Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 248-250. / Ph.D.

Cette étude s’inscrit dans le domaine de la description de la dynamique des ceintures deradiation terrestres. Elle consiste à modéliser le phénomène de diffusion radiale en travaillantavec une résolution spatio-temporelle plus fine que celle utilisée pour décrire la dynamiquedes ceintures par le biais d’une équation de diffusion. La démarche s’est organisée en troistemps. Tout d’abord, l’objectif a été d’étudier le phénomène de diffusion radiale d’un point devue théorique afin de mettre en lumière les principaux pilotes du processus et d’expliciter uneformulation des coefficients de diffusion radiale. Une fois l’expression de ces coefficientsétablie, l’objectif a ensuite été de les quantifier. Pour cela, nous avons développé desprotocoles analytiques et numériques puis des protocoles expérimentaux. Nous avons discutéles résultats obtenus ainsi que les atouts et les limites de ces protocoles. Cette étude met enévidence le rôle central de l’asymétrie des variations du champ électromagnétique et deschamps électriques induits dans le processus de diffusion radiale. Elle propose des pistes pourla quantification numérique et expérimentale de ces deux pilotes. Elle apporte également unregard critique sur les travaux de la littérature. Elle ouvre la voie pour une nouvellequantification des coefficients de diffusion basée sur une modélisation adéquate de ladynamique de l’environnement électromagnétique / This study falls within the field of the Earth’s radiation belt dynamics. It consists of modelingthe radial diffusion process based on a spatiotemporal resolution higher than the resolution atwhich radiation belt dynamics are described in terms of a diffusion equation. The approachhas been organized in three parts. First, we described radial diffusion theoretically,highlighting the main drivers of the phenomenon and giving a ready-made formula of theradial diffusion coefficients. Then, based on this formula, we aimed to quantify the radialdiffusion coefficients. In order to reach this goal, we developed analytical and numericalprocedures, and then, observational procedures. Finally, we discussed the results and the prosand cons of each method. This study highlights the central role of asymmetric variations ofthe electromagnetic fields and induced electric fields in the driving of the intensity of theradial diffusion process. It provides tracks for numerical and experimental quantification ofthese two drivers. It also provides tools for a critical review of the literature. It paves the wayfor a more accurate determination of radial diffusion coefficients based on a more precisedescription of the electromagnetic environment and its variations.

<p>One of the most conspicuous problems in space physics for the last decades has been to theoretically describe how the large parallel electric fields on auroral field lines can be generated. There is strong observational evidence of such electric fields, and stationary theory supports the need for electric fields accelerating electrons to the ionosphere where they generate auroras. However, dynamic models have not been able to reproduce these electric fields. This thesis sheds some light on this incompatibility and shows that the missing ingredient in previous dynamic models is a correct description of the electron temperature. As the electrons accelerate towards the ionosphere, their velocity along the magnetic field line will increase. In the converging magnetic field lines, the mirror force will convert much of the parallel velocity into perpendicular velocity. The result of the acceleration and mirroring will be a velocity distribution with a significantly higher temperature in the auroral acceleration region than above. The enhanced temperature corresponds to strong electron pressure gradients that balance the parallel electric fields. Thus, in regions with electron acceleration along converging magnetic field lines, the electron temperature increase is a fundamental process and must be included in any model that aims to describe the build up of parallel electric fields. The development of such a model has been hampered by the difficulty to describe the temperature variation. This thesis shows that a local equation of state cannot be used, but the electron temperature variations must be descibed as a nonlocal response to the state of the auroral flux tube. The nonlocal response can be accomplished by the particle-fluid model presented in this thesis. This new dynamic model is a combination of a fluid model and a Particle-In-Cell (PIC) model and results in large parallel electric fields consistent with in-situ observations.</p>

This thesis deals with the use of electric fields for evaluation and control of chemical systems. An electric field can result in the flow of charge across an interface between a metal and a solution, by means of chemical reactions. This interplay between electricity and chemistry, i.e. electrochemistry, is a field of crucial importance both within research and industry. Applications based on electrochemical principles encompass such diverse areas as batteries and fuel cells, pH electrodes, and the glucose monitor used by people suffering from diabetes.A major part of the present work concerns the use of static electric fields in solutions containing a non-contacted metal surface. In such a setup it is possible to control the extent of electrochemical reactions at different positions on the metal. This allows the formation and evaluation of various types of gradients on electrodes, via indirectly induced electrochemical reactions. This approach is a new and simple way of forming for instance molecular gradients on conducting surfaces. These are very advantageous in biomimetic research, because a gradient contains a huge amount of discrete combinations of for example two molecules. The basis for the technique is the use of bipolar electrochemistry. Briefly, a surface can become a bipolar electrode (an electrode that acts as both anode and cathode) when the electric field in the solution exceeds a certain threshold value, thereby inducing redox reactions at both ends. In our experiments, the driving force for these reactions will vary along the electrode surface. Since the result of an electrochemical reaction can be the deposition or removal of material from an electrode, bipolar electrochemistry can be used to create gradients of that material on a surface. In order to gain a deeper understanding of these processes, the potential and current density distributions at bipolar electrodes were investigated with different methods. Especially the use of imaging techniques was important for the visualization and analysis of the gradients. Using this knowledge, the formation of more complex gradients was facilitated, and the results were further compared to simulations based on simple conductivity models. These simulations also provided us with means to predict the behavior of new and interesting setup geometries for pattering applications.The other major part is more application driven and deals with the use of alternating electric fields for chemical analysis, a technique known as electrochemical impedance spectroscopy (EIS). In this work, EIS has been applied for the analysis of engine oils and industrial cutting fluids. Emphasis was placed on practical aspects of the measurement procedure, and on the evaluation of the results using statistical methods. It was for example shown that it was possible to simultaneously determine the amount of different contaminants in low conducting solutions. Generally, EIS is used to measure the impedance of a solution or a solid, often as a function of the frequency of the alternating electric field. The impedance of a system is closely correlated to its complex dielectric constant, and EIS can therefor be used to examine many chemical and physical processes. It is further well suited for characterizing low conducting media with little or no redox-active species. The evaluation of impedance data is often a quite complex task, which is why we have made use of statistical methods that drastically reduce the effort and quickly reveal significant intrinsic parameters.

The application of non-thermal processes pulsed electric fields (PEF) and cross-flow micro-filtration (CFMF) continuous to be studied with the purpose of controlling microorganisms in milk. Trends suggesting increased adoption include the study of Food Safety Objectives as a safety criterion, the promotion of sustainable processing, and the implementation of hurdle strategies. While the advance of gentle processing is counteracted by the risk of enhanced resistance due to microbial stress response, several techniques can be applied to quantitatively assess its impact. The objective of this project was to evaluate the effectiveness of microbial inactivation by PEF and CFMF at various steps of milk processing including shelf-life, its comparison with high temperature short time (HTST) pasteurization, and the quantitative assessment of the cross protection resistance to PEF of Escherichia coli O157:H7. Some differences in mesophilics inactivation were observed in milks (fat contents between 1.1% and 3.1%). Increasing the PEF inlet temperature decreased the treatment time by three or two-fold. The combination of CFMF/PEF yielded similar microbial reductions as CFMF/HTST. Higher inactivation of the coliforms was achieved in homogenized cream (12% fat) compared to non-homogenized. The linear relation between electrical conductivity and nutrient content (fat and solids content) was established. In a parallel study the PEF/CFMF sequence resulted in higher inactivation of mesophilics compared to CFMF/PEF and HTST. The shelf life was acceptable for CFMF/PEF and HTST after 7 days, while enterics and psychrotrophs grew more after PEF/CFMF, thermodurics did after HTST. The growth and stress of Escherichia coli O157:H7 in lactose containing broths was monitored by absorbance and fluorescence expression of stress reporters. Growth was explained using a secondary model, and stress response using mechanistic and probabilistic models. PEF inactivation was evaluated following the Weibull distribution after the cells reached stationary phase or maximum fluorescence expression. Similar resistances were observed within the cells grown in lactose broth at 10, 25 or 40°C, as within stressed cells (starved or cold shocked). Cells grown at 45 °C were more resistant compared to the cells grown in acid, high salt concentration while the ones grown at cold temperatures were the weakest. / Dairy Farmers of Ontario, Natural Sciences and Engineering Research Council.

We investigate the influence of the built-in voltage on the performance of organic bulk heterojuction solar cells that are based on a p-i-n structure. Electrical doping in the hole and the electron transport layer allows to tune their work function and hence to adjust the built-in voltage: Changing the doping concentration from 0.5 to 32 wt% induces a shift of the work function towards the transport levels and increases the built-in voltage. To determine the built-in voltage, we use electroabsorption spectroscopy which is based on an evaluation of the spectra caused by a change in absorption due to an electric field (Stark effect). For a model system with a bulk heterojunction of BF-DPB and C60, we show that higher doping concentrations in both the electron and the hole transport layer increase the built-in voltage, leading to an enhanced short circuit current and solar cell performance.

Every year, millions of tons of paper are diverted from landfills and recycled. Newspaper constitutes a large portion of total paper recycled, providing a cheap source of raw material for the paper industry and helping sustainable forestry. The recycling of newsprint paper involves the separation of ink from the newsprint, which is done either by flotation or washing. Conventional flotation processes for separating ink are not adequate for newsprint printed using flexography printing technique and with water-based ink. The removal of these flexographic water-based inks by washing is a better alternative. However, one drawback of washing is that it has lower yield. In addition, the subsequent wash filtrate is difficult and costly to decontaminate. The overall goal is to develop a combination of processes that can remove ink from a feedstock that contains up to 100% flexographic ink newsprint; in the context of process variables with known effects. In the present work the objectives are to (1) demonstrate that incorporating an electric field into a conventional deinking process improves deinking efficiency, (2) propose a mechanism of how incorporating an electric field helps to improve deinking efficiency, (3) demonstrate that an electric field can decontaminate water containing flexographic inks and identify the mechanism behind electric field clarification of water, and (4) demonstrate that by incorporating electric fields into both the flotation deinking stage and water decontamination, the target deinking efficiency can be achieved.

Mémoire (M.Eng.)-- Université du Québec à Chicoutimi, 1994. / Document électronique également accessible en format PDF. CaQCU

Thèse (D.Ing.) -- Université du Québec à Chicoutimi, 2005. / Bibliogr.: f. 133-137. Document électronique également accessible en format PDF. CaQCU

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