Calibration artefacts in radio interferometry. I. Ghost sources in WSRT data

This work investigates a particular class of artefacts, or ghost sources, in radio interferometric images. Earlier observations with (and simulations of) the Westerbork Synthesis Radio Telescope (WSRT) suggested that these were due to calibration with incomplete sky models. A theoretical framework is derived that validates this suggestion, and provides predictions of ghost formation in a two-source scenario. The predictions are found to accurately match the result of simulations, and qualitatively reproduce the ghosts previously seen in observational data. The theory also provides explanations for many previously puzzling features of these artefacts (regular geometry, PSF-like sidelobes, seeming independence on model flux), and shows that the observed phenomenon of flux suppression affecting unmodelled sources is due to the same mechanism. We demonstrate that this ghost formation mechanism is a fundamental feature of calibration, and exhibits a particularly strong and localized signature due to array redundancy. To some extent this mechanism will affect all observations (including those with non-redundant arrays), though in most cases the ghosts remain hidden below the noise or masked by other instrumental artefacts. The implications of such errors on future deep observations are discussed.Comment: 19 pages, 15 figures, submitted to MNRA

Prescribed minimum benefits – quagmire or foundation for social health reform?

No Abstract South African Medical Journal Vol. 97 (6) 2007: pp. 446-45

The use of confocal microscopy in quantifying changes in membrane potential

Monitoring the plasma membrane potential and its changes can be a time consuming and challenging task especially when conventional electrophysiological techniques are used. The use of potentiometricfluorophores, namely tetramethylrhodamine methylester (TMRM), and digital imaging devices (laser scanning confocal microscopy) provides reliable and time efficient method. Two scorpion pore-forming peptides, namely PP and OP1, were used as a tool to induce depolarization of the plasma membrane potential of neuroblastoma cell line and cardiac myocytes. Alternative methods for the neuroblastoma cells and cardiac myocytes were used. Depolarization of the neuroblastoma cells was calibrated with 140 mM KCl solution with 1 ìM valinomycin, after which intensity readers were substituted in the Nernst equation for quantification. Calibration of the alternative method used of the cardiac myocytes’ plasma membrane potential changes was calibrated with the use of 5, 20, 40, and 80 mM KCl solutions with 1 ìM valinomycin. A calibration curve was then constructed from which plasma membrane potential could be calculate

Identifying sequence variation in cation channel sperm associated genes in Cape mountain zebra (Equus zebra zebra)

The Cape mountain zebra (Equus zebra zebra) has recovered from near extinction over more than eight decades. While their numbers have increased, populations remain isolated with low genetic diversity. With more than 75 new populations being founded and more than 4800 extant animals, conservation management strategies are being implemented to mitigate risk of losses in genetic diversity and reproductive fitness. One objective is to identify reproductive characteristics that may improve population growth. Cation channel sperm (CatSper) genes play an important role in hyperactivation of sperm during fertilization. Mutations in these genes lead to reduced fertility and even infertility. Ten male zebras were sampled from a group that were translocated in 2016 in order to found a new population. Single nucleotide polymorphisms (SNPs) were identified in three of the CatSper genes (1 - 3). Lack of variation was observed in all exons, with only four SNPs being identified in the intronic regions in close proximity to exons 1, 2, 7, 8, and 9 of CatSper 1. These results may contribute to the pre-identification of males for new founder populations to ensure population growth and viability, and may be a useful tool for selection against low-producing individuals

Field anaesthesia of the African elephant (Loxodonta africana)

Immobilisation and anaesthesia of elephants may be required for various reasons, such as the capture, transport and clinical examination of captive animals, e.g. at a zoological park, or for minor surgical procedures. General anaesthesia is required for wound treatment, i.e trunk lacerations and dental surgery, or population control, i.e. laparoscopic vasectomy.http://www.sajaa.co.za/index.php/sajaaam2014mn201

Environmentally sustainable use of recycled asphalt at OR Tambo International Airport

Paper presented at the 33rd Annual Southern African Transport Conference 7-10 July 2014 "Leading Transport into the Future", CSIR International Convention Centre, Pretoria, South Africa.A new technology breakthrough was achieved during a recent Airports Company South Africa (ACSA) project where warmed asphalt was produced with Recycled Asphalt (RA) content of 55% using a foamed bitumen process. This was the highest amount of recycled asphalt ever produced in an asphalt plant in South Africa. The project involved the rehabilitation of the cargo area at OR Tambo International Airport (ORTIA). The use of this environmentally sustainable technology resulted in massive cost savings to the client and allowed the contractor to effectively work in a highly congested area using conventional asphalt paving and milling equipment. Various environmentally sustainable asphalt products have been used on ACSA airports (including foamed treated asphalt with 35% RA, haul road with only RA with a surface emulsion treatment, cold mixed RA mixes with emulsion, etc). This new approach was based on the experience gained on previous ACSA projects where RA has effectively being used. The paper will also discuss the use of RA of the full spectrum of applications from Hot mixed asphalt with small amount of RA, asphalt with high contents of RA, warm mixes with RA, cold mixes with RA (using foamed bitumen or emulsion) and the use of RA with a surface treatment.This paper was transferred from the original CD ROM created for this conference. The material was published using Adobe Acrobat 10.1.0 Technology. The original CD ROM was produced by CE Projects cc. Postal Address: PO Box 560 Irene 0062 South Africa. Tel.: +27 12 667 2074 Fax: +27 12 667 2766 E-mail: [email protected]

HIV prevention trial design in an era of effective pre-exposure prophylaxis

Pre-exposure prophylaxis (PrEP) has demonstrated remarkable effectiveness protecting at-risk individuals from HIV-1 infection. Despite this record of effectiveness, concerns persist about the diminished protective effect observed in women compared with men and the influence of adherence and risk behaviors on effectiveness in targeted subpopulations. Furthermore, the high prophylactic efficacy of the first PrEP agent, tenofovir disoproxil fumarate/emtricitabine (TDF/FTC), presents challenges for demonstrating the efficacy of new candidates. Trials of new agents would typically require use of non-inferiority (NI) designs in which acceptable efficacy for an experimental agent is determined using pre-defined margins based on the efficacy of the proven active comparator (i.e. TDF/FTC) in placebo-controlled trials. Setting NI margins is a critical step in designing registrational studies. Under- or over-estimation of the margin can call into question the utility of the study in the registration package. The dependence on previous placebo-controlled trials introduces the same issues as external/historical controls. These issues will need to be addressed using trial design features such as re-estimated NI margins, enrichment strategies, run-in periods, crossover between study arms, and adaptive re-estimation of sample sizes. These measures and other innovations can help to ensure that new PrEP agents are made available to the public using stringent standards of evidence

Nutritional supplements for people being treated for active tuberculosis

CITATION: Grobler, L. et al. 2016. Nutritional supplements for people being treated for active tuberculosis. Cochrane Database of Systematic Reviews, 6:CD006086, doi:10.1002/14651858.CD006086.pub4.The original publication is available at https://www.cochranelibrary.comBackground: Tuberculosis and malnutrition are linked in a complex relationship. Tuberculosis may cause undernutrition through increasedmetabolic demands and decreased intake, and nutritional deficiencies may worsen the disease, or delay recovery by depressing important immune functions. At present, there is no evidence-based nutritional guidance for adults and children being treated for tuberculosis. Objectives: To assess the effects of oral nutritional supplements in people being treated with antituberculous drug therapy for active tuberculosis.https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD006086.pub4/fullPublisher's versio