Eigenvalue Statistics for Random CMV Matrices

Speaker: 

Assistant Professor Mihai Stoiciu

Institution: 

Williams College

Time: 

Thursday, October 2, 2008 - 2:00pm

Location: 

RH 306

CMV matrices are the unitary analogues of one-dimensional discrete Schrodinger operators. We consider CMV matrices with random coefficients and we study the statistical distribution of their eigenvalues. For slowly decreasing random coefficients, we show that the eigenvalues are distributed according to a Poisson process. For rapidly decreasing coefficients, the the eigenvalues have rigid spacing (clock distribution). For a certain critical rate of decay we obtain the circular beta distribution.

K\"ahler-Ricci flow towards the boundary of K\"ahler cone

Speaker: 

Professor Zhou Zhang

Institution: 

University of Michigan

Time: 

Tuesday, November 18, 2008 - 4:00pm

Location: 

RH 306

As the complex version of Ricci flow, K\"ahler-Ricci flow enjoys the special feature, i.e., cohomology information for the evolving K\"ahler metric. The flow can thus be reduced to scalar level as first used by H. D. Cao in the alternative proof of Calabi's Conjecture. People have mostly been focusing on the situation when the K\"ahler class is fixed. As first considered by H. Tsuji, by allowing the class to evolve, the flow can be applied in the study of degenerate class, for example, class on the boundary of K\"ahler cone. We discuss some results in this drection. This is the geometric analysis aspect of Tian's program, which aims at applying K\"ahler-Ricci flow in the study of algebraic geometry objects with great interests.

The Shortest-Distance Multiscale Method for Generalized Fractal Analysis: Mathematical Theory and Computations

Speaker: 

Professor Haris Catrakis

Institution: 

UCI, Mechanical and Aerospace Engineering

Time: 

Monday, November 3, 2008 - 4:00pm

Location: 

RH 306

An analytical and computational method is described which
has broad applicability to studies of multiscale phenomena, such as
turbulence, with regard to fractal dimensions as well as their
scale-dependent extensions known as generalized fractal dimensions as
functions of scale. The mathematical basis of the method is the
analytical relation between the shortest-distance probability density
function and the generalized fractal dimension function. The shortest
distance refers to the distance between any randomly chosen point
location, within a reference boundary, and the nearest part of the
multiscale object of interest. These shortest distances, in addition
to being analytically related to the dimension, provide a means to
characterize the scales of level crossing sets of fluctuating fields
or of the fields themselves. We demonstrate aspects of the method
using exact analytical examples and computational tests.

On dynamical properties of the trace map

Speaker: 

Professor Anton Gorodetski

Institution: 

UCI

Time: 

Tuesday, October 21, 2008 - 4:00pm

Location: 

RH 306

By trace map we mean the following polynomial map of R^3:
T(x,y,z)= (2xy-z, x, y).

Despite of its simple form, it is related to complicated mathematical objects such as character varieties of some surfaces, Painlev\'e sixth equation, and discrete Schr\"odinger operator with Fibonacci potential. We will present some very recent results on dynamics of the trace map and discuss their applications. These is a joint project with D.Damanik.

Some divergence-free finite elements in 2D and 3D

Speaker: 

Professor Shangyou Zhang

Institution: 

University of Delaware

Time: 

Monday, October 20, 2008 - 4:00pm

Location: 

RH 306

The incompressible constraint in fluid dynamics and
the nearly incompressible condition in solid mechanics post a major
difficulty in the numerical computation, especially in the finite
element method. In 1983, Scott and Vogelius showed that the
$P_k$-$P_{k-1}$ element (approximating the velocity by continuous
piecewise-polynomials of degree $k$ and approximating the pressure by
discontinuous piecewise-polynomials of degree $k-1$) is stable and
consequently of the optimal order on 2D triangular grids for any
$k\ge 4$, provided the grids have no nearly-singular vertex.
For such a combination of mixed elements, the finite element
velocity is divergence free point wise, truly incompressible.
The 3D version of $P_k$-$P_{k-1}$ problem is still open.
We give some partial answers and present some newly discovered
divergence-free elements in this talk.

Mathematical and numerical study of Maxwells equations in negative index material

Speaker: 

Professor Jichun Li

Institution: 

Univ. of Nevada Las Vegas and IPAM at UCLA

Time: 

Monday, September 29, 2008 - 4:00pm

Location: 

RH 306

Since 2000, there has been a growing interest in the study of negative
index metamaterials across many disciplinaries. In this talk, I'll first derive
the Maxwell's equations resulting from negative index metamaterials. Then I'll discuss some time-domain mixed finite elements developed for solving these equations, followed by succinct error estimate. Finally, some numerical
results will be presented.

Rigidity of Quasi-Einstein Metrics

Speaker: 

Professor Yujen Shu

Institution: 

UC Santa Barbara

Time: 

Tuesday, December 2, 2008 - 3:00pm

Location: 

RH 306

We call a metric quasi-Einstein if the m-Bakry-Emery Ricci tensor is a constant multiple of the metric tensor. This is a generalization of Einstein metrics, which contains gradient Ricci solitons and is also closely related to the construction of the warped product Einstein metrics. We study properties of quasi-Einstein metrics and prove several
rigidity results. We also give a splitting theorem for some Kahler quasi-Einstein metrics.

New singular solutions of the critical and supercritical Nonlinear Schrodinger equation (NLS)

Speaker: 

Dr Nir Gavish

Institution: 

Tel Aviv University

Time: 

Monday, October 13, 2008 - 4:00pm

Location: 

RH 306

The study of singular solutions of the NLS goes back to the 1960s, with applications in nonlinear optics and, more recently, in BEC. Asymptotic and numerical studies conducted in the 80s showed that singular solutions of the critical NLS collapse with the Townes (R) profile at a blowup rate known as the loglog law. Recently (2003) Merle and Raphael proved this result rigorously for a large class of initial conditions. Concurrently, it was demonstrated experimentally that the profile of collapsing laser beams is given by the Townes profile. Thus, all the research that was carried out from the eighties until these days leads to the belief that the Townes profile is the only attractor of blowup solutions of the critical NLS.
In this talk I will present new families of singular solutions of the critical and supercritical NLS that collapse with a self-similar ring profile, and whose blowup rate is different from the one of the "old" singular solutions. I will show, experimentally and theoretically, that these new blowup profiles are attractors for large super-Gaussian initial conditions.
In addition, I will present in the talk a semi-static adaptive grid method we have developed for the numerical simulations involved in this study for solutions which focus over 15 orders of magnitude.

Classification of compact ancient solutions of the Curve Shortening flow and the Ricci flow on Surfaces

Speaker: 

Professor Panagiota Daskalopoulos

Institution: 

Columbia University

Time: 

Tuesday, October 14, 2008 - 4:00pm

Location: 

RH 306

We classify compact ancient solutions of the curve
shortening flow and the Ricci flow on Surfaces. We show that these are either a family of contracting circles (contracting spheres in the case of the Ricci flow on surfaces), which is a type I ancient solution,or a family of Angenent ovals (Rosenau solutions in the case of the Ricci flow on surfaces), which corresponds to a type II
solution.

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