338 research outputs found
Generalized entropies and corresponding holographic dark energy models
Using Tsallis statistics and its relation with Boltzmann entropy, the Tsallis
entropy content of black holes is achieved, a result in full agreement with a
recent study (Phys. Lett. B 794, 24 (2019)). In addition, employing Kaniadakis
statistics and its relation with that of Tsallis, the Kaniadakis entropy of
black holes is obtained. The Sharma-Mittal and R\'{e}nyi entropy contents of
black holes are also addressed by employing their relations with Tsallis
entropy. Thereinafter, relying on the holographic dark energy hypothesis and
the obtained entropies, two new holographic dark energy models are introduced
and their implications on the dynamics of a flat FRW universe are studied when
there is also a pressureless fluid in background. In our setup, the apparent
horizon is considered as the IR cutoff, and there is not any mutual interaction
between the cosmic fluids. The results indicate that the obtained cosmological
models have ) notable powers to describe the cosmic evolution from the
matter-dominated era to the current accelerating universe, and ) suitable
predictions for the universe age
Thermodynamics of charged rotating dilaton black branes with power-law Maxwell field
In this paper, we construct a new class of charged rotating dilaton black
brane solutions, with complete set of rotation parameters, which is coupled to
a nonlinear Maxwell field. The Lagrangian of the matter field has the form of
the power-law Maxwell field. We study the causal structure of the spacetime and
its physical properties in ample details. We also compute thermodynamic and
conserved quantities of the spacetime such as the temperature, entropy, mass,
charge, and angular momentum. We find a Smarr-formula for the mass and verify
the validity of the first law of thermodynamics on the black brane horizon.
Finally, we investigate the thermal stability of solutions in both canonical
and grand-canonical ensembles and disclose the effects of dilaton field and
nonlinearity of Maxwell field on the thermal stability of the solutions. We
find that for , charged rotating black brane solutions are
thermally stable independent of the values of the other parameters. For
, the solutions can encounter an unstable phase depending on the
metric parameters.Comment: 15 pages, 14 figures. We have revised the text to remove the overlap
Counterterms for Static Lovelock Solutions
In this paper, we introduce the counterterms that remove the non-logarithmic
divergences of the action in third order Lovelock gravity for static
spacetimes. We do this by defining the cosmological constant in such a way that
the asymptotic form of the metric have the same form in Lovelock and Einstein
gravities. Thus, we employ the counterterms of Einstein gravity and show that
the power law divergences of the action of Lovelock gravity for static
spacetimes can be removed by suitable choice of coefficients. We find that the
dependence of these coefficients on the dimension in Lovelock gravity is the
same as in Einstein gravity. We also introduce the finite energy-momentum
tensor and employ these counterterms to calculate the finite action and mass of
static black hole solutions of third order Lovelock gravity. Next, we calculate
the thermodynamic quantities and show that the entropy calculated through the
use of Gibbs-Duhem relation is consistent with the obtained entropy by Wald's
formula. Furthermore, we find that in contrast to Einstein gravity in which
there exists no uncharged extreme black hole, third order Lovelock gravity can
have these kind of black holes. Finally, we investigate the stability of static
charged black holes of Lovelock gravity in canonical ensemble and find that
small black holes show a phase transition between very small and small black
holes, while the large ones are stable.Comment: arXiv admin note: text overlap with arXiv:1008.0102 by other author
Thermodynamics and gauge/gravity duality for Lifshitz black holes in the presence of exponential electrodynamics
In this paper, we construct a new class of topological black hole Lifshitz
solutions in the presence of nonlinear exponential electrodynamics for
Einstein-dilaton gravity. We show that the reality of Lifshitz supporting
Maxwell matter fields exclude the negative horizon curvature solutions except
for the asymptotic AdS case. Calculating the conserved and thermodynamical
quantities, we obtain a Smarr type formula for the mass and confirm that
thermodynamics first law is satisfied on the black hole horizon. Afterward, we
study the thermal stability of our solutions and figure out the effects of
different parameters on the stability of solutions under thermal perturbations.
Next, we apply the gauge/gravity duality in order to calculate the ratio of
shear viscosity to entropy for a three-dimensional hydrodynamic system by using
the pole method. Furthermore, we study the behavior of holographic conductivity
for two-dimensional systems such as graphene. We consider linear Maxwell and
nonlinear exponential electrodynamics separately and disclose the effect of
nonlinearity on holographic conductivity. We indicate that holographic
conductivity vanishes for in the case of nonlinear electrodynamics while
it does not in the linear Maxwell case. Finally, we solve perturbative
additional field equations numerically and plot the behaviors of real and
imaginary parts of conductivity for asymptotic AdS and Lifshitz cases. We
present experimental results match with our numerical ones.Comment: 31 pages, 16 figures (some figures include two subfigures). V2: some
typos corrected, some references adde
Formulation and characterization of a novel cutaneous wound healing ointment by silver nanoparticles containing Citrus lemon leaf: A chemobiological study
Introduction: Formulating new wound-healing ointments by natural compounds is the first research priority in the developing and developed countries. This study was intended to provide green formulation of Ag-NP ointment containing Citrus lemon leaf aqueous extract and examine its capability of healing cutaneous wounds and its antioxidant and cytotoxicity activities under in vitro and in vivo conditions. Materials and methods: Different techniques, including UV�Vis and FT-IR spectroscopy, were used to characterize Ag-NPs. MTT assay was used to investigate cytotoxicity property of Ag-NPs. Antioxidant activity of Ag-NPs were examined by DPPH in the presence of butylated hydroxytoluene as positive control. Parameters of cutaneous wound healing were measured both histopathologically and biochemically. Results: Clear peak at 429 nm shown by UV�Vis spectroscopy indicated formation of Ag-NPs. In FT-IR spectroscopy, presence of many antioxidant compounds provided an excellent condition to reduce silver in Ag-NPs. FE-SEM and TEM images showed spherical Ag-NPs with an average size of 25.1 nm. The synthesized silver nanoparticles had excellent cell viability on the HUVECs line and indicated this method was nontoxic. Application of Ag-NP ointment improved wound healing parameters significantly (P � 0.01). Ag-NPs reduced wound areas, total cells, neutrophils and lymphocytes significantly (P � 0.01) and increased wound contracture, vessels, hexosamines, hydroxyl proline, hexuronic acid, fibrocytes, fibroblasts and fibrocyte/ fibroblast ratios significantly (P � 0.01). Conclusions: Once our results are verified by clinically experimental studies, Ag-NP ointment can be used as a modern one to treat several types of wounds, especially cutaneous ones, in humans. © 202
Numerical analysis of an initial design of a counter-rotating pump-turbine
Renewable sources of energy are on the rise and will continue to increase the coming decades. A common problem with the renewable energy sources is that they rely on effects which cannot be controlled, for instance the strength of the wind or the intensity of the sunlight. The ALPHEUS Horizon 2020 EU project has the aim to develop a low-head hydraulic pump-turbine which can work as a grid stabilising unit. This work presents numerical results of an initial hub-driven counter-rotating pump-turbine design within ALPHEUS. Computational fluid dynamics simulations are carried out in both prototype and model scale, for pump and turbine modes, and under steady-state and unsteady conditions. The results indicate that the initial design have a hydraulic efficiency of roughly 90 % in both modes and for a wide range of operating conditions. The unsteady simulations reveal a complex flow pattern downstream the two runners and frequency analysis show that the dominating pressure pulsations originates from the rotor dynamics. Given the promising high efficiency, this initial design makes an ideal platform to continue the work to optimise efficiency and transient operations further
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