Dissertationen: „Roll fronts“

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Langanay, Jean. "Quantification des incertitudes d'une exploitation d'un gisement d'uranium par Récupération In Situ." Electronic Thesis or Diss., Université Paris sciences et lettres, 2021. http://www.theses.fr/2021UPSLM035.

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La Lixiviation In-Situ d’uranium, ou In-Situ Recovery (ISR), est basée sur la lixiviation directe des minéraux uranifères au coeur du gisement par une solution minière injectée. Les résultats des écoulements et des réactions chimiques dans le réservoir sont difficiles à prédire en raison des incertitudes géochimiques, pétrophysiques et géologiques. Les codes de simulation de transport réactif utilisés pour modéliser l’ISR sont particulièrement sensibles à la distribution spatiale des propriétés physiques et chimiques dans le dépôt. Ainsi, la modélisation géostatistique est utilisée pour représenter l’incertitude de la répartition spatiale des propriétés géologiques. On peut représenter cette incertitude par un grand nombre de réalisations du modèle géostatistique. La propagation directe des incertitudes géologiques est difficile à résoudre en contexte industriel en raison du temps CPU nécessaire pour effectuer une simulation de l’ISR. Les travaux réalisés dans cette thèse présentent différents moyens de propager l’incertitude géologique en incertitude sur la production d’uranium avec un coût en temps de calcul réduit. On utilise pour cela la méthode de réduction de scénarios, qui permet de propager parcimonieusement l’incertitude. Un sous-ensemble de simulations géostatistiques est sélectionné pour approximer la variabilité d’un ensemble plus large. La sélection est obtenue en utilisant un proxy de la simulation de transport réactif. La principale contribution de ce travail est la construction de différents proxys pour approximer la lixiviation de l’uranium. Ils permettent de reproduire la dissimilarité des réalisations en terme de production d’uranium. Ensuite, les simulations de l’ISR effectuées dans les réalisations géostatistiques sélectionnées donnent une approximation de la variabilité de production d’uranium de l’ensemble des réalisations. Cette approximation est enfin utilisée pour quantifier les incertitudes de la production d’uranium sur des cas réels. Finalement, la propagation de l’incertitude de production de l’échelle du bloc de production à l’échelle de la mine est développée. Par ailleurs, un travail exploratoire a été mené dans le but d’utiliser des modèles de substitution du solveur de la chimie pour accélérer les simulations de transport réactif Uranium In Situ Recovery (ISR) is based on the direct leaching of the uranium ore in the deposit by a mining solution. Fluid flow and geochemical reaction in the reservoir are difficult to predict due to geological, petrophysical and geochemical uncertainties. The reactive transport simulation code used to model ISR is very sensitive to the spatial distribution of the physical and chemical properties of the deposit. Geostatistical models are used to represent the uncertainty of the spatial distribution of geological properties. The direct propagation of geological uncertainties by multiple ISR mining simulations is intractable in an industrial context. This work presents a way to propagate geological uncertainties into uranium production uncertainties at a reduced computational cost, thanks to a scenario reduction method. A subset of geostatistical simulations is built to approximate the variability of a larger set. The selection is obtained using a proxy of reactive transport simulation. The main contribution of this work is the development of different proxys to approximate the uranium leaching. They allow the discrimination of geostatistical realizations in terms of potential uranium production.Then, the ISR simulation carried out with the selected geostatistical realizations gives an approximation of the uranium production variability over the whole set of geostatistical simulations. This approximation is then used to quantify the uncertainties on the uranium production. The proposed approach is assessed on real case studies. Finally, the propagation of the uranium production uncertainty, assessed by the scenario reduction method, on mining operation planning is developped. Furthermore, an exploratory work about the use of statistical meta-models as chemistry solvers is also presented

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Pons, Tony. "Caractérisation des oxy-hydroxydes de fer et des éléments associés (S, Se, As, Mo, V, Zr) dans les environnements redox favorables aux gisements d’uranium." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112197/document.

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Ce travail présente une étude multi-échelle et multi-technique sur la caractérisation des oxy-hydroxydes de fer dans trois types de gisements d’uranium et leur encaissant. Le choix des sites d’études s’est porté sur un gisement de type roll front : Zoovch Ovoo dans le bassin crétacé de East Gobi (Mongolie) ; un autre de type tectono-lithologique : Akola/Ebba dans le bassin de Tim Mersoï (Niger) et enfin un type discordance protérozoïque : Kiggavik en bordure du bassin du Thelon (Canada). Une nouvelle approche a été mise en œuvre pour caractériser les oxy-hydroxydes de fer sur échantillons macroscopiques : la spectroscopie infrarouge de terrain en utilisant le spectromètre ASD TerraSpec®. À partir d’indices originaux calculés sur les spectres, il a été possible à la fois de caractériser les oxy-hydroxydes de fer ; seules l’hématite et la goethite ont été identifiées dans les parties oxydées des différents fronts uranifères, et de visualiser les différentes zonations d’altération le long des fronts redox. De plus, la partie visible du spectre a été utilisée pour quantifier la couleur des échantillons à travers les paramètres des systèmes ITS (Intensité – Teinte – Saturation) et de Munsell. L’étude des paramètres de couleurs a permis d’identifier une teinte spécifique pour les échantillons minéralisés étudiés : un mélange de jaune et de rouge (2,5 à 10 YR en notation de Munsell). A l’échelle des cristaux, les oxy-hydroxydes de fer ont été caractérisés par la spectroscopie micro-Raman. Cette étude a permis de mettre en évidence une différence de cristallinité des cristaux d’hématite dans les différents gisements. D’un point de vue morphologique, les cristaux de goethite du gisement de Zoovch Ovoo, seul oxy-hydroxyde de fer authigène décrit dans ce front, sont maclés en forme d’étoile à six branches, ce qui témoigne d’une cristallisation de basse température, comparé aux gisements du Niger et de Kiggavik. Cette cristallisation est principalement contrôlée par la disponibilité des ions Feᴵᴵᴵ dans le fluide, libérés par la dissolution de la pyrite en milieu oxydant et le pH. D’un point de vue chimique, les oxy-hydroxydes de fer enregistrent le passage du fluide uranifère de part leur teneur eu uranium. Et d’autre part la composition en éléments en trace qui marque la typologie du gisement, par exemple de la teneur en zirconium dans les oxy-hydroxydes de fer provenant du gisement du Niger, source d’origine volcanique. Cette typicité de la mobilité du zirconium est particulièrement bien exprimée dans les fronts uranifères d’Ebba par la précipitation de cristaux authigènes de zircon contemporains de la pechblende. Les données minéralogiques et géochimiques obtenues dans ce travail sur le gisement de Zoovch Ovoo permettent de proposer un modèle original pour sa formation : l’uranium n’a pas précipité massivement en amont du front puisqu’il n’y a pas d’auréole d’irradiation observable en cathodoluminescence dans les minéraux détritiques dans la zone oxydée. L’uranium a précipité lorsque l’eau oxydante a rencontré un faciès sédimentaire ayant un pouvoir réducteur assez fort pour permettre la réduction de l’uranium. La précipitation a lieu dans un endroit particulier de la formation : un paléo-lac où la matière organique et la pyrite sont abondantes This work presents a multi-scale and a multi-technical study for the characterization of iron oxi-hydroxides in three uranium-type deposits and host rock. The choice of sites has focused on a roll front deposit: Zoovch Ovoo in a Cretaceous basin of East Gobi (Mongolia); a tectonic-lithological type: Akola/Ebba in Tim Mersoï basin (Niger) and a Proterozoic unconformity type: Kiggavik in Thelon basin (Canada). A new approach has been implemented to characterize the iron oxi-hydroxides on macroscopic samples: field infrared spectroscopy using the ASD TerraSpec® spectrometer. From the original indexes calculated on the spectra, it was possible both to characterize the iron oxi-hydroxides; only hematite and goethite were identified in the different parts of oxidized uranium fronts, and visualize the alteration zonation along the redox front. In addition, the visible part of spectrum was used to quantify the color of samples through the IHS system parameters (Intensity – Hue – Saturation) and the Munsell system. The color setting of the study identified a specific hue for mineralized samples studied: a mixture of yellow and red (2.5 to 10YR in Munsell notation). At the crystals scale, the iron-hydroxides were characterized by µ-Raman spectroscopy. The study highlighted a difference in crystallinity of hematite crystals in different fields. From a morphological point of view, the crystals of goethite in the Zoovch Ovoo deposit, is only authigenic iron oxi-hydroxides described in this uranium front, are twinned in the form of six-pointed star, reflecting a low crystallization temperature, compared to Niger and Kiggavik deposits. This crystallization is mainly controlled by the availability of Feᴵᴵᴵ ions in the fluid, released by pyrite dissolution in an oxidizing environment and pH. From a chemical point of view, iron oxi-hydroxides record the fluid passage owing their uranium content. Secondly, the composition in trace elements marks the type of deposit, for example zirconium content in oxi-hydroxides from Niger deposit, volcanic source. This typical mobility of zirconium is particularly expressed in the uranium front in Ebba deposit by the precipitation of authigenic crystals of zircon contemporary of pitchblende. The mineralogical and geochemical data obtained in this work on the Zoovch Ovoo deposit (Mongolia) allow us to propose an original model for its formation: uranium did not precipitate massively in upstream edge of front, because not radiation halo is visible in cathodoluminescence in detrital minerals in the oxidized area. Uranium precipitated when the oxidizing water met with sedimentary facies having a fairly strong reducing power to allow uranium reduction. The precipitation occurs in a particular location of the formation: paleo-lake where organic matter and pyrite are abundant

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Rallakis, Dimitrios. "Le système métallogénique et le piège redox dans le gisement d’uranium de type roll-front de Zoovch-Ovoo, Mongolie. Rôle des porteurs du carbone et du soufre." Thesis, Université de Lorraine, 2019. http://www.theses.fr/2019LORR0079.

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L'objectif de la thèse concerne l'analyse du système matières organiques (carbone)-uranium-sulfure qui contrôle la formation du gisement d'uranium de type de roll-front au Zoovch Ovoo (Mongolie). La formation Cénomanienne du Sainshand est constituée de sédiments continentaux silicoclastiques déposés dans des milieux fluvio-lacustres. Le système global est en début de diagénèse et n'a pas été affecté par un enfouissement significatif, estimé à moins de 600 m pour une température maximale de 40°C. Le réservoir se caractérise par des sables non consolidés et des argiles silteuses. Parfois, certains lits de grès d’épaisseur décimétriques sont cimentés par des carbonates et disposés au sein de faciès silicoclastiques non consolidés. L’étude systématique des grès à ciment carbonaté a révélé la présence exclusive de dolomite. Quatre types de dolomite différents ont été reconnus. Tous ont été formés par des eaux d'origine météorique et présentent des caractéristiques isotopiques (C, O) semblables. Ils sont génétiquement liés les uns aux autres, avec de possibles épisodes de recristallisation impliquant une réincorporation progressivement moindre des éléments en traces comme les terres rares et le manganèse. Le premier type de dolomite est contrôlé par les conditions de sédimentation, tandis que les trois suivants sont contrôlés par diagenèse. Le troisième type de dolomite n'a été trouvé que dans des échantillons ayant été affectés par le roll-front alors que le quatrième est postérieur aux porteurs d'uranium. La matière organique détritique est très abondante et joue un rôle majeur dans le piégeage de l’uranium aux côtés de la pyrite. L'étude en pétrographie organique a montré que toute est d'origine végétale supérieure et immature, comme l'ont montré les mesures de réflectance de la vitrinite (<0,4%). Elle est exclusivement présente sous forme de particules détritiques et sa distribution est donc régie par l’évolution des conditions de dépôt sédimentaires. Huit générations de pyrite ont été identifiées sur la base textures et des associations minérales, avec trois types majeurs : les pyrites framboidales en sphérolites isolés, les surcroissances automorphes, et les pyrites de remplacement (épigénie). L'étude isotopique du δ34S de la pyrite a montré qu’une grande parties des pyrites s‘est formée par bio-réduction des sulfates. Les porteurs de l’uranium sont la pechblende et dans une moindre mesure la phospho-coffinite. La pechblende cimente et remplace la matière organique mais aussi les pyrites automorphes corrodées ce qui indique que l’enrichissement ou l’introduction massive de l’uranium s’est produit assez tardivement. La matière organique a piégé l’uranium de manière diffuse à des fortes concentrations, sous une forme minéralogique non accessible au MEB. Il peut s’agir de nanophases de pechblende de taille inférieure à la centaine de nanomètres. Pour expliquer ces concentrations, une préconcentration ne peut pas être totalement exclue ou un processus de diffusion piégeage lors du stade de minéralisation. La considération de l’ensemble des données indique que l’aquifère principal a été le siège probable d’activité microbienne subcontinue, qui est attestée par la formation à différentes stades de l’histoire du bassin de pyrites dont les caractéristiques isotopiques indiquent des processus complexes de fractionnement. La présence de matière organique en quantité significative et des pyrites peut expliquer l’efficacité du piège redox pour la réduction de l’uranium. Le modèle métallogénique présenté est celui d’un système mixte où un processus de type roll-front lié aux caractéristiques sédimentologiques de cette zone se superpose à un piège redox particulier dont la chimie C-S-U est assistée par les bactéries The objective of the PhD thesis concerns the analysis of the processes governing the carbon-uranium-sulfide system in the aquifers of the roll-front type Zoovch Ovoo uranium-deposit (Mongolia). The Cenomanian Sainshand Formation hosting the ore deposit contains reservoirs made of silicoclastic sediments deposited in fluvio-lacustrine settings mostly characterized by unconsolidated silty clays and sands ranging from arenite to sub-arkose. Occasionally some decimetres thick sandstone beds are dolomite cemented. Four different dolomite fabrics are recognized and classified according to their crystal boundaries and geochemistry. Isotopic analysis indicates that they were formed from meteoric waters with the carbon source being probably the detrital material itself issued from basement rock erosion. Dolomites are genetically related to each other with possible recrystallization episodes that are indicated by gradual depletion in REE and Mn. The first dolomite type was depositionally controlled, while the next three parageneses are diagenetic. The third dolomite type is found only in samples that have experienced roll-front waters, whereas the fourth post-dates uranium formation. As a result the dolomite cements paragenetic evolution is used as reference to document the whole burial history of the deposit. Organic matter particles, pyrite and uranium are very intimately related. Organic matter present in clay, silt and sand is always represented by poorly preserved detrital elements of higher plant origin and is very immature (peat stage; vitrinite reflectance <0.4%). At the scale of the sedimentary particles, organic matter complexes U(VI). However, despite a systematic association to UO2, it cannot be considered as directly involved in the reduction mechanism of uranium because of the low burial temperatures (max 50°C) and hence very limited diagenesis. Nevertheless, the investigation reveals that organic matter is the most important element in the U trapping process. Indeed, it acts as a substrate sustaining and focusing bacterial activity into specific sedimentary layers. In turn the microbial communities catalyze the reduction of sulfur, iron and especially uranium leading to two major consequences: 1) the precipitation of UO2 onto organic matter particles and 2) the formation of pyrite which acts as an additional reducer for U(VI). It appears that the uranium ore deposit at Zoovch Ovoo is primarily controlled by the distribution of the detrital organic matter in the sedimentary system as well as by the permeability network allowing the input of S, U and micro-organisms. The rather shallow aquifers probably underwent a nearly continuous bacterial activity which is responsible of many chemical features and processes controlling the U and sulfide precipitation. However, main uranium deposition events occur since the beginning of exhumation when enhanced fluid movement sustains roll-front activity. The latter displaces and combines the ingredients of the biochemical trap, allowing progressive enrichment in uranium through time

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Graham, Robert M. "The role of Southern Ocean fronts in the global climate system." Doctoral thesis, Stockholms universitet, Institutionen för geologiska vetenskaper, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-108736.

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The location of fronts has a direct influence on both the physical and biological processes in the Southern Ocean. However, until recently fronts have been poorly resolved by available data and climate models. In this thesis we utilise a combination of high resolution satellite data, model output and ARGO data to improve our basic understanding of fronts. A method is derived whereby fronts are identified as local maxima in sea surface height gradients. In this way fronts are defined locally as jets, rather than continuous-circumpolar water mass boundaries. A new climatology of Southern Ocean fronts is presented. This climatology reveals a new interpretation of the Subtropical Front. The currents associated with the Subtropical Front correspond to the western boundary current extensions from each basin, and we name these the Dynamical Subtropical Front. Previous studies have instead suggested that the Subtropical Front is a continuous feature across the Southern Ocean associated with the super gyre boundary. A comprehensive assessment of the relationship between front locations and wind stress is conducted. Firstly, the response of fronts to a southward shift in the westerly winds is tested using output from a 100 year climate change simulation on a high resolution coupled model. It is shown that there was no change in the location of fronts within the Antarctic Circumpolar Current as a result of a 1.3° southward shift in the westerly winds. Secondly, it is shown that the climatological position of the Subtropical Front is 5-10° north of the zero wind stress curl line, despite many studies assuming that the location of the Subtropical Front is determined by the zero wind stress curl. Finally, we show that the nutrient supply at ocean fronts is primarily due to horizontal advection and not upwelling. Nutrients from coastal regions are entrained into western boundary currents and advected into the Southern Ocean along the Dynamical Subtropical Front. At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.

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Nathwani, Falguni. "Fronto-striatal circuitry : role in behaviour and cognition." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619737.

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Bonnetti, Christophe. "La genèse des gisements de type roll front dans le bassin d'Erlian, Chine." Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0282/document.

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Le bassin d'Erlian localisé au NE de la Chine s'est développé au cours de l'extension continentale de la fin du Mésozoïque en Asie de l'Est. Le socle sur lequel il repose correspond à la partie orientale de la ceinture orogénique centre asiatique. Les granites indosiniens (236.8±5.8 Ma) étudiés, proviennent d'une série magmatique calco-alcaline fortement potassique dérivée de la fusion partielle d'un manteau enrichi (143Nd/144Ndi faible; epsilon Nd(t) négatif) et correspondent à des sources majeures d'U. Les systèmes fluviatiles en tresse qui dominent au cours de l'épisode post-rift du bassin, sont des environnements favorables au dépôt des sables réduits qui constituent les pièges pour les minéralisations U. Les sédiments post-rifts contiennent des concentrations syn-sédimentaires significatives en U, principalement adsorbé aux minéraux argileux. Celles-ci sont ensuite redistribuées quasi in situ au cours de l'évolution diagénétique des sédiments, s'exprimant sous forme de coffinite et de pechblende (e.g. Nuheting). La MO contenue dans ces sédiments est d'origine continentale et correspond à un kérogène de type IV immature. Enfin, le gisement roll front de Bayinwula se caractérise par un modèle biogénique. Dans la zone à pyrite, la MO est dégradée par des bactéries sulfato-réductrices. La production de H2S contribue à la dissolution des oxydes de fer/titane qui sont progressivement remplacés par la pyrite (de même que la MO), caractérisée par une signature delta 34S très négative. L'U porté par ces oxydes et la MO est libéré et peut alors être lessivé par les fluides oxydants. Le H2S produit favorise la réduction de l'U qui précipite au front sous forme de coffinite et de ningyoite The Erlian Basin located in NE China developed during the late Mesozoic continental extension in eastern Asia. This basin lies on a basement corresponding to the eastern part of the Central Asia Orogenic Belt. Indosinian magmatism (236.8±5.8 Ma) is widely represented by high-K calcalkaline granites derived from an enriched mantle (low 143Nd/144Ndi; negative epsilon Nd(t)) and correspond to major U sources. Braided fluvial systems of post-rift sediments of the Erlian Basin correspond to favorable sedimentary conditions for the genesis of permeable and reduced sandstones. Post-rift sediments contain significant synsedimentary U concentrations, mainly adsorbed on clay minerals. These pre-concentrations are redistributed in situ, during the diagenetic evolution, and mineralized as coffinite and pitchblende replacing pyrite or pyritized OM (e.g. Nuheting). The OM occurring within these sediments is mainly terrigenous and corresponds to kerogens of type IV, thermally immature. Finally, the roll front-type Bayinwula deposit is characterized by a biogenic model involving reactions between OM, U-rich Fe/Ti oxides and sulfate-reducing bacteria. In the pyrite zone, the OM is degraded by bacteria and replaced by pyrite. H2S production contributes in the dissolution of Fe/Ti oxides that are progressively epigenized into pyrite, characterized by strongly negative values of delta 34S. U concentrations from Fe/Ti oxides and OM are liberated and can be leached by oxygenated groundwater. H2S creates a reducing barrier contributing in the reduction of uranium that precipitates at the redox front as coffinite and ningyoite

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Raosa, Andrea Natalia. "Analisi sperimentale della formazione e propagazione di treni d'onda a fronte ripido (roll waves)." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amslaurea.unibo.it/710/.

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Cooper, Ian Michael. "The role of surface and diffusive processes on potential vorticity in atmospheric fronts." Thesis, University of Reading, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306836.

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Andersen, Jordan Turner. "Movement Characteristics of Front Crawl Swimming at Sprint Pace and Middle-Distance Pace: Establishing Demands on the Torso Muscles." Thesis, The University of Sydney, 2019. http://hdl.handle.net/2123/20906.

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Dry-land training of the torso muscles is common in swimming programs; however, the role of the torso muscles in front crawl is unclear. The purpose of this thesis was to establish demands on the torso muscles in front crawl from analysis of kinematic data and torso muscle activity during sprint and middle-distance swimming. In the first two studies, 3D kinematic data were analysed from swimmers swimming at sprint and 400m pace. In Study 1, the range of hip roll decreased while shoulder roll range was similar as swimming speed increased. These differences produced greater range and velocity of torso twist as swimming speed increased, indicating higher demands on the torso muscles at sprint than at 400m pace. In Study 2, Fourier analysis was used to decompose angular momentum signals to determine the impact of the flutter kick on longitudinal body rotation. The third harmonic frequency, representing effects from the flutter kick, was greater in lower limb than in upper limb angular momentum at both paces, indicating a reduction in the rotation transferred from the lower to upper limbs. This reduction was more pronounced at sprint than at 400m pace. In Study 3, 3D kinematic data and surface EMG data from internal oblique, external oblique, rectus abdominis, and lumbar and thoracic erector spinae were collected from swimmers swimming at sprint and 400m pace. Torso twist angle did not relate to EMG data and no relationships between muscle activity and torso twist acceleration could be detected. Findings from this study indicate that the torso muscles may play a greater role in stability and posture than they do in producing torso twist in front crawl. Guidelines were developed to improve dry-land training specificity for swimmers: (1) increase torso muscle demands as swimming speed increases, (2) use the torso muscles to provide stability during lower limbs movements, and (3) challenge the torso muscles to maintain torso posture while moving the upper and lower limbs.

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Schomers, Malte [Verfasser]. "Establishing action-perception circuits as a neural basis for meaning-carrying linguistic symbols – the role of frontal speech motor areas and fronto-temporal connectivity / Malte R. Schomers." Berlin : Freie Universität Berlin, 2017. http://d-nb.info/1128150646/34.

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Hebert, Benoit. "Approche quantitative par spectrométrie Vis-NIR des minéraux argileux et uranifères dans les sables du gisement de Tortkuduk, Kazakhstan." Thesis, Poitiers, 2018. http://www.theses.fr/2018POIT2268/document.

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Les gisements de type roll-front du Kazakhstan représentent près de 13% des réserves mondiales en uranium en 2015. Les minéraux argileux, présents à chaque étape du cycle minier, ont récemment suscité l’intérêt des exploitants. L’étude de la distribution et des proportions de ces minéraux dans les sédiments à l’échelle d’un gisement permettraient d’améliorer à la fois l’exploration, l’exploitation et la réhabilitation de ce type de gisement.Différentes méthodes ont été développées pour identifier et quantifier les minéraux d’intérêt à partir de la spectrométrie infrarouge (IR), une technique instrumentale rapide, adaptée à une utilisation sur le terrain. Ces méthodes ont été calibrées à l’aide d’une large base de données de spectres IR et la préparation de sables artificiels.Il est possible d’obtenir, à partir d’une seule mesure spectrale, la teneur en argiles des sables et particulièrement celle en smectite afin d’identifier les zones les plus riches et adapter l’extraction de l’uranium. L’ensemble de ces méthodes permettent de réaliser des cartographies de la répartition des minéraux argileux à l’échelle du gisement pour comprendre sa géométrie et sa mise en place.La migration des corps minéralisés à l’échelle régionale a été mise en évidence par spectrométrie de résonance paramagnétique, avec l’étude des défauts structuraux engendrés par la proximité des minéraux argileux avec les minéraux uranifères Uranium roll-front type sandstone-hosted deposits from Kazakhstan account for about 13% of the worldwide uranium reserve in 2015. Clay minerals occur at every step of the mining cycle and recently begun to be considered by mining companies.The proportions and distribution of these clay minerals in the sediments at the roll-front deposit scale could improve the exploration, exploitation and rehabilitation of such uranium deposits.Several methods were developed to identify and quantify minerals using a portable near-infrared spectrometer, a convenient and fast analytical tool for use in the field. These methods were calibrated with the help of a wide spectral database and the conception of artificial sands.The clay mineral content, and more importantly, the smectite content can be obtained from a single spectral measurement. It enables the detection of smectite-rich areas to optimise the uranium extraction process where they occur. Combination of the methods provide a mapping tool for clay minerals at the ore deposit scale, yielding information about its actual geometry and formation.Uranium ore bodies migration was observed at the ore deposit scale with the use of the electron paramagnetic resonance spectroscopy. Crystalline radiation induced defects in clay minerals that were in close contact with uranium showed records of the past migration

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Bankole, Olabode Modupe. "Transformations diagénétiques des dépôts silicoclastiques FA du bassin de Franceville au Gabon (2.2-2.0 Ga) par l'invasion de solutions oxydo-réductrices." Thesis, Poitiers, 2015. http://www.theses.fr/2015POIT2319/document.

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Dans le bassin de Franceville (Gabon), les sédiments détritiques non-métamorphosés d’âge Paléoprotérozoïque (2,15 Ga) des formations FA et FB ont fait l’objet d’une étude faciologique, pétrographique et géochimique. L’objectif était de déterminer l’origine de ces matériaux clastiques et des minéralisations uranifères associées, mais aussi d’en retracer l’histoire diagénétique à travers l’évolution des paléoconditions rédox et des fluides qui les ont percolés.La pétrographie des faciès montre que la minéralogie et la texture initiales de ces sédiments ont été fortement modifiées au cours de la diagenèse précoce. Au toît de la formation FA, les quartz-arénites faiblement granoclassées ont été très tôt cimentées par du quartz, s’opposant ainsi à l’action ultérieure de la diagenèse d’enfouissement. Dans les arènes arkosiques, la séquence paragénétique liée aux ciments authigènes suggère que les interactions fluides-roches ont été polyphasées et que les éléments chimiques nécessaires à leur précipitation trouvent leur origine dans l’altération de minéraux détritiques. Pour un ensemble lithologique donné, les effets de la diagenèse varient peu d’un faciès à l’autre, ce qui indique un fort contrôle des paramètres initiaux tels que la minéralogie, la texture et la composition du fluide poral. Par conséquent, ces faciès sédimentaires nous informent directement sur les propriétés hydrologiques qui régnaient dans le bassin sédimentaire, et sur la nature de la diagenèse précoce qui les a affectés.Les données pétrographiques et géochimiques montrent que la précipitation de l’hématite en lits ferrugineux a débuté juste après le dépôt des sédiments, dont l’altération des minéraux primaires a libéré le fer, plus tard redistribué durant la diagenèse. Ainsi, la mise en évidence d’une corrélation positive entre les valeurs de "delta" 56Fe et les rapports Fe/Mg mesurés sur échantillon total suggère que le fer se répartit entre deux pôles que sont l’hématite authigène et les silicates porteur du fer. En revanche, l’absence de relation entre les rapports Fe3+/FeT et les compositions isotopiques du fer démontre que des oxydes riches en isotopes lourds du fer préexistaient dans les sédiments lorsque la diagenèse précoce a débuté. Le fer présent initialement à l’état réduit dans des faciès sédimentaires verts s’est progressivement oxydé au cours de la diagenèse, processus à l’origine de la formation des lits ferrugineux.Dans la formation FA du Bassin de Franceville, les gisements uranifères résultent de la libération de l’uranium contenu à l’origine dans les grès oxydés des dépôts fluviatiles inférieurs puis de sa migration et de son piégeage dans les grès réduits et les mudstones silteux des formations de deltas de marée supérieures, où il s’est concentré par un mécanisme de type roll-front.L’analyse des éléments chimiques majeurs et traces des formations FA et FB indique que leurs matériaux constitutifs trouvent leur source dans des roches ignées felsiques. Tandis que les diagrammes de terres rares normalisés aux chondrites, les anomalies négatives en Eu et les rapports GdN/YbN plaident plus précisément en faveur des roches archéennes et paléoprotérozoïques. Enfin, des diagrammes discrimants et des rapports en éléments majeurs et traces montrent que, si la plupart des grès de la formation FA se sont déposés sur une marge passive, les mudstones et les grès fins des formations FA et FB ont sédimenté sur une marge continentale active en relation avec la tectonique paléoprotérozoïque de la Ceinture orogénique du Centre-Ouest de l’Afrique The FA and FB Formations clastic sediments have been subjected to detailed facies, petrographic, and geochemical analyses in relation to diagenesis, fluid flow, paleo-redox conditions, provenance, and uranium mineralization during the evolution of the unmetamorphosed Paleoproterozoic (ca 2.15 Ga) Franceville Basin, Gabon. Lithofacies analyses in combination with petrographic studies indicate that the original mineralogical and textural properties of the sediments have been greatly modified during diagenesis. The moderately sorted quartz arenite at the top of FA underwent early quartz cementation; thus preventing it from subsequent burial diagenetic processes. The inferred paragenetic sequence of authigenic cements in the arkosic arenites suggest a multiphase of fluid-rock interactions with most of the ions needed for their precipitations likely sourced during alteration of detrital precursors. The observed slight variations in the diagenetic pathways in different lithofacies associations are closely related to primary mineralogy, texture, and nature of pore fluid. This relationship suggests that depositional facies can provide an insight into the diagenetic pathways and hydrologic properties of sediments in sedimentary basins. Petrographic features coupled with whole rock geochemical and iron isotope analyses suggest that hematite precipitation in the red beds started after sediment deposition with the iron internally derived by alteration of iron-bearing minerals and redistributed during late diagenesis. Positive correlation between Fe/Mg ratio and "delta" 56Fe values of bulk samples suggests mixing relationship with end members being authigenic hematite and iron-bearing silicates. The lack of relationship between Fe3+/FeT ratios and iron isotope compositions suggest that the isotopically heavy iron oxide was already present in the sediments during early diagenesis, and was incorporated into green (reduced) facies that likely replaced red facies during diagenesis or burial. Uranium released from the lower, fluvial oxidized sandstones and added to the reduced sandstones and silty mudstones in the upper tidal-deltaic sediments potentially resulted in a uranium mineralization of a roll-front type in the FA Formation of the Franceville Basin. Major and trace element geochemical data for the FA and FB formation are consistent with sediments derived exclusively from felsic igneous source. Chondrite-normalized patterns with high LREE/HREE ratios, negative Eu anomalies, and GdN/YbN ratios favour mixture of Archean and Post-Archean felsic sources. Discriminant diagrams and elemental ratios of major and trace elements suggest deposition of most of the FA sandstone in a passive margin, while the mudstones and fine-grained sandstones of FA and FB were deposited in an active continental margin during Paleoproterozoic tectonic regimes of the West Central African Belt

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Havens, Sarah Beth. "The role of skeletal development in body size evolution of two North American frogs." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2010. http://scholarsmine.mst.edu/thesis/pdf/Havens_2010_09007dcc807be556.pdf.

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Thesis (M.S.)--Missouri University of Science and Technology, 2010. Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed June 7, 2010) Includes bibliographical references.

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Bellis, Stephen. "Catholic chaplains on the Western Front, 1915-1919 : Lancashire's pivotal role." Thesis, University of Liverpool, 2015. http://livrepository.liverpool.ac.uk/2042042/.

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An examination of the spiritual and temporal roles of Catholic chaplains in WW1 in France and Belgium. All the formative influences at home are assessed from religious, political, social, and geographic perspectives. The roles of the bishops in England and Ireland are reviewed and how their post war ambitions were interpreted at the Front are explained. Lancashire's traditional Catholic strength makes it a significant contributor, not least as the fulcrum between Irish and English catholics.

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MOHAMED, IBRAHIM ABOU EL AMAYEM IMAN. "Going the extra mile: front line manager’s role in people management." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2013. http://hdl.handle.net/2108/207905.

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The study investigates the role of front line managers in people management1 to explore how the way people are managed is expected to impact on employee attitudes and outcomes. Research on the link between HRM and organizational performance has overlooked the vital role of front line managers, however it is these managers who are increasingly charged with the enactment of many HR practices. This study seeks to address this gap through examining particularly how the employee attitudes seen in affective organizational commitment and job satisfaction are influenced by the front line managers’ leadership behavior, trustworthy behavior and by satisfaction with HR practices as they have a powerful impact on them. This paper draws on a case study based research which employs both quantitative and qualitative data analysis techniques. Data for this study was collected among 306 employees working in an Egyptian governmental entity. Data analysis and OLS regression showed that employees’ perceptions of front line managers’ leadership behavior, trustworthiness and satisfaction with HR practices have significant correlations with their affective organizational commitment and job satisfaction.

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Ingram, Clayton Bryant. "The Supervising Discipline Engineer's (SDE) role in the Front End Planning Process." Thesis, [Tuscaloosa, Ala. : University of Alabama Libraries], 2009. http://purl.lib.ua.edu/87.

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Dickerson, Darby. "Front-Page News: Newspapers and their Role in the Agenda-Setting Process." W&M ScholarWorks, 1985. https://scholarworks.wm.edu/etd/1539625313.

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18

Koski, Lisa Marie. "The role of frontal cortex in visual selective attention." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape10/PQDD_0017/NQ55350.pdf.

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19

Gough, Patricia Mary. "The role of inferior frontal cortex in language processing." Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442760.

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Muzur, Amir. "Role of Area V6A in the Parieto-Frontal Network." Doctoral thesis, SISSA, 2000. http://hdl.handle.net/20.500.11767/4652.

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The story of brain research is somehow the continuation of the ancient search for the magic stone or the life elixir. Trapped somewhere between laboratorial meticulousness, sentimental tradition, and regardless obsession, contemporary neuroscience demonstrates a very slow pace of advancing, and the only indisputable fact is that the questions at stake are of crucial importance for the improvement of life quality, intellectual satisfaction, and the discovery of real human limitations. To a young scientist, it seems very often that he has to choose between entering the chain of small discoveries leading to a great revelation after ten generations of hard work, or, on the other hand, starting to observe phenomena in a synthetical way, learning from all disciplines and directly speculating on. "cardinal questions." Unfortunately, the cruel scientific community does not encourage the latter choice, except in the case of neurophilosophers, which can never verify their ideas, and the so-called "authorities," who sometimes gained their reputation precisely from the coincidence of being at the end of a chain of "small" scientists and discoveries. One side of the medal suggests that one has only to bear practical sense for practical solutions always in mind. When one cannot any more explain the immediate practical implications of one's research, even if ephemeral, the sense of research is lost, the chain of fruitful discoveries is interrupted, the perspective of this kind of science is zero. "To get to know more about," as it is often the only argument of research papers, is only a sad deformation of science towards a hunt for grants and a comfortable status quo. Cognitive neuroscience can offer its contribution to two major fields: to technology, which can have profit from the models imitating neural networks and therefore facilitate human labour, and, par excellence, to medicine, where "practical sense" means application in therapeutic procedures. One is not obliged to test his findings directly or to convey them to industry or clinicians: it suffices if one knows in each moment what is the place of his work in the "chain" and what is the next step he (or somebody else) has to commit in order to reach that final "practical" scope. Studying one particular area of the brain-the way we have chosen-means to connect very specific disorders to very specific sites in order to become able to predict the outcome of human brain damage and to organise the adequate rehabilitation of debilitated skills. In our case, the chosen areas are located in the posterior superior parietal cortex and the defects observed primarily consider reaching, grasping, and orientation detection. Since, as yet, no efficient way of regenerating cortical tissue has been discovered, the only hope for regaining deteriorated functions is empirical rehabilitation, probably based on different manners of compensatory activities. In our case, it would be interesting to test whether the rehabilitation of one lost ability (for instance, orientation detection) would positively influence also the other skills (grasping and reaching). This and other possibilities should be the landmarks of the "chain" we joined. Nevertheless, there is another side of the medal. It is hardly known in natural sciences, but implicitly accepted in "humanities" (i.e., the group of disciplines called so because they allow human spirit to develop in its natural dimensions). According to this approach, one does not live to produce materially, but to form himself, to find out solutions to the questions he is confronted with, to narcissisticly enjoy his increasing knowledge without feeling remorse, and to make use of this know ledge by speculating and bringing sense in this way to everything around him. This state of limitlessness, which is not given to be felt by everyone, is probably in our case what Semir Zeki (1993, p. X) calls the "great fun the study of the brain can be."

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Simpson, Andrew. "The operational role of British corps command on the Western Front, 1914-18." Thesis, University College London (University of London), 2001. http://discovery.ucl.ac.uk/1349874/.

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British corps command having been neglected in the literature, this thesis sets out to assess what British corps did, and how they did it, on the Western Front during the Great War. It attempts to avoid anecdotal sources as much as possible, drawing its evidence instead as much as possible from contemporary official documents. It is a central argument here that Field Service Regulations, Part 1 (1909), was found by commanders in the BEF to be applicable throughout the war, because it was designed to be as flexible as possible, its broad principles being supplemented by training and manuals. Corps began the war in a minor role, as an extra level of command to help the C-in-C control the divisions of the BEF. With the growth in numbers and importance of artillery in 1915, divisions could not cope with the quantity of artillery allotted them, and by early 1916, the corps BGRA became the corps artillery commander (GOCRA). In addition to its crucial role in artillery control, corps was important as the highest level of operational command, discussing attack plans with Armies and divisions and being responsible for putting Army schemes into practice. Though corps tended to be prescriptive towards divisions in 1916, and Armies towards corps, a more hands-off style of command was generally practised in 1917, within the framework of FSR and the pamphlet SS13S (and others - to be used with FSR). However, the vital role of artillery still led corps to control divisions more closely than in 1915. In 1918, once the BEF had recovered from the setbacks of March and April (caused mainly by low levels of manpower facing overwhelming German infantry and artillery forces), the BEF as much as possible devolved command - even of heavy artillery - to divisions. In the Hundred Days, acting flexibly, corps only assumed a co-ordinating role when set-piece attacks were required.

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Bouton, Michelle Ashley. "The Role of Differential Nutritional Labelling on Consumers’ Food Choices and Perceptions of Healthfulness." Thesis, University of Canterbury. Management, Marketing, and Entrepreneurship, 2014. http://hdl.handle.net/10092/9048.

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Currently, nutritional labelling is difficult to interpret and time-consuming to read. This is a major problem as many consumers are overweight and resort to eating readymade meals and snacks. These are likely to be energy-dense food and beverages that are high in fat, sugar and artificial preservatives. Simplifying nutritional labels could help stem rising obesity rates. Front-of-pack labels are a tool to help overcome this problem by providing consumers with understandable, visible information to aid them into making healthier food choices. This study expands on past research by evaluating 7 separate pre-existing, proposed and fictitious front-of-pack nutritional labels. It includes Information, Image or a combination of both Information and Image based labels. Plus No label, which is a control variable to determine the effectiveness of each label. The nutritional labels were placed on a chicken salad sandwich which was kept consistent for all 14 manipulations. The nutritional components were altered to reflect either an Unhealthy or Healthy sandwich. The design of this experiment is a 2 (nutritional level: Healthy, Unhealthy) X7 (labelling system: Traffic Light, Star, Running, Walking, Third Party, Daily Intake, Caloric, None) between subjects design. The results provide evidence of the urgent need to communicate nutritional information more effectively. Images, simplicity, colour and reliability, are determining label elements that influence consumption behaviour. The results from this study help to understand behaviours associated to labels. This study draws differences between those who partake in health behaviours and those who do not. This information could help to trigger support for a new, more effective front-of-pack labelling system to be put in place globally to guide consumers in making healthier food choices.

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Derrfuss, Jan. "Functional specialization in the lateral frontal cortex : the role of the inferior frontal junction in cognitive control /." Leipzig ; München : MPI, 2005. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=014646361&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.

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Balchin, Ross. "Emotional biases in confabulation : the role of the frontal lobes." Master's thesis, University of Cape Town, 2004. http://hdl.handle.net/11427/7991.

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Bibliography: leaves 57-61. The neuropsychological understanding of confabulation has recently been enriched by the finding that confabulating patients present positive emotional biases in their false recollections. The exact mechanisms of this motivational phenomenon have been heuristically linked to the frontal lobe impairment accompanying confabulation. The present study aims at providing direct support for this claim. A patient with damage to the prefrontal cortex is examined and his performance is contrasted with two confabulating patients, a patient with non-frontal neurological damage and twenty matched controls on a number of tests of emotional processing.

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Al, Balushi Mohammed M. D. M. "The Role of Dramaturgy in Change Management in Shell Oman Marketing Company." Thesis, University of Bradford, 2018. http://hdl.handle.net/10454/17357.

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Inspired by my personal interest in the topic of dramaturgy, coupled with the continuous change programmes that Shell Oman Marketing Company (SOMC) adopts in many areas, this research attempts to explore the role of dramaturgy (Goffman 1956) in change management in SOMC. The primary question that this thesis addresses is: What is the role, impact and potential of dramaturgy in change management in SOMC? The objective is to examine the ability of dramaturgy to offer an effective method for managing change, and one that will eventually be used as an integral part of effective change management programmes in SOMC. The research consists of a case study of installing Closed Circuit Television (CCTV) system cameras in the offices of SOMC. The research was a qualitative study, conducting 22 semi-structured interviews along with unstructured observations of meetings and engagements. The research concludes that front stage performances and backstage performances are witnessed extensively in SOMC, and concludes that the boundary between front and backstage is blurred, that stories, metaphors and body language play an important role in performances, and that the audience perception of the authenticity, sincerity and genuineness of the performers is a key factor in their acceptance of the message. This research identifies a number of themes that can be added to the existing literature. The study highlighted the importance of ‘Alignment’ as a way of explaining the work that goes on in backstage and front stage performances, much part of living organisations. The term found extensively in organisational life at SOMC and many other organisations. Backstage meeting often has the goal of aligning participants to the message that has to be conveyed – the coordinated front stage performance. Therefore, alignment is a key element of the rehearsals and practices for the frontstage performances, and in bringing together the supporting team and loyalists. Another contribution of this research that is not available in other studies is that the importance of context and culture. That although metaphors and storytelling are used in many organisations across the world, they resonate particularly with Omanis because they are part of their history and culture. Hence using storytelling and metaphors in performances in SOMC can have a huge help connecting the audience with the performance.

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McPartland, Caitlin Elizabeth. "The role of Rosie : propaganda and female home-front intervention during World War Two /." Full-text of dissertation on the Internet (703 KB), 2009. http://www.lib.jmu.edu/general/etd/2009/Honors/McPartland_Caitlin/mcpartce_honors_11-11-2009.pdf.

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Kuljabekov, Alibek. "Analytical and numerical models of chemical leaching with gypsum precipitation in porous media." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0369/document.

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Dans cette thèse, nous développons le modèle phénoménologique optimisé de lessivage chimique in situ (ISL) de l'uranium par l'injection d'acide sulfurique, en prenant en compte la précipitation des espèces non-solubles telles que le gypse, qui réduisent la récupération de l'uranium. Le modèle proposé décrit le transport de masse avec des réactions chimiques hétérogènes entre le liquide et les roches solides, qui mènent à la dissolution des oxydes d'uranium et à la récupération de l'uranium sous forme liquide. Ce modèle comprend à la fois des réactions utiles, qui décrivent la dissolution de divers types d'oxydes d'uranium, et les réactions néfastes qui conduisent à la précipitation des sédiments solides (gypse), dont les flocons couvrent la surface de canaux poreux et réduisent l'efficacité des réactions utiles. Parmi les résultats qualitatifs, nous avons révélé l'existence d'un taux critique de sédimentation de gypse, en dessous duquel la récupération ultime de l'uranium est complète. En revanche, elle tend à une valeur limite inférieure à 100% lorsque le taux de sédimentation est supérieur à la valeur critique. Ce taux de récupération limite dépend de divers paramètres du processus. La théorie et la méthodologie développées dans ce travail peuvent être facilement étendues et appliquées aux autres types de minerais qui sont récupérés par la méthode de lessivage in situ, et autres types de solvant In the present thesis we develop the optimized phenomenological model of in-situ chemical leaching (ISL) of uranium by the injection of sulfuric acid, with special account for the precipitation of non-soluble species as gypsum, which reduces the uranium recovery. The suggested model describes the mass transport with heterogeneous chemical reactions between liquid and solid rocks, leading to dissolve uranium oxides and recover uranium in liquid form. It includes both useful reactions, describing the dissolution of various kinds of uranium oxides, and detrimental reactions, leading to the precipitation of solid sediments (gypsum), whose flakes cover the surface of porous channels and reduce the efficiency of useful reactions. Among the qualitative results we revealed the existence of a critical rate of gypsum sedimentation, below which the ultimate uranium recovery is complete. In contrast, it tends to a limit value lower than 100% when the sedimentation rate is higher than the critical value. This limit recovery depends on various parameters of the process. The theory and the methodology developed in this work can be easily extended and applied on other type of ores that are recovered by in-situ leaching method and other types of solvents

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Kennerley, Steven W. "The role of the medial frontal cortex in updating action representations." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422663.

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Abate, Marco, and Massimo Biei. "Role of adopting response strategies to manage the Front-End phase of a project. : An exploratory study of the Italian Innovative SMEs." Thesis, Umeå universitet, Företagsekonomi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-118300.

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The present study investigates the role of the Front-End phase within the context of Innovative Small and Medium-sized Enterprises through the project management lens, focusing on what practitioners can do to manage this phase. Taking a cue from the assumption that the Front-End phase of a project is a very critical and important stage, this study begins with a literature review on innovation and on its role among the Small and Medium-sized Enterprises, and moves to the identification of the main challengesthat an Innovative Italian Small and Medium Enterprise has to face in the Front-End phase. Particularly, the research focuses on the strategies that a project manager can implement to deal with the fuzzy nature of the Front-End phase, originated by uncertainty, equivocality and complexity. The study has an inductive approach and a cross-sectional time-horizon. A case study strategy has been employed, together with semi-structured interviews as data collection technique, involving six Italian Innovative Small and Medium-sized Enterprises identified through the framework of legal requirements provided by the European Union. Although literature poses on the same level all three elements, results show that there is a general consensus about the main role played by uncertainty. Practitioners identify several strategies to employ in order to deal with uncertainty, while the number of strategies identified to reduce equivocality and complexity is limited. Furthermore, this study identifies a correlation between the size of a company and the type of strategies employed to deal with the fuzziness. The more resource a company allocates on a project, the wider is the range of possible strategies project managers can adapt.

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Powell, Jesse Russell. "Ocean fronts in the Southern California Current System and their role in structuring zooplankton distributions, diel vertical migration, and size composition." Thesis, University of California, San Diego, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3566029.

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Ocean fronts are dynamic gradients that divide waters with differing hydrographic properties. Fronts also play important ecological roles in structuring plankton distributions, modulating primary and secondary production, and delineating predator foraging areas. Here, I utilize autonomous “ Spray” ocean gliders to describe the spatial and seasonal distribution of deep-water fronts and their impact on the plankton within the Southern California Current System (SCCS). To test the suitability of the Spray’s 750 kHz acoustic doppler profilers (ADP) for mapping zooplankton distributions, I first present results from a seatruthing study in which I mounted an ADP on a Mocness plankton net. I show that the relative mean volume backscatter (rMVBS) measured by the ADP is correlated with the summed zooplankton cross-sectional area (a proxy for biomass). I also find that the relationship between rMVBS and zooplankton biomass is strongest for zooplankters with an estimated spherical diameter greater than 1.6 mm. Observed rMVBS was best explained by euphausiid and copepod biomass. From Spray cross-shore sections between October, 2006 and December, 2011, I identified 154 distinct surface layer density fronts. The strongest and most numerous fronts occurred in spring, and were located closer to the coast, whereas summer and fall fronts were found further offshore. Fronts were weakest and least numerous in winter. Across all seasons, fronts structured plankton distributions. Horizontal gradients in physical variables (e.g., surface density, temperature, and salinity) co-varied with horizontal gradients in MVBS and Chl-a fluorescence, and the magnitude of biological gradients was higher at frontal areas compared with non-frontal areas. Frontal areas were also clearly associated with elevated Chl -a and zooplankton acoustic backscatter. Fronts divided distinct plankton habitats and associated assemblages. Chlorophyll-a fluorescence maxima and euphotic zones were deeper offshore of fronts. The amplitude of diel vertical migration by zooplankton also increased offshore, in association with increased optical transparency in the upper ocean. Additionally, ADP data indicate that zooplankton assemblages change across fronts. I employ an inverse acoustic model to estimate zooplankton size spectra, inferring that larger-bodied zooplankters contributed a greater proportion to overall biomass inshore of these fronts. Vertically-stratified zooplankton samples from both inshore and offshore regions corroborated the model results.

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Edwards, Carolyn Anne. "The role of the frontal cortex in normal age-related memory performance." Thesis, University of Bristol, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389161.

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Lee, Andy Cheung Hong. "The role of the human frontal lobes in memory encoding and retrieval." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621105.

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Seo, M. "The role of front-striatal brain circuits and dopamine in cognitive motor control of sequential behaviour." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1420697/.

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Our daily lives are filled with routine behaviours that we develop with repeated practice over time. These routine behaviours, often executed automatically without requiring much attention become an integral part of our lives. However, a seemingly effective automatic behaviour can become inappropriate or inefficient with changes in the environment and we naturally turn to a more adaptable, perceptually guided behaviour to achieve the same goal. What are the networks that mediate these automatic and perceptually guided behaviours? This thesis focuses on understanding the role of frontal-striatal circuits in the cognitive motor control of sequential behaviour, as well as the contribution of dopamine (DA) in these areas. The aim of the studies presented in this work was to address these questions from a number of perspectives. Firstly, in an awake-behaving non-human primate study the goal was to develop a behavioural task that differentiates the automatic and attention demanding sequential actions. Secondly, ensembles of neurons in the frontal cortex and the dorsal striatum were recorded simultaneously with a multichannel single unit recording system to characterise neural responses to our different task conditions and thereby investigating the role of prefrontal cortex and the dorsal striatum in these behaviours. Thirdly, we locally injected DA receptor antagonists into the dorsal striatum, during the behavioural task to examine the effects of DA on behaviour. Finally, in a study using patients with Parkinson’s disease we examined their performance in a sequence learning task from positive and negative feedback processing while they were off and on their DA medication. This approach helped to strengthen the link between findings in the non-human primate and the human subjects with specific involvement of DA or disruption of the frontal-striatal circuits in sequence learning.

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Honzík, Tomáš. "Návrh přední nápravy formule SAE." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2008. http://www.nusl.cz/ntk/nusl-228230.

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My thesis will be aimed at front axle design. I am going to design the assembly of the front axle in the program ADAMS by MSC. I am going to observe and record most of cinematic changes of the car such as change of position of vehicle roll centre ,wheel camber, geometry adjustment , wheel toe-in measuring and other necessary data. The final report is going to include strength calculation of particular axle parts. I am also going to solve the axle stabilizer including strength calculation.

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McGuire, Luke A., Francis K. Rengers, Jason W. Kean, et al. "Elucidating the role of vegetation in the initiation of rainfall-induced shallow landslides: Insights from an extreme rainfall event in the Colorado Front Range." AMER GEOPHYSICAL UNION, 2016. http://hdl.handle.net/10150/621986.

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More than 1100 debris flows were mobilized from shallow landslides during a rainstorm from 9 to 13 September 2013 in the Colorado Front Range, with the vast majority initiating on sparsely vegetated, south facing terrain. To investigate the physical processes responsible for the observed aspect control, we made measurements of soil properties on a densely forested north facing hillslope and a grassland-dominated south facing hillslope in the Colorado Front Range and performed numerical modeling of transient changes in soil pore water pressure throughout the rainstorm. Using the numerical model, we quantitatively assessed interactions among vegetation, rainfall interception, subsurface hydrology, and slope stability. Results suggest that apparent cohesion supplied by roots was responsible for the observed connection between debris flow initiation and slope aspect. Results suggest that future climate-driven modifications to forest structure could substantially influence landslide hazards throughout the Front Range and similar water-limited environments where vegetation communities may be more susceptible to small variations in climate.

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Gagnon, Danny. "The role of frontal oculomotor structures in the predictive control of eye movements /." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=85909.

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The role of the FEF/FPA and SEF in oculomotor prediction was investigated using psychophysics, functional MRI (fMRI) and TMS. The separate contribution of advance knowledge of target direction and target timing to predictive saccades, and neural activity in frontal oculomotor structures was first investigated. The greatest proportion of predictive saccades were elicited when subjects had advance knowledge of both target direction and target timing; advance knowledge of target direction increased the proportion of predictive saccades, while advance knowledge of target timing decreased saccade latencies without increasing predictive saccades. Activity was greater in the FEF for all saccade tasks with a predictable component than reflexive saccades. Activity in the FEF was higher in tasks for which saccade latencies were lower. These data suggest that target direction and target timing independently reduce saccade latencies, and that this information converges in the FEF to allow the generation of predictive saccades. In the SEF, activity was greater only in the condition when both target direction and target timing were predictable. This finding may reflect a role of the SEF in oculomotor sequencing rather than in prediction per se. In order to assess whether the FEF play a general role in oculomotor prediction, and not just in saccades, the role of the FPA in predictive pursuit was evaluated by applying TMS to the FPA and SEF during sinusoidal pursuit. TMS of the FPA modulated eye velocity both at peak target velocity and at the target turnaround. The induced changes in eye velocity occurred with a short latency, that is, before visual signals could travel from the retina to brainstem. This would suggest that TMS of the FPA likely increased the gain of the transformation of predictive signals, rather than visual signals, to motor commands. Stimulation of the SEF increased eye velocity only when applied at the target turnaround. Previous studies have demonstrated that stimulation of SEF increases eye velocity during pursuit initiation. Our finding that this facilitation also occurs at the target turnaround may berelated to similarities between pursuit initiation and the turnaround, including the necessity to rapidly increase eye velocity from zero.

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Baker, Gillian Clare. "The enigmatic protist - the taxonomic affinities of Prototheca richardsi and its role in amphibian ecology." Thesis, University of Sussex, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263149.

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Leonard, Thomas Gabriel. "The role of the frontal lobes in the encoding and recall of kinesthetic information /." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75703.

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Patients with unilateral temporal- or frontal-lobe excisions and normal control subjects were tested on four kinesthetic and two visual recall tasks. The first two studies required subjects to monitor peripheral feedback, in order to duplicate the distance or the end-position of examiner-defined arm movements. In the next two tasks, the subjects selected the movements to be recalled, and hence reliance on feedback was reduced. On the visual tests the subjects had to recall the distance traversed by a dot on a screen, or its end-position. Temporal lobectomy did not interfere with performance of the tasks, except for examiner-defined kinesthetic location. On this task, large left- or right-hippocampal resection produced an impairment following 30 s of counting. Patients with left frontal-lobe or small right frontal-lobe excisions performed normally on all tests, whereas those with large right frontal-lobe removals were impaired with both hands on the examiner-defined kinesthetic tasks. Patients with large right frontal-lobe lesions also demonstrated a delayed-recall deficit for visual distance. The results point to an important role played by the right frontal lobe in the monitoring of kinesthetic feedback both during the presentation of the movements and during the recall attempt.

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Sommer, Marc A. (Marc Alois). "The role of frontal cortex in the generation of saccadic eye movements and fixation." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/32678.

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40

Hong, Sujin. "Neural correlates of beat and metre perception : the role of the inferior frontal gyrus." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/21112.

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Temporal regularity and metrical organisation are important factors in beat and metre perception. The current thesis aims to investigate neural correlates of beat and metre perception in healthy non-musician volunteers, using functional magnetic resonance imaging (fMRI). In particular, the thesis focuses on determining the role of the Inferior Frontal Gyrus (IFG, in particular BA44/45) in beat and metre perception. The IFG has been proposed to be involved in higher order cognitive processes during various temporal sequencing, such as speech, movement, and music. Previous studies have shown that the temporal processing of rhythm activates auditory and sensorimotor areas, but the role of the IFG in rhythm perception has not yet been fully understood. Study 1 investigated beat perception in complex rhythms, in which the addition of volume accents either enhanced or weakened the beat perception, resulting in Unaccented, Beat Accented or Non-Beat Accented rhythms. Participants (N=14; 6 males) listened to rhythm pairs across all three conditions, and judged whether each rhythm pair was the same or different. Results showed that left IFG activation (BA44) was significantly greater during the Non-Beat Accented condition compared to Beat Accented condition, whereas the right IFG activation showed no significant difference between the two conditions. Study 2 investigated metre perception of a series of isochronous sequences, of which metrical organisation was grouped by 2/4 (C2), 3/4 (C3), or 4/4 (C4) using pitch accents, or remained without metrical grouping (or 1/4, C1). The same participants (N=15; 6 males) listened to the stimuli and indicated the perceived metrical grouping level. Results showed that the activation of bilateral IFG parametrically increased from C2 to C3 to C4. Interestingly, the activation was found to be significantly greater in C1 relative to C2, suggesting that involuntary subjective in C1 may increase the brain response. Converging results from both Study 1 and Study 2 demonstrated, firstly, that the bilateral IFG is involved in rhythm perception in addition to the auditory and sensorimotor areas, including primary and secondary auditory areas, supplementary motor areas, premotor areas, insula, and basal ganglia. Secondly, the left IFG (BA44) in particular was significantly modulated by the rhythmic complexity relating to both temporal regularity and metrical organisation, while showing the suppression during the Beat Accented rhythm condition of Study 1 and the binary pattern (C2) of Study 2. This thesis argues that the left IFG (BA44) may have the role the higher order cognitive processing, such as attention and prediction, in the perception of hierarchical structures in metric rhythms.

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Macleod, Mairi S. "Cognitive ageing and the role of the frontal lobes in prospective memory and planning." Thesis, University of Aberdeen, 2001. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU137019.

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A recent theory postulates that the cognitive functions associated with the frontal lobes are likely to selectively deteriorate with age (West, 1996). In line with this theory, it was predicted that an age-related decline in measures of prospective memory and planning would be observed. In order to investigate this hypothesis, a series of five experiments were conducted using groups of young, middle aged and older normal participants. In Experiment 1, participants were asked to follow a recipe while remembering to do various prospective memory tasks at the same time. Older participants performed significantly worse on all measures of prospective memory. Significant age differences in measures of planning were observed in the computerised &'34;Tower of London&'34; planning task in Experiment 2. In Experiment 3, participants were given an open-ended planning task involving allocating a list of tasks to three friends. Older participants made significantly more overall planning errors. In Experiment 4, few age differences were observed in general executive function. In Experiment 5, the role of attention in prospective memory and planning was examined. Older participants performed significantly worse than the younger participants at the prospective memory and planning tasks. Speed of information processing was more highly associated with performance on the planning and prospective memory tasks than the attentional measures. There was not enough evidence available from the two patient studies to suggest that prospective memory was differentially impaired in patients with frontal lesions. The overall results confirmed the experimental hypothesis that there is an age-related decline in prospective memory and planning. However, the extent to which these age-related declines can be attributed to selective declines in the frontal lobes remains unclear.

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Asdar, Sarah. "Climate change impact on ecosystems of Prince Edward Islands : role of oceanic mesoscale processes." Thesis, Brest, 2018. http://www.theses.fr/2018BRES0037/document.

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L’archipel du Prince Édouard est situé dans le Courant Circumpolaire Antarctique, entre le Front Subantarctique (SAF) et le front polaire (PF). Les positions de ces fronts se sont révélées très variables aux échelles interannuelles et mensuelles et ont montré une tendance à long terme à migrer vers le sud dans la région. L'activité tourbillonnaire, observée à la dorsale sud-ouest indienne, en amont de l’archipel, a également affiché une variabilité interannuelle et intra-annuelle ainsi qu’une tendance à la baisse sur ces 24 dernières années. A une échelle plus locale, nous avons souligné que les conditions aux îles sont impactées par ces tourbillons mésoéchelle produits en amont. La marée a également été mise en évidence comme jouant un rôle non négligeable dans la variabilité de la circulation entre les îles. Une configuration idéalisée a été mise en place pour la région afin d’étudier les propriétés des tourbillons et les mécanismes physiques à l’origine de leur formation. L'énergie potentielle tourbillonnaire disponible a révélé un maximum d'énergie aux alentours de 800 m de profondeur, confirmant le caractère « deep-reaching » des tourbillons. Cette activité tourbillonnaire a été montrée comme étant le résultat d'une combinaison d’instabilités barotropes et baroclines. Enfin, nous avons enquêté sur les conséquences potentielles d'une migration vers le sud du SAF dans la région des îles. Le modèle étant idéalisé, il nous a permis de simuler un déplacement vers le sud en déplaçant les conditions initiales ainsi que les conditions aux limites. Le principal résultat a été la nette diminution de l'activité mésoéchelle dans la région, ce qui pourrait avoir un impact sur les écosystèmes de l’archipel du Prince Édouard The subantarctic Prince Edward Islands lie in the Antarctic Circumpolar Current, between the Subantarctic Front (SAF) and the Polar Front (PF). These fronts positions were found to be highly variable at interannual and monthly time scales and revealed a significant long-term southward trend in the region. The intense mesoscale activity, observed upstream the islands at the South West Indian Ridge, also showed an interannual and intra-annual variability as well a decrease in eddy kinetic energy over 24 years. At a more local scale, we highlighted that the archipelago’s environment was impacted by the mesoscale features produced upstream.Tides appeared to be another important driver of variability of the circulation in between the two islands.An idealised model configuration was designed for the Prince Edward Islands region to study the mesoscale eddy properties and the physical mechanisms of their formation at the ridge. The Eddy Available Potential Energy revealed a maximum of energy around 800 m depth, confirming the deep reaching characteristic of the eddy originated in the region and suggested the presence of a local energy source at this depth. This eddies activity was shown to be the result of a combination of barotropic and baroclinic instabilities occurring at the ridge.Finally, we investigated on the potential consequences of a southward shift of the SAF in the region of the islands.Because the model was idealised, it allowed us to simulate an SAF southward shift by shifting the initial and boundary conditions. The main result was the clear decrease of mesoscale activity in the region which could potentially impact the ecosystems of the Prince Edward Islands

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Mani, Arzhang [Verfasser], Lambert [Akademischer Betreuer] Alff, and Rolf [Akademischer Betreuer] Jakoby. "Epitaxial ferroelectric all-oxide varactors for application in reconfigurable RF front ends / Arzhang Mani ; Lambert Alff, Rolf Jakoby." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2017. http://d-nb.info/1143827287/34.

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Vines, Anthony John. "The heroic manager : an assessment of Sir Douglas Haig's role as a military manager on the Western Front." Thesis, King's College London (University of London), 2016. http://kclpure.kcl.ac.uk/portal/en/theses/the-heroic-manager(cb67ab17-c1ea-4866-a6b5-1a832250dc8e).html.

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Sir Michael Howard has observed that Douglas Haig was a military manager in the mould of Ulysses S. Grant and Dwight D. Eisenhower rather than one of the “Great Captains” of military legend. Unfortunately, Howard did not elaborate. To date, this crucial aspect of Haig’s role on the Western Front has not been explored. The contention of this thesis is that Haig was an exceptional military manager who pursued the organising principle of unity-of-effort within the BEF on the Western Front to facilitate the defeat of the German Army in concert with the Allies. In 1909, Haig established unity-of-effort as the first principle of war organization in FSR-II.1 Haig did not define the precept possibly in the belief that it was a commonplace. However, a study to establish the contemporary understanding has revealed that unity-of-effort was, and is, the raison d’être of all forms of human organization including the military. It was regarded as a tangible and effective principle and not a mere rhetorical gesture or oratorical flourish. Its nature was immutable, and uniquely coordinative. Unity-of-effort found expression in its compound character, which had distinct mental, physical and moral components, specific to each organization. The principle was considered to be a normative ideal, and not an absolute standard. Haig strove to optimise unity-of-effort by developing operational, organizational and administrative doctrine in pursuit of unity-of-mental-effort; by inculcating the teachings of doctrine through progressive training methods to achieve unity-of-physical-effort; and by promoting the will to fight through sustained morale and discipline to attain unity-of-moral-effort. Haig managed the process to attain unity-of-effort through the coordinative function of the General Staff.

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Le, Bouar Erwan. "Etude des circulations ageostrophiques entre la basse et la haute troposphere. Leur role dans la formation des ondulations frontales observees pendant l'experience fronts 87." Paris 6, 1997. http://www.theses.fr/1997PA066681.

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L'objectif de cette these est de determiner le role des circulations ageostrophiques dans l'evolution des ondulations frontales. La demarche adoptee sera appliquee a l'exploitation des donnees de la toute recente experience fastex. Dans le cadre de ce travail, quatre situations frontales de l'experience fronts 87 sont comparees a l'aide de re-analyses du cepmmt pour le contexte regional a grande echelle, et de donnees de radiosondages intensifs pour le contexte local. Pour la premiere fois, le champ de vent ageostrophique est obtenu a petite meso-echelle a partir de donnees experimentales, grace a la methode de restitution avag. Cette methode est validee en fonction de criteres physiques et phenomenologiques (en utilisant les donnees de radiosondages intensifs, de radar s. T. , et des analyses du cepmmt), et s'avere superieure aux methodes qui utilisent uniquement l'equation du mouvement. La comparaison entre les differentes situations frontales permet d'observer des interactions entre haute et basse troposphere au voisinage de la plupart des zones deformees des fronts, soulignant le lien qui existe entre ces deux phenomenes. Parmi les quatre cas d'etude selectionnes, un seul correspond de facon certaine a un front ondulant. Ce cas est donc etudie en detail. Dans ce contexte, on etudie non seulement l'interaction haute-basse troposphere au voisinage de l'ondulation, mais aussi les mecanismes qui conduisent a la formation puis a la destruction de l'ondulation elle-meme. La vitesse verticale, ageostrophique par nature, joue un role clef dans l'evolution de l'ondulation, par deux effets antagonistes : d'une part elle induit un terme d'advection verticale de chaleur qui intensifie puis contribue a maintenir l'ondulation ; d'autre part, elle entraine un effet de basculement des isentropes qui tend a attenuer l'ondulation. Dans le cas etudie, le dernier effet devient, a un moment donne, preponderant et conduit a l'attenuation de l'ondulation frontale.

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Alblooshi, Fatima Khalifa. "The Role of Paratextual Elements in the Reception of Translation of Arabic Novels into English." Kent State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=kent1617719565200925.

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47

Hand, Ralf [Verfasser]. "The Role of Ocean-Atmosphere Interaction over the Gulf Stream SST-front in North Atlantic Sector Climate / Ralf Hand." Kiel : Universitätsbibliothek Kiel, 2015. http://d-nb.info/106664487X/34.

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48

Allard, Alain. "Consumer interpretation of nutrition and health messages on food products : the role of individual characteristics and front-package features." Thesis, Queen's University Belfast, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.554343.

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Under the new Regulation (1924IEC2006), consumer understanding is now one the criteria for the approval Of NH claims. This thesis focuses on consumer interpretation of NH claims as a key factor influencing expectations of product healthfulness and potential health benefits. Based on spreading activation theory and the Elaboration Likelihood Model, the thesis investigates the impact of package characteristics and personal determinants on consumer perceptions of product attributes and potential health benefits. Using a combined approach of qualitative and quantitative research methods, the research found that people's expectations of a product's healthfulness are primarily influenced by personal characteristics, and to a lesser extent, by NH claims and other front package characteristics. With regards to front package characteristics, results suggest that colour-coding nutritional information may create a negativity bias while endorsement/logo schemes may create a positivity bias in some cases. However, data show that variations in the wording of a claim only have a small impact on consumer evaluations. With regards to personal determinants, result show that people's motivation (expressed in terms of personal relevance) and their perceived understanding of the information on food products play an important part in the way consumers evaluate a product's healthfulness. Level of liking of the pictures on the package and perceived expertise of the organisation supporting NH claims were also found to have a significant influence on consumer evaluations. Furthermore, the belief that a product's health benefits increase with increasing consumption (dose insensitivity) appears to be relatively common amongst consumers. Implications for these findings are dis cussed in context, along with considerations for future research.

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Daku-Mante, Jacqueline G. "An analysis of civil disobedience with specific reference to the role of the United Democratic Front in South Africa." Diss., University of Pretoria, 2013. http://hdl.handle.net/2263/43307.

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The main objective of this study is to analyse the concept of civil disobedience by providing an overview of its historical development; its objectives and strategies, and how this was applied in South Africa by the United Democratic Front in the 1980s. The sub-objectives were to determine if civil disobedience as a concept is going through, or has gone through any notable changes since its inception; to assess the extent to which United Democratic Front policies and strategies were in accordance with civil disobedience; and to briefly compare manifestations of civil disobedience in South Africa in the pre-1994 period, with some manifestations in the post-1994 period. The study included an assessment of the Defiance Campaign, analysing its impact and demise. It focused on the ANC strategy of mass action and assessed the role of the Pan African Congress. It outlined the formation of the UDF, assessing its vision, broad principles, organisation and objectives. Certain assumptions were assessed in the concluding chapters, namely that civil disobedience has developed into a broader concept than the original concept of passive resistance; that the policies and strategies of the United Democratic Front initially resembled some aspects of civil disobedience but eventually deviated from this due to a change in strategy; and that some contemporary manifestations of civil disobedience in South Africa resemble certain methods used in the 1980s, but the objectives differ. Dissertation (MA)--University of Pretoria, 2013. lk2014 Political Sciences MA Unrestricted

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Bernard, Kim Sarah. "The role of the euthecosome pteropod, limacina retroversa, in the polar frontal zone, Southern Ocean." Thesis, Rhodes University, 2007. http://hdl.handle.net/10962/d1005449.

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The aim of the present study was to assess the ecological role of the euthecosome pteropod, Limacina retroversa, in particular, and the mesozooplankton community, in general, in the pelagic ecosystem of the Polar Frontal Zone (PFZ), Southern Ocean. Data were collected from four oceanographic surveys to the Indian sector of the PFZ during austral autumn 2000, 2002, 2004 and 2005. Copepods, mainly Calanus simillimus, Oithona similis, Clausocalanus spp. and Ctenocalanus spp., typically dominated total mesozooplankton counts, accounting for, on average, between 75.5 % and 88.1 % (Mean = 77.4 %; SD = 13.4 %) of the total, during the present investigation. Results of the study indicate that L. retroversa may, at times, contribute substantially to total mesozooplankton abundances. During the study, L. retroversa contributed between 0.0 and 30.0 % (Mean = 5.3 %; SD = 7.1 %) to total mesozooplankton numbers. Significant small-scale variability in abundance and size structure of L. retroversa and abundance of copepods was minimal. Inter-annual variability, on the other hand, was significant between some years. Total pteropod numbers were greatest during April 2002 and 2004, while copepods exhibited greatest abundances during April 2004 only. Pearson’s Correlation analysis suggested that L. retroversa abundances were positively correlated to total surface chlorophyll-a (chl-a) concentrations. The significantly lower chl-a concentrations recorded during April 2005 may explain the reduced pteropod numbers observed during that survey. The size class structure of L. retroversa comprised mainly small and mediumsized individuals during all four surveys. This corresponds well with records from the northern hemisphere (sub-Arctic and Arctic waters) where Limacina spp. are reported to exhibit maximum spawning during mid to late-summer. Higher abundances of large individuals only occurred during April 2005, when chl-a concentrations were very low; possibly the result of delayed spawning, due to reduced food availability. Ingestion rates of the four most abundant copepods, determined using the gut fluorescence technique, ranged between 159.32 ng (pigm) ind⁻¹ day⁻¹ and 728.36 ng (pigm) ind⁻¹ day⁻¹ (Mean = 321.01 ng (pigm) ind⁻¹ day⁻¹; SD = 173.91 ng (pigm) ind⁻¹ day). Ingestion rates of L. retroversa were much higher, ranging from an average of 4 28.68 ng (pigm) ind⁻¹ day⁻¹ in April 2002 to 4 196.88 ng (pigm) ind⁻¹day⁻¹in April 2005 (Mean = 4157.36 ng (pigm) ind⁻¹ day⁻¹; SD = 35.37 ng (pigm) ind⁻¹day⁻¹). Average daily grazing rates for the pteropod varied between 0.39 mg (pigm) m⁻² day⁻¹ in April 2005 and 17.69 mg (pigm) m-2 day-1 in April 2004 (Mean = 6.13 mg (pigm) m⁻² day⁻¹; SD = 11.04 mg (pigm) m⁻² day⁻¹); corresponding average daily grazing impacts ranged between 8.4 % and 139.8 % of the phytoplankton standing stock in April 2005 and 2004, respectively (Mean = 48.5 %; SD = 84.5 %). Average daily grazing rates of the four copepods ranged from 4.58 mg (pigm) m⁻² day⁻¹ to 8.77 mg (pigm) m⁻² day⁻¹ -1, during April 2002 and 2004, respectively (Mean = 6.28 mg (pigm) m⁻² day⁻¹; SD = 5.94 mg (pigm) m⁻² day⁻¹). Collectively, the copepods removed an average of between 31.6 % and 89.8 % of the phytoplankton standing stock per day, during April 2002 and 2004, respectively (Mean = 70.8 %; SD = 86.7 %). The daily grazing impact of the copepods accounted for an average of between 40.4 % and 87.8 % of the total zooplankton grazing impact, during April 2004 and 2005, respectively (Mean = 75.0 %; SD = 65.5 %). L. retroversa was responsible for an average of 52.4 % and 59.5 % of the total zooplankton grazing impact, during April 2002 and 2004, respectively. However, during April 2005, when L. retroversa numbers were significantly lower than previous years, the pteropod contributed an average of only 7.5 % to the total zooplankton grazing impact. Thus, during the present investigation,the pteropod was responsible for removing a mean of 48.9 % of the available phytoplankton (SD = 74.9 %). The predation impact of the dominant carnivorous macrozooplankton and micronekton in the PFZ was determined during April 2004 and 2005 using daily ration estimates obtained from the literature. Additionally, gut content analysis was used to determine the contribution of L. retroversa to the diet of the dominant predators. Average predation impact ranged from 1.1 % and 5.7 % of the total mesozooplankton standing stock during April 2004 and 2005, respectively (Mean = 3.8 %; SD = 12.3 %). Chaetognaths and euphausiids dominated total carnivore numbers and made the greatest contributions to total predation impact during both years. Copepods appeared to be the main prey item of the dominant carnivorous macrozooplankton-micronekton in the region. L. retroversa was only detected in the gut contents of the amphipod, Themisto gaudichaudi, but not in either of the chaetognath species (Eukrohnia hamata and Sagitta gazellae) or the myctophid fish (Electrona spp.). The pteropod was found in 19 % of amphipod guts dissected. Pearson’s Correlation analyses showed that the four major predatory zooplankton groups found in the PFZ (chaetognaths, euphausiids, amphipods and myctophid fish) were positively correlated to abundances of L. retroversa, suggesting that the pteropod might be an important prey item for many of the carnivorous macrozooplankton/micronekton in the PFZ. To conclude, L. retroversa may play an important role in the pelagic ecosystem of the PFZ, in austral autumn. However, ocean acidification and calcium carbonate undersaturation (as a result of increased anthropogenic carbon dioxide emissions), that is predicted to occur within the next 50 – 100 years, will most likely have significant implications for the Sub-Antarctic pelagic ecosystem if L. retroversa cannot adapt quickly enough to the changes.

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Dissertationen zum Thema „Roll fronts“

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