148 research outputs found

    Simulation of rear surface contamination for a simple bluff body

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    Predicting the accumulation of material on the rear surfaces of square-backed cars is important to vehicle manufacturers, as this progressively compromises rear vision, vehicle visibility and aesthetics. It also reduces the effectiveness of rear mounted cameras. Here, this problem is represented by a simple bluff body with a single sprayer mounted centrally under its rear trailing edge. A Very Large Eddy Simulation (VLES) solver is used to simulate both the aerodynamics of the body and deposition of contaminant. Aerodynamic drag and lift coefficients were predicted to within +1.3% and −4.2% of their experimental values, respectively. Wake topology was also correctly captured, resulting in a credible prediction of the rear surface deposition pattern. Contaminant deposition is mainly driven by the lower part of the wake ring vortex, which advects material back onto the rear surface. This leads to a maximum below the rear stagnation point and an association with regions of higher base pressure. The accumulation of mass is linear with time; the relative distribution changing little as the simulation progresses, implying that shorter simulations can be compared to longer experiments. Further, the rate of accumulation quickly reaches a settled mean value, suggesting utility as a metric for assessing different vehicles

    Possible magnetic field variability during the 6.7 GHz methanol maser flares of G09.62+0.20

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    (Abridged) Recently, the magnetic field induced Zeeman splitting was measured for the strongest known 6.7 GHz methanol maser, which arises in the massive star forming region G09.62+0.20. This maser is one of a handful of periodically flaring methanol masers. The 100-m Effelsberg telescope was used to monitor the 6.7 GHz methanol masers of G09.62+0.20. With the exception of a two week period during the peak of the maser flare, we measure a constant magnetic field of B_||~11+-2 mG in the two strongest maser components of G09.62+0.20 that are separated by over 200 AU. In the two week period that coincides exactly with the peak of the maser flare of the strongest maser feature, we measure a sharp decrease and possible reversal of the Zeeman splitting. The exact cause of both maser and polarization variability is still unclear, but it could be related to either background amplification of polarized emission or the presence of a massive protostar with a close-by companion. Alternatively, the polarization variability could be caused by non-Zeeman effects related to the radiative transfer of polarized maser emission.Comment: 4 pages, 3 figures, accepted for publication Astronomy and Astrophysic

    Colorectal cancer in South Africa: An assessment of disease presentation, treatment pathways and 5-year survival

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    Background. Colorectal cancer (CRC) is the fourth most common cancer in South Africa (SA), and the sixth most lethal. Approximately 25% of patients will have synchronous metastatic disease at the time of their primary CRC diagnosis. Although chemotherapy is used in most stages of the disease, surgical resection of the primary tumour and metastases remains the most successful treatment modality to achieve cure or prolong survival. To date, no data on CRC presentation and management have been published in SA.Objectives. To determine CRC presentation, general management patterns and overall survival in the SA private healthcare sector.Methods. A retrospective review of a private healthcare funder’s database from 1 January 2008 to 31 December 2015. International Statistical Classification of Diseases and Related Health Problems (10th revision) (ICD-10) diagnosis codes were used to identify colorectal cancer and liver and/or pulmonary metastatic disease. Procedure codes assigned to hospital admissions were used to identify type of surgical treatment. Chemotherapy was identified by the World Health Organization Anatomical Therapeutic Chemical Classification System of medicines. Treatment patterns were determined and 5-year survival rates for these were calculated. Survival was estimated using the Kaplan-Meier method, and Cox proportional hazards regression was used for between-group comparisons of survival. Data analysis was carried out using SAS version 9.4 for Windows.Results. A total of 3 412 patients were included in the study, 2 267 with CRC only and 1 145 with liver (LM) or pulmonary metastases (PM). The mean age was 64.1 years (range 21 - 97), and 54.6% were male; these did not differ statistically between the study groups. Twenty percent of patients with LM or PM underwent surgical resection of their metastases. Five-year survival rates following surgical resection of all disease for CRC only, CRCLM, CRCPM and CRCLMPM were 71.7%, 57.3%, 31.5% and 26.0%, respectively.Conclusions. SA CRC patients treated in the private healthcare sector have similar disease presentation to that in published international series, with similar outcomes following various treatment pathways; however, it seems that fewer resections of metastases are undertaken compared with international trends.

    New Periodic 6.7 GHz Class II Methanol Maser Associated with G358.460-0.391

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    Eight new class II methanol masers selected from the 6.7 GHz Methanol Multibeam survey catalogues I and II were monitored at 6.7 GHz with the 26m Hartebeesthoek Radio Astronomy Observatory (HartRAO) radio telescope for three years and seven months, from February 2011 to September 2014. The sources were also observed at 12.2 GHz and two were sufficiently bright to permit monitoring. One of the eight sources, namely G358.460-0.391, was found to show periodic variations at 6.7 GHz. The period was determined and tested for significance using the Lomb-Scargle, epoch-folding and Jurkevich methods, and by fitting a simple analytic function. The best estimate for the period of the 6.7 GHz class II methanol maser line associated with G358.460-0.391 is 220.0 ±\pm 0.2 day.Comment: 8 pages, 11 figures, accepted for publication in MNRAS. The appendix of 4 pages (with 16 figures) will be published as online versio

    Colorectal cancer liver metastases : management and five-year survival in a South African patient cohort

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    BACKGROUND : Approximately 25% of patients with colorectal cancer (CRC) will be diagnosed with CRC liver metastases (CRCLM) during the course of their disease. No data regarding CRCLM presentation, management and survival outcomes has been published from either the private or public health care sectors in South Africa. This study aimed to address this deficit, reporting on a private sector cohort. METHODS : A retrospective review of a private health care funder’s database from 1 January 2008 to 31 December 2015 was performed. ICD-10 diagnosis codes were used to identify CRC and CRCLM. Procedure codes assigned to hospital admissions were used to identify the type of surgical treatment. Chemotherapy was identified by the WHO Anatomical Therapeutic Chemical classification system of medicines. Treatment patterns were assessed and five-year overall survival (OS) was calculated. Survival was estimated using the Kaplan–Meier method, and Cox proportional-hazards regression was used for between group survival comparisons. RESULTS : Six hundred and one (601) of 3 412 patients presenting with CRC (17.6%) were diagnosed with CRCLM at presentation or during the follow-up period. Sixty patients with CRCLM (10.0%) underwent resection of the primary CRC and liver resection for metastases, 281 (46.8%) underwent CRC resection only, 180 (30%) received chemotherapy only, and 47 (7.8%) received no treatment. Five-year OS for these groups were 57.3%, 15.6%, 9.8% and 0% respectively. CONCLUSION : Five-year OS of the various CRCLM treatment pathways in a South African private sector population compares to results published in international series. However, a smaller proportion of patients with CRCLM underwent liver resection, compared to international studieshttp://sajs.redbricklibrary.com/index.php/sajsdm2022Surger

    The ‘ins and outs’ of faecal microbiota transplant for recurrent Clostridium difficile diarrhoea at Wits Donald Gordon Medical Centre, Johannesburg, South Africa

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    Background. Clostridium difficile-associated diarrhoea (CDAD) is a potentially life-threatening condition that is becoming increasingly common. A persistent burden of this infectious illness has been demonstrated over the past 4 years at Wits Donald Gordon Medical Centre (WDGMC), Johannesburg, South Africa, through implementation of active surveillance of hospital-acquired infections as part of the infection prevention and control programme. Oral treatment with metronidazole or vancomycin is recommended, but there is a major problem with symptomatic recurrence after treatment. Replacement of normal flora by the administration of donor stool through colonoscopy or nasogastric/duodenal routes is becoming increasingly popular.Objectives. To identify risk factors for the development of CDAD in patients referred for faecal microbiota transplant (FMT) and evaluate the safety of administration of donor stool as an outpatient procedure, including via the nasogastric route.Methods. A retrospective record review of patients with recurrent CDAD referred for FMT at WDGMC between 1 January 2012 and 31 December 2016 was conducted.Results. Twenty-seven patients were identified, all of whom fulfilled the criteria for recurrent CDAD. One-third were aged >65 years, and the majority were female. The most common risk factors were prior exposure to antibiotics or proton-pump inhibitors and underlying inflammatory bowel disease. Three procedures were carried out as inpatients and 24 in the outpatient gastroenterology unit. At 4-week follow-up, all patients reported clinical resolution of their diarrhoea after a single treatment and there were no recurrences. The FMT procedure was associated with no morbidity (with particular reference to the risk of aspiration when administered via the nasogastric route) or mortality.Conclusions. This case series confirms that FMT is a safe and effective therapy for recurrent CDAD. In most cases it can be administered via the nasogastric route in the outpatient department. We propose that the recently published South African Gastroenterology Society guidelines be reviewed with regard to recommendations for the route of administration of FMT and hospital admission. Meticulous prescription practice by clinicians practising in hospitals and outpatient settings, with particular attention to antimicrobials and chronic medication, is urgently required to prevent this debilitating and potentially life-threatening condition

    Statistical properties of 12.2 GHz methanol masers associated with a complete sample of 6.7 GHz methanol masers

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    We present definitive detection statistics for 12.2 GHz methanol masers towards a complete sample of 6.7 GHz methanol masers detected in the Methanol Multibeam survey south of declination -20 degrees. In total, we detect 250 12.2 GHz methanol masers towards 580 6.7 GHz methanol masers. This equates to a detection rate of 43.1%, which is lower than that of previous significant searches of comparable sensitivity. Both the velocity ranges and the flux densities of the target 6.7 GHz sources surpass that of their 12.2 GHz companion in almost all cases. 80 % of the detected 12.2 GHz methanol maser peaks are coincident in velocity with the 6.7 GHz maser peak. Our data support an evolutionary scenario whereby the 12.2 GHz sources are associated with a somewhat later evolutionary stage than the 6.7 GHz sources devoid of this transition. Furthermore, we find that the 6.7 GHz and 12.2 GHz methanol sources increase in luminosity as they evolve. In addition to this, evidence for an increase in velocity range with evolution is presented. This implies that it is not only the luminosity, but also the volume of gas conducive to the different maser transitions, that increases as the sources evolve. Comparison with GLIMPSE mid-infrared sources has revealed a coincidence rate between the locations of the 6.7 GHz methanol masers and GLIMPSE point sources similar to that achieved in previous studies. Overall, the properties of the GLIMPSE sources with and without 12.2 GHz counterparts are similar. There is a higher 12.2 GHz detection rate towards those 6.7 GHz methanol masers that are coincident with extended green objects.Comment: Accepted to ApJ March 2011. 28 pages, 9 figure

    Favourable outcomes for the first 10 years of kidney and pancreas transplantation at Wits Donald Gordon Medical Centre, Johannesburg, South Africa

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    Background. It is important for centres participating in transplantation in South Africa (SA) to audit their outcomes. Wits Donald Gordon Medical Centre (WDGMC), Johannesburg, SA, opened a transplant unit in 2004. The first 10 years of kidney and pancreas transplantation were reviewed to determine outcomes in respect of recipient and graft survival.Methods. A retrospective review was conducted of all kidney-alone and simultaneous kidney-pancreas (SKP) transplants performed at WDGMC from 1 January 2004 to 31 December 2013, with follow-up to 31 December 2014 to ensure at least 1 year of survival data. Information was accessed using the transplant registers and clinical records in the transplant clinic at WDGMC. The Kaplan-Meier method was used to estimate 1-, 5- and 10-year recipient and graft survival rates for primary (first graft) kidney-alone and SKP transplants.Results. The overall 10-year recipient and graft survival rates were 80.4% and 66.8%, respectively, for kidney-alone transplantation. In the kidney-alone group, children tended towards better recipient and graft survival compared with adults, but this was not statistically significant. In adults, recipient survival was significantly better for living than deceased donor type. Recipient and graft survival were significantly lower in black Africans than in the white (largest proportion in the sample) reference group. For SKP transplants, the 10-year recipient survival rate was 84.7%, while kidney and pancreas graft survival rates were 73.1% and 43.2%, respectively.Conclusion. Outcomes of the first 10 years of kidney and pancreas transplantation at WDGMC compare favourably with local and international survival data
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