Events & Seminars

2018 May 08

Dynamics Seminar: Tsviqa Lakrec (Huji)

12:00pm to 1:00pm

Location: 

Manchester 209
Consider a simple random walk on $\mathbb{Z}$ with a random coloring of $\mathbb{Z}$. Look at the sequence of the first $N$ steps taken and colors of the visited locations. From it, you can deduce the coloring of approximately $\sqrt{N}$ integers. Suppose an adversary may change $\delta N$ entries in that sequence. What can be deduced now? We show that for any $\theta<0.5,p>0$, there are $N_{0},\delta_{0}$ such that if $N>N_{0}$ and $\delta<\delta_{0}$ then with probability $>1-p$ we can reconstruct the coloring of $>N^{\theta}$ integers.
2018 Jun 19

Tomasz Rzepecki (Uniwersytet Wrocławski): Topological dynamics and Galois groups in model theory

2:15pm to 3:15pm

Location: 

Ross 70
In recent years, topological dynamics have become an important tool in model theory. I will talk about some topological dynamical results from my PhD thesis about the so-called group-like equivalence relations. I plan to give a glimpse of the motivations in model theory (mostly related to the model-theoretic Galois groups and connected components of definable groups) and to show some ideas of the proofs. I will briefly recall the required notions from topological dynamics. Some knowledge of model theory will help to understand the motivations, but otherwise, it will not be necessary.
2018 May 29

Dynamics Lunch: Matan Seidel (Huji) - "The Mass Transport Principle in Percolation Theory"

12:00pm to 1:00pm

Location: 

Manchester lounge
The Mass Transport Principle is a useful technique that was introduced to the study of automorphism-invariant percolations by Häggström in 1997. The technique is a sort of mass conservation principle, that allows us to relate random properties (such as the random degree of a vertex) to geometric properties of the graph. I will introduce the principle and the class of unimodular graphs on which it holds, as well as a few of its applications.
2018 Apr 16

Special talk: Yonatan Harpaz (Paris 13) - "Towards a universal property for Hermitian K-theory"

Lecturer: 

Yonatan Harpaz (Paris 13)
4:30pm to 5:30pm

Location: 

Ross 70

Abstract: Hermitian K-theory can be described as the "real" analogue of algebraic K-theory, and plays a motivic role similar to the role played by real topological K-theory in classical stable homotopy theory. However, the abstract framework surrounding and supporting Hermitian K-theory is less well understood than its algebraic counterpart, especially in the case when 2 is not assumed to be invertible in the ground ring.

2018 Jun 27

Analysis Seminar: Barry Simon (Caltech) "Heinävarra’s Proof of the Dobsch–Donoghue Theorem"

12:00pm to 1:00pm

Location: 

Ross Building, Room 70
Abstract: In 1934, Loewner proved a remarkable and deep theorem about matrix monotone functions. Recently, the young Finnish mathematician, Otte Heinävarra settled a 10 year old conjecture and found a 2 page proof of a theorem in Loewner theory whose only prior proof was 35 pages. I will describe his proof and use that as an excuse to discuss matrix monotone and matrix convex functions including, if time allows, my own recent proof of Loewner’s original theorem.
2018 May 29

Yuri Lima (Paris 11): Symbolic dynamics for non-uniformly hyperbolic systems with singularities

2:15pm to 3:15pm

Location: 

Ross 70
Symbolic dynamics is a tool that simplifies the study of dynamical systems in various aspects. It is known for almost fifty years that uniformly hyperbolic systems have ``good'' codings. For non-uniformly hyperbolic systems, Sarig constructed in 2013 ``good'' codings for surface diffeomorphisms. In this talk we will discuss some recent developments on Sarig's theory, when the map has discountinuities and/or critical points, such as multimodal maps of the interval and Bunimovich billiards.
2018 May 08

Dynamics Seminar: Yinon Spinka (TAU): Finitary codings of Markov random fields

2:15pm to 4:15pm

Location: 

Ross 70
Let X be a stationary Z^d-process. We say that X is a factor of an i.i.d. process if there is a (deterministic and translation-invariant) way to construct a realization of X from i.i.d. variables associated to the sites of Z^d. That is, if there is an i.i.d. process Y and a measurable map F from the underlying space of Y to that of X, which commutes with translations of Z^d and satisfies that F(Y)=X in distribution. Such a factor is called finitary if, in order to determine the value of X at a given site, one only needs to look at a finite (but random) region of Y.
2018 Apr 12

Special talk: Yonatan Harpaz (Paris 13) - "Small extensions in algebra and topology"

Lecturer: 

Yonatan Harpaz (Paris 13)
1:15pm to 2:15pm

Location: 

Ross 70
Abstract: In this talk, we will discuss the notion of small extensions in its various incarnations, from torsors under abelian groups to square-zero extensions of algebras. We will then focus on the somewhat less familiar case of small extensions of ∞-categories. Our main goal is to make this abstract concept concrete and intuitive through a variety of examples. In particular, we will advocate the point of view that small extensions of  ∞-categories offer a unifying perspective in understanding many constructions appearing in obstruction, classification, and deformation theoretic problems

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