L’amélioration des matériaux et des technologies de lentilles de contact a permis le recours de plus en plus fréquent à un type de lentille de contact à grand diamètre reposant sur la sclère : la lentille sclérale (SL). Celle-ci est majoritairement utilisée pour la réadaptation visuelle de patient vivant avec divers types de déformations cornéennes, mais également pour le traitement de maladie de surface oculaire et la correction optique de la simple erreur de réfraction lorsque les autres modalités de lentilles ne peuvent être tolérées. Ce mémoire a pour objectif d’évaluer l’influence de l’asphéricité des surfaces antérieure (ASA) et postérieure (ASP) sur la performance visuelle d’un porteur de SL chez deux groupes distincts : une cohorte de 12 participants sans anomalie cornéenne et une cohorte de 9 participants ayant un diagnostic de kératocône (KC). Lors de l’expérience, quatre différentes SL ayant différents profils d’asphéricité ont été étudiées sur l’œil droit seulement. Pour chaque SL, les mesures d’acuité visuelle à haut contraste (AVHC), l’acuité visuelle à bas contraste (AVHC) et les valeurs moyennes quadratiques (root-mean-square ou RMS) des différents coefficients d’aberrations d’ordres supérieurs (AOS) ont été compilées pour chacun de ces designs aux diamètres pupillaires 3, 4, 5 et 6 mm. Les résultats obtenus suggèrent que l’augmentation de l’ASA d’une SL portée à l’œil droit génère une augmentation de l’aberration sphérique négative, de la coma verticale et horizontale négative chez les deux groupes. L’augmentation de l’ASA entraîne toutefois une augmentation de l’AOS totale et du trèfle total chez les participants sans anomalie cornéenne. Chez le groupe de participants atteint de KC, l’augmentation de l’ASA entraîne une diminution non significative des AOS totales et une augmentation non significative de l’aberration trèfle total. Bien que des études supplémentaires soient nécessaires pour bien comprendre l’influence de l’asphéricité sur les AOS chez les participants atteints de KC, la manipulation de celle-ci permettrait de réduire l’amplitude de certains types d’AOS dans certains cas particuliers. / Improvements in materials and technology have led to the increased use of a large diameter contact lens that rests on the sclera: the scleral lens (SL). These lenses are mainly used for visual rehabilitation of patients with various types of corneal ectasia, for the treatment of ocular surface disease and also for the optical correction of simple refractive error when other lens modalities are not tolerated. The purpose of this dissertation is to evaluate the influence of anterior surface asphericity (ASA) and posterior surface asphericity (ASP) on the visual performance of a SL wearer in two distinct groups: a cohort of 12 participants with no corneal abnormalities and a cohort of 9 participants with a diagnosis of keratoconus (KC). Four different SLs with different aspheric profiles were studied on the right eye only. For each SL, high-contrast visual acuity (HCVA), low contrast visual acuity (LCVA) measurements were measured. The root-mean-square (RMS) values of the higher-order aberration (HOA) Zernike coefficients were also measured for each of these designs for a pupil diameter of 3, 4, 5 and 6 mm. The results of this study suggest that increasing the anterior asphericity of a SL worn on the right eye generates an increase in negative spherical aberration, negative vertical and horizontal coma in both groups. Increasing anterior asphericity leads to an increase in total HOA and total trefoil in participants without corneal anomalies. In the group of participants with KC, increasing asphericity results in a non-significant decrease in total HOA and a non-significant increase in total trefoil aberration. Although additional studies are needed to understand the influence of asphericity on HOA in participants with KC, the manipulation of the anterior asphericity could reduce the amplitude of some types of HOA in some cases.

The research topic is: Tools for the revision of a maintenance strategy for an explosives manufacturing plant, using asset management principles. This research has specific reference to the SASOL Prillan plant based in SASOL, Sasolburg. The purpose of this research is to identify tools for the revision of a maintenance strategy for an explosives manufacturing plant, using asset management principles. These tools must be aimed to increase the proactive work capacity index, Figure 3, and to identify and/or develop tools that can be used by the engineering team of this explosives manufacturing plant to increase equipment reliability and performance. In this research assets include people. The meaning and application of asset management principles were researched and the tools needed to combine existing efforts and future needs are discussed. The human element to ensure the successful implementation of an asset management culture was researched and attributes of leaders and a change model is presented. This research was done into the wider engineering management discipline and not only maintenance. The method used to gather data was by means of interviews of a sample group within this organization. As this manufacturing unit makes use of subject matter experts, these support functions and plant personnel that were not interviewed, were issued with questionnaires to ensure that the sample group is a fair representation of the total manufacturing facility. To obtain a holistic view of potential shortcomings within the current maintenance strategy, all disciplines and levels within this operation were interviewed and commonalities of various asset management models were determined and used to define existing problem areas. This data was used to determine statistical correlations. The case study presented in Chapter 1 indicates that there is a case for change that can improve the proactive work capacity index of the engineering team. The results of this research confirm that there is in fact a real requirement to increase spares accuracy, improve on technical training as well as a need to establish visual performance indicators (dashboard) to measure overall equipment efficiency with the goal toTools for the revision of a maintenance strategy for an explosives manufacturing plant, using asset management principles increase equipment reliability and performance. The technical training referred to in this research reflects on training of people on equipment after investment in new technology. The current spares holding strategy is lacking equipment description accuracy. Furthermore, it is recommended that the implementation of career paths and development plans for individuals must be developed to create an environment of learning. The use of user status information captured on the computerized maintenance management system (SAP R/3) can add to the management of works orders and indicate where the focus must be to complete overdue work orders. Open work orders should be used to manage expenditure, to measure planning efficiency and to manage the cash flow of the business. The use of overall equipment efficiency and engineering efficiency measures is recommended and must be visually displayed on a “dashboard”. It was recommended that the engineering and operations personnel of this manufacturing plant be trained in asset management principles and that balanced scorecards are developed to ensure that the strategies of the various departments are aligned with the business strategy. Diagram 1 best illustrates the thinking and process flow of this research. The flow diagram shows five distinct stages and the appropriate objectives and/ or elements that were considered. The dissertation is also structured in this manner. All abbreviations, acronyms and definitions used in this document were listed in APPENDIX B / Thesis (M.Ing. (Development and Management Engineering))--North-West University, Potchefstroom Campus, 2009.

The research topic is: Tools for the revision of a maintenance strategy for an explosives manufacturing plant, using asset management principles. This research has specific reference to the SASOL Prillan plant based in SASOL, Sasolburg. The purpose of this research is to identify tools for the revision of a maintenance strategy for an explosives manufacturing plant, using asset management principles. These tools must be aimed to increase the proactive work capacity index, Figure 3, and to identify and/or develop tools that can be used by the engineering team of this explosives manufacturing plant to increase equipment reliability and performance. In this research assets include people. The meaning and application of asset management principles were researched and the tools needed to combine existing efforts and future needs are discussed. The human element to ensure the successful implementation of an asset management culture was researched and attributes of leaders and a change model is presented. This research was done into the wider engineering management discipline and not only maintenance. The method used to gather data was by means of interviews of a sample group within this organization. As this manufacturing unit makes use of subject matter experts, these support functions and plant personnel that were not interviewed, were issued with questionnaires to ensure that the sample group is a fair representation of the total manufacturing facility. To obtain a holistic view of potential shortcomings within the current maintenance strategy, all disciplines and levels within this operation were interviewed and commonalities of various asset management models were determined and used to define existing problem areas. This data was used to determine statistical correlations. The case study presented in Chapter 1 indicates that there is a case for change that can improve the proactive work capacity index of the engineering team. The results of this research confirm that there is in fact a real requirement to increase spares accuracy, improve on technical training as well as a need to establish visual performance indicators (dashboard) to measure overall equipment efficiency with the goal toTools for the revision of a maintenance strategy for an explosives manufacturing plant, using asset management principles increase equipment reliability and performance. The technical training referred to in this research reflects on training of people on equipment after investment in new technology. The current spares holding strategy is lacking equipment description accuracy. Furthermore, it is recommended that the implementation of career paths and development plans for individuals must be developed to create an environment of learning. The use of user status information captured on the computerized maintenance management system (SAP R/3) can add to the management of works orders and indicate where the focus must be to complete overdue work orders. Open work orders should be used to manage expenditure, to measure planning efficiency and to manage the cash flow of the business. The use of overall equipment efficiency and engineering efficiency measures is recommended and must be visually displayed on a “dashboard”. It was recommended that the engineering and operations personnel of this manufacturing plant be trained in asset management principles and that balanced scorecards are developed to ensure that the strategies of the various departments are aligned with the business strategy. Diagram 1 best illustrates the thinking and process flow of this research. The flow diagram shows five distinct stages and the appropriate objectives and/ or elements that were considered. The dissertation is also structured in this manner. All abbreviations, acronyms and definitions used in this document were listed in APPENDIX B / Thesis (M.Ing. (Development and Management Engineering))--North-West University, Potchefstroom Campus, 2009.

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