Trace Formulas for Some Operators Related To Quadrature Domains in Riemann Surfaces

This note studies the trace formula of a class of pure operators A with finite rank self-commutators satisfying the condition that there is a finite dimensional subspace containing the image of the self-commutator and invariant with respect to A ^*. Besides, in this class, the spectrum of the operator A is covered by the projection of a union of quadrature domains in some Riemann surfaces.     

Recovering a Logic from Its Fragments by Meta-Fibring

In this paper we address the question of recovering a logic system by combining two or more fragments of it. We show that, in general, by fibring two or more fragments of a given logic the resulting logic is weaker than the original one, because some meta-properties of the connectives are lost after the combination process. In order to overcome this problem, the categories Mcon and Seq of multiple-conclusion consequence relations and sequent calculi, respectively, are introduced. The main feature of these categories is the preservation, by morphisms, of meta-properties of the consequence relations, which allows, in several cases, to recover a logic by fibring of its fragments. The fibring in this categories is called meta−fibring. Several examples of well-known logics which can be recovered by meta-fibring its fragments (in opposition to fibring in the usual categories) are given. Finally, a general semantics for objects in Seq (and, in particular, for objects in Mcon) is proposed, obtaining a category of logic systems called Log. A general theorem of preservation of completeness by fibring in Log is also obtained.     

Large Time Behaviour of Linear Functional Differential Equations

The aim of this paper is to show that the spectral theory for linear autonomous and periodic functional differential equations yields explicit formulas for the large time behaviour of solutions. Our results are based on resolvent computations and Dunford calculus and yield insight, new proofs and generalizations of results that have recently appeared in the literature.     

Algebraic Order Bounded Disjointness Preserving Operators and Strongly Diagonal Operators

Let T be an order bounded disjointness preserving operator on an Archimedean vector lattice. The main result in this paper shows that T is algebraic if and only if there exist natural numbers m and n such that n ≥ m, and T^n!, when restricted to the vector sublattice generated by the range of T^m, is an algebraic orthomorphism. Moreover, n (respectively, m) can be chosen as the degree (respectively, the multiplicity of 0 as a root) of the minimal polynomial of T. In the process of proving this result, we define strongly diagonal operators and study algebraic order bounded disjointness preserving operators and locally algebraic orthomorphisms. In addition, we introduce a type of completeness on Archimedean vector lattices that is necessary and sufficient for locally algebraic orthomorphisms to coincide with algebraic orthomorphisms.     

w-Hyponormal Operators are Subscalar

We prove that if X is a Banach space, R, S B(X), then RS is subscalar (subdecomposable) if and only if SR is. As corollaries, it is shown that w-hyponormal operators (including p-hyponormal (p > 0) and log-hyponormal operators) and their Aluthge transformations and inverse Aluthge transformations are subscalar.     

On Some Product of Two Unbounded Self-Adjoint Operators

We give a spectral analysis of some unbounded normal product HK of two self-adjoint operators H and K (which appeared in [7]) and we say why it is not self-adjoint even if the spectrum of one of the operators is sufficiently “asymmetric”. Then, we investigate the self-adjointness of KH (given it is normal) for arbitrary self-adjoint H and K by giving a counterexample and some positive results and hence finishing off with the whole question of normal products of self-adjoint operators (appearing in [1, 7, 12]). The author was supported in part by CNEPRU: B01820070020 (Ministry of Higher Education, Algeria).     

Topological Components of the Set of Composition Operators on $$H^\infty (B_N)$$

This paper characterizes the component structure of the space of composition operators acting on , both in the operator norm topology and in the topology induced by the essential norm.     

Absolute Equivalence and Dirac Operators of Commuting Tuples of Operators

In this paper we define an equivalence relation of operators on Hilbert spaces which we call absolute equivalence. Two operators are called absolutely equivalent if both the absolute value of the operators and their adjoints are unitarily equivalent. We then use the properties of this equivalence relation to study the Koszul complex of a commuting tuple of operators through the Dirac operator of the tuple.     

The algebraic uniqueness of the addition of natural numbers

As is known, multiplication is aniteration of addition within the natural numbers. We show that addition is essentially theonly associative binary operation on natural numbers whose iteration is commutative or associative. This result, in which a set determines a structure, is in a sense a converse of the classical one due to Pontrjagin [3] and Kolmogorov [1], in which certain algebraic and topological structures determine the fields of real and complex numbers and of quaternions.     

Simultaneous Approximation for Generalized Baskakov-Durrmeyer-Type Operators

The present paper deals with the study of a Durrmeyer-type integral modification of certain modified Baskakov operators. Here we study simultaneous approximation properties for these operators by using the iterative combinations. We obtain an asymptotic formula and an error estimation in terms of higher order modulus of continuity for these operators.      

Strongly regular rings and rational identities of division rings

We look at division rings in the variety of strongly regular rings and show a connection to the study of rational identities on division rings.Research partially supported by a Grant from NSERC.     

Syndetically Hypercyclic Operators

Given a continuous linear operator T L(x) defined on a separable -space X, we will show that T satisfies the Hypercyclicity Criterion if and only if for any strictly increasing sequence of positive integers such that the sequence is hypercyclic. In contrast we will also prove that, for any hypercyclic vector x X of T, there exists a strictly increasing sequence such that and is somewhere dense, but not dense in X. That is, T and do not share the same hypercyclic vectors.     

Local Spectral Theory of Linear Operators RS and SR

In this paper, we study the relation between local spectral properties of the linear operators RS and SR. We show that RS and SR share the same local spectral properties SVEP, (β), (δ) and decomposability. We also show that RS is subscalar if and only if SR is subscalar. We recapture some known results on spectral properties of Aluthge transforms.     

Toeplitz Operators on Analytic Besov Spaces

We characterize complex measures μ on the unit disk for which the Toeplitz operator T _μ is bounded or compact on the analytic Besov spaces B _p with 1 ≤ p < ∞. Research supported in part by NSF grant, DMS 0200587 (first author); and by a NSERC grant (third author).     

ℰ-complete andD-generic filters of partially ordered sets

In this paper we prove theorems which ensure the existence of -complete andD-generic filters of partially ordered sets.