10,254 research outputs found
Gravitational radiation from dynamical black holes
An effective energy tensor for gravitational radiation is identified for
uniformly expanding flows of the Hawking mass-energy. It appears in an energy
conservation law expressing the change in mass due to the energy densities of
matter and gravitational radiation, with respect to a Killing-like vector
encoding a preferred flow of time outside a black hole. In a spin-coefficient
formulation, the components of the effective energy tensor can be understood as
the energy densities of ingoing and outgoing, transverse and longitudinal
gravitational radiation. By anchoring the flow to the trapping horizon of a
black hole in a given sequence of spatial hypersurfaces, there is a locally
unique flow and a measure of gravitational radiation in the strong-field
regime.Comment: 5 revtex4 pages. Additional comment
M{\o}ller Energy for the Kerr-Newman metric
The energy distribution in the Kerr-Newman space-time is computed using the
M{\o}ller energy-momentum complex. This agrees with the Komar mass for this
space-time obtained by Cohen and de Felice. These results support the
Cooperstock hypothesis.Comment: 8 pages, 1 eps figure, RevTex, accepted for publication in Mod. Phys.
Lett.
A Cosmological Constant Limits the Size of Black Holes
In a space-time with cosmological constant and matter satisfying
the dominant energy condition, the area of a black or white hole cannot exceed
. This applies to event horizons where defined, i.e. in an
asymptotically deSitter space-time, and to outer trapping horizons (cf.
apparent horizons) in any space-time. The bound is attained if and only if the
horizon is identical to that of the degenerate `Schwarzschild-deSitter'
solution. This yields a topological restriction on the event horizon, namely
that components whose total area exceeds cannot merge. We
discuss the conjectured isoperimetric inequality and implications for the
cosmic censorship conjecture.Comment: 10 page
Energy Associated with Schwarzschild Black Hole in a Magnetic Universe
In this paper we obtain the energy distribution associated with the Ernst
space-time (geometry describing Schwarzschild black hole in Melvin's magnetic
universe) in Einstein's prescription. The first term is the rest-mass energy of
the Schwarzschild black hole, the second term is the classical value for the
energy of the uniform magnetic field and the remaining terms in the expression
are due to the general relativistic effect. The presence of the magnetic field
is found to increase the energy of the system.Comment: RevTex, 8 pages, no figures, a few points are clarified, to appear in
Int. J. Mod. Phys. A. This paper is dedicated to Professor G. F. R. Ellis on
the occasion of his 60th birthda
Construction and enlargement of traversable wormholes from Schwarzschild black holes
Analytic solutions are presented which describe the construction of a
traversable wormhole from a Schwarzschild black hole, and the enlargement of
such a wormhole, in Einstein gravity. The matter model is pure radiation which
may have negative energy density (phantom or ghost radiation) and the
idealization of impulsive radiation (infinitesimally thin null shells) is
employed.Comment: 22 pages, 7 figure
An algorithm to identify rheumatoid arthritis in primary care: a Clinical Practice Research Datalink study
Objective:
Rheumatoid arthritis (RA) is a multisystem,
inflammatory disorder associated with increased levels
of morbidity and mortality. While much research into
the condition is conducted in the secondary care
setting, routinely collected primary care databases
provide an important source of research data. This
study aimed to update an algorithm to define RA that
was previously developed and validated in the General
Practice Research Database (GPRD).
Methods:
The original algorithm consisted of two criteria. Individuals meeting at least one were considered to have RA. Criterion 1:≥1 RA Read code and a disease modifying antirheumatic drug (DMARD) without an alternative indication. Criterion 2:≥2RA Read codes, with at least one
'strong' code and no alternative diagnoses. Lists of codes for consultations and prescriptions were obtained from the authors of the original algorithm where these were available, or compiled based on the original description and clinical knowledge. 4161 people with a first Read code for RA between 1 January 2010 and 31 December 2012 were
selected from the Clinical Practice Research Datalink
(CPRD, successor to the GPRD), and the criteria applied.
Results:
Code lists were updated for the introduction of new Read codes and biological DMARDs. 3577/
4161 (86%) of people met the updated algorithm for
RA, compared to 61% in the original development
study. 62.8% of people fulfilled both Criterion 1 and
Criterion 2.
Conclusions:
Those wishing to define RA in the CPRD, should consider using this updated algorithm, rather than a single RA code, if they wish to identify only those who are most likely to have RA
Energy distribution in a BTZ black hole spacetime
We evaluate the energy distribution associated with the (2+1)-dimensional
rotating BTZ black hole. The energy-momentum complexes of Landau-Lifshitz and
Weinberg are employed for this computation. Both prescriptions give exactly the
same form of energy distribution. Therefore, these results provide evidence in
support of the claim that, for a given gravitational background, different
energy-momentum complexes can give identical results in three dimensions, as it
is the case in four dimensions.Comment: 16 pages, LaTeX; v2: comments, clarifications and references added,
version to appear in Int.J.Mod.Phys.
Energy Distribution in Melvin's Magnetic Universe
We use the energy-momentum complexes of Landau and Lifshitz and Papapetrou to
obtain the energy distribution in Melvin's magnetic universe. For this
space-time we find that these definitions of energy give the same and
convincing results. The energy distribution obtained here is the same as we
obtained earlier for the same space-time using the energy-momentum complex of
Einstein. These results uphold the usefulness of the energy-momentum complexes.Comment: 8 pages, RevTex, no figure
Gravitational waves, black holes and cosmic strings in cylindrical symmetry
Gravitational waves in cylindrically symmetric Einstein gravity are described
by an effective energy tensor with the same form as that of a massless Klein-
Gordon field, in terms of a gravitational potential generalizing the Newtonian
potential. Energy-momentum vectors for the gravitational waves and matter are
defined with respect to a canonical flow of time. The combined energy-momentum
is covariantly conserved, the corresponding charge being the modified Thorne
energy. Energy conservation is formulated as the first law expressing the
gradient of the energy as work and energy-supply terms, including the energy
flux of the gravitational waves. Projecting this equation along a trapping
horizon yields a first law of black-hole dynamics containing the expected term
involving area and surface gravity, where the dynamic surface gravity is
defined with respect to the canonical flow of time. A first law for dynamic
cosmic strings also follows. The Einstein equation is written as three wave
equations plus the first law, each with sources determined by the combined
energy tensor of the matter and gravitational waves.Comment: 10 pages, revtex. Published version with further detail
Complex lapse, complex action and path integrals
Imaginary time is often used in quantum tunnelling calculations. This article
advocates a conceptually sounder alternative: complex lapse. In the ``3+1''
action for the Einstein gravitational field minimally coupled to a Klein-Gordon
field, allowing the lapse function to be complex yields a complex action which
generates both the usual Lorentzian theory and its Riemannian analogue, and in
particular allows a change of signature between the two. The action and
variational equations are manifestly well defined in the Hamiltonian
representation, with the momentum fields consequently being complex. The
complex action interpolates between the Lorentzian and Riemannian actions as
they appear formally in the respective path integrals. Thus the complex-lapse
theory provides a unified basis for a path-integral quantum theory of gravity
involving both Lorentzian and Riemannian aspects. A major motivation is the
quantum-tunnelling scenario for the origin of the universe. Taken as an
explanation for the observed quantum tunnelling of particles, the complex-lapse
theory determines that the argument of the lapse for the universe now is
extremely small but negative.Comment: 12 pages, Te
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