Speaker: Lukas Kuhne (HUJI)

Title:  Matroids doing Algebra

Abstract:

A matroid  is a combinatorial object based on an abstraction of linear independence in vector spaces and forests in graphs. It is a classical question to determine whether a given matroid is representable as a vector configuration over a field. Such a matroid is called linear.

Speaker: Yuval Flimus (Technion)


Title: Oligarchy testing

Abstract:
Arrow's impossibility theorem states that the only voting rule satisfying certain natural requirements is a dictatorship.
Gil Kalai showed that even if we relax some of these requirements so that they only hold with high probability, we are not getting genuine new voting rules.
Arrow's theorem is just one of many paradoxes in social choice theory.

Abstract: I'll discuss  various  "ratio mixing"  properties
of transformations preserving infinite measures e.g. "Krickeberg mixing" (based on the example in Hopf's 1936 book) & "rational weak mixing". I'll also introduce a new one connected to "tied down" renewal theory.

Contains joint works with Hitoshi Nakada, Dalia Terhesiu & Toru Sera


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Meeting ID: 944 0148 4601
Password: 8w24u0

Hind Abu Saleh will speal about reducts of the real ordered field and strongly bounded structures.
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Title: Reducts of the Real Ordered Field and Strongly Bounded Structures

Abstract: Let N =〈 A ;<,.. 〉 be an o-minimal structure and let A =〈 A ;.. 〉 be a reduct of N . The structure A is called strongly bounded if every A -definable subset of A is either bounded or co-bounded. In this talk we examine additive strongly bounded structures over R and as a corollary we identify all possible reducts of 〈 R ;+, ⋅ ,< 〉 , which expand the vector space

Until recently there was known an essentially unique way to resolve singularities of varieties of 
characteristic zero in a canonical way (though there were different descriptions and proofs of correctness). 
Recently a few advances happened -- 
1) The algorithm was extended to varieties with log structures and even to morphisms -- This requires to consider 
more general logarithmic blow ups and results in a stronger logarithmic canonicity of the algorithms even for resolution 

Until recently there was known an essentially unique way to resolve singularities of varieties of 
characteristic zero in a canonical way (though there were different descriptions and proofs of correctness). 

Recently a few advances happened -- 
1) The algorithm was extended to varieties with log structures and even to morphisms -- This requires to consider 
more general logarithmic blow ups and results in a stronger logarithmic canonicity of the algorithms even for resolution 

Abstract: One of the first things we learn about a (proper) Gromov hyperbolic geodesic space X is the construction of the visual boundary of X. An ergodic theorist then learns that for a non-elementary discrete group of isometries G acting properly on X, there is an interesting family of \delta_G-quasi-conformal measures on the boundary. The parameter \delta_G is called the critical exponent of G, and is equal to the exponential growth rate of the orbit Gx in X.

This is the 4th talk in the series

Joint E-seminar of Bar-Ilan University and the Hebrew University
 This is a continuation of last week's talk

Speaker: Michael Krivelevich, Tel Aviv University
Title: Embedding large minors in weak expanders and in sparse random graphs

                         ABSTRACT

A graph G on n vertices is called an alpha-expander if the external neighborhood of every vertex subset U of size |U|<=n/2 in G has size at least alpha*|U|.