Seminars and Colloquia Schedule

Symplectic topology of rational blowdowns

Series
Geometry Topology Seminar
Time
Monday, October 29, 2012 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Yankı Lekili – University of Cambridge & Simons Center
We study some finite quotients of the A_n Milnor fibre which coincide with the Stein surfaces that appear in Fintushel and Stern's rational blowdown construction. We show that these Stein surfaces have no exact Lagrangian submanifolds by using the already available and deep understanding of the Fukaya category of the A_n Milnor fibre coming from homological mirror symmetry. On the contrary, we find Floer theoretically essential monotone Lagrangian tori, finitely covered by the monotone tori that we studied in the A_n Milnor fibre. We conclude that these Stein surfaces have non-vanishing symplectic cohomology. This is joint work with M. Maydanskiy.

Variational method for speckle reduction in coherent imaging systems

Series
Applied and Computational Mathematics Seminar
Time
Monday, October 29, 2012 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Hyenkyun Woo – Georiga Tech CSE –
The fully developed speckle(multiplicative noise) naturally appears in coherent imaging systems, such as synthetic aperture radar imaging systems. Since the speckle is multiplicative, it makes difficult to interpret observed data. In this talk, we introduce total variation based variational model and convex optimization algorithm(linearized proximal alternating minimization algorithm) to efficiently remove speckle in synthetic aperture radar imaging systems. Numerical results show that our proposed methods outperform the augmented Lagrangian based state-of-the-art algorithms.

Curvature and (contact) topology

Series
Research Horizons Seminar
Time
Wednesday, October 31, 2012 - 12:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
John Etnyre – Georgia Tech, School of Math
Contact geometry is a beautiful subject that has important interactions with topology in dimension three. In this talk I will give a brief introduction to contact geometry and discuss its interactions with Riemannian geometry. In particular I will discuss a contact geometry analog of the famous sphere theorem and more generally indicate how the curvature of a Riemannian metric can influence properties of a contact structure adapted to it.

Stein fillings of planar open books.

Series
Geometry Topology Student Seminar
Time
Wednesday, October 31, 2012 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 006.
Speaker
Amey Kaloti – Georgia Tech
The goal of this talk is to study geography and classification problem for Stein fillings of contact structures supported by planar open books. In the first part we will prove that for contact structures supported by planar open books Stein fillings have a finite geography. In the second part we will outline an approach to classify Stein fillings of manifolds supported by planar open books.

Coupled diffusions and systemic risk

Series
Mathematical Finance/Financial Engineering Seminar
Time
Wednesday, October 31, 2012 - 15:05 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
J.-P. Fouque – Department of Statistics and Applied Probability, University of California Santa Barbara,

Hosted by Christian Houdre and Liang Peng

We present a simple model of diffusions coupled through their drifts in a way that each component mean-reverts to the mean of the ensemble. In particular, we are interested in the number of components reaching a "default" level in a given time. This coupling creates stability of the system in the sense that there is a large probability of "nearly no default". However, we show that this "swarming" behavior also creates a small probability that a large number of components default corresponding to a "systemic risk event". The goal is to illustrate systemic risk with a toy model of lending and borrowing banks, using mean-field limit and large deviation estimates for a simple linear model. In the last part of the talk we will show some recent work with Rene Carmona on a "Mean Field Game" version of the previous model and the effects of the game on stability and systemic risk.

Explorations in Burgers turbulence: integrability and exact solutions

Series
Stochastics Seminar
Time
Thursday, November 1, 2012 - 15:05 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Ravi Srinivasan – University of Texas at Austin
Burgers turbulence is the study of Burgers equation with random initial data or forcing. While having its origins in hydrodynamics, this model has remarkable connections to a variety of seemingly unrelated problems in statistics, kinetic theory, random matrices, and integrable systems. In this talk I will survey these connections and discuss the crucial role that exact solutions have played in the development of the theory.

shadowing

Series
Dynamical Systems Working Seminar
Time
Thursday, November 1, 2012 - 16:30 for 1 hour (actually 50 minutes)
Location
Skiles 06
Speaker
Rafael de la Llave – Georgia Tech
"Shadowing" in dynamical systems is the property that an approximate orbit (satisfying some additional properties) can be followed closely by a true orbit. This is a basic tool to construct complicated orbits since construction of approximate orbits is sometimes easier. It is also important in applications since numerical computations produce only approximate orbits and it requires an extra argument to show that the approximate ofbit produced by the computer corresponds to a real orbit. There are three standard mechanicsms for shadowing: Hyperbolicity, topological methods, shadowing of minimizers. We will present hyperbolicity.

Efficient active and semi-supervised algorithms for Two-sided Disjunctions

Series
ACO Student Seminar
Time
Friday, November 2, 2012 - 13:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Steven Ehrlich – College of Computing, Georgia Tech
We present a new algorithm learning the class of two-sided disjunctions in semi-supervised PAC setting and in the active learning model. These algorithms are efficient and have good sample complexity. By exploiting the power of active learning we are able to find consistent, compatible hypotheses -- a task which is computationally intractable in the semi-supervised setting.

Prospective Student Day

Series
Other Talks
Time
Friday, November 2, 2012 - 14:00 for 3.5 hours
Location
Skiles 006
Speaker
John Etnyre – School of Mathematics, Georgia Tech
This will be an afternoon event, and light refreshments will be served. Students will visit our school, hear about graduate degree options available in the School of Mathematics, learn about requirements for admission, as well as meet our faculty and current graduate students. Check the schedule of events.

Tiling simply connected regions by rectangles

Series
Combinatorics Seminar
Time
Friday, November 2, 2012 - 15:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Jed Yang – Math, UCLA –

Given a set of tiles on a square grid (think polyominoes) and a region, can we tile the region by copies of the tiles? In general this decision problem is undecidable for infinite regions and NP-complete for finite regions. In the case of simply connected finite regions, the problem can be solved in polynomial time for some simple sets of tiles using combinatorial group theory; whereas the NP-completeness proofs rely heavily on the regions having lots of holes. We construct a fixed set of rectangular tiles whose tileability problem is NP-complete even for simply connected regions.This is joint work with Igor Pak.

Atlanta Lecture Series in Combinatorics and Graph Theory VII

Series
Other Talks
Time
Saturday, November 3, 2012 - 13:00 for 1 hour (actually 50 minutes)
Location
Emory University
Speaker
Featured Speaker Penny Haxell – University of Waterloo
Emory University, the Georgia Institute of Technology and Georgia State University, with support from the National Security Agency and the National Science Foundation, are hosting a series of 9 mini-conferences from November 2010 - April 2013. The seventh in the series will be held at Emory University on November 3-4, 2012. This mini-conference's featured speaker is Dr. Penny Haxell, who will give two one-hour lectures. Additionally, there will be five one-hour talks and seven half-hour talks given by other invited speakers. See all titles, abstracts, and schedule.