7,638 research outputs found
Macroscopic Expression Connecting the Rate of Energy Dissipation and Violation of the Fluctuation-Response Relation
A direct connection between the magnitude of the violation of the
fluctuation-response relation (FRR) and the rate of energy dissipation is
presented in terms of field variables of nonequilibrium systems. Here, we
consider the density field of a colloidal suspension either in a relaxation
process or in a nonequilibrium steady state driven by an external field. Using
a path-integral representation of the temporal evolution of the density field,
we find an equality that relates the magnitude of the violation of the FRR for
scalar and vector potentials of the velocity field to the rate of energy
dissipation for the entire system. Our result demonstrates that the violation
of the FRR for field variables captures the entropic component of the
dissipated free energy.Comment: 4 pages, a major reviso
Sublattice Asymmetric Reductions of Spin Values on Stacked Triangular Lattice Antiferromagnet CsCoBr
We study the reductions of spin values of the ground state on a stacked
triangular antiferromagnet using the spin-wave approach. We find that the spin
reductions have sublattice asymmetry due to the cancellation of the molecular
field. The sublattice asymmetry qualitatively analyzes the NMR results of
CsCoBr.Comment: 5pages, 5figure
Sum rule for response function in nonequilibrium Langevin systems
We derive general properties of the linear response functions of
nonequilibrium steady states in Langevin systems. These correspond to extension
of the results which were recently found in Hamiltonian systems [A. Shimizu and
T. Yuge, J. Phys. Soc. Jpn. {\bf 79}, 013002 (2010)]. We discuss one of the
properties, the sum rule for the response function, in particular detail. We
show that the sum rule for the response function of the velocity holds in the
underdamped case, whereas it is violated in the overdamped case. This implies
that the overdamped Langevin models should be used with great care. We also
investigate the relation of the sum rule to an equality on the energy
dissipation in nonequilibrium Langevin systems, which was derived by Harada and
Sasa.Comment: 8 page
Super and Sub-Poissonian photon statistics for single molecule spectroscopy
We investigate the distribution of the number of photons emitted by a single
molecule undergoing a spectral diffusion process and interacting with a
continuous wave laser field. The spectral diffusion is modeled based on a
stochastic approach, in the spirit of the Anderson-Kubo line shape theory.
Using a generating function formalism we solve the generalized optical Bloch
equations, and obtain an exact analytical formula for the line shape and
Mandel's Q parameter. The line shape exhibits well known behaviors, including
motional narrowing when the stochastic modulation is fast, and power
broadening. The Mandel parameter, describing the line shape fluctuations,
exhibits a transition from a Quantum sub-Poissonian behavior in the fast
modulation limit, to a classical super-Poissonian behavior found in the slow
modulation limit. Our result is applicable for weak and strong laser field,
namely for arbitrary Rabi frequency. We show how to choose the Rabi frequency
in such a way that the Quantum sub-Poissonian nature of the emission process
becomes strongest. A lower bound on is found, and simple limiting behaviors
are investigated. A non-trivial behavior is obtained in the intermediate
modulation limit, when the time scales for spectral diffusion and the life time
of the excited state, become similar. A comparison is made between our results,
and previous ones derived based on the semi-classical generalized
Wiener--Khintchine theorem.Comment: 14 Phys. Rev style pages, 10 figure
Generating extremal neutrino mixing angles with Higgs family symmetries
The existence of maximal and minimal mixing angles in the neutrino mixing
matrix motivates the search for extensions to the Standard Model that may
explain these angles. A previous study (C.I.Low and R.R.Volkas,
Phys.Rev.D68,033007(2003)), began a systematic search to find the minimal
extension to the Standard Model that explains these mixing angles. It was found
that in the minimal extensions to the Standard Model which allow neutrino
oscillations, discrete unbroken lepton family symmetries only generate neutrino
mixing matrices that are ruled out by experiment. This paper continues the
search by investigating all models with two or more Higgs doublets, and an
Abelian family symmetry. It is found that discrete Abelian family symmetries
permit, but cannot explain, maximal atmospheric mixing, however these models
can ensure theta_{13}=0.Comment: Minor modifications, references added, typos corrected. LaTeX, 16
page
Analysis of f-p model for octupole ordering in NpO2
In order to examine the origin of octupole ordering in NpO2, we propose a
microscopic model constituted of neptunium 5f and oxygen 2p orbitals. To study
multipole ordering, we derive effective multipole interactions from the f-p
model by using the fourth-order perturbation theory in terms of p-f hopping
integrals. Analyzing the effective model numerically, we find a tendency toward
\Gamma_{5u} antiferro-octupole ordering.Comment: 4 pages, 3 figure
Incipient order in the t-J model at high temperatures
We analyze the high-temperature behavior of the susceptibilities towards a
number of possible ordered states in the t-J-V model using the high-temperature
series expansion. From all diagrams with up to ten edges, reliable results are
obtained down to temperatures of order J, or (with some optimism) to J/2. In
the unphysical regime, t<J, large superconducting susceptibilities are found,
which moreover increase with decreasing temperatures, but for t>J, these
susceptibilities are small and decreasing with decreasing temperature; this
suggests that the t-J model does not support high-temperature
superconductivity. We also find modest evidence of a tendency toward nematic
and d-density wave orders.
ERRATUM: Due to an error in the calculation, the series for d-wave
supeconducting and extended s-wave superconducting orders were incorrect. We
recalculate the series and give the replacement figures. In agreement with our
earlier findings, we still find no evidence of any strong enhancement of the
superconducting susceptibility with decreasing temperature. However, because
different Pade approximants diverge from each other at somewhat higher
temperatures than we originally found, it is less clear what this implies
concerning the presence or absence of high-temperature superconductivity in the
t-J model.Comment: 4 pages, 5 eps figures included; ERRATUM 2 pages, 3 eps figures
correcting the error in the series for superconducting susceptibilitie
Granular Scale Magnetic Flux Cancellations in the Photosphere
We investigate the evolution of 5 granular-scale magnetic flux cancellations
just outside the moat region of a sunspot by using accurate spectropolarimetric
measurements and G-band images with the Solar Optical Telescope aboard Hinode.
The opposite polarity magnetic elements approach a junction of the
intergranular lanes and then they collide with each other there. The
intergranular junction has strong red shifts, darker intensities than the
regular intergranular lanes, and surface converging flows. This clearly
confirms that the converging and downward convective motions are essential for
the approaching process of the opposite-polarity magnetic elements. However,
motion of the approaching magnetic elements does not always match with their
surrounding surface flow patterns in our observations. This suggests that, in
addition to the surface flows, subsurface downward convective motions and
subsurface magnetic connectivities are important for understanding the approach
and collision of the opposite polarity elements observed in the photosphere. We
find that the horizontal magnetic field appears between the canceling opposite
polarity elements in only one event. The horizontal fields are observed along
the intergranular lanes with Doppler red shifts. This cancellation is most
probably a result of the submergence (retraction) of low-lying photospheric
magnetic flux. In the other 4 events, the horizontal field is not observed
between the opposite polarity elements at any time when they approach and
cancel each other. These approaching magnetic elements are more concentrated
rather than gradually diffused, and they have nearly vertical fields even while
they are in contact each other. We thus infer that the actual flux cancellation
is highly time dependent events at scales less than a pixel of Hinode SOT
(about 200 km) near the solar surface.Comment: Accepted for publication in the Astrophysical Journa
A statistical mechanics model for free-for-all airplane passenger boarding
I present and discuss a model for the free-for-all passenger boarding which
is employed by some discount air carriers. The model is based on the principles
of statistical mechanics where each seat in the aircraft has an associated
energy which reflects the preferences of the population of air travelers. As
each passenger enters the airplane they select their seats using Boltzmann
statistics, proceed to that location, load their luggage, sit down, and the
partition function seen by remaining passengers is modified to reflect this
fact. I discuss the various model parameters and make qualitative comparisons
of this passenger boarding model with models which involve assigned seats. This
model can also be used to predict the probability that certain seats will be
occupied at different times during the boarding process. These results may be
of value to industry professionals as a useful description of this boarding
method. However, it also has significant value as a pedagogical tool since it
is a relatively unusual application of undergraduate level physics and it
describes a situation with which many students and faculty may be familiar.Comment: version 1: 4 pages 2 figures version 2: 7 pages with 5 figure
Quantum scalar field in D-dimensional static black hole space-times
An Euclidean approach for investigating quantum aspects of a scalar field
living on a class of D-dimensional static black hole space-times, including the
extremal ones, is reviewed. The method makes use of a near horizon
approximation of the metric and -function formalism for evaluating the
partition function and the expectation value of the field fluctuations
. After a review of the non-extreme black hole case, the extreme
one is considered in some details. In this case, there is no conical
singularity, but the finite imaginary time compactification introduces a cusp
singularity. It is found that the -function regularized partition
function can be defined, and the quantum fluctuations are finite on the
horizon, as soon as the cusp singularity is absent, and the corresponding
temperature is T=0.Comment: 9 pages, LaTe
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