Search results for " Operator"

Rate of growth of frequently hypercyclic functions

2010

AbstractWe study the rate of growth of entire functions that are frequently hypercyclic for the differentiation operator or the translation operator. Moreover, we prove the existence of frequently hypercyclic harmonic functions for the translation operator and we study the rate of growth of harmonic functions that are frequently hypercyclic for partial differentiation operators.

Prefazione al libro di Vanessa Dioguardi, L'immagine della destinazione turistica come costruzione sociale, Franco Angeli, Milano, 2009.

2009

Approximation problems in linear and non-linear analysis

2023

En esta tesis estudiamos problemas relacionados con aplicaciones de varios tipos que alcanzan su norma u operadores que alcanzan su radio numérico. Tras un capítulo introductorio donde se comentan las notaciones, los principales conceptos, y un resumen histórico del estado del arte, hay 4 capítulos de contenido matemático donde se estudian diversos tipos de problemas. En el capítulo 2, se estudian clases de operadores entre espacios de Banach tales que cuando casi alcanzan su norma (respectivamente, su radio numérico) en un punto (respectivamente, un estado), necesariamente la alcanzan en un punto cercano (respectivamente, en un estado cercano). Se obtienen resultados positivos para dominio…

Beurling ultradistributions of Lp-growth

2003

We study the convolutors and the surjective convolution operators acting on spaces of ultradistributions of Lp-growth. In the case p = 2 we obtain complete characterizations. Some results on hypoellipticity are also included.  2003 Elsevier Science (USA). All rights reserved.

Unbounded derivations and *-automorphisms groups of Banach quasi *-algebras

2018

This paper is devoted to the study of unbounded derivations on Banach quasi *-algebras with a particular emphasis to the case when they are infinitesimal generators of one parameter automorphisms groups. Both of them, derivations and automorphisms are considered in a weak sense; i.e., with the use of a certain families of bounded sesquilinear forms. Conditions for a weak *-derivation to be the generator of a *-automorphisms group are given.

Continuous frames for unbounded operators

2021

Few years ago G\u{a}vru\c{t}a gave the notions of $K$-frame and atomic system for a linear bounded operator $K$ in a Hilbert space $\mathcal{H}$ in order to decompose $\mathcal{R}(K)$, the range of $K$, with a frame-like expansion. These notions are here generalized to the case of a densely defined and possibly unbounded operator on a Hilbert space $A$ in a continuous setting, thus extending what have been done in a previous paper in a discrete framework.

Fredholm operator families ?II

1984

First, we give a characterization of semi-Fredholm operators (i.e. those which are left or right invertible modulo compact operators) on Hausdorff tvs which generalizes the usual one in the context of Banach spaces. Then we consider a class of semi-Fredholm operator families on tvs which include both the "classical" semi-Fredholm operator valued functions on Banach spaces (continuous in the norm sense), and families of the form T + Kn, where Kn is a collectively compact sequence which converges strongly to O. For these families we prove a general stability theorem.

Factorization of strongly (p,sigma)-continuous multilinear operators

2013

We introduce the new ideal of strongly-continuous linear operators in order to study the adjoints of the -absolutely continuous linear operators. Starting from this ideal we build a new multi-ideal by using the composition method. We prove the corresponding Pietsch domination theorem and we present a representation of this multi-ideal by a tensor norm. A factorization theorem characterizing the corresponding multi-ideal - which is also new for the linear case - is given. When applied to the case of the Cohen strongly -summing operators, this result gives also a new factorization theorem.

Property (w) for perturbations of polaroid operators

2008

Abstract A bounded linear operator T ∈ L ( X ) acting on a Banach space satisfies property ( w ) , a variant of Weyl’s theorem, if the complement in the approximate point spectrum σ a ( T ) of the Weyl essential approximate-point spectrum σ wa ( T ) is the set of all isolated points of the spectrum which are eigenvalues of finite multiplicity. In this note, we study the stability of property ( w ) for a polaroid operator T acting on a Banach space, under perturbations by finite rank operators, by nilpotent operators and, more generally, by algebraic operators commuting with T.

Operators which have a closed quasi-nilpotent part

2002

We find several conditions for the quasi-nilpotent part of a bounded operator acting on a Banach space to be closed. Most of these conditions are established for semi-Fredholm operators or, more generally, for operators which admit a generalized Kato decomposition. For these operators the property of having a closed quasi-nilpotent part is related to the so-called single valued extension property.