This thesis is devoted to the deposition of intermetallic thin films by laser ablation deposition (LAD) and their characterization. Pulsed laser ablation and subsequent deposition of the ablated vapours produces films under conditions very far away from equilibrium. Besides the film, which forms directly by quenching the vapour or plasma on substrate, one also obtains under certain conditions micron and sub-micron sized spherical droplets of alloy melt on to the film. The latter travel at very high velocities and impinge on the substrate resulting in a very high rate of heat transfer during solidification from liquid state. Therefore, in this work it was possible to study the microstructure evolution depending on quenching rates of different sized droplets and compare with the extreme case of vapour/plasma quenching. The compositions selected correspond to the intermetallic compounds in Al-Fe, Al-Ni and Ti-Si binary systems. Pre-alloyed targets of the appropriate intermetallic compositions were used for ablation by laser. The deposition system has been designed and built in-house. The characterization is mainly done by transmission electron microscopy (TEM). The study focuses on microstructure and phase evolution within these intermetallic films at room temperature, at elevated temperature and during heating the room temperature deposited films in heating stage inside the TEM.

<p>Radio frequency ablation (RFA) is a commonly used minimally invasive method of treating liver cancer tumours which utilises RF current for heating tumour tissue up to a lethal temperature. RF current is generated by a power generator and applied to the tumour by an electrode which is inserted into the tumour either during percutaneous or open surgery. </p><p>RFA is a method that has great advantages compared to traditional surgical resection of tumours due to minimal invasiveness, it can be used for a greater number of patients and enables repeated treatments. Even though there are many advantages coupled to RFA there are still some problems and difficulties associated with the method. One of these problems is the cooling effect from large vessel blood flow within the liver, the so called heat sink effect.</p><p>The aim of this master thesis work has been to develop a theoretical finite element model of RFA within Comsol Multiphysics software. This theoretical model has been used to simulate blood perfusion effects on resulting ablation volume. The effects from different large vessel blood flow parameters has been investigated, these parameters are: blood flow velocity, blood vessel diameter and distance between blood vessel and RF electrode. A factorial design has been utilised to setup parameter levels for the different simulations. A linear- and a second degree regression model has been calculated based on simulation results. The parameter with largest impact on simulative ablation volume and the interaction effects between the parameters were determined from the regression model coefficients. In addition to this has two simulations been performed, modelling perfused- and unperfused liver tissue, in order to investigate the effects resulting from microvascular perfusion.</p><p>The result shows that the parameter with largest impact on simulative ablation volume are the distance, it was also shown that there are a small interactional effects between diameter and distance, where a small distance increases the effect from a varying diameter. Modelled microvascular perfusion was shown to give a decrease in simulative ablation volume. A shortage of this master thesis work is the lack of experimental verification of the developed model. </p>

Dans l'industrie nucléaire, les peintures murales doivent être décontaminées à la fin de vie des installations ou lors d'opération de maintenance. L'ablation par laser de la peinture permet de réduire considérablement le volume de déchets engendrés lors de l'opération, par rapport aux techniques actuelles. <br />Les peintures sont constituées d'une base polymérique dans laquelle des charges et des pigments sont inclus. Le dépôt d'énergie du faisceau laser dans ce milieu diffusant est étudié à l'aide d'un modèle de diffusion multiple, et de mesures de réflexion / transmission de faisceau à travers des couches minces.<br />L'ablation des peintures est analysée avec plusieurs lasers Nd : YAG et un laser TEA-CO2, permettant de faire varier la fluence, la longueur d'onde, la durée de l'impulsion, la cadence de tir et le nombre de tirs appliqué. Des bancs optiques ont été réalisés, et des tests paramétriques permettent de définir les paramètres optimaux de l'ablation, en terme d'efficacité de l'ablation.<br />L'ablation à haute cadence de tir est étudiée à l'aide d'un pyromètre optique et d'un modèle thermique spécifiquement développé. Les mesures et la modélisation permettent de mettre en évidence l'accumulation de chaleur qui apparaît lors de l'utilisation de laser à haute cadence. Cette accumulation permet de réduire les fluences seuils d'ablation et d'augmenter les efficacités d'ablation. <br />Une analyse de l'interaction et des régimes d'ablation est proposée sur la base des résultats expérimentaux et des modèles, et permet l'optimisation du procédé de décontamination.

Bedingt durch die zunehmende Prävalenz der Rhythmusstörung Vorhofflimmern mit den assoziierten Morbiditäts- und Mortalitätsrisiken ist die Entwicklung und Etablierung kurativer Therapieverfahren von klinischem und wissenschaftlichem Interesse. Entsprechend dem pathophysiologischen Verständnis der Arrhythmie-induzierenden Triggeraktivität und des Arrhythmie-erhaltenden Flimmersubstrat mit der vorrangigen anatomisch-strukturellen Lokalisation beider Entitäten im Übergangsbereich der großen Pulmonalvenentrichter in den posterioren linken Vorhof wurden katheterinterventionelle Ablationskonzepte als potentiell kurative Therapien entwickelt. Limitationen der praktischen Umsetzung theoretischer Linienkonzepte ergeben sich aus komplexen anatomischen Gegebenheiten und instabilen Zugangsbedingungen infolge Atmung und kardialer Mobilität. Aufbauend auf non-fluoroskopischen Navigationssystemen wurden Verfahren für vollständig Modell-integrierte Ansätze der Ablationslinienplatzierung entwickelt, bei denen Planung, Durchführung und Validierung der Ablation an anatomisch korrekten dreidimensionalen CT-Modellen des linken Vorhofes erfolgen. Zur Verbesserung instabiler Zugangsbedingungen wurden Verfahren der Katheternavigation mittels steuerbaren Schleusensystemen eingeführt und in entsprechenden Studien mit klinischen Endpunkten validiert. Zu objektivierbaren Erfassung von Energietransfer und myokardialer Läsionsbildung während der Ablation wurden katheterinterventionelle Kontakttechnologien, die auf der Messung lokaler komplexer Impedanzen zwischen Katheter und Gewebe beruhen, in der ersten klinischen Anwendung erprobt und validiert. Mit diesen technologischen Entwicklungen gelangen eine zunehmend akkuratere klinische Umsetzung theoretischer Ablationskonzepte und damit eine Etablierung des Therapiekonzeptes als klinisches Standardverfahren. Eine zur Abschätzung des Nutzen/Risiko-Profils nötige detaillierte Komplikationsanalyse stellte die Ösophagusverletzung als schwerste Komplikation heraus, die mit 0,3% selten auftrat, aber für nahezu alle langfristigen Folgeschäden verantwortlich war. Entwicklungen zur periprozeduralen Visualisierung des Ösophagus mit paralleler intraösophagealer Temperaturmessung sind Ansätze zur Vermeidung dieser Komplikation in der Zukunft. Bedingt durch das Auftreten und die postinterventionelle Zunahme asymptomatischer Flimmerrezidive ist die Frage eines objektiven Vorhofflimmermonitorings von entscheidender Bedeutung für die Beurteilung der Effektivität der Ablation sowie weitergehende klinische und wissenschaftliche Fragestellungen; wie die Indikation zur Antikoagulation oder den Vergleich von Rhythmus- und Frequenzkontrolle. 7-Tage-LzEKGs und transtelephonische EKGs wurden als Standard zum Monitoring innerhalb klinischer Vorhofflimmerstudien etabliert. Entwicklungen im Bereich implantierbarer kontinuierlicher Rhythmusmonitore werden in Zukunft das Netz zur Erfassung asymptomatischen Vorhofflimmerns weiter verdichten.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2001. / Bibliography: leaves 109-115. Also available online.

Sarahsaurus aurifontanalis is the most recent sauropodomorph dinosaur to be discovered and named from the Early Jurassic of North America. The dinosaur is represented by a mostly complete and articulated holotype specimen that preserves a unique manual phalangeal count of 2-3-4-2-2 and accessory pubic foramen adjacent to the obturator foramen. The holotype of Sarahsaurus comprises a braincase and isolated cranial elements, but the skull previously referred to this taxon, MCZ 8893, can only be provisionally referred to Sarahsaurus until additional crania are found associated with postcranial material. Sarahsaurus comes from the middle third of the Kayenta Formation, which is considered to be Early Jurassic in age despite the absence of a radiometric date from that unit. A new technique used to obtain a U-Pb radiometric date from the type quarry of Sarahsaurus in the Kayenta Formation was influenced by secondary uranium enrichment in the open system of the fossil bone. That suggests that uranium within the Kayenta Formation may be the result of the movement of groundwater during the Laramide orogeny in the Late Cretaceous and Early Eocene, and lends support to the hypothesis that the uplift of the Colorado Plateau began relatively early in Late Cretaceous to the Eocene. / text

Two separate heat transfer problems that involve jet flows impinging on a reacting target are studied through modeling and experimentation. The first system is an ablating carbon-carbon specimen exposed to high heat fluxes from an oxy-acetylene torch which has applications in atmospheric re-entry vehicles. The second system involves the penetration of hot gases into the void space in a compartment. The fire protection stands to benefit from knowledge of this system, both in building component design and informing firefighting personnel. Both problems can be modeled as a jet flow impinging on a flat surface where hot gases from the jet lead to primarily convective heat transfer. Ablation experiments are outlined and a theoretical framework is developed. A serial inversion technique is tested for predicting the recession rate observed in the experiments. A novel inversion technique that takes advantage of parallel computing is developed to circumvent the shortcomings of the serial technique. These techniques are then compared to synthetically generated and experimental data for different data streams and error signals. Compartment-scale experiments were conducted to test hot gas penetration into void spaces. Anecdotal evidence was observed outside of the intended test section prompting further investigation into the mechanics of ignition in void spaces. A theoretical framework is established to predict possibility of ignition under varied environmental factors. A leakage-scale experiment is constructed to gain insight into conditions that result in ignition of materials in void spaces. / text

A recently-developed experimental technique based on the sublimation of naphthalene, which enables imaging of the dispersion of a passive scalar using planar laser-induced fluorescence (PLIF), is applied to a Mach 5 turbulent boundary layer and a NASA Orion capsule flowfield. To enable the quantification of naphthalene PLIF images, quantitative fluorescence and quenching measurements were made in a temperature- and pressure-regulated test cell. The test cell measurements were of the naphthalene fluorescence lifetime and integrated fluorescence signal over the temperature range of 100 K to 525 K and pressure range of 1 kPa to 40 kPa in air. These data enabled the calculation of naphthalene fluorescence yield and absorption cross section over the range of temperatures and pressures tested, which were then fit to simple functional forms for use in the calibration of the PLIF images. Quantitative naphthalene PLIF images in the Mach 5 boundary layer revealed large-scale naphthalene vapor structures that were regularly ejected out to wall distances of approximately y/δ = 0.6 for a field of view that spanned 3δ to 5δ downstream of the trailing edge of the naphthalene insert. The magnitude of the calculated naphthalene mole fraction in these structures at y/δ = 0.2 ranged from approximately 1-6% of the saturation mole fraction at the wind tunnel recovery temperature and static pressure. An uncertainty analysis showed that the uncertainty in the inferred naphthalene mole fraction measurements was ± 20%. Mean mole fraction profiles collected at different streamwise locations were normalized by the mole fraction measured at the wall and a characteristic height of the scalar boundary layer, causing the profiles to collapse into one “universal” mole fraction profile. Two-dimensional fields of naphthalene mole fraction were also obtained simultaneously with velocity by using particle image velocimetry (PIV) and PLIF. The images show large-scale naphthalene vapor structures that coincide with regions of relatively low streamwise velocity. The covariance of naphthalene mole fraction with velocity indicates that an ejection mechanism is transporting low-momentum, high-scalar-concentration fluid away from the wall, resulting in the protrusions of naphthalene vapor evident in the instantaneous PLIF images. Lastly, naphthalene PLIF was used to visualize the dispersion of gas-phase ablation products on a scaled Orion capsule model at four different angles of attack at Mach 5. High concentrations of scalar were imaged in the capsule recirculation region. Additionally, intermittent turbulent structures were visualized on the heat shield surface, particularly for the 12° and 52° AoA cases.

In the past decade, there has been an increased interest in magnetostrictive materials for micro actuators and sensors. Of particular importance are the Fe₂R intermetallics, where R = Tb, Dy. In this study, films of Tb[subscript 0.3]Dy[subscript 0.7]Fe[subscript 1.92] were prepared by three laser processing techniques (pulsed laser deposition, flat plate ablation and laser ablation of microparticles) to explore the effect of processing parameters on particle size, crystallinity and magnetic properties. The laser used in the experiments was a KrF laser with a 12 ns pulse width. Pulsed laser deposition of an alloyed target in vacuum produces dense amorphous films with the similar composition to the target, low coercivity (46 Oe) and good magnetostriction ([lambda][subcript two horizontal lines] = 305 ppm at 2300 Oe). Flat plate ablation and laser ablation of microparticles produced amorphous nanoparticles at 1 atm. The particles were subsequently jet deposited onto substrates to form thick films. Nanoparticle films produced by flat plate ablation resulted in oxidized and segregated particles due to extended, non-uniform plume expansion, laser target modification, and open porosity. Laser ablation of microparticles produced thick films with M[subscript s] = 13.8 emu/g. Two types of annealing treatments were performed to close porosity and increase Youngs modulus. Annealing of LAM films at temperatures up to 700°C in-situ and 950°C in a reducing atmosphere did not result in coarsening of the particles or crystallization of the Laves phase due to the core-shell structure of nanoparticles (rare earth oxide shell, Fe rich core) brought about by oxidation-induced segregation.

A new technique is developed that uses planar laser-induced fluorescence (PLIF) imaging of sublimated naphthalene to image the transport of ablation products in a hypersonic boundary layer. The primary motivation for this work is to understand scalar transport in hypersonic boundary layers and to develop a database for validation of computational models. The naphthalene is molded into a rectangular insert that is mounted flush with the floor of a Mach 5 wind tunnel. The distribution of naphthalene in the boundary layer is imaged by using PLIF, where the laser excitation is at 266 nm and the fluorescence is collected in the range of 320 to 380 nm. To investigate the use of naphthalene PLIF as a quantitative diagnostic technique, a series of experiments is conducted to determine the linearity of the fluorescence signal with laser fluence, as well as the temperature and pressure dependencies of the signal. The naphthalene fluorescence at 297 K is determined to be linear for laser fluence that is less than about 200 J/m². The temperature dependence of the naphthalene fluorescence signal is found at atmospheric pressure over the temperature range of 297K to 525K. A monotonic increase in the fluorescence is observed with increasing temperature. Naphthalene fluorescence lifetime measurements were also made in pure-air and nitrogen environments at 300 K over the range 1 kPa to 40 kPa. The results in air show the expected Stern-Volmer behavior with decreasing lifetimes at increasing pressure, whereas nitrogen exhibits the opposite trend. Preliminary PLIF images of the sublimated naphthalene are acquired in a Mach 5 turbulent boundary layer. Relatively low signal-to-noise-ratio images were obtained at a stagnation temperature of 345 K, but much higher quality images were obtained at a stagnation temperature of 380 K. The initial results indicate that PLIF of sublimating naphthalene may be an effective tool for studying scalar transport in hypersonic flows. / text