10,014 research outputs found
Energy and entropy of relativistic diffusing particles
We discuss energy-momentum tensor and the second law of thermodynamics for a
system of relativistic diffusing particles. We calculate the energy and entropy
flow in this system. We obtain an exact time dependence of energy, entropy and
free energy of a beam of photons in a reservoir of a fixed temperature.Comment: 14 pages,some formulas correcte
Momentum of an electromagnetic wave in dielectric media
Almost a hundred years ago, two different expressions were proposed for the
energy--momentum tensor of an electromagnetic wave in a dielectric. Minkowski's
tensor predicted an increase in the linear momentum of the wave on entering a
dielectric medium, whereas Abraham's tensor predicted its decrease. Theoretical
arguments were advanced in favour of both sides, and experiments proved
incapable of distinguishing between the two. Yet more forms were proposed, each
with their advocates who considered the form that they were proposing to be the
one true tensor. This paper reviews the debate and its eventual conclusion:
that no electromagnetic wave energy--momentum tensor is complete on its own.
When the appropriate accompanying energy--momentum tensor for the material
medium is also considered, experimental predictions of all the various proposed
tensors will always be the same, and the preferred form is therefore
effectively a matter of personal choice.Comment: 23 pages, 3 figures, RevTeX 4. Removed erroneous factor of mu/mu_0
from Eq.(44
Gaussian noise and time-reversal symmetry in non-equilibrium Langevin models
We show that in driven systems the Gaussian nature of the fluctuating force
and time-reversibility are equivalent properties. This result together with the
potential condition of the external force drastically restricts the form of the
probability distribution function, which can be shown to satisfy
time-independent relations. We have corroborated this feature by explicitly
analyzing a model for the stretching of a polymer and a model for a suspension
of non-interacting Brownian particles in steady flow.Comment: 6 pages, submitted to PR
The role of Joule heating in the formation of nanogaps by electromigration
We investigate the formation of nanogaps in gold wires due to
electromigration. We show that the breaking process will not start until a
local temperature of typically 400 K is reached by Joule heating. This value is
rather independent of the temperature of the sample environment (4.2-295 K).
Furthermore, we demonstrate that the breaking dynamics can be controlled by
minimizing the total series resistance of the system. In this way, the local
temperature rise just before break down is limited and melting effects are
prevented. Hence, electrodes with gaps < 2 nm are easily made, without the need
of active feedback. For optimized samples, we observe quantized conductance
steps prior the gap formation.Comment: including 7 figure
Gravitational backreaction in cosmological spacetimes
We develop a new formalism for the treatment of gravitational backreaction in
the cosmological setting. The approach is inspired by projective techniques in
non-equilibrium statistical mechanics. We employ group-averaging with respect
to the action of the isotropy group of homogeneous and isotropic spacetimes
(rather than spatial averaging), in order to define effective FRW variables for
a generic spacetime. Using the Hamiltonian formalism for gravitating perfect
fluids, we obtain a set of equations for the evolution of the effective
variables; these equations incorporate the effects of backreaction by the
inhomogeneities. Specializing to dust-filled spacetimes, we find regimes that
lead to a closed set of backreaction equations, which we solve for small
inhomogeneities. We then study the case of large inhomogeneities in relation to
the proposal that backreaction can lead to accelerated expansion. In
particular, we identify regions of the gravitational state space that
correspond to effective cosmic acceleration. Necessary conditions are (i) a
strong expansion of the congruences corresponding to comoving observers, and
(ii) a large negative value of a dissipation variable that appears in the
effective equations (i.e, an effective "anti-dissipation").Comment: 36 pages, latex. Extended discussion on results and on relation to
Lemaitre-Tolman-Bondi models. Version to appear in PR
Energy dissipation and violation of the fluctuation-response relation in non-equilibrium Langevin systems
The fluctuation-response relation is a fundamental relation that is
applicable to systems near equilibrium. On the other hand, when a system is
driven far from equilibrium, this relation is violated in general because the
detailed-balance condition is not satisfied in nonequilibrium systems. Even in
this case, it has been found that for a class of Langevin equations, there
exists an equality between the extent of violation of the fluctuation-response
relation in the nonequilibrium steady state and the rate of energy dissipation
from the system into the environment [T. Harada and S. -i. Sasa, Phys. Rev.
Lett. 95, 130602 (2005)]. Since this equality involves only experimentally
measurable quantities, it serves as a proposition to determine experimentally
whether the system can be described by a Langevin equation. Furthermore, the
contribution of each degree of freedom to the rate of energy dissipation can be
determined based on this equality. In this paper, we present a comprehensive
description on this equality, and provide a detailed derivation for various
types of models including many-body systems, Brownian motor models,
time-dependent systems, and systems with multiple heat reservoirs.Comment: 18 pages, submitted to Phys. Rev.
Transport properties of highly asymmetric hard-sphere mixtures
The static and dynamic properties of binary mixtures of hard spheres with a diameter ratio of sigma(B)/sigma(A)= 0.1 and a mass ratio of m(B)/m(A)= 0.001 are investigated using event driven molecular dynamics. The contact values of the pair correlation functions are found to compare favorably with recently proposed theoretical expressions. The transport coefficients of the mixture, determined from simulation, are compared to the predictions of the revised Enskog theory using both a third-order Sonine expansion and direct simulation Monte Carlo. Overall, the Enskog theory provides a fairly good description of the simulation data, with the exception of systems at the smallest mole fraction of larger spheres (x(A)=0.01) examined. A "fines effect" was observed at higher packing fractions, where adding smaller spheres to a system of large spheres decreases the viscosity of the mixture; this effect is not captured by the Enskog theory
Cationic exchange in nanosized ZnFe2O4 spinel revealed by experimental and simulated near-edge absorption structure
The non-equilibrium cation site occupancy in nanosized zinc ferrites (6-13
nm) with different degree of inversion (0.2 to 0.4) was investigated using Fe
and Zn K-edge x-ray absorption spectroscopy XANES and EXAFS, and magnetic
measurements. The very good agreement between experimental and ab-initio
calculations on the Zn K-edge XANES region clearly show the large
Zn2+(A)--Zn2+[B] transference that takes place in addition to the
well-identified Fe3+[B]--Fe3+(A) one, without altering the long-range
structural order. XANES spectra features as a function of the spinel inversion
were shown to depend on the configuration of the ligand shells surrounding the
absorbing atom. This XANES approach provides a direct way to sense cationic
inversion in these spinel compounds. We also demonstrated that a mechanical
crystallization takes place on nanocrystalline spinel that causes an increase
of both grain and magnetic sizes and, simultaneously, generates a significant
augment of the inversion.Comment: 5 pages, 5 eps figures, uses revtex4, corrected table
Lower bounds on dissipation upon coarse graining
By different coarse-graining procedures we derive lower bounds on the total
mean work dissipated in Brownian systems driven out of equilibrium. With
several analytically solvable examples we illustrate how, when, and where the
information on the dissipation is captured.Comment: 11 pages, 8 figure
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