18,267 research outputs found
Probing the gravitational geon
The Brill-Hartle gravitational geon construct as a spherical shell of small
amplitude, high frequency gravitational waves is reviewed and critically
analyzed. The Regge-Wheeler formalism is used to represent gravitational wave
perturbations of the spherical background as a superposition of tensor
spherical harmonics and an attempt is made to build a non-singular solution to
meet the requirements of a gravitational geon. High-frequency waves are seen to
be a necessary condition for the geon and the field equations are decomposed
accordingly. It is shown that this leads to the impossibility of forming a
spherical gravitational geon. The attempted constructs of gravitational and
electromagnetic geons are contrasted. The spherical shell in the proposed
Brill-Hartle geon does not meet the regularity conditions required for a
non-singular source and hence cannot be regarded as an adequate geon construct.
Since it is the high frequency attribute which is the essential cause of the
geon non-viability, it is argued that a geon with less symmetry is an unlikely
prospect. The broader implications of the result are discussed with particular
reference to the problem of gravitational energy.Comment: Replaced with revised version (substantial changes and additions,
conclusions unchanged), 36 pages, LaTex, 3 figures available from the author
Evaluation of anomalies observed on film from S-190A flight system calibration test
Due to a persistent problem of scratched film from testing of the Skylab S-190A system, a series of tests were designed to identify the cause of the film scratching. The procedures followed in this test for pretest handling and packaging of the film, the makeup of the rolls for processing, and the results of the processed film evaluation are reported
Stability of Gravitational and Electromagnetic Geons
Recent work on gravitational geons is extended to examine the stability
properties of gravitational and electromagnetic geon constructs. All types of
geons must possess the property of regularity, self-consistency and
quasi-stability on a time-scale much longer than the period of the comprising
waves. Standard perturbation theory, modified to accommodate time-averaged
fields, is used to test the requirement of quasi-stability. It is found that
the modified perturbation theory results in an internal inconsistency. The
time-scale of evolution is found to be of the same order in magnitude as the
period of the comprising waves. This contradicts the requirement of slow
evolution. Thus not all of the requirements for the existence of
electromagnetic or gravitational geons are met though perturbation theory. From
this result it cannot be concluded that an electromagnetic or a gravitational
geon is a viable entity. The broader implications of the result are discussed
with particular reference to the problem of gravitational energy.Comment: 40 pages, 5 EPS figures, uses overcite.st
Initial bound state studies in light-front QCD
We present the first numerical QCD bound state calculation based on a
renormalization group-improved light-front Hamiltonian formalism. The QCD
Hamiltonian is determined to second order in the coupling, and it includes
two-body confining interactions. We make a momentum expansion, obtaining an
equal-time-like Schrodinger equation. This is solved for quark-antiquark
constituent states, and we obtain a set of self-consistent parameters by
fitting B meson spectra.Comment: 38 pages, latex, 5 latex figures include
Context Dependence, MOPs,WHIMs and procedures Recanati and Kaplan on Cognitive Aspects in Semantics
After presenting Kripke’s criticism to Frege’s ideas on context dependence of thoughts, I present two recent attempts of considering cognitive aspects of context dependent expressions inside a truth conditional pragmatics or semantics: Recanati’s non-descriptive modes of presentation (MOPs) and Kaplan’s ways of having in mind (WHIMs). After analysing the two attempts and verifying which answers they should give to the problem discussed by Kripke, I suggest a possible interpretation of these attempts: to insert a procedural or algorithmic level in semantic representations of indexicals. That a function may be computed by different procedures might suggest new possibilities of integrating contextual cognitive aspects in model theoretic semanti
On the Size of Hadrons
The form factor and the mean-square radius of the pion are calculated
analytically from a parametrized form of a wave function. The
numerical wave function was obtained previously by solving numerically an
eigenvalue equation for the pion in a particular model. The analytical formulas
are of more general interest than just be valid for the pion and can be
generalized to the case with unequal quark masses. Two different
parametrizations are investigated. Because of the highly relativistic problem,
noticable deviations from a non-relativistic formula are obtained.Comment: 14 pages, minor typos corrected, several points clarified, results
unchange
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