1,809 research outputs found
André Pretorius Collection index
No full textThis index describes the Andre Pretorius collection which consists of material collected by André Pretorius (1935-2006), author, photographer and conservationist. The material pertains mainly to the areas in the Western, Northern and Eastern Cape. The collection contains photographs ; newspaper clippings ; articles ; brochures ; correspondence contained in 3 filing cabinets (4 drawers each)
Meningiomas occurring during long-term survival after treatment for childhood cancer
No full textChildhood cancer is rare but improvements in treatment over the past five decades have resulted in a cohort of more than 30,000 long-term survivors of childhood cancer in the UK with more added annually. These long-term survivors are at risk of late effects of cancer treatment which replace original tumour recurrence as the leading cause of premature death. Second neoplasms are a particular risk and in the central nervous system meningiomas occur increasingly with increased radiation dose to central nervous system tissue and length of time after exposure, resulting in a 500-fold increase above that expected in the normal population by 40 years of follow up. This multidisciplinary author group and others met to discuss the issue. Our pooled information, and consensus that screening should only follow symptoms, was published online by the Royal College of Radiologists in 2013. We outline here the current knowledge and management of these neoplasms secondary to childhood cancer treatment
Radiology secrets plus.
No full textRev. ed. of: Radiology secrets / E. Scott Pretorius, Jeffrey A. Solomon. c2006.Includes bibliographical references and index
Observational constraints on the evolution of cataclysmic variable stars
No full textI provide observational constraints on the size and period distribution of the Galactic cataclysmic variable (CV) population, and derive the implications that these constraints have for the theory of CV evolution. The results are based on quantitative modelling applied to three observational CV samples, two of which are newly constructed here. Large differences between the size and other properties of the known sample of CVs and the predictions of the theory of binary star evolution have long been recognized. However, because all existing observational CV samples suffer from strong selection effects, observational biases, must be taken into account before it is possible to tell whether there are real inconsistencies. In order to address this, I implement a Monte Carlo method to model selection effects in observed CV samples, and make a new measurement of the space density of CVs. I illustrate the effects of the biases that are introduced by several of the most common observational strategies for identifying CVs. Also, by simulating the selection criteria of the Palomar-Green (PG) Survey, I show that selection effects cannot reconcile the relative sizes of the long- and short-period CV populations predicted by standard CV evolution theory with the observed sample. k The selection criteria used to define most CV samples (including the PG sample) discriminate heavily against the discovery of intrinsically faint, short-period systems. The situation can be improved by selecting systems for the presence of emission lines; I have therefore constructed a homogeneous new sample of 17 CVs, selected on the basis of Ha emission from the AAO/UKST SuperCOSMOS Ha Survey (SHS). I present observations of the CVs discovered in this search, and use the sample to constrain the properties of the intrinsic CV population. I show that even very generous allowance for selection effects is not sufficient to reconcile the ratio of short- to long-period CVs predicted by standard CV evolution theory with the observed sample, confirming the result based on the PG survey. The most likely implication is that short-period systems evolve faster than predicted by the disrupted magnetic braking model. This would require that an angular momentum loss mechanism besides gravitational radiation acts on CVs with orbital periods below the period gap. To bring the model into agreement with observations, the rate of angular momentum loss below the period gap must be increased by a factor of at least 3, unless the model also overestimates the angular momentum loss rate of long-period CVs. In order to constrain the size of the Galactic CV population, I construct a small, but purely X-ray flux-limited sample of CVs, using the ROSAT North Ecliptic Pole (NEP) survey. The sample includes only 4 systems, 2 of which are new discoveries. Orbital periods are measured for both these systems from time-resolved spectroscopy, and the distances of all the CVs in this sample are estimated. The space density of the CV population represented by the sample is l.lij)!? x 10~5pc~3. I also place upper limits on the space density of any population of CVs too faint to be included in the NEP survey—if the overall space density of CVs is as high as 2 x 10~4 pc~3 (as has been predicted theoretically), the vast majority of CVs must have X-ray luminosities below ~ 2 x 1029ergs~1.</p
An H?-selected sample of cataclysmic variables – I. Observations of newly discovered systems
No full textStrong selection effects are present in observational samples of cataclysmic variables (CVs), complicating comparisons to theoretical predictions. The selection criteria used to define most CV samples discriminate heavily against the discovery of short-period, intrinsically faint systems. The situation can be improved by selecting CVs for the presence of emission lines. For this reason, we have constructed a homogeneous sample of CVs selected on the basis of H? emission. We present discovery observations of the 14 CVs and two additional CV candidates found in this search. The orbital periods of 11 of the new CVs were measured; all are above 3 h. There are two eclipsing systems in the sample, and one in which we observed a quasi-periodic modulation on a ?1000 s time-scale. We also detect the secondary star in the spectrum of one system, and measure its spectral type. Several of the new CVs have the spectroscopic appearance of nova-like variables, and a few display what may be SW Sex star behaviour. In a companion paper, we discuss the implications of this new sample for CV evolution
Comment on "Kerr Black Holes as Particle Accelerators to Arbitrarily High Energy"
No full textA Comment on the Letter by Máximo Bañados, Joseph Silk, and Stephen M. West [Phys. Rev. Lett. 103, 111102 (2009)]
Impaired DNA repair and genomic stability in hereditary tyrosinemia type 1
No full textThe autosomal recessive disorder, hereditary tyrosinemia type 1 (HT1), is caused by a defective fumarylacetoacetate hydrolase enzyme. Consequently intermediate metabolites such as fumarylacetoacetate, succinylacetone and p-hydroxyphenylpyruvic acid accumulate. Characteristic to HT1 is the development of hepatocellular carcinoma, irrespective of dietary intervention or pharmacological treatment. Carcinogenesis may occur through a chromosomal instability mutator phenotype or a microsatellite instability phenotype, and deficient DNA repair may be a contributing factor thereof. The purpose of this study was to investigate the expression of DNA repair proteins, and the possible occurrence of microsatellite instability in HT1. Gene expression analyses show low expression of hOGG1 and ERCC1 in HT1 patient lymphocytes. Results from microsatellite instability analyses show allelic imbalance on chromosome 7 of the fah−/− mouse genome, and instability of the D2S123, D5S346 and (possibly) D17S250 microsatellite markers, in HT1 patient lymphocytes
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