Events & Seminars

2019 Apr 30

Dynamics Seminar: Iftach Dayan (TAU) "Random walks on the 1-dim torus and an application to normal numbers on fractals"

2:15pm to 3:15pm

Location: 

Ross 70
Abstract: We show that under certain conditions, a random walk on the 1-dim torus by affine expanding maps has a unique stationary measure. We then use this result to show that given an IFS of contracting similarity maps of the real line with a uniform contraction ratio 1/D, where D is some integer > 1, under some suitable condition, almost every point in the attractor of the given IFS (w.r.t. a natural measure) is normal to base D.
2019 Mar 13

Set Theory Seminar - Tom Benhamou (TAU), "Projections of Tree-Prikry forcing"

2:00pm to 3:30pm

Location: 

Ross 63
Title: Projections of Tree-Prikry forcing. Abstract: Gitik, Kanovei and Koepke proved that if U is a normal measure over \kappa then the projections of Prikry forcing with U is essentially Prikry forcing with U. The questions remains regarding to the Tree-Prikry forcing. Gitik and B. showed that without normality, it is possible that a Tree-Prikry generic sequence adds a Add(\kappa,1) generic function. In this talk we wish to examine which forcing notions can be projections of Tree-Prikry forcing under different large cardinals assumptions.
2019 Mar 27

Set Theory Seminar - Ralf Schindler (Munster), "Paradoxical" sets with no well-ordering of the reals

2:00pm to 3:30pm

Location: 

Ross 63
Title: "Paradoxical" sets with no well-ordering of the reals Abstract: By a Hamel basis we mean a basis for the reals, R, construed as a vecor space over the field of rationals. In 1905, G. Hamel constructed such a basis from a well-ordering of R. In 1975, D. Pincus and K. Prikry asked "whether a Hamel basis exists in any model in which R cannot be well ordered." About two years ago, we answered this positively in a joint paper with M. Beriashvili, L. Wu, and L. Yu. In more recent joint work, additionally with J. Brendle and F. Castiblanco we constructed a model of
2019 Mar 20

Set Theory Seminar - Tom Benhamou (TAU) (part II)

2:00pm to 3:30pm

Location: 

Ross 63
Title: Projections of Tree-Prikry forcing. Abstract: Gitik, Kanovei and Koepke proved that if U is a normal measure over \kappa then the projections of Prikry forcing with U is essentially Prikry forcing with U. The questions remains regarding to the Tree-Prikry forcing. Gitik and B. showed that without normality, it is possible that a Tree-Prikry generic sequence adds a Add(\kappa,1) generic function. In this talk we wish to examine which forcing notions can be projections of Tree-Prikry forcing under different large cardinals assumptions.
2019 May 01

Set Theory Seminar - Thomas Gilton (UCLA): Abraham-Rubin-Shelah Open Coloring Axiom with a large continuum

2:00pm to 3:30pm

Location: 

Ross 63

Abstract: In their 1985 paper, the above three authors introduced a consistent generalization of Ramsey's theorem to pairs of countable ordinals, which we abbreviate as $OCA_{ARS}$. This axiom asserts that for any continuous coloring (with respect to an appropriate topology) of pairs of countable ordinals, there is a decomposition of $\omega_1$ into countably-many homogeneous sets. The key to their argument is to construct Preassignments of Colors.
2019 Mar 12

Dynamics Seminar: Terry Soo (KU) Finitary isomorphism of Bernoulli flows

2:15pm to 3:15pm

Location: 

Ross 70
A powerful theory due to Ornstein and his collaborators has been successfully applied to many random systems to show that they are isomorphic to independent and identically distributed systems. The isomorphisms provided by Ornstein's theory may not be finitary, that is, effectively realizable in practice. Despite the large number of systems known to be Bernoulli, there are only a handful of cases where explicit finitary isomorphisms have been constructed. In this talk, we will discuss classical and recent constructions, and some long standing open problems.
2019 May 22

Analysis seminar: Yoel Grinshpon "Fluctuations of linear statistics for Schroedinger operators with a random decaying potential"

12:00pm to 1:00pm

Location: 

Ross 70
Title: Fluctuations of linear statistics for Schroedinger operators with a random decaying potential Abstract: Linear statistics provide a tool for the analysis of fluctuations of random measures and have been extensively studied for various models in random matrix theory. In this talk we discuss the application of the same philosophy to the analysis of the finite volume eigenvalue counting measure of one dimensional Schroedinger operators and demonstrate it with some interesting results in the case of a random decaying potential. This is joint work with Jonathan Breuer and Moshe White.
2019 Mar 13

Analysis Seminar: Yehuda Pinchover (Technion) "How large can Hardy-weight be?"

12:00pm to 1:00pm

Location: 

Ross 70
Title: How large can Hardy-weight be? Abstract: In the first part of the talk we will discuss the existence of optimal Hardy-type inequalities with 'as large as possible' Hardy-weight for a general second-order elliptic operator defined on a noncompact Riemannian manifold, while the second part of the talk will be devoted to a sharp answer to the question: "How large can Hardy-weight be?"
2019 Jan 23

T&G: Sylvain Cappell (NYU), Atiyah-Bott classes and extending representations of fundamental groups of 3-manifolds from part of the boundary

1:00pm to 2:00pm

Location: 

Room 70, Ross Building, Jerusalem, Israel
We consider the problem of extending a representation of the fundamental group of 3-manifolds from part of the boundary surfaces. Applications to links will be discussed. Combining this with some cohomology classes of Atiyah and Bott leads to new multivariable polynomial invariants of 3-manifolds with boundary. This is joint work with Edward Miller. No background in 3-dimensional topology will be assumed in this survey and research talk.
2019 Mar 19

Dynamics Seminar: Elon Lindenstrauss (HUJI) - Double variational principle for mean dimension

2:15pm to 3:15pm

Mean dimension is a topological invariant of dynamical systems introduced by Gromov that measures the number of parameters per iteration needed to describe a trajectory in the system. We characterize this invariant (at least for dynamical systems with the marker property, such as infinite minimal systems) using a min-max principle, where choices of both a metric on the topological space and an invariant probability measure on the system are varied. The work I will report on is joint work with M. Tsukamoto.
2019 Jan 15

T&G: Michael Khanevsky (Technion), Geometry of sets of Hamiltonian isotopic curves in a symplectic surface

2:00pm to 3:30pm

Location: 

Room 209, Manchester Building, Jerusalem, Israel
Given two Hamiltonian isotopic curves in a surface, one would like to tell whether they are "close" or "far apart". A natural way to do that is to consider Hofer's metric which computes mechanical energy needed to deform one curve into the other. However due to lack of tools the large-scale Hofer geometry is only partially understood. On some surfaces (e.g. S^2) literally nothing is known.

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