Dissertations / Theses on the topic 'Osmotic processes in cells'

Subject of this master's thesis is the observation of influence of external environment on the living cells with the use of multimodal holographic microscope. The theoretical part is summarising the development of the holographic microscopy at IPE FME BUT. The theoretical part also describes multimodal holographic microscope, which allows non-invasive observing of living cells. The thesis also covers construction of the microscope, basic working instructions and the hologram processing method. The main subject of the thesis is the research on the topic of chemotaxis and osmotic processes in the cells. Experiments were designed for the purpose of this thesis to cover topics mentioned above. The experimental part of the thesis deals with cultivation of the cells, preparation of the sample and observation chambers and processing of the data. This part later focuses directly on the laboratory measurements. In all experiments, cells K2 (full name LW13K2) were observed.

El procesado de alimentos conlleva, en mayoría de los casos, la generación de subproductos o residuos que pueden ser reutilizados o revalorizados mediante la utilización de técnicas de separación por membrana. Estas técnicas ofrecen la posibilidad de tratar las soluciones en condiciones de operación muy suaves, y no comportan en mayoría de las ocasiones, una alteración de los componentes a recuperar. Actualmente, las técnicas de separación por membrana, debido a su alta calidad y relativamente bajos costes, se encuentran completamente integradas en la mayoría de procesos productivos que requieren de una etapa de separación. Sin embargo, la investigación en el área de las técnicas de separación por membrana sigue abriendo nuevos campos de aplicación, que surgen con la mejora de las condiciones tecnológicas de los equipos y la posibilidad de obtener nuevas membranas adaptables a necesidades específicas.

En concreto, en este proyecto se utilizaron técnicas de separación por membranas para concentrar soluciones de azúcar procedentes de deshidratación osmótica (en adelante OD). El principal objetivo fue estudiar el potencial de varias técnicas de separación, haciendo hincapié en los flujos obtenidos durante la reconcentración y en la calidad de la solución reconcentrada.

La deshidratación osmótica es un tratamiento que permite una eliminación parcial del agua en un alimento y/o la incorporación de solutos de una manera controlada, respetando la calidad inicial del producto. El proceso consiste en introducir los alimentos en una solución hipertónica, controlando las condiciones de operación para favorecer, en mayor o menor grado la incorporación de solutos y la deshidratación del alimento. La aplicación de OD puede resultar en la mejora de las propiedades nutricionales y funcionales de los alimentos y en la reducción de la energía requerida para la deshidratación. El principal problema de la aplicación industrial de la OD radica en la gestión de la solución procedente del proceso. La reutilización de esta solución plantea una doble ventaja: primero desde el punto de vista ambiental, ya que se elimina un efluente del proceso que a menudo no puede ser vertido directamente, y segundo el ahorro económico que representa la recuperación de las materias primas que muchas veces contienen solutos de importante valor económico.

Los métodos de separación por membrana utilizados para recuperar las soluciones de OD fueron los siguientes: nanofiltración, osmosis directa y destilación osmótica por membranas. La nanofiltración (NF) presenta altos niveles de retención y un menor gasto de energía que la osmosis inversa, y en la industria azucarera se aplica como uno de los pasos en la clarificación y concentración de jarabes. En los procesos de contactores de membranas: osmosis directa (DO) y destilación osmótica por membranas (OMD), a diferencia de los procesos basados en el tamizaje, el flujo depende solamente de la diferencia de potencial osmótico. Las únicas presiones hidráulicas requeridas son las necesarias para bombear la solución de azúcar y la solución osmótica hasta la superficie de la membrana. Estas características hacen que estos procesos presenten como muy prometedores para la reconcentración de soluciones de azúcar de concentraciones elevadas.

Los experimentos de filtración se llevaron a cabo utilizando plantas piloto diseñadas y construidas expresamente para el presente proyecto. Durante todos los procesos de separación por membranas, se empleó como solución modelo una solución de sacarosa a diferentes concentraciones (5-60 ºBrix), debido a que las soluciones aplicadas en la deshidratación osmótica de frutas son habitualmente soluciones de azucares (sacarosa, glucosa o jarabes).

Durante los experimentos de NF se evaluó el funcionamiento de las membranas planas: Desal5 DK (GE- Osmonics), MPF-34 (Koch Membrane), NFT-50 (DSS) y tubulares: MPT-34 (Koch Membrane) y AFC 80 (PCIMembranes). Además de la solución de azúcar de diferentes concentraciones (5-20 ºBrix), se concentraron zumos de pera y manzana.


La reconcentración mediante osmosis directa se realizó utilizando dos modos de operación: off-site e on-site. En el modo off-site, la reconcentración por ósmosis directa se llevó a cabo en una planta de filtración provista de un módulo plano o tubular, dependiendo de la membrana. En el módulo se llevó a cabo la concentración. En el modo on-site, la deshidratación se realizaba conjuntamente con la reconcentración de la solución osmótica. La solución de reconcentración de la osmosis directa en off-site (offsiteDO) fue NaCl, mientras la solución de reconcentración de la osmosis directa on-site (on-site DO) fue una solución de sacarosa más concentrada que la solución osmótica (60 para una solución osmótica de 40 y 68 para una solución de 50 ºBrix). Para garantizar el flujo de agua entre las dos soluciones y altas retenciones de azúcar durante la off-site DO, se utilizaron membranas de NF planas (Desal5-DK y MPF-34) y tubulares (MPT-34 y AFC80). La reconcentración por osmosis directa on-site se levó a cabo empleando una membrana de microfiltración (Durapore, Millipore), ya que la solución de reconcentración (SS) es la misma que la solución osmótica y la alta viscosidad de la SS restringe mucho el flujo de agua si se utiliza una membrana más densa.

En la deshidratación por membranas (OMD) se utilizaron membranas hidrófobas (11806, Sartorius) que presentan una retención teórica del 100 %. Se comparó el rendimiento de dos soluciones de reconcentración: NaCl y CaCl2.

Con el fin de obtener información referente a la influencia de las propiedades de las membranas sobre el desarrollo del proceso de concentración de las soluciones procedentes de la deshidratación osmótica, se realizó un estudio detallado de las propiedades de las membranas aplicadas mediante AFM, SEM, FTIR, ángulo de contacto y medidas de potencial zeta. Con la finalidad de generar soluciones osmóticas para someterlas a reconcentración, y también para disponer de productos procedentes de deshidratación osmótica con soluciones frescas que pudieran compararse con aquellas procedentes de OD con solución reconcentrada, se deshidrataron diferentes lotes de manzana (Granny Smith) con soluciones de sacarosa de 40, 50 y 60 ºBrix. Estas pruebas permitieron determinar también el tímelo de operación para una máxima pérdida de agua con relativamente poca impregnación de las manzanas. Después de cada experimento se analizaron los siguientes parámetros: concentración de azúcar, pH, absorbancia a 420 nm de las soluciones y humedad de las manzanas.

La nanofiltración, aplicada en la primera fase del presente estudio, resultó ser viable solamente para la reconcentración de soluciones de concentraciones hasta 24 ºBrix. El aumento de la temperatura de 25 hasta 35 ºC para las dos membranas tubulares ocasionó un incremento del flujo de permeado, y el mismo efecto tuvo el aumento de presión transmembranaria de 8 a 12 bar.

Se comprobó que el factor más importante para la eficacia del proceso es disponer de una membrana que combine altos flujos y retenciones durante el proceso. La deposición de las partículas de sacarosa y/o los zumos se caracterizó mediante SEM y la topología de la capa filtrante de la membrana se identificó usando AFM. La topología de la capa filtrante de las membranas era diferente para cada una de ellas, a pesar de que todas estaban preparadas con el mismo material (poliamida). En las imágenes de los cortes transversales de las membranas realizados con SEM, se observaron los cambios en la estructura de las membranas producidos por la aplicación de presión durante los experimentos y las altas temperaturas empleadas durante su acondicionamiento. Gracias a las imágenes de SEM se pudo verificar también la eficacia del proceso de acondicionamiento de membranas.

A diferencia de NF, tanto la ósmosis directa como la destilación osmótica por membrana permiten la reconcentración de soluciones concentradas de sacarosa (hasta60 ºBrix). La eficacia de estas dos últimas técnicas se evaluó en unción de los flujos de agua obtenidos.

El sistema de ósmosis directa on-site propuesto para la reconcentración de las soluciones de OD permitió reutilizar las soluciones osmóticas como mínimo cuatro veces. Para la solución osmótica de 40 ºBrix la humedad de las manzanas fue similar utilizando solución fresca o reconcentrada. En cambio, una solución osmótica de 50 ºBrix, la pérdida de agua de las manzanas fue mayor cuando la deshidratación osmótica se llevó a cabo con reconcentración on-site de la solución osmótica. Los análisis de concentración de azúcar de las soluciones osmóticas y de la solución de reconcentración indican que la membrana elegida para los experimentos facilita el transporte óptimo de solutos y agua entre las dos soluciones. Además, el sistema de reconcentración por membrana propuesto es muy sencillo y de bajo coste porque no requiere presurización.

La osmosis directa en off-site proporcionó flujos mucho mayores que los obtenidos con el sistema on-site (1.3 kg/m2h para la solución osmótica de 50 ºBrix respecto a 0.0023 kg/m2h durante on-site DO para la misma solución). Sin embargo, el transporte de solutos de la solución de reconcentración hacía la solución osmótica puede ser considerado un obstáculo para su aplicación a escala industrial.

Los flujos de agua más elevados fueron obtenidos utilizando la OMD (2.01 kg/m2h para la solución osmótica de 50 ºBrix y con CaCl2 con la solución de reconcentración). Otra gran ventaja de este proceso es la retención de solutos que proporciona, hecho confirmado por los análisis realizados.

El estudio sobre el transporte durante los procesos de contactores de membranas indicó que la viscosidad es la propiedad limitante para la solución osmótica y la actividad de agua/alta presión osmótica como la propiedad más importante a la hora de elegir una solución de reconcentración. Para todos los procesos de separación aplicados, el aumento de la concentración de azúcar de la solución osmótica comporta una disminución notable del flujo de agua.

El desarrollo de un posible proceso de deshidratación osmótica con una etapa de reconcentración de la solución osmótica mediante procesos con contactores de membrana ha permitido calcular el área requerida para realizar la reconcentración: 3.6,9.7, 1608 m2 para OMD, off-site DO e on-site DO, respectivamente.

Las conclusiones del trabajo confirman la posibilidad de utilizar procesos por membrana para realizar la reconcentración de soluciones osmóticas. No obstante se ha constatado que técnicas más tradicionales basadas en diferencias de presión (NF) no son

En el caso del almacenamiento de los residuos radioactivos los flujos osmóticos pueden ser relevantes y requieren un análisis en detalle. El residuo nuclear bituminizado (BW) será almacenado mediante contenedores en cavidades excavadas en la Boom Clay, que es una arcilla marina que presenta propiedades favorables para limitar y retrasar la migración de los contaminantes radioactivos. La interacción entre los dos materiales es un proceso acoplado químico-hidro-mecánico y depende de la respuesta hidromecánica de la Boom Clay y del BW. En condiciones de almacenamiento, el contacto del BW, que contienen cantidades importantes de NaNO3, con el agua subterránea induce la hidratación por gradientes osmóticos y el consiguiente hinchamiento, además de la difusión de la sal disuelta hacia la Boom Clay. Se pueden distinguir dos tipos de afecciones: la perturbación geomecánica causada por el hinchamiento del BW y el aumento de presión en el BW y cambio de las distribución de tensiones en la roca, y la perturbación físico química por la migración de grandes cantidades de sales. El objetivo de esta tesis es: (i) Mejorar la comprensión de los procesos que controlan la absorción de agua y el consecuente hinchamiento del BW que contengan sales (NaNO3), y (ii) Investigar los posibles efectos de la concentración de fluidos de los poros sobre el hinchamiento, la compresibilidad y comportamiento de corte de la Boom Clay. En primer lugar, se ha desarrollado una formulación para el análisis de la deformación inducida por la disolución de sales en medio poroso con contacto con agua. Las ecuaciones planteadas incluyen los flujos acoplados de agua y soluto. Se presenta también un trabajo teórico que ayuda a la comprensión del comportamiento mecánico del BW. Se considera este material como una mezcla de bitumen y cristales de NaNO3. Se ha desarrollado un modelo elasto-viscoplástico que describe el comportamiento de fluencia del BW considerando el comportamiento de fluencia de sus constituyentes. El modelo constitutivo elasto-viscoplástico ha sido implementado en el programa CODE_BRIGHT. Los resultados se han comparado con observaciones experimentales. Se ha estudiado el comportamiento a largo plazo del BW en contacto con agua al simular ensayos de hinchamiento por absorción de agua bajo condiciones confinadas. El análisis numérico ha demostrado ser capaz de proporcionar una representación satisfactoria de los principales patrones observados en su comportamiento. En lo que respecta al segundo objetivo de la tesis, se ha propuesto una formulación para el análisis de las deformaciones inducidas por procesos osmóticos en un medio poroso de doble estructura. Esta formulación distingue dentro del material un nivel micro-estructural y otro macro-estructural con cambios químicos que tienen un efecto significativo en la micro-estructura. Se han obtenido las ecuaciones básicas que describen los flujos acoplados de agua y solutos y el transporte de sus componentes a través de los macroporos así como las ecuaciones de balance de masa para agua y soluto en los macroporos y microporos. La formulación propuesta ha sido aplicada particularmente para analizar cualitativamente el efecto de la succión osmótica sobre el hinchamiento de los suelos arcillosos. Se han analizado los efectos a corto y largo plazo. Se ha investigado también la influencia del aumento de la concentración del fluido en los poros sobre las propiedades geotécnicas y el comportamiento de la Boom Clay no saturada. Se ha llevado a cabo un programa sistemático de investigación experimental, con control de succión osmótica y matricial, con el fin de investigar el efecto del incremento de la concentración del fluido de poros sobre la resistencia de corte y el cambio volumétrico bajo condiciones edométricas. Se ha observado, que bajo condiciones parcialmente saturadas, un cambio en la salinidad provoca una disminución en la compresibilidad y en la resistencia de corte del material.
For deep storage of high-level nuclear waste osmotic flows can be significant and so require a careful analysis. In Belgium, The bituminized nuclear waste (BW) named Eurobitum contained in metallic drums will be placed inside a tunnel or a shaft excavated in the Boom Clay, which is 100 m thick marine clay presenting favourable properties to limit and delay the migration of the leached radionuclides over extended periods of time. In Geological disposal conditions, contact of the bituminized radioactive waste which contains high amounts of highly soluble salt (NaNO3) with groundwater will result in water uptake and swelling of the waste and in subsequent diffusion of the dissolved salt through the host clay formation. Basically, two types of disturbance can be distinguished: A geo-mechanical perturbation, caused by the swelling of the waste and the increase of the pressure in and around the waste and a physico-chemical perturbation by the release of large amounts of NaNO3 and other soluble salts. In this context the aim of this thesis is: (i) to improve the understanding of the processes controlling the water uptake and the subsequent swelling of bituminized waste containing soluble salts (NaNO3), and (ii) to investigate of the possible effects of the increase of pore fluid concentration on swelling, compressibility and shear behaviour of Boom Clay. A formulation has been proposed for the analysis of deformation induced by dissolution of salts in porous media in contact with water. The equations include the effect of coupled transport phenomena and the formulation has been included as an extension in the coupled THM program CODE_BRIGHT. A theoretical and experimental work aiming at understanding the mechanical behaviour of the Bituminized Waste has been presented.This material is considered for this purpose as a mixture of bitumen and crystals of NaNO3. An elasto-viscoplastic model has been developed that describes the creep behaviour of BW considering the constituents' creep behaviour. The elasto-viscoplastic constitutive model has been implemented into CODE_BRIGHT. The modelling results have been compared with the experimental data. The impact of osmotic forces on the swelling of the material has been investigated by simulating water uptake swelling tests under confined conditions and comparing the predictions with experimental results. The numerical analysis has proven to be able to furnish a satisfactory representation of the main observed patterns of the behaviour. In regard to the second objective of this thesis, a formulation has been proposed for the analysis of deformations induced by osmotic processes in double structure porous media. The formulation is based on the distinction within the material of a microstructural and a macrostructural levels with chemical changes having a significant effect on the microstructure. A macroscopic description of the system is provided. Then the basic equations describing coupled flows of water and solutes and the transport of its components through macropores and mass balance equations for water and solute in macro and micro pores have been obtained. The proposed formulation has been particularly applied to analyze qualitatively the effect of osmotic suction on swelling of clayey soils. Transient and long term effects have been analyzed. The influence of pore fluid concentration on the geotechnical properties and behavior of Boom Clay under partially saturated conditions has been investigated. A systematic experimental research program involving osmotic suction and matric suction controlled experiments has been carried to investigate the effect of the increase of pore fluid concentration on shear strength and on the volume change behaviour under odometer stress state conditions. It has been observed that under partially saturated conditions a change in salinity causes a decrease in compressibility and shear strength.

Japanese eels (Anguilla japonicas) are snakelike fishes living in waters in the Asian region. In contrast to most fishes which are stenohalines that can only live in waters with a narrow range of salinity, Japanese eels are classified as euryhalines that can habitat in a broad range of salinity. As the lifecycle of Japanese eels consists of stages across fresh and seawater districts, a well-developed osmoregulation mechanism is needed to balance the intra- and extra- cellular osmolarity of the fishes throughout the seawater acclimation process. While fish gills are one of the organs that separating the ambient water and the inner body fluid of the fish, the fish gills of the Japanese eels have been studied as one of the most crucial organs for osmoregulation purposes. Yet, the osmoregulation and survival strategies of Japanese eels under hyperosmotic stress has not been fully elucidated. In chapter 2, this study has performed a transcriptome study on the ex vivo gill filament model of the Japanese eel to profile the molecular responses after a hypertonic treatment of 4 hours or 8 hours. The experiment is aimed to mimic the gill cells exposed to seawater in the seawater acclimation process of Japanese eels. A profile of differential expressed genes (DEGs) has been revealed that 577 DEGs were commonly upregulated and 711 DEGs were commonly downregulated in both 4- and 8-hours hypertonic treatment. Functional analysis and annotation have been processed with these DEGs, including Ingenuity Canonical Pathways analysis and gene ontology. These analyses have revealed that the cellular homeostasis of the gill cells has been disrupted and cell death responses has been induced by osmotic stress. The results have raises a concern that the maintenance of cellular viability and a cell death regulation mechanism are needed for the fishes to survive in the early stage of seawater acclimation. In chapter 3, this chapter demonstrated that gill cells in Japanese eels are susceptible to apoptosis when they are exposed to hyperosmotic treatments in both in vitro gill cell and the ex vivo gill filament model. To maintain the viability of the gills cells, two inhibitors of apoptosis, XIAP, and survivin, were seen to be expressed in gills cells. The expression of XIAP and survivin were upregulated by dexamethasone, which is an agonist mimicking the effect of cortisol on fishes in seawater acclimation. Meanwhile, the expression levels of the apoptosis executor, caspase 3, were downregulated. These data suggested that with the regulation of cortisol express in the fishes, XIAP and survivin are effective apoptosis regulators in the gill cells of Japanese eels. The study has demonstrated the molecular responses of the gills of Japanese eels exposed to hyperosmotic stress at the transcriptional level and post-translational level by using transcriptome studies and protein study respectively. The study has paved cell death regulation to be another the key field to study in understanding the ability of salinity tolerance in euryhalines.

Un excès de charge hydraulique, ou surpression, est fréquemment observé dans les formations argileuses de très faible perméabilité et l’origine de cet excès de charge est une question importante pour comprendre les mouvements d’eau et de solutés. Le but de la thèse a consisté à étudier et quantifier l’importance de chacun des processus responsables de l’excès de charge de 30 +/- 10 m observé dans la formation argileuse du Toarcien/Domérien de Tournemire (Aveyron). Le cœur de la thèse consiste en la caractérisation des processus d’osmose chimique et thermique, un flux d’eau sous un gradient de concentration et de température, respectivement. Cette caractérisation s’est faite expérimentalement et par le biais de modèles théoriques reproduisant les interactions entre la surface chargée des argiles et la solution de pore: l’exclusion anionique pour l’osmose chimique et la modification des propriétés de l’eau à proximité de la surface pour la thermo-osmose. Les expériences ont été réalisées sur échantillons d’argilite et dans un forage équipé d’une chambre de test à Tournemire en induisant un gradient de concentration ou de température à travers un échantillon ou entre le forage et la formation. L’efficacité d’osmose chimique la perméabilité thermo-osmotique sont ensuite obtenus par la simulation de l’évolution des pressions. En parallèle, le profil de composition de l’eau porale a été établi de manière indirecte avec un modèle géochimique. Le calcul du profil de charge hydraulique dans la formation, qui considère aussi le comportement hydromécanique de l’argilite, montre que seuls les processus osmotiques et hydrauliques sont à l’origine de l’excès de charge hydraulique.

Cell cultivation in bioreactors would benefit from developed monitoring systems with online real-time imaging to evaluate cell culture conditions and processes. This opportunity can be provided with the newly developed in situ Microscope also called ISM. The ISM probe is mounted into the wall of a bioreactor and consists of a measurement zone with an illuminating light source to obtain real-time images of moving cells in suspension. The instrument is linked to advanced imaging analysis software which can be specifically adapted for the objects in study. The aim of this project is to analyze the T lymphocyte cell line Jurkat T cells using the ISM equipment and identify specific features of the cells that can be obtained. The results show that the equipment and linked software are suitable for monitoring cell density, cell size distribution and cell surface analysis of the Jurkat cells during cultivation. The ISM could also detect induced changes in cell size caused by osmotic shifts and the course of an infection occurring in the cell suspension using a developed software for online real-time monitoring.

Adaptive responses allow cells to maintain their growth as well as their proliferative potential under diverse stress conditions. It is known that, growth and proliferation can be suppressed by intense stress, but maintained under tolerable stress conditions under which cells can induce compensatory responses. The kinase mTOR is a central regulator of proliferative and growing capacity in mammalian cells, and has been shown to be sensitive to diverse stressors. However, little is known about the role played by mTOR in the adaptive responses that cells utilize to resist stress and maintain their growth capacity. We addressed this question in the context of osmotic stress, to which cells can adapt by inducing the transcription of specialized genes. We showed that mTOR is active under moderate osmostress conditions and regulates the induction of a set of genes by mechanisms dependent and independent of NFAT5, the main transcription factor involved in the transcription of genes upon hypertonic stress. In addition, we observed that the overall set of genes whose induction was sensitive to mTOR activity is enriched in regulators of growth and proliferation. We also have identified REDD1 and REDD2 as two osmostress and mTOR-dependent induced genes, which previously had been characterized in other stress contexts acting as negative regulators of the mTORC1 pathway. We observed that mTOR promoted changes in chromatin predisposing it towards a transcriptional permissive configuration, with higher levels of acetylated histone H4 and increased recruitment of active RNA-pol II to promoters as well as transcribed regions. Altogether, the results described in this thesis reveal a new role for the mTOR kinase in the regulation of gene expression to facilitate the cellular adaptive response upon osmostress.
Las respuestas adaptativas frente al estrés permiten a las células mantener su crecimiento así como su potencial proliferativo. Aunque se ha establecido que el crecimiento y la proliferación celular pueden inhibirse en respuesta a un estrés intenso, en situaciones de estrés tolerable las células pueden mantener su crecimiento y proliferación mediante la inducción de respuestas compensatorias. La quinasa mTOR es una proteína clave para el mantenimiento de la capacidad proliferativa y del crecimiento en las células de mamífero; además se ha descrito que es sensible a varios estreses. Sin embargo, poco se sabe acerca del papel que juega en las respuestas de adaptación que son utilizadas por las células para resistir el estrés y mantener así su capaciad de crecimiento. Nuestro trabajo se ha centrado en el ámbito del estrés osmótico, en cuyo caso las células pueden adaptarse mediante la transcripción de diversos genes especializados. Nuestro estudio demuestra que mTOR se encuentra activo en condiciones moderadas de estrés osmótico y regula la indución de un conjunto de genes mediante mecanismos dependientes e independientes de NFAT5, el principal factor de transcripción responsable de la transcripción de genes en respuesta a un estrés hipertónico. Además, observamos que la mayoría de los genes cuya inducción es sensible a la actividad de mTOR tienen funciones en la regulación del crecimiento y de la proliferación. También hemos identificado a REDD1 y REDD2 como genes que se inducen en respuesta a estrés osmótico dependientes de mTOR, y que con anterioridad se habían caracterizado en otros escenarios de estrés actuando como reguladores negativos de la ruta de señalización de mTORC1. Por último hemos observado que mTOR origina cambios en la cromatina, promoviendo una configuración permisiva para la transcripción, con un incremento de la acetilación de la histona H4 y un aumento en el reclutamiento de la forma activa de la RNA-polimerasa II en los promotores y regiones transcritas de ciertos genes. En resumen, los resultados descritos en esta tesis muestran un nuevo papel de la quinasa mTOR en la regulación de la expresión génica facilitando así la respuesta de adaptación celular frente al estrés osmótico.

Dye-sensitized solar cells (DSCs) have attained considerable attention during the last decade because of the potential of becoming a low cost alternative to silicon based solar cells. Although efficiencies exceeding 10% in full sunlight have been presented, major improvements of the system are however limited. Electron transport is one of the processes in the cell and is of major importance for the overall performance. It is further a complex process because the transport medium is a mesoporous film and the pores are completely filled by an electrolyte with high ionic strength, resulting in electron-ion interactions. Therefore, present models describing electron transport include simplifications, which limit the practical use, in terms of improving the DSC, because the included model parameters usually have an effective nature. This thesis focuses in particular on the influence of the mesoporous film on electron transport and also on the influence of electron-ion interactions. In order to model diffusion, which is assumed to be the transport process for electrons in the DSC, Brownian motion simulations were performed and spatial restrictions, representing the influence of the mesoporous film, were introduced by using representative models for the structure. The simulations revealed that the diffusion coefficient is approximately half the value for electrons and ions in mesoporous systems. To study the influence of ions, a simulation model was constructed in where electric fields were calculated with respect to the net charge densities, resulting from the different charge carrier distributions. The simulations showed that electron transport is highly dependent on the nature of the ions, supporting an ambipolar diffusion transport model. Experimentally, it was found that the transport process is dependent on the wavelength of the incident light; we found that the extracted current was composed of two components for green light illumination, one fast and one slow. The slow component showed similar trends as the normal current. Also we found that the transport coefficient scaled linearly with film thickness for a fixed current, which questions diffusion as transport process. Other experiments, investigating various effects in the DSC, such as the effect of different cations in the electrolyte, are also presented.
QC 20100708

L'energia fotovoltaica s'ha convertit en una de les alternatives més populars com a font d'energia renovable. Es basa en la transformació directa de radiació solar en electricitat. Es troba disponible a escala global i a més no necessita de cap transformador per convertir l'energia mecànica en energia elèctrica, el que fa que sigui fàcil d'implementar. Avui en dia, el material més utilitzat per a aplicacions fotovoltaiques segueix sent el silici. En canvi, el desenvolupament de noves tecnologies, més barates, fàcils de processar i que a més poden utilitzar-se en substrats flexibles, ha sorgit com a alternativa al silici. De totes elles, les perovskita basades en halurs de plom s'han convertit en una de les millors opcions per a la comunitat científica a causa de les excel·lents propietats fotovoltaiques que presenta. Tot i que les eficiències dels dispositius preparats amb perovskita han arribat al 25%, un valor que es troba molt proper al seu màxim teòric, els processos que tenen lloc en aquests dispositius encara no són del tot coneguts. En aquesta tesi es tracta d'obtenir informació sobre els processos dels transportadors de càrrega, des de com es generen fins a la recombinació, tant en les interfícies com a l'interior del propi material. Per això, s'han utilitzat diferents tècniques de caracterització avançades com el fotovoltatge transitori (TPV), la fotocorrent transitòria (TPC), l'extracció de càrrega (CE) i l’espectroscòpia d'absorció transitòria en l'escala del femtosegon (FSTA), obtenint importants conclusions sobre pèrdues i processos que afecten la recombinació de transportadors de càrrega que porten a pitjors eficiències
La energía fotovoltaica se ha convertido en una de las alternativas más populares como fuente de energía renovable. Se basa en la transformación directa de radiación solar en electricidad. Se encuentra disponible a escala global y además no precisa de ningún transformador para convertir la energía mecánica en energía eléctrica, lo que hace que sea fácil de implementar. Hoy en día, el material más utilizado para aplicaciones fotovoltaicas sigue siendo el silicio. En cambio, el desarrollo de nuevas tecnologías, más baratas, fáciles de procesar y que además pueden utilizarse en sustratos flexibles, ha surgido como alternativa al silicio. De todas ellas, las perovskitas basadas en haluros de plomo se han convertido en una de las mejores opciones para la comunidad científica debido a las excelentes propiedades fotovoltaicas que presenta. Aunque las eficiencias de los dispositivos preparados con perovskitas han alcanzado el 25%, un valor que se encuentra muy cercano a su máximo teórico, los procesos que tienen lugar en estos dispositivos aún no son del todo conocidos. En esta tesis se trata de obtener información acerca de los procesos de los transportadores de carga, desde cómo se generan hasta la recombinación, tanto en las interfaces como en el interior del propio material. Para ello, se han utilizado distintas técnicas de caracterización avanzadas como el fotovoltaje transitorio (TPV), fotocorriente transitoria (TPC), la extracción de carga (CE) y la espectrocopía de absorción transitoria en la escala del femtosegundo (fsTA), obteniendo importantes conclusiones sobre pérdidas
Photovoltaics have become one of the most popular renewable source of energy. Photovoltaic technologies transform sunlight into electricity, and they are also available worldwide, and they do not depend on the conversion of motive power, making this technology quite easy to implement. Nowadays, silicon is still the most used material for photovoltaics. Anyway, new photovoltaic technologies have emerged as alternatives to silicon, as they are cheaper, easier to process, and, they are possible to use on flexible substrates. Among them, lead halide perovskites have become one of the most popular choice in the scientific community, due to the great properties that this material presents. While efficiencies have risen above 25%, which is close to their maximum theoretical limit, there is still debate about the processes happening in the device. In this thesis, we try to gain insight into charge carrier processes from their generation to their recombination at both perovskite interfaces, and also in the bulk of the material. Using advanced characterization techniques, such as transient photovoltage (TPV), transient photocurrent (TPC), charge extraction (CE), and femtosecond transient absorption spectroscopy (fsTA) we obtained important findings about charge carrier losses, and artifacts affecting charge carrier recombination in functional devices that lead to lower power conversion efficiencies.

I present in this thesis a wide analysis of stochastic and deterministic models of the vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptor (VEGFR) on human umbilical vein endothelial cells (HUVEC). Firstly, the analysis addresses the contribution of ligand induced dimerisation, receptor competition between VEGFR1 and VEGFR2 and immediate or delayed dimers phosphorylation in the overall behaviour of the VEGFR/VEGF system. The analysis is based on van Kampen approximation of the solution of the corresponding master equations and matrix-analytic techniques to analyse different signalling hypotheses upon ligand stimulation. Secondly two mathematical models are provided, with accompanying quantitative experimental data, for binding and trafficking properties of VEGFR on HUVECs, which propose a theoretical dependence of ERK phosphorylation and transport rate of receptors from the Golgi to the cell surface on these properties. The signal for ERK phosphorylation or perturbation of transport rate is generated by intrinsic VEGFR tyrosine kinase activation via VEGF binding at the cell surface, and terminated by receptor/growth factor complex internalisation and degradation. Presented in this thesis models consist of kinetic equations which describe the binding, internalisation, recycling and synthesis of VEGF and VEGFR, along with a simple expression for the dependence of ERK phosphorylation or receptor synthesis on VEGFR/VEGF dynamics.

This thesis describes the development of a fast rate method for the deposition of high quality CdS and CdTe thin films. The technique uses Pulsed DC Magnetron Sputtering (PDCMS). Surprisingly, the technique produces highly stable process conditions. CREST is the first laboratory worldwide to show that pulsed DC power may be used to deposit CdS and CdTe thin films. This is a very promising process technology with potential for eventual industrial deployment. The major advantage is that the process produces high deposition rates suitable for use in solar module manufacturing. These rates are over an order of magnitude faster than those obtained by RF sputtering. In common with other applications it has also been found that the energetics of the pulsed DC process produce excellent thin film properties and the power supply configuration avoids the need for complex matching circuits. Conventional deposition methodologies for CdS, Chemical Bath Deposition (CBD) and CdTe thin films, Electrodeposition (ED), have been chosen as baselines to compare film properties with Pulsed DC Magnetron Sputtering (PDCMS). One of the issues encountered with the deposition of CdS thin films (window layers) was the presence of pinholes. A Plasma cleaning process of FTO-coated glass prior to the deposition of the CdS/CdTe solar cell has been developed. It strongly modifies and activates the TCO surface, and improves the density and compactness of the deposited CdS thin film. This, in turn, improves the optical and morphological properties of the deposited CdS thin films, resulting in a higher refractive index. The pinhole removal and the increased density allows the use of a much thinner CdS layer, and this reduces absorption of blue spectrum photons and thereby increases the photocurrent and the efficiency of the thin film CdTe cell. Replacing the conventional magnetic stirrer with an ultrasonic probe in the chemical bath (sonoCBD) was found to result in CdS films with higher optical density, higher refractive index, pinhole and void-free, more compact and uniform along the surface and through the thickness of the deposited material. PDCMS at 150 kHz, 500 W, 2.5 μs, 2 s, results in a highly stable process with no plasma arcing. It allows close control of film thickness using time only. The CdS films exhibited a high level of texture in the <001> direction. The grain size was typically ~50 nm. Pinholes and voids could be avoided by reducing the working gas pressure using gas flows ii below 20 sccm. The deposition rate was measured to be 1.33 nm/s on a rotating substrate holder. The equivalent deposition rate for a static substrate is 8.66 nm/s, which is high and much faster than can be achieved using a chemical bath deposition or RF magnetron sputtering. The transmission of CdS can be improved by engineering the band gap of the CdS layer. It has been shown that by adding oxygen to the working gas pressure in an RF sputtering deposition process it is possible to deposit an oxygenated CdS (CdS:O) layer with an improved band gap. In this thesis, oxygenated CdS films for CdTe TF-PV applications have been successfully deposited by using pulsed DC magnetron sputtering. The process is highly stable using a pulse frequency of 150 kHz and a 2.5 μs pulse reverse time. No plasma arcing was detected. A range of CdS:O films were deposited by using O2 flows from 1 sccm to 10 sccm during the deposition process. The deposition rates achieved using pulsed DC magnetron sputtering with only 500 W of power to the magnetron target were in the range ~1.49 nm/s ~2.44 nm/s, depending on the oxygen flow rate used. The properties of CdS thin films deposited by pulsed DC magnetron sputtering and chemical bath deposition have been studied and compared. The pulsed DC magnetron sputtering process produced CdS thin films with the preferred hexagonal <001> oriented crystalline structure with a columnar grain growth, while sonoCBD deposited films were polycrystalline with a cubic structure and small grainy crystallites throughout the thickness of the films. Examination of the PDCMS deposited CdS films confirmed the increased grain size, increased density, and higher crystallinity compared to the sonoCBD CdS films. The deposition rate for CdS obtained using pulsed DC magnetron sputtering was 2.86 nm/s using only 500 W power on a six inch circular target compared to the much slower (0.027 nm/s) for the sonoChemical bath deposited layers. CdTe thin films were grown on CdS films prepared by sonoCBD and Pulsed DC magnetron sputtering. The results showed that the deposition technique used for the CdS layer affected the growth and properties of the CdTe film and also determined the deposition rate of CdTe, being 3 times faster on the sputtered CdS. PDCMS CdTe layers were deposited at ambient temperature, 500 W, 2.9 μs, 10 s, 150 kHz, with a thickness of approximately 2 μm on CdS/TEC10 coated glass. The layers appear iii uniform and smooth with a grain size less than 100 nm, highly compact with the morphology dominated by columnar grain growth. Stress analysis was performed on the CdTe layers deposited at room temperature using different gas flows. Magnetron sputtered thin films deposited under low gas pressure are often subject to compressive stress due to the high mobility of the atoms during the deposition process. A possible way to reduce the stress in the film is the post-deposition annealing treatment. As the lattice parameter increased; the stress in the film is relieved. Also, a changing the deposition substrate temperature had an effect on the microstructure of CdTe thin films. Increasing the deposition temperature increased the grain size, up to ~600 nm. CdTe thin films with low stress have been deposited on CdS/TEC10 coated glass by setting the deposition substrate temperature at ~200°C and using high argon flows ~ 70 sccm Ar. Finally, broadband multilayer ARCs using alternate high and low refractive index dielectric thin films have been developed to improve the light transmission into solar cell devices by reducing the reflection of the glass in the extended wavelength range utilised by thin-film CdTe devices. A four-layer multilayer stack has been designed and tested, which operates across the wavelength range used by thin-film CdTe PV devices (400 850 nm). Optical modelling predicts that the MAR coating reduces the WAR (400-850 nm) from the glass surface from 4.22% down to 1.22%. The application of the MAR coating on a thin-film CdTe solar cell increased the efficiency from 10.55% to 10.93% or by 0.38% in absolute terms. This is a useful 3.6% relative increase in efficiency. The increased light transmission leads to improvement of the short-circuit current density produced by the cell by 0.65 mA/cm2. The MAR sputtering process developed in this work is capable of scaling to an industrial level.

There are long-standing hypotheses that endogenous ion currents act to control cell dynamics in development, wound healing and regeneration. However, the mechanisms employed by cells to detect the electric field (EF) and translate it into a discernable message to drive specific cell behaviors, such as migration, proliferation and differentiation, are not well understood. A better understanding of how cells are able to sense EFs and react to them is vital to understanding physiological mechanisms are involved in regeneration. Ion channel signaling provides a reasonable suspect for mediating these effects based on their documented involvement in proliferation, migration and differentiation. To investigate mechanisms underlying ionic regulation of critical cellular processes in non-excitable cells, a novel, in vivo assay was developed to screen multiple pharmacological inhibitors of ion channels during larval A. mexicanum tail regeneration. This assay was used to identify individual channels that were then targeted for further analysis regarding their involvement in the regenerative process. Chapter 2 presents data from a study that indicates that a wound-like response can be generated in an invertebrate model by application of exogenous, low-amplitude sine-wave electrical stimulation. This was characterized by recruitment of hemocytes at the stimulation site which was dependent on voltage-gated potassium channels. Chapter 3 presents data from a comprehensive and systematic screen of pharmacological compounds against larval salamander tail regeneration that indicates 8 specific target ion channels. This chapter also describes results indicating specific mechanisms by which these channels may be perturbing regeneration. Chapter 4 presents data that indicate that the Anoctamin 1 channel identified in the aforementioned screen is a regulator of cellular proliferation. This is shown to be accomplished via amplification of intracellular calcium surges and a subsequent increase in the activity of the p44/42 MAPK signaling cascade.

Solid oxide fuel cells (SOFCs) represent a next generation energy source with high energy conversion efficiency, low pollutant emission, good flexibility with a wide variety of fuels, and excellent modularity suitable for distributed power generation. As an electrochemical energy conversion device, SOFC’s performance and reliability depend sensitively on the catalytic activity and stability of the electrode materials. To date, however, the development of electrode materials and microstructures is still based largely on trial-and-error methods because of inadequate understanding of the mechanisms of the electrode processes. Identifying key descriptors/properties of electrode materials or functional heterogeneous interfaces, especially under in situ conditions, may provide guidance to the design of electrode materials and microstructures. This thesis aims to gain insight into the electrochemical and catalytic processes occurring on the electrode surfaces using unique characterization tools with superior sensitivity, high spatial resolution, and excellent surface specificity applicable under in situ/operando conditions. Carbon deposition on nickel-based anodes is investigated with in situ Raman spectroscopy and SERS. Analysis shows a rapid nucleation of carbon deposition upon exposure to small amount of propane. Such nucleation process is sensitive to the presence of surface coating (e.g., GDC) and the concentration of steam. In particular, operando analysis of the Ni-YSZ boundary indicates special function of the interface for coking initiation and reformation. The coking-resistant catalysts (BaO, BZY, and BZCYYb) are systematically studied using in situ Raman spectroscopy, SERS, and EFM. In particular, time-resolved Raman analysis of the surface functional groups (-OH, -CO3, and adsorbed carbon) upon exposure to different gas atmospheres provides insight into the mechanisms related to carbon removal. The morphology and distribution of early stage carbon deposition are investigated with EFM, and the impact of BaO surface modification is evaluated. The surface species formed as a result of sulfur poisoning on nickel-based anode are examined with SERS. To identify the key factors responsible for sulfur tolerance, model cells with welldefined electrode-electrolyte interfaces are systematically studied. The Ni-BZCYYb interface exhibits superior sulfur tolerance. The oxygen reduction kinetics on LSCF, a typical cathode material of SOFC, is studied using model cells with patterned electrodes. The polarization behaviors of these micro- electrodes, as probed using a micro-probe impedance spectroscopy system, were correlated with the systematically varied geometries of the electrodes to identify the dominant paths for oxygen reduction under different electrode configurations. Effects of different catalyst modifications are also evaluated to gain insight into the mechanisms that enhance oxygen reduction activity. The causes of performance degradation of LSCF cathodes over long term operation are investigated using SERS. Spectral features are correlated with the formation of surface contamination upon the exposure to air containing Cr vapor, H2O, and CO2. Degradation in cathode performance occurs under normal operating conditions due to the poisoning effect of Cr from the interconnect between cells and the high operating temperature. The surface-modified LSCF cathode resists surface reactions with Cr vapor that impairs electrode performance, suggesting promising ways to mitigate performance degradation.

Thesis (Honors)--Ohio State University, 2006.
Title from first page of PDF file. Document formatted into pages: contains 20 p.; also includes graphics. Includes bibliographical references (p. 17-20). Available online via Ohio State University's Knowledge Bank.

Amino acid transport is controlled by a system of transporter proteins whose function remains poorly defined in CHO cells. In this thesis, the relationship between amino acid transporter activity and culture performance parameters was investigated and used as a basis to explore new opportunities for improving cell line productivity. Transcriptomic analysis of transporter expression was first performed in two non-producing CHO cell lines and one antibody-producing CHO cell line during fed-batch cultures. Seven transporters were highly expressed across the three cell lines (ASCT1, CAT-1, GLAST, LAT1, SNAT2, xCT and y+LAT2). For all cell lines, the cystine-glutamate xCT transporter was significantly upregulated at stationary phase and formed part of a larger adaptive response to support the cellular availability of glutathione. The antibodyproducing cell line also upregulated ASCT1 and LAT1 transporter expression during stationary phase, which allowed the cells to maintain a high consumption rate of amino acids abundant in the antibody. Cells were next treated with inhibitors that block amino acid transport through individual or groups of transporters. Inhibition results confirmed that xCT transport activity is a key determinant of culture viability in all cell lines, and along with LAT1, also supports specific productivity during late-stage culture in the antibody-producing cell line. A directed evolution strategy was subsequently developed to increase xCT transport capability in the host. Evolved host cells demonstrated an increased capacity for GSH synthesis, increased resistance to a ROS insult, and a heritable improvement in cell growth but were not able to outperform the unevolved host in the transient production of an IgG. Finally, a mechanistic model to describe essential amino acid transport processes in CHO cells was constructed from transcriptomic and inhibitor data. This model can be used to direct future optimisation of amino acid concentrations in culture media to maximise cell growth and antibody production.

Pour ce travail de thèse, le dépôt électrochimique de Ni/Cu est étudié en tant qu’alternative à la sérigraphie à base de pates d’Ag et Al pour métalliser les cellules solaires en silicium cristallin. Cette technique a le potentiel d’améliorer la qualité des contacts métalliques et d’augmenter l’efficacité des cellules solaires en silicium. Les métaux utilisés étant moins coûteux, une diminution des coûts de production est envisageable. Cependant, le dépôt Ni/Cu doit être amélioré pour une application industrielle dans le domaine photovoltaïque.L’objectif de cette thèse est d’étudier les différentes étapes du procédé de dépôt de Ni/Cu sur des cellules solaires n-PERT bifaciales afin de comprendre les mécanismes physicochimiques impliqués et résoudre les différents verrous relatifs à cette technique.La première étape, qui consiste à ouvrir selectivement les couches dielectriques par ablation laser, a été optimisée en choisissant des paramètres limitant l’endommagement du silicium sous-jacent. Un mécanisme d’ablation a également été proposé. La désoxydation et l’activation au palladium du silicium, ont été étudiés dans deux milieux fluorés (HF et NaHF2). De meilleurs résultats en terme de gravure du SiOx et d’activation ont été obtenus avec NaHF2. L’inhomogénité du dépôt de nickel a soulignée l’importance de réaliser ce dépôt dans l’obscurité. Une mauvaise adhérence sur surface polie a été observée et des axes d’amélioration ont été proposés. L’impact de paramètres de recuit non adaptés sur le rendement des cellules a été étudié. Un procédé de plating Ni/Cu optimisé a été developpé et des rendements similaires aux références sérigraphiées ont été obtenus
In this thesis work, Ni/Cu electrochemical deposition (“plating”) is studied as an alternative to the mainstream screen-printing technique based on Ag and Al metallic pastes to produce industrial c-Si solar cells. Ni/Cu plating has the potential to improve the quality of metallic contacts and increase c-Si solar cell efficiency. The use of cheaper metals is a strong asset to reduce the production costs. However, Ni/Cu plating is still at an introductory phase and there are some issues to deal with.The goal of this thesis is to investigate the successive steps of Ni/Cu plating process for bifacial n-PERT c-Si solar cells and understand the physico-chemical phenomena involved to address the related issues.On the first step, laser ablation parameters have been optimized to selectively ablate the dielectric layers while limiting the impact on the underlying Si. An ablation mechanism has also been proposed. Next steps of deoxidation and Pd activation of Si surface have been studied in two fluoride media (HF and NaHF2). NaHF2 provided higher SiOx etching rates and better Si surface activation. Next, homogeneity issues of Ni electroless deposition have been found, highlighting the need to make the deposition in dark conditions. Poor adherence on polished surface has been observed and areas of improvement have been suggested. The impact of non-optimized annealing parameters on cells conversion efficiencies has been demonstrated. The Ni/Cu plating process has been improved similar efficiencies than those of screen-printed reference cells have been achieved

Thin film chalcogenide solar cells are promising photovoltaic technologies. Cu(In,Ga)Se2 (CIGS)-based devices are already produced at industrial scale and record laboratory efficiency surpasses 22 %. Cu2ZnSn(S,Se)4 (CZTS) is an alternative material that is based on earth-abundant elements. CZTS device efficiency above 12 % has been obtained, indicating a high potential for improvement. In this thesis, in-line vacuum, sputtering-based processes for the fabrication of complete thin film chalcogenide solar cells on stainless steel substrates are studied. CIGS absorbers are deposited in a one-step high-temperature process using compound targets. CZTS precursors are first deposited by room temperature sputtering and absorbers are then formed by high temperature crystallization in a controlled atmosphere. In both cases, strategies for absorber layer improvement are identified and implemented. The impact of CZTS annealing temperature is studied and it is observed that the absorber grain size increases with annealing temperature up to 550 °C. While performance also improves from 420 to 510 °C, a drop in all solar cell parameters is observed for higher temperature. This loss is caused by blisters forming in the absorber during annealing. Blister formation is found to originate from gas entrapment during precursor sputtering. Increase in substrate temperature or sputtering pressure leads to drastic reduction of gas entrapment and hence alleviate blister formation resulting in improved solar cell parameters, including efficiency. An investigation of bandgap grading in industrial CIGS devices is conducted through one-dimensional simulations and experimental verification. It is found that a single gradient in the conduction band edge extending throughout the absorber combined with a steeper back-grading leads to improved solar cell performance, mainly due to charge carrier collection enhancement. The uniformity of both CIGS and CZTS 6-inch solar cells is assessed. For CZTS, the device uniformity is mainly limited by the in-line annealing process. Uneven heat and gas distribution resulting from natural convection phenomenon leads to significant lateral variation in material properties and device performance. CIGS solar cell uniformity is studied through laterally-resolved material and device characterization combined with SPICE network modeling. The absorber material is found to be laterally homogeneous. Moderate variations observed at the device level are discussed in the context of large area sample characterization. Power conversion efficiency values above 15 % for 225 cm2 CIGS cells and up to 5.1 % for 1 cm2 CZTS solar cells are obtained.

Thesis (PhD (Chemical Engineering))--Cape Peninsula University of Technology, 2019
The South African wine industry is constantly facing several challenges which affect the quality of wine, the local/global demand and consequently the revenue generated. These challenges include the ongoing drought, bush fires, climate change and several liquor amendment bills aimed at reducing alcohol consumption and alcohol outlets in South Africa. It is therefore critical for the wine industry to expand and find alternative ways in which sub-standard or surplus wine grapes can be used to prevent income losses and increase employment opportunities. Traditional Balsamic Vinegar (TBV) is a geographically and legislative protected product produced only in a small region in Italy. However, the methodology can be used to produce similar vinegars in other regions. Balsamic-styled vinegar (BSV), as defined in this thesis, is a vinegar produced by partially following the methods of TBV while applying process augmentation techniques. Balsamic-styled vinegar is proposed to be a suitable product of sub-standard quality or surplus wine grapes in South Africa. However, the production of BSV necessitates the use of cooked (high sugar) grape must which is a less favourable environment to the microorganisms used during fermentation. Factors that negatively affect the survival of the microorganisms include low water activity due to the cooking, high osmotic pressure and high acidity. To counteract these effects, methods to improve the survival of the non-Saccharomyces yeasts and acetic acid bacteria used are essential. The primary aim of this study was to investigate several BSV process augmentation techniques such as, aeration, agitation, cell immobilization, immobilized cell reusability and oxygen mass transfer kinetics in order to improve the performance of the microbial consortium used during BSV production. The work for this study was divided into four (4) phases. For all the phases a microbial consortium consisting of non-Saccharomyces yeasts (n=5) and acetic acid bacteria (n=5) was used. Inoculation of the yeast and bacteria occurred simultaneously. The 1st phase of the study entailed evaluating the effect of cells immobilized by gel entrapment in Ca-alginate beads alongside with free-floating cells (FFC) during the production of BSV. Two Ca-alginate bead sizes were tested i.e. small (4.5 mm) and large (8.5 mm) beads to evaluate the effects of surface area or bead size on the overall acetification rates. Ca-alginate beads and FFC fermentations were also evaluated under static and agitated (135 rpm) conditions. The 2nd phase of the study involved studying the cell adsorption technique for cell immobilization which was carried-out using corncobs (CC) and oak wood chips (OWC), while comparing to FFC fermentations. At this phase of the study, other vinegar bioreactor parameters such as agitation and aeration were studied in contrast to static fermentations. One agitation setting (135 rpm) and two aeration settings were tested i.e. high (0.3 vvm min−1) and low (0.15 vvm min−1) aeration conditions. Furthermore, to assess the variations in cell adsorption capabilities among individual yeast and AAB cells, the quantification of cells adsorbed on CC and OWC prior- and post-fermentation was conducted using the dry cell weight method. The 3rd phase of the study entailed evaluating the reusability abilities of all the matrices (small Ca-alginate beads, CC and OWC) for successive fermentations. The immobilized cells were evaluated for reusability on two cycles of fermentation under static conditions. Furthermore, the matrices used for cell immobilization were further analysed for structure integrity by scanning electron microscopy (SEM) before and after the 1st cycle of fermentations. The 3rd phase of the study also involved the sensorial (aroma and taste) evaluations of the BSV’s obtained from the 1st cycle of fermentation in order to understand the sensorial effects of the Ca-alginate beads, CC and OWC on the final BSV. The 4th phase of the study investigated oxygen mass transfer kinetics during non-aerated and aerated BSV fermentation. The dynamic method was used to generate several dissolved oxygen profiles at different stages of the fermentation. Consequently, the data obtained from the dynamic method was used to compute several oxygen mass transfer parameters, these include oxygen uptake rate ( 𝑟𝑟𝑂𝑂2 ), the stoichiometric coefficient of oxygen consumption vs acid yield (𝑌𝑌𝑂𝑂/𝐴𝐴), the oxygen transfer rate (𝑁𝑁𝑂𝑂2 ), and the volumetric mass transfer coefficients (𝐾𝐾𝐿𝐿𝑎𝑎). During all the phases of the study samples were extracted on weekly intervals to evaluate pH, sugar, salinity, alcohol and total acidity using several analytical instruments. The 4th phase of the study involved additional analytical tools, i.e. an oxygen µsensor to evaluate dissolved oxygen and the ‘Speedy breedy’ to measure the respiratory activity of the microbial consortium used during fermentation. The data obtained from the 1st phase of the study demonstrated that smaller Ca-alginate beads resulted in higher (4.0 g L-1 day−1) acetification rates compared to larger (3.0 g L-1 day−1) beads, while freely suspended cells resulted in the lowest (0.6 g L-1 day−1) acetification rates. The results showed that the surface area of the beads had a substantial impact on the acetification rates when gel entrapped cells were used for BSV fermentation. The 2nd phase results showed high acetification rates (2.7 g L-1 day−1) for cells immobilized on CC in contrast to cells immobilized on OWC and FFC, which resulted in similar and lower acetification rates. Agitated fermentations were unsuccessful for all the treatments (CC, OWC and FFC) studied. Agitation was therefore assumed to have promoted cell shear stress causing insufficient acetification during fermentations. Low aerated fermentations resulted in better acetification rates between 1.45–1.56 g L-1 day−1 for CC, OWC and FFC. At a higher aeration setting, only free-floating cells were able to complete fermentations with an acetification rate of 1.2 g L-1 day−1. Furthermore, the adsorption competence data showed successful adsorption on CC and OWC for both yeasts and AAB with variations in adsorption efficiencies, whereby OWC displayed a lower cell adsorption capability compared to CC. On the other hand, OWC were less efficient adsorbents due to their smooth surface, while the rough surface and porosity of CC led to improved adsorption and, therefore, enhanced acetification rates. The 3rd phase results showed a substantial decline in acetification rates on the 2nd cycle of fermentations when cells immobilized on CC and OWC were reused. While cells entrapped in Ca-alginate beads were able to complete the 2nd cycle of fermentations at reduced acetification rates compared to the 1st cycle of fermentations. The sensory results showed positive ratings for BSV’s produced using cells immobilized in Ca-alginate beads and CC. However, BSV’s produced using OWC treatments were neither ‘liked nor disliked’ by the judges. The SEM imaging results further showed a substantial loss of structural integrity for Ca-alginate beads after the 1st cycle fermentations, with minor changes in structural integrity of CC being observed after the 1st cycle fermentations. OWC displayed the same morphological structure before and after the 1st cycle fermentations which was attributed to their robustness. Although Ca-alginate beads showed a loss in structural integrity, it was still assumed that Ca-alginate beads provided better protection against the harsh environmental conditions in contrast to CC and OWC adsorbents due to the acetification rates obtained on both cycles. The 4th phase data obtained from the computations showed that non-aerated fermentations had a higher 𝑌𝑌𝑂𝑂/𝐴𝐴, 𝑟𝑟𝑂𝑂2 , 𝑁𝑁𝑂𝑂2 and a higher 𝐾𝐾𝐿𝐿𝑎𝑎 . It was clear that aerated fermentations had a lower aeration capacity due to an inappropriate aeration system design and an inappropriate fermentor. Consequently, aeration led to several detrimental biochemical changes in the fermentation medium thus affecting 𝐾𝐾𝐿𝐿𝑎𝑎 and several oxygen mass transfer parameters which serve as a driving force. Overall, it was concluded that the best method for BSV production is the use of cells entrapped in small alginate beads or cells adsorbed on CC under static and non-aerated fermentations. This conclusion was based on several factors such as cell affinity/cell protection, acetification rates, fermentation period and sensorial contributions. However, cells entrapped in Ca-alginate beads had the highest acetification rates. The oxygen mass transfer computations demonstrated a high 𝐾𝐾𝐿𝐿𝑎𝑎 when Ca-alginate beads were used under static-non-aerated conditions compared to fermentations treated with CC. Therefore, a fermentor with a high aeration capacity needs to be designed to best suit the two BSV production systems (Ca-alginate beads and CC). It is also crucial to develop methods which can increase the robustness of Ca-alginate beads in order to improve cell retention and reduce the loss of structural integrity for subsequent cycles of fermentation. Studies to define parameters used for upscaling the BSV production process for large scale productions are also crucial.

Leader cells are a fundamental biological process that have only been investigated since the early 2000s. These cells have often been observed emerging at the edge of an artificial wound in 2D epithelial cell collective invasion, created with either a mechanical scrape from a pipette tip or from the removal of a plastic, physical blocker. During migration, the moving cells maintain cell-cell contacts, an important quality of collective migration; the leader cells originate from either the first or the second row, they increase in size compared to other cells, and they establish ruffled lamellipodia. Recent studies in 3D have also shown that cells emerging from an invading collective group that also exhibit leader-like properties. Exactly how leader cells influence and interact with follower cells as well as other cells types during collective migration, however, is another matter, and is a subject of intense investigation between many different labs and researchers. The majority of leader cell research to date has involved epithelial cells, but as collective migration is implicated in many different pathogenic diseases, such as cancer and wound healing, a better understanding of leader cells in many cell types and environments will allow significant improvement to therapies and treatments for a wide variety of disease processes. In fact, more recent studies on collective migration and invasion have broadened the field to include other cell types, including mesenchymal cancer cells and fibroblasts. However, the proper technology for picking out dynamic, single cells within a moving and changing cell population over time has severely limited previous investigation into leader cell formation and influence over other cells. In line with these previous studies, we not only bring new technology capable of dynamically monitoring leader cell formation, but we propose that leader cell behavior is more than just an epithelial process, and that it is a critical physiological process in multiple cell types and diseases.

An investigation has been made into the structure and properties of polycrystalline CuxS-CdS solar cells in order to develop an improved understanding of some of the processes which lead to unsatisfactory reproducibility and long term stability of the characteristics of these devices. The cells studied during this project were fabricated using vacuum evaporation for production of the CdS base layer and the well known chemical exchange process in a CuCl solution for formation of the CuxS layer. In view of the non-uniform thickness of the CuxS layer and non-planar structure of the Cu, S-CdS interface, it was found to be necessary to employ a variety of different characterisation techniques to monitor changes in the structure and properties of the devices. These techniques included I/V, C-V, spectral response and sheet resistance measurements, electrochemical analysis, cathodoluminescence spectroscopy and Rutherford backscattering. Detailed consideration was given to the influence of the conditions of formation on the properties of each cell component, in order to establish procedures necessary for the production of reproducible structures. particular attention was paid to the rate of growth of the CuxS layer and a theoretical analysis was developed to account for the time dependence of the growth in mean thickness of the CuxS layer in terms of the contributions associated with growth at the surface of the CdS layer and in the CdS grain boundary regions. The grain boundary contribution was found to be very sensitive to the CdS grain structure and to the previous treatment given to the CdS layer. Pre-annealing in air at 2000C enhanced the grain boundary penetration while the effect of ion implantation (with either Cu or Zn ions) was found to depend on the initial structure and the implantation conditions, but substantial improvements in the photovoltaic conversion efficiency were shown to be possible as a result of such treatment.The rate of degradation of cells exposed to air was also found to be dependent on the previous history of the cell. An increased concentration of Cd in the CuxS film (due to diffusion from the CdS layer) appeared to reduce the rate of qegradation while use of the standard stabilizing treatment (deposition of Cu overlayer followed by annealing in air) was shown to reduce interfacial diffusion as well as protecting the front surface of the CuxS layer against oxidation.

A conceptual framework for the design and performance evaluation of flexible manufacturing cells (FMCS) based on the strategic objectives of firms was developed. Four different types of manufacturing task profiles were identified based on the primary manufacturing task, product characteristics, and manufacturing system characteristics of a strategic business unit (SBU). Performance measures were discussed for each of the manufacturing task profiles, and the task profiles of firms likely to implement FMCs were identified.

A methodology, based on the analytic hierarchy process (AHP), introduced by Saaty, was developed to prioritize the manufacturing objectives of an FMC. The implications of each of the manufacturing objectives for an FMC were hypothesized and related performance measures identified. An interactivecomputer-based model, based on the theory of closed network-ofâ queues, was then developed to aid in the preliminary design and evaluation on an FMC.

Field work was cariied out to determine the practical applicability of the conceptual framework. Visits to a company in the Southeastem United States were made and an analysis of the FMC being developed in the Department of Industrial Engineering and Operations Research, at Virginia Tech was conducted.

The framework developed in this research was used to determine the manufacturing task profile of the company, identify key performance measures, and exercise the AHP methodology for one cell. Operational measures were then calculated for the FMC, using the computer-based model.

Master of Science

Nowadays mono- and multicrystalline silicon have the highest market share of all PV technologies but thin film solar cells based on CdTe or Cu(In,Ga)Se2 (CIGS) absorbers recently show promising high power conversion efficiency values and due to their short energy payback time, minimal use of high purity material and low cost, they attract more and more attention. However, one concern of thin film PV based on CdTe or CIGS is the use of scare elements like tellurium or indium and gallium which could become a bottleneck if the technology wants to scale up to the terawatt level. Therefore, there is a high interest to replace these scare elements by more abundant ones and find suitable earth abundant photovoltaic absorbers. Cu2ZnSnSe4 (CZTSe) or Cu2ZnSnS4 (CZTS) and its sulphur-selenide solid solution are promising candidates to replace CIGS as absorber material due to its composition of more earth abundant elements. In literature CZTSe and CZTS are referred to as kesterite due to its crystal structure. However, there is still a large gap between power conversion efficiencies of solar cells based on kesterite absorber material and more established thin film solar cells, thus intensive research is still necessary to close this gap. The main goal of this thesis was to develop and optimize heterostructure solar cells based on Cu2ZnSnSe4 absorbers, by cost effective physical vapour deposition (PVD) and chemical based processes. Special focus is put on an improved understanding of the influence of the surface properties of kesterite absorbers on device performance and furthermore to optimize the front interface, i.e. buffer layer as well as the kesterite absorber layer itself. A detailed study investigating the influence of the surface chemistry on device performance is presented. After a chemical etching to remove unwanted ZnSe secondary phases formed during CZTSe absorber synthesis a low temperature post deposition annealing at 200ºC of the full solar cell is necessary to improve device efficiencies from below 3% to over 8%. X-ray photoelectron spectroscopy (XPS) surface analysis showed that this post deposition annealing promotes the diffusion of Zn towards the surface and Cu towards the bulk resulting in a Zn enriched and Cu depleted surface region, which is crucial for high device performance. Additionally experimental surface treatments confirm the necessity of a Cu-poor and Zn-rich surface and the reason for this beneficial surface composition are discussed in detail. Furthermore, the CdS buffer layer which is typically used in kesterite based heterostructures solar cells was optimized and allowed improvements in device performance of 1% absolute. This optimization was further extended to Cd-free ZnS(O,OH) buffer layer. Efficiencies close to that of CdS reference solar cells could be achieved using optimized ZnS(O,OH) buffer layer. Additionally to the front interface optimization, a Ge assisted crystallization process for nanocrystalline CZTSe precursors was developed which largely increase grain growth and boost open circuit voltages (Voc) to promising high values due to the elimination of deep defects. Since the low Voc values is identified of one of the main bottlenecks of kesterite technology, the improvements achieved are highly promising and give important insight for further possible optimizations.
Los compuestos Cu2ZnSnSe4 (CZTSe), Cu2ZnSnS4 (CZTS) y Cu2ZnSnSexS4-x (CZTSSe) también conocidos como kesteritas debido a su estructura, presentan propiedades prometedoras para sustituir a la tecnología de células solares de capa fina basadas en Cu(In,Ga)Se2, evitando el problema potencial que podría generar el uso de indio y galio. A día de hoy, las eficiencias obtenidas en dispositivos de CIGS, son bastante mayores que las reportadas para dispositivos de kesteritas, debido entre otras razones a la diferencia en la madurez de dicha tecnología. Por lo tanto, es necesario un estudio más profundo de los materiales y dispositivos basados en kesteritas, enfocado a aumentar los valores de eficiencia de los dispositivos. El objetivo principal de esta Tesis Doctoral es el desarrollo y optimización de células solares con capas absorbentes basadas en el compuesto CZTSe por métodos de bajo coste incluyendo procesos de deposición física en fase vapor, así como también por procesos químicos. Se ha prestado especial interés en aumentar el conocimiento sobre la influencia de las propiedades de la superficie de la capa absorbente en el funcionamiento de las células solares. Estos estudios incluyen la optimización de la capa de kesterita, y también de su interfaz con la capa “buffer” o semiconductor tipo n en la heterounión. Se incluye un estudio detallado de la influencia de las propiedades químicas de la superficie del absorbente en la eficiencia de los dispositivos. Además, se presentan los estudios de optimización de la capa buffer basada en CdS y de capas buffer libres de Cd, usando como alternativa ZnS(O,OH), donde se obtuvieron eficiencias comparables con las de los dispositivos de referencia fabricados con CdS. Finalmente, se presenta un estudio de recristalización asistida por una capa nanométrica de Ge depositada en los precursores nano cristalinos. Se demuestra que este proceso induce un aumento significativo del crecimiento de los granos del absorbedor, reduciendo la presencia de defectos profundos eléctricamente activos que resultan perjudiciales para las propiedades de los dispositivos fotovoltaicos. Las mejoras presentadas en este estudio son altamente prometedoras y conducen hacia nuevas rutas de optimización en la fabricación de estos dispositivos.

EBAG9 (estrogen receptor-binding fragment-associated gene 9) hat als unabhängiger prognostischer Marker viel Aufmerksamkeit erregt, da in einigen Tumoren hohe Expressionsraten und Tumorentwicklung korrelieren. In diesen Fällen ist eine hohe EBAG9 Expression häufig mit einer schlechten klinischen Prognose verbunden. EBAG9 ist ein ubiquitär exprimiertes Golgi Protein. Aktuelle Daten demonstrieren, dass es in sekretorischen Zellen an der regulierten Exozytose und an der zytotoxischen Funktion von Lymphozyten beteiligt ist. In epithelialen Zellen führt es zur Generierung von Tumor-assoziierten O-Glykanen, welche ein Erkennungsmerkmal vieler Krebsarten sind. In dieser Arbeit wurde der pathogenetische Zusammenhang zwischen EBAG9 Expression und der Veränderung des zellulären Glykoms untersucht. Um einen tieferen Einblick in die zelluläre Funktion von EBAG9 in epithelialen Zellen zu gewinnen, wurden Zellen mit tumorähnlicher EBAG9 Expression verwendet. Innerhalb dieser Arbeit wurde demonstriert, dass EBAG9 mit anterograden COPI Vesikeln assoziiert und zwischen dem ER-Golgi intermediären Kompartiment und cis-Golgi pendelt. EBAG9 verursacht eine Verzögerung des anterograden Transportes vom ER zum Golgi und verändert die Lokalisation von Komponenten der ER Qualitätskontrolle und des Glycosylierungsapparates. Auf der anderen Seite beschleunigt die verminderte Expression von EBAG9 den Proteintransport durch den Golgi und verstärkt die Aktivität von Mannosidase II. Mechanistisch betrachtet verhindert EBAG9 die Rekrutierung von ArfGAP1 an die Membran. Dies beeinträchtigt das Auflösen der COPI Vesikelhülle und somit die Fusion von Vesikeln am cis-Golgi. Damit agiert EBAG9 in epithelialen Zellen als negativer Regulator des COPI-abhängigen ERGolgi Transportes und stellt damit ein neues phatogenetisches Prinzip dar, bei dem die Beeinflussung des intrazellulären Transportes zu der Entstehung von Tumor-assoziierten Glykanen führt.
The estrogen receptor-binding fragment-associated gene 9 (EBAG9) has received increased attention as an independent prognostic marker for disease-specific survival since in some human tumor entities high expression levels correlate with tumor progression and poor clinical prognosis. Interestingly, EBAG9 was identified as an ubiquitously expressed Golgi protein. Recent data demonstrate an involvement in regulated exocytosis in secretory cells and the cytotoxic functions of lymphocytes. However, EBAG9 is expressed in essentially all mammalian tissues, and in epithelial cells it has been identified as a modulator of tumorassociated O-linked glycan expression, a hallmark of many carcinomas. This thesis addresses the pathogenetic link between EBAG9 expression and the alteration of the cellular glycome. To gain further insights into the cellular functions of EBAG9 in epithelial cells, tumor-associated EBAG9 overexpression was mimicked in living cells. It was demonstrated that EBAG9 associates with anterograde COPI-coated carriers and shuttles between the ER-Golgi intermediate compartment and cis-Golgi stacks. EBAG9 overexpression imposes a delay in anterograde ER-to-Golgi transport and mislocalizes components of the ER quality-control and glycosylation machinery. Conversely, EBAG9 downregulation accelerates glycoprotein transport through the Golgi and enhances mannosidase activity. Functionally, EBAG9 impairs ArfGAP1 recruitment to membranes and consequently, interferes with the disassembly of the coat lattice at the cis-Golgi prior to fusion. Thus, EBAG9 acts as a negative regulator of a COPI-dependent ER-to-Golgi transport pathway in epithelial cells and represents a novel pathogenetic principle in which interference with intracellular membrane trafficking results in the emergence of a tumor-associated glycome.

Epithelial ovarian cancer frequently metastasizes to the omentum, a process that requires pro-angiogenic activation of local microvascular endothelial cells (ECs) by tumour-secreted factors. We have previously shown that ovarian cancer cells secrete factors, other than vascular endothelial growth factor (VEGF), with possible roles in metastatic angiogenesis including the lysosomal proteases cathepsin L (CathL) and cathepsin D (CathD), and insulin-like growth factor binding protein 7 (IGFBP7). However, the mechanisms by which these factors may contribute to omental endothelial angiogenic changes are unknown. Therefore the aims of this thesis were a) to examine disease relevant human omental microvascular endothelial cell (HOMEC) proliferation, migration and angiogenesis tube-formation induced by CathL, CathD and IGFBP7; b) to investigate whether CathL and CathD act via a proteolytic or non-proteolytic mechanism; c) to identify activated downstream intracellular signalling cascades in HOMECs and their activation in proliferation and migration; and finally d) to identify activated cell surface receptors by these factors. CathL, CathD and IGFBP7 significantly induced proliferation and migration in HOMECs, with CathL and CathD acting in a non-proteolytic manner. Proteome-profiler and ELISA data identified increased phosphorylation of the ERK1/2 and AKT (protein kinase B) pathways in HOMECs in response to these factors. CathL induced HOMEC proliferation and migration via the ERK1/2 pathway, whereas, although CathD-induced proliferation was mediated by activation of ERK1/2, its migratory effect was dependent on both ERK1/2 and AKT pathways. Interestingly, CathL induced secretion of galectin-1 (Gal1) from HOMECs which in turn significantly induced HOMEC proliferation via ERK1/2. However, none of the ERK1/2 or AKT pathways was observed to be active in Gal1-induced HOMEC migration. Interestingly, Gal1-induced proliferation and migration were significantly inhibited by L-glucose, suggesting a role for a receptor with extracellular sugar moieties. IGFBP7-induced migration was shown to be mediated via activation of the ERK1/2 pathway only. CathL, Gal1 and IGFBP7 significantly induced angiogenesis tube-formation in HOMECs which was not observed in CathD-treated cells. Receptor tyrosine kinase array revealed activation of Tie-1 and VEGF receptor type 2 (VEGFR2) in CathL and IGFBP7-treated HOMECs respectively. In conclusion, all CathL, CathD, Gal1 and IGFBP7 have the potential to act as proangiogenic factors in the metastasis of ovarian cancer to the omentum. These in vitro data suggest all four factors activate intracellular pathways which are involved in well-known angiogenesis models.

Polymer electrolyte membrane fuel cells (PEMFCs) are a promising alternative to combustion engines and batteries in vehicles. PEMFCs are more efficient than combustion engines, and cars powered by PEMFCs tend to have longer ranges than battery powered cars and has a short fuelling time. To gain significant market shares, the costs of PEMFCs need to be reduced. This work aims to achieve this by improving the production process of bipolar plates, which significantly contribute to the total cost of fuel cells. In conventional production methods bipolar plates are formed by stamping at room temperature which limits the degree of deformation that can be achieved before exceeding the structural integrity of the material. It is expected that stamping at elevated temperatures will increase the forming limit of the material and therefore the flexibility in forming the channel geometry of bipolar plates. This has the potential to simplify the manufacturing process and improve the resulting performance of fuel cells.  The goal of this thesis is to establish to what degree the forming at elevated temperatures facilitates higher degrees of deformation. Different heating methods are benchmarked and analysed numerically in order to identify the most suitable one for stamping experiments at elevated temperatures. Out of six investigated heating concepts, direct resistive heating is identified as the most suitable one. The suitability of the concept is supported by numerical simulations. The direct resistive heating system is designed and integrated into the existing experimental setup.  Four flow channel geometries with channel widths of 1 mm, 0.8 mm, 0.6 mm, and 0.56 mm are investigated in stamping experiments using the identified heating method. Samples are formed at 150 °C, 300 °C, 600 °C, and 900 °C. Hexagonal Boron Nitride is used as a lubricant. The stamping experiments performed at elevated temperatures indicate that the formability of the bipolar plates improves as compared to the cold-formed reference experiments. The best results are obtained at 900 °C where the average channel depth, which can be formed before cracks are observed in the samples, could be improved by 27% compared to channels formed at room temperature.
Polymerelektrolytmembranbränsleceller (PEMFC) är ett lovande alternativ till förbränningsmotorer och batterier i fordon. Fordon som drivs av PEMFC har en längre räckvidd än batteridrivna bilar och behöver bara några minuter för att tanka. PEMFC kan drivas utan utsläpp av växthusgaser. För att få betydande marknadsandelar måste tillverkningskostnaderna för dessa bränsleceller minskas. Detta kan uppnås genom att förbättra produktionsprocessen. Dessutom kan en förbättrad prestanda för bränslecellen leda till en minskning av storlek, materialanvändning och därmed produktionskostnader. Denna uppsats undersöker stämpling av metalliska bipolära plattor, som har en betydande del av kostnaden för en PEMFC. I konventionella produktionsmetoder bildas flödesfältgeometrin vid omgivningstemperaturer vilket begränsar den grad av deformation som kan uppnås innan materialets strukturella gränser överskrids. Det förväntas att stämpling vid förhöjd temperatur ökar formningsgränsen för materialet och därför flexibiliteten vid formning av kanalgeometrin. Detta förväntas förenkla tillverkningsprocessen och förbättra bränslecellens resultat. Målet med denna avhandling är att testa denna hypotes och fastställa hur förhöjda temperaturer underlättar högre deformationsgrader. För att uppnå detta används olika uppvärmningsmetoder som riktmärken och analyseras numeriskt för att identifiera den lämpligaste metoden för experiment med hetstämpling. Av sex undersökta värmekoncept identifieras direkt resistiv uppvärmning som den mest lämpliga. Konceptets lämplighet stöds av numeriska simuleringar. Det direktresistiva uppvärmningssystemet är utformat och integrerat i den befintliga experimentella installationen. Fyra olika kanalgeometrier undersöks. Prover bildas vid 150 ° C, 300 ° C, 600 ° C och 900 ° C. Hexagonal bornitrid används som smörjmedel. Stämplingsexperimenten utförda vid förhöjda temperaturer indikerar att de bipolära plattornas formbarhet förbättras jämfört med de kallformade referensexperimenten. De bästa resultaten erhålls vid 900 ° C där det genomsnittliga kanaldjupet, som kan bildas innan sprickor observeras i proverna, skulle kunna förbättras med 27% jämfört med formningen vid rumstemperatur.

En aquesta tesi s'han dut a terme dos tipus d'estudis diferents. L'objectiu del primer era la preservació del semen de porcí a 15ºC i el del segon eren els co-cultius homòlegs de cèl·lules epitelials de l'oviducte i espermatozoides de porcí.
Pel que fa al primer estudi, s'ha observat que l'addició de la prostaglandina F2α i àcid hialurònic a les dosis seminals no malmena la qualitat espermàtica i que la tolerància dels espermatozoides als canvis d'osmolalitat del medi es pot correlacionar proves de fertilitat i prolificitat..
Respecte el segon, s'ha determinat que les cèl·lules oviductals afecten els paràmetres espermàtics i que la presència d'espermatozoides sobreexpressa els gens que codifiquen per les proteïnes de xoc tèrmic. Així, se suggereix que aquestes proteïnes tenen algun paper en els processos reproductius que tenen lloc a l'oviducte, malgrat que s'hagi observat, mitjançant la tècnica de la interferència de l'RNA, que la HSP90AA1 no està implicada en el perllongament de la viabilitat espermàtica.
In this thesis, two different studies have been conducted. The aim of the first experimental chapter was boar sperm preservation at 15ºC, the second dealing with in vitro homologous co-culture of oviductal epithelial cells (OEC) and spermatozoa.
Regarding the first, it has been observed that the addition of prostaglandin F2α and hyaluronic acid do not cause any harm on sperm quality, and the osmotic tolerance of spermatozoa can be correlated with fertility and prolificacy rates of a given ejaculate.
As far as the second study is concerned, OEC specifically affect sperm functional parameters and the presence of spermatozoa upregulates the expression of some genes encoding for heat shock proteins. Some role in the reproductive processes taking place in the oviduct is therefore suggested for this protein family, even though it has been observed, by means of RNA interference, that HSP90AA1 is not the protein involved in prolonging sperm survival.

Cells, either as unicellular organisms or as part of a tissue of a multicellular organism, can acquire different functions thanks to their capability of changing their expression state. The enzyme synthesis, cell division or cell differentiation are some examples of these functions. The turning on and off of them lie in the mechanisms by which cells are able to integrate the information they perceive from the environment. Frequently, cells exhibit different responses under the same stimulus or environment. These probabilistic processes, whose behaviours are not univocal, are known as "cellular decision making". We can classify these processes according to the range at which the decision is made. We denominate cell-autonomous decision those in which of each cell chooses its response independently of the choice of the other cells of the population. By contrast, if the decision is made collectively by the whole population, it is classified as non autonomous. This second type of decisions involve mechanisms of cell-to-cell communication that mediate in the choices the cells and so, some spatial distributions of the different cell states can arise. The capability of cellular decision making processes of performing a variety of responses under a same signal is given by the multistability and the stochasticity of their dynamics. While multistability is underlain by the nonlinear interactions of the elements involved in genetic regulation, stochasticity arises from the discrete nature of biochemical reactions and the thermal fluctuations of the cellular environment. These two characteristics motivate the study of these processes from Systems Dynamics the point of view, by identifying cell states with system attractors. This Thesis focuses on the study of the general dynamical mechanisms that control cellular decision making processes. The main goal is to connect the properties of the decision with the relevant dynamical behaviour of the system while it is being made. We have analysed the properties of cellular decisions in two systems: a system with cell-autonomous dynamics, where cells choose their state regardless the choice of the others; and a system where the decision is made jointly by all the tissue. In this second system, cells interact through a cell-to-cell communication that takes place at first neighbours. From these interactions, different pattern solutions arise, where different different cell types are spatially distributed along the tissue. Finally, it has been analysed the role that a specific choice, whose probability value is well known, plays in the functionality of an organism. The chosen system to study these consequences has been a process of differentiation that the parasite that causes malaria in humans performs.
Cada célula, ya se como organismo unicelular o formando parte de un organismo multicelular, tiene que desarrollar distintas funciones a lo largo de su vida. Algunos ejemplos de estas funciones son tales como la síntesis de encimas, dividirse o diferenciarse en otro tipo celular. La activación y desactivación de muchas de estas funciones está sujeta a la integración de la información que la célula percibe de su entorno. A menudo, las células exhiben respuestas distintas bajo un mismo estímulo o bajo unas mismas condiciones del entorno. Estos procesos probabilísticos son conocidos como "toma de decisiones celulares". Estos eventos celulares se puede desarrollar de forma autónoma por cada célula, o de forma colectiva por toda una población o tejido. En este segundo caso, se requiere de algún mecanismo que medie en la comunicación entre células. Esta capacidad de estos sistemas de producir una variedad de respuestas es otorgada por la multiestabilidad y estocasticidad de sus dinámicas. Estas características motivan el estudio de estos procesos desde la perspectiva de la Dinámica de Sistemas, identificando los estados celulares a los atractores del sistema. Esta Tesis se centra en el estudio de los mecanismos dinámicos genéricos que controlan la toma de decisiones celulares. Se ha caracterizado la conexión entre las propiedades de una decisión y el mecanismo subyacente que la genera. Dos tipos decisiones autónomas han sido analizadas de acuerdo a esta perspectiva. También se ha estudiado los mecanismos dinámicos que llevan a la selección de un patrón espacial concreto en un escenario de decisión no autónoma, en el que las células interactúan entre sí a primeros vecinos mediante una inhibición lateral. Estas decisiones han revelado como la simetría especial de la señal inductora de las mismas afecta a la solución final alcanzada por el tejido. Finalmente, se ha analizado el papel que la probabilidad de una decisión concreta y bien conocida puede desarrollar en la viabilidad del organismo implicado. El sistema de estudio escogido ha sido un proceso de diferenciación que lleva a cabo el parásito responsable de causar la malaria en humanos.

Semiconductor multijunction solar cell is a cutting-edge photovoltaic technology aimed at developing a frontier solution to the clean energy demand and environmental problem. Due to the efficient photoabsorption and energy conversion in the visible and near-infrared spectral ranges of the solar spectrum, the multijunction solar cell structures have shown an unprecedented application potential by demonstrating a solar conversion efficiency of over 44 %. Among various multijunction solar cell structural designs, the GaxIn1-xP/GaAs double-junction tandem structure is considered as the most fundamental building block for developing the industry-standard triple- and even more junction photovoltaic cells with super high efficiency. Therefore, obtaining a better and more in-depth understanding of physical properties of the GaxIn1-xP/GaAs double-junction tandem device structure, especially some fundamental optoelectronic processes in the individual structural layer, including photoexcitation, transport and the mid-way recombination of charge carriers, is crucial for further improving the energy conversion efficiency. In this thesis, the mid-way radiative recombination, diffusion transport, localization mechanism, and photocurrent spectra of charge carriers in the GaxIn1-xP/GaAs double-junction tandem solar cells grown on GaAs substrates with different misorientation angles were investigated in detail. Our main findings are summarized as below. Efficient radiative recombination of carriers in the GaxIn1-xP/GaAs double-junction tandem solar cell samples was demonstrated by using electroluminescence (EL) and photoluminescence (PL) techniques. The radiative recombination intensity was shown to be dependent on the intrinsic material-related parameters such as the doping concentration, growth thickness and the substrate misorientation angle both experimentally and theoretically. The radiative recombination was thus revealed to be an important loss channel of carriers in the GaxIn1-xP/GaAs double-junction tandem solar cells. Super strong transverse diffusion of minority carriers in the top GaxIn1-xP subcell was found by the micro-EL image surveying. Theoretical simulation on the experimental data shows that the minority carrier diffusion length is as long as ~93 μm at a forward bias of 2.75 V, which is ~30 times longer than that of unbiased GaxIn1-xP epilayer. Origin of this super transverse diffusion was argued, and its influence on device performance was also discussed. Significant correlations of carrier localization and luminescence behaviors with the substrate misorientation angle in the top GaxIn1-xP subcells were unveiled by excitation intensity- and temperature-dependent PL. The large difference in potential energy profile of GaxIn1-xP layers, caused by the different degrees of atomic ordering, was argued to interpret the observed PL distinctions. Vertical transport and photoresponse mechanisms of charge carriers in the GaxIn1-xP/GaAs double-junction tandem solar cells were studied by temperature- and reverse bias-dependent photocurrent (PC) spectroscopy. Both the temperature and reverse bias were shown to have significant impact on the device photoresponse, in particular on the photoresponse due to the absorption of photons with energy above the bandgap of GaAs and GaxIn1-xP, namely the supra-bandgap photoresponse. A model was proposed to simulate the observed temperature- and reverse-bias dependence of the supra-bandgap photoresponse.
published_or_final_version
Physics
Doctoral
Doctor of Philosophy

Il sistema immunitario è un esempio di un sistema biologico caratterizzato da varie scale di complessità che può essere modellizzato con un approccio fisico ricorrendo agli strumenti dei sistemi complessi, e in particolare ai processi stocastici. Si tratta di un argomento indubbiamente affascinante, dal momento che il sistema immunitario gioca un ruolo fondamentale nel proteggere l’organismo dalle minacce esterne. In particolare la parte del sistema immunitario cosiddetta adattiva, di cui fanno parte le T-cells, è in grado di produrre una risposta specifica modulando costantemente il numero di cellule che esprimono ciascun recettore, in base al variare della composizione del pool di patogeni con cui l’organismo interagisce. Dunque le T-cells formano un insieme, detto repertorio, in continua evoluzione, che contiene informazioni sulle sfide affrontate dal sistema immunitario di un individuo. Oltre a poter modellizzare la risposta a uno stimolo specifico, come può essere un’infezione o un vaccino, altrettanto importante come punto di partenza è investigare il funzionamento di base del sistema immunitario in individui sani. Il presente lavoro si propone dunque di studiare la dinamica naturale del repertorio delle T-cells, intesa come l’evoluzione dinamica quando l’interazione con l’ambiente non è dominata da uno stimolo forte e preciso. Inserendosi nel solco tracciato dai modelli stocastici per il sistema immunitario, lo scopo è quello di analizzare dati di individui sani e identificare una dinamica stocastica di base, con un approccio data-driven. A questo scopo vengono considerati diversi modelli che tengono conto della stocasticità intrinseca nel sistema o dell’interazione con l’ambiente, e viene costruita un’analisi che permette di discriminare quale sia il meccanismo dominante. Viene inoltre tracciato un quadro di inferenza statistica per determinare i parametri di tali modelli.

This thesis explores three routes to alleviating the economic barriers to proton exchange membrane fuel cells through reducing, recycling and removing platinum group metals (PGMs). The reduction of PGM content is explored using electrochemistry to assess the novel materials produced when combining fullerene based compounds with electron beam lithography. This technique yields the potential to precisely control the distance between platinum (or other metal) atoms embedded within carbon materials. It is shown that the material alters the onset potential of proton reduction compared to glassy carbon and the methodology for study is developed. The recycling of PGMs is demonstrated by testing the electrochemical behaviour and particle structure of deposited palladium within biomass produced through biohydrometallurgy. Electron microscopy and electrochemistry is used to investigate the biohydrometallurgy process and how the substrate, leachate and reducing agent effect both the particles produced and the electrochemistry observed. Concluding that the un-processed materials may function as future electrocatalysts without further processing steps. The removal of PGM content is investigated, through the electrochemical characterisation of the adsorbed layers and solutions of phosphomolybdic acid, singularly substituted vanadophosphomolybdic acid and doubly substituted vanadophosphomolybdic acid. Describing the complicated multi-electron, multi-step redox chemistry of the potential mediator species, with specific focus on electrode material and the effect of pH.