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No description available.

This work investigates the effects of long range hydrodynamic fibre-fibre interactions on the orientation state of a semi-dilute, rigid fibre suspension flowing through a linear contracting channel under laminar flow conditions. The effects of fibre-fibre interactions are modeled mathematically, the governing equations solved numerically and the predicted results compared with experimental observations. The theoretical model is based on the assumption that the orientation state of the suspension can be completely described by a probability distribution function and that fibre-fibre interactions are random in nature, thus giving rise to a diffusion-type process. The orientation distribution evolves spatially according to a Fokker-Plank type equation using closure equations for the rotary diffusion coefficient advanced by either (i) Folgar and Tucker (J. Reinforced Plast. Comp. 3 98–119 1984) or (ii) Koch (Phys. Fluids 7(8) 2086–2088 1995). Each of these two closure models for the rotary diffusion coefficient contains an unknown empirical constant that must be determined from experiments. These were fit to experimental data along the central streamline of the contraction as a function of fibre concentration. The diffusion coefficient was found to first increase with increasing suspension concentration up to a maximum, and then decrease with concentration above this point. This non-monotonic behavior was attributed to fibre flocculation, a mechanism not considered in the relationships for the rotary diffusion coefficient. The theoretical model is then extended to predict fibre orientation over the entire plane of the contraction and the two-way momentum coupling between the fluid and fibre phases were investigated numerically. The results show that the structure of the flow field within the contraction is significantly altered when the fibre phase is considered, demonstrating the non-negligible effect of the momentum exchange between the two phases. Comparison is made between the predicted orientation state of the suspension with experimental observations over the contraction plane. Good agreement was found between the model predictions and the experimental observations except in a small region near the solid boundaries. These near wall discrepancies were attributed to an inability to correctly handle the wall boundary conditions in the fibre orientation model.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 177-190). Also available via the Internet.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 140-147).

Ce travail concerne le développement de méthodes de commandes avancées pour les suspensions automobiles afin d'améliorer la tenue de route des véhicules et le confort des passagers, tout en respectant les contraintes technologiques liées aux actionneurs de suspension (passivité, non-linéarités, limite structurelle). Dans la 1ère partie, nous proposons deux schémas de commande par approche LPV polytopique (Linéaire à Paramètre Variant) et Stabilisation Forte (Strong Stabilization) avec optimisation par algorithme génétique pour résoudre les conflits confort/tenue de route et confort/débattement de suspension. Dans la 2ème partie, pour résoudre le problème complet de commande de suspensions semi-actives, nous développons d'abord une stratégie générique pour les systèmes LPV généraux soumis à la saturation des actionneurs et à des contraintes d'état. Le problème est étudié sous la forme de résolution d'inégalités linéaires matricielles (LMI) qui permettent de synthétiser un contrôleur LPV et un gain anti wind-up garantissant la stabilité et la performance du système en boucle fermée. Ensuite, cette stratégie est appliquée au cas de la commande des suspensions semi-actives. Les méthodes proposées sont validées par une évaluation basée sur un critère industriel et des simulations effectuées sur un modèle non-linéaire de quart de véhicule. / This work concerns the development of advanced control methods for automotive suspensions to improve road holding and passenger comfort, while satisfying the technological constraints related to the suspension actuators (passivity, nonlinearity, structural limit). In the first part, we propose two control schemes by polytopic LPV (Linear Parameter Varying) approach and by Strong Stabilization with genetic algorithm optimization to solve the comfort/handling and comfort/suspension travel conflits. In the second part, to solve the full semi-active suspension problem, we develop first a generic strategy for general LPV systems subject to actuator saturation and state constraints. The problem is studied in the form of resolution matrix of linear inequalities (LMI) that allows synthesizing an LPV controller and an anti-windup gain to ensure the stability and performance of the closed-loop system. Second, the theoretical result is applied to the case of semi-active suspension control. The proposed methods are validated by an evaluation based on an industrial standard and simulations on a nonlinear quarter vehicle model.

A estabilização de suspensões de alumina é essencial para a fabricação de vários produtos, especialmente na indústria cerâmica e com o controle das propriedades que se pode atingir usando polímeros como agentes estabilizantes. Na busca de processos industriais que preservem o meio ambiente, polímeros sintéticos podem ser substituídos por biopolímeros, com a vantagem adicional de encontrar usos nobres para rejeitos, como quitina, da qual se obtêm a quitosana e ligninas. Nesta tese, os derivados carboximetilados de celulose, a carboximetilcelulose (CMC) e quitosana, a carboximetilquitosana (CMQ) foram preparados e caracterizados por Espectroscopia de Ressonância Magnética Nuclear de Próton (1HRMN), Espectroscopia na Região do Infravermelho (FTIR), Termogravimetria (TG), Calorimetria Diferencial Exploratória (DSC), Difração de raios X, Cromatografia de Exclusão por Tamanho (SEC). O derivado obtido da lignina, a carboximetil-lignina, (CML) foi caracterizado por Espectroscopia na Região do Infravermelho (FTIR), Termogravimetria (TG), Calorimetria Diferencial Exploratória (DSC). Os três derivados obtidos foram usados como agentes estabilizantes para suspensões aquosas de alumina. A reação de carboximetilação ocorreu em meio heterogêneo, gerando derivados solúveis em água. O grau de substituição (GS) para as carboximetilceluloses foi determinado por 1HRMN, obtendo-se valores de 0,7; 1,3 e 1,8 para as três amostras analisadas nesse trabalho. Para as carboximetilquitosanas, o GS foi determinado por FTIR e análise elementar sendo obtidos valores de 0,6 e 0,8 para duas amostras de CMQ. O valor de GS de 0,5 para carboximetil-lignina foi obtido por titulação potenciomêtrica. Os derivados CMC, CMQ e CML permitiram a estabilização de suspensões de alumina, como demonstrado em medidas de tamanho de partículas, potencial zeta e viscosidade. De relevância especial foi a estabilização em altos valores de pHs, incluindo o ponto de carga zero, pcz, no qual a atração entre as partículas de alumina, de cargas opostas, é máxima, levando a aglomeração de partículas em suspensões sem agentes de estabilização. A distribuição de tamanhos de partícula também foi afetada positivamente com a incorporação dos derivados. De maneira geral, os resultados com os derivados foram promissores em termos de potencial zeta e tamanho de partícula no pcz da alumina, o intervalo de interesse deste trabalho. O destaque é para o derivado de celulose, a CMC GS 1,3 que obteve a melhor performance dentre todos do derivados levando aos menores valores de viscosidade para a suspensão, salientando que esta foi preparada com alto teor de sólidos, nas mesmas condições de suspensões utilizadas em processamentos cerâmicos,. Foi importante também a estabilização ao longo do tempo das suspensões contendo CMC, CMQ e CML, pois o tamanho médio de partícula permaneceu invariável por períodos de até 2 horas, tempo suficiente para processos de moldagem de cerâmicos como extrusão, injeção, tap-casting. O uso de derivados carboximetilados de lignina, quitosana e celulose, como agentes estabilizantes de suspensões de alumina, abre caminho para novas aplicações de produtos obtidos a partir de fontes naturais e renováveis, em substituição aos tradicionalmente usados, oriundos de fontes fósseis. / The stabilization of alumina suspensions is crucial for the fabrication of various products, especially in the ceramic industry, with fine control of materials properties being reached using polymers as stabilizing agents. In this context, in the search for environmentally-friendly industrial processes, synthetic polymers may be replaced with biopolymers, with the added advantage of providing noble uses for waste materials such as those deriving from lignins and chitosans. In this thesis, carboxymethylated cellulose (CMC) and chitosan (CMQ) were prepared and characterized with proton nuclear magnetic resonance (1HNMR), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), differential scanning calorimetry (DSC), X-ray diffraction and size exclusion chromatography (SEC). Carboxymethylated lignin (CML) was characterized with Fourier Transform infrared (FTIR) spectroscopy, thermogravimetry (TG) and DSC. These three derivatives were used as stabilizing agents in aqueous solutions of alumina. The carboxymethylation reaction was carried out in a heterogeneous medium yielding water-soluble derivatives. GS values of 0.7, 1.3 and 1.8 for CMC were obtained with 1HNMR measurements, while values of 0.6 and 0.8 for CMQ were determined using FTIR and elemental analysis. For CML, GS = 0.5 was found using potentiometric titration. The success of the carboxymethylation was confirmed via 1HNMR measurements. The effectiveness of the derivatives CMC, CMQ and CML as stabilizing agents was proven by measuring the size distribution of particles, viscosity and zeta potential of alumina suspensions. Of particular relevance was the stabilization at high pHs, including the point of zero charge (pcz) for which attraction between oppositely charged particles is maximum, where alumina particles normally agglomerate in the absence of stabilizing agents. The particle size distributions were also affected positively by incorporation of the derivatives. Overall, the data presented indicated that CML was responsible for optimized results for the zeta potential and mean particle size at the pzc of alumina suspensions. The CMC with GS = 1.3 exhibited the best performance with the lowest viscosity values at the pcz, even in dispersions with high contents of solid materials which are the conditions prevailing in ceramic processes. Also worth mentioning was the stability over time of the alumina suspensions incorporating CMQ, CML and CMC, with the average particle size remaining the same for 1-2 hours, which is a sufficient period of time for ceramic molding processes such as extrusion, injection and tap-casting. The use of carboxymethylated derivatives of lignin, chitosan and cellulose as stabilizing agents opens the way for the development of new products from natural and renewable sources, to replace those materials traditionally used which are obtained from fossil sources.

Magister Pharmaceuticae - MPharm / Co-crystals are a solid phase phenomena that could enhance the physicochemical properties of an active pharmaceutical ingredient. A co-crystal has never been incorporated into a liquid dosage form with the assurance of maintaining its co-crystal state until absorption under defined conditions. This study aims to develop a liquid formulation with a nevirapine co-crystal. A protocol was developed to investigate all the five co-formers that were used to make the nevirapine co-crystals to-date. The most appropriate co-former was selected for a liquid dosage form to study the integrity and the scaling up of the co-crystal in a suspension formulation. Co-formers used were viz. saccharin, glutaric acid, salicylic acid, rac-tartaric acid and maleic acid. These were characterized according to their physical, chemical, pharmacological and pharmaceutical properties. A grading scale was used to select the most appropriate co-former for a suspension formulation. Comparatively, saccharin produced the best combination of physical, chemical, pharmacological and pharmaceutical properties, especially with regard to the particle size and the specific gravity which proved to be very useful as optimal criteria for suspension formulation. Upon selection of the ideal co-former, scale-up of the nevirapine saccharin co-crystal was performed from a small scale of 350 mg to a large scale of 5 g. Nevirapine-saccharin (NVSC) co-crystals were prepared utilizing the slow evaporation technique, using methanol as the solvent and the percentage yield of the co-crystals were > 80 %. The identity of co-crystals was confirmed using hot stage microscopy (HSM), differential scanning calorimetry (DSC), fourier transform infra- red (FTIR) and thermogravimetric analysis (TGA). Three co-crystal suspension formulations were prepared using the excipients identified in the branded, Viramune® suspension, with each formulation containing viscosity enhancers such as aerosil 200, carbopol 971G and carbopol 974P. To ascertain the co- crystal integrity in the suspension, it was filtered and the filtrate was identified with DSC and FTIR while the filtered solution was identified with ultraviolet spectroscopy (UV). The co-crystal suspension formulation with optimal pH, viscosity and assurance of co-crystal integrity was the carbopol 974P formulation. The UV and DSC of the filtrate of the suspension revealed that the co-crystal had not separated into its individual components and remained intact while in suspension form irrespective of the excipients added. This formulation proceeded to the quality control stage. It was assessed for its pH, viscosity and dissolution according to the USP 32 standards and compared to the branded nevirapine suspension, Viramune ®, presently on the market. The suspension was characterized for particle size, zeta potential and polydispersity index. The dissolution results assayed by High Performance Liquid Chromatography (HPLC) revealed a drug release of 86 % in the Viramune® suspension while the NVSC co- crystal suspension achieved a drug release of 94% within 30 minutes of dissolution. / National Research Foundation (NRF)

This work investigates the effects of long range hydrodynamic fibre-fibre interactions on the orientation state of a semi-dilute, rigid fibre suspension flowing through a linear contracting channel under laminar flow conditions. The effects of fibre-fibre interactions are modeled mathematically, the governing equations solved numerically and the predicted results compared with experimental observations. The theoretical model is based on the assumption that the orientation state of the suspension can be completely described by a probability distribution function and that fibre-fibre interactions are random in nature, thus giving rise to a diffusion-type process. The orientation distribution evolves spatially according to a Fokker-Plank type equation using closure equations for the rotary diffusion coefficient advanced by either (i) Folgar and Tucker (J. Reinforced Plast. Comp. 3 98–119 1984) or (ii) Koch (Phys. Fluids 7(8) 2086–2088 1995). Each of these two closure models for the rotary diffusion coefficient contains an unknown empirical constant that must be determined from experiments. These were fit to experimental data along the central streamline of the contraction as a function of fibre concentration. The diffusion coefficient was found to first increase with increasing suspension concentration up to a maximum, and then decrease with concentration above this point. This non-monotonic behavior was attributed to fibre flocculation, a mechanism not considered in the relationships for the rotary diffusion coefficient. The theoretical model is then extended to predict fibre orientation over the entire plane of the contraction and the two-way momentum coupling between the fluid and fibre phases were investigated numerically. The results show that the structure of the flow field within the contraction is significantly altered when the fibre phase is considered, demonstrating the non-negligible effect of the momentum exchange between the two phases. Comparison is made between the predicted orientation state of the suspension with experimental observations over the contraction plane. Good agreement was found between the model predictions and the experimental observations except in a small region near the solid boundaries. These near wall discrepancies were attributed to an inability to correctly handle the wall boundary conditions in the fibre orientation model. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

No description available.