28 research outputs found
Evolution of fNL to the adiabatic limit
We study inflationary perturbations in multiple-field models, for which zeta
typically evolves until all isocurvature modes decay--the "adiabatic limit". We
use numerical methods to explore the sensitivity of the nonlinear parameter fNL
to the process by which this limit is achieved, finding an appreciable
dependence on model-specific data such as the time at which slow-roll breaks
down or the timescale of reheating. In models with a sum-separable potential
where the isocurvature modes decay before the end of the slow-roll phase we
give an analytic criterion for the asymptotic value of fNL to be large. Other
examples can be constructed using a waterfall field to terminate inflation
while fNL is transiently large, caused by descent from a ridge or convergence
into a valley. We show that these two types of evolution are distinguished by
the sign of the bispectrum, and give approximate expressions for the peak fNL.Comment: v1: 25 pages, plus Appendix and bibliography, 6 figures. v2: minor
edits to match published version in JCA
Restoring Holographic Dark Energy in Brane Cosmology
We present a generalized version of holographic dark energy arguing that it
must be considered in the maximally subspace of a cosmological model. In the
context of brane cosmology it leads to a bulk holographic dark energy which
transfers its holographic nature to the effective 4D dark energy. As an
application we use a single-brane model and we show that in the low energy
limit the behavior of the effective holographic dark energy coincides with that
predicted by conventional 4D calculations. However, a finite bulk can lead to
radically different results.Comment: 11 pages, version published in Phys. Lett.
Cosmological perturbations in Palatini modified gravity
Two approaches to the study of cosmological density perturbations in modified
theories of Palatini gravity have recently been discussed. These utilise,
respectively, a generalisation of Birkhoff's theorem and a direct linearization
of the gravitational field equations. In this paper these approaches are
compared and contrasted. The general form of the gravitational lagrangian for
which the two frameworks yield identical results in the long-wavelength limit
is derived. This class of models includes the case where the lagrangian is a
power-law of the Ricci curvature scalar. The evolution of density perturbations
in theories of the type is investigated numerically. It is
found that the results obtained by the two methods are in good agreement on
sufficiently large scales when the values of the parameters (b,c) are
consistent with current observational constraints. However, this agreement
becomes progressively poorer for models that differ significantly from the
standard concordance model and as smaller scales are considered
Holographic Dark Energy in Braneworld Models with a Gauss-Bonnet Term in the Bulk. Interacting Behavior and the w =-1 Crossing
We apply bulk holographic dark energy in general braneworld models with a
Gauss-Bonnet term in the bulk and an induced gravity term and a perfect fluid
on the brane. Without making any additional assumptions we extract the
Friedmann equation on the physical brane and we show that a
- coupling arises naturally by the full 5D dynamics. The
low-energy (late-time) evolution reveals that the effective 4D holographic dark
energy behaves as ``quintom'', that is it crosses the phantom divide
during the evolution. In particular, the Gauss-Bonnet contribution decreases
the present value of , while it increases the growing rate of
with , in comparison with the case where such a term is
absent.Comment: 16 pages, version published in Phys. Lett.
Geodesic motion in the neighbourhood of submanifolds embedded in warped product spaces
We study the classical geodesic motions of nonzero rest mass test particles
and photons in (3+1+n)- dimensional warped product spaces. An important feature
of these spaces is that they allow a natural decoupling between the motions in
the (3+1)-dimensional spacetime and those in the extra n dimensions. Using this
decoupling and employing phase space analysis we investigate the conditions for
confinement of particles and photons to the (3+1)- spacetime submanifold. In
addition to providing information regarding the motion of photons, we also show
that these motions are not constrained by the value of the extrinsic curvature.
We obtain the general conditions for the confinement of geodesics in the case
of pseudo-Riemannian manifolds as well as establishing the conditions for the
stability of such confinement. These results also generalise a recent result of
the authors concerning the embeddings of hypersurfaces with codimension one.Comment: 8 pages, 1 figure. To appear in General Relativity and Gravitation as
a contributed paper to Mashhoon Festschrif
A DFT Study on the Interaction of Doped Carbon Nanotubes with H2S, SO2 and Thiophene
The interactions of simple and Al-, B-, N-, S-, P-, and Si-doped carbon nanotubes with three sulfur-containing molecules (H2S, SO2, and thiophene) were investigated to assess their adsorption potencies and sensor abilities. The DFT method was used to calculate the adsorption energies and natural bond orbitals parameters. In addition, population analyses were performed to calculate the energy gaps and reactivity parameters. The results showed an exothermic interaction of H2S, SO2, and thiophene with simple and doped carbon nanotubes, while the maximum negative adsorption energies belong to Al- and B-containing complexes. Furthermore, evaluation of second-order perturbation energies (obtained from natural bond orbitals calculations) confirmed that the highest energies were related to B- and Al-containing intramolecular interactions. The results revealed the favorability of adsorption of SO2 by nanotubes (B- and Al-doped carbon nanotubes, in particular) compared with the other examined adsorbates
Molecular dynamics study of biodegradation of azo dyes via their interactions with AzrC azoreductase
<p>Azo dyes are one of the most important class of dyes, which have been widely used in industries. Because of the environmental pollution of azo dyes, many studies have been performed to study their biodegradation using bacterial systems. In present work, the AzrC of mesophilic gram-positive <i>Bacillus</i> sp<i>.</i> B29 has been considered to study its interaction with five common azo dyes (orange G, acid red 88, Sudan I, orange I, and methyl red). The molecular dynamics simulations have been employed to study the interaction between AzrC and azo dyes. The trajectory was confirmed using root mean square deviation and the root mean square fluctuation analyses. Then, the hydrogen bond and alanine scanning analyses were performed to reveal active site residues. Phe105 (A), Phe125 (B), Phe172 (B), and Pro132 (B) have been found as the most important hydrophobic residues whereas Asn104 (A), Tyr127 (B), and Asn187 (A) have key role in making hydrogen bond. The results of molecular mechanics Poisson–Boltzmann surface area and molecular mechanics generalized Born surface area calculations proved that the hydrophobic azo dyes like Acid red 88 binds more tightly to the AzrC protein. The calculated data suggested MR A 121 (B) I as a potential candidate for improving the AzrC–MR interactions.</p
Protective role of green tea on malathion-induced testicular oxidative damage in rats
Objective: To examine effects of total green tea extract, a potent free radical scavenger on testicular tissue oxidative status.
Methods: 32 male albino rats of Wistar strain were divided into four groups, every group restricted 8 animals: (i) control rats; (ii) green tea-treated control rats; (iii) malathion rats; (iv) malathion-treated green tea rats. Animals received malathion 150 mg/kg and green tea 30 mg/kg for 24 h intraperitoneally. At the end of the treatment period, rat testis tissues were quickly removed and analyzed. Diameter of seminiferous tubules and germinal cell thickness, spermatogonia sertoli cells, primary spermatocytes, spermatids and leydig cell were evaluated. Also, oxidative stress evaluation was conducted based on total antioxidant capacity (TAC), lipid peroxidation (LPO) and total thiol molecules (TTM) in homogenate testis tissues.
Results: The results showed that total green tea extract improve oxidative damages against malathion group. Light photomicrograph of seminiferous tubules in malathion-treated group showed noticeable reduced height of germinal epithelium and disorganization of the tubules. An increased intestinal tissue was also observed. Primary spermatocytes were located distance from basal lamina indicating it induced damages to the intestinal tissue. While seminiferous tubules in malathion exposed and green tea extract-treated were normal.
Conclusion: This study demonstrated the effectiveness of TGTE on oxidative stress and testicular tissue damage induced in malathion in infertility disorders