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2006, Glasgow Mathematical Journal
In this paper we present some results about wV (weak property V of Pełczyński) or property wV * (weak property V * of Pełczyński) in Banach spaces. We show that E has property wV if for any reflexive subspace F of E * , ⊥ F has property wV. It is shown that G has property wV if under some condition K w * (E * , F *) contains the dual of G. Moreover, it is proved that E * contains a copy of c 0 if and only if E contains a copy of 1 where E has property wV *. Finally, the identity between L(C(, E), F) and WP(C(, E), F) is investigated.
Studia Mathematica, 2010
In this paper we show several characterizations of weakly compact sets in Banach spaces: Given a bounded closed convex set C of a Banach space X, the following statements are equivalent: i) C is weakly compact; ii) C can be affinely uniformly embedded into a reflexive Banach space; iii) there exists an equivalent norm of X such that it admits the w2R-property on C; iv) there is a continuous and w * -lower semi-continuous (l.s.c.) semi-norm p on the dual X * with p ≥ sup C such that p 2 is everywhere Fréchet differentiable in X * ; and as a consequence, the space X is a weakly compactly generated (WCG) space if and only if there exists a continuous and w * -l.s.c. Fréchet smooth (not necessarily equivalent) norm on X * .
1974
An operator T: X-*y iX 9 y are Banach spaces) is unconditionally converging (uc) if it maps weakly unconditionally converging series into unconditionally converging series. It is known that T' (the dual of T ) is a uc operator if and only if T is i-f-cosingular. The X^ -cosingular' operator is classified and then used to characterize Banach spaces with property V (studied by Pelczynski).
Proceedings of the Royal Society of Edinburgh: Section A Mathematics, 2010
The strong* topology s * (X) of a Banach space X is defined as the locally convex topology generated by the seminorms x → Sx for bounded linear maps S from X into Hilbert spaces. The w-right topology for X, ρ(X), is a stronger locally convex topology, which may be analogously characterised by taking reflexive Banach spaces in place of Hilbert spaces. For any Banach space Y , a linear map T : X → Y is known to be weakly compact precisely when T is continuous from the w-right topology to the norm topology of Y . The main results deal with conditions for, and consequences of, the coincidence of these two topologies on norm bounded sets. A large class of Banach spaces, including all C * -algebras, and more generally, all JB * -triples, exhibit this behaviour.
2003
The Banach space $E$ has the weakly compact approximation property (W.A.P. for short) if there is a constant $C < \infty$ so that for any weakly compact set $D \subset E$ and $\epsilon > 0$ there is a weakly compact operator $V: E \to E$ satisfying $\sup_{x\in D} || x - Vx || < \epsilon$ and $|| V|| \leq C$. We give several examples of Banach spaces both with and without this approximation property. Our main results demonstrate that the James-type spaces from a general class of quasi-reflexive spaces (which contains the classical James' space $J$) have the W.A.P, but that James' tree space $JT$ fails to have the W.A.P. It is also shown that the dual $J^*$ has the W.A.P. It follows that the Banach algebras $W(J)$ and $W(J^*)$, consisting of the weakly compact operators, have bounded left approximate identities. Among the other results we obtain a concrete Banach space $Y$ so that $Y$ fails to have the W.A.P., but $Y$ has this approximation property without the uniform bound $C$.
Indagationes Mathematicae (Proceedings), 1973
arXiv: General Topology, 2015
Being motivated by the famous Kaplansky theorem we study var- ious sequential properties of a Banach space E and its closed unit ball B, both endowed with the weak topology of E. We show that B has the Pytkeev property if and only if E in the norm topology contains no isomorphic copy of l1, while E has the Pytkeev property if and only if it is finite-dimensional. We extend Schluchtermann and Wheeler's result from (27) by showing that B is a (separable) metrizable space if and only if it has countable cs � -character and is a k-space. As a corollary we obtain that B is Polish if and only if it has countable cs � -character and is y Cech-complete, that supplements a result of Edgar and Wheeler (8).
Nonlinear Analysis: Theory, Methods & Applications, 2012
We study the stability properties of the class of weak*-extensible spaces introduced by Wang, Zhao, and Qiang showing, among other things, that weak*-extensibility is equivalent to having a weak*-sequentially continuous dual ball (in short, w*SC) for duals of separable spaces or twisted sums of w*SC spaces. This shows that weak*-extensibility is not a 3-space property, solving a question posed by Wang, Zhao, and Qiang. We also introduce a restricted form of weak*-extensibility, called separable weak*-extensibility, and show that separably weak*-extensible Banach spaces have the Gelfand-Phillips property, although they are not necessarily w*SC spaces.
Archiv der Mathematik, 1990
2021
Any Lipschitz map f : M → N between two pointed metric spaces may be extended in a unique way to a bounded linear operator f : ℱ(M) →ℱ(N) between their corresponding Lipschitz-free spaces. In this paper, we give a necessary and sufficient condition for f to be compact in terms of metric conditions on f. This extends a result by A. Jiménez-Vargas and M. Villegas-Vallecillos in the case of non-separable and unbounded metric spaces. After studying the behavior of weakly convergent sequences made of finitely supported elements in Lipschitz-free spaces, we also deduce that f is compact if and only if it is weakly compact.
Glasgow Mathematical Journal, 2011
In this paper we study non-complemented spaces of operators and the embeddability of ℓ∞ in the spaces of operators L(X, Y), K(X, Y) and Kw*(X*, Y). Results of Bator and Lewis [2, 3] (Bull. Pol. Acad. Sci. Math.50(4) (2002), 413–416; Bull. Pol. Acad. Sci. Math.549(1) (2006), 63–73), Emmanuele [8–10] (J. Funct. Anal.99 (1991), 125–130; Math. Proc. Camb. Phil. Soc.111 (1992), 331–335; Atti. Sem. Mat. Fis. Univ. Modena42(1) (1994), 123–133), Feder [11] (Canad. Math. Bull.25 (1982), 78–81) and Kalton [16] (Math. Ann.208 (1974), 267–278), are generalised. A vector measure result is used to study the complementation of the spaces W(X, Y) and K(X, Y) in the space L(X, Y), as well as the complementation of K(X, Y) in W(X, Y). A fundamental result of Drewnowski [7] (Math. Proc. Camb. Phil. Soc. 108 (1990), 523–526) is used to establish a result for operator-valued measures, from which we obtain as corollaries the Vitali–Hahn–Saks–Nikodym theorem, the Nikodym Boundedness theorem and a Banach s...
arXiv (Cornell University), 1991
A Banach space E is said to have Property (w) if every (bounded linear) operator from E into E ′ is weakly compact. We give some interesting examples of James type Banach spaces with Property (w). We also consider the passing of Property (w) from E to C(K, E).
2007
In this note we revise and survey some recent results established in (8). We shall show that for each Banach space X, there exists a locally convex topology for X, termed the "Right Topology", such that a linear map T, from X into a Banach space Y, is weakly compact, precisely when T is a continuous map from X, equipped with the "Right" topology, into Y equipped with the norm topology. We provide here a new and shorter proof of this result. We shall also survey the results concerning sequentially Right-to-norm continuous operators.
arXiv: Optimization and Control, 2016
We provide sufficient conditions for a Banach space Y to be weakly sequentially complete. These conditions are expressed in terms of the existence of directional derivatives for cone convex mappings with values in Y .
Mathematische Annalen, 2004
Suppose ∞ → X. We construct examples of bounded sets M ⊂ X, such that M w * ⊂ X + 1 2 B X * , but coM w * ⊂ X + αB X * * for any α < 1. These examples show that the previous results of the authors on quantitative versions of Krein's theorem are optimal.
Matematicki Vesnik, 2012
In this note we show that weakly compact operators from a Banach space X into a complete (LB)-space E need not factorize through a reflexive Banach space. If E is a Fréchet space, then weakly compact operators from a Banach space X into E factorize through a reflexive Banach space. The factorization of operators from a Fréchet or a complete (LB)-space into a Banach space mapping bounded sets into relatively weakly compact sets is also investigated.
arXiv (Cornell University), 2020
Based on the concept of unbounded absolutely weakly convergence, we give new characterizations of L-weakly compact sets. As applications, we find some properties of order weakly compact operators. Also, a new characterizations of order continuous Banach lattices are obtained.
Positivity
Based on the concept of unbounded absolutely weakly convergence, we give new characterizations of L-weakly compact sets. As applications, we find some properties of order weakly compact operators. Also, a new characterizations of order continuous Banach lattices are obtained.
Bulletin of the Australian Mathematical Society, 1989
Let X be a completely regular space. We denote by Cb(X) the Banach space of all real-valued bounded continuous functions on X endowed with the supremum-norm.In this paper we prove some characterisations of weakly compact operators defined from Cb(X) into a Banach space E which are continuous with respect to fit, βt, βr and βσ introduced by Sentilles.We also prove that (Cb,(X), βi), i = t, τσ , has the Dunford-Pettis property.
Integral Equations and Operator Theory, 1999
We prove that a weakly compact operator from H ~ or any of its even duals into an arbitrary Banach space is uniformly convexifying. By using this, we establish three dicothomies: (i) every operator defined on H ~ or any of its even duals either fixes a copy of g~ or factors through a Banach space having the Banach-Saks property; (2) every quotient of H cc or any of its even duals either contains a copy of s or is super-reflexive; (3) eve N subspace of LI/H~ or any of its even duals either contains a complemented copy of ~i or is super-reflexive.
Israel Journal of Mathematics, 1977
THEOREM 1. Let X be a Banach space. (a) If X* has a closed subspace in which no normalized sequence converges weak* to zero, then I, is isomorphic to a subspace of X. (b) If X* contains a bounded sequence which has no weak* convergent subsequence, then X contains a separable subspace whose dual is not separable.
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