15,887 research outputs found
Crystallography on Curved Surfaces
We study static and dynamical properties that distinguish two dimensional
crystals constrained to lie on a curved substrate from their flat space
counterparts. A generic mechanism of dislocation unbinding in the presence of
varying Gaussian curvature is presented in the context of a model surface
amenable to full analytical treatment. We find that glide diffusion of isolated
dislocations is suppressed by a binding potential of purely geometrical origin.
Finally, the energetics and biased diffusion dynamics of point defects such as
vacancies and interstitials is explained in terms of their geometric potential.Comment: 12 Pages, 8 Figure
Axial-vector currents and tau mesonic decays
A general expression of the axial-vector current is presented, in which both
the effects of the chiral symmetry breaking and the spontaneous chiral symmetry
breaking are included. A new resonance formula of the axial-vector meson is
derived and in the limit of this formula doesn't go back
to the ``chiral limit``. The studies show that the dominance of the
axial-vector meson is associated with the satisfaction of PCAC. The dominance
of pion exchange is companied by the strong anomaly of PCAC.Comment: 8 pages, talk presented at the Fourth International Workshop on tau
Lepton Physivs, Este Park, Colorado, Sept. 15-19, 199
Study of CP violation in D->VV decay at BESIII
In this paper, we intend to study the problem of CP violation in meson by
decay mode in which the T violating triple-product correlation is
examined. That would undoubtedly be another excellent probe of New Physics
beyond Standard Model. For the neutral , we focus on direct CP violation
without considering oscillation. Experimentally, by a full
angular analysis one may obtain such CP violating signals, and particularly it
is worth mentioning that the upcoming large data samples at BES-III in
Beijing will provide a great opportunity to perform it.Comment: 5 pages, 2 tables and 1 figure, version to appear in Phys. Lett.
Linking motion-induced blindness to perceptual filling-in
AbstractâMotion-induced blindnessâ and âperceptual filing-inâ are two phenomena in which perceptually salient stimuli repeatedly disappear and reappear after prolonged viewing. Despite the many similarities between MIB and PFI, two differences suggest that they could be unrelated phenomena: (1) An area surrounded by background stimuli can be perceived to disappear completely in PFI but not in MIB and (2) high contrast stimuli are perceived to disappear less easily in PFI but, remarkably enough, more easily in MIB. In this article we show that the apparent differences between MIB and PFI disappear when eccentricity, contrast, and perceptual grouping are taken into account and that both are most likely caused by the same underlying mechanism
On Maximum-Likelihood Decoding of Time-Varying Trellis Codes
Decoding complexity of convolutional and trellis codes by Viterbi decoder can be reduced by applying suggested merging algorithm to the Forney code trellis. The algorithm can be applied for every trellis section separately, which is convenient for time-varying codes, and it outputs the minimal trellis of the section. In case of convolutional codes, the same minimal trellis of every section can be obtained from the syndrome trellis of proposed split code
COLD GASS, an IRAM Legacy Survey of Molecular Gas in Massive Galaxies: III. Comparison with semi-analytic models of galaxy formation
We compare the semi-analytic models of galaxy formation of Fu et al. (2010),
which track the evolution of the radial profiles of atomic and molecular gas in
galaxies, with gas fraction scaling relations derived from the COLD GASS survey
(Saintonge et al 2011). The models provide a good description of how condensed
baryons in galaxies with gas are partitioned into stars, atomic and molecular
gas as a function of galaxy stellar mass and surface density. The models do not
reproduce the tight observed relation between stellar surface density and
bulge-to-disk ratio for this population. We then turn to an analysis of
the"quenched" population of galaxies without detectable cold gas. The current
implementation of radio-mode feedback in the models disagrees strongly with the
data. In the models, gas cooling shuts down in nearly all galaxies in dark
matter halos above a mass of 10**12 M_sun. As a result, stellar mass is the
observable that best predicts whether a galaxy has little or no neutral gas. In
contrast, our data show that quenching is largely independent of stellar mass.
Instead, there are clear thresholds in bulge-to-disk ratio and in stellar
surface density that demarcate the location of quenched galaxies. We propose
that processes associated with bulge formation play a key role in depleting the
neutral gas in galaxies and that further gas accretion is suppressed following
the formation of the bulge, even in dark matter halos of low mass.Comment: 12 figures, accepted for publication in MNRAS, the COLD GASS data is
available at http://www.mpa-garching.mpg.de/COLD_GASS/data.shtm
High-precision geometry of a double-pole pulsar
High time resolution observations of PSR B0906-49 (or PSR J0908-4913) over a
wide range of frequencies have enabled us to determine the geometry and beam
shape of the pulsar. We have used the position angle traverse to determine
highly-constrained solutions to the rotating vector model which show
conclusively that PSR B0906-49 is an orthogonal rotator. The accuracy obtained
in measuring the geometry is unprecedented. This may allow tests of high-energy
emission models, should the pulsar be detected with GLAST. Although the impact
parameter, beta, appears to be frequency dependent, we have shown that this is
due to the effect of interstellar scattering. As a result, this pulsar provides
some of the strongest evidence yet that the position angle swing is indeed
related to a geometrical origin, at least for non-recycled pulsars. We show
that the beam structures of the main pulse and interpulse in PSR B0906-49 are
remarkably similar. The emission comes from a height of ~230 km and is
consistent with originating in a patchy cone located about half way to the last
open field lines. The rotation axis and direction of motion of the pulsar
appear to be aligned.Comment: accepted for publication in MNRAS, 7 pages, 4 figure
Pair Production of Charged Higgs Bosons from Bottom-Quark Fusion
For very large values of , charged Higgs boson pair production at
the Large Hadron Collider (LHC) from the scattering of two bottom quarks can
proceed dominantly. We investigated the cross sections of charged Higgs boson
pair production via the subprocess at the LHC including
the next-to-leading order (NLO) QCD corrections in the minimal supersymmetric
standard model (MSSM). We find that the NLO QCD corrections can significantly
reduce the dependence of the cross sections on the renormalization and
factorization scales.Comment: small changes are mad
Non-existence of stationary two-black-hole configurations: The degenerate case
In a preceding paper we examined the question whether the spin-spin repulsion
and the gravitational attraction of two aligned sub-extremal black holes can
balance each other. Based on the solution of a boundary value problem for two
separate (Killing-) horizons and a novel black hole criterion we were able to
prove the non-existence of the equilibrium configuration in question. In this
paper we extend the non-existence proof to extremal black holes.Comment: 18 pages, 2 figure
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