1,151 research outputs found
Quantum Statistical Relation for black holes in nonlinear electrodynamics coupled to Einstein-Gauss-Bonnet AdS gravity
We consider curvature-squared corrections to Einstein-Hilbert gravity action
in the form of Gauss-Bonnet term in D>4 dimensions. In this theory, we study
the thermodynamics of charged static black holes with anti-de Sitter (AdS)
asymptotics, and whose electric field is described by nonlinear electrodynamics
(NED). These objects have received considerable attention in recent literature
on gravity/gauge dualities.
It is well-known that, within the framework of anti de-Sitter/Conformal Field
Theory (AdS/CFT) correspondence, there exists a nonvanishing Casimir
contribution to the internal energy of the system, manifested as the vacuum
energy for global AdS spacetime in odd dimensions. Because of this reason, we
derive a Quantum Statistical Relation directly from the Euclidean action and
not from the integration of the First Law of thermodynamics. To this end, we
employ a background-independent regularization scheme which consists in the
addition to the bulk action of counterterms that depend on both extrinsic and
intrinsic curvatures of the boundary (Kounterterm series). This procedure
results in a consistent inclusion of the vacuum energy and chemical potential
in the thermodynamic description for Einstein-Gauss-Bonnet AdS gravity
regardless the explicit form of the NED Lagrangian.Comment: 22 pages, no figures; 3 references and a subsection on Thermodynamic
Charges added; Final version for PR
Topological regularization and self-duality in four-dimensional anti-de Sitter gravity
It is shown that the addition of a topological invariant (Gauss-Bonnet term)
to the anti-de Sitter (AdS) gravity action in four dimensions recovers the
standard regularization given by holographic renormalization procedure. This
crucial step makes possible the inclusion of an odd parity invariant
(Pontryagin term) whose coupling is fixed by demanding an asymptotic (anti)
self-dual condition on the Weyl tensor. This argument allows to find the dual
point of the theory where the holographic stress tensor is related to the
boundary Cotton tensor as , which
has been observed in recent literature in solitonic solutions and hydrodynamic
models.
A general procedure to generate the counterterm series for AdS gravity in any
even dimension from the corresponding Euler term is also briefly discussed.Comment: 13 pages, no figures; enlarged discussion on self-duality condition
for AAdS spacetimes, references added, final version for PR
EVALUATION OF THE ANTIOXIDANT ACTIVITY OF THE FLAVONOIDS ISOLATED FROM HELIOTROPIUM SINUATUM RESIN USING ORACFL, DPPH AND ESR METHODOLOGIES
Indexación: Web of Science; Scielo.The antioxidant capacity has been determined for a number of flavonoid compounds from Heliotropium sinuatum, a plant that grows in arid areas in the north of Chile. The methodologies used were: ORAC(FL) (oxygen radical absorbance capacity - fluorescein), DPPH (2,2-diphenyl-2-picrylhydrazyl) bleaching and electron spin resonance (ESR). These compounds were studied in homogeneous and heterogeneous media. The results showed that the 7-o-methyleriodictiol and 3-o-methylisorhamnetin are those with the highest antioxidant capacity.http://ref.scielo.org/m82cz
Xenoestrogens released from lacquer coatings in food cans
We present data showing that some foods preserved in lacquer-coated cans and the liquid in them may acquire estrogenic activity. Hormonal activity was measured using the E-screen bioassay. The biological activity of vegetables packed in cans was a result of plastic monomers used in manufacturing the containers. The plastic monomer bisphenol-A, identified by mass spectrometry, was found as a contaminant not only in the liquid of the preserved vegetables but also in water autoclaved in the cans. The amount of bisphenol-A in the extracts accounted for all the hormonal activity measured. Although the presence of other xenoestrogens cannot be ruled out, it is apparent that all estrogenic activity in these cans was due to bisphenol-A leached from the lacquer coating. The use of plastic in food-packaging materials may require closer scrutiny to determine whether epoxy resins and polycarbonates contribute to human exposure to xenoestrogens.This work was supported by grant 94/1551
from the Fondo de Investigaciones Sanitarias (FIS), Spanish Ministry of Health
Uniqueness of static decompositions
We classify static manifolds which admit more than one static decomposition
whenever a condition on the curvature is fullfilled. For this, we take a
standard static vector field and analyze its associated one parameter family of
projections onto the base. We show that the base itself is a static manifold
and the warping function satisfies severe restrictions, leading us to our
classification results. Moreover, we show that certain condition on the
lightlike sectional curvature ensures the uniqueness of static decomposition
for Lorentzian manifolds.Comment: 14 page
Black strings in AdS_5
We present non-extremal magnetic black string solutions in five-dimensional
gauged supergravity. The conformal infinity is the product of time and S^1xS_h,
where S_h denotes a compact Riemann surface of genus h. The construction is
based on both analytical and numerical techniques. We compute the holographic
stress tensor, the Euclidean action and the conserved charges of the solutions
and show that the latter satisfy a Smarr-type formula. The phase structure is
determined in the canonical ensemble, and it is shown that there is a first
order phase transition from small to large black strings, which disappears
above a certain critical magnetic charge that is obtained numerically. For
another particular value of the magnetic charge, that corresponds to a twisting
of the dual super Yang-Mills theory, the conformal anomalies coming from the
background curvature and those arising from the coupling to external gauge
fields exactly cancel. We also obtain supersymmetric solutions describing waves
propagating on extremal BPS magnetic black strings, and show that they possess
a Siklos-Virasoro reparametrization invariance.Comment: 40 pages, 7 figures, JHEP3. v2: minor corrections, 2 references
added. v3: typos in holographic stress tensor corrected, 3 references adde
Hamilton-Jacobi Counterterms for Einstein-Gauss-Bonnet Gravity
The on-shell gravitational action and the boundary stress tensor are
essential ingredients in the study of black hole thermodynamics. We employ the
Hamilton-Jacobi method to calculate the boundary counterterms necessary to
remove the divergences and allow the study of the thermodynamics of
Einstein-Gauss-Bonnet black holes.Comment: 21 pages, LaTe
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