102 research outputs found
FABRICATION OF TANTALUM CAPSULES FOR LAMPRE I REACTOR
Tantalum fabrication methods primarily for use as a container for molten plutonium are described. One method involved the rolling of a Ta billet into sheet of the desired age, cutting a circular blank, and deep drawing the tantalum blank through successive stages into the desimed shape. Another method used for the fabrication of Ta containers consisted of a combination of impact extrusion and ironing. This method involved the extrusion of the cast billet into rod, swaging the rod to a suitable diameter, and cutting it into slugs of the desired length. The slugs were then impact rod, swaging the rid ti a suitable diameter, and cutting it into slugs of the desired length. The slugs were then impact extruded into heavy walled containers. These starting containers were then taken through successive dies where the wall thickness was ironed down to the desired gage. (auth
Exact Solutions of Five Dimensional Anisotropic Cosmologies
We solve the five dimensional vacuum Einstein equations for several kinds of
anisotropic geometries. We consider metrics in which the spatial slices are
characterized as Bianchi types-II and V, and the scale factors are dependent
both on time and a non-compact fifth coordinate. We examine the behavior of the
solutions we find, noting for which parameters they exhibit contraction over
time of the fifth scale factor, leading naturally to dimensional reduction. We
explore these within the context of the induced matter model: a Kaluza-Klein
approach that associates the extra geometric terms due to the fifth coordinate
with contributions to the four dimensional stress-energy tensor.Comment: 11 page
Evolution of high-frequency gravitational waves in some cosmological models
We investigate Isaacson's high-frequency gravitational waves which propagate
in some relevant cosmological models, in particular the FRW spacetimes. Their
time evolution in Fourier space is explicitly obtained for various metric forms
of (anti--)de Sitter universe. Behaviour of high-frequency waves in the
anisotropic Kasner spacetime is also described.Comment: 14 pages, 8 figures, to appear in Czech. J. Phy
The General Solution of Bianchi Type Vacuum Cosmology
The theory of symmetries of systems of coupled, ordinary differential
equations (ODE) is used to develop a concise algorithm in order to obtain the
entire space of solutions to vacuum Bianchi Einstein Field Equations (EFEs).
The symmetries used are the well known automorphisms of the Lie algebra for the
corresponding isometry group of each Bianchi Type, as well as the scaling and
the time re-parametrization symmetry. The application of the method to Type
VII_h results in (a) obtaining the general solution of Type VII_0 with the aid
of the third Painlev\'{e} transcendental (b) obtaining the general solution of
Type with the aid of the sixth Painlev\'{e} transcendental (c) the
recovery of all known solutions (six in total) without a prior assumption of
any extra symmetry (d) The discovery of a new solution (the line element given
in closed form) with a G_3 isometry group acting on T_3, i.e. on time-like
hyper-surfaces, along with the emergence of the line element describing the
flat vacuum Type VII_0 Bianchi Cosmology.Comment: latex2e source file, 27 pages, 2 tables, no fiure
Empty singularities in higher-dimensional Gravity
We study the exact solution of Einstein's field equations consisting of a
()-dimensional static and hyperplane symmetric thick slice of matter, with
constant and positive energy density and thickness , surrounded by
two different vacua. We explicitly write down the pressure and the external
gravitational fields in terms of and , the pressure is positive and
bounded, presenting a maximum at an asymmetrical position. And if
is small enough, the dominant energy condition is satisfied
all over the spacetime. We find that this solution presents many interesting
features. In particular, it has an empty singular boundary in one of the vacua.Comment: 13 page
Lesbian and bisexual women's experiences of sexuality-based discrimination and their appearance concerns
Lesbian and bisexual women frequently experience sexuality-based discrimination, which is often based on others' judgements about their appearance. This short article aims to explore whether there is a relationship between lesbian and bisexual women's experiences of sexuality-based discrimination and their satisfaction with the way that they look. Findings from an online survey suggest that discrimination is negatively related to appearance satisfaction for lesbian women, but not for bisexual women. It is argued that this difference exists because lesbian appearance norms are more recognisable and distinctive than bisexual women's appearance norms
Future non-linear stability for reflection symmetric solutions of the Einstein-Vlasov system of Bianchi types II and VI
Using the methods developed for the Bianchi I case we have shown that a
boostrap argument is also suitable to treat the future non-linear stability for
reflection symmetric solutions of the Einstein-Vlasov system of Bianchi types
II and VI. These solutions are asymptotic to the Collins-Stewart solution
with dust and the Ellis-MacCallum solution respectively. We have thus
generalized the results obtained by Rendall and Uggla in the case of locally
rotationally symmetric Bianchi II spacetimes to the reflection symmetric case.
However we needed to assume small data. For Bianchi VI there is no
analogous previous result.Comment: 30 page
Domain Wall Spacetimes: Instability of Cosmological Event and Cauchy Horizons
The stability of cosmological event and Cauchy horizons of spacetimes
associated with plane symmetric domain walls are studied. It is found that both
horizons are not stable against perturbations of null fluids and massless
scalar fields; they are turned into curvature singularities. These
singularities are light-like and strong in the sense that both the tidal forces
and distortions acting on test particles become unbounded when theses
singularities are approached.Comment: Latex, 3 figures not included in the text but available upon reques
Generalized Quantum Theory of Recollapsing Homogeneous Cosmologies
A sum-over-histories generalized quantum theory is developed for homogeneous
minisuperspace type A Bianchi cosmological models, focussing on the particular
example of the classically recollapsing Bianchi IX universe. The decoherence
functional for such universes is exhibited. We show how the probabilities of
decoherent sets of alternative, coarse-grained histories of these model
universes can be calculated. We consider in particular the probabilities for
classical evolution defined by a suitable coarse-graining. For a restricted
class of initial conditions and coarse grainings we exhibit the approximate
decoherence of alternative histories in which the universe behaves classically
and those in which it does not. For these situations we show that the
probability is near unity for the universe to recontract classically if it
expands classically. We also determine the relative probabilities of
quasi-classical trajectories for initial states of WKB form, recovering for
such states a precise form of the familiar heuristic "J d\Sigma" rule of
quantum cosmology, as well as a generalization of this rule to generic initial
states.Comment: 41 pages, 4 eps figures, revtex 4. Modest revisions throughout.
Physics unchanged. To appear in Phys. Rev.
Exact Hypersurface-Homogeneous Solutions in Cosmology and Astrophysics
A framework is introduced which explains the existence and similarities of
most exact solutions of the Einstein equations with a wide range of sources for
the class of hypersurface-homogeneous spacetimes which admit a Hamiltonian
formulation. This class includes the spatially homogeneous cosmological models
and the astrophysically interesting static spherically symmetric models as well
as the stationary cylindrically symmetric models. The framework involves
methods for finding and exploiting hidden symmetries and invariant submanifolds
of the Hamiltonian formulation of the field equations. It unifies, simplifies
and extends most known work on hypersurface-homogeneous exact solutions. It is
shown that the same framework is also relevant to gravitational theories with a
similar structure, like Brans-Dicke or higher-dimensional theories.Comment: 41 pages, REVTEX/LaTeX 2.09 file (don't use LaTeX2e !!!) Accepted for
publication in Phys. Rev.
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