Radioactive silicon as a marker in thin-film silicide formation

A new technique using radioactive 31Si (half-life =2.62 h), formed in a nuclear reactor, as a marker for studying silicide formation is described. A few hundred angstroms of radioactive silicon is first deposited onto the silicon substrate, followed immediately by the deposition of a few thousand angstroms of the metal. When the sample is heated, a silicide is first formed with the radioactive silicon. Upon further silicide formation, this band of radioactive silicide can move to the surface of the sample if silicide formation takes place by diffusion of the metal or by silicon substitutional and/or vacancy diffusion. However, if the band of radioactive silicide stays at the silicon substrate interface it can be concluded that silicon diffuses by interstitial and/or grain-boundary diffusion. This technique was tested by studying the formation of Ni2Si on silicon at 330 °C. From a combination of ion-beam sputtering, radioactivity measurement, and Rutherford backscattering it is found that the band of radioactive silicide moves to the surface of the sample during silicide formation. From these results, implanted noble-gas marker studies and the rate dependence of Ni2Si growth on grain size, it is concluded that nickel is the dominant diffusing species during Ni2Si formation, and that it moves by grain-boundary diffusion

Dissociation mechanism for solid-phase epitaxy of silicon in the Si <100>/Pd2Si/Si (amorphous) system

Solid-phase epitaxial growth (SPEG) of silicon was investigated by a tracer technique using radioactive 31Si formed by neutron activation in a nuclear reactor. After depositing Pd and Si onto activated single-crystal silicon substrates, Pd2Si was formed with about equal amounts of radioactive and nonradioactive Si during heating at 400 °C for 5 min. After an 1-sec annealing stage (450-->500 °C in 1 h) this silicide layer, which moves to the top of the sample during SPEG, is etched off with aqua regia. From the absence of radioactive 31Si in the etch, it is concluded that SPEG takes place by a dissociation mechanism rather than by diffusion

Chronic non-communicable diseases in black South African population living in a low-resource community

A thesis submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg in fulfilment of the requirements for the degree of Doctor of Philosophy Johannesburg 2016Introduction: The African continent, particularly sub-Saharan Africa, is facing a high burden of disease from the human immunodeficiency virus (HIV) pandemic and nutritional deficiencies, while at the same time, facing ever increasing rates of cardiovascular diseases (CVDs). The mortality rates from CVD are almost equal to the death rates from communicable diseases. In Sub-Saharan countries CVD prevention and management faces many barriers. One such difficulty is the shortage of data for the descriptive epidemiology of CVD risk factors. In an attempt to address this shortage of data, we established the Heart of Soweto (HOS) study in one of the largest African urban communities in South Africa. The purpose of this study was to identify and describe some of the factors contributing to the emergence of chronic diseases of lifestyle, such as heart disease, high blood pressure, diabetes and obesity in a black urban African population, within the framework of the HOS study. We also investigated the impact of a dietary intervention on cardiac function in subjects with chronic heart failure (CHF) in this black urban cohort. Methods: Data was collected as part of the “Heart of Soweto” (HOS) study, which was a prospectively designed registry that recorded data relating to the presentation, investigation and treatment of patients with newly diagnosed cardiovascular disease presenting to Chris Hani Baragwanath Hospital (CHBH), Soweto in 2006. Data collected included socio-demographic profile and all major cardiovascular diagnoses. Heart disease was defined as non-communicable (ND) e.g. coronary artery disease or communicable (CD) e.g. rheumatic heart disease. A survey was also conducted on consecutive patients attending two pre-selected primary care clinics in Soweto (644 and 667 patients from the Mandela Sisulu and Michael Maponya clinics, respectively). Data collected included, ethnicity, duration of residence in Soweto, highest level of education and employment status. Clinical data collected included prior or current diagnoses of diabetes and hypertension and pharmacological therapy related to the treatment of hypertension, as well as smoking status and exposure to second-hand smoking. Weight, height, and waist and hip circumference were measured. Questions were asked regarding the duration of night-time sleep and napping during the day. Descriptive studies were undertaken at the Heart Failure Clinic at CHBH, Soweto to firstly describe the food choices and macro-and micronutrients intake of 50 consecutive patients presenting with heart failure using an interviewer-administered quantitative food frequency questionnaire (QFFQ). Food data were translated into nutrient data using the Medical Research Council (MRC) Food Finder 3, 2007, which is based on South African food composition tables. Secondly we performed a randomized controlled study of a multidisciplinary, community-based, chronic HF management program in Soweto, compared with usual care, at CHBH Heart Failure Clinic located at the Soweto Cardiovascular Research Unit (SOCRU), or at the General Cardiac ix Clinic (standard care) in Soweto. In this study 49 consenting, eligible patients were individually randomized on a 1:1 basis to either usual care or to the study intervention and cardiac function was measured before and after the intervention. Results: Data collected at Chris Hani Baragwanath hospital (CHBH) cardiology clinic from 5328 suspected cases of heart disease, demonstrated that the most prevalent form of heart disease was hypertensive heart failure (22.0%). It was found that those participants who presented with ND (35.0%) were older and had higher BMI and mean systolic blood pressure (SBP) and diastolic blood pressure (DBP) than those with CD (39.0%; all comparisons p<0.001). Within this cohort of 5328 de novo cases of heart disease, 2505 (47%) were diagnosed with HF, of which 697 (28%) were diagnosed with r i g h t h e a r t f a i l u r e ( RHF). There were more women than men diagnosed with RHF (379 vs. 318 cases), and on an adjusted basis, compared with the remainder of the Heart of Soweto cohort (n = 4631), RHF cases were more likely to be African (adjusted OR 2.33, 95% CI 1.59 – 3.41), with a history of smoking (OR 1.72, 95% CI 1.42 – 2.10), a lower body mass index (OR 0.96, 95% CI 0.94 – 0.97 per kg/m2) and were less likely to have a family history of heart disease (OR 0.79, 95% CI 0.64 – 0.96). Data collected at 2 primary health care clinics in Soweto from 862 women (mean age 41 ± 16 years and mean BMI 29.9 ± 9.2 kg/m2) and 449 men (38 ± 14 years and 24.8 ± 8.3 kg/m2) indicated that in females, former smokers had a higher BMI (p<0.001) than current smokers, while exposure to second hand smoking was associated with a lower BMI (p<0.001) in both genders. Longer sleep duration in females was associated with a lower BMI (p=0.01). Napping during the day for > 30 minutes in males was related to a lower BMI and waist circumference (β=-0.03, p<0.05 for both) and lower systolic (β=-0.02, p<0.05) and diastolic BP (β=-0.02, p<0.05). Longer night time sleep duration was associated with lower diastolic (β=0.004, p<0.01) and systolic BP (β=0.003, p<0.05) in females. Within this same cohort, o b e s i t y w a s m o r e p r e v a l e n t i n f e m a l e s ( 4 1 . 8 % ) t h a n m a l e s ( 1 4 . 1 % ; p < 0 . 0 0 1 ) , 16% (n = 205) had an abnormal 12- lead ECG with more men than women showing a major abnormality (24% vs. 11%; OR 2.63, 95% CI 1.89–3.46). Of 99 cases (7.6%) subject to advanced cardiologic assessment, 29 (2.2%) had newly diagnosed heart disease which included hypertensive heart failure (13 women vs. 2 men, OR 4.51 95% CI 1.00–21.2), coronary artery disease (n = 3), valve disease (n = 3), dilated cardiomyopathy (n = 3) and 2 cases of acute myocarditis. Nutritional deficiencies were observed in a cohort presenting with HF at the cardiology outpatient clinic, CHBH. In women, food choices likely to negatively impact on heart health included added sugar [consumed by 75%: median daily intake (interquartile range) 16 g (10–20)], sweet drinks [54%: 310 ml (85–400)] and salted snacks [61%: 15 g (2–17)]. Corresponding figures for men were added sugar [74%: 15 g (10–15)], sweet drinks [65%: 439 ml (71–670)] and salted snacks [74%: 15 g (4–22)]. The women’s intake of calcium, vitamin C and vitamin E was only 66%, 37% and 40% of the age-specific requirement, respectively. For men, equivalent figures were 66%, 87% and 67%, respectively. Mean sodium intake was 2 372 g/day for men and 1 972 g/day for women, 470 and 294% respectively, of daily recommended intakes (DRI). In men, vitamin C intake was 71 ± 90 (79% of DRI). Similarly, in women vitamin C intake was 66 ± 80 (88% of DRI). Data collected from our HF management programme study supported the deficient intake of vitamin C in African subjects presenting with heart failure. Thus, plasma vitamin C concentrations (normal range 23 – 85 μmol/L) were markedly deficient in both standard care [6.53 (3.80, 9.22) μmol/L] and managed care [3.65 (1.75, 8.23) μmol/L] groups. In terms of clinical presentation, males were significantly older (49.9 ± 10.9 years; p<0.005) than females (37.2 ± 12.8) and at follow-up females had a significantly higher ejection fraction (34.8 ± 9.56 %) than males (29.5 ± 8.27; p<0.05) and when the groups were combined, the ejection fraction was significantly higher (32.2 ± 9.27; p<0.05) at follow-up compared to baseline (29.9 ± 8.80). We found that heart rate was significantly lower at follow-up (89.9 ± 14.6 beats/min) compared to baseline (93.4 ± 17.2; p<0.05) only in the managed care group. Furthermore, if diastolic blood pressure increased over the follow-up period, ejection fraction fell by 5.98% (p=0.009) in comparison to cases where diastolic blood pressure remained the same or fell. In addition, thiamine levels at baseline correlated negatively with systolic blood pressure (r=-0.68, p=0.04) at follow-up. Conclusion: Non-communicable heart disease and other diseases of lifestyle, such as high blood pressure, obesity and diabetes, are drastically increasing in Sub-Saharan Africa in general and in a black urban African community, such as Soweto, specifically. Soweto can clearly be described as a community in epidemiological and nutrition transition and is facing a double or even triple burden of disease. This is a community that is still being burdened by historically prevalent forms of communicable or infectious diseases juxtaposed against people who have lived their whole lives in Soweto and are increasingly suffering from newer or non-communicable diseases of lifestyle. Women seem to be especially burdened by this increase in non-communicable diseases, with a predominance of women suffering from heart disease and obesity. Certain exacerbating risk factors have been identified from the HOS in this community, namely the gender specific effects of sleep, smoking and other environmental factors on BMI and blood pressure, and the adverse effects of changing dietary patterns particularly the increased consumption of refined and processed foods, high in sugar, salt and fats and insufficient intakes of fruits and vegetables. Although there are some limitations to our HF management study, it serves as an indication that targeted, culturally sensitive care, adapted to an urban African population, might contribute to improved patient outcomes. However, prevention should always be our first priority through community-based and gender specific screening and the development and implementation of targeted prevention programs.MT201

Gene Technology in Winemaking: New Approaches to an Ancient Art

For the last century, the availability of pure culture yeast has improved reproducibility in wine fermentations and product quality. However, there is not a single wine yeast strain that possesses an ideal combination of oenological characteristics that are optimised for the task set by today´s leading winemakers. With new developments in modern winemaking there has arisen an urgent need to modify wine yeast strains in order to take full advantage of technology and to satisfy the demands of the sophisticated wine consumers. The combined use of mutagenesis, hybridisation and recombinant DNA methods have significantly increased the genetic diversity that can be introduced into Saccharomyces cerevisiae strains. The overall aim of the strain development programmes extends far beyond the primary role of wine yeast to catalyse the rapid and complete conversion of grape sugars into alcohol and carbon dioxide without distorting the flavour of the final product. Starter cultures of S. cerevisiae must now possess a range of other properties that differ with the type and style of wine to be made and the technical requirements of the winery. Our strain development programme focuses on a number of targets that are amenable to a genetic approach, including strain security and quality control, the increase of fermentation and processing efficiencies, and the enhancement of the sensorial quality and health properties of wine and other grape-based beverages. However, successful commercialisation of transgenic wine yeasts will depend on a multitude of scientific, technical, economic, marketing, safety, regulatory, legal and ethical issues. Therefore, it would be foolish to entertain unrealistic expectations over rapid commercialisation and short-term benefits. However, it will be equally unwise to deny the potential advantages of genetically improved wine yeasts to both the winemaker and consumer in the third millennium

Vibration problems of skips in mine shafts : the effect of compressive forces in the guides

Investigations into problems involving the vibration of conveyances in deep mining shafts have led to the identification of 'slamming' as a significant event in the initiation of large perturbations in the motion of the skip. Slamming occurs when the flexible rollers on the skip which normally act on the guides are inoperative. The primary concern is that this slamming event can give rise to large lateral loads on the shaft steelwork and is therefore a factor which limits the speed at which the skip can be drawn up the shaft. This study extends previous work to investigate the influence of compressive forces in the guides on the response of the skip and the steelwork. These forces are induced as a result of mining operations and lead to a decrease in the transverse stiffness of the guides. A mathematical model of the slamming event is formulated and a numerical solution for a specific case is performed. An alternative simplified solution is discussed and compared to the initial formulation, with the aim of facilitating the use of previous research results. A model to simulate the response of the skip when the skip rollers are functional is formulated, and numerical solutions of different examples are given. An important conclusion is that the compressive forces can significantly reduce the transverse stiffness of the guides, and should be taken into account in future designs. Bibliography: pages 86-88

Critical Collapse of the Massless Scalar Field in Axisymmetry

We present results from a numerical study of critical gravitational collapse of axisymmetric distributions of massless scalar field energy. We find threshold behavior that can be described by the spherically symmetric critical solution with axisymmetric perturbations. However, we see indications of a growing, non-spherical mode about the spherically symmetric critical solution. The effect of this instability is that the small asymmetry present in what would otherwise be a spherically symmetric self-similar solution grows. This growth continues until a bifurcation occurs and two distinct regions form on the axis, each resembling the spherically symmetric self-similar solution. The existence of a non-spherical unstable mode is in conflict with previous perturbative results, and we therefore discuss whether such a mode exists in the continuum limit, or whether we are instead seeing a marginally stable mode that is rendered unstable by numerical approximation.Comment: 11 pages, 8 figure

Heat transfer in two and three-dimensional single span greenhouses

Abstract: The purpose of this paper is to investigate the heat transfer in two-dimensional and three-dimensional cavities representing a single span greenhouse. This investigation is conducted numerically using Computational Fluid Dynamics (CFD). The heat transfer and temperature fields driven by buoyancy forces are investigated. The research commences with the validation of a few fundamental geometries used as the building blocks for a large commercial greenhouse. The first fundamental geometry is a square filled with air. The CFD results for a square cavity are first evaluated against experimental results found in the literature for both two and three dimensional cavities. The heat transfer inside the cavities is then investigated and compared to those found in the literature. A reasonably good comparison between the numerical CFD results and the experimental results was found for both the two- and three-dimensional cavities. Based on the validated CFD models, two three-dimensional single span greenhouses containing a pitched roof were investigated to determine the effect of design alterations on the heat transfer within the cavity. The results were also compared to two-dimensional greenhouses with a 30 and 45 degree roof angle respectively. Results found that there are significant differences between the two and three-dimensional cases when the average Nusselt number is considered, especially for a greenhouse containing a roof angle of 45 degrees. Temperature distributions were also found to vary significantly throughout the three-dimensional greenhouses

Two-dimensional quantum black holes: Numerical methods

We present details of a new numerical code designed to study the formation and evaporation of 2-dimensional black holes within the CGHS model. We explain several elements of the scheme that are crucial to resolve the late-time behavior of the spacetime, including regularization of the field variables, compactification of the coordinates, the algebraic form of the discretized equations of motion, and the use of a modified Richardson extrapolation scheme to achieve high-order convergence. Physical interpretation of our results will be discussed in detail elsewhere

The effect of geometrical electrical cable configurations on heat transfer in cable ducts

Abstract: Please refer to full text to view abstrac

Critical success factors for instrumentation and control projects within the power industry in South Africa

Abstract: Instrumentation and control projects entail an upgrade or refurbishment of a portion of the current process control system. The changes introduced present integration challenges to people, the plant and operating guidelines and procedures. The successful implementation of these time sensitive projects depends on factors such as change management effectiveness, stakeholder investment and competency of the project team. Project success factors identified across the lifecycle of the project enables the organization to filter down on challenges and risks contained within each project phase. The research identifies critical success factors specific to instrumentation and control projects within the South African power industry. The framework is developed through the descriptive analysis of feedback received from key stakeholders within the organization