1,155 research outputs found
Testing Born-Infeld electrodynamics in waveguides
Waveguides can be employed to test non-linear effects in electrodynamics. We
solve Born-Infeld equations for TE waves in a rectangular waveguide. We show
that the energy velocity acquires a dependence on the amplitude, and harmonic
components appear as a consequence of the non-linear behavior.Comment: 3 pages. To appear in PR
Plasmonic nanoparticle enhanced photocurrent in GaN/InGaN/GaN quantum well solar cells
We demonstrate enhanced external quantum efficiency and current-voltage characteristics due to scattering by 100 nm silver nanoparticles in a single 2.5 nm thick InGaN quantum well photovoltaic device. Nanoparticle arrays were fabricated on the surface of the device using an anodic alumina template masking process. The Ag nanoparticles increase light scattering, light trapping, and carrier collection in the III-N semiconductor layers leading to enhancement of the external quantum efficiency by up to 54%. Additionally, the short-circuit current in cells with 200 nm p-GaN emitter regions is increased by 6% under AM 1.5 illumination. AFORS-Het simulation software results were used to predict cell performance and optimize emitter layer thickness
Tunneling and delocalization in hydrogen bonded systems: a study in position and momentum space
Novel experimental and computational studies have uncovered the proton
momentum distribution in hydrogen bonded systems. In this work, we utilize
recently developed open path integral Car-Parrinello molecular dynamics
methodology in order to study the momentum distribution in phases of high
pressure ice. Some of these phases exhibit symmetric hydrogen bonds and quantum
tunneling. We find that the symmetric hydrogen bonded phase possesses a
narrowed momentum distribution as compared with a covalently bonded phase, in
agreement with recent experimental findings. The signatures of tunneling that
we observe are a narrowed distribution in the low-to-intermediate momentum
region, with a tail that extends to match the result of the covalently bonded
state. The transition to tunneling behavior shows similarity to features
observed in recent experiments performed on confined water. We corroborate our
ice simulations with a study of a particle in a model one-dimensional double
well potential that mimics some of the effects observed in bulk simulations.
The temperature dependence of the momentum distribution in the one-dimensional
model allows for the differentiation between ground state and mixed state
tunneling effects.Comment: 14 pages, 13 figure
The quantum algebra of superspace
We present the complete set of , quantum algebras associated to
massive superparticles. We obtain the explicit solution of these algebras
realized in terms of unconstrained operators acting on the Hilbert space of
superfields. These solutions are expressed using the chiral, anti-chiral and
tensorial projectors which define the three irreducible representations of the
supersymmetry on the superfields. In each case the space-time variables are
non-commuting and their commutators are proportional to the internal angular
momentum of the representation. The quantum algebra associated to the chiral or
the anti-chiral projector is the one obtained by the quantization of the
Casalbuoni-Brink-Schwarz (superspin 0) massive superparticle. We present a new
superparticle action for the (superspin 1/2) case and show that their wave
functions are the ones associated to the irreducible tensor multiplet.Comment: 20 pages;changes in the nomenclatur
Naive mean field approximation for image restoration
We attempt image restoration in the framework of the Baysian inference.
Recently, it has been shown that under a certain criterion the MAP (Maximum A
Posterior) estimate, which corresponds to the minimization of energy, can be
outperformed by the MPM (Maximizer of the Posterior Marginals) estimate, which
is equivalent to a finite-temperature decoding method. Since a lot of
computational time is needed for the MPM estimate to calculate the thermal
averages, the mean field method, which is a deterministic algorithm, is often
utilized to avoid this difficulty. We present a statistical-mechanical analysis
of naive mean field approximation in the framework of image restoration. We
compare our theoretical results with those of computer simulation, and
investigate the potential of naive mean field approximation.Comment: 9 pages, 11 figure
Housing prices and multiple employment nodes: is the relationship nonmonotonic?
Standard urban economic theory predicts that house prices will decline with distance from the central business district. Empirical results have been equivocal, however. Disjoints between theory and empirics may be due to a nonmonotonic relationship between house prices and access to employment arising from the negative externalities associated with proximity to multiple centres of employment. Based on data from Glasgow (Scotland), we use gravity-based measures of accessibility estimated using a flexible functional form that allows for nonmonotonicity. The results are thoroughly tested using recent advances in spatial econometrics. We find compelling evidence of a nonmonotonic effect in the accessibility measure and discuss the implications for planning and housing policy
Stability and Quasinormal Modes of Black holes in Tensor-Vector-Scalar theory: Scalar Field Perturbations
The imminent detection of gravitational waves will trigger precision tests of
gravity through observations of quasinormal ringing of black holes. While
General Relativity predicts just two polarizations of gravitational waves, the
so-called plus and cross polarizations, numerous alternative theories of
gravity predict up to six different polarizations which will potentially be
observed in current and future generations of gravitational wave detectors.
Bekenstein's Tensor-Vector-Scalar (TeVeS) theory and its generalization fall
into one such class of theory that predict the full gamut of six polarizations
of gravitational waves. In this paper we begin the study of quasinormal modes
(QNMs) in TeVeS by studying perturbations of the scalar field in a spherically
symmetric background. We show that, at least in the case where superluminal
propagation of perturbations is not present, black holes are generically stable
to this kind of perturbation. We also make a unique prediction that, as the
limit of the various coupling parameters of the theory tend to zero, the QNM
spectrum tends to times the QNM spectrum induced by scalar
perturbations of a Schwarzschild black hole in General Relativity due to the
intrinsic presence of the background vector field. We further show that the QNM
spectrum does not vary significantly from this value for small values of the
theory's coupling parameters, however can vary by as much as a few percent for
larger, but still physically relevant parameters.Comment: Published in Physical Review
Multi-State Image Restoration by Transmission of Bit-Decomposed Data
We report on the restoration of gray-scale image when it is decomposed into a
binary form before transmission. We assume that a gray-scale image expressed by
a set of Q-Ising spins is first decomposed into an expression using Ising
(binary) spins by means of the threshold division, namely, we produce (Q-1)
binary Ising spins from a Q-Ising spin by the function F(\sigma_i - m) = 1 if
the input data \sigma_i \in {0,.....,Q-1} is \sigma_i \geq m and 0 otherwise,
where m \in {1,....,Q-1} is the threshold value. The effects of noise are
different from the case where the raw Q-Ising values are sent. We investigate
which is more effective to use the binary data for transmission or to send the
raw Q-Ising values. By using the mean-field model, we first analyze the
performance of our method quantitatively. Then we obtain the static and
dynamical properties of restoration using the bit-decomposed data. In order to
investigate what kind of original picture is efficiently restored by our
method, the standard image in two dimensions is simulated by the mean-field
annealing, and we compare the performance of our method with that using the
Q-Ising form. We show that our method is more efficient than the one using the
Q-Ising form when the original picture has large parts in which the nearest
neighboring pixels take close values.Comment: latex 24 pages using REVTEX, 10 figures, 4 table
Policy-based management for body-sensor networks
Accepted versio
Active plasmonic devices and optical metamaterials
We studied active near-infrared metamaterials based on phase transition of vanadium oxide thin films, asymmetrically coupled split-ring resonators for narrowing resonance line-widths , field effect modulation of plasmon propagation and 3D single layer, plasmonic negative-index metamaterials
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