Optical and X-ray Properties of CAL 83: I. Quasi-periodic Optical and Supersoft Variability

We have studied the long-term (~ years) temporal variability of the prototype supersoft X-ray source (SSS) CAL 83 in the LMC, using data from the MACHO and OGLE projects. The CAL 83 light curve exhibits dramatic brightness changes of ~1 mag on timescales of ~450 days, and spends typically ~200 days in the optical low state. Combined with archival XMM-Newton X-ray observations these represent the most extensive X-ray/optical study to date of this system, and reveal in much greater detail that the X-ray light curve is anti-correlated with the optical behaviour. This is remarkably similar to the behaviour of the "transient" SSS, RX J0513.9-6951, where the SSS outbursts recur on a timescale of ~168 days, and also anti-correlate with the optical flux. We performed simple blackbody fits to both high and low state X-ray spectra, and find that the blackbody temperature and luminosity decrease when the optical counterpart brightens. We interpret these long-term variations in terms of the limit-cycle model of Hachisu & Kato (2003a), which provides further support for these systems containing massive (~1.3 Msun) white dwarfs. In addition, we have refined their orbital periods in the MACHO and OGLE-III light curves to values of 1.047529(1) days and 0.762956(5) days for CAL 83 and RX J0513.9-6951, respectively.Comment: 9 pages, 8 figures, 3 tables, accepted for publication in MNRA

Die gebruik van die metadiskoerskategorie “bewyse” as voorvereiste vir suksesvolle argumentatiewe skryfwerk op tersiêre vlak

Hierdie artikel werp lig op die gebruik van Hyland (2004:139) se metadiskoerskategorie “bewyse” in eerstejaar-universiteitstudente se akademiese, argumentatiewe skryfwerk. ʼn Kwasi-eksperimentele navorsingsontwerp is gebruik ten einde kwantitatiewe data in te samel rakende die invloed wat ʼn intervensie sal hê op die deelnemers se gebruik van en verwysing na bronne volgens die Noordwes-Universiteit se amptelike verwysingstyl. Ten einde eties om te gaan met akademiese bronne, is dit belangrik dat studente reeds vroeg in hulle universiteitsloopbaan bewus gemaak behoort te word van die erkenning van bronne wat in tekste geraadpleeg word. ʼn Handontleding en vergelyking van twee korpora, bestaande uit 109 tekste elk (woordtotale van onderskeidelik 54 586 en 56 151), is gedoen. Daar is bevind dat, ten spyte van die beperkte hoeveelheid tyd wat aan die onderrig van die metadiskoerskategorie “bewyse” afgestaan is, dit wel ʼn positiewe invloed het op die erkenning van bronne en die korrekte verwysing daarna volgens die Harvardstyl.Sleutelwoorde: Metadiskoers, Akademiese Argumentasie, Plagiaat, Bewyse, Akademiese Geletterdheid, Eerstejaar-universiteitstudente, Kwasi-eksperimen

Teaching problem-solving competency in Business Studies at secondary school level

The high unemployment rate in South Africa compels potential entrepreneurs to start their own businesses in order to survive. Often this is with little or no formal training or education in entrepreneurship. Since problem recognition and problem-solving are amongst the most crucial competencies required for a successful entrepreneurial career, this study aimed to determine whether the application of an extended curriculum with a strong focus on active learning in a business-simulated set-up will enhance this competency. The performance of a specific group of Grade 11 Business Studies learners in this study was measured, both before and after they had been exposed to such an extended curriculum in different experimental settings (intervention). Assessments were done qualitatively through observations and interviews, and quantitatively, by means of question-based scenarios. The findings revealed that the intervention enhanced learners’ entrepreneurial competencies concerning problem recognition and problem-solving considerably. This also contributed to these learners’ positive approach towards Business Studies. In this article, it is argued that practical exposure in a business-simulated set-up will not only result in enhanced entrepreneurial proficiency in school learners, but also contribute to an accelerated pace of economic growth and job creation in our country.Keywords: active learning; business-simulated set-up; entrepreneurship; extended curriculum; problem-solvin

Treatment of Tuberculous Meningitis and Its Complications in Adults.

PURPOSE OF REVIEW: Tuberculous meningitis (TBM) is a global health problem. In this review, we systematically evaluate the evidence for current and emerging antimicrobials, host-directed therapies and supportive managements. RECENT FINDINGS: Current antimicrobial regimes do not factor the differing ability of drugs to cross the blood-brain barrier. Rifampicin may be more effective at higher doses yet the most recent clinical trial failed to demonstrate survival benefit at 15 mg/kg/day. Dose finding studies suggest that higher doses still may be safe and more effective. Fluoroquinolones are currently listed as important second-line agents in drug-resistant TBM; however, a survival benefit as a first-line agent has yet to be shown. Linezolid may be a promising antimicrobial with good central nervous system penetrance. Dexamethasone reduces mortality in HIV-uninfected individuals yet evidence for its use in HIV co-infection is lacking. Aspirin has anti-inflammatory and anti-thrombotic properties. Small studies have demonstrated efficacy in reducing stroke but further research is required to better understand its effect on controlling the host inflammatory response. Discovery of genetic polymorphisms may direct individualized immune therapies and mediators of the innate immune response may provide targets for the development of novel therapies. There is at present no significant evidence base to guide management of hydrocephalus in HIV co-infection. Further clinical trial data is required to improve treatment outcomes in TBM in particularly in regard to the value of high-dose rifampicin, newer antimicrobials with improved central nervous system penetration and host-directed therapies. Supportive measures in particular the management of hydrocephalus in HIV co-infection should be an area for future research

AE Aquarii: A Short Review

The nova-like variable AE Aquarii has been continuously studied since its discovery on photographic plates in 1934. In this short review the peculiar multi-wavelength properties of AE Aquarii will be reviewed and explained in context of its evolution from a high mass transfer phase, during which period it could have been a supersoft X-ray source (SSS)