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Previous Lectures

Dr. A. Debernardi, Bar-Ilan University
14/01/2019 - 14:00 - 15:15

We will discuss some problems related to Hankel transforms of \textbf{real-valued} general monotone functions,
some of them generalize previously known results, and some others are completely new. To mention some, we give
a criterion for uniform convergence of Hankel transforms, and we also give a solution to Boas' problem in this
context. In particular, the latter implies a generalization of the well-known Hardy-Littlewood inequality for
Fourier transforms.

Prof. David Shoikhet, Holon Institute of Technology, Israel
07/01/2019 - 14:00 - 15:45

This talk is based on joint work with Mark Elin and Toshiyuki Sugawa. Let $f$
\ be the infinitesimal generator of a one-parameter semigroup $\left\{
F_{t}\right\} _{t>0}$ of holomorphic self-mappings of the open unit disk,
i.e., $f=\lim_{t\rightarrow 0}\frac{1}{t}\left( I-F_{t}\right) .$ In this
work, we study properties of the resolvent family $R=\left\{ \left(
I+rf\right) ^{-1}\right\} _{r>0}$ \ in the spirit of geometric function
theory. We discovered, in particular, that $R$ forms an inverse Loewner
chain and consists of starlike functions of order $\alpha >1/2$. Moreover,
each element of $R$ satisfies the Noshiro-Warshawskii condition $\left(
\func{Re}\left[ \left( I+rf\right) ^{-1}\right] ^{\prime }\left( z\right)
>0\right) .$ This, in turn, implies that all elements of $R$ are also
holomorphic generators. Finally, we study the existence of repelling fixed
points of this family.

Prof. Elchanan Mossel, Massachusets Institute of Technology, USA
24/12/2018 - 14:00 - 15:25

Two important results in Boolean analysis highlight the role of majority functions in the theory
of noise stability. Benjamini, Kalai, and Schramm (1999) showed that a boolean monotone function
is noise-stable if and only if it is correlated with a weighted majority. Mossel, O’Donnell, and
Oleszkiewicz (2010) showed that simple majorities asymptotically maximize noise stability among
low influence functions. In the talk, we will discuss and review progress from the last decade
in our understanding of the interplay between Majorities and noise-stability. In particular, we
will discuss a generalization of the BKS theorem to non-monotone functions, stronger and more
robust versions of Majority is Stablest and the Plurality is Stablest conjecture. We will also
discuss what these results imply for voting.

Prof. D. Ryabogin, Kent State University, Ohio, USA
17/12/2018 - 14:00 - 15:30

In  1956, Busemann and Petty  posed a series of questions about
symmetric convex bodies, of which only the first one has been solved.
Their fifth problem asks the following.

Let K be  an origin symmetric convex body in the n-dimensional Euclidean
space and let H_x be a hyperplane passing through the origin orthogonal to
a unit direction x. Consider a hyperplane G parallel to H_x and supporting
to K and let              C(K,x)=vol(K\cap H_x)dist (0, G).
If  there exists a constant C such that for all directions x we have
C(K,x)=C, does it follow that K is an ellipsoid?

We give an affirmative answer to this problem for bodies sufficiently
close to the Euclidean ball in the Banach-Mazur distance. This is a joint
work with Maria Alfonseca, Fedor Nazarov and Vlad Yaskin.

Dr. Eli Shamovich, University of Waterloo, Waterloo, Ontario, Canada
10/12/2018 - 15:05 - 16:00

In this talk, we will discuss what is special about the Hardy spaces $H^2(\mathbb{D})$ and its
multiplier algebra $H^{\infty}(\mathbb{D})$, from the point of view of operators algebras and
function theory. I will present two generalizations of the pair $H^2$ and $H^{\infty}$ to the
multivariable setting. One commutative and one noncommutative. We will then discuss a natural
classification question that arises in the multivariable setups of algebras of analytic functions
on subvarieties of the unit ball. These algebras arise naturally as universal operator algebras
of a class of row contractions. Only basic familiarity with operators on Hilbert spaces and complex
analysis is assumed.

Prof. Boris Rubin, Louisiana State University, USA
10/12/2018 - 14:00 - 15:00

The horospherical Radon transform integrates functions on the n-dimensional real
hyperbolic space over d-dimensional horospheres, where d is a fixed integer, $1\le d\le n-1$.
Using the tools of real analysis, we obtain sharp existence conditions and explicit inversion
formulas for these transforms acting on smooth functions and functions belonging to $L^p$. The
case d = n-1 agrees with the classical Gelfand-Graev transform which was studied before in
terms of the distribution theory on rapidly decreasing smooth functions. The results for
$L^p$-functions and the case d < n-1 are new. This is a joint work with William O. Bray.

Dr. A. Kuleshov, Moscow State University, Russia
03/12/2018 - 14:00 - 15:10

We prove that each function of one variable forming a continuous finite sum of ridge functions

on a convex body belongs to the VMO space on every compact interval of its domain. Also, we prove that for the existence of finite limits of the functions of one variable forming the sum at the 

corresponding boundary points of their domains, it suffices to assume the Dini condition on the 

modulus of continuity of some continuous sum of ridge functions on a convex body E at some boundary point. Further, we prove that the obtained (Dini) condition is sharp.

Prof. E. Liflyand, Bar-Ilan University
26/11/2018 - 14:00 - 15:50

Asymptotic-wise results for the Fourier transform of a function of convex type are proved.
Certain refinement of known one-dimensional results due to Trigub gives a possibility to
obtain their multidimensional generalizations.

Prof. Dmitry Karp, Institute of Applied Mathematics, Far Eastern Branch of Russian Academy of Sciences, Russia
12/11/2018 - 14:00 - 15:25

We investigate conditions for the logarithmic complete
monotonicity of a quotient of two products of gamma functions, where
the argument of each gamma function has a different scaling factor. We
give necessary and sufficient conditions in terms of non-negativity of
some elementary functions and some more practical sufficient
conditions in terms of parameters. Further, we study the representing
measure in Bernstein’s theorem for both equal and non-equal scaling
factors. This leads to conditions on the parameters under which Meijer’s
G-function or Fox’s H-function represents an infinitely divisible
probability distribution on the positive half-line.

Dr. Yuki Takahashi, Bar-Ilan University
05/11/2018 - 14:00 - 15:15

We consider Iterated Function Systems of linear fractional transformations, and show that the
Hausdorff dimension of the attractor is given by the Bowen's pressure formula, if the Iterated
Function Systems satisfy the exponential separation condition. We also show that almost every
finite collections of $GL_n( \mathbb{R} )$ matrices are Diophantine if the matrices have positive
entries. This is a joint work with Boris Solomyak.

Prof. Andrei Lerner, Bar-Ilan University
26/10/2018 - 14:05 - 15:05

We construct an example showing the sharpness of certain weighted weak type (1,1) bounds
for the Hilbert transform. This is joint work with Fedor Nazarov and Sheldy Ombrosi.

Dr. Naomi Feldheim, Bar-Ilan University
22/10/2018 - 14:00 - 15:20

It is known that the Fourier transform of a measure which vanishes on [-a,a]
must have asymptotically at least a/pi zeroes per unit interval.
One way to quantify this further is using a probabilistic model:
Let f be a Gaussian stationary process on R whose spectral measure vanishes on [-a,a].
What is the probability that it has no zeroes on an interval of length L?
Our main result shows that this probability is at most e^{-c a^2 L^2}, where c>0 is an absolute constant.
This settles a question which was open for a while in the theory of Gaussian processes.
I will explain how to translate the probabilistic problem to a problem of minimizing weighted
L^2 norms of polynomials against the spectral measure, and how we solve it using tools from
harmonic and complex analysis. Time permitting, I will discuss lower bounds.
Based on a joint work with Ohad Feldheim, Benjamin Jaye, Fedor Nazarov and Shahaf Nitzan (arXiv:1801.10392).

Prof. Yuval Peres, Microsoft Research
15/10/2018 - 14:00 - 15:00

In the trace reconstruction problem, an unknown string $x$ of $n$ bits is observed through the deletion channel, which deletes each bit with some constant probability $q$, yielding a contracted string. How many independent outputs (traces) of the deletion channel are needed to reconstruct $x$ with high probability?


The best lower bound known is of order $n^{1.25}$. Until 2016, the best upper bound available was exponential in the square root of $n$. With Fedor Nazarov, we improve the square root to a cube root using complex analysis (bounds for Littlewood polynomials on the unit circle). This upper bound is sharp for reconstruction algorithms that only use this statistical information. (Similar results were obtained independently and concurrently by De, O’Donnell and Servedio). If the string $x$ is random and $q<1/2$, we can show a subpolynomial number of traces suffices by comparison to a biased random walk. (Joint work with Alex Zhai, FOCS 2017). With Nina Holden and Robin Pemantle (COLT 2018), we removed the restriction $q<1/2$ for random inputs.

Prof. Yuval Peres, Microsoft Research
15/10/2018 - 14:00 - 15:10

In the trace reconstruction problem, an unknown string $x$ of $n$ bits is observed through
the deletion channel, which deletes each bit with some constant probability $q$, yielding
a contracted string. How many independent outputs (traces) of the deletion channel are needed
to reconstruct $x$ with high probability?
The best lower bound known is of order $n^{1.25}$. Until 2016, the best upper bound available
was exponential in the square root of $n$. With Fedor Nazarov, we improve the square root to
a cube root using complex analysis (bounds for Littlewood polynomials on the unit circle).
This upper bound is sharp for reconstruction algorithms that only use this statistical information.
(Similar results were obtained independently and concurrently by De, O’Donnell and Servedio). If
the string $x$ is random and $q<1/2$, we can show a subpolynomial number of traces suffices by
comparison to a biased random walk. (Joint work with Alex Zhai, FOCS 2017). With Nina Holden and
Robin Pemantle (COLT 2018), we removed the restriction $q<1/2$ for random inputs.

Prof. Anatoly Golberg, Holon Institute of Technology
11/06/2018 - 14:00 - 15:45

We study the asymptotic behavior of the ratio $|f(z)|/|z|$ as $z\to 0$ for homeomorphic mappings
differentiable almost everywhere in the unit disc with non-degenerated Jacobian. The main tools
involve the length-area functionals and angular dilatations depending on some real number $p.$
The results are applied to homeomorphic solutions of a nonlinear Beltrami equation. The estimates
are illustrated by examples.

Prof. Vladimir Golubyatnikov, Sobolev institute of mathematics, Novosibirsk, Russia
14/05/2018 - 15:05 - 16:00

We study geometry and combinatorial structures of phase portrait of some nonlinear
kinetic dynamical systems as models of circular gene networks in order to find conditions
of existence of cycles of these systems. Some sufficient conditions of existence of their
stable cycles are obtained as well.

Rachel Greenfeld, Bar-Ilan University
14/05/2018 - 14:00 - 15:00

A set $\Omega$ in $R^d$ is called spectral if the space $L^2(\Omega)$ admits an orthogonal basis consisting of exponential
functions. Which sets $\Omega$ are spectral? This question is known as "Fuglede's spectral set problem".
In the talk we will be focusing on the case of product domains, namely, when $\Omega = AxB$.
In this case, it is conjectured that $\Omega$ is spectral if and only if the factors A and B are both spectral.
We will discuss some new results, joint with Nir Lev, supporting this conjecture, and their applications
to the study of spectrality of convex polytopes.

Prof. Ya. Krasnov, Bar-Ilan University
07/05/2018 - 14:00 - 15:45

Many well-known (classes of) differential equations  may be viewed as an equation in a certain
commutative nonassociative algebra. We develop further the principal idea of L. Markus for deriving
algebraic properties of solutions to ODEs and PDEs directly from the equations defining them.
Our main purpose is a) to show how the algebraic formalism can be applied with great success to a
remarkably elegant description of the geometry of curves being solutions to homogeneous polynomial ODEs,
and, on the other hand, b) to motivate the recent interest in applications of nonassociative algebra
methods to PDEs. More precisely, given a differential equation on an algebra A, we are interested in
the following two problems:

1. Which properties of the differential equation determine certain algebraic structures on $A$ such as
to be power associative, unital or division algebra.

2. In the converse direction, which properties of $A$ imply certain qualitative information about the
differential equation, for example topological equivalent classes, existence of a bounded, periodic,
ray solutions, ellipticity, etc.

We also define and discuss syzygies between Peirce numbers which provide an effective tool for our study.
(Some results here are based on a recent joint work with V. Tkachev.)

Dr. Serge Itshak Lukasuewicz, Bar-Ilan University
30/04/2018 - 14:00 - 15:35

The Chazarain-Poisson summation formula for Riemannian manifolds (which generalizes the Poisson Summation formula)
computes the distribution trace. In the case of Riemannian surfaces with constant (sectional) curvature, we study
the holomorphic extension of the shifted trace. We have three generic cases according to the sign of the curvature:
the sphere, the torus and the compact hyperbolic surfaces of negative constant curvature. We use the shifted
Laplacian in order to be able to use the Selberg trace formula. Our results concern the case of the torus, the case
of a compact Riemannian surfaces with constant (sectional) negative curvature, and the case of a compact Riemannian
manifold of dimension $n$ and constant curvature, $n\ge 3$.

Prof. Yosef Yomdin, Weizmann Institute
16/04/2018 - 14:00 - 15:15

Smooth parametrization consists in a subdivision of a mathematical object under consideration into simple pieces,
and then parametric representation of each piece, while keeping control of high order derivatives. Main examples
for this talk are C^k or analytic parametrizations of semi-algebraic and o-minimal sets.
We provide an overview of some results, open and recently solved problems on smooth parametrizations, and their
applications in several apparently rather separated domains: Smooth Dynamics, Diophantine Geometry, and Analysis.
The structure of the results, open problems, and conjectures in each of these domains shows in many cases a
remarkable similarity, which we plan to stress.
We consider a special case of smooth parametrization: ``doubling coverings” (or “conformal invariant Whitney coverings”),
and “Doubling chains”. We present some new results on the complexity bounds for doubling coverings, doubling chains,
and on the resulting bounds in Kobayashi metric and Doubling inequalities. We plan also to present a short report on
a remarkable progress, recently achieved in this (large) direction by two independent groups (G. Binyamini, D. Novikov,
on one side, and R. Cluckers, J. Pila, A. Wilkie, on the other).

Dr. Bochen Liu, Bar-Ilan University
09/04/2018 - 14:00 - 15:35

Given a measure on a subset of Euclidean spaces. The $L^2$ spherical averages of the Fourier transform of this measure was originally used to attack Falconer distance conjecture, via Mattila’s integral. In this talk, we will consider pinned distance problem, a stronger version of Falconer distance problem, and show that spherical averages imply the same dimensional threshold on both problems. In particular, with the best known spherical averaging estimates, we improve a result of Peres and Schlag on pinned distance problem significantly. The idea is to reduce the pinned distance problem to an integral where spherical averages apply. The key new ingredient is an identity between square functions.

Prof. Elza Farkhi, Tel-Aviv University
19/03/2018 - 14:00 - 15:40

The talk surveys joint works with T. Donchev and more recent ones with R. Baier.
We discuss some (continuous and discrete) versions of the celebrated Filippov
theorem on approximate solutions of differential (and difference) equations and
inclusions that  extend classical stability results for differential equations
with continuous and discontinuous right-hand sides. We present some applications
related to numerical solution of differential equations and inclusions.

Prof. Richard Kerner, University Pierre et Marie Curie - Sorbonne Universit\'es Paris, France
05/03/2018 - 14:00 - 15:35

We discuss cubic and ternary algebras which are a direct generalization of Grassmann
and Clifford algebras, but with $Z_3$-grading replacing the usual $Z_2$-grading.
Elementary properties and structures of such algebras are discussed, with special interest
in low-dimensional ones, with two or three generators.
Invariant antisymmetric quadratic and cubic forms on such algebras are introduced, and it
is shown how the $SL(2,C)$ group arises naturally in the case of lowest dimension, with
two generators only, as the symmetry group preserving these forms.
We also show how the calculus of differential forms can be extended to include also second
differentials $d^2 x^i$, and how the $Z_3$ grading naturally appears when we assume that
$d^3 = 0$ instead of $d^2 = 0$.
Ternary analogue of the commutator is introduced, and its relation with usual Lie algebras
investigated, as well as its invariance properties.
We shall also discuss certain physical applications In particular, $Z_3$-graded gauge theory
is briefly presented, as well as ternary generalization of Pauli's exclusion principle and
ternary Dirac equation for quarks.

Prof. Boris Solomyak Bar-Ilan University
15/01/2018 - 14:00 - 15:30

Let $\mu$ be a finitely-supported measure on $SL_{2}(\mathbb{R})$ generating a non-compact and 
totally irreducible subgroup, and let $\nu$ be the associated stationary (Furstenberg) measure. 
We prove that if the support of $\mu$ is ``Diophantine,'' then
where $h_{RW}(\mu)$ is the random walk entropy of $\mu$, $\dim$ denotes pointwise dimension, 
and $\chi$ is the Lyapunov exponent of the random walk generated by $\mu$.
In particular, for every $\delta>0$, there is a neighborhood $U$ of the identity in 
$SL_{2}(\mathbb{R})$ such that if $\mu$ has support in $U$ on matrices with algebraic entries, 
is atomic with all atoms of size at least $\delta$, and generates a group which is non-compact 
and totally irreducible, then its stationary measure $\nu$ satisfies  $\dim\nu=1$.
This is a joint work with M. Hochman.
In my talk, I will try to explain the concepts and motivate the result.

Prof. Shai Dekel, Tel-Aviv University
08/01/2018 - 14:00 - 15:15

Maximal and atomic Hardy spaces $H^p$ and $H_A^p$ , $0 < p = 1$, are considered in
the setting of a doubling metric measure space in the presence of a non-negative
self-adjoint operator whose heat kernel has Gaussian localization. It is shown that
$H^p = H_A^p$ with equivalent norms.

Dr. Nadav Yesha, King's College, London, UK
25/12/2017 - 15:05 - 16:00

In this talk we discuss the fine scale $L^2$-mass distribution of toral Laplace
eigenfunctions with respect to random position. For the 2-dimensional torus, under
certain flatness assumptions on the Fourier coefficients of the eigenfunctions and
generic restrictions on energy levels, both the asymptotic shape of the variance
and the limiting Gaussian law are established, in the optimal Planck-scale regime.
We also discuss the 3-dimensional case, where the asymptotic behaviour of the variance
is analysed in a more restrictive scenario. This is joint work with Igor Wigman.

Dr. Boaz Slomka, University of Michigan, USA
25/12/2017 - 14:00 - 15:00

Abstract: We present a construction of convex bodies from Borel measures on ${\mathbb R}^n$. 
This construction allows us to study natural extensions of problems concerning the approximation 
of convex bodies by polytopes. In particular, we study a variation of the vertex index which, in 
a sense, measures how well a convex body can be inscribed into a polytope with small number of 
vertices. We discuss several estimates for these quantities, as well as an application to bounding 
certain average norms. Based on joint work with Han Huang.

Prof. A. Golberg, Holon Institute of Technology
11/12/2017 - 14:00 - 15:30

We consider the classes of homeomorphisms of domains in $\mathbb R^n$ with $p$-moduli
of the families of curves and surfaces integrally bounded from above and below. These
classes essentially extend the well-known classes of mappings such as quasiconformal,
quaiisometric, Lipschitzian, etc.
In the talk, we survey the known results in this field but mainly establish new differential
properties of such mappings. A collection of related open problems will also be presented.

Prof. Nir Lev, Bar-Ilan University
04/12/2017 - 14:00 - 15:10

Let $\mu$ be a positive, finite measure on $R^d$. Is it possible to construct a 

Fourier system which would constitute a frame in the space $L^2(\mu)$ ?

In the talk, I will explain the notion of a Fourier frame, discuss what is known 

about the problem, and present some recent results.

Prof. M. Levin, Bar-Ilan University
13/11/2017 - 14:00 - 15:40

We will consider the connections between very well uniformly distributed sequence
in s-torus,  Quasi-Monte Carlo integration and the lattice points problem for parallelepiped.
Lattices are determined here from totally reel algebraic number fields and  from "totally reel"
functional fields.

Dr. Ami Viselter University of Haifa
06/11/2017 - 14:00 - 15:20

We will discuss convolution semigroups of states on locally
compact quantum groups. They generalize the families of distributions
of Levy processes from probability. We are particularly interested
in semigroups that are symmetric in a suitable sense. These are proved
to be in one-to-one correspondence with KMS-symmetric Markov semigroups
on the $L^{\infty}$ algebra that satisfy a natural commutation condition,
as well as with non-commutative Dirichlet forms on the $L^2$ space
that satisfy a natural translation invariance condition. This Dirichlet
forms machinery turns out to be a powerful tool for analyzing convolution
semigroups as well as proving their existence. We will use it to derive
geometric characterizations of the Haagerup Property and of Property (T)
for locally compact quantum groups, unifying and extending earlier
partial results. We will also show how examples of convolution semigroups
can be obtained via a cocycle twisting procedure. Based on joint work
with Adam Skalski.

Prof. David Levin, Tel-Aviv University
30/10/2017 - 14:00 - 15:55

Iterated Function Systems (IFS) have been at the heart of fractal geometry
almost from its origin, and several generalizations for the notion of IFS have
been suggested. Subdivision schemes are widely used in computer graphics and
attempts have been made to link limits generated by subdivision schemes to
fractals generated by IFS. With an eye towards establishing connection between
non-stationary subdivision schemes and fractals, this talk introduces a non-stationary
extension of Banach fixed-point theorem. We introduce the notion of ”trajectories of
maps defined by function systems” which may be considered as a new generalization of
the traditional IFS. The significance and the convergence properties of ’forward’ and
’backward’ trajectories is presented. Unlike the ordinary fractals which are self-similar
at different scales, the attractors of these trajectories may have different structures
at different scales. Joint work with Nira Dyn and Puthan Veedu Viswanathan.

Dr. Humberto Rafeiro, Pontificia Universidad Javeriana, Bogota, Colombia
12/06/2017 - 14:00 - 15:35

In this talk we will discuss the boundedness of the maximal operator
with rough kernel in some non-standard function spaces, e.g. vari-
able Lebesgue spaces, variable Morrey spaces, Musielak-Orlicz spaces,
among others. We will also discuss the boundedness of the Riesz po-
tential operator with rough kernel in variable Morrey spaces. This is
based on joint work with S. Samko.

Dr. Ami Viselter, Haifa University
22/05/2017 - 14:00 - 15:10

Kazhdan's Property (T) is a notion of fundamental importance, with numerous applications 
in various fields of mathematics such as abstract harmonic analysis, ergodic theory and 
operator algebras. By using Property (T), Connes was the first to exhibit a rigidity 
phenomenon of von Neumann algebras. Since then, the various forms of Property (T) have 
played a central role in operator algebras, and in particular in Popa's deformation/rigidity 
This talk is devoted to some recent progress in the notion of Property (T) for locally 
compact quantum groups. Most of our results are concerned with second countable discrete 
unimodular quantum groups with low duals. In this class of quantum groups, Property (T) is 
shown to be equivalent to Property (T)$^{1,1}$ of Bekka and Valette. As applications, we 
extend to this class several known results about countable groups, including theorems on 
"typical" representations (due to Kerr and Pichot) and on connections of Property (T) with 
spectral gaps (due to Li and Ng) and with strong ergodicity of weakly mixing actions on a 
particular von Neumann algebra (due to Connes and Weiss).
Joint work with Matthew Daws and Adam Skalski.
The talk will be self-contained: no prior knowledge of quantum groups or Property (T) for groups is required.

Dr. Yu. Kolomoitsev, University of Luebeck, Germany
15/05/2017 - 14:00 - 15:40

The talk is devoted to the Lebesgue constants of polyhedral partial sums of the Fourier series. 
New upper and lower estimates of the Lebesgue constant in the case of anisotropic dilations of 
general convex polyhedra will be presented. The obtained estimates generalize and give sharper 
versions of the corresponding results of E.S. Belinsky (1977), A.A.Yudin and V.A. Yudin (1985), 
J.M. Ash and L. De Carli (2009), and J.M. Ash (2010).

Prof. E. Shustin, Tel-Aviv University
08/05/2017 - 14:00 - 15:30

Milnor fibers of isolated hypersurface singularities carry the most important information on the singularity. We review the works by A'Campo and Gusein-Zade, who showed that, in the case of real plane curve singularities, one can use special deformations (so-called morsifications) in order to recover the topology of the Milnor fiber, intersection form in vanishing homology, monodromy operator and other invariants. We prove that any real plane curve singularity admits a morsification and discuss its relation to the Milnor fiber, which is still an open problem of the complex-analytic nature. Joint work with P. Leviant.

Prof. Amos Nevo, Technion
27/03/2017 - 14:00 - 15:30

Euclidean lattice points counting problems, the primordial example of which is the Gauss circle problem, are an important topic in classical analysis. Their non-Euclidean analogs in irreducible symmetric spaces (such as hyperbolic spaces and the space of positive-definite symmetric matrices) are equally significant, and we will present an approach to establishing such results in considerable generality. Our method is based on dynamical arguments together with representation theory and non-commutative harmonic analysis, and produces the current best error estimate in the higher rank case. We will describe some of the remarkably diverse applications of lattice point counting problems, as time permits.

Prof. Michael I. Ganzburg, Hampton University, Virginia, USA
20/03/2017 - 14:00 - 15:40

In this talk we discuss asymptotic relations between sharp constants of approximation theory
in a general setting. We first present a general model that includes a circle of problems of
finding sharp or asymptotically sharp constants in some areas of univariate and multivariate
approximation theory, such as inequalities for approximating elements, approximation of individual
elements, and approximation on classes of elements. Next we discuss sufficient conditions that
imply limit inequalities and equalities between various sharp constants. Finally, we present
applications of these results to sharp constants in Bernstein-V. A. Markov type inequalities of
different metrics for univariate and multivariate trigonometric and algebraic polynomials and
entire functions of exponential type.

Bochen Liu, University of Rochester, NY, USA
13/02/2017 - 14:00 - 16:00

I will discuss how large the Hausdorff dimension of a set $E\subset{\mathbb R}^d$ needs to be 
 to ensure that it contains vertices of an equilateral triangle. An argument due to Chan, Laba 
 and Pramanik (2013) implies that a Salem set of large Hausdorff dimension contains equilateral 
 triangles. We prove that, without assuming the set is Salem, this result still holds in dimensions 
 four and higher. In ${\mathbb R}^2$, there exists a set of Hausdorff dimension $2$ containing no 
 equilateral triangle (Maga, 2010).
I will also introduce some interesting parallels between the triangle problem in Euclidean space 
and its counter-part in vector spaces over finite fields. It is a joint work with Alex Iosevich.

Prof. Michael Megrelishvili, Bar-Ilan University
23/01/2017 - 14:00 - 15:30

Tame dynamical systems were introduced by A. K\"{o}hler in 1995 and their theory was 
developed during last decade in a series of works by several authors. Connections to 
other areas of mathematics like: Banach spaces, model theory, tilings, cut and project 
schemes were established. A metric dynamical $G$-system $X$ is tame if every element 
$p \in E(X)$ of the enveloping semigroup $E(X)$ is a limit of a sequence of elements 
from $G$. In a recent joint work with Eli Glasner we study the following general question:
which finite coloring $G \to \{0, \dots ,d\}$ of a discrete countable group $G$ defines a 
tame minimal symbolic system $X \subset \{0, \dots ,d\}^G$. Any Sturmian bisequence 
$\Z \to \{0,1\}$ on the integers is an important prototype.
As closely related directions we study cutting coding functions coming from circularly ordered 
systems. As well as generalized Helly's sequential compactness type theorems about families 
with bounded total variation. We show that circularly ordered dynamical systems are tame and 
that several Sturmian like symbolic  $G$-systems are circularly ordered.

Prof. D. Kerner, Ben-Gurion University
16/01/2017 - 14:00 - 15:05

Linear algebra over a field have been studied for centuries. In many branches of math one 
faces matrices over a ring, these came e.g. as "matrices of functions" or "matrices depending 
on parameters". Linear algebra over a (commutative, associative) ring is infinitely more 
complicated. Yet, some particular questions can be solved.
 I will speak about two problems: block-diagonalization (block-diagonal reduction) of matrices 
and stability of matrices under perturbations by higher-order-terms.

Prof. S. Alesker, Tel-Aviv University
09/01/2017 - 14:00 - 17:35

Finitely additive measures on convex convex sets are called valuations. Valuations continuous in
the Hausdorff metric are of special interest and have been studied in convexity for a long time.
In this talk I will present a non-traditional method of constructing continuous valuations using
various Monge-Ampere (MA) operators, namely the classical complex MA operator and introduced by
the speaker quaternionic MA operators (if time permits, I will briefly discuss also octonionic case).
In several aspects analytic properties of the latter are very similar to the properties of the former,
but the geometric meaning is different. The construction of the quaternionic MA operator uses
non-commutative determinants.

Prof. Nir Lev, Bar-Ilan University
19/12/2016 - 14:00 - 15:45

By a crystalline measure in R^d one means a measure whose support and 
spectrum are both discrete closed sets. I will survey the subject and 
discuss recent results obtained jointly with Alexander Olevskii.

Tomer Manket, Bar-Ilan University
05/12/2016 - 14:00 - 15:30

Differential inequalities and their connection to normality (and quasi normality) have been studied since Marty’s Theorem in 1935. We discuss when these inequalities imply some degree of normality, and present a new result, joint with S. Nevo and J. Grahl.

Prof. Shahar Nevo, Bar-Ilan University
28/11/2016 - 14:00 - 15:00

Following Marty's Theorem we present recent results about differential inequalities that imply (or not) some degree of normality. We deal with inequalities with reversed sign of inequality than that in Marty's Theorem, i.e. $|f^(k)(z)|> h(|f(z))$.

Prof. Shahar Nevo, Bar-Ilan University
28/11/2016 - 14:00 - 15:55

Following Marty's Theorem we present recent results about differential inequalities that imply (or not) some degree of normality. We deal with inequalities with reversed sign of inequality than that in Marty's Theorem, i.e. $|f^(k)(z)|> h(|f(z))$.

Prof. E. Liflyand, Bar-Ilan University
21/11/2016 - 14:00 - 15:15

Earlier and recent one-dimensional estimates and asymptotic relations for the
cosine and sine Fourier transform of a function of bounded variation are refined
in such a way that become applicable for obtaining multidimensional asymptotic
relations for the Fourier transform of a function with bounded Hardy variation.

Prof. V. Derkach, Vasyl Stus Donetsk University, Ukraine
14/11/2016 - 14:00 - 15:35

Selfadjoint extensions of a closed symmetric operator A in a Hilbert
space with equal de ficiency indices were described by in the 30s by
J. von Neumann. Another approach, based on the notion of abstract boundary
triple originates to the works of J.W. Calkin and was developed by M.I. Visik,
G.Grubb, F.S.Rofe-Beketov, M.L.Gorbachuck, A.N.Kochubei and others.
By Calkin's approach all selfadjoint extensions of the symmetric operator A can
be parametrized via "multivalued" selfadjoint operators in an auxiliary Hilbert spaces.
Spectral properties of these extensions can be characterized in terms of the abstract
Weyl function, associated to the boundary triple. In the present talk some recent
developments in the theory of boundary triples will be presented. Applications to
boundary value problems for Laplacian operator in bounded domains with smooth and
rough boundaries will be discussed.

Prof. Tatiana Savina Ohio University, Athens, OH, USA
20/06/2016 - 15:05 - 16:00

A Muskat problem describes an evolution of the interface  $\Gamma (t)\subset{\mathbb R}^{2}$  between two immiscible fluids, occupying regions $\Omega _1$ and $\Omega _2$ in a Hele-Shaw cell. The interface evolves due to the presence of sinks and sources located in $\Omega _j$, $j=1,2$.
The case where one of the fluids is effectively inviscid, that is, it  has a constant pressure, is called
one-phase problem.  This case has been studied extensively. Much less progress has been made for the two-phase problem, the Muskat problem.
The main difficulty of the two-phase problem is the fact that the pressure on the interface, separating the fluids, is unknown. In this talk we introduce a notion of a two-phase mother body (the terminology comes from the potential theory) as a union of two distributions $\mu _j$  with integrable densities of sinks and sources, allowing to control the evolution of the interface, such that $\rm{supp}\, \mu _j \subset\Omega _j$. We use the Schwarz function approach and the introduced two-phase mother body to find the evolution of the curve $\Gamma (t)$  as well as two harmonic functions $p_j$, the pressures,  defined almost everywhere in $\Omega_j$ and satisfied prescribed boundary conditions on $\Gamma (t)$.

Rachel Greenfeld Bar-Ilan University
20/06/2016 - 14:00 - 15:00

A bounded set O in R^d is called spectral if the space L^2(O) admits an orthogonal basis consisting of
exponential functions. In 1974 Fuglede conjectured that spectral sets can be characterized geometrically
by their ability to tile the space by translations. Although since then spectral sets have been intensively
studied, the connection between spectrality and tiling is still unresolved in many aspects.
I will focus on cylindric sets and discuss a new result, joint with Nir Lev, on the spectrality of such sets.
Since also the tiling analogue of the result holds, it provides a further evidence of the strong connection
between these two properties.

Prof. A. Lerner, Bar-Ilan University
30/05/2016 - 14:00 - 15:10

In this talk we survey several recent results establishing a pointwise domination of Calder\'on-Zygmund 
operators by sparse operators defined by
$${\mathcal A}_{\mathcal S}f(x)=\sum_{Q\in {\mathcal S}}\Big(\frac{1}{|Q|}\int_Qf\Big)\chi_{Q}(x),$$
where ${\mathcal S}$ is a sparse family of cubes from ${\mathbb R}^n$.
In particular, we present a simple proof of M. Lacey's theorem about Calder\'on-Zygmund operators
with Dini-continuous kernels in its quantitative form obtained by T. Hyt\"onen-L. Roncal-O. Tapiola.

Prof. Pauline Lafitte-Godillon, D\'epartement de Math\'ematiques & Laboratoire MICS, France
23/05/2016 - 14:00 - 16:00

Evans and Portilheiro introduced in 2004 the functional framework that allows to tackle 
the problem of a forward-backward diffusion equation with a cubic-like diffusion function, 
that is classically ill-posed. The key is to consider its ``entropy'' formulation
determined by considering the equation as the singular limit of a third-order
pseudo-parabolic equation. Obtaining numerical simulations is not easy, since
the ill-posedness related to the negativity of the diffusion coefficient induces
severe oscillations. However, we showed that, in 1D, the regularization offered by
the basic Euler in time-centered finite differences in space renders a fairly
good numerical solution, except for the fact that the entropy condition is
violated. We thus proposed an adapted entropic scheme in 1D. The finite volume framework 
has since allowed us to prove new properties of the problem.

Prof. Galia Dafni, Concordia University, Montreal, Canada
09/05/2016 - 14:00 - 15:40

The theory of real Hardy spaces has been applied to the study of partial
differential equations in many different contexts.  In the 1990's, one of main results
in this direction was the div-curl lemma of Coifman, Lions, Meyer and Semmes.   We
discuss some variants of this lemma in the context of the local Hardy spaces of Goldberg,
and of weighted Hardy spaces.  This is joint work with Der-Chen Chang and Hong Yue.

Prof. V. Ryazanov, Institute of Applied Mathematics and Mechanics, Ukraine
11/04/2016 - 15:05 - 16:05

For the nondegenerate Beltrami equations in the quasidisks and, in particular, in smooth
Jordan domains, we prove the existence of regular solutions of the Riemann–Hilbert problem
with coefficients of bounded variation and boundary data that are measurable with respect
to the absolute harmonic measure (logarithmic capacity).

Prof. F. Abdullayev, Mersin University, Turkey
11/04/2016 - 14:00 - 15:05

For a system of polynomials  orthonormal with weight on a curve in the complex plane,
the problem of sharp estimates of these polynomials is of considerable importance.
We discuss known conditions and inequalities and present certain refinements of them.

Prof. R. Trigub
28/03/2016 - 14:00 - 15:40

For functions $f(x_{1},x_{2})=f_{0}\big(\max\{|x_{1}|,|x_{2}|\}\big)$ from
$L_{1}(\mathbb{R}^{2})$, sufficient and necessary conditions for the belonging of their Fourier transform
$\widehat{f}$ to $L_{1}(\mathbb{R}^{2})$ as well as of a function $t\cdot \sup\limits_{y_{1}^{2}+y_{2}^{2}\geq
t^{2}}\big|\widehat{f}(y_{1},y_{2})\big|$ to $L_{1}(\mathbb{R}^{1}_{+})$. As for the positivity of $\widehat{f}$ on
$\mathbb{R}^{2}$, it is completely reduced to the same question on $\mathbb{R}^{1}$ for a function

Prof. D. Leviatan, Tel-Aviv University
21/03/2016 - 14:00 - 15:55

It is quite obvious that one should expect that the degree of constrained approximation
be worse than the degree of unconstrained approximation. However, it turns out that in certain cases
we can deduce the behavior of the degrees of the former from information about the latter.

Let $E_n(f)$ denote the degree of approximation of $f\in C[-1,1]$,
by algebraic polynomials of degree $<n$, and assume that we know
that for some $\alpha>0$ and $\Cal N\ge1$,
$$n^\alpha E_n(f)\leq1,\quad n\geq\Cal N.$$
Suppose that $f\in C[-1,1]$, changes its monotonicity or convexity $s\ge0$ times in $[-1,1]$ ($s=0$ means that $f$
is monotone or convex, respectively). We are interested in what may be said about its degree of
approximation by polynomials of degree $<n$ that are comonotone or coconvex with
$f$. Specifically, if $f$ changes its monotonicity or convexity at
$Y_s:=\{y_1,\dots,y_s\}$ ($Y_0=\emptyset$) and the degrees of comonotone and coconvex approximation
are denoted by $E^{(q)}_n(f,Y_s)$, $q=1,2$, respectively. We investigate when can one say that
$$n^\alpha E^{(q)}_n(f,Y_s)\le c(\alpha,s,\Cal N),\quad n\ge\Cal N^*,$$
for some $\Cal N^*$. Clearly, $\Cal N^*$, if it exists at all (we prove it
always does), depends on $\alpha$, $s$ and $\Cal N$. However, it turns
out that for certain values of $\alpha$, $s$ and $\Cal N$, $\Cal N^*$ depends also
on $Y_s$, and in some cases even on $f$ itself, and this dependence is essential.

Prof. A. Golberg, Holon Institute of Technology
14/03/2016 - 14:00 - 16:00
We consider classes of mappings (with controlled moduli) whose $p$-module of the families of curves/surfaces
is restricted by integrals containing measurable functions and arbitrary admissible metrics. In the talk we
discuss various properties of mappings with controlled moduli including their differential features (Lusin's
$N-$ and  $N^{-1}$-conditions, Jacobian bounds, estimates for distortion dilatations, H\"older/logarithmically
H\"older continuity) and the topological structure (openness, discreteness, invertibility, finiteness of the
multiplicity function). This allows us to investigate the interconnection between mappings of bounded and finite
distortion defined analytically and mapping with controlled moduli having no analytic assumptions.
Prof. Vladimir Rovenski, University of Haifa
18/01/2016 - 14:00 - 16:00

Recent decades brought increasing interest in Finsler spaces $(M,F)$,
especially, in extrinsic geometry of their hypersurfaces.
Randers metrics (i.e., $F=\alpha+\beta$, $\alpha$ being the norm of a Riemannian structure
and $\beta$ a 1-form of $\alpha$-norm smaller than $1$ on~$M$),
appeared in Zermelo's control problem, are of special interest.

After a short survey of above, we will discuss
Integral formulae, which provide obstructions for existence of foliations
(or compact leaves of them) with given geometric properties.
The first known Integral formula (by G.\,Reeb) for codimension-1 foliated closed manifolds tells us that
the total mean curvature $H$ of the leaves is zero (thus, either $H\equiv0$ or $H(x)H(y)<0$  for some $x,y\in M$).

Using a unit normal to the leaves of a codimension-one foliated $(M,F)$,
we define a new Riemannian metric $g$ on $M$, which for Randers case depends nicely on $(\alpha,\beta)$.
For that $g$ we derive several geometric invariants of a foliation in terms of $F$;
then express them in terms of invariants of $\alpha$ and~$\beta$.
Using our results \cite{rw2} for Riemannian case, we present new Integral formulae
for codimension-one foliated $(M, F)$ and $(M, \alpha+\beta)$.
Some of them generalize Reeb's formula.

Prof. Tobias Hartnick, Technion
04/01/2016 - 14:30 - 16:00

The study of aperiodic point sets in Euclidean space is a classical topic in harmonic analysis, 
combinatorics and geometry. Aperiodic point sets in R^3 are models for quasi-crystals, and in 
this context it is of interest to study their diffraction measure, i.e. the way they scatter an 
incoming laser or x-ray beam. By a classical theorem of Meyer, every sufficiently regular 
aperiodic point set in a Euclidean space is a shadow of a periodic one in a larger locally 
compact abelian group. The diffraction of these "model sets" can be computed in terms of a 
certain group of irrational rotations of an associated torus.

In this talk, I will review the classical theory of diffraction of Euclidean model sets and then 
explain how the theory generalizes to model sets in arbitrary (non-abelian) locally compact groups. 
We will explain the construction of new examples of different flavours, and how the classical 
theory has to be modified in order to accomodate these new examples. We will focus on the case 
of model sets in groups admitting a Gelfand pair, since for these the (spherical) diffraction 
theory is particularly accessible.

No previous knowledge of model sets or diffraction theory is assumed. 
This is based on joint work with Michael Bjorklund and Felix Pogorzelski.

Prof. A. Golberg, Holon Institute of Technology
04/01/2016 - 14:00 - 16:00

We consider classes of mappings (with controlled moduli) whose $p$-module of the families of curves/surfaces is restricted by integrals containing measurable functions and arbitrary admissible metrics. In the talk we discuss various properties of mappings with controlled moduli including their differential features (Lusin's  $N-$ and  $N^{-1}$-conditions, Jacobian bounds, estimates for distortion dilatations, H\"older/logarithmically H\"older continuity) and the topological structure (openness, discreteness, invertibility, finiteness of the multiplicity function). This allows us to investigate the interconnection between mappings of bounded and finite distortion defined analytically and mapping with controlled moduli having no analytic assumptions.

Dr. Panagiotis Mavroudis, University of Crete, Greece
21/12/2015 - 14:00 - 20:35

Let $\Omega$ be an open 0-symmetric subset of $\mathbb R^d$ which contains 0 and
f a continuous positive definite function vanishing off O, that is,
supp f is contained in the closure of $\Omega$. The problem is to approximate
f by a continuous positive definite function F supported in $\Omega$. We prove
this when 1. d=1. 2 $\Omega$ is strictly star-shaped 3. f is a radial function.
We also consider the following problem: Given a measure $\mu$
supported in $\Omega$, does  there exist an extremal function for the problem
$\sup \int f d\mu$, where the sup is taken over the cone of continuous
 positive definite functions f supported in $\Omega$ with f(0)=1?

Dr. Nir Lev, Bar-Ilan University
07/12/2015 - 14:00 - 23:05

A function f on the real line is said to tile by translates
along a discrete set $\Lambda$ if the sum of all the functions
f(x-\lambda), $\lambda \in \Lambda$, is equal to one identically.
Which functions can tile by translates, and what can be said
about the translation set $\Lambda$? I will survey the subject and
discuss some recent results joint with Mihail Kolountzakis.

Prof. E. Liflyand Bar-Ilan University
23/11/2015 - 14:00 - 18:20

New relations between the Fourier transform of a function of bounded
variation and the Hilbert transform of its derivative are revealed.
The main result is an asymptotic formula for the {\bf cosine} Fourier
transform. Such relations have previously been known only for the sine
Fourier transform. Interrelations of various function spaces are studied
in this context, first of all of two types of Hardy spaces. The obtained
results are used for proving completely new results on the integrability
of trigonometric series.

Prof. Y. Krasnov Bar-Ilan University
16/11/2015 - 14:00 - 18:00

Consider a polynomial map $f: C^n\to C^n$, vanishing at some point $z_0$ in $C^n$. In differential equations, such points are called
equilibria of the vector field $z' = f(z)$, or their singular points. The question is "how singular". Can we quantify the singularity of $f$ at $z_0$?
Attempting only to demystify the problem, in this presentation we make an effort to quantify singularity in the sense of differential equations
and also discuss connections of this theory to analysis, topology and commutative algebra.

Prof. M. Cwikel, Technion
09/11/2015 - 14:00 - 15:30

It is now more than 52 years since Studia Mathematica received Alberto
Calder\'on's very remarkable paper about his theory of complex
interpolation spaces. And one of the questions which Calder\'on
implicitly asked in that paper, by solving it in a significant special
case, is apparently still open today:


After briefly surveying attempts to solve this question over several
decades, I will also report on a few new partial answers obtained
recently, some of them (arXiv:1411.0171) jointly with Richard
Rochberg. Among other things there is an interplay with Jaak Peetre's
"plus-minus" interpolation method, (arXiv:1502.00986) a method which
probably deserves to be better known. Banach lattices and UMD spaces
also have some roles to play.

Several distinguished mathematicians have expressed the belief that
that the general answer to this question will ultimately turn out to be
negative. Among other things, I will try to hint at where a counterexample
might perhaps be hiding. You are all warmly invited to seek it out,
or prove that it does not exist.

A fairly recent survey which discusses this question is available at

Prof. Ognyan Kounchev IZKS, University of Bonn, Germany Institute of mathematics and informatics, Bulgarian Academy of Sciences
26/10/2015 - 14:00 - 01/11/2015 - 11:30

We present a new construction of Hardy spaces on the Klein-Dirac
quadric; we show that the quadric is obtained as a complexification of the
unit ball in R^n. We introduce also Hardy spaces on complexified
multidimensional annulus.
We show some natural properties of these Hardy spaces, in particular,
Cauchy type formula, and Brothers Riesz type theorem.
We prove applications to the multidimensional Moment problem,
multidimensional Interpolation theory, and Cubature formulas.

Prof. S. Krushkal, Bar-Ilan University
08/06/2015 - 14:00 - 15:00

We provide restricted negative answers to the Royden-Sullivan problem
whether any Teichm\"{u}ller space of dimension greater than $1$
is biholomorphically equivalent to bounded domain in a complex Banach
space. The only known result here is Tukia's theorem of 1977 that there is
a real analytic homeomorphism of the universal Teichm\"{u}ller
space onto a convex domain in some Banach space.
   We prove:
(a) Any Teichm\"{u}ller space $\mathbf T(0,n)$ of the punctured spheres
(the surfaces of genus zero) with sufficiently large number of punctures
$(n \ge n_0 > 4)$ cannot be mapped biholomorphically onto a bounded
convex domain in $\mathbf C^{n-3}$.
(b) The universal Teichm\"{u}ller space is not biholomorphically equivalent
to a bounded convex domain in uniformly convex Banach space, in
particular, to convex domain in the Hilbert space.
  The proofs involve the existence of conformally rigid domains established
by Thurston and some interpolation results for bounded univalent functions. 

Prof. Palle Jorgensen, University of Iowa, USA
01/06/2015 - 14:00 - 15:00

The class of fractals referred to are those which may be specified by a finite system of affine transformations,
assuming contractive scaling; and their corresponding selfsimilar measures, $\mu$. They include standard Cantor
spaces such as the middle third, and the planar Sierpinski caskets in various forms, and their corresponding
selfsimilar measures, but the class is more general than this; including fractals realized in $\mathbb R^d$, for
$d > 2$.
In part 1, we motivate the need for wavelets in the harmonic analysis of these selfsimilar measures $\mu$. While
classes of the Hilbert spaces $L^2(\mu)$ have Fourier bases, it is known (the speaker and Pedersen) that many do
not, for example the middle third Cantor can have no more than two orthogonal Fourier frequencies.
In part 2 of the talk, we outline a construction by the speaker and Dutkay to the effect that all the affine systems
do have wavelet bases; this entails what we call thin Cantor spaces.

Prof. Mikhail Zaidenberg, Fourier Institute, Grenoble, France
28/05/2015 - 14:00 - 15:00
Given complex affine algebraic varieties $X$ and $Y$, the general Zariski Cancellation Problem asks whether the existence 
of an isomorphism $X\times\mathbb{C}^n\cong Y\times\mathbb{C}^n$ implies that $X\cong Y$.
Or, in other words, whether varieties with isomorphic cylinders should be isomorphic. This occurs to be true for affine 
curves (Abhyankar, Eakin, and Heinzer $'72$)  and false for affine surfaces (Danielewski $'89$).
The special Zariski Cancellation Problem asks the same question provided that $Y=\mathbb{C}^k$. In this case, the answer 
is "yes" in dimension $k=2$ (Miyanishi-Sugie $'80$ and Fujita $'79$), and unknown in higher dimensions, where the situation 
occurs to be quite mysterious (indeed, over a field of positive characteristic, there is a recent counter-example due to Neena Gupta $'14$).
The birational counterpart of the special Zariski Cancellation Problem asks whether stable rationality implies rationality.  The answer 
occurs to be negative; the first counter-example was constructed by Beauville, Colliot-Th\'el\`ene, Sansuc, and Swinnerton-Dyer $'85$. 
We will survey on the subject, both on some classical results and on a very recent development, reporting in particular on a joint 
work with Hubert Flenner and Shulim Kaliman.
Prof. A. Danielyan, University of South Florida, Tampa, USA
18/05/2015 - 15:05 - 16:05
The talk is devoted to some bounded approximation and interpolation problems and theorems in
the unit disc related to the work of P. Fatou, W. Rudin, L. Carleson, L. Zalcman, and other authors.
Among other results, a new theorem due to S. Gardiner on radial interpolation will be presented.
We also show that the classical Rudin-Carleson interpolation theorem is a simple corollary of
Fatou's much older interpolation theorem (of 1906).
Prof. V. Maz'ya, University of Liverpool and University of Linkoeping
18/05/2015 - 14:00 - 15:00
A number of topics in the qualitative spectral analysis of the  Schr\"odinger operator $-\Delta + V$
are surveyed. In particular,  results concerning the positivity and semiboundedness of this operator.
The attention is focused on conditions both necessary and sufficient, as well as on their sharp corollaries.
Prof. B. Rubin, Louisiana State University, Baton Rouge, USA
04/05/2015 - 14:00 - 15:00
The Radon transform $R$ assigns to a function $f$ on $R^n$  a collection 
of integrals of that function over   hyperplanes in $R^n$. Suppose 
that $Rf$ vanishes on  all hyperplanes that do not meet a fixed convex 
set. {\it Does it follow that $f$ is zero in the exterior of that set?}
I am planning to discuss new results related to this question and  the
corresponding injectivity problems. If time allows, some   projectively
equivalent modifications of $R$ will be considered.
Prof. S. Yakovenko, Weizmann Institute
20/04/2015 - 14:00 - 15:00
I will describe the current state of affairs in both the original Hilbert 16th problem 
(on limit cycles of polynomial planar vector fields) and its relaxed version on zeros of 
Abelian integrals. It turns out that the latter belong to a natural class of Q-functions 
described by integrable systems of linear differential equations with quasiunipotent monodromy, 
defined over the field of rational numbers. Functions of this class admit explicit (albeit very 
excessive) bounds for the number of their isolated zeros in a way similar to algebraic functions. 
This result lies at the core of the solution of the infinitesimal Hilbert problem, achieved with 
Gal Binyamini and Dmitry Novikov.
The talk is aimed at a broad audience.
Prof. R. Trigub, Donetsk National University, Ukraine
13/04/2015 - 14:00 - 15:00

In the problem of summability at a point at which the derivative of indefinite
integral exists for Fourier series and Fourier integrals of integrable functions
a new sufficient condition is obtained. In the case of "arithmetic means" the
corresponding condition is also necessary.
Exact rates of approximation by the classical Gauss-Weierstrass, Bochner-Riesz,
and Marcinkiewicz-Riesz means, as well as by non-classical Bernstein-Stechkin means
are found.
These problems are related to the representability of a function as an absolutely
convergent Fourier integral. For this, new conditions are obtained, while for radial functions
even a criterion.

Prof. P. Shvartsman, Technion
19/01/2015 - 14:00 - 15:00

For each positive integer $m$ and each $p>2$ we characterize bounded simply connected
Sobolev $W^m_p$-extension domains $\Omega$ in $R^2$. Our criterion is expressed in terms of
certain intrinsic subhyperbolic metrics in $\Omega$. Its proof is based on a series of results related
to the existence of special chains of squares joining given points $x$ and $y$ in $\Omega$.

An important geometrical ingredient for obtaining these results is a new ''Square Separation Theorem''.
It states that under certain natural assumptions on the relative positions of a point $x$ and a square
$S\subset\Omega$ there exists a similar square $Q\subset\Omega$ which touches $S$ and has
the property that $x$ and $S$ belong to distinct connected components of $\Omega\setminus Q$.

 This is a joint work with Nahum Zobin.

Michael Twito, University of Sydney Australia
12/01/2015 - 15:05 - 16:05

The triply truncated solutions of the first Painlev\'e equation were specified by Boutroux 
in his famous paper of 1913 as those having no poles (of large modulus) except in one sector 
of angle $2\pi/5$. There are five such solutions and each of them can be obtained from any 
other one by applying a certain symmetry transformation. One of these solutions is real on 
the real axis. We will discuss a characteristic property of this solution (discovered by Prof. 
Joshi, and Prof. Kitaev), different from the asymptotic description given by Boutroux.

Prof. B. Solomyak
12/01/2015 - 14:00 - 15:00

For $\lambda\in (0,1)$, the Bernoulli convolution measure $\nu_\lambda$ may be defined as the distribution 
of the random series $\sum_{n=0}^\infty \pm \lambda^n$, where the signs are chosen independently with equal 
probabilities. For $\lambda =1/3$, this is the familiar Cantor-Lebesgue measure (up to a linear change of variable). 
The Fourier transform of $\nu_\lambda$ has an infinite product formula:
$$\widehat{\nu}_\lambda(t) = \prod_{n=0}^\infty \cos(2\pi \lam^n t).$$
The properties of $\nu_\lambda$ and their Fourier transforms have been studied since the 1930's by many mathematicians, 
among them Jessen, Wintner, Erd\H{o}s, Salem, Kahane, Garcia. In particular, it was proved by Erd\H{o}s and Salem that 
$\widehat{\nu}_\lambda(t)$ does not vanish at infinity (i.e. $\nu_\lambda$ is not a Rajchman measure) if and only if 
$1/\lambda$ is a Pisot number (an algebraic integer greater than one with all conjugates inside the unit circle). 
However, very little is known about the rate of decay, especially for specific $\lambda$, as opposed to "typical" ones. 
In this talk I will survey known results and open problems in this direction. Recently in a joint work with A. Bufetov 
we proved that if $1/\lam$ is an algebraic integer with at least one conjugate outside of the unit circle, then the 
Fourier transform of $\nu_\lam$ has at least a logarithmic decay rate at infinity.

Prof. A. Eremenko, Purdue University
05/01/2015 - 14:00 - 15:00

This is a joint work with Walter Bergweiler.
We construct differential equations of the form w"+Aw=0, where $A$ 
is an entire function of finite order, with the property that two 
linearly independent solutions have finite exponent of convergence 
of zeros. This solves a problem proposed by Bank and Laine in 1982.

Dr. M. ELENA LUNA-ELIZARRARAS ́ Departamento de Matem ́aticas E.S.F.M. del I.P.N. 07338 M ́exico D.F.,
29/12/2014 - 14:00 - 15:00

In recent years the study of quaternionic linear spaces has been widely developed
by mathematicians and has been widely used by physicists. At the same
time it turns out that some basic and fundamental properties of those spaces
are not treated properly and this requires to develop the corresponding theory.
In this talk we will analyze certain peculiarities of the situation via the notion
of quaternionic extension of real and complex linear spaces as well as using the
notion of internal quaternionization. We will see, for example, how the norms of
some operators behave when they are “quaternionically extended”.

Dr. Nir Lev, Bar-Ilan University
22/12/2014 - 14:00 - 15:00

Hecke, Ostrowski and Kesten characterized the intervals on the circle
for which the ergodic sums of their indicator function, under an
irrational rotation, stay at a bounded distance from their integral
with respect to the Lebesgue measure on the circle.
In this talk I will discuss this phenomenon in multi-dimensional setting.
Based on joint work with Sigrid Grepstad.

Prof. Z. Balanov, University of Texas at Dallas
15/12/2014 - 14:00 - 15:00

Topological methods based on the usage of degree theory have proved
themselves to be an important tool for qualitative studying of solutions to
nonlinear differential systems (including such problems as existence,
uniqueness, multiplicity, bifurcation, etc.).

During the last twenty years the equivariant degree theory emerged in Non-
linear Analysis. In short, the equivariant degree is a topological tool
allowing “counting” orbits of solutions to symmetric equations in the same
way as the usual Brouwer degree does, but according to their symmetry
properties. This method is an alternative and/or complement to the
equivariant singularity theory developed by M. Golubitsky et al., as well as
to a variety of methods rooted in Morse theory/Lusternik–Schnirelman theory.

In fact, the equivariant degree has different faces reflecting a diversity of
symmetric equations related to applications. In the two talks, I will discuss
three variants of the equivariant degree: (i) non-parameter equivariant
degree, (ii) twisted equivariant degree with one parameter, and (iii)
gradient equivariant degree. Each of the three variants of equivariant degree
will be illustrated by appropriate examples of applications: (i) boundary
value problems for vector symmetric pendulum equation, (ii) Hopf bifurcation
in symmetric neural networks (simulation of legged locomotion), and (iii)
bifurcation of relative equilibria in Lennard-Jones three-body problem.

The talk is addressed to a general audience, without any special knowledge
of the subject.

Itay Londner, Tel-Aviv University
08/12/2014 - 14:00 - 09/12/2014 - 13:20

In the talk, which is joint work with Alexander Olevskii, I will present our study of the
relationship between the existence of arithmetic progressions with specified lengths and
step sizes and lower Riesz bounds of complex exponentials indexed by a set of integers
$\Lambda$ on subsets of the circle.

Prof. R. Trigub, Donetsk National University, Ukraine
01/12/2014 - 14:00

The following problems (or a part of them) will be discussed.
1. Generalization of the Abel-Poisson summation method. 
2. Generalization of the Riemann-Lebesgue lemma.
3. Strengthening of the Hardy-McGehee-Pigno-Smith inequality.
4. Generalization of the Euler-Maclaurin formula.
5. Absolute convergence of grouped Fourier series.
6. Comparison of linear differential operators with constant coefficients.
7. Positive definite functions and splines.
8. Strong converse theorems in approximation theory. Bernstein-Stechkin polynomials.

Prof. M. Sodin, Tel-Aviv University
24/11/2014 - 14:00

We study the influence the angular distribution of zeroes of the Taylor
series with pseudo-random and random coefficients, and show that the
distribution of zeroes is governed by certain autocorrelations of the
coefficients. Using this guiding principle, we consider several examples
of random and pseudo-random sequences $\xi$ and, in particular, answer
some questions posed by Chen and Littlewood in 1967.

As a by-product we show that if $\xi$ is a stationary random
integer-valued sequence, then either it is periodic, or its spectral
measure has no gaps in its support. The same conclusion is true if $\xi$
is a complex-valued stationary ergodic sequence that takes values from a
uniformly discrete set (joint work with Alexander Borichev and Alon Nishry).

Prof. M. Agranovsky, Bar-Ilan University
17/11/2014 - 14:00 - 23:00

Nodal sets are zero loci of Laplace eigenfunctions (e.f.). Study of nodal sets is important
for understanding wave processes. The geometry of a single nodal set may be very complicated
and hardly can be well understood. More realistic might be describing geometry of sets which
are nodal for a large family of e.f. (the condition of simultaneous vanishing, resonanse, of
a large packet of e.f., on a large set, is overdetermined and hence may be expected to occur
only for exclusive sets).

Indeed, it was proved that common nodal curves for large, in different senses, families
of e.f. in $\mathbb R^2$ are straight lines (non-periodic case: Quinto and the speaker, ’96; periodic
case: Bourgain and Rudnick, ’11). It was conjectured that in a Euclidean space of
arbitrary dimension, common nodal hypersurfaces for large families of e.f. are cones, more precisely,
are translates of zero sets of harmonic homogeneous polynomials.

The talk will be devoted to a recent result confirming the conjecture for ruled hypersurfaces
in $\mathbb R^3$. Relation to the injectivity problem for the spherical Radon transform will be explained.

Prof. M. Sodin, Tel-Aviv University
17/11/2014 - 14:00 - 23:10

We study the influence the angular distribution of zeroes of the Taylor
series with pseudo-random and random coefficients, and show that the
distribution of zeroes is governed by certain autocorrelations of the
coefficients. Using this guiding principle, we consider several examples
of random and pseudo-random sequences $\xi$ and, in particular, answer
some questions posed by Chen and Littlewood in 1967.

As a by-product we show that if $\xi$ is a stationary random
integer-valued sequence, then either it is periodic, or its spectral
measure has no gaps in its support. The same conclusion is true if $\xi$ 
is a complex-valued stationary ergodic sequence that takes values from a 
uniformly discrete set (joint work with Alexander Borichev and Alon Nishry).

Avner Kiro, Tel-Aviv University
03/11/2014 - 14:00 - 17/11/2014 - 23:00

The talk is will be devoted to two  questions in the theory of quasianalytic  
Carleman classes. The first one is how to describe the image of a quasianalytic 
Carleman class under Borel's map $f\to\{f^{(n)}(0)/n!\}_{n\geq 0}$ ?    
The second one is how to sum the formal Taylor series of functions  in quasianalytic Carleman classes? In the talk, I will present a method of Beurling that gives a solution to both of the problems for some quasianalytic Carleman classes. If time permits, I will also discuss the image problem in some non-quasianalytic classes.

Prof. Bert Schreiber, Wayne State University, Detroit, USA
02/06/2014 - 14:00

We will begin by introducing the notion of hypergroup, give some examples, 
and describe the convolution of measures on a hypergroup. After a review of 
some basic operator space theory, we shall describe how to extend the notion 
of convolution to the space of completely bounded multilinear forms on a cartesian 
product of spaces of continuous functions on hypergroups, thus making that space 
into a Banach algebra. When the hypergroups are commutative, we introduce and study 
a notion of Fourier transform in this setting.

Prof. V. Rabinovich, National Polytechnic Institute of Mexico
26/05/2014 - 14:00

The talk is devoted to applications of the limit operators to the study of
essential spectra and exponential decay of eigenfunctions of the discrete
spectra for Schr\"{o}dinger and Dirac operators for wide classes of
potentials. Outline of the talk:

1) Fredholm property and location of the essential spectrum of systems of
partial differential operators with variable bounded coefficients;

2) Exponential estimates of solutions of systems of partial differential
operators with variable bounded coefficients;

3) Location of the essential spectrum of Schr\"{o}dinger and Dirac operators
and exponential estimates of eigenfunctions of the discrete spectrum.

Prof. Gershon Kresin, Ariel University
19/05/2014 - 14:00

Two types of optimal estimates for derivatives of analytic functions
with bounded real part are considered. The first of them is a pointwise
inequality for derivatives of analytic functions in the complement
of a convex closed domain in ${\mathbb C}$. The second type of inequalities
is a limit relation for derivatives of analytic functions in an arbitrary proper
subdomain of ${\mathbb C}$. Optimal estimates for derivatives of a vector
field with bounded harmonic components as well as optimal estimates for the
divergence of an elastic displacement field and pressure in a fluid in
subdomains of ${\mathbb R}^n$ are discussed.

Prof. L. De Carli, Florida International University
12/05/2014 - 14:00

Let $D$ be a domain of $\R^d$; we say that $L^2(D)$ has an exponential basis if there exists   

sequence  of functions ${\mathcal B}=\{ e^{2\pi i \langle s_m x\rangle}\}_{ m \in Z^d}$,      
with $s_m\in\R^d$, with the following property:  every function in $L^2(D)$ can be written in 
a unique way   as  $\sum_{m\in\Z^d}  c_m  e^{ 2\pi i \langle s_m, x\rangle} $,  with $c_m  \in  \C$.  
For example, $\{ e^{2\pi i mx}\} _{m \in Z}$  is  an exponential basis  of $L^2(0, 1 )$.  
Exponential bases are very useful in the application, especially when they are orthogonal; however,  
the existence   or non-existence of exponential  bases is proved only on  very  special  domains of $\R^d$. 
In particular, it is not known whether the  unit ball in $\R^2$ has an exponential basis or not.

An important property of exponential bases is their stability. That is, if $\{ e^{2\pi i \langle s_m, 
x\rangle}\}_{ m \in Z^d}$  is an exponential basis of $L^2(D)$ and $\Delta=\{\delta_m\}_{ m \in Z^d} $ is  
a sequence of  sufficiently small  real number,  then also $\{ e^{2\pi i \langle s_m+\delta_m,  
x\rangle}\}_{ m \in Z^d}$  is an exponential basis of $L^2(D)$.   In this talk  I will discuss the existence 
and stability of exponential bases on special 2-dimensional domains called trapezoids.
I will also generalize a celebrate  theorem by M. Kadec  and obtain stability bounds for exponential bases on  domains of $\R^d$.
The result that I will present in my talk are part of joint projects with my students A. Kumar and S. Pathak.


Prof. E. Liflyand, Bar-Ilan University
07/04/2014 - 14:00

If a function and its conjugate (in a special sense) both have 
bounded variation, then their Fourier transforms are integrable. 
This recent extension of a classical (for Fourier series) Hardy-
Littlewood theorem gives rise to new thoughts and results.

Dr. R. Bessonov, TAU, St-Petersburg State University.
31/03/2014 - 14:00

The aim of this talk is to present a simple two-sided estimate for the
operator norm of a finite Hankel matrix in terms of its standard
symbol. We will also discuss several reformulations and consequences
of this estimate, including the classical Fefferman's duality theorem
for the Hardy space $H^1$.

Dr. R.V. Bessonov, TAU, St.Petersburg State University
31/03/2014 - 14:00

The aim of this talk is to present a simple two-sided estimate for the
operator norm of a finite Hankel matrix in terms of its standard
symbol. We will also discuss several reformulations and consequences
of this estimate, including the classical Fefferman's duality theorem
for the Hardy space $H^1$.

Dr. Shimon Brooks, Bar-Ilan University
24/03/2014 - 14:00

We consider the wave flow on a surface of constant negative curvature.  
For short times, the propagation is approximated by the geodesic flow, with 
errors controlled by the “semiclassical expansion” coming from geometric optics.  
In negative curvature, this expansion is useful up the Ehrenfest time $|\log{\hbar}|$, 
after which the error terms in the expansion become as large as the main term.  It is 
believed that the approximation of wave propagation by the geodesic flow should hold 
for much larger times, perhaps all the way up to the Heisenberg time $1/\hbar$. However, 
we show that this cannot hold in general, and exhibit explicit examples where the semiclassical 
approximation breaks down at a constant multiple of Ehrenfest time. These examples come from 
Eisenstein series on the modular surface, and are intimately tied to the arithmetic structure, 
and highly non-generic.  We will also discuss these non-generic features of the arithmetic setting, 
and whether this breakdown at the Ehrenfest time is likely to be a more generic phenomenon or not.
Includes joint work with Roman Schubert.

Prof. Yakov Krasnov, Bar-Ilan University
10/03/2014 - 14:00

The aim of this work is to establish a number of elementary
properties about the topology and algebra of real quadratic homogeneous
mapping and Ricatti type ODEs  occurring in non-associative algebras.
We construct a series of examples of the quadratic vector field to
show the impact of their spectral properties into qualitative theory.

Prof. Yu. Kolomoitsev, Inst. Applied Math. Mech., Donetsk, Ukraine
03/03/2014 - 14:00

We present sharp Ul’yanov type inequalities for fractional moduli of smoothness and K-functionals for the values of the parameters: 0<p<1, p<q. We also provide a generalization of Kolyada's inequality and relations between fractional moduli of smoothness of a function and  its derivatives in the spaces L_p, 0<p<1.

Prof. Yu. Kolomoitsev, Inst. Applied Math. Mech., Donetsk, Ukraine
24/02/2014 - 15:05

We present new sufficient conditions for Fourier multipliers. These conditions are given in terms of simultaneous
behavior of (quasi-)norms of a function in different Lebesgue and Besov spaces. We also provide some sufficient
conditions for the representation of a function as an absolute convergence Fourier integrals in terms of belonging
of a function simultaneously to several spaces of smooth functions.

Prof. V. Maz'ya, University of Liverpool and University of Linkoeping
24/02/2014 - 14:00

We discuss sharp continuity and regularity results for solutions of the
polyharmonic equation in an arbitrary open set. The absence of
information about  geometry of the domain puts the question of
regularity properties  beyond the scope of applicability of the methods
devised previously, which typically rely on specific geometric assumptions.
Positive results have been available only when the domain is
sufficiently smooth, Lipschitz or diffeomorphic to a polyhedron.

The techniques developed recently  allow  to establish the
boundedness of derivatives of solutions to the Dirichlet problem for the
polyharmonic equation  under no restrictions on the underlying domain
and to show that the order of the derivatives is maximal. An appropriate
notion of polyharmonic capacity  is introduced which
allows one to describe the precise correlation between the smoothness of
solutions and the geometry of the domain.

We also study the 3D Lam\'e system and establish its weighted
 positive definiteness for a certain range of elastic constants. By modifying
 the general theory developed by Maz'ya (Duke, 2002), we then show, under the
 assumption of weighted positive definiteness, that the divergence
 of the classical Wiener integral for a boundary point guarantees the
continuity of solutions to the Lam\'e system at this point.

The talk is based on my joint work with S.Mayboroda (Minnesota) and Guo Luo (Caltech)

Prof. Matania Ben-Artzi, Hebrew University, Jerusalem
13/01/2014 - 14:00

 First-order systems of partial differential equations appear
in many areas of physics, from the Maxwell equations to the Dirac
    The aim of the talk is to describe a general method for the study of
the spectral density of all such systems, connecting it to traces on the
(geometric-optical)  "slowness surfaces" .
    The Holder continuity of the spectral density leads to a derivation of
the limiting absorption principle and global spacetime estimates
  (based on joint work with Tomio Umeda).

Prof. A. Iosevich, University of Rochester, NY, USA
06/01/2014 - 14:00

The beautiful and extensive Coifman-Meyer theory, developed in the 70s and 80s to study
singular multi-linear operators does not apply to many naturally arising operators with
positive kernels. We shall describe some elementary approaches to such operators and apply
them to some problems in geometric measure theory and classical harmonic analysis.

Prof. Simeon Reich, The Technion
30/12/2013 - 14:00

H. H. Bauschke and J. M. Borwein showed that in the space of all tuples of bounded,
closed and convex subsets of a Hilbert space with a nonempty intersection, a typical
tuple has the bounded linear regularity property. This property is important because
it leads to the convergence of infinite products of the corresponding nearest point
projections to a point in the intersection.
We show that the subset of all tuples possessing the bounded linear
regularity property has a porous complement. Moreover, our result is
established in all normed spaces and for tuples of closed and convex sets
which are not necessarily bounded. This is joint work with A. J. Zaslavski.

Dr. Roman Shubert, University of Bristol, UK
23/12/2013 - 14:00

We derive an extension of the standard time-dependent WKB theory, which can be applied
to propagate coherent states and other strongly localized states for long times. It in
particular allows us to give a uniform description of the transformation from a localized
coherent state into a delocalized Lagrangian state, which takes place at the Ehrenfest time.
The main new ingredient is a metaplectic operator that is used to modify the initial state
in a way that the standard time-dependent WKB theory can then be applied for the propagation.
This is based on joint work with Raul Vallejos and Fabricio Toscano, but in this talk we will
focus on the special case of propagation on a manifold of negative curvature.

Prof. A. Golberg, Holon Institute of Technology
09/12/2013 - 14:00

~We consider the generic discrete open mappings in ${\mathbb R}^n$ under which the perturbation of extremal lengths of curve collections is controlled integrally via $\int Q(x)\eta^p(|x-x_0|)
dm(x)$ with $n-1<p<n$, where $Q$ is a measurable function on ${\mathbb R}^n$ and $\int\limits_{r_1}^{r_2} \eta(r) dr \ge 1$ for any $\eta$ on a given interval $[r_1,r_2].$ The main results state that the family of all open discrete mappings of above type is normal under appropriate restrictions on the majorant $Q.$

We also provide conditions ensuring the local H\"older continuity
of such mappings with respect to euclidian distances (in the general case with respect to their
logarithms). The inequalities defining the continuity are sharp with respect to
the order.

This is a joint work with R. Salimov and E. Sevost'yanov.

Prof. M. Elin, Ort Braude, Karmiel
25/11/2013 - 14:00

It is well known that the geometric nature of semigroup trajectories essentially depends on the semigroup type. 
In this work, we concentrate on parabolic type semigroups of holomorphic self-mappings of the open unit disk and of the right
half-plane, and study the structure of semigroup trajectories near the Denjoy--Wolff point.  In particular, we find the limit
order of contact and the limit curvature of trajectories and their `closeness’,  determine whether these trajectories have
asymptotes. For these purposes, we suggest that two terms in the asymptotic power expansion of semigroup generators are known.
Our methods are based on the asymptotic expansion of a semigroup  that we find on the first step. Inter alia, this enable us
to establish a new rigidity property for semigroups of parabolic type.

The talk is based on a joint work with F. Jacobzon.

Prof. Victor Palamodov, Tel-Aviv University
18/11/2013 - 14:00

A generalization of Newton's attraction theorem will be discussed.
The same analytic method is applied for reconstruction in photoacoustic geometry.

Dr. Shahar Nevo, Bar-Ilan University
11/11/2013 - 14:00

We extend Caratheodory's generalization of Montel's fundamental normality test
to "wandering" exceptional functions (i.e. depending on the respective function in the
family under consideration), and we give a corresponding result on shared functions.
Furthermore, we prove that if we have a family of pairs (a,b) of functions meromorphic
in a domain such that a and b uniformly "stay away from each other " , then the families
of the functions a resp.  b are normal. The proofs are based on a "simultaneous rescaling"
version of Zalcman's Lemma. We also introduce a somewhat "strange" result about some
sharing wandering values assumptions that imply normality.

Dr. Anna Novikova, Weizmann Institute of Sciences
28/10/2013 - 14:00

Let $X$ be Banach space, $(\Omega,\Sigma)$ is a measure space, where $\Omega$
is a set and $\Sigma$ is a $\sigma$-algebra of subsets of $\Omega.$ If $m:\Sigma\rightarrow X$ is
a $\sigma$-additive $X$-valued measure, then the range of $m$ is the set $m(\Sigma)=\{m(A):
\ A\in\Sigma.\}$ The measure $m$ is {\it non-atomic} if for every set $A\in\Sigma$ with $m(A)>0,$
there exist $B\subset A,B\in\Sigma$ such that $m(B)\neq0$ and $m(A \backslash B)\neq0.$
$X$-valued measure we will call {\it Lyapunov measure} if the closure of its range is convex.
And Banach space $X$ is {\it Lyapunov space} if every $X$-valued non-atomic measure is Lyapunov.

Theorem. Let X be Banach space with unconditional basis, q-concave, $q<\infty$, and which doesn't contain isomorphic copy of $l_2.$
Then X is Lyapunov space.

Prof. V. Goldshtein, Ben-Gurion University
21/10/2013 - 14:00
We show that Brennan's conjecture about integrability of
derivatives of conformal homeomorphisms is equivalent to boundedness
of composition operators on homogeneous Sobolev spaces $L^{1,p}$.
This result is used for description of embedding operators of
homogeneous Sobolev spaces $L^{1,p}$ into weighted Lebesgue spaces
with so-called "conformal weights" induced by the conformal
homeomorphisms of simply connected plane domains to the unit disc.
Applications to elliptic boundary value problems will be discussed.
Dr. Etienne Le Masson, Universit´e Paris-Sud 11, ORSAY, FRANCE
17/06/2013 - 14:00

I will present a quantum ergodicity theorem on large regular graphs.
This is a result of spatial equidistribution of most eigenfunctions of the discrete Laplacian
in the limit of large regular graphs. It is analogous to the quantum ergodicity theorem on
Riemannian manifolds, which is concerned with the eigenfunctions of the Laplace-Beltrami operator
in the high frequency limit. I will also talk about pseudo-differential calculus on regular graphs,
one of the tools constructed for the proof of the theorem.

This is a joint work with Nalini Anantharaman.

Yehonatan Salman
10/06/2013 - 14:00

This presentation is devoted to the problem of
recovering a function from its spherical means with
centers located on an ellipsoid $\Sigma$ in the two- and
three-dimensional spaces. We will show how to
generalize methods for obtaining inverse
formulas for the case when $\Sigma$ is a sphere to the
case when $\Sigma$ is an ellipsoid.

Yehonatan Salman
10/06/2013 - 14:00

This presentation is devoted to the problem of
recovering a function from its spherical means with
centers located on an ellipsoid $\Sigma$ in the two- and
three-dimensional spaces. We will show how to
generalize methods for obtaining inverse
formulas for the case when $\Sigma$ is a sphere to the
case when $\Sigma$ is an ellipsoid.

Prof. V. Maz'ya, University of Liverpool and University of Linkoeping
13/05/2013 - 14:00

We discuss sharp continuity and regularity results for solutions of the
polyharmonic equation in an arbitrary open set. The absence of
information about  geometry of the domain puts the question of
regularity properties  beyond the scope of applicability of the methods
devised previously, which typically rely on specific geometric assumptions.
Positive results have been available only when the domain is
sufficiently smooth, Lipschitz or diffeomorphic to a polyhedron.

The techniques developed recently  allow  to establish the
boundedness of derivatives of solutions to the Dirichlet problem for the
polyharmonic equation  under no restrictions on the underlying domain
and to show that the order of the derivatives is maximal. An appropriate
notion of polyharmonic capacity  is introduced which
allows one to describe the precise correlation between the smoothness of
solutions and the geometry of the domain.

We also study the 3D Lam\'e system and establish its weighted
 positive definiteness for a certain range of elastic constants. By modifying
 the general theory developed by Maz'ya (Duke, 2002), we then show, under the
 assumption of weighted positive definiteness, that the divergence
 of the classical Wiener integral for a boundary point guarantees the
continuity of solutions to the Lam\'e system at this point.

The talk is based on my joint work with
 S.Mayboroda (Minnesota) and Guo Luo (Caltech)

Dr. Daniel Alayon-Solarz, Bar-Ilan University
22/04/2013 - 14:00

In this talk we will introduce a definition of Generalized Analytic Functions
(in the sense of Vekua), in elliptic complex numbers. One advantage of this definition 
is that its Canonical Form is more general than Vekua's and in many cases the reduction
from the elliptic and linear partial differential equation of first order can be done  
without solving an associated Beltrami equation. Finally, using techniques of Vekua we 
will show that these functions satisfy a representation formula that generalizes the   
Similarity Principle in the ordinary case.                                             

Prof. S. Favorov, Kharkov University, Ukraine
08/04/2013 - 14:00

We introduce a notion of r-convexity for subsets of the complex
plane. It is a pure geometric characteristic that generalizes the        
usual notion of convexity. Next, we investigate subharmonic              
functions that grow near the boundary in unbounded domains with          
r-convex compact complement. We obtain the Blaschke-type bounds          
for its Riesz measure and, in particular, for zeros of unbounded         
analytic functions  in unbounded domains. These results are based        
on a certain estimates for Green functions on complements of some        
neighborhoods of $r$-convex compact set. Also, we apply our              
results in perturbation theory of linear operators in a Hilbert          
space. More precisely, we find quantitative estimates for the rate       
of condensation of the discrete spectrum of a perturbed operator         
near its the essential spectrum.                                         

Dr. Sigrid Grepstad, Norwegian University of Science and Technology
11/03/2013 - 14:00

Let S be a bounded, Riemann measurable set in R^d, and L 
be a lattice. By a theorem of Fuglede, if S tiles R^d with         
translation set L, then S has an orthogonal basis of exponentials. 
We show that, under the more general condition that S multi-tiles  
R^d with translation set L, S has a Riesz basis of exponentials. The
proof is based on Meyer's quasicrystals. This is a joint work with 
Nir Lev.                                                           

Dr. Krystal Taylor, Technion
04/03/2013 - 14:00

A classical theorem due to Mattila says that if $A,B       
\subset {\Bbb R}^d$ of Hausdorff dimension $s_A, s_B$, respectively, 
with $s_A+s_B \ge d$, $s_B>\frac{d+1}{2}$ and $dim_{{\mathcal H}}(A  
\times B)=s_A+s_B\ge d$, then                                        
$$ dim_{{\mathcal H}}(A \cap (z+B)) \leq s_A+s_B-d$$ for almost every
$z \in {\Bbb R}^d$, in the sense of Lebesgue measure.                
We obtain a variable coefficient variant of this result in which we  
are able to replace the Hausdorff dimension with the upper Minkowski 
dimension on the left-hand-side of the first inequality.  This is    
joint work with Alex Iosevich and Suresh Eswarathasan.  Fourier      
Integral Operator bounds and other techniques of harmonic analysis   
play a crucial role in our investigation.                            

Dr. Daniel Reem, IMPA, Rio de Janeiro, Brasil
23/01/2013 - 14:00

Recently S. Artstein-Avidan and V. Milman have developed an    
abstract duality theory and proved the following remarkable    
result: up to linear terms, the only fully order preserving    
operator (namely, an invertible operator whose inverse also    
preserves the pointwise order between functions) acting        
on the class of lower semicontinuous proper convex functions   
defined on R^n is the identity operator, and the only fully    
order reversing operator acting on the same set is the         
Fenchel conjugation (Legendre transform). We establish         
a suitable extension of their result to infinite dimensional   
Banach spaces.                                                 
This is a joint work with Alfredo N. Iusem and Benar F. Svaiter

Prof. A. Lerner, Bar-Ilan University
14/01/2013 - 14:00

The $A_2$ conjecture says that the $L^2(w)$ operator norm            
of any Calder\'on-Zygmund operator is bounded linearly by the $A_2$  
constant of the weight $w$.                                          
This conjecture was completely solved in 2010 by T. Hyt\"onen.       
The proof was based on a rather difficult representation of a general
Calder\'on-Zygmund operator in terms of the Haar shift operators.    
In this talk we shall discuss a recent simpler proof completely      
avoiding the notion of the Haar shift operator.                      

Dr. Nir Lev, Bar-Ilan University
31/12/2012 - 14:00

 We consider an extremal configuration of points on a manifold, called Fekete points,
and study their equidistribution through their relation to Beurling-Landau theory            
of sampling and interpolation (joint work with Joaquim Ortega-Cerda).                        

Prof. Fedor Pakovich, Ben-Gurion University
24/12/2012 - 14:00

A classification of commuting rational functions, that is of rational   
solutions of the functional equation A(X)=X(A), was obtained in the beginning of  
the past century by Fatou, Julia, and Ritt. In the talk we will present a solution
of a more general problem of description of semiconjugate rational functions, that
is of rational solutions of the functional equation A(X)=X(B) in terms of groups  
acting properly discontinuously on the Riemann sphere or complex plane.           

Prof. Y. Yomdin, Weizmann Institute
17/12/2012 - 14:00

I plan to discuss a recent  
progress in Eckhoff Conjecture obtained via "Algebraic Sampling" approach, and a general
bound on sampling accuracy provided by a combination of Kolmogorov's entropy and       
Johnson-Lindenstrauss dimensionality reduction. This is a joint work with D. Batenkov. 

Dr. Leo Tzou, Academy of Finland/University of Helsinki
10/12/2012 - 14:00


The problem of determining the electrical conductivity of a body by                                                                                                                             
making voltage and current measurements on the object's surface has                                                                                                                             
various applications. We will look at the connection between this applied analysis problem with seemingly unrelated fields such as symplectic geometry  
and differential topology as well as geometric scattering theory.                                                       
Prof. Daoud Bshouty, Technion
26/11/2012 - 14:00

 The Nitsche conjecture was solved recently by Iwaniec, Kovalov and Onninen and in the same
paper they pose the same problem from Teichmuller domain onto Teiuchmuller
domain. We present a solution to this problem.

Dr. Shimon Brooks, Bar-Ilan University
19/11/2012 - 14:00

We will discuss the case of surfaces of constant negative curvature; in particular,
we will explain how to construct examples of sufficiently weak quasimodes that do not
satisfy QUE, and show how they fit into the larger theory.

Dr. Daniel Spector
12/11/2012 - 14:00

 In this talk I will discuss some recent results obtained in                    
collaboration with G. Leoni on new characterizations of Sobolev spaces for                
arbitrary open sets. The motivation for such a characterization stems from a              
2001 paper of Bourgain, Brezis, and Mironescu that gives a related one for                
smooth and bounded domains, and an open question on the extension of these                
results to arbitrary open sets.                                                           

Dr. Nathan Keller
05/11/2012 - 14:00

In 1996, Talagrand established a lower bound on the second-level Fourier
coefficients of a monotone Boolean function, in terms of its first-level coefficients.
This lower bound and its enhancements were used in various applications to
correlation inequalities, noise sensitivity, geometry, percolation, etc.
In this talk we present a new proof of Talagrand's inequality, which is somewhat
simpler than the original proof, and allows to generalize the result easily to
non-monotone functions (with influences replacing the first-level coefficients) and
to more general measures on the discrete cube. We then apply our proof to obtain
a quantitative version of a theorem of Benjamini-Kalai-Schramm on the relation
between influences and noise sensitivity.
Time permitting, we shall present recent results and open questions, related
to an application of Talagrand's lower bound to correlation inequalities.

The first part of the talk is joint work with Guy Kindler.

Prof. R. Trigub, Donetsk National University, Ukraine
29/10/2012 - 14:00

The talk consists of two parts.

1) Fourier multipliers and absolute convergence of Fourier integrals.
Based on the paper by Liflyand-Samko-Trigub "The Winer
algebra of absolutely convergent Fourier integrals: an overview",
Analysis and Math. Physics 2(2012), 1-68.

2) Comparison of linear differential operators with constant coefficients
by their norms in  $L_p,$ $1\le p\le \infty$. In particular, three criteria
of comparison are obtained for functions on the circle, on the axis, and on
the half-axis, as well as one sharp inequality.

Tal Weissblat
18/06/2012 - 14:00

In the talk we first review the highly anisotropic Hardy spaces].  We  then discuss a careful approximation
argument that is needed when analyzing dual spaces of Hardy spaces. One cannot assume that a linear
functional, uniformly bounded on all atoms, is automatically bounded
on spaces that have atomic representations (e.g. Hardy spaces).

Prof. Vitaly E. Maiorov, Technion
04/06/2012 - 14:00

We characterize the radial basis functions whose
scattered shifts form a fundamental system in
 the space $L_{p}(\rrd)$. In particular, we show that for any even function $h$ from the space
 $L_{2,{\rm loc}}(\rrd)$
 the space formed by all possible linear combinations of
 shifted radial basis functions $h(\|x+a\|)$, $a\in \rrd$, is dense in the
 space $L_p(\rrd)$, $1\le p\le 2$, if
 and only if the function $h$ is not a polynomial.

E. Liflyand, Bar-Ilan University
21/05/2012 - 14:00
In this talk we discuss various conditions of the
integrability of the Fourier transform of a function of bounded
variation and their connections to the behavior of the Hilbert
transform of a related function. Correspondingly, the considered
spaces of functions with integrable Fourier transform are intimately
related with the real Hardy space. One of the most important
connections for the two transforms is given by the space introduced
(for different purposes) by Johnson and Warner.
Prof. Anatoly Golberg, Holon Institute of Technology
14/05/2012 - 14:00

The classical Teichm\"uller-Wittich-Belinskii theorem implies
the conformality of a planar continuous mapping at a point under rather
general integral restrictions for the dilatation of this mapping
near the point.
This theorem is very rich in applications and has been generalized
by many authors in various directions (weak conformality, differentiability,
multidimensional analogs, etc.).
Certain complete generalizations are due to Reshetnyak and  Bishop, Gutlyanskii, Martio, Vuorinen.


I will show in the talk that the assumptions under which the main results have been obtained,

can be essentially weakened and give much stronger estimate
for the limit of $|f(x)|/|x|$ as $x$ approaches $0$.
We essentially improve the underlying modular technique.

Dmitry Faifman
30/04/2012 - 14:00

We study to which extent the Poisson summation formula determines the Fourier transform. The answer is positive under certain technical smoothness and rate of decay conditions. This study leads to a class of unitary operators on L^2 that satisfy a weighted form of the Poisson summation formula, which we explicitly diagonalize, with eigenvalues related to associated L-functions.

Prof. Shiri Artstein, Tel-Aviv University
23/04/2012 - 14:00
I shall describe the polarity transform for functions, were it came
from, and some of its properties, especially in comparison with the
well known Legendre transform ("duality" versus "polarity").
Then we shall study its (sub)differential structure, and show that
it may be used to solve new families of first order Hamilton--Jacobi type
equations as well as some second order Monge-Ampere type equations.
The first part is based on joint work with Vitali Milman, and the second
part on joint work with Yanir Rubinstein. 
, Swinburne University of Technology, Hawthorn, Australia Prof. V.P. Gurarii
16/04/2012 - 15:05

The Euler-Gauss linear transformation formula for the
hypergeometric function was extended by Goursat for the case of
logarithmic singularities. By replacing the perturbed Bessel
differential equation by a monodromic functional equation, and
studying this equation separately from the differential equation by
an appropriate Laplace-Borel technique, we associate with the latter
equation another monodromic relation in the dual complex plane. This
enables us to prove a duality theorem and to extend Goursat's
formula to much larger classes of functions.

Prof. Rovenski Vladimir, University of Haifa
16/04/2012 - 14:00



Let $(M^{n+p},g)$ be a closed Riemannian manifold, and $\pi: M\to B$
a smooth fiber bundle with compact and orientable $p$-dimensional
fiber $F$. Denote by $D_F$ ($D$) the distribution tangent
(orthogonal, resp.) to fibers.

We discuss conformal flows of the metric restricted to $D$ with the
speed proportional to

(i) the divergence of the mean curvature vector $H$ of $D$,

(ii) the mixed scalar curvature $Sc_{mix}$ of the distributions.
     (If $M$ is a surface, then $Sc_{mix}$ is the gaussian curvature $K$).

For (i), we show that the flow is equivalent to the heat flow of the
1-form dual to $H$, provided the initial 1-form is $D_F$-closed. We
use known long-time existence results for the heat flow to show that
our flow has a global solution $g_t$. It converges to a limiting
metric, for which $D$ is harmonic (i.e., $H=0$); actually under some
topological assumptions we can prescribe $H$.

For (ii) on a twisted product, we observe that $H$ satisfies the
Burgers type PDE, while the warping function satisfies the heat
equation; in this case the metrics $g_t$ converge to the product.

We consider illustrative examples of flows similar to (i) and (ii)
on a surface (of revolution), they yield convection-diffusion PDEs
for curvature of $D$-curves (parallels) and solutions -- non-linear

For $M$ with general $D$, we modify the flow (ii) with the help of a
measure of ``non-umbilicity" of $D_F$, and the integrability tensor
of $D$, while the fibers are totally geodesic. Let $\lambda_0$ be
the smallest eigenvalue of certain Schrödinger operator on the
fibers. We assume $H$ to be $D_F$-potential and show that

-- $H$ satisfies the forced Burgers type PDE;

-- the flow has a unique solution converging to a metric, for which
   and $H$ depends only on the $D$-conformal class of the initial metric.

-- if $D$ had constant rate of ``non-umbilicity" on fibers, then the
limiting metric
   has the properties: $Sc_{mix}$ is quasi-positive, and $D$ is harmonic.

Prof. CHONG KYU HAN, Seoul National University, Republic of Korea
26/03/2012 - 14:00
By using the generalized Frobenius theorems we study
the existence of solutions of overdetermined PDE systems. In
particular, we discuss local geometry of Levi-forms associated with
the minimality and the existence of complex submanifolds of generic
CR manifolds.
Prof. Walter Trebels, Technical University, Darmstadt, Germany
19/03/2012 - 14:00

Define on $\, L^p({\mathbb R}^n),\, p\ge 1,$  moduli of smoothness of order
$\, r,\, r \in {\mathbb N},$ by
\omega_r(t,f)_p:=\sup _{|h| <t} \| \Delta_h^rf\|_p\, ,\quad t>0,\; \;
\Delta_hf(\cdot)= f(\cdot +h)-f(\cdot),\; \Delta_h^r=\Delta_h \Delta^{r-1}_h .
Trivially one has $\, \omega_r(t,f)_p \lesssim \omega_k(t,f)_p\, ,\;
k<r.$ Its converse is known as Marchaud inequality. M.F. Timan 1958
proved a sharpening of the converse, nowadays called
{\it sharp Marchaud inequality}, which in the present context takes the
\omega_k(t,f)_p \lesssim t^k \left( \int_{t}^{\infty} [s^{-k}
\omega_r(u,f)_p]^q \frac{du}{u} \right)^{1/q},\qquad  t>0,\quad k<r.
where $\, q:=\min (p,2),\, 1<p<\infty.$
Here we will show that the sharp Marchaud inequality as well as further
sharp inequalities for moduli of smoothness like Ulyanov  and Kolyada type
ones  are equivalent to  (known) embeddings
between Besov and potential spaces.\\
 To this end  one has to make
use of moduli of smoothness of fractional order which can be
characterized by Peetre's (modified) $\, K$-functional, living on $\,
L^p$ and associated Riesz potential spaces. Limit cases  of
the Holmstedt formula (connecting different $\, K$-functionals) show
that the embeddings imply the desired inequalities.
Conversely, the embeddings result from the inequalities for moduli of
smoothness by limit procedures.

Prof. Mikhail Zaidenberg, Institut Fourier, Grenoble, France
12/03/2012 - 14:00
This is a survey talk on special cellular automata related
to the game `Lights out'. This game, commercialized by `Tiger
Electronics', became a source of inspiration for the work of Sutner,
Goldwasser-Klostermayer-Ward, Barua-Sarkar,
Hunziker-Machiavello-Park e.a.