Seminar Calendar
for events the day of Tuesday, September 14, 2010.

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Questions regarding events or the calendar should be directed to Tori Corkery. 
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Tuesday, September 14, 2010

Topology Seminar
11:00 am   in 241 Altgeld Hall,  Tuesday, September 14, 2010
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Submitted by rezk.
Charles Rezk (UIUC Math)
Subgroups of elliptic curves
Abstract: I will talk about the moduli of subgroups of elliptic curves, following the treatment of Katz-Mazur. Then I'll describe some interesting relationships between the moduli of subgroups of various kinds; if time permits, I'll talk about what this has to do with algebraic topology.

Number Theory
1:00 pm   in 241 Altgeld Hall,  Tuesday, September 14, 2010
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Submitted by berndt.
Harold Diamond (UIUC)
Two Results on Beurling Generalized Numbers
Abstract: A sequence of Beurling generalized primes (g-primes) is an increasing, unbounded sequence of numbers exceeding 1. The semigroup it generates under multiplication is called the associated sequence of g-integers. No additive structure is assumed for g-integers. A survey will be given of two major theorems in the area: Kahane's L^2 proof of the prime number theorem and the DMV oscillation theorem.

Logic seminar
1:00 pm   in Altgeld Hall 345,  Tuesday, September 14, 2010
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Submitted by vddries.
Lou van den Dries (UIUC Math)
The o-minimal Hauptvermutung
Abstract: This is the first of several talks on Shiota's proof of the o-minimal Hauptvermutung which he has circulated in a preprint. This first talk will discuss the general background. The second talk will be on Friday September 17.

Graduate Geometry and Topology Seminar
2:00 pm   in 345 Altgeld Hall,  Tuesday, September 14, 2010
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Submitted by lukyane2.
Nat Stapleton (UIUC)
Stacks and Descent
Abstract: We will motivate the definition of a stack providing all of the necessary prerequisites. We will also discuss several examples and generalizations.

Study Seminar in Analysis and Geometry
3:00 pm   in 347 Altgeld Hall,  Tuesday, September 14, 2010
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Submitted by jmmackay.
John Mackay (Department of Mathematics, University of Illinois)
The Heisenberg group does not admit a bi-Lipschitz embedding into L^1
Abstract: We will discuss the recent result of Cheeger and Kleiner which shows that the Heisenberg group (with its natural Carnot-Caratheodory metric) does not admit a bi-Lipschitz embedding into the Banach space L^1. (This result gives a natural counterexample to the Goemans-Linial conjecture regarding the Sparsest Cut problem in computer science.)
The proof involves ideas including: differentiation with Banach space targets, cut metrics, and the geometry of the Heisenberg group. All these notions will be defined and explained.

[This seminar meets from 3-4:50 with a break halfway when you can escape.]

Graph Theory and Combinatorics
3:00 pm   in 241 Altgeld Hall,  Tuesday, September 14, 2010
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Submitted by west.
Hehui Wu (UIUC Math)
Decomposition of sparse graphs into forests and a graph with bounded degree
Abstract: For d≥k+1, we prove a sharp sparseness condition for decomposability into k forests and a graph having maximum degree at most d. Consequences include that every graph with fractional arboricity at most k+d/(k+d+1) has such a decomposition. For d≤k+1, we prove that every graph with fractional arboricity at most k+d/(2k+2) decomposes into k+1 forests having maximum degree at most d. This result implies the Nine Dragon Tree (NDT) Conjecture for the case k=d+1. This is joint work with Seog-jin Kim, Alexandr V. Kostochka, Douglas B. West, and Xuding Zhu.