Dissertations / Theses on the topic 'Earth divers'

My stoneware sculptures in my MFA final project were named Earth Divers because clay as a material is earth and clay is also symbolic of the Earth. The way that I physically dive into clay up to my elbows is a poetic performance. The sculptures were built in sections horizontally and then stacked vertically. I began the process by first making life size plaster molds of the human figure taken from live people. Earth Divers take their architectural structure specifically from the organic curves of the negative voids that are characteristic of the plaster figure molds. I built into these plaster molds a block or brick like section. I then removed the large block sections from the molds and stacked the sections one on top of the other combining the figurative and architectural structures with gothic influence. The sculptor, Stephen De Staebler, who works in a similar fashion, describes his work as, "... first laying the figure down and later standing it in a vertical position." The way of life that was lost with the manufacturing past of my family at Castone Brick is found in the use of industrial nostalgia by modeling I-beam shapes as part of the structure of the stacked sections. I also fired nuts, bolts, and washers of various sizes in the clay that build the surface of the human forms. The square nut seen in my work is no longer being manufactured and is symbolic of the passing of the industrial age in America. Finally, to build the surfaces of my sculptures I used slips, glazes, and a variety of clays on top of clay, and laid glass fragments on the horizontal surfaces to create a look of pooled water when my work was fired similar to what I have seen in the Lehman Caves in Baker, Nevada. "I believe there is a force in this world that lives beneath the surface, something primitive and wild that awakens when you need an extra push just to survive, like wild flowers that bloom after a fire turns the forest black. Most people are afraid of it and keep it buried deep inside themselves. But, there will always be a few people who have the courage to love what is untamed inside us." (Tim McGraw)

Le comportement des structures sous certains types d'actions tels que les séismes nécessite une bonne connaissance du comportement des matériaux composants sous des charges cycliques. Dans cette étude, le modèle de comportement cyclique du béton est basé sur la théorie de l'endommagement, sur la mécanique des milieux continus et la thermodynamique des processus irréversibles. Ce modèle tient compte des déformations résiduelles et de la perte de raideur due à la fissuration. Dans son application, les effets biaxiaux et le fluage ne sont pas pris en considération. Le comportement des armatures est considéré élasto - plastique parfait. Une amélioration importante pour l'application du modèle a été de définir une méthode d'identification des paramètres à partir des données physiques obtenues dans les essais classiques de contrôle du béton et d'une expression analytique de la loi de comportement d'usage courant. Le modèle uniaxial est introduit dans un code numérique pour structures planes. La structure à analyser est découpée en plusieurs éléments de poutres. Chaque élément est représenté par un certain nombre de sections. La section est divisée en plusieurs fibres soumises à une sollicitation uniaxiale. Chaque fibre suit sa propre histoire conforme au modèle ci-dessus, mais sa déformation respecte la loi de planéité de la section considérée. Des essais de validation ont été réalisés sur des éprouvettes cylindriques sous charges cycliques de compression, sur des poteaux courts sous compression - traction cyclique et sur des poteaux sous flexion alternée et effort normal constant. La comparaison modèle - essais apporte des résultats encourageants pour l'analyse des structures en béton armé sous charges cycliques.

Master of Science
Department of Geology
Iris M. Totten
Problem-based learning in the sciences has been demonstrated to be a successful educational approach to engage students and increase content knowledge. However, the power of collaborative learning to engage students, increase content knowledge and develop problem-solving skills in the sciences has not yet been fully researched. Collaborative learning has an enormous potential not only to foster student learning, but also to increase interest in the sciences and promote cutting-edge education strategies worldwide. Collaborative learning tactics in this study take place within the virtual learning environment entitled “GeoWorlds.” GeoWorlds is an online educational gaming program within the Second Life 3-D Teen Grid. The curriculum was developed as a collaborative, investigative and engaging program to promote learning of Earth science content. The program allows students to be submersed-in and explore different geologic time periods; enabling them to observe species and geological structures while interacting with one another to complete tasks. This study investigates the educational impact, emotional response and overall feedback of the GeoWorlds virtual learning environment on Midwest ninth graders.

Thesis: Ph. D., Joint Program in Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references.
While aerobic respiration is typically invoked as the dominant mass-balance sink for organic matter in the upper ocean, many other biological and abiotic processes can degrade particulate and dissolved substrates on globally significant scales. The relative strengths of these other remineralization processes - including mechanical mechanisms such as dissolution and disaggregation of sinking particles, and abiotic processes such as photooxidation - remain poorly constrained. In this thesis, I examine the biogeochemical significance of various alternative pathways of organic matter remineralization using a combination of field experiments, modeling approaches, geochemical analyses, and a new, high-throughput lipidomics method for identification of lipid biomarkers. I first assess the relative importance of particle-attached microbial respiration compared to other processes that can degrade sinking marine particles. A hybrid methodological approach - comparison of substrate-specific respiration rates from across the North Atlantic basin with Monte Carlo-style sensitivity analyses of a simple mechanistic model - suggested sinking particle material was transferred to the water column by various biological and mechanical processes nearly 3.5 times as fast as it was directly respired, questioning the conventional assumption that direct respiration dominates remineralization. I next present and demonstrate a new lipidomics method and open-source software package for discovery and identification of molecular biomarkers for organic matter degradation in large, high-mass-accuracy HPLC-ESI-MS datasets. I use the software to unambiguously identify more than 1,100 unique lipids, oxidized lipids, and oxylipins in data from cultures of the marine diatom Phaeodactylum tricornutum that were subjected to oxidative stress. Finally, I present the results of photooxidation experiments conducted with liposomes - nonliving aggregations of lipids - in natural waters of the Southern Ocean. A broadband polychromatic apparent quantum yield (AQY) is applied to estimate rates of lipid photooxidation in surface waters of the West Antarctic Peninsula, which receive seasonally elevated doses of ultraviolet radiation as a consequence of anthropogenic ozone depletion in the stratosphere. The mean daily rate of lipid photooxidation (50 ± 11 pmol IP-DAG L⁻¹ d⁻¹, equivalent to 31 ± 7 [mu]g C m⁻³ d⁻¹) represented between 2 and 8 % of the total bacterial production observed in surface waters immediately following the retreat of the sea ice.
by James R. Collins.
Ph. D.

This thesis investigates how increased global mean temperatures on Earth, induced by the increase in the luminosity of the Sun as it ages, change the types of habitable environments on the planet at local scales over the next 3 Gyr. Rising temperatures enhance silicate weathering rates, reducing atmospheric CO₂ levels to below the threshold for photosynthesis, while simultaneously pushing environments past the temperature tolerances of plant and animal species. This leads to the end of all plant life and animal life (due to reduced food, O₂ and H₂O availability, as well as higher temperatures) within the next 1 Gyr. The reduction in the extent of the remaining microbial biosphere due to increasing temperatures and rapid ocean evaporation is then modelled, incorporating orbital parameter changes until all known types of life become extinct; a maximum of 2.8 Gyr from the present. The biosignatures associated with these changes are determined and the analysis extended to Earth-like extrasolar planets nearing the end of their habitable lifetimes. In particular, the stages in the main sequence evolutions of Sun-like stars within 10 pc are evaluated and used to extrapolate the stage that an Earth-analogue planet would be at in its habitable evolution, to determine the best candidate systems for a far-future Earth-analogue biosphere, highlighting the Beta Canum Venaticorum system as a good target. One of the most promising biosignatures for a microbial biosphere on the far-future Earth (and similar planets) may be CH₄, which could reach levels in the atmosphere that make it more readily detectable than it is for a present-day Earth-like atmosphere. Determining these biosignatures will help expand the search for life to the wider range of environments that will be found as the habitable exoplanet inventory grows and planets are found at different stages in their habitable evolution.

The discovery of ultra-high pressure (UHP), super-reduced (SuR), and continental crust-derived minerals in ophiolitic chromitites worldwide challenged the previous hypotheses for chromitite formation and motivated the proposal of complex geodynamic models involving UHP conditions of formation for the chromite or recycling of the ophiolitic rocks down to the Mantle Transition Zone (410 – 660 km depth). This thesis investigates in detail the chromitites and the associated ophiolitic rocks from the Moa-Baracoa massif, eastern Cuba, and Bou Azzer, Morocco, with emphasis on identifying the presence of exotic minerals, interpreting their formation, and understanding the related geodynamic processes. The interaction of preexisting chromitites with evolved tholeiitic melts that triggered Fe-Ti-Zr metasomatism in the Potosí chromitites (eastern Cuba) is carefully investigated here. There is evidence of coarse granular textures and strongly variable mineralogy composed of recrystallized/neoformed Fe3+-Ti-rich chromite, Ti-rich amphibole, clinopyroxene, orthopyroxene, olivine, Mg-rich ilmenite, Zr-bearing oxides and silicates, and Fe-Cu-Ni sulfides. Thorough petrographic analysis coupled with the chemical composition of the mineral phases allowed to determine the sequence of mineral formation and to propose a two-stage genetic model: 1) the crystallization of an evolved MORB liquid, via fractional crystallization, produced water-rich residual melts strongly enriched in incompatible elements, and 2) batches of this evolved melt escaped and extensively reacted and metasomatized the surrounding chromitites. U/Pb dating of baddeleyite indicates that the age of the metasomatic event (134.4 ± 14 Ma) matches the age of magmatism related to ophiolite construction in eastern Cuba. The high-Al chromitites of eastern Cuba contain exotic minerals of the three categories: diamond, oriented clinopyroxene and rutile lamellae, graphite-like amorphous carbon, moissanite, native Cu and Si, Fe-Mn alloys, zircon, corundum, and quartz. The studied diamond grains are nanometric in size, located in CH4-bearing fluid inclusions within olivine, and systematically associated with a typical serpentinization mineral assemblage composed of serpentine and magnetite. Textural-mineralogical evidences indicate that nanodiamond formed during low-pressure and low-temperature serpentinization in super-reduced microenvironments (log[fO2;MPa]=−45.3; ΔlogfO2[Iron-Magnetite]=−6.5). The other SuR minerals (moissanite, graphite-like amorphous carbon, native elements, and alloys) also formed in super-reduced CH4-rich microenvironments. On the other hand, nominally UHP phases such as the clinopyroxene lamellae formed as exsolutions after the crystallization of chromite or can represent silicate melt inclusions attached to the growing chromite grains. Oriented rutile lamellae formed after the interaction of chromitites with mafic magma. Finally, continental crust-derived minerals, such as zircon, likely represent xenocrystic material derived from the subducting slab that was entrapped by the chromitite parental melts. The investigation of the Neoproterozoic Bou Azzer chromitites (Morocco) allowed the comparison with the younger Cretaceous Cuban chromitites and other Phanerozoic and Precambrian chromitites. It was possible to determine that the Bou Azzer chromitites formed in the fore-arc setting during subduction-initiation with two stages of evolution: 1) formation of intermediate-Cr chromitites from fore-arc basalts (FAB), and 2) formation of high-Cr chromitites after boninitic melts. These chromitites host inclusions of platinum group minerals and exotic minerals. The unusual mineralogy includes oriented clinopyroxene lamellae, moissanite, native Cu, diaspore, and zircon formed after chromite crystallization and post-magmatic serpentinization processes, thus completely ruling out UHP conditions. Altogether, the results of these investigations represent the first descriptions of exotic minerals in the Cuban and Moroccan ophiolites. The corresponding discussions allowed to reject hypotheses of ultra-high pressure formation or recycling for the studied chromitites and the associated ophiolitic sequences and to ultimately provide simpler formation models for the exotic minerals. Additionally, the investigation provided definitive evidence for the formation of metastable nanodiamond, and other SuR phases, during serpentinization of the oceanic lithosphere at low-pressure and low-temperature conditions. Therefore, the presence of diamond in oceanic rocks, in particular chromitites, cannot be taken as a general indication of deep mantle recycling.
En aquesta tesi doctoral s’investiguen en detall les cromitites ofiolítiques de Cuba Oriental i de Bou Azzer, Marroc, per tal d’identificar la presència de minerals exòtics d’ultra-alta pressió, formats en condicions superreduïdes o derivats de l’escorça continental, i interpretar-ne la formació. Els resultats representen la primera descripció de minerals exòtics en aquestes ofiolites i les respectives discussions han permès descartar condicions d’ultra alta pressió per les cromitites i les roques associades i proposar models de formació simples relacionats amb la serpentinització de la litosfera oceànica pels minerals exòtics. S’ha investigat la interacció de líquids toleítics evolucionats amb cromitites preexistents a la zona de Potosí, Cuba, i es proposa un model de formació en dues etapes: primer la cristal·lització d’un magma de tipus MORB genera, mitjançant cristal·lització fraccionada, magmes residuals enriquits en elements incompatibles, i posteriorment alguns d’aquests magmes residuals s’escapen i reaccionen amb les cromitites. A les cromitites ofiolítiques de Cuba Oriental s’ha pogut identificar diamant, lamel·les orientades de clinopiroxè i de rútil, fases superreduïdes (carboni amorf, moissanita, Si i Cu natiu, aliatges de Fe-Mn) i minerals derivats de l’escorça continental. Els grans de diamant són de mida nanomètrica, es troben en inclusions fluides juntament amb metà, serpentina i magnetita. Totes les evidències indiquen que els nanodiamants es van formar durant la serpentinització en ambients superreduïts en condicions de baixa pressió i temperatura, igual que la resta de minerals superreduïts. En canvi, les lamel·les de clinopiroxè es van formar com a exsolucions degut a la cristal·lització de la cromita i les lamel·les de rútil es van formar per la interacció de les cromitites amb gabres. Finalment, el zircó podria representar material de la placa subduint atrapat pels magmes dels quals va cristal·litzar posteriorment la cromita. La investigació de les cromitites neoproterozoiques de Bou Azzer ha permès determinar la seva formació en una zona d’avant-arc durant l’inici de subducció, diferenciant dos estadis de formació relacionats amb basalts d’avant-arc (FAB) i boninites. Aquestes cromitites contenen inclusions de minerals del grup del platí i de minerals exòtics com són lamel·les de clinopiroxè, moissanita, Cu natiu, diàspora i zircó, similar a les cromitites de Cuba.

Introducció La creixent utilització de tuneladores de gran diàmetre EPBs (Earth Pressure Balance), ha comportat l'aparició de nous riscos i dificultats per als serveis d'emergències, que haurien de conèixer amb detall i disposar de procediments d'intervenció específics. Les tuneladores EPBs es caracteritzen per treballar mantenint el front d'excavació pressuritzat per a evitar despreniments al cap de tall. Aquestes condicions hiperbàriques en la zona de treball comporten una dificultat afegida a les ja existents en els treballs de manteniment i recanvi de les eines de tall: temperatura i humitat ambiental elevades, treballs d'alçada (10 -12 m. aprox.), manipulació d'eines pesades que precisen d'instal·lacions de suport, perill de despreniments, etc. Es requereix de personal acreditat, qualificat i format adequadament per a cicles controlats de compressió, treball i descompressió. Segons la normativa actual a Espanya es precisa de l'acreditació de cabussador professional per a poder treballar en condicions hiperbàriques. Les empreses constructores han d'articular importants mesures de seguretat i comptar, entre altres, amb la presència d'un Servei Preventiu d'Assistència Sanitària Immediata capaç de poder resoldre amb eficàcia i eficiència un accident en aquest àmbit tant complex fins a l'arribada dels serveis d'emergències. El personal sanitari i de rescat ha de disposar d'un perfil clarament prehospitalari amb experiència i formació específiques en medicina hiperbàrica i d'emergències degudament acreditades. Objectius Avaluar les mesures preventives proposades i implementades pel IEM amb el suport d'empreses del busseig professional i dels serveis preventius de la UTE Túnel Sabadell. Objectius específics Descriure les condicions fisiològiques dels treballadors prèvies i posteriors a la intervenció hiperbàrica. Valorar l'evolució dels seus paràmetres fisiològics. Generar una guia de prevenció i seguretat per als treballs en tuneladores EPBs Materials i mètodes La població objecte de l'estudi van ser 60 cabussadors professionals que treballaven en condicions hiperbàriques. La població de control, 30 mecànics de la tuneladora, que treballaven en condicions normobáriques. Com a lloc i temps de l'estudi es va determinar que fora durant les obres de construcció del túnel del metro de Sabadell. Com a mesures preventives i de control es van implementar les que van ser elaborades “ad hoc” i van ser especificades en el Pla d'Emergències de la UTE Túnel Sabadell. Les variables d'estudi que es van determinar, i que van ser preses a peu de tuneladora, van ser: Pressió arterial (PA), Freqüència cardíaca (FC), Freqüència respiratòria (FR), Temperatura (Temp °C), Saturació d'oxigen (SpO2), Carboxihemoglobina (SpCO) i la Metahemoglobina (SpMet). Resultats El grup control té una mitjana d'edat de 38,5 anys amb una desviació estàndard (DE) de 7,3 anys, amb un mínim de 26 i un màxim de 54. El grup de treball hiperbàric té una mitjana d'edat de 32,3 anys i una DE de 6,7 anys, amb un mínim de 21 i un màxim de 51. La diferència de la mitjana d'edat 6,2 anys entre els treballadors és significativa amb

Introducción. La creciente utilización de tuneladoras de gran diámetro EPBs (Earth Pressure Balance), ha comportado la aparición de nuevos riesgos y dificultades para los servicios de emergencias, que deberían conocerlos con detalle y disponer de procedimientos de intervención específicos. Las tuneladoras EPBs se caracterizan por trabajar manteniendo el frente de excavación presurizado para evitar desprendimientos en la cabeza de corte. Estas condiciones hiperbáricas en la zona de trabajo comportan una dificultad añadida a las ya existentes en los trabajos de mantenimiento y recambio de las herramientas de corte: temperatura y humedad ambiente elevadas, trabajos de altura (10 -12 m. aprox.), manipulación de herramientas pesadas que precisan de instalaciones de soporte, peligro de desprendimientos, etc. Se requiere de personal acreditado, cualificado y formado adecuadamente para ciclos controlados de compresión, trabajo y descompresión. Según la normativa actual en España se precisa de la acreditación de buzo profesional para poder trabajar en condiciones hiperbáricas. Las empresas constructoras deben articular importantes medidas de seguridad y contar, entre otras, con la presencia de un Servicio Preventivo de Asistencia Sanitaria Inmediata capaz de poder resolver con eficacia y eficiencia un accidente en este complejo ámbito hasta la llegada de los servicios de emergencias. El personal sanitario y de rescate debe disponer de un perfil claramente prehospitalario con experiencia y formación específicas en medicina hiperbárica y de emergencias debidamente acreditadas. Objetivos Evaluar las medidas preventivas propuestas e implementadas por el IEM con el soporte de empresas del buceo profesional y de los servicios preventivos de la UTE Túnel Sabadell. Objetivos específicos Describir las condiciones fisiológicas de los trabajadores previas y posteriores a la intervención hiperbárica Valorar la evolución de sus parámetros fisiológicos. Generar una guía de prevención y seguridad para los trabajos en tuneladoras EPBs Materiales y métodos La población objeto del estudio fueron 60 buzos profesionales que trabajaban en condiciones hiperbáricas La población de control, 30 mecánicos de la tuneladora, que trabajaban en condiciones normobáricas. Como lugar y tiempo del estudio se determinó que fuera durante las obras de construcción del túnel del metro de Sabadell. Como medidas preventivas y de control se implementaron las que fueron elaboradas “ad-hoc” y fueron especificadas en el Plan de Emergencias de la UTE Túnel Sabadell. Las variables de estudio que se determinaron, y que fueron tomadas a pie de tuneladora, fueron: Presión arterial (PA), Frecuencia cardíaca (FC), Frecuencia respiratoria (FR), Temperatura (Temp °C), Saturación de oxígeno (SpO2), Carboxihemoglobina (SpCO) y la Metahemoglobina (SpMet). Resultados El grupo control tiene una media de edad de 38,5 años con una desviación estándar (DE) de 7,3 años, con un mínimo de 26 y un máximo de 54. El grupo de trabajo hiperbárico tiene una media de edad de 32,3 años y una DE de 6,7 años, con un mínimo de 21 y un máximo de 51. La diferencia de la media de edad 6,2 años entre los trabajadores es significativa con p<0,001. El grupo control ha efectuado 98 entradas, con una media de 3,2 y una DE de 2,8. El grupo hiperbárico tiene 366 entradas con una media de 6,1 y una DE de 4,6. La diferencia de media de entradas por trabajador es significativa con p<0,05. El tiempo en el fondo (TF) del personal a presión es de una media de 147 minutos y una DE 35,3. En los trabajadores normobáricos el TF es de 189 minutos y una DE de 93. El tiempo de descompresión tiene una media de 18 minutos con una DE de 6,4 minutos habiendo realizado un número de paradas de media 185 y de 0,6 minutos Los trabajadores hiperbáricos han trabajado a una presión relativa media de 1,1 bars con una DE de 0,25 bars. Conclusiones Todos los trabajadores hiperbáricos presentaron unas condiciones fisiológicas adecuadas previas a la intervención. A su salida presentaron todos los buceadores un perfil fisiológico de normalidad. No se encontraron diferencias, ni estadísticas ni fisiológicas, significativas entre grupo estudio y control en ninguno de los parámetros valorados. La falta de accidentes y/o incidentes mínimamente destacables permiten concluir que el conjunto de medidas preventivas propuestas e implementadas por el IEM, con el soporte de empresas del buceo profesional y de los servicios preventivos de la UTE Túnel Sabadell, fueron acertadas. La respuesta en urgencias y emergencias, y evidentemente en las tuneladoras EPBs, requiere de personal altamente cualificado y preparado para trabajar de forma integral y coordinada con el resto de los cuerpos operativos. La prevención, la seguridad y una respuesta eficiente en emergencias es responsabilidad de todos.
Introduction Growing use of EPBs (Earth pressure balance) high diameter tunneling machines has incurred the appearance of new risks and difficulties for the emergency services, that should know in detail and have specific intervention proceedings. EPBs tunneling machines are characterized for the maintenance of the pressurized excavation front to avoid rockfall. These hyperbaric conditions in the working area entail an additional difficulty to the already existing in the maintenance work and replacement of the cutting tools: elevated temperature and environmental humidity, height jobs (10 – 12 m approximately), heavy tool manipulation that require support installations, rock fall danger, etc. Accredited, qualified and formed personnel is required for controlled cycles of compression, work and decompression. According to the actual regulation in Spain, the professional diver accreditation is required to be able to work in hyperbaric conditions. Constructor enterprises have to articulate important security measures and count, among others, with the presence of a Preventive Service of Immediate Sanitary Assistance able to efficiently and effectively solve an accident in this complex environment until the emergency services arrival. The sanitary and rescue personnel must have a clear prehospitalary profile with experience and formation in hyperbaric medicine and emergencies correctly accredited. Objectives To evaluate the preventive measures proposed and implemented by the IEM with the support of professional diving enterprises and the preventive services of the UTE Túnel Sabadell. Specific objectives To describe the physiological conditions of workers previous and posterior to the hyperbaric intervention. To evaluate the evolution of their physiological parameters. To generate a guide of prevention and security to the workers in EPBs tunneling machines. Materials and methods Study population was formed by 60 professional divers who worked in hyperbaric conditions. Control population was formed by 30 mechanics of the tunneling machine who worked in normobaric conditions. Place and time of the study were determined to be during the construction process of the Sabadell underground. Preventive and control measures were elaborated and implemented “ad hoc” and specified in the Emergency Plan of the UTE Túnel Sabadell. Studied variables were determined and measured near the tunneling machine were: arterial pressure, cardiac frequency, respiratory frequency, temperature, oxygen saturation, carboxyhemoglobin and metahemoglobin. Results Control group has a mean age of 38.5 years with a standard deviation (SD) of 7.3 years, a minimum of 26 and a maximum of 54. Hyperbaric work group has a mean age of 32.3 years, with a SD of 6.7 years, a minimum of 21 and a maximum of 51. The different mean age of 6.2 years between workers is significant with p<0.001. Control group has performed 98 entries, with a mean of 3.2 and a SD of 2.8. Hyperbaric group has 366 entries, with a mean of 6.1 and a SD of 4.6. Difference between entry means per worker is significant with p<0.05. Time in the tunnel (TT) of pressure working personnel is a mean of 147 minutes with a SD of 35.3. In normobaric workers the TT is of 189 minutes with a SD of 93. Decompression time has a mean of 18 minutes with a SD of 6.4 minutes having performed a mean stop number of 185 and of 0.6 minutes. Hyperbaric workers have worked at a relative mean pressure of 1.1 bars with a SD of 0.25 bars. Conclusions All hyperbaric workers showed adequate physiological conditions prior to the intervention. After leaving the tunnel, all divers had a normal physiological profile. No differences, nor statistical or physiological, significant differences were found between the study group and the control group in any of the parameters assessed. The lack of remarkable accidents and / or incidents allowed us to conclude that the set of the preventive measures proposed and implemented by the IEM and supported by companies of the professional diving and the preventive services of the UTE Tunnel Sabadell, were adequate. The response in emergencies and obviously in the EPB tunneling machines, requires highly qualified personnel to work in a comprehensive and coordinated way with the other operating groups. Prevention, security and an efficient response in emergencies is the responsibility of everyone.

L’ingestion de sables et de cendres volcaniques par les moteurs d’avion conduit à la formation de dépôts silicatés (CMAS) qui s’infiltrent dans la porosité du revêtement barrière thermique (BT) en zircone yttriée des aubes de turbine. De nouvelles compositions de BT issues du système ZrO2-RE2O3 (RE = La-Lu) sont donc envisagées. En effet, leur réactivité chimique au contact des CMAS peut conduire à la formation de phases cristallisées, notamment la phase apatite Ca2RE8(SiO4)6O2, qui bloquent l’infiltration du CMAS. Cependant, divers silicates du système CaO-RE2O3-SiO2 sont susceptibles d’entrer en compétition avec sa formation et de plus, la composition du CMAS varie selon les régions survolées. L’objectif de ces travaux de thèse est de déterminer l’influence de la composition du CMAS et de la terre rare sur les mécanismes réactionnels de dissolution et de précipitation. Divers oxydes RE2O3 à basicité croissante (RE = Yb, Dy, Gd, Sm et Nd) et un CMAS de composition simplifiée du système CaO-Al2O3-SiO2 (CAS) ont été choisis. Des teneurs fixes en MgO et Fe2O3 ont été ensuite ajoutées au CAS en faisant varier le rapport CaO/SiO2 entre 0,4 et 1,6. Les phases apatite et cyclosilicate Ca3RE2(Si3O9)2 ont également été synthétisées afin d’étudier leur dissolution. Il est montré que le mécanisme de dissolution des RE2O3 est indirect, les équilibres locaux établis avec cet oxyde imposant systématiquement la formation de la phase apatite. Sa cristallisation est favorisée par un rayon cationique RE3+ proche de celui de Ca2+. Lorsque l’écart est important, la nucléation de la phase cyclosilicate est rapidement observée dans le CAS avec une répartition préférentielle de ces cations RE3+ dans les sites de coordinence 6. La solubilité en RE dans le liquide silicaté augmente avec la basicité de l’oxyde RE2O3 et en présence de MgO et Fe2O3. La variation de composition du CMAS modifie la nature des phases à l’équilibre. Leurs limites de solubilité en RE sont inférieures à celles de la phase apatite, ce qui réduit d’autant leur vitesse de redissolution dans le liquide silicaté
Fine particles of sand, dust or volcanic ashes ingested by aircraft engines are well-known to damage Thermal Barrier Coatings (TBC) when they infiltrate their porous microstructure as molten silicate (CMAS). They are mainly constituted of CaO-MgO-Al2O3-SiO2 in variable proportions and also contain metallic oxides. RE2Zr2O7 compositions are TBC candidate materials as they have shown efficiency to mitigate CMAS infiltration due to their reactivity with synthetic CMAS. Indeed, the dissolution reaction leads to rapid sealing of the topcoat porosity mainly due to the formation of crystalline Ca2Gd8(SiO4)6O2 apatite. However, many rare-earth silicates are likely to compete with apatite crystallization and little is known on reaction kinetics and thermodynamics involving RE2O3 and multi-component CMAS system. This work aims to determine the influence of CMAS and rare earth composition on dissolution and precipitation mechanisms. A simplified CAS was first selected with eutectic (1170°C), 65SiO2-26CaO-9Al2O3 (mol. %) composition. Dissolution of various RE2O3 with increasing basicity (RE = Yb, Dy, Gd, Sm and Nd) as well as synthetic apatite and cyclosilicate Ca3RE2(Si3O9)2 phases was then performed at 1200°C in CAS-melt. Finally, fixed MgO and Fe2O3 contents were added to CAS melt with an increasing CaO/SiO2 ratio. The results showed that RE2O3 dissolution mechanism is indirect. Apatite formation results from local equilibrium at the interface with solid RE2O3 whatever the rare earth and CMAS composition. Its crystallization is favored when Ca2+ and RE3+ ionic radii are close as they are both distributed within 9-fold coordination sites. Conversely, Ca and RE mismatch leads to rapid nucleation of cyclosilicate phase in CAS as they are preferentially distributed within a 6-fold coordination site. MgO and Fe2O3 addition in CAS as well as RE2O3 basicity tend to increase RE solubility in silicate melt. Phases in thermodynamic equilibrium strongly depend on CMAS composition but generally exhibits lower RE solubility and dissolution rate in melt than apatite

A large data set comprising normal-mode eigenfrequencies, quality factors and splitting functions, Earth's mass and moment of inertia, surface-wave phase anomalies and dispersion curves, body-wave arrivals and traveltime curves, as well as long-period waveforms is inverted to obtain the distribution of elastic properties, shear attenuation and density in the Earth's interior. We address three fundamental aspects of global seismology by reconciling and modeling data sets with several methodological improvements, such as accounting for radial and azimuthal anisotropy, development of better methods for crustal corrections, and devising novel regularization and parameterization schemes. In the first contribution, we incorporate normal-mode splitting functions with other seismological data sets to examine the variation of anisotropic shear-wave velocity in the Earth's mantle. Our preferred anisotropic model, S362ANI+M, has strong isotropic velocity anomalies in the transition zone while the anisotropy is restricted to the upper 300~km in the mantle. When radial anisotropy is allowed throughout the mantle, large-scale anisotropic patterns are observed in the lowermost mantle with v_SV > v_SH beneath Africa and South Pacific and v_SH > v_SV beneath several circum-Pacific regions. However, small improvements in fits to the data on adding anisotropy at depth leave the question open on whether large-scale radial anisotropy is required in the transition zone and in the lower mantle. We demonstrate the utility of mode-splitting data in reducing the tradeoffs between even-degree variations of isotropic velocity and anisotropy in the lowermost mantle. We then devise a methodology to detect seismological signatures of chemical heterogeneity using scaling relationships between shear velocity, density and compressional velocity in the Earth's mantle. Several features reported in earlier tomographic studies persist with the inclusion of new and larger data sets; anti-correlation between bulk-sound and shear velocities in the lowermost mantle as well as an increase in velocity scaling (nu=dlnv_S/dlnv_P) with depth in the lower mantle are found to be robust. Many spheroidal and toroidal modes are largely incompatible with perfect correlations between density and shear-velocity variations in the lowermost mantle. A way to fit concurrently the various data sets is by allowing independent density perturbations in the lowermost mantle. Our preferred joint model consists of denser-than-average anomalies (~1% peak-to-peak) at the base of the mantle roughly coincident with the low-velocity superplumes. The relative variation of shear velocity, density and compressional velocity in this study disfavors a purely thermal contribution to heterogeneity in the lowermost mantle. In the third contribution, we introduce an approach to construct a 1-D reference model that is consistent with crustal heterogeneities and various asphericities in the Earth's mantle. We demonstrate that the crust contributes substantially to fundamental-mode dispersion curves when the nonlinear effects of its thickness and velocity variations are taken into consideration. We apply appropriate crustal corrections and perform several iterations to converge to our preferred radial model NREM1D, which is anisotropic in the upper mantle and smooth across the 220-km discontinuity for all physical parameters. Radial anisotropy in the shallowest mantle, with a maximum at ~150~km depth, is required to fit global averages of fundamental-mode Rayleigh and Love wave dispersion (25--250s). NREM1D also predicts arrival times of major mantle and core phases in agreement (+/- 0.5s) with a recent isotropic velocity model that was optimized for earthquake location. The new reference Earth model NREM1D introduced here is easily extendable due to its modular construction as a linear combination of radial basis functions and can be used for earthquake location, spherical-earth normal mode calculations, and as a starting model in studies of lateral heterogeneity.

This dissertation addresses key questions raised in Human Geography and Economic Geography concerning scale and the production of space, alternative economic geographies and co-operative economic development. It is the product of a five year ethnographic investigation with co-operative enterprises in Western Massachusetts and the broader Connecticut River Valley of Western New England. It explores neglected questions about how subjects are producing co-operative economic identities, enterprises and development strategies amid capitalist cultural dominance; and how structural, financial and governmental aspects of their enterprises participate in cultivating the desire and capacity to expand co-operative space. In line with poststructuralist feminist perspectives within and outside the disciplines of Human and Economic Geography, each chapter challenges ontological presumptions often made about the economy, scale, power and size and offers theoretical contributions based upon empirical research with co-operative enterprises.The three chapters of this dissertation explore the co-production of co-operative space and subjects; the "practices of scale" in the Valley Alliance of Worker Co-operatives; and co-operative development in a regional context. They challenge the presumptions that space and economy are (and must be) structured by capitalism; power is constituted by hierarchy, size and "scale"; and subjects and subjectivity are insignificant to the project of constructive development. Contrary to structuralist critiques of worker co-operatives based upon size, political conservatism and vulnerability, I argue that worker owned enterprises empower workers despite capitalist cultural dominance and relative size.

Orientação : Ana Maria Duque de Araújo Munhoz ; co-orientação : Florbela Maria Benjamim Soares
Em aquacultura, tanto a nível mundial como nacional, a ocorrência de parasitoses externas é relativamente frequente e causa perdas significativas para os aquacultores. Os organismos pertencentes à classe Monogenea (Filo Platyhelminte), que afetam normalmente as brânquias e pele dos hospedeiros, são dos mais comumente encontrados. Neste estudo, avaliaram-se diversos factores na adesão dos ovos dos monogéneos tais como, os substratos utilizados, fio controlo de algodão, plástico, policloreto de vinilo (PVC), madeira e macroalga (Ulva spp.), o tempo de imersão dos substratos, o efeito das diferentes operações de aquacultura e a densidade de produção nos tanques em cultivo. Foram realizados três ensaios: no primeiro, comparou-se o efeito de cinco e dez dias de imersão dos substratos no mesmo tanque de terra; no segundo, avaliou-se o efeito de duas operações de aquacultura (pesca e remoção/manipulação de ostras) e no terceiro comparou-se a adesão dos ovos de monogéneos entre os tanques com diferentes densidades de produção. Também foram estudados em todos os ensaios, quais os substratos que promoviam a maior e menor adesão de ovos. De acordo com os resultados, o factor tempo (cinco e dez dias) não influenciou o número de ovos aderidos aos substratos. Nos tanques de terra onde decorreram operações de aquacultura verificou-se um menor número de adesão dos ovos e no tanque com maior densidade de produção houve uma maior adesão dos ovos. Concluiu-se que os substratos que tiveram a maior adesão de ovos de monogéneos foi o plástico e aquele com menor adesão foi a macroalga.
External parasitosis causes a lot of losses to aquacultures globally and in Portugal. Monogenea class (Phylum Platyhelminth) organisms that usually affects hosts’ gills and skin are one of the most commonly found in aquaculture. This study analyses how the adhesion varies due to different factors such as the substrates, control, plastic, polyvinyl chloride (PVC), wood and macroalgae (Ulva spp.), exposure time, effect of different aquaculture operations and fish production density. Three different assays were performed: in the first one the effect of five and ten days for different substrates in the same pond was compared; in the second, the effect of two aquaculture operations (fishery and removal/manipulation oysters) was evaluated and in the third the eggs adhesion between ponds with different production densities was studied. Furthermore, in every assay it was checked which substrate had a major and minor adhesion. According to the results, exposure time (five and ten days) doesn’t influence the number of eggs in the substrates. There was a smaller number of eggs in the earth ponds with aquaculture operations and in the pond with highest production density there was a higher egg adhesion. It was also found that plastic and macroalgae were the two substrates with biggest and smallest number of monogeneans eggs.