Les grandes éruptions explosives (10 to 1000 km3/eruption) ont été l’un des sujets principaux d’étude de la volcanologie moderne car elles représentent des éruptions de grand impact sur la nature et sur les installations humaines sur Terre. Les pétrologues ont démontré que la proportion de cristaux dans les produits de ces éruptions peut être utilisée pour étudier les dynamiques pré-éruptives de la plomberie magmatique et contraindre les échelles de temps des processus magmatiques. Plus précisément, de nombreuses études ont prouvé que ces cristaux peuvent être remobilisés en des temps courts de 10 à 100 ans avant l’éruption, ce qui rend ces systèmes significativement dynamiques. Plusieurs éruptions ignimbritiques d’un volume de l’ordre de la dizaine de km3 ont été reconnues en Dominique (Arc des Petites Antilles). Nous présentons ici, sur la base d’une étude stratigraphique détaillée, une étude pétrologique des ponces de la phase plinienne qui débute les trois éruptions ponceuses majeures de la Dominique : Layou (~51kyrs cal BP), Roseau (~33kyrs cal BP) et Grand Fond (~24kyrs cal BP). En combinant une étude pétrologique des produits naturels et des produits issus des travaux de pétrologie expérimentale, nous proposons un modèle complet des réservoirs à l’origine des trois éruptions. Les magmas sont des dacites à forte teneur en cristaux (~30%), comprenant plagioclases, orthopyroxènes, clinopyroxènes, amphiboles et oxydes. Les expériences d’équilibre de phases sur ces dacites ont permis de contraindre les conditions de stockage à 850°C, 400 MPa (16 km), ~ΔNNO+1 et une teneur en eau pré-éruptive de ~6-8 wt % pour les trois éruptions. Les orthopyroxènes ont été utilisés pour étudier les dynamiques pré-éruptives du système magmatique. Par une analyse systématique (« Crystal system analysis ») de leur zonation nous avons défini différents environnements magmatiques et leur connections. Les échelles de temps des dynamiques pré-éruptives sont calculées par modélisation de l’interdiffusion Fe-Mg dans les orthopyroxènes. Les caractéristiques chimiques et texturales des orthopyroxènes montrent que ~80-85% des cristaux sont non-zonés, tandis que 15-20% présentent une zonation multiple, normale ou inverse, avec prévalence de cette dernière. Les cristaux non zonés représentent l’environnement magmatique principal, alors que les zonés suggèrent une perturbation pré-éruptive du réservoir. Le « crystal system analysis » appliqué à ces derniers suggère la présence de 4 environnements magmatiques (MEs), avec un mouvement principal des cristaux vers des MEs de compositions moins évoluées, lié à la zonation inverse des cristaux. Cependant, la composition des inclusions vitreuses des orthopyroxènes, montre que les différents MEs sont en équilibre avec un verre de même composition. Ces considérations, couplées aux résultats d’équilibres de phases, nous permettent de définir le réservoir comme un environnement fortement cristallisé (~30%), modérément froid (~850°C) et fortement oxydé (~ΔNNO+1) possédant 80-85% de cristaux non-zonés, remobilisé par un réchauffement de 25-30°C produit par l’injection d’un magma plus chaud sous-jacent. La modélisation de l’interdiffusion Fe-Mg dans les orthopyroxènes indique que le réchauffement s’est produit ~10 ans avant chaque éruption. Ce processus crée la zonation inverse retrouvée dans 15-20% des orthopyroxènes et développe un panache thermique interne au réservoir qui est responsable de l’hétérogénéité cristalline retrouvée dans les échantillons / Large silicic eruptions (tens to hundreds of km3/eruption) have been a main subject of study for modern volcanology as they represent volcanic events of great impact on environment and human settlement on Earth. Petrologists have demonstrated that the crystal “cargo” of these eruptions can be used to unravel the pre-eruptive dynamic of their magmatic plumbing system and constrain timescales of the related magmatic processes. Specifically, several studies have proved that this “crystal cargo” can be remobilized and brought to eruption in short timescales of decades to centuries, making these systems more dynamic than previously believed.Several ignimbritic eruptions with a volume of the order of ~10 km3 have been recognized in Dominica (Lesser Antilles arc). On the basis of a detailed chronostratigraphy of the deposits, we present an integrated petrological study of the plinian fallout deposit of the latest three ignimbritic eruptions of Layou (~51kyrs cal BP), Roseau (~33kyrs cal BP) and Grand Fond (~24kyrs cal BP). We combine natural and experimental petrology to investigate the prevailing storage conditions within the reservoir that fed each eruption. Whole rocks are all dacites with crystal contents of ~30%, comprising plagioclase (An50-78), orthopyroxene (En47-63), clinopyroxene (Wo44-45), amphibole (Mg# 0.52-0.60) and Fe-Ti oxide (Mag71-75 and Ilm86-87) and rhyolitic residual melt. Pre-eruptive storage conditions of 850 (±5) °C, 400 MPa (16 km depth), ~ΔNNO+1 and melt water content of ~6-8wt% were determined for all studied eruptions through phase equilibria experiments. Orthopyroxenes were used to investigate the architecture and pre-eruptive dynamics of the plumbing system through a crystal system analysis (CSA) combined to a Fe-Mg diffusion modelling. Textural and chemical features of analysed orthopyroxenes prove that for all eruptions ~80-85% of crystals are unzoned while 15-20% present clear normal, reverse and multiple zoning, with reverse zoning being prevalent. Unzoned crystals represent the main magmatic environment (ME) while reverse zoned ones suggest a pre-eruptive perturbation of the reservoir. 4 MEs are evidenced, with a main movement of crystals towards MEs of less evolved composition, linked with the observed reverse zoning. Nevertheless, major element composition of orthopyroxene-hosted melt inclusions shows that all MEs are in equilibrium with the same melt. Combining results on natural and experimental petrology we can define the reservoirs as a highly crystalline (~30%), moderately cold (850°C) and highly oxidized (~ΔNNO+1) environment with 80-85% of unzoned orthopyroxenes, and 15-20% of zoned orthopyroxenes recording a heating process of 25-30°C, possibly produced by an underplating hotter magma that is responsible of the rejuvenation of the reservoir. By modelling the diffusional relaxation of Fe-Mg chemical gradient on zoned orthopyroxenes, we argue that this heating occurs in short timescales of ~10 years prior to each eruption. This heating process develops, over the considered eruptive time, a plume heating geometry able to bring together, on the scale of the hand sample, crystals of different magmatic environments (MEs)

Hartstoffschichten ermöglichen die Verbesserung bewährter und die Entwicklung neuartiger Produkte. Bei geringstem Materialaufwand lassen sich mit solchen Schichten Wirkungen erzielen, die auf eine andere Weise nicht erreichbar wären. Dünne Hartstoffschichten bis 10 µm werden seit Jahrzehnten zum Verschleißschutz von Werkzeugen und Bauteilen eingesetzt. Der zu den PVD-Verfahren zählende Vakuumbogenprozess (Arc-PVD) wird in der Industrie in großem Umfang zur Abscheidung nitridischer Hartstoffschichten eingesetzt. Als besonders vorteilhaft sind dabei die hohe Ionenenergie im fast vollständig ionisierten Plasma, die damit verbundenen hervorragenden Schichteigenschaften (Mikrohärte, Haftung, Struktur) und die relativ unkomplizierte, robuste und flexible Anlagentechnik anzusehen. Im Rahmen dieser Arbeit wurde ein nanostrukturierte AlCr(Si)N/TiN Hartstoffsystem entwickelt, welches sich mit dem Arc-PVD-Prozess homogen in Schichtdicken größer 50 µm aufbringen lässt und damit neue Einsatzbereiche für die Hartstoffbeschichtung eröffnet. Durch das definierte Schichtdesign im Nanometermaßstab kann einerseits das Eigenspannungsniveau stark abgesenkt werden und zusätzlich wird das Wachstum von Defektstrukturen unterdrückt. Die gewonnen Erkenntnisse bei der Herstellung dicker Schichten ermöglichen auch Verbesserungen der Eigenschaften dünner Schichten bis 10 µm.

Coral terrace surveys and U-series ages of coral and mollusk shells yield a surface uplift rate of ~0.6 m/ka for Kisar Island. The small island is located NE of Timor in the active Banda Arc of Indonesia. Based on this rate, Kisar first emerged from the ocean as recently as ~450 ka. Terrace surveys show warping that follows a pattern of east-west striking folds, which are along strike of thrust-related folds of similar wavelength imaged by a seismic reflection profile just offshore. This deformation shows that the emergence of Kisar can be attributed to forearc closure along the south-dipping Kisar Thrust. Terrace morphology and coral ages are best explained by recognizing major terraces as mostly growth terraces and minor terraces as mostly erosional into older growth terraces. All reliable and referable coral U-series ages are marine isotope stage (MIS) 5e (118-128 ka), which encrusted the coast up to 60 m elevation. All coral samples are found below 6 m elevation, but a tridacna (giant clam) shell in growth position at 95 m elevation yields an age of 195 +/- 31 ka, which corresponds to MIS Stage 7. Loose deposits of coral fragments found on top of low terraces between 8 and 20 m elevation yield ages of < 100 years and may represent paleotsunami deposits from previously undocumented seismic activity in the region. The metamorphic rocks of Kisar, Indonesia, which correlate with the Aileu Metamorphic Complex of East Timor, record the breakup of a supercontinent with associated rifting, metamorphism from arc-continent collision, and the growth and exhumation of a new orogenic belt. The protoliths of these rocks are mostly psammitic with minor basaltic and felsic igneous rocks. Geochemical analyses of mafic meta-igneous rocks show rift affinities that are likely related to rifting of Gondwana and later breakup in the Jurassic Period. The Aileu Complex is overlain by younger sedimentary rocks deposited on the northern passive margin of Australia, which collided with the Banda Arc in latest Miocene time. This collision caused metamorphism of the distal edge of the continental margin rocks at conditions of 600-700°C at 6-8 kbar and up to 700-850°C at 8-9 kbar locally, corresponding to depths from 25 to 30 km. These rocks were then rapidly uplifted and exhumed. U-Pb analysis of detrital zircons indicates a Permian to Late Jurassic age of the sedimentary sources and confirm an Australian provenance. The timing of metamorphism of the Aileu Complex is poorly constrained by previous studies, of which only a white mica cooling age of 5.36 +/- 0.05 Ma proved reliable. Prior apatite fission track studies show that all tracks are partially to completely annealed suggesting recent rapid cooling. A domal geometry of the island above the sea floor is expressed in the pinnacle shape. Foliations on Kisar Island generally strike parallel to the coastline, which is may be suggestive of doming. The Kisar Thrust, which is imaged in offshore seismic reflection data, may indicate that the doming corresponds to diapirism into the hinge of an active thrust-related anticline or diapirism of buoyant continental material along the thrust itself.

Deux groupes de poissons ont été nourris avec des diètes différent uniquement par leur teneur en acide gras. Trois acides gras principaux divergeaient dans leur concentration (18:ln-9, 18:2n-6, 22:6n-3). La composition en acide gras des principales classes de phospholipides des membranes mitochondriales a été modifiée par la diète, mais la somme des AG saturés, mono-insaturés et polyinsaturés est demeurée constante. Les proportions de phosphatidylcholine et phosphatidylethanolamine ont aussi été modifiées par la diète. À l'opposé, les propriétés fonctionnelles de la chaîne oxydative, à part les taux non-phosphorylants, étaient inchangées. Ces résultats suggèrent que les truites contrôlent la composition des AG dans les classes de phospholipides afin de maintenir les activités fonctionnelles. La diète semble avoir peu d'effet sur les propriétés fonctionnelles de la chaîne oxydative lesquelles conservent leur grande dépendance sur la taille des individus.

Extension at oceanic spreading centers ranges from ultra-slow (dominantly tectonic) to ultra-fast spreading (dominantly magmatic). This variation is reflected in the morphology of the spreading ridge segments and the magmatic productivity observed on the seafloor. These relationships are well understood at Mid-Ocean Ridges (MOR), but less is known about spreading centers above subduction zones. This study is part of a larger initiative to create the first 1:1,000,000 scale geological maps of different subduction zones at the Indo-Australian margin. This is a region of some of the fastest-growing crust on Earth and exhibits prolific magmatic-hydrothermal activity in back-arc basins. Previous work has shown that crustal growth associated with westward subduction of the Pacific Plate is characterized by highly distributed extension in back-arc basins, with numerous and simultaneously active spreading centers. In the NW Lau Basin, two of the spreading centers are punctuated by large-scale magmatic centers that coincide with anomalous mantle input (as documented by large-scale mantle helium anomalies) − features that are not well known in other basins. Detailed mapping at 1:200,000 scale shows that these spreading centers are related to near-field transcurrent faulting that developed in the early stages of the Lau back-arc basin. Translation across two oppositely moving fault zones induced rotation of the intervening crust and two anomalous spreading centers (Rochambeau Rifts and the Northwest Lau Spreading Center) opened obliquely to these structures. Both show inflated axial volcanic ridges that may be a product of an anomalous melt supply relative to the spreading rate. The marked variation in the morphology and magmatic output are thought to be controlled by input of melt from adjacent sources (Samoan plume) or the channeling of melt into a zone of thicker pre-existing crust, or both. These findings have important implications for understanding the origins of large-scale magmatic input in back-arc basins, where many fossil ore deposits have formed, thus providing important guides for resource exploration in ancient volcanic terranes on land.

The objective of this research was to establish a relationship between arc spot weld shear strength and the arc time used to form the weld. Lap shear tests were performed on both 3/4 in. and 5/8 in. nominal diameter welds. Each weld was formed in one-, two-, or four-layers of sheet steel ranging from 22 gauge (0.028 in.) to 16 gauge (.057 in.). Three distinct time series were tested for each unique weld size, thickness of sheet steel and layer configuration. The first of these series were the full-time welds. The two remaining series, 2/3-time and 1/3-time welds, had arc times equal to 2/3 and 1/3 of the average full-time weld arc time, respectively. Both weld shear strength tests and weld sectioning were performed for each series of weld. Strength tests were performed on a minimum of three specimens from every weld series. If the strength of any specimen deviated by over ten percent from the mean strength, an additional specimen was tested, helping to better understand the true behavior of the weld. Comparisons were made between the strengths of full-time, 2/3-time and 1/3-time welds. Comparisons were also made between the observed strength of each weld and the strengths calculated using the 2001 AISI Specification. Each sectioning test involved measuring and documenting the visual diameter, average diameter and effective diameter of the weld. Weld penetrations were also documented as sufficient or insufficient and any porosity was noted. A single sectioning test was performed for each full-time series, while three were performed for every 2/3-time and 1/3-time series. The data taken from the strength tests and the sectioning samples proved that welds formed using reduced arc times were considerably smaller and weaker than full-time welds. The tests also proved that proper penetration is not dependent on the arc time, but is instead a function of the welding current and sheet steel thickness. / Master of Science

No description available.

Management of data with a time dimension increases the overhead of storage and query processing in large database applications especially with the join operation, which is a commonly used and expensive relational operator whose processing is dependent on the size of the input relations. An index-based approach has been shown to improve the processing of a join operation, which in turn, improves the performance of querying historical data. Temporal data consist of tuples associated with a time interval value having a valid life span of different lengths. With join processing on temporal data, since tuples with longer life spans tend to overlap a greater number of joining tuples, they are likely to be accessed more often. The efficient performance of a temporal join depending on index-clustered data is the main theme studied and researched in this work. The presence of intervals having an extended data range in temporal data makes the join evaluation harder because temporal data are intrinsically multidimensional. Some temporal join processing methods create duplicates of tuples with long life spans to achieve clustering of similar data, which improves the performance on tuples that tend to be accessed more frequently. The proposed Hilbert-Temporal Join (Hilbert-TJ) join algorithm overcomes the need of data duplication by mapping temporal data into Hilbert curve space that is inherently clustered, thus allowing for fast retrieval and storage. A balanced B+ tree index structure was implemented to manage and query the data. The query method identifies data pages containing matching tuples that intersect a multidimensional region. Given that data pages consist of contiguously mapped points on the curve, the query process successively traverses along the curve to determine the next page that intersects the query region by iteratively partitioning the data space. The proposed Adaptive Replacement Cache-Temporal Data (ARC-TD) buffer replacement policy is built upon the Adaptive Replacement Cache (ARC) policy by favoring the cache retention of data pages in proportion to the average life span of the tuples in the buffer. By giving preference to tuples having long life spans, a higher cache hit ratio was evident. The caching priority is also balanced between recently and frequently accessed data. An evaluation and comparison study of the proposed Hilbert-TJ algorithm determined the relative performance with respect to a nested-loop join, a sort-merge join, and a partition-based join algorithm that use a multiversion B+ tree (MVBT) index. The metrics are based on a comparison between the processing time (disk I/O time plus CPU time), cache hit ratio, and index storage size needed to perform the temporal join. The study was conducted with comparisons in terms of the Least Recently Used (LRU), Least Frequently Used (LFU), ARC, and the new ARC-TD buffer replacement policy. Under the given conditions, the expected outcome was that by reducing data redundancy and considering the longevity of frequently accessed temporal data, better performance was achieved. Additionally, the Hilbert-TJ algorithm offers support to both valid-time and transaction-time data.

Call number: LD2668 .T4 1957 T82 / Master of Science

This work was primarily motivated by the industrial need for control of problems associated with the Gas Tungsten Arc Welding (GTAW) of small bore titanium and austenitic stainless steel tubes. These include: pore creation and entrapment in the weld zone, and variability of the fusion zone geometry. The primary aim of this study was the development of a low current orbital plasma welding capability using a structured approach which could lead to defect minimisation. The methodology should also have the potential to be used in a number of different conditions, extending the use of plasma welding in both melt-in and keyhole modes for the orbital welding of small bore tubes. The project originally involved the modification of a totally enclosed orbital GTAW welding head for low current welding operations. It was established that for the current range required for small bore and small to medium thickness tubes, the use of a solid copper torch was sufficient to provide the required heat absorption. A stable arc was produced even for very low current values (down to 7A) while arc voltages were within the operating range of a standard GTA welding power source. Procedural (i.e. off line) control was adopted for identification and optimisation of welding parameters. Since no procedure was available for the proposed welds it was necessary to generate the parameters required for the production of consistent weld profiles. Simultaneously, an expert system has been developed for the determination of optimum process parameters based on empirical models, developed using statistical techniques. Parameter combinations were selected based on physical as well as statistical relevance, providing a measure of confidence when predicting the required weld bead output characteristics. The approach also indicates the influence of the major input parameters on weld bead geometry and defect formation, such as undercut. Two quality acceptance criteria were employed during this investigation, weld bead dimensional accuracy, and the type and seriousness of defects present (penetration / burn-through, porosity and undercut). Off line programming was utilised to control heat build up and to ensure welds were obtained with the desired geometry and minimal defect levels. The end result was the development of a prototype system for low current orbital plasma welding (in both melt-in and keyhole mode) of small bore tubes in a totally enclosed head. Tolerant procedures for low current orbital melt-in and particularly keyhole welding have been generated and a systematic methodology for the prediction and optimisation of welding procedures based on predetermined criteria has been developed.