202,619 research outputs found
A New Lower Bound for the Distinct Distance Constant
The reciprocal sum of Zhang sequence is not equal to the Distinct Distance
Constant. This note introduces a -sequence with larger reciprocal sum, and
provides a more precise estimation of the reciprocal sums of Mian-Chowla
sequence and Zhang sequence.Comment: 4 pages, 3 ancillary table
Eigenvalue estimates for the Dirac-Schr\"odinger operators
We give new estimates for the eigenvalues of the hypersurface Dirac operator
in terms of the intrinsic energy-momentum tensor, the mean curvature and the
scalar curvature. We also discuss their limiting cases as well as the limiting
cases of the estimates obtained by X. Zhang and O. Hijazi in [13] and [10]. We
compare these limiting cases with those corresponding to the Friedrich and
Hijazi inequalities. We conclude by comparing these results to intrinsic
estimates for the Dirac-Schr\"odinger operator D_f = D - f/2.Comment: 22 pages, LaTeX, to appear in Journal of Geometry and Physic
New Models for X-Ray Synchrotron Radiation from the Remnant of Supernova 1006 AD
Galactic cosmic rays up to energies of around 10^15 eV are assumed to
originate in supernova remnants (SNRs). The shock wave of a young SNR like SN
1006 AD can accelerate electrons to energies greater than 1 TeV, where they can
produce synchrotron radiation in the X-ray band. A new model (SRESC) designed
to model synchrotron X-rays from Type Ia supernovae can constrain values for
the magnetic-field strength and electron scattering properties, with
implications for the acceleration of the unseen ions which dominate the
cosmic-ray energetics. New observations by ASCA, ROSAT, and RXTE have provided
enormously improved data, which now extend to higher X-ray energies. These data
allow much firmer constraints. We will describe model fits to these new data on
SN 1006 AD, emphasizing the physical constraints that can be placed on SNRs and
on the cosmic-ray acceleration process.Comment: 10 pages, 2 figures. to appear in "Cosmic Explosions", proceeding of
the 10th Annual October Astrophysics Conference (ed. S.S. Holt and W. W.
Zhang) LaTex aipproc.st
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