Events & Seminars

2015 Dec 31

Groups & dynamics: Thang Neguyen (Weizmann) - Rigidity of quasi-isometric embeddings

10:00am to 11:00am

Location: 

Ross building, Hebrew University of Jerusalem, (Room 70)
To every topological group, one can associate a unique universal
minimal flow (UMF): a flow that maps onto every minimal flow of the
group. For some groups (for example, the locally compact ones), this
flow is not metrizable and does not admit a concrete description.
However, for many "large" Polish groups, the UMF is metrizable, can be
computed, and carries interesting combinatorial information. The talk
will concentrate on some new results that give a characterization of
metrizable UMFs of Polish groups. It is based on two papers, one joint
2015 Nov 24

Dynamics & probability: Yaar Salomon (Stonybrook) "The Danzer problem and a solution to a related problem of Gowers"

2:00pm to 3:00pm

Location: 

Manchester building, Hebrew University of Jerusalem, (Room 209)
The Danzer problem and a solution to a related problem of Gowers
Is there a point set Y in R^d, and C>0, such that every convex
set of volume 1 contains at least one point of Y and at most C? This
discrete geometry problem was posed by Gowers in 2000, and it is a special
case of an open problem posed by Danzer in 1965. I will present two proofs
that answers Gowers' question with a NO. The first approach is dynamical;
we introduce a dynamical system and classify its minimal subsystems. This
2015 Dec 02

Dynamics & probability: Ron Rosenthal (ETHZ) "Local limit theorem for certain ballistic random walks in random environments"

2:00pm to 3:00pm

Location: 

Ross 70
Title: Local limit theorem for certain ballistic random walks in random
environments
Abstract: We study the model of random walks in random environments in
dimension four and higher under Sznitman's ballisticity condition (T').
We prove a version of a local Central Limit Theorem for the model and also
the existence of an equivalent measure which is invariant with respect
to the point of view of the particle. This is a joint work with Noam Berger
and Moran Cohen.
2015 Nov 10

Dynamics & probability: Ariel Rapaport (HUJI) " Self-affine measures with equal Hausdorff and Lyapunov dimensions"

2:00pm to 3:00pm

Location: 

Manchester building, Hebrew University of Jerusalem, (Room 209)
Title: Self-affine measures with equal Hausdorff and Lyapunov dimensions
Abstract:
Let μ be the stationary measure on ℝd which corresponds to a self-affine iterated function system Φ and a probability vector p. Denote by A⊂Gl(d,ℝ) the linear parts of Φ. Assuming the members of A contract by more than 12, it follows from a result by Jordan, Pollicott and Simon, that if the translations of Φ are drawn according to the Lebesgue measure, then dimHμ=min{D,d} almost surely. Here D is the Lyapunov dimension, which is an explicit constant defined in terms of A and p.
2015 Nov 17

Dynamics & probability: Sebastian Donoso (HUJI), "Topological structures and the pointwise convergence of some averages for commuting transformations"

2:00pm to 3:00pm

Location: 

Manchester building, Hebrew University of Jerusalem, (Room 209)
Title: Topological structures and the pointwise convergence of some averages for commuting transformations
Abstract: ``Topological structures'' associated to a topological dynamical
system are recently developed tools in topological dynamics. They have
several applications, including the characterization of topological
dynamical systems, computing automorphisms groups and even the pointwise
convergence of some averages.  In this talk I will discuss some developments
of this subject, emphasizing applications to the pointwise convergence of
2015 Nov 02

Combinatorics seminar

Repeats every week every Monday until Sun Nov 08 2015 .
11:00am to 1:00pm

Abstract:
Expander graphs have many wonderful properties, and have been an immensely useful and fruitful area of research in both applicative and theoretical fields. There has been a lot of interest recently in the study of higher dimensional generalizations of expanders to d-uniform hypergraphs. Many competing definitions have been proposed, and different definitions may be appropriate depending on the property of expanders that we wish to preserve.
2015 Nov 03

Dynamics lunch: Or Landesberg (HUJI)

12:00pm to 1:00pm

Location: 

Manchester building, Hebrew University of Jerusalem, (Room 209)
Title: On the Mixing Property for Hyperbolic Systems [following a paper by Martine Babillot]
2016 Nov 01

Dynamics & probability

Repeats every week every Tuesday until Tue Jan 24 2017 except Tue Nov 01 2016.
2:00pm to 3:00pm

2:00pm to 3:00pm
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2:00pm to 3:00pm

Location: 

Manchester building, Hebrew University of Jerusalem, (Room 209)
Given a Z^d shift of finite type and a finite range shift-invariant interaction, we present sufficient conditions for efficient approximation of pressure and, in particular, topological entropy. Among these conditions, we introduce a combinatorial analog of the measure-theoretic property of Gibbs measures known as strong spatial mixing and we show that it implies many desirable properties in the context of symbolic dynamics. Next, we apply our
2017 Mar 16

Basic Notions: Benjy Weiss (HUJI) - What are amenable groups and why are groups non-amenable

4:00pm to 5:15pm

Location: 

Ross 70
Title: What are amenable groups and why are groups non-amenable
Abstract: I will give an introduction to amenable
groups and explain the result of Kevin Whyte that a
countable non-amenable group admits a
"translation-like" action by a non-abelian free group.
I will also discuss (without proof) a measure theoretic
analogue of this result due to D. Gaboriau and R. Lyons.
2017 Mar 23

Basic Notions: Benjy Weiss (HUJI) - What are amenable groups and why are groups non-amenable II

4:00pm to 5:15pm

Location: 

Ross 70
Title: What are amenable groups and why are groups non-amenable
Abstract: I will give an introduction to amenable
groups and explain the result of Kevin Whyte that a
countable non-amenable group admits a
"translation-like" action by a non-abelian free group.
I will also discuss (without proof) a measure theoretic
analogue of this result due to D. Gaboriau and R. Lyons.
2017 Mar 09

Basic Notions: Benjy Weiss (HUJI) - What are amenable groups and why are groups non-amenable

4:00pm to 5:15pm

Location: 

Ross 70
Title: What are amenable groups and why are groups non-amenable
Abstract: I will give an introduction to amenable
groups and explain the result of Kevin Whyte that a
countable non-amenable group admits a
"translation-like" action by a non-abelian free group.
I will also discuss (without proof) a measure theoretic
analogue of this result due to D. Gaboriau and R. Lyons.

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