4,723 research outputs found
Observational Constraints on Phantom Crossing DGP Gravity
We study the observational constraints on the Phantom Crossing DGP model. We
demonstrate that the crossing of the phantom divide does not occur within the
framework of the original Dvali-Gabadadze-Porrati (DGP) model or the DGP model
developed by Dvali and Turner. By extending their model in the framework of an
extra dimension scenario, we study a model that realizes crossing of the
phantom divide. We investigate the cosmological constraints obtained from the
recent observational data of Type Ia Supernovae, Cosmic Microwave Background
anisotropies, and Baryon Acoustic Oscillations. The best fit values of the
parameters with 1 (68%) errors for the Phantom Crossing DGP model are
, . We find that
the Phantom Crossing DGP model is more compatible with the observations than
the original DGP model or the DGP model developed by Dvali and Turner. Our
model can realize late-time acceleration of the universe, similar to that of
CDM model, without dark energy due to the effect of DGP gravity. In
our model, crossing of the phantom divide occurs at a redshift of .Comment: 17 pages, 9 figures, 1 table, Accepted for publication in
International Journal of Modern Physics
MEDIA OPTIMIZATION FOR BIOPROTEINS PRODUCTION FROM CHEAPER CARBON SOURCE
There are high demands for animal and human food supply especially protein, which is an important dietary component. Agricultural wastes, cheap carbon sources- which are rich and have high energy, can be used for producing the value added bioprotein. A lab scale study was carried out to optimize the media composition for bioprotein production from a cheaper carbon source - wheat flour using potential strain, which was selected earlier by screening different microorganisms. The performance of the selected strain was enhanced by media optimization with varied substrate concentration, nitrogen sources and nutrient supplementation according to the central composite design from STATISTICA software. Statistical optimization was carried out to evaluate the polynomial regression model through effect of linear, quadratic and interaction of the factors. The maximum biomass produced was 21.89 g/L with optimum fermentation conditions of wheat flour (4 g/L), nitrogen concentration (0.5 g/L), nutrient concentration (0.1 g/L), and four days of fermentation
Accelerating Universe as Window for Extra Dimensions
Homogeneous cosmological solutions are obtained in five dimensional space
time assuming equations of state and where p
is the isotropic 3 - pressure and , that for the fifth dimension. Using
different values for the constants k and many known solutions are
rediscovered. Further the current acceleration of the universe has led us to
investigate higher dimensional gravity theory, which is able to explain
acceleration from a theoretical view point without the need of introducing dark
energy by hand. We argue that the terms containing higher dimensional metric
coefficients produce an extra negative pressure that apparently drives an
acceleration of the 3D space, tempting us to suggest that the accelerating
universe seems to act as a window to the existence of extra spatial dimensions.
Interestingly the 5D matter field remains regular while the \emph{effective}
negative pressure is responsible for the inflation. Relaxing the assumptions of
two equations of state we also present a class of solutions which provide early
deceleration followed by a late acceleration in a unified manner. Interesting
to point out that in this case our cosmology apparently mimics the well known
quintessence scenario fuelled by a generalised Chaplygin-type of fluid where a
smooth transition from a dust dominated model to a de Sitter like one takes
place.Comment: 20 pages,3 figure
Reconstructing the potentials for the quintessence and tachyon dark energy, from the holographic principle
We propose an holographic quintessence and tachyon models of dark energy. The
correspondence between the quintessence and tachyon energy densities with the
holographic density, allows the reconstruction of the potentials and the
dynamics for the quintessence and tachyon fields, in flat FRW background. The
proposed infrared cut-off for the holographic energy density works for two
cases of the constant : for we reconstructed the holographic
quintessence model in the region before the crossing for the EoS
parameter. The cosmological dynamics for was also reconstructed for
the holographic quintessence and tachyon models.Comment: 21 pages, 18 figures, 2 table
Reconstructing generalized ghost condensate model with dynamical dark energy parametrizations and observational datasets
Observations of high-redshift supernovae indicate that the universe is
accelerating at the present stage, and we refer to the cause for this cosmic
acceleration as ``dark energy''. In particular, the analysis of current data of
type Ia supernovae (SNIa), cosmic large-scale structure (LSS), and the cosmic
microwave background (CMB) anisotropy implies that, with some possibility, the
equation-of-state parameter of dark energy may cross the cosmological-constant
boundary () during the recent evolution stage. The model of ``quintom''
has been proposed to describe this crossing behavior for dark energy. As
a single-real-scalar-field model of dark energy, the generalized ghost
condensate model provides us with a successful mechanism for realizing the
quintom-like behavior. In this paper, we reconstruct the generalized ghost
condensate model in the light of three forms of parametrization for dynamical
dark energy, with the best-fit results of up-to-date observational data.Comment: 8 pages, 3 figures; references added; accepted for publication in
Mod. Phys. Lett.
Impact of Cycle Time on Potential CTS
Upper limb musculoskeletal symptoms and upper-limb musculoskeletal disorders (MSDs) have been found to be common in the working population. Carpal tunnel syndrome (CTS) is the most commonly studied entrapment neuropathy caused by compression of the median nerve as it passes through the carpal tunnel beneath the flexor retinaculum. The present study is conducted among person engaged in connecting rod manufacturing industry to check effect of cycle time of operation on potential CTS symptoms. The study sample consists of 103 workers for data collection. The study was conducted by questionnaire, physical examination, wrist angle evaluation and on job observation. Correlation analysis and Correlation analysis using IBM SPSS 20, it is revealed that Value of Pearson correlation coefficient is found to be -0.930 which is same as the value calculated manually. So analysis by SPSS 20 also confirms that there is very high negative correlation between cycle time and percentage of CTS sufferers
Phantom universe from CPT symmetric QFT
Inspired by the generalization of quantum theory for the case of
non-Hermitian Hamiltonians with CPT symmetry, we construct a simple classical
cosmological scalar field based model describing a smooth transition from
ordinary dark energy to the phantom one
A Tracker Solution for a Holographic Dark Energy Model
We investigate a kind of holographic dark energy model with the future event
horizon the IR cutoff and the equation of state -1. In this model, the
constraint on the equation of state automatically specifies an interaction
between matter and dark energy. With this interaction included, an accelerating
expansion is obtained as well as the transition from deceleration to
acceleration. It is found that there exists a stable tracker solution for the
numerical parameter , and smaller than one will not lead to a physical
solution. This model provides another possible phenomenological framework to
alleviate the cosmological coincidence problem in the context of holographic
dark energy. Some properties of the evolution which are relevant to
cosmological parameters are also discussed.Comment: 10 pages, 3 figures; accepted for publication in Int.J.Mod.Phys.
Cosmic Mimicry: Is LCDM a Braneworld in Disguise ?
For a broad range of parameter values, braneworld models display a remarkable
property which we call cosmic mimicry. Cosmic mimicry is characterized by the
fact that, at low redshifts, the Hubble parameter in the braneworld model is
virtually indistinguishable from that in the LCDM cosmology. An important point
to note is that the \Omega_m parameters in the braneworld model and in the LCDM
cosmology can nevertheless be quite different. Thus, at high redshifts (early
times), the braneworld asymptotically expands like a matter-dominated universe
with the value of \Omega_m inferred from the observations of the local matter
density. At low redshifts (late times), the braneworld model behaves almost
exactly like the LCDM model but with a renormalized value of the cosmological
density parameter \Omega_m^{LCDM}. The redshift which characterizes cosmic
mimicry is related to the parameters in the higher-dimensional braneworld
Lagrangian. Cosmic mimicry is a natural consequence of the scale-dependence of
gravity in braneworld models. The change in the value of the cosmological
density parameter is shown to be related to the spatial dependence of the
effective gravitational constant in braneworld theory. A subclass of mimicry
models lead to an older age of the universe and also predict a redshift of
reionization which is lower than z_{reion} \simeq 17 in the LCDM cosmology.
These models might therefore provide a background cosmology which is in better
agreement both with the observed quasar abundance at z \gsim 4 and with the
large optical depth to reionization measured by the Wilkinson Microwave
Anisotropy Probe.Comment: 22 pages, 4 figures. A subsection and references added; main results
remain unchanged. Accepted for publication in JCA
Experimental investigation of inter-modal cross-gain modulation and transient effects in a two mode group erbium doped fiber amplifier
We report what we believe to be the first experimental study of inter-modal cross-gain modulation and associated transient effects as different spatial modes and wavelength channels are added and dropped within a two-mode amplifier for SDM transmission
- …