343 research outputs found
Return to driving after traumatic brain injury : a British perspective
Primary Objective: to identify current legal situation, and professional practice in assisting persons with traumatic brain injury (TBI) to return to safe driving after injury.
Methods and Procedures
A brief review of relevant literature, a description of the current statutory and quasi-statutory authorities regulating return to driving after TBI in the UK, and a description of the nature and resolution of clinical and practical dilemmas facing professionals helping return to safe driving after TBI. Each of the 15 UK mobility centres was contacted and literature requested; in addition a representative of each centre responded to a structured telephone survey.
Main Outcome and Results: The current situation in Great Britain is described, with a brief analysis of the strengths and weaknesses both of the current statutory situation, and also the practical situation (driving centres), with suggestions for improvements in practice.
Conclusion
Although brain injury may cause serious limitations in driving ability, previous drivers are not routinely assessed or advised regarding return to driving after TBI
Nucleosynthesis in Advective Accretion Disks Around Galactic and Extra-Galactic Black Holes
We compute the nucleosynthesis of materials inside advective disks around
black holes. We show that composition of incoming matter can change
significantly depending on the accretion rate and accretion disks. These works
are improvements on the earlier works in thick accretion disks of Chakrabarti,
Jin & Arnett (1987) in presence of advection in the flow.Comment: Latex pages including figures. Kluwer Style files included. Appearing
in `Observational Evidence for Black Holes in the Universe', ed. Sandip K.
Chakrabarti, Kluwer Academic Publishers (DORDRECHT: Holland
Accretion Disks Around Black Holes: Twenty Five Years Later
We study the progress of the theory of accretion disks around black holes in
last twenty five years and explain why advective disks are the best bet in
explaining varied stationary and non-stationary observations from black hole
candidates. We show also that the recently proposed advection dominated flows
are incorrect.Comment: 30 Latex pages including figures. Kluwer Style files included.
Appearing in `Observational Evidence for Black Holes in the Universe', ed.
Sandip K. Chakrabarti, Kluwer Academic Publishers (DORDRECHT: Holland
Theory of disk accretion onto supermassive black holes
Accretion onto supermassive black holes produces both the dramatic phenomena
associated with active galactic nuclei and the underwhelming displays seen in
the Galactic Center and most other nearby galaxies. I review selected aspects
of the current theoretical understanding of black hole accretion, emphasizing
the role of magnetohydrodynamic turbulence and gravitational instabilities in
driving the actual accretion and the importance of the efficacy of cooling in
determining the structure and observational appearance of the accretion flow.
Ongoing investigations into the dynamics of the plunging region, the origin of
variability in the accretion process, and the evolution of warped, twisted, or
eccentric disks are summarized.Comment: Mostly introductory review, to appear in "Supermassive black holes in
the distant Universe", ed. A.J. Barger, Kluwer Academic Publishers, in pres
Foundations of Black Hole Accretion Disk Theory
This review covers the main aspects of black hole accretion disk theory. We
begin with the view that one of the main goals of the theory is to better
understand the nature of black holes themselves. In this light we discuss how
accretion disks might reveal some of the unique signatures of strong gravity:
the event horizon, the innermost stable circular orbit, and the ergosphere. We
then review, from a first-principles perspective, the physical processes at
play in accretion disks. This leads us to the four primary accretion disk
models that we review: Polish doughnuts (thick disks), Shakura-Sunyaev (thin)
disks, slim disks, and advection-dominated accretion flows (ADAFs). After
presenting the models we discuss issues of stability, oscillations, and jets.
Following our review of the analytic work, we take a parallel approach in
reviewing numerical studies of black hole accretion disks. We finish with a few
select applications that highlight particular astrophysical applications:
measurements of black hole mass and spin, black hole vs. neutron star accretion
disks, black hole accretion disk spectral states, and quasi-periodic
oscillations (QPOs).Comment: 91 pages, 23 figures, final published version available at
http://www.livingreviews.org/lrr-2013-
Admission to hospital following head injury in England: Incidence and socio-economic associations
BACKGROUND:
Head injury in England is common. Evidence suggests that socio-economic factors may cause variation in incidence, and this variation may affect planning for services to meet the needs of those who have sustained a head injury.
METHODS:
Socio-economic data were obtained from the UK Office for National Statistics and merged with Hospital Episodes Statistics obtained from the Department of Health. All patients admitted for head injury with ICD-10 codes S00.0–S09.9 during 2001–2 and 2002–3 were included and collated at the level of the extant Health Authorities (HA) for 2002, and Primary Care Trust (PCT) for 2003. Incidence was determined, and cluster analysis and multiple regression analysis were used to look at patterns and associations.
Results: 112,718 patients were admitted during 2001–2 giving a hospitalised incidence rate for England of 229 per 100,000. This rate varied across the English HA's ranging from 91–419 per 100,000. The rate remained unchanged for 2002–3 with a similar magnitude of variation across PCT's. Three clusters of HA's were identified from the 2001–2 data; those typical of London, those of the Shire counties, and those of Other Urban authorities. Socio-economic factors were found to account for a high proportion of the variance in incidence for 2001–2. The same pattern emerged for 2002–3 at the PCT level. The use of public transport for travel to work is associated with a
decreased incidence and lifestyle indicators, such as the numbers of young unemployed, increase the incidence.
CONCLUSION:
Head injury incidence in England varies by a factor of 4.6 across HA's and PCT's.
Planning head injury related services at the local level thus needs to be based on local incidence
figures rather than regional or national estimates. Socio-economic factors are shown to be
associated with admission, including travel to work patterns and lifestyle indicators, which suggests
that incidence is amenable to policy initiatives at the macro level as well as preventive programmes
targeted at key groups
Inside-Out Evacuation of Transitional Protoplanetary Disks by the Magneto-Rotational Instability
How do T Tauri disks accrete? The magneto-rotational instability (MRI)
supplies one means, but protoplanetary disk gas is typically too poorly ionized
to be magnetically active. Here we show that the MRI can, in fact, explain
observed accretion rates for the sub-class of T Tauri disks known as
transitional systems. Transitional disks are swept clean of dust inside rim
radii of ~10 AU. Stellar coronal X-rays ionize material in the disk rim,
activating the MRI there. Gas flows from the rim to the star, at a rate limited
by the depth to which X-rays ionize the rim wall. The wider the rim, the larger
the surface area that the rim wall exposes to X-rays, and the greater the
accretion rate. Interior to the rim, the MRI continues to transport gas; the
MRI is sustained even at the disk midplane by super-keV X-rays that Compton
scatter down from the disk surface. Accretion is therefore steady inside the
rim. Blown out by radiation pressure, dust largely fails to accrete with gas.
Contrary to what is usually assumed, ambipolar diffusion, not Ohmic
dissipation, limits how much gas is MRI-active. We infer values for the
transport parameter alpha on the order of 0.01 for GM Aur, TW Hyd, and DM Tau.
Because the MRI can only afflict a finite radial column of gas at the rim, disk
properties inside the rim are insensitive to those outside. Thus our picture
provides one robust setting for planet-disk interaction: a protoplanet interior
to the rim will interact with gas whose density, temperature, and transport
properties are definite and decoupled from uncertain initial conditions. Our
study also supplies half the answer to how disks dissipate: the inner disk
drains from the inside out by the MRI, while the outer disk photoevaporates by
stellar ultraviolet radiation.Comment: Accepted to Nature Physics June 7, 2007. The manuscript for
publication is embargoed per Nature policy. This arxiv.org version contains
more technical details and discussion, and is distributed with permission
from the editors. 10 pages, 4 figure
The magnetic nature of disk accretion onto black holes
Although disk accretion onto compact objects - white dwarfs, neutron stars,
and black holes - is central to much of high energy astrophysics, the
mechanisms which enable this process have remained observationally elusive.
Accretion disks must transfer angular momentum for matter to travel radially
inward onto the compact object. Internal viscosity from magnetic processes and
disk winds can in principle both transfer angular momentum, but hitherto we
lacked evidence that either occurs. Here we report that an X-ray-absorbing wind
discovered in an observation of the stellar-mass black hole binary GRO J1655-40
must be powered by a magnetic process that can also drive accretion through the
disk. Detailed spectral analysis and modeling of the wind shows that it can
only be powered by pressure generated by magnetic viscosity internal to the
disk or magnetocentrifugal forces. This result demonstrates that disk accretion
onto black holes is a fundamentally magnetic process.Comment: 15 pages, 2 color figures, accepted for publication in Nature.
Supplemental materials may be obtained by clicking
http://www.astro.lsa.umich.edu/~jonmm/nature1655.p
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