3,307 research outputs found
The evolution of a warped disc around a Kerr black hole
We consider the evolution of a warped disc around a Kerr black hole, under
conditions such that the warp propagates in a wavelike manner. This occurs when
the dimensionless effective viscosity, alpha, that damps the warp is less than
the characteristic angular semi-thickness, H/R, of the disc. We adopt
linearized equations that are valid for warps of sufficiently small amplitude
in a Newtonian disc, but also account for the apsidal and nodal precession that
occur in the Kerr metric. Through analytical and time-dependent studies, we
confirm the results of Demianski & Ivanov, and of Ivanov & Illarionov, that
such a disc takes on a characteristic warped shape. The inner part of the disc
is not necessarily aligned with the equator of the hole, even in the presence
of dissipation. We draw attention to the fact that this might have important
implications for the directionality of jets emanating from discs around
rotating black holes.Comment: 8 pages, 6 figures, to be published in MNRA
Preliminary results on performance testing of a turbocharged rotary combustion engine
The performance of a turbocharged rotary engine at power levels above 75 kW (100 hp) was studied. A twin rotor turbocharged Mazda engine was tested at speeds of 3000 to 6000 rpm and boost pressures to 7 psi. The NASA developed combustion diagnostic instrumentation was used to quantify indicated and pumping mean effect pressures, peak pressure, and face to face variability on a cycle by cycle basis. Results of this testing showed that a 5900 rpm a 36 percent increase in power was obtained by operating the engine in the turbocharged configuration. When operating with lean carburetor jets at 105 hp (78.3 kW) and 4000 rpm, a brake specific fuel consumption of 0.45 lbm/lb-hr was measured
The appropriate use of radiography in clinical practice: a report of two cases of biomechanical versus malignant spine pain
BACKGROUND: To describe the evaluation, treatment, management and referral of two patients with back pain with an eventual malignant etiology, who were first thought to have a non-organic biomechanical disorder. CLINICAL FEATURES: The study was a retrospective review of the clinical course of two patients seen by a chiropractor in a multi-disciplinary outpatient facility, who presented with what was thought to be non-organic biomechanical spine pain. Clinical examination by both medical and chiropractic physicians did not indicate the need for radiography in the early course of management of either patient. Upon subsequent re-evaluation, it was decided that certain clinical factors required investigation with advanced imaging. In one instance, the patient responded to conservative care of low back pain for nine weeks, after which she developed severe pain in the pelvis. In the second case, the patient presented with signs and symptoms consistent with uncomplicated musculoskeletal pain that failed to respond to a course of conservative care. He was referred for medical therapy which also failed to relieve his pain. In both patients, malignancy was eventually discovered with magnetic resonance imaging and both patients are now deceased, resulting in an inability to obtain informed consent for the publication of this manuscript. CONCLUSION: In these two cases, the prudent use of diagnostic plain film radiography did not significantly alter the appropriate long-term management of patients with neuromusculoskeletal signs and symptoms. The judicious use of magnetic resonance imaging was an effective procedure when investigating recalcitrant neuromusculoskeletal pain in these two patients
Are there brown dwarfs in globular clusters?
We present an analytical method for constraining the substellar initial mass
function in globular clusters, based on the observed frequency of transit
events. Globular clusters typically have very high stellar densities where
close encounters are relatively common, and thus tidal capture can occur to
form close binary systems. Encounters between main sequence stars and
lower-mass objects can result in tidal capture if the mass ratio is > 0.01. If
brown dwarfs exist in significant numbers, they too will be found in close
binaries, and some fraction of their number should be revealed as they transit
their stellar companions. We calculate the rate of tidal capture of brown
dwarfs in both segregated and unsegregated clusters, and find that the tidal
capture is more likely to occur over an initial relaxation time before
equipartition occurs. The lack of any such transits in recent HST monitoring of
47 Tuc implies an upper limit on the frequency of brown dwarfs (< 15 % relative
to stars) which is significantly below that measured in the galactic field and
young clusters.Comment: MNRAS in pres
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