1,893 research outputs found
Thermodynamics of interacting entropy-corrected holographic dark energy in a non-flat FRW universe
A so-called "entropy-corrected holographic dark energy" (ECHDE), was recently
proposed to explain the dark energy-dominated universe with the help of quantum
corrections to the entropy-area relation in the setup of loop quantum
cosmology. Using this new definition, we investigate its thermodynamical
features including entropy and energy conservation. We describe the
thermodynamical interpretation of the interaction between ECHDE and dark matter
in a non-flat universe. We obtain a relation between the interaction term of
the dark components and thermal fluctuation. Our study further generalizes the
earlier works [M.R. Setare and E.C. Vagenas, Phys. Lett. B 666 (2008) 111; B.
Wang et al., Phys. Lett. B 662 (2008) 1] in this direction.Comment: 14 pages, no figure, accepted by Int. J. Mod. Phys.
Entropy Corrections for Schwarzschild and Reissner-Nordstr\"om Black Holes
Schwarzschild black hole being thermodynamically unstable, corrections to its
entropy due to small thermal fluctuations cannot be computed. However, a
thermodynamically stable Schwarzschild solution can be obtained within a cavity
of any finite radius by immersing it in an isothermal bath. For these boundary
conditions, classically there are either two black hole solutions or no
solution. In the former case, the larger mass solution has a positive specific
heat and hence is locally thermodynamically stable. We find that the entropy of
this black hole, including first order fluctuation corrections is given by:
{\cal S} = S_{BH} - \ln[\f{3}{R} (S_{BH}/4\p)^{1/2} -2]^{-1} + (1/2)
\ln(4\p), where is its Bekenstein-Hawking entropy and is the
radius of the cavity. We extend our results to four dimensional
Reissner-Nordstr\"om black holes, for which the corresponding expression is:
{\cal S} = S_{BH} - \f{1}{2} \ln [ {(S_{BH}/\p R^2) ({3S_{BH}}/{\p R^2} -
2\sqrt{{S_{BH}}/{\p R^2 -\a^2}}) \le(\sqrt{{S_{BH}}/{\p R^2}} - \a^2 \ri)}/
{\le({S_{BH}}/{\p R^2} -\a^2 \ri)^2} ]^{-1} +(1/2)\ln(4\p). Finally, we
generalise the stability analysis to Reissner-Nordstr\"om black holes in
arbitrary spacetime dimensions, and compute their leading order entropy
corrections. In contrast to previously studied examples, we find that the
entropy corrections in these cases have a different character.Comment: 6 pages, Revtex. References added, minor changes. Version to appear
in Class. Quant. Gra
Deformation of Codimension-2 Surface and Horizon Thermodynamics
The deformation equation of a spacelike submanifold with an arbitrary
codimension is given by a general construction without using local frames. In
the case of codimension-1, this equation reduces to the evolution equation of
the extrinsic curvature of a spacelike hypersurface. In the more interesting
case of codimension-2, after selecting a local null frame, this deformation
equation reduces to the well known (cross) focusing equations. We show how the
thermodynamics of trapping horizons is related to these deformation equations
in two different formalisms: with and without introducing quasilocal energy. In
the formalism with the quasilocal energy, the Hawking mass in four dimension is
generalized to higher dimension, and it is found that the deformation of this
energy inside a marginal surface can be also decomposed into the contributions
from matter fields and gravitational radiation as in the four dimension. In the
formalism without the quasilocal energy, we generalize the definition of slowly
evolving future outer trapping horizons proposed by Booth to past trapping
horizons. The dynamics of the trapping horizons in FLRW universe is given as an
example. Especially, the slowly evolving past trapping horizon in the FLRW
universe has close relation to the scenario of slow-roll inflation. Up to the
second order of the slowly evolving parameter in this generalization, the
temperature (surface gravity) associated with the slowly evolving trapping
horizon in the FLRW universe is essentially the same as the one defined by
using the quasilocal energy.Comment: Latex, 61 pages, no figures; v2, type errors corrected; v3,
references and comments are added, English is improved, to appear in JHE
Static flow on complete noncompact manifolds I: short-time existence and asymptotic expansions at conformal infinity
In this paper, we study short-time existence of static flow on complete
noncompact asymptotically static manifolds from the point of view that the
stationary points of the evolution equations can be interpreted as static
solutions of the Einstein vacuum equations with negative cosmological constant.
For a static vacuum we also compute the asymptotic expansions of
and at conformal infinity.Comment: 25 page
Geometric and thermodynamic properties in Gauss-Bonnet gravity
In this paper, the generalized second law (GSL) of thermodynamics and entropy
is revisited in the context of cosmological models in Gauss-Bonnet gravity with
the boundary of the universe is assumed to be enclosed by the dynamical
apparent horizon. The model is best fitted with the observational data for
distance modulus. The best fitted geometric and thermodynamic parameters such
as equation of state parameter, deceleration parameter and entropy are derived.
To link between thermodynamic and geometric parameters, the "entropy rate of
change multiplied by the temperature" as a model independent thermodynamic
state parameter is also derived. The results show that the model is in good
agreement with the observational analysis.Comment: 13 pages, 13 figures, to be published in Astrophysics and Space Sc
Short-range interactions in a two-electron system: energy levels and magnetic properties
The problem of two electrons in a square billiard interacting via a
finite-range repulsive Yukawa potential and subjected to a constant magnetic
field is considered. We compute the energy spectrum for both singlet and
triplet states, and for all symmetry classes, as a function of the strength and
range of the interaction and of the magnetic field. We show that the
short-range nature of the potential suppresses the formation of ``Wigner
molecule'' states for the ground state, even in the strong interaction limit.
The magnetic susceptibility shows low-temperature paramagnetic peaks
due to exchange induced singlet-triplet oscillations. The position, number and
intensity of these peaks depend on the range and strength of the interaction.
The contribution of the interaction to the susceptibility displays paramagnetic
and diamagnetic phases as a function of .Comment: 12 pages,6 figures; to appear in Phys. Rev.
Peristaltic Transport of a Couple Stress Fluid: Some Applications to Hemodynamics
The present paper deals with a theoretical investigation of the peristaltic
transport of a couple stress fluid in a porous channel. The study is motivated
towards the physiological flow of blood in the micro-circulatory system, by
taking account of the particle size effect. The velocity, pressure gradient,
stream function and frictional force of blood are investigated, when the
Reynolds number is small and the wavelength is large, by using appropriate
analytical and numerical methods. Effects of different physical parameters
reflecting porosity, Darcy number, couple stress parameter as well as amplitude
ratio on velocity profiles, pumping action and frictional force, streamlines
pattern and trapping of blood are studied with particular emphasis. The
computational results are presented in graphical form. The results are found to
be in good agreement with those of Shapiro et. al \cite{r25} that was carried
out for a non-porous channel in the absence of couple stress effect. The
present study puts forward an important observation that for peristaltic
transport of a couple stress fluid during free pumping when the couple stress
effect of the fluid/Darcy permeability of the medium, flow reversal can be
controlled to a considerable extent. Also by reducing the permeability it is
possible to avoid the occurrence of trapping phenomenon
Optimised Method for the Production and Titration of Lentiviral Vectors Pseudotyped with the SARS-CoV-2 Spike
The use of recombinant lentivirus pseudotyped with the coronavirus Spike protein of SARS-CoV-2 would circumvent the requirement of biosafety-level 3 (BSL-3) containment facilities for the handling of SARS-CoV-2 viruses. Herein, we describe a fast and reliable protocol for the transient production of lentiviruses pseudotyped with SARS-CoV-2 Spike (CoV-2 S) proteins and green fluorescent protein (GFP) reporters. The virus titer is determined by the GFP reporter (fluorescent) expression with a flow cytometer. High titers (>1.00 E+06 infectious units/ml) are produced using codon-optimized CoV-2 S, harbouring the prevalent D614G mutation and lacking its ER retention signal. Enhanced and consistent cell entry is achieved by using permissive HEK293T/17 cells that were genetically engineered to stably express the SARS-CoV-2 human receptor ACE2 along with the cell surface protease TMPRSS2 required for efficient fusion. For the widespread use of this protocol, its reagents have been made publicly available. Graphic abstract: Production and quantification of lentiviral vectors pseudotyped with the SARS-CoV-2 Spike glycoprotein
Defect ferromagnetism induced by lower valence cation doping:Li-doped SnO(2)nanoparticles
To explore the role of Li in establishing room-temperature ferromagnetism in SnO2, the structural, electronic and magnetic properties of Li-doped SnO(2)compounds were studied for different size regimes, from nanoparticles to bulk crystals. Li-doped nanoparticles show ferromagnetic ordering plus a paramagnetic contribution for particle sizes in the range of 16-51 nm, while pure SnO(2)and Li-doped compounds below and above this particular size range are diamagnetic. The magnetic moment is larger for compositions where the Li substitutes for Sn than for compositions where Li prevalently occupies interstitial sites. The observed ferromagnetic ordering in Li-doped SnO(2)nanoparticles is mainly due to the holes created when Li substitutes at a Sn site. Conversely, Li acts as an electron donor and electrons from Li may combine with holes to decrease ferromagnetism when lithium mainly occupies interstitial sites in the SnO(2)lattice
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