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Texas A&M University
Mathematics

Working Seminar in Groups, Dynamics, and Operator Algebras

Spring 2020

 

Date:February 21, 2020
Time:3:00pm
Location:BLOC 220
Speaker:Konrad Wrobel, Texas A&M University
Title:Ornstein Theory I: Bernoulli Shifts and the Rokhlin Lemma
Abstract:Ornstein theory is a collection of techniques used to prove the Orstein Isomorphism Theorem, a beautiful and deep result which gives a complete classification of Bernoulli shifts by their entropy. Bernoulli shifts arise in many contexts including the theory of flows on manifolds, stochastic processes, transformations of the torus, symbolic coding, statistical mechanics, and ergodic theory. I'll introduce Bernoulli shifts and state the Kolmogorov-Ornstein Isomorphism Theorem. Then, I'll discuss a geometric representation of the Bernoulli shift in the form of the Rokhlin Lemma.

Date:February 27, 2020
Time:3:00pm
Location:BLOC 220
Speaker:James O'Quinn
Title:Ornstein Theory II: Stacks and Gadgets
Abstract:This talk will be a continuation of the talk given last week. During this talk, The geometric representation of p.m.p. actions given by the Rokhlin lemma will be developed even further, which will lead to the definitions of gadgets and their labeling properties. Chapters 3 & 4 of the following notes will be covered: https://www.impan.pl/~gutman/The%20Theory%20of%20Bernoulli%20Shifts.pdf

Date:March 5, 2020
Time:3:00pm
Location:BLOC 220
Speaker:Konrad Wrobel
Title:Ornstein Theory III: Metrics on Partitions and Gadgets
Abstract:Last time, we were introduced to gadgets which are one of the basic tools in Ornstein's proof. This time we'll consider some metrics on partitions and a metric on gadgets. We'll then observe the properties of these metrics and how they relate to isomorphism of actions. This is primarily taken from chapter 5 of Paul Shields' book https://www.impan.pl/~gutman/The%20Theory%20of%20Bernoulli%20Shifts.pdf.