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Series: Analysis Seminar

Consider three partitions of integers a=(a_1\ge a_2\ge ... \ge a_n\ge 0), b=(b_1\ge b_2\ge ... \ge b_n \ge 0), and
c=(c_1\ge \ge c_2\ge ... \ge c_n\ge 0). It is well-known that a triple of partitions (a,b,c) that satisfies the so-call Littlewood-Richardson rule describes the eigenvalues of the sum of nXn Hermitian matricies, i.e., Hermitian matrices A, B, and C such that A+B=C with a (b and c respectively) as the set of eigenvalues of A (B and C respectively). At the same time such triple also describes the Jordan decompositions of a nilpotent matrix T, T resticts to an invarint subspace M, and T_{M^{\perp}} the compression of T onto the M^{\perp}. More precisely, T is similar to J(c):=J_(c_1)\oplus J_(c_2)\oplus ... J_(c_n)$, and T|M is similar to J(a) and T_{M^{\perp}} is similar to J(b). (Here J(k) denotes the Jordan cell of size k with 0 on the diagonal.) In addition, these partitions must also satisfy the Horn inequalities. In this talk I will explain the connections between these two seemily unrelated objects in matrix theory and why the same combinatorics works for both. This talk is based on the joint work with H. Bercovici and K. Dykema.

Series: Analysis Seminar

Asymptotics for L2 Christoffel functions are a classical topic in orthogonal polynomials. We present asymptotics for Lp Christoffel functions for measures on the unit circle. The formulation involves an extremal problem in Paley-Wiener space. While there have been estimates of the Lp Christoffel functions for a long time, the asymptotics are noew for p other than 2, even for Lebesgue measure on the unict circle.

Series: Analysis Seminar

A brief overview of some integrable and exactly-solvable Schroedinger equations with trigonometric potentials of Calogero-Moser-Sutherland type is given.All of them are characterized bya discrete symmetry of the Hamiltonian given by the affine Weyl group,a number of polynomial eigenfunctions and eigenvalues which are usually quadratic in the quantum number, each eigenfunction is an element of finite-dimensionallinear space of polynomials characterized by the highest root vector, anda factorization property for eigenfunctions. They admitan algebraic form in the invariants of a discrete symmetry group(in space of orbits) as 2nd order differential operator with polynomial coefficients anda hidden algebraic structure. The hidden algebraic structure for $A-B-C-D$-series is related to the universal enveloping algebra $U_{gl_n}$. For the exceptional $G-F-E$-seriesnew infinite-dimensional finitely-generated algebras of differential operatorswith generalized Gauss decomposition property occur.

Series: Analysis Seminar

In this talk, we investigate the structures of C*-algebras generated by
collections of linear-fractionally-induced composition operators and
either the forward shift or the ideal of compact operators. In the
setting of the classical Hardy space, we present a full characterization
of the structures, modulo the ideal of compact operators, of
C*-algebras generated by a single linear-fractionally-induced
composition operator and the forward shift. We apply the structure
results to compute spectral information for algebraic combinations of
composition operators. We also discuss related results for C*-algebras
of operators on the weighted Bergman spaces.

Series: Analysis Seminar

Series: Analysis Seminar

In this talk we discuss some nonlinear transformations between moment
sequences. One of these transformations is the following: if (a_n)_n
is a non-vanishing Hausdorff moment sequence then the sequence defined
by 1/(a_0 ... a_n) is a Stieltjes moment sequence. Our approach is
constructive and use Euler's idea of developing q-infinite products in
power series. Some others transformations will be considered as well as
some relevant moment sequences and analytic functions related to them.
We will also propose some conjectures about moment transformations
defined by means of continuous fractions.

Series: Analysis Seminar

The classification theorem for a C_0 operator describes its
quasisimilarity class by means of its Jordan model. The purpose of this
talk will be to investigate when the relation between the operator and
its model can be improved to similarity. More precisely, when the
minimal function of the operator T can be written as a product of inner
functions satisfying the so-called (generalized) Carleson condition, we
give some natural operator theoretic assumptions on T that guarantee
similarity.

Series: Analysis Seminar

Using integral formulas based on Green's theorem and in
particular a lemma of Uchiyama, we give simple proofs of comparisons
of different BMO norms without using the John-Nirenberg inequality
while we also give a simple proof of the strong John-Nirenberg
inequality. Along the way we prove the inclusions of BMOA in the dual
of H^1 and BMO in the dual of real H^1. Some difficulties of the
method and possible future directions to take it will be suggested at
the end.

Series: Analysis Seminar

In the first part of the talk we will give a brief survey of significant
results going from S. Brown pioneering work showing the existence of
invariant subspaces for subnormal operators (1978) to Ambrozie-Muller
breakthrough asserting the same conclusion for the adjoint of a
polynomially bounded operator (on any Banach space) whose spectrum
contains the unit circle (2003). The second part will try to give some
insight of the different techniques involved in this series of results,
culminating with a brilliant use of Carleson interpolation theory for
the last one. In the last part of the talk we will discuss additional
open questions which might be investigated by these techniques.

Series: Analysis Seminar