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Sequential closures of σ -subalgebras for a vector measure

Werner J. Ricker — 1996

Commentationes Mathematicae Universitatis Carolinae

Let X be a locally convex space, m : Σ X be a vector measure defined on a σ -algebra Σ , and L 1 ( m ) be the associated (locally convex) space of m -integrable functions. Let Σ ( m ) denote { χ E ; E Σ } , equipped with the relative topology from L 1 ( m ) . For a subalgebra 𝒜 Σ , let 𝒜 σ denote the generated σ -algebra and 𝒜 ¯ s denote the closure of χ ( 𝒜 ) = { χ E ; E 𝒜 } in L 1 ( m ) . Sets of the form 𝒜 ¯ s arise in criteria determining separability of L 1 ( m ) ; see [6]. We consider some natural questions concerning 𝒜 ¯ s and, in particular, its relation to χ ( 𝒜 σ ) . It is shown that 𝒜 ¯ s Σ ( m ) and moreover,...

Optimal domains for the kernel operator associated with Sobolev's inequality

Guillermo P. CurberaWerner J. Ricker — 2003

Studia Mathematica

Refinements of the classical Sobolev inequality lead to optimal domain problems in a natural way. This is made precise in recent work of Edmunds, Kerman and Pick; the fundamental technique is to prove that the (generalized) Sobolev inequality is equivalent to the boundedness of an associated kernel operator on [0,1]. We make a detailed study of both the optimal domain, providing various characterizations of it, and of properties of the kernel operator when it is extended to act in its optimal domain....

Criteria for weak compactness of vector-valued integration maps

Susumu OkadaWerner J. Ricker — 1994

Commentationes Mathematicae Universitatis Carolinae

Criteria are given for determining the weak compactness, or otherwise, of the integration map associated with a vector measure. For instance, the space of integrable functions of a weakly compact integration map is necessarily normable for the mean convergence topology. Results are presented which relate weak compactness of the integration map with the property of being a bicontinuous isomorphism onto its range. Finally, a detailed description is given of the compactness properties for the integration...

Operator ideal properties of vector measures with finite variation

Susumu OkadaWerner J. RickerLuis Rodríguez-Piazza — 2011

Studia Mathematica

Given a vector measure m with values in a Banach space X, a desirable property (when available) of the associated Banach function space L¹(m) of all m-integrable functions is that L¹(m) = L¹(|m|), where |m| is the [0,∞]-valued variation measure of m. Closely connected to m is its X-valued integration map Iₘ: f ↦ ∫f dm for f ∈ L¹(m). Many traditional operators from analysis arise as integration maps in this way. A detailed study is made of the connection between the property L¹(m) = L¹(|m|) and the...

Characterizing Fréchet-Schwartz spaces via power bounded operators

Angela A. AlbaneseJosé BonetWerner J. Ricker — 2014

Studia Mathematica

We characterize Köthe echelon spaces (and, more generally, those Fréchet spaces with an unconditional basis) which are Schwartz, in terms of the convergence of the Cesàro means of power bounded operators defined on them. This complements similar known characterizations of reflexive and of Fréchet-Montel spaces with a basis. Every strongly convergent sequence of continuous linear operators on a Fréchet-Schwartz space does so in a special way. We single out this type of "rapid convergence" for a sequence...

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