21,866 research outputs found
Calder\'on-Zygmund operators in the Bessel setting for all possible type indices
In this paper we adapt the technique developed in [17] to show that many
harmonic analysis operators in the Bessel setting, including maximal operators,
Littlewood-Paley-Stein type square functions, multipliers of Laplace or
Laplace-Stieltjes transform type and Riesz transforms are, or can be viewed as,
Calder\'on-Zygmund operators for all possible values of type parameter
in this context. This extends the results obtained recently in [7],
which are valid only for a restricted range of .Comment: 12 page
On fundamental harmonic analysis operators in certain Dunkl and Bessel settings
We consider several harmonic analysis operators in the multi-dimensional
context of the Dunkl Laplacian with the underlying group of reflections
isomorphic to (also negative values of the multiplicity
function are admitted). Our investigations include maximal operators,
-functions, Lusin area integrals, Riesz transforms and multipliers of
Laplace and Laplace-Stieltjes transform type. Using the general
Calder\'on-Zygmund theory we prove that these objects are bounded in weighted
spaces, , and from into weak .Comment: 26 pages. arXiv admin note: text overlap with arXiv:1011.3615 by
other author
Riesz-Jacobi transforms as principal value integrals
We establish an integral representation for the Riesz transforms naturally
associated with classical Jacobi expansions. We prove that the Riesz-Jacobi
transforms of odd orders express as principal value integrals against kernels
having non-integrable singularities on the diagonal. On the other hand, we show
that the Riesz-Jacobi transforms of even orders are not singular operators. In
fact they are given as usual integrals against integrable kernels plus or
minus, depending on the order, the identity operator. Our analysis indicates
that similar results, existing in the literature and corresponding to several
other settings related to classical discrete and continuous orthogonal
expansions, should be reinvestigated so as to be refined and in some cases also
corrected.Comment: 30 page
Intrinsic Parameters of GRB990123 from Its Prompt Optical Flash and Afterglow
We have constrained the intrinsic parameters, such as the magnetic energy
density fraction (), the electron energy density fraction
(), the initial Lorentz factor () and the Lorentz factor
of the reverse external shock (), of GRB990123, in terms of the
afterglow information (forward shock model) and the optical flash information
(reverse shock model). Our result shows: 1) the inferred values of
and are consistent with the suggestion that they may be universal
parameters, comparing to those inferred for GRB970508; 2) the reverse external
shock may have become relativistic before it passed through the ejecta shell.
Other instrinsic parameters of GRB990123, such as energy contained in the
forward shock and the ambient density are also determined and discussed
in this paper.Comment: 5 pages, MN LaTeX style, a few changes made according to referee's
suggestions, references up dated, MNRAS accepte
Theory of the Magnetic Moment in Iron Pnictides
We show that the combined effects of spin-orbit, monoclinic distortion, and
p-d hybridization in tetrahedrally coordinated Fe in LaOFeAs invalidates the
naive Hund's rule filling of the Fe d-levels. The two highest occupied levels
have one electron each but as a result of the p-d hybridization have very
different on-site repulsions. As a result, electrons in the upper level are
more itinerant while those in the lower level are more localized. It is the
xy-projection of the spin in the lower level that orders antiferromagnetically
as the z-components of the spins in the two levels is shown to be vanishingly
small in the ground state. The resulting magnetic moment is highly anisotropic
with an in-plane value of per Fe and a z-projection of
, both of which are in agreement with experiment. As a consequence,
we arrive the minimal model that describes the electronic properties of
LaOFeAs.Comment: Published Versio
Piezas toroides de arcilla en yacimientos ibéricos
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