3,281 research outputs found
Energy and Momentum Distributions of the Magnetic Solution to (2+1) Einstein-Maxwell Gravity
We use Moeller's energy-momentum complex in order to explicitly evaluate the
energy and momentum density distributions associated with the three-dimensional
magnetic solution to the Einstein-Maxwell equations. The magnetic spacetime
under consideration is a one-parametric solution describing the distribution of
a radial magnetic field in a three-dimensional AdS background, and representing
the superposition of the magnetic field with a 2+1 Einstein static
gravitational field.Comment: LaTex, 13 pages; v2 clarifying comments and references added,
Conclusions improved, to appear in Mod. Phys. Lett.
Interacting Kasner-type cosmologies
It is well known that Kasner-type cosmologies provide a useful framework for
analyzing the three-dimensional anisotropic expansion because of the
simplification of the anisotropic dynamics. In this paper relativistic
multi-fluid Kasner-type scenarios are studied. We first consider the general
case of a superposition of two ideal cosmic fluids, as well as the particular
cases of non-interacting and interacting ones, by introducing a
phenomenological coupling function . For two-fluid cosmological scenarios
there exist only cosmological scaling solutions, while for three-fluid
configurations there exist not only cosmological scaling ones, but also more
general solutions. In the case of triply interacting cosmic fluids we can have
energy transfer from two fluids to a third one, or energy transfer from one
cosmic fluid to the other two. It is shown that by requiring the positivity of
energy densities there always is a matter component which violates the dominant
energy condition in this kind of anisotropic cosmological scenarios.Comment: Accepted for publication in Astrophysics &Space Science, 8 page
No Black Hole Theorem in Three-Dimensional Gravity
A common property of known black hole solutions in (2+1)-dimensional gravity
is that they require a negative cosmological constant. In this letter, it is
shown that a (2+1)-dimensional gravity theory which satisfies the dominant
energy condition forbids the existence of a black hole to explain the above
situation.Comment: 3 pages, no figures, to be published in Physical Review Letter
Magnetically charged solutions via an analog of the electric-magnetic duality in (2+1)-dimensional gravity theories
We find an analog of the electric-magnetic duality, which is a
transformation between magnetic and electric sectors of the static and
rotationally symmetric solutions in a class of (2+1)-dimensional
Einstein-Maxwell-Dilaton gravity theories. The theories in our consideration
include, in particular, one parameter class of theories continuously connecting
the Banados-Teitelboim-Zanelli (BTZ) gravity and the low energy string
effective theory. When there is no charge, we have or
symmetry, depending on a parameter that specifies each theory. Via the
transformation, we obtain exact magnetically charged solutions from the known
electrically charged solutions. We explain the relationship between the
transformation and symmetry, and comment on the -duality of the
string theory.Comment: 10 pages, RevTe
Properties of Solutions in 2+1 Dimensions
We solve the Einstein equations for the 2+1 dimensions with and without
scalar fields. We calculate the entropy, Hawking temperature and the emission
probabilities for these cases. We also compute the Newman-Penrose coefficients
for different solutions and compare them.Comment: 16 pages, 1 figures, PlainTeX, Dedicated to Prof. Yavuz Nutku on his
60th birthday. References adde
Evolution of high-frequency gravitational waves in some cosmological models
We investigate Isaacson's high-frequency gravitational waves which propagate
in some relevant cosmological models, in particular the FRW spacetimes. Their
time evolution in Fourier space is explicitly obtained for various metric forms
of (anti--)de Sitter universe. Behaviour of high-frequency waves in the
anisotropic Kasner spacetime is also described.Comment: 14 pages, 8 figures, to appear in Czech. J. Phy
Spherical and planar three-dimensional anti-de Sitter black holes
The technique of dimensional reduction was used in a recent paper (Zanchin et
al, Phys. Rev. D66, 064022,(2002)) where a three-dimensional (3D)
Einstein-Maxwell-Dilaton theory was built from the usual four-dimensional (4D)
Einstein-Maxwell-Hilbert action for general relativity. Starting from a class
of 4D toroidal black holes in asymptotically anti-de Sitter (AdS) spacetimes
several 3D black holes were obtained and studied in such a context. In the
present work we choose a particular case of the 3D action which presents
Maxwell field, dilaton field and an extra scalar field, besides gravity field
and a negative cosmological constant, and obtain new 3D static black hole
solutions whose horizons may have spherical or planar topology. We show that
there is a 3D static spherically symmetric solution analogous to the 4D
Reissner-Nordstr\"om-AdS black hole, and obtain other new 3D black holes with
planar topology. From the static spherical solutions, new rotating 3D black
holes are also obtained and analyzed in some detail.Comment: 27 pages, uses "iopclass" files (Latex2e
On the static solutions in gravity with massive scalar field in three dimensions
We investigate circularly symmetric static solutions in three-dimensional
gravity with a minimally coupled massive scalar field. We integrate numerically
the field equations assuming asymptotic flatness, where black holes do not
exist and a naked singularity is present. We also give a brief review on the
massless cases with cosmological constant.Comment: 11 pages, LaTeX, 1 Postscript figure. Some changes were don
Supergravity with cosmological constant and the AdS group
It is shown that the supersymmetric extension of the Stelle-West formalism
permits the construction of an action for -dimensional N=1 supergravity
with cosmological constant genuinely invariant under the Since the
action is invariant under the supersymmetric extension of the group, the
supersymmetry algebra closes off shell without the need for auxiliary fields.
The limit case , i.e. -dimensional N=1 supergravity invariant
under the Poincar\'{e} supergroup is also discussed.Comment: 10 page
Impact of Obesity on Perioperative Morbidity and Mortality Following Pancreaticoduodenectomy
Background: Obesity has been implicated as a risk factor for perioperative and postoperative complications. The aim of this study was determine the impact of obesity on morbidity and mortality in patients undergoing pancreaticoduodenectomy (PD).
Study Design: Between January 2000 and July 2007, 262 patients underwent PD at Thomas Jefferson University Hospital (TJUH), of whom 240 had complete data, including body mass index (BMI) for analysis. Data on BMI, preoperative parameters, operative details, and post-operative course were collected. Patients were categorized as obese (BMI \u3e30 kg/m2), overweight (25≤BMI\u3c30), or normal weight (BMI\u3c25). Complications were graded according to previous published scales. Other endpoints included length of postoperative hospital stay, blood loss, and operative duration. Analyses were performed using univariate and multivariable models.
Results: There were 103 (42.9%) normal weight, 71 (29.6%) overweight and 66 (27.5%) obese patients. There were 5 perioperative deaths (2.1%) with no differences across BMI categories. A significant difference in median operative duration and blood loss between obese and normal weight patients was identified (439vs. 362.5minutes, p= 0.0004; 650 vs. 500 ml, p=0.0139). Furthermore, median length of stay was marginally significantly longer for by BMI (9.5 vs. 8 days, p=0.095). While there were no significant differences in superficial wound infections, obese patients did have an increased rate of serious complications compared to normal weight patients (24.2% vs. 13.6%, respectively; p=0.10).
Conclusions: Obese patients undergoing PD have a significantly increased blood loss and longer operative time, but do not have a significantly increased length of postoperative hospital stay or rate of serious complications. These findings should be considered when assessing patients for operation and when counseling patients regarding operative risk, but do not preclude obese individuals from undergoing definitive pancreatic surgery
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