2,281 research outputs found
Radiation Information from 1958 δ2
The telemetered radiation information from the satellite 1958 δ2
(Sputnik III) has been analyzed for sixty-two separate passes recorded
in College, Alaska. The data indicate a dependence of radiation intensity
on altitude in the range 250-500 km. Both the high and low
energy components apparently contribute to the overall increase of
intensity with altitude, but the presence of a continuous afterglow
in the scintillating crystal prevented detailed interpretation of the
results.IGY Project No. 32.42
NSF Grant No. Y/32.42/268Ye
Self-force on a scalar charge in radial infall from rest using the Hadamard-WKB expansion
We present an analytic method based on the Hadamard-WKB expansion to
calculate the self-force for a particle with scalar charge that undergoes
radial infall in a Schwarzschild spacetime after being held at rest until a
time t = 0. Our result is valid in the case of short duration from the start.
It is possible to use the Hadamard-WKB expansion in this case because the value
of the integral of the retarded Green's function over the particle's entire
past trajectory can be expressed in terms of two integrals over the time period
that the particle has been falling. This analytic result is expected to be
useful as a check for numerical prescriptions including those involving mode
sum regularization and for any other analytical approximations to self-force
calculations.Comment: 22 pages, 2 figures, Physical Review D version along with the
corrections given in the erratu
Point Charge Self-Energy in the General Relativity
Singularities in the metric of the classical solutions to the Einstein
equations (Schwarzschild, Kerr, Reissner -- Nordstr\"om and Kerr -- Newman
solutions) lead to appearance of generalized functions in the Einstein tensor
that are not usually taken into consideration. The generalized functions can be
of a more complex nature than the Dirac \d-function. To study them, a
technique has been used based on a limiting solution sequence. The solutions
are shown to satisfy the Einstein equations everywhere, if the energy-momentum
tensor has a relevant singular addition of non-electromagnetic origin. When the
addition is included, the total energy proves finite and equal to , while
for the Kerr and Kerr--Newman solutions the angular momentum is .
As the Reissner--Nordstr\"om and Kerr--Newman solutions correspond to the point
charge in the classical electrodynamics, the result obtained allows us to view
the point charge self-energy divergence problem in a new fashion.Comment: VI Fridmann Seminar, France, Corsica, Corgeze, 2004, LaTeX, 6 pages,
2 fige
On Special Re-quantization of a Black Hole
Quantized expressions for the gravitational energy and momentum are derived
from a linearized theory of teleparallel gravity. The derivation relies on a
second-quantization procedure that constructs annihilation and creation
operators for the graviton. The resulting gravitational field is a collection
of gravitons, each of which has precise energy and momentum. On the basis of
the weak-field approximation of Schwarzschild's solution, a new form for the
quantization of the mass of a black hole is derived.Comment: 4 page
Combustion of solid carbon rods in zero and normal gravity
In order to investigate the mechanism of carbon combustion, spectroscopic carbon rods were resistance ignited and burned in an oxygen environment in normal and zero gravity. Direct mass spectrometric sampling was used in the normal gravity tests to obtain concentration profiles of CO2, CO, and O2 as a function of distance from the carbon surface. The experimental concentrations were compared to those predicted by a stagnant film model. Zero gravity droptower tests were conducted in order to assess the effect of convection on the normal gravity combustion process. The ratio of flame diameter to rod diameter as a function of time for oxygen pressures of 5, 10, 15, and 20 psia was obtained for three different diameter rods. It was found that this ratio was inversely proportional to both the oxygen pressure and the rod diameter
Bohmian trajectories and the Path Integral Paradigm. Complexified Lagrangian Mechanics
David Bohm shown that the Schr{\"o}dinger equation, that is a "visiting card"
of quantum mechanics, can be decomposed onto two equations for real functions -
action and probability density. The first equation is the Hamilton-Jacobi (HJ)
equation, a "visiting card" of classical mechanics, to be modified by the
Bohmian quantum potential. And the second is the continuity equation. The
latter can be transformed to the entropy balance equation. The Bohmian quantum
potential is transformed to two Bohmian quantum correctors. The first corrector
modifies kinetic energy term of the HJ equation, and the second one modifies
potential energy term. Unification of the quantum HJ equation and the entropy
balance equation gives complexified HJ equation containing complex kinetic and
potential terms. Imaginary parts of these terms have order of smallness about
the Planck constant. The Bohmian quantum corrector is indispensable term
modifying the Feynman's path integral by expanding coordinates and momenta to
imaginary sector.Comment: 14 pages, 3 figures, 46 references, 48 equation
Cauchy-characteristic Evolution of Einstein-Klein-Gordon Systems: The Black Hole Regime
The Cauchy+characteristic matching (CCM) problem for the scalar wave equation
is investigated in the background geometry of a Schwarzschild black hole.
Previously reported work developed the CCM framework for the coupled
Einstein-Klein-Gordon system of equations, assuming a regular center of
symmetry. Here, the time evolution after the formation of a black hole is
pursued, using a CCM formulation of the governing equations perturbed around
the Schwarzschild background. An extension of the matching scheme allows for
arbitrary matching boundary motion across the coordinate grid. As a proof of
concept, the late time behavior of the dynamics of the scalar field is
explored. The power-law tails in both the time-like and null infinity limits
are verified.Comment: To appear in Phys. Rev. D, 9 pages, revtex, 5 figures available at
http://www.astro.psu.edu/users/nr/preprints.htm
Environmental risk factors for autism
Autism is a devastating childhood condition that has emerged as an increasing social concern just as it has increased in prevalence in recent decades. Autism and the broader category of autism spectrum disorders are among the increasingly seen examples in which there is a fetal basis for later disease or disorder. Environmental, genetic, and epigenetic factors all play a role in determining the risk of autism and some of these effects appear to be transgenerational. Identification of the most critical windows of developmental vulnerability is paramount to understanding when and under what circumstances a child is at elevated risk for autism. No single environmental factor explains the increased prevalence of autism. While a handful of environmental risk factors have been suggested based on data from human studies and animal research, it is clear that many more, and perhaps the most significant risk factors, remain to be identified. The most promising risk factors identified to date fall within the categories of drugs, environmental chemicals, infectious agents, dietary factors, and other physical/psychological stressors. However, the rate at which environmental risk factors for autism have been identified via research and safety testing has not kept pace with the emerging health threat posed by this condition. For the way forward, it seems clear that additional focused research is needed. But more importantly, successful risk reduction strategies for autism will require more extensive and relevant developmental safety testing of drugs and chemicals
Interacting classical and quantum particles
We apply Hall and Reginatto's theory of interacting classical and quantum
ensembles to harmonically coupled particles, with a view to understanding its
experimental implications. This hybrid theory has no free parameters and makes
distinctive predictions that should allow it to be experimentally distinguished
from quantum mechanics. It also bears on the questions of quantum measurement
and quantum gravity.Comment: 7 pages, 6 figure
Regularity of Cauchy horizons in S2xS1 Gowdy spacetimes
We study general S2xS1 Gowdy models with a regular past Cauchy horizon and
prove that a second (future) Cauchy horizon exists, provided that a particular
conserved quantity is not zero. We derive an explicit expression for the
metric form on the future Cauchy horizon in terms of the initial data on the
past horizon and conclude the universal relation A\p A\f=(8\pi J)^2 where
A\p and A\f are the areas of past and future Cauchy horizon respectively.Comment: 17 pages, 1 figur
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