15,422 research outputs found
Exact Persistence Exponent for One-dimensional Potts Models with Parallel Dynamics
We obtain \theta_p(q) = 2\theta_s(q) for one-dimensional q-state
ferromagnetic Potts models evolving under parallel dynamics at zero temperature
from an initially disordered state, where \theta_p(q) is the persistence
exponent for parallel dynamics and \theta_s(q) = -{1/8}+
\frac{2}{\pi^2}[cos^{-1}{(2-q)/q\sqrt{2}}]^2 [PRL, {\bf 75}, 751, (1995)], the
persistence exponent under serial dynamics. This result is a consequence of an
exact, albeit non-trivial, mapping of the evolution of configurations of Potts
spins under parallel dynamics to the dynamics of two decoupled reaction
diffusion systems.Comment: 13 pages Latex file, 5 postscript figure
Semi-Empirical Bound on the Chlorinr-37 Solar Neutrino Experiment
The Kamiokande measurement of energetic Boron-8 neutrinos from the sun is
used to set a lower bound on the contribution of the same neutrinos to the
signal in the \Chlorine\ experiment. Implications for Beryllium-7 neutrinos are
discussed.Comment: Latex, 6 pages + 1 postscript figure (included). UTAPHY-HEP-
Counter-rotating Accretion Disks
We consider accretion disks consisting of counter-rotating gaseous components
with an intervening shear layer. Configurations of this type may arise from the
accretion of newly supplied counter-rotating gas onto an existing co-rotating
gas disk. For simplicity we consider the case where the gas well above the disk
midplane is rotating with angular rate and that well below has the
same properties but is rotating with rate . Using the Shakura-Sunyaev
alpha turbulence model, we find self-similar solutions where a thin (relative
to the full disk thickness) equatorial layer accretes very rapidly, essentially
at free-fall speed. As a result the accretion speed is much larger than it
would be for an alpha disk rotating in one direction. Counter-rotating
accretion disks may be a transient stage in the formation of counter-rotating
galaxies and in the accretion of matter onto compact objects.Comment: 7 pages, 3 figures, aas2pp4.sty, submitted to Ap
Dynamics of a metastable state nonlinearly coupled to a heat bath driven by an external noise
Based on a system-reservoir model, where the system is nonlinearly coupled to
a heat bath and the heat bath is modulated by an external stationary Gaussian
noise, we derive the generalized Langevin equation with space dependent
friction and multiplicative noise and construct the corresponding Fokker-Planck
equation, valid for short correlation time, with space dependent diffusion
coefficient to study the escape rate from a metastable state in the moderate to
large damping regime. By considering the dynamics in a model cubic potential we
analyze the result numerically which are in good agreement with the theoretical
prediction. It has been shown numerically that the enhancement of rate is
possible by properly tuning the correlation time of the external noise.Comment: 13 pages, 5 figures, Revtex4. To appear in Physical Review
The Spatial Correlation of Bent-Tail Galaxies and Galaxy Clusters
We have completed a deep radio continuum survey covering 86 square degrees of
the Spitzer-South Pole Telescope deep field to test whether bent-tail galaxies
are associated with galaxy clusters. We present a new catalogue of 22 bent-tail
galaxies and a further 24 candidate bent-tail galaxies. Surprisingly, of the 8
bent-tail galaxies with photometric redshifts, only two are associated with
known clusters. While the absence of bent-tail sources in known clusters may be
explained by effects such as sensitivity, the absence of known clusters
associated with most bent-tail galaxies casts doubt upon current models of
bent-tail galaxies.Comment: Accepted by MNRA
Recommended from our members
An Examination of Motivation to Change and Neural Alcohol Cue Reactivity Following a Brief Intervention.
Background: Brief interventions represent a promising psychological intervention targeting individuals with heavy alcohol use. Motivation to change represents an individual's openness to engage in a behavior change strategy and is thought to be a crucial component of brief interventions. Neuroimaging techniques provide a translational tool to investigate the neurobiological mechanisms underlying potential mediators of treatment response, including motivation to change. Therefore, this study aimed to examine the effect of a brief intervention on motivation to change drinking behavior and neural alcohol taste cue reactivity. Methods: Non-treatment-seeking heavy drinkers were randomized to receive a brief drinking intervention (n = 22) or an attention-matched control (n = 24). Three indices of motivation to change were assessed at baseline and after the intervention or control session: importance, confidence, and readiness. Immediately following the intervention or control session, participants also underwent an functional magnetic resonance imaging (fMRI) during which they completed an alcohol taste cues paradigm. Results: There was a significant effect of the brief intervention on increasing ratings of importance of changing drinking behavior, but not on ratings of confidence or readiness to change. Ratings of importance after the intervention or control session were associated with neural alcohol taste cue reactivity, but notably, this effect was only significant for participants who received the intervention. Individuals in the intervention condition showed a positive association between ratings of importance and activation in the precuneus, posterior cingulate, and insula. Conclusions: The brief drinking intervention was successful at improving one dimension of motivation to change among non-treatment-seeking heavy drinkers. The brief intervention moderated the relationship between ratings of importance and brain activation in circuitry associated with interoceptive awareness and self-reflection. Together, findings represent an initial step toward understanding the neurobiological mechanisms through which a brief intervention may improve motivation to change
Floating Spherical Gaussian Orbital (FSGO) Studies with a Model Potential: Methane, Silane & Germane
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Synchrotron aging and the radio spectrum of SN 1993J
We combine the GMRT low frequency radio observations of SN 1993J with the VLA
high frequency radio data to get a near simultaneous spectrum around day 3200
since explosion. The low frequency measurements of the supernova determine the
turnover frequency and flux scale of the composite spectrum and help reveal a
steepening in the spectral index, , in the optically
thin part of the spectrum. This is the first observational evidence of a break
in the radio spectrum of a young supernova. We associate this break with the
phenomenon of synchrotron aging of radiating electrons. From the break in the
spectrum we calculate the magnetic field in the shocked region independent of
the equipartition assumption between energy density of relativistic particles
and magnetic energy density. We determine the ratio of these two energy
densities and find that this ratio is in the range: . We also predict the nature of the evolution of the synchrotron break
frequency with time, with competing effects due to diffusive Fermi acceleration
and adiabatic expansion of the radiative electron plasma.Comment: 12 pages, 2 figures. Accepted for publication in ApJ
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