Modified-Truncation Finite Difference Schemes for Geophysical Flows

Speaker: 

Professor Don Jones

Institution: 

Arizona State University

Time: 

Tuesday, November 21, 2006 - 3:00pm

Location: 

MSTB 254

We describe a method to improve both the accuracy and computational efficiency of a given finite difference scheme used to simulate a geophysical flow. The resulting modified scheme is at least as accurate as the original, has the same time step, and often uses the same spatial stencil. However, in certain parameter regimes it is higher order. As examples we apply the method to the shallow water equations, the Navier-Stokes equations, and to a sea breeze model.

Analytic continuation of random analytic functions

Speaker: 

Stanislav Molchanov

Institution: 

UNCC

Time: 

Thursday, October 26, 2006 - 2:00pm

Location: 

MSTB 254

We consider random Taylor series and the random $\dzeta$-functions. We prove non-continuation results for both, in case of independent random variables. Also, if the series defined by a stationary process can be continued beyond the radius of convergence we show that the process is deterministic.

Best constants in a class of multiplicative inequalities for derivatives.

Speaker: 

Professor Alexei Ilyin

Institution: 

Visiting UCI

Time: 

Tuesday, October 31, 2006 - 3:00pm

Location: 

MSTB 254

Best constants are found for a class of multiplicative inequalities
that give an estimate of the C-norm of a function in terms of the product
of the L_2-norms of the powers of the Laplace operator.
Special attention is given to functions defined on the sphere S^n.

"On a splitting scheme for the nonlinear Schrodinger equation in a random medium"

Speaker: 

Professor Renaud Marty

Institution: 

UCI

Time: 

Monday, November 6, 2006 - 11:00am

Location: 

MSTB 256

We consider a nonlinear Schr\"odinger equation (NLS) with random
coefficients, in a regime of separation of scales corresponding to
diffusion approximation. The primary goal is to propose and
study an efficient numerical scheme in this framework. We use a
pseudo-spectral splitting scheme and we establish the order of the
global error. In particular we show that we can take an integration step
larger than the smallest scale of the problem, here the correlation
length of the random medium. We study
the asymptotic behavior of the numerical solution in the diffusion
approximation regime.

Universality for mathematical and physical systems

Speaker: 

Professor Percy Deift

Institution: 

Courant Institute

Time: 

Thursday, November 2, 2006 - 4:00pm

Location: 

MSTB 254

All physical systems in equilibrium obey the laws of
thermodynamics. In other words, whatever the precise nature of the
interaction between the atoms and molecules at the microscopic level,
at the macroscopic level, physical systems exhibit universal behavior in
the sense that they are all governed by the same laws and formulae of
thermodynamics.

The speaker will recount some recent history of universality ideas in
physics starting with Wigner's model for the scattering of neutrons
off large nuclei and show how these ideas have led mathematicians to
investigate universal behavior for a variety of mathematical systems.
This is true not only for systems which have a physical origin, but also
for systems which arise in a purely mathematical context such as the
Riemann hypothesis, and a version of the card game solitaire called
patience sorting.

Detecting the trail of a random walker in random scenery.

Speaker: 

Professor Noam Berger

Institution: 

UCLA

Time: 

Tuesday, May 9, 2006 - 1:00pm

Location: 

MSTB 254

Let G be a transient graph, and flip a fair coin at each vertex.
This gives a distribution P. Now start a random walk from a vertex v, and
retoss the coin at each visited vertex, this time with probability 0.75
for heads and probability 0.25 for tails. The eventual configuration of
the coins gives a distribution Q. Are P and Q absolutely continuous w.r.t.
each other? are they singular? (i.e. can you tell whether a random walker
had tampered with the coins or not?) In the talk I'll answer to this
question for various graphs and various types of random walk. Based on
joint work with Y. Peres.

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