General Relativistic Magnetohydrodynamic Simulations of Black Hole Accretion Disks

Observations are providing increasingly detailed quantitative information about the accretion flows that power such high energy systems as X-ray binaries and active galactic nuclei. Analytic models of such systems must rely on assumptions such as regular flow geometry and a simple, parameterized stress. Global numerical simulations offer a way to investigate the basic physical dynamics of accretion flows without these assumptions. For black hole accretion studies one solves the equations of general relativistic magnetohydrodynamics. Magnetic fields are of fundamental importance to the structure and evolution of accretion disks because magnetic turbulence is the source of the anomalous stress that drives accretion. We have developed a three-dimensional general relativistic magnetohydrodynamic simulation code to evolve time-dependent accretion systems self-consistently. Recent global simulations of black hole accretion disks suggest that the generic structure of the accretion flow is usefully divided into five regimes: the main disk, the inner disk, the corona, the evacuated funnel, and the funnel wall jet. The properties of each of these regions are summarized.Comment: invited review at the conference "Stellar-mass, Intermediate-mass, and Supermassive Black Holes", held in Kyoto, Japan, Octorber 28-31, 2003, to be published in Progress of Theoretical Physics Supplemen

Scattering of a Long Cosmic String by a Rotating Black Hole

The scattering of a straight, infinitely long string by a rotating black hole is considered. We assume that a string is moving with velocity v and that initially the string is parallel to the axis of rotation of the black hole. We demonstrate that as a result of scattering, the string is displaced in the direction perpendicular to the velocity by an amount kappa(v,b), where b is the impact parameter. The late-time solution is represented by a kink and anti-kink, propagating in opposite directions at the speed of light, and leaving behind them the string in a new ``phase''. We present the results of the numerical study of the string scattering and their comparison with the weak-field approximation, valid where the impact parameter is large, b/M >> 1, and also with the scattering by a non-rotating black hole which was studied in earlier works.Comment: 27 pages, 14 figures, to be published in Classical and Quantum Gravit

A near-infrared study of the star forming region RCW 34

We report the results of a near-infrared imaging study of a $7.8 \times 7.8$ arcmin$^2$ region centered on the 6.7 GHz methanol maser associated with the RCW 34 star forming region using the 1.4m IRSF telescope at Sutherland. A total of 1283 objects were detected simultaneously in J, H, and K for an exposure time of 10800 seconds. The J-H, H-K two-colour diagram revealed a strong concentration of more than 700 objects with colours similar to what is expected of reddened classical T Tauri stars. The distribution of the objects on the K {\it vs} J-K colour-magnitude diagram is also suggestive that a significant fraction of the 1283 objects is lower mass pre-main sequence stars. We also present the luminosity function for the subset of about 700 pre-main sequence stars and show that it suggests ongoing star formation activity for about $10^7$ years. An examination of the spatial distribution of the pre-main sequence stars shows that the fainter (older) part of the population is more dispersed over the observed region and the brighter (younger) subset is more concentrated around the position of the O8.5V star. This suggests that the physical effects of the O8.5V star and the two early B-type stars on the remainder of the cloud out of which they formed, could have played a role in the onset of the more recent episode of star formation in RCW 34.Comment: Accepted for publication in The Astronomical Journa

DEFERENCE AND DIFFÉRANCE: judicial review and the perfect gift

The highest courts in both Canada and South Africa have expressedthemselves in favour of an approach of deference as respect in the review of administrative action. The notion of deference as respect derives from the thinking of David Dyzenhaus, who has developed a theory of democracy in support of this approach to judicial review. Dyzenhaus’ model of review attempts to steer clear from the problems he associates particularly with positivism and liberalism. Dyzenhaus’ model of review furthermore attempts to allow space for the administration to play a significant role in giving effect to democratic values, on the understanding that all such decisions need to be reasonably justifiable. In this article the views of Dyzenhaus are contrasted with those of Jacques Derrida, especially insofar as the latter has reflected on the relation between law and justice, as well as concepts such as the gift and democracy. The argument developed in this article is that Dyzenhaus’ model of review, despite its many positive features, needs to be rethought with reference to the perfect gift, unconditional justice and democracy to come. Such a rethinking is required because of the limited conception of justice – as simply ‘our’ justice – in Dyzenhaus’ model

Afrikaans as sangtaal*

Eerstens: Sang, wat een van die onderafdelings vorm van die breë begrip „musiek”, wat op sy beurt weer een van die vertakkings is van die nog breër begrip „kuns”. Aan definisies van kuns en meer spesifiek van musiek is daar geen gebrek nie. Laat ons vir die huidige volstaan met die volgende: Musiek is die sinvolle rangskikking van musikale klanke in ’n sinvolle ritmiese verband. Sang, as een van die middele waarmee musiek gemaak word, maak gebruik van die menslike stem wat daartoe in staat is om verskillende toonhoogtes voort te bring in ’n vinniger of stadiger opeenvolging met mekaar. Die menslike stem kan slegs een toonhoogte op ’n gegewe moment voortbring, en die derde groot element van musiek nl. harmonie (die ander twee is melodie en ritme en is implisiet in die bogenoemde definisie) kan alleen dán na vore kom wanneer een stem in kombinasie met een of meer ander stemme of instrumente aan- gewend word

Global General Relativistic Magnetohydrodynamic Simulations of Accretion Tori

This paper presents an initial survey of the properties of accretion flows in the Kerr metric from three-dimensional, general relativistic magnetohydrodynamic simulations of accretion tori. We consider three fiducial models of tori around rotating, both prograde and retrograde, and nonrotating black holes; these three fiducial models are also contrasted with axisymmetric simulations and a pseudo-Newtonian simulation with equivalent initial conditions to delineate the limitations of these approximations.Comment: Submitted to ApJ. 30 pages, 21 figures. Animations and high-resolution version of figures available at http://www.astro.virginia.edu/~jd5

Puerperale tubale onderbining met plaaslike verdowing

No Abstrac

Sports imaging for the general practitioner

No Abstract

Morbidity profile of admissions to GF Jooste Hospital, Manenberg, Cape Town

Background Secondary hospitals play an important, yet overlooked, role in reflecting public health status, both locally and nationally. Relatively few reports analysing the causes of secondary hospital admissions exist, which is especially unfortunate in the case of developing countries, considering the huge numbers of admissions and people at risk. In developing countries like South Africa, the quality of records varies among institutions. Some hospitals have computerised data, while others may keep no records whatsoever. A major problem facing the quality of hospital records is the constant shortage of staff in rural and urban hospitals. Thorough documentation is essential in providing an invaluable database for researchers, but morbidity statistics are unfortunately scarce.GF Jooste Hospital in Manenberg is the busiest hospital in Cape Town – serving 1.1 million people, with 224 beds and over 12 000 admissions annually. Budgetary constraints in the South African public health sector means that providing healthcare services at higher levels than necessary is too costly. Because hospitals consume the largest share of the public healthcare budget, they have been the focus in cost cutting. In particular, the budgets of referral (tertiary or teaching) hospitals have been trimmed in order to promote primary and secondary care. It is imperative to identify those services that are required most at secondary hospitals in order to improve budgeting and, more appropriately, train doctors and medical students for the job at hand. Identifying the morbidity profile of the population for which the hospital caters can aid the optimal utilisation of the available resources, as well as focusing the continuing medical education of hospital physicians. We determined disease patterns of admissions over a three-year period (2001-2003), primarily as insight towards optimal hospital resource management.Methods A retrospective study examined ward records, totalling 36 657 admissions, from which a random sample (N=608) was selected. A stratified sample (N=462) was constructed, considering the relative proportions admitted to the wards. The International Statistical Classification of Diseases (ICD) directed diagnosis sorting. Disease prevalence was expressed as the percentage of patients allocated to each ICD category among those admitted to the hospital and respective wards and, additionally, the percentage of diagnoses for each ICD subcategory among patients assigned to each major category.Results Trauma (represented by ICD categories S/T 23% and V/X/Y 16%), specifically assault-related, was most prevalent. This was followed by circulatory diseases (22%) and infectious diseases (19%), dominated by HIV (61%) and associated diseases like TB (57%). The age of the patients ranged from 13 to 87 (mean: 40 years), with the 20 to 30-year-olds predominating. Surgical patients were younger (mean: 35 years) than medical (mean: 45 years). In the medical wards, infectious (39% in men; 38% in women) and circulatory aetiologies (39% and 41% in men and women respectively) dominated. In the surgical wards, the trend varied according to sex: assault (43%) and other injuries (61%) for males; pregnancy-related (42%) for females.Conclusion The morbidity distribution reflects the ills affecting South African urban society, with young trauma admissions predominating. The hospital's budget is insufficient, considering its population's demands.For full text click here: SA Fam Pract 2006;48(6):15-15