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Graphene has displayed much promise as an electrical conductor and as a optical material. To date there is a large body of literature dedicated to the equilibrium properties of graphene. In this thesis the properties of graphene out of equilibrium are probed. Through combined optical and transport measurements the behaviour of hot electrons are probed at temperatures over five orders of magnitude from 50mK to 2000K. This wide range of temperatures allows access to the behaviour of quantum corrections at the lowest temperatures to the highest energy phonon modes. From ultrafast femtosecond laser pulses to steady state heating from an electric field the cooling of hot electron populations through coupling to various phonon modes in the graphene and the substrate are explored. Additionally the effect of an electric field on the weak localisation correction to the conductivity was separated from heating effects using applied magnetic fields combined with careful modelling of the heat transport properties of the graphene. Finally the desorption dynamics of oxygen bound to the surface are shown using a combination of transport and two pulse correlation technique using an ultrafast laser. Surprisingly the cooling of hot carriers in graphene at low energies shows substrate surface phonons as an important cooling mechanism, highlighting the importance of substrate choice in future graphene devices. In contrast at the very highest energy scales accessed only by photoexcitation the cooling is shown not to be influenced by the presence of a substrate, but out-of-plane phonon modes increase cooling of the hot optical phonons.

Thesis MMed (Paediatrics), Faculty of Health Sciences, University of the Witwatersrand / INTRODUCTION: Improved survival of VLBW infants is raising several management issues. An example is that of growth and growth monitoring. AIM OF THE STUDY: To assess the growth of a cohort of VLBW infants born at CMJAH from term CGA to 20 months CGA. METHODS: A retrospective chart review was conducted on 139 VLBW infants (birth weight ≤ 1500g) born at CMJAH between 1 July 2006 and 28 February 2007. RESULTS: Comparison with a term growth reference showed initial growth failure followed by gradual catch up growth but with persistent deficits in length for age. Comparison with international VLBW references showed similar growth for weight and head circumference for age but with deficits in length for age. Growth parameters of the study sample were similar to those of other South African VLBW infants. CONCLUSION: Growth and growth monitoring in VLBW infants is complicated by characteristic growth patterns, high associated morbidity, controversies surrounding ideal growth and lack of an ideal growth reference. Significant deficits in length for age in the study sample may have been due to the large proportion of infants born SGA and the high prevalence of stunting in South African children. Current recommendations for growth monitoring of VLBW infants include the use of a VLBW reference up to two years CGA followed by a term growth reference thereafter

Introduction Various authors have proposed that there may be altered hip rotation range of motion (ROM) in patients with low back pain (LBP). However, limited studies have been conducted to investigate the association between hip rotation ROM and LBP specifically in distance runners. The aim of this study was to determine whether there is an association between hip rotation ROM and non-specific LBP in distance runners. Methods A cross-sectional design was used to look at the relationship between hip rotation ROM and LBP. Thirty five runners with LBP (24 males, 11 females) and 51 runners without LBP (29 males, 22 females) participated in the study. A questionnaire was used to divide participants into LBP and no LBP groups and to evaluate certain factors specific to LBP. Passive rotation ROM was measured in prone position using a hand-held inclinometer. Results Results showed no statistically significant difference (p>0.05) in hip rotation ROM between the two groups. Furthermore, no statistically significant difference (p>0.05) was found for factors specific to running, between the two groups. Conclusion Although no association was found between hip rotation ROM and LBP in distance runners, further research is needed into other possible causative factors of LBP in distance runners. Keywords Low back pain, hip biomechanics, hip mobility, hip rotation, sports and running Operational definitions  Low back pain (LBP): pain and discomfort located below the costal margins and above the gluteal folds, with or without associated leg pain (Van Tulder et al 2006).  Non-specific LBP: pain not attributable to a clearly recognisable pathology (Koes et al 2006).  Healthy distance runner: a runner who has had no LBP symptoms within the last 6 months.  Time trial: an unofficial road running race in which participants are timed individually over a set distance, in this case, 4km.

A research report submitted to the Faculty of Health Sciences Witwatersrand University, Johannesburg in partial fulfillment of the requirements for the degree of Master of Medicine in Family Medicine Johannesburg, South Africa 2017 / Background: Low birth weight (LBW) is an important risk factor for infant developmental problems, morbidity and mortality. Low birth weight babies are twenty times more likely to die during the neonatal period than their normal weight counterparts. Although risk factors for low birth weight vary from one community to another, maternal risk factors for low birth weight in the South Rand Hospital (Johannesburg, Gauteng) catchment area have not been investigated. The objective of this study was to determine maternal risk factors for low birth weight in South Rand Hospital, Johannesburg. Method: This 1: 1 matched case-control study was conducted on a total of 480 mothers who delivered babies at South Rand Hospital between 1 January 2013 and 31 December 2014. The cases were 240 mothers who delivered singleton term live LBW babies. They were matched with an equal number of controls. Results: Conditional logistic regression showed that, no anaemia in the third trimester (OR=0.54, 95% CI= 0.30-0.99), immigration status (OR= 0.46, 95% CI= 0.25- 0.85) and four or more antenatal care clinic attendance (OR=0.36, 95% C.I= 0.12- 0.76) were protective factors, while smoking during pregnancy (OR= 8.69, 95% CI= 2.70-28.35) predisposes to delivering a LBW baby. Conclusion: The results showed that smoking during pregnancy is a risk factor for LBW, while maternal third-trimester haemoglobin level of 11g/dl or more, immigrant status, and more than three ANC visits were protective factors for delivering LBW baby. / MT2017

The research reported in this dissertation centered around the prevalence and factors associated with low back pain (LBP) among the undergraduate physiotherapy students at the University of the Witwatersrand. Physiotherapy students are prone to LBP due to a flexion posture while studying, lifting patients and working. After pathology, muscle activity is influenced, affecting optimal function of the spine. Preventative strategies can minimise recurrences of LBP. Physiotherapy students enrolled for 2010 at the University of the Witwatersrand participated in a cross-sectional prevalence study. A questionnaire, multi-stage fitness test and physical assessment were completed. Statistical analysis was done with univariate analysis for associations with LBP. The study revealed that the lifetime LBP prevalence was 35.6% among all four physiotherapy year groups. The prevalence increased from first year to third year but unexpectedly decreased in the fourth year group. Significant associations with LBP were posterior-anterior mobilisations on L4 (p=0.003) and L5 (p≤0.001) centrally, left lumbar multifidus (LM) cross-sectional area (p=0.02), right obliquus internus abdominis (p=0.02) and transversus abdominis (TrA) thickness at rest (p=0.03), both TrA during contraction, left (p=0.02) and right (p=0.01), as well as the pull of the TrA during contraction on the left (p=0.03). The present work is the first study to show measurements with ultrasound imaging of LM and TrA on physiotherapy students. The prevalence of LBP might be reduced if students are more aware of LBP and consequential muscle imbalances that might perpetuate the problem. The dissertation concludes with a discussion of future research avenues. It is suggested that an intervention to make students aware of LBP and risk assessments in South Africa will help to identify and address hazards in the workplace.

São propostos modelos de 4 e de 12 vértices na rede quadrada para explicar a transição de fases antiferroelétrica observada no ácido quadrático (H IND. 2C IND. 4O IND. 4). A energia livre do modelo básico de 4 vértices se anula identicamente. A solução do modelo iônico de 12 vértices na aproximação de Bethe apresenta uma transição de segunda ordem. A existência desta transição de fases é assegurada por meio de um argumento de Peierls . A transição de fases do modelo de 12 vértices também é estudada pela técnica do grupo de renormalização fenomenológico. Conclui-se que a temperatura critica exata deve ser sistematicamente inferior àquela prevista pela aproximação de Bethe. Há evidências de que nü = 1. A mesma técnica foi empregada no estudo de um modelo de 16 vértices equivalente ao modelo de Ising, reproduzindo- se com boa precisão os cálculos exatos. Resultados experimentais mais recentes para O ácido quadrático indicam urna transição de primeira ordem. Mostra- se então que um modelo compressível de 12 vértices apresenta urna transição descontinua na aproximação de Bethe. / We consider 4 and 12 vertex models on the square lattice for the antiferroelectric phase transition in crystals of squaric acid (H IND. 2C IND. 4O IND. 4). The free energy of the basic 4 vertex model vanishes identically. In the framework of the Bethe approximation, the ionic 12 vertex model gives a second order phase transition. We use a Peierls argument to show that a phase transition does indeed occur in this model. Also, the phase transition in the 12 vertex model is studied by means of phenomenological renormalization group calculations. The exact critical temperature seems to be always lower than the prediction of the Bethe approximation. We present evidences that nü = 1 for this model. The same calculations were done for a 16 vertex model which is equivalent to the Ising model, the exact results being reproduced with good precision. Recent experimental data seem to support that the transition in squaric acid is indeed of first order. A compressible 12 vertex model is then shown to give a discontinuous transition.

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São propostos modelos de 4 e de 12 vértices na rede quadrada para explicar a transição de fases antiferroelétrica observada no ácido quadrático (H IND. 2C IND. 4O IND. 4). A energia livre do modelo básico de 4 vértices se anula identicamente. A solução do modelo iônico de 12 vértices na aproximação de Bethe apresenta uma transição de segunda ordem. A existência desta transição de fases é assegurada por meio de um argumento de Peierls . A transição de fases do modelo de 12 vértices também é estudada pela técnica do grupo de renormalização fenomenológico. Conclui-se que a temperatura critica exata deve ser sistematicamente inferior àquela prevista pela aproximação de Bethe. Há evidências de que nü = 1. A mesma técnica foi empregada no estudo de um modelo de 16 vértices equivalente ao modelo de Ising, reproduzindo- se com boa precisão os cálculos exatos. Resultados experimentais mais recentes para O ácido quadrático indicam urna transição de primeira ordem. Mostra- se então que um modelo compressível de 12 vértices apresenta urna transição descontinua na aproximação de Bethe. / We consider 4 and 12 vertex models on the square lattice for the antiferroelectric phase transition in crystals of squaric acid (H IND. 2C IND. 4O IND. 4). The free energy of the basic 4 vertex model vanishes identically. In the framework of the Bethe approximation, the ionic 12 vertex model gives a second order phase transition. We use a Peierls argument to show that a phase transition does indeed occur in this model. Also, the phase transition in the 12 vertex model is studied by means of phenomenological renormalization group calculations. The exact critical temperature seems to be always lower than the prediction of the Bethe approximation. We present evidences that nü = 1 for this model. The same calculations were done for a 16 vertex model which is equivalent to the Ising model, the exact results being reproduced with good precision. Recent experimental data seem to support that the transition in squaric acid is indeed of first order. A compressible 12 vertex model is then shown to give a discontinuous transition.