Seminars and Colloquia by Series

Tuesday, April 16, 2013 - 11:00 , Location: Skiles 006 , Benedict Gross , Harvard University , Organizer: Greg Blekherman
The problem of finding rational solutions to cubic equations is central in number theory, and goes back to Fermat. I will discuss why these equations are particularly interesting, and the modern theory of elliptic curves that has developed over the past century, including the Mordell-Weil theorem and the conjecture of Birch and Swinnerton-Dyer. I will end with a description of some recent results of Manjul Bhargava on the average rank.
Thursday, April 11, 2013 - 11:00 , Location: Skiles 006 , Mark Pollicott , University of Warwick , Organizer: Greg Blekherman
The study of mechanical linkages is a very classical one, dating back to the Industrial Revolution.   In this talk we will discuss the geometry of the configuration spaces in some simple idealized examples and, in particular, their curvature and geometry.  This leads to an interesting quantitative description of their dynamical behaviour.
Thursday, April 4, 2013 - 11:00 , Location: Skiles 006 , Ed Saff , Vanderbilt University , Organizer: Greg Blekherman
While this could be a lecture about our US Congress, it instead deals with problems that are asymptotically related to best-packing and best-covering. In particular, we discuss how to efficiently generate N points on a d-dimensional manifold that have the desirable qualities of well-separation and optimal order covering radius, while asymptotically having a prescribed distribution. Even for certain small numbers of points like N=5,  optimal arrangements with regard to energy and polarization can be a challenging problem.
Thursday, March 14, 2013 - 11:00 , Location: Skiles 006 , Jack Xin , UC Irvine , Organizer: Greg Blekherman
Front propagation in fluid flows arise in power generation of automobile engines, forest fire spreading, and material interfaces of solidification to name a few. In this talk, we introduce the level set formulation and the resulting Hamilton-Jacobi equation, known as G-equation in turbulent combustion. When the fluid flow has enough intensity, G-equation becomes non-coercive and non-linearity no longer dominates. When front curvature and flow stretching effects are included, the extended G-equation is also non-convex. We discuss recent progress in analysis and computation of homogenization and large time front speeds in cellular flows (two dimensional Hamiltonian flows) from both Lagrangian and Eulerian perspectives, and the recovery of experimental observations from the G-equations.
Thursday, March 7, 2013 - 11:00 , Location: Skiles 006 , Alexander Barvinok , University of Michigan , Organizer: Greg Blekherman
Given a d-dimensional convex body C containing the origin in its interior and a real t>1, we seek to construct a polytope P with as few vertices as possible such that P is contained in C and C is contained in tP. I plan to present a construction which breaks some long-held records and is nearly optimal for a wide range of parameters d and t. The construction uses the maximum volume ellipsoid, the John decomposition of the identity and its recent sparsification by Batson, Spielman and Srivastava, Chebyshev polynomials, and some tensor algebra.
Thursday, February 28, 2013 - 11:00 , Location: Skiles 006 , Dmitry Dolgopyat , Univ. of Maryland , Organizer:
The classical Weyl equidistribution theorem says that if v is a non-resonant vector then the sequence v, 2v, 3v... is uniformly distributed on a torus. In this talk we discuss the rate of convergence to the uniform distribution. This is a joint work with Bassam Fayad.
Thursday, February 21, 2013 - 11:00 , Location: Skiles 006 , Mathias Drton , University of Washington , , Organizer: Greg Blekherman
Statistical modeling amounts to specifying a set of candidates for what the probability distribution of an observed random quantity might be.  Many models used in practice are of an algebraic nature in thatthey are defined in terms of a polynomial parametrization.  The goal of this talk is to exemplify how techniques from computational algebraic geometry may be used to solve statistical problems thatconcern algebraic models.  The focus will be on applications in hypothesis testing and parameter identification, for which we will survey some of the known results and open problems.
Friday, February 8, 2013 - 15:00 , Location: Skiles 005 , Van Vu , Yale University , Organizer: Greg Blekherman
Random matrix theory is a fast developing topic with connections to so many areas of mathematics: probability, number theory, combinatorics, data analysis, mathematical physics, to mention a few. The determinant is one of the most studied matrix functionals. In our talk, we are going to  give a brief survey on the studies  of this functional, dated back to Turan in the 1940s. The main focus will be on recent developments that establish the limiting law in various models.
Friday, December 7, 2012 - 16:00 , Location: Skiles 006 , Joan Birman , Columbia University , Organizer: John Etnyre

Kickoff of the Tech Topology Conference from December 7-9, 2012.

This will be a Colloquium talk, aimed at a general audience.  The topic is the curve complex, introduced by Harvey in 1974. It's a simplicial complex, and was introduced as a tool to study mapping class groups of surfaces. I will discuss recent joint work with Bill Menasco about new local pathology in the curve complex, namely that its geodesics can have dead ends and even double dead ends.
Thursday, November 8, 2012 - 11:00 , Location: Skiles 006 , Sebastain Schreiber , UC Davis , , Organizer: Greg Blekherman
Populations, whether they be viral particles, bio-chemicals, plants or animals, are subject to intrinsic and extrinsic sources of stochasticity. This stochasticity in conjunction with nonlinear interactions between individuals determines to what extinct populations are able to persist in the long-term. Understanding the precise nature of these interactive effects is a central issue in population biology from theoretical, empirical, and applied perspectives. For the first part of this talk, I will discuss, briefly, the relationship between attractors of deterministic models and quasi-stationary distributions of their stochastic, finite population counterpoints i.e. models accounting for demographic stochasticity. These results shed some insight into when persistence should be observed over long time frames despite extinction being inevitable. For the second part of the talk, I will discuss results on stochastic persistence and boundedness for stochastic models accounting for environmental (but not demographic) noise. Stochastic boundedness asserts that asymptotically the population process tends to remain in compact sets. In contrast, stochastic persistence requires that the population process tends to be "repelled" by some "extinction set." Using these results, I will illustrate how environmental noise can facilitate coexistence of competing species and how dispersal in stochastic environments can rescue locally extinction prone populations. Empirical work on Kansas prairies, acorn woodpecker populations, and microcosm experiments demonstrating these phenomena will be discussed.