1,121 research outputs found
Electromagnetic Fields of Slowly Rotating Magnetized Gravastars
We study the dipolar magnetic field configuration and present solutions of
Maxwell equations in the internal background spacetime of a a slowly rotating
gravastar. The shell of gravastar where magnetic field penetrated is modeled as
sphere consisting of perfect highly magnetized fluid with infinite
conductivity. Dipolar magnetic field of the gravastar is produced by a circular
current loop symmetrically placed at radius at the equatorial plane.Comment: 5 pages, 2 figures, accepted for publication to Mod. Phys. Lett.
Poison sedge can kill stock
POISON SEDGE was first suspected of being toxic to livestock in Western Australia nearly 80 years ago.
Sudden deaths of sheep grazing areas on which poison sedge grew have been reported from many regions from Geraldton to Scott River.
This article reports a case of poisoning in the field, and the experimental reproduction of poison sedge toxicity in pen-fed sheep
The effect of self-selected complementary therapies on cancer patients\u27 quality of life and symptom distress: A prospective cohort study in an integrative oncology setting
Objective: To examine the effectiveness of a multifaceted complementary therapies intervention, delivered in a systematic manner within an Australian public hospital setting, on quality of life and symptom distress outcomes for cancer patients.
Methods: Adults receiving treatment for any form of cancer were eligible to participate in this study. Self-referred participants were offered a course of six complementary therapy sessions. Measures were administered at baseline, and at the third and sixth visit. The primary outcomes were quality of life and symptom distress. Linear mixed models were used to assess change in the primary outcomes.
Results: In total, 1376 cancer patients participated in this study. The linear mixed models demonstrated that there were significant improvements in quality of life and significant reductions in symptom distress over six sessions. Body-based therapies demonstrated significantly superior improvement in quality of life over counselling, but no other differences between therapies were identified. Reduced symptom distress was not significantly associated with any particular type of therapy.
Conclusion: A self-selected complementary therapies intervention, provided in an Australian public hospital by accredited therapists, for cancer patients significantly mproved quality of life and reduced symptom distress. The effect of this intervention on quality of life has particular salience, since cancer impacts on many areas of people’s lives and impairs quality of life
Perturbations on steady spherical accretion in Schwarzschild geometry
The stationary background flow in the spherically symmetric infall of a
compressible fluid, coupled to the space-time defined by the static
Schwarzschild metric, has been subjected to linearized perturbations. The
perturbative procedure is based on the continuity condition and it shows that
the coupling of the flow with the geometry of space-time brings about greater
stability for the flow, to the extent that the amplitude of the perturbation,
treated as a standing wave, decays in time, as opposed to the amplitude
remaining constant in the Newtonian limit. In qualitative terms this situation
simulates the effect of a dissipative mechanism in the classical Bondi
accretion flow, defined in the Newtonian construct of space and time. As a
result of this approach it becomes impossible to define an acoustic metric for
a conserved spherically symmetric flow, described within the framework of
Schwarzschild geometry. In keeping with this view, the perturbation, considered
separately as a high-frequency travelling wave, also has its amplitude reduced.Comment: 8 pages, no figur
Implications of nonlinearity for spherically symmetric accretion
We subject the steady solutions of a spherically symmetric accretion flow to
a time-dependent radial perturbation. The equation of the perturbation includes
nonlinearity up to any arbitrary order, and bears a form that is very similar
to the metric equation of an analogue acoustic black hole. Casting the
perturbation as a standing wave on subsonic solutions, and maintaining
nonlinearity in it up to the second order, we get the time-dependence of the
perturbation in the form of a Li\'enard system. A dynamical systems analysis of
the Li\'enard system reveals a saddle point in real time, with the implication
that instabilities will develop in the accreting system when the perturbation
is extended into the nonlinear regime. The instability of initial subsonic
states also adversely affects the temporal evolution of the flow towards a
final and stable transonic state.Comment: 14 pages, ReVTeX. Substantially revised with respect to the previous
version. Three figures and a new section (Sec. VI) adde
Secular instability in quasi-viscous disc accretion
A first-order correction in the -viscosity parameter of Shakura and
Sunyaev has been introduced in the standard inviscid and thin accretion disc. A
linearised time-dependent perturbative study of the stationary solutions of
this "quasi-viscous" disc leads to the development of a secular instability on
large spatial scales. This qualitative feature is equally manifest for two
different types of perturbative treatment -- a standing wave on subsonic
scales, as well as a radially propagating wave. Stability of the flow is
restored when viscosity disappears.Comment: 15 pages, 2 figures, AASTeX. Added some new material and upgraded the
reference lis
Evolution of transonicity in an accretion disc
For inviscid, rotational accretion flows driven by a general pseudo-Newtonian
potential on to a Schwarzschild black hole, the only possible fixed points are
saddle points and centre-type points. For the specific choice of the Newtonian
potential, the flow has only two critical points, of which the outer one is a
saddle point while the inner one is a centre-type point. A restrictive upper
bound is imposed on the admissible range of values of the angular momentum of
sub-Keplerian flows through a saddle point. These flows are very unstable to
any deviation from a necessarily precise boundary condition. The difficulties
against the physical realisability of a solution passing through the saddle
point have been addressed through a temporal evolution of the flow, which gives
a non-perturbative mechanism for selecting a transonic solution passing through
the saddle point. An equation of motion for a real-time perturbation about the
stationary flows reveals a very close correspondence with the metric of an
acoustic black hole, which is also an indication of the primacy of
transonicity.Comment: 18 page
A Toy Model for Blandford-Znajek Mechanism
A toy model for the Blandford-Znajek mechanism is investigated: a Kerr black
hole with a toroidal electric current residing in a thin disk around the black
hole. The toroidal electric current generates a poloidal magnetic field
threading the black hole and disk. Due to the interaction of the magnetic field
with remote charged particles, the rotation of the black hole and disk induces
an electromotive force, which can power an astrophysical load at remote
distance. The power of the black hole and disk is calculated. It is found that,
for a wide range of parameters specifying the rotation of the black hole and
the distribution of the electric current in the disk, the power of the disk
exceeds the power of the black hole. The torque provided by the black hole and
disk is also calculated. The torque of the disk is comparable to the torque of
the black hole. As the disk loses its angular momentum, the mass of the disk
gradually drifts towards the black hole and gets accreted. Ultimately the power
comes from the gravitational binding energy between the disk and the black
hole, as in the standard theory of accretion disk, instead of the rotational
energy of the black hole. This suggests that the Blandford-Znajek mechanism may
be less efficient in extracting energy from a rotating black hole with a thin
disk. The limitations of our simple model and possible improvements deserved
for future work are also discussed.Comment: 16 pages, 4 figures. Accepted for publication in Physical Review
Effects of organic plant oils and role of oxidation on nutrient utilization in juvenile rainbow trout (Oncorhynchus mykiss)
The study compared the effect of four either fresh or force oxidized organic plant oils in diets for juvenile rainbow trout (Oncorhynchus mykiss) in which 47% of conventional LT fish meal protein was substituted by a mixture of 3 organic plant protein concentrates. Fish oil was completely substituted with either organic linseed oil; rape seed oil; sunflower oil or grape seed oil and evaluated based on feed intake, feed utilization, growth and digestibility. None of the plant oils affected feed intake and growth parameters. Organic plant oils had all a positive effect on lipid digestibility as compared with the fish oil based control diet, despite the very different FA profiles. The organic vegetable oils did not undergo autoxidation, as opposed to the fish oil control for which lipid digestibility was significantly negative influenced
On the orbital and physical parameters of the HDE 226868/Cygnus X-1 binary system
In this paper we explore the consequences of the recent determination of the
mass m=(8.7 +/- 0.8)M_Sun of Cygnus X-1, obtained from the Quasi-Periodic
Oscillation (QPO)-photon index correlation scaling, on the orbital and physical
properties of the binary system HDE 226868/Cygnus X-1. By using such a result
and the latest spectroscopic optical data of the HDE 226868 supergiant star we
get M=(24 +/- 5)M_Sun for its mass. It turns out that deviations from the third
Kepler law significant at more than 1-sigma level would occur if the
inclination i of the system's orbital plane to the plane of the sky falls
outside the range 41-56 deg: such deviations cannot be due to the first
post-Newtonian (1PN) correction to the orbital period because of its smallness;
interpreted in the framework of the Newtonian theory of gravitation as due to
the stellar quadrupole mass moment Q, they are unphysical because Q would take
unreasonably large values. By conservatively assuming that the third Kepler law
is an adequate model for the orbital period we obtain i=(48 +/- 7) deg which
yields for the relative semimajor axis a=(42 +/- 9)R_Sun. Our estimate for the
Roche's lobe of HDE 226868 is r_M = (21 +/- 6)R_Sun.Comment: Latex2e, 7 pages, 1 table, 4 figures. To appear in ApSS (Astrophysics
and Space Science
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