1,361 research outputs found
Electromagnetic Boundary Conditions Defined in Terms of Normal Field Components
A set of four scalar conditions involving normal components of the fields D
and B and their normal derivatives at a planar surface is introduced, among
which different pairs can be chosen to represent possible boundary conditions
for the electromagnetic fields. Four such pairs turn out to yield meaningful
boundary conditions and their responses for an incident plane wave at a planar
boundary are studied. The theory is subsequently generalized to more general
boundary surfaces defined by a coordinate function. It is found that two of the
pairs correspond to the PEC and PMC conditions while the other two correspond
to a mixture of PEC and PMC conditions for fields polarized TE or TM with
respect to the coordinate defining the surface
Inhomogeneous Big-Bang Nucleosynthesis in Light of Recent Observations
We consider inhomogeneous big bang nucleosynthesis in light of the present
observational situation. Different observations of He-4 and D disagree with
each other, and depending on which set of observations one uses, the estimated
primordial He-4 corresponds to a lower baryon density in standard big bang
nucleosynthesis than what one gets from deuterium. Recent Kamiokande results
rule out a favorite particle physics solution to this tension between He-4 and
D. Inhomogeneous nucleosynthesis can alleviate this tension, but the more
likely solution is systematics in the observations. The upper limit to Omega_b
from inhomogeneous nucleosynthesis is higher than in standard nucleosynthesis,
given that the distance scale of the inhomogeneity is near the optimal value,
which maximizes effects of neutron diffusion. Possible sources of baryon
inhomogeneity include the QCD and electroweak phase transitions. The distance
scale of the inhomogeneities arising from the electroweak transition is too
small for them to have a large effect on nucleosynthesis, but the effect may
still be larger than some of the other small corrections recently incorporated
to SBBN codes.Comment: 12 pages, 8 figures, REVTe
Backward-wave regime and negative refraction in chiral composites
Possibilities to realize a negative refraction in chiral composites in in
dual-phase mixtures of chiral and dipole particles is studied. It is shown that
because of strong resonant interaction between chiral particles (helixes) and
dipoles, there is a stop band in the frequency area where the backward-wave
regime is expected. The negative refraction can occur near the resonant
frequency of chiral particles. Resonant chiral composites may offer a root to
realization of negative-refraction effect and superlenses in the optical
region
Homogenization principles and effect of mixing on dielectric behavior
This paper consists of two parts. First, a review of classical mixing principles lists the multitude of the various ways to characterize the effective permittivity of heterogeneous materials. Different connections between the various mixing formulas are underlined and the homogenization principles are classified into families of mixing rules. The second part emphasizes and analyzes the richness of the manner how the mixing process is able to create new types of dielectric behaviors, in particular with respect to enhancement of dielectric polarization, shifts of the dispersion parameters, and emergence of new effects in electrical response.Non Peer reviewe
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