8,037 research outputs found
Surface plasmon polariton propagation around bends at a metal-dielectric interface
We analyze theoretically the propagation of surface plasmon polaritons about
a metallic corner with a finite bend radius, using a one-dimensional model
analogous to the scattering from a finite-depth potential well. We obtain
expressions for the energy reflection and transmission coefficients in the
short wavelength limit, as well as an upper bound for the transmittance. In
certain cases we find that propagation on non-planar interfaces may result in
lower losses than on flat surfaces, contrary to expectation. In addition, we
also find that the maximum transmittance depends non-monotonously on the bend
radius, allowing increased transmission with decreasing radius.Comment: For higher-quality figures, see
http://darkwing.uoregon.edu/~noeckel/papers.php#xref2
Classical small systems coupled to finite baths
We have studied the properties of a classical -body system coupled to a
bath containing -body harmonic oscillators, employing an model
which is different from most of the existing models with . We have
performed simulations for -oscillator systems, solving
first-order differential equations with and , in order to calculate the time-dependent energy exchange between the
system and the bath. The calculated energy in the system rapidly changes while
its envelope has a much slower time dependence. Detailed calculations of the
stationary energy distribution of the system (: an energy per
particle in the system) have shown that its properties are mainly determined by
but weakly depend on . The calculated is analyzed with the
use of the and - distributions: the latter is derived with
the superstatistical approach (SSA) and microcanonical approach (MCA) to the
nonextensive statistics, where stands for the entropic index. Based on
analyses of our simulation results, a critical comparison is made between the
SSA and MCA. Simulations have been performed also for the -body ideal-gas
system. The effect of the coupling between oscillators in the bath has been
examined by additional () models which include baths consisting of
coupled linear chains with periodic and fixed-end boundary conditions.Comment: 30 pages, 16 figures; the final version accepted in Phys. Rev.
Curvature-induced radiation of surface plasmon polaritons propagating around bends
We present a theoretical study of the curvature-induced radiation of surface
plasmon polaritons (SPPs) propagating around bends at metal-dielectric
interfaces. We explain qualitatively how the curvature leads to distortion of
the phase front, causing the fields to radiate energy away from the
metal-dielectric interface. We then quantify, both analytically and
numerically, radiation losses and energy transmission efficiencies of SPPs
propagating around bends with varying radii- as well as sign-of-curvature.Comment: 9 pages, 8 figures, submitted to Physical Review
Proton-neutron alignment in the yrast states of Ge and Ge
The Ge and Ge nuclei are studied by means of the shell model
with the extended Hamiltonian, which succeeds in reproducing
experimentally observed energy levels, moments of inertia and other properties.
The investigation using the reliable wave-functions predicts T=0, J=9
one-proton-one-neutron () alignment in the orbit, at high spins
(, and ) in these even-even nuclei. It
is shown that a series of the even- positive-parity yrast states (observed
up to for Ge) consists of the ground-state band and successive
three bands with different types of particle alignments (two-neutron, ,
two-proton-two-neutron) in the orbit.Comment: 4 pages, 5 figures, to be published in Pyhs. Rev.
An augmented moment method for stochastic ensembles with delayed couplings: I. Langevin model
By employing a semi-analytical dynamical mean-field approximation theory
previously proposed by the author [H. Hasegawa, Phys. Rev. E {\bf 67}, 041903
(2003)], we have developed an augmented moment method (AMM) in order to discuss
dynamics of an -unit ensemble described by linear and nonlinear Langevin
equations with delays. In AMM, original -dimensional {\it stochastic} delay
differential equations (SDDEs) are transformed to infinite-dimensional {\it
deterministic} DEs for means and correlations of local as well as global
variables. Infinite-order DEs arising from the non-Markovian property of SDDE,
are terminated at the finite level in the level- AMM (AMM), which
yields -dimensional deterministic DEs. Model calculations have been made
for linear and nonlinear Langevin models. The stationary solution of AMM for
the linear Langevin model with N=1 is nicely compared to the exact result. The
synchronization induced by an applied single spike is shown to be enhanced in
the nonlinear Langevin ensemble with model parameters locating at the
transition between oscillating and non-oscillating states. Results calculated
by AMM6 are in good agreement with those obtained by direct simulations.Comment: 18 pages, 3 figures, changed the title with re-arranged figures,
accepted in Phys. Rev. E with some change
An augmented moment method for stochastic ensembles with delayed couplings: II. FitzHugh-Nagumo model
Dynamics of FitzHugh-Nagumo (FN) neuron ensembles with time-delayed couplings
subject to white noises, has been studied by using both direct simulations and
a semi-analytical augmented moment method (AMM) which has been proposed in a
recent paper [H. Hasegawa, E-print: cond-mat/0311021]. For -unit FN neuron
ensembles, AMM transforms original -dimensional {\it stochastic} delay
differential equations (SDDEs) to infinite-dimensional {\it deterministic} DEs
for means and correlation functions of local and global variables.
Infinite-order recursive DEs are terminated at the finite level in the
level- AMM (AMM), yielding -dimensional deterministic DEs. When a
single spike is applied, the oscillation may be induced if parameters of
coupling strength, delay, noise intensity and/or ensemble size are appropriate.
Effects of these parameters on the emergence of the oscillation and on the
synchronization in FN neuron ensembles have been studied. The synchronization
shows the {\it fluctuation-induced} enhancement at the transition between
non-oscillating and oscillating states. Results calculated by AMM5 are in
fairly good agreement with those obtained by direct simulations.Comment: 15 pages, 3 figures; changed the title with correcting typos,
accepted in Phys. Rev. E with some change
Theory of Magnetic Short--Range Order for High-T_c Superconductors
A theory of magnetic short--range order for high-- cuprates is presented
on the basis of the one--band ----Hubbard model combining the
four--field slave--boson functional integral technique with the Bethe cluster
method. The ground--state phase diagram evaluated self--consistently at the
saddle--point and pair--approximation levels shows the experimentally observed
suppression of magnetic long--range order in the favour of a paraphase with
antiferromagnetic short--range order. In this phase the uniform static spin
susceptibility consists of interrelated itinerant and local parts and increases
upon doping up to the transition to the Pauli paraphase. Using realistic values
of the Hubbard interaction we obtain the cusp position and the doping
dependence of the zero--temperature susceptibility in reasonable agreement with
experiments on .Comment: 3 pages, 2 Postscript figure, Proc. Int. Conf. SCES Zuerich
Switzerland Aug. 96, to appear in Physica
Monte Carlo simulations of pulse propagation in massive multichannel optical fiber communication systems
We study the combined effect of delayed Raman response and bit pattern
randomness on pulse propagation in massive multichannel optical fiber
communication systems. The propagation is described by a perturbed stochastic
nonlinear Schr\"odinger equation, which takes into account changes in pulse
amplitude and frequency as well as emission of continuous radiation. We perform
extensive numerical simulations with the model, and analyze the dynamics of the
frequency moments, the bit-error-rate, and the mutual distribution of amplitude
and position. The results of our numerical simulations are in good agreement
with theoretical predictions based on the adiabatic perturbation approach.Comment: Submitted to Physical Review E. 8 pages, 5 figure
Optimal reconstruction of magnetopause structures from Cluster data
The Grad-Shafranov (GS) reconstruction technique, a single-spacecraft based data analysis method for recovering approximately two-dimensional (2-D) magnetohydrostatic plasma/field structures in space, is improved to become a multi-spacecraft technique that produces a single field map by ingesting data from all four Cluster spacecraft into the calculation. The plasma pressure, required for the technique, is measured in high time resolution by only two of the spacecraft, C1 and C3, but, with the help of spacecraft potential measurements available from all four spacecraft, the pressure can be estimated at the other spacecraft as well via a relationship, established from C1 and C3 data, between the pressure and the electron density deduced from the potentials. Consequently, four independent field maps, one for each spacecraft, can be reconstructed and then merged into a single map. The resulting map appears more accurate than the individual single-spacecraft based ones, in the sense that agreement between magnetic field variations predicted from the map to occur at each of the four spacecraft and those actually measured is significantly better. Such a composite map does not satisfy the GS equation any more, but is optimal under the constraints that the structures are 2-D and time-independent. Based on the reconstruction results, we show that, even on a scale of a few thousand km, the magnetopause surface is usually not planar, but has significant curvature, often with intriguing meso-scale structures embedded in the current layer, and that the thickness of both the current layer and the boundary layer attached to its earthward side can occasionally be larger than 3000km
Optimal reconstruction of magnetopause structures from Cluster data
The Grad-Shafranov (GS) reconstruction tech- nique, a single-spacecraft based data analysis method for recovering approximately two-dimensional (2-D) magneto- hydrostatic plasma/field structures in space, is improved to become a multi-spacecraft technique that produces a single field map by ingesting data from all four Cluster spacecraft into the calculation. The plasma pressure, required for the technique, is measured in high time resolution by only two of the spacecraft, C1 and C3, but, with the help of spacecraft po- tential measurements available from all four spacecraft, the pressure can be estimated at the other spacecraft as well via a relationship, established from C1 and C3 data, between the pressure and the electron density deduced from the poten- tials. Consequently, four independent field maps, one for each spacecraft, can be reconstructed and then merged into a single map. The resulting map appears more accurate than the individual single-spacecraft based ones, in the sense that agreement between magnetic field variations predicted from the map to occur at each of the four spacecraft and those actually measured is significantly better. Such a composite map does not satisfy the GS equation any more, but is op- timal under the constraints that the structures are 2-D and time-independent. Based on the reconstruction results, we show that, even on a scale of a few thousand km, the magne- topause surface is usually not planar, but has significant cur- vature, often with intriguing meso-scale structures embedded in the current layer, and that the thickness of both the current layer and the boundary layer attached to its earthward side can occasionally be larger than 3000 km
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