Seminars and Colloquia by Series

Thursday, August 28, 2008 - 15:00 , Location: Skiles 269 , Mikhail Lifshits , School of Mathematics, Georgia Tech , Organizer: Heinrich Matzinger
We consider a random field of tensor product type X and investigate the quality of approximation (both in the average and in the probabilistic sense) to X by the processes of rank n minimizing the quadratic approximation error. Most interesting results are obtained for the case when the dimension of parameter set tends to infinity. Call "cardinality" the minimal n providing a given level of approximation accuracy. By applying Central Limit Theorem to (deterministic) array of covariance eigenvalues, we show that, for any fixed level of relative error, this cardinality increases exponentially (a phenomenon often called "intractability" or "dimension curse") and find the explosion coefficient. We also show that the behavior of the probabilistic and average cardinalities is essentially the same in the large domain of parameters.
Thursday, August 28, 2008 - 12:00 , Location: Skiles 255 , Sergey Norin , Mathematics, Princeton University , Organizer: Robin Thomas
The problem of generating random integral tables from the set of all nonnegative integral tables with fixed marginals is of importance in statistics. The Diaconis-Sturmfels algorithm for this problem performs a random walk on the set of such tables. The moves in the walk are referred to as Markov bases and correspond to generators of a certain toric ideal. When only one and two-way marginals are considered, one can naturally associate a graph to the model. In this talk, I will present a characterization of all graphs for which the corresponding toric ideal can be generated in degree four, answering a question of Develin and Sullivant. I will also discuss some related open questions and demonstrate applications of the Four Color theorem and results on clean triangulations of surfaces, providing partial answers to these questions. Based on joint work with Daniel Kral and Ondrej Pangrac.
Wednesday, August 27, 2008 - 12:00 , Location: Skiles 255 , Tom Trotter, Teena Carroll, Luca Dieci , School of Mathematics, Georgia Tech , Organizer:
* Dr. Trotter: perspective of the hiring committee with an emphasis on research universities.
* Dr. Carroll: perspective of the applicant with an emphasis on liberal arts universities.
* Dr. Dieci: other advice, including non-academic routes.
Series: PDE Seminar
Tuesday, August 26, 2008 - 15:00 , Location: Skiles 255 , Eldad Haber , Mathematics & Computer Science, Emory University , Organizer:
Optimization problems with PDE constraints are commonly solved in different areas of science and engineering. In this talk we give an introduction to this field. In particular we discuss discretization techniques and effective linear and nonlinear solvers. Examples are given from inverse problems in electromagnetics.
Monday, August 25, 2008 - 16:30 , Location: Skiles 269 , Francisco J. Beron-Vera , Marine & Atmospheric Science, University of Miami , Organizer: Haomin Zhou
The connection between transport barriers and potential vorticity (PV) barriers in PV-conserving flows is investigated with a focus on zonal jets in planetary atmospheres. A perturbed PV-staircase model is used to illustrate important concepts. This flow consists of a sequence of narrow eastward and broad westward zonal jets with a staircase PV structure; the PV-steps are at the latitudes of the cores of the eastward jets. Numerically simulated solutions to the quasigeostrophic PV conservation equation in a perturbed PV-staircase flow are presented. These simulations reveal that both eastward and westward zonal jets serve as robust meridional transport barriers. The surprise is that westward jets, across which the background PV gradient vanishes, serve as robust transport barriers. A theoretical explanation of the underlying barrier mechanism is provided, which relies on recent results relating to the stability of degenerate Hamiltonians under perturbation. It is argued that transport barriers near the cores of westward zonal jets, across which the background PV gradient is small, are found in Jupiter's midlatitude weather layer and in the Earth's summer hemisphere subtropical stratosphere.
Monday, August 25, 2008 - 16:00 , Location: Skiles 255 , Maria Clara Nucci , Dept. of Mathematics and Informatics, University of Perugia , Organizer: Jeff Geronimo
In any standard course of Analytical Mechanics students are indoctrinated that a Lagrangian have a profound physical meaning (kinetic energy minus potential energy) and that Lagrangians do not exist in the case of nonconservative system.  We present an old and regretfully forgotten method by Jacobi which allows to find many nonphysical Lagrangians of simple physical models (e.g., the harmonic oscillator) and also of nonconservative systems (e.g., the damped oscillator).  The same method can be applied to any equation of second-order, and extended to fourth-order equations as well as systems of second and first order. Examples from Physics, Number Theory and Biology will be provided.
Series: PDE Seminar
Tuesday, August 19, 2008 - 15:00 , Location: Skiles 255 , Giovanni Leoni , Carnegie Mellon University, Pittsburgh , Organizer:
In this talk we will discuss some recent existence and regularity results for equilibrium configurations of epitaxially strained crystalline films.