976 research outputs found
Study of direct versus orbital entry for Mars missions. Volume 2 - Parametric studies, final analyses, conceptual designs
Parametric data, systems analyses, and space capsule design concepts - direct versus orbital entry for Mars mission
Robertson-Walker fluid sources endowed with rotation characterised by quadratic terms in angular velocity parameter
Einstein's equations for a Robertson-Walker fluid source endowed with
rotation Einstein's equations for a Robertson-Walker fluid source endowed with
rotation are presented upto and including quadratic terms in angular velocity
parameter. A family of analytic solutions are obtained for the case in which
the source angular velocity is purely time-dependent. A subclass of solutions
is presented which merge smoothly to homogeneous rotating and non-rotating
central sources. The particular solution for dust endowed with rotation is
presented. In all cases explicit expressions, depending sinusoidally on polar
angle, are given for the density and internal supporting pressure of the
rotating source. In addition to the non-zero axial velocity of the fluid
particles it is shown that there is also a radial component of velocity which
vanishes only at the poles. The velocity four-vector has a zero component
between poles
Study of a soft lander/support module for Mars missions. Volume 1 - Summary Final summary report
Soft lander support module for Mars missions - summar
Study of direct versus orbital entry for Mars missions. Volume 1 - Summary Final report, 26 Mar. - 1 Jul. 1968
Mission and subsystem parametric analyses to evaluate direct and orbital entry modes for soft landing capsules on Mar
Average observational quantities in the timescape cosmology
We examine the properties of a recently proposed observationally viable
alternative to homogeneous cosmology with smooth dark energy, the timescape
cosmology. In the timescape model cosmic acceleration is realized as an
apparent effect related to the calibration of clocks and rods of observers in
bound systems relative to volume-average observers in an inhomogeneous geometry
in ordinary general relativity. The model is based on an exact solution to a
Buchert average of the Einstein equations with backreaction. The present paper
examines a number of observational tests which will enable the timescape model
to be distinguished from homogeneous cosmologies with a cosmological constant
or other smooth dark energy, in current and future generations of dark energy
experiments. Predictions are presented for: comoving distance measures; H(z);
the equivalent of the dark energy equation of state, w(z); the Om(z) measure of
Sahni, Shafieloo and Starobinsky; the Alcock-Paczynski test; the baryon
acoustic oscillation measure, D_v; the inhomogeneity test of Clarkson, Bassett
and Lu; and the time drift of cosmological redshifts. Where possible, the
predictions are compared to recent independent studies of similar measures in
homogeneous cosmologies with dark energy. Three separate tests with indications
of results in possible tension with the Lambda CDM model are found to be
consistent with the expectations of the timescape cosmology.Comment: 22 pages, 12 figures; v2 discussion, references added, matches
published versio
Charged Dilaton Black Holes with a Cosmological Constant
The properties of static spherically symmetric black holes, which are either
electrically or magnetically charged, and which are coupled to the dilaton in
the presence of a cosmological constant, are considered. It is shown that such
solutions do not exist if the cosmological constant is positive (in arbitrary
spacetime dimension >= 4). However, asymptotically anti-de Sitter black hole
solutions with a single horizon do exist if the cosmological constant is
negative. These solutions are studied numerically in four dimensions and the
thermodynamic properties of the solutions are derived. The extreme solutions
are found to have zero entropy and infinite temperature for all non-zero values
of the dilaton coupling constant.Comment: 12 pages, epsf, phyzzx, 4 in-text figures incl. (minor typos fixed, 1
reference added
Study of direct versus orbital entry for Mars missions. Volume 6 - Appendix D - Subsystem studies and parametric data Final report
Subsystems analyses and parametric data on configurations for direct versus orbital entry for Mars mission
Black Hole Area in Brans-Dicke Theory
We have shown that the dynamics of the scalar field
in Brans-Dicke theories of gravity makes the surface area of the black hole
horizon {\it oscillatory} during its dynamical evolution. It explicitly
explains why the area theorem does not hold in Brans-Dicke theory. However, we
show that there exists a certain non-decreasing quantity defined on the event
horizon which is proportional to the black hole entropy for the case of
stationary solutions in Brans-Dicke theory. Some numerical simulations have
been demonstrated for Oppenheimer-Snyder collapse in Brans-Dicke theory.Comment: 12 pages, latex, 5 figures, epsfig.sty, some statements clarified and
two references added, to appear in Phys. Rev.
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