1,582 research outputs found
Quasinormal Modes of Kerr Black Holes in Four and Higher Dimensions
We analytically calculate to leading order the asymptotic form of quasinormal
frequencies of Kerr black holes in four, five and seven dimensions. All the
relevant quantities can be explicitly expressed in terms of elliptical
integrals. In four dimensions, we confirm the results obtained by Keshest and
Hod by comparing the analytic results to the numerical ones.Comment: 14 pages, 7 figure
Quantum Stress Tensor Fluctuations and their Physical Effects
We summarize several aspects of recent work on quantum stress tensor
fluctuations and their role in driving fluctuations of the gravitational field.
The role of correlations and anticorrelations is emphasized. We begin with a
review of the properties of the stress tensor correlation function. We next
consider some illuminating examples of non-gravitational effects of stress
tensors fluctuations, specifically fluctuations of the Casimir force and
radiation pressure fluctuations. We next discuss passive fluctuations of
spacetime geometry and some of their operational signatures. These include
luminosity fluctuations, line broadening, and angular blurring of a source
viewed through a fluctuating gravitational field. Finally, we discuss the
possible role of quantum stress tensor fluctuations in the early universe,
especially in inflation. The fluctuations of the expansion of a congruence of
comoving geodesics grows during the inflationary era, due to non-cancellation
of anticorrelations that would have occurred in flat spacetime. This results in
subsequent non-Gaussian density perturbations and allows one to infer an upper
bound on the duration of inflation. This bound is consistent with adequate
inflation to solve the horizon and flatness problems.Comment: 15 pages, 1 figure; invited talk presented at the 3rd Mexican Meeting
on Experimental and Theoretical Physics, Mexico City, September 10-14, 200
Exact Master Equation and Quantum Decoherence of Two Coupled Harmonic Oscillators in a General Environment
In this paper we derive an exact master equation for two coupled quantum
harmonic oscillators interacting via bilinear coupling with a common
environment at arbitrary temperature made up of many harmonic oscillators with
a general spectral density function. We first show a simple derivation based on
the observation that the two-harmonic oscillator model can be effectively
mapped into that of a single harmonic oscillator in a general environment plus
a free harmonic oscillator. Since the exact one harmonic oscillator master
equation is available [Hu, Paz and Zhang, Phys. Rev. D \textbf{45}, 2843
(1992)], the exact master equation with all its coefficients for this two
harmonic oscillator model can be easily deduced from the known results of the
single harmonic oscillator case. In the second part we give an influence
functional treatment of this model and provide explicit expressions for the
evolutionary operator of the reduced density matrix which are useful for the
study of decoherence and disentanglement issues. We show three applications of
this master equation: on the decoherence and disentanglement of two harmonic
oscillators due to their interaction with a common environment under Markovian
approximation, and a derivation of the uncertainty principle at finite
temperature for a composite object, modeled by two interacting harmonic
oscillators. The exact master equation for two, and its generalization to ,
harmonic oscillators interacting with a general environment are expected to be
useful for the analysis of quantum coherence, entanglement, fluctuations and
dissipation of mesoscopic objects towards the construction of a theoretical
framework for macroscopic quantum phenomena.Comment: 35 pages, revtex, no figures, 2nd version, references added, to
appear in PR
Electromagnetic energy and energy flows in photonic crystals made of arrays of parallel dielectric cylinders
We consider the electromagnetic propagation in two-dimensional photonic
crystals, formed by parallel dielectric cylinders embedded a uniform medium.
The frequency band structure is computed using the standard plane-wave
expansion method, and the corresponding eigne-modes are obtained subsequently.
The optical flows of the eigen-modes are calculated by a direct computation
approach, and several averaging schemes of the energy current are discussed.
The results are compared to those obtained by the usual approach that employs
the group velocity calculation. We consider both the case in which the
frequency lies within passing band and the situation in which the frequency is
in the range of a partial bandgap. The agreements and discrepancies between
various averaging schemes and the group velocity approach are discussed in
detail. The results indicate the group velocity can be obtained by appropriate
averaging method.Comment: 23 pages, 5 figure
Trapping effects on inflation
We develop a Lagrangian approach based on the influence functional method so
as to derive self-consistently the Langevin equation for the inflaton field in
the presence of trapping points along the inflaton trajectory. The Langevin
equation exhibits the backreaction and the fluctuation-dissipation relation of
the trapping. The fluctuation is induced by a multiplicative colored noise that
can be identified as the the particle number density fluctuations and the
dissipation is a new effect that may play a role in the trapping with a strong
coupling. In the weak coupling regime, we calculate the power spectrum of the
noise-driven inflaton fluctuations for a single trapping point and studied its
variation with the trapping location. We also consider a case with closely
spaced trapping points and find that the resulting power spectrum is blue.Comment: 13 pages, 2 figure
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Neural plasticity in common forms of chronic headaches
Headaches are universal experiences and among the most common disorders. While headache may be physiological in the acute
setting, it can become a pathological and persistent condition.The mechanisms underlying the transition from episodic to chronic
pain have been the subject of intense study. Using physiological and imaging methods, researchers have identified a number of
different forms of neural plasticity associated with migraine and other headaches, including peripheral and central sensitization,
and alterations in the endogenous mechanisms of pain modulation. While these changes have been proposed to contribute to
headache and pain chronification, some findings are likely the results of repetitive noxious stimulation, such as atrophy of brain
areas involved in pain perception and modulation. In this review, we provide a narrative overview of recent advances on the
neuroimaging, electrophysiological and genetic aspects of neural plasticity associated with the most common forms of chronic
headaches, including migraine, cluster headache, tension-type headache, and medication overuse headache
Gender Determination using Fingerprint Features
Several previous studies have investigated the gender difference of the fingerprint features. However, regarding to the statistical significance of such differences, inconsistent results have been obtained. To resolve this problem and to develop a method for gender determination, this work proposes and tests three fingertip features for gender determination. Fingerprints were obtained from 115 normal healthy adults comprised of 57 male and 58 female volunteers. All persons were born in Taiwan and were of Han nationality. The age range was18-35 years. The features of this study are ridge count, ridge density, and finger size, all three of which can easily be determined by counting and calculation. Experimental results show that the tested ridge density features alone are not very effective for gender determination. However, the proposed ridge count and finger size features of left little fingers are useful, achieving a classification accuracy of 75% (P-valu
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