553 research outputs found
Long time-scale variability in GRS1915+105
We present very high resolution hydrodynamical simulations of accretion discs
in black hole X-ray binaries accreting near the Eddington limit. The results
show that mass loss, irradiation and tidal interactions all have a profound
effect on the observed behaviour of long period X-ray transients. In
particular, the interplay of all of these effects in the outer regions of the
accretion disc is able to drive long time-scale (weeks to years) variability is
these objects, and is a possible origin for some of the extreme variability of
GRS1915+105.Comment: 7 pages, 9 figures (2 in colour), accepted for publication in MNRA
The steady-state structure of accretion discs in central magnetic fields
We develop a new analytic solution for the steady-state structure of a thin
accretion disc under the influence of a magnetic field that is anchored to the
central star. The solution takes a form similar to that of Shakura and Sunyaev
and tends to their solution as the magnetic moment of the star tends to zero.
As well as the Kramer's law case, we obtain a solution for a general opacity.
The effects of varying the mass transfer rate, spin period and magnetic field
of the star as well as the opacity model applied to the disc are explored for a
range of objects. The solution depends on the position of the magnetic
truncation radius. We propose a new approach for the identification of the
truncation radius and present an analytic expression for its position.Comment: 11 pages, 7 figures, accepted by MNRA
Accretion disc dynamics in extreme mass ratio compact binaries
An analysis is presented of a numerical investigation of the dynamics and
geometry of accretion discs in binary systems with mass ratios q < 0.1,
applicable to ultra-compact X-ray binaries, AM CVn stars and very short period
cataclysmic variables. The steady-state geometry of the disc in the binary
reference frame is found to be quite different from that expected at higher
mass ratios. For q ~ 0.1, the disc takes on the usual elliptical shape, with
the major axis aligned perpendicular to the line of centres of the two stars.
However, at smaller mass ratios the elliptical gaseous orbits in the outer
regions of the disc are rotated in the binary plane. The angle of rotation
increases with gas temperature, but is found to vary inversely with q. At q =
0.01, the major axis of these orbits is aligned almost parallel to the line of
centres of the two stars. These effects may be responsible for the similar disc
structure inferred from Doppler tomography of the AM CVn star GP Com
(Morales-Rueda et al. 2003), which has q = 0.02. The steady-state geometry at
low mass ratios is not predicted by an inviscid, restricted three-body model of
gaseous orbits; it is related to the effects of tidal-viscous truncation of the
disc near the Roche lobe boundary. Since the disc geometry can be inferred
observationally for some systems, it is proposed that this may offer a useful
diagnostic for the determination of mass ratios in ultra-compact binaries.Comment: 17 pages, 9 figures, 7 in colour. Accepted for publication in MNRAS.
Plain article formatting to get round arXiv problems with mn2e.st
Texas Oil and Gas Case Law Update
As the Texas economy enjoys the impact of robust oil and gas exploration and development spurred on by the shale drilling boom, Texas courts continue to experience similarly swollen dockets of oil and gas disputes. The Texas Supreme Court remained active in the energy sector in the 2011-2012 term with significant opinions affecting the areas of pipeline condemnation, exploration and production industry contracts, and lessor-lessee relations. Texas intermediate appellate courts also issued dozens of opinions touching various aspects of the industry from title and conveyancing disputes to lease operating issues. The following update will address the significant Texas Supreme Court opinions from the 2011-2012 term as well as selected cases from the intermediate appellate courts
Hydrodynamic modelling of accretion flows
In the proceedings of this, and of several recent close binary conferences,
there have been several contributions describing smoothed particle
hydrodynamics simulations of accretion disks. It is apposite therefore to
review the numerical scheme itself with emphasis on its advantages for disk
modelling, and the methods used for modelling viscous processes.Comment: 3 pages, to appear in proceedings of IAU Colloquium 194: Compact
binaries in the galaxy and beyon
Reconstructing the Topology on Monoids and Polymorphism Clones of the Rationals
We show how to reconstruct the topology on the monoid of endomorphisms of the rational numbers under the strict or reflexive order relation, and the polymorphism clone of the rational numbers under the reflexive relation. In addition we show how automatic homeomorphicity results can be lifted to polymorphism clones generated by monoids
Classification of some countable descendant-homogeneous digraphs
For finite q, we classify the countable, descendant-homogeneous digraphs in
which the descendant set of any vertex is a q-valent tree. We also give
conditions on a rooted digraph G which allow us to construct a countable
descendant-homogeneous digraph in which the descendant set of any vertex is
isomorphic to G.Comment: 16 page
Characterization of cyclic nucleotide phosphodiesterase isoenzymes in the human ureter and their functional role in vitro
Intracavernous Calcitonin-gene Related Peptide Plus Prostaglandin E 1. Possible Alternative to Penile Implants in Selected Patients.
Propeller-activated resonances and the fate of short-period cataclysmic variables
We show that the combination of a weak magnetic propeller and accretion disc resonances can effectively halt accretion in short-period cataclysmic variables (CVs) for large fractions of their lifetimes. This may help to explain the discrepancy between the observed and predicted orbital period distributions of CVs at short periods. Orbital resonances cause the disc to become eccentric, allowing material to fall back on to the donor star or out of the system. A weak magnetic field on a rapidly spinning primary star propels disc material outwards, allowing it to access these resonances. Numerical and analytic calculations show that this state can be long lived (âŒ1011 yr). This is because the magnetic propeller is required only to maintain access to the resonances, and not to push matter out of the Roche lobe, so that the spin-down time-scale is much longer than that for a classical propeller mode
- âŠ