37,717 research outputs found
Maximal function and Multiplier Theorem for Weighted Space on the Unit Sphere
For a family of weight functions invariant under a finite reflection group,
the boundedness of a maximal function on the unit sphere is established and
used to prove a multiplier theorem for the orthogonal expansions with respect
to the weight function on the unit sphere. Similar results are also established
for the weighted space on the unit ball and on the standard simplex.Comment: 24 pages, to appear in J. Funct. Analysi
Thermal and Non-thermal radiation from pulsars: hints of physics
Thermal and non-thermal radiation from pulsars carries significant
information from surface and would have profound implications on the state of
dense matter in compact stars. For the non-thermal radio emission, subpulse
drifting phenomena suggest the existence of Ruderman-Sutherland-like
gap-sparking and strong binding of particles on pulsar polar caps. While
conventional neutron star models can hardly provide such a high binding energy,
the strong self-bound surface of quark-cluster stars can naturally solve this
problem. As for the thermal one, the featureless X-ray spectra of pulsars may
indicate a bare surface without atmosphere, and the ultrarelativistic fireball
of gamma-ray bursts and supernovae would also require strong self-bound
surfaces. Recent achievements in measuring pulsar mass and mass-radius relation
further indicate a stiff equation of state and a self-bound surface. Therefore,
we conjecture that matters inside pulsar-like compact stars could be in a
quark-cluster phase. The surface of quark-cluster stars is chromatically
confined and could initially be bare. Such a surface can not only explain above
features, but may also promote a successful core-collapse supernova, and the
hydro-cyclotron oscillation of the electron sea above the surface could be
responsible for those absorption features detected in the X-ray spectrum.Comment: 4 pages, contribution to the ERPM conferences, Zielona Gora, April
201
Polynomial Approximation in Sobolev Spaces on the Unit Sphere and the Unit Ball
This work is a continuation of the recent study by the authors on
approximation theory over the sphere and the ball. The main results define new
Sobolev spaces on these domains and study polynomial approximations for
functions in these spaces, including simultaneous approximation by polynomials
and relation between best approximation to a function and to its derivatives.Comment: 16 page
Moduli of Smoothness and Approximation on the Unit Sphere and the Unit Ball
A new modulus of smoothness based on the Euler angles is introduced on the
unit sphere and is shown to satisfy all the usual characteristic properties of
moduli of smoothness, including direct and inverse theorem for the best
approximation by polynomials and its equivalence to a -functional, defined
via partial derivatives in Euler angles. The set of results on the moduli on
the sphere serves as a basis for defining new moduli of smoothness and their
corresponding -functionals on the unit ball, which are used to characterize
the best approximation by polynomials on the ball.Comment: 63 pages, to appear in Advances in Mat
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