All Seminars

Show:
Title: Non-backtracking walk centrality for directed networks
Seminar: Numerical Analysis and Scientific Computing
Speaker: Francesca Arrigo of University of Strathclyde
Contact: Michele Benzi, benzi@mathcs.emory.edu
Date: 2017-04-28 at 1:00PM
Venue: W301
Download Flyer
Abstract:
The talk is motivated by a practical issue: walk-based centrality measures regard all walks of the same length as being equally important, whereas it is intuitively reasonable to rule out certain classes of walk. We focus here on non-backtracking walks. The theory of zeta functions provides an expression for the generating function of non-backtracking walk counts on a directed network. This expression can be used to produce a centrality measure that eliminates backtracking walks at no cost. The new centrality measure may be interpreted as standard Katz on a modified network, where self loops are added, and where non-reciprocated edges are augmented with negative weights. We also give a multilayer interpretation of the new centrality measure, where (negatively) weighted walks between layers compensate for backtracking walks on the only non-empty layer. We further show that the radius of convergence of the generating function is determined by the spectrum of a three-by-three block matrix involving the original adjacency matrix. This gives a means to choose appropriate values of the attenuation parameter and, in particular, we show that we obtain a larger range of choices for the attenuation parameter than that obtained for standard Katz. By studying the effect of pruning operations on the network (i.e., removing nodes), we show that there is potential for the non-backtracking centrality to be computed more cheaply than Katz for appropriate network structures. Studying the limit as the attenuation parameter approaches its upper bound allows us to propose an eigenvector-based non-backtracking centrality measure in this directed network setting. We illustrate the centrality measure on a synthetic network, where it is shown to eliminate a localization effect present in standard Katz centrality. We also give results for real networks. Finally, we discuss some preliminary results on the non-backtracking version of the total communicability and of some alternating walk-based centrality measures.\\ \\This talk is based on joint work with Prof. Peter Grindrod (University of Oxford, UK), Prof. Desmond J. Higham (University of Strathclyde, UK), and Dr. Vanni Noferini (University of Essex, UK).
Title: The excedance algebra and box polynomials
Seminar: Algebra
Speaker: Cyrus Hettle of Univeristy of Kentucky
Contact: David Zureick-Brown, dzb@mathcs.emory.edu
Date: 2017-04-25 at 4:00PM
Venue: W306
Download Flyer
Abstract:
The excedance algebra, given by the noncommutative quotient Z/(ba-a-b-ab), is motivated by a recurrence for a permutation statistic. We examine this algebra and a related matrix construction known as the excedance matrix. We then consider properties of the box polynomials, which arise from applying the finite difference operator to monomials and whose coefficients are the entries of the rightmost column of the excedance matrix. Evaluating these polynomials yields a variety of identities involving set partition enumeration. We extend these identities using restricted growth words and a new operator called the fast Fourier operator. This talk is based on joint work with Richard Ehrenborg and Dustin Hedmark.
Title: Reconstructing the Tree of Life
Seminar: N/A
Speaker: Shel Swenson of Emory University
Contact: TBA
Date: 2017-04-24 at 2:30PM
Venue: W301
Download Flyer
Abstract:
TBA
Title: On a problem in Euclidean Ramsey Theory
Seminar: Combinatorics
Speaker: Adril Arman of The University of Manitoba
Contact: Dwight Duffus, dwight@mathcs.emory.edu
Date: 2017-04-21 at 4:00PM
Venue: W303
Download Flyer
Abstract:
An old open problem in Euclidean Ramsey theory asks if the points in $E^3$ are coloured in red and blue, does there exist either a red pair of points at unit distance or six collinear blue points separated by unit distances? After a short survey of related problems, I will give a positive answer to this problem and outline the proof. This talk is based on a joint work with Sergei Tsaturian.
Title: Embedded Systems: Arduino Programming for Autonomous Racing Cars
Seminar: N/A
Speaker: Lanny Sitanayah of Clemson University
Contact: Ken Mandelberg, km@mathcs.emory.edu
Date: 2017-04-19 at 2:30PM
Venue: W301
Download Flyer
Abstract:
mall, low-cost, low-power sensing devices are transforming science and society, making it possible to transform the deployment of new applications and allow the collection and analysis of data far beyond the scale of what was previously possible. A commercially available embedded platform, such as Arduino, helps developers to prototype embedded systems easier, faster, and in a fun way. One of Arduino's fun projects is autonomous car, where a racing car must be able to move without a remote control. The car should be able to move forward, avoid any obstacles, stop and reverse if necessary, without any user input apart from turning it on. In this talk, we are going to learn how to control the electronic speed control and the steering servo of the car using an Arduino.
Title: Athens-Atlanta Joint Number Theory Seminar
Seminar: Algebra
Speaker: Gopal Prasad and Rachel Pries of University of Michigan and Colorado State University
Contact: David Zureick-Brown, dzb@mathcs.emory.edu
Date: 2017-04-18 at 4:00PM
Venue: Room 208
Download Flyer
Abstract:
Rachel Pries (4pm) \\ Title: Galois action on homology of Fermat curves \\ Abstract: We prove a result about the Galois module structure of the Fermat curve using commutative algebra, number theory, and algebraic topology. Specifically, we extend work of Anderson about the action of the absolute Galois group of a cyclotomic field on a relative homology group of the Fermat curve. By finding explicit formulae for this action, we determine the maps between several Galois cohomology groups which arise in connection with obstructions for rational points on the generalized Jacobian. Heisenberg extensions play a key role in the result. This is joint work with R. Davis, V. Stojanoska, and K. Wickelgren. \\ Gopal Prasad (5:15pm) \\ Title: Weakly commensurable Zariski-dense subgroups of semi-simple groups and isospectral locally symmetric spaces \\ Abstract. I will discuss the notion of weak commensurability of Zariski-dense subgroups of semi-simple groups. This notion was introduced in my joint work with Andrei Rapinchuk (Publ. Math. IHES 109(2009), 113-184), where we determined when two Zariski-dense S-arithmetic subgroups of absolutely almost simple algebraic groups over a field of characteristic zero can be weakly commensurable. These results enabled us to prove that in many situations isospectral locally symmetric spaces of simple real algebraic groups are necessarily commensurable. This settled the famous question "Can one hear the shape of a drum?" of Mark Kac for these spaces. The arguments use algebraic and transcendental number theory.
Title: Point Processes and Asynchronous Event Sequence Analysis
Seminar: N/A
Speaker: Hongteng Xu of Georgia Institute of Technology
Contact: TBA
Date: 2017-04-17 at 4:00PM
Venue: White Hall 112
Download Flyer
Abstract:
Real-world interactions among multiple entities, such as user behaviors in social networks, job hunting and hopping, and diseases and their complications, often exhibit self-triggering and mutually-triggering patterns. For example, a tweet of a twitter user may trigger further responses from her friends. A disease of a patient may trigger other complications. Temporal point processes, especially Hawkes processes and correcting processes, have a capability to capture the triggering patterns quantitatively. This talk aims to introducing basic concepts of point processes and proposing a series of cutting-edge techniques for practical applications. In particular, the Granger causality analysis of Hawkes processes, the clustering problem of event sequences, the combination of deep learning and point processes, and some interesting applications will be discussed.\\ \\ Bio: Hongteng Xu is a Ph.D. candidate in the School of Electrical and Computer Engineering, Georgia Tech, jointly supervised by Prof. Hongyuan Zha (CSE) and Prof. Mark A. Davenport (ECE). At the same time, he is a research assistant in the College of Computing at Georgia Tech. He received his Bachelor Degree in Electronic and Information Engineering from Tianjin University in 2010 and his dual Master Degree in ECE from Shanghai Jiao Tong University and Georgia Tech in 2013. His research interests include machine learning and its applications, e.g., computer vision and data mining. Currently, he has published over 20 papers on top conferences and journals.
Title: Question Answering with User Generated Content
Defense: Dissertation
Speaker: Denis Savenkov of Emory University
Contact: Denis Savenkov, denis.savenkov@emory.edu
Date: 2017-04-13 at 4:00PM
Venue: W306
Download Flyer
Abstract:
Modern search engines have made dramatic progress in answering many user questions, especially about facts, such as those that might be retrieved or directly inferred from a knowledge base. However, many other more complex factual, opinion or advice questions, are still largely beyond the competence of computer systems. For such information needs users still have to dig into the "10 blue links" of search results and extract relevant information. As conversational agents become more popular, question answering (QA) systems are increasingly expected to handle such complex questions and provide users with helpful and concise information. In my dissertation I develop new methods to improve the performance of question answering systems for a diverse set of user information needs using various types of user-generated content, such as text documents, community question answering archives, knowledge bases, direct human contributions, and explore the opportunities of conversational settings for information seeking scenarios.
Title: A characterization of Toric pairs
Seminar: Algebra
Speaker: Morgan Brown of University of Miami
Contact: David Zureick-Brown, dzb@mathcs.emory.edu
Date: 2017-04-11 at 4:00PM
Venue: W306
Download Flyer
Abstract:
Toric varieties are ubiquitous in algebraic geometry. They have a rich combinatorial structure, and give the simplest examples of log Calabi-Yau varieties. \\ We give a simple criterion for characterizing when a log Calabi-Yau pair is toric, which answers a case of a conjecture of Shokurov. This is joint work with James McKernan, Roberto Svaldi, and Runpu Zong.
Title: Statistical and informatics methods for analyzing next generation sequencing data
Defense: Dissertation
Speaker: Li Chen of Emory University
Contact: Li Chen, li.chen@emory.edu
Date: 2017-04-10 at 9:00AM
Venue: CNR 2001
Download Flyer
Abstract:
TBA