Seminar Calendar
for events the day of Thursday, September 1, 2011.

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Questions regarding events or the calendar should be directed to Tori Corkery.
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Thursday, September 1, 2011

BCDE Math/Physics Seminar
12:00 pm   in Loomis 464,  Thursday, September 1, 2011
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Submitted by katz.
 Organizational MeetingAbstract: This seminar is being resurrected and co-organized by Sheldon Katz and Mike Stone, with a focus on the connections between Mathematics and Physics, particularly in the areas of geometry, topology, and algebra.

Number Theory
1:00 pm   in 241 Altgeld Hall,  Thursday, September 1, 2011
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Submitted by berndt.
 Jayadev Athreya (UIUC Math)Ergodic theory of the BCZ mapAbstract: In their study of Farey fracitons, Boca-Cobeli-Zaharescu introduced a piecewise-linear Lebesgue measure preserving map of the Farey triangle $x, y: 0 < x, y \leq 1, x+y >1$. They posed the question of ergodicity of this map. In joint work with Yitwah Cheung, we show that the map is ergodic with respect to Lebesgue measure by displaying it as a first return map for horocycle flow on the modular surface. We obtain corollaries on the distribution of gaps for Farey fractions which had previously been known using analytic number theory methods. We also obtain results on cusp excursions for horocycles.

Group Theory Seminar
1:00 pm   in 347 Altgeld Hall ,  Thursday, September 1, 2011
 Del Edit Copy
Submitted by kapovich.
 Ilya Kapovich (UIUC Math)On the fibers of the Cannon-Thurston map for word-hyperbolic free-by-cyclic groupsAbstract: Let $\phi\in Aut(F_N)$ be an atoroidal iwip automorphism of a free group $F_N$, $N\ge 3$ and let $M_\phi=F_N\rtimes_\phi \mathbb Z$ be the mapping torus group of $\phi$. The group $M_\phi$ is Gromov-hyperbolic and it follows from the work of Mitra that the inclusion $i:F_N\to M_\phi$ extends to a continuous surjective map between the hyperbolic boundaries $\hat i: \partial F_N\to\partial M_\phi$, called the "Cannon-Thurston map". We prove that for any $\phi$ as above the map $\hat i$ is finite-to-one and that the preimage of every point of $\partial M_\phi$ has cardinality $\le 2N$. This talk is based on joint work with Martin Lustig.