752 research outputs found
Thermodynamic relations in a driven lattice gas: numerical exprements
We explore thermodynamic relations in non-equilibrium steady states with
numerical experiments on a driven lattice gas. After operationally defining the
pressure and chemical potential in the driven lattice gas, we confirm
numerically the validity of the integrability condition (the Maxwell relation)
for the two quantities whose values differ from those for an equilibrium
system. This implies that a free energy function can be constructed for the
non-equilibrium steady state that we consider. We also investigate a
fluctuation relation associated with this free energy function. Our result
suggests that the compressibility can be expressed in terms of density
fluctuations even in non-equilibrium steady states.Comment: 4 pages, 4 figure
A Comparison of Exergaming Interfaces for Use in Rehabilitation Programs and Research
Exergames or active video games are video games with interfaces that require active involvement and the exertion of physical force by participants. These exergames are designed to track body motion and provide both fun and exercise for game players. Numerous video game console companies have designed exergaming interfaces that are becoming very popular. This paper examines the nature of the interfaces and explores the possibility of using these interfaces for rehabilitation programs and research. While many systems exist, this paper will focus on three major players: Sony PlayStation Move, Nintendo Wii, and Microsoft Xbox 360 Kinect. Comparisons include the technical specifications, the motion sensed by each interface, and the motion required in each therapeutic activity type. Discussion addresses the research implications of using these tools
Thermodynamics with long-range interactions: from Ising models to black-holes
New methods are presented which enables one to analyze the thermodynamics of
systems with long-range interactions. Generically, such systems have entropies
which are non-extensive, (do not scale with the size of the system). We show
how to calculate the degree of non-extensivity for such a system. We find that
a system interacting with a heat reservoir is in a probability distribution of
canonical ensembles. The system still possesses a parameter akin to a global
temperature, which is constant throughout the substance. There is also a useful
quantity which acts like a {\it local temperatures} and it varies throughout
the substance. These quantities are closely related to counterparts found in
general relativity. A lattice model with long-range spin-spin coupling is
studied. This is compared with systems such as those encountered in general
relativity, and gravitating systems with Newtonian-type interactions. A
long-range lattice model is presented which can be seen as a black-hole analog.
One finds that the analog's temperature and entropy have many properties which
are found in black-holes. Finally, the entropy scaling behavior of a
gravitating perfect fluid of constant density is calculated. For weak
interactions, the entropy scales like the volume of the system. As the
interactions become stronger, the entropy becomes higher near the surface of
the system, and becomes more area-scaling.Comment: Corrects some typos found in published version. Title changed 22
pages, 2 figure
Nonequilibrium Linear Response for Markov Dynamics, II: Inertial Dynamics
We continue our study of the linear response of a nonequilibrium system. This
Part II concentrates on models of open and driven inertial dynamics but the
structure and the interpretation of the result remain unchanged: the response
can be expressed as a sum of two temporal correlations in the unperturbed
system, one entropic, the other frenetic. The decomposition arises from the
(anti)symmetry under time-reversal on the level of the nonequilibrium action.
The response formula involves a statistical averaging over explicitly known
observables but, in contrast with the equilibrium situation, they depend on the
model dynamics in terms of an excess in dynamical activity. As an example, the
Einstein relation between mobility and diffusion constant is modified by a
correlation term between the position and the momentum of the particle
Galaxy rotation curves: the effect of j x B force
Using the Galaxy as an example, we study the effect of j x B force on the
rotational curves of gas and plasma in galaxies. Acceptable model for the
galactic magnetic field and plausible physical parameters are used to fit the
flat rotational curve for gas and plasma based on the observed baryonic
(visible) matter distribution and j x B force term in the static MHD equation
of motion. We also study the effects of varied strength of the magnetic field,
its pitch angle and length scale on the rotational curves. We show that j x B
force does not play an important role on the plasma dynamics in the
intermediate range of distances 6-12 kpc from the centre, whilst the effect is
sizable for larger r (r > 15 kpc), where it is the most crucial.Comment: Accepted for publication in Astrophysics & Space Science (final
printed version, typos in proofs corrected
Triggering Threshold Spacecraft Charging with Changes in Electron Emission from Materials
Modest changes in spacecraft charging conditions can lead to abrupt changes in the spacecraft equilibrium, from small positive potentials to large negative potentials relative to the space plasma; this phenomenon is referred to as threshold charging. It is well known that temporal changes of the space plasma environment (electron plasma temperature or density) can cause threshold charging. Threshold charging can also result from by temporal changes in the juxtaposition of the spacecraft to the environment, including spacecraft orbit, orientation, and geometry. This study focuses on the effects of possible changes in electron emission properties of representative spacecraft materials. It is found that for electron-induced emission, the possible threshold scenarios are very rich, since this type of electron emission can cause either positive or negative charging. Alternately, modification of photon- or ion-induced electron emission is found to induce threshold charging only in certain favorable cases. Changes of emission properties discussed include modifications due to: contamination, degradation and roughening of surfaces and layered materials; biasing and charge accumulation; bandstructure occupation and density of states caused by heat, optical or particle radiation; optical reflectivity and absorptivity; and inaccuracies and errors in measurements and parameterization of materials properties. An established method is used here to quantitatively gauge the relative extent to which these various changes in electron emission alter a spacecraft’s charging behavior and possibly lead to threshold charging. The absolute charging behavior of a hypothetical flat, two-dimensional satellite panel of a single material (either polycrystalline conductor Au or the polymeric polyimide Kapton™ H) is modeled as it undergoes modification and concomitant changes in spacecraft charging in three representative geosynchronous orbit environments, from full sunlight to full shade (eclipse) are considered
Can the Pioneer anomaly be of gravitational origin? A phenomenological answer
In order to satisfy the equivalence principle, any non-conventional mechanism
proposed to gravitationally explain the Pioneer anomaly, in the form in which
it is presently known from the so-far analyzed Pioneer 10/11 data, cannot leave
out of consideration its impact on the motion of the planets of the Solar
System as well, especially those orbiting in the regions in which the anomalous
behavior of the Pioneer probes manifested itself. In this paper we, first,
discuss the residuals of the right ascension \alpha and declination \delta of
Uranus, Neptune and Pluto obtained by processing various data sets with
different, well established dynamical theories (JPL DE, IAA EPM, VSOP). Second,
we use the latest determinations of the perihelion secular advances of some
planets in order to put on the test two gravitational mechanisms recently
proposed to accommodate the Pioneer anomaly based on two models of modified
gravity. Finally, we adopt the ranging data to Voyager 2 when it encountered
Uranus and Neptune to perform a further, independent test of the hypothesis
that a Pioneer-like acceleration can also affect the motion of the outer
planets of the Solar System. The obtained answers are negative.Comment: Latex2e, 26 pages, 6 tables, 2 figure, 47 references. It is the
merging of gr-qc/0608127, gr-qc/0608068, gr-qc/0608101 and gr-qc/0611081.
Final version to appear in Foundations of Physic
Electroweak Symmetry Breaking via UV Insensitive Anomaly Mediation
Anomaly mediation solves the supersymmetric flavor and CP problems. This is
because the superconformal anomaly dictates that supersymmetry breaking is
transmitted through nearly flavor-blind infrared physics that is highly
predictive and UV insensitive. Slepton mass squareds, however, are predicted to
be negative. This can be solved by adding D-terms for U(1)_Y and U(1)_{B-L}
while retaining the UV insensitivity. In this paper we consider electroweak
symmetry breaking via UV insensitive anomaly mediation in several models. For
the MSSM we find a stable vacuum when tanbeta < 1, but in this region the top
Yukawa coupling blows up only slightly above the supersymmetry breaking scale.
For the NMSSM, we find a stable electroweak breaking vacuum but with a chargino
that is too light. Replacing the cubic singlet term in the NMSSM superpotential
with a term linear in the singlet we find a stable vacuum and viable spectrum.
Most of the parameter region with correct vacua requires a large superpotential
coupling, precisely what is expected in the ``Fat Higgs'' model in which the
superpotential is generated dynamically. We have therefore found the first
viable UV complete, UV insensitive supersymmetry breaking model that solves the
flavor and CP problems automatically: the Fat Higgs model with UV insensitive
anomaly mediation. Moreover, the cosmological gravitino problem is naturally
solved, opening up the possibility of realistic thermal leptogenesis.Comment: 27 pages, 3 figures, 1 tabl
Generalized thermodynamics and Fokker-Planck equations. Applications to stellar dynamics, two-dimensional turbulence and Jupiter's great red spot
We introduce a new set of generalized Fokker-Planck equations that conserve
energy and mass and increase a generalized entropy until a maximum entropy
state is reached. The concept of generalized entropies is rigorously justified
for continuous Hamiltonian systems undergoing violent relaxation. Tsallis
entropies are just a special case of this generalized thermodynamics.
Application of these results to stellar dynamics, vortex dynamics and Jupiter's
great red spot are proposed. Our prime result is a novel relaxation equation
that should offer an easily implementable parametrization of geophysical
turbulence. This relaxation equation depends on a single key parameter related
to the skewness of the fine-grained vorticity distribution. Usual
parametrizations (including a single turbulent viscosity) correspond to the
infinite temperature limit of our model. They forget a fundamental systematic
drift that acts against diffusion as in Brownian theory. Our generalized
Fokker-Planck equations may have applications in other fields of physics such
as chemotaxis for bacterial populations. We propose the idea of a
classification of generalized entropies in classes of equivalence and provide
an aesthetic connexion between topics (vortices, stars, bacteries,...) which
were previously disconnected.Comment: Submitted to Phys. Rev.
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