39 research outputs found
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
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
General Relativistic Radiant Shock Waves in the Post-Quasistatic Approximation
An evolution of radiant shock wave front is considered in the framework of a
recently presented method to study self-gravitating relativistic spheres, whose
rationale becomes intelligible and finds full justification within the context
of a suitable definition of the post-quasistatic approximation. The spherical
matter configuration is divided into two regions by the shock and each side of
the interface having a different equation of state and anisotropic phase. In
order to simulate dissipation effects due to the transfer of photons and/or
neutrinos within the matter configuration, we introduce the flux factor, the
variable Eddington factor and a closure relation between them. As we expected
the strength of the shock increases the speed of the fluid to relativistic
values and for some critical ones is larger than light speed. In addition, we
find that energy conditions are very sensible to the anisotropy, specially the
strong one. As a special feature of the model, we find that the contribution of
the matter and radiation to the radial pressure are the same order of magnitude
as in the mant as in the core, moreover, in the core radiation pressure is
larger than matter pressure.Comment: To appear in Journal of Physics:Conference Series:"XXIX Spanish
Relativity Meeting (ERE 2006): Einstein's Legacy: From the Theoretical
Paradise to Astrophysical Observations
Compact anisotropic spheres with prescribed energy density
New exact interior solutions to the Einstein field equations for anisotropic
spheres are found. We utilise a procedure that necessitates a choice for the
energy density and the radial pressure. This class contains the constant
density model of Maharaj and Maartens (Gen. Rel. Grav., Vol 21, 899-905, 1989)
and the variable density model of Gokhroo and Mehra (Gen. Rel. Grav., Vol 26,
75-84, 1994) as special cases. These anisotropic spheres match smoothly to the
Schwarzschild exterior and gravitational potentials are well behaved in the
interior. A graphical analysis of the matter variables is performed which
points to a physically reasonable matter distribution.Comment: 22 pages, 3 figures, to appear in Gen. Rel. Gra
On surface tension for compact stars
In an earlier treatment it was demonstrated that general relativity gives
higher values of surface tension in strange stars with quark matter than
neutron stars.We generate the modified Tolman-Oppenheimer-Volkoff equation to
incorporate anisotropic matter and use this to show that pressure anisotropy
provides for a wide range of behaviour in the surface tension than is the case
with isotropic pressures. In particular it is possible that anisotropy
drastically decreases the value of the surface tension.Comment: 8 pages, To appear in J. Astrophys. Astro
Comparison of three nucleic acid-based tests for detecting Anaplasma marginale and Anaplasma centrale in cattle
Several nucleic acid-based assays have been developed for detecting Anaplasma marginale and
Anaplasma centrale in vectors and hosts, making the choice of method to use in endemic areas
difficult. We evaluated the ability of the reverse line blot (RLB) hybridisation assay, two nested
polymerase chain reaction (nPCR) assays and a duplex real-time quantitative polymerase
chain reaction (qPCR) assay to detect A. marginale and A. centrale infections in cattle (n = 66) in
South Africa. The lowest detection limits for A. marginale plasmid DNA were 2500 copies by
the RLB assay, 250 copies by the nPCR and qPCR assays and 2500, 250 and 25 copies of
A. centrale plasmid DNA by the RLB, nPCR and qPCR assays respectively. The qPCR assay
detected more A. marginale- and A. centrale-positive samples than the other assays, either as
single or mixed infections. Although the results of the qPCR and nPCR tests were in agreement
for the majority (38) of A. marginale-positive samples, 13 samples tested negative for A. marginale
using nPCR but positive using qPCR. To explain this discrepancy, the target sequence region
of the nPCR assay was evaluated by cloning and sequencing the msp1β gene from selected field
samples. The results indicated sequence variation in the internal forward primer (AM100) area
amongst the South African A. marginale msp1β sequences, resulting in false negatives. We
propose the use of the duplex qPCR assay in future studies as it is more sensitive and offers the
benefits of quantification and multiplex detection of both Anaplasma spp.The
National Research Foundation (NRF) of South Africa
(grant number 81840 awarded to Dr Nicola Collins) and
Technology Innovation Agency (TIA), Tshwane Animal
Health Cluster (grant TAHC12-00037 awarded to Professor
Marinda Oosthuizen).http://www.ojvr.org/am2017GeneticsVeterinary Tropical Disease
Using Lie Symmetry Analysis to Solve a Problem That Models Mass Transfer from a Horizontal Flat Plate
We use Lie symmetry analysis to solve a boundary value problem that arises in chemical engineering, namely, mass transfer during the contact of a solid slab with an overhead flowing fluid. This problem was earlier tackled using Adomian decomposition method (Fatoorehchi and Abolghasemi 2011), leading to the Adomian series form of solution. It turns out that the application of Lie group analysis yields an elegant form of the solution. After introducing the governing mathematical model and some preliminaries of Lie symmetry analysis, we compute the Lie point symmetries admitted by the governing equation and use these to construct the desired solution as an invariant solution
Dataset: Blood parasites of South African cranes
The study investigated the occurrence, systematics, phylogenetic relationships and ecology (geographical distribution and host-parasite relationships) of haemosporidian parasites from selected populations of cranes (order: Gruiformes) in South African in order to document their prevalence and diversity. It contributes to (1) our understanding of the diversity of avian Haemosporidia of priority avian species (2) the expansion of host range and geographical distribution of these parasites (3) additional information on the barcodes of priority avian taxa for which there is paucity of information. Blood samples were collected from three South African cranes species from selected conservation facilities. DNA was extracted from the samples and analysed by PCR. The cytochrome b gene was sequenced from positive samples. The prevalence of the parasites was determined. Genetic distances, haplotype networks and nucleotide diversity (π) were calculated to estimate genetic diversity. Evolutionary relationships of the new sequences were determined by phylogenetic analysis. Parasite DNA was detected in cranes from 10 facilities, with an overall prevalence of 37.41%. Overall haplotype diversity was high (Hd=0.927) with low nucleotide diversity (π=0.099). A total of 15 lineages (cyt b haplotypes) were identified from South African cranes, with 11 being unique South African haplotypes, composed of three Leucocytozoon haplotypes (Hd=0.600; π=0.038), seven for Haemoproteus (Hd=0.81; π=0.046) and five for Plasmodium species (Hd=0.895; π=0.050). Haemoproteus antigonis was the most common and diverse species and is reported for the first time in South African birds by this study. Metadata (locality, date of collection, species, sex, age, Biobank reference number), PCR results, sequence alignment and sequence data (MalAvi lineages, GenBank Accession numbers, genetic distances) are presented. These data contribute valuable information that can be used in subsequent studies. Highlights: haemosporidian infections (Plasmodium, Haemoproteus and Leucocytozoon spp.) in cranes in South Africa are common and genetically diverse; 15 unique lineages and six distinct species are described, two of these are novel species of captive bred cranes in South African; this is the first report on the occurrence of Haemoproteus antigonis in South Africa and confirmation of cranes as the only hosts of H. antigonis.THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV