Implementation of the Quantum Hall Effect based precision resistance measurement system

The integer Quantum Hall Effect (QHE) occurs when a two-dimensional electron gas (2DEG) is subjected to a strong perpendicular magnetic field and when the system is cooled to low temperatures. The QHE harbours a wealth of unique phenomena. Of interest is the existence of the Quantum Hall Resistance (QHR) which had found to be related to two fundamental constants of nature via the von Klitzing constant h e 2 , where e is the charge of the electron and h Planck’s constant. This thesis investigates the properties of the QHE in a low dimensional electron gas system. The von Klitzing constant is determined as well as the electron density n2D and mobility µ of the material measured. The results are compared to the accepted value of the von Klitzing constant as determined by the metrological community. The average von Klitzing constant obtained is 25 783.637 Ω within an accuracy of 1.13 × 10−12. Our results are further interpreted using the Landau quantum mechanical model of electron transport in perpendicular magnetic field. The measurement of standard resistances utilising a standard DC resistance measurement system were also undertaken at the National Metrology Institute of South Africa (NMISA). This ties in with the ongoing project of NMISA to develop an in-house quantum Hall measurement system to provide the full traceability for resistance standard measurements in the Republic of South Africa. The device measured utilised a GaAs/AlGaAs heterostructure structure, grown via Molecular Beam Epitaxy (MBE). A micron sized Hall bar with Ohmic contacts was patterned using standard clean room procedures. Magnetotransport measurements at low temperatures, sub 200 mK were carried out on the device. The transverse and longitudinal resistances were obtained and plotted against the perpendicular magnetic field. Quantum Hall plateaus and Shubnikov de-Haas (SdH) oscillations were observed. Properties of the heterostructure such as the electron density (n2D) and mobility (µ) were determined. The n2D obtained was 2.27 × 1011 cm−2 with µ at 3.5 × 105 cm2V−1 s −1 . All results were compared to current literature values

Performance of High School Students in Vhembe District

Despite the attempts by South African government to make education accessible to all by introducing free food and free textbooks at the primary school level, there is still high failure rate in mathematics and science in high schools in the country. This study makes attempt to establish some factors that affect the performance of students, especially in science subjects in high schools in the Vhembe district in the Limpopo province. A survey was conducted in 17 high schools randomly sampled in the Vhembe district. Purposive sampling was used to get the grade 11 and 12 students and their teachers. About 700 students, 70 teachers and 17 principals were interviewed. The study concludes that the overall pass rate is 70% but the rate in mathematics and science is hardly 40%; and the key factors affecting performance are lack of laboratory for practical, awards, shuffling and textbooks. The study recommends that science laboratories be built in schools, textbooks be supplied in good time and teachers to motivate students by giving awards

An ethical reflection on the DOTS programme in South Africa: adherence, vulnerable populations, benefits, and burdens

The introduction of the Directly Observed Treatment Short course (DOTS) recommended by the World Health Organization (WHO) in 1991 was developed as the ideal public health measure for the treatment and management of tuberculoisis (TB) (Naidoo, Dick & Cooper 2008:1). However, despite attempts to cure and control tuberculosis, two million new cases are reported in the sub-Saharan region of Africa. The problem of TB in South Africa is made worse by the high incidence and prevalence of HIV/AIDS. There are many contributing factors that may play a part in South Africa’s low cure rate such as unequal national drug distribution, lack of healthcare personnel, patient superstitions and myths concerning tuberculosis. I have touched upon some of these issues. But in this research report I have mainly concentrated on the South African DOTS programme and some of the ethical issues involved in the problem of patient adherence as it concerns the fair societal distribution of burdens and benefits. I have used the ethical framework for public health ethics for my analysis as proposed by Nancy Kass, and also placed a special focus on adherence problems as they concern vulnerable populations. Quality of the DOTS programme in South Africa such as staff attitudes towards TB patients and poor communication skills, nursing care, broken equipment, dirty facilities, absenteeism may contribute towards non-adherence. Moreover, poor quality healthcare services may encourage TB patients to seek alternative treatment other than hospital care thereby increasing their vulnerability to infection and disease progression. Cultural differences in health care and practices may be a barrier to the effective distribution of quality healthcare

The challenges arising from the application of the ‘gross income definition to illegal income.’

Master of Law in Taxation. University of KwaZulu-Natal, Durban 2016.Abstract available in PDF file

Yield and quality parameters of tomato cultivars as affected by different soilless production systems and beneficial micro-organisms.

Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.Most tomato cultivars used for commercial food production are imported into South Africa. Optimal growing conditions for these specific cultivars need to be determined, as wrong cultivar choices can lead to great financial losses. Lack of information on selecting well-performing cultivars may lead to lower yield or unacceptable fruit quality. Information on the performance of tomato cultivars under South African conditions, utilizing plastic tunnels or shadenet structures under soilless cultivation is still very limited. Soilless cultivation of vegetables is becoming a preferable over in-soil cultivation due to the improved yield and quality of produce, efficient water and nutrients usage by the crop; furthermore, the grower can regulate nutrient solution, electrical conductivity and pH of the nutrient solution. To identify the optimal system for growing tomatoes hydroponically, the performance of four tomato cultivars (‘FA593’, ‘Miramar’, ‘FiveOFive’ and ‘Malory’) under different growing conditions was evaluated: directly planted in soil under 40% shadenet with drip irrigation, a closed hydroponic system under 40% shadenet, an open bag system under 40% shadenet, or an open-bag system in a temperature controlled as well as a non-temperature controlled tunnel. The study revealed that ‘Miramar’ performed better than the other cultivars in all production systems, with the exception of soil cultivation where there were no differences amongst the four cultivars. Fruit cracking was found to be directly correlated with fruit size, as the large-sized cultivars ‘Malory’ and ‘FA593’ were more susceptible than the other two cultivars. Plants grown under shadenet were prone to fruit cracking and raincheck as well as early blight. Higher yields were obtained when plants were produced in the open bag system under temperature controlled conditions and in the closed system under shadenet. Growing tomatoes in the non-temperature controlled tunnel resulted in high incidences of fruit cracking, poor yield and pre-mature fruit ripening probably due to high and fluctuating temperatures under such conditions. The average marketable yield was 88% and 59% of the total yield in the temperature controlled and non-temperature controlled tunnels, respectively. A further experiment was carried out to improve yield and quality of tunnel tomatoes using beneficial micro-organisms, i.e., arbuscular mycorrhiza fungi (AMF) at different nutrient concentrations. Tomato seedlings were treated with Mycoroot™ containing four mycorrhiza species (Glomus etunicatum, Paraglomus occultum, Glomus clarum and Glomus mossea) at transplanting and subsequently transferred to either a temperature controlled or a non-temperature controlled tunnel under the recommended (100%) or reduced (75 and 50%) nutrient concentrations. Sawdust was used as a growing medium in this experiment. Application of AMF neither enhanced plant growth, yield, nor fruit mineral nutrient concentrations; although fruit Mn and Zn concentrations in the temperature controlled tunnel increased significantly following AMF application. Plants grown in the non-temperature controlled tunnel had significantly poorer plant growth, and lower yield and lower fruit mineral concentrations, compared with fruit from plants in the temperature controlled tunnel. Tomato plants in the non-temperature controlled tunnel had higher levels of micro-elements in leaf tissue, compared with those in the temperature controlled tunnel. The highest yields were obtained from plants fertigated with 75% of the recommended nutrient concentration, as compared with the 100 and 50% nutrient concentrations. When coir was subsequently used as the growing medium, Mycoroot™ applied at seeding and transplanting did not enhance mycorrhizal colonization or fruit quality. Growing tomatoes under reduced nutrient supply reduced the total soluble solids in the juice of the fruit, but improved total and marketable yield, as well as the number of marketable fruit. This effect was more substantial in the temperature controlled than in the non-temperature controlled tunnel. Fruit firmness and leaf chlorophyll concentrations were significantly higher in plants grown in the temperature controlled tunnel. Growing tomatoes in sawdust improved the leaf Mn and Ca concentration over that of tomato plants grown in coir. Mycorrhizal colonisation did not have a beneficial effect on tomato yield and quality. The study indicated that cultivar selection was important in obtaining the highest yield and quality of tomato using the closed hydroponic system under shadenet and the open bag hydroponic system in the temperature controlled tunnel. Temperature controlled tunnels with a pad–and-fan cooling system are still an effective way of cooling the tunnel environment which resulted in high yield and high quality of tomatoes with a higher fruit mineral content than that obtained under non-temperature controlled conditions where only natural ventilation is relied on. Results also demonstrated that mycorrhizal colonization in soilless condition has limited beneficial effects in allowing for better nutrient uptake and thereby for improved yield and quality of tomatoes. Further studies, including different media, nutrient composition and concentrations, need to be carried out to investigate the possible causes of AMF failure to improve yield, despite good AMF root colonization

Alternative off school Business Models that Enhance Multiple Intelligences in Kenyan Schools

Promotion of individual development and self-fulfillment amongst students in Kenya is among the national goals of education. To accomplish this goal it is imperative that, development of Multiple Intelligences in schools is put into perspective. To date, relatively little research has investigated the ways students Multiple Intelligences should be enhanced in Kenya. Consequently, this study was devised to examine alternative off school business management models that enhance Multiple Intelligences among secondary students in Kenya. The study was guided by the Multiple Intelligence Theory and Management Competency Framework. The study target population was 150 secondary schools in Elgeyo Marakwet. Data was collected using questionnaire, document analysis and interview. The data was analyzed qualitatively using thematic approach and quantitatively using percentages, means, standard deviation and simple linear regression. Data was presented in tables. The findings indicated that schools management was managing traditional models of enhancing multiple intelligences thus majority of the students’ abilities were not developed. Alternative off school business management models were found to be effective in enhancing multiple intelligences among students though majority of the schools had not adopted them. The study recommends that managing and facilitating entrepreneurship programmes should be promoted to enable students to show case abilities in different intelligences

Monitoring CD27 expression to evaluate Mycobacterium tuberculosis activity in HIV-1 infected individuals in vivo.

The level of bacterial activity is only poorly defined during asymptomatic Mycobacterium tuberculosis (MTB) infection. The objective was to study the capacity of a new biomarker, the expression of the T cell maturation marker CD27 on MTB-specific CD4 T cells, to identify active tuberculosis (TB) disease in subjects from a MTB and HIV endemic region. The frequency and CD27 expression of circulating MTB-specific CD4 T cells was determined in 96 study participants after stimulation with purified protein derivative (PPD) using intracellular cytokine staining for IFNgamma (IFNγ). Subjects were then stratified by their TB and HIV status. Within PPD responders, a CD27(-) phenotype was associated with active TB in HIV(-) (p = 0.0003) and HIV(+) (p = 0.057) subjects, respectively. In addition, loss of CD27 expression preceded development of active TB in one HIV seroconverter. Interestingly, in contrast to HIV(-) subjects, MTB-specific CD4 T cell populations from HIV(+) TB-asymptomatic subjects were often dominated by CD27(-) cells. These data indicate that down-regulation of CD27 on MTB-specific CD4 T cell could be used as a biomarker of active TB, potentially preceding clinical TB disease. Furthermore, these data are consistent with the hypothesis that late, chronic HIV infection is frequently associated with increased mycobacterial activity in vivo. The analysis of T cell maturation and activation markers might thus be a useful tool to monitor TB disease progression

Effect of genital herpes on cervicovaginal HIV shedding in women co-infected with HIV AND HSV-2 in Tanzania.

To compare the presence and quantity of cervicovaginal HIV among HIV seropositive women with clinical herpes, subclinical HSV-2 infection and without HSV-2 infection respectively; to evaluate the association between cervicovaginal HIV and HSV shedding; and identify factors associated with quantity of cervicovaginal HIV. Four groups of HIV seropositive adult female barworkers were identified and examined at three-monthly intervals between October 2000 and March 2003 in Mbeya, Tanzania: (1) 57 women at 70 clinic visits with clinical genital herpes; (2) 39 of the same women at 46 clinic visits when asymptomatic; (3) 55 HSV-2 seropositive women at 60 clinic visits who were never observed with herpetic lesions; (4) 18 HSV-2 seronegative women at 45 clinic visits. Associations of genital HIV shedding with HIV plasma viral load (PVL), herpetic lesions, HSV shedding and other factors were examined. Prevalence of detectable genital HIV RNA varied from 73% in HSV-2 seronegative women to 94% in women with herpetic lesions (geometric means 1634 vs 3339 copies/ml, p = 0.03). In paired specimens from HSV-2 positive women, genital HIV viral shedding was similar during symptomatic and asymptomatic visits. On multivariate regression, genital HIV RNA (log10 copies/mL) was closely associated with HIV PVL (β = 0.51 per log10 copies/ml increase, 95%CI:0.41-0.60, p<0.001) and HSV shedding (β = 0.24 per log10 copies/ml increase, 95% CI:0.16-0.32, p<0.001) but not the presence of herpetic lesions (β = -0.10, 95%CI:-0.28-0.08, p = 0.27). HIV PVL and HSV shedding were more important determinants of genital HIV than the presence of herpetic lesions. These data support a role of HSV-2 infection in enhancing HIV transmissibility

Characterization of envelope function of transmitted viruses circulating in Mbeya, Tanzania, and its impact on disease progression

An understanding of the biological characteristics of transmitted viruses provides important insights into HIV pathogenesis and informs vaccine development. The aim of the study was to characterize env function of transmitted viruses and its role in disease progression