京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18538号 / 理博第4014号 / 新制||理||1579(附属図書館) / 31438 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 國友 浩, 教授 杉本 茂樹, 教授 田中 貴浩 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

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An analysis to determine physical and spatial patterns of the surface latent heat flux (LHF) and near surface (5m) salinity (NSS) beneath tropical cyclones (TCs) in the North Atlantic and eastern North Pacific basins during the first 24 hours of rapid intensification (RI) was conducted using empirical orthogonal function (EOF) analysis. To determine if these patterns were unique to RI, TC RI cases were compared to three non-RI intensification thresholds, 10 kt, 15 kt and 20 kt, for both LHF and NSS. Though similarities exist between non-RI and RI cases physical and spatial patterns unique to the RI cases did exist. Sea surface temperatures associated with statistically identified TC groups were assessed for their potential influence on RI. While inconclusive in the eastern North Pacific, NSS in the Atlantic may play a role for RI TCs in areas affected by river discharge from South America.

Groundwater chemistry is highly variable and dependent on environmental conditions, and it is not entirely understood how all these factors contribute to groundwater chemistry. This study aims to examine some of the factors that contribute to groundwater heterogeneity in the Amazon Rainforest. This was done by collecting groundwater samples from piezometers in three different regions of the Amazon Basin in Brazil, and then analyzing them in the lab for cations and anions, as well as dissolved inorganic and organic carbon. Environmental conditions were measured in the field using portable probes. The results were analyzed and compared with previously established figures for tropical forests. Statistical analyses were performed using SPSS and R in order to establish correlations and linear relationships between the studied variables.Understanding how groundwater supplies are affected is important for being able to predict and manage environmental change that can degrade groundwater sources. This knowledge could also help in developing strategies for groundwater remediation efforts in areas where supplies are contaminated.

[pt] Analisa-se a resistência térmica da parede de trocadores de calor tipo tubo-placa. Quatro modelos do trocador, imersos em um fluido são considerados; uma placa com tubos paralelos e igualmente espaçados sobre uma das superfícies; dois cilindros ocos, um com tubos uniformemente distribuídos sobre a superfície interna e segundo a direção circunferencial e finalmente uma esfera oca com distribuição paralela e uniforme de tubos sobre a superfície interna. Em todos os casos, a analise baseia-se na existência de fluxo uniforme de calor entre tubo e placa, extendendo-se porém, para a placa plana, a condição de fluxo conectivo. Os resultados mostraram um aumento considerável na resistência térmica da placa quando as razões(largura do tubo/ distancia entre tubos) e/ou (espessura da placa/ distancia entre tubos) diminuem ocasionando um estrangulamento das linhas de fluxo do calor através da placa. Essa resistência mostrouse-se também ser uma função crescente da resistência térmica do fluido externo e da condutividade térmica da placa, e crescer também com o aumento da resistência, obteve-se para os modelos cilíndricos, desvios de até 10 por cento, ao passo que valores até 3 (três) vezes maiores que aqueles foram obtidos para o modelo esférico. Um exemplo típico de uma aplicação sub-ocêanica é feito com o modelo cilíndrico de tubos axiais, usando-se titânio com material da parede do vaso. / [en] The thermeal costriction resisteance in the wall of a tube-plate heat excchanger in analyzed in this study. Four heat exchanger models, are considered; a flat plate with parallel tubes aqual spaced on one of the surfaces; two hollow cylindrs, one with tube uniformaly distributed axially over the inside surface and the other with tubes uniformly distributed circumferencially: and finally a hollow shere with a parallel distribution of tubes uniformly spaced on the inside surface. In each of the geometries it is assumed that the heat flux from the tubes is uniform. In addition, the condition of covective heat transfer from the tubes is considered for the case of the flat plate. The outer surface of the plate is cooled convectively. The results show a considerable increase in the therminal resitance of teh when the ratios (tube midth/tube spacing) and/or ( wall thickness/tube spacing) decreases, giving rise to the pincirg of the lines of heat flux through the plate. This resistance is shown also to be an increasing fuction of the therminal resistance of the fluid that flows in the tubes. Using the results of the rectangular model (flat plate) as a reference, it is found that the resistance for the cylindrical models differs model differs by up to 3 times greater. As an example of the application of the data obtained in this study, a desing of a deep seen cylindrical vessel made of titanium with axially distributed tubes is considered.

We investigate the properties of two distinct disordered systems: the two-species predator-prey Lotka-Volterra model with rate variability, and an elastic line model to simulate vortex lines in type-II superconductors. We study the effects of intrinsic demographic variability with inheritance in the reaction rates of the Lotka-Volterra model via zero-dimensional Monte Carlo simulations as well as two-dimensional lattice simulations. Individuals of each species are assigned inheritable predation efficiencies during their creation, leading to evolutionary dynamics and thus population-level optimization. We derive an effective subspecies mean-field theory and compare its results to our numerical data. Furthermore, we introduce environmental variability via quenched spatial reaction-rate randomness. We investigate the competing effects and relative importance of the two types of variability, and find that both lead to a remarkable enhancement of the species densities, while the aforementioned optimization effects are essentially neutral in the densities. Additionally, we collected extinction time histograms for small systems and find a marked increase in the stability of the populations against extinction due to the presence of variability. We employ an elastic line model to investigate the steady-state properties and non-equilibrium relaxation kinetics of magnetic vortex lines in disordered type-II superconductors. To this end, we developed a versatile and efficient Langevin molecular dynamics simulation code, allowing us to do a careful study of samples with or without vortex-vortex interactions or disorder allows us to disentangle the various complex relaxational features present in this system and investigate their origin. In particular, we compare disordered samples with randomly distributed point defects versus correlated columnar defects. We extract two-time quantities such as the mean-square displacement, the height and density correlations, to investigate the relaxation kinetics of the system of flux lines. Additionally, we compare the steady-state mean velocity and gyration radius as a function of an external driving current in the presence of point-like and columnar disorder. We validate our simulation algorithm by matching our results against a previously-used Monte Carlo algorithm, verifying that these microscopically quite distinct methods yield similar results even in out-of-equilibrium settings. / Ph. D.

Second-generation biofuels have the potential to replace fossil fuels in the energy economy without negatively impacting the food supply. An effective biocatalyst must be able to convert all sugars found in lignocellulosic hydrolysates to biofuels. Few microbes exist in that have both a wide substrate range and high ethanol yields necessary for this process. Mixed culture biotechnology is a promising alternative to the use of single organisms in the production of fuels from lignocellulosic biomass. These systems mimic natural processes for the degradation of lignocellulose and exploit the native capabilities of each microbe. The segregation of metabolic pathways allows for the individual optimization of each step in the process. Preliminary work with a consortium capable of saccharification and fermentation showed promise, but the dynamics were poorly understood. Metabolic modeling is a powerful tool for understanding the interactions between microbes in mixed cultures. The development of accurate models of mixed culture metabolism will help drive the engineering of these systems for industrial applications. In this dissertation, dynamic flux balance analysis is applied to mixed culture systems by combining mathematical reconstructions of pure culture metabolism. By tuning the inoculum to sugar concentration, simulations of Saccharomyces cerevisiae and Escherichia coli mutants engineered to ferment a specific substrate display the potential for improved ethanol production over pure cultures. A framework for translating model predictions to experimental systems was developed for a co-culture of S. cerevisiae and xylose-specific E. coli. The consumption of sugar mixtures was optimized through this method, but the inability of the predicted gains in ethanol production to be replicated in experimental systems reveals the importance of selecting microbes with similar optimal growth conditions. The more compatible microbes S. cerevisiae and Scheffersomyces stipitis were modeled under microaerobic conditions to optimize ethanol production from a mixture of glucose and xylose. To further demonstrate the ability of these systems to ferment lignocellulosic hydrolysates, the effect of furan inhibitors on pure and co-cultures was assessed through modeling and experiment. The work presented here represents the first steps towards engineering and optimizing a microbial consortium for the production of ethanol from lignocellulosic biomass.

<p> An experimental investigation is reported for water boiling at atmospheric pressure on a copper surface. Bubble nucleation at an artificial site was observed for five heat fluxes between 11,000 and 20,000 BTU/Hr Ft^2, and subcooling from 0° to about 30°F. Using Wiebe's correlation for heat flux and superheat layer thickness, four mathematical models were tested. The measured results are found to provide excellent agreement with the Han and Griffith model for bubble nucleation.</p> / Thesis / Master of Engineering (MEngr)

<p> The objective of this investigation was to examine the potential of the point heat-flux meter in studying the dynamic heat transfer process in a scraped-surface heat exchanger.</p> <p> The heat-flux meters were an integral part of the copper heat exchanger which was steam-heated. Water was passed through the equipment as a thin film. The steam condensate was collected for measurement.</p> <p> Mathematical analysis related the transient differential temperature of the detector with the transient applied heat flux. A mathematical model was found that would estimate the instantaneous heat flux from the heat-flux-meter experimental temperature difference.</p> <p> Instantaneous and time-average local heat fluxes were measured by the heat-flux meter and the condensate respectively. The meter accuracy was -7000 Btu/hr sq ft.</p> <p> The heat-flux meter can be used in studying dynamic heat transfer processes.</p> / Thesis / Master of Engineering (MEngr)

The primary objective of this study is to develop a sliding interface method for simulations involving relative rotational grid motion suitable for unstructured grid topologies. The present method alleviates computationally expensive grid deformation, remeshing, and hole cutting procedures. Rotational motion is accomplished by rigidly rotating a subdomain representing the moving component. At the subdomain interface boundary, the faces along the interfaces are extruded into the adjacent subdomain to create new volume elements and provide a one-cell overlap. These new volume elements close the control volumes for the nodes on the interface surface and allow a flux to be computed across the subdomain interface. An interface flux is computed independently for each subdomain. The values of the solution variables and other quantities for the nodes created by the extrusion process are found by interpolation. The extrusion is done so that the interpolation will maintain information as localized as possible. A parallel implementation of the neighbor search is used to find the extruded points in the adjacent subdomain. The method has been implemented in a parallel, node-centered finite volume, high-resolution viscous flow solver. The method does not impose any restrictions on the subdomain interface aside from the axisymmetric limitation required for rotational motion. In addition, the grid on the subdomain interface is arbitrary. The boundary surfaces between the two subdomains can have independent grids from one another. They do not have to connect in a one-to-one manner and there are no symmetry or pattern restrictions placed on the surface grid. A variety of numerical simulations were performed on several small-scale model problems to examine conservation of the interface flux. Overall flux conservation errors were found to be comparable to that for fully connected and fully conservative simulations. In addition, excellent agreement was obtained with both theoretical and experimental results. Three large-scale applications were also used to validate the method and highlight some of the advantages of the sliding interface method compared to the current state-of- the-art for unstructured grid applications. This sliding interface method requires no geometric modifications and has significantly shorter run times Furthermore, there were no apparent adverse effects on the numerical solutions by not strictly enforcing flux conservation at the subdomain boundary.