The glacial history of the Tibetan Plateau has long been a contentious topic with widely different reconstructions. For Tanggula Shan, an extensive mountain range on the central Tibetan Plateau, multiple glacial reconstruc- tions and studies on the glacial chronology have been presented. However, the glacial geomorphological record has been sparse resulting in insufficient data to fully infer the area’s palaeoglaciology. Focussing on four landform categories, glacial valleys, marginal moraines, hummocky terrain, and glacial lineations; a glacial geomorphological map was produced, using Landsat 7 ETM+ satellite imagery, SRTM digital elevation model, and Google Earth. This map, together with GIS analyses and available cosmogenic exposure and electron spin reso- nance ages from the study area, was used to investigate the extent of former glaciations. Cosmogenic exposure and electron spin resonance ages range from 18.4 ± 1.6 to 203.4 ± 33.2 ka (recalculated using the CRONUS calculator). The extent of the glacial footprint is restricted to the high mountain areas, and is similar in extent to earlier glacial reconstructions. This glacial footprint can tentatively be explained by a monsoonal influence in the southeast, with the influence diminishing to the northwest. Alternatively, the precipitation gradient might have resulted in cold-based ice in the west and warm-based ice in the east. These variations in ice regime could have left fewer traces of glaciation in the west, than in the east. There is no evidence supporting an ice sheet covering the entire Tibetan Plateau. Rather, the available data support a smaller ice field in the high mountain areas, with a maximum extent well before the Last Glacial Maximum.

No description available.

La frontière de plaque transpressive Nord Caraïbe s'exprime dans la région d'Haïti par un partitionnement de la déformation entre deux failles décrochantes et des chevauchements. L'étude de données de bathymétrie, de sismique réflexion, et de fonctions récepteur apporte des contraintes sur la structure et le fonctionnement de cette frontière de plaque en transpression en mer et à terre. Les données de bathymétrie des campagnes Haïti-SIS 1 et 2 nous ont permis de cartographier précisément le grand système de failles décrochantes senestres et leur segmentation. L'étude des profils de sismique réflexion a mis en évidence l'existence de structures pré-existantes à l'activité du décrochement EPGFZ en mer. Nous avons également identifié un domaine crustal distinct, que nous avons relié au plateau océanique Caribéen. L'étude des déformations actuelles en mer nous permet de montrer que la faille EPGFZ est principalement décrochante, avec une composante compressive qui augmente vers l'Est. Les estimations de raccourcissement restent cependant très faibles (2 à 3%) en comparaison des estimations faites par les modélisations GPS. A terre en Haïti, nous avons imagé l'épaisseur crustale grâce à une étude de fonctions récepteur. Les épaisseurs imagées délimitent trois domaines différents. Nous proposons que ces domaines correspondent à trois ensembles géologiques distincts, composés respectivement de l'arc Crétacé des Grandes Antilles au Nord, du plateau océanique Caraïbe au Sud, et d'une croûte continentale au centre. Cette croûte pourrait être sous-charriée par du matériel dense provenant de la subduction d'une portion du plateau océanique Caribéen sous Haïti. / The Northern Caribbean transpressive plate boundary is expressed in Haiti by the partitioning of the deformation between two strike-slip faults and compressive structures. Bathymetric, seismic reflection and receiver-functions studies are methods used here to constrain the structure and the dynamic of the Northern Caribbean transpressive plate boundary offshore and onshore. The bathymetric data acquired during the Haiti-SIS cruises provide a detailed mapping of the geometry and segmentation of the senestrial strike-slip fault systems. The seismic profiles in the Jamaica Passage show that basin structures exist prior to the initiation of the EPGFZ and are cross-cut and folded by the EPGFZ. We identify a distinct crustal domain that we relate to the Caribbean large igneous province. The present deformations offshore show that the EPGFZ is primary strike-slip, with an increasing compressive component of the deformation toward the east. The shortening estimates are very small (2 to 3%) compared to the short-term GPS modeling estimates. Onshore in Haiti, we image the crustal structure from a receiver-functions study. The crustal thickness is ~23 km in the northern part of Haiti, ~22 km in the southern part of Haiti and ~41 km in the middle part, delimiting 3 distinct domains. We propose that these domains correspond to 3 geological distinct terranes: the Cretaceous volcanic arc in the north, the oceanic igneous province in the south, and in between a continental crust underthrusted by dense material. The underthrusted material could be a subducted portion of the Caribbean large igneous province under the Trans-Haitian fold-and-thrust belt.

Please read the abstract in the section 06back of this document / Dissertation (MSc)--University of Pretoria, 2009. / Centre for Wildlife Management / unrestricted

In the last decade aluminium started to be considered as an alternative to steel to produce car body panels, especially considering the strict demands to decrease fuel consumption which require vehicle weight reduction. In order to keep their leading role, steel companies have to produce stronger materials to reduce the thickness of steel sheets used in cars and are now considering non-conventional steel making processes. The purpose of this PhD research was to investigate the possibility of strengthening thin sheets of interstitial free steel (IF steel) by using carbon rich films deposited on the steel surface using Physical Vapour Deposition (PVD). These films then act as a carbon reservoir which upon heat treatment release carbon in the IF steel and strengthen it. Coated tensile coupons 200 μm thick were annealed at different temperatures under high vacuum. Tensile tests show that a 100 MPa increase in yield stress can be obtained after annealing at 430 ˚C for 1h in high vacuum. The effects of annealing environment, film thickness and prestrain on carbon diffusion were also investigated. It was shown that carbon diffusion from the film to the IF steel substrate is limited by the film transformation into cementite at temperatures equal or higher than 530 ˚C. All tensile curves showed a plastic instability known as Lüders plateau, which is undesirable as it results in surface markings on the deformed part. FEM analyses were performed to find ways to suppress the Lüders plateau, proving that increasing strain-hardening or having a graded instead of uniform carbon content through thickness can suppress or limit Lüdering. The possibility of creating a through thickness gradient of microstructure was investigated as it could suppress Lüdering and result in higher strength. For these tests, FeC coated coupons were induction heated to 820 ˚C followed by water quenching. After only 2 minutes of heat treatment the yield stress was increased by 250 MPa and the ultimate tensile strength reached 400 MPa. With an annealing of 4 minutes, the Lüders plateau was fully suppressed and the microstructure consisted in ferrite grains and TiC nanocarbides. This work demonstrates that FeC films can be effectively used to diffuse carbon into steel and that a significant increase in mechanical properties can be obtained after a heat treatment of only a few minutes.

This thesis applies a novel method of change detection, the Landsat Image Stack Trend Analysis method to the monitoring of retrogressive thaw slumps in the Richardson Mountains, NWT. This method represents a significant improvement upon previous methods of thaw slump monitoring, which utilized air photos and high-resolution satellite imagery. This method applies Tasseled Cap brightness, wetness and greenness indices to Landsat TM/ETM images acquired between 1985 and 2011 and analyzes the temporal change of each pixel for the different indices values. This method is useful in retrogressive thaw slump monitoring in two ways. First, by creating a map showing the linear change over time from 1985 to 2011, retrogressive thaw slumps can be easily identified, as they are more dynamic than the surrounding tundra. In total, 251 thaw slumps were identified within an area of roughly 18 000km2. Second, thaw slump activity, from initiation, growth and stabilization can be studied by plotting the annual vegetation index pixel values of adjacent pixels in a thaw slump. This method allows for the efficient extraction of annual thaw slump headwall retreat rates, provided the availability of cloud-free imagery. The retreat rates of 16 slumps were extracted, which were found to have an average annual retreat rate of 11.8 m yr-1.

Des épisodes à Dinophysis affectent périodiquement l'exploitation des fruits de mer dans le Bassin d'Arcachon. Le réseau de surveillance interne au Bassin d'Arcachon montre que Dinophysis est advecté de l'océan ouvert. Le but de cette étude est de déterminer l'origine de Dinophysis. Des campagnes en mer sur le plateau continental Aquitain ont permis d'identifier une zone propice au développement de Dinophysis au large de Capbreton. Les épisodes à Dinophysis dans le bassin d'Arcachon se produisent suite à des vents d'Ouest qui induisent des courants vers le Sud d'après la littérature. L'étude des données hydrodynamiques acquises pendant les campagnes met en évidence un processus complexe et nouveau suite aux vents d'Ouest: de forts courants le long de la côte vers le Nord capables de transporter Dinophysis de Capbreton jusqu'au Bassin d'Arcachon. Un travail de modélisation a permis de reproduire ce courant et d'étudier son mécanisme particulier lié coin Sud-Est du Golfe de Gascogne. / Abstract

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22113号 / 理博第4540号 / 新制||理||1652(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 福田 洋一, 教授 岩田 知孝, 准教授 深畑 幸俊 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

It is widely accepted that the late Pliocene spans a time with globally warmer conditions compared to today. Regional specifics in temperature patterns from this period, however, remain poorly known. In this study, we reconstruct quantitatively late Pliocene climates for eight sites at the southeastern border of the Qinghai-Tibet Plateau (SBTP), based on palaeobotanical data compiled from published sources using the Coexistence Approach (CoA), and analyze anomalies with respect to modern climates. The reconstructed temperatures indicate that in the late Pliocene, the northwestern part of the study area was cooler than its southern part. This spatial differentiation in temperature was largely due to differences in altitude: the northwest of the SBTP probably had higher altitudes than the south at that time. Mean annual temperatures (MATs) were around 1. °C higher than today, suggesting a cooling trend since the late Pliocene. Our data show that summer temperatures have declined significantly since the late Pliocene while winter temperatures have remained similar to those of the present, different from observations in other territories. The unexpected summer and winter temperature changes can be explained by the regional orogenic uplift plus the global cooling. The eastward extrusion of the Qinghai-Tibet Plateau might have blocked the southward cold high pressure of the winter monsoon and forced it to circumvent the eastern flank of the plateau, weakening its impact on the SBTP. The post-Pliocene mountain uplift increased the overall altitude of the region, which caused the temperature decline for both summer and winter. The reconstructed summer precipitation was lower while the winter precipitation was higher than today, suggesting a weaker monsoon climate during the late Pliocene.

Thesis (Ph. D.)--Boston University, 1991. / Interest in deep sea microbiota was stimulated by recent discoveries of productive redox communities associated with hydrothermal vents and brine seeps, and based on bacterial chemolithotrophy. This study investigates microbial destruction of mussel shells from a redox community at the base of the Florida Escarpment (3360 m), in comparison with microbial boring in shells of typical, low productivity areas of the ocean floor. An assemblage of eukaryotic and prokaryotic periostracum borers and their boring traces were discovered in shells of Bathymodiolus mussels from the base of the Florida Escarpment, and characterized. Microbial destruction of this protective layer results in colonization of secondary microbial inhabitants inside boreholes, and exposes the underlying mineralized shell to colonization and destruction by microbial endoliths. Microbial consumption of periostracum often proceeds in successive waves. These organisms show different "foraging" behaviors and leave accordingly varied boring patterns. These activities create a labyrinth of pits, holes and tunnels which, in tum, provide sheltered microenvironments for secondary microbial settlers, including primary producers, which all constitute an abundant food source for numerous ciliates and gastropods observed on the shells. This concerted attack on the periostracum eventually leads to the exposure of the mineralized shell. Such exposed areas are characterized by [TRUNCATED]