3,237 research outputs found
Statistical-mechanical theory of the overall magnetic properties of mesocrystals
The mesocrystal showing both electrorheological and magnetorheological
effects is called electro-magnetorheological (EMR) solids. Prediction of the
overall magnetic properties of the EMR solids is a challenging task due to the
coexistence of the uniaxially anisotropic behavior and structural transition as
well as long-range interaction between the suspended particles. To consider the
uniaxial anisotropy effect, we present an anisotropic Kirkwood-Fr\"{o}hlich
equation for calculating the effective permeabilities by adopting an explicit
characteristic spheroid rather than a characteristic sphere used in the
derivation of the usual Kirkwood-Fr\"{o}hlich equation. Further, by applying an
Ewald-Kornfeld formulation we are able to investigate the effective
permeability by including the structural transition and long-range interaction
explicitly. Our theory can reduce to the usual Kirkwood-Fr\"{o}hlich equation
and Onsager equation naturally. To this end, the numerical simulation shows the
validity of monitoring the structure of EMR solids by detecting their effective
permeabilities.Comment: 14 pages, 1 figur
Casimir Energies and Pressures for -function Potentials
The Casimir energies and pressures for a massless scalar field associated
with -function potentials in 1+1 and 3+1 dimensions are calculated. For
parallel plane surfaces, the results are finite, coincide with the pressures
associated with Dirichlet planes in the limit of strong coupling, and for weak
coupling do not possess a power-series expansion in 1+1 dimension. The relation
between Casimir energies and Casimir pressures is clarified,and the former are
shown to involve surface terms. The Casimir energy for a -function
spherical shell in 3+1 dimensions has an expression that reduces to the
familiar result for a Dirichlet shell in the strong-coupling limit. However,
the Casimir energy for finite coupling possesses a logarithmic divergence first
appearing in third order in the weak-coupling expansion, which seems
unremovable. The corresponding energies and pressures for a derivative of a
-function potential for the same spherical geometry generalizes the TM
contributions of electrodynamics. Cancellation of divergences can occur between
the TE (-function) and TM (derivative of -function) Casimir
energies. These results clarify recent discussions in the literature.Comment: 16 pages, 1 eps figure, uses REVTeX
Scattering-free plasmonic optics with anisotropic metamaterials
We develop an approach to utilize anisotropic metamaterials to solve one of
the fundamental problems of modern plasmonics -- parasitic scattering of
surface waves into free-space modes, opening the road to truly two-dimensional
plasmonic optics. We illustrate the developed formalism on examples of
plasmonic refractor and plasmonic crystal, and discuss limitations of the
developed technique and its possible applications for sensing and imaging
structures, high-performance mode couplers, optical cloaking structures, and
dynamically reconfigurable electro-plasmonic circuits
On the ground state energy for a penetrable sphere and for a dielectric ball
We analyse the ultraviolet divergencies in the ground state energy for a
penetrable sphere and a dielectric ball. We argue that for massless fields
subtraction of the ``empty space'' or the ``unbounded medium'' contribution is
not enough to make the ground state energy finite whenever the heat kernel
coefficient is not zero. It turns out that for a penetrable
sphere, a general dielectric background and the dielectric ball. To our
surprise, for more singular configurations, as in the presence of sharp
boundaries, the heat kernel coefficients behave to some extend better than in
the corresponding smooth cases, making, for instance, the dilute dielectric
ball a well defined problem.Comment: 18 pages, 1 figure, subm. to Phys. Rev.
Casimir Energy for a Spherical Cavity in a Dielectric: Applications to Sonoluminescence
In the final few years of his life, Julian Schwinger proposed that the
``dynamical Casimir effect'' might provide the driving force behind the
puzzling phenomenon of sonoluminescence. Motivated by that exciting suggestion,
we have computed the static Casimir energy of a spherical cavity in an
otherwise uniform material. As expected the result is divergent; yet a
plausible finite answer is extracted, in the leading uniform asymptotic
approximation. This result agrees with that found using zeta-function
regularization. Numerically, we find far too small an energy to account for the
large burst of photons seen in sonoluminescence. If the divergent result is
retained, it is of the wrong sign to drive the effect. Dispersion does not
resolve this contradiction. In the static approximation, the Fresnel drag term
is zero; on the mother hand, electrostriction could be comparable to the
Casimir term. It is argued that this adiabatic approximation to the dynamical
Casimir effect should be quite accurate.Comment: 23 pages, no figures, REVTe
Observability of the Bulk Casimir Effect: Can the Dynamical Casimir Effect be Relevant to Sonoluminescence?
The experimental observation of intense light emission by acoustically
driven, periodically collapsing bubbles of air in water (sonoluminescence) has
yet to receive an adequate explanation. One of the most intriguing ideas is
that the conversion of acoustic energy into photons occurs quantum
mechanically, through a dynamical version of the Casimir effect. We have argued
elsewhere that in the adiabatic approximation, which should be reliable here,
Casimir or zero-point energies cannot possibly be large enough to be relevant.
(About 10 MeV of energy is released per collapse.) However, there are
sufficient subtleties involved that others have come to opposite conclusions.
In particular, it has been suggested that bulk energy, that is, simply the
naive sum of , which is proportional to the volume, could
be relevant. We show that this cannot be the case, based on general principles
as well as specific calculations. In the process we further illuminate some of
the divergence difficulties that plague Casimir calculations, with an example
relevant to the bag model of hadrons.Comment: 13 pages, REVTe
Optical nonlinearity enhancement of graded metal-dielectric composite films
We have derived the local electric field inside graded metal-dielectric
composite films with weak nonlinearity analytically, which further yields the
effective linear dielectric constant and third-order nonlinear susceptibility
of the graded structures. As a result, the composition-dependent gradation can
produce a broad resonant plasmon band in the optical region, resulting in a
large enhancement of the optical nonlinearity and hence a large figure of
merit.Comment: 11 pages, 2 figures. To be published in Europhysics Letter
Analytic Perturbation Theory: A New Approach to the Analytic Continuation of the Strong Coupling Constant into the Timelike Region
The renormalization group applied to perturbation theory is ordinarily used
to define the running coupling constant in the spacelike region. However, to
describe processes with timelike momenta transfers, it is important to have a
self-consistent determination of the running coupling constant in the timelike
region. The technique called analytic perturbation theory (APT) allows a
consistent determination of this running coupling constant. The results are
found to disagree significantly with those obtained in the standard
perturbative approach. Comparison between the standard approach and APT is
carried out to two loops, and threshold matching in APT is applied in the
timelike region.Comment: 16 pages, REVTeX, 7 postscript figure
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