12,551 research outputs found
Proof of the Generalized Second Law for Quasistationary Semiclassical Black Holes
A simple direct explicit proof of the generalized second law of black hole
thermodynamics is given for a quasistationary semiclassical black hole.Comment: 12 pages, LaTeX, report Alberta-Thy-10-93 (revision of paper in
response to Phys. Rev. Lett. referees' comments, which suffered a series of
long delays
Single-level resonance parameters fit nuclear cross-sections
Least squares analyses of experimental differential cross-section data for the U-235 nucleus have yielded single level Breit-Wigner resonance parameters that fit, simultaneously, three nuclear cross sections of capture, fission, and total
Spinning Down a Black Hole With Scalar Fields
We study the evolution of a Kerr black hole emitting scalar radiation via the
Hawking process. We show that the rate at which mass and angular momentum are
lost by the black hole leads to a final evolutionary state with nonzero angular
momentum, namely .Comment: 4 pages (including 3 postscript figures), Revtex, uses epsf.tex,
twocolumn.sty and header.sty (included). Submitted to Physical Review Letter
Evaporation of a Kerr black hole by emission of scalar and higher spin particles
We study the evolution of an evaporating rotating black hole, described by
the Kerr metric, which is emitting either solely massless scalar particles or a
mixture of massless scalar and nonzero spin particles. Allowing the hole to
radiate scalar particles increases the mass loss rate and decreases the angular
momentum loss rate relative to a black hole which is radiating nonzero spin
particles. The presence of scalar radiation can cause the evaporating hole to
asymptotically approach a state which is described by a nonzero value of . This is contrary to the conventional view of black hole
evaporation, wherein all black holes spin down more rapidly than they lose
mass. A hole emitting solely scalar radiation will approach a final asymptotic
state described by . A black hole that is emitting scalar
particles and a canonical set of nonzero spin particles (3 species of
neutrinos, a single photon species, and a single graviton species) will
asymptotically approach a nonzero value of only if there are at least 32
massless scalar fields. We also calculate the lifetime of a primordial black
hole that formed with a value of the rotation parameter , the minimum
initial mass of a primordial black hole that is seen today with a rotation
parameter , and the entropy of a black hole that is emitting scalar or
higher spin particles.Comment: 22 pages, 13 figures, RevTeX format; added clearer descriptions for
variables, added journal referenc
Measuring software technology
Results are reported from a series of investigations into the effectiveness of various methods and tools used in a software production environment. The basis for the analysis is a project data base, built through extensive data collection and process instrumentation. The project profiles become an organizational memory, serving as a reference point for an active program of measurement and experimentation on software technology
Black Hole Motion in Entropic Reformulation of General Relativity
We consider a system of black holes -- a simplest substitute of a system of
point particles in the mechanics of general relativity -- and try to describe
their motion with the help of entropic action: a sum of the areas of black hole
horizons. We demonstrate that such description is indeed consistent with the
Newton's laws of motion and gravity, modulo numerical coefficients, which
coincide but seem different from unity. Since a large part of the modern
discussion of entropic reformulation of general relativity is actually based on
dimensional considerations, for making a next step it is crucially important to
modify the argument, so that these dimensionless parameters acquire correct
values.Comment: 6 page
An experimental investigation of two large annular diffusers with swirling and distorted inflow
Two annular diffusers downstream of a nacelle-mounted fan were tested for aerodynamic performance, measured in terms of two static pressure recovery parameters (one near the diffuser exit plane and one about three diameters downstream in the settling duct) in the presence of several inflow conditions. The two diffusers each had an inlet diameter of 1.84 m, an area ratio of 2.3, and an equivalent cone angle of 11.5, but were distinguished by centerbodies of different lengths. The dependence of diffuser performance on various combinations of swirling, radially distorted, and/or azimuthally distorted inflow was examined. Swirling flow and distortions in the axial velocity profile in the annulus upstream of the diffuser inlet were caused by the intrinsic flow patterns downstream of a fan in a duct and by artificial intensification of the distortions. Azimuthal distortions or defects were generated by the addition of four artificial devices (screens and fences). Pressure recovery data indicated beneficial effects of both radial distortion (for a limited range of distortion levels) and inflow swirl. Small amounts of azimuthal distortion created by the artificial devices produced only small effects on diffuser performance. A large artificial distortion device was required to produce enough azimuthal flow distortion to significantly degrade the diffuser static pressure recovery
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