Seminar Calendar
for events the day of Tuesday, March 1, 2011.

.
events for the
events containing

Questions regarding events or the calendar should be directed to Tori Corkery.
    February 2011            March 2011             April 2011
Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa
1  2  3  4  5          1  2  3  4  5                   1  2
6  7  8  9 10 11 12    6  7  8  9 10 11 12    3  4  5  6  7  8  9
13 14 15 16 17 18 19   13 14 15 16 17 18 19   10 11 12 13 14 15 16
20 21 22 23 24 25 26   20 21 22 23 24 25 26   17 18 19 20 21 22 23
27 28                  27 28 29 30 31         24 25 26 27 28 29 30



Tuesday, March 1, 2011

Topology Seminar
11:00 am   in 241 Altgeld Hall,  Tuesday, March 1, 2011
 Del Edit Copy
Submitted by mando.
 HIsham Sati (University of Maryland)M-theory and elliptic cohomology

Joint Ergodic Theory/Differential Geometry
1:00 pm   in 243 Altgeld Hall,  Tuesday, March 1, 2011
 Del Edit Copy
Submitted by jathreya.
 Steve Lalley (University of Chicago)Self-Intersections of Closed Curves and Closed Geodesics on Negatively Curved SurfacesAbstract: Fix a compact surface M with a Riemannian metric of constant curvature -1. From among all closed geodesics on M of length no greater than x, choose one at random; let L be its length, and let N be the number of its transversal self-intersections. A simple argument shows that as x gets large N / x^2 converges almost surely to a constant K. How big are the fluctuations of N around the mean? We will argue that they are of order x, and that [ N - K L^2 ]/x converges in distribution, most likely not to a Gaussian distribution. On the other hand, if the closed geodesic is instead chosen at random from among all closed geodesics on M represented by (conjugacy classes of) elements in the fundamental group with word length (in the natural generators) no larger than x, then fluctuations of N are of order x^(3/2), and the limit distribution is Gaussian. Part of this is joint work with Moira Chas.

Logic Seminar
1:00 pm   in 345 Altgeld Hall,  Tuesday, March 1, 2011
 Del Edit Copy
Submitted by phierony.
 Philipp Hieronymi (UIUC)An analogue of the Baire Category TheoremAbstract: I will show that every definably complete expansion of an ordered field satisfies an analogue of the Baire Category Theorem. For a preprint, see http://arxiv.org/abs/1101.1194 . This is the first of two lectures. The second one will be on Friday March 4 at 4pm.

Geometry Seminar
2:00 pm   in 243 Altgeld Hall,  Tuesday, March 1, 2011
 Del Edit Copy
Submitted by sba.
 Gregory Galperin (Eastern Illinois University)Making invisible objectsAbstract: In my talk, I will show some examples of "invisible geometric objects". This means that light bends around an object, causing it to become as if it were invisible. When designing such objects, the billiard law of reflection will play a crucial role. The main example in my talk will concern the billiard reflection for ellipses and hyperbolas. To prove that the reflection in my design is indeed billiard, it is necessary to prove a tricky lemma about an angle bisector of a triangle. If time permits, I will provide a proof for this lemma. Everyone (especially students!) are invited to visit the talk. No prior knowledge is required; all necessary definitions and explanations will be given during the talk.

Probability Seminar
2:00 pm   in 347 Altgeld Hall,  Tuesday, March 1, 2011
 Del Edit Copy
Submitted by rsong.
 Prof. Krishna Athreya (Iowa State University)Coalescence in Galton-Watson branching treesAbstract: Pick two individuals at random by srswor in the nth generation of a Galton-Watson branching tree and trace their family lines back in time till they meet. Call that generation Xn. In this talk we discuss the limit behaviour of the distribution of Xn for the four cases:1

Study Seminar in Geometry and Analysis
3:00 pm   in 347 Altgeld Hall,  Tuesday, March 1, 2011
 Del Edit Copy
Submitted by jathreya.
 Piotr Przytycki (UIUC)Shalom-Tao arguments for Gromov's polynomial growth theoremAbstract: We give an outline of the proof of Shalom-Tao of the Gromov theorem on groups of polynomial growth. The proof follows the approach of Kleiner, but avoids using the Tits Alternative and energy arguments. We also give an account of Shalom-Tao effective version of Gromov theorem.

Graph Theory and Combinatorics
3:00 pm   in 241 Altgeld Hall,  Tuesday, March 1, 2011
 Del Edit Copy
Submitted by west.
 Ping Hu (UIUC Math)Chromatic thresholds of hypergraphsAbstract: Let F be a family of graphs. The chromatic threshold of F is the infimum of the values c such that the subfamily of F consisting of graphs G with minimum degree at least c|V(G)| has bounded chromatic number. This was defined by Andrásfai, Erdős and Sós in 1974 for Kl-free graphs. Łuczak and Thommassé showed how to use Vapnik-Chervonenkis dimension to give a new short proof that the chromatic threshold of triangle-free graphs is at most 1/3. They also generalized VC-dimension to paired VC-dimension and used it to give a new proof that C5-free graphs have chromatic threshold 0. We generalize the concept for hypergraphs. Besides surveying results for graphs, this talk will focus on constructions providing lower bounds on chromatic threshold for various hypergraphs. Our constructions are based on an idea of Hajnal, using the Kneser graph. (Joint work with József Balogh, Jane Butterfield, John Lenz, and Dhruv Mubayi.)