3,913 research outputs found
Casimir effect across a layered medium
Using nonstandard recursion relations for Fresnel coefficients involving
successive stacks of layers, we extend the Lifshitz formula to configurations
with an inhomogeneous, n-layered, medium separating two planar objects. The
force on each object is the sum of a Lifshitz like force and a force arising
from the inhomogeneity of the medium. The theory correctly reproduces very
recently obtained results for the Casimir force/energy in some simple systems
of this kind. As a by product, we obtain a formula for the force on an
(unspecified) stack of layers between two planar objects which generalizes our
previous result for the force on a slab in a planar cavity.Comment: 5 pages, 1 figure, presented at QFEXT1
Recursion relations for generalized Fresnel coefficients: Casimir force in a planar cavity
We emphasize and demonstrate that, besides using the usual recursion
relations involving successive layers, generalized Fresnel coefficients of a
multilayer can equivalently be calculated using the recursion relations
involving stacks of layers, as introduced some time ago [M. S. Tomas, Phys.
Rev. A 51, 2545 (1995)]. Moreover, since the definition of the generalized
Fresnel coefficients employed does not imply properties of the stacks, these
nonstandard recursion relations can be used to calculate Fresnel coefficients
not only for local systems but also for a general multilayer consisting of
various types (local, nonlocal, inhomogeneous etc.) of layers. Their utility is
illustrated by deriving a few simple algorithms for calculating the
reflectivity of a Bragg mirror and extending the formula for the Casimir force
in a planar cavity to arbitrary media.Comment: 5 pages, 2 figures, slightly expande
The scattering of a cylindrical invisibility cloak: reduced parameters and optimization
We investigate the scattering of 2D cylindrical invisibility cloaks with
simplified constitutive parameters with the assistance of scattering
coefficients. We show that the scattering of the cloaks originates not only
from the boundary conditions but also from the spatial variation of the
component of permittivity/permeability. According to our formulation, we
propose some restrictions to the invisibility cloak in order to minimize its
scattering after the simplification has taken place. With our theoretical
analysis, it is possible to design a simplified cloak by using some peculiar
composites like photonic crystals (PCs) which mimic an effective refractive
index landscape rather than offering effective constitutives, meanwhile
canceling the scattering from the inner and outer boundaries.Comment: Accepted for J. Phys.
Theoretical framework of entangled-photon generation from biexcitons in nano-to-bulk crossover regime with planar geometry
We have constructed a theoretical framework of the biexciton-resonant
hyperparametric scattering for the pursuit of high-power and high-quality
generation of entangled photon pairs. Our framework is applicable to
nano-to-bulk crossover regime where the center-of-mass motion of excitons and
biexcitons is confined. Material surroundings and the polarization correlation
of generated photons can be considered. We have analyzed the entangled-photon
generation from CuCl film, by which ultraviolet entangled-photon pairs are
generated, and from dielectric microcavity embedding a CuCl layer. We have
revealed that in the nano-to-bulk crossover regime we generally get a high
performance from the viewpoint of statistical accuracy, and the generation
efficiency can be enhanced by the optical cavity with maintaining the high
performance. The nano-to-bulk crossover regime has a variety of degrees of
freedom to tune the entangled-photon generation, and the scattering spectra
explicitly reflect quantized exciton-photon coupled modes in the finite
structure.Comment: 18 pages, 10 figure
Dissipation in intercluster plasma
We discuss dissipative processes in strongly gyrotropic, nearly collisionless
plasma in clusters of galaxies (ICM). First, we point out that Braginsky
theory, which assumes that collisions are more frequent that the system's
dynamical time scale, is inapplicable to fast, sub-viscous ICM motion. Most
importantly, the electron contribution to collisional magneto-viscosity
dominates over that of ions for short-scale Alfvenic motions. Thus, if a
turbulent cascade develops in the ICM and propagates down to scales
kpc, it is damped collisionally not on ions, but on electrons. Second, in high
beta plasma of ICM, small variations of the magnetic field strength, of
relative value , lead to development of anisotropic pressure
instabilities (firehose, mirror and cyclotron). Unstable wave modes may provide
additional resonant scattering of particles, effectively keeping the plasma in
a state of marginal stability. We show that in this case the dissipation rate
of a laminar, subsonic, incompressible flows scales as inverse of plasma beta
parameter. We discuss application to the problem of ICM heating.Comment: 4 pages, accepted by ApJ Let
Shearing Box Simulations of the MRI in a Collisionless Plasma
We describe local shearing box simulations of turbulence driven by the
magnetorotational instability (MRI) in a collisionless plasma. Collisionless
effects may be important in radiatively inefficient accretion flows, such as
near the black hole in the Galactic Center. The MHD version of ZEUS is modified
to evolve an anisotropic pressure tensor. A fluid closure approximation is used
to calculate heat conduction along magnetic field lines. The anisotropic
pressure tensor provides a qualitatively new mechanism for transporting angular
momentum in accretion flows (in addition to the Maxwell and Reynolds stresses).
We estimate limits on the pressure anisotropy due to pitch angle scattering by
kinetic instabilities. Such instabilities provide an effective ``collision''
rate in a collisionless plasma and lead to more MHD-like dynamics. We find that
the MRI leads to efficient growth of the magnetic field in a collisionless
plasma, with saturation amplitudes comparable to those in MHD. In the saturated
state, the anisotropic stress is comparable to the Maxwell stress, implying
that the rate of angular momentum transport may be moderately enhanced in a
collisionless plasma.Comment: 20 pages, 9 figures, submitted to Ap
Computation and visualization of Casimir forces in arbitrary geometries: non-monotonic lateral forces and failure of proximity-force approximations
We present a method of computing Casimir forces for arbitrary geometries,
with any desired accuracy, that can directly exploit the efficiency of standard
numerical-electromagnetism techniques. Using the simplest possible
finite-difference implementation of this approach, we obtain both agreement
with past results for cylinder-plate geometries, and also present results for
new geometries. In particular, we examine a piston-like problem involving two
dielectric and metallic squares sliding between two metallic walls, in two and
three dimensions, respectively, and demonstrate non-additive and non-monotonic
changes in the force due to these lateral walls.Comment: Accepted for publication in Physical Review Letters. (Expected
publication: Vol. 99 (8) 2007
Augmented EPA with augmented EFIE method for packaging analysis
It is evident that the low frequency full wave electromagnetic modelling is necessary for IC packaging analysis. Considering the complexity, it is very difficult to solve the whole problem directly. Even though the domain decomposition method is a legitimate approach for these types of problems, the domain decomposition method based on the equivalence principle has the low frequency breakdown issue. In this paper, we developed a low frequency augmented equivalence principle algorithm (AEPA) with the augmented electric field integral equation (AEFIE) for packaging and IC analysis. On the equivalence surfaces, not only the electric current and the magnetic current, but also the electric charge and the magnetic charge are used to capture the low frequency couplings. Inside each AEPA box, AEFIE is applied to maintain the low frequency accuracy. As a result, we are able to solve low frequency domain decomposition problems and apply it to IC packaging analysis.published_or_final_versionThe 2010 IEEE Electrical Design of Advanced Packaging & Systems Symposium (EDAPS), Singapore, 7-9 December 2010. In Proceedings of EDAPS, 2010, p. 1-
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