1,190 research outputs found
Band-Gap Engineering in two-dimensional periodic photonic crystals
A theoretical investigation is made of the dispersion characteristics of
plasmons in a two-dimensional periodic system of semiconductor (dielectric)
cylinders embedded in a dielectric (semiconductor) background. We consider both
square and hexagonal arrangements and calculate extensive band structures for
plasmons using a plane-wave method within the framework of a local theory. It
is found that such a system of semiconductor-dielectric composite can give rise
to huge full band gaps (with a gap to midgap ratio ) within which
plasmon propagation is forbidden. The most interesting aspect of this
investigation is the huge lowest gap occurring below a threshold frequency and
extending up to zero. The maximum magnitude of this gap is defined by the
plasmon frequency of the inclusions or the background as the case may be. In
general we find that greater the dielectric (and plasmon frequency) mismatch,
the larger this lowest band-gap. Whether or not some higher energy gaps appear,
the lowest gap is always seen to exist over the whole range of filling fraction
in both geometries. Just like photonic and phononic band-gap crystals,
semiconducting band-gap crystals should have important consequences for
designing useful semiconductor devices in solid state plasmas.Comment: 16 pages, 5 figure
The Hard X-ray emission of the blazar PKS 2155--304
The synchrotron peak of the X-ray bright High Energy Peaked Blazar (HBL) PKS
2155304 occurs in the UV-EUV region and hence its X-ray emission (0.6--10
keV) lies mostly in the falling part of the synchrotron hump. We aim to study
the X-ray emission of PKS 2155304 during different intensity states in
20092014 using XMMNewton satellite. We studied the spectral curvature of
all of the observations to provide crucial information on the energy
distribution of the non-thermal particles. Most of the observations show
curvature or deviation from a single power-law and can be well modeled by a log
parabola model. In some of the observations, we find spectral flattening after
6 keV. In order to find the possible origin of the X-ray excess, we built the
Multi-band Spectral Energy distribution (SED). We find that the X-ray excess in
PKS 2155--304 is difficult to fit in the one zone model but, could be easily
reconciled in the spine/layer jet structure. The hard X-ray excess can be
explained by the inverse Comptonization of the synchrotron photons (from the
layer) by the spine electrons.Comment: 14 pages, 7 Figures, Accepted for publication in Ap
Impact of 50% ethanolic extract of Calendula officinalis (flower) on the reproductive function of male albino rats (Rattus norvegicus)
Oral administration to male rats of 200mg kg-1 body weight of an extract of Calendula officinalis flowers every day for 60 days did not cause loss of body weight, but decreased significantly the weight of the testis, epididymis, seminal vesicle and ventral prostate. Sperm motility as well as sperm density were reduced significantly, resulting in 80% loss of fertility.Serum testosterone levels showed highly significant reduction. Total protein and sialic acid in the testis, epididymis, seminal vesicles and ventral prostate decreased significantly, and testicular cholesterol was elevated. All measured haematological parameters were unchanged
Viscoelastic response of sonic band-gap materials
A brief report is presented on the effect of viscoelastic losses in a high
density contrast sonic band-gap material of close-packed rubber spheres in air.
The scattering properties of such a material are computed with an on-shell
multiple scattering method, properties which are compared with the lossless
case. The existence of an appreciable omnidirectional gap in the transmission
spectrum, when losses are present, is also reported.Comment: 5 pages, 4 figures, submitted to PR
Theoretical analysis of acoustic stop bands in two-dimensional periodic scattering arrays
This paper presents a theoretical analysis of the recently reported
observation of acoustic stop bands in two-dimensional scattering arrays
(Robertson and Rudy, J. Acoust. Soc. Am. {\bf 104}, 694, 1998). A
self-consistent wave scattering theory, incorporating all orders of multiple
scattering, is used to obtain the wave transmission. The band structures for
the regular arrays of cylinders are computed using the plane wave expansion
method. The theoretical results compare favorably with the experimental data.Comment: 18 pages, 4 page
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