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1
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Dieudonné operators on the space of Bochner integrable functions

100%
Nowak M.
Banach Center Publications
|
2011
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tom 92
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nr 1
279-282
EN
A bounded linear operator between Banach spaces is called a Dieudonné operator ( = weakly completely continuous operator) if it maps weakly Cauchy sequences to weakly convergent sequences. Let (Ω,Σ,μ) be a finite measure space, and let X and Y be Banach spaces. We study Dieudonné operators T: L¹(X) → Y. Let $i_{∞}: L^{∞}(X) → L¹(X)$ stand for the canonical injection. We show that if X is almost reflexive and T: L¹(X) → Y is a Dieudonné operator, then $T∘i_{∞}: L^{∞}(X) → Y$ is a weakly compact operator. Moreover, we obtain that if T: L¹(X) → Y is a bounded linear operator and $T∘i_{∞}: L^{∞}(X) → Y$ is weakly compact, then T is a Dieudonné operator.
2
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A Riesz representation theory for completely regular Hausdorff spaces and its applications

100%
Nowak M.
Open Mathematics
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2016
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tom 14
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nr 1
474-496
EN
Let X be a completely regular Hausdorff space, E and F be Banach spaces. Let Cb(X, E) be the space of all E-valued bounded, continuous functions on X, equipped with the strict topology β. We develop the Riemman-Stieltjes-type Integral representation theory of (β, || · ||F) -continuous operators T : Cb(X, E) → F with respect to the representing Borel operator measures. For X being a k-space, we characterize strongly bounded (β, || · ||F)-continuous operators T : Cb(X, E) → F. As an application, we study (β, || · ||F)-continuous weakly compact and unconditionally converging operators T : Cb(X, E) → F. In particular, we establish the relationship between these operators and the corresponding Borel operator measures given by the Riesz representation theorem. We obtain that if X is a k-spaceand E is reflexive, then (Cb(X, E), β) has the V property of Pełczynski.
3
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Bochner representable operators on Köthe-Bochner spaces

100%
Nowak M.
Commentationes Mathematicae
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2008
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tom 48
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nr 2
EN
Let \(E\) be a Banach function space and \(X\) be a real Banach space. We study Bochner representable operators from a Köthe-Bochner space \(E(X)\) to a Banach space \(Y\). We consider the problem of compactness and weak compactness of Bochner representable operators from \(E(X)\) (provided with the natural mixed topology) to \(Y\).
4
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Topological properties of some spaces of continuous operators

100%
Nowak M.
Discussiones Mathematicae, Differential Inclusions, Control and Optimization
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2016
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tom 36
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nr 1
79-86
EN
Let X be a completely regular Hausdorff space, E and F be Banach spaces. Let $C_b(X,E)$ be the space of all E-valued bounded continuous functions on X, equipped with the strict topology β. We study topological properties of the space $L_{β}(C_{b}(X,E),F)$ of all $(β,||·||_{F})$-continuous linear operators from $C_{b}(X,E)$ to F, equipped with the topology $τ_{s}$ of simple convergence. If X is a locally compact paracompact space (resp. a P-space), we characterize $τ_{s}$-compact subsets of $L_{β}(C_{b}(X,E),F)$ in terms of properties of the corresponding sets of the representing operator-valued Borel measures. It is shown that the space $(L_{β}(C_{b}(X,E),F),τ_{s})$ is sequentially complete if X is a locally compact paracompact space.
5
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Dunford-Pettis operators on the space of Bochner integrable functions

100%
Nowak M.
Banach Center Publications
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2011
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tom 95
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nr 1
353-358
EN
Let (Ω,Σ,μ) be a finite measure space and let X be a real Banach space. Let $L^Φ(X)$ be the Orlicz-Bochner space defined by a Young function Φ. We study the relationships between Dunford-Pettis operators T from L¹(X) to a Banach space Y and the compactness properties of the operators T restricted to $L^Φ(X)$. In particular, it is shown that if X is a reflexive Banach space, then a bounded linear operator T:L¹(X) → Y is Dunford-Pettis if and only if T restricted to $L^∞(X)$ is $(τ(L^∞(X),L¹(X*)),||·||_Y)$-compact.
6
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Order-bounded operators from vector-valued function spaces to Banach spaces

100%
Nowak M.
Banach Center Publications
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2005
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tom 68
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nr 1
109-114
EN
Let E be an ideal of L⁰ over a σ-finite measure space (Ω,Σ,μ). For a real Banach space $(X,||·||_X)$ let E(X) be a subspace of the space L⁰(X) of μ-equivalence classes of strongly Σ-measurable functions f: Ω → X and consisting of all those f ∈ L⁰(X) for which the scalar function $||f(·)||_X$ belongs to E. Let E(X)˜ stand for the order dual of E(X). For u ∈ E⁺ let $D_u ( = {f ∈ E(X): ||f(·)||_X ≤ u})$ stand for the order interval in E(X). For a real Banach space $(Y,||·||_Y)$ a linear operator T: E(X) → Y is said to be order-bounded whenever for each u ∈ E⁺ the set $T(D_u)$ is norm-bounded in Y. In this paper we examine order-bounded operators T: E(X) → Y. We show that T is order-bounded iff T is $(τ(E(X),E(X)˜),||·||_Y)$-continuous. We obtain that every weak Dunford-Pettis operator T: E(X) → Y is order-bounded. In particular, we obtain that if a Banach space Y has the Dunford-Pettis property, then T is order-bounded iff it is a weak Dunford-Pettis operator.
7

Topological properties of the complex vector lattice of bounded finitely additive mesures

100%
Nowak M.
Commentationes Mathematicae
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2013
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tom 53
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nr 2
EN
Let \(\Sigma\) be a \(\sigma\)-algebra of subsets of a non-empty set \(\Omega\). Let \(ba(\Sigma)\) be the complex vector lattice of bounded finitely additive measures \(\mu:\Sigma\rightarrow\mathbb{C}\). We study locally solid topologies on \(ba(\Sigma)\). We develop the duality theory of \(ba(\Sigma)\), provided with locally convex-solid topologies.
8
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Linear operators on non-locally convex Orlicz spaces

64%
Nowak M., Oelke A.
Banach Center Publications
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2008
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tom 79
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nr 1
157-165
EN
We study linear operators from a non-locally convex Orlicz space $L^Φ$ to a Banach space $(X,||·||_X)$. Recall that a linear operator $T:L^Φ → X$ is said to be σ-smooth whenever $uₙ\longrightarrow\limits^{(o)} 0$ in $L^Φ$ implies $||T(uₙ)||_X → 0$. It is shown that every σ-smooth operator $T:L^Φ → X$ factors through the inclusion map $j:L^Φ → L^{Φ̅}$, where Φ̅ denotes the convex minorant of Φ. We obtain the Bochner integral representation of σ-smooth operators $T:L^Φ → X$. This extends some earlier results of J. J. Uhl concerning the Bochner integral representation of linear operators defined on a locally convex Orlicz space.
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