3,311 research outputs found
UMD-valued square functions associated with Bessel operators in Hardy and BMO spaces
We consider Banach valued Hardy and BMO spaces in the Bessel setting. Square
functions associated with Poisson semigroups for Bessel operators are defined
by using fractional derivatives. If B is a UMD Banach space we obtain for
B-valued Hardy and BMO spaces equivalent norms involving -radonifying
operators and square functions. We also establish characterizations of UMD
Banach spaces by using Hardy and BMO-boundedness properties of g-functions
associated to Bessel-Poisson semigroup
Area Littlewood-Paley functions associated with Hermite and Laguerre operators
In this paper we study Lp-boundedness properties for area Littlewood-Paley
functions associated with heat semigroups for Hermite and Laguerre operator
Connection between type B (or C) and F factorizations and construction of algebras
In a recent paper (Del Sol Mesa A and Quesne C 2000 J. Phys. A: Math. Gen. 33
4059), we started a systematic study of the connections among different
factorization types, suggested by Infeld and Hull, and of their consequences
for the construction of algebras. We devised a general procedure for
constructing satellite algebras for all the Hamiltonians admitting a type E
factorization by using the relationship between type A and E factorizations.
Here we complete our analysis by showing that for Hamiltonians admitting a type
F factorization, a similar method, starting from either type B or type C ones,
leads to other types of algebras. We therefore conclude that the existence of
satellite algebras is a characteristic property of type E factorizable
Hamiltonians. Our results are illustrated with the detailed discussion of the
Coulomb problem.Comment: minor changes, 1 additional reference, final form to be published in
JP
UMD Banach spaces and square functions associated with heat semigroups for Schr\"odinger and Laguerre operators
In this paper we define square functions (also called Littlewood-Paley-Stein
functions) associated with heat semigroups for Schr\"odinger and Laguerre
operators acting on functions which take values in UMD Banach spaces. We extend
classical (scalar) L^p-boundedness properties for the square functions to our
Banach valued setting by using \gamma-radonifying operators. We also prove that
these L^p-boundedness properties of the square functions actually characterize
the Banach spaces having the UMD property
Polarization Properties of Extragalactic Radio Sources and Their Contribution to Microwave Polarization Fluctuations
We investigate the statistical properties of the polarized emission of
extragalactic radio sources and estimate their contribution to the power
spectrum of polarization fluctuations in the microwave region. The basic
ingredients of our analysis are the NVSS polarization data, the multifrequency
study of polarization properties of the B3-VLA sample (Mack et al. 2002) which
has allowed us to quantify Faraday depolarization effects, and the 15 GHz
survey by Taylor et al. (2001), which has provided strong constraints on the
high-frequency spectral indices of sources. The polarization degree of both
steep- and flat-spectrum at 1.4 GHz is found to be anti-correlated with the
flux density. The median polarization degree at 1.4 GHz of both steep- and
flat-spectrum sources brighter than mJy is . The data by Mack et al. (2002) indicate a substantial mean Faraday
depolarization at 1.4 GHz for steep spectrum sources, while the depolarization
is undetermined for most flat/inverted-spectrum sources. Exploiting this
complex of information we have estimated the power spectrum of polarization
fluctuations due to extragalactic radio sources at microwave frequencies. We
confirm that extragalactic sources are expected to be the main contaminant of
Cosmic Microwave Background (CMB) polarization maps on small angular scales. At
frequencies GHz the amplitude of their power spectrum is expected to be
comparable to that of the -mode of the CMB. At higher frequencies, however,
the CMB dominates.Comment: 10 pages, A&A in pres
-boundedness properties for the maximal operators for semigroups associated with Bessel and Laguerre operators
In this paper we prove that the generalized (in the sense of Caffarelli and
Calder\'on) maximal operators associated with heat semigroups for Bessel and
Laguerre operators are weak type
(1,1). Our results include other known ones and our proofs are simpler than
the ones for the known special cases.Comment: 8 page
Andropigios de los Ortópteros de Navarra (Orthoptera).
Se presenta la descripción de los andropigios de las 64 especies de Ortópteros -sensu strictus- de Navarra, en 32 Láminas con 297 figuras
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