On Commuting Families Of Subnormal Operatores
On local spectral properties of operators in Banach spaces
On some constructions of new triangular norms.
We discuss the properties of two types of construction of a new t-norm from a given t-norm proposed recently by B. Demant, namely the dilatation and the contraction. In general, the dilatation of a t-norm is an ordinal sum t-norm and the continuity of the outgoing t-norm is preserved. On the other hand, the contraction may violate the continuity as well as the non-continuity of the outgoing t-norm. Several examples are given.
On the essential order spectrum
On the genericity of nonvanishing instability intervals in Hills equation
On the local spectral properties of weighted shift operators
We study the local spectral properties of both unilateral and bilateral weighted shift operators.
On The Set Of Operators Having A Given Simply Connected Spectral Set.
On the singular spectrum of discrete Schrödinger operator
On von Neumann's inequality.
Opérateurs de Riesz dont le coeur analytique est fermé
Dans ce travail nous donnons plusieurs caractérisations, en termes spectraux, d'opérateurs de Riesz dont le coeur analytique est fermé. Notamment, nous montrons que pour un opérateur de Riesz T, le coeur analytique est fermé si et seulement si sa dimension est finie si et seulement si zéro est isolé dans le spectre de T si et seulement si T = Q + F avec QF = FQ = 0, F de rang fini et Q quasinilpotent. Ce dernier résultat montre qu'un opérateur de Riesz dont le coeur analytique est fermé admet la...
Operator theory and the Carathéodory metric.
Operators acting on certain Banach spaces of analytic functions.
Operators on spaces of analytic functions
Let be the operator of multiplication by z on a Banach space of functions analytic on a plane domain G. We say that is polynomially bounded if for every polynomial p. We give necessary and sufficient conditions for to be polynomially bounded. We also characterize the finite-codimensional invariant subspaces and derive some spectral properties of the multiplication operator in case the underlying space is Hilbert.
Operators with thin spectral sets.
Operator-valued n-harmonic measure in the polydisc
An operator-valued multi-variable Poisson type integral is studied. In Section 2 we obtain a new equivalent condition for the existence of a so-called regular unitary dilation of an n-tuple T=(T₁,...,Tₙ) of commuting contractions. Our development in Section 2 also contains a new proof of the classical dilation result of S. Brehmer, B. Sz.-Nagy and I. Halperin. In Section 3 we turn to the boundary behavior of this operator-valued Poisson integral. The results obtained in this section improve upon...