Seminars archive

Upcoming Seminars
Mon 05/19/2008 2:00pm	Dissertation Defense Localization Phenomena in Matrix Functions: Theory and Algorithms Nader Razouk, Emory University Venue: Mathematics and Science Center, Room W303 Download printable flyer (PDF, 38 kB)
Mon 05/19/2008 4:00pm	Dissertation Defense Problems in Extremal Combinatorics Andrzej Dudek, Emory University Contact: Andrzej Dudek, adudek@emory.edu Venue: Mathematics and Science Center, Room W304 Download printable flyer (PDF, 45.8 kB)
Thu 05/22/2008 4:00pm	Seminar: Numerical Analysis and Scientific Computing Computing the joint spectral radius of a family of matrices. Nicola Guglielmi, Universita` dell'Aquila Contact: Alessandro Veneziani, ale@mathcs.emory.edu Venue: Mathematics and Science Center, Room W301 Download printable flyer (PDF, 39.7 kB) Show abstract We address the problem of the computation of the spectral radius of a family of matrices. We briefly describe the extension of the concept of polytope to the complex space and outline the main geometric properties of such an object. Then we consider the norms determined by the complex polytopes and illustrate a possible algorithm for the approximation of the joint spectral radius of a family of matrices which is based on these complex polytope norms. As an example for our technique we consider the set of two matrices recently analyzed by Blondel, Nesterov and Theys to disprove the finiteness conjecture. This is a joint work with Marino Zennaro (Universit\`{a} di Trieste, Italy).
Past Seminars
Thu 05/08/2008 4:00pm	Dissertation Defense Polya's Theorem with Zeros Mari Castle, Emory University Contact: Victoria Powers, vicki@mathcs.emory.edu Venue: Mathematics and Science Center, Room W201 Download printable flyer (PDF, 55.6 kB)
Mon 05/05/2008 1:00pm	Seminar: Computer Science Novelty and Diversity in Search Evaluation Charles Clarke, University of Waterloo Contact: Eugene Agichtein, eugene@mathcs.emory.edu Venue: Mathematics and Science Center, Room W301 Download printable flyer (PDF, 38.8 kB) Show abstract Evaluation measures act as objective functions to be optimized by Web search engines and other information retrieval systems. Such objective functions must accurately reflect user requirements, particularly when tuning systems and learning ranking functions. Ambiguity in queries and redundancy in retrieved documents represent two areas where current evaluation measures poorly reflect these requirements. In this talk, I will present a framework for evaluation that systematically rewards novelty and diversity. This framework is developed into a specific evaluation measure based on cumulative gain. The feasibility of the approach is demonstrated using a test collection based on the TREC question answering track. Biography: Charles Clarke is an Associate Professor in the School of Computer Science at the University of Waterloo. His research interests cover a wide range of topics related to information search and retrieval, including question answering, XML, program analysis, filesystem search, user interfaces, and statistical NLP.
Fri 05/02/2008 3:00pm	Seminar: Combinatorics Cleaning d-regular graphs with brushes Pawel Pralat, Dalhousie University, Canada Contact: Vojtech Rodl, rodl@mathcs.emory.edu Venue: Mathematics and Science Center, Room W201 Download printable flyer (PDF, 37.4 kB) Show abstract A model for cleaning a graph with brushes was recently introduced. We consider the minimum number of brushes needed to clean d-regular graphs in this model, focusing on the asymptotic number for random d-regular graphs. We use a degree-greedy algorithm to clean a random d-regular graph on n vertices (with dn even) and analyze it using the differential equations method to find the (asymptotic) number of brushes needed to clean a random d-regular graph using this algorithm (for fixed d). We further show that for any d-regular graph on n vertices at most n(d+1)/4 brushes suffice, and prove that for fixed large d, the minimum number of brushes needed to clean a random d-regular graph on n vertices is asymptotically almost surely n(d+o(d))/4. \ (Joint work with Noga Alon and Nick Wormald.)
Fri 04/25/2008 3:00pm	Seminar: Computer Science Maps and Math: Geographic Information Systems and Spatial Analysis Dr. Lance Waller, Emory University Venue: Mathematics and Science Center, Room W306 Download printable flyer (PDF, 42.3 kB) Show abstract The use of maps to reveal spatial patterns and associations has a long history. More recently, maps and spatial patterns have been used in order to try to understand underlying processes driving the patterns. For example, public health researchers may be interested in investigating whether cases of childhood cancer clustered around toxic waste sites, or conservation biologists may be interested in whether beach construction impacts nesting patterns for endangered sea turtles in Florida. Geographic information systems offer a powerful mechanism for linking spatially referenced data from different sources in order to address questions like these. In this presentation, we will review the basic structure of geographic information systems, central concepts to their use in research, and examples from the fields of epidemiology, disease ecology, conservation biology, and neurology. \ Bio: \ Dr. Waller received his PhD in Operations Research from Cornell University in 1992. His interests involve statistical analysis of spatially referenced data. Examples include tests of spatial clustering of disease cases, for example around a hazardous waste site; small area estimation; hierarchical models with spatially structured random effects; and spatial point process models. Recent applications include spatiotemporal mapping of disease rates, statistical methods for assessing environmental justice, the analysis of spatial trends in Lyme disease incidence and reporting, spatial modelling of the spread of raccoon rabies, and point process analysis of sea turtle nesting locations in Florida. He is interested in both the statistical methodology, and the environmental and epidemiologic models involved in the analysis of this type of data. He teaches courses in spatial biostatistics, applied linear models, and Geographic Information Systems (GIS) in Public Health.
Fri 04/25/2008 1:00pm	Seminar: SIAM Student Chapter Ranking Theory: models and applications Anjela Y. Govan, North Carolina State University Contact: Tobias Graf, tgraf4@emory.edu Venue: Mathematics and Science Center, Room W306 Download printable flyer (PDF, 47.6 kB)
Mon 04/21/2008 4:00pm	Evans-Hall Lecture Evans-Hall Lecture: "Truveo: A Video Search Engine" Adam Beguelin, Venue: Mathematics and Science Center, Room E208 Download printable flyer (PDF, 24.2 kB)
Fri 04/18/2008 3:00pm	Seminar: Computer Science Coupling Query Languages with Structural Indexes Dr. George Fletcher, Washington State University Contact: James Lu, jlu@mathcs.emory.edu Venue: Mathematics and Science Center, Room W306 Download printable flyer (PDF, 42.8 kB) Show abstract Index data structures are crucial for efficient database query processing. Typically, such indexes are built over the data values which occur in the underlying database instance. Alternatively, indexes can be built over the "structure" of the instance. For example, indexes for XML have been proposed which capture the hierarchical structure of the data. The relationships between query languages and such structural indexes, however, are not clearly understood. In this talk we introduce a new methodology for coupling languages and indexes that is aimed towards a better understanding of the use of structural indexes for efficient query evaluation. We focus on the important case of the XML query language XPath, identifying XPath fragments which are ideally coupled with the newly introduced P(k)-partition, which has its definition grounded in the well known A(k) structural indexes. We will then discuss how these couplings are utilized to investigate fundamental questions about the use of structural indexes to accelerate XPath query processing. his is joint work with colleagues at Indiana University, Hasselt University, and the University of Antwerp, with results published in PODS 2006 and DBPL 2007. \ Bio: \ George Fletcher is an assistant professor of computer science at Washington State University, Vancouver. Dr. Fletcher's research interests are in database systems and theory, with a current focus on problems of data integration and sharing in web-scale information systems. Dr. Fletcher received his PhD in 2007 from Indiana University where he held the Paul W. Purdom Fellowship in Informatics.
Thu 04/17/2008 4:00pm	Colloquium Metric Space Inversions and Quasihyperbolic Geometry Prof. David Herron, University of Cincinnati Contact: Shanshuang Yang, syang@mathcs.emory.edu Venue: Mathematics and Science Center, Room W201 Download printable flyer (PDF, 41.1 kB) Show abstract The class of Euclidean spatial conformal mappings is generated by reflections across planes and inversions about spheres. We briefly recall the concept of Euclidean inversion about a sphere, and then define a notion of inversion valid in the general metric space setting and establish several basic facts concerning these. For example, they are quasimoebius homeomorphisms and quasihyperbolically bilipschitz. Just as in the Euclidean setting, sphericalization can be realized as a special case of inversion. Certain important geometric properties are preserved under inversion. For example, both inversion and sphericalization preserve the class of uniform subspaces. \ We introduce a notion called annular quasiconvexity and demonstrate that a space is quasiconvex and annular quasiconvex if and only if its inversions and its sphericalizations also enjoy these properties. Moreover, in the presence of an annular quasiconvex ambient space, we obtain improved quantitative information describing how uniformity constants change. Examples of metric spaces that are quasiconvex and annular quasiconvex include Banach spaces and upper regular Loewner spaces; the latter includes Carnot groups and certain Riemannian manifolds with non-negative Ricci curvature.
Tue 04/15/2008 4:00pm	Seminar: Algebra Lie superalgebras: geometry and cohomology Dan Nakano, University of Georgia Contact: Skip Garibaldi, skip@mathcs.emory.edu Venue: Mathematics and Science Center, Room W303 Download printable flyer (PDF, 42.2 kB) Show abstract Let $g$ be a simple classical Lie superalgebra. In this talk we will construct subalgebras with detect the relative cohomology of $g$ with respect to $g_0$ through the use of invariant theory. This will allow us to define rank varieties and develop a theory of support varieties for modules over the Lie superalgebra. Later in the talk, we will indicate how these varieties provide a geometric interpretation of the combinatorial description of the defect of $g$ and the atypicality of simple $g$-supermodules due to Kac and Wakimoto.
Fri 04/11/2008 3:00pm	Seminar: Computational and Life Sciences Integrated Genomics Approaches to Discovering the Genetic Basis of Complex Traits in Inbred Mouse Strains Eleazar Eskin, University of California, Los Angeles Contact: Liana Smith, smit42@emory.edu Venue: Mathematics and Science Center, Room W201 Download printable flyer (PDF, 42.2 kB) Show abstract Inbred mouse strains are a very powerful and well studied human disease and complex trait model. A tremendous amount of information is available for various inbred strains including phenotypic information stored in the Mouse Phenome Database (MPD) and high-throughput genomic data such as expression microarray data. \ Recently, several high density SNP maps have also been developed for inbred mouse stains. These resources combined with what is already known about mouse genetics in terms of quantitative trait loci (QTLs) and known pathways, make inbred mouse strains an ideal model system. \ We present results of our analyses which combines multiple types of data in order to understand the genetic basis of complex traits. We perform whole genome association analysis of the mouse SNP maps over the phenotypes in the MPD. We describe how we augment our association analysis results with information from expression data, known pathways and QTLs. We demonstrate the how our approach is able to discover many regions in the mouse genome associated with phenotypes and how many of our predictions are consistent with genes known to influence specific traits.