Events & Seminars

2020 May 25

Combinatorics: Yuval Flimus (Technion)

11:00am to 1:00pm

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.
2020 May 26

Jon Aaronson (TAU) On mixing properties of infinite measure preserving transformations

2:00pm to 3:00pm

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


Join Zoom Meeting

Meeting ID: 944 0148 4601
Password: 8w24u0
2020 May 20

Logic Seminar - Hind Abu Saleh "Reducts of the Real Ordered Field and Strongly Bounded Structures"

12:00pm to 2:00pm

Location: 

Zoom: Meeting ID: 928 6821 1553 Password: 829281
Hind Abu Saleh will speal about reducts of the real ordered field and strongly bounded structures.
.
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
2020 May 28

Basic Notions: Michael Tenkin "Resolution: classical, relative and weighted"

4:00pm to 5:15pm

Location: 

Join Zoom Meeting https://huji.zoom.us/j/98768675115?pwd=WnZOZUpuVmpoNGkrYWQxanNVWkQzUT09,

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 
2020 May 21

Basic Notions: Michael Tenkin "Resolution: classical, relative and weighted"

4:00pm to 5:15pm

Location: 

Join Zoom Meeting https://huji.zoom.us/j/98768675115?pwd=WnZOZUpuVmpoNGkrYWQxanNVWkQzUT09


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 
2020 Jun 02

Dynamics seminar : Rhiannon Dougall (Bristol) Critical exponents for subgroups of isometries of negatively curved spaces

2:00pm to 3:00pm


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.
2020 Jun 29

Combinatorics: Dan Hefez (Ariel)

11:00am to 1:00pm

In this talk we will study the so-called perturbed model which is a graph distribution of the form G \cup \mathbb{G}(n,p), where G is an n-vertex graph with edge-density at least d > 0, and d is independent of n.

We are interested in the threshold of the following anti-Ramsey property: every proper edge-colouring of G \cup \mathbb{G}(n,p) yields a rainbow copy of K_s. We have determined this threshold for every s.   

Based on joint work with Elad Aigner-Horev, Oran Danon and Shoham Letzter.

2020 Jun 08

Combinatorics: Bannai Eiichi (Kyushu University)

11:00am to 12:45pm

Location: 

Zoom

Speaker: Bannai Eiichi (Kyushu University)

Title:
On unitary t-designs


Abstract: 

The purpose of design theory is for a given space $M$ to find good finite subsets $X$ of $M$ that approximate the whole space $M$ well. There are many design theories for various spaces $M$. If $M$ is the sphere $S^{n-1}$ then such $X$ are called spherical designs. If $M$ is the unitary group $U(d)$, then such $X$ are called unitary designs. 

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