Dissertations / Theses: 'Grenat de fer'

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Grosseau, Philippe. "Synthèse et étude du grenat de fer et d'yttrium." Phd thesis, Ecole Nationale Supérieure des Mines de Saint-Etienne, 1993. http://tel.archives-ouvertes.fr/tel-00844349.

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Les pièces polycristallines de grenat de fer et d'yttrium Y₃Fe₅O₁₂ (YIG) utilisées en hyperfréquences doivent présenter une densité très proche de la valeur théorique. Industriellement, ces pièces sont élaborées par frittage de la poudre qui est préparée par réaction entre les oxydes Y₂O₃ et Fe₂O₃. Ce travail concerne l'étude de deux procédés d'élaboration des poudres de YIG qui sont la réaction entre oxydes et la coprécipitation. Dans les deux cas, la formation de la pérovskite de fer et d'yttrium YFeO₃ (YIP) précède la formation du grenat. Lors de la synthèse par coprécipitation, la quantité de YIP formée est cependant fortement influencée par la présence d'impuretés ou de dopants (résidus de synthèse, substitution du fer par l'aluminium). L'influence des paramètres d'élaboration sur les caractéristiques physico-chimiques des poudres et leur aptitude au frittage est étudiée. Il apparait alors que les deux procèdes permettent l'obtention de pièces correctement densifiées présentant de faibles pertes magnétiques d'insertion. Tout écart a la stœchiométrie doit être évité, mais la détérioration des propriétés magnétiques n'est importante qu'à partir du moment où il y a présence dans le matériau d'une phase étrangère au grenat.

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Deb, Marwan. "Spectroscopie magnéto-optique de grenat magnétique de bismuth fer : études statique et dynamique." Versailles-St Quentin en Yvelines, 2013. http://www.theses.fr/2013VERS0065.

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Cette thèse a pour objectif d’étudier d’une manière approfondie les propriétés magnétiques, magnéto-optiques (MO) et électroniques du grenat de bismuth fer (Bi3Fe5O12, BIG). BIG est un nouveau matériau magnétique transparent connu pour ces propriétés MO exceptionnelles. Une partie de ce travail présente l’étude spectroscopique des propriétés MO statiques de BIG effectuée sur une large gamme d’épaisseur (5nm-220nm) d’énergie photonique (1. 7eV- 4. 2eV) et de température (5K-740K). Cette étude a permis de comprendre plusieurs propriétés intrinsèques de ce matériau complexe telles que ses cycles d’hystérésis anormaux et sa structure de bande électronique. La deuxième partie porte sur l’étude de la dynamique de l’aimantation. Nous avons montré que l’excitation de BIG par une impulsion laser femtoseconde de polarisation linéaire ou circulaire initie une précession cohérente de l’aimantation
The objective of this thesis is the extensive study of the magnetic, magneto-optical (MO) and electronic properties of the bismuth iron garnet (Bi3Fe5O12, BIG). BIG is a novel transparent magnetic material with exceptional MO properties. The first part of the thesis presents the studies of the static MO properties of BIG performed over a wide range of thickness (5nm-220nm) of photon energy (5nm-220nm) and of temperature (5K-740K). The obtained results have allowed understanding several intrinsic properties of this complex material such as its abnormal hysteresis loops and its electronic band structure. In the second part of the thesis, the optically induced magnetization dynamics has been studied. We have demonstrated that the excitation of BIG with linearly or circularly polarized femtosecond laser pulse triggers a coherent precession of the magnetization

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Gilles, Bruno. "Etude par rayons X rasants des effets de l'implantation de silicium dans le silicium et de fer dans un grenat." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb37597890r.

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HOUPERT, CHANTAL. "Modifications structurales et magnetiques d'oxydes de fer de type grenat, hexaferrite et spinelle irradies par des ions lourds de haute energie." Caen, 1989. http://www.theses.fr/1989CAEN2030.

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Quelques oxydes de fer de type grenat, hexaferrite et spinelle ont ete irradies par les ions lourds de haute energie du ganil. Les ions xe de 27 mev/n induisent la formation de traces latentes continues qui ont ete caracterisees par spectroscopie mossbauer, microscopie electronique haute resolution et par des mesures d'aimentation. Elles ont permis d'introduire une structure en couches de la trace latente dont la formation apparait obeir a un mecanisme a seuil. La trace est continue et cylindrique au-dessus d'une valeur seuil de l'energie deposee par chocs electroniques; elle est formee de defauts isoles et allonges en-dessous. L'irradiation induit par ailleurs un changement des proprietes magnetiques et structurales des materiaux etudies: l'orientation anisotrope du champ magnetique hyperfin, dans le grenat y#3fe#5o#1#2 et les spinelles afe#2o#4 (a=ni, mg, zn); des changements de sites des ions fe#3#+ qui induisent l'apparition d'une aimantation spontanee dans znfe#2o#4; l'amorphisation des materiaux aux fluences les plus elevees. Les composes amorphes presentent un comportement speromagnetique mais il subsiste une faible fraction aimantee de type metamagnetique. La temperature a laquelle se fait l'irradiation n'influence pas de facon generale le volume amorphise

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Grange, Olivier. "Synthese et etude de films minces de grenat d'yttrium-fer obtenus par pulverisation par un faisceau d'ions issu d'une source kaufman." Paris 7, 1988. http://www.theses.fr/1988PA077219.

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Obtention par une procede en deux etapes: depot, sur des substrats monocristallins des produits pulverises par le bombardement d'une cible de yig polycristalline stchiometrique par un faisceau d'ions ar energetique issu d'une source kaufman puis recuit sous oxygene au-dessus de 750#oc. Etude de la dependance de l'angle d'ejection, de l'energie et de l'incidence des ions sur la composition de la couche mince

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Qassym, Lilia. "Etude et mise au point de ferrites de structure grenat à basse température de frittage pour intégration dans les circulateurs hyperfréquences." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS479/document.

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Les systèmes embarqués dans les aéronefs comme dans les véhicules spatiaux doivent impérativement se conformer aux impératifs de masse et de volume mais aussi de coût. Les modules actifs pour antenne à balayage électronique constituent, dans ce cadre, un enjeu stratégique majeur en termes de masse, de volume et de fiabilité. Dans une antenne à balayage électronique actuelle, on peut trouver jusqu’à 1000 modules, chacun étant équipé d’un circulateur-isolateur afin de garantir ses performances. La technologie des circulateurs et des isolateurs à ferrite reste la plus performante en termes d’isolation et de pertes d’insertion. Elle est de plus totalement passive et ne demande aucune énergie extérieure pour son fonctionnement. Elle reste néanmoins coûteuse car la fabrication industrielle de ces dispositifs consiste à assembler mécaniquement de nombreuses pièces usinées précisément : céramiques magnétiques et diélectriques, aimants, conducteurs en cuivre et pièces en métal magnétique doux. De plus, le niveau d’intégration recherché nécessite de réduire les dimensions sans augmenter les pertes pour des niveaux de puissance qui peuvent être importants. S’inspirant des composants céramiques multicouches (condensateurs et inductances) ainsi que de la technologie LTCC (Low Temperature Cofired Ceramics), une nouvelle voie de fabrication de ces composants, en rupture avec les technologies d’assemblage traditionnelles, est abordée dans ces travaux de thèse. L’idée consiste à réaliser par cofrittage le cœur du composant qui est le plus délicat à ajuster et qui détermine le volume final. Les ferrites qui constituent actuellement le cœur des circulateurs sont principalement des grenats ferrimagnétiques fabriqués par des techniques céramiques classiques et frittés à haute température (> 1400°C). Pour les rendre compatibles de la technologie LTCC, il est nécessaire de diminuer leur température de frittage. Les températures visées doivent être inférieures à 1000°C pour pouvoir cofritter avec des parties métalliques en or et si possible être proches de 900°C pour espérer cofritter avec de l’argent. Dans ce contexte, l’objectif de ce travail de thèse était de mettre au point des grenats ferrimagnétiques pour des applications en hyperfréquences présentant des températures de frittage proche de 900°C. Ces ferrites ont alors été utilisés pour la réalisation de circulateurs hyperfréquences, composants indispensables dans les systèmes de Radars et de télécommunications. De plus, des études d’optimisation des propriétés magnétiques et diélectriques de ces ferrites ont aussi été réalisées pour adapter le ferrite aux conditions de fonctionnement (gamme de fréquence et niveau de puissance)
Embedded systems in aircraft must comply with the requirements of mass, volume and cost. The active modules of electronic scanning antenna are, in this context, a strategic challenge in terms of mass, volume and reliability. Today, there are up to 1000 modules per antenna, each one containing a circulator-isolator in order to guarantee its performances. The technology of ferrite circulators and isolators remains the most efficient in terms of isolation and insertion losses. It is also fully passive as no external energy is required to work. However this technology is expensive due to complex mechanical assembling of the different materials: magnetic and dielectric ceramics, magnets, conductors made of copper and soft metallic material. The integration of such devices also requires the reduction of dimensions without increasing losses for power levels that can be high. Based on by multilayer ceramic components (capacitors and inductors) as well as Low Temperature Cofired Ceramics (LTCC) technology, a new way of manufacturing these components, is investigated in this PhD work.. The idea is to be able to cofire the heart of the component which is the most difficult to adjust and also determines the final volume. The ferrites which currently constitute the core of the circulators are ferrimagnetic garnets synthetized by using a conventional ceramic process and sintered at high temperature (> 1400°C). To make them compatible with LTCC technology, it is essential to reduce their sintering temperature. The targeted temperatures must be less than 1000°C in order to cofire with gold metal parts and, if possible, close to 900°C for circulators with silver. In this context, the objective of this PhD work was to develop a ferrimagnetic garnet for microwave applications with sintering temperatures close to 900°C. This ferrite was then used for the preparation of microwave circulators which are essential components in radar and telecommunications systems. In addition, studies of optimization of the magnetic and dielectric properties have also been carried out to meet the operating requirements (frequency band and power level)

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Juraszek, Jean. "Dommages induits par irradiation aux ions lourds dans des matériaux magnétiques : multicouches metalliques Fe/Tb et grenat isolant Y 3Fe 5O 1 2." Rouen, 2000. http://www.theses.fr/2000ROUES016.

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Ce travail concerne l'étude de l'endommagement induit par excitation électronique dans des multicouches Tb/Fe et dans le grenat de fer-yttrium. Les multicouches ont été préparées par évaporation sous ultra-vide et irradiées par des ions de différents pouvoirs d'arrêt électronique au GANIL. Les transformations structurales et magnétiques ont été caractérisées par réflectométrie et diffraction des rayons X, microscopie électronique à transmission haute résolution, mesures d'aimantation et spectrométrie Mössbauer par électrons de conversion. Dans le cas des ions Pb ou U, une forte interdiffusion entraine une perte de la structure en couche et de l'anisotropie magnétique perpendiculaire. L'efficacité de mélange est d'autant plus grande que l'épaisseur des couches de fer et que la vitesse des ions est faible. Une modélisation des cinétiques d'endommagement des couches de fer, ainsi que des variations avec la fluence de la direction des moments magnétiques, a été utilisée pour estimer le diamètre des zones de mélange ainsi que la longueur de diffusion induite. Des plans sondes de 5 7Fe déposés à différents endroits dans la couche de fer naturelle ont permis d'étudier sélectivement les interfaces abruptes Tb-sur-Fe, les interfaces diffuses Fe-sur-Tb et le Cur cristallin des couches de fer pour différents pouvoirs d'arrêt électronique. A partir d'un pouvoir d'arrêt électronique seuil, une démixtion du fer et du terbium est observée à basse fluence à l'interface Fe-sur-Tb. On observe uniquement un mélange interatomique à l'interface Tb-sur-Fe. Ce mélange est indépendant du sens de parcours des ions à travers l'interface. Dans les grenats Y 3Fe 5O 1 2 irradiés aux ions Pb de haute énergie, la détermination des fractions volumiques des différentes phases introduites par irradiation nous a permis de proposer un modèle phénoménologique permettant de déterminer les sections efficaces des différents domaines.

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Ziborov, Georgy. "Optimisation des propriétés cristallines et magnétiques des grenats de ferrimagnétiques pour des applications en spintronique." Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALY043.

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Le développement moderne des technologies de l'information, telles que les mémoires et les opérations logiques, exige des technologies plus rapides, plus denses, non volatiles et à faible consommation d'énergie. Cela a donné lieu à des recherches importantes dans le domaine de la spintronique, ou de l'électronique de spin, qui repose sur l'idée d'exploiter les degrés de liberté de charge et de spin de l'électron. Les oxydes ferrimagnétiques, en particulier les grenats de fer aux terres rares (ReIG), sont au cœur de ce domaine. Ces matériaux présentent un grand potentiel d'utilisation dans les dispositifs magnétiques à base d'isolant qui génèrent des courants de spin purs. Les ReIG présentent des propriétés magnétiques uniques qui en font des candidats prometteurs pour les applications spintroniques à base d'isolant, notamment la stabilisation des skyrmions et la propagation des ondes de spin. Ces applications nécessitent toutefois la fabrication de films de grenat d'une épaisseur de l'ordre du nanomètre.Dans ce travail, nous avons optimisé la fabrication de films minces épitaxiés de ReIG, en particulier de YIG et de TmIG à magnétisation perpendiculaire, par une technique de pulvérisation à radiofréquence et un post-recuit, ce qui a permis d'obtenir des films ultraminces épitaxiés de haute qualité d'une épaisseur de 3 nm. La structure hétéroépitaxiale et la qualité cristalline des films fabriqués ont été confirmées par des mesures aux rayons X. Les mesures in situ des ReIG pendant le processus de recuit ont également été effectuées, ce qui nous a permis de déterminer la dynamique de cristallisation séparée en deux phases simultanées : la cristallisation du grenat et la diffusion. Il a été déterminé que la phase de cristallisation des ReIGs n'est pas linéaire, et la modélisation du processus à l'aide de l'approche Johnson-Mehl-Avrami-Kolmogorov (JMAK) a été développée, avec la correction du processus de diffusion du substrat vers la couche de grenat.Les propriétés magnétiques des ReIG ont été étudiées et, afin de les optimiser pour stabiliser des textures magnétiques plus petites telles que des domaines en bandes ou des bulles, plusieurs manières de réduire l'anisotropie effective ont été étudiées. Deux d'entre elles, à savoir l'optimisation des paramètres de recuit et la fabrication de bicouches YIG/TmIG avec différents axes d'aimantation facile, se sont avérées très efficaces. Cela nous a permis d'ajuster l'anisotropie effective pour stabiliser les domaines en bandes et les bulles magnétiques à la rémanence. Les études de la dynamique de l'aimantation du ReIG ont montré que ses propriétés dépendent fortement de la composition du grenat et, par conséquent, du processus de fabrication et des conditions de la procédure de recuit. Un optimum de ces contraintes a été trouvé permettant de préserver le faible amortissement des ReIGs.Les études synchrotron des ReIG ont démontré la différence de composition du grenat entre la couche à l'interface et la surface et ont confirmé la présence d'une couche non magnétique, créée par la diffusion du substrat dans la couche de grenat. Cet effet a été observé pendant les études de cristallisation, et l'épaisseur approximative de cette couche ≈2 nm a été déterminée à partir de mesures de rayons X durs et mous
Modern development of information technologies such as memory storages and logic operations demands for faster, denser, non-volatile and low power-consuming technologies. This has driven significant research in the area of spintronics, or spin-electronics, which is based on the idea of exploiting both the charge and spin degrees of freedom of the electron. A key focus in this field is on ferrimagnetic oxides, in particular Rare-earth Iron Garnets (ReIG). These materials show great potential for use in insulator-based magnetic devices that generate pure spin currents. ReIGs exhibit unique magnetic properties, making them promising candidates for insulator spintronics applications, including skyrmion stabilization and spin wave propagation. These applications, however, require the fabrication of nanometer-thick garnet films.In this work, we optimized the fabrication of epitaxial thin films of ReIG, in particular YIG and perpendicularly magnetized TmIG. This was performed via radio frequency sputtering technique and post-annealing, allowing to obtain high quality epitaxial ultrathin films down to 3 nm. The heteroepitaxial structure and crystalline quality of the fabricated films was confirmed with X-ray measurements. The in-situ measurements of ReIGs during the annealing process were performed as well, which allowed us to determine the crystallization dynamics separated in two simultaneous phases: garnet crystallization and diffusion. It was determined that the ReIGs crystallization phase is not linear, and the modeling of the process using Johnson-Mehl-Avrami-Kolmogorov (JMAK) approach was developed, with the correction to the diffusion process from the substrate to the garnet layer.The magnetic properties of ReIGs were studied and, in order to optimize them to stabilize smaller magnetic textures like stripe domains or bubbles, several ways of reducing effective anisotropy were investigated. Two of them, including the optimization of the annealing parameters and the fabrication of YIG/TmIG bilayers with different easy magnetization axis, turned out to be quite efficient. This allowed us to tune the effective anisotropy to stabilize stripe domains and magnetic bubbles at remanence. The studies of the ReIG magnetization dynamics demonstrated that its properties highly depend on the garnet composition, and, therefore, on the fabrication process and the annealing procedure conditions. An optimum of these constrains was found allowing to preserve the low damping of ReIGs.The synchrotron studies of ReIGs demonstrated the difference in the garnet composition between the layer at the interface and the surface and confirmed the presence of a non-magnetic layer, created due to the substrate diffusion into the garnet layer. This effect was observed during the crystallization studies, and the approximate thickness of this layer ≈2 nm was determined from both hard and soft X-ray measurements

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Kirouane, Souad. "Conception et réalisation d'un isolateur coplanaire en bande X pour des applications télécoms." Thesis, Saint-Etienne, 2010. http://www.theses.fr/2010STET4002.

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La minimisation des circuits et la montée en fréquence constituent deux enjeux importants des systèmes de communication du futur. Cela nécessite un haut degré d'intégration, des performances plus élevées à coût réduit. Ce travail a pour objectif la conception et la réalisation de nouveaux isolateurs réalisés sur ligne coplanaire asymétrique à base de deux types de matériaux ferrite : hexaferrite de baryum (BaM) et grenat d’yttrium et de fer (YIG). La première étude, présentée sur une structure coplanaire à couche de BaM, a été effectuée pour montrer la faisabilité d’un isolateur à déplacement de champ dans la bande 40-50 GHz. La seconde a utilisé le YIG saturé pour des applications autour de 10 GHz. La nouvelle structure d’isolateur utilise le phénomène physique de déplacement de champ lorsqu’elle est polarisée par un champmagnétique continu. Elle est constituée d’une ligne coplanaire asymétrique gravée sur une couche ou un substrat magnétique et d’un demi-plan de masse arrière. Plusieurs séries de prototypes ont été fabriquées puis caractérisées à partir d’un banc de mesure hyperfréquence composé d’un testeur sous pointes à trois accès et d’un analyseur vectoriel de réseaux. Les résultats expérimentaux sont très encourageants car nous obtenons des pertes d’insertion faibles, dans le meilleur des cas inférieures à 1 dB et une isolation de plus de 16 dB
The minimization of circuits and the increasing frequency are two important issues of future communication systems. That requires a high degree of integration, higher performance at reduced cost. This work aims to design and implementation of new isolators on coplanar line based on two types of ferrite materials: barium hexaferrite (BaM) and garnet and yttrium iron (YIG). The first study presented on a planar layer of BaM leads to the feasibility of the isolator of field displacement in the 40-50 GHz band. The second one concerns the use of saturated YIG for applications around 10 GHz. The magnetic field displacement phenomenon appears when the magnetic substrate is polarized by a D.C. magnetic field. The new isolator structure is made from an asymmetric coplanar line put on a layer or magnetic substrate with a half ground plane placed under this substrate. Several sets of prototypes are fabricated and characterized from a measurement bench which is composed by a microwave prober and a vector network analyzer. The experimental results are very promising because low insertion loss (less than 1 dB) and isolation (over 16 dB) have been obtained

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Zahwe, Oussama. "Conception et Réalisation d'un Circulateur Coplanaire à Couche Magnétique de YIG en Bande X pour des Applications en Télécommunications." Phd thesis, Université Jean Monnet - Saint-Etienne, 2009. http://tel.archives-ouvertes.fr/tel-00419725.

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Dans le domaine des hyperfréquences, les composants passifs actuellement commercialisés, de type circulateurs ou isolateurs, sont fabriqués de façon unitaire à partir des substrats de ferrite et avec des structures microruban ou triplaque. La miniaturisation et l'intégration des ces circulateurs nécessitent de disposer d'une couche mince magnétique qui possède des propriétés magnétiques proche des matériaux massifs. Ce travail s'intéresse donc à deux points particuliers pour la réalisation du circulateur : miniaturisation et fabrication collective. Les travaux relatés dans ce manuscrit ont pour objectif la conception et la réalisation d'un circulateur coplanaire à couche magnétique de YIG en bande X pour des applications en télécommunications. L'étude présentée débute la mise en place d'un processus de dimensionnement. A partir des travaux de Bosma, les règles de design sont mises en place de façon analytique pour un circulateur triplaque. Après avoir affiné les dimensions de façon numérique, les résultats sont transposés à la structure coplanaire et optimisés à l'aide d'un simulateur électromagnétique. Plusieurs structures de circulateur en couche mince et couche massive sont utilisées. Les épaisseurs vont de 16 à 1000 µm. Plusieurs séries de prototypes sont fabriquées puis caractérisées à partir d'un banc de mesure hyperfréquence composé d'un testeur sous pointes à trois accès et d'un analyseur vectoriel de réseaux. Les résultats expérimentaux de différents prototypes de différentes épaisseurs sont présentés tout en dressant une comparaison avec les rétro-simulations en 3D. Une réflexion sur les résultats généraux est réalisée et nous proposons des pistes pour l'amélioration des performances de nos prototypes.

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Rochet, Antonine. "Manipulation optique de vortex d'Abrikosov individuels dans les supraconducteurs et applications." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0148/document.

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À l'interface entre l'optique, le magnétisme et la supraconductivité, nous cherchons à dévelop-per de nouveaux concepts pour la manipulation optique, la génération et l'étude des vortex d'Abrikosov individuels dans des systèmes supraconducteurs. D'une part, nous démontrons l'efficacité d'une méthode optique de génération spontanée d'une paire de vortex/anti-vortex par effet Kibble Zurek basée sur l'utilisation d'une impulsion laser focalisée à la surface d'un film supraconducteur. C'est une technique en champ lointain, rapide qui permet de créer et piéger une paire dans le condensat supraconducteur à une position stable et reproductible. Cette expérience est également adaptée à l'étude du scénario Kibble-Zurek, relatif à la nucléation spontanée de défauts topologiques, tels que les vortex d'Abrikosov, lors de transitions de phase rapides du second ordre. D'autre part, nous présentons les résultats d'une expérience pompe-sonde visant à étudier l'effet Faraday inverse dans le grenat de BiLuIG servant à l'imagerie magnéto-optique des vortex. Nous montrons qu'il est possible de générer un champ magnétique femtoseconde de plusieurs Tesla localisé dans le grenat grâce à une impulsion laser ultra-courte de polarisation circulaire. Ces résultats nous permettent d'étudier les conditions expérimentales pour une génération de paires de vortex/anti-vortex par méthode magnéto-optique, basée sur l'application d'un fort champ magnétique à la surface du supraconducteur. La possibilité de manipuler et générer les vortex, véritables nano-objets de l'état supraconducteur, offre des perspectives prometteuses quant au développement du contrôle optique de micro-circuits supraconducteurs tels que les jonctions Josephson
At the interface between optics, magnetism and superconductivity, we want to develop new concepts for the optical manipulation, the generation and the study of individual Abrikosov vortices in superconducting systems. On one hand, we demonstrate the efficiency of an optical method to perform spontaneous generation of a single vortex/anti-vortex pair by Kibble Zurek effect, based on a laser pulse focused at the superconductor film surface. It is a fast far field method to create and trap a pair into the superconducting condensate at a reproducible and stable position. This experiment is also adapted to the study of the Kibble Zurek mechanism, describing nucleation of topological defects such as Abrikosov vortices during a fast second order phase transition. On the other hand, we present the results of a pomp-probe experiment to the study the inverse Faraday effect into a BiLuIG garnet used for magneto-optical imaging of vortices. We show the possibility to produce a strong femtosecond magnetic field of a few Tesla localized into the garnet with a circularly polarized ultra-short laser pulse. Those results lead to the determination of the experimental conditions necessary to generate a vortex/anti-vortex pair with a magneto-optical method based on the application of a strong magnetic field close to the superconductor surface. Fast optical manipulation and generation of vortices, which are intrinsic nano-objects of the superconducting state, should enable the development of optically driven superconducting micro-circuits such as Josephson junctions

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Ravel, Frédéric. "Contribution à l'étude de l'implantation fer dans les grenats par microscopie électronique en transmission." Grenoble 1, 1986. http://www.theses.fr/1986GRE10127.

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Etude des effets de l'implantation d'ions fers dans y::(3)al::(5)o::(12),gd::(3)ga::(5)o::(12) et y::(3)fe::(5)o::(12) par differentes techniques (microscopie electronique en transmission, retrodiffusion rutherford, diffraction rx). Les changements structuraux et les modifications des proprietes magnetiques dus a l'implantation sont etudies avant et apres recuit

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Ravel, Frédéric. "Contribution à l'étude de l'implantation fer dans les grenats par microscopie électronique en transmissions." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb37600668n.

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Abdel, Samad Bassel. "Elaboration, étude et caractérisation de couches minces dans les grenats de fer et d'yttrium : applications dans le domaine télécommunication." Saint-Etienne, 2009. http://www.theses.fr/2009STET4007.

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Le travail de thèse a commencé par l'élaboration des couches minces de grenat de fer et d'yttrium (YIG) au laboratoire DIOM de Saint-Etienne, par pulvérisation cathodique radio fréquence. Une centaine d'échantillons a été réalisée en faisant varier les conditions de dépôt : débit d'argon, débit d'oxygène, chauffage du substrat et recuit sous air et sous vide. La caractérisation magnéto-optique et magnétique des échantillons a été réalisée par l'étude de l'effet Faraday, de l'effet Kerr, le VSM permettant de vérifier les propriétés magnétiques des couches minces. L'état de surface des échantillons a été analysé par microscopie électronique à balayage. La mesure de l'épaisseur des couches est réalisée par un profilomètre. La technique de caractérisation par rétrodiffusion d'ions α (RBS) réalisée par une équipe du CNRS au Liban, a permis de déterminer la stœchiométrie des différents échantillons. L'état cristallin des échantillons a été réalisé par l'analyse de diffractions des rayons X, ces travaux ont abouti à certaines améliorations. Le travail présente également le design du circulateur coplanaire, l'élaboration des couches magnétiques, de la réalisation de la structure en salle blanche (Laboratoire Hubert Curien) et en finalité sur la caractérisation des dispositifs. Les circulateurs que nous avons réalisés présentent un effet non-réciproque très intéressant, y compris pour des épaisseurs de ferrite très faibles (8µm)
The thesis work began with the preparation of thin films of yttrium iron garnet (YIG) in DIOM Laboratory at Saint-Etienne, by radio frequency sputtering. Hundreds of samples was elaborated by varying the deposition conditions : argon flow, oxygen flow, heating the substrate during deposition and annealed in air and vacuum. The magneto-optical and magnetic characterization samples was performed by studying the Faraday effect, the Kerr effect, and the VSM to check the magnetic properties of the films. The surface samples were analyzed by scanning electron microscopy. Measuring the thickness of the films was achieved by a profilometer. The technique of characterization by Rutherford backscatter (RBS) performed at CNRS team in Lebanon, was determined the stoichiometry of samples. The crystalline state of samples was performed by X-ray diffraction ; this work has resulted in some improvments. This work also presente the design of a coplanar circulator, development of the magnetic films, the elaboration of its structure in a clean room (Hubert Curien Laboratory) and finally on the characterization of the devices. The circulator that we've made presente an interesting non-reciprocal effect, for small ferrite films thicknesses of (8µm)

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15

Kornilios, Nicolas. "Contribution à l'étude de grenats implantés en ions 57Fe par effet Mössbauer." Lyon 1, 1986. http://www.theses.fr/1986LYO10084.

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Etude de monocristaux de y::(3)fe::(5)o::(12), y::(3)al::(5)o::(12) et gd::(3)ga::(5)o::(12) implantes avec **(u)5**(7) (100 kev, 10**(16)-10**(17) ions/cm**(2)). Determination des etats chimiques du fer, influence des elements de la matrice sur la nature des phases formees. Caracterisation des couches superficielles au cours des traitements thermiques par spectrometrie moessbauer, diffraction rx en incidence rasante, microscopie electronique a transmission et retrodiffusion rutherford; mise en evidence de l'oxydation du fer implante au dessus de 650**(o)c, de la recristallisation du grenat vers 850**(o)c, de la formation des oxydes (deal)::(2)o::(3), (fega)::(2)o::(3) et fe::(2)o::(3). Possibilite de transition de morin a la temperature ambiante apres recuit a 1200**(o)-1300**(o)c

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16

Chowne, Peter. "Aspects of later prehistoric settlement in Lincolnshire : a study of the Western Fen margin and Bain Valley." Thesis, University of Nottingham, 1988. http://eprints.nottingham.ac.uk/14364/.

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The objective of this research was to examine the development of settlement in Lincolnshire during the 4th-1st millennia B.C. by a detailed investigation of two contrasting areas, the western fen margin and the Bain Valley. To understand how the fen margin settlements evolved it was necessary to study the development of the ancient landscape. This was achieved by a combination of fieldwalking, examination of aerial photographs and by recording fenland drainage sections. By studying the soils and their depositional history it was possible to relate drying out and flooding episodes to the traditional fenland sequences. The excavation of a Bronze Age and Iron Age settlement at Billingborough was described in detail and compared with similar remains from other sites. The Bain Valley was studied by a combination of survey and excavation. An area between Ludford and Tattershall was investigated by fieldwalking transects across the valley and onto the Wolds. A detailed survey of two flint scatters was undertaken. The results of two major excavations at Tattershall Thorpe were presented. One was a Neolithic settlement with associated ceramics and lithic industry the other an Iron Age defended enclosure with waterlogged ditch deposits. The two study areas were then compared, contrasted and discussed in a broader context. Results of the research suggest that a mixed agricultural economy developed on the western fen margin in the Bronze Age and a predominantly pastoral economy in the Bain Valley and on the Wolds. Early in the 1st millennium, in a period of increasing wetness and flooding, settlement patterns changed with the Witham Valley becoming the focus of attention a role it continued to play in the Iron Age. A shift towards semi-urban settlement takes place in the 1st century B.C. with the formation of major Iron Age centres. Extensive land divisions also appear at this time and it is suggested that these may relate to the territories of these centres.

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17

Teurtrie, Adrien. "Towards a magnetic semiconductor using Ca and Y co-substituted bismuth iron garnet thin films." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS464.

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Ce travail s'inscrit dans le domaine des oxydes multifonctionnels pour l'électronique "tout-oxyde" afin de développer un matériau semi-conducteur magnétique combinant à la fois des porteurs de charge et un ordre magnétique. Le couplage de ces deux propriétés à 300 K est un enjeu majeur qui permettrait de contrôler le magnétisme par un champ électrique ou les porteurs de charge par un champ magnétique. De nombreux travaux ont été réalisés sur le dopage de semi-conducteurs classiques comme GaAs (DMS) ou des oxydes semi-conducteurs comme ZnO (DMO) par des cations magnétiques 3d. Pour les DMS, le couplage entre les propriétés électriques et magnétiques n'est présent que jusqu'à 190 K. Tandis qu'une température de Curie (Tc) de 900 K est atteinte pour les DMO sans toutefois présenter de couplage avec les propriétés électriques. Dans cette thèse, l'approche inverse a été appliquée où des cations aliovalents et/ou isovalents sont en substitution au sein d'un oxyde magnétique isolant afin d'induire des porteurs de charge. Le grenat de bismuth fer (BIG) présente des propriétés remarquables dont la rotation Faraday géante induite par la présence de Bi, un couplage magnéto-électrique à 300 K et Tc de 660 K résultant du couplage ferrimagnétique entre les sous-réseaux tétraédriques et octaédriques de fer. Des calculs théoriques montrent que la structure électronique du BIG favoriserait un transport électronique polarisé en spin.La croissance de grenats de fer riche en Bi ne pouvant pas être réalisée sous forme de monocristaux massifs, des films de BIG co-dopés à l'Y (0.2 à 0.5 Y par formule unitaire) et au Ca (0 à 0.3 Ca par formule unitaire) sur le site du Bi ont été synthétisés par dépôt laser pulsé sur un substrat isostructural. Le Ca²⁺ tend à induire la formation de Fe³⁺/⁴⁺ et une conduction de type p alors que le co-dopage d'Y³⁺ permet de maintenir constante la concentration de Bi (2.5 par formule unitaire) préservant la rotation Faraday géante.Les films présentent une phase grenat majoritaire bien cristallisée et epitaxiée. Une phase minoritaire d'hématite faiblement cristallisée et texturée est aussi présente sans toutefois former de chemin de percolation. Cette phase n'est pas détectable par diffraction des rayons X et n’altère pas les propriétés physiques des films. La distribution des dopants et des charges au sein de ces films a été étudiée notamment par microscopie électronique (Cs-STEM) et spectroscopie de pertes d’énergie des électrons (EELS) jusqu’à l’échelle atomique. Le Ca et l'Y se substituent dans la maille de grenat sans former d’agrégats. Les films présentent une sous-stoechiométrie en oxygène s'ajustant à l'aide de recuits sous atmosphère contrôlée tout en conservant leurs propriétés structurales et microstructurales. Ces grenats co-dopés au Ca et à l'Y présentent un comportement semi-conducteur de type p (ρ(450 K)=3x10⁴ Ω cm) tandis que le BIG dopé uniquement à l'Y révèle un comportement semi-conducteur de type n (ρ(450 K)=10¹ Ω cm) ; ce qui est dix ordres de grandeur inférieur au grenat d’yttrium fer. En outre, les films de type n montrent un changement de résistivité réversible de trois ordres de grandeur lors de recuits sous atmosphère inerte ou oxydante. La présence de Fe⁴⁺ au sein des films de type p n'a pas pu être mise en évidence ni par EELS ni par spectroscopie d'absorption des rayons X ; les porteurs de type p sont à priori compensés par des lacunes d'oxygène. Les films de type n présentent une concentration de porteurs correspondant à 12% de Fe²⁺ principalement localisés sur les sites tétraédriques du fer. Les films conservent une rotation Faraday géante ainsi qu’une Tc> 590 K.La présence simultanée d’un comportement semi-conducteur de type p ou n, d’une Tc> 600 K, d’une rotation Faraday géante ainsi que des calculs indiquant la polarisation en spin du haut de la bande de valence font de ces phases de BIG co-dopés à l'Y et au Ca des candidats prometteurs en tant que semi-conducteur magnétique
This work belongs to the field of multifunctional oxides for "all-oxide" electronics in order to develop a magnetic semiconductor i.e. combining the presence of both charge carriers and a magnetic order. The coupling of these two properties at 300 K is a major challenge that would allow the control of magnetism by an electric field or the control of charge carriers by a magnetic field. Many works were carried out on the doping of conventional semiconductors such as GaAs (DMS) or semiconductor oxides such as ZnO (DMO) by 3d magnetic cations. For DMS, the coupling between the electrical and magnetic properties is only present up to 190 K. While a Curie temperature (Tc) of 900 K is achieved for DMOs without however presenting a coupling with the electrical properties.In this thesis, the inverse approach was applied by substituting aliovalent and/or isovalent cations within an insulating magnetic oxide in order to induce charge carriers. Bismuth iron garnet (BIG) has remarkable properties including the giant Faraday rotation induced by the presence of Bi, a magneto-electric coupling at 300K and a Tc of 660 K resulting from the ferrimagnetic coupling between the tetrahedral and octahedral iron sublattices. Theoretical calculations show that the electronic structure of BIG would favor a spin-polarized electronic transport.The growth of Bi-rich iron garnets cannot be obtained in the form of bulk single crystals. Thus, BIG films co-substituted with Y (0.2 to 0.5 Y per formula unit) and Ca (0 to 0.3 Ca per formula unit) on the Bi site have been synthesized by pulsed laser deposition on an isostructural substrate. The Ca²⁺ tends to induce the formation of Fe³⁺/⁴⁺ and a p-type conduction while the co-substitution of Y³⁺ allows to keep the concentration of Bi (2.5 per formula unit) preserving the giant Faraday rotation.The films are mostly composed of a well crystallised and epitaxial garnet phase. A minor secondary phase of weakly crystallized and textured hematite is also present but does not form a percolation path. This phase is not detectable by X-ray diffraction and does not alter the physical properties of the films. The distribution of dopants and charges within these films was studied notably by electron microscopy (Cs-STEM) and electron energy loss spectroscopy (EELS) down to the atomic scale. Ca and Y substitute within the garnet lattice without forming aggregates. The oxygen stoichiometry of the films can be adjusted by means of controlled atmosphere annealing while maintaining their structural and microstructural properties. These Ca and Y co-substituted garnets have a p-type semiconductor behaviour (ρ(450 K)=3x10⁴ Ω cm) while the Y-only substituted BIG exhibits a n-type semiconductor behavior (ρ(450 K)=10¹ Ω cm) ; this resistivity is ten orders of magntitude lower than that of yttrium iron garnet. In addition, n-type films exhibit a reversible resistivity change of three orders of magnitude upon annealing under an inert or oxidizing atmosphere. The presence of Fe⁴⁺ in p-type films could not be identified neither by EELS nor by X-ray absorption spectroscopy as p-type charge carriers are a priori compensated by oxygen vacancies. N-type films have a carrier concentration corresponding to 12% of Fe²⁺ mainly located on the Fe tetrahedral sites. The films conserved the giant Faraday rotation Faraday and a Tc> 590 K.The simultaneous presence of either n- or p-type semiconductor behaviour, a Tc> 600 K, a giant Faraday rotation and calculations indicating a spin-polarization of the top of the valence band make these Y and Ca co-substituted BIG phases promising candidates as magnetic semiconductors

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18

Chassé, Mathieu. "Geochemical and crystal-chemical processes of scandium enrichment from the mantle to lateritic contexts - Contribution to the understanding of the processes of critical metals enrichment." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066282/document.

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L'approvisionnement en métaux rares est devenu un sujet de préoccupation majeur du fait de nombreuses incertitudes géopolitiques et de leur utilisation croissante dans des produits de haute technologie. Cependant, pour assurer l'approvisionnement, des progrès doivent être accomplis dans la compréhension de la ressource. Parmi les métaux rares, la demande potentielle pour le scandium (Sc) est croissante, du fait de son utilisation dans des alliages de haute technologie ainsi que dans les piles à combustible. L'approvisionnement n'est actuellement pas assuré mais les gisements latéritiques sont des cibles prometteuses. Le Sc pourrait devenir un sous-produit de nombreuses latérites nickélifères, et même le principal produit des minerais latéritiques à fortes teneurs découverts dans l'est australien. Pour comprendre l'origine de ces enrichissements latéritiques en Sc, nous avons étudié les processus géochimiques et cristallochimiques qui forment l'un de ces gisements (Syerston–Flemington, Nouvelle-Galle du Sud). Une méta-analyse des études géochimiques portant sur les roches et minéraux mantelliques, qui forment les roches mères de toutes les latérites enrichies en Sc connues à ce jour, révèle que les lithotypes les plus favorables sont les cumulats à clinopyroxène ou amphibole. Cette étude montre aussi un changement drastique dans la compatibilité du Sc avec la profondeur dans le manteau, allant d'incompatible dans le faciès à spinelle à compatible dans le faciès à grenat. Cette dualité est particulièrement intéressante pour tracer la profondeur de fusion partielle des roches extrusives.Une étude intégrée combinant diffraction des rayons X, analyses chimiques en roche totale et à l'échelle microscopique, ainsi que l'absorption des rayons X, a été menée dans le but de comprendre les processus de concentration du Sc durant l'altération latéritique. Les profils latéritiques riches en Sc résultent de la dissolution des minéraux primaires présentant des enrichissements en Sc légers, mais significatifs. Ensuite, le Sc est piégé successivement par les smectites, puis les oxydes de fer après la dissolution des phases argileuses. Les teneurs en Sc reflètent la haute capacité d'adsorption de cet élément par la goethite. Avec les mécanismes de dissolution–précipitation formant des générations successives de goethite, cette capacité préserve l'immobilité du Sc alors que la plupart des autres éléments sont lessivés, amenant à de hautes concentrations résiduelles
The supply of rare metals has become a great concern due to the combination of geopolitical uncertainties and increasing use in new high-technology materials. However, to secure supply, progress on the understanding of the resource is needed. Among rare metals, there is a growing potential demand for scandium (Sc), resulting from its use in high-performance alloys and solid oxide fuel cells. The current supply is not guaranteed but lateritic deposits are a promising target. Scandium could become a by-product of many nickel laterites, and even the main product of high-grade lateritic Sc ores in eastern Australia. To understand the origin of lateritic Sc enrichment, we investigated the geochemical and crystal-chemical processes forming one of these deposits (Syerston–Flemington, New South Wales). A meta-analysis of geochemical studies on mantle-derived rocks and minerals, which form the parent rocks of all known Sc-enriched laterites reveals that the most favourable lithotypes are cumulates of clinopyroxene or amphibole. It also shows a drastic change in the compatibility of Sc with increasing depth in the mantle, ranging from incompatible in the spinel facies to compatible in the garnet facies. This dichotomy is of great interest for tracing the depth of partial melting of extrusive rocks.Integrated X-ray diffraction, whole-rock and microscopic chemical analyses and X-ray absorption spectroscopy have been used to understand the processes that concentrate Sc during lateritisation. Scandium-rich lateritic profiles result from the dissolution of primary minerals containing slight but significant Sc enrichment, followed by successive trapping by smectite and iron oxides after dissolution of the clay phases. Scandium grades reflect the high capacity of goethite to adsorb this element. Along with mechanisms of dissolution–precipitation forming successive generations of goethite, it preserves Sc immobility while most other elements are leached, leading to high residual concentrations of Sc

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19

Valette, Pascale. "Dynamique de paroi de domaines magnetiques dans des grenats ferrimagnetiques." Paris 6, 1987. http://www.theses.fr/1987PA066654.

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Etude des oscillations de parois de domaines magnetiques de couches de grenats substitues (gdbipr)::(3)(alfe)::(5)o::(12) et bi::(3)(algafe)::(5)o::(12) par effet faraday a 6328 a et sous un champ magnetique d'une frequence allant jusqu'a 50mhz. L'intensite lumineuse transmise est mesuree en fonction de la frequence et de l'intensite du champ applique. Deux modeles de parois sont correles aux resultats experimentaux. Un modele de paroi non isolee sans ligne de bloch est en accord avec les resultats experimentaux

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20

Ou, Zhirong. "US post-war monetary policy and the Great Moderation : was the Fed doing a good job?" Thesis, Cardiff University, 2011. http://orca.cf.ac.uk/54463/.

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Using indirect inference based on a VAR this thesis confronts the US data from 1972 to 2007 with a standard New Keynesian model in which either an optimal timeless policy or a Taylor rule is assumed prevails. By comparing the models' performance in fitting the dynamics and size of the data, it finds in both the episodes of the Great Acceleration and the Great Moderation that the Fed's underlying behaviour was better understood as the timeless optimum either under standard calibration or under estimation. The implication is that to the final analysis the Great Moderation is a result of improved environment as the volatility of shocks has fallen, rather than one occurred as policy improved. Smaller Fed managerial errors caused the moderation in inflation. Smaller supply shocks caused the moderation in output and smaller demand shocks the moderation in interest rates. In either episode the same model with differing Taylor rules of the standard sorts generally fails to fit the data well. But the optimal timeless rule model could have generated data in which Taylor rule regressions could have been discovered, creating an illusion that the Fed was following such policies and that the improved economy was caused by changed pattern of these.

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21

Neu, Roene Ellen Medellia. "An Investigation of Source Water Feeding Buck Creek, Great Sand Dunes National Monument and Preserve." Bowling Green State University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1100552677.

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22

Chassé, Mathieu. "Geochemical and crystal-chemical processes of scandium enrichment from the mantle to lateritic contexts - Contribution to the understanding of the processes of critical metals enrichment." Electronic Thesis or Diss., Paris 6, 2017. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2017PA066282.pdf.

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L'approvisionnement en métaux rares est devenu un sujet de préoccupation majeur du fait de nombreuses incertitudes géopolitiques et de leur utilisation croissante dans des produits de haute technologie. Cependant, pour assurer l'approvisionnement, des progrès doivent être accomplis dans la compréhension de la ressource. Parmi les métaux rares, la demande potentielle pour le scandium (Sc) est croissante, du fait de son utilisation dans des alliages de haute technologie ainsi que dans les piles à combustible. L'approvisionnement n'est actuellement pas assuré mais les gisements latéritiques sont des cibles prometteuses. Le Sc pourrait devenir un sous-produit de nombreuses latérites nickélifères, et même le principal produit des minerais latéritiques à fortes teneurs découverts dans l'est australien. Pour comprendre l'origine de ces enrichissements latéritiques en Sc, nous avons étudié les processus géochimiques et cristallochimiques qui forment l'un de ces gisements (Syerston–Flemington, Nouvelle-Galle du Sud). Une méta-analyse des études géochimiques portant sur les roches et minéraux mantelliques, qui forment les roches mères de toutes les latérites enrichies en Sc connues à ce jour, révèle que les lithotypes les plus favorables sont les cumulats à clinopyroxène ou amphibole. Cette étude montre aussi un changement drastique dans la compatibilité du Sc avec la profondeur dans le manteau, allant d'incompatible dans le faciès à spinelle à compatible dans le faciès à grenat. Cette dualité est particulièrement intéressante pour tracer la profondeur de fusion partielle des roches extrusives.Une étude intégrée combinant diffraction des rayons X, analyses chimiques en roche totale et à l'échelle microscopique, ainsi que l'absorption des rayons X, a été menée dans le but de comprendre les processus de concentration du Sc durant l'altération latéritique. Les profils latéritiques riches en Sc résultent de la dissolution des minéraux primaires présentant des enrichissements en Sc légers, mais significatifs. Ensuite, le Sc est piégé successivement par les smectites, puis les oxydes de fer après la dissolution des phases argileuses. Les teneurs en Sc reflètent la haute capacité d'adsorption de cet élément par la goethite. Avec les mécanismes de dissolution–précipitation formant des générations successives de goethite, cette capacité préserve l'immobilité du Sc alors que la plupart des autres éléments sont lessivés, amenant à de hautes concentrations résiduelles
The supply of rare metals has become a great concern due to the combination of geopolitical uncertainties and increasing use in new high-technology materials. However, to secure supply, progress on the understanding of the resource is needed. Among rare metals, there is a growing potential demand for scandium (Sc), resulting from its use in high-performance alloys and solid oxide fuel cells. The current supply is not guaranteed but lateritic deposits are a promising target. Scandium could become a by-product of many nickel laterites, and even the main product of high-grade lateritic Sc ores in eastern Australia. To understand the origin of lateritic Sc enrichment, we investigated the geochemical and crystal-chemical processes forming one of these deposits (Syerston–Flemington, New South Wales). A meta-analysis of geochemical studies on mantle-derived rocks and minerals, which form the parent rocks of all known Sc-enriched laterites reveals that the most favourable lithotypes are cumulates of clinopyroxene or amphibole. It also shows a drastic change in the compatibility of Sc with increasing depth in the mantle, ranging from incompatible in the spinel facies to compatible in the garnet facies. This dichotomy is of great interest for tracing the depth of partial melting of extrusive rocks.Integrated X-ray diffraction, whole-rock and microscopic chemical analyses and X-ray absorption spectroscopy have been used to understand the processes that concentrate Sc during lateritisation. Scandium-rich lateritic profiles result from the dissolution of primary minerals containing slight but significant Sc enrichment, followed by successive trapping by smectite and iron oxides after dissolution of the clay phases. Scandium grades reflect the high capacity of goethite to adsorb this element. Along with mechanisms of dissolution–precipitation forming successive generations of goethite, it preserves Sc immobility while most other elements are leached, leading to high residual concentrations of Sc

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23

Kinský, Jiří. "Velká deprese a Velká recese: role měnové politiky USA." Master's thesis, Vysoká škola ekonomická v Praze, 2014. http://www.nusl.cz/ntk/nusl-206710.

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The thesis analysis the primary causes of the Great Depression and Great Recession in the US. The author is looking for common signs of these crisis with special attention to monetary policy, which is considered as a crucial. The author aims to analyze economic and political measures that accompanied the crisis. The first part deals with the Fed policy including its origin, the roaring twenties, the stock Exchange crash, anti-crisis economical and political measures during the crisis and there is also written about the theoretical interpretation of the different schools of economics. The second part deals with causes of Great Recession, the government sponsored enterprises, the housing bubble or federal emergency programs. Further, it discussed the credit expansion and the Fed´s policy and in the end the author offers an comparison of both crisis and presents his own view on the issue.

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24

Contreras-Luna, Rafael. "Russia's Great Power ambitions : the role of Siberia, the Russian Far East, and the Arctic in Russia's contemporary relations with Northeast Asia." Thesis, Durham University, 2016. http://etheses.dur.ac.uk/12034/.

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Being at the confluence of two worlds – East and West – has had long-term influence on how Russia has thought of its national identity, in particular prompting the question: to what extent is it joining or resisting these two worlds? This thesis argues that Russia’s self-perception of being a great power – greatpowerness - defines its status and position in the world. This ‘greatpowerness’ is a central element of Russia’s national identity and exerts huge influence in the country’s foreign policy making. Under the presidency of Vladimir Putin, Russia has established a long-term project to develop and improve living conditions in Asiatic Russia, and advance its integration into Northeast Asia. This thesis pursues a research study focusing on these problems: Russia’s insistence on its great power status and the idea of Russia as a great power straddling the West and Asia as a key demand of national identity. The thesis tries to explain how Russian foreign policy reflects this; but also how Asiatic Russia remains a central element defining and promoting this national identity and its quest for great power status. This thesis aims to examine how the aforementioned ideas relate to the apparent necessity of Russia to develop Asiatic Russia and integrate it into Northeast Asia and the broader Asia-Pacific region, pointing out to the dilemmas between cooperation and security issues. The function and perception of Asiatic Russia has never been exclusively internal or external but has always arisen out of the interaction of the two. Therefore this thesis does not only study changes in Asiatic Russia in the post-Soviet period; but also the new external conditions in Northeast Asia. This thesis attempts to connect three aspects—national identity, geographical settings, and external strategy, to determine the place of Siberia, the Russian Far East, and the Arctic in Russia’s contemporary relations with Northeast Asian countries.

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25

Flores, Norma Lisa. "When Fear is Substituted for Reason: European and Western Government Policies Regarding National Security 1789-1919." Bowling Green State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1350932743.

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26

Christie, Ross. "'Britain's crisis of confidence' : how Whitehall planned Britain's retreat from the extra-European world, 1959-1968." Thesis, University of Stirling, 2004. http://hdl.handle.net/1893/2018.

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This thesis attempts to give an account of how Whitehall planned Britain's withdrawal from extra-European commitments in the years 1959-1968, demonstrating that foreign policy development was essentially a cross-departmental process, involving a synthesis of views articulated by the Treasury, Board of Trade, Ministry of Defence, Colonial Office, Commonwealth Relations Office, as well as the Foreign Office. More specifically, the thesis is concerned with the direct effects of the interplay of different departmental policies on British retrenchment from Africa, the Middle East, and the Far East. Most accounts of how ministers and officials approached the subject of withdrawal from international commitments lack any substantive analysis of documentary evidence, a fact attributable to the 'thirty-year rule'. Many academic works also contain a reference to 'delusions of grandeur' as the main explanation as to why Whitehall guided a tentative course in extracting Britain from its remaining overseas obligations. By examining Whitehall's attempts to review future policy, usually on an inter-departmental basis, this thesis questions the commonly held assumption that an outdated imperial sentiment permeated the political establishment until economic reality, namely the devaluation of sterling in November 1967, forced Britain to confront the fragility of its position. Developing and expanding upon previous scholarship, this thesis makes a contribution to historical knowledge by providing the first sustained and unified study of how the highest echelons of Whitehall framed Britain's long-term strategic aims in the late 1950s and 1960s. This thesis is a contribution to administrative, diplomatic and military history, and provokes a number of questions. To what extent, for example, did economic considerations inform the decisions of leading policy-makers? Did a misjudgment over the strength of British 'power' lead to the pursuit of inappropriate foreign policy objectives? How was foreign policy affected by defence policy? What influence did the Treasury exert over high foreign policy? Did the influence of civil servants vary according to policy issues and the personalities involved? In what ways did the views of the departments responsible for economic matters differ from those in charge of defence policy on the priority attached to military expenditure? To what extent did the Foreign Office and Ministry of Defence disagree on matters regarding Britain's overseas commitments and possessions? In answering such questions, this thesis casts new light on how Whitehall, between 1959 and 1968, reduced the scope of Britain's international commitments, redirecting the central thrust of British foreign policy away from extra-European commitments towards Europe.

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Lahoubi, Mahieddine. "Structures magnétiques non colinéaires et transitions de phases dans les grenats ferrimagnétiques de terbium et d'yttrium." Grenoble 1, 1986. http://www.theses.fr/1986GRE10068.

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Determination par diffraction neutronique de la structure magnetique de tb::(3)fe::(5)o::(12) et de son evolution en fonction de la temperature de 4,2k a 650k (t::(n)=560k); analyse theorique des representation des groupes d'espace cubique ia3d rhomboedrique r**(3c) et application aux spectres de diffraction. Etude, par des mesures d'aimantation, du comportement de tb::(3)fe::(5)o::(12) et de tb::(x)y::(3-x)fe::(5)o::(12) (x=1,98; 1,0 et 0,37) en presence de champs magnetiques intenses, appliques selon les directions cristallographiques principales; mise en evidence de nombreuses transitions de reorientation de spin et determination des diagrammes de phases, entre 4,2 et 300k. Cas particulier du compose a x=0,37 qui presente une transition due a un croisement de niveaux de l'ion tb

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Vicente, Beaufils Bénédicte. "L’expression de la culture de l’eau dans l’Alhambra : poids de la réalité et pouvoir de l’imaginaire." Rennes 2, 2008. http://tel.archives-ouvertes.fr/tel-00401425/fr/.

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A Grenade comme dans toute la Péninsule, l’Alhambra se révèle, incontestablement, comme l’expression la plus aboutie de la culture musulmane de l’eau. Inspirés des plus grandes civilisations antérieures, les Nasrides sont effectivement parvenus à compléter ce legs ancestral pour le transformer en une véritable culture de l’eau en Espagne ; il leur fallait pour cela non seulement une implication dans la vie quotidienne et religieuse des habitants, mais également au niveau architectural, par le biais de l’esthétisme et du ludisme. Ce fait étant établi, il est intéressant de se pencher plus avant sur l’héritage de cette culture au sein de l’Alhambra. Car force est de constater que ce legs, aujourd’hui, revêt deux aspects distincts. Bien entendu, il nous faut le considérer en termes matériels puisque cette culture s’exprime encore de nos jours pleinement dans l’architecture même des palais et jardins du joyau nasride de Grenade. Mais nous ne pouvons ni ne devons oublier que cette culture s’est également longtemps exprimée à travers le domaine de l’imaginaire, parfois même en dehors et au détriment de cette réalité matérielle et historique du monument. En ce sens, il nous semble important de nous interroger sur le pouvoir de ces deux héritages de la culture nasride de l’eau aujourd’hui, et leur dimension respective dans les mentalités actuelles concernant l’Alhambra
In Granada, just like in the whole peninsula, Alhambra is definitaly the most advanced expression of Muslim water culture heritage. Inspired by previous generations, the Nasride people has modified this tradition into a real Spanish water culture tradition. To do so, it had to penetrate inhabitants everyday and religious life, as well as to influence architecture through estheticism and fun. That being said, one should take a closer look into the heritage of that culture within Alhambra, as this heritage has nowadays two different aspects. On the one hand, those should be considered from a material point of view, as the study of the architecture of the palaces and gardens of nasride jewel of Granada will reveal its influence. But on the other hand, one can not and one should not forget that that culture has strongly expressed itself in the imaginary of the local people, sometimes even against its contemporary material and historical reality. With those two aspects in mind, it is important to us to question not only the power of both of those heritages on today’s nasrid culture of water, but also the influence of each heritage in contemporary people relationship with Alhambra

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Iglesias, Rogers Graciela. "British liberators : the role of volunteers in the Spanish forces during the Peninsular War (1808-1814)... and far beyond." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.669998.

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Lamaczová, Michaela. "Federální rezervní systém v letech 2000-2011." Master's thesis, Vysoká škola ekonomická v Praze, 2010. http://www.nusl.cz/ntk/nusl-85863.

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Dissertation deals with the Federal reserve system, which is the central Bank of the United states of America. The dissertation is supposed to analyze monetary politics of FED with regard to the possible connection of this institution with the last financial crisis. Chapter nbr. I. introduces short history of the central banking in the USA, the situation before FED was created, circumstances with the enactment of Federal Reserve act from 1913, followed by foundation of FED and first of all about its task during the period of Great depression in the 30th of the 20th century. Enclosed is the overview of critical economical opinions how the FED was functioning. The second part of the dissertation describes the monetary politics of FED before the crisis years 2000-2007. It evaluates the main steps the FED undertook to prevent or alleviate the incomming crisis. Further it evaluates these steps with recommendations of renowned and respected economists. Next chapter deals with the mortgage market crisis and with the monetary politics of FED between the years 2007-2011. This chapter also describes different situation of FED and European central bank and their monetary politics as a reaction to the mortgage crisis. Fourth and last chapter is aimed at the possible cause of the financial crisis and present development of FED.

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Abidin, Shamharir. "Audit market concentration and auditor choice in the UK." Thesis, University of Stirling, 2006. http://hdl.handle.net/1893/119.

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Auditing has an important role in the corporate governance process and is essential in ensuring confidence in the reliability of financial information. It is important to understand the reasons why, given the costs involved, companies change their auditor and choose a particular level of audit assurance. To date, however, only a limited number of studies on auditor choice issues are available, especially in the UK setting. Further, since the downfall of Andersen, the audit market environment has changed significantly, creating a new audit environment to be researched. In light of these recent developments, the objectives of this thesis are to address both concentration and auditor choice issues. It is divided into two separate but interrelated parts. The first part of this thesis provides evidence on audit market concentration in the UK domestic listed company market from 1998 to 2003. The effect of Andersen’s demise on both audit market concentration and audit fees is examined. Using four different size measures (number of audits, audit fees, clients’ total assets and sales), three measures of concentration are calculated. Results show that the UK audit market has now clearly surpassed the tight oligopoly threshold and, despite auditing significantly fewer clients in 2003 than in 1998, the B5/4 managed to increase their fee dominance. In particular, the decline in B5/4 ‘number of clients’ market share was mainly due to their lower share of the newly-listed companies audit market. On the other hand, the slight increase in B5/4 audit fee market share was due to the net impact of leavers concentrating the B5/4 share and joiners diluting it. Voluntary switches to/from the B5/4 had a relatively small impact on B5/4 market share for both measures. Following Andersen’s acquisition by Deloitte & Touche, market levels of audit fee and audit fee rate (audit fee scaled by total assets) have increased markedly, suggesting that more audit effort is being expended as a way to restore confidence about audit quality after the damage caused by Andersen’s alleged misconduct. The acquisition has also contributed to a further increase in ‘audit fee’ market concentration for the 4-firm concentration ratio (CR4) and in the overall Hirschman-Herfindahl Index measure. Although, Deloitte & Touche gained significant market share in terms of both audit fees and number of audits through its acquisition of Andersen, it is PricewaterhouseCoopers that continues to hold the largest market share. Deloitte & Touche retained 93 former Andersen clients (74%), 21 (17%) moved to another B5/4 auditor and 11 (9%) chose a non-B5/4 firm. While former Andersen clients paid higher audit fees, in aggregate, the increase was, perhaps surprisingly, less than for the market as a whole. At the industry level, the B4 firms dominated all sectors, the highest non-B5/4 market share in any industry being just 8%. In 2003, PricewaterhouseCoopers was the leader in 18 out of 34 sectors. The second part of the thesis is divided into two separate studies – auditor change determinants and new auditor selection determinants. These studies use a sample of non financial auditor change companies to test logistic regression models of the determinants of auditor change and new auditor selection. The determinant variables include auditee, auditor and audit characteristics. This part also examines the sensitivity of results to alternative functional forms of the basic model specification. Two definitions of auditor quality – brand name auditor and specialism, are employed. Internal governance issues such as audit committee independence, the duality of chairman/CEO as well as the size/quality of the incumbent auditor were found to be significant determinants of auditor change. Expected future growth in the company, rather than past growth, and audit fee reduction were positively related to audit change probability. Result also suggests that companies changed auditor to improve the perception of auditor independence. By contrast, in the new auditor selection models, corporate governance variables did not appear to be important in determining a different quality (brand-name) auditor. Only the chairman/CEO duality variable was weakly and negatively significant, suggesting that duality is associated with a change to a lower quality auditor. Growing companies are more likely to change to a brand name auditor, consistent with the inability of smaller firms to provide services across an international market. Contrary to agency theory predictions, the results show that a company experiencing increased leverage is less likely to choose a B5/4 auditor, suggesting that B5/4 auditors are being selective in avoiding risky clients. Higher audit fees are paid to new auditors by companies that changed from non-B5/4 to B5/4, reflecting a B5/4 fee premium. However, the higher NAS fee result is contrary to initial expectations. Typically, far fewer variables were significant in the models with audit quality proxied by industry specialism. For the specialism models based on audit fee market share, there is counter-intuitive evidence that a company with a large number of subsidiaries is less likely to move to a specialist auditor from a non-specialist. New specialist auditors were more likely to be preferred when a company experienced an increase in current accruals or a reduction in leverage. In general, the results for these models were less strong and were dependent upon the specialist definition adopted. Finally, the thesis provides evidence that the choice of time variant model (ex-ante, contemporaneous or ex-post) made no significant difference to the overall results. The one exception concerns the ‘growth’ variable, where companies are found to change auditor in anticipation of future growth, rather than as a response to past growth. Further, the use of alternative proxy variables does not greatly influence the regression results. One important exception to this general observation concerns the brand name proxy. When brand name was defined as tier12 (to include Grant Thornton and BDO) the significance level was improved in all models. This suggests that, to some degree, Grant Thornton and BDO are viewed as quality service providers closer in quality to B5/4 than to other smaller audit firms.

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Fero, Barbara <1983&gt. "Studies on the dual in Mycenaean, in the Homeric poetry and in the Attic Theatre of the 5th century — morphological, dialectal and stylistical variations." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5940/1/fero-barbara-tesi.pdf.

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The present dissertation focuses on the dual number in Ancient Greek in a diachronical lapse stretching from the Mycenaean age to the Attic Drama and Comedy of the 5th century BC. In the first chapter morphological issues are addressed, chiefly in a comparative perspective. The Indo European evidence on the dual is hence gathered in order to sketch patterns of grammaticalisation and paradigmatisation of specific grams, growing increasingly functional within the Greek domain. In the second chapter syntactical problems are tackled. After a survey of scholarly literature on the Greek dual, we engage in a functional and typological approach, in order to disentangle some biased assessments on the dual, namely its alleged lack of regularity and intermittent agreement. Some recent frameworks in General Linguistics provide useful grounds for casting new light on the subject. Internal Reconstruction, for instance, supports the facultativity of the dual in each and every stage of its development; Typology and the Animacy Hierarcy add precious cross linguistical insight on the behaviour of the dual toward agreement. Glaring differences also arise as to the adoption — or avoidance — of the dual by different authors. Idiolectal varieties prove in fact conditioned by stylistical and register necessity. By means of a comparison among Epics, Tragedy and Comedy it is possible to enhance differences in the evaluation of the dual, which led sometimes to forms of ‘censure’ — thus triggering the onset of competing strategies to express duality. The last two chapters delve into the tantalising variety of the Homeric evidence, first of all in an account of the notorious issue of the Embassy of Iliad IX, and last in a commentary of all significant Homeric duals — mostly represented by archaisms, formulae, and ad hoc coinages.
La dissertazione verte sullo stato del duale in Greco, a partire dalle testimonianze attestate le tavolette micenee, attraverso l'epica omerica, fino alla produzione teatrale attica di quinto secolo. Il primo capitolo, di taglio morfologico, investiga il duale da un punto di vista flessionale, osservando come cronologicamente si verifichi un sempre maggiore inquadramento in paradigmi, grazie all'azione pervasiva di adeguamenti analogici. Il secondo capitolo si propone di smantellare alcuni falsi assunti che hanno dominato la critica, quali la mancanza di regolarità del duale, sempre visto 'in punto di morte'. Lungi dall'esser morente, il duale appare piuttosto facoltativo - come la Tipologia linguistica sembra confermare. Attraverso l'Animacy Hierarchy è possibile osservare tendenze e un certo grado di coerenza interna nell'adozione del duale. Infine, il diverso comportamento rispetto al duale dell'epica e degli autori tragici, con la controprova offerta da Aristofane, denuncia una diversa percezione stilistica della marca nei due àmbiti - in altre parole, un diverso livello di registro. L'ultima parte della trattazione si dedica alle questioni più propriamente omeriche, vertendo sul duale inclusivo, sulla nota ambasciata del IX canto dell'Iliade, e su un commentario a tutte le forme di duale portatrici di peculiarità morfologiche, arcaizzanti, formulari.

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Takhar, Opinderjit Kaur. "Sikh groups in Britain and their implications for criteria related to Sikh identity." Thesis, University of South Wales, 2001. https://pure.southwales.ac.uk/en/studentthesis/sikh-groups-in-britain-and-their-implications-for-criteria-related-to-sikh-identity(25232d84-48de-4227-bee1-d0cb6c2394f5).html.

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This thesis examines Sikh groups in Britain and the implications these have for criteria related to the issue of Sikh identity. Five groups have been selected. They are: the Guru Nanak Nishkam Sewak Jama; the Namdharis; the Ravidasls; the Valmikis; and the Sikh Dharma of the Western Hemisphere, which is also frequently associated with the Healthy, Happy, Holy Organization (3HO). The thesis begins with a historical analysis of Sikhism, to discover what it meant to be a Sikh in the days of the founder of the faith, Guru Nanak, and during the time of the successive Gurus. Political and social issues related to the development of Sikhism and emerging Sikh identity are examined also at the outset. Each group has its own unique contribution to make towards highlighting certain indicators and inhibitors of a Sikh identity. Thus, an important part of the present thesis is to examine the beliefs and practices of each group in order to assess its contribution towards a Sikh identity. Each group has unique leaders and founders; it is interesting, therefore, to see what implications the leaders' backgrounds and teachings have on the ethos of the group studied. The present thesis has aimed to highlight the implications of five groups ~ who have in the present and/or in the past have Sikh connections ~ on issues related to Sikh identity. This has been undertaken by continuous reference to four fundamental questions. A thematic approach was adopted for concluding the thesis. Each of the themes arose as significant factors developed throughout the research. The themes illustrate areas that are responsible for the promotion, as well as the hindering, of a uniform Sikh identity among the groups. The five themes that emerged were: (1) The concept of Guru in Sikhism; (2) Leaders and founders; (3) The role of the Rehat Maryada in relation to Sikh identity; (4) Caste and the Panth; (5) The issue of Sikh identity in relation to Punjabi ethnicity. The present research has shown that there are no overall dominant criteria with which to assess the Sikh identity of the Sikh community as a whole. Thus, contrary, to prevalent views about the Sikhs, there are many different "types" of Sikhs present today. I have suggested a federal identity of the Sikh community as a whole. This implies a unity of Sikhs worldwide but independence in the interpretation of Sikhism for the different groups. A federal identity might mean one or two core beliefs such as the acceptance of the Sikh Gurus' teachings and belief in the Sikh Absolute -- but, further than that, it is up to the individual group to express its unique beliefs and practices.

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Park, David B. "The Administration of Unemployment Relief by the State of Texas during the Great Depression, 1929-1941." Thesis, University of North Texas, 2020. https://digital.library.unt.edu/ark:/67531/metadc1703286/.

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During the Great Depression, for the first time in its history, the federal government provided relief to the unemployed and destitute through myriad New Deal agencies. This dissertation examines how "general relief" (direct or "make-work") from federal programs—primarily the Emergency Relief and Construction Act (ERCA) and Federal Emergency Relief Administration (FERA)—was acquired and administered by the government of Texas through state administrative agencies. These agencies included the Chambers of Commerce (1932-1933), Unofficial Texas Relief Commission (1933), Texas Rehabilitation and Relief Commission (1933), Official Texas Relief Commission (1933-1934), Texas Relief Commission Division of the State Board of Control (1934), and the Department of Public Welfare (1939). Overall, the effective administration of general relief in the Lone Star State was undermined by a political ideology that persisted from, and was embodied by, the "Redeemer" Constitution of 1876.

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Piliarkinová, Eva. "Komparácia menovej politiky FED-u v období Veľkej depresie a hospodárskej a finančnej krízy 2007 - 2009." Master's thesis, Vysoká škola ekonomická v Praze, 2012. http://www.nusl.cz/ntk/nusl-113963.

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The main goal of this thesis is comparison of FEDs monetary policy in times of Great Depression and financial crisis 2007 -- 2009. Both of them began when the speculative bubble burst (in the first case it was in stock market, in the second one it occurred in real estate market). The effect of speculative bubbles bursting had very negative impact on global economic system. The FEDs monetary reaction to the both crises was very different. It differentiates in many aspects -- in times of Great Depression FED acted passive -- did not provide large open market purchases, did not lowered the interest rate quick enough to avoid the money stock fall-down. In current crisis, FED did not repeat mistakes made during Great Depression. In response to the market pressure, FED created several unconventional tools to support liquidity of depository institutions, primary dealers and commercial paper market. Via these new-invented programs, FED did not allow the money stock to fall and as the financial strains eased, they slowly disappeared. Besides these liquidity programs, FED supported economy with fast interest rate lowering and providing quantitative easing. Steps taken by FED helped to stabilize financial markets.

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Crews, Chris G. "Fortress of Fear and Borders of Control: How the U.S Media Constructs Mexican Immigrants as a National Security Threat." Ohio : Ohio University, 2007. http://www.ohiolink.edu/etd/view.cgi?ohiou1185568102.

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Chan, Ho Fai. "Essays on top scholars: A scientometrics approach." Thesis, Queensland University of Technology, 2017. https://eprints.qut.edu.au/104383/1/Ho%20Fai_Chan_Thesis.pdf.

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This thesis contributes to the scientometrics literature by providing empirical evidence on a number of aspects in academia focusing on the most prominent scholars. It comprises eight individual studies examining topics on recognition, research performance, impact, biases and collaboration patterns in academia.

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Shaw, James Adam. "'The Great Desideratum in Government' : James Madison, Benjamin Constant, and the Liberal-Republican framework for political neutrality." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/the-great-desideratum-in-government-james-madison-benjamin-constant-and-the-liberalrepublican-framework-for-political-neutrality(f9d6c46c-3dac-4f8d-9d7b-955aa66d3045).html.

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The liberal and republican traditions of political thought are commonly treated as divergent political-philosophical doctrines which existed in a state irreconcilable opposition in late eighteenth-century France and America. The present study challenges this notion through examining the concept of political neutrality as discussed and expounded in the political and constitutional writings of James Madison and Benjamin Constant. In seeking to account for not only why, but also how, both thinkers endeavoured to construct political systems geared toward securing the production of neutral laws, this thesis explores and highlights the complex interdependent relationship between the liberal and republican philosophical traditions in late eighteenth- and early nineteenth-century political theory. It is argued that in their desire to construct political-constitutional systems tailored toward guaranteeing the materialisation of neutral laws, Madison and Constant incorporated republican, or ‘Real Whig’, concepts into their respective constitutional strategies. Their shared objective, it is shown, was to form limited and neutral states through exploiting the diversity of public opinion in such a way that would render popular sovereignty self-neutralising. More specifically, this thesis suggests that both Madison and Constant placed considerable emphasis on de-legitimising particular justifications for legislative action, and that their respective efforts in this area were motivated by a desire to restrict the legislature to the promotion of objective, and impartially-conceived, accounts of the public good. Thus through examining Madison’s and Constant’s attempts to form neutral states, this thesis challenges the traditional account of the development of modern liberalism through pointing to the existence of an autonomous liberal-republican philosophy in post-revolutionary French and American political thought. It is argued that this hybrid political philosophy – which underpinned the constitutionalisms advanced by both Madison and Constant – had as its principal objective the reconciliation of the practice of popular governance with the restoration and maintenance negative individual liberty. Both thinkers, in other words, exploited republican concepts and institutions in order to realise the distinctly liberal end of forming limited and neutral states.

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Vicente, Beaufils Bénédicte Saez Ricardo. "L'expression de la culture de l'eau dans l'Alhambra poids de la réalité et pouvoir de l'imaginaire /." Rennes : Université Rennes 2, 2009. http://tel.archives-ouvertes.fr/tel-00401425/fr.

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Reynolds, Teddy. "Pulling back the curtain : an examination of the English Defence League and their use of Facebook." Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/6927.

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As social media becomes an integral part of our daily lives, and groups seek to utilize this medium to facilitate activism, understanding the nature of these communications and the impact of the content on the individual user becomes a valid area of interest. When one then considers that extremist and terrorist groups have found social media to be an inexpensive and effective means for communication, radicalization, recruitment and member mobilization, the need for this understanding becomes critical. This research seeks to provide just such an understanding in its examination of Far-Right English Defence League and their use of Facebook during a period of increased activism and online growth. Important elements of this work include an understanding of the legal and ethical issues surrounding the collection of online content, particularly in extremist environments; the role of traditional media in their coverage of the group and whether the comments of the members reflect the group's mission statement of the characterization of traditional media; the ability to enhance data segregation and analysis through the development and use of specialized software; and most importantly the findings from the data analysis. Contained within these findings is an understanding of the intricacies of online participation in extremist social media. These include insights into overall traffic generation, the use of links within communications and their impact on the member traffic, and how the group narrative put forth by the administrator is reflected in the dialogue of the users. The most important finding was an understanding of individual user participation within the group and how, even with such an inexpensive and pervasive media outlet, activist groups still struggle to overcome the problem of participation. That this knowledge can be applied in a meaningful way in counter extremist and counter terrorism efforts was an interesting and satisfying development.

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Raterron, Paul Cordier Patrick. "Contribution à l'étude des propriétés thermodynamiques et rhéologiques des silicates." Villeneuve d'Ascq : Université des sciences et technologies de Lille, 2007. https://iris.univ-lille1.fr/dspace/handle/1908/460.

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Reproduction de : Habilitation à diriger des recherches : Sciences physiques : Lille 1 : 2005.
N° d'ordre (Lille 1) : 457. Textes et résumé en français. Titre provenant de la page de titre du document numérisé. Bibliogr. en fin de chapitre.

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Chien, Hung-Ju. "Developing a digital nervous system for enhancing effectiveness of construction management and increasing commercial benefit in the UK construction industry." Thesis, University of South Wales, 2003. https://pure.southwales.ac.uk/en/studentthesis/developing-a-digital-nervous-system-for-enhancing-effectiveness-of-construction-management-and-increasing-commercial-benefit-in-the-uk-construction-industry(eae650ad-778f-4873-ab37-e1717dbbd4bc).html.

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Information and Communication Technology (ICT) facilitates better communication within the construction industry and has the potential to change the industry beyond recognition. The aim of this research is to develop a theoretical Digital Nervous System (DNS) model for the UK construction industry to enable companies to improve their corporate business performance. To accomplish the aim of the research, the author conducted extensive secondary and primary data collection. Two primary research techniques were adopted to elicit data and information from respondents, these were; questionnaire surveys and structured interviews. A comprehensive review of secondary data was undertaken, this included a review of published literature, both in print and electronic format. A theoretical DNS model has been proposed by the author in this research. This DNS model is able to support and integrate the following functions: To manage inner-company operations more efficiently using Enterprise Resource Planning (ERP) and Intranet technology. To use Extranets to improve communication with business partners by sharing up-to-date information. To exploit the potential of the Internet to increase interaction with the public, interest groups and potential clients. To create commercial benefits available to the construction industry through the use of e-Commerce. The potential benefits of utilising a DNS model for a construction organisation are significant. The possible improvements that can be attributed to adopting the DNS model proposed by the author of this research include: • Reduction in an organisation's costs and construction time. • Improved profits. • Reduction in defects and waste. • Increase in productivity and client satisfaction.

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Lau, Alice Man Sze. "Assessment for learning in higher education." Thesis, University of South Wales, 2013. https://pure.southwales.ac.uk/en/studentthesis/assessment-for-learning-in-higher-education(3dbf6052-980d-45d8-b059-6be56c13dc59).html.

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The thesis is about assessment for learning. It aims to examine the gap between theory and practice in assessment for learning through a case study approach. By examining closely the assessment practice in one higher education institution in the UK, the thesis presents a number of original contributions to the literature, knowledge base and practice of assessment for learning. The thesis challenges the established literature in assessment for learning and proposes that the literature should move away from the dichotomised view of summative and formative assessment. The thesis also highlights the lack of an explicit theoretical underpinning in assessment for learning and proposes that the social constructivist approach should be made more explicit in the assessment for learning literature. With the case study demonstrating that lecturers often take a surface approach towards assessment for learning principles, the thesis proposes that dialogue needs to be seen as the common thread in assessment for learning. By understanding that assessment for learning is about a process that involves meaningful dialogue between 1) tutors and tutors, 2) tutors and learners, 3) learners and peers and finally 4) learners themselves, lecturers will be presented with a new knowledge base to re-consider their assessment practice. The case study also reveals that lecturers from certain disciplines found the notion of assessment for learning aligned with their disciplines more readily. This finding together with the contributions to literature and knowledge base will present a new perspective towards assessment for learning and look to inform practice that will result in a deep approach to assessment for learning.

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Hammarström, (Gimleström) Dag. "Konstruktion av ett kapningsverktyg för pappersreglar." Thesis, Karlstads universitet, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-78669.

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Start-up företaget Wood Tube har utvecklat en ny typ av miljövänlig byggregel gjord av papper. Pappersreglar är en ny produkt som ännu inte finns på marknaden, men som kan komma att innebära stora fördelar för byggindustrin och snickare i fråga om pris, miljövänlighet och förbättrad arbetsmiljö. Det tänkta användningsområdet är att ersätta plåtreglar som ram i icke-bärande innerväggar, men det finns även stor potential i andra applikationer, såsom i möbler. Pappersreglarna tillverkas i standardlängder och ska kapas på plats ute på det aktuella bygget, i dagsläget genom sågning. Detta projekt går ut på att utveckla ett specialanpassat kapningsverktyg som ska möjliggöra en enkel och smidig kapning av dessa reglar, i syfte att göra lösningen mer attraktiv för potentiella kunder. Inom detta projekt har enklare tester utförts som indikerar att klippning är den metod med störst möjlighet till måluppfyllelse. En kravspecifikation har tagits fram och innefattar bland annat att verktyget ska drivas utan el, vara portabelt, ej avge sågspån, motstå korrosion och kunna klippa pappersreglar av olika dimensioner. Ett klippande sax-koncept väljs efter nyttjande av systematiska metoder för konceptgenerering och urval. Mycket inspiration till verktyget hämtas från konkurrentanalys av en grensax med kugg-utväxling av märket Fiskars. Egna tester har utförts för att ta reda på pappersreglarnas klippbarhet och kapningsverktygets tänkta lastfall. Konstruktionsarbetet utförs med Brain-Aided-Design (BAD), Pen-Aided-Design (PAD) och Computer-Aided-Design (CAD), och inkluderar även riskanalyser (FMEA) samt hållfasthetsberäkningar. Slutligen har ett specialiserat kapningsverktyg utvecklats för att snabbt och enkelt kunna klippa miljövänliga pappersreglar från Wood Tube.
Wood Tube is a start-up company with a new invention, environmental-friendly building bars made out of paper. The product is not yet available on the market, but these bars are likely to be a lot cheaper and easier to use for carpenters when building drywall, where the bars will replace the commonly used plate metal bars for framing. These bars are manufactured in standard lengths and are supposed to be cut on site to fit the local application. As of now they are sawn with a hand saw. This project is about developing a new specialized cutting-tool for easy and fast cutting of the Wood Tube paper bars, with the idea that a customised tool will make the paper bars even more attractive to carpenters and other potential customers. Tests indicate that cutting with shear-blades is the cutting method with the highest probability to meet the product requirements, which include requirements such as the tool being manually powered, highly portable, does not produce sawdust, is resistant to corrosion and being able to cut paper bars of different dimensions. Using systematic methods for generating concepts and the final selection, this results in a handheld scissors-concept, similar to a lopper. A lot of inspiration for the tool has come from the benchmarking of a lopper with gears from the brand Fiskars. Tests have been performed to determine the cuttability of the paper bars, as well as to predict the loads which will be exerted on the cutting tool. The cutting tool is designed using the methods Brain-Aided-Design (BAD), Pen-Aided-Design (PAD) and Computer-Aided-Design (CAD), along with calculations for tool-strength and risk-analysis (FMEA). The end result are blueprints for a tool which has been specifically developed for cutting paper bars from Wood Tube.

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45

Paris, Stuart David. "Using artificial neural networks to forecast changes in national and regional price indices for the UK residential property market." Thesis, University of South Wales, 2008. https://pure.southwales.ac.uk/en/studentthesis/using-artificial-neural-networks-to-forecast-changes-in-national-and-regional-price-indices-for-the-uk-residential-property-market(593fb5b7-d955-4012-b50e-18ecae3c18fd).html.

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The residential property market accounts for a substantial proportion of UKeconomic activity. However, there is no reliable forecasting service to predict theperiodic housing market crises or to produce estimates of long-term sustainablevalue. This research examined the use of artificial neural networks, trained usingnational economic, social and residential property transaction time-series data, toforecast trends within the housing market. Artificial neural networks have previously been applied successfully to produceestimates of the open market value of a property over a limited time period withinsub-markets. They have also been applied to the prediction of time-series data in anumber of fields, including finance. This research sought to extend their applicationto time-series of house prices in order to forecast changes in the residential propertymarket at national and regional levels. Neural networks were demonstrated to be successful in producing time-seriesforecasts of changes in the housing market, particularly when combined in simplecommittees of networks. They successfully modelled the direction, timing and scaleof annual changes in house prices, both for an extremely volatile and difficult period(1987 to 1991) and for the period 1999 to 2001. Poor initial forecasting results forthe period 2002 onwards were linked to new conditions in the credit and housingmarkets, including changes in the loan to income ratio. Self-organising maps wereused to identify the onset of new market conditions. Neural networks trained with asubset of post-1998 data added to the training set improved their forecastingperformance, suggesting that they were able to incorporate the new conditions intothe models. Sensitivity analysis was used to identify and rank the network input variables underdifferent market conditions. The measure of changes in the house price index itselfwas found to have the greatest effect on future changes in prices. Predictionsurfaces were used to investigate the relationship between pairs of input variables. The results show that artificial neural networks, trained using national economic,social and residential property transaction time-series data, can be used to forecaststrends within the housing market under various market conditions.

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Sjöblom, Matilda. "Greta Knutson och surrealismen : en studie av Greta Knutsons senare stilperiod utifrån verken La Surprise, Feu dans la maison och Det stulna brevet." Thesis, Södertörns högskola, Institutionen för kultur och lärande, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:sh:diva-26302.

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Denna uppsats undersöker hur den svenska konstnären Greta Knutson historiskt sett har kanoniserats i relation till sitt förhållande med den kände dadaisten Tristan Tzara och den franska surrealiströrelsen under 1920- och 1930-talet. Knutson hade en lång och produktiv karriär och uppsatsens intention är att flytta fokus från de tidiga dagarna i Paris med surrealisterna till hennes senare konstnärliga period, räknad från slutet på 1960-talet fram till hennes död 1983. Min tes är att en radikal stilförändring då skedde till ett, paradoxalt nog, mer surrealistisk konstnärligt uttryck. Med hjälp av Griselda Pollock och det teoretiska begreppet ”kanonisering” ifrågasätts varför denna senare period i stort har gått förbi konsthistorien och hur Knutsons relation till surrealismen sett ut. Genom en formalistisk analys presenteras därefter verken La Surprise, Feu dans la maison och Det stulna brevet, vilka är representativa för Knutsons senare konstnärliga period.
This essay examines how Swedish born artist Greta Knutson has been historically canonised in reference to her relationship with the famous Dadaist Tristan Tzara and the French surrealist movement of the 1920’s and 1930’s. Knutson had a long and productive career and the overall purpose of my essay is to change focus from the early days in Paris with the Surrealists into her later artistic period, counted from the late 1960’s until her death in 1983. It is claimed here that she then made a radical change of style into, paradoxically, a more surrealistic artistic expression. Through Griselda Pollock and the term “canonisation” I’m exploring and questioning why Knutson’s later career has gone unnoticed in art history and I’m also looking at Knutson’s relation to surrealism. Through a formalistic analysis the artworks La Surprise, Feu dans la maison and Det stulna brevet are presented, which are representative for Knutson’s later artistic period.

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Hayot, Carbonero Christine. "Sainfoin (Onobrychis viciifolia), a forage legume with great potential for sustainable agriculture : an insight on its morphological, agronomical, cytological and genetic characterisation." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/sainfoin-onobrychis-viciifolia-a-forage-legume-with-great-potential-for-sustainable-agriculture-an-insight-on-its-morphological-agronomical-cytological-and-genetic-characterisation(dd6093b5-a50c-4f65-b0ae-fe0c856a5849).html.

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Sainfoin (Onobrychis viciifolia), is a traditional forage legume whose agricultural use has been in constant decrease in Western Europe since the 1960's. However, growing evidence suggests that it may be of great interest in the context of sustainable agriculture, thanks to numerous beneficial properties (nutritional, environmental and anthelmintic). In the frame of a large project network, an extensive O. viciifolia (and other Onobrychis species) germplasm has been gathered and several accessions were grown in small plots on an experimental field at NIAB, Cambridge. Measurements of morphological and agronomical traits were performed on these plots. Cytological and molecular genetics studies were also carried on the germplasm.Accessions were found to be highly variable in their agronomical traits, with differences in productivity. It was observed that O. viciifolia was relatively resistant to diseases, but that persistence was the main difficulty to overcome. O. viciifolia accessions were also found to be variable in their morphological traits. Statistical analyses on both morphological and agronomical traits showed strong links with accessions' geographic origins. The most important trend observed is a general distinction between Western European accessions and accessions from the rest of the world.It was found that most O. viciifolia were tetraploids, suggesting that agricultural domestication led to polyploidy. Other Onobrychis species were found to be either diploid or tetraploid with varying basic chromosome numbers, which tends to confirm the assumption that an aneuploidy event occurred in Onobrychis genetic history.AFLP and SSR fingerprinting were attempted to investigate O. viciifolia genetic diversity. The potential of these techniques was shown, but the latest improvements needed to obtain solid data were not achieved during this study. Still, it was shown that molecular marker assisted breeding programmes can be elaborated for O. viciifolia.Phylogenetic analyses were performed through sequencing of different DNA regions. Substantial genetic diversity was observed among O. viciifolia accessions, with again a general distinction between Western European accessions and accessions from the rest of the world. A clarification of the Onobrychis genus is suggested, as it appeared that many species must be synonyms, and that many taxonomic sections are weakly supported.Overall, it appeared that O. viciifolia potential has probably not been fully exploited, and that there is an important potential for improvement in the gemplasm studied here. Due to its superiority in animal husbandry and agroecologic impact, O. viciifolia improvement can be suggested as a valuable alternative to extensively used forage legumes.

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Miranda, O'Shea Flavia. "A Psychoanalytic Interpretation : Jay Gatsby’s Id, Superego, Ego, and Core Issues." Thesis, Högskolan Kristianstad, Fakulteten för lärarutbildning, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:hkr:diva-20170.

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The present essay attempts a psychoanalytic interpretation of F. Scott Fitzgerald’s Jay Gatsby’s id, superego, ego, and core issues. The first stage of the paper offers an analysis of Gatsby’s id, superego and ego; and finds that the id largely rules his behaviour, with few instances where the ego takes control and manifests the superego. The second stage proposes that three psychoanalytic core issues are identifiable in the character of Gatsby: fear of abandonment, low self-esteem and insecure or unstable sense of self. Through the lens of Psychoanalytic Criticism, the present essay looks at fictional literature in order to gain insight into the human psyche, in hopes of discussing and spreading awareness about mental health.

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Godrant, Aurélie. "The role of superoxide in iron acquisition by marine phytoplankton." Brest, 2009. http://www.theses.fr/2009BRES2061.

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Le rôle clef du fer dans le cycle biogéochimique du carbone et de l’azote dans l’océan a été mis en évidence au cours de la dernière décennie. Une des découvertes majeures récentes en océanographie biologique est la limitation de la croissance du phytoplancton par la disponibilité en fer dans au moins 40% de l’océan mondial. Or, la chimie de cet élément dans l’océan est particulièrement complexe et la forme sous laquelle il est disponible pour le phytoplancton reste encore mal connue. Plusieurs mécanismes sont utilisés par le phytoplancton marin pour améliorer la solubilité du fer en eau de mer et parvenir à absorber les quantités suffisantes en fer nécessaires à leur survie. Un de ces mécanismes implique la production de radicaux superoxyde en milieu extracellulaire, ce qui accroît la bio-disponibilité du fer en eau de mer en réduisant la forme Fe(III) sous forme Fe(II), plus bio-disponible aux cellules de phytoplancton. Les objectifs principaux de ce travail étaient de i) développer une méthode appropriée pour détecter la production de superoxyde en milieu extracellular par n’importe quelle cellule de phytoplancton marin, et ii) examiner la relation entre la production extracellulaire de superoxyde et l’absorption du fer par la cyanobactérie Trichodesmium erythraeum IMS101. Une méthode de détection du superoxyde a été développée, qui utilise du red-CLA ou du MCLA, deux sondes chimiluminescentes spécifiques à la détection du superoxyde, qui ont donné des résultats fiables, même sur de très faibles quantités d’échantillons. En effet, comparée aux autres méthodes employées, la détection de la production du superoxyde par microplaques permet de réduire le volume d’échantillon par 10, et de réduire le temps d’analyse de tréplicats d’un échantillon, d’un blanc et de trois standards à 10 minutes. De plus, cette méthode présente une large gamme de travail avec une limite de détection de 0,076 pmol/s, ce qui lui confère un grand avantage pour le travail sur le phytoplancton marin. Les taux de production de superoxyde en milieu extracellulaire par la cyanobatérie Trichodesmium erythraeum ont été mesurés en condition de laboratoire et allaient de 0,93 à 16,21 pmol/trichome/h. La limitation en fer des cellules de Trichodesmium résultat en une augmentation de ce taux de production, qui a été multiplié par un facteur 2,9 entre les cellules non limitées et les cellules limitées en fer. Il a aussi été montré que la production de superoxyde suivait un rythme diurne avec une forte augmentation du taux de production en milieu du cycle « jour», spécialement marqué pour les cultures maintenues en milieu pauvre en fer. Les taux de production extracellulaire de superoxyde et d’absorption du fer par Trichodesmium ont été mesurés simultanément sur des cultures pré-limitées ou non limitées en fer. Les taux d’absorption étaient 10 fois plus élevés pour les cultures non limitées, sauf lorsqu’un composé réducteur (acide ascorbique) était ajouté. Dans ce cas, les taux d’absorption des deux cultures étaient similaires. De plus, les deux cultures ont montré une plus grande aptitude à absorber le fer lié à des ligands faibles comme le citrate. Dans l’ensemble, les résultats ont montré une relation entre la production de superoxyde et l’absorption de fer par Trichodesmium, mais aucune influence directe entre ces deux processus n’a pu être démontrée. La méthode de détection du superoxyde par microplaque a été utilisée lors de campagnes sur la Grande Barrière de corail en Australie. L’analyse de deux blooms de Trichodesmium a montré de forts taux de production de superoxyde, en cohérence avec les analyses effectuées au laboratoire. De plus, l’utilisation de cette méthode (entre autres) a permis de démontrer une accumulation d’espèces Fe(II) en concentrations biologiquement significatives, quand la concentration en superoxyde dans l’eau de mer était inférieure à 1 nM. Par contre, lorsque cette concentration se trouvait supérieure à 1nM, la plupart des espèces réduites (Fe(II)) étaient réoxidées, ce qui résultait en un fort taux de production de peroxyde d’hydrogène du à la dismutation du superoxyde. Dans l’ensemble, cette étude a permis le développement d’une méthode de détection de la production de superoxyde par le phytoplancton marin en milieu extracellulaire qui peut être utilisée au laboratoire ou en conditions d’étude sur le terrain. Nous avons aussi démontré que les cellules de Trichodesmium erythraeum IMS101 produisent de grandes quantités de superoxyde, en particulier lorsqu’elles sont limitées en fer. L’étude des taux d’absorption du fer par ces même cellules a démontré une forte relation entre ce processus et la production de superoxyde par les cellules: ces résultats sont en accord avec l’hypothèse que le modèle d’absorption du fer par le phytoplancton marin «Fe’» serait fortement influencé par ce type d’organisme capable de modifier l’équilibre redox du milieu présent à la surface des cellules
It is hypothesised that, under iron limitation, phytoplankton cells develop biochemical mechanisms to increase their iron uptake efficiency with one of these mechanisms involving the production of superoxide in the extracellular environment that increases the bioavailability of iron in seawater by reducing Fe(III) to the more soluble Fe(II). The main objectives of this work were 1) to develop an appropriate method to detect extracellular production of superoxide by marine phytoplankton, and 2) to examine the relationship between extracellular production of superoxide and iron acquisition by Trichodesmium erythraeum. A method to measure superoxyde production is described using red-CLA and MCLA probes, yielding considerable improvement for analysis compared to other available methods. Extracellular superoxide production and iron uptake rates were measured simultaneously on iron replete and iron deplete Trichodesmium erythraeum IMS 101 laboratory cultures : iron starvation leads to a 2. 9-fold increase in superoxide production rate and 10-fold decrease in the iron uptake rate (except when a reducing compound was added) compared to iron replete cultures. Extracellular superoxide production shows a pronounced circadian rythm in iron deplete cultures, but less so in iron replete cultures. Overall, no direct impact of extracellular superoxide production by Trichodesmium is observed, but both processes are shown to be related. Both iron deplete and iron replete cultures demonstrate greater ability to uptake iron bound to weaker iron-binding ligands such as citrate. Application of the method to field studies in the Great Barrier Reef lagoon showed an accumulation of biologically significant concentrations of reduced trace metals including Fe(II) when the concentration of superoxide was lower than 1 nM. When the concentration of superoxide was higher than 1 nM, most of the reduced species were oxidised resulting in high rates of hudrogen peroxide production rates, consistent with laboratory studies. Overall, this thesis permitted the development of a method to detect superoxide production rates by marine phytoplankton cells that could be used routinely in field studies. The observations are in accord with the conclusion that fit the ongoing hypothesis that the extablished Fe' uptake model for phytoplankton would be strongly influenced by such organisms that are able to modify the redox equilibrium of the solution at their cells surface

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Oussalah, Tarik. "Comportement des sables sous sollicitation d’impact à faible vitesse : application au dimensionnement de couches de sol protégeant les structures des impacts rocheux." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSET004/document.

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Les sols sont utilisés dans différents dispositifs de protection contre les chutes de blocs rocheux : pour couvrir des structures exposées, telles que les tunnels ou les galeries, ou construire des merlons. Une campagne d’essais expérimentaux instrumentés a été menée pour compléter l’observation des phénomènes, en particulier pour mieux caractériser la distribution spatio-temporelle de pression induite à l’interface entre la couche de sol protectrice et la structure, dans différentes configurations d’impact. Plusieurs configurations d’impacts ont été considérées, caractérisées par l’épaisseur de sable (D), le diamètre équivalent du bloc rocheux (B, ou sa masse) et sa hauteur de chute libre (H). L’étude paramétrique expérimentale a comporté 43 essais, combinant systématiquement différentes valeurs de D, B et H de l’ordre de celles rencontrées en pratique. Suite au dépouillement des mesures, une expression de la pression induite à l’interface sol-structure pendant un impact au sommet de la couche de sol protectrice a été proposée. La démarche exposée pour établir, dans une configuration d’impact D, B et H, les valeurs des paramètres qui caractérisent les cinq grandeurs décrivant la distribution spatio-temporelle de pression induite à l’interface sol-structure, peut être appliquée à d’autres natures de sols ou densités de compactage. Par ailleurs, un modèle numérique tridimensionnel simple de calcul en déformations, en dynamique explicite, a été développé. Le comportement en déformations du sol a été représenté par un modèle élastoplastique, avec critère de rupture de Mohr-Coulomb et faible dilatance. Les calculs ont été réalisés avec le logiciel ABAQUS. Enfin, une méthode de dimensionnement des couches de sol en protection de structures a été proposée. Cette méthode comporte deux étapes : (1) Pour la configuration d’impact B, D, H considérée, utiliser l’expression développée dans cette étude pour définir la distribution spatio-temporelle de pression induite à l’interface sol-structure, puis (2) Calculer en dynamique la structure soumise à cette impulsion de pression
An extensive experimental parametric study has been carried out to characterize how impact loads of low velocity (lower than 100 km/h) are transmitted to a structure through a protective sand layer. Different rock fall conditions have been considered, corresponding to actual conditions in current practice. The experimental program consisted of 43 full scale impact tests on a sand layer protecting a concrete foundation mat, combining three sand layer thicknesses (1, 1.5 and 2 m), impacting blocs of equivalent diameters in the range of 0.42 to 1.79 m and five free falling heights, up to 33 m. Based on the analysis of pressure cells measurements for the different rock fall conditions, the pressure induced at the interface between the protective sol layer and the structure by an impact was expressed in terms of impact conditions, defined by layer thickness (D), size of the impacting bloc (B) and height of free fall (H). Procedures to derive the model parameters from the tests are explained in detail. A numerical model was developed to simulate an impact on a structure protected by a soil layer based on a deformation analysis approach. The Finite Element code ABAQUS was used. The bloc, the soil and the structure were considered as different bodies, having contact conditions between them. The stress‐strain relationship in the soil was assumed to be elastoplastic. Friction angle and dilation angles were derived from laboratory tests on the sand. The elastic modulus was assumed constant, equal to usual values for compacted sands. An approach is proposed for the design of soil layers to protect structures from impacting loads due to rock falls

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Dissertations / Theses on the topic 'Grenat de fer'

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