2,225 research outputs found
Taub-NUT/Bolt Black Holes in Gauss-Bonnet-Maxwell Gravity
We present a class of higher dimensional solutions to Gauss-Bonnet-Maxwell
equations in dimensions with a U(1) fibration over a -dimensional
base space . These solutions depend on two extra parameters, other
than the mass and the NUT charge, which are the electric charge and the
electric potential at infinity . We find that the form of metric is
sensitive to geometry of the base space, while the form of electromagnetic
field is independent of . We investigate the existence of
Taub-NUT/bolt solutions and find that in addition to the two conditions of
uncharged NUT solutions, there exist two other conditions. These two extra
conditions come from the regularity of vector potential at and the fact
that the horizon at should be the outer horizon of the black hole. We
find that for all non-extremal NUT solutions of Einstein gravity having no
curvature singularity at , there exist NUT solutions in
Gauss-Bonnet-Maxwell gravity. Indeed, we have non-extreme NUT solutions in
dimensions only when the -dimensional base space is chosen to be
. We also find that the Gauss-Bonnet-Maxwell gravity has
extremal NUT solutions whenever the base space is a product of 2-torii with at
most a 2-dimensional factor space of positive curvature, even though there a
curvature singularity exists at . We also find that one can have bolt
solutions in Gauss-Bonnet-Maxwell gravity with any base space. The only case
for which one does not have black hole solutions is in the absence of a
cosmological term with zero curvature base space.Comment: 23 pages, 3 figures, typos fixed, a few references adde
Two-Dimensional Black Holes and Planar General Relativity
The Einstein-Hilbert action with a cosmological term is used to derive a new
action in 1+1 spacetime dimensions. It is shown that the two-dimensional theory
is equivalent to planar symmetry in General Relativity. The two-dimensional
theory admits black holes and free dilatons, and has a structure similar to
two-dimensional string theories. Since by construction these solutions also
solve Einstein's equations, such a theory can bring two-dimensional results
into the four-dimensional real world. In particular the two-dimensional black
hole is also a black hole in General Relativity.Comment: 11 pages, plainte
Charged null fluid collapse in anti-de Sitter spacetimes and naked singularities
We investigate the occurrence of naked singularities in the spherically
symmetric, plane symmetric and cylindrically symmetric collapse of charged null
fluid in an anti-de Sitter background. The naked singularities are found to be
strong in Tipler's sense and thus violate the cosmic censorship conjecture, but
not hoop conjecture.Comment: 8 pages, No figure
Collapsing shells of radiation in anti-de Sitter spacetimes and the hoop and cosmic censorship conjectures
Gravitational collapse of radiation in an anti-de Sitter background is
studied. For the spherical case, the collapse proceeds in much the same way as
in the Minkowski background, i.e., massless naked singularities may form for a
highly inhomogeneous collapse, violating the cosmic censorship, but not the
hoop conjecture. The toroidal, cylindrical and planar collapses can be treated
together. In these cases no naked singularity ever forms, in accordance with
the cosmic censorship. However, since the collapse proceeds to form toroidal,
cylindrical or planar black holes, the hoop conjecture in an anti-de Sitter
spacetime is violated.Comment: 4 pages, Revtex Journal: to appear in Physical Review
Area Regge Calculus and Discontinuous Metrics
Taking the triangle areas as independent variables in the theory of Regge
calculus can lead to ambiguities in the edge lengths, which can be interpreted
as discontinuities in the metric. We construct solutions to area Regge calculus
using a triangulated lattice and find that on a spacelike hypersurface no such
discontinuity can arise. On a null hypersurface however, we can have such a
situation and the resulting metric can be interpreted as a so-called refractive
wave.Comment: 18 pages, 1 figur
Relativistic Static Thin Disks with Radial Stress Suport
New solutions for static non-rotating thin disks of finite radius with
nonzero radial stress are studied. A method to introduce either radial pressure
or radial tension is presented. The method is based on the use of conformal
transformations.Comment: 19 pages, LaTeX, 7 figures, submitted to Class. Quan. Gra
The Quantum Propagator for a Nonrelativistic Particle in the Vicinity of a Time Machine
We study the propagator of a non-relativistic, non-interacting particle in
any non-relativistic ``time-machine'' spacetime of the type shown in Fig.~1: an
external, flat spacetime in which two spatial regions, at time and
at time , are connected by two temporal wormholes, one leading from
the past side of to t the future side of and the other from the
past side of to the future side of . We express the propagator
explicitly in terms of those for ordinary, flat spacetime and for the two
wormholes; and from that expression we show that the propagator satisfies
completeness and unitarity in the initial and final ``chronal regions''
(regions without closed timelike curves) and its propagation from the initial
region to the final region is unitary. However, within the time machine it
satisfies neither completeness nor unitarity. We also give an alternative proof
of initial-region-to-final-region unitarity based on a conserved current and
Gauss's theorem. This proof can be carried over without change to most any
non-relativistic time-machine spacetime; it is the non-relativistic version of
a theorem by Friedman, Papastamatiou and Simon, which says that for a free
scalar field, quantum mechanical unitarity follows from the fact that the
classical evolution preserves the Klein-Gordon inner product
Does the Clinical Frailty Scale at Triage Predict Outcomes From Emergency Care for Older People?
Study objective:
We determine whether the Clinical Frailty Scale applied at emergency department (ED) triage is associated with important service- and patient-related outcomes.
Methods:
We undertook a single-center, retrospective cohort study examining hospital-related outcomes and their associations with frailty scores assessed at ED triage. Participants were aged 65 years or older, registered on their first ED presentation during the study period at a single, centralized ED in the United Kingdom. Baseline data included age, sex, Clinical Frailty Scale score, National Early Warning Score–2 and the Charlson Comorbidity Index score; outcomes included length of stay, readmissions (any future admissions), and mortality (inhospital or out of hospital) up to 2 years after ED presentation. Survival analysis methods (standard and competing risks) were applied to assess associations between ED triage frailty scores and outcomes. Unadjusted incidence curves and adjusted hazard ratios are presented.
Results:
A total of 52,562 individuals representing 138,328 ED attendances were included; participants’ mean age was 78.0 years, and 55% were women. Initial admission rates generally increased with frailty. Mean length of stay after 30- or 180-day follow-up was relatively low; all Clinical Frailty Scale categories included patients who experienced zero days’ length of stay (ie, ambulatory care) and patients with relatively high numbers of inhospital days. Overall, 46% of study participants were readmitted by the 2-year follow-up. Readmissions increased with Clinical Frailty Scale score up until a score of 6 and then attenuated. Mortality rates increased with increasing frailty; the adjusted hazard ratio was 3.6 for Clinical Frailty Scale score 7 to 8 compared with score 1 to 3.
Conclusion:
Frailty assessed at ED triage (with the Clinical Frailty Scale) is associated with adverse outcomes in older people. Its use in ED triage might aid immediate clinical decisionmaking and service configuration
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