Department of

# Mathematics

Seminar Calendar
for events the day of Thursday, November 17, 2005.

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events for the
events containing

Questions regarding events or the calendar should be directed to Tori Corkery.
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Thursday, November 17, 2005

12:00 pm in 464 Loomis,Thursday, November 17, 2005

#### Questions about open and closed string theories suggested by twisted K-theory and elliptic cohomology

###### Matt Ando (UIUC Math)

1:00 pm in 241 Altgeld Hall,Thursday, November 17, 2005

#### Nonlinear recurrences with rational generating functions, and certain number triangles

###### Ken Stolarsky (UIUC Math)

Abstract: There is a notable equivalence between rational generating functions, exponential polynomials, and linear recurrences. We show that some nonlinear recurrences also have rational generating functions, and that they are connected with certain number triangles that have divisibility properties.

1:00 pm in Altgeld Hall 347,Thursday, November 17, 2005

#### Separable subgroups of the mapping class groups

###### Ben McReynolds (University of Texas, Austin)

Abstract: In joint work with Chris Leininger, we separated several well known classes of subgroups of the mapping class groups. I will describe some of the results and proofs with focus on the separability of solvable subgroups.

2:00 pm in 243 Altgeld Hall,Thursday, November 17, 2005

#### Zeros of derivatives and normal families

###### W.K. Hayman, F.R.S. (Imperial College, London (visiting Purdue University))

3:00 pm in 243 Altgeld Hall,Thursday, November 17, 2005

#### Solution to General Baer Splitting Problem

###### Phillip Griffith   [email] (UIUC Math)

3:00 pm in 241 Altgeld Hall,Thursday, November 17, 2005

#### Orbifold cohomology of abelian symplectic reductions

###### Tara Holm   [email] (University of Connecticut)

Abstract: I will talk about the topology of symplectic (and other) quotients. I will briefly review Kirwan's techniques for proving that the restriction map from the equivariant cohomology of the originial space to the ordinary cohomology of the symplectic reduction is a surjection. I will show how this result can be used to understand various aspects of the topology of quotients, focusing on the theme of orbifolds and computing the Chen-Ruan orbifold cohomology ring of symplectic reductions by torus actions.

4:00 pm in 245 Altgeld Hall,Thursday, November 17, 2005

#### Computation and Generalizations of the Douady-Earle Extension

###### William Abikoff (University of Connecticut - Storrs)

Abstract: In collaboration with Clifford Earle and others, we have developed a computational approach to the conformally natural extension due to Douady and Earle. In the disk, their early method extends homeomorphisms of the boundary of the disk D to homeomorphisms of D. A more general setting, that arises quite naturally, are the degree 1 monotone maps ofthe circle; that result will be discussed together with the iterative algorithm that provides the extension. Some generalizations arise from the algorithmic approach; open questions will be mentioned. Host: George Francis