Seminar Calendar
for events the day of Thursday, April 20, 2017.

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Questions regarding events or the calendar should be directed to Tori Corkery.
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Thursday, April 20, 2017

Number Theory Seminar
11:00 am   in 241 Altgeld Hall,  Thursday, April 20, 2017
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Submitted by sahlgren.
Robert Lemke Oliver (Tufts University)
To Be Announced

Geometry, Groups and Dynamics/GEAR
12:00 pm   in 243 Altgeld Hall,  Thursday, April 20, 2017
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Submitted by cuyanik2.
Michelle Chu (UT Austin Math)
To Be Announced
Abstract: TBA

Math-Physics Seminar
12:30 pm   in 464 Loomis Laboratory,  Thursday, April 20, 2017
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Submitted by katz.
Aitor Lewkowycz (Stanford Physics)
To Be Announced

Analysis Seminar
2:00 pm   in 243 Altgeld Hall,  Thursday, April 20, 2017
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Submitted by fboca.
Alexander Gorokhovsky (University of Colorado Boulder)
TBA

Mathematics Colloquium
4:00 pm   in 245 Altgeld Hall,  Thursday, April 20, 2017
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Submitted by kapovich.
Mark Sapir (Centennial Professor, Vanderbilt University, and George A. Miller Visiting Professor, Univ. of Illinois)
Tarski numbers
Abstract: It is known since Hausdorff, Banach and Tarski that one can decompose a 2-sphere into 4 pieces, move the pieces using rotations of the sphere, and obtain two spheres of the same radius (assuming the Axiom of Choice). Thus a sphere with the group of rotations acting on it has a paradoxical decomposition with 4 pieces. In general if we have a group G acting on a set X, then the Tarski number of X is the minimal number of pieces in a paradoxical decomposition of X. For example, if G acts on itself by left multiplication, then we can talk about the Tarski number of G. I will show how to use Golod-Shafarevich groups to prove that the set of possible Tarski numbers of groups is infinite. I will also show how to use l_2-Betti numbers of groups and cost of group actions to construct groups with Tarski numbers 5 and 6. Note that 4, 5 and 6 are the only numbers that are currently known to be Tarski numbers of groups. This is a joint work with Gili Golan and Mikhail Ershov.

LAS Teaching Excellence Awards Ceremony
5:00 pm   in Alice Campbell Alumni Center ,  Thursday, April 20, 2017
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Submitted by seminar.
LAS Teaching Excellence Awards
Abstract: The LAS Teaching Excellence Awards ceremony will be held from 5-7 pm on Thursday, April 20, 2017, at the Alice Campbell Alumni Center.