Thesis (M.S.)--University of Wisconsin--Madison, 1965. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 49-50.

Th. doct.--Sci. des matériaux--Paris 6, 1997. / Bibliogr. p. 148-153. Résumé en français et en anglais. 1998 d'après la déclaration de dépôt légal.

Soit $F_n$ le groupe libre de rang $n$. On considère le groupe $IA_n$ des automorphismes de $F_n$ qui agissent trivialement sur son abélianisé. Deux filtrations canoniques de $IA_n$ sont définies : la première est sa suite centrale descendante $\Gamma_*$ ; la seconde est la filtration d’Andreadakis $\mathcal A_*$, définie à partir de l’action sur $F_n$. Le problème d’Andreadakis est l’étude de la différence entre ces deux filtrations. Après avoir mis en place un cadre général pour l’étude de telles filtrations et des filtrations sur les algèbres de groupes qui leur sont associées, nous étudions différentes versions de ce problème. En particulier, nous examinons sa restriction à certains sous-groupes de $IA_n$ : nous montrons que les deux filtrations coïncident si on les restreint aux groupes triangulaires et aux groupes de tresses. Nous examinons aussi le problème stable : nous montrons que le morphisme canonique entre les algèbres de Lie associées aux filtrations est surjectif si $n$ est assez grand devant le degré considéré. Nous étudions également une version $p$-restreinte du problème, calculant au passage l’algèbre de Lie du groupe de congruence. Les méthodes employées sont essentiellement d’ordre algébrique. Elles proviennent de la théorie combinatoire des groupes ainsi que d’outils développés pour l’étude des groupes de difféotopie, et sont souvent reformulées avec un langage catégorique approprié. / Let $F_n$ be the free group on $n$ generators. Consider the group $IA_n$ of automorpisms of $F_n$ acting trivially on its abelianization. There are two canonical filtrations on $IA_n$: the first one is its lower central series $\Gamma_*$; the second one is the Andreadakis filtration $\mathcal A_*$, defined from the action on $F_n$. Andreadakis asked if and how these filtrations were different. We begin by describing a framework adapted to the study of such filtrations and their counterparts on group algebras. We then study several versions of the problem. In particular, we look at its restriction to some subgroups of $IA_n$ : we show that the two filtration coïncide when restricted to the triangular subroups and to braid groups. We also consider a stable version of the problem : we establish that the canonical morphism between the associated graded Lie rings is surjective when $n$ is big enough compared to a fixed degree. We also investigate a $p$-restricted version of the Andreadakis problem, and provide a calculation of the Lie algebra of the classical congruence group. Our methods are algebraic in nature. The tools come from combinatorial group theory and the study of mapping class groups; we often introduce some categorical langage to reformulate them.

The lack of a suitable system for hot gas cleaning is the greatest obstacle to the development of gasification combined-cycle power generation. In this work, a shallow 0.15 m diameter fluidised bed of 1 mm sand particles was used as a filter for 0.5-10 mum gasifier char particles redispersed in nitrogen at 700-900°C and 1 bar a. Earlier work has suggested that, for a correctly-designed low free-area distributor, initial collection efficiencies greater than 99% at 2 could be realised but that poor retention limits the overall filtration efficiency. As an aid to retention, heavy fuel oil was sprayed continuously into the bed using a concentric-tubs atomiser. With this arrangement, theoretically-predicted filtration efficiencies were approached for particles below; 7 mum in size, but the overall performance was seriously marred by secondary aerosol originating from the addition of the oil itself. The results suggested that two modes of filter operation are possible; at lower gas and retention-aid flowrates the challenging aerosol is retained on the collector; at higher gas and retention-aid flov/rates the challenging aerosol is agglomerated and re-emitted from the bed in a distribution with a larger mean size. The operation of various instruments for particle size measurement below 10 mum has been reviewed, and their capabilities have been compared by experiment. The method selected (collection in a liquid impinger, followed by off-line analysis by "Coulter Counter") is described in detail. The addition of a liquid retention-aid to a fluidised bed can cause modification of its fluidisation behaviour, leading eventually to catastrophic defluidisation. Theoretical and experimental aspect of these effects are discussed, leading to the development of an experimental method for direct measurement of interparticle forces, and an expression for the transition condition between Geldart's (1973) groups A and B.

A dupla filtração pode ser considerada como uma das mais promissoras tecnologias para tratamento de água, estimando-se que grande parte das necessidades de tratamento poderiam ser satisfeitas com o uso desta tecnologia. Alguns aspectos ainda não devidamente esclarecidos até o presente sobre esta tecnologia estão relacionados ao tratamento de água com turbidez elevada. Com a montagem e operação de uma instalação piloto, constituída de dois sistemas de dupla filtração (sistema 1: filtro ascendente de areia grossa e filtro descendente de areia e sistema 2: filtro ascendente de pedregulho e filtro descendente de areia), foi realizada uma investigação experimental com águas de estudo preparadas com caulinita (água tipo I com turbidez em torno de 100 uT e água tipo II com turbidez em torno de 300 uT). A coagulação foi realizada com o sulfato de alumínio, sem o uso de alcalinizante ou de acidificante, para que resultasse potencial zeta próximo de zero. A operação de ambos os sistemas foi efetuada com e sem descargas de fundo intermediárias nos filtros ascendentes, e foram variadas as taxas de filtração em ambos os filtros (de 120 a 240 m&sup3/m&sup2.d nos filtros ascendentes e de 180 a 300 m&sup3/m&sup2.d nos filtros descendentes). Concluiu-se principalmente que os dois sistemas foram capazes de produzir água filtrada com turbidez consistentemente menor que 0,5 uT e que a produção efetiva de água depende da turbidez da água de estudo, das taxas de filtração, da execução das descargas de fundo intermediárias e da carga hidráulica disponível para retenção de sólidos. / Double filtration may be considered one of the most important technologies for water treatment. It has been estimated that most of water treatment can be efficiently achieved with the use of this technology, although some design and operational aspects related to the high turbidity of the influent water have not been fully studied until the present time. A pilot plant was built comprising two double filtration systems (system 1 with an upflow coarse sand filter followed by a downflow fine sand filter; system 2 with an upflow gravel filter followed by a downflow filter identical to that used in system 1). The experimental investigation was carried out using influent waters prepared with kaolin (water type I with turbidity of approximately 100 NTU and water type II with turbidity of approximately 300 NTU). Coagulation was accomplished by using aluminum sulfate (no acid or alkaline products) so that the zeta potential resulted approximately zero. The operation of both systems was carried out with and without intermediate down flushes during the runs. Filtration rates in the filters of both systems varied from 120 to 240 m&sup3/m&sup2.d in the upflow filters and from 180 to 300 m&sup3/m&sup2.d in downflow filters. It was mainly concluded that both systems resulted capable to produce filtered water with turbidity consistently lower than 0.5 NTU and that the net production was related to the influent water turbidity, filtration rates, execution of intermediate down flushes and the hydraulic head provided for solids retention in both filter of each double filtration system.

Mechatronics involves the combination of the disciplines of Mechanical Engineering and Electrical Engineering with computer technology. The purpose of this work is to incorporate mechatronics technology into a novel experimental apparatus and perform a series of experiments to generate data on the filter cycle using this novel technique. The experimental data generated are compared with results obtained from a selection of existing theoretical models which successfully demonstrates the advantages of the novel technology used.

Malgré les ressources importantes en eau de la République Centrafricaine 70 % de la population ne dispose pas d’eau potable et la question se pose cruellement de potabiliser l’eau . Nous nous sommes intéressés à la technique d'adsorption sur une brique locale comme adsorbant aisément accessible pour purifier l'eau en milieu rural. Après traitement acide et dépôt de ferrihydrite à pH fixé, la brique s’est avérée être un bon adsorbant par échanges d'ions. Le composite obtenu, permet ainsi la rétention de cations métalliques tels : Fe2+, Pb2+, Zn2+, Cu2+, Ni2+, Cd2+ et UO2+ et selon le traitement préalable d'anions tels les phosphates grâce aux charges opposées entre la surface du solide et les ions dans l'eau. L’influence de paramètres : temps de contact, température, masse d’adsorbant et pH, ont été pris en compte. La régénération sur colonne a été effectuée par une solution de NaCl ou de NaClO. L’étude analytique de cycles d’adsorption/désorption sur colonne a mis en évidence l’implication des espèces H+ et Na+ à l’interface « brique-eau ». Pour justifier nos hypothèses, diverses techniques ont été utilisées: Diffraction RX, MEB /EDS, IRTF, BET, RMN 23Na, 29Si, 27Al, 1H. Les mesures des adsorptions ont été suivies in situ par potentiométrie et conductimétrie.Les isothermes d'adsorption, la cinétique et thermodynamie des processus hétérogènes mis en jeu ont été abordés. Les mesures électrocinétiques ont confirmé l'implication de forces électrostatiques dans le mécanisme d'adsorption. / Despite the great ressources of water in Centrafrican Republic, drinking water is not accessible for about 70% of the population in this country. To resolve this problem, waters need to be treated. We have chosen the adsorption technique,by using a local brick as adsorbant in the purification of water in rural region. After acid treatment and deposition of ferrihydrite at a fixed pH, brick was found to be a good adsorbant in the elimination : Fe2+, Pb2+, Zn2+,Cu2+, Ni2+, Cd2+, UO2+. This adsorption process was also applied to phosphates elimination. The effects of the parameters: contact time, temperature, mass of material, and pH were taken into account. Column regeneration was performed either by using NaCl solution or NaClO as eluent. The analytical studies of adsorption/desorption cycles on the column showed the implication of H+ and Na+ ions at the "brick-water" interface. Depending upon the treatment used, cations or anions could be adsorbed owing to the existence of opposite charges between solid surface and ions in water. To ascertain our assumptions, several techniques were used : X-Ray diffraction, SEM /EDS, FTIR, BET, 23Na, 29Si, 27Al, and 1H NMR. Adsorption measurements were also followed by potentiometry and conductimetry. Adsorption isotherms, kinetics and thermodynamie of heterogeneous processes involved were addressed. Electrokinetic measurements conformed the involvement of electrostatic forces in the adsorption mechanism.

<div>Bacteria which enter a viable but non-culturable state cannot be concentrated by enrichment. This means they may not reach a detectable concentration for PCR methods - especially in the presence of sample compounds which may act as PCR reaction inhibitors. An alternative strategy for concentration of bacteria from aqueous samples is explored in this work using tangential flow filtration. The effectiveness of this technology to concentrate pathogens from food-derived samples was previously demonstrated; however, losses of bacteria to the filtration system can still be high (i.e. recovery of bacteria is low). </div><div>The goal of this research was to maximize recovery of pathogenic microorganisms from hollow fiber filtration processes while also maximizing flux. In this way, high recovery filtration conditions could be selected while keeping filtration time low. It was hypothesized that flux would have relatively lower impact on final recovery of bacteria at high shear rates (27,000 1/s) which are sufficient to remove attached bacteria on surfaces. It was hypothesized that these high shear rates would not cause loss of bacterial viability, and the main cause of bacterial losses during filtration would be accumulation on the membrane surface.</div><div>To test these hypotheses, single fiber filter modules (both microfilters and ultrafilters with 0.5 mm inner diameter), were constructed and used to concentrate GFP-producing Escherichia coli at a wide range of flux conditions. Post-concentration, fluorescence micrographs of bisected hollow fibers illustrated patterns of bacterial accumulation along the length of the fiber. A simple recovery model was constructed to predict recovery as a function of flux and shear rate, and predictions were compared against the experimental data. </div><div>Both in the experiments and in the simple recovery model developed in this dissertation, recoveries near 90% were achievable at high shear rates when flux was ≤0.5 mL min-1 cm-2. This amounted to a 3-hour filtration time for a 225 mL sample. Compared to a filtration with only 30% recovery, detectable bacteria concentrations could be achieved with lower starting concentrations – ~5 CFU/mL starting concentration versus at least 15 CFU/mL. Given these high recoveries (determined with plating methods on agar) occurred at high pressure and shear conditions, it was determined the filtration did not affect bacterial viability. </div><div>In addition to using the model to predict recovery at various shear and flux conditions, it would be helpful to predict module designs or concentration strategies which could improve bacterial recoveries from the filter. One strategy, explored with preliminary data, was to pre-develop a layer of bacteria on the filter surface prior to concentrating samples. </div><div>Understanding and reducing the losses of bacteria during tangential flow filtration could enable detection of dilute levels of viable but non-culturable microorganisms; in addition, sensitivity of detection could be improved for quickly concentration culturable microorganisms in food and water samples.</div><div><br></div>

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