Seminars and Colloquia by Series

Geometric combinatorics, graphs and hypergraphs

Series
Other Talks
Time
Monday, February 25, 2013 - 11:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Gil KalaiHebrew University and Yale University
In the lecture I will describe how several questions in geometric combinatorics translate into questions about graphs and hypergraphs. 1. Borsuk's problem. 2. Tverberg theorem and Tverberg's type problems. Tverberg's theorem asserts that (r-1)(d+1)+1 points in d-space can be divided into r parts whose convex hull intersect. I will discuss situations where less points admit such a partition and connections with graph theory. (For more background, look at this MO question Tverberg partitions with less than (r-1)(d+1)+1 points<http://mathoverflow.net/questions/88718/tverberg-partitions-with-less-than-r-1d11-points> ) 3. Helly type theorems and conditions on induced subgraphs and sub-hypergraphs. I will explain the origin to the following conjecture of Meshulam and me: There is an absolute upper bound for the chromatic number of graphs with no induced cycles of length divisible by 3. 4. Embedding of 2-dimensional complexes and high dimensional minors. I will discuss the following conjecture: A 2-dimensional simplicial complex with E edges and F 2-dimensional faces that can be embedded into 4-space satisfies F < 4e. (For more background see my post *F ≤ 4E*<http://gilkalai.wordpress.com/2013/02/01/f-4e/> )

Georgia Scientific Computing Symposium

Series
Other Talks
Time
Saturday, February 23, 2013 - 08:30 for 8 hours (full day)
Location
Georgia State University
Speaker
Georgia Scientific Computing SymposiumGeorgia State University
The purpose of the GSC Symposium is to provide an opportunity for professors, postdocs, and graduate students in the Atlanta area to meet in an informal setting, to exchange ideas, and to highlight local scientific computing research. Certainly, the symposium is open to whole mathematics and computer sciences communities. The previous meetings were held at Emory University (2009), Georgia Institute of Technology (2010), Emory University (2011) and University of Georgia (2012). The 2013 GSC Symposium will be held at the Georgia State University campus and is organized by Alexandra Smirnova and Vladimir Bondarenko in the Department of Mathematics and Statistics, Georgia State. The following researchers have agreed to give invited plenary lectures: Hao Gao, Department of Mathematics and Computer Science, Department of Radiology and Imaging Sciences, Emory University; Guillermo Goldsztein, School of Mathematics, Georgia Institute of Technology; Yi Jiang, Department of Mathematics and Statistics, Georgia State University; Caner Kazanci, Department of Mathematics, University of Georgia; Brani Vidakovic, College of Engineering, Georgia Institute of Technology. There will be poster sessions. Anyone attending this symposium may present a poster. We especially encourage graduate students and postdocs to use this opportunity displaying their research results. Please register at the Symposium website.

Long paths and cycles in random subgraphs of graphs with large minimum degree

Series
Combinatorics Seminar
Time
Friday, February 22, 2013 - 15:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Choongbum LeeM.I.T.
For a given finite graph G of minimum degree at least k, let G_{p} be a random subgraph of G obtained by taking each edge independently with probability p. We prove that (i) if p \ge \omega/k for a function \omega=\omega(k) that tends to infinity as k does, then G_p asymptotically almost surely contains a cycle (and thus a path) of length at least (1-o(1))k, and (ii) if p \ge (1+o(1))\ln k/k, then G_p asymptotically almost surely contains a path of length at least k. Our theorems extend classical results on paths and cycles in the binomial random graph, obtained by taking G to be the complete graph on k+1 vertices. Joint w/ Michael Krivelevich (Tel Aviv), Benny Sudakov (UCLA).

Resonances for manifolds with hyperbolic ends

Series
Math Physics Seminar
Time
Friday, February 22, 2013 - 15:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
David BorthwickEmory University
Abstract: In this talk we will survey some recent developments in the scattering theory of complete, infinite-volume manifolds with ends modeled on quotients of hyperbolic space. The theory of scattering resonances for such spaces is in many ways parallel to the classical case of eigenvalues on a compact Riemann surface. However, it is only relatively recently that progress has been made in understanding the distribution of these resonances. We will give some introduction to the theory of resonances in this context and try to sketch this recent progress. We will also discuss some interesting outstanding conjectures and present numerical evidence related to these.

The Riemann-Roch theorem for graphs and applications

Series
ACO Student Seminar
Time
Friday, February 22, 2013 - 13:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Matt BakerSchool of Mathematics, Georgia Tech
We will begin by formulating the Riemann-Roch theorem for graphs, due to the speaker and Norine. We will then describe some refinements and applications. Refinements include a Riemann-Roch theorem for tropical curves, proved by Gathmann-Kerber and Mikhalkin-Zharkov, and a Riemann-Roch theorem for metrized complexes of curves, proved by Amini and the speaker. Applications include a new proof by Cools-Draisma-Payne-Robeva of the Brill-Noether theorem in algebraic geometry, a generalization by Amini and the speaker of the Eisenbud-Harris theory of limit linear series, and a new Chabauty-Coleman style bound for the number of rational points on an algebraic curve over the rationals, proved recently by Katz and Zureick-Brown.

Conormals and contact homology VI

Series
Geometry Topology Working Seminar
Time
Friday, February 22, 2013 - 11:30 for 1.5 hours (actually 80 minutes)
Location
Skiles 006
Speaker
John EtnyreGa Tech
In this series of talks I will begin by discussing the idea of studying smooth manifolds and their submanifolds using the symplectic (and contact) geometry of their cotangent bundles. I will then discuss Legendrian contact homology, a powerful invariant of Legendrian submanifolds of contact manifolds. After discussing the theory of contact homology, examples and useful computational techniques, I will combine this with the conormal discussion to define Knot Contact Homology and discuss its many wonders properties and conjectures concerning its connection to other invariants of knots in S^3.

Subcubic triangle-free graphs have fractional chromatic number at most 14/5

Series
Graph Theory Seminar
Time
Thursday, February 21, 2013 - 12:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Zdenek DvorakCharles University and Georgia Tech
Every subcubic triangle-free graph on n vertices contains an independent set of size at least 5n/14 (Staton'79). We strengthen this result by showing that all such graphs have fractional chromatic number at most 14/5, thus confirming a conjecture by Heckman and Thomas. (Joint work with J.-S. Sereni and J. Volec)

Applications of Algebraic Geometry in Statistics

Series
School of Mathematics Colloquium
Time
Thursday, February 21, 2013 - 11:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Mathias DrtonUniversity of Washington
Statistical modeling amounts to specifying a set of candidates for what the probability distribution of an observed random quantity might be. Many models used in practice are of an algebraic nature in thatthey are defined in terms of a polynomial parametrization. The goal of this talk is to exemplify how techniques from computational algebraic geometry may be used to solve statistical problems thatconcern algebraic models. The focus will be on applications in hypothesis testing and parameter identification, for which we will survey some of the known results and open problems.

The Essential Norm of Operators on the Bergman Space.

Series
Analysis Seminar
Time
Wednesday, February 20, 2013 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Brett WickGeorgia Tech
In this talk, we will characterize the compact operators on Bergman spaces of the ball and polydisc. The main result we will discuss shows that an operator on the Bergman space is compact if and only if its Berezin transform vanishes on the boundary and additionally this operator belongs to the Toeplitz algebra. We additionally will comment about how to extend these results to bounded symmetric domains, and for "Bergman-type" function spaces.

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