12,488 research outputs found
Neutrino Bremsstrahlung Process in highly degenerate magnetized electron gas
In this article the neutrino bremsstrahlung process is considered in presence
of strong magnetic field, though the calculations for this process in absence
of magnetic field are also carried out simultaneously. The electrons involved
in this process are supposed to be highly degenerate and relativistic. The
scattering cross sections and energy loss rates for both cases, in presence and
absence of magnetic field, are calculated in the extreme-relativistic limit.
Two results are compared in the range of temperature K K and magnetic field G at a fixed density
, a typical environment during the cooling of magnetized
neutron star. The interpretation of our result is briefly discussed and the
importance of this process during the stellar evolution is speculated.Comment: 12 pages including 2 figures and 1 tabl
Programmable telemetry system Patent
Time division multiplexed telemetry transmitting system controlled by programmed memor
On the dependence of the avalanche angle on the granular layer thickness
A layer of sand of thickness h flows down a rough surface if the inclination
is larger than some threshold value theta which decreases with h. A tentative
microscopic model for the dependence of theta with h is proposed for rigid
frictional grains, based on the following hypothesis: (i) a horizontal layer of
sand has some coordination z larger than a critical value z_c where mechanical
stability is lost (ii) as the tilt angle is increased, the configurations
visited present a growing proportion $_s of sliding contacts. Instability with
respect to flow occurs when z-z_s=z_c. This criterion leads to a prediction for
theta(h) in good agreement with empirical observations.Comment: 6 pages, 2 figure
The use of implicit evidence for relevance feedback in web retrieval
In this paper we report on the application of two contrasting types of relevance feedback for web retrieval. We compare two systems; one using explicit relevance feedback (where searchers explicitly have to mark documents relevant) and one using implicit relevance feedback (where the system endeavours to estimate relevance by mining the searcher's interaction). The feedback is used to update the display according to the user's interaction. Our research focuses on the degree to which implicit evidence of document relevance can be substituted for explicit evidence. We examine the two variations in terms of both user opinion and search effectiveness
Saltatory drift in a randomly driven two-wave potential
Dynamics of a classical particle in a one-dimensional, randomly driven
potential is analysed both analytically and numerically. The potential
considered here is composed of two identical spatially-periodic saw-tooth-like
components, one of which is externally driven by a random force. We show that
under certain conditions the particle may travel against the averaged external
force performing a saltatory unidirectional drift with a constant velocity.
Such a behavior persists also in situations when the external force averages
out to zero. We demonstrate that the physics behind this phenomenon stems from
a particular behavior of fluctuations in random force: upon reaching a certain
level, random fluctuations exercise a locking function creating points of
irreversibility which the particle can not overpass. Repeated (randomly) in
each cycle, this results in a saltatory unidirectional drift. This mechanism
resembles the work of an escapement-type device in watches. Considering the
overdamped limit, we propose simple analytical estimates for the particle's
terminal velocity.Comment: 14 pages, 6 figures; appearing in Journal of Physics: Condensed
Matter, special issue on Molecular Motors and Frictio
Is the quantum world composed of propensitons?
In this paper I outline my propensiton version of quantum theory (PQT). PQT is a fully micro-realistic version of quantum theory that provides us with a very natural possible solution to the fundamental wave/particle problem, and is free of the severe defects of orthodox quantum theory (OQT) as a result. PQT makes sense of the quantum world. PQT recovers all the empirical success of OQT and is, furthermore, empirically testable (although not as yet tested). I argue that Einstein almost put forward this version of quantum theory in 1916/17 in his papers on spontaneous and induced radiative transitions, but retreated from doing so because he disliked the probabilistic character of the idea. Subsequently, the idea was overlooked because debates about quantum theory polarised into the Bohr/Heisenberg camp, which argued for the abandonment of realism and determinism, and the Einstein/Schrödinger camp, which argued for the retention of realism and determinism, no one, as a result, pursuing the most obvious option of retaining realism but abandoning determinism. It is this third, overlooked option that leads to PQT. PQT has implications for quantum field theory, the standard model, string theory, and cosmology. The really important point, however, is that it is experimentally testable. I indicate two experiments in principle capable of deciding between PQT and OQT
Far-from-constant mean curvature solutions of Einstein's constraint equations with positive Yamabe metrics
In this article we develop some new existence results for the Einstein
constraint equations using the Lichnerowicz-York conformal rescaling method.
The mean extrinsic curvature is taken to be an arbitrary smooth function
without restrictions on the size of its spatial derivatives, so that it can be
arbitrarily far from constant. The rescaled background metric belongs to the
positive Yamabe class, and the freely specifiable part of the data given by the
traceless-transverse part of the rescaled extrinsic curvature and the matter
fields are taken to be sufficiently small, with the matter energy density not
identically zero. Using topological fixed-point arguments and global barrier
constructions, we then establish existence of solutions to the constraints. Two
recent advances in the analysis of the Einstein constraint equations make this
result possible: A new type of topological fixed-point argument without
smallness conditions on spatial derivatives of the mean extrinsic curvature,
and a new construction of global super-solutions for the Hamiltonian constraint
that is similarly free of such conditions on the mean extrinsic curvature. For
clarity, we present our results only for strong solutions on closed manifolds.
However, our results also hold for weak solutions and for other cases such as
compact manifolds with boundary; these generalizations will appear elsewhere.
The existence results presented here for the Einstein constraints are
apparently the first such results that do not require smallness conditions on
spatial derivatives of the mean extrinsic curvature.Comment: 4 pages, no figures, accepted for publication in Physical Review
Letters. (Abstract shortenned and other minor changes reflecting v4 version
of arXiv:0712.0798
Second Law of Thermodynamics with Discrete Quantum Feedback Control
A new thermodynamic inequality is derived which leads to the maximum work
that can be extracted from multi-heat baths with the assistance of discrete
quantum feedback control. The maximum work is determined by the free-energy
difference and a generalized mutual information content between the
thermodynamic system and the feedback controller. This maximum work can exceed
that in conventional thermodynamics and, in the case of a heat cycle with two
heat baths, the heat efficiency can be greater than that of the Carnot cycle.
The consistency of our results with the second law of thermodynamics is ensured
by the fact that work is needed for information processing of the feedback
controller
The Effects of a Core Stabilization Training Program on the Performance of Functional Tasks in Firefighters
International Journal of Exercise Science 17(4): 602-610, 2024. The purpose of this study was to observe if core stabilization training plays a significant role in firefighter time-to-completion during a functional performance test. A within subjects study design was used in which subjects (n = 13, 84.6% male, 33.7 ± 7.4 years of age, 91.06 ± 13.29 kg, 25.79 ± 6.55 percent body fat, 8.96 ± 7.51 years of firefighting experience) completed two performance tests (pre and post core training), comprised of 7 firefighter-specific exercises performed while wearing a 22.68 kg weight vest to mimic typical firefighter equipment. Between testing sessions, subjects were prescribed specific core stabilization exercises to perform at least three days a week for a total of 4 weeks. Time-to-completion was significantly quicker between the first (300.89 ± 42.11s) and second (256.92 ± 34.31s) performance testing, on average by 43.8 seconds (p \u3c 0.001). Body mass index (p = 0.065) and rating of perceived exertion during testing (p = 0.084) did not significantly decrease across the course of the study. Adequate fitness is essential to firefighters’ job task performance. Data from this study suggests that regular core stabilization training may assist in optimizing the effectiveness, and potentially safety, of firefighters’ performance in high intensity functional skills
A Note on Non-equilibrium Work Fluctuations and Equilibrium Free Energies
We consider in this paper, a few important issues in non-equilibrium work
fluctuations and their relations to equilibrium free energies. First we show
that Jarzynski identity can be viewed as a cumulant expansion of work. For a
switching process which is nearly quasistatic the work distribution is sharply
peaked and Gaussian. We show analytically that dissipation given by average
work minus reversible work , decreases when the process becomes more and
more quasistatic. Eventually, in the quasistatic reversible limit, the
dissipation vanishes. However estimate of - the probability of violation of
the second law given by the integral of the tail of the work distribution from
to , increases and takes a value of in the quasistatic
limit. We show this analytically employing Gaussian integrals given by error
functions and Callen-Welton theorem that relates fluctuations to dissipation in
process that is nearly quasistatic. Then we carry out Monte Carlo simulation of
non-equilibrium processes in a liquid crystal system in the presence of an
electric field and present results on reversible work, dissipation, probability
of violation of the second law and distribution of workComment: 15 pages, 4 figure
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