3,694 research outputs found
A Continuous Injection Plasma Model for the X-Ray/Radio Knots in Kpc-Scale Jets of AGN
We consider the evolution of a spherically expanding plasma cloud, where
there is continuous injection of non-thermal electrons. We compute the time
dependent electron distribution and resultant photon spectra taking into
account synchrotron, adiabatic and inverse Compton cooling. This model is
different from previous works where, instead of a continuous injection of
particles, a short injection period was assumed. We apply this model to the
radio/optical knots in the large scale jets of AGN, detected in X-rays by {\it
Chandra} and find that the overall broadband spectral features can be
reproduced. It is shown that for some sources, constraints on the X-ray
spectral index (by a longer {\it Chandra} observation) will be able to
differentiate between the different models. This in turn will put a strong
constraint on the acceleration mechanism active in these sources.Comment: Accepted for publications in the Astrophysical Journal Letter
Black Hole Entropy from Spin One Punctures
Recent suggestion, that the emission of a quantum of energy corresponding to
the asymptotic value of quasinormal modes of a Schwarzschild black hole should
be associated with the loss of spin one punctures from the black hole horizon,
fixes the Immirzi parameter to a definite value. We show that saturating the
horizon with spin one punctures reproduces the earlier formula for the black
hole entropy, including the correction with definite coefficient (-
3/2) for large area.Comment: 4 pages. RevTe
Optimizing Information Freshness in Wireless Networks under General Interference Constraints
Age of information (AoI) is a recently proposed metric for measuring
information freshness. AoI measures the time that elapsed since the last
received update was generated. We consider the problem of minimizing average
and peak AoI in a wireless networks, consisting of a set of source-destination
links, under general interference constraints. When fresh information is always
available for transmission, we show that a stationary scheduling policy is peak
age optimal. We also prove that this policy achieves average age that is within
a factor of two of the optimal average age. In the case where fresh information
is not always available, and packet/information generation rate has to be
controlled along with scheduling links for transmission, we prove an important
separation principle: the optimal scheduling policy can be designed assuming
fresh information, and independently, the packet generation rate control can be
done by ignoring interference. Peak and average AoI for discrete time G/Ber/1
queue is analyzed for the first time, which may be of independent interest
BTZ Black Hole Entropy from Ponzano-Regge Gravity
The entropy of the BTZ black hole is computed in the Ponzano-Regge
formulation of three-dimensional lattice gravity. It is seen that the correct
semi-classical behaviour of entropy is reproduced by states that correspond to
all possible triangulations of the Euclidean black hole.Comment: 11 pages LaTeX, 3 eps figures, some minor clarifications added,
result unchange
Reductions for the Stable Set Problem
One approach to finding a maximum stable set (MSS) in a graph is to try to reduce the size of the problem by transforming the problem into an equivalent problem on a smaller graph. This paper introduces several new reductions for the MSS problem, extends several well-known reductions to the maximum weight stable set (MWSS) problem, demonstrates how reductions for the generalized stable set problem can be used in conjunction with probing to produce powerful new reductions for both the MSS and MWSS problems, and shows how hypergraphs can be used to expand the capabilities of clique projections. The effectiveness of these new reduction techniques are illustrated on the DIMACS benchmark graphs, planar graphs, and a set of challenging MSS problems arising from Steiner Triple Systems
Quantum Aspects of Black Hole Entropy
This survey intends to cover recent approaches to black hole entropy which
attempt to go beyond the standard semiclassical perspective. Quantum
corrections to the semiclassical Bekenstein-Hawking area law for black hole
entropy, obtained within the quantum geometry framework, are treated in some
detail. Their ramification for the holographic entropy bound for bounded
stationary spacetimes is discussed. Four dimensional supersymmetric extremal
black holes in string-based N=2 supergravity are also discussed, albeit more
briefly.Comment: 13 Pages Revtex with 3 eps figures; based on plenary talk given at
the International Conference on Gravitation and Cosmology, Kharagpur, India,
January, 2000 One reference adde
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