Mask Projection Microstereolithography (MPSLA) is an additive manufacturing process capable for fabricating true three-dimensional microparts and hence, holds promise as a potential micro-fabrication process for micro-machine components. With only a few MPSLA systems developed and studied so far, the research in this field is inchoate and experimental in nature. The process of curing a micropart using an MPSLA system has not been analytically modeled and no literature on process planning for MPSLA is available. In order to employ the MPSLA technology for microfabrication, it is necessary to model its part building process and formulate a process planning method to cure dimensionally accurate microparts. As a part of this thesis, an MPSLA system is designed and assembled. The process of curing a single layer using this system is analytically modeled as the Layer cure model. The Layer cure model is formulated in two steps. First, the irradiance received by the resin surface is modeled as a function of the system parameters (Irradiance model). Then, the resin used in the system is characterized to experimentally determine its working curve. The Irradiance model and the resin characterization enable us to compute the dimensions of any layer cured using our MPSLA system in terms of the process parameters. The Layer cure model has been validated by curing test layers on our system. Finally, the Layer cure model has been inverted to formulate a process planning method to cure layers of the required dimensions. Using this process planning method, it is possible to cure layers within a dimensional error of 3%.

Obesity and physical inactivity (PI) are major health problems world-wide, and leading contributors to the high incidence of overweight, cardiovascular and metabolic diseases in children both globally and in South Africa in particular. Despite the importance of physical activity (PA), health-related physical fitness (HRPF) and body composition to health, very few studies have investigated the longitudinal relationship between these variables in children. Three articles based on this research were written in which a total of 283 adolescent learners (111 boys and 172 girls) with a mean age of 14.90±0.72 years from the Physical Activity and Health Longitudinal Study (PAHLS) participated. The students’ physical characteristics were measured using the protocol of the International Society for the Advancement of Kinanthropometry (ISAK); the EUROFIT test protocol and International Physical Activity Questionnaire (IPAQ) were used to assess the children’s HRPF and PA levels, respectively. In the first article, the results showed that girls had a slightly higher significant BMI (21.43±4.37 kg/m²) than the boys (20.01±3.71kg/m²) (p=0.002), and were substantially more overweight (32.4%) and fatter (%body fat=26.01±8.51) than the boys (17.1%)). A total of 85 (30%), 78 (27.5%) and 88 (31.1%) of the students had low, moderate and high PA involvement. It was concluded that girls were more overweight and less active than boys. The second article examined the relationships between body composition, health-related fitness and PA. Inverse relationships were found between BMI and the health-related fitness items of SBJ and BAH. Furthermore, BMI negatively associated with SAR and endurance performance, especially in girls. Percentage body fat was negatively related to SBJ, BAH, SAR and endurance performance. The aim of the third article was to evaluate the longitudinal development of HRPF, anthropometry and body composition status among the children. Regression coefficients showed that changes in BMI were inversely associated with those in health-related physical fitness. The changes in %BF were negatively associated with SBJ, BAH and aerobic capacity (VO2max) in the boys and girls. The results also yielded a low significantly positive association between changes in WHtR and SBJ in both genders, while low inverse associations were found between WHtR and BAH in girls, and VO2max in both genders. It is concluded that the incidence of overweight and PI was especially high in girls and excessive fatness negatively affected the girls’ fitness performances. Changes in BMI, % body fat and WHtR were negatively related with the children’s strength and running performances, especially among the girls in which the relative increase in overweight negatively affected their endurance running and static strength performances. In view of the health implications of the findings, it is necessary to create an enabling environment and opportunities to promote physically active lifestyles and develop life-long positive attitudes towards PA among students. Community-based strategies targeted at facilitating sustainable PA intervention programmes in schools are recommended. / PhD (Human Movement Science), North-West University, Potchefstroom Campus, 2014

Obesity and physical inactivity (PI) are major health problems world-wide, and leading contributors to the high incidence of overweight, cardiovascular and metabolic diseases in children both globally and in South Africa in particular. Despite the importance of physical activity (PA), health-related physical fitness (HRPF) and body composition to health, very few studies have investigated the longitudinal relationship between these variables in children. Three articles based on this research were written in which a total of 283 adolescent learners (111 boys and 172 girls) with a mean age of 14.90±0.72 years from the Physical Activity and Health Longitudinal Study (PAHLS) participated. The students’ physical characteristics were measured using the protocol of the International Society for the Advancement of Kinanthropometry (ISAK); the EUROFIT test protocol and International Physical Activity Questionnaire (IPAQ) were used to assess the children’s HRPF and PA levels, respectively. In the first article, the results showed that girls had a slightly higher significant BMI (21.43±4.37 kg/m²) than the boys (20.01±3.71kg/m²) (p=0.002), and were substantially more overweight (32.4%) and fatter (%body fat=26.01±8.51) than the boys (17.1%)). A total of 85 (30%), 78 (27.5%) and 88 (31.1%) of the students had low, moderate and high PA involvement. It was concluded that girls were more overweight and less active than boys. The second article examined the relationships between body composition, health-related fitness and PA. Inverse relationships were found between BMI and the health-related fitness items of SBJ and BAH. Furthermore, BMI negatively associated with SAR and endurance performance, especially in girls. Percentage body fat was negatively related to SBJ, BAH, SAR and endurance performance. The aim of the third article was to evaluate the longitudinal development of HRPF, anthropometry and body composition status among the children. Regression coefficients showed that changes in BMI were inversely associated with those in health-related physical fitness. The changes in %BF were negatively associated with SBJ, BAH and aerobic capacity (VO2max) in the boys and girls. The results also yielded a low significantly positive association between changes in WHtR and SBJ in both genders, while low inverse associations were found between WHtR and BAH in girls, and VO2max in both genders. It is concluded that the incidence of overweight and PI was especially high in girls and excessive fatness negatively affected the girls’ fitness performances. Changes in BMI, % body fat and WHtR were negatively related with the children’s strength and running performances, especially among the girls in which the relative increase in overweight negatively affected their endurance running and static strength performances. In view of the health implications of the findings, it is necessary to create an enabling environment and opportunities to promote physically active lifestyles and develop life-long positive attitudes towards PA among students. Community-based strategies targeted at facilitating sustainable PA intervention programmes in schools are recommended. / PhD (Human Movement Science), North-West University, Potchefstroom Campus, 2014

There are unique cases when designing products where a prototype is required to demonstrate critical operations of a system or subsystem such that it will serve as a basis for how the design will move forward. These prototypes are oftentimes on the critical design path. Due to the fact there is typically some aspect of a prototype that is not well understood there can be a considerable amount of uncertainty associated with the amount of resources needed to design such a prototype. The goal of this thesis is to address how to systematically reduce uncertainty for the purpose of creating a robust cost estimate. This statement does highlight the problem of defining what a robust estimate is, which results in addressing the key question driving this research: "When is enough information gathered to generate a robust estimate for the design of prototype systems?" The crux of the problem lies in how to characterize the interactions and uncertainty associated with cost, schedule, and performance. Additionally, the breakdown of a prototype system into its subsystems results in errors exist at each division. The result is a cost estimation method that has been generated by leveraging the principles of design methodology. Two test cases are applied including one theoretical model, and one project from the Georgia Tech Research Institute (GTRI). The GTRI project was work performed for the Georgia Department of Transportation related to the filling of cracks on asphalt road surfaces. These examples are evaluated from the view point of the Validation Square in order to verify the effectiveness beyond example problems.

Obesity in children and adolescents is on the rise and is a major risk factor for chronic disease, thus posing one of the greatest public health challenges for the 21st century. Although adolescent obesity is increasing in all ethnic groups, its prevalence is higher in non–Caucasian populations. A possible explanation for ethnic differences in the development of obesity could be ethnic differences in resting metabolic rate (RMR). A low RMR would pre–dispose an ethnic group to obesity. In South Africa limited research has been published with regards to body composition (BC) and RMR in adolescents and the possible association of RMR with BC. The first aim of this study, therefore, was to determine differences in BC and RMR between 14 year old black and Caucasian South African adolescents from the Tlokwe municipality of the North West Province, South– Africa. The second aim was to investigate whether significant relationships between the body composition characteristics body mass index (BMI), percentage body fat (%BF), fat free mass (FFM) and RMR exist in this group. The baseline data of participants in the Physical Activity and Health Longitudinal Study (PAHLS) was used. Anthropometric measurements included stature, body mass, triceps and subscapular skinfolds, and waist girth to determine BMI, %BF, FFM and waist–to–height ratio (WHTR). RMR was measured by the FitMate Pro Indirect Calorimetry (Cosmed). An independent t–test was used to compare the two groups (black vs. Caucasian, boys and girls respectively) with regards to body composition and RMR. Pearson correlation coefficients (adjusted for gender and ethnicity) were calculated, to study the relationship between RMR and body composition. Significant difference levels were set at p<0.05. The present cross–sectional results revealed significant differences in BC and RMR in black and Caucasian adolescents of the Tlokwe municipality, with Caucasian adolescents of both genders having a higher RMR and FFM compared to their counterpart black adolescents. The results further indicated that Caucasian adolescents were significantly (p<0.05) taller, heavier and had a higher %BF, WHTR, FFM and RMR than the black adolescents of both genders. Boys of both ethnicities had a higher RMR than the girls, with black girls having the lowest RMR. Both underweight and overweight/obesity were present in both ethnic groups and genders emphasizing the double burden of disease prevalent in South Africa. The overweight/obese group of both ethnicities had a higher FFM and RMR than the normal and underweight group. After adjusting for gender and ethnicity a high non–significant negative relationship was observed between RMR and FFM in the overweight group. The reasons for these persistent differences in ethnic groups for RMR in adolescents are not clear. A positive association between anthropometric indicators of BC and RMR influenced by gender and ethnicity was indicated. Whether the observed ethnic differences in RMR predict future weight gain and obesity awaits the results of longitudinal analyses. It is suggested that intervention programmes be implemented focusing on the prevention of obesity in adolescents, but especially black adolescent girls, as they are indicated to be the group more prone to obesity. These results supported the literature findings and identified the need for longitudinal data regarding RMR and BC in adolescents. The PAHL–Study will continue to follow–up these adolescents over a period of time as some of the conclusions made will further be cleared, including whether the observed ethnic differences in RMR predict future weight gain and obesity. / Thesis (M.Sc. (Biokinetics))--North-West University, Potchefstroom Campus, 2012.

Obesity in children and adolescents is on the rise and is a major risk factor for chronic disease, thus posing one of the greatest public health challenges for the 21st century. Although adolescent obesity is increasing in all ethnic groups, its prevalence is higher in non–Caucasian populations. A possible explanation for ethnic differences in the development of obesity could be ethnic differences in resting metabolic rate (RMR). A low RMR would pre–dispose an ethnic group to obesity. In South Africa limited research has been published with regards to body composition (BC) and RMR in adolescents and the possible association of RMR with BC. The first aim of this study, therefore, was to determine differences in BC and RMR between 14 year old black and Caucasian South African adolescents from the Tlokwe municipality of the North West Province, South– Africa. The second aim was to investigate whether significant relationships between the body composition characteristics body mass index (BMI), percentage body fat (%BF), fat free mass (FFM) and RMR exist in this group. The baseline data of participants in the Physical Activity and Health Longitudinal Study (PAHLS) was used. Anthropometric measurements included stature, body mass, triceps and subscapular skinfolds, and waist girth to determine BMI, %BF, FFM and waist–to–height ratio (WHTR). RMR was measured by the FitMate Pro Indirect Calorimetry (Cosmed). An independent t–test was used to compare the two groups (black vs. Caucasian, boys and girls respectively) with regards to body composition and RMR. Pearson correlation coefficients (adjusted for gender and ethnicity) were calculated, to study the relationship between RMR and body composition. Significant difference levels were set at p<0.05. The present cross–sectional results revealed significant differences in BC and RMR in black and Caucasian adolescents of the Tlokwe municipality, with Caucasian adolescents of both genders having a higher RMR and FFM compared to their counterpart black adolescents. The results further indicated that Caucasian adolescents were significantly (p<0.05) taller, heavier and had a higher %BF, WHTR, FFM and RMR than the black adolescents of both genders. Boys of both ethnicities had a higher RMR than the girls, with black girls having the lowest RMR. Both underweight and overweight/obesity were present in both ethnic groups and genders emphasizing the double burden of disease prevalent in South Africa. The overweight/obese group of both ethnicities had a higher FFM and RMR than the normal and underweight group. After adjusting for gender and ethnicity a high non–significant negative relationship was observed between RMR and FFM in the overweight group. The reasons for these persistent differences in ethnic groups for RMR in adolescents are not clear. A positive association between anthropometric indicators of BC and RMR influenced by gender and ethnicity was indicated. Whether the observed ethnic differences in RMR predict future weight gain and obesity awaits the results of longitudinal analyses. It is suggested that intervention programmes be implemented focusing on the prevention of obesity in adolescents, but especially black adolescent girls, as they are indicated to be the group more prone to obesity. These results supported the literature findings and identified the need for longitudinal data regarding RMR and BC in adolescents. The PAHL–Study will continue to follow–up these adolescents over a period of time as some of the conclusions made will further be cleared, including whether the observed ethnic differences in RMR predict future weight gain and obesity. / Thesis (M.Sc. (Biokinetics))--North-West University, Potchefstroom Campus, 2012.