2,616 research outputs found
Gravitational Lensing Bound On The Average Redshift Of Gamma Ray Bursts In Models With Evolving Lenses
Identification of gravitationally lensed Gamma Ray Bursts (GRBs) in the BATSE
4B catalog can be used to constrain the average redshift of the GRBs.
In this paper we investigate the effect of evolving lenses on the of
GRBs in different cosmological models of universe. The cosmological parameters
$\Omega$ and $\Lambda$ have an effect on the of GRBs. The other factor
which can change the of GRBs is higher in evolving model of galaxies as compared to
non-evolving models of galaxies.Comment: 23 pages,one plain LaTeX file with three postscript figures This is
modified version with recent BATSE efficiency parameter and with the latest F
paramete
Magnetic domain walls in constrained geometries
Magnetic domain walls have been studied in micrometer-sized Fe20Ni80 elements
containing geometrical constrictions by spin-polarized scanning electron
microscopy and numerical simulations. By controlling the constriction
dimensions, the wall width can be tailored and the wall type modified. In
particular, the width of a 180 degree Neel wall can be strongly reduced or
increased by the constriction geometry compared with the wall in unconstrained
systems.Comment: 4 pages, 6 figure
Strongly Secure and Efficient Data Shuffle On Hardware Enclaves
Mitigating memory-access attacks on the Intel SGX architecture is an
important and open research problem. A natural notion of the mitigation is
cache-miss obliviousness which requires the cache-misses emitted during an
enclave execution are oblivious to sensitive data. This work realizes the
cache-miss obliviousness for the computation of data shuffling. The proposed
approach is to software-engineer the oblivious algorithm of Melbourne shuffle
on the Intel SGX/TSX architecture, where the Transaction Synchronization
eXtension (TSX) is (ab)used to detect the occurrence of cache misses. In the
system building, we propose software techniques to prefetch memory data prior
to the TSX transaction to defend the physical bus-tapping attacks. Our
evaluation based on real implementation shows that our system achieves superior
performance and lower transaction abort rate than the related work in the
existing literature.Comment: Systex'1
Towards an improved understanding of eta --> gamma^* gamma^*
We argue that high-quality data on the reaction
will allow one to determine the double off-shell form factor in a model-independent way with controlled accuracy. This is
an important step towards a reliable evaluation of the hadronic light-by-light
scattering contribution to the anomalous magnetic moment of the muon. When
analyzing the existing data for in the range of
total energies , we demonstrate that the
double off-shell form factor is
consistent with the commonly employed factorization ansatz at least for
, if the effect of the meson is taken into account.
However, better data are needed to draw firm conclusions.Comment: 7 pages, 3 figure
Consequences of gravitational radiation recoil
Coalescing binary black holes experience an impulsive kick due to anisotropic
emission of gravitational waves. We discuss the dynamical consequences of the
recoil accompanying massive black hole mergers. Recoil velocities are
sufficient to eject most coalescing black holes from dwarf galaxies and
globular clusters, which may explain the apparent absence of massive black
holes in these systems. Ejection from giant elliptical galaxies would be rare,
but coalescing black holes are displaced from the center and fall back on a
time scale of order the half-mass crossing time. Displacement of the black
holes transfers energy to the stars in the nucleus and can convert a steep
density cusp into a core. Radiation recoil calls into question models that grow
supermassive black holes from hierarchical mergers of stellar-mass precursors.Comment: 5 pages, 4 figures, emulateapj style; minor changes made; accepted to
ApJ Letter
Phylogeny, character evolution, and biogeography of the gondwanic moss family Hypopterygiaceae (Bryophyta)
Phylogenetic relationships among the seven genera of the Hypopterygiaceae,
represented by 14 of the 21 species recognized in the family, were reconstructed based
on variation in nucleotide sequences of six nuclear, mitochondrial, and plastid loci
Regge Calculus in Teleparallel Gravity
In the context of the teleparallel equivalent of general relativity, the
Weitzenbock manifold is considered as the limit of a suitable sequence of
discrete lattices composed of an increasing number of smaller an smaller
simplices, where the interior of each simplex (Delaunay lattice) is assumed to
be flat. The link lengths between any pair of vertices serve as independent
variables, so that torsion turns out to be localized in the two dimensional
hypersurfaces (dislocation triangle, or hinge) of the lattice. Assuming that a
vector undergoes a dislocation in relation to its initial position as it is
parallel transported along the perimeter of the dual lattice (Voronoi polygon),
we obtain the discrete analogue of the teleparallel action, as well as the
corresponding simplicial vacuum field equations.Comment: Latex, 10 pages, 2 eps figures, to appear in Class. Quant. Gra
Gauge theory of disclinations on fluctuating elastic surfaces
A variant of a gauge theory is formulated to describe disclinations on
Riemannian surfaces that may change both the Gaussian (intrinsic) and mean
(extrinsic) curvatures, which implies that both internal strains and a location
of the surface in R^3 may vary. Besides, originally distributed disclinations
are taken into account. For the flat surface, an extended variant of the
Edelen-Kadic gauge theory is obtained. Within the linear scheme our model
recovers the von Karman equations for membranes, with a disclination-induced
source being generated by gauge fields. For a single disclination on an
arbitrary elastic surface a covariant generalization of the von Karman
equations is derived.Comment: 13 page
How black holes get their kicks: Gravitational radiation recoil revisited
Gravitational waves from the coalescence of binary black holes carry away
linear momentum, causing center of mass recoil. This "radiation rocket" effect
has important implications for systems with escape speeds of order the recoil
velocity. We revisit this problem using black hole perturbation theory,
treating the binary as a test mass spiraling into a spinning hole. For extreme
mass ratios (q = m1/m2 << 1) we compute the recoil for the slow inspiral epoch
of binary coalescence very accurately; these results can be extrapolated to q ~
0.4 with modest accuracy. Although the recoil from the final plunge contributes
significantly to the final recoil, we are only able to make crude estimates of
its magnitude. We find that the recoil can easily reach ~ 100-200 km/s, but
most likely does not exceed ~ 500 km/s. Though much lower than previous
estimates, this recoil is large enough to have important astrophysical
consequences. These include the ejection of black holes from globular clusters,
dwarf galaxies, and high-redshift dark matter halos.Comment: 4 pages, 2 figures, emulateapj style; minor changes made; accepted to
ApJ Letter
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