Représentation d’un semigroupe d’opérateurs sur un espace par des noyaux. Remarques sur deux articles de S.E. Kuznetsov
Some general representation formulae for (C₀) m-parameter operator semigroups with rates of convergence are obtained by the probabilistic approach and multiplier enlargement method. These cover all known representation formulae for (C₀) one- and m-parameter operator semigroups as special cases. When we consider special semigroups we recover well-known convergence theorems for multivariate approximation operators.
Soit une distribution dissipative sur un groupe de Lie et soit une représentation fortement continue de dans un espace de Banach. Supposons à support compact. Il y a deux façons évidentes de définir un opérateur fermé : une faible et une forte. Le résultat principal de cet article est que l’on obtient le même résultat et que engendre un semi-groupe fortement continu d’opérateurs.
In the first part of the paper, some criteria of continuity of representations of a Polish group in a Banach algebra are given. The second part uses the result of the first part to deduce automatic continuity results of Baire morphisms from Polish groups to locally compact groups or unitary groups. In the final part, the spectrum of an element in the range of a strongly but not norm continuous representation is described.
We prove that some regularity conditions on unbounded representations of topological abelian semigroups with countable spectral conditions induce a certain stability result extending the well-known Arendt-Batty-Lyubich-Vũ theorem.
Under suitable conditions we prove the wellposedness of small time-varied delay equations and then establish the robust stability for such systems on the phase space of continuous vector-valued functions.