9,408 research outputs found
Hard thermal loops with a background plasma velocity
I consider the calculation of the two and three-point functions for QED at
finite temperature in the presence of a background plasma velocity. The final
expressions are consistent with Lorentz invariance, gauge invariance and
current conservation, pointing to a straightforward generalization of the hard
thermal loop formalism to this physical situation. I also give the resulting
expression for the effective action and identify the various terms.Comment: 11 pages, no figure
The transition to irreversibility in sheared suspensions: An analysis based on a mesoscopic entropy production
We study the shear-induced diffusion effect and the transition to
irreversibility in suspensions under oscillatory shear flow by performing an
analysis of the entropy production associated to the motion of the particles.
We show that the Onsager coupling between different contributions to the
entropy production is responsible for the scaling of the mean square
displacement on particle diameter and applied strain. We also show that the
shear-induced effective diffusion coefficient depends on the volume fraction
and use Lattice-Boltzmann simulations to characterize the effect through the
power spectrum of particle positions for different Reynolds numbers and volume
fractions. Our study gives a thermodynamic explanation of the the transition to
irreversibility through a pertinent analysis of the second law of
thermodynamics.Comment: 17 pages, 3 figures, paper submitted tp phys rev
The Electrodynamics of Inhomogeneous Rotating Media and the Abraham and Minkowski Tensors II: Applications
Applications of the covariant theory of drive-forms are considered for a
class of perfectly insulating media. The distinction between the notions of
"classical photons" in homogeneous bounded and unbounded stationary media and
in stationary unbounded magneto-electric media is pointed out in the context of
the Abraham, Minkowski and symmetrized Minkowski electromagnetic
stress-energy-momentum tensors. Such notions have led to intense debate about
the role of these (and other) tensors in describing electromagnetic
interactions in moving media. In order to address some of these issues for
material subject to the Minkowski constitutive relations, the propagation of
harmonic waves through homogeneous and inhomogeneous, isotropic plane-faced
slabs at rest is first considered. To motivate the subsequent analysis on
accelerating media two classes of electromagnetic modes that solve Maxwell's
equations for uniformly rotating homogeneous polarizable media are enumerated.
Finally it is shown that, under the influence of an incident monochromatic,
circularly polarized, plane electromagnetic wave, the Abraham and symmetrized
Minkowski tensors induce different time-averaged torques on a uniformly
rotating materially inhomogeneous dielectric cylinder. We suggest that this
observation may offer new avenues to explore experimentally the covariant
electrodynamics of more general accelerating media.Comment: 29 pages, 4 figures. Accepted for publication in Proc. Roy. Soc.
The Relationship Between Sociodemographics and Environmental Values Across Seven European Countries
Given the importance of environmental values (altruistic, biospheric, and egoistic) to pro-environmental behavior, it would be useful to segment the population – an approach known as market segmentation – to tailor pro-environmental messages more effectively. Sociodemographic variables are popular targets for segmentation, as such variables are often knowable in the absence of more nuanced information about individuals. However, evidence for the relationship between sociodemographics and environmental values is sparse, and contradictory. We examined the extent to which popular sociodemographic variables (gender, age, income, education, urbanization level, and political orientation) were predictive of environmental values for 11,820 participants across seven European countries. Overall, sociodemographics were hardly related to environmental values. Only gender and political orientation were weakly but significantly related to environmental values, whereby men and right-wingers showed weaker altruistic and biospheric, and stronger egoistic, values than women and left-wingers. We conclude that sociodemographic variables cannot be considered a suitable proxy for environmental values, and thus that behavior-change campaigns might be more impactful when focused on alternative segmentation strategies in relation to environmental aims
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
Energy conservation for dynamical black holes
An energy conservation law is described, expressing the increase in
mass-energy of a general black hole in terms of the energy densities of the
infalling matter and gravitational radiation. For a growing black hole, this
first law of black-hole dynamics is equivalent to an equation of Ashtekar &
Krishnan, but the new integral and differential forms are regular in the limit
where the black hole ceases to grow. An effective gravitational-radiation
energy tensor is obtained, providing measures of both ingoing and outgoing,
transverse and longitudinal gravitational radiation on and near a black hole.
Corresponding energy-tensor forms of the first law involve a preferred time
vector which plays the role for dynamical black holes which the stationary
Killing vector plays for stationary black holes. Identifying an energy flux,
vanishing if and only if the horizon is null, allows a division into
energy-supply and work terms, as in the first law of thermodynamics. The energy
supply can be expressed in terms of area increase and a newly defined surface
gravity, yielding a Gibbs-like equation, with a similar form to the so-called
first law for stationary black holes.Comment: 4 revtex4 pages. Many (mostly presentational) changes; emphasizes the
definition of gravitational radiation in the strong-field regim
Modes of Growth in Dynamic Systems
Regardless of a system's complexity or scale, its growth can be considered to
be a spontaneous thermodynamic response to a local convergence of down-gradient
material flows. Here it is shown how growth can be constrained to a few
distinct modes that depend on the availability of material and energetic
resources. These modes include a law of diminishing returns, logistic behavior
and, if resources are expanding very rapidly, super-exponential growth. For a
case where a system has a resolved sink as well as a source, growth and decay
can be characterized in terms of a slightly modified form of the predator-prey
equations commonly employed in ecology, where the perturbation formulation of
these equations is equivalent to a damped simple harmonic oscillator. Thus, the
framework presented here suggests a common theoretical under-pinning for
emergent behaviors in the physical and life sciences. Specific examples are
described for phenomena as seemingly dissimilar as the development of rain and
the evolution of fish stocks.Comment: 16 pages, 6 figures, including appendi
Statistical mechanics in the context of special relativity II
The special relativity laws emerge as one-parameter (light speed)
generalizations of the corresponding laws of classical physics. These
generalizations, imposed by the Lorentz transformations, affect both the
definition of the various physical observables (e.g. momentum, energy, etc), as
well as the mathematical apparatus of the theory. Here, following the general
lines of [Phys. Rev. E {\bf 66}, 056125 (2002)], we show that the Lorentz
transformations impose also a proper one-parameter generalization of the
classical Boltzmann-Gibbs-Shannon entropy. The obtained relativistic entropy
permits to construct a coherent and selfconsistent relativistic statistical
theory, preserving the main features of the ordinary statistical theory, which
recovers in the classical limit. The predicted distribution function is a
one-parameter continuous deformation of the classical Maxwell-Boltzmann
distribution and has a simple analytic form, showing power law tails in
accordance with the experimental evidence. Furthermore the new statistical
mechanics can be obtained as stationary case of a generalized kinetic theory
governed by an evolution equation obeying the H-theorem and reproducing the
Boltzmann equation of the ordinary kinetics in the classical limit.Comment: 14 pages, no figures, proof correction
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