On the $\sigma_2$-scalar curvature and its application

Speaker: 

Professor Yuxin Ge

Institution: 

University Paris 12 & U. Washington

Time: 

Tuesday, March 11, 2008 - 4:00pm

Location: 

MSTB 254

In this talk, we establish an analytic foundation for a fully non-linear equation $\frac{\sigma_2}{\sigma_1}=f$ on manifolds with positive scalar curvature. This equation arises from conformal geometry. As application, we prove that, if a compact 3-dimensional manifold $M$ admits a riemannian metric with positive scalar curvature and $\int
\sigma_2\ge 0$, then topologically $M$ is a quotient of sphere.

Onsager's Conjecture and a Model for Turbulence

Speaker: 

Professor Susan Friedlander

Institution: 

USC and UIC

Time: 

Thursday, February 21, 2008 - 4:00pm

Location: 

MSTB 254

We discuss properties of a shell type model for the inviscid fluid equations. We prove that the forced system has a unique equilibrium which is an exponential global attractor. Every solution blows up in H^5/6 in finite time . After this time, all solutions stay in H^s, s

3D Euler in a 2D Symmetry Plane: Preliminary Computations

Speaker: 

Dr. Miguel Bustamante

Institution: 

University of Warwick, UK

Time: 

Friday, November 9, 2007 - 2:00pm

Location: 

MSTB 254

Initial results from new calculations of interacting anti-parallel Euler vortices are presented with the objective of understanding the origins of singular scaling presented by Kerr (1993) and the lack thereof by Hou and Li (2006). Core profiles designed to reproduce the two results are presented, new more robust
analysis is proposed, and new criteria for when calculations should be terminated are given. Most of the analysis is on a $512\times 128 \times 2048$ mesh, with new analysis on a just completed $1024\times 256\times 2048$ used to confirm trends. The qualitative conclusions of Kerr (1993) are supported, but most of the proposed scaling laws will have to be modified. Assume enstrophy growth like $\Omega\sim (T_c-t)^{-\gamma_\Omega}$ and vorticity growth like $||\omega||_\infty \sim (T_c-t)^{-\gamma}$. Present results would support $\gamma_\Omega\rightarrow 1/4-1/2$ and $\gamma>$. The results are not conclusive since they require higher resolution calculations (work in progress) to further confirm the trends.

Random sampling and probability

Speaker: 

Professor Richard Bass

Institution: 

University of Connecticutt

Time: 

Tuesday, November 20, 2007 - 11:00am

Location: 

MSTB 254

The ``random sampling'' in the title has nothing whatsoever to
do with statistics. Instead, it refers to the perfect reconstruction of
a band-limited function from samples, a classical problem of
Fourier analysis and signal processing. With deterministic sampling,
almost everything is known in one dimension and almost nothing
is known in higher dimensions. It turns out that one loses very little in
efficiency by using random sampling, and in return one can use
probabilistic techniques to get some interesting theoretical results.
This is joint work with Karlheinz Gr\"ochenig.

Martingale Functions of Brownian Motion and Its Local Time at 0

Speaker: 

Professor Patrick Fitzsimmons

Institution: 

UCSD

Time: 

Tuesday, November 6, 2007 - 11:00am

Location: 

MSTB 254

Let $B = (B_t: t\ge 0)$ be a real-valued Brownian motion and let
$L = (L_t: t\ge 0)$ denote its local time in state 0. We present a characterization of the measurable functions $H$ such that $M_t = H(B_t,L_t)$
is a continuous local martingale. It turns out that the class of such functions is considerably wider when one relaxes the smoothness conditions that would be needed for a facile application of It\^o's formula.

Measuring the Anisotropic Behavior of Higher Order Derivative Tensors and Optimal Meshes for Picewise Polynomial Interpolation

Speaker: 

Associated Professor Weiming Cao

Institution: 

The University of Texas at San Antonio

Time: 

Monday, December 3, 2007 - 4:00pm

Location: 

MSTB 254

The error of piecewise polynomial interpolation on anisotropic meshes
is determined by the geometric features of the elements (size,
orientation,
and aspect ratio) and the higher order derivatives of the interpolated
function. In this talk we introduce some quantities to measure the
anisotropic behavior of higher order derivative tensors.
Based on these measures, we derive the error estimates for interpolations
on anisotropic meshes that are quasi-uniform under a given Riemannian
metric.
By using the inertia properties for matrix eigenvalues, we can
identify the optimal mesh metrics leading to the smallest interpolation
error in various norms. Numerical results indicate that the smallest
error is attained exactly on meshes generated with the optimal metrics
as predicted.

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