Le développement de matériaux piézoélectriques innovants pour la réalisation de transducteurs, de capteurs ou d'actionnneurs nécessite la mise en oeuvre de dispositifs de caractérisation performants. Dans ce contexte, ce document propose des méthodes de modélisation de la propagation d'ondes ultrasonores dans des structures multicouches ou a gradients continus de propriétés. Au préalable, deux méthodes de caractérisation, ont été exposées et appliquées à des céramiques de type PZT. L'une d'entre elle, appelée méthode de spectroscopie de transmission, utilise une mise en forme matricielle de l'équation de propagation des ondes accoustiques. Cette formulation analytique facilite la résolution de l'équation de propagation, et permet également une représentation des phénomènes de transmissions d'ondes à travers une structure. La validité de ces modèles est clairement établie à travers des hétérostructures piézoélectriques. / The developpement of innovative piezoelectric materials for achievement of transducers, sensors or actuators requires the implementation of hight performance of characterization method. In this context, this document proposes two methods modeling the ultrasonic wave propagation in multilayered structures and continutes graded materials. Prior, two models of characterizations were presented and applied for PZT ceramics. They use a matrix formalism of the equation of accoustic waves. This analytical formulation facilitates the resolution of the propagation equation of propagation, and facilitate the representation of the phenomena of wave transmission through a structure. The validity of these models is clearly established through comparisons of results from finite element and measurement in piezoelectric heterostructures.

La notion du développement de l’Afrique est essentiellement liée à son histoire, et particulièrement à celle des indépendances. Les peuples d’Afrique espéraient que l’accession à l’indépendance politique, allait suivre une indépendance économique, synonyme du développement humain. Mais tel ne fut pas le cas. A son tour, l’éducation, au lieu de former des personnes capables d’apporter leur savoir être et leur savoir faire à la construction d’une société juste pour le développement, elle s’est contenté d’importer la forme scolaire occidentale et de mettre en place des politiques économiques libérales. Aujourd’hui, il n’est plus question de reprendre ce chemin. Le développement n’aura aucun sens s’il n’est pas solidaire, authentique et intégral. Ce travail s’inscrit dans une démarche consistant à construire une version authentiquement africaine du développement. Celle-ci est indissociable d’une philosophie de l’éducation pour l’Afrique, dont l’exploitation et la construction seront les objectifs de cette thèse. Un penseur s’est déjà engagé sur cette voie : c’est Jacques Maritain. En s’opposant à une philosophie libérale de l’éducation, il a ouvert les perspectives d’une éducation au développement solidaire. Dans le contexte de l’Amérique latine, un autre penseur et pédagogue, Paulo Freire, a réfléchi sur un paradigme éducatif alternatif. La recherche d’une nouvelle philosophie éducative pour l’Afrique passe par l’étude comparative de ces deux auteurs contemporains. / The notion of the development of Africa is primarily tributary to its history and specifically to that of its independence. The African people expected that the accession to political independence would be followed by the economical independence that is instrumental in human development. The African Educational system has imported the western education prototype and has put in place free market policies instead of training/educating/moulding individuals capable of contributing with their intellectual and practical knowledge towards the making of a fair society that enhances development. To date, it is out of question to stick to this model. Development will not have any meaning if it is not genuine, showing solidarity and inclusiveness. This work is intended to conceive a typically genuine African model of development. This is ultimately linked /inseparable to the African philosophy of education whose concerns and making will constitute the objectives of this thesis. A philosopher, Jacques Maritain has already explored that possibility. While opposing the liberal education system, he has opened prospects to education for [development that shows solidarity /communal development] . Within Latin America’s context, another philosopher and educationist, Paulo Freire, has considered an alternative education paradigm. The search for a new philosophy of education for Africa is tributary to the comparative study of these two contemporary scholars.

Thesis (M.B.A.)--University of Hong Kong, 1985.

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published_or_final_version / Physics / Doctoral / Doctor of Philosophy

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Typescript, etc.

A project report submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering. / This project is a part of a research programme by Eskom to develop power station rotary regenerative air heaters that are more compatible with South African coal properties. Large costs are involved in the replacement of air heater surfaces due to the erosion caused by the abrasive South African coal ash. The performance of an air heater L governed by numerous parameters, some of which (such as erosion) are unpredictable. A laborar: 'v testing facility which can produce a real-situation environment for air heater research is not only impractical but also expensive. Hence it has been decided to generate a computer simulation model of a power station air heater. The various alternatives for the improvement of existing air heaters will be assessed using this computer model. Extensive information regarding the influence of various parameters such as thermal performance, erosion, flow resistance, corrosion, etc. is necessary as input to the simulation model. Various test facilities have been commissioned to obtain this information. This project is an experimental study on the thermal performance of the regenerative air heater heating elements using a thermal test facility situated at the Eskom Technology Research and Investigations centre in Johannesburg. The facility uses the single-blow transient technique to establish the heat transfer coefficients of various air heater heating elements. Ten different types of heating elements were tested and the results were analysed .. These test results and recommendations give useful indications for power station application even before the final simulation model is available. The primary objective of this project was to find the heat transfer coefficient and also to make correlations between Colburn j factor, Fanning friction factor and Reynolds number. Packs were tested for various air tlow rates, ranging from Reynolds number 1200 to 6000. The test results were analysed and the correlations were made. A detailed uncertainty analysis was done and found that the results are showing less than 7 % error which is acceptable. The consistency of the test results was tested by a repeatability test and the results were quite satisfactory. The single blow method used in this project considered the longitudinal conduction within the material and it can accommodate any arbitrary inlet fluid temperature history. A comparative study of the various packs was done and traced certain trends. The high density packs gave better heat transfer and high pressure drop. The packs with alternate corrugated and flat plates had lower heat transfer performance, due to the fact that the tlat plates do not create such turbulence to the flow to reduce the boundary layer thickness to enhance the heat transfer. In short the flat plates only add weight to the pack, making it heavier than other packs. Based on the correlations and trends obtained from the analysis, some recommendations are also made. A further modification of the test facility was recommended to include a wider range of flow from very low Reynolds number to very high. This is necessary to find whether the packs with flat plates really perform better for highly turbulent tlow. The non - adiabatic nature of the side wall has to be considered for better reliability of the results. Some other recommendations are made to make the testing of packs more convenient. / Andrew Chakane 2018

A dissertation presented in fulfilment of the requirements for the Degree of Master of Science in Engineering DECEMBER 1982 / Although transpiration cooling has been demonstrated to keep the metal surface temperatures, in a gar turbine, below that at which oxidation occurs even though the hot gas temperatures are in excess of the metals melting temperature, few experimental studies have been conducted on the heat transfer aspects of transpiration cooling. Especially the effect blowing has on a turbulent boundary layer that has developed over a porous surface that is heated by the mainstream. Many studies have involved the blowing or suction oi the boundary layer through heated porous plates. Trans. an cooling was exper cntally investigated by making use of an existing wind tunnel which was modified so as to simulate the heat transfer phenomenon resulting from blowing coolant through a porous wall into a heated mainstream. The existing wind tunnel was designed and commissioned by Krieg (13) who considered the momentum transfer aspects of transpiration cooling. The solution of the momentum equation by Krieg forms the basis from which this investigation was developed, the original solution procedure being put forward by Cebeci and Smith (7). Krieg developed a generalised two-dimensional finite-differunce compute* program to solve the incompressible momentum equations describing a blown boundary layer. This program was further developed as part of this effort to solve the compressible momentum and neigy equations so as to account for the heat transfer in the blown boundary layer. The program is used to predict the experimental results obtained from the literature as well is those ottained during the nine experimental runs on the wind tunnel. Freestream flow velocities varied from 4,^5 m/s to 14,95 m/s with correspoi ;.ng temperatures of 44,95°C and 33,00eC respectively. The blowing fr tion F, was varied from 0,0059 to a maximum of , temperature of 40°C. The numerically calculated profiles and tho: » obi lined expurim ntally, as well as one set presented by another researcher, compared well. Finally, recommendations for future studies have been suggested.

Cette étude de cas qualitative pose de nombreuses questions théoriques et managériales dans la cadre de la recherche sur les entreprises familiales. Elle a la particularité de se dérouler sur une période de quatre années durant laquelle, un chercheur a pu vivre au coeur de l’organisation au quotidien à travers une approche ethnographique en utilisant la technique de l’observation participante. Ce dispositif méthodologique de recherche, rare et original, a permis d’être au plus près du terrain, permettant ainsi de confronter des éléments issus de la littérature organisationnelle consacrée aux entreprises familiales et les réalités quotidiennes d’une entreprise familiale qui vit un processus de transmission. Cette étude de cas aura permis au chercheur de vivre une étape clé du processus de transmission, celle de la transmission managériale. En d’autres termes, il s’agit de la transmission par le fondateur du leadership et du pouvoir managérial aux potentiels successeurs familiaux issus de la 2nde génération. Nous cherchons à comprendre comment des construits essentiels comme la confiance et la psychological ownership peuvent influencer les comportements des parties prenantes (membres familiaux et non-familiaux). En analysant les antécédents et les conséquences comportementales et attitudinales de ces deux construits principaux, et en les confrontant aux enjeux liés à cette entreprise familiale du Moyen-Orient, nous avons pu identifier les facteurs organisationnels, institutionnels et culturels qui impactent le processus de transmission. / This qualitative case study poses many theoretical and managerial questions in the context of research on family businesses. It has the distinction of taking place over a period of four years during which a researcher could live at the heart of the organization on a daily basis through an ethnographic approach using the participant observation method. This rare and original method of research has allowed him to be closer to the field, thus enabling the confrontation of family business literature and the daily realities of a family business experiencing a succession process. This case study has allowed the researcher to experience a stage in the succession process, that of managerial succession. In other words, it is the transmission by the founder of leadership and managerial power to potential family successors from the 2nd generation. We seek to understand how essential constructs such as trust and psychological ownership can influence the stakeholders’ behaviors (family and non-family members). By analyzing the antecedents as well as the behavioral and attitudinal consequences of these two main constructs, and by confronting them with the stakes related to this Middle Eastern family business, we were able to identify the organizational, institutional and cultural factors which impact the process of succession.