499 research outputs found
Survival in equilibrium step fluctuations
We report the results of analytic and numerical investigations of the time
scale of survival or non-zero-crossing probability in equilibrium step
fluctuations described by Langevin equations appropriate for
attachment/detachment and edge-diffusion limited kinetics. An exact relation
between long-time behaviors of the survival probability and the autocorrelation
function is established and numerically verified. is shown to exhibit
simple scaling behavior as a function of system size and sampling time. Our
theoretical results are in agreement with those obtained from an analysis of
experimental dynamical STM data on step fluctuations on Al/Si(111) and Ag(111)
surfaces.Comment: RevTeX, 4 pages, 3 figure
A Perturbative Calculation of the Electromagnetic Form Factors of the Deuteron
Making use of the effective field theory expansion recently developed by the
authors, we compute the electromagnetic form factors of the deuteron
analytically to next-to-leading order (NLO). The computation is rather simple,
and involves calculating several Feynman diagrams, using dimensional
regularization. The results agree well with data and indicate that the
expansion is converging. They do not suffer from any ambiguities arising from
off-shell versus on-shell amplitudes.Comment: 22 pages, 8 figures. Discussion of effective range theory added,
typos correcte
Isocurvature forecast in the anthropic axion window
We explore the cosmological sensitivity to the amplitude of isocurvature
fluctuations that would be caused by axions in the "anthropic window" where the
axion decay constant f_a >> 10^12 GeV and the initial misalignment angle
Theta_i << 1. In a minimal Lambda-CDM cosmology extended with subdominant
scale-invariant isocurvature fluctuations, existing data constrain the
isocurvature fraction to alpha < 0.09 at 95% C.L. If no signal shows up, Planck
can improve this constraint to 0.042 while an ultimate CMB probe limited only
by cosmic variance in both temperature and E-polarisation can reach 0.017,
about a factor of five better than the current limit. In the parameter space of
f_a and H_I (Hubble parameter during inflation) we identify a small region
where axion detection remains within the reach of realistic cosmological
probes.Comment: 14 pages, 4 figures; v2: matches published versio
Critical Exponents for Three-Dimensional Superfluid--Bose-Glass Phase Transition
The critical phenomenon of the zero temperature superfluid--Bose-glass phase
transition for hard-core bosons on a three-dimensional disordered lattice is
studied using a quantum real-space renormalization-group method. The
correlation-length exponent and the dynamic exponent z are computed. The
critical exponent z is found to be 2.5 for compressible states and 1.3 for
incompressible states. The exponent is shown to be insensitive to z as
that in the two-dimensional case, and has value roughly equal to 1.Comment: 11 pages, REVTE
Disordered Boson Systems: A Perturbative Study
A hard-core disordered boson system is mapped onto a quantum spin 1/2
XY-model with transverse random fields. It is then generalized to a system of
spins with an arbitrary magnitude S and studied through a 1/S expansion. The
first order 1/S expansion corresponds to a spin-wave theory. The effect of weak
disorder is studied perturbatively within such a first order 1/S scheme. We
compute the reduction of the speed of sound and the life time of the Bloch
phonons in the regime of weak disorder. Generalizations of the present study to
the strong disordered regime are discussed.Comment: 27 pages, revte
Effects of electrical stimulation of dorsal raphe nucleus on neuronal response properties of barrel cortex layer IV neurons following long-term sensory deprivation
Abstract: Objective To evaluate the effect of electrical stimulation of dorsal raphe nucleus (DRN) on response properties of layer IV barrel cortex neurons following long-term sensory deprivation. Methods: Male Wistar rats were divided into sensory-deprived (SD) and control (unplucked) groups. In SD group, all vibrissae except the D2 vibrissa were plucked on postnatal day one, and kept plucked for a period of 60 d. After that, whisker regrowth was allowed for 8-10 d. The D2 principal whisker (PW) and the D1 adjacent whisker (AW) were either deflected singly or both deflected in a serial order that the AW was deflected 20 ms before PW deflection for assessing lateral inhibition, and neuronal responses were recorded from layer IV of the D2 barrel cortex. DRN was electrically stimulated at inter-stimulus intervals (ISIs) ranging from 0 to 800 ms before whisker deflection. Results: PW-evoked responses increased in the SD group with DRN electrical stimulation at ISIs of 50 ms and 100 ms, whereas AW-evoked responses increased at ISI of 800 ms in both groups. Whisker plucking before DRN stimulation could enhance the responsiveness of barrel cortex neurons to PW deflection and decrease the responsiveness to AW deflection. DRN electrical stimulation significantly reduced this difference only in PW-evoked responses between groups. Besides, no DRN stimulation-related changes in response latency were observed following PW or AW deflection in either group. Moreover, condition test (CT) ratio increased in SD rats, while DRN stimulation did not affect the CT ratio in either group. There was no obvious change in 5-HT2A receptor protein density in barrel cortex between SD and control groups. Conclusion: These results suggest that DRN electrical stimulation can modulate information processing in the SD barrel cortex
Generalizations of Gronwall-Bihari Inequalities on Time Scales
We establish some nonlinear integral inequalities for functions defined on a
time scale. The results extend some previous Gronwall and Bihari type
inequalities on time scales. Some examples of time scales for which our results
can be applied are provided. An application to the qualitative analysis of a
nonlinear dynamic equation is discussed.Comment: This is a preprint of an article accepted (16/May/2008) for
publication in the "Journal of Difference Equations and Applications"; J.
Difference Equ. Appl. is available online at http://www.informaworld.co
Formation of superdense hadronic matter in high energy heavy-ion collisions
We present the detail of a newly developed relativistic transport model (ART
1.0) for high energy heavy-ion collisions. Using this model, we first study the
general collision dynamics between heavy ions at the AGS energies. We then show
that in central collisions there exists a large volume of sufficiently
long-lived superdense hadronic matter whose local baryon and energy densities
exceed the critical densities for the hadronic matter to quark-gluon plasma
transition. The size and lifetime of this matter are found to depend strongly
on the equation of state. We also investigate the degree and time scale of
thermalization as well as the radial flow during the expansion of the
superdense hadronic matter. The flow velocity profile and the temperature of
the hadronic matter at freeze-out are extracted. The transverse momentum and
rapidity distributions of protons, pions and kaons calculated with and without
the mean field are compared with each other and also with the preliminary data
from the E866/E802 collaboration to search for experimental observables that
are sensitive to the equation of state. It is found that these inclusive,
single particle observables depend weakly on the equation of state. The
difference between results obtained with and without the nuclear mean field is
only about 20\%. The baryon transverse collective flow in the reaction plane is
also analyzed. It is shown that both the flow parameter and the strength of the
``bounce-off'' effect are very sensitive to the equation of state. In
particular, a soft equation of state with a compressibility of 200 MeV results
in an increase of the flow parameter by a factor of 2.5 compared to the cascade
case without the mean field. This large effect makes it possible to distinguish
the predictions from different theoretical models and to detect the signaturesComment: 55 pages, latex, + 39 figures available upon reques
Relativistic Calculation of the Meson Spectrum: a Fully Covariant Treatment Versus Standard Treatments
A large number of treatments of the meson spectrum have been tried that
consider mesons as quark - anti quark bound states. Recently, we used
relativistic quantum "constraint" mechanics to introduce a fully covariant
treatment defined by two coupled Dirac equations. For field-theoretic
interactions, this procedure functions as a "quantum mechanical transform of
Bethe-Salpeter equation". Here, we test its spectral fits against those
provided by an assortment of models: Wisconsin model, Iowa State model,
Brayshaw model, and the popular semi-relativistic treatment of Godfrey and
Isgur. We find that the fit provided by the two-body Dirac model for the entire
meson spectrum competes with the best fits to partial spectra provided by the
others and does so with the smallest number of interaction functions without
additional cutoff parameters necessary to make other approaches numerically
tractable. We discuss the distinguishing features of our model that may account
for the relative overall success of its fits. Note especially that in our
approach for QCD, the resulting pion mass and associated Goldstone behavior
depend sensitively on the preservation of relativistic couplings that are
crucial for its success when solved nonperturbatively for the analogous
two-body bound-states of QED.Comment: 75 pages, 6 figures, revised content
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