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Les alliages à mémoire de forme (AMF) sont des matériaux métalliques qui présentent des propriétés thermomécaniques particulières, et notamment l’effet mémoire de forme. L’étude réalisée durant la thèse concerne la création de systèmes actifs double-sens à l'aide de fils AMF à effet mémoire simple-sens. Trois modèles analogiques simples, représentant trois catégories de solutions constructives, ont été développés. Ces modèles correspondent à des types de couplages mécaniques différents entre un (ou des) fil(s) AMF et une structure mécanique. Par exemple, le modèle le plus simple consiste à utiliser un unique fil AMF couplé à un système mécanique constitué d’une structure monolithique déformable. Lorsque l’on chauffe l’AMF, on active l’effet mémoire de forme, ce qui entraîne une déformation de la structure. Lorsque l’on refroidit l’AMF, la rigidité propre de la structure entraîne une déformation dans le sens inverse à celui de la phase de chauffage. Plusieurs démonstrateurs ont été également construits et analysés durant la thèse. Cette étude montre la possibilité de concevoir des structures actives pilotées par des AMF, ce qui ouvre des perspectives pour le contrôle des déformations ou des contraintes dans des structures. / Shape memory alloys (SMA) are metallic materials that have particular thermomechanical properties, including the shape memory effect. The study carried out during the thesis concerns the creation of two-way active systems using SMA wires exhibiting one-way memory effect. Three simple analog models, representing three classes of constructive solutions, have been developed. These models correspond to different types of mechanical coupling between one (or more) SMA wire(s) and a mechanical structure. For example, the simplest configuration is a single SMA wire coupled to a mechanical system consisting of a deformable monolithic structure. When the SMA is heated, the shape memory effect is activated, which causes the deformation of the structure. When cooling the SMA, the inherent rigidity of the structure causes a deformation in the opposite direction to that of the heating phase. Several demonstrators were also constructed and analyzed during the thesis. This study demonstrates the possibility of designing active structures driven by SMAs, which opens prospects for the control of deformations or stresses in structures.

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M-PESA (a mobile banking service in Kenya) was introduced to offer a person-to-person money transfer service. Its extensive adoption and appropriation for purposes other than person-to-person transfers has influenced the technology providers (Safaricom) to widen their services beyond their original intentions. M-PESA provides a wide range of financial services including services for people who were previously unbanked. Users of M-PESA can now pay different utilities, those without credit cards can purchase products online, others can repay loans to microfinance institutions, pay insurance premiums, withdraw money from ATMs, use it as Point of Sale Payment and open savings accounts. This research examines the existence of “bi-directional” influences between technology and society by taking M-PESA business users as a case. It specifically investigates how M-PESA as a technology has influenced the business environment in Kenya and how the design of M-PESA has in turn been influenced by its adoption. The research adopts the Adaptive Structuration Theory as the theoretical framework and interpretive case study research as a methodological approach. Interviews with different stakeholders in the industry were used to collect data. Data was analyzed using Diachronic Analysis. The results of the research show that there is a “bi-directional” influence between technology and people as they affect each other over time. Mobile technologies shape the way businesses operate, allowing them to provide new services and improve existing ones. At the same time, usage and adoption trends affect the design of mobile technologies. Over time, technology is adapted to accommodate the new needs of businesses and other needs in the wider community. This research shows that the impact of technology depends not only on its functionality but also on its use and appropriation in society. / Dissertation (MCom)--University of Pretoria, 2011. / Informatics / unrestricted

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