1,026 research outputs found
Gravitational Charged Perfect Fluid Collapse in Friedmann Universe Models
This paper is devoted to study the gravitational charged perfect fluid
collapse in the Friedmann universe models with cosmological constant. For this
purpose, we assume that the electromagnetic field is so weak that it does not
introduce any distortion into the geometry of the spacetime. The results
obtained from the junction conditions between the Friedmann and the
Reissner-Nordstrm de-Sitter spacetimes are used to solve the field
equations. Further, the singularity structure and mass effects of the
collapsing system on time difference between the formation of apparent horizons
and singularity have been studied. This analysis provides the validity of
Cosmic Censorship Hypothesis. It is found that the electric field affects the
area of apparent horizons and their time of formation.Comment: 17 pages, accepted for publication in Astrophys. Space Sc
Nonextensive Entropies derived from Form Invariance of Pseudoadditivity
The form invariance of pseudoadditivity is shown to determine the structure
of nonextensive entropies. Nonextensive entropy is defined as the appropriate
expectation value of nonextensive information content, similar to the
definition of Shannon entropy. Information content in a nonextensive system is
obtained uniquely from generalized axioms by replacing the usual additivity
with pseudoadditivity. The satisfaction of the form invariance of the
pseudoadditivity of nonextensive entropy and its information content is found
to require the normalization of nonextensive entropies. The proposed principle
requires the same normalization as that derived in [A.K. Rajagopal and S. Abe,
Phys. Rev. Lett. {\bf 83}, 1711 (1999)], but is simpler and establishes a basis
for the systematic definition of various entropies in nonextensive systems.Comment: 16 pages, accepted for publication in Physical Review
Superconductivity in the Nb2SnC compound
Nb2SnC is a member of the large family of lamellar materials that crystallize
in the hexagonal structure with space group P63/mmc which are isomorphs with
Cr2AlC, also named H-phase. In spite of the great number of compounds which
belong to this family, the superconductivity has been reported only for two
cases: Mo2GaC and Nb2SC. In this work we show that superconductivity can be
observed in Nb2SnC depending on the synthesis method used. The quality of the
superconductor is strongly dependent of the synthesis method and the optimal
results were reached for samples synthesized at 2.5 GPa and 523 +/- 50oC. This
sample showed a critical temperature close to 7.8K, revealed from magnetization
and transport measurement, the highest critical temperature reported up to now
for an H-phase.Comment: paper with 12 pages and 4 figure
Nature of singularity formed by the gravitational collapse in Husain space-time with electromagnetic field and scalar field
In this work, we have investigated the outcome of gravitational collapse in
Husain space-time in the presence of electro-magnetic and a scalar field with
potential. In order to study the nature of the singularity, global behavior of
radial null geodesics have been taken into account. The nature of singularities
formed has been thoroughly studied for all possible variations of the
parameters. These choices of parameters has been presented in tabular form in
various dimensions. It is seen that irrespective of whatever values of the
parameters chosen, the collapse always results in a naked singularity in all
dimensions. There is less possibility of formation of a black hole. Hence this
work is a significant counterexample of the cosmic censorship hypothesis.Comment: 9 pages, 19 figure
Variable Modified Chaplygin Gas in Anisotropic Universe with Kaluza-Klein Metric
In this work, we have consider Kaluza-Klein Cosmology for anisotropic
universe where the universe is filled with variable modified chaplygin gas
(VMCG). Here we find normal scalar field and the self interacting
potential to describe the VMCG Cosmology. Also we graphically
analyzed the geometrical parameters named {\it statefinder parameters} in
anisotropic Kaluza-Klein model. Next, we consider a Kaluza-Klein model of
interacting VMCG with dark matter in the Einstein gravity framework. Here we
construct the three dimensional autonomous dynamical system of equations for
this interacting model with the assumption that the dark energy and the dark
matter are interact between them and for that we also choose the interaction
term. We convert that interaction terms to its dimensionless form and perform
stability analysis and solve them numerically. We obtain a stable scaling
solution of the equations in Kaluza-Klein model and graphically represent
solutions.Comment: 11 pages, 13 figure
Exciton swapping in a twisted graphene bilayer as a solid-state realization of a two-brane model
It is shown that exciton swapping between two graphene sheets may occur under
specific conditions. A magnetically tunable optical filter is described to
demonstrate this new effect. Mathematically, it is shown that two turbostratic
graphene layers can be described as a "noncommutative" two-sheeted
(2+1)-spacetime thanks to a formalism previously introduced for the study of
braneworlds in high energy physics. The Hamiltonian of the model contains a
coupling term connecting the two layers which is similar to the coupling
existing between two braneworlds at a quantum level. In the present case, this
term is related to a K-K' intervalley coupling. In addition, the experimental
observation of this effect could be a way to assess the relevance of some
theoretical concepts of the braneworld hypothesis.Comment: 15 pages, 3 figures, final version published in European Physical
Journal
Space-time inhomogeneity, anisotropy and gravitational collapse
We investigate the evolution of non-adiabatic collapse of a shear-free
spherically symmetric stellar configuration with anisotropic stresses
accompanied with radial heat flux. The collapse begins from a curvature
singularity with infinite mass and size on an inhomogeneous space-time
background. The collapse is found to proceed without formation of an even
horizon to singularity when the collapsing configuration radiates all its mass
energy. The impact of inhomogeneity on various parameters of the collapsing
stellar configuration is examined in some specific space-time backgrounds.Comment: To appear in Gen. Relativ. Gra
Polyphenols journey through blood-brain barrier towards neuronal protection
Age-related complications such as neurodegenerative disorders are increasing and remain cureless.
The possibility of altering the progression or the development of these multifactorial diseases through
diet is an emerging and attractive approach with increasing experimental support. We examined
the potential of known bioavailable phenolic sulfates, arising from colonic metabolism of berries, to
infuence hallmarks of neurodegenerative processes. In silico predictions and in vitro transport studies
across blood-brain barrier (BBB) endothelial cells, at circulating concentrations, provided evidence for
diferential transport, likely related to chemical structure. Moreover, endothelial metabolism of these
phenolic sulfates produced a plethora of novel chemical entities with further potential bioactivies.
Pre-conditioning with phenolic sulfates improved cellular responses to oxidative, excitotoxicity and
infammatory injuries and this attenuation of neuroinfammation was achieved via modulation of
NF-κB pathway. Our results support the hypothesis that these small molecules, derived from dietary
(poly)phenols may cross the BBB, reach brain cells, modulate microglia-mediated infammation and
exert neuroprotective efects, with potential for alleviation of neurodegenerative diseases.info:eu-repo/semantics/publishedVersio
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