the explanations of Young live on today in engineering textbooks, though in certain cases it has been pointed out that they lead to anomolous predictions (which are effectively avoided in the Gaussian variational framework). I will discuss a fundamentally new direction in mathematical capillarity which is motivated by an effort to harmonize the heuristic and rigorous elements of the theory and has other important applications as well.

Two applications of Riemannian geometry: Thermal stresses in solid mechanics and density preserving maps in machine learning.

Series
Research Horizons Seminar
Time
Wednesday, April 4, 2012 - 12:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Arkadaş Özakın – Georgia Tech Research Institute
I will present two "real life" applications of Riemannian geometry,one in the field of continuum mechanics, another in the field ofmachine learning (nonlinear dimensionality reduction). I will providequick introductions in order to make the talk accessible to anaudience with no background in either field.

From birational invariants to elections

Series
Research Horizons Seminar
Time
Wednesday, March 28, 2012 - 12:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Anton Leykin – Georgia Tech
This talk will traverse several topics in singularity theory, algebraic analysis, complex analysis, algebraic geometry, and statistics. I will outline effective methods to compute the log canonical threshold, a birational invariant of an algebraic variety, as well as its potential statistical applications.

A combinatorial construction of a non-measurable set

Series
Research Horizons Seminar
Time
Wednesday, March 7, 2012 - 12:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Robin Thomas – Georgia Tech
I will present a construction of a non-measurable set using the fundamental fact that a graph with no odd cycles is 2-colorable. That will not take very long, even though I will prove everything from first principles. In the rest of the time I will discuss the Axiom of Choice and some unprovable statements. The talk should be accessible to undergraduates.

Isoperimetric and Functional Inequalities on Discrete Spaces

Series
Research Horizons Seminar
Time
Wednesday, February 22, 2012 - 12:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Prasad Tetali – Georgia Tech
Following exciting developments in the continuous setting of manifolds (and other geodesic spaces), in joint works with various collaborators, I have explored discrete analogs of the interconnection between several functional and isoperimetric inequalities in discrete spaces. Such inequalities include concentration, transportation, modified versions of the logarithmic Sobolev inequality, and (most recently) displacement convexity. I will attempt to motivate and review some of these connections and illustrate with examples. Time permitting, computational aspects of the underlying functional constants and other open problems will also be mentioned.

Train tracks and entropy

Series
Research Horizons Seminar
Time
Wednesday, February 8, 2012 - 12:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Dan Margalit – Georgia Tech
To any self-map of a surface we can associate a real number, called the entropy. This number measures, among other things, the amount of mixing being effected on the surface. As one example, you can think about a taffy pulling machine, and ask how efficiently the machine is stretching the taffy. Using Thurston's notion of a train track, it is actually possible to compute these entropies, and in fact, this is quite easy in practice. We will start from the basic definitions and proceed to give an overview of Thurston's theory. This talk will be accessible to graduate students and advanced undergraduates.

A Survey of Some Results Related to Roth's Theorem

Series
Research Horizons Seminar
Time
Wednesday, January 25, 2012 - 12:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Ernie Croot – School of Mathematics, Georgia Tech
In this talk I will survey some recent results related to Roth's Theorem on three-term arithmetic progressions. The basic problem in this area is to determine the largest subset S of the integers in {1,...,n} containing no triple of the form x, x+d, x+2d. Roth showed back in the 1950's that the largest such set S has size o(n), and over the following decades his result has been considerably improved upon.

FINITE TIME DYNAMICS: the first steps and outlook.

Series
Research Horizons Seminar
Time
Wednesday, January 18, 2012 - 12:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Leonid A. Bunimovich – Georgia Tech
It is well known that typically equations do not have analytic (expressed by formulas) solutions. Therefore a classical approach to the analysis of dynamical systems (from abstract areas of Math, e.g. the Number theory to Applied Math.) is to study their asymptotic (when an independent variable, "time", tends to infinity) behavior. Recently, quite surprisingly, it was demonstrated a possibility to study rigorously (at least some) interesting finite time properties of dynamical systems. Most of already obtained results are surprising, although rigorously proven. Possible PhD topics range from understanding these (already proven!) surprises and finding (and proving) new ones to numerical investigation of some systems/models in various areas of Math and applications, notably for dynamical analysis of dynamical networks. I'll present some visual examples, formulate some results and explain them (when I know how).

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