In this thesis, the results from a geophysical mapping and coring campaign of Lagoa das Furnas are presented. Specific focus is placed on the origin of a subaqueous volcanic cone mapped in the southern part of the lake. Lagoa das Furnas is a crater lake within the Furnas volcanic centre which is located on the island of São Miguel in the Azores archipelago. The Furnas volcanic centre has a long history of earthquakes and volcanic activity. The area is relatively well-studied, except for the lake floor. Therefore, a high resolution geophysical and geological mapping survey was conducted at Lagoa das Furnas. Sidescan sonar was used to map the surface of the lake floor and single beam sonar was used to acquire sub-bottom profiles. In addition to the geophysical mapping, sediment surface sampling and core drilling were carried out followed by geochemical analyses of the retrieved material. The mapped data permitted a characterisation of the floor of Lagoa das Furnas and revealed several volcanic features including fumarole activity and a volcanic cone in the southern part of the lake. In order to unravel the origin of this cone several methods were applied, including analyses of tephra and minerals collected from the cone itself and from nearby deposits of two known eruptions Furnas I and Furnas 1630. Sedimentological, petrological, geochemical and geochronological studies of pyroclastic deposits from the cone suggest a subaqueous eruption linked to the Furnas 1630 eruption. The chemistry of glass and crystal fragments sampled from the cone suggests that it is composed of more evolved magma than that of the main Furnas 1630 implying that the lake cone is likely a product of the last eruptional phase. Historical documents reveal three lakes in Furnas valley before the 1630 eruption. Two of these lakes were lost due the eruption and the remaining lake is most likely Lagoa das Furnas and consequently did exist before the 1630 eruption.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20602号 / 理博第4317号 / 新制||理||1620(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 山路 敦, 教授 山 明, 准教授 伊藤 正一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The crater wear of alumina coated WC-Co cutting tools is thought to be influenced by the chemical reactions between the coating and the workpiece material. Three different crystal orientations ((001), (012), and (100) of alpha alumina CVD coatings are examined in combination with four workpiece materials of steel to establish what reactions are present, and the extent of diffusion. The alumina coatings and workpiece materials were pressed together as diffusion couples and heat treated at 1250- 1300°C for 10-20hours. It was fond that the types of inclusions present in the workpiece were more impactful on the chemical wear of the coating than the crystal orientation of the coating. EDS measurements show significant amounts of W and Co on the surface of the coatings and on the steel surfaces after heat treatment. This is thought to be connected to the migration of Co through the coating in cooling cracks and other impurities. In the surface of the coating, areas of solidified Co-rich structure have been found, implying that Co has formed an alloy with Fe, C, Al, and W with sufficiently low melting temperature to partially melt during the heat treatment. This has been confirmed as possible by simulations in Thermo-calc. Turning tests and scratch tests were made with the same combinations of coatings and workpiece material and show differences in adhesion of workpiece material on the different coating orientations. The 100-orientation has been found to have the most adhered workpiece material, the reason for this being its higher surface roughness. Ultimately no noticeable differences in chemical reactivity between the coating crystal orientations was found. The Co diffusion though the coating occurred for all the coating orientations and further experiments in turning with the different workpiece materials are required to determine the effect of Ca-rich inclusions on the magnitude of chemical wear. / <p>Handledare på företag:</p><p>Susanne Norgren </p><p>Doc.  Ph.D,  Group Expert Materials Design</p>

We study numerical methods for solving the nonlinear porous medium and Navier-Lame problems. When coupled together, these equations model the flow of exhaust through a porous medium, soil, and the effects that the pressure has on the soil in terms of spatial displacement. For the porous medium equation we use the Crank-Nicolson time stepping method with a spectral discretization in space. Since the Navier-Lame equation is a boundary value problem, it is solved using a finite element method where the spatial domain is represented by a triangulation of discrete points. The two problems are coupled by using approximations of solutions to the porous medium equation to define the forcing term in the Navier-Lame equation. The spatial displacement solutions can be used to approximate the strain and stress imposed on the soil. An analysis of these physical properties shows whether or not the material ceases to act as an elastic material and instead behaves like a plastic which will tell us if the soil has failed and a crater has formed. Analytical as well as experimental tests are used to find a good balance for solving the porous medium and Navier-Lame equations both accurately and efficiently.

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<p>Digital elevation models (DEM) can be used for a multitude of applications. Under ideal circumstances, calibration of a remotely acquired estimate of topographic elevation is calibrated through use of ground control points (GCP) which would be ubiquitous, seamlessly joining remotely sensed data and high accuracy check points. In reality there are many areas on the earth’s surface which are difficult, expensive, or dangerous to access. Under these circumstances, the acquisition of GCPs may not be realistic and relative DEMs must be used. Innovative methods must then be used to determine the relative error associated with a DEM in a given study area. The method presented in this paper compares three DEMs (ASTER, CDED, SRTM) derived from independent acquisition systems to determine their relative errors.</p> <p>The ASTER DEM data was chosen for a lineament analysis study in north central Ontario, Canada. This study used a quantitative digital approach to determine the density of lineaments mimicking the geometry of the northern Sudbury Igneous Complex contact (SIC). The study revealed a lineament density at ~25km north of the northern SIC contact, suggesting a ring structure from an ancient multi-ring impact basin. This argument is supported by findings of the pattern of plagioclase clouding intensities in Matachewan dykes in the vicinity of the ring structure. The orientation of the dykes may have some connection to the faulting and block rotation caused by crater wall collapse.</p> <p>Paleomagnetic data from the norite in the SIC and Foy Offset dyke combined with an unconstrained magnetic inversion of the Foy Offset dyke suggest that the Sudbury Structure has not been folded, but instead has been deformed by brittle deformation.</p> / Master of Science (MSc)

Titanium alloys are major materials used in the airplane industry, and prospects show that airplane production will double in the next 20 years. Consequently, the demand for cutting tools for machining of titanium alloys will increase. The primary problem when machining titanium alloys is their low thermal conductivity. Crater wear is the main factor limiting tool life, and is generally caused by thermal diffusion due to high temperatures in the tool-chip interface. This master’s thesis was performed in collaboration with Sandvik Coromant, with the prospect to increase knowledge of how diffusion and chip formation influences crater wear progression. The aim was to study tool wear of cutting tools when turning Ti–6Al–4V. This was done by testing two different rake face geometries, both coated and uncoated, at cutting speeds of 30–115 m/min. Diffusion was investigated to learn about the impact it has on crater wear. Chips were examined to investigate chip formation and shear strain. The coated modified rake face insert showed less crater wear only for the initial few seconds of machining. Uncoated inserts with a modified rake face showed higher diffusion rate and faster crater wear progression than did standard inserts. The standard inserts showed twice as long tool life as did the modified inserts. No significant differences in the chip formation mechanism were found between modified and standard inserts. Cracks were found within shear bands that were thinner than usual, which suggest that the generation of cracks allows less shear deformation.

A pesquisa tem como objetivo compreender a evolução da drenagem e do relevo na cratera de Colônia e entorno, no setor meridional do Planalto Paulistano, em São Paulo-SP. Parte-se da hipótese de que o relevo da área resulta da degradação de uma zona de estruturas concêntricas, formada em conjunto com a cratera, por impacto de bólido extraterrestre. Essas estruturas seriam atribuídas a um ou mais mecanismos, entre eles: a) controle exercido por um sistema de falhas radiais e concêntricos, b) estratificação do alvo, c) pico anelar em cratera complexa, d) ejecta fluidificada e e) fluidificação de finos, que resultaram na geração de uma zona de formas concêntricas no entorno da cratera. Após sua formação, o relevo da cratera e seu entorno foram degradados pela drenagem, que promoveu trabalho erosivo mais intenso a leste que a oeste, produzindo níveis hipsométricos menores a leste. Com base na proposta metodológica de Oliveira (2003), elabora-se uma descrição do relevo e da drenagem para identificar elementos sugestivos de condicionamento geológico produzido pela estrutura de impacto, por meio de fotointerpretação, trabalhos de campo e morfometria. A partir dos dados de hipsometria, rupturas de declividade e lineamentos da drenagem, descartam-se os mecanismos de estratificação do alvo, pico anelar e ejecta fluidificada, restando apenas o sistema de falhas radiais e concêntricos e a fluidificação de finos como possibilidades em aberto, cujo teste definitivo dependerá da disponibilidade de dados geofísicos detalhados. Os dados de morfometria, por sua vez, sugerem maior trabalho erosivo efetuado pelos rios da bacia do Jurubatuba que do Embu-Guaçu, respondendo pela assimetria altimétrica leste-oeste da zona de formas concêntricas e do anel colinoso da cratera de impacto e pela abertura da drenagem a leste, em conjunto com o condicionamento dado pelas linhas estruturais geradas tectonicamente. A presença de anomalias de drenagem e sua correlação com as integrais hipsométricas, por sua vez, são indicativas de modificação tectônica da drenagem, posterior à sua delineação condicionada pela estrutura de impacto. / This research aims to comprehend the relief and drainage evolution in the Colônia crater and surrounding areas, in the southern sector of the Paulistano Plateau, São Paulo-SP. We advance a hypothesis such as the morphology of the area results from degradation of a zone of concentric structures, originated at the same time as the crater, by extraterrestrial bolide impact. These structures are due to one or more mechanisms, among them: a) system of concentric and radial fractures, b) target stratification, c) peak ring in a complex impact structure, d) fluidized ejecta and e) fluidization of fine sediments, which generated a zone of concentric forms around the crater. After its formation, the relief of the crater and surroundings was degraded by drainage, which promoted a more intense erosive work to East than West, producing lower hypsometric levels to East. Based on the methodological proposal of Oliveira (2003), we elaborated a description of the topography and drainage to indentify suggestive elements for geological conditioning produced by the impact structure, by means of photointerpretation, fieldwork and morphometric measurements. From hypsometric data and slope break and drainage lineations analysis, we discard the hypothesis of: target stratification, peak ring and fluidized ejecta, leaving only those of concentric and radial fractures and fluidization of fine sediments, as open possibilities, whose final test will depend on the availability of detailed geophysical data. The morphometric data suggest greater erosive work performed by the Jurubatuba drainage basin than by Embu-Guaçu, responding by hypsometric East-West asymmetry of the craters raised ring and surroundings. This still accounts for the position of its drainage exutory, to East, together with structural lines tectonically generated. The presence of drainage anomalies and their correlation with the hypsometric integrals are indicative of tectonic modification of drainage, after its delineation conducted by the impact structure.