All Seminars
| Title: Considering the importance of realism in virtual reality |
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| and Awards Ceremony: Annual Evans/Hall Lecture Series |
| Speaker: Dr. Doug Bowman of Virginia Tech |
| Contact: Erin Nagle, erin@mathcs.emory.edu |
| Date: 2013-04-29 at 4:00PM |
| Venue: MSC E208 |
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| Abstract: It is often implied or assumed that the ultimate goal of virtual reality (VR) systems is the perfect reproduction of reality. It seems that the objective is making graphics, audio, haptics, physics, and interaction as indistinguishable from the real world as possible. In other words, the hypothetical Star Trek Holodeck is seen as the gold standard of VR systems. The word "reality" is even part of the name of the field! However, increasing realism can have a steep cost, and evidence for the benefits of higher levels of realism is often lacking. In this talk, I want to take a step back to evaluate how, when, and why high levels of realism are desirable. I will review a decade of research in my group focusing on understanding the effects of various types of realism in VR systems, and will draw some potentially surprising conclusions about where research efforts should be focused and how much realism is enough. Along the way, I will share some lessons learned about life in academia and a career in research. |
| Title: Datacenter-scale Cloud Management: Experience, Insights and Future Challenges |
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| Seminar: Computer Science |
| Speaker: Ada Gavrilovska of Georgia Tech |
| Contact: Li Xiong, lxiong@mathcs.emory.edu |
| Date: 2013-04-26 at 3:00PM |
| Venue: MSC W301 |
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| Abstract: Datacenter scale cloud platforms continue to exhibit increases in the scale and diversity of their infrastructure -- cores, servers, enclosures, I/O -- and the workloads they host -- number and type of applications, virtual machines, etc. This results in significant challenges in the ability to effectively manage these platforms, to provide high resource utilization while also meeting client performance expectations, and to further evaluate the effectiveness of such management operation. In this talk, I will present our ongoing efforts toward management of compute, I/O and energy resources in cloud platforms, and will provide data regarding the insights we gained in the behavior of the management processes themselves, including their failures. For the results gathered in our experimental approach we use publicly available cloud traces as well as a range of popular cloud and enterprise workloads. Our evaluation with real cloud applications illustrate additional challenges due to the interactions of the cloud-level management processes and those present in modern cloud runtimes, like Hadoop. |
| Title: A new proof of the known cases of Sidorenko's conjecture |
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| Seminar: Combinatorics |
| Speaker: Leonardo Nagami Coregliano of The University of Toronto and the University of Sao Paulo |
| Contact: Dwight Duffus, dwight@mathcs.emory.edu |
| Date: 2013-04-26 at 4:00PM |
| Venue: MSC W303 |
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| Abstract: One of the simplests statements of Sidorenko's conjecture is an inequality bounding the homomorphism density from a bipartite graph to a non-empty graph. Due to extensive research the conjecture has been established for various classes of bipartite graphs. The proofs, however, are often complicated and seem to have little relation to one another. Recently (in a yet unpublished paper), Balázs Szegedy gave a new, unified proof of all known cases for which Sidorenko's conjecture has been established. Our aim in this talk is to give some idea of how this proof goes and to discuss which cases it covers. |
| Title: Equations for Hilbert modular surfaces |
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| Seminar: Algebra |
| Speaker: Abhinav Kumar of MIT |
| Contact: David Zureick-Brown, dzb@mathcs.emory.edu |
| Date: 2013-04-24 at 3:00PM |
| Venue: W306 |
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| Abstract: I will describe a method to compute models for Hilbert modular surfaces $Y_{-}(D)$, parametrizing principally polarized abelian surfaces with real multiplication by the full ring of integers in the quadratic field of discriminant D, through moduli spaces of elliptic K3 surfaces. I will also show a couple of applications of these explicit equations, in number theory and in geometry/dynamics. |
| Title: Domination in 3-edge-colored complete graphs |
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| Seminar: Combinatorics |
| Speaker: Daniel Kral of The University of Warwick |
| Contact: Dwight Duffus, dwight@mathcs.emory.edu |
| Date: 2013-04-19 at 4:00PM |
| Venue: MSC W303 |
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| Abstract: Erdos, Faudree, Gould, Gyarfas, Rousseau and Schelp proved that for every complete graph of order $n$ with edges colored with three colors, there exist a set $X$ of 22 vertices and a color $c$ such that the number of vertices in $X$ or joined to a vertex of $X$ by an edge of color $c$ is at least $2n/3$. They also conjectured that the bound of 22 can be lowered to 3. We improve the bound to 4. The talk is based on joint work with Chun-Hung Liu, Jean-Sebastien Sereni, Peter Whalen and Zelealem Yilma. |
| Title: Differential Approximations of the Radiative Transport Equation |
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| Seminar: Numerical Analysis and Scientific Computing |
| Speaker: Qiwei Sheng of The University of Iowa |
| Contact: Hao Gao, haog@mathcs.emory.edu |
| Date: 2013-04-18 at 2:00PM |
| Venue: MSC E408 |
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| Abstract: Abstract: The radiative transport equation (RTE) arises in a variety range of applications in sciences and engineering. It is challenging to solve RTE numerically due to its integro-differential form and high dimension. For highly forward-peaked media, it is even more difficult to solve RTE since accurate numerical solutions require a high resolution of the direction variable, leading to prohibitively large amount of computations. For this reason, various approximations of RTE have been proposed in the literature. This talk is devoted to the introduction and analysis of a family of differential approximations of the RTE. |
| Title: Image Deblurring with Krylov Subspace Methods |
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| Seminar: Numerical Analysis and Scientific Computing |
| Speaker: Per Christian Hansen of Technical University of Denmark |
| Contact: James Nagy, nagy@mathcs.emory.edu |
| Date: 2013-04-17 at 12:50PM |
| Venue: W306 |
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| Abstract: Image deblurring, i.e., reconstruction of a sharper image from a blurred and noisy one, involves the solution of a large and very ill-conditioned system of linear equations, and regularization is needed in order to compute a stable solution. Krylov subspace methods are often ideally suited for this task: their iterative nature is a natural way to handle such large-scale problems, and the underlying Krylov subspace provides a convenient mechanism to regularized the problem by projecting it onto a low-dimensional "signal subspace" adapted to the particular problem. In this talk we consider the three Krylov subspace methods CGLS, MINRES, and GMRES. We describe their regularizing properties, and we discuss some computational aspects such as preconditioning and stopping criteria. |
| Title: Uniform Hypergraphs Containing no Grids |
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| Seminar: Combinatorics |
| Speaker: Miklos Ruszinko of Hungarian Academy of Science and Memphis University |
| Contact: Andrzej Rucinski, andrzej@mathcs.emory.edu |
| Date: 2013-04-15 at 3:00PM |
| Venue: MSC W303 |
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| Abstract: A hypergraph is called an $r\times r$ {\em grid} if it is isomorphic to a pattern of $r$ horizontal and $r$ vertical lines, i.e., a family of sets $\{A_1, \dots ,A_r, B_1,\dots ,B_r\}$ such that $A_i\cap A_j=B_i\cap B_j=\emptyset$ for $1\le i |
| Title: Subcubic triangle-free graphs have fractional chromatic number at most 14/5 |
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| Seminar: Combinatorics |
| Speaker: Zdenek Dvorak of The Georgia Institute of Technology |
| Contact: Dwight Duffus, dwight@mathcs.emory.edu |
| Date: 2013-04-12 at 4:00PM |
| Venue: MSC W303 |
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| Abstract: Every subcubic triangle-free graph on n vertices contains an independent set of size at least $5n/14$ (Staton'79). We strengthen this result by showing that all such graphs have fractional chromatic number at most 14/5, thus confirming a conjecture by Heckman and Thomas.\\ \\ This is joint work with J.-S. Sereni and J. Volec. |
| Title: Gradient Descent Methods for Large-Scale Linear Inverse Problems |
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| Defense: Honors thesis |
| Speaker: Chen (Cool) Cheng of Emory University |
| Contact: James Nagy, nagy@mathcs.emory.edu |
| Date: 2013-04-11 at 4:00PM |
| Venue: W306 |
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| Abstract: Iterative gradient descent methods are frequently used for ill-posed inverse problems because they are suitable for large models and they are cheap to work with. In this thesis, we explore three different types of gradient descent methods: the Landweber method, method of steepest descent, and the Barzilai-Borwein method. Specifically, we also compare the efficiency of these methods to the conjugate gradient method. The thesis begins with an introduction to the history and application of the gradient descent methods and to the methods tested, and follows with convergence analysis and numerical experience on real images. Ways to accelerate and smooth the BB method are also included. |