863 research outputs found
Extreme objects with arbitrary large mass, or density, and arbitrary size
We consider a generalization of the interior Schwarzschild solution that we
match to the exterior one to build global C^1 models that can have arbitrary
large mass, or density, with arbitrary size. This is possible because of a new
insight into the problem of localizing the center of symmetry of the models and
the use of principal transformations to understand the structure of space.Comment: 20 pages, 6 figures. Fixed one reference. Added a new equatio
Separating expansion from contraction: generalized TOV condition, LTB models with pressure and CDM
We discuss the existence of a dividing shell separating expanding and
collapsing regions in spherically symmetric solutions with pressure. We obtain
gauge invariant conditions relating not only the intrinsic spatial curvature of
the shells to the ADM mass, but also a function of the pressure which we
introduce that generalises the Tolman-Oppenheimer-Volkoff equilibrium
condition, in the framework of a 3+1 spacetime splitting. We consider the
particular case of a Lema\^itre-Tolman-Bondi dust models with a cosmological
constant (a -CDM model) as an example of our results.Comment: Proceedings of 'Invisible Universe International Conference', Paris,
June 29- July 3, 2009 ; 5pp, 4 fig
Separating expansion from contraction and generalizing TOV condition in spherically symmetric models with pressure
We investigate spherically symmetric solutions with pressure and discuss the
existence of a dividing shell separating expanding and collapsing regions. We
perform a 3+1 splitting and obtain gauge invariant conditions relating not only
the intrinsic spatial curvature of the shells to the ADM mass, but also a
function of the pressure which we introduce that generalises the
Tolman-Oppenheimer-Volkoff equilibrium condition. We consider the particular
case of a Lema\^itre-Tolman dust models with a cosmological constant (a
-CDM model) as an example of our results.Comment: 4pp, 1fig, AIP Conference: Proc. XXXI Spanish Relat. Meeting, ERE08,
Salamanca, Spain, 15-19 Sept., 2008 Septembre, Salamanca, Espagn
Gravity of a static massless scalar field and a limiting Schwarzschild-like geometry
We study a set of static solutions of the Einstein equations in presence of a
massless scalar field and establish their connection to the Kantowski-Sachs
cosmological solutions based on some kind of duality transformations. The
physical properties of the limiting case of an empty hyperbolic spacetime
(pseudo-Schwarzschild geometry) are analyzed in some detail.Comment: 13 pages, 4 figure
Eleven spherically symmetric constant density solutions with cosmological constant
Einstein's field equations with cosmological constant are analysed for a
static, spherically symmetric perfect fluid having constant density. Five new
global solutions are described.
One of these solutions has the Nariai solution joined on as an exterior
field. Another solution describes a decreasing pressure model with exterior
Schwarzschild-de Sitter spacetime having decreasing group orbits at the
boundary. Two further types generalise the Einstein static universe.
The other new solution is unphysical, it is an increasing pressure model with
a geometric singularity.Comment: 19 pages, 5 figures, 1 table, revised bibliography, corrected eqn.
(3.11), typos corrected, two new reference
Electrooptical scanning of film
Scan-in scan-out flying spot scanning system recognizes three different levels of transmissivity within a frame. It selectively acts on these levels either to intensify the illumination or to extend the duration of the illuminating spot to any picture element. Thus it improves the ratio of signal to tube noise in the cameras output
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