Search results for "Compact space"

Compactness and $s$-numbers for polynomials

2018

Quasi-compactness of dominated positive operators andC o-semigroups

1991

Hilbert-Schmidt Hankel operators on the Segal-Bargmann space

2004

This paper considers Hankel operators on the Segal-Bargmann space of holomorphic functions onCn\mathbb {C}^nthat are square integrable with respect to the Gaussian measure. It is shown that in the case of a bounded symbolg∈L∞(Cn)g \in L^{\infty }(\mathbb {C}^n)the Hankel operatorHgH_gis of the Hilbert-Schmidt class if and only ifHg¯H_{\bar {g}}is Hilbert-Schmidt. In the case where the symbol is square integrable with respect to the Lebesgue measure it is known that the Hilbert-Schmidt norms of the Hankel operatorsHgH_gandHg¯H_{\bar {g}}coincide. But, in general, if we deal with bounded symbols, only the inequality‖Hg‖HS≤2‖Hg¯‖HS\|H_g\|_{HS}\leq 2\|H_{\bar {g}}\|_{HS}can be proved. The resul…

On compactness of the difference of composition operators

2004

Abstract Let φ and ψ be analytic self-maps of the unit disc, and denote by C φ and C ψ the induced composition operators. The compactness and weak compactness of the difference T = C φ − C ψ are studied on H p spaces of the unit disc and L p spaces of the unit circle. It is shown that the compactness of T on H p is independent of p ∈[1,∞). The compactness of T on L 1 and M (the space of complex measures) is characterized, and examples of φ and ψ are constructed such that T is compact on H 1 but non-compact on L 1 . Other given results deal with L ∞ , weakly compact counterparts of the previous results, and a conjecture of J.E. Shapiro.

A note on monolithic scattered compacta

2015

Abstract For a Banach space E, it is well-known that a necessary condition for E to have the controlled separable complementation property (CSCP, for short) is that the dual unit ball B E ⁎ be monolithic in the weak-star topology. We prove here that when X is a scattered first countable locally compact space, then monolithicity of X turns out to be sufficient for C 0 ( X ) to enjoy the CSCP.

Toward a quasi-Möbius characterization of invertible homogeneous metric spaces

2020

We study locally compact metric spaces that enjoy various forms of homogeneity with respect to Mobius self-homeomorphisms. We investigate connections between such homogeneity and the combination of isometric homogeneity with invertibility. In particular, we provide a new characterization of snowflakes of boundaries of rank-one symmetric spaces of non-compact type among locally compact and connected metric spaces. Furthermore, we investigate the metric implications of homogeneity with respect to uniformly strongly quasi-Mobius self-homeomorphisms, connecting such homogeneity with the combination of uniform bi-Lipschitz homogeneity and quasi-invertibility. In this context we characterize spac…

On $p$-Dunford integrable functions with values in Banach spaces

2018

[EN] Let (Omega, Sigma, mu) be a complete probability space, X a Banach space and 1 X. Special attention is paid to the compactness of the Dunford operator of f. We also study the p-Bochner integrability of the composition u o f: Omega->Y , where u is a p-summing operator from X to another Banach space Y . Finally, we also provide some tests of p-Dunford integrability by using w*-thick subsets of X¿.

Some remarks on nonsmooth critical point theory

2006

A general min-max principle established by Ghoussoub is extended to the case of functionals f which are the sum of a locally Lipschitz continuous term and of a convex, proper, lower semicontinuous function, when f satisfies a compactness condition weaker than the Palais-Smale one, i.e., the so-called Cerami condition. Moreover, an application to a class of elliptic variational-hemivariational inequalities in the resonant case is presented. © Springer Science+Business Media B.V. 2007.

Locally compact groups which are just not compact

2010

A Just-Non-Compact group, or briefly a JNC group, is a Hausdorff topological group which is not a compact group but all of whose proper Hausdorff quotients are compact groups. Intuitively, it is clear that these groups are rich in compact quotients. Locally compact JNC groups are largely described in the present paper.

WEAKLY COMPACT HOMOMORPHISMS BETWEEN SMALL ALGEBRAS OF ANALYTIC FUNCTIONS

2001

The weak compactness of the composition operator CΦ(f) = f ○ Φ acting on the uniform algebra of analytic uniformly continuous functions on the unit ball of a Banach space with the approximation property is characterized in terms of Φ. The relationship between weak compactness and compactness of these composition operators and general homomorphisms is also discussed.