864 research outputs found
A Proof of the Generalized Second Law for Two-Dimensional Black Holes
We investigate the generalized second law for two-dimensional black holes in
equilibrium (Hartle-Hawking) and nonequilibrium (Unruh) with the heat bath
surrounding the black holes. We obtain a simple expression for the change of
total entropy in terms of covariant thermodynamic variables, which is valid not
only for the Hartle-Hawking state but also for the Unruh state up to leading
order, without assuming a quasi-stationary evolution of the black holes. Using
this expression, it is shown that the rate of local entropy production is
non-negative in the two-dimensional black hole systems.Comment: 15 pages, boundary condition of static black hole is added to clarify
the situation, abstract and section 4 (concluding remarks) is rewritten, and
minor corrections, references adde
Trends in sexually transmitted infections in general practice 1990-2000: population based study using data from the UK general practice research database
Objective: To describe the contribution of primary care to the
diagnosis and management of sexually transmitted infections in
the United Kingdom, 1990-2000, in the context of increasing
incidence of infections in genitourinary medicine clinics.
Design: Population based study.
Setting: UK primary care.
Participants: Patients registered in the UK general practice
research database.
Main outcome measures: Incidence of diagnosed sexually
transmitted infections in primary care and estimation of the
proportion of major such infections diagnosed in primary care.
Results: An estimated 23.0% of chlamydia cases in women but
only 5.3% in men were diagnosed and treated in primary care
during 1998-2000, along with 49.2% cases of non-specific
urethritis and urethral discharge in men and 5.7% cases of
gonorrhoea in women and 2.9% in men. Rates of diagnosis in
primary care rose substantially in the late 1990s.
Conclusions: A substantial and increasing number of sexually
transmitted infections are diagnosed and treated in primary
care in the United Kingdom, with sex ratios differing from
those in genitourinary medicine clinics. Large numbers of men
are treated in primary care for presumptive sexually
transmitted infections
Could biodiversity loss have increased Australia’s bushfire threat
Ecosystem engineers directly or indirectly affect the availability of resources
through changing the physical state of biotic and/or abiotic materials. Fossorial
ecosystem engineers have been hypothesized as affecting fire behaviour through
altering litter accumulation and breakdown, however, little evidence of this has
been shown to date. Fire is one of the major ecological processes affecting biodiversity
globally. Australia has seen the extinction of 29 of 315 terrestrial mammal
species in the last 200 years and several of these species were ecosystem engineers
whose fossorial actions may increase the rate of leaf litter breakdown. Thus, their
extinction may have altered the rate of litter accumulation and therefore fire ignition
potential and rate of spread. We tested whether a reduction in leaf litter was
associated with sites where mammalian ecosystem engineers had been reintroduced
using a pair-wise, cross-fence comparison at sites spanning the Australian continent.
At Scotia (New South Wales), Karakamia (Western Australia) and Yookamurra
(South Australia) sanctuaries, leaf litter mass ( 24%) and percentage cover
of leaf litter ( 3%) were significantly lower where reintroduced ecosystem engineers
occurred compared to where they were absent, and fire behaviour modelling
illustrated this has substantial impacts on flame height and rate of spread. This
result has major implications for fire behaviour and management globally wherever
ecosystem engineers are now absent as the reduced leaf litter volumes where they
occur will lead to decreased flame height and rate of fire spread. This illustrates
the need to restore the full suite of biodiversity globally.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1469-17952017-12-31hb2016Centre for Wildlife Managemen
Origami World
We paste together patches of to find solutions which describe two
4-branes intersecting on a 3-brane with non-zero tension. We construct
explicitly brane arrays with Minkowski, de Sitter and Anti-de Sitter geometries
intrinsic to the 3-brane, and describe how to generalize these solutions to the
case of , , where -branes intersect on a 3-brane. The
Minkowski and de Sitter solutions localize gravity to the intersection, leading
to 4D Newtonian gravity at large distances. We show this explicitly in the case
of Minkowski origami by finding the zero-mode graviton, and computing the
couplings of the bulk gravitons to the matter on the intersection. In de Sitter
case, this follows from the finiteness of the bulk volume. The effective 4D
Planck scale depends on the square of the fundamental 6D Planck scale, the
radius and the angles between the 4-branes and the radial
direction, and for the Minkowski origami it is . If this may account for the Planck-electroweak hierarchy even if , with a possibility for sub-millimeter corrections to the
Newton's law. We comment on the early universe cosmology of such models.Comment: plain LaTeX, 23 pages + 2 .eps figure
Non-linear instability of Kerr-type Cauchy horizons
Using the general solution to the Einstein equations on intersecting null
surfaces developed by Hayward, we investigate the non-linear instability of the
Cauchy horizon inside a realistic black hole. Making a minimal assumption about
the free gravitational data allows us to solve the field equations along a null
surface crossing the Cauchy Horizon. As in the spherical case, the results
indicate that a diverging influx of gravitational energy, in concert with an
outflux across the CH, is responsible for the singularity. The spacetime is
asymptotically Petrov type N, the same algebraic type as a gravitational shock
wave. Implications for the continuation of spacetime through the singularity
are briefly discussed.Comment: 11 pages RevTeX, two postscript figures included using epsf.st
Thermodynamics of charged and rotating black strings
We study thermodynamics of cylindrically symmetric black holes. Uncharged as
well as charged and rotating objects have been discussed. We derive surface
gravity and hence the Hawking temperature and entropy for all these cases. We
correct some results in the literature and present new ones. It is seen that
thermodynamically these black configurations behave differently from
spherically symmetric objects
Corrections to Hawking-like Radiation for a Friedmann-Robertson-Walker Universe
Recently, a Hamilton-Jacobi method beyond semiclassical approximation in
black hole physics was developed by \emph{Banerjee} and
\emph{Majhi}\cite{beyond0}. In this paper, we generalize their analysis of
black holes to the case of Friedmann-Robertson-Walker (FRW) universe. It is
shown that all the higher order quantum corrections in the single particle
action are proportional to the usual semiclassical contribution. The
corrections to the Hawking-like temperature and entropy of apparent horizon for
FRW universe are also obtained. In the corrected entropy, the area law involves
logarithmic area correction together with the standard inverse power of area
term.Comment: 10 pages, no figures, comments are welcome; v2: references added and
some typoes corrected, to appear in Euro.Phys.J.C; v3:a defect corrected. We
thank Dr.Elias Vagenas for pointing out a defect of our pape
Wormholes in AdS
We construct a few Euclidean supergravity solutions with multiple boundaries.
We consider examples where the corresponding boundary field theory is well
defined on each boundary. We point out that these configurations are puzzling
from the AdS/CFT point of view. A proper understanding of the AdS/CFT
dictionary for these cases might yield some information about the physics of
closed universes.Comment: 38 pages, 2 figures, harvmac. v2: minor typos corrected and
references adde
Equatorial circular orbits in the Kerr-de Sitter spacetimes
Equatorial motion of test particles in the Kerr-de Sitter spacetimes is
considered. Circular orbits are determined, their properties are discussed for
both the black-hole and naked-singularity spacetimes, and their relevance for
thin accretion discs is established.Comment: 24 pages, 19 figures, REVTeX
Energy Distribution associated with Static Axisymmetric Solutions
This paper has been addressed to a very old but burning problem of energy in
General Relativity. We evaluate energy and momentum densities for the static
and axisymmetric solutions. This specializes to two metrics, i.e., Erez-Rosen
and the gamma metrics, belonging to the Weyl class. We apply four well-known
prescriptions of Einstein, Landau-Lifshitz, Papaterou and Mller to
compute energy-momentum density components. We obtain that these prescriptions
do not provide similar energy density, however momentum becomes constant in
each case. The results can be matched under particular boundary conditions.Comment: 18 pages, accepted for publication in Astrophysics and SpaceScienc
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