Seminar Calendar
for events the day of Tuesday, April 12, 2011.

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Questions regarding events or the calendar should be directed to Tori Corkery.
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Tuesday, April 12, 2011

Topology Seminar
11:00 am   in 241 Altgeld Hall,  Tuesday, April 12, 2011
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Submitted by mando.
 Marcy Robertson (U. Western Ontario)Spaces of operad structuresAbstract: A multicategory, also known as a colored operad, is simply an operad with many objects. While operads encode families of algebras in a symmetric monoidal category of interest, multicategories encode more complex algebraic structures such as modules, bimodules, and morphisms between algebras. In this talk we focus on studying maps between multicategories enriched in simplicial sets or symmetric spectra. We show that the space of maps between any two multicategories can be computed as the moduli of a certain small category of bimodules. Time permitting, we will discuss applications of this theory to computing invariants of cosimplicial spaces.

Harmonic Analysis and Differential Equations
1:00 pm   in Altgeld Hall 347,  Tuesday, April 12, 2011
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Submitted by berdogan.
 Marius Beceanu (Rutgers)To Be Announced

Number Theory Seminar
1:00 pm   in 241 Altgeld Hall,  Tuesday, April 12, 2011
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Submitted by pppollac.
 Ken Stolarksy (UIUC Math)Variations on a Theme by ChebyshevAbstract: (Please note: there will be a substantial overlap with my 499 talk of March 9.) We survey developments stemming from the Chebyshev polynomials. These interact with many areas including geometry, combinatorics, and number theory. They also suggest some open problems in number theory.

Probability Seminar
2:00 pm   in 347 Altgeld Hall,  Tuesday, April 12, 2011
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Submitted by vzh.
 Misha Chertkov   [email] (Los Alamos Natl Lab)Lagrangian Turbulence: From Theory to AlgorithmsAbstract: In this colloquium-style talk I will review foundations of the theory of particles and fields (Lagrangian and Eulerian) in turbulence, discuss predictions of anomalous scaling in passive scalar turbulence and two-dimensional turbulence (regime of inverse cascade with a condensate), and then explain how the theory helps to design inference and learning algorithms reconstructing velocity field from particle measurements.

Geometry Seminar
2:00 pm   in 243 Altgeld Hall,  Tuesday, April 12, 2011
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Submitted by sba.
 Zoltan Furedi (UIUC)Spheres and boxes enclosing a large fraction of pointsAbstract: We overview a few applications of Turan graph theory in extremal combinatorial geometry. An example of results (and questions): we show that any n point set P (in general position) in the three dimensional space contains a pair x,y\in P such that the open ball B(x,y) with diameter [xy] contains n/30 additional members of P.

Topology Theme Seminar
2:00 pm   in 241 Altgeld Hall,  Tuesday, April 12, 2011
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Submitted by franklan.
 Nat Stapleton (UIUC)The thick subcategory theoremAbstract: We will discuss the thick subcategory theorem and how it relates to the telescope conjecture. We will also sketch a proof of the theorem.

Graph Theory and Combinatorics
3:00 pm   in 241 Altgeld Hall,  Tuesday, April 12, 2011
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Submitted by west.
 Andrew Treglown (University of Birmingham, U.K.)Matchings in 3-uniform hypergraphsAbstract: A theorem of Tutte characterises the graphs that have a perfect matching. In contrast, a result of Garey and Johnson implies that the decision problem whether an r-uniform hypergraph contains a perfect matching is NP-complete for r>2. So it is natural to seek simple sufficient conditions that ensure a perfect matching. Given an r-uniform hypergraph H, the degree of a k-tuple (x1,…,xk) of vertices is the number of edges in H containing x1,…,xk. The minimum vertex degree of H is the minimum of these degrees over all 1-tuples. The minimum codegree of H is the minimum of all the degrees over all (r-1)-tuples of vertices in H. In recent years there has been significant progress on this problem. In 2009, Rödl, Ruciński and Szemerédi characterised the minimum codegree that ensures a perfect matching in an r-uniform hypergraph. Much less is known about minimum vertex degree conditions for perfect matchings in r-uniform hypergraphs. In the case r=3, Hàn, Person, and Schacht asymptotically determined the minimum vertex degree that ensures a perfect matching. In this talk we discuss a result that determines this threshold exactly. (Joint work with Daniela Kühn and Deryk Osthus.)

Ergodic Theory
4:00 pm   in 347 Altgeld Hall,  Tuesday, April 12, 2011
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Submitted by jathreya.
 Howard Masur (University of Chicago)Ergodicity of the Weil-Petersson geodesic flowAbstract: This is joint work with Keith Burns and Amie Wilkinson. Let $\Sigma$ be a surface of genus g with n punctures. We assume 3g-3+n>0. Associated to \Sigma is the Teichmuller space. This is the space of hyperbolic metrics one can put on \Sigma, up to isotopy. The mapping class group acts on the Teichmuller space with quotient, the Riemann moduli space \cal M(\Sigma). There are a number of interesting metrics on \cal M(\Sigma); one of which is the Weil-Petersson metric. It is a Riemannian metric of negative curvature and finite volume but it is not complete. In this talk I will discuss the background on this metric and the following theorem. Theorem: The Weil-Petersson geodesic flow is ergodic on \cal M(\Sigma).