Le but de cette thèse est donc de mettre en œuvre la méthode µPEEC pour évaluer, sans avoir recours à des simulations ni à des mesures, la réluctance de circuits magnétiques simples en 2D et ce, afin de prédire leur comportement électromagnétique dès les phases de conception. Cela revient à chercher le champ créé par un brin conducteur rectiligne placé dans une fenêtre ronde ou rectangulaire de circuit magnétique comportant ou non un entrefer. Cette étude s'inscrit dans le cadre d'une recherche plus vaste, visant à élaborer le circuit équivalent de transformateurs, avant la réalisation de prototypes, afin d'optimiser ces composants au sein de leurs applications. Avant d'atteindre ce but, différentes étapes ont été franchies progressivement, en s'aidant de solutions analytiques et de simulations par éléments finis pour valider nos approches.

Cette étude propose une unification des formulations mono- et multi-moments de la distribution granulométrique des pluies (DSD pour " drop size distribution ") proposées dans la littérature dans le cadre des techniques de mise à l'échelle (scaling). On considère dans un premier temps que la DSD normalisée par la concentration en gouttes (Nt, moment d'ordre 0 de la DSD) peut s'écrire comme une fonction de densité de probabilité (ddp) du diamètre normalisé par un diamètre caractéristique (Dc). Cette ddp, notée g(x) avec x=D/Dc, aussi appelé distribution générale, semble être bien représentée par une loi gamma à deux paramètres. Le choix d'un diamètre caractéristique particulier, le rapport des moments d'ordre 4 et 3, conduit à une relation d'auto-consistance entre les paramètres de la fonction g(x). Deux méthodes différentes, fondées sur 3 moments particuliers de la DSD (M0, M3 et M4) ou bien sur des moments multiples (de M0 à M6) sont proposées pour l'estimation des paramètres et ensuite évaluées sur 3 ans d'observations de DSD recueillies à Alès dans le cadre de l'Observatoire Hydrométéorologique Méditerranéen Cévennes-Vivarais (OHMCV). Les résultats révèlent que: 1) les deux méthodes d'estimation des paramètres ont des performances équivalentes; 2) malgré la normalisation, une grande variabilité de la DSD est toujours observée dans le jeu de données mis à l'échelle. Ce dernier point semble résulter de la diversité des processus micro-physiques qui conditionnent la forme de la DSD.Cette formulation est ensuite adaptée pour une mise à l'échelle avec un ou deux moments de la DSD en introduisant des modèles en loi puissance entre des moments dits de référence (par exemple l'intensité de la pluie R et / ou le facteur de réflectivité radar Z) et les moments expliqués (concentration en gouttes Nt, diamètre caractéristique Dc). De manière analogue à la première partie du travail, deux méthodes sont proposées pour estimer des paramètres climatologiques des DSD mises à l'échelle par un ou deux DSD moment(s). Les résultats montrent que: 1) la méthode d'estimation a un impact significatif pour la formulation de mise à l'échelle par un seul moment; 2) le choix du moment de référence dépend des objectifs d'étude: par exemple, le modèle mis à l'échelle par des moments d'ordre élevé produit une bonne performance pour les grosses gouttes mais pas pour les petites; 3) l'utilisation de deux moments au lieu d'un seul améliore significativement la performance du modèle pour représenter les DSD.Notre modèle est ensuite appliqué pour analyser la variabilité inter- événementielle selon trois paramètres (Nt, Dc et μ, ce dernier paramètre µ décrivant la forme de la fonction gamma). Différentes séquences de pluie ont été identifiées de façon subjective pour l'événement pluvieux intense des 21-22 octobre 2008 par des changements brusques des moments et/ou paramètres dans les séries temporelles correspondantes. Ces phases de pluie sont liées à des processus météorologiques différents. Une relation préliminaire est établie entre les observations radar et la variation des paramètres des DSD au sol telle que mesurée par le disdromètre. Les formulations de mise à l'échelle sont également appliquées pour des estimations des densités de flux d'énergie cinétique des précipitations à partir de l'intensité de la pluie et / ou de la réflectivité radar. Les résultats confirment que l'utilisation de deux moments (R et Z) améliore significativement les performances de ces modèles, malgré les caractéristiques d'échantillonnage très différentes des radars et des pluviomètres. Cette application ouvre des perspectives intéressantes pour la spatialisation de l'énergie cinétique des pluies dans le cadre des études sur le pouvoir érosif des pluies.

Dans ce travail de thèse nous nous sommes intéressés principalement à la récupération de l'énergie mécanique et plus particulièrement l'énergie vibratoire. Cette technologie repose sur l'utilisation des transducteurs résonants, ces dispositifs permettent d'amplifier l'amplitude de vibration et donc de stocker d'avantage d'énergie mécanique dans le convertisseur à la résonance. La quantité de l'énergie en sortie du convertisseur chute lorsque la fréquence de vibration n'est plus égale à la fréquence de résonance, il est donc nécessaire d'assurer un asservissement de la fréquence de résonance de la structure de récupération d'énergie vibratoire sur la fréquence de vibration, si possible sur tout le spectre fréquentiel que couvre la source de vibration. L'objectif de la thèse est de proposer des solutions, à basse consommation, permettant d'assurer un ajustement dynamique en temps réel de la fréquence de résonance en fonction de la fréquence de vibration. Les travaux de cette thèse s'articulent autour de trois solutions : 1) Ajustement de la fréquence de résonance par application d'un champ électrique dans un matériau piézoélectrique 2) Ajustement de la fréquence de résonance par adaptation de la charge électrique d'un matériau piézoélectrique 3) Amplification du mouvement vibratoire par technique de rebond Une modélisation et optimisation à la fois de la plage de fréquence de fonctionnement et de la conversion mécano-électrique ont été réalisées. Trois structures ont été développées et testées et permettent de valider chacune des trois approches. Enfin, une électronique très basse consommation a été mise au point pour asservir en temps réel la fréquence de résonance sur la fréquence de la source de vibration et optimiser le taux d'énergie électrique extraite du système (pour maintenir un facteur de qualité de la structure optimum).

This study examined the energy dependence of cancer cells. Glucose was found to be their main energy source. It seems possible to use this dependence to advantage in the fight against cancer. A novel experiment to reduce the blood glucose supply and utilisation was proposed. It entailed caloric restriction, suppression of glucose secretion by the liver as well as suppression of stress hormones (which elevates glucose levels). This minimises the blood glucose value. As a last step, anti-insulin is provided to inhibit cancer cells to utilise the glucose. The cancer cells are thus deprived of their main energy source. This should lead to a reduction or elimination of tumours and will aid in preventing their development. Although feasible, this method turned out to be too expensive to perform the necessary clinical trials to prove the hypothesis. Next, the focus shifted to cancer prevention. The human energy system was analysed with the goal to reduce the circulating glucose level. The main focus here was metabolised CHO energy consumption. A previously proposed unit – the Equivalent Teaspoon Sugar, or ets , was used to quantify energy with. It was shown that cancer risk increases significantly when the recommended ets consumption per day is exceeded. Furthermore, it was shown that including fibre in a meal reduces the ets value of the meal. One gram of fibre leads to a reduction of around 0.6 ets . The link between exercise, stress, fibre, their resulting blood glucose levels and cancer were quantified in terms of ets . Exercise expends ets , while stress causes the liver to secrete more ets . Experimental data was analysed to confirm the relationships. In conclusion an equation was formulated to describe the combined effect of all these elements on the energy system. One’s total daily ets consumption can be obtained from the equation, and it was linked to one’s cancer risk. Adapting a lifestyle that ensures the correct daily ets intake will lead to a significant reduction in cancer risk. This study proved that cancer cells are very dependent on sugar and a restriction of this energy source forces them into regression. Using this knowledge to advantage may help in the combat one of the biggest killers of our time – cancer. / Thesis (Ph.D. (Electrical and Electronic Engineering))--North-West University, Potchefstroom Campus, 2012

Background: Modern culture has stereotyped the divine female body as one that is continually getting leaner, with the internalization of the “thin” ideal possibly resulting in body dissatisfaction, disturbances in body image and exploitation of extreme weight control measures. These shoddy eating behaviours/attitudes may involve body mass and figure anxiety, sub-optimal nutrition or insufficient energy intake (possibly even a combination of both) and use of pathogenic weight control measures (PWCM). Furthermore, low energy availability can be a consequence of disordered eating (DE) behaviour, but can also inadvertently emerge in the absence of clinical eating disorders, DE behaviours and/or restricted dietary intake. Various researchers have concluded that dancers are overly-concerned about dieting and their body mass, and tend to be discontented with their bodies. Every organ system in the body may potentially be negatively affected as a result of the ensuing undernourishment and/or weight loss related to poor nutritional behaviour. The aim of the study was to investigate the DE behaviour, PWCM use, body image and energy status of a group of University female dancers Methods: Fifty two volunteer (18-30 years) dancers (n=26) matched by controls (n=26) of the same race, and comparable age and body mass index were recruited. DE behaviour was assessed with the Eating disorder inventory-3 (EDI3), Cognitive dietary restraint (CDR) subscale of the Three-factor eating questionnaire (TFEQ) and EDI3 referral form (EDI3-RF) behavioural questions. Body image was assessed using the Body Silhouette Assessment Scale. Energy status was assessed using a 5-day weighed food record to measure energy intake and Actiheart® monitor to measure energy expenditure. Results: Dancers presented with significantly higher EDI3-Drive for thinness, EDI3-Body dissatisfaction and TFEQ-CDR raw subscale scores when compared to controls. Furthermore, the majority of dancers scored above the designated cut-off scores for the EDI3-Drive for thinness (46.2%), EDI3-Body dissatisfaction (61.5%), EDI-Bulimia (53.9%) and TFEQ-CDR (52.0%) subscales. Bingeing was the most common PWCM used by both dancers and controls (19.2% vs. 23.1%), followed by weight loss ≥ 9kg within the preceding 6 months (11.5% vs. 15.4%). Vomiting (7.7%), laxatives (11.5%) and excessive exercise (19.2%) for weight loss were used only by the dancers. Current body weight was significantly different to desired body weight for the dancers only (p=0.0004). The discrepancy between current and ideal body image, also termed Feel Minus Ideal Discrepancy (FID), was significantly different between dancers and controls, and indicated that controls were content with their body silhouette while dancers were inclined to want to lose weight. A negative energy balance was found in 80.8% of both dancers and controls. The energy availability of 48.0% of dancers and 52.0% of controls was between 30 and 45 kcal/kg fat-free mass/day. A total of 65.4% of dancers and 38.5% of controls reported to be currently trying to lose weight. Conclusion: Irrespective of the limitations of this study, noteworthy observations were made pertaining to the DE behaviour, body image, and energy status of a group of South African student women dancers. This group of South African university women dancers were vulnerable to DE behaviour, had a propensity to be greatly displeased with their body image, and possessed a low energy status possibly because they were trying to lose weight. / Thesis (MSc (Nutrition))--North-West University, Potchefstroom Campus, 2013.

Obesity is affecting an increasingly larger proportion of adolescents in the world, and this can be attributed to low resting metabolic rate (RMR) as well as reduced physical activity (PA) levels. Little is known about objectively determined habitual PA and RMR in 16 year old African adolescents. The purpose of this study is twofold. Firstly, to determine the objectively measured PA status of adolescents and secondly, to determine the relationship that exists between RMR and PA in 16 year old adolescents. Two hundred and twenty six (226) adolescents aged sixteen (16) wore the Actiheart® monitor, combined accelerometry and heart rate for seven (7) consecutive days. Six high schools were recruited to take part in the study: two from town (high socio-economic status) and four from the township (low socio-economic status) of the Potchefstroom area of the North West Province of South Africa. Times spent in moderate to vigorous physical activity, physical activity counts per minute (CPM), total energy expenditure (TEE), active energy expenditure (AEE) and physical activity levels (PAL) were assessed using the Actiheart®. The participants’ RMR was measured by indirect calorimetry using the Fitmate Pro (Cosmed, Italy). All data analyses were performed with the SPSS Version 20 software (IBM SPSS, II). The descriptive statistics (mean and standard deviations) as well as independent t-tests and Mann-Whitney U test were performed to determine differences between ethnicity and genders and to calculate practical significance. A Type I error rate of p ≤ 0.05 was used for statistical significance. To investigate the relationship between RMR and physical activity regression analysis was performed with adjustment for gender, race and fat free mass. Results: Significantly higher PAL (1.57 ± 0.15) were determined in girls compared to boys (PAL = 1.41 ± 0.10). Black adolescents indicated significant higher PAL (1.53 ± 0.14) compared to white adolescents (1.45 ± 0.16). On average, regardless of race or gender, the participants were more active on weekdays than weekends. The current study shows that girls spent more minutes/day in moderate to vigorous physical activity (MVPA) than the boys. The results show that 16.4% of the study sample was either overweight or obese. After adjustment for gender, ethnicity and FFM, linear regression between RMR and moderate-to-vigorous PA yielded an r2 = 0.46 (p ˂ 0.05.) Conclusion: Objectively determined PA of adolescents in South Africa indicates that only one third of adolescents are meeting the recommended 60 minutes of daily MVPA. Gender and race specific interventions are needed to increase habitual physical activity levels in adolescents. Given the fact that the studied sample did not meet recommended daily physical activity and the adverse effect of inactivity and chronic diseases of life style, urgent strategies to inculcate the culture of regular physical activity as a preventative measure of chronic diseases of life style are needed. Behaviour that is carried on into adulthood is established during adolescence. Civic health efforts should focus on encouraging adolescent involvement in regular moderate-to-vigorous PA, which will subsequently increase RMR and lower the risk of the development of non-communicable chronic diseases such as obesity. Further local research is needed to confirm the association between RMR and PA in the local population. / Thesis (MSc (Biokinetics))--North-West University, Potchefstroom Campus, 2013.

This study examined the energy dependence of cancer cells. Glucose was found to be their main energy source. It seems possible to use this dependence to advantage in the fight against cancer. A novel experiment to reduce the blood glucose supply and utilisation was proposed. It entailed caloric restriction, suppression of glucose secretion by the liver as well as suppression of stress hormones (which elevates glucose levels). This minimises the blood glucose value. As a last step, anti-insulin is provided to inhibit cancer cells to utilise the glucose. The cancer cells are thus deprived of their main energy source. This should lead to a reduction or elimination of tumours and will aid in preventing their development. Although feasible, this method turned out to be too expensive to perform the necessary clinical trials to prove the hypothesis. Next, the focus shifted to cancer prevention. The human energy system was analysed with the goal to reduce the circulating glucose level. The main focus here was metabolised CHO energy consumption. A previously proposed unit – the Equivalent Teaspoon Sugar, or ets , was used to quantify energy with. It was shown that cancer risk increases significantly when the recommended ets consumption per day is exceeded. Furthermore, it was shown that including fibre in a meal reduces the ets value of the meal. One gram of fibre leads to a reduction of around 0.6 ets . The link between exercise, stress, fibre, their resulting blood glucose levels and cancer were quantified in terms of ets . Exercise expends ets , while stress causes the liver to secrete more ets . Experimental data was analysed to confirm the relationships. In conclusion an equation was formulated to describe the combined effect of all these elements on the energy system. One’s total daily ets consumption can be obtained from the equation, and it was linked to one’s cancer risk. Adapting a lifestyle that ensures the correct daily ets intake will lead to a significant reduction in cancer risk. This study proved that cancer cells are very dependent on sugar and a restriction of this energy source forces them into regression. Using this knowledge to advantage may help in the combat one of the biggest killers of our time – cancer. / Thesis (Ph.D. (Electrical and Electronic Engineering))--North-West University, Potchefstroom Campus, 2012

Background: Modern culture has stereotyped the divine female body as one that is continually getting leaner, with the internalization of the “thin” ideal possibly resulting in body dissatisfaction, disturbances in body image and exploitation of extreme weight control measures. These shoddy eating behaviours/attitudes may involve body mass and figure anxiety, sub-optimal nutrition or insufficient energy intake (possibly even a combination of both) and use of pathogenic weight control measures (PWCM). Furthermore, low energy availability can be a consequence of disordered eating (DE) behaviour, but can also inadvertently emerge in the absence of clinical eating disorders, DE behaviours and/or restricted dietary intake. Various researchers have concluded that dancers are overly-concerned about dieting and their body mass, and tend to be discontented with their bodies. Every organ system in the body may potentially be negatively affected as a result of the ensuing undernourishment and/or weight loss related to poor nutritional behaviour. The aim of the study was to investigate the DE behaviour, PWCM use, body image and energy status of a group of University female dancers Methods: Fifty two volunteer (18-30 years) dancers (n=26) matched by controls (n=26) of the same race, and comparable age and body mass index were recruited. DE behaviour was assessed with the Eating disorder inventory-3 (EDI3), Cognitive dietary restraint (CDR) subscale of the Three-factor eating questionnaire (TFEQ) and EDI3 referral form (EDI3-RF) behavioural questions. Body image was assessed using the Body Silhouette Assessment Scale. Energy status was assessed using a 5-day weighed food record to measure energy intake and Actiheart® monitor to measure energy expenditure. Results: Dancers presented with significantly higher EDI3-Drive for thinness, EDI3-Body dissatisfaction and TFEQ-CDR raw subscale scores when compared to controls. Furthermore, the majority of dancers scored above the designated cut-off scores for the EDI3-Drive for thinness (46.2%), EDI3-Body dissatisfaction (61.5%), EDI-Bulimia (53.9%) and TFEQ-CDR (52.0%) subscales. Bingeing was the most common PWCM used by both dancers and controls (19.2% vs. 23.1%), followed by weight loss ≥ 9kg within the preceding 6 months (11.5% vs. 15.4%). Vomiting (7.7%), laxatives (11.5%) and excessive exercise (19.2%) for weight loss were used only by the dancers. Current body weight was significantly different to desired body weight for the dancers only (p=0.0004). The discrepancy between current and ideal body image, also termed Feel Minus Ideal Discrepancy (FID), was significantly different between dancers and controls, and indicated that controls were content with their body silhouette while dancers were inclined to want to lose weight. A negative energy balance was found in 80.8% of both dancers and controls. The energy availability of 48.0% of dancers and 52.0% of controls was between 30 and 45 kcal/kg fat-free mass/day. A total of 65.4% of dancers and 38.5% of controls reported to be currently trying to lose weight. Conclusion: Irrespective of the limitations of this study, noteworthy observations were made pertaining to the DE behaviour, body image, and energy status of a group of South African student women dancers. This group of South African university women dancers were vulnerable to DE behaviour, had a propensity to be greatly displeased with their body image, and possessed a low energy status possibly because they were trying to lose weight. / Thesis (MSc (Nutrition))--North-West University, Potchefstroom Campus, 2013.

Obesity is affecting an increasingly larger proportion of adolescents in the world, and this can be attributed to low resting metabolic rate (RMR) as well as reduced physical activity (PA) levels. Little is known about objectively determined habitual PA and RMR in 16 year old African adolescents. The purpose of this study is twofold. Firstly, to determine the objectively measured PA status of adolescents and secondly, to determine the relationship that exists between RMR and PA in 16 year old adolescents. Two hundred and twenty six (226) adolescents aged sixteen (16) wore the Actiheart® monitor, combined accelerometry and heart rate for seven (7) consecutive days. Six high schools were recruited to take part in the study: two from town (high socio-economic status) and four from the township (low socio-economic status) of the Potchefstroom area of the North West Province of South Africa. Times spent in moderate to vigorous physical activity, physical activity counts per minute (CPM), total energy expenditure (TEE), active energy expenditure (AEE) and physical activity levels (PAL) were assessed using the Actiheart®. The participants’ RMR was measured by indirect calorimetry using the Fitmate Pro (Cosmed, Italy). All data analyses were performed with the SPSS Version 20 software (IBM SPSS, II). The descriptive statistics (mean and standard deviations) as well as independent t-tests and Mann-Whitney U test were performed to determine differences between ethnicity and genders and to calculate practical significance. A Type I error rate of p ≤ 0.05 was used for statistical significance. To investigate the relationship between RMR and physical activity regression analysis was performed with adjustment for gender, race and fat free mass. Results: Significantly higher PAL (1.57 ± 0.15) were determined in girls compared to boys (PAL = 1.41 ± 0.10). Black adolescents indicated significant higher PAL (1.53 ± 0.14) compared to white adolescents (1.45 ± 0.16). On average, regardless of race or gender, the participants were more active on weekdays than weekends. The current study shows that girls spent more minutes/day in moderate to vigorous physical activity (MVPA) than the boys. The results show that 16.4% of the study sample was either overweight or obese. After adjustment for gender, ethnicity and FFM, linear regression between RMR and moderate-to-vigorous PA yielded an r2 = 0.46 (p ˂ 0.05.) Conclusion: Objectively determined PA of adolescents in South Africa indicates that only one third of adolescents are meeting the recommended 60 minutes of daily MVPA. Gender and race specific interventions are needed to increase habitual physical activity levels in adolescents. Given the fact that the studied sample did not meet recommended daily physical activity and the adverse effect of inactivity and chronic diseases of life style, urgent strategies to inculcate the culture of regular physical activity as a preventative measure of chronic diseases of life style are needed. Behaviour that is carried on into adulthood is established during adolescence. Civic health efforts should focus on encouraging adolescent involvement in regular moderate-to-vigorous PA, which will subsequently increase RMR and lower the risk of the development of non-communicable chronic diseases such as obesity. Further local research is needed to confirm the association between RMR and PA in the local population. / Thesis (MSc (Biokinetics))--North-West University, Potchefstroom Campus, 2013.

In order to be sustainable, companies have to adapt in the ever–changing market and economic conditions which are often unpredictable. The adaptation to these challenges rests with employees who have to stay motivated and psychologically well. The environmental working conditions are often undesirable The objective of this study was to evaluate the psychometric performance of the Utrecht Work Engagement Scale (UWES) and the Oldenburg Burnout inventory (OLBI) within the cement factory. A random sampling approach was adopted by distributing a questionnaire for the purposes of achieving the general research objective with an availability sample (N = 187). The UWES and OLBI were administered. Exploratory factor analysis, descriptive statistics, Cronbach alpha coefficients, Pearson product–moment correlations and MANOVA's were used to analyse the data. The outcome of the study through literature review confirmed that work engagement and burnout are two important components of employee wellbeing. The factor loadings of the UWES and OLBI resulted in a two–factor structure for both the UWES and OLBI. The two factor structure for the UWES were labelled as Vigour/Dedication and Absorption. The twofactor structure for the OLBI was labelled Disengagement and Exhaustion. A small number of items were retained for the OLBI. The internal consistency of the UWES was found to be well above the acceptable level with the alpha coefficients exceeding 0,70. The internal consistency for the OLBI was found to be lower than the 0,70 level. Data analysis further showed that correlations between engagement and burnout were statistically insignificant. Data analysis also showed that there were no vi significant differences for age and gender for both engagement and burnout, however there is a significant difference in race and language with regard to engagement but none for burnout. Limitations within the study were identified and recommendations for future research were made. / Thesis (M.A. (Industrial Psychology))--North-West University, Potchefstroom Campus, 2011.