1,591,299 research outputs found
Electrovacuum Near-horizon Geometries in Four and Five Dimensions
Associated to every stationary extremal black hole is a unique near-horizon
geometry, itself a solution of the field equations. These latter spacetimes are
more tractable to analyze and most importantly, retain properties of the
original black hole which are intrinsic to the event horizon. After reviewing
general features of near-horizon geometries, such as SO(2,1) symmetry
enhancement, I report on recent work on stationary, charged extremal black hole
solutions of the Einstein-Maxwell equations with a negative cosmological
constant in four dimensions and present a classification of near-horizon
geometries of black holes on this kind. In five dimensions, charged extremal
black hole solutions to minimal (gauged) supergravity, which arises naturally
in string theory and the gauge theory/gravity correspondence, are considered. I
consider the classification of near-horizon geometries for the subset of such
black holes which are supersymmetric. Recent progress on the classification
problem in the general extremal, non-supersymmetric case is also discussed.Comment: Invited contribution to a special issue of Classical and Quantum
Gravity on the 19th International Conference on General Relativity and
Gravitation, Mexico City, July 5-9, 201
Scaling regimes and critical dimensions in the Kardar-Parisi-Zhang problem
We study the scaling regimes for the Kardar-Parisi-Zhang equation with noise
correlator R(q) ~ (1 + w q^{-2 \rho}) in Fourier space, as a function of \rho
and the spatial dimension d. By means of a stochastic Cole-Hopf transformation,
the critical and correction-to-scaling exponents at the roughening transition
are determined to all orders in a (d - d_c) expansion. We also argue that there
is a intriguing possibility that the rough phases above and below the lower
critical dimension d_c = 2 (1 + \rho) are genuinely different which could lead
to a re-interpretation of results in the literature.Comment: Latex, 7 pages, eps files for two figures as well as Europhys. Lett.
style files included; slightly expanded reincarnatio
Application of Cryogenic Treatment to Extend the Life of the TiAlN-Coated Tungsten Carbide Milling Cutter
Cutting tools are important to the manufacturing industry since they will affect production efficiency and product quality. Cryogenic treatment can improve the material properties by decreasing residual stress, stabilizing dimensional accuracy, and increasing wear resistance. The purpose of this study is to investigate the feasibility and effect of cryogenic treatment on the performance of TiAlN-coated tungsten carbide milling cutters for machining the Inconel alloy 625 in terms of different testing methods (e.g., hardness, wear resistance, residual stress, microstructure, and tool life test). Experimental results indicate that after cryogenic treatment there is less wear, the microstructure is denser, residual stress is decreased, the adhesion of coating and tungsten carbide is improved, and the tool life is effectively improved
Discovery of {\gamma}-ray pulsation and X-ray emission from the black widow pulsar PSR J2051-0827
We report the discovery of pulsed {\gamma}-ray emission and X-ray emission
from the black widow millisecond pulsar PSR J2051-0827 by using the data from
the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope and
the Advanced CCD Imaging Spectrometer array (ACIS-S) on the Chandra X-ray
Observatory. Using 3 years of LAT data, PSR J2051-0827 is clearly detected in
{\gamma}-ray with a signicance of \sim 8{\sigma} in the 0.2 - 20 GeV band. The
200 MeV - 20 GeV {\gamma}-ray spectrum of PSR J2051-0827 can be modeled by a
simple power- law with a photon index of 2.46 \pm 0.15. Significant (\sim
5{\sigma}) {\gamma}-ray pulsations at the radio period were detected. PSR
J2051-0827 was also detected in soft (0.3-7 keV) X-ray with Chandra. By
comparing the observed {\gamma}-rays and X-rays with theoretical models, we
suggest that the {\gamma}-ray emission is from the outer gap while the X-rays
can be from intra-binary shock and pulsar magnetospheric synchrotron emissions.Comment: 10 pages, 4 figures, accepted by ApJ on Jan 28, 201
Effect of Diethylenetriamine and Triethylamine sensitization on the critical diameter of Nitromethane
In this work, the critical diameter for detonation was measured for Nitromethane (NM) sensitized with two different amines: Diethylenetriamine (DETA) and Triethylamine (TEA). The critical diameter in glass and polyvinylchloride tubes is found to decrease rapidly as the amount of sensitizer is increased, then increase past a critical amount of sensitizer. Thus the critical diameter reaches a minimum at a critical concentration of sensitizer. It was also found that the critical diameter is lower with DETA than with TEA
Quark-Gluon-Plasma Formation at SPS Energies?
By colliding ultrarelativistic ions, one achieves presently energy densities
close to the critical value, concerning the formation of a quark-gluon-plasma.
This indicates the importance of fluctuations and the necessity to go beyond
the investigation of average events. Therefore, we introduce a percolation
approach to model the final stage ( fm/c) of ion-ion collisions, the
initial stage being treated by well-established methods, based on strings and
Pomerons. The percolation approach amounts to finding high density domains, and
treating them as quark-matter droplets. In this way, we have a {\bf realistic,
microscopic, and Monte--Carlo based model which allows for the formation of
quark matter.} We find that even at SPS energies large quark-matter droplets
are formed -- at a low rate though. In other words: large quark-matter droplets
are formed due to geometrical fluctuation, but not in the average event.Comment: 7 Pages, HD-TVP-94-6 (1 uuencoded figure
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