All Seminars
| Title: Modeling Temporal Dynamics of User Generated Content |
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| Defense: Dissertation |
| Speaker: Yu Wang of Emory Unviersity |
| Contact: Yu Wang, yu.wang@emory.edu |
| Date: 2014-09-29 at 10:15AM |
| Venue: PAIS 561 |
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| Abstract: The evolving nature of user generated content (UGC) lays the key characteristics of Web 2.0. The evolution process in UGC offers valuable evidence to explain the content dynamics in the past and predict trends in the future. In this thesis, we design models to analyze content evolution patterns of UGC in three granularities: words, topics and sentiment. More specifically, this thesis investigates content evolution in the following aspects: (1) on word-level dyanmics: analyzing word frequency change in collaboratively generated content and using historical word frequencies to better weigh the words in ranking functions; (2) on topic-level dynamics: learning temporal transition patterns of topics in microblog streams and predict future topics according to historical posts; (3) on sentiment-level dynamics: estimating and understanding different sentiment change patterns of popular political topics across different user groups. We show that the developed models enable new applications in UGC, such as improving content-based ranking, anticipating future popular topics and visualizing and interpreting sentiment dynamics. |
| Title: Computing free surface flows of viscoplastic fluids |
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| Seminar: Numerical Analysis and Scientific Computing |
| Speaker: Maxim Olshanskii of University of Houston |
| Contact: Michele Benzi, benzi@mathcs.emory.edu |
| Date: 2014-09-26 at 12:00PM |
| Venue: MSC W301 |
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| Abstract: Free surfaces flows of yield stress fluids are common in nature and in engineering applications. Viscoplastic models, such as the Herschel-Bulkley model, are often used to describe the complex rheology of such fluids and predict fluids dynamics with reasonable accuracy. The numerical modeling and analysis of the phenomena is a challenging task due to the non-trivial coupling of complex fluid dynamics and free surface evolution.\\ \\ In this talk we discuss an approach for numerical simulation of free surface flows of viscoplastic incompressible fluids. The approach features adaptive Cartesian grids and a splitting technique for numerical time integration. We shall point to several open problems in the mathematical and numerical analysis of equations governing free surface flows of viscoplastic fluids. |
| Title: An algebraic approach to enumerating field extensions |
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| Seminar: Algebra |
| Speaker: Frank Thorne of University of South Carolina |
| Contact: David Zureick-Brown, dzb@mathcs.emory.edu |
| Date: 2014-09-22 at 4:00PM |
| Venue: W302 |
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| Abstract: Building on previous work of Cohen and several of his collaborators, I will discuss the use Kummer theory and class field theory to enumerate field extensions of low degree. We obtain an explicit Dirichlet series representation, in the form of a finite sum of Euler products, for the set of field extensions with Galois group $S_3, A_4, S_4$, or $D_l$ (l an odd prime) with fixed resolvent. This has a variety of interesting consquences, including results on the Shintani zeta function as well as an extension of the Scholz reflection principle, which I will describe. Most of this is joint work with Henri Cohen, and one part is also joint with Simon Rubinstein-Salzedo. |
| Title: On the Distribution of Moonshine |
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| Seminar: Algebra |
| Speaker: Michael Griffin of Emory |
| Contact: David Zureick-Brown, dzb@mathcs.emory.edu |
| Date: 2014-09-16 at 4:00PM |
| Venue: W306 |
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| Abstract: Monstrous moonshine expresses distinguished modular functions in terms of the representation theory of the Monster. The celebrated observations that \[ (*) 1=1, 196884=196883+1, 21493760=1+196883+21296876,\ldots \] illustrate the case of $J(z)=j(z)-744$, where the coefficients are sums of the dimensions of the 194 irreducible representations of the Monster. Such formulas are dictated by the structure of the graded monstrous moonshine modules. Here we use the modularity of the moonshine modules to address the open problem of obtaining exact formulas for the multiplicities of the irreducible components of the moonshine modules. These formulas imply that such multiplicities are asymptotically proportional to dimensions. |
| Title: A connection between coupled and penalty projection time-stepping schemes with FE spatial discretization for the Navier-Stokes equations |
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| Seminar: Numerical Analysis and Scientific Computing |
| Speaker: Leo Rebholz of Clemson University |
| Contact: Michele Benzi, benzi@mathcs.emory.edu |
| Date: 2014-09-12 at 12:00PM |
| Venue: MSC W301 |
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| Abstract: We prove that in finite element settings where the divergence-free subspace of the velocity space has optimal approximation properties, the solution of Chorin-Temam projection methods for Navier-Stokes equations equipped with grad-div stabilization with parameter $\gamma$, converge to the associated coupled method solution with rate $\gamma^{-1}$ as $\gamma\rightarrow \infty$. We prove this first for backward Euler schemes, and then extend the results to BDF2 schemes, and finally to schemes with outflow boundary conditions. Several numerical experiments are given which verify the convergence rate, and show how using projection methods in this setting with large grad-div stabilization parameters improves accuracy. |
| Title: Shifted convolution L-functions |
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| Seminar: Algebra |
| Speaker: Ken Ono of Emory |
| Contact: David Zureick-Brown, dzb@mathcs.emory.edu |
| Date: 2014-09-09 at 4:00PM |
| Venue: W306 |
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| Abstract: Rankin-Selberg convolution L-functions are important functions in number theory. Their properties play a central role in many of deepest works on the Ramanujan-Petersson Conjecture. In a recent paper, Hoffstein and Hulse defined generalizations of these L-functions, the so-called ``shifted-convolution" L-functions. They obtained the meromorphic continuation of the functions in many cases. Here we consider symmetrizations of these L-functions, and we exactly evaluate their special values at diagonal weights for all shifts. This is joint work with Michael Mertens. |
| Title: Pursuit and Evasion |
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| Colloquium: N/A |
| Speaker: Imre Leader of University of Cambridge |
| Contact: Dwight Duffus, dwight@mathcs.emory.edu |
| Date: 2014-09-08 at 4:00PM |
| Venue: MSC W303 |
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| Abstract: In Rado's famous "lion and man" problem, a man and a lion are in a circular arena. The lion wants to catch the man, and the man does not want to be caught by the lion. Each can run at the same speed. Who wins? We will start with some background on this kind of "continuous pursuit" problem, including the solution that was eventually given by Besicovitch. We will then move on to some surprising recent developments. |
| Title: What is the limit of a line bundle on a non normal variety? |
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| Seminar: Algebra |
| Speaker: Jesse Kass of USC |
| Contact: David Zureick-Brown, dzb@mathcs.emory.edu |
| Date: 2014-09-02 at 4:00PM |
| Venue: W306 |
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| Abstract: On a nonnormal variety, the limit of a family of line bundles is not always a line bundle. What is the limit? I will present an answer to this question and give some applications. Time permitting, I will discuss connections with Néron models, autoduality, and recent work of R. Hartshorne and C. Polini. |
| Title: Applying Diploid Method to Improve Read-mapping and Analysis Based on NGS Data |
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| Defense: Dissertation |
| Speaker: Shuai Yuan of Emory University |
| Contact: Shuai Yuan, shuaiyuan@emory.edu |
| Date: 2014-07-25 at 1:00PM |
| Venue: Grace Crum Rollins (GCR), Room 537 |
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| Abstract: Applying Diploid Method to Improve Read-mapping and Analysis Based on NGS Data Abstract: Next generation sequencing (NGS) technologies have been applied extensively in many areas of genetics and genomics research. A fundamental problem when comes to analyzing NGS data is mapping short sequencing reads back to the reference genome. Most of existing software packages rely on a single uniform reference genome and do not automatically take into the consideration of genetic variants. On the other hand, large proportions of incorrectly mapped reads affect the correct interpretation of the NGS experimental results. In this presentation, I will talk about a method that produces a personalized diploid reference genome based on all known genetic variants of that particular individual. Using such a reference genome can improve mapping accuracy and significantly reduce the bias toward reference allele in allele-specific expression analysis. By incorporating the imputation into the diploid method, genotype calling and SNP discovery results will also be improved. |
| Title: Modeling User Attention and Interaction on the Web |
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| Defense: Dissertation |
| Speaker: Dmitry Lagun of Emory University |
| Contact: Dmitry Lagun, dlagun@emory.edu |
| Date: 2014-07-22 at 12:00PM |
| Venue: MSC W301 |
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| Abstract: Analysis of user attention and Web page examination behavior, collected with specialized eye tracking equipment, has offered numerous insights about how online users examine content of the Web pages and remains a valuable tool for Web researchers and developers. Unfortunately, eye tracking technology is currently available for relatively small scale user studies, due to its high costs and the effort associated with participant recruitment. In this thesis we develop several alternatives to eye tracking for studying user attention and behavior. We start by introducing ViewSer - a method based on idea restricted focus viewing, that allows measuring attention for thousands of participants. Then, we develop a probabilistic model that infers most likely position of user’s gaze on the screen from user interactions and web page content. Our model outperforms current state of the art for gaze position prediction that only uses behavioral signals. In addition to the methodological contributions, this thesis develops several important applications in web search and medical domain. First, we describe a scalable approach for extracting frequent mouse cursor movement patterns from large scale cursor data. Second, we demonstrate how these patterns could be used to improve quality of search relevance estimation and search result ranking. Third, we show that attention measured with cursor and viewport position could be used to improve automatic summarization. Lastly, we show how restricted focus viewing could be adapted to develop an automated diagnostic of memory impairment that could be administered over the Web anywhere in the world. Together, the techniques developed and evaluated in this thesis substantially advance the state of the art and enable novel important practical applications. |