Local spectral multiplicity of a linear operator with respect to a measure

Let T be a bounded linear operator in a separable Banach space X and let μ be a nonnegative measure in χ with compact support. A function m_T,μ is considered that is defined μ-a.e. and has nonnegative integers or +∞ as values. This function is called the local multiplicity of T with respect to the measure μ. This function has some natural properties, it is invariant under similarity and quasisimilarity; the local spectral multiplicity of a direct sum of operators equals the sum of local multiplicities, and so on. The definition is given in terms of the maximal diagonalization of the operator T. It is shown that this diagonalization is unique in the natural sense. A notion of a system of generalized eigenvectors, dual to the notion of diagonalization, is discussed. Some examples of evaluation of the local spectral multiplicity function are given. Bibliography:10 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 222, 1995, pp. 293–306.     

Neighborhoods with respect to a categorical closure operator

We introduce and study a concept of neighborhoods with respect to a categorical closure operator. The concept, which is based on using pseudocomplements in subobject lattices, naturally generalizes the classical neighborhoods in topological spaces and we show that it behaves accordingly. We investigate also separation and compactness defined in a natural way by the help of the neighboorhoods introduced.     

Complementary means with respect to a nonsymmetric invariant mean

Aequationes mathematicae - It is known that if a bivariate mean K is symmetric, continuous and strictly increasing in each variable, then for every mean M there is a unique mean $$N,$$ such that K...     

Variational composition of a monotone operator and a linear mapping with applications to elliptic PDEs with singular coefficients

This paper proposes a regularized notion of a composition of a monotone operator with a linear mapping. This new concept, called variational composition, can be shown to be maximal monotone in many cases where the usual composition is not. The two notions coincide, however, whenever the latter is maximal monotone. The utility of the variational composition is demonstrated by applications to subdifferential calculus, theory of measurable multifunctions, and elliptic PDEs with singular coefficients.     

Neighborhoods and convergence with respect to a closure operator

We study neighborhoods with respect to a categorical closure operator. In particular, we discuss separation and compactness obtained from neighborhoods in a natural way and compare them with the usual closure separation and closure compactness. We also introduce a concept of convergence based on using centered systems of subobjects, which naturally generalizes the classical filter convergence in topological spaces. We investigate behavior of the convergence introduced and show, among others, that it relates to the separation and compactness in natural ways.     

On the Ornstein-Uhlenbeck operator in spaces with respect to invariant measures

We consider a class of elliptic and parabolic differential operators with unbounded coefficients in , and we study the properties of the realization of such operators in suitable weighted spaces.

     

Estimates of operator polynomials in the space Lp with respect to the multiplier norm

The paper is devoted to the determination of an analog of J, von Neumann's inequality for the space L^p.The fundamental result of the paper is: If T is an absolute contraction in the space L^p(X,F,μ) (i.e., |T|_L1≤1) and |T|_L∞≤1) then for every polynomial ϕ one has where S is the shift operator in the space. On the basis of this theorem, one finds a theorem on substitutions in the space of multipliers. One gives applications of the inequality (1) to the weighted shift operators in the space It turns out that under some natural restrictions on the weight, inequality (1) becomes an equality for such operators. One also presents a proof of J. von Neumann's inequality based on the approximation of a contraction in a Hilbert space by unitary operators. Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 65, pp. 133–148, 1976. The author wishes to express his thanks to N. K. Nikol'skii for suggesting the problem and for his interest in the paper.     

The Forsythe-Motzkin method for singular linear operator equations

Convergence of the gradient method of Forsythe and Motzkin to a generalized solution of a singular linear operator equation is established.     

Simplicity of principal eigenvalue for p-Laplace operator with singular indefinite weight

Given a connected open set and a function w ∈L^N/p(Ω) if 1 < p < N and w ∈L^r (Ω) for some r ∈(1, ∞) if p ≧ N, with we prove that the positive principal eigenvalue of the problem

Existence of measures invariant with respect to a semigroup of continuous open mappings of a locally compact topological space

Translated from Matematicheskie Zametki, Vol. 57, No. 3, pp. 415–421, March, 1995.     

The topological asymptotic with respect to a singular boundary perturbation

The aim of the topological sensitivity analysis is to obtain an asymptotic expansion of a design functional with respect to the insertion of a small hole in the domain. The question that we address here is what happens if the hole is located at the boundary of the domain and what happens if the boundary is not regular. The adjoint method and the domain truncation technique are proposed to solve this problem. As a model example, we consider the Laplace equation in a domain with a corner. To cite this article: B. Samet, C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

General forms of operator algebras on Pontrjagin space with neutral invariant subspaces

In this paper, we classify the general symmetric operator algebras on Pontrjagin space into six classes by using of symmetric ideals, and give the general forms for all the general symmetric operator algebras in each class.