623 research outputs found
The marginally stable Bethe lattice spin glass revisited
Bethe lattice spins glasses are supposed to be marginally stable, i.e. their
equilibrium probability distribution changes discontinuously when we add an
external perturbation. So far the problem of a spin glass on a Bethe lattice
has been studied only using an approximation where marginally stability is not
present, which is wrong in the spin glass phase. Because of some technical
difficulties, attempts at deriving a marginally stable solution have been
confined to some perturbative regimes, high connectivity lattices or
temperature close to the critical temperature. Using the cavity method, we
propose a general non-perturbative approach to the Bethe lattice spin glass
problem using approximations that should be hopeful consistent with marginal
stability.Comment: 23 pages Revised version, hopefully clearer that the first one: six
pages longe
A unified stability property in spin glasses
Gibbs' measures in the Sherrington-Kirkpatrick type models satisfy two
asymptotic stability properties, the Aizenman-Contucci stochastic stability and
the Ghirlanda-Guerra identities, which play a fundamental role in our current
understanding of these models. In this paper we show that one can combine these
two properties very naturally into one unified stability property
Evolution of the double neutron star merging rate and the cosmological origin of gamma-ray burst sources
Evolution of the coalescence rate of double neutron stars (NS) and neutron
star -- black hole (BH) binaries are computed for model galaxies with different
star formation rates. Assuming gamma-ray bursts (GRB) to originate from NS+NS
or NS+BH merging in distant galaxies, theoretical logN--logS distributions and
tests of gamma-ray bursts (GRB) are calculated for the first time
taking the computed merging rates into account. We use a flat cosmological
model (Omega=1) with different values of the cosmological constant Lambda and
under various assumptions about the star formation history in galaxies. The
calculated source evolution predicts a 5-10 times increase of the source
statistics at count rates 3-10 times lower than the exising BATSE sensitivity
limit. The most important parameter in fitting the 2nd BATSE catalogue is the
initial redshift of star formation, which is found to be z_*=2-5 depending on a
poorly determined average spectral index of GRB.Comment: 13 pages, compressed uuencoded postscript, 6 figures. This paper has
been accepted for publication in the Astrophysical Journal part
Remote detection of traces of high energetic materials
The possibility of remote detection of traces of high energetic materials using laser fragmentation/laser-induced fluorescence (LF/LIF) method is studied. Experimental data on the remote visualization of traces of trinitrotoluene, hexogen, composition B, octogen, and tetryl obtained at a distance of 5 m with a scanning lidar detector of traces of high energetic materials are presented
Analyzing X-Ray Pulsar Profiles: Geometry and Beam Pattern of Her X-1
We report on our analysis of a large sample of energy dependent pulse
profiles of the X-ray binary pulsar Hercules X-1. We find that all data are
compatible with the assumption of a slightly distorted magnetic dipole field as
sole cause of the asymmetry of the observed pulse profiles. Further the
analysis provides evidence that the emission from both poles is equal. We
determine an angle of 20 deg between the rotation axis and the local magnetic
axis. One pole has an offset of 5 deg from the antipodal position of the other
pole. The beam pattern shows structures that can be interpreted as pencil- and
fan-beam configurations. Since no assumptions on the polar emission are made,
the results can be compared with various emission models. A comparison of
results obtained from pulse profiles of different phases of the 35-day cycle
indicates different attenuation of the radiation from the poles being
responsible for the change of the pulse shape during the main-on state. These
results also suggest the resolution of an ambiguity within a previous analysis
of pulse profiles of Cen X-3, leading to a unique result for the beam pattern
of this pulsar as well. The analysis of pulse profiles of the short-on state
indicates that a large fraction of the radiation cannot be attributed to the
direct emission from the poles. We give a consistent explanation of both the
evolution of the pulse profile and the spectral changes with the 35-day cycle
in terms of a warped precessing accretion disk.Comment: 24 pages, 12 figures. To appear in ApJ 529 #2, 1 Feb 200
Behavior of nonlinear dielectric response and features of elastic properties in a PZT-Based multicomponent system
- …