61 research outputs found
Variable Modified Chaplygin Gas and Accelerating Universe
In this letter, I have proposed a model of variable modified Chaplygin gas
and shown its role in accelerating phase of the universe. I have shown that the
equation of state of this model is valid from the radiation era to quiessence
model. The graphical representations of statefinder parameters characterize
different phase of evolution of the universe. All results presented in the
letter concerns the case .Comment: 7 Latex pages, 5 figures, revtex styl
Role of Modified Chaplygin Gas as a Dark Energy Model in Collapsing Spherically Symmetric Cloud
In this work, gravitational collapse of a spherical cloud, consists of both
dark matter and dark energy in the form of modified Chaplygin gas is studied.
It is found that dark energy alone in the form of modified Chaplygin gas forms
black hole. Also when both components of the fluid are present then the
collapse favors the formation of black hole in cases the dark energy dominates
over dark matter. The conclusion is totally opposite to the usually known
results.Comment: 7 Latex Pages, RexTex style, No figure
Holographic Dark Energy Scenario and Variable Modified Chaplygin Gas
In this letter, we have considered that the universe is filled with normal
matter and variable modified Chaplygin gas. Also we have considered the
interaction between normal matter and variable modified Chaplygin gas in FRW
universe. Then we have considered a correspondence between the holographic dark
energy density and interacting variable modified Chaplygin gas energy density.
Then we have reconstructed the potential of the scalar field which describes
the variable modified Chaplygin cosmology.Comment: 4 latex pages, no figures, RevTeX styl
Gravitational Collapse in Higher Dimensional Husain Space-Time
We investigate exact solution in higher dimensional Husain model for a null
fluid source with pressure and density are related by the following
relations (i) , (ii) (variable
modified Chaplygin) and (iii) (polytropic). We have studied
the nature of singularity in gravitational collapse for the above equations of
state and also for different choices of the of the parameters and
namely, (i) , constant (generalized Chaplygin), (ii) constant
(modified Chaplygin). It is found that the nature of singularity is independent
of these choices of different equation of state except for variable Chaplygin
model. Choices of various parameters are shown in tabular form. Finally,
matching of Szekeres model with exterior Husain space-time is done.Comment: 12 latex pages, No figure, RevTex styl
Material and device characterization of Type-II InAs/GaSb superlattice infrared detectors
This work investigates midwave infrared Type-II InAs/GaSb superlattice (SL) grown by molecular beam epitaxy on GaSb substrate. In order to compensate the natural tensile strain of the InAs layers, two different shutter sequences have been explored during the growth. The first one consists of growing an intentional InSb layer at both interfaces (namely GaSb-on-InAs and InAs-on-GaSb interfaces) by migration enhanced epitaxy while the second uses the antimony-for-arsenic exchange to promote an ‘InSb-like’ interface at the GaSb-on-InAs interface. SLs obtained via both methods are compared in terms of structural, morphological and optical properties by means of high-resolution x-ray diffraction, atomic force microscopy and photoluminescence spectroscopy. By using the second method, we obtained a nearly strain-compensated SL on GaSb with a full width at half maximum of 56 arcsec for the first-order SL satellite peak. Relatively smooth surface has been achieved with a root mean square value of about 0.19 nm on a 2 µm × 2 µm scan area. Finally, a p-i-n device structure having a cut-off wavelength of 5.15 µm at 77 K has been demonstrated with a dark-current level of 8.3 × 10−8 A/cm2 at −50 mV and a residual carrier concentration of 9.7 × 1014 cm−3, comparable to the state-of-the-art
Demonstration of large ionization coefficient ratio in AlAs0.56Sb0.44 lattice matched to InP
The electron and hole avalanche multiplication characteristics have been measured in bulk AlAs0.56Sb0.44 p-i-n and n-i-p homojunction diodes, lattice matched to InP, with nominal avalanche region thicknesses of ~0.6 μm, 1.0 μm and 1.5 μm. From these and data from two much thinner devices, the bulk electron and hole impact ionization coefficients (α and β respectively), have been determined over an electric-field range from 220-1250 kV/cm for α and from 360-1250 kV/cm for β for the first time. The α/β ratio is found to vary from 1000 to 2 over this field range, making it the first report of a wide band-gap III-V semiconductor with ionization coefficient ratios similar to or larger than that observed in silicon
Dynamics of Logamediate and Intermediate Scenarios in the Dark Energy Filled Universe
We have considered a model of two component mixture i.e., mixture of
Chaplygin gas and barotropic fluid with tachyonic field. In the case, when they
have no interaction then both of them retain their own properties. Let us
consider an energy flow between barotropic and tachyonic fluids. In both the
cases we find the exact solutions for the tachyonic field and the tachyonic
potential and show that the tachyonic potential follows the asymptotic
behavior. We have considered an interaction between these two fluids by
introducing a coupling term. Finally, we have considered a model of three
component mixture i.e., mixture of tachyonic field, Chaplygin gas and
barotropic fluid with or without interaction. The coupling functions decays
with time indicating a strong energy flow at the initial period and weak stable
interaction at later stage. To keep the observational support of recent
acceleration we have considered two particular forms (i) Logamediate Scenario
and (ii) Intermediate Scenario, of evolution of the Universe. We have examined
the natures of the recent developed statefinder parameters and slow-roll
parameters in both scenarios with and without interactions in whole evolution
of the universe.Comment: 28 pages, 20 figure
Dynamics of interacting phantom and quintessence dark energies
We present models, in which phantom energy interacts with two different types
of dark energies including variable modified Chaplygin gas (VMCG) and new
modified Chaplygin gas (NMCG). We then construct potentials for these cases. It
has been shown that the potential of the phantom field decreases from a higher
value with the evolution of the Universe.Comment: 7 pages, 6 figures, accepted for publication in Astrophysics and
Space Scienc
Role of Brans-Dicke Theory with or without self-interacting potential in cosmic acceleration
In this work we have studied the possibility of obtaining cosmic acceleration
in Brans-Dicke theory with varying or constant (Brans- Dicke
parameter) and with or without self-interacting potential, the background fluid
being barotropic fluid or Generalized Chaplygin Gas. Here we take the power law
form of the scale factor and the scalar field. We show that accelerated
expansion can also be achieved for high values of for closed Universe.Comment: 12 Latex pages, 20 figures, RevTex styl
Interaction between Tachyon and Hessence (or Hantom) dark energies
In this paper, we have considered that the universe is filled with tachyon,
hessence (or hantom) dark energies. Subsequently we have investigated the
interactions between tachyon and hessence (hantom) dark energies and calculated
the potentials considering the power law form of the scale factor. It has been
revealed that the tachyonic potential always decreases and hessence (or hantom)
potential increases with corresponding fields. Furthermore, we have considered
a correspondence between the hessence (or hantom) dark energy density and new
variable modified Chaplygin gas energy density. From this, we have found the
expressions of the arbitrary positive constants B0 and C of new variable
modified Chaplygin gas
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