Giambelli compatible point processes

Speaker: 

Eugene Strahov

Institution: 

Caltech

Time: 

Thursday, May 4, 2006 - 2:00pm

Location: 

MSTB 254

We distinguish a class of random point processes which we call
Giambelli compatible point processes. Our definition was partly
inspired by determinantal identities for averages of products and
ratios of characteristic polynomials for random matrices.
It is closely related to the classical Giambelli formula for Schur symmetric functions.

We show that orthogonal polynomial ensembles, z-measures on
partitions, and spectral measures of characters of generalized
regular representations of the infinite symmetric group generate
Giambelli compatible point processes. In particular, we prove
determinantal identities for averages of analogs of characteristic
polynomials for partitions.

Our approach provides a direct derivation of determinantal
formulas for correlation functions

The geometry of $p$-harmonic morphisms

Speaker: 

Professor Yelin Ou

Institution: 

UC Riverside

Time: 

Tuesday, February 21, 2006 - 4:00pm

Location: 

MSTB 254

$p$-Harmonic morphisms are maps between
Riemannain manifolds that preserve solutions of $p$-
Laplace's equation. They are characterized as horizontally
weakly conformal $p$-harmonic maps so, locally, they are
solutions of an over-determined system of PDEs. I will talk
about some background of $p$-harmonic morphisms, some
calssifications and constructions of such maps, and some
applications related to minimal surfaces and biharmnonic
maps.

On phase transitions for homopolymers and hetereopolymers.

Speaker: 

Professor Michael Cranston

Institution: 

UCI

Time: 

Tuesday, January 31, 2006 - 11:00pm

Location: 

MSTB 254

Given the measure on random walk paths $P_0$ and a Hamiltonian $H$ the Gibbs perturbation of $H$ defined by
$$\frac{dP_{\beta,t}}{dP_0}=Z^{-1}_{\beta,t}\exp\{\beta H(x)\}$$
with
$$Z_{\beta,t}=\int \exp\{-\beta H(x)\}dP_0(x)$$
gives a new measure on paths $x$ which can be viewed as polymers.
In the case $H(x)=\int_0^t\delta_0(x_{s})ds(\int_0^t\delta_0(x_{s})dW_s)$ we say the resulting measure is concentrated on "homopolymers" ("heteropolymers") and are interested in the influence of dimension and $\beta$ on their behavior.

Phase coexistence of gradient Gibbs measures

Speaker: 

Professor Marek Biskup

Institution: 

UCLA

Time: 

Tuesday, February 21, 2006 - 11:00pm

Location: 

MSTB 254

A gradient Gibbs measure is the projection to the gradient variables $\eta_b=\phi_y-\phi_x$
of the Gibbs measure of the form
$$
P(\textd\phi)=Z^{-1}\exp\Bigl\{-\beta\sum_{\langle x,y\rangle}V(\phi_y-\phi_x)\Bigr\}\textd\phi,
$$
where $V$ is a potential, $\beta$ is the inverse temperature and $\textd\phi$ is the product
Lebesgue measure. The simplest example is the (lattice) Gaussian free field
$V(\eta)=\frac12\kappa\eta^2$. A well known result of Funaki and Spohn (and Sheffield)
asserts that, for any uniformly-convex $V$, the possible infinite-volume measures of this type are
characterized by the \emph{tilt}, which is a vector $u\in\R^d$ such that
$E(\eta_b)=u\cdot b$ for any (oriented) edge $b$. I will discuss a simple example
for which this result fails once $V$ is sufficiently non-convex thus showing that
the conditions of Funaki-Spohn's theory are generally optimal. The underlying
mechanism is an order-disorder phase transition known, e.g., from the context
of the $q$-state Potts model with sufficiently large $q$. Based on joint work
with Roman Koteck\'y.

Estimation and Prediction with HIV Treatment Interruption Data

Speaker: 

H. Thomas Banks

Institution: 

Center for Research in Scientific Computation, N.C. State University

Time: 

Thursday, February 16, 2006 - 4:00pm

Location: 

MSTB 254

We consider longitudinal clinical data for HIV patients undergoing treatment interrupt
ions. We use a nonlinear dynamical mathematical model in attempts to fit individual pa
tient data. A statistically-based censored data method is combined with inverse proble
m techniques to estimate dynamic parameters. The predictive capabilities of this appro
ach are demonstrated by comparing simulations based on estimation of parameters using
only half of the longitudinal observations to the full longitudinal data sets.

The loop-erased random walk and the uniform spanning tree on the four-dimensional discrete torus.

Speaker: 

Professor Jason Schweinsberg

Institution: 

UCSD

Time: 

Tuesday, February 14, 2006 - 11:00pm

Location: 

MSTB 254

Let x and y be points chosen uniformly at random
from the four-dimensional discrete torus with side length n.
We show that the length of the loop-erased random walk from
x to y is of order n^2 (log n)^{1/6}, resolving a conjecture
of Benjamini and Kozma. We also show that the scaling limit
of the uniform spanning tree on the four-dimensional discrete
torus is the Brownian continuum random tree of Aldous. Our
proofs use the techniques developed by Peres and Revelle,
who studied the scaling limits of the uniform spanning tree
on a large class of finite graphs that includes the
d-dimensional discrete torus for d >= 5, in combination with
results of Lawler concerning intersections of
four-dimensional random walks.

New Periodic Orbit of the Classical N-Body Problem

Speaker: 

Professor Michael Nauenberg

Institution: 

UCSC

Time: 

Thursday, April 13, 2006 - 4:00pm

Location: 

MSTB 124

Since the discovery in 1993 of the figure-8 orbit by Cris Moore, a large number of periodic orbits for equal n masses have been found having beautiful symmetries and topologies. Most of these orbits are either planar or have been obtained from perturbation of planar orbits.

Recently Moore and I have found also a number of new three-dimensional periodic orbits of this kind which have cubic symmetries. We found these orbits by symmetry considerations, and by minimizing numerically the action integral directly as a function of the Fourier coefficients for the periodic orbit coordinates. I will review some of the early history of periodic orbits, discuss our method, and present video animations of recent results.

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