Understanding the structure of minerals at the atomic scale: a new perspective enabled by advanced microscopy

From oxides to ores and rocks, minerals are the most prevalent materials on Earth. The majority of their properties are the direct result of their microstructure. The investigation of their structure at the nano and micron scale is routinely carried out using techniques such as optical and electron microscopy, X-ray diffraction or secondary ion mass spectrometry. However, these techniques are usually limited in resolution, either spatially or chemically. More recently, atom probe tomography (APT) has emerged as a powerful microscopy technique that can provide 3D maps showing the position and atomic mass of individual atoms with sub-nanometre resolution. The non-conductive character of most minerals, both thermally and electrically, makes their investigation by APT challenging, from sample preparation to data interpretation. However, with the relatively recent development of focused ion beam sample preparation techniques and ultra-violet laser-assisted local electrode atom probe, the APT study of large band gap materials such as oxides has become more successful in the last decade. Advanced microscopy techniques such as transmission Kikuchi diffraction (TKD) or electron backscattered diffraction (EBSD) can also be used in combination with APT, and bring a new perspective to the investigation of the atomic scale structure of minerals, leading to a better understanding of their structure – properties relationships. The overall purpose of this thesis is to develop and apply new methods and techniques for the characterization of the structure of minerals at the atomic scale. This is achieved by means of various advanced microscopy techniques, which are applied to a selection of important scientific questions. By using a combination of APT, TKD, EBSD and transmission electron microscopy we investigate intergranular corrosion in stainless steels, the atomic structure of dental enamel and the robustness of zircon as a geological dating accessory. In this work, intergranular corrosion mechanisms in a commercial austenitic stainless steel (ASS) were revealed using EBSD and correlative TKD/TEM. Characterization by APT of the intergranular iron-chromium spinel formed during corrosion of the ASS revealed new insights at the atomic scale on its role towards the fast corrosion rate of the ASS. With the combined use of EBSD, TKD and APT, the atomic scale distribution of trace elements within dislocations in deformed mineral zircons was investigated for the first time to review the robustness of zircon for radiogenic dating. By using APT and TEM, new structural and elemental analysis of human dental enamel at the atomic scale provided unprecedented information for our understanding of human tooth decay

Montrapon: mutations d'un quartier bisontin et de son image

Le quartier de Montrapon, situé au nord-ouest de la ville, est, avec Palente-Les-Orchamps, l'un des tout premiers quartiers d'HLM bisontins: ses 1 084 logements ont été occupés entre 1954 et 1956. Sa bonne image s'est dégradée dès les années 70 et, au début des années 80, Montrapon était devenu l'un des quartiers de Besançon où les problèmes étaient les plus aigus, en particulier en son centre, la place P. De Coubertin appelée "place noire" en raison de son insécurité. En 1983. la municipalité lance un projet de réhabilitation dont l'essentiel est achevé en 1993. Physiquement, le quartier a beaucoup changé, en particulier dans la zone centrale de la place P. De Coubertin. Mais qu 'en est- il de l' image? Comment les Rapomontois voient-ils actuellement leur quartier ? Les Bisontins en ont-ils une meilleure image

The adoption of advanced feed-in tariffs in Ontario : a case of institutional layering

En mai 2009, l’Ontario a adopté la Loi sur l’énergie verte et devint ainsi la première juridiction en Amérique du Nord à promouvoir l’énergie renouvelable par le biais de tarifs de rachat garantis. En novembre 2010, dans son Plan énergétique à long terme, la province s’est engagée à déployer 10,700 MW en capacité de production d’énergie renouvelable non-hydroélectrique par 2018. Il s’agit de la cible de déploiement la plus élevée dans ce secteur au Canada. Les infrastructures de production et de distribution d’électricité comprennent des coûts d’installation élevés, une faible rotation des investissements et de longs cycles de vie, facteurs qui servent habituellement à ancrer les politiques énergétiques dans une dynamique de dépendance au sentier. Depuis le début des années 2000, cependant, l’Ontario a commencé à diverger de sa traditionnelle dépendance aux grandes centrales hydroélectriques, aux centrales à charbon et aux centrales nucléaires par une série de petits changements graduels qui feront grimper la part d’énergie renouvelable dans le mix énergétique provincial à 15% par 2018. Le but de ce mémoire est d’élucider le mécanisme de causalité qui a sous-tendu l’évolution graduelle de l’Ontario vers la promotion de l’énergie renouvelable par le biais de tarifs de rachat garantis et d’une cible de déploiement élevée. Ce mémoire applique la théorie du changement institutionnel graduel de Mahoney et Thelen au cas du développement de politiques d’énergie renouvelable en Ontario afin de mieux comprendre les causes, les modes et les effets du changement institutionnel. Nous découvrons que le contexte canadien de la politique énergétique favorise la sédimentation institutionnelle, c’est-à-dire un mode changement caractérisé par de petits gains favorisant l’énergie renouvelable. Ces gains s’accumulent pourtant en transformation politique importante. En Ontario, la mise sur pied d’une vaste coalition pour l’énergie renouvelable fut à l’origine du changement. Les premiers revendicateurs de politiques favorisant l’énergie renouvelable – les environnementalistes et les premières entreprises d’approvisionnement et de service en technologies d’énergie renouvelable – ont dû mettre sur pied un vaste réseau d’appui, représentant la quasi-totalité de la société ontarienne, pour faire avancer leur cause. Ce réseau a fait pression sur le gouvernement provincial et, en tant que front commun, a revendiqué l’énergie renouvelable non seulement comme solution aux changements climatiques, mais aussi comme solution à maints autres défis pressants de santé publique et de développement économique. La convergence favorable d’un nombre de facteurs contextuels a certes contribué à la réussite du réseau ontarien pour l’énergie renouvelable. Cependant, le fait que ce réseau ait trouvé des alliés au sein de l’exécutif du gouvernement provincial s’est révélé d’importance cruciale quant à l’obtention de politiques favorisant l’énergie renouvelable. Au Canada, les gouvernements provinciaux détiennent l’ultime droit de veto sur la politique énergétique. Ce n’est qu’en trouvant des alliés aux plus hauts échelons du gouvernement que le réseau ontarien pour l’énergie renouvelable a pu réussir.In May 2009, Ontario adopted the Green Energy and Green Economy Act and became the first jurisdiction in North America to promote renewable energy through advanced feed-in tariffs. In November 2010, in its Long-Term Energy Plan, the province pledged to deploy 10,700 MW of non-hydroelectric renewable energy capacity by 2018, the highest such target in Canada. Electricity production and distribution infrastructure is characterized by high setup costs, low capital stock turnover and long life spans, factors that traditionally entrench energy policy in path-dependent trajectories. Since the early 2000’s, however, Ontario has diverged from its historic reliance on large hydro, coal and nuclear through a series of gradual policy shifts set to expand renewable energy’s share in the overall supply mix to 15% by 2018. The purpose of this thesis is to uncover the causal mechanism behind Ontario`s gradual shift toward the promotion of renewable energy through advanced feed-in tariffs, accompanied by high deployment targets. The thesis applies Mahoney & Thelen’s theory of gradual institutional change to the case of renewable energy policy development in Ontario, providing new insight into the causes, modes and effects of institutional change. The thesis finds that the Canadian energy policy context favors a layering pattern of change, characterized by small, yet cumulative, renewable energy policy gains. The driving force of this process involves coalition building. To achieve renewable energy policy gains, Ontario`s first renewable energy proponents, mostly environmental groups and early renewable energy supply and service firms, had to build a wide-ranging, multi-stakeholder network of allies and lobby government from a unified front, presenting renewable energy as a solution not only to climate change but a combination of other immediately pressing public health and economic challenges. Elements of timing greatly aided the renewable energy network’s campaign. Ultimately, however, the thesis finds that, given provincial governments` ultimate veto power over energy policy, finding allies in the top echelons of government was most crucial to the renewable energy network`s success

La diversité des interactions plantes-pollinisateurs : Un pré-requis indispensable à la stabilité des écosystèmes

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Synthèse et caractérisation d’oxydes mixtes de type MgAlCe pour l’oxydation catalytique de l’acide acétique

AbstractMgAl mixed oxide catalysts were prepared by co-precipitation and sol–gel methods. On each catalyst, cerium is deposited on the surface (0.14 mol%) in order to improve its reducibility. MgAlCe0.14_cp and MgAlCe0.14_sg catalysts have shown interesting properties caused by various oxygen species (O22−, O2− and/or O2−) located on the surface of the materials and provided by ceria (CeO2). In fact, the oxygen-storage capacity of these catalysts is increased for MgAlCe0.14_sg, whereas a synergy effect appears for MgAlCe0.14_cp. The results have shown that the reducibility of the catalysts is not related to the preparation method. However, the basicity of the catalysts prepared by the co-precipitation method is higher than that of the catalysts prepared by the sol–gel method. This basicity gives a high activity to co-precipitated catalysts, which is limited by the possible formation of carbonates during the oxidation reaction of acetic acid

Homogeneous light in shade-house experiment overestimates carbon gains in Norway maple seedlings

We set up a shade-house experiment with Norway maple growing at two light intensities typical of a disturbed and undisturbed forest canopy from either a homogeneous or a dynamic regime that mimics sunflecks. We show that although horticultural-grade shade-cloths can be finely tuned to provide daily averages of any light intensity, they do not appropriately mimic natural forest understories which are characterized by dynamic light environments composed of intense but short direct light events interspaced with prolonged period of low diffuse light. The results suggest that replicating the dynamic light environment of forests could be very important in experiments aimed at identifying the traits responsible for invasiveness in exotic species in forest understories, such as Norway maple in North America

Semi-automated stereoradiographic upper limb 3D reconstructions using a combined parametric and statistical model: a preliminary study

PURPOSE: Quantitative assessment of 3D clinical indices may be crucial for elbow surgery planning. 3D parametric modeling from bi-planar radiographs was successfully proposed for spine and lower limb clinical investigation as an alternative for CT-scan. The aim of this study was to adapt this method to the upper limb with a preliminary validation. METHODS: CT-scan 3D models of humerus, radius and ulna were obtained from 20 cadaveric upper limbs and yielded parametric models made of geometric primitives. Primitives were defined by descriptor parameters (diameters, angles...) and correlations between these descriptors were found. Using these correlations, a semi-automated reconstruction method of humerus using bi-planar radiographs was achieved: a 3D personalized parametric model was built, from which clinical parameters were computed [orientation and projections on bone surface of trochlea sulcus to capitulum (CTS) axis, trochlea sulcus anterior offset and width of distal humeral epiphysis]. This method was evaluated by accuracy compared to CT-scan and reproducibility. RESULTS: Points-to-surface mean distance was 0.9 mm (2 RMS = 2.5 mm). For clinical parameters, mean differences were 0.4-1.9 mm and from 1.7° to 2.3°. All parameters except from angle formed by CTS axis and bi-epicondylar axis in transverse plane were reproducible. Reconstruction time was about 5 min. CONCLUSIONS: The presented method provides access to morphological upper limb parameters with very low level of radiation. Preliminary in vitro validation for humerus showed that it is fast and accurate enough to be used in clinical daily practice as an alternative to CT-scan for total elbow arthroplasty pre operative evaluation