1,361 research outputs found
Measuring Nonequilibrium Temperature of Forced Oscillators
The meaning of temperature in nonequilibrium thermodynamics is considered by
using a forced harmonic oscillator in a heat bath, where we have two effective
temperatures for the position and the momentum, respectively. We invent a
concrete model of a thermometer to testify the validity of these different
temperatures from the operational point of view. It is found that the measured
temperature depends on a specific form of interaction between the system and a
thermometer, which means the zeroth law of thermodynamics cannot be immediately
extended to nonequilibrium cases.Comment: 8 page
Incorporating Memory Effects in Phase Separation Processes
We consider the modification of the Cahn-Hilliard equation when a time delay
process through a memory function is taken into account. We then study the
process of spinodal decomposition in fast phase transitions associated with a
conserved order parameter. Finite-time memory effects are seen to affect the
dynamics of phase transition at short times and have the effect of delaying, in
a significant way, the process of rapid growth of the order parameter that
follows a quench into the spinodal region. These effects are important in
several systems characterized by fast processes, like nonequilibrium dynamics
in the early universe and in relativistic heavy-ion collisions.Comment: 5 pages, 2 eps figures. Version in press Phys. Lett.
Vortex length, vortex energy and fractal dimension of superfluid turbulence at very low temperature
By assuming a self-similar structure for Kelvin waves along vortex loops with
successive smaller scale features, we model the fractal dimension of a
superfluid vortex tangle in the zero temperature limit. Our model assumes that
at each step the total energy of the vortices is conserved, but the total
length can change. We obtain a relation between the fractal dimension and the
exponent describing how the vortex energy per unit length changes with the
length scale. This relation does not depend on the specific model, and shows
that if smaller length scales make a decreasing relative contribution to the
energy per unit length of vortex lines, the fractal dimension will be higher
than unity. Finally, for the sake of more concrete illustration, we relate the
fractal dimension of the tangle to the scaling exponents of amplitude and
wavelength of a cascade of Kelvin waves.Comment: 12 pages, 1 figur
Correlations of Globular Cluster Properties: Their Interpretations and Uses
Correlations among the independently measured physical properties of globular
clusters (GCs) can provide powerful tests for theoretical models and new
insights into their dynamics, formation, and evolution. We review briefly some
of the previous work, and present preliminary results from a comparative study
of GC correlations in the Local Group galaxies. The results so far indicate
that these diverse GC systems follow the same fundamental correlations,
suggesting a commonality of formative and evolutionary processes which produce
them.Comment: An invited review, to appear in "New Horizons in Globular Cluster
Astronomy", eds. G. Piotto, G. Meylan, S.G. Djorgovski, and M. Riello, ASPCS,
in press (2003). Latex file, 8 pages, 5 eps figures, style files include
Phenomenological approach to the critical dynamics of the QCD phase transition revisited
The phenomenological dynamics of the QCD critical phenomena is revisited.
Recently, Son and Stephanov claimed that the dynamical universality class of
the QCD phase transition belongs to model H. In their discussion, they employed
a time-dependent Ginzburg-Landau equation for the net baryon number density,
which is a conserved quantity. We derive the Langevin equation for the net
baryon number density, i.e., the Cahn-Hilliard equation. Furthermore, they
discussed the mode coupling induced through the {\it irreversible} current.
Here, we show the {\it reversible} coupling can play a dominant role for
describing the QCD critical dynamics and that the dynamical universality class
does not necessarily belong to model H.Comment: 13 pages, the Curie principle is discussed in S.2, to appear in
J.Phys.
Attenuation and damping of electromagnetic fields: Influence of inertia and displacement current
New results for attenuation and damping of electromagnetic fields in rigid
conducting media are derived under the conjugate influence of inertia due to
charge carriers and displacement current. Inertial effects are described by a
relaxation time for the current density in the realm of an extended Ohm's law.
The classical notions of poor and good conductors are rediscussed on the basis
of an effective electric conductivity, depending on both wave frequency and
relaxation time. It is found that the attenuation for good conductors at high
frequencies depends solely on the relaxation time. This means that the
penetration depth saturates to a minimum value at sufficiently high
frequencies. It is also shown that the actions of inertia and displacement
current on damping of magnetic fields are opposite to each other. That could
explain why the classical decay time of magnetic fields scales approximately as
the diffusion time. At very small length scales, the decay time could be given
either by the relaxation time or by a fraction of the diffusion time, depending
whether inertia or displacement current, respectively, would prevail on
magnetic diffusion.Comment: 21 pages, 1 figur
Pain in patients with equal radiographic grades of osteoarthritis in both knees: the value of gray scale ultrasound
SummaryObjectivesTo investigate the association of ultrasound (US) features with pain and the functional scores in patients with equal radiographic grades of osteoarthritis (OA) in both knees.MethodsFifty-six consecutive patients with knee OA: 85 symptomatic knees (81 knees with medial pain) and 27 asymptomatic knees, and 10 healthy patients without knee OA as a control were enrolled. US was done by two ultrasonographers blinded to patient diagnoses. US features were semiquantitatively scored (0–3) when appropriate.ResultsIn the OA group, common US findings were marginal osteophyte, suprapatellar synovitis, suprapatellar effusion (SPE), medial meniscus protrusion, medial compartment synovitis (MCS), lateral compartment synovitis, and Baker's cyst. Only SPE and MCS were significantly associated with knee pain. Visual analog pain scale (VAS) scores on motion were positively linearly associated with SPE and MCS (P < 0.01). Only MCS was degree-dependently associated with VAS scores at rest, the Western Ontario and McMaster Universities pain subscale, and the presence of medial knee pain (P < 0.01) after adjustments for age, gender, body mass index (BMI), radiographic grade, and other US features. In the control group, no US features were associated with knee pain.ConclusionsUS inflammation features, including SPE and MCS, were positively linearly associated with knee pain in motion. MCS was also degree-dependently associated with pain at rest and the presence of medial knee pain. These findings show that synovitis was one important predictive factor of pain. Further studies to confirm the association of US features and pain are warranted
Stability of inflationary solutions driven by a changing dissipative fluid
In this paper the second Lyapunov method is used to study the stability of
the de Sitter phase of cosmic expansion when the source of the gravitational
field is a viscous fluid. Different inflationary scenarios related with
reheating and decay of mini-blackholes into radiation are investigated using an
effective fluid described by time--varying thermodynamical quantities.Comment: 17 pages, LaTeX 2.09, 2 figures. To be published in Classical and
Quantum Gravit
Hyperbolic subdiffusive impedance
We use the hyperbolic subdiffusion equation with fractional time derivatives
(the generalized Cattaneo equation) to study the transport process of
electrolytes in media where subdiffusion occurs. In this model the flux is
delayed in a non-zero time with respect to the concentration gradient. In
particular, we obtain the formula of electrochemical subdiffusive impedance of
a spatially limited sample in the limit of large and of small pulsation of the
electric field. The boundary condition at the external wall of the sample are
taken in the general form as a linear combination of subdiffusive flux and
concentration of the transported particles. We also discuss the influence of
the equation parameters (the subdiffusion parameter and the delay time) on the
Nyquist impedance plots.Comment: 10 pages, 5 figure
A causal model of radiating stellar collapse
We find a simple exact model of radiating stellar collapse, with a shear-free
and non-accelerating interior matched to a Vaidya exterior. The heat flux is
subject to causal thermodynamics, leading to self-consistent determination of
the temperature . We solve for exactly when the mean collision time
is constant, and perturbatively in a more realistic case of variable
. Causal thermodynamics predicts temperature behaviour that can
differ significantly from the predictions of non-causal theory. In particular,
the causal theory gives a higher central temperature and greater temperature
gradient.Comment: Latex [ioplppt style] 9 pages; to appear Class. Quantum Gra
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