649 research outputs found
A new algorithm for anisotropic solutions
We establish a new algorithm that generates a new solution to the Einstein
field equations, with an anisotropic matter distribution, from a seed isotropic
solution. The new solution is expressed in terms of integrals of an isotropic
gravitational potential; and the integration can be completed exactly for
particular isotropic seed metrics. A good feature of our approach is that the
anisotropic solutions necessarily have an isotropic limit. We find two examples
of anisotropic solutions which generalise the isothermal sphere and the
Schwarzschild interior sphere. Both examples are expressed in closed form
involving elementary functions only.Comment: 16 pages, to appear in Pramana - J. Phy
Anisotropic static solutions in modelling highly compact bodies
Einstein field equations for anisotropic spheres are solved and exact
interior solutions obtained. This paper extends earlier treatments to include
anisotropic models which accommodate a wider variety of physically viable
energy densities. Two classes of solutions are possible. The first class
contains the limiting case for the energy density which
arises in many astrophysical applications. In the second class the singularity
at the center of the star is not present in the energy density. The models
presented in this paper allow for increasing and decreasing profiles in the
behavior of the energy density.Comment: 9 pages, to appear in Pramana - J. Phy
Complete adiabatic waveform templates for a test-mass in the Schwarzschild spacetime: VIRGO and Advanced LIGO studies
Post-Newtonian expansions of the binding energy and gravitational wave flux
truncated at the {\it same relative} post-Newtonian order form the basis of the
{\it standard adiabatic} approximation to the phasing of gravitational waves
from inspiralling compact binaries. Viewed in terms of the dynamics of the
binary, the standard approximation is equivalent to neglecting certain
conservative post-Newtonian terms in the acceleration. In an earlier work, we
had proposed a new {\it complete adiabatic} approximant constructed from the
energy and flux functions. At the leading order it employs the 2PN energy
function rather than the 0PN one in the standard approximation, so that,
effectively the approximation corresponds to the dynamics where there are no
missing post-Newtonian terms in the acceleration. In this paper, we compare the
overlaps of the standard and complete adiabatic templates with the exact
waveform in the adiabatic approximation of a test-mass motion in the
Schwarzschild spacetime, for the VIRGO and the Advanced LIGO noise spectra. It
is found that the complete adiabatic approximants lead to a remarkable
improvement in the {\it effectualness} at lower PN ( 3PN) orders, while
standard approximants of order 3PN provide a good lower-bound to the
complete approximants for the construction of effectual templates. {\it
Faithfulness} of complete approximants is better than that of standard
approximants except for a few post-Newtonian orders. Standard and complete
approximants beyond the adiabatic approximation are also studied using the
Lagrangian templates of Buonanno, Chen and Vallisneri.Comment: Proceedings of the GWDAW-9, Accepted for publication in Class. Quant.
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Evolving wormhole geometries
We present here analytical solutions of General Relativity that describe
evolving wormholes with a non-constant redshift function. We show that the
matter that threads these wormholes is not necessarily exotic. Finally, we
investigate some issues concerning WEC violation and human traversability in
these time-dependent geometries.Comment: 12 pages latex, 3 figures, to appear in Phys. Rev. D., Title
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Analytic Behaviour of Competition among Three Species
We analyse the classical model of competition between three species studied
by May and Leonard ({\it SIAM J Appl Math} \textbf{29} (1975) 243-256) with the
approaches of singularity analysis and symmetry analysis to identify values of
the parameters for which the system is integrable. We observe some striking
relations between critical values arising from the approach of dynamical
systems and the singularity and symmetry analyses.Comment: 14 pages, to appear in Journal of Nonlinear Mathematical Physic
The emergence of insecticide resistance in central Mozambique and potential threat to the successful indoor residual spraying malaria control programme
Background: Malaria vector control by indoor residual spraying was reinitiated in 2006 with DDT in ZambĂ©zia province, Mozambique. In 2007, these efforts were strengthened by the Presidentâs Malaria Initiative. This manuscript reports on the monitoring and evaluation of this programme as carried out by the Malaria Decision Support Project.
Methods: Mosquitoes were captured daily through a series of 114 window exit traps located at 19 sentinel sites, identified to species and analysed for sporozoites. Anopheles mosquitoes were collected resting indoors and tested for insecticide resistance following the standard WHO protocol. Annual cross sectional household parasite surveys were carried out to monitor the impact of the control programme on prevalence of Plasmodium falciparum in children aged 1 to 15 years.
Results: A total of 3,769 and 2,853 Anopheles gambiae s.l. and Anopheles funestus, respectively, were captured from window exit traps throughout the period. In 2010 resistance to the pyrethroids lambda-cyhalothrin and permethrin and the carbamate, bendiocarb was detected in An. funestus. In 2006, the sporozoite rate in An. gambiae s.s. was 4% and this reduced to 1% over 4 rounds of spraying. The sporozoite rate for An. funestus was also reduced from 2% to 0 by 2008. Of the 437 Anopheles arabiensis identified, none were infectious. Overall prevalence of P. falciparum in the sentinel sites fell from 60% to 32% between October 2006 and October 2008.
Conclusion: Both An. gambiae s.s. and An. funestus were controlled effectively with the DDT-based IRS programme in ZambĂ©zia, reducing disease transmission and burden. However, the discovery of pyrethroid resistance in the province and Mozambiqueâs policy change away from DDT to pyrethroids for IRS threatens the gains made here
Static charged perfect fluid spheres in general relativity
Interior perfect fluid solutions for the Reissner-Nordstrom metric are
studied on the basis of a new classification scheme. General formulas are found
in many cases. Explicit new global solutions are given as illustrations. Known
solutions are briefly reviewed.Comment: 23 pages, Revtex (galley), journal version, to appear in Phys.Rev.
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