The aim of this paper is to prove the existence and convergence theorems for cyclic contractions. We introduce a notion called proximally complete pair (A,B) on a metric space, which unify the earlier notions that are used to prove the existence of a best proximity point for a cyclic contraction. By observing geometrical properties on a Hilbert space, we introduce Pythagorean property and use t...

The paper deals with semigroups of operators associated with delay diierential equation: _ x(t) = Ax(t) + L 1 x(t ? h) + L 2 xt; where A is the innnitesimal generator of an analytic semigroup on a Hilbert space X and L 1 , L 2 are densely deened closed operators in X and L 2 (?h; 0;X) respectively. The adjoint semigroupof the solution semigroupof the delay diierentialequation is characterized. ...

We consider various quotients of the C*-algebra of bounded operators on a nonseparable Hilbert space, and prove in some cases that, consistently, there are many outer automorphisms.

We show that each reflexive finite-dimensional subspace of operators is hyperreflexive. This gives a positive answer to a problem of Kraus and Larson. We also show that each n– dimensional subspace of Hilbert space operators is [ √ 2n]–hyperreflexive.

As usual, we equip an infinite-dimensional separable Hilbert space 2 by such nonzero σ -finite Borel measures which are invariant with respect to everywhere dense vector subspaces and study duality between such measures and Baire category. Section 1 contains constructions of nontrivialσ -finite Borel measures, which are defined in the infinite-dimensional separable Hilbert space 2 and are invar...

In this paper, we will study some connections between Hilbert algebras and binary block-codes.With these codes, we can eassy obtain orders which determine suplimentary properties on these algebras. We will try to emphasize how, using binary block-codes, we can provide examples of classes of Hilbert algebras with some properties, in our case, classes of semisimple Hilbert algebras and classes of...

For each triple of positive numbers p,q,r ≥ 1 and each commutative C-algebra with identity 1 and the set s( ) of states on , the set r ( ) of all matrices A = [ajk] over such that φ[A [r] ] := [φ(|ajk|r )] defines a bounded operator from p to q for all φ ∈ s( ) is shown to be a Banach algebra under the Schur product operation, and the norm ||A|| = |||A|||p,q,r = sup{||φ[A[r] ]||1/r : φ ∈ s( )}....

An algebra of bounded linear operators on a Hilbert space is called strongly compact whenever each of its bounded subsets is relatively compact in the strong operator topology. The concept is most commonly studied for two algebras associated with a single operator T : the algebra alg(T ) generated by the operator, and the operator’s commutant com(T ). This paper focuses on the strong compactnes...

Uncountably many mutually non-isomorphic product systems (that is, continuous tensor products of Hilbert spaces) of types II0 and III are constructed by probabilistic means (random sets and off-white noises), answering four questions of W. Arveson.

A classical result of Grothendieck and Lidskii says that the trace formula (that the trace of a nuclear operator is the sum of its eigenvalures provided the sequence of eigenvalues is absolutely summable) holds in Hilbert spaces. In 1988 Pisier proved that weak Hilbert spaces satisfy the trace formula. We exhibit a much larger class of Banach spaces, called Γ-spaces, that satisfy the trace form...