Compactness for Kahler-Einstein manifolds of negative constant scalar curvature

Speaker: 

Jian Song

Institution: 

Rutgers, The State University of New Jersey

Time: 

Tuesday, April 3, 2018 - 3:00pm to 4:00pm

Location: 

RH 306

We discuss general compactness results for Kahler-Einstein manifolds of negative scalar curvature and geometric Kahler-Einstein metrics on smoothable semi-log canonical models. 

 

Joint with Differential Geometry Seminar.

Asymptotic analysis of multi-class queues with random order of service .

Speaker: 

Reza Aghajani

Institution: 

UCSD

Time: 

Saturday, December 2, 2017 - 3:20pm to 4:10pm

Location: 

NS2 1201

The random order of service (ROS) is a natural scheduling policy for systems where no ordering of customers can or should be established. Queueing models under ROS have been used to study molecular interactions of intracellular components in biology. However, these models often assume exponential distributions for processing and patience times, which is not realistic especially when operations such as binding, folding, transcription and translation are involved. We study a multi-class queueing model operating under ROS with reneging and generally distributed processing and patience times. We use measure-valued processes to describe the dynamic evolution of the network, and establish a fluid approximation for this representation. Obtaining a fluid limit for this network requires a multi-scale analysis of its fast and slow components, and to establish an averaging principle in the context of measure-valued process. In addition, under slightly more restrictive assumptions on the patience time distribution, we introduce a reduced, function-valued fluid model that is described by a system of non-linear Partial Differential Equations (PDEs). These PDEs, however, are non-standard and the analysis of their existence, uniqueness and stability properties requires new techniques.

Harnack inequality for degenerate balanced random random walks.

Speaker: 

Jean-Dominique Deuschel

Institution: 

Technische Universitat, Berlin

Time: 

Saturday, December 2, 2017 - 2:00pm to 2:50pm

Location: 

NS2 1201

We consider an i.i.d. balanced environment  $\omega(x,e)=\omega(x,-e)$, genuinely d dimensional on the lattice and show that there exist a positive constant $C$ and a random radius $R(\omega)$ with streched exponential tail such that every non negative

$\omega$ harmonic function $u$ on the ball  $B_{2r}$ of radius $2r>R(\omega)$,

we have $\max_{B_r} u <= C \min_{B_r} u$.

Our proof relies on a quantitative quenched invariance principle

for the corresponding random walk in  balanced random environment and

a careful analysis of the directed percolation cluster.

This result extends Martins Barlow's Harnack's inequality for i.i.d.

bond percolation to the directed case.

This is joint work with N.Berger  M. Cohen and X. Guo.

On the Navier-Stokes equation with rough transport noise.

Speaker: 

James-Michael Leahy

Institution: 

USC

Time: 

Saturday, December 2, 2017 - 11:20am to 12:10pm

Location: 

NS2 1201

In this talk, we present some results on the existence of weak-solutions of the Navier-Stokes equation perturbed by transport-type rough path noise with periodic boundary conditions in dimensions two and three. The noise is smooth and divergence free in space, but rough in time. We will also discuss the problem of uniqueness in two dimensions. The proof of these results makes use of the theory of unbounded rough drivers developed by M. Gubinelli et al.

 

As a consequence of our results, we obtain a pathwise interpretation of the stochastic Navier-Stokes equation with Brownian and fractional Brownian transport-type noise. A Wong-Zakai theorem and support theorem follow as an immediate corollary. This is joint work with Martina Hofmanov\'a and Torstein Nilssen.

Deviations of random matrices and applications.

Speaker: 

Roman Vershynin

Institution: 

UCI

Time: 

Saturday, December 2, 2017 - 10:00am to 10:50am

Location: 

NS2 1201

Uniform laws of large numbers provide theoretical foundations for statistical learning theory. This lecture will focus on quantitative uniform laws of large numbers for random matrices. A range of illustrations will be given in high dimensional geometry and data science.

Algebraic constructions of Markov duality functions

Speaker: 

Jeffrey Kuan

Institution: 

Columbia University

Time: 

Friday, December 8, 2017 - 3:00pm to 4:00pm

Location: 

RH 306

Markov duality in spin chains and exclusion processes has found a wide variety of applications throughout probability theory. We review the duality of the asymmetric simple exclusion process (ASEP) and its underlying algebraic symmetry. We then explain how the algebraic structure leads to a wide generalization of models with duality, such as higher spin exclusion processes, zero range processes, stochastic vertex models, and their multi-species analogues.

The Projection of some Random Cantor sets and the Decay Rate of the Favard length.

Speaker: 

Shiwen Zhang

Institution: 

Michigan State

Time: 

Friday, January 12, 2018 - 2:00pm

Location: 

Rh 340N

The Favard length of a set E has a probabilistic interpretation: up to a constant factor, it is the probability that the Buffon's needle, a long line segment dropped at random, hits E. In this talk, we study the Favard length of some random Cantor sets of dimension 1. Replace the unit disc by 4 disjoint sub-discs of radius 1/4 inside. By repeating this operation in a self-similar manner and adding a random rotation in each step, we can generate a random Cantor set D. Let D_n be the n-th generation in the construction, which is comparable to the 4^{-n}-neighborhood of D. We are interested in the decay rate of the Favard length of these sets D_n as n tends to infinity, which is the likelihood (up to a constant) that the Buffon's needle will fall into the 4^{-n}-neighborhood of D. It is well known that the lower bound for such 1-dimensional set is constant multiple of 1/n. We show that the upper bound of the Favard length of D_n is also constant multiple of 1/n in the average sense.

 

Uniformity of the Möbius function in F_q[t]

Speaker: 

Lê Thái Hoàng

Institution: 

University of Mississippi

Time: 

Thursday, March 15, 2018 - 3:00pm to 4:00pm

Host: 

Location: 

RH 306

The Möbius randomness principle states that the Möbius function μ does not correlate with simple or low complexity sequences F(n), that is, we have non-trivial bounds for sums ∑ μ(n) F(n).

By analogy between the integers and the ring F_q[t] of polynomials over a finite field F_q, we study this principle in the latter setting and expect that for f in F_q[t], μ(f)  does not correlate with low degree polynomials evaluated at the coefficients of f. In this talk, I will talk about our results in the linear and quadratic case. This is joint work with Pierre-Yves Bienvenu.

Short generating functions and their complexity

Speaker: 

Danny Nguyen

Institution: 

UCLA

Time: 

Thursday, March 1, 2018 - 3:00pm to 4:00pm

Location: 

RH 306

Short generating functions were first introduced by Barvinok to enumerate integer points in polyhedra. Adding in Boolean operations and projection, they form a whole complexity hierarchy with interesting structure. We study them in the computational complexity point of view. Assuming standard complexity assumption, we show that these functions cannot effectively represent certain truncated theta functions. Along the way, we will draw connection to ordinary number theoretic objects, such as the set of prime or square numbers. This talk assumes no prior knowledge of the subject. Some open questions will be offered at the end. Joint work with Igor Pak.

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