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Le besoin de substituts pour vaisseaux sanguins de petit calibre a attiré une attention considérable sur le développement de constructions artérielles dans des bioréacteurs à partir de systèmes d’échafaudage. Les gels formés à partir de collagène reconstitué représentent des substrats idéaux pour le remodelage du à l’activité cellulaire, mais leur faible résistance et élasticité limitent leur utilisation comme échafaudages pour la régénération du tissu vasculaire. Ces caractéristiques proviennent de la perte d’organisation structurelle liée au processus d’extraction du collagène. Dans ce contexte, l’objectif de ce projet était d’améliorer les propriétés mécaniques des gels de collagène afin de supporter la croissance et la maturation du tissu vasculaire sous contrainte cyclique. En considérant l’importance de l’état d’agrégation du collagène pour les propriétés mécaniques des tissus natifs, la stratégie de ce projet a été de modifier la microstructure des matrices de collagène reconstitué en agissant sur trois aspects : 1) les interactions intermoléculaires et la fibrillogenèse ont été ajustées en variant les paramètres expérimentaux (pH, température, force ionique et concentration du collagène); 2) des liaisons covalentes ont été introduites afin de fixer des fibrilles voisines; 3) les gels ont été compactés et les fibrilles alignées grâce à l’action de remodelage des cellules. Des mesures de spectrophotométrie et des images par MEB ont confirmé les effets des conditions expérimentales et du remodelage sur la microstructure des gels. Notamment, la présence des cellules a permis la formation de matrices plus compactes et orientées, surtout en présence de contraintes mécaniques. Des essais mécaniques ont démontré que les stratégies adoptées ont engendré le renforcement de la structure. En particulier, des essais cycliques ont établi que la variation des conditions expérimentales combinée à la réticulation ont produit des matrices dont l’hystérèse diminue et l’élasticité augmente. En conclusion, l’ensemble de ces études a permis la réalisation à court terme (24-48 h) de structures à base de collagène présentant une résistance mécanique, une rigidité et une élasticité accrues. Ces résultats suggèrent que ces matrices sont de bons candidats comme supports pour la régénération de tissus vasculaires sous conditionnement cyclique. / The need for small-caliber vascular replacements has attracted considerable attention on the development of scaffold-based vascular constructs in bioreactors. Reconstituted collagen gels represent ideal substrates for cell-mediated remodeling, but their low strength and low elasticity, limits their application as scaffold for the regeneration of the vascular tissue. These features result from collagen extraction and the consequent loss of structural organization. The objective of this project was to improve the mechanical performances of collagen gels in order to support the growth and the maturation of the vascular tissue under cyclic conditioning. Considering how fundamental collagen assembly is for the mechanical behavior of native tissues, the microstructure of reconstituted collagen lattices was modified by working on three aspects: 1) The intermolecular interactions and the aggregation of collagen monomers were tailored by modulating the experimental conditions, including pH, temperature, ionic strength and collagen concentration; 2) Inter-fibril crosslinking was carried out in order to fix neighboring collagen fibrils through their reactive side chains; 3) Gels were compacted and fibrils were aligned through cell-mediated remodeling. Spectrophotometric analyses and SEM confirmed the effects of changes in experimental conditions and cell-mediated remodeling on collagen gels microstructure. Notably, the presence of SMCs lead to tighter and highly oriented lattices, moreover in the presence of mechanical constraints. Mechanical tests showed that the adopted procedures contributed to the stiffening of collagen lattices. In particular, the modulation of the experimental conditions combined with crosslinking lead to lattices presenting lower hysteresis and higher elasticity as shown by cyclic tests. In conclusion, this study produced, in a short time (24-48 h), collagen gel-based lattices with improved stiffness, strength, and elastic recoil. The results suggest that these lattices are serious candidates for the role of temporary supports during the maturation period under cyclic loading.

La présence d’hydrogène en solution dans l’aluminium liquide entraîne la formation de porosités une fois celui-ci solidifié. C’est pourquoi il est important de bien mesurer la quantité de gaz dissous dans le métal. La méthode de Sieverts, utilisée par d’autres expérimentateurs dans le passé, montre certaines faiblesses et une nouvelle méthode plus fiable et versatile est proposée afin de valider les résultats obtenus précédemment. Après plusieurs tests et améliorations au montage et à la méthodologie, des résultats prometteurs ont été obtenus. En fait, un phénomène attribuable à la dissolution de l’hydrogène dans l’aluminium a été observé. En faisant quelques hypothèses, ces résultats ont permis de valider le modèle mathématique en obtenant une valeur de la solubilité de l’hydrogène dans l’aluminium près de celle des autres expérimentateurs. Suite à ces essais, de nouvelles améliorations ont été apportées au montage et une nouvelle méthodologie de mesure est proposée pour les expérimentations futures. / The presence of hydrogen in solution in liquid aluminium leads to the formation of porosities after the solidification. For this reason, a good measurement of the quantity of gas dissolve in the molten metal should be made. The Sieverts’ method, used by the precedents experimenters, shows some weaknesses and a new method more reliable and versatile is proposed to validate the results formerly obtained. After several tests and ameliorations to the measurement system, some promising results were obtained. A phenomenon that can be attributed to the dissolution of hydrogen in liquid aluminium was observed. By making some assumptions, these results were used to validate the mathematical model by obtaining a value of the solubility of hydrogen in aluminum near the other experimenters. Following that, new ameliorations were made to the system and that a new measurement methodology is proposed for the future experimentations.

Thesis (M.S.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on November 11, 2008) Includes bibliographical references.

"Submitted in partial fulfillment of the requirements for the degree of Master of Business Administration from the Naval Postgraduate School, June 2009." / Advisor(s): Henderson, David R. ; Melese, Francois. "June 2009." "MBA professional report"--Cover. Description based on title screen as viewed on July 14, 2009. Author(s) subject terms: Economics of landmines, demining, economic impact of landmines, solutions to landmine problem, alternatives to demining, cost-benefit analysis of demining, finance of demining, structure of demining organizations. Includes bibliographical references (p. 113-115). Also available in print.

Texte remanié de: Diss.--Rechts--Sarrebruck--Rechts- und Wirtschaftwissenschaftlichen Fakultät der Universität des Saarlandes, 1985. / Bibliogr. p. 219-232. Index.

Th. doct.-ing.--Génie géol. et minier--Nancy--I.N.P.L., 1980.

Th. univ.--Sci.--Nancy--I.N.P.L., 1979.

Embodied in three main parts, this study incorporates field observations, theoretical modelling and geochemical data to interpret the various aspects of the copper mineralization at Afton Mines. Part I describes and interprets mineral distributions within and about the Afton orebody. The copper mineralization occurred in a roof pendant environment characterized by a diversified array of rock types with intricate mutual relationships. Excluding the large scale zoning of pyrite and magnetite established by Carr and Reed (1976) and the apparent association of hydrothermal biotite with ore, distribution of most primary and secondary minerals is rather sporadic. High temperature alterations at Afton probably proceeded with a low ratio of fluid to rock such that primary mineralogy was able to control the appearance of secondary minerals. The absence of intense phyllic and argillic alterations is interpreted to be caused by the lack of abundant meteoric water participating in the hypogene mineralization event. Intense carbonate alteration, however, is likely to be indicative of concentrated juvenile hydrothermal activity. The mode of occurrence of ore minerals, on the other hand, suggests that supergene alteration at Afton was dominated by irreversible mineral-solution interactions. The extent of the alteration at depth appears to be largely fracture-controlled. Part II presents a thermodynamic reconstruction of the supergene alteration at Afton. It is demonstrated that the dominance of native copper and the lack of copper enrichment in the supergene zone are related to the relatively mafic composition of the wall rocks and the absence of abundant sulfides in the hypogene zone. Supergene alteration of porphyry copper deposits in general can be interpreted in the framework of a log f-log f plot with respect to two arbitrary "limiting" curves characterized by extreme values of acidic and basic pH respectively. The closer a reacting fluid evolves parallel to the upper or acidic "limiting" curve, the more likely is the formation of a well-developed leached cap with an enriched supergene ore blanket underneath. In contrast, a reacting fluid evolving parallel and close to the lower or basic "limiting" curve will lead to a spectrum of copper oxides and native copper with little enrichment. Part III summarizes and relates major element geochemical data, petrographic observations and field evidence to the evolution and copper mineralization of the various intrusive phases of the Iron Mask batholith. The four major phases of the batholith, namely, the Iron Mask Hybrid, Pothook, Sugarloaf and Cherry Creek units, appear to be related by the process of fractional crystallization. The Afton protore is likely a by-product of magmatic differentiation generated at the early Cherry Creek stage when portions of the fractionating magma intruded into a subvolcanic environment. Mineralogical characteristics of the orebody, including the scarcity of molybdenite, reflect significant influence of host rock geochemistry on late stage copper mineralization and the associated hypogene alteration. Taking into account all the information acquired, the evolution of the Afton orebody appears to have involved four major events: i) fractional crystallization of a parent Iron Mask magma at depth with continual magnetite separation; ii) transfer of portions of the early Cherry Creek magma to a subvolcanic environment where rapid cooling enhanced supersaturation of copper sulfides and where some loss of sulfur occurred through volcanic emanations; iii) local trapping of late magmatic fluid to remobilize and concentrate the originally disseminated sulfides to form the hypogene ore; and iv) subsequent supergene alteration constrained to take place in a basic pH domain to stabilize abundant native copper without much enrichment. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Doctorat en sciences appliquées / Autres membres du jury :MMs Glansdorff et Jaumotte / info:eu-repo/semantics/nonPublished