On Calabi's strong maximum principle via local Dirichlet forms

Speaker: 

Prof. Kazuhiro Kuwae

Institution: 

Yokohama, visiting UCSD

Time: 

Tuesday, February 3, 2004 - 11:00am

Location: 

MSTB 254

I will talk on a generalization of classical Calabi's strong maximum (1957) in the framework of Dirichlet forms associated with strong Feller diffusion processes.
The proof is stochastic and the result can be applicable to a singular geometric space appeared in the measured Gromov-Hausdorff convergence (precisely in the convergence by spectral distance by Kasue Kumura) of compact Riemannian manifolds with uniform lower Ricci curvature and uniform upper diameter.

Attractors for equations of mathematical physics

Speaker: 

Prof, Mark Vishik

Time: 

Thursday, February 5, 2004 - 4:00pm

Location: 

MSTB 254

The lecture will cover the following topics:
1. Global attractor for an autonomous evolution equation. Examples. between the attractor and the family of complete solutions.
2. Fractal dimension of a global attractor. Examples.
3. Nonautonomous evolution equations and corresponding processes. Uniform global attractor of a process.
4. Global attractor of the nonautonomous 2D Navier Stokes system. Translation-compact forcing term. Relation between the uniform attractor and the family of complete solutions. Nonautonomous 2D Navier-Stokes system with a simple attractor.
5. Kolmogorov epsilon-entropy of the global attractor of a nonautonomous equation. Estimates of the epsilon-entropy. Examples.
6. Some open problems.

Geometric Motion in Plasmas

Speaker: 

Prof. Marshall Slemrod

Institution: 

University of Wisconsin

Time: 

Thursday, January 29, 2004 - 4:00pm

Location: 

MSTB 254

This talk outlines recent work by Feldman, Ha, and Slemrod on the dynamics of the sheath boundary layer which occurs in a plasma consisting of ions and electrons. The equations for the motion are derived from the classical Euler- Poisson equations. Of particular interest is that the boundary layer interface moves via motion by mean curvature where the acceleration of the front (not the velocity) is proportional to the mean curvature of the front.

Nonlinear theory of self-similar crystal growth and melting

Speaker: 

Prof. John Lowengrub

Institution: 

UC Irvine

Time: 

Monday, January 26, 2004 - 4:00pm

Location: 

MSTB 254

In this talk, we demonstrate the existence of non-circular shape-invariant (self-similar) growing and melting two dimensional crystals. This work is motivated by the recent three dimensional studies of Cristini and Lowengrub in which the existence of self-similar shapes was suggested using linear analysis and dynamical numerical simulations. Here, we develop a nonlinear theory of self-similar crystal growth and melting. Because the analysis is qualitatively independent of the number of dimensions, we focus on a perturbed two-dimensional circular crystal growing or melting in a liquid ambient. Using a spectrally accurate quasi-Newton method, we demonstrate that there exist nonlinear self-similar shapes with k-fold dominated symmetries. A critical heat flux J_k is associated with each shape. In the isotropic case, k is arbitrary and only growing solutions exist. When the surface tension is anisotropic, k is determined by the form of the anisotropy and both growing and melting solutions exist. We discuss how these results can be used to control crystal morphologies during growth. This is joint work with Shuwang Li, Perry Leo and Vittorio Cristini.

This is joint work with Shuwang Li, Perry Leo and Vittorio Cristini.

The Ten Martini Problem

Speaker: 

Prof. J. Puig

Institution: 

Universitat de Barcelona, Spain

Time: 

Thursday, January 29, 2004 - 2:00pm

Location: 

MSTB 254

In this talk we will consider the spectrum of the Almost Mathieu operator, \[ \left(H_{b,\phi} x\right)_n= x_{n+1} +x_{n-1} + b \cos\left(2 \pi n\omega + \phi\right)x_n, \] on $l^2(\mathbb{Z})$. We will show that for $b \ne 0,\pm 2$ and $\omega$ Diophantine the spectrum of the operator is a Cantor subset of the real line. This solves the so-called ``Ten Martini Problem'', for these values of $b$ and $\omega$.

The proof uses a combination of results on reducibility, localization and duality for the Almost Mathieu operator, and its associated eigenvalue equation, sometimes called the Harper equation.

Finally, we will also show that for $|b|\ne 0$ small enough or large enough all spectral gaps predicted by the Gap Labelling theorem are open.

Evolutionary Game Dynamics in Finite Populations

Speaker: 

Prof. Christine Taylor

Institution: 

Massachusetts Institute of Technology

Time: 

Friday, January 30, 2004 - 2:00pm

Location: 

MSTB 254

We study the evolutionary game dynamics of a two-strategy game. In infinite populations, the well-known replicator equations describe the deterministic evolutionary dynamics. There are three generic selection scenarios. The dynamics of a finite group of players has received little attention. We provide a framework for studying stochastic evolutionary game dynamics in finite populations. We define a Moran process with frequency dependent fitness. We find that there are eight selection scenarios. And for a given payoff matrix, a number of these sceanrios can occur for different population size. Our results have interesting applications in biology and economics. In particular, we obtain new results on the evolution of cooperation in the classic repeated Prisoner's Dilemma game. We show that a single cooperator using a reciprocal strategy such as Tit-For-Tat can invade a population of defectors with a probability that corresponds to a net selective advantage. We specify the conditions for natural selection to favor the emergence of cooperation and derive conditions for evolutionary stability in finite populations.

L-FUNCTIONS AND GALOIS THEORY

Speaker: 

Prof. Richard Taylor

Institution: 

Harvard University

Time: 

Friday, January 30, 2004 - 4:00pm

Location: 

MSTB 254

I will first recall some examples of L-functions and indicate some of the ways they have been important in algebraic number theory. I will then describe what appears to be their intimate connection with Galois theory (eg the Fontaine-Mazur conjectures), as well as touching on their relationship with algebraic geometry and automorphic forms. Finally, I will discuss what can be proved in this direction.

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