Speaker: Boaz Slomka (Open U.) Title: On Hadwiger's covering problem
Abstract: A long-standing open problem, known as Hadwiger’s covering problem, asks what is the smallest natural number N(n) such that every convex body in R^n can be covered by a union of the interiors of N(n) of its translates.
In this talk, I will discuss some history of this problem and its close relatives, and present more recent results, including a general upper bound for N(n).
Title: Some recent results on sublinear algorithms for graph related properties
Abstract: I will describe property testing of (di)graph properties in bounded degree graph models, and talk about a characterization of the 1-sided error testable monotone graph properties and the 1-sided error testable hereditary graph properties in this model. I will introduce the notion of configuration-free properties and talk about some graph theoretic open problems.
Abstract: When are two elements in a given group conjugate? We solve this problem for the group of tree almost-automorphisms. These are homeomorphisms of the tree boundary which locally look like tree automorphisms. The solution is tied with the dynamics of the group action on the tree boundary. This work is joint with W. Lederle.
Manchester Building (Hall 2), Hebrew University Jerusalem
Hamiltonian Floer cohomology was invented by A. Floer to prove the Arnold conjecture: a Hamiltonian diffemorphism of a closed symplectic manifold has at least as many periodic orbits as the sum of the Betti numbers. A variant called Symplectic cohomology was later defined for certain non compact manifolds, including the cotangent bundle of an arbitrary closed smooth manifold. The latter is the setting for classical mechanics of constrained systems. Read more about Colloquium: Yoel Groman (HUJI) - Floer homology of the magnetic cotangent bundle
I will define the notions described in the title, and ask if they are equivalent. I will present a proof showing that they are in case the theory is NIP. The proof is essentially the proof of the fact that the lack of distality is witnessed by a sequence of singletons by Pierre Simon’s.
Repeats every week every Monday until Sun Dec 15 2019 .
1:00pm to 2:00pm
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1:00pm to 2:00pm
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1:00pm to 2:00pm
Location:
Mathematics, Faculty Lounge
This semester will be devoted to resolution of singularities -- a process that modifies varieties at the singular locus so that the resulting variety becomes smooth. For many years this topic had the reputation of very technical and complicated, though rather elementary.
In fact, the same resolution algorithm can be described in various settings, including schemes, algebraic varieties or complex analytic spaces.
Abstract: We consider generic translation flows corresponding to Abelian differentials on flat surfaces of genus $g\ge 2$. These flows are weakly mixing by the Avila-Forni theorem. Recently Forni obtained Hoelder estimates on spectral measures for almost all translation flows, following earlier work by Bufetov and myself in genus two. Combining Forni's idea with our methods, we extended our proof to the case of arbitrary genus $g\ge 2$. It is based on a vector form of the Erd\H{o}s-Kahane argument, which I will try to explain.
This is a joint work with A. Bufetov.
Model-theoretic proofs of partition theorems for semigroups.
Abstract: Partition theorems have the following form. Let "regular" be some notion for a structure S; theorem: for every finite partition of S there is a "regular" set inside a cell of the partition.
