1,753 research outputs found
A study of high power argon laser optics Final report, 15 Apr. 1967 - 14 Apr. 1968
Window degradation in high power argon laser optic
A study of high power argon laser optics Interim scientific report, 15 Apr. - 31 Oct. 1967
Argon laser optimal component degredation at high power level
On marginally outer trapped surfaces in stationary and static spacetimes
In this paper we prove that for any spacelike hypersurface containing an
untrapped barrier in a stationary spacetime satisfying the null energy
condition, any marginally outer trapped surface cannot lie in the exterior
region where the stationary Killing vector is timelike. In the static case we
prove that any marginally outer trapped surface cannot penetrate into the
exterior region where the static Killing vector is timelike. In fact, we prove
these result at an initial data level, without even assuming existence of a
spacetime. The proof relies on a powerful theorem by Andersson and Metzger on
existence of an outermost marginally outer trapped surface.Comment: 22 pages, 3 figures; 1 reference added, 1 figure changed, other minor
change
Singularity-Free Cylindrical Cosmological Model
A cylindrically symmetric perfect fluid spacetime with no curvature
singularity is shown. The equation of state for the perfect fluid is that of a
stiff fluid. The metric is diagonal and non-separable in comoving coordinates
for the fluid. It is proven that the spacetime is geodesically complete and
globally hyperbolic.Comment: LaTeX 2e, 8 page
Stationary axisymmetric exteriors for perturbations of isolated bodies in general relativity, to second order
Perturbed stationary axisymmetric isolated bodies, e.g. stars, represented by
a matter-filled interior and an asymptotically flat vacuum exterior joined at a
surface where the Darmois matching conditions are satisfied, are considered.
The initial state is assumed to be static. The perturbations of the matching
conditions are derived and used as boundary conditions for the perturbed Ernst
equations in the exterior region. The perturbations are calculated to second
order. The boundary conditions are overdetermined: necessary and sufficient
conditions for their compatibility are derived. The special case of
perturbations of spherical bodies is given in detail.Comment: RevTeX; 32 pp. Accepted by Phys. Rev. D. Added references and extra
comments in introductio
Generalisation of the Einstein-Straus model to anisotropic settings
We study the possibility of generalising the Einstein--Straus model to
anisotropic settings, by considering the matching of locally cylindrically
symmetric static regions to the set of on locally rotationally
symmetric (LRS) spacetimes. We show that such matchings preserving the symmetry
are only possible for a restricted subset of the LRS models in which there is
no evolution in one spacelike direction. These results are applied to spatially
homogeneous (Bianchi) exteriors where the static part represents a finite
bounded interior region without holes. We find that it is impossible to embed
finite static strings or other locally cylindrically symmetric static objects
(such as bottle or coin-shaped objects) in reasonable Bianchi cosmological
models, irrespective of the matter content. Furthermore, we find that if the
exterior spacetime is assumed to have a perfect fluid source satisfying the
dominant energy condition, then only a very particular family of LRS stiff
fluid solutions are compatible with this model.
Finally, given the interior/exterior duality in the matching procedure, our
results have the interesting consequence that the Oppenheimer-Snyder model of
collapse cannot be generalised to such anisotropic cases.Comment: LaTeX, 24 pages. Text unchanged. Labels removed from the equations.
Submitted for publicatio
Symmetry-preserving matchings
In the literature, the matchings between spacetimes have been most of the
times implicitly assumed to preserve some of the symmetries of the problem
involved. But no definition for this kind of matching was given until recently.
Loosely speaking, the matching hypersurface is restricted to be tangent to the
orbits of a desired local group of symmetries admitted at both sides of the
matching and thus admitted by the whole matched spacetime. This general
definition is shown to lead to conditions on the properties of the preserved
groups. First, the algebraic type of the preserved group must be kept at both
sides of the matching hypersurface. Secondly, the orthogonal transivity of
two-dimensional conformal (in particular isometry) groups is shown to be
preserved (in a way made precise below) on the matching hypersurface. This
result has in particular direct implications on the studies of axially
symmetric isolated bodies in equilibrium in General Relativity, by making up
the first condition that determines the suitability of convective interiors to
be matched to vacuum exteriors. The definition and most of the results
presented in this paper do not depend on the dimension of the manifolds
involved nor the signature of the metric, and their applicability to other
situations and other higher dimensional theories is manifest.Comment: LaTeX, 19 page
Meanings & motives. Experts debating tobacco addiction.
Over the last 50 years, tobacco has been excluded from and then included in the category of addictive substances. We investigated influences on these opposing definitions and their application in expert witness testimony in litigation in the 1990s and 2000s. A scientist with ties to the tobacco industry influenced the selection of a definition of addiction that led to the classification of tobacco as a "habituation" in the 1964 Surgeon General's Advisory Committee report. Tobacco was later defined as addictive in the 1988 surgeon general's report. Expert witnesses for tobacco companies used the 1964 report's definition until Philip Morris Tobacco Company publicly changed its position in 1997 to agree that nicotine was addictive. Expert witnesses for plaintiffs suing the tobacco industry used the 1988 report's definition, arguing that new definitions were superior because of scientific advance. Both sides viewed addiction as an objective entity that could be defined more or less accurately
The Eight Forms of Corrosion & the Corrective Measures
Corrosion has been justifiably attributed to cause more loss in money than any other single factor. Corrosion has also been an important factor in causing some outstanding cases of failure.
Valuable information for the solution of a corrosion failure can often be obtained through careful observation of the corroded test specimens or, failed equipment. Corr-osion can be classified by the eight forms in which it manifests itself, the basis for this classification being the appearance of the corroded metal. Some of these eight forms are unique and distinct but all of them are to varying degrees interrelate
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