139 research outputs found
Experimental investigations related to ionospheric probing, Part 1 Final report
D region simulation by ultraviolet photoionization of nitric oxid
Spacelike Ricci Inheritance Vectors in a Model of String Cloud and String Fluid Stress Tensor
We study the consequences of the existence of spacelike Ricci inheritance
vectors (SpRIVs) parallel to for model of string cloud and string fluid
stress tensor in the context of general relativity. Necessary and sufficient
conditions are derived for a spacetime with a model of string cloud and string
fluid stress tensor to admit a SpRIV and a SpRIV which is also a spacelike
conformal Killing vector (SpCKV). Also, some results are obtained.Comment: 11 page
Ricci Collineations of the Bianchi Type II, VIII, and IX Space-times
Ricci and contracted Ricci collineations of the Bianchi type II, VIII, and IX
space-times, associated with the vector fields of the form (i) one component of
is different from zero and (ii) two components of are
different from zero, for , are presented. In subcase (i.b), which
is , some known solutions are found, and in subcase
(i.d), which is , choosing ,
the Bianchi type II, VIII, and IX space-times is reduced to the
Robertson-Walker metric.Comment: 12 Pages, LaTeX, 1 Table, no figure
Classification of Spherically Symmetric Static Spacetimes according to their Matter Collineations
The spherically symmetric static spacetimes are classified according to their
matter collineations. These are studied when the energy-momentum tensor is
degenerate and also when it is non-degenerate. We have found a case where the
energy-momentum tensor is degenerate but the group of matter collineations is
finite. For the non-degenerate case, we obtain either {\it four}, {\it five},
{\it six} or {\it ten} independent matter collineations in which four are
isometries and the rest are proper. We conclude that the matter collineations
coincide with the Ricci collineations but the constraint equations are
different which on solving can provide physically interesting cosmological
solutions.Comment: 15 pages, no figure, Late
Killing tensors in pp-wave spacetimes
The formal solution of the second order Killing tensor equations for the
general pp-wave spacetime is given. The Killing tensor equations are integrated
fully for some specific pp-wave spacetimes. In particular, the complete
solution is given for the conformally flat plane wave spacetimes and we find
that irreducible Killing tensors arise for specific classes. The maximum number
of independent irreducible Killing tensors admitted by a conformally flat plane
wave spacetime is shown to be six. It is shown that every pp-wave spacetime
that admits an homothety will admit a Killing tensor of Koutras type and, with
the exception of the singular scale-invariant plane wave spacetimes, this
Killing tensor is irreducible.Comment: 18 page
Matter collineations of Spacetime Homogeneous G\"odel-type Metrics
The spacetime homogeneous G\"odel-type spacetimes which have four classes of
metrics are studied according to their matter collineations. The obtained
results are compared with Killing vectors and Ricci collineations. It is found
that these spacetimes have infinite number of matter collineations in
degenerate case, i.e. det, and do not admit proper matter
collineations in non-degenerate case, i.e. det. The degenerate
case has the new constraints on the parameters and which characterize
the causality features of the G\"odel-type spacetimes.Comment: 12 pages, LaTex, no figures, Class. Quantum.Grav.20 (2003) 216
Projective dynamics and first integrals
We present the theory of tensors with Young tableau symmetry as an efficient
computational tool in dealing with the polynomial first integrals of a natural
system in classical mechanics. We relate a special kind of such first
integrals, already studied by Lundmark, to Beltrami's theorem about
projectively flat Riemannian manifolds. We set the ground for a new and simple
theory of the integrable systems having only quadratic first integrals. This
theory begins with two centered quadrics related by central projection, each
quadric being a model of a space of constant curvature. Finally, we present an
extension of these models to the case of degenerate quadratic forms.Comment: 39 pages, 2 figure
Effect of fosmidomycin on metabolic and transcript profiles of the methylerythritol phosphate pathway in Plasmodium falciparum
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