55 research outputs found
Lax pair tensors and integrable spacetimes
The use of Lax pair tensors as a unifying framework for Killing tensors of
arbitrary rank is discussed. Some properties of the tensorial Lax pair
formulation are stated. A mechanical system with a well-known Lax
representation -- the three-particle open Toda lattice -- is geometrized by a
suitable canonical transformation. In this way the Toda lattice is realized as
the geodesic system of a certain Riemannian geometry. By using different
canonical transformations we obtain two inequivalent geometries which both
represent the original system. Adding a timelike dimension gives
four-dimensional spacetimes which admit two Killing vector fields and are
completely integrable.Comment: 10 pages, LaTe
Generalized plane-fronted gravitational waves in any dimension
We study the gravitational waves in spacetimes of arbitrary dimension. They
generalize the pp-waves and the Kundt waves, obtained earlier in four
dimensions. Explicit solutions of the Einstein and Einstein-Maxwell equations
are derived for an arbitrary cosmological constant.Comment: Revtex, 18 pages, no figure
Energy-momentum and angular momentum of Goedel universes
We discuss the Einstein energy-momentum complex and the Bergmann-Thomson
angular momentum complex in general relativity and calculate them for
space-time homogeneous Goedel universes. The calculations are performed for a
dust acausal model and for a scalar-field causal model. It is shown that the
Einstein pseudotensor is traceless, not symmetric, the gravitational energy is
"density" is negative and the gravitational Poynting vector vanishes.
Significantly, the total (gravitational and matter) energy "density" fro the
acausal model is zero while for the casual model it is negative.The
Bergmann-Thomson angular momentum complex does not vanish for both G\"odel
models.Comment: an amended version, 24 pages, accepted to PR
Goedel, Penrose, anti-Mach: extra supersymmetries of time-dependent plane waves
We prove that M-theory plane waves with extra supersymmetries are necessarily
homogeneous (but possibly time-dependent), and we show by explicit construction
that such time-dependent plane waves can admit extra supersymmetries. To that
end we study the Penrose limits of Goedel-like metrics, show that the Penrose
limit of the M-theory Goedel metric (with 20 supercharges) is generically a
time-dependent homogeneous plane wave of the anti-Mach type, and display the
four extra Killings spinors in that case. We conclude with some general remarks
on the Killing spinor equations for homogeneous plane waves.Comment: 20 pages, LaTeX2
Obtaining a class of Type O pure radiation metrics with a cosmological constant, using invariant operators
Using the generalised invariant formalism we derive a class of conformally
flat spacetimes whose Ricci tensor has a pure radiation and a Ricci scalar
component. The method used is a development of the methods used earlier for
pure radiation spacetimes of Petrov types O and N respectively. In this paper
we demonstrate how to handle, in the generalised invariant formalism,
spacetimes with isotropy freedom and rich Killing vector structure. Once the
spacetimes have been constructed, it is straightforward to deduce their
Karlhede classification: the Karlhede algorithm terminates at the fourth
derivative order, and the spacetimes all have one degree of null isotropy and
three, four or five Killing vectors.Comment: 29 page
Type O pure radiation metrics with a cosmological constant
In this paper we complete the integration of the conformally flat pure
radiation spacetimes with a non-zero cosmological constant , and , by considering the case . This is a
further demonstration of the power and suitability of the generalised invariant
formalism (GIF) for spacetimes where only one null direction is picked out by
the Riemann tensor. For these spacetimes, the GIF picks out a second null
direction, (from the second derivative of the Riemann tensor) and once this
spinor has been identified the calculations are transferred to the simpler GHP
formalism, where the tetrad and metric are determined. The whole class of
conformally flat pure radiation spacetimes with a non-zero cosmological
constant (those found in this paper, together with those found earlier for the
case ) have a rich variety of subclasses with zero,
one, two, three, four or five Killing vectors
New solutions in 3D gravity
We study gravitational theory in 1+2 spacetime dimensions which is determined
by the Lagrangian constructed as a sum of the Einstein-Hilbert term plus the
two (translational and rotational) gravitational Chern-Simons terms. When the
corresponding coupling constants vanish, we are left with the purely Einstein
theory of gravity. We obtain new exact solutions for the gravitational field
equations with the nontrivial material sources. Special attention is paid to
plane-fronted gravitational waves (in case of the Maxwell field source) and to
the circularly symmetric as well as the anisotropic cosmological solutions
which arise for the ideal fluid matter source.Comment: Revtex, 21 pages, no figure
M-theory on a Time-dependent Plane-wave
We propose a matrix model on a homogeneous plane-wave background with 20
supersymmetries. This background is anti-Mach type and is equivalent to the
time-dependent background. We study supersymmetries in this theory and
calculate the superalgebra. The vacuum energy of the abelian part is also
calculated. In addition we find classical solutions such as graviton solution,
fuzzy sphere and hyperboloid.Comment: 19pages, no figures, LaTeX, JHEP3.cl
Teeth of the red fox Vulpes vulpes (L., 1758) as a bioindicator in studies on fluoride pollution
An examination was made of fluoride content in the mandibular first molars of the permanent teeth of the red fox Vulpes vulpes living in north-west (NW) Poland. The teeth were first dried to a constant weight at 105°C and then ashed. Fluorides were determined potentiometrically, and their concentrations were expressed in dry weight (DW) and ash. The results were used to perform an indirect estimation of fluoride pollution in the examined region of Poland. The collected specimens (nâ=â35) were classified into one of the three age categories: immature (im, 6â12 months), subadult (subad, from 12 to 20 months) and adult (ad, >20 months). The mean concentrations (geometric mean) of fluoride were similar in the im and subad groups (230 and 296 mg/kg DW and 297 and 385 mg/kg ash, respectively), and significantly smaller than in the ad group (504 and 654 mg/kg, respectively, in DW and ash). Basing on other reports that the âŒ400 mg/kg DW concentration of fluoride in bones in the long-lived wild mammals generally reflects the geochemical background, it was found that 57% of the foxes in NW Poland exceeded this value by 9% to 170%. This indirectly reflects a moderate fluoride contamination in the tested region
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