Unitary dilations of multi-parameter semigroups of operators
Unitary equivalence and decompositions of finite systems of closed densely defined operators in Hilbert spaces [Book]
Unitary equivalence of operators and dilations
Given two contractions T and T' such that T'-T is an operator of finite rank, we prove, under some conditions, the unitary equivalence of the unitary parts of the minimal isometric dilations (respectively minimal co-isometric extensions) of T and T'.
Unitary Equivalence of Stark Hamiltonians.
Unitary extensions of isometries, generalized interpolation and band extensions
The aim of this paper is to give a very brief account of some applications of the method of unitary extensions of isometries to interpolation and extension problems.
Unitary Mappings Between Multiresolution Analyses of L... (R) and a Parametrization of Low-Pass Filters.
Unitary parts of generalized Hankel operators
Unitary representations of solvable Lie groups
Universal Compressions of Representations of H... (G).
Universal estimates of the spectral radius
Universal images of universal elements
We furnish several necessary and sufficient conditions for the following property: For a topological space X, a continuous selfmapping S of X and a family τ of continuous selfmappings of X, the image under S of every τ-universal element is also τ-universal. An application in operator theory, where we extend results of Bourdon, Herrero, Bes, Herzog and Lemmert, is given. In particular, it is proved that every hypercyclic operator on a real or complex Banach space has a dense invariant linear manifold...
Universal interpolating sequences on some function spaces
Let be the Hilbert space with reproducing kernel . This paper characterizes some sufficient conditions for a sequence to be a universal interpolating sequence for .
Universal Jamison spaces and Jamison sequences for C₀-semigroups
An increasing sequence of positive integers is said to be a Jamison sequence if for every separable complex Banach space X and every T ∈ ℬ(X) which is partially power-bounded with respect to , the set is at most countable. We prove that for every separable infinite-dimensional complex Banach space X which admits an unconditional Schauder decomposition, and for any sequence which is not a Jamison sequence, there exists T ∈ ℬ(X) which is partially power-bounded with respect to and has the...
Universal Spectra and Tijdeman's Conjecture on Factorization of Cyclic Groups.
Universal stability of Banach spaces for ε -isometries
Let X, Y be real Banach spaces and ε > 0. A standard ε-isometry f: X → Y is said to be (α,γ)-stable (with respect to for some α,γ > 0) if T is a linear operator with ||T|| ≤ α such that Tf- Id is uniformly bounded by γε on X. The pair (X,Y) is said to be stable if every standard ε-isometry f: X → Y is (α,γ)-stable for some α,γ > 0. The space X[Y] is said to be universally left [right]-stable if (X,Y) is always stable for every Y[X]. In this paper, we show that universally right-stable...
Universal Taylor series with maximal cluster sets.
Universal zero solutions of linear partial differential operators
A generalized approach to several universality results is given by replacing holomorphic or harmonic functions by zero solutions of arbitrary linear partial differential operators. Instead of the approximation theorems of Runge and others, we use an approximation theorem of Hörmander.
Universality of derivative and antiderivative operators with holomorphic coefficients
We prove some conditions on a sequence of functions and on a complex domain for the existence of universal functions with respect to sequences of certain derivative and antiderivative operators related to them. Conditions for the equicontinuity of those families of operators are also studied. The conditions depend upon the "size" of the domain and functions. Some earlier results about multiplicative complex sequences are extended.
Universality of the best determined terms method
The properties are studied of the best determined terms method with respect to an a priori decomposition . The universal approximation to the normal solution of the first kind Fredholm integral equation is found.