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This study has investigated the take-up, at a range of South African tertiary institutions, of Open Educational Resources (OER) designed for mathematics teacher education. Although numerous studies (e.g. Darling-Hammond, 2006; Jonassen & Rohrer-Murphy, 1999; Loughran, 2006) have identified criteria for the development of quality materials for teacher education, and have investigated ways in which these have been and should be used, little attention has been paid to the implications of these findings for the use of OER in teacher education. In 2006 the South African Institute of Distance Education (SAIDE) initiated the ACEMaths project to pilot a collaborative materials design and adaptation process in response to a Department of Education call for large scale teacher upgrading programmes leading to an Advanced Certificate in Education (ACE) in priority areas. Nine South African tertiary institutions formed the collaborative group for the development of Mathematics teacher education materials. Six of these institutions committed to using the pilot materials in their teacher education programmes in 2007. Methodologically, the research is a case study of cases (Adler & Reed, 2002), in which the varying uses of the materials in these six institutional sites constituted the individual cases. At each site data were gathered from session observations, questionnaires and interviews. Artefacts, such as examples of customised materials, were also collected. Cross case analysis revealed that institutions used the ACEMaths materials in both similar and different ways and in a range of programmes. Findings from this analysis and their implications for both initial inter-institutional designing and subsequent intra-institutional re-designing and re-use of OER are discussed.

Les travaux de cette thèse focalisent sur la résolution de deux problèmes majeurs des électrodes positives de systèmes Li-O2, dus à la nature du produit de décharge formé pendant la réaction de réduction de l'oxygène, en milieux Li+ : Lithium peroxyde (Li2O2). Le premier problème est lié au processus de formation de ce dernier (étapes successives de nucléation électrochimiques et de dismutation chimique d'un intermédiaire : le superoxide de lithium), qui conduit à la formation de très grosses particules de peroxyde lithium à la surface de l'électrode. Du fait de leurs taille et de leur résistivité ( le gap du peroxyde de lithium est de 5 eV), il est impossible de recharger de manière efficace et à 100% ce dernier. Cependant, ce problème peut être résolu, grâce à l'ajout d'un additif, qui permet le transport d'électron en solution, et qui peut (en théorie), recharger les particules de Li2O2, détachées de l'électrode. Un très bon candidat a été trouvé dans cette étude, qui a prouvé de très bonne performances pour l'amélioration du processus de recharge, et un effet bénéfique supplémentaire a été caractérisé sur le potentiel de décharge, grâce à un effet catalytique (augmentation du potentiel de réduction de 230 mV). Cependant, cette solution demande de repenser totalement le design actuel des systèmes Li-O2, car ce composé (soluble) peut facilement traverser le séparateur, vers l'électrode de lithium (et causer une autodécharge importante ainsi qu'une boucle de recharge infinie). Le second problème est lié à une autre caractéristique du peroxyde de lithium : sa réactivité. De fait, c'est un base forte au sens de Lewis (en accord avec la théorie HSAB), et réagit de manière importante avec les constituants de l'électrodes (réactivité avec le liant PVDF, mais aussi avec les solvant, le sel et le support carboné de l'électrode). Il est donc nécessaire de trouver un moyen de protéger ce dernier, et une solution proposé dans ce manuscrit a été de réaliser la déposition d'une couche nanométrique de Nb2O5, qui a pour but d'éviter tout contact direct entre le carbone, et le peroxyde de lithium (réaction entre ces deux derniers, qui conduit à la formation d'un composé avec un gap de 7 eV : le carbonate de lithium). Le dépôt fut étudié sur un carbone graphitisé (Zoltek Panex 30) qui, de manière surprenante, a été très résistant versus le peroxyde de lithium. Malheureusement, la présence du dépôt à la surface du tissus n'a pas protégé l'électrode, mais a plutôt eu l'effet inverse, car des traceurs de la formation de carbonate de lithium ont pu être observé (alors qu'aucun traceur n'était détecté sur le tissu nu). Le Nb2O5 a donc été écarté, et d'autres composés doivent être testés dans de futures études, pour cette application. / The present PhD work focuses on solving two major issues of the Li-O2 positive electrodes, both being linked with the nature of the discharge product formed during the Oxygen Reduction Reaction, in Lithium cation electrolyte: Lithium peroxide (Li2O2). The first issue is related to the Discharge mechanism (consecutives Electrochemical nucleation and chemical disproportionation of an intermediate, lithium superoxide), which lead to the formation of large particles of lithium peroxide on the electrode surface. Owing to their size and resistivity (bandgap of lithium peroxide : 5 eV), it is nearly impossible to re-charge efficiently the electrode. This issue can be solved, thanks to the dissolution of an additive in solution, that promote the transport of electrons, and allow the oxidation of large discharge particles (in theory, even the ones disconnected from the electrode). A very good compound was found to efficiently work as a redox shuttle (enhanced Oxygen Evolution reaction), with also a highly beneficial effect for the ORR, with a catalysis effect that allowed to increase the onset of the ORR of 230 mV. However, this solution require a engineering of the practical system as this additive could cross from the positive electrode to the negative side (lithium) and trigger capacity loss and infinite charging loop. The second issue is linked to its reactivity. As a matter of fact, it is an hard base (according to HSAB theory), which reacts readily with a large panel of electrodes component (reactivity toward the PvDf binder, solvent, salts, but also with the carbon material, used as the positive electrode). As such, it is necessary to find a way to protect the latter, and a solution proposed in this work was to use Atomic Layer deposition of Niobium pentoxide (Nb2O5), in order to form a very thin deposit, which was supposed to prevent any contact between the discharge product, and the carbon support (consumption of Carbon, with formation of a large bandgap compound : Lithium carbonate). The deposition was conducted onto a graphitized carbon cloth (Zoltek Panex 30), which surprisingly proved to be highly resistant toward lithium peroxide. Sadly, the presence of the deposit did not protect the electrode but rather made it weaker, with tracers of the formation lithium carbonate. This compound was thus not considered anymore, and others deposits are yet needed to be tested in future studies.

Background: Current studies in radiotherapy aim to develop better methods for curing patients fromcancer. Since different types of radiation interact with biological matter in various ways, the resultsof their interaction and their effectiveness with respect to the biological damage to cells have ageneral investigation interest. Aim: The work in this project aims to use a mathematical model to fit a pre-existing data onclonogenic survival of cells irradiated by different types of radiation and report the fittingparameters. Various radiobiological concepts were investigated and compared between differentradiation qualities used in this work. Materials and Methods: The repairable-conditionally repairable (RCR) damage model parametrisedwith respect to the linear energy transfer (LET) of the cell oxygenation was used for fittingexperimental cell survival data for human salivary gland cells irradiated in oxic and hypoxicconditions with protons, 12C-, 20Ne- and 3He-ions. Results: Good consistency with the entire cell survival data was achieved. RCR-model was robustenough to achieve agreement with cell survival data for LET values excluded from fitting procedure.Slope of cell survival curves for the three ions increased up to optimal LET value reaching maximumthere and it decreased at higher LETs. RBE of 3He-ions showed the most rapid increase in low-LETregion and reached a higher maximum as compared with other ions. RBE of the three ions increasedapproximately in the same LET region as a and c parameters of RCR-model, but no underlyingradiobiological mechanism could explain any of curve shape similarities. The RBE of 12C-ions reachedmaximum approximately at 126 keV/μm, which is the optimal LET that could possibly correspond tothe steepest cell survival curve. It was observed how the cell oxygenation became less important forcell irradiation with very high LET values. Conclusion: The results showed that it is feasible to use the RCR model to fit the broad range of cellsurvival curves corresponding to different radiation qualities and the assessment of their relativebiological effectiveness in oxic and hypoxic irradiation conditions. RCR-model may have a possible application in cell irradiation with other ion beams than those used in this work.

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