## Seminars and Colloquia by Series

Series: Other Talks
Thursday, January 28, 2010 - 11:00 , Location: Skiles 249 , Provost Gary Schuster , President's Office, Georgia Tech , Organizer:
Series: Other Talks
Monday, December 7, 2009 - 08:00 , Location: University of Alabama, Birmingham , , University of Alabama, Birmingham , Organizer: John McCuan

The Southeast Geometry Seminar is a series of semiannual one-day events focusing on geometric analysis. These events are hosted in rotation by the following institutions:

• The University of Alabama at Birmingham
• The Georgia Institute of Technology
• Emory University
• The University of Tennessee Knoxville

The following five speakers will give presentations on topics that include geometric analysis, and related fields, such as partial differential equations, general relativity, and geometric topology.

• Natasa Sesum (U Penn)
• Alexandru Ionescu (U Wisconsin)
• Sergiu Klainerman (Princeton U)
• Alex Freire (U Tennessee Knoxville)
• Christian Hainzl (UAB)

A poster session will be hosted.  There will also be an evening public lecture by plenary speaker Sergiu Klainerman entitled The Mathematical Magic of Black Holes.

Series: Other Talks
Friday, December 4, 2009 - 15:00 , Location: Skiles 168 , Michelle Delcourt and Leo Chen , School of Mathematics, Georgia Tech , Organizer: Matt Baker

Leo Chen: The Shape and Stability of a Flexible Sheet in a von Karman Vortex Street

Michelle Delcourt: Dessin and Manturov bracket shuffles
In this talk we will explore the connections between knot theory and combinatorics. Links are related to Grothendieck's dessins d'enfants. Cartographic one-vertex dessins can be represented by chord diagrams. The diagrams can be recorded as "words" using a finite alphabet (k-bracket parenthesis system). Many combinatorial objects are related to these Manturov bracket structures.

Series: Other Talks
Wednesday, December 2, 2009 - 13:00 , Location: Skiles 255 , Kangkang Wang , School of Mathematics, Georgia Tech , Organizer: Matt Baker
We will present a sheaf-theoretic proof of the Riemann-Roch theorem for projective nonsingular curves.
Series: Other Talks
Wednesday, November 25, 2009 - 13:00 , Location: Skiles 255 , Matt Baker , School of Mathematics, Georgia Tech , Organizer: Matt Baker
We will state Serre's fundamental finiteness and vanishing results for the cohomology of coherent sheaves on a projective algebraic variety. As an application, we'll prove that the constant term of the Hilbert Polynomial does not depend on the projective embedding, a fact which is hard to understand using classical (non-cohomological) methods.
Series: Other Talks
Wednesday, November 18, 2009 - 13:00 , Location: Skiles 255 , Doug Ulmer , Ga Tech , Organizer: John Etnyre
In the 60s, Grothendieck had the remarkable idea of introducing a new kind of topology where open coverings of X are no longer collections of subsets of X, but rather certain maps from other spaces to X.  I will give some examples to show why this is reasonable and what one can do with it.
Series: Other Talks
Wednesday, November 11, 2009 - 13:00 , Location: Skiles 255 , Farbod Shokrieh , Ga Tech , Organizer: John Etnyre
We will show that the construction of derived functors satisfy the required universal property.I will then show that, for any ringed space, the abelian category of all sheaves of Modules has enough injectives. We achieve this by first characterizing injective abelian groups (Baer's theorem).The relation with Cech cohomology will also be studied. In particular, I will show that the first Cech and Grothendieck sheaf cohomology groups are isomorphic for any topological space (without using spectral sequences).
Series: Other Talks
Friday, November 6, 2009 - 15:00 , Location: Skiles 154 , Sergio Almada , Georgia Tech , Organizer:
We consider the Stochastic Differential Equation $dX_\epsilon=b(X_\epsilon)dt + \epsilon dW$ . Given a domain D, we study how the exit time and the distribution of the process at the time it exits D behave as \epsilon goes to 0. In particular, we cover the case in which the unperturbed system $\frac{d}{dt}x=b(x)$ has a unique fixed point of the hyperbolic type. We will illustrate how the behavior of the system is in the linear case. We will remark how our results give improvements to the study of systems admitting heteroclinic or homoclinic connections.  We will outline the general proof in two dimensions that requires normal form theory from differential equations. For higher dimensions, we introduce a new kind of non-smooth stochastic calculus.
Series: Other Talks
Wednesday, November 4, 2009 - 13:00 , Location: Skiles 255 , Farbod Shokrieh , Ga Tech , Organizer: John Etnyre
We will continue the study of derived functors between abelian categories. I will show why injective objects are needed for the construction. I will then show that, for any ringed space, the abelian category of all sheaves of Modules has enough injectives. The relation with Cech cohomology will also be studied.
Series: Other Talks
Wednesday, October 28, 2009 - 11:00 , Location: ISyE Executive Classroom , Pushkar Tripathi , ACO, Computing Science and Systems, Georgia Tech , Organizer:

Organizer: Daniel Dadush, ACO Student, ISyE

Applications in complex systems such as the Internet have spawned recent interest in studying situations involving multiple agents with their individual cost or utility functions. We introduce an algorithmic framework for studying combinatorial problems in the presence of multiple agents with submodular cost functions. We study several fundamental covering problems (Vertex Cover, Shortest Path, Perfect Matching, and Spanning Tree) in this setting and establish tight upper and lower bounds for the approximability of these problems. This talk is based on joint work with Gagan Goel, Chinmay Karande and Wang Lei. This is a joint ACO/DOS seminar, so please come a little early for pizza and refreshments sponsored by ACO.