12 research outputs found
Energy and Momentum Distributions of Kantowski and Sachs Space-time
We use the Einstein, Bergmann-Thomson, Landau-Lifshitz and Papapetrou
energy-momentum complexes to calculate the energy and momentum distributions of
Kantowski and Sachs space-time. We show that the Einstein and Bergmann-Thomson
definitions furnish a consistent result for the energy distribution, but the
definition of Landau-Lifshitz do not agree with them. We show that a signature
switch should affect about everything including energy distribution in the case
of Einstein and Papapetrou prescriptions but not in Bergmann-Thomson and
Landau-Lifshitz prescriptions.Comment: 12 page
Origin of volatiles in the Main Belt
We propose a scenario for the formation of the Main Belt in which asteroids
incorporated icy particles formed in the outer Solar Nebula. We calculate the
composition of icy planetesimals formed beyond a heliocentric distance of 5 AU
in the nebula by assuming that the abundances of all elements, in particular
that of oxygen, are solar. As a result, we show that ices formed in the outer
Solar Nebula are composed of a mix of clathrate hydrates, hydrates formed above
50 K and pure condensates produced at lower temperatures. We then consider the
inward migration of solids initially produced in the outer Solar Nebula and
show that a significant fraction may have drifted to the current position of
the Main Belt without encountering temperature and pressure conditions high
enough to vaporize the ices they contain. We propose that, through the
detection and identification of initially buried ices revealed by recent
impacts on the surfaces of asteroids, it could be possible to infer the
thermodynamic conditions that were present within the Solar Nebula during the
accretion of these bodies, and during the inward migration of icy
planetesimals. We also investigate the potential influence that the
incorporation of ices in asteroids may have on their porosities and densities.
In particular, we show how the presence of ices reduces the value of the bulk
density of a given body, and consequently modifies its macro-porosity from that
which would be expected from a given taxonomic type.Comment: Accepted for publication in MNRA
The Energy of Regular Black Hole in General Relativity Coupled to Nonlinear Electrodynamics
According to the Einstein, Weinberg, and M{\o}ller energy-momentum complexes,
we evaluate the energy distribution of the singularity-free solution of the
Einstein field equations coupled to a suitable nonlinear electrodynamics
suggested by Ay\'{o}n-Beato and Garc\'{i}a. The results show that the energy
associated with the definitions of Einstein and Weinberg are the same, but
M{\o}ller not. Using the power series expansion, we find out that the first two
terms in the expression are the same as the energy distributions of the
Reissner-Nordstr\"{o}m solution, and the third term could be used to survey the
factualness between numerous solutions of the Einstein field eqautions coupled
to a nonlinear electrodynamics.Comment: 11 page
The comet Halley dust and gas environment
Quantitative descriptions of environments near the nucleus of comet P /Halley have been developed to support spacecraft and mission design for the flyby encounters in March, 1986. To summarize these models as they exist just before the encounters, we review the relevant data from prior Halley apparitions and from recent cometary research. Orbital elements, visual magnitudes, and parameter values and analysis for the nucleus, gas and dust are combined to predict Halley's position, production rates, gas and dust distributions, and electromagnetic radiation field for the current perihelion passage. The predicted numerical results have been useful for estimating likely spacecraft effects, such as impact damage and attitude perturbation. Sample applications are cited, including design of a dust shield for spacecraft structure, and threshold and dynamic range selection for flight experiments. We expect that the comet's activity may be more irregular than these smoothly varying models predict, and that comparison with the flyby data will be instructive.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43774/1/11214_2004_Article_BF00175326.pd
An axially symmetric scalar and the Teleparallelism
An axially symmetric scalar field is considered in teleparallel gravity. We calculate, respectively, the tensor, the vector and the axial-vector parts of torsion and energy, momentum and angular momentum in the ASSF. We find the vector parts are in the radial and e^θ directions, the axial-vector, momentum and angular momentum vanish identically, but the energy distribution is different from zero. The vanishing axial-vector part of torsion gives us the result that there occurs no deviation in the spherical symmetry of the spacetime. Consequently, there exists no inertia field with respect to a Dirac particle, and the spin vector of a Dirac particle becomes constant. The result for the energy is the same as obtained by Radinschi. Next, this work also (a) supports the viewpoint of Lessner that the Møller energy-momentum complex is a powerful concept for the energy-momentum, (b) sustains the importance of the energy-momentum definitions in the evaluation of the energy distribution of a given spacetime, and (c) supports the hypothesis by Cooperstock that the energy is confined to the region of non-vanishing energy-momentum tensor of the matter and all non-gravitational fields
Localization of energy for a regular black hole solution in an asymptotically de Sitter spacetime geometry
The energy and momentum distributions of a regular black hole in a four-dimensional, asymptotically de Sitter spacetime geometry are computed, whereby the Einstein, Landau-Lifshitz, Weinberg and Moller energy-momentum complexes are utilized. It is found, for all prescriptions applied, that the momentum distribution vanishes, while the energy distribution depends on the mass parameter M, the electric charge Q, and the cosmological constant Lambda. In addition, various limiting cases are discussed