All Seminars

Title: Asymptotics of Resonances for Radial Potential Scattering in Hyperbolic Space
Defense: Dissertation
Speaker: Catherine Crompton of Emory University
Contact: Catherine Crompton, lcrompt@emory.edu
Date: 2012-06-14 at 1:00PM
Venue: W306
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Abstract:
It is shown that for scattering by a spherically symmetric potential with compact support in $\mathbb{H}^{n+1}$, the resonance counting function $N(r)$ is asymptotic to $Cr^{n+1}$. $C$ is found explicitly, and is shown to depend only on the dimension and the radius of support of the potential.
Title: Leibniz, Nilakantha, Euler and Pi
Seminar: Algebra and Number Theory
Speaker: Manuel Ojanguren of EPFL
Contact: R. Parimala, parimala@mathcs.emory.edu
Date: 2012-05-08 at 3:00PM
Venue: W304
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Abstract:
This elementary talk will discuss some historical and mathematical aspects of different series involving $\pi$ that were discovered between 1400 and 1995.
Title: Searching for social meanings in social media
Seminar: Computer Science
Speaker: Jacob Eisenstein of Georgia Institute of Technology
Contact: Eugene Agichtein, eugene@mathcs.emory.edu
Date: 2012-05-04 at 3:00PM
Venue: MSC W201
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Abstract:
Social interaction is increasingly conducted through online platforms such as Facebook and Twitter, leaving a recorded trace of millions of individual interactions. While some have focused on the supposed deficiencies of social media with respect to more traditional communication channels, language in social media features the same rich connections with personal and group identity, style, and social context. However, social media's unique set of linguistic affordances causes social meanings to be expressed in new and perhaps surprising ways. This talk will describe research that builds on large-scale social media corpora using analytic tools from statistical machine learning. I will focus on some of the ways in which social media data allow us to go beyond traditional sociolinguistic methods, but I will also discuss lessons from the sociolinguistics literature for the new generation of "big data" research. This research includes collaborations with David Bamman, Brendan O'Connor, Tyler Schnoebelen, Noah A. Smith, and Eric P. Xing.
Title: A Subconvexity Bound for Rankin-Selberg L-functions in the Level Aspect
Seminar: Algebra
Speaker: Riad Masri of Texas A\&M University
Contact: Zachary A. Kent, kent@mathcs.emory.edu
Date: 2012-05-01 at 3:00PM
Venue: W304
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Abstract:
We will discuss the subconvexity problem for Rankin-Selberg L-functions in the level aspect in the case both forms are allowed to vary. We will show how to establish a bound of this type for a certain natural family of L-functions. This is joint work with Sheng-Chi Liu.
Title: Capturing Butterfly Effects
Lecture: Annual Evans/Hall Lecture Series
Speaker: Dr. Sarah Day of College of William and Mary
Contact: Erin Nagle, erin@mathcs.emory.edu
Date: 2012-05-01 at 4:00PM
Venue: MSC E208
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Abstract:
The Butterfly Effect, also known as sensitive dependence on initial conditions, is one of the defining properties of chaotic systems. Lorenz famously found evidence of this effect in his numerical simulations of a simplified weather model, now known as the Lorenz system. Since then, researchers have grappled with how to use dramatic increases in computing power to study the dynamics of systems known to misbehave, sometimes in very dramatic ways. I will discuss recent work in developing a computational approach for measuring the Butterfly Effect and other types of dynamics. This approach uses tools from many subfields of mathematical research and, when successful, produces mathematically rigorous results. As illustration, I will show computer-assisted proofs for a few model systems and discuss how this approach ties into, or sometimes challenges, prior theoretical work in the rapidly growing and evolving field of dynamical systems research.
Title: Dynamic coloring and list dynamic coloring of planar graphs
Seminar: Combinatorics
Speaker: Sang June Lee of Emory University
Contact: Dwight Duffus, dwight@mathcs.emory.edu
Date: 2012-04-27 at 4:00PM
Venue: W306
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Abstract:
Title: An Eisenstein Measure for Unitary Groups
Seminar: Algebra and Number Theory
Speaker: Ellen Eischen of Northwestern University
Contact: Zachary A. Kent, kent@mathcs.emory.edu
Date: 2012-04-24 at 3:00PM
Venue: W304
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Abstract:
One approach to constructing certain p-adic L-functions relies on construction of a p-adic family of Eisenstein series. I will explain how to construct such a family for certain unitary groups. As part of the talk, I will explain how to p-adically interpolate certain values of both holomorphic and non-holomorphic Eisenstein series. I will also mention some applications to number theory and beyond.
Title: Past, Present, and Future Parallel Programming Paradigms and Numerical Algorithms
Seminar: Numerical Analysis and Scientific Computing
Speaker: Rebecca Hartman-Baker of Oak Ridge National Laboratory
Contact: Alexis Aposporidis, aapospo@emory.edu
Date: 2012-04-24 at 4:00PM
Venue: MSC W201
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Abstract:
As computing resources, needs, and goals have evolved, parallel programming paradigms have changed. The evolution of high-end computer architecture (from organic to mechanical to digital and from single-core computers to vector-based, multicore-based, and hybrid CPU/GPGPU-based machines) has necessitated the continuing development of new parallel programming paradigms and numerical algorithms. In this talk, I discuss the development of numerical algorithms throughout the history of numerical computing placed within their historical and architectural contexts, and the implications of future architectures on numerical methods.
Title: Geometrization of sub-hyperbolic semi-rational branched coverings
Seminar: Analysis and Differential Geometry
Speaker: Professor Tao Cheng of East China Normal University
Contact: Shanshuang Yang, syang@mathcs.emory.edu
Date: 2012-04-24 at 4:00PM
Venue: MSC W301
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Abstract:
Given a sub-hyperbolic semi-rational branched covering of the sphere, which is not CLH-equivalent to a rational map, it must have the non-empty canonical Thurston obstruction. By using this canonical Thurston obstruction, we will discuss how to decompose such a dynamical system into several sub-dynamical systems. Then we will show that each of these sub-dynamical systems is either a post-critically finite type branched covering or a sub-hyperbolic semi-rational type branched covering.
Title: The best way to choose a winner
Seminar: Combinatorics
Speaker: Vicki Powers of Emory University
Contact: Dwight Duffus, dwight@mathcs.emory.edu
Date: 2012-04-20 at 4:00PM
Venue: W306
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Abstract:
What could be easier than choosing the winner of an election?    Just ask the voters to choose their favorite and pick the candidate with the most votes.    It turns out that if there are  more than two candidates, all sorts of paradoxes and undesirable outcomes can, and do, happen. For example, in 1998, Jesse Ventura was elected governor of Minnesota with 37\% of the vote, even though more than half of the voters preferred either of the the other two candidates.   So what is the best way to hold a multicandidate election?    Arrow's Impossibility Theorem says  that there is NO good way to choose a winner when there are more than two candidates in the sense that whatever method is chosen,  there is always the possibility of an undesirable outcome.   A natural question to ask for various election methods is how likely is a ``bad" outcome?  In this talk we will introduce Social Choice Theory and Arrow's Theorem and look at one desirable property of social choice methods -- the Condorcet Winner Criterion (CWC).   We will discuss a way to measure the likelihood of the CWC being violated and use this to compare different social choice methods.