Stochatically modeled reaction networks : positive recurrence and mixing times.

Speaker: 

Jinsu Kim

Institution: 

UCI

Time: 

Tuesday, December 4, 2018 - 11:00am to 12:00pm

Host: 

Location: 

306 RH

 

A reaction network is a graphical configuration that describes an interaction between species (molecules). If the abundances of the network system is small, then the randomness inherent in the molecular
interactions is important to the system dynamics, and the abundances are modeled stochastically as a jump by jump fashion continuous-time Markov chain. One of challenging issues facing researchers who study biological

systems is the often extraordinarily complicated structure of their interaction networks. Thus, how to characterize network structures that induce characteristic behaviors of the system dynamics is one of the major open questions in this literature.

In this talk, I will provide an analytic approach to find a class of reaction networks whose associated Markov process has a stationary distribution. Moreover I will talk about the convergence rate for the process to its stationary distribution with the mixing time.

Higher algebra and arithmetic

Speaker: 

Lars Hesselholt

Institution: 

Nagoya University and Copenhagen University

Time: 

Thursday, February 21, 2019 - 4:00pm to 5:00pm

Host: 

Location: 

RH 306

This talk concerns a twenty-thousand-year old mistake: The natural numbers record only the result of counting and not the process of counting. As algebra is rooted in the natural numbers, the higher algebra of Joyal and Lurie is rooted in a more basic notion of number which also records the process of counting. Long advocated by Waldhausen, the arithmetic of these more basic numbers should eliminate denominators. Notable manifestations of this vision include the Bökstedt-Hsiang-Madsen topological cyclic homology, which receives a denominator-free Chern character, and the related Bhatt-Morrow-Scholze integral p-adic Hodge theory, which makes it possible to exploit torsion cohomology classes in arithmetic geometry. Moreover, for schemes smooth and proper over a finite field, the analogue of de Rham cohomology in this setting naturally gives rise to a cohomological interpretation of the Hasse-Weil zeta function by regularized determinants, as envisioned by Deninger.

Model Theory for Real-valued Structures

Speaker: 

H. Jerome Keisler

Institution: 

University of Wisconsin

Time: 

Monday, January 28, 2019 - 4:00pm

Location: 

RH 440R

Metric structures are like first-order structures except that the formulas take truth values in the unit interval, and instead of equality there is a distance predicate with respect to which every function and predicate is uniformly continuous.  Pre-metric structures are similar the distance predicate is only a pseudo-metric.  In recent years the model theory of metric and pre-metric structures has been successfully developed in a way that is closely parallel to first order model theory, with many applications to analysis.

We consider general structures, where formulas still have truth values in the unit interval, but the predicates and functions need not be continuous with respect to a distance predicate.  It is shown that every general structure can be expanded to a pre-metric structure by adding a distance predicate that is a uniform limit of formulas.  Moreover, any two such expansions have the same notion of uniform convergence.  This can be used to extend almost all of the model theory of metric structures to general structures in a precise way.  For instance, the notion of a stable theory extends in a natural way to general structures, and the main results carry over.

Volume estimates for tubes around submanifolds using integral curvature bounds

Speaker: 

Yousef Chahine

Institution: 

UC Santa Barbara

Time: 

Tuesday, December 4, 2018 - 4:00pm to 5:00pm

Host: 

Location: 

RH 306

We generalize an inequality of E. Heintze and H. Karcher for the volume of tubes around minimal submanifolds to an inequality based on integral bounds for k-Ricci curvature. Even in the case of a pointwise bound this generalizes the classical inequality by replacing a sectional curvature bound with a k-Ricci bound. This work is motivated by the estimates of Petersen-Shteingold-Wei for the volume of tubes around a geodesic and generalizes their estimate. Using similar ideas we also prove a Hessian comparison theorem for k-Ricci curvature which generalizes the usual Hessian and Laplacian comparison for distance functions from a point and give several applications.

On the probability that a stationary Gaussian process with spectral gap remains non-negative on a long interval

Speaker: 

Ben Jaye

Institution: 

Clemson University

Time: 

Tuesday, March 5, 2019 - 3:00pm

Host: 

Location: 

RH 306

In this talk, we shall study certain aspects of the long term behavior of stationary Gaussian process through building polynomials on the unit circle.  No prior knowledge of, or familiarity with, Gaussian processes are required to understand this talk.  Joint work with Naomi Feldheim, Ohad Feldheim, Fedor Nazarov, and Shahaf Nitzan.

 Is $\aleph_1$-categoricity absolute for atomic models?

Speaker: 

Chris Laskowski

Institution: 

University of Maryland

Time: 

Monday, February 4, 2019 - 2:00pm

Location: 

340N RH

In first order logic, the Baldwin-Lachlan characterization of $\aleph_1$-categorical
theories implies that the notion is absolute between transitive models of set theory.  
Here, we seek a similar characterization for having a unique atomic model of size $\aleph_1$.
At present, we have several conditions that imply many non-isomorphic atomic models of size $\aleph_1$.
Curiously, even though the results are in ZFC, their proofs rely on forcing.
This is joint work with John Baldwin and Saharon Shelah.

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