Seminar Calendar
for events the week of Thursday, March 5, 2015.

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events for the
events containing

Questions regarding events or the calendar should be directed to Tori Corkery.
    February 2015            March 2015             April 2015
Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa
1  2  3  4  5  6  7    1  2  3  4  5  6  7             1  2  3  4
8  9 10 11 12 13 14    8  9 10 11 12 13 14    5  6  7  8  9 10 11
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22 23 24 25 26 27 28   22 23 24 25 26 27 28   19 20 21 22 23 24 25
29 30 31               26 27 28 29 30



Monday, March 2, 2015

Symplectic & Poisson Geometry Seminar
12:00 pm   in 341 AH,  Monday, March 2, 2015
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Submitted by jawatts.
 Susan Tolman (UIUC Math)Non-Hamiltonian actions with isolated fixed pointsAbstract: Let a circle act symplectically on a closed symplectic manifold $M$. If the action is Hamiltonian, we can pass to the reduced space; moreover, the fixed set largely determines the cohomology and Chern classes of $M$. In particular, symplectic circle actions with no fixed points are never Hamiltonian. This leads to the following important question: What conditions force a symplectic action with fixed points to be Hamiltonian? Frankel proved that Kahler circle actions with fixed points on Kahler manifolds are always Hamiltonian. In contrast, McDuff constructed a non-Hamiltonian symplectic circle action with fixed tori. Despite significant additional research, the following question is still open: Does there exists a non-Hamiltonian symplectic circle action with isolated fixed points? The main goal of this talk is to answer this question by constructing a non-Hamiltonian symplectic circle action with exactly 32 fixed points on a closed six-dimensional symplectic manifold. Based in part on joint work with J. Watts.

Operator Algebra Learning Seminar
5:00 pm   in 241 Altgeld Hall,  Monday, March 2, 2015
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Submitted by mjunge.
 Li Gao/Mathew Wiersma:Khintchine/Tensor products of group $C^*$-algebras admitting a continuum of $C^*$-normsAbstract: The first half of the talk will finish the Khintchine p<1 business. Second talk: It is known that $C^*$-algebras admit unique $C^*$-norms, but this is not true in general for dense $*$-subalgebras of $C^*$-algebras. For example, the algebraic tensor product $A\otimes B$ of $C^*$-algebras $A$ and $B$ may admit multiple $C^*$-norms. We will show that if $\Gamma$ is a discrete group containing a copy of a noncommutative free group, then $C^*_r(\Gamma)\otimes C^*_r(\Gamma)$ and $C^*(\Gamma)\otimes C^*_r(\Gamma)$ admit a continuum of $C^*$-norms.

Tuesday, March 3, 2015

Topology Seminar
11:00 am   in 243 Altgeld Hall,  Tuesday, March 3, 2015
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Submitted by cmalkiew.
 Thomas Nikolaus   [email] (Regensburg)Aspects of (twisted) differential cohomologyAbstract: We will start by explaining the concept of differential cohomology and its classical application to conformal embeddings and Chern-Simons invariants. Then we generalize this to arbitrary cohomology theories and explain how to obtain a useful integration theory and applications. We also want to explain twisted aspects and a factorization of the Becker-Gottlieb transfer. Finally, if time permits we explain differential algebraic K-theory for a field of intergers in a number ring and the transfer index conjecture.

Geometry, Groups and Dynamics/GEAR Seminar
1:00 pm   in Altgeld Hall 243,  Tuesday, March 3, 2015
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Submitted by kapovich.
 Catherine Pfaff (Bielefeld)Dense geodesic rays in the quotient of Outer spaceAbstract: In 1981 Masur proved the existence of a dense Teichmueller geodesic in moduli space. As some form of analogue, we construct dense geodesic rays in certain subcomplexes of the $Out(F_r)$ quotient of outer space. This is joint work in progress with Yael Algom-Kfir.

Harmonic Analysis and Differential Equations
1:00 pm   in 347 Altgeld Hall,  Tuesday, March 3, 2015
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Submitted by laugesen.
 Stanley Snelson   [email] (U of Chicago Mathematics)Regularity and long-time behavior of nonlocal heat flowsAbstract: We consider a nonlocal parabolic system with a singular target space. Caffarelli and Lin showed that a well-known optimal eigenvalue partition problem could be reformulated as a constrained harmonic mapping problem into a singular space. We show that the gradient flow corresponding to this problem is Lipschitz continuous in space, and study the regularity of a resulting free interface problem. We also show that the flow converges to a stationary solution of the constrained mapping problem as time approaches infinity. Time permitting, we will also discuss some related ongoing work involving more general non-smooth target spaces.

Logic Seminar
1:00 pm   in 345 Altgeld Hall,  Tuesday, March 3, 2015
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Submitted by ssolecki.
 Slawomir Solecki (UIUC)Partial homogeneity of dual Fraisse limits and homogeneity of the pseudo-arcAbstract: The pseudo-arc is the generic compact connected subset of the plane (or the Hilbert cube). By a fundamental result of Bing, it is homogeneous as a topological space. By work of Irwin and myself, the pseudo-arc is represented as a quotient of a dual Fraisse limit, which allows for a discretization of a continuous situation. (The limit is automatically "dually" homogeneous, but not "directly" homogeneous, so Bing's result does not follow.) In this joint work with Tsankov, we determine partial "direct" homogeneity of the limit, which involves combinatorial and basic "dual" model theoretic arguments (e.g., a notion of dual type). Further, we prove a transfer theorem, through which we recover Bing's result from our partial homogeneity. Time permitting, I will make comments on the possible generality of the method.

Graph Theory and Combinatorics Seminar
3:00 pm   in 241 Altgeld Hall,  Tuesday, March 3, 2015
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Submitted by molla.
 Theodore Molla   [email] (UIUC Math)Arbitrary Orientations of Hamilton Cycles in DigraphsAbstract: Let n be sufficiently large. Every digraph G on n vertices with minimum indegree and minimum outdegree at least n/2 contains every orientation of a Hamilton cycle except when n is even and G is isomorphic to one of two digraphs. Furthermore, both of these two exceptional digraphs have minimum indegree and minimum outdegree exactly n/2 and contain every orientation of a Hamilton cycle except the orientation in which every pair of consecutive edges alternate direction. Our result improves on an approximate result of Häggkvist and Thomason from 1995. Along with the proof of this result, we will discuss some of the innovative ideas employed in Häggkvist and Thomason's result and how these ideas can be used in a proof of the precise result. This is joint work with Louis DeBiasio, Daniela Kühn, Deryk Osthus and Amelia Taylor.

4:00 pm   in 243 Altgeld Hall,  Tuesday, March 3, 2015
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Submitted by ackrmnn2.
 Zhenghui Huo (UIUC Math)The Bergman kernel on some Reinhardt domains Abstract: We provide a new method to compute the Bergman kernel on some Reinhardt domains. We express the kernel on certain domain in $\mathbb C^{n+1}$ in terms of an already known kernel on a domain in $\mathbb C^n$ and a first order differential operator. We find, for example, an exact formula for the kernel on $\{(z_1,z_2,w)\in \mathbb C^{3};e^{|w|^2}|z_1|^2+|z_2|^2<1\}$.

Wednesday, March 4, 2015

Integrability and Representation Theory
3:00 pm   in 345 Altgeld Hall,  Wednesday, March 4, 2015
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Submitted by nevins.
 Darlayne Addabo (UIUC)Dynkin and Euclidean Diagrams, and Quivers, Part IIAbstract: This will be a continuation of last week's talk.

Math 499: Introduction to Graduate Mathematics
4:00 pm   in 245 Altgeld Hall,  Wednesday, March 4, 2015
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Submitted by laugesen.
 Elena Fuchs (Department of Mathematics, University of Illinois at Urbana-Champaign)Thin groups from different points of viewAbstract: Thin subgroups of GL_n(Z) are essentially ones that are infinite index in their Zariski closure. We discuss how interest in these groups has recently arisen in number theory, and what (very different) kinds of questions have come up as a result.

Thursday, March 5, 2015

Number Theory Seminar
11:00 am   in 241 Altgeld Hall,  Thursday, March 5, 2015
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Submitted by ford.
 Michael Zieve (U Michigan)A classification of non-generic rational functions, with applicationsAbstract: I will explain recent work with Danny Neftin which describes all complex rational functions of sufficiently large degree whose crucial invariants are not those of a random rational function. I will present several consequences of this result, including refinements of Hilbert's irreducibility theorem, a generalization of Mazur's theorem on rational torsion on elliptic curves, a description of the possible image sizes of rational functions over finite fields, and a result about reducibility of polynomials of the form $f(x)-g(y)$.

Math-Physics Seminar
12:30 pm   in 464 Loomis Laboratory,  Thursday, March 5, 2015
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Submitted by katz.
 Finn Larsen (Michigan Physics)Logarithmic Corrections to Black Hole EntropyAbstract: Logarithmic corrections to supersymmetric black holes offer a unique window into the precistion black hole entropy. Related considerations play a role in several other current directions of research. We present a selfcontained and elementary on-shell computation of these corrections that takes advantage of the symmetries in the near horizon geometry. For bulk modes interactions are incorporated using group theory alone. The spectrum of boundary states is identified explicitly. The final result is the sum of elementary contributions in 4D, 2D, and 0D.

Geometry, Groups and Dynamics/GEAR Seminar
1:00 pm   in 243 Altgeld Hall,  Thursday, March 5, 2015
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Submitted by clein.
 Chris Leininger (UIUC Math)Homology and dynamics of pseudo-AnosovsAbstract: I'll explain a connection between a pseudo-Anosov homeomorphism's stretch factor, and its action on homology. This provides a kind of interpolation between a result of Penner and our prior work with Farb and Margalit, and answers a question of Ellenberg. This is joint work with Agol and Margalit.

Analysis Seminar
2:00 pm   in 243 Altgeld Hall,  Thursday, March 5, 2015
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Submitted by tumanov.
 Kai Rajala (University of Jyväskylä)Uniformization of metric surfacesAbstract: We discuss uniformization results for metric spaces that are homeomorphic to the euclidean plane or sphere and have locally finite Hausdorff 2-measure. We give a necessary and sufficient condition for such spaces to be quasiconformally equivalent to a euclidean space. We also discuss connections to quasisymmetric parametrization problems.

2:00 pm   in 140 Henry Administration Bldg,  Thursday, March 5, 2015
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Submitted by amalik10.
 Junxian Li (UIUC Math)Zeros of families of L- functions Abstract: In order to study the zeros of the Riemann zeta function, Spira considered a family of approximations of the Riemann zeta function defined as $\zeta_N(s)=\sum_{n \leq N} n^{-s}+\chi(s)\sum_{n\leq N} n^{1-s}$. These functions approximate to the Riemann zeta function as $N$ goes to $\infty$. He also proved all the zeros of $\zeta_1(s)$ and $\zeta_2(s)$ lie on the critical line, and suggested infinitely many zeros off the critical line. Montgomery and Gonek studied the zeros of this family and obtained asymptotic formulas for the number of zeros up to height $T$ within a critical strip and on the critical line, which implies that 100% of the complex zeros lie on the critical line as $T$ goes to $\infty$ provided $N$ is not too large compared to $T$. We investigated the zeros of approximations of Hecke L-functions associated to cusp forms and Dedekind zeta functions and discovered similar behaviors. This is a joint work with A. Roy and A. Zaharescu.

Analysis Seminar
2:00 pm   in 243 Altgeld Hall,  Thursday, March 5, 2015
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Submitted by tumanov.
 Kai Rajala (University of Jyväskylä)Uniformization of metric surfacesAbstract: We discuss uniformization results for metric spaces that are homeomorphic to the euclidean plane or sphere and have locally finite Hausdorff 2-measure. We give a necessary and sufficient condition for such spaces to be quasiconformally equivalent to a euclidean space. We also discuss connections to quasisymmetric parametrization problems.

Joint Algebraic Geometry and Commutative Algebra Seminar
3:00 pm   in 243 Altgeld Hall,  Thursday, March 5, 2015
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Submitted by mastroe2.
 John Little (College of the Holy Cross)Cubic surfaces and error-control codesAbstract: In a very interesting application of algebraic geometry, Goppa's construction from the 1980's has led to some very good error-control codes. Goppa's original method started from an algebraic curve over a finite field and produces codes by two dual constructions. Recently, there has been interest in extending this construction to make use of higher-dimensional varieties over finite fields in similar ways. We will discuss how some ideas of M. Zarzar can be applied to the test case of codes from cubic surfaces over a finite field. The classical geometry of the 27 lines on a smooth cubic surface, in combination with their arithmetic properties determine the parameters of the corresponding codes.

Mathematics Colloquium
4:00 pm   in 245 Altgeld Hall,  Thursday, March 5, 2015
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Submitted by seminar.
 Karen Smith (Michigan)The Magic of Prime Characteristic Abstract: Many a calculus student has used the trick (x+y)^p = x^p + y^p to dramatically simplify calculations and sometimes even prove remarkable statements unbelievable to their professors. In this lecture, I hope to show you a context where this trick is valid: the world of "characteristic p." This trick has been used to understand complex varieties better---for example, to see that certain cohomology groups vanish or that certain kinds of differential forms exist. It has been used to show that rings of invariants for nice group actions has a particularly nice structure. Most recently, it has been used to show that a natural class of combinatorial algebras called cluster algebras" arising in many contexts have especially nice properties. The latter work is joint with Angelica Benito, Greg Muller and Jenna Rajchgot.

Friday, March 6, 2015