Page 1 Next

Displaying 1 – 20 of 50

Showing per page

An Exposition of the Connection between Limit-Periodic Potentials and Profinite Groups

Z. Gan (2010)

Mathematical Modelling of Natural Phenomena

We classify the hulls of different limit-periodic potentials and show that the hull of a limit-periodic potential is a procyclic group. We describe how limit-periodic potentials can be generated from a procyclic group and answer arising questions. As an expository paper, we discuss the connection between limit-periodic potentials and profinite groups as completely as possible and review some recent results on Schrödinger operators obtained in this...

An introduction to Rota’s universal operators: properties, old and new examples and future issues

Carl C. Cowen, Eva A. Gallardo-Gutiérrez (2016)

Concrete Operators

The Invariant Subspace Problem for Hilbert spaces is a long-standing question and the use of universal operators in the sense of Rota has been an important tool for studying such important problem. In this survey, we focus on Rota’s universal operators, pointing out their main properties and exhibiting some old and recent examples.

An operator-theoretic approach to truncated moment problems

Raúl Curto (1997)

Banach Center Publications

We survey recent developments in operator theory and moment problems, beginning with the study of quadratic hyponormality for unilateral weighted shifts, its connections with truncated Hamburger, Stieltjes, Hausdorff and Toeplitz moment problems, and the subsequent proof that polynomially hyponormal operators need not be subnormal. We present a general elementary approach to truncated moment problems in one or several real or complex variables, based on matrix positivity and extension. Together...

Composition operators in the Dirichlet series setting

Hervé Queffélec (2007)

Banach Center Publications

In this work, we begin with a survey of composition operators on the Hardy space H² and on the Wiener algebra A⁺ of absolutely convergent Taylor series, with special emphasis on their compactness, or invertibility, or isometric character. The main results are due respectively to J. Shapiro and D.~Newman. In a second part, we present more recent results, due to Gordon and Hedenmalm on the one hand, and to Bayart, the author et al. on the other hand, concerning the analogues of H² and A⁺ in the setting...

Fixed point and continuation results for contractions in metric and gauge spaces

M. Frigon (2007)

Banach Center Publications

We present an overview of generalizations of Banach's fixed point theorem and continuation results for contractions, i.e., results establishing that the existence of a fixed point is preserved by suitable homotopies. We will consider single-valued and multi-valued contractions in metric and in gauge spaces.

Fredholm determinants

Henry McKean (2011)

Open Mathematics

The article provides with a down to earth exposition of the Fredholm theory with applications to Brownian motion and KdV equation.

La figura espectral del producto tensorial de dos operadores.

Carlos Bosch Giral, Carlos Hernández Garciadiego, Elena de Oteyza (1982)

Revista Matemática Hispanoamericana

Sea H un espacio de Hilbert complejo, separable y de dimensión infinita. Denotaremos por L(H) al álgebra de todos los operadores acotados en H. Carl Pearcy en 1977 introdujo el concepto de figura espectral de un operador T en L(H) [13]. Sin lugar a dudas hay dos resultados que hacen de la figura espectral de un operador un concepto importante. El primero se debe a Brown, Douglas y Fillmore:"Dos operadores esencialmente normales son débilmente equivalentes si y sólo si tienen la misma figura espectral".El...

Currently displaying 1 – 20 of 50

Page 1 Next