10,250 research outputs found
Flame sprayed dielectric coatings improve heat dissipation in electronic packaging
Heat sinks in electronic packaging can be flame sprayed with dielectric coatings of alumina or beryllia and finished off with an organic sealer to provide high heat and electrical resistivity
Depolarization volume and correlation length in the homogenization of anisotropic dielectric composites
In conventional approaches to the homogenization of random particulate
composites, both the distribution and size of the component phase particles are
often inadequately taken into account. Commonly, the spatial distributions are
characterized by volume fraction alone, while the electromagnetic response of
each component particle is represented as a vanishingly small depolarization
volume. The strong-permittivity-fluctuation theory (SPFT) provides an
alternative approach to homogenization wherein a comprehensive description of
distributional statistics of the component phases is accommodated. The
bilocally-approximated SPFT is presented here for the anisotropic homogenized
composite which arises from component phases comprising ellipsoidal particles.
The distribution of the component phases is characterized by a two-point
correlation function and its associated correlation length. Each component
phase particle is represented as an ellipsoidal depolarization region of
nonzero volume. The effects of depolarization volume and correlation length are
investigated through considering representative numerical examples. It is
demonstrated that both the spatial extent of the component phase particles and
their spatial distributions are important factors in estimating coherent
scattering losses of the macroscopic field.Comment: Typographical error in eqn. 16 in WRM version is corrected in arxiv
versio
Towards gravitationally assisted negative refraction of light by vacuum
Propagation of electromagnetic plane waves in some directions in
gravitationally affected vacuum over limited ranges of spacetime can be such
that the phase velocity vector casts a negative projection on the time-averaged
Poynting vector. This conclusion suggests, inter alia, gravitationally assisted
negative refraction by vacuum.Comment: 6 page
Depolarization regions of nonzero volume in bianisotropic homogenized composites
In conventional approaches to the homogenization of random particulate
composites, the component phase particles are often treated mathematically as
vanishingly small, point-like entities. The electromagnetic responses of these
component phase particles are provided by depolarization dyadics which derive
from the singularity of the corresponding dyadic Green functions. Through
neglecting the spatial extent of the depolarization region, important
information may be lost, particularly relating to coherent scattering losses.
We present an extension to the strong-property-fluctuation theory in which
depolarization regions of nonzero volume and ellipsoidal geometry are
accommodated. Therein, both the size and spatial distribution of the component
phase particles are taken into account. The analysis is developed within the
most general linear setting of bianisotropic homogenized composite mediums
(HCMs). Numerical studies of the constitutive parameters are presented for
representative examples of HCM; both Lorentz-reciprocal and
Lorentz-nonreciprocal HCMs are considered. These studies reveal that estimates
of the HCM constitutive parameters in relation to volume fraction, particle
eccentricity, particle orientation and correlation length are all significantly
influenced by the size of the component phase particles
Scattering loss in electro-optic particulate composite materials
The effective permittivity dyadic of a composite material containing
particulate constituent materials with one constituent having the ability to
display the Pockels effect is computed, using an extended version of the
strong-permittivity-fluctuation theory which takes account of both the
distributional statistics of the constituent particles and their sizes.
Scattering loss, thereby incorporated in the effective electromagnetic response
of the homogenized composite material, is significantly affected by the
application of a low-frequency (dc) electric field
Robust and Efficient Sifting-Less Quantum Key Distribution Protocols
We show that replacing the usual sifting step of the standard
quantum-key-distribution protocol BB84 by a one-way reverse reconciliation
procedure increases its robustness against photon-number-splitting (PNS)
attacks to the level of the SARG04 protocol while keeping the raw key-rate of
BB84. This protocol, which uses the same state and detection than BB84, is the
m=4 member of a protocol-family using m polarization states which we introduce
here. We show that the robustness of these protocols against PNS attacks
increases exponentially with m, and that the effective keyrate of optimized
weak coherent pulses decreases with the transmission T like T^{1+1/(m-2)}
Testing Error Correcting Codes by Multicanonical Sampling of Rare Events
The idea of rare event sampling is applied to the estimation of the
performance of error-correcting codes. The essence of the idea is importance
sampling of the pattern of noises in the channel by Multicanonical Monte Carlo,
which enables efficient estimation of tails of the distribution of bit error
rate. The idea is successfully tested with a convolutional code
Surface disinfection challenges for Candida auris: an in-vitro study
The emerging pathogenic multidrug-resistant yeast Candida auris is an important source of healthcare-associated infections and of growing global clinical concern. The ability of this organism to survive on surfaces and withstand environmental stressors creates a challenge for eradicating it from hospitals. A panel of C. auris clinical isolates was evaluated on different surface environments against the standard disinfectant sodium hypochlorite and high-level disinfectant peracetic acid. C. auris was shown to selectively tolerate clinically relevant concentrations of sodium hypochlorite and peracetic acid in a surface-dependent manner, which may explain its ability to successfully persist within the hospital environment
Justification of the coupled-mode approximation for a nonlinear elliptic problem with a periodic potential
Coupled-mode systems are used in physical literature to simplify the
nonlinear Maxwell and Gross-Pitaevskii equations with a small periodic
potential and to approximate localized solutions called gap solitons by
analytical expressions involving hyperbolic functions. We justify the use of
the one-dimensional stationary coupled-mode system for a relevant elliptic
problem by employing the method of Lyapunov--Schmidt reductions in Fourier
space. In particular, existence of periodic/anti-periodic and decaying
solutions is proved and the error terms are controlled in suitable norms. The
use of multi-dimensional stationary coupled-mode systems is justified for
analysis of bifurcations of periodic/anti-periodic solutions in a small
multi-dimensional periodic potential.Comment: 18 pages, no figure
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