A characterization for the spectral capacity of a finite system of operators
A Characterization of Riesz Operators.
A characterization of some subsets of S-essential spectra of a multivalued linear operator
We characterize some S-essential spectra of a closed linear relation in terms of certain linear relations of semi-Fredholm type.
Certain invariant subspaces for operators with rich eigenvalues.
Commutativity of compact selfadjoint operators
The relationship between the joint spectrum γ(A) of an n-tuple of selfadjoint operators and the support of the corresponding Weyl calculus T(A) : f ↦ f(A) is discussed. It is shown that one always has γ(A) ⊂ supp (T(A)). Moreover, when the operators are compact, equality occurs if and only if the operators mutually commute. In the non-commuting case the equality fails badly: While γ(A) is countable, supp(T(A)) has to be an uncountable set. An example is given showing that, for non-compact operators,...
Comparison of joint spectra for certain classes of commuting operators
Concept of the spectral sets in Wachs spaces, I.
Contributi all'analisi spettrale algebrica
Ein Äquikonvergenzsatz für eine Klasse von singulären Differentialoperatoren.
Ein „merkwürdiges” Spektrum für nichtlineare Operatoren
We define a spectrum for Lipschitz continuous nonlinear operators in Banach spaces by means of a certain kind of "pseudo-adjoint" and study some of its properties.
Erratum to "Operators on spaces of analytic functions" (Studia Math, 108 (1994), 49-54)
Exponential bounds for noncommuting systems of matrices
It is shown that a finite system T of matrices whose real linear combinations have real spectrum satisfies a bound of the form . The proof appeals to the monogenic functional calculus.
Fourier-like methods for equations with separable variables
It is well known that a power of a right invertible operator is again right invertible, as well as a polynomial in a right invertible operator under appropriate assumptions. However, a linear combination of right invertible operators (in particular, their sum and/or difference) in general is not right invertible. It will be shown how to solve equations with linear combinations of right invertible operators in commutative algebras using properties of logarithmic and antilogarithmic mappings. The...
Function theory in sectors
It is shown that there is a one-to-one correspondence between uniformly bounded holomorphic functions of n complex variables in sectors of ℂⁿ, and uniformly bounded functions of n+1 real variables in sectors of that are monogenic functions in the sense of Clifford analysis. The result is applied to the construction of functional calculi for n commuting operators, including the example of differentiation operators on a Lipschitz surface in .
Generalization of von Neumann's spectral sets and integral representation of operators
In search of the invisible spectrum
In this paper, we begin the study of the phenomenon of the “invisible spectrum” for commutative Banach algebras. Function algebras, formal power series and operator algebras will be considered. A quantitative treatment of the famous Wiener-Pitt-Sreider phenomenon for measure algebras on locally compact abelian (LCA) groups is given. Also, our approach includes efficient sharp estimates for resolvents and solutions of higher Bezout equations in terms of their spectral bounds. The smallest “spectral...
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