The primary objectives of the described research were to examine the underlying physical phenomena occurring during flame/obstacles interactions in various chambers of low L/D ratio and to develop a new empirical equation for explosion venting. A literature review suggested that the propagating flame/obstacle interactions in enclosures with large L/D ratio (&gt 2) result in flame acceleration and subsequent pressure build-up during a gas explosion. However, the interactions in practical situations with small L/D &lt 2 were not extensively studied. In this thesis the first investigation involved the flame interaction with different single and multiple obstacles in a 1/20th model of real enclosure. Results provided the basis for flame propagation, local flame displacement speed probability density functions (pdfs), mean flame velocity and explosion pressure. The second investigation of the study involved the flame interaction with multiple bars within chambers of different L/D ratios. The results provided mean flame velocities on each stage, as a function of nondimensional time, and pressure developments as a function of L/D ratio. The final investigation is associated with gas explosion venting. The predictive ability between existing models on explosion venting and experimental results obtained in this thesis were undertaken and found to be deficient. Consequently a new empirical model for predicting explosion venting was developed. The new model was validated with experimental data published in literature.

Certain new realities, such as the liberalisation of the skies and increased air traffic in South Africa are bound to test the existing safety strategies, regulations and maintenance of standards. In order to obtain a picture of the future architecture and the standard of aviation safety in South Africa, the mental models of stakeholders in the industry were investigated in a qualitative, study. A qualitative interpretive research design was followed. The research question was: What are the mental models of key stakeholders in the aviation safety environment and how does this need to be accounted for in the development of an aviation safety strategy, in a Southern African context? In order to obtain a broad spectrum of the social constructs of key stakeholders with regard to aviation safety and to enhance the trustworthiness of the information, three research interventions or information gathering processes were applied. These were the individual interviews through Kelly’s Repertory Grid (Rep Grid) technique, outcomes analysis of the job of a safety manager through a focus group process and a scenario development process (in this sequence). Data was then considered in relation to certain theoretical perspectives, as well as realities in the aviation safety environment in Southern Africa. The study identified pertinent gaps between the mental models elicited from research participants during individual interventions and those elicited during group interventions, as well as a disparity between their mental models and the demands of the aviation safety environment in Southern Africa and the international community. The participants’ individual mental models (or theories in use) focused more on micro systems and symptoms of “unsafety” than the broader systemic relationships and problems. Tendencies towards silo-thinking and single loop learning were indicated. In contrast with the individual mental models, the collective or shared mental models of the participants, elicited during group interventions, represented a more systemic view and a more effective or desired model with regard to aviation safety. The broader system together with its interrelated elements, entropy and unpredictability, as well as critical elements that need to be accounted for in an aviation strategy, were identified. These were, amongst others, effective coordinated regulation and safety oversight on national and regional level; risk management; international recognition; legitimacy; authorisation and market access for airlines; maintenance of standards; international cooperation; and training. It also became clear that safety cannot be understood and managed by focussing on Newtonian laws without a proper appreciation of human factors. Other important perspectives that were identified are the need for the establishment of a study-field for aviation psychology and effective human factors training; as well as the need for a regional regulatory function in Southern Africa. / Prof.J.S Uys

M.Ing. / In the mining industry safety is a primary concern. Especially so when it comes to the large conveyances transporting people, equipment and ore up and down the shaft. Even though it has occurred seldomly, a so-called "slack rope event" - when the conveyance gets stuck in its guides - is extremely dangerous. If the conveyance should become freed it will fall freely until all the slack rope has been taken up and then whiplash. The immense strain could lead to complete failure of the rope or suspension mechanisms. The large deceleration rates experienced could in itself be sufficient to cause serious injury or even death to passengers. A strategy to alleviate this danger, originated by Greenway and Hymers (41), is to have passive energy absorber units in parallel to the suspension mechanism of the conveyance. In the event of an emergency the suspension mechanism will be detached and the absorbers will then be activated, safely absorbing the kinetic energy the conveyance has gained. The dynamic behaviour of the system with and without the energy absorbers in a free fall situation was studied and it was clear that the hazards associated with a slack rope event could be successfully alleviated using the energy absorbers. The question that now presented itself was, which energy absorbing mechanism should be used in this application. An encompassing set of qualifying criteria was subsequently set and after extensive research and evaluation the cyclic plastic bending energy absorber was deemed to be most suitable for this application, as also suggested by Greenway and Hymers (41). The device uses a metal element being bent and unbent while being pulled through a set of rollers. The kinetic energy is transformed to plastic metal deformation and dissipated as low grade heat. Further research was then done on this energy absorbtion device. It revealed a substantial amount of background information and two approximate equations for prediction of the resistive force delivered by the device. It was subsequently attempted to find an analytical solution from first principles, to predict the resistive force and characteristic behaviour of the device. Two solutions were obtained, using different approaches to the problem. A number of experiments were then conducted to study the actual characteristics and behaviour of the device. After manipulation of the results it was found that non-dimensional parameters could be formulated which would make it possible to predict the behaviour of full-scale prototypes using small-scale models. Upon comparing the experimental results with the analytical solutions it was found that the two analytical solutions provide an upper and lower bound to the experimental results. Finite element analysis was also utilized to characterize the behaviour of the device and to attempt to predict the resistive force the device delivers. The finite element models revealed some interesting characteristics of the device and mimicked the behaviour of the actual device. However, the resistive force values obtained, deviated slightly more from the experimental values than the scaling method or the analytical solutions. It is thus possible to predict the behaviour of the cyclicplastic- bending energy absorber by utilizing scaling techniques, analytical solutions or the finite element method. The cyclic-plastic-bending energy absorber has a wide spectrum of applications as it is a very versatile and reliable energy absorber.

Lupane and Hwange districts fall under natural region IV and V and lie in the semi-arid regions of Zimbabwe with low and erratic mean annual rainfall not exceeding 600mm. Seventy percent of Zimbabwe’s population lives in communal areas, whose livelihood is based on agriculture. The communities in these areas mainly practice mixed farming systems. However, crop production is constrained by water availability and suitable production techniques. As a result households in these areas are experiencing worsening levels of household food insecurity. Two irrigation schemes were identified for this study and these are located in these two districts. Tshongokwe irrigation scheme is located in Lupane district and Lukosi irrigation scheme is located in Hwange district and these irrigation schemes are about 25 hectares in size. Lupane and Hwange districts are considered to be one of the most food insecure areas in the country because of the frequent droughts and unreliable rainfall in the region. The major tool of enquiry in this study was the questionnaire which was used to collect data from the households that farm on irrigated land and those that farm on dryland farming. Household and farm characteristics were collected using structured questionnaires with the help of locally recruited and trained enumerators. Agricultural production, household consumption and marketing of agricultural produce were accessed using the questionnaire to establish problems experienced by farmers. The main objective of this study was to investigate the determinants of household food security using a logistic regression model. The model was initially fitted with thirteen variables, selected from factors identified by previous researchers that affect food security in communal areas. Six variables were found to be significant at 1, 5 and 10 percent significance level and all had the expected signs except farm size. These factors include access to irrigation, farm size, cattle ownership, fertilizer application, household size and per capita aggregate production. The results obtained were further analyzed to compute partial effects on continuous variables and change in probabilities on the discrete variables for the significant factors in the logistic regression model. Analysis of partial effects revealed that household size, farm size, cattle ownership and per capita aggregate production lead to a greater probability of household being food secure. Change in probability results showed that having access to irrigation and using fertilizer can increase the probability of household being food secure The findings of this study highlight a positive and significant relationship between access to irrigation, fertilizer application, cattle ownership, per capita aggregate production to household food security. Household size and farm size have a negative and significant relationship on household food security. This study shows the effectiveness of irrigated farming over dryland farming in the semi-arid areas. The results show increased agricultural production, crop diversification and higher incomes from irrigation farming as compared to dry land farming. Irrigation farming has enabled many households to diversify their source of income and generate more income. Irrigation has enabled households with irrigation not only to feed themselves throughout the year but also to invest on non-agricultural goods and services from incomes received from crop sales Based on the results from the logistic regression model, it can be concluded that household size, farm size, per capita aggregate production, cattle ownership, fertilizer application and access to irrigation have a positive effect on household food security and the magnitude of changes in conditional probabilities have an impact on household food security.

Through the use of standards the fire-control problem can be divided into its many phases, and specifications set for its solution. Fire-control standards fall into two classes, (1) the overall fire-control objective, and (2) standards to be met in attaining that objective. The former, or primary standards, serve to keep the various phases of fire-control at the most economically justifiable level. The latter, or secondary standards, ensure that all fire-control efforts conform with the primary standards. A full schedule of fire-control standards is presented. A system for assessing presuppression and suppression, first presented in 1932, was revised and elaborated for application as a current secondary standard. The principal feature of this system is that certain specifications must be met by the many phases of presuppression and prevention efforts before a numerical rating indicating adequacy is obtained. A different scale of rating should be set up for each fire-control unit, depending on the purposes of forest management and the nature of the fire hazard. Fire-control standards were analyzed from a theoretical point of view and a new primary standard, called the actuarial standard, was developed. Data from three Ranger Districts on Vancouver Island were studied through the actuarial assessment of past fire-control costs and damage, past fire danger, and expected trends. It was found that the actuarial standard was the only one of the three major standards that provided an adequate analysis of the fire-control problem on a given area and produced realistic results. A new secondary standard, called the local incentive standard is also presented. This standard relies on the value of enthusiasm and personal incentive in obtaining good results from fire-control employees. Dealing with burned area, this standard establishes the allowable annual burn by decreasing the past average burned area by 10 per cent each year. / Forestry, Faculty of / Graduate

The United States has the world’s largest road network with over 4.1 million miles of roads supporting more than 260 million of registered automobiles including around 11 million of heavy trucks. Such a large road network challenges the road and traffic management systems such as condition assessment and traffic monitoring. To assess the road conditions and track the traffic, currently, multiple facilities are required simultaneously. For instance, vehicle-based image techniques are available for pavements’ mechanical behavior detection such as cracks, high-speed vehicle-based profilers are used upon request for the road ride quality evaluation, and inductive loops or strain sensors are deployed inside pavements for traffic data collection. Having multiple facilities and systems for the road conditions and traffic information monitoring raises the cost for the assessment and complicates the process. In this study, an integrated system is developed to simultaneously monitor the road condition and traffic using in-pavement strain-based sensors, which will phenomenally simplify the road condition and traffic monitoring. To accomplish such a superior system, this dissertation designs an innovative integrated sensing system, installs the integrated system in Minnesota's Cold Weather Road Research Facility (MnROAD), monitors the early health conditions of the pavements and ride quality evaluation, investigates algorithms by using the developed system for traffic data collection especially weigh-in-motion measurements, and optimizes the system through optimal system design. The developed integrated system is promising to use one system for multiple purposes, which gains a considerable efficiency increase as well as a potential significant cost reduction for intelligent transportation system. / USDOT (U.S. Department of Transportation) / MPC (Mountain-Plains Consortium)

research report submitted to the Faculty of Science, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Science. School of Physics. Johannesburg, 2015. / Protection against accidental criticality is of utmost importance due to the potential of extremely high doses (such as the 17 Sv in the case of the Toikamura accident) to personnel involved in a criticality accident. In this study a criticality study is performed on a storage facility for uranium-containing residue. A criticality safety evaluation is the method used to determine the criticality safety of a system. Various internationally accepted methods exist which can be used during a criticality safety evaluation, including the use of a validated calculational technique. The three-dimensional Monte Carlo code, MCNP, was used in this study to determine multiplication factors, keff, for several different theoretical storage configurations. The internationally accepted subcritical limit of keff = 0.95 was used to determine whether a specific configuration is safe in terms of criticality. This study determines whether the theoretical storage configurations will be safe in terms of criticality, and it also evaluates the influence of various moderators on the multiplication factor, as well as the effect of distance between individual canisters on the multiplication factor. This criticality safety evaluation aims to show that the proposed theoretical storage configurations are safe in terms of criticality. It also provides recommendations of how the storage capacity can be increased, based on the results of the study.

A research report submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in partial fulfillment of the requirements for the degree of Master of Medicine in Diagnostic Radiology Johannesburg 2019 / Introduction: Neonates in a neonatal ICU or high care unit are a high-risk population. Besides a vulnerability to medical and surgical conditions, which often require radiological investigation, they are also at risk from the effects of radiation used in imaging. These risks increase with radiation dose. Numerous studies have assessed the dose due to primary radiation, however few have assessed the secondary radiation dose, and none have quantified the dose over time. Aim: To quantify the secondary radiation dose in our neonatal high care unit in order to determine if additional protective measures from secondary radiation are necessary. Method: A prospective analytic study was undertaken using multiple thermoluminescent devices in a cubicle of a neonatal high care unit, and control dosimeters outside the unit. Dosimeters were deployed for a 4 week period. Simultaneously, data was collected on patient numbers, and the X-rays performed in the unit. Results were compared to reference ranges for primary and secondary radiation (2-3 mSv per annum). Results: The average secondary radiation dose was 0.108mGy (p=0.6553) over 4 weeks, less than the expected background radiation dose of 0.17 – 0.25mGy. There was a large number of patients moving through the unit during the study period (89), with an average of 14 patients in the unit at a time, however this did not result a large number of X-ray exposures. Twenty one percent of patients were in the unit for less than a day, and 49 % were admitted for less than 3 days. Sixteen patients (18%) had X-ray investigations, with a total of 21 investigations and 30 exposures. Thirty percent of primary radiation dose was due to repeat exposures. Patients receiving X-rays had an average of 2 X-ray examinations (range: 1 to 4 studies) performed, with an average Entrance Skin Dose of 196.7µSv (0.197mGy) – range 77 to 554µSv (0.077mGy to 0.554mGy). There was no statistically significant difference between weeks or zones (p=0.1060 and p=0.8237 respectively), and differences in primary radiation doses was likely due to chance. Conclusion: Additional measures to protect patients in the unit from secondary radiation are unnecessary. There was a low probability of patients having a radiological investigation in the neonatal high care unit, and secondary radiation doses were not measurably higher than background radiation. / TL (2019)

No description available.

No description available.