2,064 research outputs found
Pull-through procedure as treatment for coloanal anastomotic dehiscence following laparoscopic total mesorectal excision
On the Universality of the Entropy-Area Relation
We present an argument that, for a large class of possible dynamics, a
canonical quantization of gravity will satisfy the Bekenstein-Hawking
entropy-area relation. This result holds for temperatures low compared to the
Planck temperature and for boundaries with areas large compared to Planck area.
We also relate our description, in terms of a grand canonical ensemble, to
previous geometric entropy calculations using area ensembles.Comment: 6 page
String-Loop Corrected Magnetic Black Holes
We discuss the form of the string-loop-corrected effective action obtained by
compactification of the heterotic string theory on the manifold
or on its orbifold limit and the loop-corrected magnetic black hole solutions
of the equations of motion. Effective 4D theory has N=2 local supersymmetry.
Using the string-loop-corrected prepotential of the N=2 supersymmetric theory,
which receives corrections only from the string world sheets of torus topology,
we calculate the loop corrections to the tree-level gauge couplings and solve
the loop-corrected equations of motion. At the string-tree level, the effective
gauge couplings decrease at small distances from the origin, and in this region
string-loop corrections to the gauge couplings become important. A possibility
of smearing the singularity of the tree-level supersymmetric solution with
partially broken supersymmetry by quantum corrections is discussed.Comment: Improved version. Mixing of the dilaton with other moduli properly
taken into account. Explanatory notes adde
Cane vs. wood molasses used as preservatives for grass silage.
Cover title.Includes bibliographical references
Macroscopic and Microscopic Entropy of Near-Extremal Spinning Black Holes
A seven parameter family of five-dimensional black hole solutions depending
on mass, two angular momenta, three charges and the asymptotic value of a
scalar field is constructed. The entropy is computed as a function of these
parameters both from the Bekenstein-Hawking formula and from the degeneracies
of the corresponding D-brane states in string theory. The expressions agree at
and to leading order away from extremality.Comment: 7 pages, harvma
Brane Baldness vs. Superselection Sectors
The search for intersecting brane solutions in supergravity is a large and
profitable industry. Recently, attention has focused on finding localized forms
of known `delocalized' solutions. However, in some cases, a localized version
of the delocalized solution simply does not exist. Instead, localized separated
branes necessarily delocalize as the separation is removed. This phenomenon is
related to black hole no-hair theorems, i.e. `baldness.' We continue the
discussion of this effect and describe how it can be understood, in the case of
Dirichlet branes, in terms of the corresponding intersection field theory. When
it occurs, it is associated with the quantum mixing of phases and lack of
superselection sectors in low dimensional field theories. We find surprisingly
wide agreement between the field theory and supergravity both with respect to
which examples delocalize and with respect to the rate at which this occurs.Comment: 26 pages, ReVTeX, 2 figures, reference added, version to appear in
PR
Properties of the ionised plasma in the vicinity of the neutron-star X-ray binary EXO 0748-676
Aims. We present the spectral analysis of a large set of XMM-Newton observations of EXO 0748-676, a bright dipping low-mass X-ray binary. In particular, we focus on the dipping phenomenon as a result of changes in the properties of the ionised gas close to the source.Methods. We analysed the high-resolution spectra collected with the reflection grating spectrometer on board XMM-Newton. We studied dipping and persistent spectra separately. We used the Epic data to constrain the broad-band continuum. We explored two simple geometrical scenarios for which we derived physical quantities of the absorbing material like the density, size, and mass.Results. We find that the continuum is absorbed by a neutral gas, and by both a collisionally (temperature T similar to 70 eV) and photoionised (ionisation parameter log xi similar to 2.5) absorbers. Emission lines from OVII and OVIII are also detected. This is the first time that evidence of a collisionally ionised absorber has been found in a low-mass X-ray binary. The collisionally ionised absorber may be in the form of dense (n > 10(14) cm(-3)) filaments, located at a distance r greater than or similar to 10(11) cm. During dips, the photoionised absorber significantly increases its column density (factor 2-4) while becoming less ionised. This strengthens the idea that the colder material of the accretion stream impinging the disc is passing on our line of sight during dips. In this scenario, we find that the distance from the neutron star to the impact region (similar to 5 x 10(10) cm) is similar to the size of the neutron star's Roche lobe. The gas observed during the persistent state may have a flattened geometry. Finally, we explore the possibility of the existence of material forming an initial, hotter portion of a circumbinary disc.</p
Tachyon Field Quantization and Hawking Radiation
We quantize the tachyon field in a static two dimensional dilaton gravity
black hole background,and we calculate the Hawking radiation rate. We find that
the thermal radiation flux, due to the tachyon field, is larger than the
conformal matter one. We also find that massive scalar fields which do not
couple to the dilaton, do not give any contribution to the thermal radiation,
up to terms quadratic in the scalar curvature.Comment: 13 pages, Latex file, 1 figure available upon reques
Quantum Black Hole Evaporation
We investigate a recently proposed model for a full quantum description of
two-dimensional black hole evaporation, in which a reflecting boundary
condition is imposed in the strong coupling region. It is shown that in this
model each initial state is mapped to a well-defined asymptotic out-state,
provided one performs a certain projection in the gravitational zero mode
sector. We find that for an incoming localized energy pulse, the corresponding
out-going state contains approximately thermal radiation, in accordance with
semi-classical predictions. In addition, our model allows for certain acausal
strong coupling effects near the singularity, that give rise to corrections to
the Hawking spectrum and restore the coherence of the out-state. To an
asymptotic observer these corrections appear to originate from behind the
receding apparent horizon and start to influence the out-going state long
before the black hole has emitted most of its mass. Finally, by putting the
system in a finite box, we are able to derive some algebraic properties of the
scattering matrix and prove that the final state contains all initial
information.Comment: 37 pages (figs 2 and 3 included as uuencoded compressed tar file),
Latex, needs epsf.tex, PUPT-1395, IASSNS-HEP-93/25 (revised version has minor
corrections, one reference added
- …