Buoyant plumes in cold fresh water are of interest because of the possibility of buoyancy reversal due to the nonlinear relation between temperature and density in water. Thus an initially rising plume may become a fountain. This project aims to mathematically model such plumes and fountains using numerical simulation by the means of a commercial software, Comsol Multiphysics. Both turbulent and lam- inar cases were investigated in different geometries, and with the assumption that density is a quadratic function of temperature. The turbulent flow cases as con- sidered here in this thesis are relevant to practical applications such as industrial discharge in cold lakes: whereas, the laminar flow case relates to laboratory experi- ments which are typically at scales too small for the flow to be turbulent. Previous investigation on warm discharge placed more attention on the biological implications of the spread along the lake bed, and not interested in analysing the dynamics of such flow, which turns out to be our focus. Furthermore, investigations on buoyant plumes that become negatively buoyant at later time (fountain flow) as considered previously, are based on the assumption that density is a linear function of tem- perature: where entrainment always reduces buoyancy. Whereas, the consideration of the temperature of maximum density is crucial and realistic in many practical situations, especially the power station warm discharge. Mixing is then bound to produce a mixture that is denser than both the discharge and the ambient water if receiving water is less than Tm: where this situation differs from plumes with linear mixing properties. Therefore, our focus is to better fathom the behaviour of warm discharge so as to give a detailed description of the flow, and also to observe buoyancy reversal whenever water that is denser than both the discharge and the receiving water is produced. The simulations were carried out for Prandtl number Pr = 7 & 11.4 and over the ranges of Froude number 0.1 ≤ Fr ≤ 5 and Reynolds numbers 50 ≤ Re ≤ 106, with source temperatures that are assumed to be higher than the temperature of maximum density Tm, and the ambient water below the Tm. Our results show some distinct behaviours from those experimental investigations by Bukreev, who also considered warm discharge where water that has temperature above the temperature Tm is initiated into a medium below Tm. The results here also showed some differences from those investigations with the linear dependence relation assumption.

xv, 108 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / Studies on seismic attenuation are an important complement to those on seismic velocity, especially when interpreting results in terms of temperature. But estimation of attenuation (t*) is more computationally involved and prone to contamination by noise, especially signal-generated noise. We have examined the effects of various forms of synthetic noise on t* estimation using time and frequency domain methods with varying window lengths and data frames of reference. We find that for S-waves, error due to noise can be reduced by rotating the data into the estimated polarization direction of the signal, but unless the exact nature of the noise is known, no method or window size is clearly preferable. We recommend the use of multiple estimation methods including a careful assessment of the uncertainty associated with each estimate, which is used as a weight during inversion for 1/Q. Our synthetic tests demonstrate that the misfit between actual and estimate-predicted traces or spectra correlates with t* error, and a similar relationship is suggested for real data. Applying this approach to data from the Yellowstone Intermountain Seismic Array, we employ two important constraints during inversion. First, we scale the misfit values so that the resulting weights are comparable in magnitude to the squares of the eventual data residuals. Second, we smooth the model so that the maximum attenuation (1/Q) does not exceed a value which would totally explain the observed velocity anomaly. The tomographic models from all the estimation methods are similar, but in the vicinity of the Yellowstone mantle plume, S-wave models show greater attenuation than do P-wave models. We attribute this difference to greater focusing by the plume of S-waves. All models show relatively high attenuation for the plume at depth, but above 250 km attenuation in the plume drops rapidly to values less than those of the surrounding mantle. We attribute this drop to the onset of partial melting, which dehydrates the olivine crystals, suppressing dislocation mobility and thereby attenuation. These attenuation models suggest excess plume temperatures at depth which are too low to support a plume origin in the lower mantle. This dissertation includes unpublished co-authored material. / Committee in charge: Eugene Humphreys, Chairperson, Geological Sciences; Emilie Hooft Toomey, Member, Geological Sciences; Douglas Toomey, Member, Geological Sciences; James Isenberg, Outside Member, Mathematics

Cenozoic tectonics of the Pacific Northwest (PNW) and the associated mantle structures are remarkable, the latter revealed by EarthScope seismic data. In this thesis we model teleseismic body waves constrained by ambient-noise surface waves and teleseismic receiver function analysis in order to recover better-controlled higher resolution images of the PNW continuously from the surface of the crust to the base of the upper mantle. We focus on and have clearly imaged two major upper mantle structures: (1) the high-velocity Farallon slab (the "Siletzia curtain") extending vertically beneath the Challis-Kamloops-Absaroka volcanic flareup (~53-47 Ma) of western Idaho and central Washington; and (2) a high-velocity anomaly beneath the Wallowa Mountains of northeast Oregon associated with the main Columbia River flood basalts source region. The proximity of these two structures along with the tectono-magmatic history of the PNW leads us to reexamine the origin of the Columbia River Basalts ~ 16 Ma. This thesis includes co-authored material submitted for publication.

Part 1 The viscosity of silicate melts is a fundamental physical property that determines the mobility and transport behaviour of magma on the surface and in planetary interiors. The viscosity of liquid fayalite (Fe2SiO4), the Fe-rich end-member of the abundant upper mantle mineral olivine, was determined up to 9.2 GPa and 1850 °C using in situ falling sphere viscometry and X-ray radiography imaging. The viscosity of liquid fayalite was found to decrease with pressure both along the melting curve and an isotherm, with temperature having very little influence on viscosity at high pressure. This work is the first to determine the viscosity of a highly depolymerized silicate melt at high pressure as only recent advances in experimental techniques have allowed the difficulties associated with studying depolymerized liquids at high pressure to be overcome. The results are in contrast with previous studies on moderately depolymerized silicate melts such as diopside and peridotite which found viscosity to initially increase with pressure. In accordance with recent in situ structural measurements on liquid fayalite, the viscosity decrease is likely a result of the increase in Fe-O coordination with pressure. The results show that the behaviour of silicate melts at depth is strongly dependent on the melt structure and composition. Part 2 The magnitude of the thermal anomaly at hotspot locations has a fundamental influence on the dynamics of mantle melting and therefore has an important role in shaping the surface of our planet. The North Atlantic Igneous Province (NAIP) is the surface expression of a major mantle plume and is unique in the fact that it has a complete magmatic history. The highest 3He/4He volcanic rocks on Earth are found in the early NAIP picrites of West Greenland and Bafin Island and high 3He/4He rocks are still erupted on Iceland today. However, the relationship between 3He/4He and mantle plumes has remained enigmatic. The main aim of this work is to use the ideal opportunity provided by the NAIP to investigate the relationship between temperature, mantle melting dynamics and helium isotopes within a mantle plume. The magmatic temperatures of a suite of picrites and primitive basalts spanning the spatial and temporal range of the NAIP was determined using traditional olivine-melt thermometry, a forward mantle melting model and the newly developed Al-in-olivine thermometer. This study is the first to provide a detailed petrologic approach to investigating the mantle temperature of the NAIP throughout its magmatic history and is the first to compare all three techniques in detail. The Al-in-olivine thermometer was found to be the most robust proxy for mantle temperature. The early stage of volcanic activity in the NAIP is associated with the arrival of the ancestral Iceland plume head and resulted in a uniform temperature anomaly with Al-in-olivine temperatures 250-300° above that of ambient MORB across an area 2000 km in diameter. In addition, the temperature of the plume is shown to have been subject to large temperature fluctuations on a timescale of 107 years and is currently increasing, which has had profound effects on the melting dynamics and bathymetry of the North Atlantic region. Using existing and new 3He/4He measurements, no clear relationship between 3He/4He and temperature is observable. However, it is noted that the maximum 3He/4He of primitive basalts from the NAIP has decreased through time. These relationships are explicable if the high 3He/4He reservoir is located in either the core or the core-mantle boundary (CMB), from which helium diffuses into the lower mantle. The high 3He=4He signature is incorporated into a plume when it breaks away from the base of the mantle and over the lifetime of the plume, the 3He/4He source is gradually depleted. The temperature of the plume can vary independently in responses to heat flow at the CMB, which is in turn related to changes in mantle convection. Global plate tectonics and mantle processes are therefore intricately linked with melting dynamics at hotspot locations.

O cálculo de dispersão de plumas é uma ferramenta empregada para se estimar o alcance dos poluentes emitidos por uma chaminé nas suas redondezas. É empregada nos países desenvolvidos há alguns anos e recentemente vem sendo exigida pelas agências ambientais brasileiras como um dos requisitos para concessão das licenças de operação. Baseia-se em um cálculo gaussiano, onde os dados de entrada são as taxas de emissão, os dados físicos da chaminé, dados meteorológicos e topográficos. Como é uma técnica recente no Brasil, este trabalho se propõe a fazer uma descrição da metodologia e suas etapas, indicando quais são os dados mais relevantes e quais simplificações podem ser feitas. O estudo de caso foi realizado nas instalações das Indústrias Nucleares do Brasil (INB). Os resultados indicaram que a influência de edificações adjacentes à fonte emissora é um dos parâmetros mais importantes, seguido da influência do relevo da região. Foi também realizada uma comparação entre os dois softwares comerciais existentes, o ISCST3, de maior complexidade, e o SCREEN mais simplificado, e indicou que o SCREEN pode ser usado como uma ferramenta de avaliação inicial, quando todos os dados de entrada necessários para se usar o ISCST3 não estão disponíveis / The plume dispersion modeling is a tool used to estimate the pollutants distribution in the vicinities of a chimney. It has been widely used in developed countries for a long time and now is started to be used by Brazilian environmental agencies as one of the requirements to obtain the operation license. It is based on a Gaussian modeling where input data are the emissions rate, physical data from the stack, meteorological data, and topographical characteristics. As this technique recently used in Brazil, this work proposes to describe the methodology and its steps, indicating the most relevant parameters, the possible simplifications, and details necessary. The case study was done at the site of Indústrias Nucleares do Brasil (INB). The results indicated that the edifications near the emission source are the most relevant parameter, followed by the topographical characteristics. A comparison was also done between the two commercial softwares available, the ISC3, with more details, and the SCREEN with simpler features. The results indicated that the SCREEN software can be used as an initial evaluation tool, whenever all input data necessary to process ICS3 are not available

Une fontaine peut se créer quand la flottabilité d'un rejet vertical s'oppose à sa quantité de mouvement. Ce type d'écoulement connaît beaucoup d'applications que ce soit dans la nature (panaches issus des éruptions volcaniques) ainsi que dans l'industrie du bâtiment (chauffage et refroidissement) ou dans le domaine des risques (rejets accidentel de gaz lourd). Dans cette thèse, nous nous focalisons sur l'étude des fontaines turbulentes miscibles. Dans le premier chapitre nous reformulons le modèle théorique de Morton et al. (1956) pour traiter le cas des fontaines en milieu linéairement stratifié. La résolution de ce modèle permet d'obtenir des relations analytiques pour la hauteur de la fontaine et sa hauteur d'étalement. Ce modèle est, par la suite, étendu au cas des panaches et des jets turbulents en milieu linéairement stratifié. Dans le second chapitre, nous proposons un modèle théorique permettant d'étudier une fontaine turbulente miscible en régime établi. Pour calibrer ce modèle, des simulations numériques aux grandes échelles (LES) sont utilisées pour obtenir une estimation des valeurs des constantes associées aux phénomènes d'échanges turbulents entre les parties ascendante et descendante de la fontaine. L'objectif du dernier chapitre est d'apporter, à partir d'expérimentations en laboratoire, des informations quantitatives sur l'influence de forts écarts de masses volumiques dans les écoulements de type fontaine. Les expériences sont réalisées pour des fontaines gazeuses (mélange air/hélium) en régime établi. / A fountain can occur when the buoyancy of a vertically released fluid opposes its momentum. Such flows have many applications in nature (plumes issuing from volcanic eruption), building industry (cooling or heating) or in the area of risk management (accidental release of heavy dangerous gas). In this thesis, we focus on the study of miscible turbulent fountains. In the first chapter, we revisit the theoretical model of Morton et al. (1956) to handle the case of fountains in linearly stratified fluid. The resolution of this model allows us to obtain analytical relations for the fountain height as well as the spreading height of its horizontal layer. This model is subsequently extended to the case of turbulent jets and plumes in linearly stratified fluid. In the second chapter, we propose a theoretical model for the study of a turbulent miscible fountain in a steady state. To calibrate this model, large eddy simulations (LES) are used to obtain an estimate of the values of the constants associated with the additional terms appearing in the equations. The objective of the final chapter is to provide, from laboratory experiments, quantitative information on the influence of strong density differences on the behaviour of a turbulent fountain. These experiments shows that all the classical relations valid for the Boussinesq case can be extended to the non-Boussinesq case by using an appropriate definition of the Froude number.

No description available.

Anthropogenic activities such as uranium mining and milling, nuclear weapons production, and nuclear reprocessing have left a legacy of groundwater and soil contaminated with uranium that needs to be addressed. Therefore, developing new remediation technologies to sequester uranium in situ is crucial. The objective of the study was to determine if low-cost commercially available unrefined humic substances, such as Huma-K, can be used to facilitate uranium sorption to minerals in soil and sediment. Sediments from the saturated zone beneath the F-Area seepage basins at the Savannah River Site (SRS) in South Carolina were used for the present study. The SRS site is analogous to many contaminated locations where groundwater acidity enhances uranium and other contaminants mobility. First, a variety of techniques were applied to characterize Huma-K and SRS sediment. Characterization studies showed that Huma-K possesses functional groups that have an acidic nature such as carboxyl and phenol groups. For SRS sediment, a mineral composition of mainly quartz (93.2%), kaolinite (5.1%), and goethite (1.1%) was identified. Second, the interactions between Huma-K and SRS sediment were investigated through batch experiments. Sorption, homogeneous precipitation, and surfaced-induced precipitation were observed to be enhanced at pH 4. However, Huma-K removal from solution decreased with an increase of pH. The sorption behavior was not able to be described by any of the models employed (pseudo-first, pseudo-second, Langmuir, and Freundlich). Third, the interactions between uranium and SRS sediment with and without Huma-K amendment were investigated. In acidic conditions (pH 3-5), the sorption capacity of SRS sediment amended with Huma-K was significantly increased compared to plain sediment. At circumneutral conditions, uranium removal from solution decreased for SRS sediment amended with Huma-K, compared with plain sediments, likely as a result of the formation of aqueous uranium-humic complexes. In summary, the results from the present study suggest that Huma-K, and likely other unrefined humate products, has the characteristics and effects necessary to be suitable for subsurface injection to remediate uranium in acidic groundwater conditions. The treatment zone will persist as long as the pH does not increase sufficiently to cause soil-bound Huma-K to be released, remobilizing uranium.

No description available.

The presented research discusses the design, analysis, and testing of a low current, LaB6 heaterless hollow cathode for space propulsion applications. A heaterless design using LaB6 is chosen to reduce complexity and increase electrical power efficiency and robustness. Argon propellant is used due to its more favorable breakdown voltage characteristics compared to xenon. An original model for the insert region plasma is derived by combining several analyses in literature. This model allows the simultaneous calculation of many plasma and thermal parameters in the cathode using only two completely unobtrusive measurements, and requires several assumptions which are common in hollow cathode research. The design of the cathode and its subsystems are presented in detail. No diagnostics were used in the cathode except direct voltage measurements in the power circuit. A discussion of emitter poisoning and ignition behavior is presented. The cathode is characterized by measuring anode and keeper voltages as a function of anode current and propellant flow rate, with the cathode discharging directly to a flat metal anode. Results are consistent with those obtained by previous investigations of argon hollow cathodes. This data is used with the derived plasma model to calculate the dependence of various parameters on current and flow rate. A discussion of the spot-plume transition behavior is presented. Finally, insights and design improvements are discussed based on the experimental results. / Master of Science / In recent years, the space industry has seen rapidly accelerating growth due to the continuing advancement of technology. A critical area of spacecraft technology is the spacecraft’s propulsion system, which allows the vehicle to achieve and maintain its desired orbit or trajectory through space. One class of propulsion systems known as “electric propulsion” uses electrical power to accelerate the fuel of the spacecraft. These types of propulsion systems are far more efficient than traditional propulsion systems, which use chemical reactions to create thrust. One of the main components of certain types of electric propulsion systems is the hollow cathode, which initiates and sustains the thruster operation. In this research, a hollow cathode with several non-conventional characteristics is developed and tested. First of all, standard hollow cathodes use a heater to bring the cathode up to operational temperature, but this design is heaterless which offers several benefits to the cathode and electrical power system designs. Secondly, the cathode uses a non-conventional choice of material for the “emitter”, which emits electrons when heated and allows the cathode to operate. Lastly, while typical electric propulsion systems use xenon for fuel, this cathode uses argon which has several benefits over xenon including cost. An overview of electric propulsion is presented, as well as a new physics-based model of this type of cathode that allows useful calculations based on simple measurements. The design and test results of the cathode are discussed in detail, with several interesting and insightful behaviors that were noted during testing. Heaterless cathodes have the potential to improve the efficiency, cost, and weight of electric propulsion systems, and this research therefore contributes to an important field for the future of space exploration.