23,244 research outputs found
New Coordinates for de Sitter Space and de Sitter Radiation
We introduce a simple coordinate system covering half of de Sitter space. The
new coordinates have several attractive properties: the time direction is a
Killing vector, the metric is smooth at the horizon, and constant-time slices
are just flat Euclidean space. We demonstrate the usefulness of the coordinates
by calculating the rate at which particles tunnel across the horizon. When
self-gravitation is taken into account, the resulting tunneling rate is only
approximately thermal. The effective temperature decreases through the emission
of radiation.Comment: LaTeX, 10 pages; v2. references added; v3. minor sign errors fixed,
reference added, journal versio
Holographic dual of the five-point conformal block
We present the holographic object which computes the five-point global
conformal block in arbitrary dimensions for external and exchanged scalar
operators. This object is interpreted as a weighted sum over infinitely many
five-point geodesic bulk diagrams. These five-point geodesic bulk diagrams
provide a generalization of their previously studied four-point counterparts.
We prove our claim by showing that the aforementioned sum over geodesic bulk
diagrams is the appropriate eigenfunction of the conformal Casimir operator
with the right boundary conditions. This result rests on crucial inspiration
from a much simpler -adic version of the problem set up on the Bruhat-Tits
tree.Comment: 20 pages + references, several figures. v2: Minor typos fixed,
matches published versio
The Volume of Black Holes
We propose a definition of volume for stationary spacetimes. The proposed
volume is independent of the choice of stationary time-slicing, and applies
even though the Killing vector may not be globally timelike. Moreover, it is
constant in time, as well as simple: the volume of a spherical black hole in
four dimensions turns out to be just . We then consider
whether it is possible to construct spacetimes that have finite horizon area
but infinite volume, by sending the radius to infinity while making discrete
identifications to preserve the horizon area. We show that, in three or four
dimensions, no such solutions exist that are not inconsistent in some way. We
discuss the implications for the interpretation of the Bekenstein-Hawking
entropy.Comment: 8 pages, revte
The unreasonable effectiveness of experiments in constraining nova nucleosynthesis
Classical nova explosions arise from thermonuclear ignition in the envelopes of accreting white dwarfs in close binary star systems. Detailed observations of novae have stimulated numerous studies in theoretical astrophysics and experimental nuclear physics. These phenomena are unusual in nuclear astrophysics because most of the thermonuclear reaction rates thought to be involved are constrained by experimental measurements. This situation allows for rather precise statements to be made about which measurements are still necessary to improve the nuclear physics input to astrophysical models. We briefly discuss desired measurements in these environments with an emphasis on recent experimental progress made to better determine key rates.Postprint (published version
Energy Conservation and Hawking Radiation
The conservation of energy implies that an isolated radiating black hole
cannot have an emission spectrum that is precisely thermal. Moreover, the
no-hair theorem is only approximately applicable. We consider the implications
for the black hole information puzzle.Comment: 6 pages, LaTex; v2: references adde
A Comparison of Moderate Oral Sedation Drug Regimens for Pediatric Dental Treatment: A Pilot Study
Purpose: Compare moderate oral sedation of pediatric patients using Hydroxyzine and Meperidine with either Diazepam or Midazolam in management of pediatric dental patients.
Methods: Randomized, double-blind, crossover pilot study of patients 3 to 7 years of age requiring two sedation visits. Frankl and Houpt behavior scores recorded at injection time, initiation of treatment and 100% oxygen at end of treatment. Postoperative phone call surveys conducted within eight hours and within 24 hours of discharge. Wilcoxon Signed-Rank tests, Fisher’s Exact Chi-squared test and 0.10 significance level.
Results: 25 subjects completed 35 sedations. Eight participants completed both treatments and demonstrated significantly higher total Houpt Scores with Diazepam at all treatment stages. Frankl scores favored Diazepam at injection time. More abnormal behavior was found with Midazolam, less memory of the visit with Diazepam, but longer sleep time with Diazepam.
Conclusions: Sedation with the Hydroxyzine, Meperidine and Diazepam regimen may allow for a better overall sedation experience. Postoperative monitoring is essential. The results are promising and demonstrate the value of a larger study on sedation with Diazepam
A phenomenological study of the impact of knowledge intensity and environmental velocity on in source or hosted contact centres.
Contact centres exist in order to focus the final step of the intra organisational value chain which then delivers optimalcustomer satisfaction. In this paper we analyse a centre with a view to investigating the impact of outsourcing or the inhouselocus of provision. Such centres exhibit agency/principal characteristics, bringing knowledge management into sharp focus, aspects of information intensity which impact on the organisational dynamics, and the learning of the employees. A phenomenological approach to determine the essence of the activities was deployed rather than a methodological initiative based post positivistic strategic analysis. The characteristics of contact centres investigated
coalesce into two distinct categories; a framework to depict this is presented
Rindler-AdS/CFT
In anti-de Sitter space a highly accelerating observer perceives a Rindler
horizon. The two Rindler wedges in AdS_{d+1} are holographically dual to an
entangled conformal field theory that lives on two boundaries with geometry R x
H_{d-1}. For AdS_3, the holographic duality is especially tractable, allowing
quantum-gravitational aspects of Rindler horizons to be probed. We recover the
thermodynamics of Rindler-AdS space directly from the boundary conformal field
theory. We derive the temperature from the two-point function and obtain the
Rindler entropy density precisely, including numerical factors, using the Cardy
formula. We also probe the causal structure of the spacetime, and find from the
behavior of the one-point function that the CFT "knows" when a source has
fallen across the Rindler horizon. This is so even though, from the bulk point
of view, there are no local signifiers of the presence of the horizon. Finally,
we discuss an alternate foliation of Rindler-AdS which is dual to a CFT living
in de Sitter space.Comment: 29 Pages, 4 Figures, citations adde
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