Dissertations / Theses on the topic 'Heterogeneous phase'
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Khan, Shahid Amin. "Phase transformations in heterogeneous steels." Thesis, University of Cambridge, 1990. https://www.repository.cam.ac.uk/handle/1810/221888.
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Khong, Teck Meng. "Heterogeneous gas phase reactions for the production of chemically bonded phases." Thesis, Birkbeck (University of London), 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246077.
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Mirza, Amin Ruhul. "Developments in supported aqueous-phase catalysis." Thesis, University of Bath, 1999. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311179.
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Inceesungvorn, B. "Silver based heterogeneous catalysts for selective gas phase reactions." Thesis, Queen's University Belfast, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.517231.
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Franc, Jacques. "Two-phase flow properties upscaling in heterogeneous porous media." Phd thesis, Toulouse, INPT, 2018. http://oatao.univ-toulouse.fr/21684/1/FRANC_Jacques.pdf.
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The groundwater specialists and the reservoir engineers share the same interest in simulating multiphase flow in soil with heterogeneous intrinsic properties. They also both face the challenge of going from a well-modeled micrometer scale to the reservoir scale with a controlled loss of information. This upscaling process is indeed worthy to make simulation over an entire reservoir manageable and stochastically repeatable. Two upscaling steps can be defined: one from the micrometer scale to the Darcy scale, and another from the Darcy scale to the reservoir scale. In this thesis, a new second upscaling multiscale algorithm Finite Volume Mixed Hybrid Multiscale Methods (Fv-MHMM) is investigated. Extension to a two-phase flow system is done by weakly and sequentially coupling saturation and pressure via IMPES-like method.
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Seeley, Lane Howard. "Heterogeneous nucleation of ice from supercooled water /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/9783.
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Ferguson, Robert James. "Seismic imaging in heterogeneous anisotropic media by nonstationary phase shift." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0016/NQ49493.pdf.
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Deshpande, Kiran B. "Study of transport limited heterogeneous reaction in the dispersed phase." Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.419600.
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Young, Matthew J. "Studying liquid-phase heterogeneous catalysis using the atomic force microscope." Diss., Kansas State University, 2016. http://hdl.handle.net/2097/32852.
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Doctor of PhilosophyDepartment of Chemical Engineering
Peter H. Pfromm
Characterization of the interactions of hydrogen with catalytic metal surfaces and the mass transfer processes involved in heterogeneous catalysis are important for catalyst development. Although a range of technologies for studying catalytic surfaces exists, much of it relies on high-vacuum conditions that preclude in-situ research. In contrast, atomic force microscopy (AFM) provides an opportunity for direct observation of surfaces under or near actual reaction conditions. Tapping-mode AFM was explored here because it expands AFM beyond the usual topographic information toward speciation and other more subtle surface information. This work describes using phase-angle data from tapping-mode AFM to follow the interactions of hydrogen with palladium. Both gas-solid and liquid-solid interfaces were studied. Real-time AFM phase-angle data allowed for the observation of multiphase mass transfer to and from the surface of palladium at atmospheric pressure and room temperature without the need for complex sample preparation. The AFM observations were quantitatively benchmarked against and confirm mass transfer predictions based on bulk hydrogen diffusion estimates. Additionally, they support recent studies that demonstrate the existence of multiple hydrogen states during interactions with palladium surfaces.
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French, Christopher. "Transparent heterogeneous terrestrial optical communication networks with phase modulated signals." Thesis, Aston University, 2012. http://publications.aston.ac.uk/19237/.
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This thesis presents a large scale numerical investigation of heterogeneous terrestrial optical communications systems and the upgrade of fourth generation terrestrial core to metro legacy interconnects to fifth generation transmission system technologies. Retrofitting (without changing infrastructure) is considered for commercial applications. ROADM are crucial enabling components for future core network developments however their re-routing ability means signals can be switched mid-link onto sub-optimally configured paths which raises new challenges in network management. System performance is determined by a trade-off between nonlinear impairments and noise, where the nonlinear signal distortions depend critically on deployed dispersion maps. This thesis presents a comprehensive numerical investigation into the implementation of phase modulated signals in transparent reconfigurable wavelength division multiplexed fibre optic communication terrestrial heterogeneous networks. A key issue during system upgrades is whether differential phase encoded modulation formats are compatible with the cost optimised dispersion schemes employed in current 10 Gb/s systems. We explore how robust transmission is to inevitable variations in the dispersion mapping and how large the margins are when suboptimal dispersion management is applied. We show that a DPSK transmission system is not drastically affected by reconfiguration from periodic dispersion management to lumped dispersion mapping. A novel DPSK dispersion map optimisation methodology which reduces drastically the optimisation parameter space and the many ways to deploy dispersion maps is also presented. This alleviates strenuous computing requirements in optimisation calculations. This thesis provides a very efficient and robust way to identify high performing lumped dispersion compensating schemes for use in heterogeneous RZ-DPSK terrestrial meshed networks with ROADMs. A modified search algorithm which further reduces this number of configuration combinations is also presented. The results of an investigation of the feasibility of detouring signals locally in multi-path heterogeneous ring networks is also presented.
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Sreeranganathan, Arun. "Realistic micromechanical modeling and simulation of two-phase heterogeneous materials." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24607.
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Thesis (Ph.D.)--Materials Science and Engineering, Georgia Institute of Technology, 2008.Committee Chair: Gokhale, Arun; Committee Member: Gall, Kenneth; Committee Member: Garmestani, Hamid; Committee Member: Kurtis, Kimberly; Committee Member: Thadhani, Naresh
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Jiang, Shuaiyu. "Design of Photocatalysts for Efficient Heterogeneous and Heterogeneous/Homogeneous Photocatalytic Carbon Dioxide Reduction Systems." Thesis, Griffith University, 2021. http://hdl.handle.net/10072/403252.
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Environment and energy security issues derived from the immoderate consumption of finite fossil fuels have promoted the discovery of environment friendly and sustainable energy conversion strategy. The burning of fossil fuels led to large amount output of carbon dioxide (CO2), which can either cause global warming if emitted to the atmosphere freely or become abundant feedstock if utilised properly. Photocatalytic CO2 reduction reaction can convert CO2 into more valuable carbonaceous molecules, such as carbon monoxide (CO), methane (CH4), formic acid (HCOOH), or even alcohols, by harnessing infinite solar energy, and this process will contribute to alleviate both above issues. In this process, catalysis materials play a key role, and reasonable designed reaction system can provide supportive platform for catalysts to achieve desirable performance. Numerous studies have focused on developing advanced catalysts and various configuration of CO2 reduction. However, current CO2 reduction system are still encountering with enormous challenges, including the competition of hydrogen evolution reaction (HER), further leap in activity, diversity of products and complexity of reaction mechanism and active sites. This thesis aims to improve the performance of traditional heterogenous photocatalysis in gaseous phase CO2 reduction by enhancing the light utilization and mass transfer efficiency and develop new photosensitised homogeneousheterogenerous system for enhanced selectivity and activity in CO2 reduction.
Hierarchical hollow-shell nanomaterials have attracted numerous attentions in multidisciplinary research, especially in photocatalysis area, due to their unique structure and outstanding properties. However, current hard-templating synthesis methods are mainly capable of fabricating hierarchical hollow-shell structure composed with singular component and binary semiconductors, while show some drawbacks to synthesize more complicated compositions. Rational fabricating hierarchical hollow-shell structure composed with multinary semiconductor or semiconductors’ heterojunction remains challenging. In Chapter 2, the wide applicability of a unique one-pot hard-template method was discussed. With the strategy of fixing one component into templating agent (e.g. sucrose) at very beginning, followed by stepwise adsorption of other species, this method was capable of fabricating hierarchical hollow-shell structure composed of multinary semiconductor and semiconductors’ heterojunction. Besides, gaseous phase CO2 photoreduction reactions under high pressure condition were tested on synthesized hierarchical hollow-shell semiconductors’ heterojunction samples which achieved high selectivity and activity towards carbonaceous products.
Highly selective photocatalytic CO2 reduction into CO and methane (CH4) by solidgas interface reaction mode is achieved under ambient pressure on elaborately designed hollow sphere based TiO2/SrTiO3 heterostructures. The synthesized three-dimensional hierarchical hollow multi-shelled TiO2/SrTiO3 spheres (HoMSs-TS) are an assembly of well-organized shells composed of interconnected anatase TiO2 and perovskite SrTiO3 nanoparticles (NPs). This hierarchical structure features multiple porous shells and subunits, which not only serve to maximize light utilization, but also facilitate mass transport during the gaseous phase photocatalytic process. Moreover, the heterojunctions between TiO2 and SrTiO3 provide synergistic enhancement of the charge transfer and separation process, which is equally critically important in the selective photocatalytic CO2 reduction reaction (CO2RR). These advantages empower the HoMSs-TS to effectively suppress hydrogen evolution and ease the selective production of CO and CH4. This work is described in Chapter 3 of this thesis.
Photosensitized heterogeneous CO2 reduction (PHCR), especially the Ru-Co based PHCR system, has emerged as a promising visible-photocatalytic photocatalysis system for converting CO2 into value-added chemicals, however, challenged by the hydrogen evolution reaction (HER) induced low selectivity. Chapter 4 of this thesis reports a PHCR system that couples Ru(bpy)3^2+ homogeneous sensitizer with (001) faceted ultrathin LiCoO2 nanosheets heterogeneous photocatalyst with completely suppressed HER to yield 100% carbonaceous products. The experimental and theoretical studies reveal that the favored CO2 adsorption on the exposed Li on (001) faceted LiCoO2 surface is responsible for the suppressed HER.
Despite recent progress in discovering various photocatalysts, realizing high performance in sensitised homo-hetero CO2 reduction and disclosing CO2 activation site remain challenging. In the work of Chapter 5, we report the synergistic effect of superficial Co-O nano layer and heterogenous Co metallic in enhancing PHCR system. The conductive heterogenous cobalt metallic core composed of face-centred cubic (fcc)cubic Co and hexagonal closest packed (hcp) Co was formed by heat treatment of Co3O4 in reductive atmosphere and can effectively improve the conductivity of photogenerated electron. Moreover, an in situ formed thin oxide shell on the surface provided active sites for CO2 reduction reaction. Owing to the synergistic effect, the performance in photosensitised CO2 reduction into CO is about 1.7 times comparing to that of Co3O4 nanosheets under the same reaction condition. This discovery provides a promising approach for the design of other materials for energy conversion.
This thesis significantly contributes innovative knowledge in material science and CO2 reduction system through: (i) designing novel 3D structured heterogeneous photocatalyst with high photocatalytic CO2 reduction performance toward CO and CH4; (ii) developing gaseous phase CO2 reduction to suppress hydrogen evolution reaction (HER); (iii) reviewing the development of photosensitised homogeneous-heterogeneous CO2 reduction, and developing new approach to improve the selectivity by manipulating exposed ion as active site; (iv) probing the in situ formation of oxidised nanolayer around metallic core and investigating the synergetic effect of interface of oxidised layer and heterogenous metallic core in improving CO2 reduction performance in PHCR reaction system.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
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Bazzazi, Hojjat. "Synchronization in Heterogeneous Networks of Hippocampal Interneurons." Thesis, University of Waterloo, 2005. http://hdl.handle.net/10012/1086.
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The hippocampus is one of the most intensely studied brain structures and the oscillatory activity of the hippocampal neurons is believed to be involved in learning and memory consolidation. Therefore, studying rhythm generation and modulation in this structure is an important step in understanding its function. In this thesis, these phenomena are studied via mathematical models of networks of hippocampal interneurons. The two types of neural networks considered here are homogenous and heterogenous networks. In homogenous networks, the input current to each neuron is equal, while in heterogenous networks, this assumption is relaxed and there is a specified degree of heterogeneity in the input stimuli. A phase reduction technique is applied to the neural network model of the hippocampal interneurons and attempts are made to understand the implications of heterogeneity to the existence and stability of the synchronized oscillations. The Existence of a critical level of heterogeneity above which the synchronized rhythms are not stable is established, and linear analysis is applied to derive expressions for estimating the perturbations in the network frequency and timing of the neural spikes. The mathematical techniques developed in this thesis are general enough to be applied to models describing other types of neurons not considered here. Possible biological implications include the application of high frequency local stimulation to alleviate the synchronous neural oscillations in pathological conditions such as epilepsy and Parkinson's disease and the possible role of heterogeneity in controlling the rhythm frequency and switching between various cognitive states.
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Slater, John Clark, and John Clark Slater. "Numerical Modelling of Two-Phase Flow in Heterogeneous, Anisotropic Porous Media." Thesis, The University of Arizona, 1996. http://hdl.handle.net/10150/626830.
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A numerical model for flow of two immiscible, incompressible fluids in a two-dimensional,
incompressible, heterogeneous, and possibly anisotropic porous medium is developed. The
numerical model actually incorporates two different formulations. One formulation solves
for the wetting-phase pressure and saturation as primary unknowns, while the other
formulation solves for the wetting-phase pressure and capillary pressure. Both formulations
of the model are verified through comparison with an analytical solution for two-phase flow.
The formulations exhibit differing degrees of internal mass balance. One of the model
formulations is used to simulate a laboratory experiment involving the inundation of a
heterogeneous sand pack by tetrachloroethylene (PCE). PCE distributions implied by the
numerical model agree reasonably well with observed distributions, although no quantitative
distribution data were available.
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Alves, Jose Alberto da Conceicao. "New highlights on mechanisms of heterogeneous liquid-phase catalytic transfer reduction." Thesis, University of Liverpool, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317971.
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Nikolopoulos, Panagiotis. "Mass transfer in non-aqueous phase liquid contaminated heterogeneous porous media." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611535.
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Nagy, Dávidné. "Visible light response semiconductor nanomaterials for heterogeneous photocatalysis in liquid phase." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/33062.
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The development of sustainable and green technologies powered by renewable energy sources is highly desired to address the growing global energy need and water scarcity problems. Heterogeneous photocatalysis emerged in the past decades as promising solar-powered technology for environmental remediation applications such as wastewater treatment. The photoactivity of the materials is believed to be governed by complex mechanisms, still it was shown that it may be critically dependent on the following material properties (i) ability and effectiveness to absorb incident photons, (ii) charge separation efficiency, (iii) charge utilization efficiency, (iv) morphology including the size and shape of the nanostructure and its distribution and (v) the crystal structure, phase composition and crystallinity ... etc. Hence, most strategies aiming to improve the performance of photocatalytic materials may focus on one or more of the aforementioned aspects. Beside developing new materials or modifying existing systems, the development of sustainable, easy-to-operate systems are highly desired for developing countries such as Africa where almost half of the population are affected by water scarcity of some sort. For this motivation the immobilization of powder catalyst could be one attractive solution. In this thesis three experimental systems are presented. In the first two the effect of material properties on the photoactivity whereas in the third chapter the immobilization of powder catalyst was investigated. The first experimental project aimed to study the effect of synthesis parameters of WO3 nanostructures on its morphology, phase composition, optical properties and ultimately on the photoactivity. Understanding the role of process parameters to gain control over the material properties is still a challenge but is of great interest in photocatalysis. Here, a hydrothermal synthesis method was employed to synthesize WO3 nanostructures with various morphologies, crystal phases and optical properties. The effect of the solution pH, the polymeric surface modulator and the added EtOH was investigated on the material properties and on the photocatalytic activities. It was found that the crystal structure and the morphology of WO3 was influenced by the solution pH in the first place. It was proposed that stabilization effects between the crystal phase and the morphology could also influence the crystallization process beside supersaturation. It was revealed that despite the highest surface area of W-2.01-P20E, reduced oxidation state did not promote high photo-response. Instead the photoactivity of WO3 was seen as the compromise of the material properties including the optical, structural properties and the oxidation state. In the second experimental project the effect of Ag co-catalysis was studied on TiO2- Cu2O heterostructure formation. Coupling a wide band gap (TiO2) and a narrow band gap (Cu2O) semiconductor could benefit from extended light absorption properties and additionally from enhanced charged separation. In this study a facile wet chemical synthesis method was coupled with a UV treatment step to fabricate TiO2-Ag-CuxO ternary hybrid nano-materials. The effect of the Ag loading (1-5%) and the synthesis sequence of the Ag deposition step was evaluated on the material properties as well as on the visible photocatalytic activity. It was revealed that both the amount and the order of the Ag-deposition altered the material properties considerably. Typically TiO2/CuxO/Ag (TCA) catalysts had better visible light absorption properties but reduced affinity to adsorb methyl orange (MO) to their surface. Whereas, TiO2/Ag/CuxO (TAC) catalysts in general had better dye adsorption properties relative to TCA and had more efficient decoloration properties under visible light. TOC and HPLC-MS analysis revealed that MO and possibly its degradation products were mainly mineralized and/or adsorbed to the surface of TAC catalyst with 5% nominal Ag content in the visible process generating limited amount of byproducts in the final solution. The third experimental project focused on the immobilization of the previously prepared powder TiO2-Cu2O nanostructure. In this work a fluorine-doped tin oxide (FTO) glass sheet was used as a substrate and the doctor-blade coating technique has been employed to make TiO2-Cu2O thin films. Although this technique has a widespread use in the fabrication of solar cells to the best of our knowledge this is the first report on supported TiO2-Cu2O photocatalytic systems prepared by this method. To optimize the performance of the TiO2- Cu2O thin film under visible light irradiation, the chemical composition of the doctor-blading paste and the temperature of the final thermal treatment step was studied. It was found that both the paste composition and the heat treatment step played an important role in the material properties. When the film contained ethyl cellulose the minimum temperature to remove organic additives was 350 °C. Whereas for the films containing only alpha terpineol 300 °C was sufficient. It was revealed that the higher temperature treatment resulted in more oxidized films which were also shown in their deeper colour. The most effective film under visible light irradiation was TC-0-300 which contained no cellulose and was treated at the lowest temperature.
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Al-Nayili, Abbas. "Novel Lewis acidic zeolites as heterogeneous catalysts for liquid phase chemistry." Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/107295/.
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Porous Lewis acids are rapidly emerging heterogeneous catalysts, particularly for the upgrading of biorenewable feedstocks, due to their ability to coordinate lone-electron pairs from oxygen atom, hence inducing molecular rearrangements and cleavage. As such, this study tackles one of the most important challenges in liquid phase catalytic chemistry, namely the design of novel Lewis acidic zeolites to act as heterogeneous catalysts for liquid phase applications. Lewis acidic (Sn-BEA) zeolites are typically synthesised by highly complicated hydrothermal synthesis procedures, which have significant downsides preventing industrial application. In addition to technical difficulties, some drawbacks minimize the effectiveness of Sn-BEA in industrial interest. Amongst these limitations are 1) long crystallization time (40 days), 2) the large crystallite sizes obtained via typical hydrothermal synthesis, resulting in mass-transfer issues, and 3) the low Sn amount (typically < 2 wt.%), resulting in low space-time yield. Furthermore, a relatively amount of undesirable HF is required to induce crystallisation. Therefore, much academic and industrial research is currently devoted to the development of new methodologies for preparing Lewis-acid zeolite catalysts with higher or similar activity. The broad context at this doctoral dissertation is to investigate the potential of acid leaching (i.e., demetallation) of commercial (Al-containing) BEA zeolite as a simple, versatile, and scalable method to introduce different amounts of active centers (Sn) in zeolites, using solid-state incorporation (SSI). To evaluate the activity of the synthesized catalysts, the study focused firstly on the Meerwein-Ponndorf-Verley (MPV) transfer hydrogenation of carbonyl compounds and isomerization of glucose. Owing to the low activity of Sn-BEA micropores catalyst for the activation of bulky molecules, mesopores are subsequently created via top-down alkaline treatment to synthesis hierarchical Lewis-acid porous zeolite (Sn-h*-BEA), by employing the post-synthetic demetallation route. This catalyst, was evaluated in reactions that involve bulky molecules, such as cyclooctanone (C8) and cyclododecanone (C12). Sn-h*-BEA was found to be active, selective and more stable for continuous operation than its purely microporous analogue. Subsequent work focused on the catalytic valorisation of bio-renewable feedstock, which often relies upon multi-stage processing of highly-functionalised substrates, resulting in selectivity and process engineering challengers. Later parts of this thesis therefore report the synthesis of a novel acid-base bifunctional catalyst [Sn-Al] BEA which contains Sn-related Lewis acid sites and Al-related BrØnsted acid sites. This bifunctional catalyst has been tested, as a catalyst for the cascade catalytic transfer hydrogenation and etherification of furfural, under batch as well as continuous flow reaction condition. With this catalyst, furfural was first converted by Lewis acid Sn(Ⅳ) framework sites to form furfural alcohol via transfer hydrogenation from the solvent. Subsequently, furfuryl alcohol etherification with the solvent is catalysed by the BrØnsted acid (Al) framework to produce corresponding alkyl furfuryl ether. Such ethers are highly desirable as bio renewable fuel additives.
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Kruger, Dawid. "Gas phase heterogeneous catalyst performance testing in laboratory fixed-bed reactors." Master's thesis, Faculty of Engineering and the Built Environment, 2019. http://hdl.handle.net/11427/31115.
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Activity, selectivity and stability are invariably among the key factors of the performance of a catalyst. In the development of catalysts these properties are often screened for a range of materials and formulations. Interpretation of these key performance indicators are prone to various confounding effects. Here, performance testing of solid, porous catalysts for gas phase reactions in tubular fixed bed reactors is considered. Transport limitations and particularly internal mass transfer limitations are often cited in this case. Many have given general discussions and guides for effective catalyst performance testing, reviewed or put forward theoretical descriptions for transport phenomena and have measured and correlated associated transport coefficients. Some quantitative requirements and the relative importance of different effects have been found to remain unclear. Here, some of these aspects are addressed by the development of 3 catalyst testing criteria. Specifically, an upper limit is derived for the chemical conversion in a firstorder reaction such that differential rate conditions are established, a lower limit on the chemical conversion is applied to limit the loss of precision in conversion measurements, and an expression is derived to limit the effect of pressure drop across a catalyst bed on the observed rate of a first-order reaction. The prevalence and sensitivity of these and other transport limitation criteria were investigated theoretically in the context of the low-temperature (LT) water-gas shift (WGS) reaction over a Cu/ZnO/Al2O3 catalyst in a laboratory scale performance test. Factorial combination of some commonly manipulated experimental parameters (reactant feed rate, temperature, catalyst particle size, catalyst loading, dilution fraction and reactor tube size) was employed in this regard. The upper conversion limit, the internal mass transfer criterion and the radial heat transfer criterion were found to be particularly severe. So too, to a lesser extent, were the axial dispersion and pressure drop criteria, and the lower conversion limit. The sensitivity analysis indicated optima in the varied experimental parameters and yielded insights into effective control of different effects by selection of process conditions. Application of the set of criteria in an experimental performance test was demonstrated using a proprietary medium-temperature (MT), WGS catalyst under reaction at temperatures of 275 °C, 300 °C and 375 °C, 1 atm total pressure, dry feed composition of 10% CO, 10% CO2, 70% H2, 10% N2, steam-to-dry gas ratio of 0.5 and 158 h-1 weight hourly space velocity (WHSV). The catalyst was found to have near total selectivity towards the WGS reaction with activities of 12.2 ± 1.1, 17.1 ± 0.5 and 24.9 ± 1.5 µmol/s.gcat at 275 °C, 300 °C and 375 °C respectively. This corresponds to an activation energy of 39 ± 2 kJ/mol; a value within range of what is reported in literature for similar catalysts. This experiment also served to compare experimental and predicted internal mass transfer limitations by testing catalyst particles of different mean sizes. This catalyst as well as a CuO/ZnO/Al2O3 catalyst precursor was characterised in respect of their pore size distributions (N2 physisorption and mercury intrusion porosimetry (MIP)), particle size distributions (by photo- and microscopic analysis), bulk and particle densities and product gas compositions (by gas chromatography) to enable evaluation of the various criteria employed. Evaluation of the various criteria indicated that, theoretically, the considered confounding effects had a negligible effect on the measured catalytic activities for the catalyst sample with the smallest mean particle size, while the larger particles experienced only internal mass transfer limitations. Different models considered for effective diffusivities all under-predicted values when compared to the effective diffusivities inferred from the reaction-diffusion experiments. Predictions ranged to within factors of 3 – 20 of the experimental values, depending on whether pore size distribution data were derived from MIP or physisorption data. Here, the lack of characterisation of the macro-porosity by N2 physisorption resulted in more severe under-estimations of the effective diffusivities than the equivalent estimations made with MIP data. The best prediction was made by the ‘parallel-path pore’ model by Johnson & Stewart (1965) using MIP data. Predictions of internal mass transfer limitations varied in a similar manner. It is noted that the simplifications of the highly complex porous catalyst by these model combinations introduce large sources of error in the prediction of internal mass transfer limitations.
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Harding, Nathan. "Critical phenomena in spatial epidemic models with heterogeneous social dynamics." Thesis, University of Sydney, 2020. https://hdl.handle.net/2123/23410.
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Epidemics are a constant threat, able to bring the entire world to a halt in the case of extreme outbreaks. Computational epidemiology seeks to understand the spread of disease at a population rather than individual level. In this understanding, the field hopes to predict the spread of disease by either simulating microscopic interactions giving rise to infection, or by using mean-field models to emulate the average resultant epidemic spread. This knowledge can be used to predict the future spread of disease and create specific intervention strategies which exploit our understanding of disease spread. The epidemic threshold, the level of infectiousness below which epidemics will not persist, but above which, large levels of infections are maintained, is key to this epidemic analysis. In this pursuit, understanding criticality in the form of the epidemic threshold is frequently studied, however many questions remain unanswered. Another significant challenge to epidemic modeling is the accurate representation of population mobility, as it forms the basis of long range transmission events, and its accuracy directly impacts the relevance of a model to real scenarios. In particular, moving beyond a static treatment of mobility factors into dynamic treatments presents a significant additional step in both modeling and criticality analysis. Specifically, some open challenges addressed in this thesis are: i) Understanding critical thresholds of epidemics in the language of statistical mechanics where phase transitions are rigorously defined. ii) Improving frameworks for the treatment of mobility in epidemic models and criticality analysis of models with dynamic mobility. iii) Extending analysis of critical phenomena for epidemic models with dynamic mobility . iv) Understanding the specific implications of Australian demographics, mobility and geography on the critical dynamics of epidemic spread.
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Oliveira, Pisco Angela. "Drug resistance mechanisms in cancer heterogeneous populations." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/drug-resistance-mechanisms-in-cancer-heterogeneous-populations(a5f2d318-3fd2-4491-84a5-fd2d69ac1b40).html.
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The development of drug resistance during treatment is possibly the most important factor hampering the success of cancer therapy. In order to survive in the presence of chemotherapeutic drugs cells must quickly adapt to their altered environment. This may involve a collective stress response of interacting cells, whose mechanism is not yet clear. In the course of this work we interrogated the conceptual framework used to describe cancer and examined different aspects of drug resistance. While the main focus was on the role of ABC transporters in the rapid acquisition of drug resistance following a short period of drug treatment, the long-term adaptation to continuous drug treatment was also studied. As a tangent to this subject, the possible role of endocytosis in the process of adaptation to continuous presence of drug and subsequent resistance was also assessed. Cancer cell populations inexorably develop resistance to therapeutic treatment. In addition to selection of genetic variants, resistance may arise through two possible non-genetic mechanisms, (1) Darwinian selection of cells occupying (non-genetic) resistant microstates, or (2) Lamarckian instruction, in which cells adopt a resistant (treatment) induced phenotype. To examine the relative contribution of these two mechanisms we studied the population dynamics of leukemic cells (HL60 cell line) following treatment with the mitotic inhibitor vincristine. Single-cell analysis and mathematical modelling of state transition kinetics demonstrated that the appearance of multi-drug resistance phenotype within 24h was overwhelmingly the result of instruction. Transcriptome dynamics pointed towards a genome-wide state transition into a stress response state. Resistance induction correlated with Wnt pathway upregulation and was suppressed by beta-catenin knockdown, revealing a new opportunity for early therapeutic intervention against the development of drug resistance. By addressing the adaptation of the cell culture to prolonged drug treatment we observed that the survivor cells mounted a cellular response that neutralised the cytotoxic stress. That response involved the stabilisation of a transcriptome state that confers drug resistance. Our results suggested that the positive correlation between Wnt signalling and ABC transporters expression is important not only for the short-term survival but also for the enduring MDR phenotype. As we explored population heterogeneity we realised that the dead cells might also help the rest of the population to survive. Thus, our results support the need for examining the role of each population fraction, and ultimately each individual cell, in the overall story of cancer adaptation towards multidrug resistance. Subsequently we examined the differential endocytic behaviour between drug-sensitive and drug-resistant cells. By combining confocal time-lapse microscopy with flow cytometry we demonstrated that fluid-phase endocytosis was reduced in the resistant cells. The differences in the endocytic pathway only became noticeable after MDR1 expression has become constitutive, suggesting another protective role of the ABC transporters. All the results obtained support the idea that acquired drug resistance is not simply the passive selection of pre-existing mutants but can be accelerated by active adaptation. Cancer treatment is a double-edge sword: while the weakest cells die, the survivors cope cell-autonomously with the therapeutic perturbation.
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Ravenelle, Ryan M. "Heterogeneous catalysts in aqueous phase reforming environments: an investigation of material stability." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42921.
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There are many problems associated with the use of fossil fuels to produce fuels and chemicals, and lignocellulosic biomass stands as a promising alternative fuel/chemical feedstock. Large scale processing of biomass will likely take place in high temperature liquid water due to the low vapor pressure and polar nature of carbohydrates. However, little is known about the material stability of these catalysts in high temperature aqueous phase environments. This dissertation aims to investigate the structural integrity of some common catalytic materials under typical biomass reforming conditions. There are 3 main objectives of this study: 1) identify potentially stable candidates from commonly used materials, 2) understand the mechanism(s) by which these catalysts degrade, 3) design/modify catalysts in an effort to increase their hydrothermal stability. The two main materials investigated in this work are zeolites (faujasite, ZSM-5) and γ-Al2O3 as these are commonly used as catalysts and catalyst supports. A number of physicochemical techniques were used to characterize the materials as a function of treatment time at conditions relevant for biomass reforming. For zeolites, the major findings are that ZSM-5 framework is highly stable whereas faujasite stability depends on the Si/Al ratio, where silicon rich materials are less stable. For γ-Al2O3 based catalysts, it was found that the alumina support hydrates and undergoes a phase transformation to form crystalline boehmite (AlOOH) with a subsequent loss in surface area and Lewis acid sites. When metal particles are present on the support, the phase change kinetics are slowed. The role of metal precursor on the stability of γ-Al2O3 supported catalysts was also explored, and it was found that the precursor used in catalyst synthesis changes the boehmite formation kinetics and also affects alumina support dissolution. The final thrust aims to stabilize a Pt/γ-Al2O3 catalyst by depositing silicon on the catalyst surface. The silicon modification is effective in protecting the catalyst from boehmite formation upon exposure to hot liquid water while also stabilizing metal particles against sintering. Additionally, an increase in turnover number for hydrogen production via aqueous phase reforming of sorbitol was observed.
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Roy, Babli. "Studies on Solid-Phase Organic Reactions & Catalysis: Greener Approaches." Thesis, University of North Bengal, 2016. http://ir.nbu.ac.in/handle/123456789/2761.
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Messele, Selamawit Ashagre. "Homogeneous and heterogeneous aqueous phase oxidation of phenol with fenton-like processes." Doctoral thesis, Universitat Rovira i Virgili, 2014. http://hdl.handle.net/10803/283319.
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A les passades dècades, s’han desenvolupat diverses tècniques basades en l’oxidació química a fi de superar els inconvenients associats al tractament d’aigües residuals industrials. Els processos d’oxidació avançada (AOPs) són efectius en la degradació de contaminants no biodegradables presents en aigües residuals i freqüentment permeten una quasi total degradació sota condicions raonables de pressió i temperatura. Entre elles, el procés Fenton és àmpliament utilitzat malgrat els seus molts inconvenients, com sensibilitat al pH, formació de fangs i pèrdua de les espècies actives. Aquest treball dissenya diferents alternatives de millora d’aquests inconvenients usant processos basats en Fenton per a l’oxidació homogènia i heterogènia de fenol. Així, l’addició d’agents quelants permet ampliar el rang efectiu de pH. Així mateix, l’ús de nanoferro zero valent suportat sobre materials carbonosos millora la capacitat d’eliminació i suprimeix la requerida separació del fang d’hidròxid de ferro.En las pasadas décadas, se desarrollaron diversas técnicas basadas en la oxidación química para superar los inconvenientes asociados al tratamiento de aguas residuales industriales. Los procesos de oxidación avanzada (AOPs) son efectivos en la degradación de contaminantes no biodegradables presentes en aguas residuales y frecuentemente permiten una casi total degradación bajo condiciones razonables de presión y temperatura. Entre ellas, el proceso Fenton es ampliamente utilizado pese a sus muchos inconvenientes, como sensibilidad al pH, formación de fangos y pérdida de las especies activas. Este trabajo diseña diferentes alternativas de mejora de estos inconvenientes usando procesos basados en Fenton para la oxidación homogénea y heterogénea de fenol. Así, la adición de agentes quelantes permite ampliar el rango efectivo de pH. Igualment, el uso de nanohierro cero valente soportado sobre materiales carbonosos mejora la capacidad de eliminación y suprime la requerida separación del fango de hidróxido de hierro.
In the last decades, various chemical oxidation techniques have been developed to overcome the inconveniences associated to conventional treatment of industrial wastewaters. Advanced oxidation processes (AOPs) have been reported to be effective for the degradation of soluble organic contaminants from wastewaters containing non-biodegradable organic pollutants, because they can often provide an almost total degradation, under reasonably mild conditions of temperature and pressure. Among them, Fenton process is widely implemented, although it has many drawbacks such as pH sensitivity, formation of sludge and loss of active species. Therefore, this work is specially focused on different alternatives to overcome the above drawbacks using Fenton-like processes for homogeneous and heterogeneous oxidation of phenol. Thus, the addition of chelating agents allowed broading the pH range of efficient operation. In turn, the use of nano zero valent iron supported on carbon materials enhances the removal performance and eliminates the subsequent separation of iron hydroxide sludge.
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Kennedy, Karen Alyce. "Characterization of Phase Equilibrium associated with Heterogeneous Polymerizations in Supercritical Carbon Dioxide." NCSU, 2003. http://www.lib.ncsu.edu/theses/available/etd-10092003-214255/.
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This thesis details research to understand the phase equilibrium associated with heterogeneous polymerizations in supercritical carbon dioxide (scCO2), particularly the polymerization of vinylidene fluoride (VF2) in scCO2. Knowledge of the equilibrium between the supercritical fluid and polymer phases may be applied to understanding the mechanisms involved in heterogeneous polymerizations in scCO2. Several experimental systems were developed and/or utilized for measuring the phase equilibrium. These included a system for measuring the swelling of solid polymer particles in the presence of scCO2, a system for measuring the mass sorption and diffusion of supercritical fluids into the polymer phase, and a system for measuring the partitioning of reactant species between the polymer and supercritical fluid phases. The sorption and swelling of poly(vinylidene fluoride) (PVDF) was measured at conditions similar to those of the polymerizations. The Sanchez-Lacombe equation of state was applied to modeling the binary and ternary phase equilibria for the VF2-CO2-PVDF system. Carbon dioxide exhibits a favorable interaction with PVDF that is enhanced at increasing fluid densities. Additionally, the monomer exhibits a favorable interaction with PVDF that improves the mass sorption into the polymer phase and expands the tunability of the fluid to change the polymer properties. The impact of the phase equilibrium on the precipitation polymerization of vinylidene fluoride in scCO2 is discussed. The bimodal molecular weight distribution of PVDF synthesized in CO2 could be due, in part, to the sorption of VF2 into the polymer phase and the plasticization of the polymer to facilitate propagation of the polymer chains to high molecular weights within the polymer particles. This dissertation provides a foundation for understanding the impact of the phase equilibrium on heterogeneous polymerizations in supercritical carbon dioxide. It provides techniques for identifying and improving conditions for polymerizations in supercritical carbon dioxide and optimizing CO2-based processes of a heterogeneous nature.
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Ju, Xiumin. "Reductive Dehalogenation of Gas-phase Trichloroethylene using Heterogeneous Catalytic and Electrochemical Methods." Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1366%5F1%5Fm.pdf&type=application/pdf.
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FERNANDEZ, FABRICIO. "NUMERICAL MODELLING OF TWO-PHASE FLOW AND CONTAMINANT TRANSPORT IN HETEROGENEOUS MEDIA." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2015. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=33644@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
PROGRAMA DE EXCELENCIA ACADEMICA
O objetivo deste trabalho é ser uma contribuição ao entendimento dos mecanismos envolvidos na migração por gravidade dos compostos orgânicos chamados de DNAPLs, quando eles são liberados em meios porosos e em meios porosos fraturados, para aportar ao desenvolvimento de tecnologias efetivas orientadas principalmente à localização e à remediação do sistema subterrâneo contaminado. Primeiramente são apresentados os conceitos elementares envolvidos nos modelos matemáticos que descrevem o fluxo bifásico em meios porosos, o processo de modelagem de um problema geral da natureza, os modelos conceituais, os matemáticos e os numéricos, e a aplicabilidade dos modelos conceituais conforme a considerações de escala. Em segundo lugar, são desenvolvidas as equações matemáticas que governam os fenômenos em estudo e são apresentadas as soluções às equações governantes a partir de técnicas computacionais e esquemas de integração numérica. As equações do fluxo bifásico são resolvidas mediante técnicas de elementos finitos mistos hibridizados (EFHM) e elementos finitos descontínuos (GD), e as equações do transporte de contaminantes são resolvidas mediante a técnica dos elementos finitos convencionais (EF). Seguidamente são avaliados numericamente problemas de transporte de contaminantes em 1D e 2D, problemas de transporte de contaminantes com transferência de massa, problemas de fluxo bifásico em 2D, e problemas acoplados envolvendo tanto fluxo bifásico como transporte de contaminantes com transferência de massa. Finalmente, são apresentadas as conclusões do trabalho desenvolvido bem como sugestões para trabalhos futuros.
The objective of this work is to contribute to the understanding of the mechanisms involved in the gravity migration of organic compounds, called DNAPLs, when they are released in a porous media and in a fractured porous media, and to contribute to the development of effective technologies mainly oriented to the location and remediation of contaminated underground system. Firstly, some basic concepts are presented, especially those involved in the mathematical models that describe the two-phase flow in porous media, the conceptual models, the mathematical models, as well as the numerical models. Secondly, the mathematical equations that govern the phenomena under study are developed and the solutions to the governing equations from computational techniques and numerical integration schemes are presented. The biphasic flow equations are solved using mixed and hybridized finite element techniques (EFHM) and discontinuous finite element (GD), and the contaminant transport equations are solved by the conventional technique of finite element (FE). Then, some problems are numerically evaluated in 1D and 2D, such as transport of contaminants with and without mass transfer, two-phase flow problems in 2D, and attached problems involving both biphasic flow and contaminant transport with mass transfer. Finally, the conclusions of this thesis as well as the suggestions for future works are presented.
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Schnitzer, Jill. "Liquid phase hydroformylation by zeolite supported rhodium." Thesis, Virginia Tech, 1985. http://hdl.handle.net/10919/45732.
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The purpose of this research was to directly compare the behavior of zeolites containing rhodium with that of homogeneous rhodium species as catalysts for liquid phase hydroformylation of 1-hexene in order to study the effects of zeolite immobilization. NaX zeolite was cation exchanged with several rhodium salts and used as hydroformylation catalysts at 50°C and 125°C in the presence of: triphenylphosphine (PPh₃), dimethylphenylphosphine (PMe₂Ph), and the poison for zeolite surface and solution rhodium: triphenylmethylmercaptan (Ph₃CSH). The results of these experiments were compared with those of several homogeneous catalysts under similar conditions.
It was found that previously reported results of intrazeolitic activity with RhNaX at 50°C were probably incorrect, since, the addition of PMe₂Ph, Ph₃CSH, or both, virtually halted all reactivity of RhNax.
The catalytic results at 125°C did not conclusively indicate the location of the active rhodium. Thus, intrazeolitic activity at 125°C may or may not have been observed, and needs further investigation.
Reaction profiles were obtained for several of the catalyst systems, using an automatic sampling system. From these profiles, it was found that the addition of excess PMe₂Ph halted isomerization of 1-hexene to 2-hexenes for the zeolite-supported rhodium, and hindered, but did not stop isomerization for the homogeneous catalysts. Also, as expected, it was observed that the homogeneous catalysts reacted to completion faster than the heterogeneous catalyst.
In addition, the effects of such treatments as preheating in air and precarbonylation of the heterogeneous catalysts were studied. Pretreatments had no effect upon the catalysis. Also, no activity was observed from the heterogeneous catalysts at 125°C unless phosphines were present.
Finally, the hydrogenation of 1-hexene was studied. Heterogeneous and homogeneous rhodium catalysts showed hydrogenation activity which was accompanied by isomerization at 60°C and 125°C.Master of Science
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Niessner, Jennifer. "Multi-scale modeling of multi-phase-multi-component processes in heterogeneous porous media." Stuttgart Inst. für Wasserbau, 2006. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-27697.
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Ab, Rahim Mohd Hasbi. "Heterogeneous gold, palladium and copper based catalysts for liquid phase oxidation of methane." Thesis, Cardiff University, 2011. http://orca.cf.ac.uk/55125/.
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The oxidation of lower alkanes especially methane to methanol under mild reaction conditions is one of the most challenging task for industry and academia. At present, indirect utilisation via synthesis gas is the only commercially viable process for methanol production. Therefore, this study intends to investigate the direct oxidation of methane to methanol using a novel low temperature approach. Recently, gold based supported catalysts have been found to be highly effective oxidation catalysts where a number of important discoveries have been made such as in hydrogen peroxide synthesis and selective oxidation of alcohols to aldehydes. Due to these recent advances, further work into the oxidation of carbon-hydrogen bonds especially methane by gold and gold-palladium alloyed nanoparticles was the central topic of this study. As a proof of concept for the following studies, oxidation of primary C-H bonds in toluene and toluene derivatives were carried out in a high pressure stirred autoclave with molecular oxygen as oxidant. It was evident that Au-Pd supported catalyst is capable in oxidising primary C-H bonds on toluene and toluene derivatives at lower temperature with high catalytic activity based on turnover number (TON) compared to available heterogeneous catalysts reported in literature. However, these catalysts are ineffective in the oxidation of methane with oxygen under mild conditions with water as solvent and temperature below 90 °C. In view of this, hydrogen peroxide has been used as oxidant and it was shown that Au-Pd supported nanoparticles are active for the oxidation of methane giving high selectivity to methanol especially in the reactions carried out with hydrogen peroxide generated using an in-situ approach. Methane oxidation reactions were carried out in aqueous medium. The main products were methanol, methyl hydroperoxide and only carbon dioxide as overoxidation product. Investigations of reaction conditions such as concentration of oxidant, reaction time, reaction temperature and pressure of methane were investigated. It was found that the activity and selectivity of the catalyst was highly dependant on these variables. Oxygenate productivity was found to increase by increasing the H2O 2 or H2/O2 concentration and methane pressure. Longer reaction times were detrimental to the methanol selectivity where overoxidation reaction occurred. Interestingly, the Au-Pd catalytic system was able to oxidise methane to methanol at temperatures as low as 2 °C. The applicability of the developed catalytic system was tested on ethane oxidation reaction and it successfully produced ethanol as the major product. The oxygenate productivity was higher as compared to methane due to the solubility factor and the difference in the strength of carbon-hydrogen bonds. The catalyst preparation method and pretreatment were shown to be very important in the formation of active catalysts. The Au-Pd alloy having Au core-palladium shell structure with PdO dominance on the surface and bigger particle size was preferred than analogue catalyst consists of Au and Pd in metallic state with smaller particle size. In addition to that, the choice of support is crucial and this study discovered TiO: as a preferred support where it could assist in stabilising the active hydroperoxy species. The Au:Pd ratio was also found to be an important variable, and equal weight ratio between Au and Pd was shown to be the optimised ratio for methane oxidation either using addition of H2O2 or in-situ H2O2 approach. The synergistic effect of Au and Pd was confirmed by superior catalytic activity compared to monometallic catalysts. Reaction mechanism was proposed and it was based on catalytic evaluation data, stability of the products and oxidation with radical scavengers. The proposed mechanism was in line with the theoretical modelling studies on similar catalytic systems. Optimisation of Au based supported catalyst with copper as co-metal supported on TiO2 was shown to improve the oxygenate productivity and methanol selectivity as well as enhanced the H2O 2 utilisation. In particular, trimetallic 5wt%AuPdl.0wt%Cu/TiO 2 synthesised via impregnation method and calcined in static air gave more than double turn over frequency (TOF = 1.404) with methanol selectivity around 83% as compared to bimetallic 5wt%Au-Pd/TiO2 catalyst (TOF = 0.692, methanol selectivity = 49%). It was suggested in this study that copper is responsible in enhancing the formation of intermediate methyl hydroperoxide species and in some extent to block the non-selective sites for hydrogen peroxide decomposition and hydrogenation by disrupting the surface structure of Au-Pd alloy whilst at the same time maintaining the active sites (Au-Pd alloy) responsible for selective formation of methanol. The oxidation state of copper was shown to be the main factor in controlling the catalytic activity and selectivity. Copper in a combination of multiple oxidation states was preferred than single oxidation state.
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PASSOS, NATHALIA CHRISTINA DE SOUZA TAVARES. "NUMERICAL PROCEDURES FOR THE ANALYSIS OF TWO PHASE FLOW IN HETEROGENEOUS POROUS MEDIA." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2013. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=23193@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
A modelagem numérica precisa de reservatórios de petróleo ainda é um desafio, devido às heterogeneidades do meio poroso e à existência de estruturas geológicas com geometrias complexas, tais como: fraturas, estratificações e heterogeneidades, que influenciam decisivamente o escoamento dos fluidos através dessas formações. O presente trabalho analisa a implementação de duas formulações numéricas aplicadas ao fluxo bifásico em meios porosos em que se procura contornar as dificuldades mencionadas acima. Inicialmente, avalia-se uma formulação numérica que emprega um processo em três passos: o método dos elementos finitos, EF, para a solução da equação da pressão, intermediariamente, utiliza-se o método de Raviart-Thomas de mais baixa ordem, RT 0, para melhor aproximação da velocidade, e a resolução da equação da saturação pelo método dos elementos finitos descontínuos, MEFD. Também é avaliada uma formulação na qual se utiliza o método dos elementos finitos mistos e híbridos, EFH, para aproximar a equação da pressão, e o método MEFD para aproximar somente a equação de saturação. O estudo dessas formulações busca avaliar a conservação de massa e analisar o esforço computacional despendido. São apresentados exemplos que avaliam cada uma das formulações em comparação com resultados da literatura.
Accurate numerical modeling of oil reservoirs is still a challenge due to heterogeneity of the porous medium and the existence of geological structures with complex geometries, such as fractures, stratifications and heterogeneities that decisively influence the flow of fluids through these formations. This paper analyzes two numerical formulations of two-phase flow that seek to circumvent the difficulties mentioned. Initially, it evaluates a numerical formulation that employs a three step process: the finite element method, for solving the pressure equation, intermediately, it uses the lowest-order Raviart-Thomas, RT 0,to the best approximation of the flow velocities, and finally the solution of the saturation equation by discontinuous finite element method (MEFD). Additionally, a formulation which utilizes the mixed and hybrid finite element method (EFH), to approximate the pressure equation, and uses MEFD to approximate the saturation equation. Both implemented formulations aim to assess the mass conservation and to analyze the necessary computational effort. Examples are presented which evaluate each of the formulations as compared with results existing in literature.
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Fu, Xin 1973. "Stochastic analysis of dense nonaqueous phase liquid dissolution in naturally heterogeneous subsurface systems." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/29283.
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Thesis (Ph. D .)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, February 2003.Includes bibliographical references (p. 186-192).
Field-scale Dense Nonaqueous Phase Liquid (DNAPL) dissolution in three-dimensional heterogeneous subsurface systems is investigated using a stochastic approach that treats the variability of flow properties as three-dimensional random fields. A steady-state, quasi-static DNAPL saturation distribution in a source zone is derived, based on the previous research to describe the field-scale nonuniform residual DNAPL distribution. A local-scale dissolution model is generalized from the laboratory experimental results. Effective transport and dissolution properties are obtained by a stochastic analysis, which includes nonstationarity in the concentration field to address both boundary and downstream effects. An extrapolation of the effective properties is performed for the large spatial variability of hydraulic and dissolution parameters. The extrapolation is evaluated using a unique two-zone model that simplifies the continuous DNAPL distribution to two components: low permeability lens zone with high DNAPL saturation and a surrounding permeable zone with low DNAPL saturation. The agreement between the two-zone model results with stochastic solutions demonstrates the adequacy of the extrapolation of the latter. Four field sites with different geological settings and hydraulic characteristics are evaluated using effective properties: the Borden site, the Cape Cod aquifer, the Savannah River Site and the Hanford site.
(cont.) The theoretical prediction is compared with the DNAPL concentration data from the Hanford site, where millions of pounds carbon tetrachloride were dumped in disposal facilities. In spite of the error and uncertainty involved in the field data, there is reasonable agreement between the field observations and the predicted mean DNAPL concentration field. It is concluded that the dominant factor affecting the field-scale DNAPL dissolution is the variability of the dissolution rate coefficient, which is a function of spatial distribution of DNAPL and permeability. The bypassing effect, reflecting the diversion of water flow around zones of high DNAPL saturation with low aqueous relative permeability, is another important factor that can reduce the effective dissolution rate significantly. The limitations of the study are discussed regarding the data collection and further evaluation of the extrapolation.
by Xin Fu.
Ph.D .
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Xu, Chunli. "Preparation and characterisation of MgO : a heterogeneous basic catalyst for liquid phase reactions." Thesis, Cardiff University, 2006. http://orca.cf.ac.uk/55646/.
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We systematically studied the preparation method of magnesium oxide as cheap heterogeneous basic catalysts, and found a very simple method to obtain MgO with high surface area and high catalytic activity. Furthermore, the structure of MgO was characterized using many techniques, such as BET, TGA, XRD and SEM. The relationship of catalytic activity and structure of MgO has been investigated in detail. At last, the obtained MgO was used in the liquid phase reactions, including Meerwein-Pondorf-Verley reaction, Michael addition, Knoevenagel condensation, transesterification of vegetable oil to biodiesel and synthesis of P-Keto 1,3-dithianes. The prepared magnesium oxide catalyst was used in the liquid phase Meerwein-Pondorf-Verley reaction of benzaldehyde with alcohol. Effect of preparation method on the catalytic activity and structure of MgO has been investigated in detail. The experimental result showed that the optimal calcination temperature was 450 °C. Lithium supported magnesium oxide was also studied. Magnesium oxide obtained using a novel but simple procedure was systematically investigated as a heterogeneous base catalyst for the Michael addition and Knoevenagel condensation. The activity of MgO was studied in detail, together with the effects of solvent and of substrate on the catalytic activity for each type of reaction. A key finding is that the formation of enols affected the activity of MgO. The preparation method and activity of MgO was determined and compared with CaO. MgO was used for the first time as a heterogeneous basic catalyst to synthesis P-keto-1,3-dithianes from conjugated ynones and ynoates. It was found that MgO is an active catalyst with activity better than or comparable with previously identified homogeneous or heterogeneous catalysts for this reaction. The effect of preparation methods on the activity of MgO is described. Transesterification of vegetable oil to biodiesel with MgO as catalyst was studied at 60 °C and 200 °C, respectively. Effect of methanol-to-oil molar ratio, catalyst loading, reaction temperature and calcination temperature was investigated. 90% yield can be obtained at 60 °C for 3h, and 80% at 200 °C for 15min. The results showed that the prepared MgO was active for the synthesis of biodiesel.
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Paul, Maren. "Simulation of two-phase flow processes in heterogeneous porous media with adaptive methods." [S.l. : s.n.], 2003. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB12168132.
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Papafotiou, Alexandros. "Numerical investigations of the role of hysteresis in heterogeneous two-phase flow systems." [S.l. : s.n.], 2008. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-35679.
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Herbert, Ross James. "Modelling studies on the impact of heterogeneous ice nucleation on mixed-phase clouds." Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/7291/.
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Clouds are a critical component of Earth’s climate and hydrological cycle. The formation of ice in the atmosphere, especially at lower altitudes, can substantially impact the evolution of clouds and their radiative properties, and represents the initiation of the cold rain precipitation process. In mixed-phase clouds quantitatively understanding the interactions between ice and liquid, and the subsequent impact on the cloud development, is fundamentally dependent on the process of ice formation and its representation within cloud models. Experiments show that ice nucleating particles (INPs) exhibit variability in both freezing efficiency and time-dependent behaviour. The variability in freezing efficiency is currently well characterised and represented, but variability in time-dependence is poorly characterised and rarely represented in models and parameterisations. The primary aim of this thesis is to understand the role that time-dependence plays in the freezing behaviour of droplets, and secondly to examine the sensitivity of mixed-phase clouds to time-dependence in immersion mode freezing. It is initially found that CNT-based models are unable to reproduce the observed time-dependent behaviour. A new model is therefore presented that uniquely incorporates the variability in both freezing efficiency and time-dependent behaviour; this is applied to experimental data to understand the manifestation of time-dependence in experiments. The model is then used to derive a new theoretical framework for use in experimental analysis and cloud modelling studies. The framework is underpinned by the finding that the temperature dependence (named λ) of the nucleation rate coefficient solely determines the time-dependent behaviour observed in droplet freezing experiments. New and existing experimental data is used to demonstrate the ability for the framework to reconcile data obtained on different timescales with different experimental methods. Finally, an efficient and representative parameterisation is used to explore the sensitivity of mixed-phase clouds to time-dependence. Using a series of increasingly complex models (0D to 2D) it is shown that the inclusion of time-dependence impacts cloud properties in regimes where the updraught speed is relatively low.
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Dumbre, D. K. "Selective liquid phase alcohol oxidation and heck- type coupling reactions using heterogeneous catalysts." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2008. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2701.
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Jha, A. "Development of heterogeneous catalysts for liquid phase hydroxyalkylation and oxidation of phenolic compounds." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2013. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/1927.
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Sayar, Sepideh. "Heat Transfer During Melting and Solidification in Heterogeneous Materials." Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/36147.
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A one-dimensional model of a heterogeneous material consisting of a matrix with embedded separated particles is considered, and the melting or solidification of the particles is investigated. The matrix is in imperfect contact with the particles, and the lumped capacity approximation applies to each individual particle. Heat is generated inside the particles or is transferred from the matrix to the particles coupled through a contact conductance. The matrix is not allowed to change phase and energy is either generated inside the matrix or transferred from the boundaries, which is initially conducted through the matrix material. The physical model of this coupled, two-step heat transfer process is solved using the energy method.
The investigation is conducted in several phases using a building block approach. First, a lumped capacity system during phase transition is studied, then a one-dimensional homogeneous material during phase change is investigated, and finally the one-dimensional heterogeneous material is analyzed. A numerical solution based on the finite difference method is used to solve the model equations. This method allows for any kind of boundary conditions, any combination of material properties, particle sizes and contact conductance. In addition, computer programs, using Mathematica, are developed for the lumped capacity system, homogeneous material, and heterogeneous material. Results show the effects of control volume thickness, time step, contact conductance, material properties, internal sources, and external sources.Master of Science
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Beydoun, Hassan. "Advances in Heterogeneous Ice Nucleation Research: Theoretical Modeling and Measurements." Research Showcase @ CMU, 2017. http://repository.cmu.edu/dissertations/793.
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In the atmosphere, cloud droplets can remain in a supercooled liquid phase at temperatures as low as -40 °C. Above this temperature, cloud droplets freeze via heterogeneous ice nucleation whereby a rare and poorly understood subset of atmospheric particles catalyze the ice phase transition. As the phase state of clouds is critical in determining their radiative properties and lifetime, deficiencies in our understanding of heterogeneous ice nucleation poses a large uncertainty on our efforts to predict human induced global climate change. Experimental challenges in properly simulating particle-induced freezing processes under atmospherically relevant conditions have largely contributed to the absence of a well-established model and parameterizations that accurately predict heterogeneous ice nucleation. Conversely, the sparsity of reliable measurement techniques available struggle to be interpreted by a single consistent theoretical or empirical framework, which results in layers of uncertainty when attempting to extrapolate useful information regarding ice nucleation for use in atmospheric cloud models. In this dissertation a new framework for describing heterogeneous ice nucleation is developed. Starting from classical nucleation theory, the surface of an ice nucleating particle is treated as a continuum of heterogeneous ice nucleating activity and a particle specific distribution of this activity g is derived. It is hypothesized that an individual particle species exhibits a critical surface area. Above this critical area the ice nucleating activity of a particle species can be described by one g distribution, 𝑔, while below it 𝑔 expresses itself expresses externally resulting in particle to particle variability in ice nucleating activity. The framework is supported by cold plate droplet freezing measurements for dust and biological particles in which the total surface area of particle material available is varied. Freezing spectra above a certain surface area are shown to be successfully fitted with 𝑔 while a process of random sampling from 𝑔 can predict the freezing behavior below the identified critical surface area threshold. The framework is then extended to account for droplets composed of multiple particle species and successfully applied to predict the freezing spectra of a mixed proxy for an atmospheric dust-biological particle system. The contact freezing mode of ice nucleation, whereby a particle induces freezing upon collision with a droplet, is thought to be more efficient than particle initiated immersion freezing from within the droplet bulk. However, it has been a decades’ long challenge to accurately measure this ice nucleation mode, since it necessitates reliably measuring the rate at which particles hit a droplet surface combined with direct determination of freezing onset. In an effort to remedy this longstanding deficiency a temperature controlled chilled aerosol optical tweezers capable of stably isolating water droplets in air at subzero temperatures has been designed and implemented. The new temperature controlled system retains the powerful capabilities of traditional aerosol optical tweezers: retrieval of a cavity enhanced Raman spectrum which could be used to accurately determine the size and refractive index of a trapped droplet. With these capabilities, it is estimated that the design can achieve ice supersaturation conditions at the droplet surface. It was also found that a KCl aqueous droplet simultaneously cooling and evaporating exhibited a significantly higher measured refractive index at its surface than when it was held at a steady state temperature. This implies the potential of a “salting out” process. Sensitivity of the cavity enhanced Raman spectrum as well as the visual image of a trapped droplet to dust particle collisions is shown, an important step in measuring collision frequencies of dust particles with a trapped droplet. These results may pave the way for future experiments of the exceptionally poorly understood contact freezing mode of ice nucleation.
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Zheng, Xiaobo. "A Computational Investigation of Hydrocarbon Cracking: Gas Phase and Heterogeneous Catalytic Reactions on Zeolites." Diss., Tucson, Arizona : University of Arizona, 2006. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1455%5F1%5Fm.pdf&type=application/pdf.
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Fagerlund, Fritjof. "Experimental and Modelling Studies on the Spreading of Non-Aqueous Phase Liquids in Heterogeneous Media." Doctoral thesis, Uppsala universitet, Institutionen för geovetenskaper, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7430.
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Non-Aqueous Phase Liquids (NAPLs) include commonly occurring organic contaminants such as gasoline, diesel fuel and chlorinated solvents. When released to subsurface environments their spreading is a complex process of multi-component, multi-phase flow. This work has strived to develop new models and methods to describe the spreading of NAPLs in heterogeneous geological media. For two-phase systems, infiltration and immobilisation of NAPL in stochastically heterogeneous, water-saturated media were investigated. First, a methodology to continuously measure NAPL saturations in space and time in a two-dimensional experiment setup, using multiple-energy x-ray-attenuation techniques, was developed. Second, a set of experiments on NAPL infiltration in carefully designed structures of well-known stochastic heterogeneity were conducted. Three detailed data-sets were generated and the importance of heterogeneity for both flow and the immobilised NAPL architecture was demonstrated. Third, the laboratory experiments were modelled with a continuum- and Darcy’s-law-based multi-phase flow model. Different models for the capillary pressure (Pc) – fluid saturation (S) – relative permeability (kr) constitutive relations were compared and tested against experimental observations. A method to account for NAPL immobility in dead-end pore-spaces during drainage was introduced and the importance of accounting for hysteresis and NAPL entrapment in the constitutive relations was demonstrated. NAPL migration in three-phase, water-NAPL-air systems was also studied. Different constitutive relations used in modelling of three-phase flow were analysed and compared to existing laboratory data. To improve model performance, a new formulation for the saturation dependence of tortuosity was introduced and different scaling options for the Pc-S relations were investigated. Finally, a method to model the spreading of multi-constituent contaminants using a single-component multi-phase model was developed. With the method, the migration behaviour of individual constituents in a mixture, e.g. benzene in gasoline, could be studied, which was demonstrated in a modelling study of a gasoline spill in connection with a transport accident.Flerfasföroreningar innefattar vanligt förekommande organiska vätskor som bensin, dieselolja och klorerade lösningsmedel. Spridningen av dessa föroreningar i mark är komplicerad och styrs av det samtidiga flödet av organisk vätska, vatten och markluft samt utbytet av komponenter (föroreningar) mellan de olika faserna. Detta arbete syftade till att utveckla nya metoder och modeller för att studera spridningen av flerfasföroreningar i mark: (i) En metodik utvecklades för att i laboratorium noggrant och kontinuerligt mäta hur en organisk vätska är rumsligt fördelad i en tvådimensionell experimentuppställning. Metoden baserades på röntgenutsläckning för olika energinivåer. (ii) Infiltration av organisk vätska i vattenmättade medier studerades för olika konfigurationer av geologisk heterogenitet. I experimentuppställningen packades olika sandmaterial noggrant för att konstruera en välkänd, stokastiskt heterogen struktur. Spridningsprocessen dokumenterades i tre detaljerade mätserier och heterogenitetens påverkan på flöde och kvarhållning av den organiska vätskan påvisades. (iii) Experimenten simulerades med en numerisk modell. Olika modeller prövades för att beskriva de grundläggande relationerna mellan kapillärtryck (Pc) vätskehalt (S) och relativ permeabilitet (kr) för detta tvåfassystem av vatten och organisk vätska. En relation infördes för att beskriva partiell orörlighet hos den organiska vätskan i porer vars halsar tillfälligt blockeras av vatten då mediet avvattnas. Vikten av att i de grundläggande relationerna ta hänsyn till hysteresis och kvarhållning av organisk fas visades. (iv) Olika Pc-S-kr relationer för trefassystem av vatten, organisk vätska och markluft testades mot befintliga experimentella data. En ny relation för hur slingrigheten (eng. tortuosity) beror av vätskehalten infördes i kr-S relationen och olika möjligheter för att skala Pc-S relationen analyserades. (v) En modelleringsmetodik utvecklades för att studera spridningen av flerkomponentsföroreningar. Med metoden kunde spridningsbeteendet hos enskilda, särskilt skadliga komponenter som t.ex. bensen särskiljas då ett bensinutsläpp i samband med en transportolycka simulerades.
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Nguyen, Van Qui [Verfasser], Bernd [Akademischer Betreuer] Ondruschka, and Rainer [Akademischer Betreuer] Beckert. "Carbon nanotubes : innovative heterogeneous gas phase catalysts / Qui Nguyen Van. Gutachter: Bernd Ondruschka ; Rainer Beckert." Jena : Thüringer Universitäts- und Landesbibliothek Jena, 2012. http://d-nb.info/1019969954/34.
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Harton, Shane Edward. "Investigation of Polymer Phase Behavior at Heterogeneous Polymer-Polymer Interfaces using Secondary Ion Mass Spectrometry." NCSU, 2006. http://www.lib.ncsu.edu/theses/available/etd-03012006-131419/.
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Changes in the thermodynamic behavior of polymer blends from bulk to heterogeneous interfaces is investigated using secondary ion mass spectrometry (SIMS). The use of a magnetic sector spectrometer (CAMECA IMS-6f) is fully explored in order to determine the optimal conditions in which to probe polymer surfaces and heterogeneous interfaces using three bilayer film systems, namely polystyrene (PS) with poly(methyl methacrylate) (PMMA), poly(cyclohexyl methacrylate) (PCHMA) with PMMA, and PS with poly(2-vinylpyridine) (P2VP). Two primary ion beams have been employed, O2+ with detection of positive secondary ions, and Cs+ with detection of negative secondary ions. It was found that each polymer thin film system must be closely investigated in order to determine the optimal conditions for depth profiling using SIMS. Three types of systems were further investigated using SIMS.
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Radivojevic, Dejan M. "Liquid phase heterogeneous catalysis - deeper insight novel transient response technique with ESI-MS as a detector /." Enschede : University of Twente [Host], 2008. http://doc.utwente.nl/59040.
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Papafotiou, Alexandros [Verfasser]. "Numerical investigations of the role of hysteresis in heterogeneous two-phase flow systems / von Alexandros Papafotiou." Stuttgart : Inst. für Wasserbau, 2008. http://d-nb.info/997170352/34.
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Al-Dhahli, Adnan. "Pore- to field-scale modelling of three-phase flow processes in heterogeneous reservoirs with arbitrary wettability." Thesis, Heriot-Watt University, 2013. http://hdl.handle.net/10399/2646.
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Most reservoirs, such as carbonate reservoirs not only have structural heterogeneities (e.g. complexly shaped geobodies or fractures). But they also have distributed wettabilities and are mixed- to oil-wet. The interplay of structural and wettability heterogeneities impacts sweep efficiency and oil recovery. Choosing the appropriate Improved Oil Recovery (IOR) or Enhanced Oil Recovery (EOR) technique based on adequate predictions of oil recovery requires a sound understanding of the fundamental controls on fluid flow in mixed- to oil-wet andstructurally complex rocks. The underlying multiphase flow processes are modelled with physically robust flow functions, i.e. relative permeability and capillary pressure functions. Obtaining these flow functions is a challenging task, especially when three fluid phases coexist, such as during Water-Alternating-Gas (WAG) injection. In this work we use pore-network modelling, a reliable and physically based simulation tool, to predict three-phase flow functions. We have developed a new three-phase flow pore-network model for rocks with arbitrary wettability, which allows us to analyse the fundamental multi-phase displacement processes. Unlike other models, our model combines three main features: (I) A novel thermodynamic criterion for formation and collapse of oil layers that strongly depends on the fluid spreading behaviour and the rock wettability. The model hence captures film/layer flow of oil accurately, which impacts, in particular, the oil relative permeability at low oil saturation and hence the accurate prediction of residual oil. (II) Multiple displacement chains, where injection of one phase at the inlet triggers a chain of interface displacements throughout the network. This allows accurate modelling of the mobilization of disconnected phase clusters that arise during higher order (WAG) floods. (III) The model takes as input realistic 3D pore-networks extracted from pore-space reconstruction methods and Computed Tomography (CT) images, preserving both topology and pore shape of the rock. The model comprises a constrained set of parameters that can be tuned to mimic the wetting state of a given reservoir. We have validated our model against available experimental data for a range of wettabilities. We demonstrate the importance of film and layer flow for the continuity of the various phases during subsequent WAG cycles and for the residual oil saturations. A sensitivity analysis has been carried out with the full 3D model to predict three-phase relative permeabilities and residual oil saturations for WAG cycles under various wetting conditions with different flood end-points and for different rock types. This revealed a wide range of three-phase relative permeabilities and residual saturations. The pore-scale generated three-phase flow functions have then been used in a heterogeneous reservoir model. Here we demonstrate their impact on the sweep efficiency after gas injection and WAG for a range of realistic wettability scenarios. We show that the uncertainty in flow functions can be as big as the geological uncertainty in a reservoir model that was history matched for an extended waterflood.
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Gunatilleke, Wilarachchige D. C. B. "Analysis and New Applications of Metal Organic Frameworks (MOF): Thermal Conductivity of a Perovskite-type MOF and Incorporation of a Lewis Pair into a MOF." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7514.
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Metal organic frameworks have gained much attention due to their tunable pore sizes and very high surface areas. With the discovery many of these type materials the need has raised to look into new applications of theses porous frameworks. This thesis focuses on the synthesis of a new perovskite-type metal organic framework and measurement of its thermal conductivity in search of its applicability as a thermoelectric material. The second part of this work focuses on the synthesis of a metal organic framework incorporated with a Lewis pair for the first time. The optimum loading amount of the Lewis pair into the framework was also investigated.
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Bühl, Johannes. "Combined lidar and radar observations of vertical motions and heterogeneous ice formation in mixed-phase layered clouds." Doctoral thesis, Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-171998.
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Im Rahmen der Arbeit wurden Lidar- und Wolkenradarmessungen von troposphärischen Schichtwolken durchgeführt und ausgewertet, um den Zusammenhang zwischen Vertikalwinden und Eisbildung in diesen Wolken zu untersuchen. Der Eis- und Flüssigwassergehalt von Schichtwolken wurde mit einer Kombination aus Raman-Lidar und Wolkenradar untersucht. Die vertikalen Windbewegungen an der Wolkenunterkante wurden mit einem Doppler-Lidar aufgezeichnet. Durch die Auswertung vorangegangener Messkampagnen konnte die Vertikalwindstatistik in mittelhohen Schichtwolken zwischen den Standorten Leipzig und Praia (Kap Verde) verglichen werden. Messverfahren für die Vertikalwindmessung mit Doppler-Lidar wurden im Rahmen dieser Arbeit weiterentwickelt. In Zusammenarbeit mit dem Deutschen Wetterdienst wurde außerdem die Kombination von Doppler-Lidar, Wolkenradar und Wind-Profiler getestet.
Die Eisbildungseffizienz in der Troposphäre wurde im Temperaturbereich zwischen 0 und -40°C für den Standort Leipzig untersucht und sowohl mit vorangegangenen Lidarmessungen, als auch mit aktuellen Satellitenmessungen verglichen. Zum ersten Mal wurde außerdem die statistische Verteilung von Vertikalwinden an der Basis von Mischphasenwolken dargestellt.
Es wurde festgestellt, dass sich bei einer Temperatur von (-9 +/- 3)°C bereits in 50% der Schichtwolken über Leipzig Eis bildet. Zwischen -15 und 0°C wurden Verhältnisse zwischen Eis- und Flüssigwasserpfad zwischen 0,1 und 0,0001 abgeschätzt. Im Rahmen der Messgenauigkeit wurden zwischen den Standorten Leipzig und Praia keine Unterschiede in der Vertikalwindstatistik festgestellt.
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Yomogida, Kiyoshi. "Amplitude and phase variations of surface waves in a laterally heterogeneous earth : ray- and beam-theoretical approach." Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/58419.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1986.Microfiche copy available in Archives and Science
Bibliography: leaves 198-208.
by Kiyoshi Yomogida.
Ph.D.