811 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
Single-particle and collective excitations in quantum wires made up of vertically stacked quantum dots: Zero magnetic field
We report on the theoretical investigation of the elementary electronic
excitations in a quantum wire made up of vertically stacked self-assembled
InAs/GaAs quantum dots. The length scales (of a few nanometers) involved in the
experimental setups prompt us to consider an infinitely periodic system of
two-dimensionally confined (InAs) quantum dot layers separated by GaAs spacers.
The the Bloch functions and the Hermite functions together characterize the
whole system. We then make use of the Bohm-Pines' (full) random-phase
approximation in order to derive a general nonlocal, dynamic dielectric
function. Thus developed theoretical framework is then specified to work within
a (lowest miniband and) two-subband model that enables us to scrutinize the
single-particle as well as collective responses of the system. We compute and
discuss the behavior of the eigenfunctions, band-widths, density of states,
Fermi energy, single-particle and collective excitations, and finally size up
the importance of studying the inverse dielectric function in relation with the
quantum transport phenomena. It is remarkable to notice how the variation in
the barrier- and well-widths can allow us to tailor the excitation spectrum in
the desired energy range. Given the advantage of the vertically stacked quantum
dots over the planar ones and the foreseen applications in the single-electron
devices and in the quantum computation, it is quite interesting and important
to explore the electronic, optical, and transport phenomena in such systems
Au9+ swift heavy ion irradiation of Zn[CS(NH2)2]3SO4 crystal: Crystalline perfection and optical properties
The single crystal of tris(thiourea)zinc sulphate (Zn[CS(NH2)2]3SO4) was
irradiated by 150 MeV Au9+ swift heavy ions and analyzed in comparison with
pure crystal for crystalline perfection and optical properties. The Fourier
transform infrared and x-ray powder diffraction inferred that swift ions lead
the disordering and breaking of molecular bonds in lattice without formation of
new structural phases. High resolution X-ray diffraction (HRXRD) revealed the
abundance of point defects, and formation of mosaics and low angle grain
boundaries in the irradiated region of crystal. The swift ion irradiation found
to affect the lattice vibrational modes and functional groups significantly.
The defects induced by heavy ions act as the color centers and resulted in
enhance of photoluminescence emission intensity. The optical transparency and
band gap found to be decreased.Comment: 7 page
MoTe2: A Type-II Weyl Topological Metal
Based on the ab initio calculations, we show that MoTe2, in its
low-temperature orthorhombic structure characterized by an X-ray diffraction
study at 100 K, realizes 4 type-II Weyl points between the N-th and N+1-th
bands, where N is the total number of valence electrons per unit cell. Other
WPs and nodal lines between different other bands also appear close to the
Fermi level due to a complex topological band structure. We predict a series of
strain-driven topological phase transitions in this compound, opening a wide
range of possible experimental realizations of different topological semimetal
phases. Crucially, with no strain, the number of observable surface Fermi arcs
in this material is 2 - the smallest number of arcs consistent with
time-reversal symmetry.Comment: Published versio
Buffalo Rearing System in Bhadawari Breeding Tract
Bhadawari buffalo is one of the recognized buffalo breeds in India, known for high milk fat content, which may go as high as 14% (Kushwaha et al., 2012). Zachariah (1941) had first described this breed as “Bhadawan” buffalo – the best breed of buffaloes in Uttar Pradesh and found in the districts of Agra and Etah (Central India). Presently Bhadawari Buffaloes are found in the ravines of Yamuna and Chambal rivers spread over in the states of Uttar Pradesh and Madhya Pradesh. These buffaloes have adapted to the harsh conditions of the ravines with undulating topography, thorny and scanty bushes, climatic stress and draught conditions. The buffaloes are of medium size with medium to low milk yield having high fat content. Animals are of copper color, have two white rings on the lower side of the neck and legs are comparatively shorter. Indiscriminate crossbreeding with Murrah buffaloes, for increasing milk production, during the last 3-4 decades has reduced the number of Bhadawari buffaloes in the region. Looking into the need to conserve this gene pool, Indian Council of Agricultural Research has initiated efforts on conservation and improvement of Bhadawari buffaloes at Indian Grassland and Fodder Research Institute, Jhansi (IGFRI) under Network program in the year 2001. The present study was conducted to collect the information regarding existing buffalo rearing practices adopted by the farmers in the Bhadawari breeding tract
Scattering of elastic waves by periodic arrays of spherical bodies
We develop a formalism for the calculation of the frequency band structure of
a phononic crystal consisting of non-overlapping elastic spheres, characterized
by Lam\'e coefficients which may be complex and frequency dependent, arranged
periodically in a host medium with different mass density and Lam\'e
coefficients. We view the crystal as a sequence of planes of spheres, parallel
to and having the two dimensional periodicity of a given crystallographic
plane, and obtain the complex band structure of the infinite crystal associated
with this plane. The method allows one to calculate, also, the transmission,
reflection, and absorption coefficients for an elastic wave (longitudinal or
transverse) incident, at any angle, on a slab of the crystal of finite
thickness. We demonstrate the efficiency of the method by applying it to a
specific example.Comment: 19 pages, 5 figures, Phys. Rev. B (in press
Development and characterization of a fibroblastic-like cell line from caudal fin of the red-line torpedo, Puntius denisonii (Day) (Teleostei: Cyprinidae)
A fibroblastic-like cell line was established from the
ornamental ¢sh, red-line torpedo (Puntius denisonii).
The red-line torpedo fin (RTF) cell line is being maintained
in Leibovitz’s L-15 mediumsupplementedwith
10% fetal bovine serum (FBS) for over 1year at 28 1C
on a continuous basis in normal atmosphere. The
growth rate of RTF cells increased as the FBS proportion
increased from 5% to 20% at 28 1C with optimum
growth at the concentrations of 10% FBS. The
morphology of RTF cell was predominantly fibroblastic
like. Propagation of these cell lines was serum dependent,
with a low plating efficiency (o15%).
Karyotyping analysis of RTF cells at the 25th passage
indicated that the modal chromosome number was
2n550. The cell line was cryopreserved in liquid nitrogen
at �196 1C and could be recovered from storage
after 6 months with good cell viability.
Polymerase chain reaction amplification of a fragment
of two mitochondrial genes, 16S rRNA and
CO1, con¢rmed the identity of these cell lines with
those reported from this animal species, confirming
that the cell lines originated from P. denisonii. The
bacterial extracellular products from Vibrio cholerae
MTCC3904 and Aeromonas hydrophila were found to
be toxic to RTF. The cell lines were not susceptible to
viral nervous necrosis virus, a marine ¢sh virus
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