All Seminars
| Title: Blind Image Restoration in Modern Ground-Based Astronomy |
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| Colloquium: Numerical Analysis and Scientific Computing |
| Speaker: Stuart Jefferies of Department of Physics and the Institute for Astronomy, University of Hawaii |
| Contact: Jim Nagy, nagy@mathcs.emory.edu |
| Date: 2011-11-03 at 4:00PM |
| Venue: MSC W201 |
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| Abstract: Driven by the never-ending quest for better resolution, ground-based astronomy continues its march toward using telescopes with larger and larger apertures. Current “large aperture” (8m-10m) telescopes will soon be eclipsed by 30m-50m behemoths. However, as with any telescope with an aperture of more than about 0.3m, realizing the full resolving power of these telescopes requires the combined use of adaptive optics compensation and image restoration (due to turbulence in the Earth’s atmosphere). Because the characteristics of the image blur are typically unknown, blind deconvolution, where both the target object and the blurring function are estimated from the observed data, is the restoration technique of choice. I will give an overview of blind deconvolution and describe some recent advances that allow us to obtain high-quality imagery under turbulence conditions which, up until now, have been thought unsuitable for high-resolution imaging. |
| Title: Quadratic forms over the rational function field of a field having cohomological dimension 1 |
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| Seminar: Algebra and number theory |
| Speaker: David Leep of University of Kentucky |
| Contact: R. Parimala, parimala@mathcs.emory.edu |
| Date: 2011-11-01 at 3:00PM |
| Venue: MSC E406 |
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| Abstract: In 2003, Colliot-Thelene and Madore constructed a system of two quadratic forms in 5 variables defined over a field of cohomological dimension 1 having no nontrivial common zero lying in the field. This gave the first counterexample to a claim Armand Brumer made in a 1978 paper. I will briefly explain their counterexample, then greatly generalize the counterexample using techniques from the algebraic theory of quadratic forms, and then give a far simpler proof for the wider class of counterexamples. |
| Title: List colorings of infinite graphs |
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| Seminar: Combinatorics |
| Speaker: Peter Komjath of Eotvos Lorand University and Emory University |
| Contact: Dwight Duffus, dwight@mathcs.emory.edu |
| Date: 2011-10-28 at 4:00PM |
| Venue: W306 |
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| Abstract: After a short reminder of things like alephs and well ordering, we consider the notions of coloring number and list-chromatic number for infinite graphs and compare them with the chromatic number and each other, and calculate the list chromatic number for some complete bipartite graphs. We state some theorems essentially saying that, for uncountable graphs, the list chromatic number can be equal to the coloring number, to the chromatic number, but not both. |
| Title: The Rost invariant for groups of type $A$ |
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| Seminar: Algebra and Number Theory |
| Speaker: Anne Queguiner-Mathieu of Paris XIII and Paris-Est |
| Contact: R. Parimala, parimala@mathcs.emory.edu |
| Date: 2011-10-25 at 3:00PM |
| Venue: MSC E406 |
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| Abstract: We discuss an invariant due to Rost for torsors under simple simply connected groups with values in degree three Galois cohomology. We will explain how one can provide an exact formula to compute the Rost invariant of a torsor under the group $SL_1(A)$ of norm 1 elements in a central simple algebra. This talk is based on a joint work with Philippe Gille. |
| Title: Tensor products of division algebras |
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| Seminar: Algebra and Number Theory |
| Speaker: David J. Saltman of CCR Princeton |
| Contact: Skip Garibaldi, skip@mathcs.emory.edu |
| Date: 2011-10-25 at 4:00PM |
| Venue: MSC E406 |
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| Abstract: If $F$ is algebraically closed, and $F_i \supset F$ are field extensions, then $F_1 \otimes_F F_2$ is always a domain. It thus makes sense to conjecture that if $D_i/F_i$ are division algebras (meaning $F_i$ is the center of $D_i$ and $D_i/F_i$ is finite dimensional), then $D_1 \otimes_F D_2$ is a (noncommutative) domain. We will show that this is often true, but not always. We will concentrate on the case that $F$ has characteristic 0 and that the $D_i/F_i$ have prime degree. We also hope to draw attention to the interesting properties of $F_1 \otimes_F F_2$ and how they relate to our problem. Along the way we will make use of Picard varieties and elliptic curves. |
| Title: Recommendation Services for Location-Based Social Networks |
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| Seminar: Computer Science |
| Speaker: Wang-Chien Lee of The Pennsylvania State University |
| Contact: Li Xiong, lxiong@mathcs.emory.edu |
| Date: 2011-10-21 at 3:00PM |
| Venue: MSC W301 |
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| Abstract: With the rapid development of mobile devices, wireless networks and Web 2.0 technology, a number of location-based social networking services (LBSNs), e.g., Foursquare, Whrrl, Facebook Place, Google Latitude, Loopt, and Brightkite, have emerged in recent years. These LBSNs allow users to establish cyber links to their friends or other users, and share tips and experiences of their visits to plentiful point-of-interests (POIs), e.g., restaurants, stores, cinema theaters, etc. Recommendation services, e.g., POI recommendation service that suggests new POIs to users in order to help them explore new places and know their cities better, are essential for LBSNs and thus receiving a lot of research interests. In this talk, I will introduce some recommendation services for LBSNs and present our research effort and results for enabling some of these recommendation services.\\ \\ Bio: \\ Wang-Chien Lee is an Associate Professor of Computer Science and Engineering at Pennsylvania State University, where he leads the Pervasive Data Access (PDA) Research Group to pursue cross-area research in database systems, pervasive/mobile computing, and networking. He is particularly interested in developing data management techniques (including accessing, routing, indexing, caching, aggregation, dissemination, and query processing) for supporting complex queries and location-based services in a wide spectrum of networking and mobile environments such as peer-to-peer networks, mobile ad-hoc networks, wireless sensor networks, and wireless broadcast systems. Meanwhile, he also works on XML, security, information integration/retrieval, and object-oriented databases. He has published more than 200 technical papers on these topics. |
| Title: First-Fit is Linear on $(r+s)$-free Posets |
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| Seminar: Combinatorics |
| Speaker: Kevin Milans of The University of South Carolina |
| Contact: Dwight Duffus, dwight@mathcs.emory.edu |
| Date: 2011-10-21 at 4:00PM |
| Venue: W306 |
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| Abstract: First-Fit is an online algorithm that partitions the elements of a poset into chains. When presented with a new element $x$, First-Fit adds $x$ to the first chain whose elements are all comparable to $x$. In 2004, Pemmaraju, Raman, and Varadarajan introduced the Column Construction Method to prove that when $P$ is an interval order of width $w$, First-Fit partitions $P$ into at most $10w$ chains. This bound was subsequently improved to $8w$ by Brightwell, Kierstead, and Trotter, and independently by Narayanaswamy and Babu. The poset $r+s$ is the disjoint union of a chain of size $r$ and a chain of size $s$. A poset is an interval order if and only if it does not contain $2+2$ as an induced subposet. Bosek, Krawczyk, and Szczypka proved that if $P$ is an $(r+r)$-free poset of width $w$, then First-Fit partitions $P$ into at most $3rw^2$ chains and asked whether the bound can be improved from $O(w^2)$ to $O(w)$. We answer this question in the affirmative. By generalizing the Column Construction Method, we show that if $P$ is an $(r+s)$-free poset of width $w$, then First-Fit partitions $P$ into at most $8(r-1)(s-1)w$ chains. This is joint work with Gwena\"el Joret. |
| Title: Galois algebras, Hasse principle and induction-restriction methods |
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| Seminar: Algebra and number theory |
| Speaker: Eva Bayer-Fluckiger of Swiss Federal Institute of Technology, Lausanne |
| Contact: R. Parimala, parimala@mathcs.emory.edu |
| Date: 2011-10-18 at 3:00PM |
| Venue: MSC E406 |
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| Abstract: The aim of this talk is to prove a local-global principle for the existence of self-dual normal bases for Galois algebras. The proof involves a restriction-induction result for $G$-quadratic forms (provided $G$ has the ``odd determinant property") that is of independent interest. |
| Title: Angles and quasiconformal mappings in space |
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| Seminar: Analysis and Differential Geometry |
| Speaker: Wenfei Zou of Emory University |
| Contact: Wenfei Zou, wzou3@emory.edu |
| Date: 2011-10-18 at 4:00PM |
| Venue: MSC W301 |
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| Abstract: Quasiconformal mappings are natural generalizations of conformal mappings. Angles are preserved under conformal mappings. It is interesting to investigate how angles interact with quasiconformal mappings. In the complex plane, Agard and Gehring studied how angles change under quasiconformal mappings and how angles are used to characterize quasiconformal mappings. In this talk I will discuss how to generalize these results to higher dimension. |
| Title: Abelian varieties with big monodromy |
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| Seminar: Algebra and Number Theory |
| Speaker: David Zureick-Brown of Emory University |
| Contact: TBA |
| Date: 2011-10-13 at 3:00PM |
| Venue: MSC E406 |
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| Abstract: Serre proved in 1972 that the image of the adelic Galois representation associated to an elliptic curve E without complex multiplication has open image; moreover, he also proved that for an elliptic curve over Q the index of the image is always divisible by 2 (and in particular never surjective). More recently, Greicius in his thesis gave criteria for surjectivity and gave an explicit example of an elliptic curve E over a number field K with surjective adelic representation. Soon after, Zywina, building on earlier work of Duke, Jones, and others, proved that the adelic image `random' elliptic curve is maximal. In this talk I will explain recent work with David Zywina in which we generalize these theorems and prove that a random abelian variety in a family with big monodromy has maximal image of Galois. I'll explain the analytic and geometric techniques used in previous work and the new geometric ideas -- in particular, Nori's method of semistable approximation-- needed to generalized to higher dimension. |