All Seminars

Title: CANCELED
Seminar: Algebra
Speaker: Eva Bayer-Fluckiger of EPFL
Contact: David Zureick-Brown, dzb@mathcs.emory.edu
Date: 2013-10-23 at 5:00PM
Venue: W306
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Abstract: This is a joint work with Tingyu Lee and Parimala. Let k be a global field of characteristic not 2, let E be an etale k-algebra with involution, and let q be a quadratic space over k. The aim of this talk is to give necessary and sufficient conditions for the orthogonal group O(q) to contain a maximal torus of type E.

Title: Characterization of Quasiconformal mapping, and extremal length decomposition and upper bound of QED constant for finitely connected domains
Seminar: Analysis and Differential Geometry
Speaker: Wenfei Zou of Emory University
Contact: Wenfei Zou, wzou3@emory.edu
Date: 2013-10-22 at 4:00PM
Venue: W302
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Abstract: The talk includes two parts. For the first part, it is known that Conformal mapping preserves the measure of angle. The Quasiconformal mapping is a natural generalization of the conformal mapping. Some measure of angle named topological angle can be defined to characterize Quasiconformal mappings. I will discuss these results in higher dimension. For the second part, quasiextremal distance domains (QED) are a class of domains introduced by Gehring and Martio in connection with Quasiconformal mapping theories. I will discuss a decomposition theorem about the extremal length of a curve family within the finitely connected QED domain. Moreover, I will discuss the result of sharp upper bound for QED constant of finitely connected domain on the complex plane.

Title: On the arithmetic of surfaces
Seminar: Algebra
Speaker: Yuri Tschinkel of Courant Institute
Contact: David Zureick-Brown, dzb@mathcs.emory.edu
Date: 2013-10-18 at 10:00AM
Venue: W304
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Abstract: I will discuss new geometric constructions arising in the study of rational points on algebraic surfaces over global fields (joint with B. Hassett).

Title: Maximum induced decomposition of graphs
Seminar: Combinatorics
Speaker: Zeinab Maleki of The University of Illinois - UC
Contact: Dwight Duffus, dwight@mathcs.emory.edu
Date: 2013-10-18 at 4:00PM
Venue: W306
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Abstract:

Title: Dynamical Processes in Time-varying Networks
Type: Joint Physics and MathCS Seminar
Speaker: Prof. Alessandro Vespignani of Northeastern University
Contact: Michele Benzi, benzi@mathcs.emory.edu
Date: 2013-10-17 at 2:30PM
Venue: MSC: E300
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Abstract: Network modeling plays a critical role in identifying statistical regularities and structural principles common to many systems. The large majority of recent modeling approaches however are connectivity driven and provide a time-aggregated representation that may fail to describe the instantaneous and fluctuating dynamics of many networks. I will present a generative model framework for time-varying network by defining the activity potential, a time invariant function characterizing the agents' interactions.\\ \\ I will show the definition of the activity driven class of models, capable of encoding the instantaneous time description of the network dynamics. This class of models provides an explanation of structural features such as the presence of hubs, which simply originate from the heterogeneous activity of agents. Within this framework, highly dynamical networks can be described analytically, allowing a quantitative discussion of the biases induced by the time-aggregated representations in the analysis of dynamical processes. In particular I will consider diffusive and contagion processes and their control strategies and develop a block variable mean-field approach that allows the derivation of the equations describing the evolution of the contagion process concurrently to the network dynamic.\\ \\

Title: Pathologies of the Brauer-Manin obstruction
Seminar: Algebra
Speaker: Jean-Louis Colliot Thelene of Paris-Sud
Contact: David Zureick-Brown, dzb@mathcs.emory.edu
Date: 2013-10-09 at 4:00PM
Venue: W306
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Abstract: In 1970, Manin used the Brauer group of varieties to account for most known counterexamples to the Hasse principle over number field. In 1999, A. Skorobogatov produced the first unconditional examples of varieties without rational point not accounted for by the Brauer-Manin obtruction. Simpler examples were produced by B. Poonen in 2010. We present even simpler examples. This is joint work with A. P\'al and A. Skorobogatov.

Title: Expander families and variation of Galois representations
Seminar: Algebra
Speaker: Chris Hall of University of Wyoming
Contact: David Zureick-Brown, dzb@mathcs.emory.edu
Date: 2013-10-02 at 4:00PM
Venue: W306
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Abstract: Given a pair of curves U,V over the complex numbers, one can associate to a finite unramified map $V \to U$ a finite Cayley-Schreier graph. In this talk we consider families of maps $V_i \to U$ indexed by a parameter i such that the family of associated graphs is an expander family. As we will explain, the expander hypothesis has remarkable geometric implications, e.g. the set of $V_i$ such that the gonality of $V_i$ is less than your favorite positive number N is finite. We will also explain some of the arithmetic implications, e.g. for all but finitely many $V_i$, there are only many points on $V_i$ defined over some extension of K of degree at most N. As one an application, we can derive results on the variation of Galois representations in a one-parameter family of abelian varieties defined over a number field.

Title: Rational and quadratic preperiodic points for quadratic polynomials
Seminar: Algebra
Speaker: Xander Faber of Joining IDA/CCS
Contact: David Zureick-Brown, dzb@mathcs.emory.edu
Date: 2013-09-25 at 4:00PM
Venue: W306
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Abstract: Let f be a quadratic polynomial with coefficients in a number field K. The action of f on the affine line induces a dynamical system. Many researchers have speculated on and provided evidence for uniform bounds on the number of K-rational points with finite orbit under this action: such points are called preperiodic. I will survey what is expected and what is known, and then I will describe some new contributions by myself and my collaborators John Doyle and David Krumm when K=Q or when K is a quadratic number field.

Title: A Space-Time Finite Element Method for PDEs posed on Eveolving Surfaces
Seminar: Numerical Analysis and Scientific Computing
Speaker: Maxim A. Olshanskii of University of Houston
Contact: James Munch, jmunch@emory.edu
Date: 2013-09-23 at 4:00PM
Venue: W304
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Abstract:

Title: A problem of Erdos and Sós on 3-graphs
Seminar: Combinatorics
Speaker: Jan Volec of University of Warwick
Contact: Vojtech Rodl, rodl@mathcs.emory.edu
Date: 2013-09-23 at 4:00PM
Venue: MSC W301
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Abstract: We show that for every epsilon > 0 there exist delta > 04 and natural number n_0 such that every 3-uniform hypergraph on n >= n_0 vertices with the property that every k-vertex subset, where k is at least deltan, induces at least (1/4 + epsilon)(k choose 3) edges, contains K4- as a subgraph, where K4- is the 3-uniform hypergraph on 4 vertices with 3 edges. This question was originally raised by Erdos and Sos. The constant 1/4 is the best possible.