This is an announcement for the paper "Metrical characterization
of super-reflexivity and linear type of Banach spaces" by Florent
Baudier.
Abstract: We prove that a Banach space X is not super-reflexive if
and only if the hyperbolic infinite tree embeds metrically into X.
We improve one implication of J.Bourgain's result who gave a metrical
characterization of super-reflexivity in Banach spaces in terms of
uniforms embeddings of the finite trees. A characterization of the
linear type for Banach spaces is given using the embedding of the
infinite tree equipped with a suitable metric.
Archive classification:
Mathematics Subject Classification: 46B20; 51F99
Remarks: to appear in Archiv der Mathematik
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Submitted from: florent.baudier(a)univ-fcomte.fr
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This is an announcement for the paper "Even infinite dimensional
real Banach spaces" by Valentin Ferenczi and Eloi Medina Galego.
Abstract: This article is a continuation of a paper of the first
author \cite{F} about complex structures on real Banach spaces. We
define a notion of even infinite dimensional real Banach space, and
prove that there exist even spaces, including HI or unconditional
examples from \cite{F} and $C(K)$ examples due to Plebanek \cite{P}.
We extend results of \cite{F} relating the set of complex structures
up to isomorphism on a real space to a group associated to inessential
operators on that space, and give characterizations of even spaces
in terms of this group. We also generalize results of \cite{F} about
totally incomparable complex structures to essentially incomparable
complex structures, while showing that the complex version of a
space defined by S. Argyros and A. Manoussakis \cite{AM} provide
examples of essentially incomparable complex structures which are
not totally incomparable.
Archive classification:
Mathematics Subject Classification: 46B03; 47A53.
Remarks: 22 pages
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85kb.
Submitted from: ferenczi(a)ccr.jussieu.fr
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This is an announcement for the paper "Examples and counterexamples
of type I isometric shifts" by Jesus Araujo.
Abstract: We provide examples of nonseparable spaces $X$ for which
$C(X)$ admits an isometric shift of type I, which solves in the
negative a problem proposed by Gutek {\em et al.} (J. Funct. Anal.
{\bf 101} (1991), 97-119). We also give two independent methods for
obtaining separable examples. The first one allows us in particular
to construct examples with infinitely many nonhomeomorphic components
in a subset of the Hilbert space $\ell^2$. The second one applies
for instance to sequences adjoined to any $n$-dimensional compact
manifold (for $n \ge 2$) or to the Sierpi\'nski curve. The combination
of both techniques lead to different examples involving a convergent
sequence adjoined to the Cantor set: one method for the case when
the sequence converges to a point in the Cantor set, and the other
one for the case when it converges outside.
Archive classification: Functional Analysis; General Topology
Mathematics Subject Classification: Primary 47B38; Secondary 46E15,
47B33, 47B37, 54D65, 54H20
Remarks: 41 pages. No figures. AMS-LaTeX
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Submitted from: araujoj(a)unican.es
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http://front.math.ucdavis.edu/math.FA/0703892
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http://arXiv.org/abs/math.FA/0703892
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This is an announcement for the paper "Intersection bodies and
generalized cosine transforms" by Boris Rubin.
Abstract: Intersection bodies represent a remarkable class of
geometric objects associated with sections of star bodies and
invoking Radon transforms, generalized cosine transforms, and the
relevant Fourier analysis. We review some known facts and give them
new proofs. The main focus is interrelation between generalized
cosine transforms of different kinds and their application to
investigation of certain family of intersection bodies, which we
call lambda-intersection bodies. The latter include k-intersection
bodies (in the sense of A. Koldobsky) and unit balls of finite-dimensional
subspaces of $L_p$-spaces. In particular, we show that restriction
of the spherical Radon transforms and the generalized cosine
transforms onto lower dimensional subspaces preserves their
integral-geometric structure. We apply this result to the study
of sections of lambda-intersection bodies. A number of new
characterizations of this class of bodies and examples are given.
Archive classification:
Mathematics Subject Classification: 44A12; 52A38
Remarks: 36 pages
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195kb.
Submitted from: borisr(a)math.lsu.edu
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