Search results for "Nuclear operator"
showing 4 items of 14 documents
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…
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.
Evolution semigroups and time operators on Banach spaces
2010
AbstractWe present new general methods to obtain shift representation of evolution semigroups defined on Banach spaces. We introduce the notion of time operator associated with a generalized shift on a Banach space and give some conditions under which time operators can be defined on an arbitrary Banach space. We also tackle the problem of scaling of time operators and obtain a general result about the existence of time operators on Banach spaces satisfying some geometric conditions. The last part of the paper contains some examples of explicit constructions of time operators on function spaces.