All Seminars

Title: Maximal Chains and Antichains in Finite Partially Ordered Sets
Seminar: Combinatorics
Speaker: Dwight Duffus of Emory University
Contact: Dwight Duffus, dwight@mathcs.emory.edu
Date: 2009-10-16 at 4:00PM
Venue: W306
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Abstract:
Fix integers n and k with n at least k, and n, k > 2. With Bill Sands, we proved that if P is a finite partially ordered set and every maximal chain C of P has between n and n + (n - k)/k - 2) elements, then P must contain k pairwise disjoint maximal antichains. We also constructed a family of examples to show that these inequalities are tight. We raised and made observations about the dual problem, which Dave Howard and Tom Trotter [Georgia Tech] have recently solved.
Title: Counting Problems in Number Theory
Colloquium: Number Theory
Speaker: Manjul Bhargava of Princeton
Contact: R. Parimala, parimala@mathcs.emory.edu
Date: 2009-10-15 at 5:30PM
Venue: MSC E208
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Abstract:
There are some objects in number theory that are particularly fundamental -- examples include "number fields", "class groups", and "elliptic curves" -- yet very little is known about how many such objects there are having given invariants, or how these objects are distributed with respect to these invariants. In this talk, I will try to describe why number theorists are so interested in these questions, and will discuss a few recent results that give some answers.
Title: On Subgrid Pressure Modeling in Incompressible CFD
Seminar: Numerical Analysis and Scientific Computing
Speaker: Maxim Olshanskii of Moscow State University
Contact: Michele Benzi, benzi@mathcs.emory.edu
Date: 2009-10-13 at 4:00PM
Venue: W306
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Abstract:
In the talk we discuss a variational multiscale approach for the pressure subgrid modeling in the Galerkin method for incompressible Navier-Stokes equations. We relate the approach with a stabilization procedure of least-square type known as grad-div stabilization and consider the search of optimal stabilization parameters as a trade-off between mass and energy balance in the discrete system. Application to numerical simulation of laminar and turbulent flows is studied
Title: Informatics-based Quality Improvement in Healthcare: an Analytic Information Warehouse
Seminar: Computer Science
Speaker: Andrew Post of Emory University
Contact: Li Xiong, lxiong@mathcs.emory.edu
Date: 2009-10-09 at 3:00PM
Venue: MSC W301
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Abstract:
An increasing volume of patient data in clinical data warehouses makes possible the identification and analysis of populations with therapeutic responses, outcomes and clinical care processes that are reflected by multivariate trends and patterns over time. This presentation will describe a grid-based software system that is under development at Emory, the Analytic Information Warehouse (AIW), that aims to facilitate discovery and query of those patterns. The AIW will provide controlled terminology support in queries. It will also provide analytic services for extracting concepts from unstructured text, de-identification, discovering features of a patient population and predicting responses and outcomes. Schema adaptors will support connecting to Emory Healthcare's existing clinical data warehouse and other research and clinical databases with appropriate levels of security. These capabilities ultimately will provide broad support to Emory Healthcare and researchers in risk factor identification, prediction, and evaluation of interventions to improve patient care quality and outcomes.\\ \\ Bio:\\ \\ Andrew Post, MD, PhD is a Clinical Informatics Architect at Emory University's Center for Comprehensive Informatics, and Assistant Professor in the Department of Biomedical Engineering. Dr. Post completed an MD at the University of Pennsylvania, and a fellowship and PhD in Biomedical Informatics at the University of Pittsburgh. He is faculty lead of an Analytic Information Warehouse supporting informatics-based quality improvement and research at Emory. He has conducted research in temporal pattern detection, clinical decision support, clinical user interfaces and the promotion of cross-disciplinary collaborations in clinical and translational research environments. His roles have included hospital and research information systems planning.
Title: Chocolate key cryptography: a delicious way to send secret messages
Demonstration: for undergraduates
Speaker: Ezra Brown of Virginia Tech
Contact: Skip Garibaldi, skip@mathcs.emory.edu
Date: 2009-10-08 at 7:00PM
Venue: MSC W201
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Abstract:
The art and science of secure communication is called cryptography. To send someone a secret message, you need two things: (1) a message scrambler ("the cryptosystem"), and (2) a piece of information that tells the sender and the receiver just how the scrambling is done ("the key"). Keeping the key in the right hands and out of the wrong hands is a major problem for cryptographers, and public key cryptography is a solution to this problem that is at work on every computer and in every network in the world. This talk is about Chocolate Key Cryptography, which is a way to describe a certain public key cryptosystem that is easy to learn, fun, interactive, and delicious. Biographical Sketch: Ezra (Bud) Brown grew up in New Orleans, has degrees from Rice and LSU, and has been at Virginia Tech since 1969, where he is currently Alumni Distinguished Professor of Mathematics. Although most of his research has been in number theory and combinatorics, he once wrote a paper with a sociologist. During the summers, he works on problems of cryptography with an unnamed government agency. He has been honored with some teaching and writing awards. He enjoys singing in operas, playing jazz piano, and gardening, and he occasionally bakes biscuits for his students.
Title: A characterization of the polar reflectors
Seminar: Analysis and Differential Geometry
Speaker: Anastasia Svishcheva of Emory University
Contact: Vladimir Oliker, oliker@mathcs.emory.edu
Date: 2009-10-06 at 4:00PM
Venue: MSC W301
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Abstract:
I will speak about the characterization of the polar reflectors (duality transformations of the set of reflectors), i.e. the sufficient conditions for the transformation to be polarity.
Title: (Re-) Discovering Lost Web Pages
Seminar: Computer Science
Speaker: Michael Nelson of Old Dominion University
Contact: Joan Smith, jsmit52@emory.edu
Date: 2009-10-02 at 3:00PM
Venue: MSC W301
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Abstract:
Missing web pages (pages that return the "404 Page Not Found" error) are part of the browsing experience. So too are pages whose owners failed to renew their domain and whose old URls now have unexpected content. Users that encounter a missing page or unexpected page may try to use search engines to discover either the same page at a new location or a similar, "good enough" page to satisfy their information needs, but this can be laborious. To address this need, we are developing a semi-automated framework to assist users to first discover the topic of the missing page, and then locate the same or similar page at a new URl.\\ \\ We have been investigating a number of techniques to discover the "aboutness" of an unknown web page. If the page is in the internet Archive's Wayback Machine or in a search engine cache, the user may be satisfied with the old copy. If an old copy is insufficient, we can use either the page's title or generate a lexical signature to serve as a queiry to a search engine to find the resource. A lexcial signature is a 5-7 word "abstract" of a document that is suitable for using as a queiry to a search engine. The performance of titles and lexcial signatures are comparable, with both achieving over 60 percent success. The combination of titles and lexical signatures from link neighborhoods as well as using tags from del.icio.us, but at this point neither method performs well.\\ \\ Speaker Bio:\\ Michael L. Nelson is an associate professor of computer science at Old Dominion University. Prior to joining ODU, he worked at NASA Langley Research Center from 1991-2002. He is co-editor of the OAI-PMH and OAI-ORE specifications and is a 2007 recipient of an NSF CAREER award. In 2008, Dr. Nelson was named a "Digital Preservation Pioneer" by the Library of Congress. He has developed many digital libraries, including the NASA technical Report Server. His research interests include repository-object interaction and alternative approaches to digital preservation. More information about Dr. Nelson can be found at http://www.cs.odu.edu/~min/
Title: Vertex-coloring edge-weightings
Seminar: Combinatorics
Speaker: Michal Karonski of Mathematics and Computer Science, Emory University and Faculty of Mathematics and Computer Science, Adam Mickiewicz University
Contact: Dwight Duffus, dwight@mathcs.emory.edu
Date: 2009-10-02 at 4:00PM
Venue: W306
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Abstract:
A weighting of the edges of a graph with integer weights gives rise to a weighting of the vertices, the weight of a vertex being the sum of the weights of its incident edges. It is natural to consider edge weighting where we require that adjacent vertices have different weights, that is, that the vertex weighting induce a proper coloring of the graph.\\ \\ Conjecture [Karonski, Luczak and Thomason, 2001]. Edges of every graph that does not contain a component isomorphic to an edge can be weighted with the integers {1,2,3} such that the resultant vertex weighting is a proper coloring.\\ \\ In my talk I will discuss some recent developments regarding the above conjecture.
Title: CAT(0) Cubical Complexes in Group Theory
Seminar: Topology
Speaker: Professor Michah Sageev of Technion University
Contact: Emily Hamilton, emh@mathcs.emory.edu
Date: 2009-09-29 at 3:00PM
Venue: MSC E408
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Abstract:
Title: The Near-Field Single Reflector Problem, a Generalized Legendre Transform and Breaking of the Monge-Kantorovich Optimality Property
Seminar: Analysis and Differential Geometry
Speaker: Tobias Graf of Emory University
Contact: Vladimir Oliker, oliker@mathcs.emory.edu
Date: 2009-09-29 at 4:00PM
Venue: MSC W301
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Abstract:
In recent years, the framework of Monge-Kantorovich optimal transport has proven quite successful in the design of innovative optical systems. A major improvement from a theoretical point of view as well as for practical applications is the design of free-form lenses and mirrors. The optimal transport approach has been applied to a variety of design problems for systems consisting of one or two lenses or reflectors. A classical problem in optical design is the so-called illumination or near-field single reflector problem. In this problem, one needs to design a reflecting surface such that the rays emitted from a non-isotropic source are reflected in such a way to create a prescribed in advance illumination pattern on a given target set at a finite distance. In this talk, we will discuss how the near-field problem fits into a generalized optimal transport framework and how solutions to this transport problem are related to solutions of the near-field problem.