5,843 research outputs found
A heat pump at a molecular scale controlled by a mechanical force
We show that a mesoscopic system such as Feynman's ratchet may operate as a
heat pump, and clarify a underlying physical picture. We consider a system of a
particle moving along an asymmetric periodic structure . When put into a
contact with two distinct heat baths of equal temperature, the system transfers
heat between two baths as the particle is dragged. We examine Onsager relation
for the heat flow and the particle flow, and show that the reciprocity
coefficient is a product of the characteristic heat and the diffusion constant
of the particle. The characteristic heat is the heat transfer between the baths
associated with a barrier-overcoming process. Because of the correlation
between the heat flow and the particle flow, the system can work as a heat pump
when the particle is dragged. This pump is particularly effective at molecular
scales where the energy barrier is of the order of the thermal energy.Comment: 7 pages, 5 figures; revise
Scale-dependent bias of galaxies and mu-type distortion of the cosmic microwave background spectrum from single-field inflation with a modified initial state
We investigate the phenomenological consequences of a modification of the
initial state of a single inflationary field. While single-field inflation with
the standard Bunch-Davies initial vacuum state does not generally produce a
measurable three-point function (bispectrum) in the squeezed configuration,
allowing for a non-standard initial state produces an exception. Here, we
calculate the signature of an initial state modification in single-field
slow-roll inflation in both the scale-dependent bias of the large-scale
structure (LSS) and mu-type distortion in the black-body spectrum of the cosmic
microwave background (CMB). We parametrize the initial state modifications and
identify certain choices of parameters as natural, though we also note some
fine-tuned choices that can yield a larger bispectrum. In both cases, we
observe a distinctive k^-3 signature in LSS (as opposed to k^-2 for the
local-form). As a non-zero bispectrum in the squeezed configuration correlates
a long-wavelength mode with two short-wavelength modes, it induces a
correlation between the CMB temperature anisotropy on large scales with the
temperature-anisotropy-squared on very small scales; this correlation persists
as the small-scale anisotropy-squared is processed into mu-type distortions.
While the local-form mu-distortion turns out to be too small to detect in the
near future, a modified initial vacuum state enhances the signal by a large
factor owing to an extra factor of k_1/k. For example, a proposed
absolutely-calibrated experiment, PIXIE, is expected to detect this correlation
with a signal-to-noise ratio greater than 10, for an occupation number of about
0.5 in the observable modes. Relatively calibrated experiments such as Planck
and LiteBIRD should also be able to measure this effect, provided that the
relative calibration between different frequencies meets the required
precision. (Abridged)Comment: 14 pages, 6 figures. Matches version in PRD. Improved explanation in
Sec. IV; added references and corrected typo
Relativistic stars with purely toroidal magnetic fields
We investigate the effects of the purely toroidal magnetic field on the
equilibrium structures of the relativistic stars. The master equations for
obtaining equilibrium solutions of relativistic rotating stars containing
purely toroidal magnetic fields are derived for the first time. To solve these
master equations numerically, we extend the Cook-Shapiro-Teukolsky scheme for
calculating relativistic rotating stars containing no magnetic field to
incorporate the effects of the purely toroidal magnetic fields. By using the
numerical scheme, we then calculate a large number of the equilibrium
configurations for a particular distribution of the magnetic field in order to
explore the equilibrium properties. We also construct the equilibrium sequences
of the constant baryon mass and/or the constant magnetic flux, which model the
evolution of an isolated neutron star as it loses angular momentum via the
gravitational waves. Important properties of the equilibrium configurations of
the magnetized stars obtained in this study are summarized as follows ; (1) For
the non-rotating stars, the matter distribution of the stars is prolately
distorted due to the toroidal magnetic fields. (2) For the rapidly rotating
stars, the shape of the stellar surface becomes oblate because of the
centrifugal force. But, the matter distribution deep inside the star is
sufficiently prolate for the mean matter distribution of the star to be
prolate. (3) The stronger toroidal magnetic fields lead to the mass-shedding of
the stars at the lower angular velocity. (4) For some equilibrium sequences of
the constant baryon mass and magnetic flux, the stars can spin up as they lose
angular momentum.Comment: 13 figures, 7 tables, submitted to PR
Hidden heat transfer in equilibrium states implies directed motion in nonequilibrium states
We study a class of heat engines including Feynman's ratchet, which exhibits
a directed motion of a particle in nonequilibrium steady states maintained by
two heat baths. We measure heat transfer from each heat bath separately, and
average them using a careful procedure that reveals the nature of the heat
transfer associated with directed steps of the particle. Remarkably we find
that steps are associated with nonvanishing heat transfer even in equilibrium,
and there is a quantitative relation between this ``hidden heat transfer'' and
the directed motion of the particle. This relation is clearly understood in
terms of the ``principle of heat transfer enhancement'', which is expected to
apply to a large class of highly nonequilibrium systems.Comment: 4 pages, 4 figures; revise
Kink Solution in a Fluid Model of Traffic Flows
Traffic jam in a fluid model of traffic flows proposed by Kerner and
Konh\"auser (B. S. Kerner and P. Konh\"auser, Phys. Rev. E 52 (1995), 5574.) is
analyzed. An analytic scaling solution is presented near the critical point of
the hetero-clinic bifurcation. The validity of the solution has been confirmed
from the comparison with the simulation of the model.Comment: RevTeX v3.1, 6 pages, and 2 figure
Non-axisymmetric oscillations of rapidly rotating relativistic stars by conformal flatness approximation
We present a new numerical code to compute non-axisymmetric eigenmodes of
rapidly rotating relativistic stars by adopting spatially conformally flat
approximation of general relativity. The approximation suppresses the radiative
degree of freedom of relativistic gravity and the field equations are cast into
a set of elliptic equations. The code is tested against the low-order f- and
p-modes of slowly rotating stars for which a good agreement is observed in
frequencies computed by our new code and those computed by the full theory.
Entire sequences of the low order counter-rotating f-modes are computed, which
are susceptible to an instability driven by gravitational radiation.Comment: 3 figures. To appear in Phys.Rev.
Leaf area index and topographical effects on turburlent diffusion in a deciduous forest
In order to investigate turbulent diffusion in a deciduous forest canopy, wind velocity
measurements were conducted from late autumn of 2009 to early spring of 2010, using an observation tower
20 m in height located in the campus of Kanazawa University. Four sonic anemometers mounted on the
tower recorded the average wind velocities and temperatures, as well as their fluctuations, at four different
heights simultaneously. Two different types of data sets were selected, in which the wind velocities, wind
bearings and atmospheric stabilities were all similar, but the Leaf Area Indexes (LAI's) were different.
Vertical profiles of average wind velocities were found to have an approximately exponential profile in each
case. The characteristic length scales of turbulence were evaluated by both von Karman's method and the
integral time scale deduced from the autocorrelation from time-series analyses. Both methods produced
comparable values of eddy diffusivity for the cases with some foliage during late autumn, but some
discrepancy in the upper canopy layer was observed when the trees did not have their leaves in early spring.
It was also found that the eddy diffusivities generally take greater values at higher positions, where the wind
speeds are large. Anisotropy of eddy diffusivities between the vertical and horizontal components was also
observed, particularly in the cases when the canopy does not have leaves, when the horizontal eddy
diffusivities are generally larger than the vertical ones. On the other hand, the anisotropy is less visible when
the trees have some foliage during autumn. The effects of topography on the turbulent diffusion were also
investigated, including evaluation of the non-zero time-averaged vertical wind velocities. The results show
that the effects are marginal for both cases, and can be neglected as far as diffusion in the canopy is
concerned
Entropy and Nonlinear Nonequilibrium Thermodynamic Relation for Heat Conducting Steady States
Among various possible routes to extend entropy and thermodynamics to
nonequilibrium steady states (NESS), we take the one which is guided by
operational thermodynamics and the Clausius relation. In our previous study, we
derived the extended Clausius relation for NESS, where the heat in the original
relation is replaced by its "renormalized" counterpart called the excess heat,
and the Gibbs-Shannon expression for the entropy by a new symmetrized
Gibbs-Shannon-like expression. Here we concentrate on Markov processes
describing heat conducting systems, and develop a new method for deriving
thermodynamic relations. We first present a new simpler derivation of the
extended Clausius relation, and clarify its close relation with the linear
response theory. We then derive a new improved extended Clausius relation with
a "nonlinear nonequilibrium" contribution which is written as a correlation
between work and heat. We argue that the "nonlinear nonequilibrium"
contribution is unavoidable, and is determined uniquely once we accept the
(very natural) definition of the excess heat. Moreover it turns out that to
operationally determine the difference in the nonequilibrium entropy to the
second order in the temperature difference, one may only use the previous
Clausius relation without a nonlinear term or must use the new relation,
depending on the operation (i.e., the path in the parameter space). This
peculiar "twist" may be a clue to a better understanding of thermodynamics and
statistical mechanics of NESS.Comment: 31 pages, 4 figure
An expression for stationary distribution in nonequilibrium steady state
We study the nonequilibrium steady state realized in a general stochastic
system attached to multiple heat baths and/or driven by an external force.
Starting from the detailed fluctuation theorem we derive concise and suggestive
expressions for the corresponding stationary distribution which are correct up
to the second order in thermodynamic forces. The probability of a microstate
is proportional to where
is the excess entropy change.
Here is the difference between two kinds of conditioned
path ensemble averages of excess heat transfer from the -th heat bath whose
inverse temperature is . Our expression may be verified experimentally
in nonequilibrium states realized, for example, in mesoscopic systems.Comment: 4 pages, 2 figure
Losing Weight: A KECK Spectroscopic Survey of the Massive Cluster of Galaxies RX J1347-1145
We present a sample of 47 spectroscopically confirmed members of RX
J1347-1145, the most luminous X-ray cluster of galaxies discovered to date.
With two exceptions, all the galaxies in this sample have red B-R colors and
red spectral indices, with spectra similar to old local ellipticals. Using all
47 cluster members, we derive a mean redshift of 0.4509\pm 0.003, and a
velocity dispersion of 910\pm130 km/sec, which corresponds to a virial mass of
4.4 x 10^{14} h^{-1} Solar masses with an harmonic radius of 380 h^{-1} kpc.
The derived total dynamical mass is marginally consistent with that deduced
from the cluster's X-ray emission based on the analysis of ROSAT/ASCA images
(Schindler et al. 1997), but not consistent with the more recent X-ray analyses
of Allen (2000), Ettori, Allen & Fabian (2001) and Allen, Schmidt & Fabian
(2002). Furthermore, the dynamical mass is significantly smaller than that
derived from weak lensing (Fischer & Tyson 1997) and from strong lensing (Sahu
et al. 1998). We propose that these various discrepant mass estimates may be
understood if RX J1347-1145 is the product of two clusters caught in the act of
merging in a direction perpendicular to the line of sight, although there is no
evidence from the galaxy redshift distribution supporting this hypothesis. Even
with this hypothesis, a significant part of the extremely high X-ray luminosity
must still arise from non-virialized, presumably shocked, gas. Finally, we
report the serendipitous discovery of a lensed background galaxy at z=4.083
which will put strong constraints on the lensing mass determination once its
counter-image is securely identified.Comment: Minor changes to conform to version accepted by Ap
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