O presente trabalho teve como objetivo estudar diferentes tecnologias na extração de óleo da semente de gergelim e de compostos fenólicos e proteínas da torta de gergelim. Este estudo está dividido em quatro partes. O objetivo da primeira parte do trabalho foi extrair compostos fenólicos de diferentes tortas de nozes e sementes nas mesmas condições e comparar o teor de tais compostos e a atividade antioxidante dos extratos. Nessa fase, foram utilizadas nos experimentos tortas das sementes de girassol, linhaça e gergelim, e das nozes amêndoa, pecã, macadâmia e avelã. O extrato da torta de noz pecã apresentou o maior teor de todos os compostos fenólicos analisados, seguido pelo extrato da torta de semente de girassol e de avelã. Essas amostras também apresentaram as maiores atividades antioxidantes. As etapas seguintes do trabalho focaram-se no gergelim. A segunda parte do trabalho teve como objetivo a otimização da extração, pela metodologia convencional, de fenólicos totais e lignanas da torta de gergelim. Inicialmente, um modelo polinomial de segunda ordem foi utilizado para predição dos resultados, mediante a variação da temperatura, concentração de etanol e razão, sólido/solvente. As variáveis de resposta foram as concentrações de fenólicos totais, de sesamina e de sesaminol triglicosídeo e a atividade antioxidante dos extratos obtidos. Entre os compostos analisados, o sesaminol triglicosídeo está presente em maior quantidade na torta de gergelim. A razão sólido/solvente e a concentração de etanol foram os fatores que mais afetaram a extração, enquanto a temperatura demonstrou uma influência reduzida. Na terceira etapa, o escopo da pesquisa foi a avaliação de metodologias alternativas na extração desses mesmos compostos e, também, de proteínas. As tecnologias usadas foram as de campo elétrico pulsado (CEP) e de descargas elétricas de alta tensão (DEAT). A análise da aplicação de CEP e de DEAT foi realizada usando essas tecnologias como pré-tratamentos ao processo de extração com solvente. Os resultados demonstraram que as técnicas foram eficazes e aumentaram os rendimentos do processo para fenólicos totais, lignanas e proteínas da torta. O uso de diferentes porcentagens de etanol também se mostrou significativo nessa etapa, entretanto, esse efeito foi reduzido quando utilizadas as tecnologias elétricas. Da mesma forma, o efeito da temperatura na etapa difusiva foi menor quando os pré-tratamento foram utilizados. Os comportamentos observados sugerem que a aplicação de CEP e DEAT aumenta a eficiência da extração de compostos de interesse. Por fim, na quarta parte do trabalho, objetivou-se melhorar a eficiência do processo de extração do óleo de gergelim aplicando as tecnologias previamente citadas. Esses experimentos demonstraram um efeito significativo dos tratamentos de CEP e DEAT e um aumento na quantidade de óleo extraído com o aumento da energia aplicada às sementes. O uso de DEAT gerou um aumento maior na quantidade de óleo extraído, se comparado à tecnologia de CEP. / The goal of the present work was to study different technologies in the extraction of oil from sesame seed and phenolic compounds and proteins from sesame cake. This study is divided in four parts. The first part aimed to extract water-soluble compounds from different seed and nut cakes under the same conditions and compare the phenolic content and antioxidant activity of the extracts. For the first portion of the study, seed cakes of sunflower, pumpkin, flaxseed and defatted sesame, and nut cakes of almond, pecan, macadamia and hazelnut were used in the experiments. The extract from pecan nut cake presented the highest amounts of all compounds analyzed, followed by sunflower seed and hazelnut cake extracts. These samples also had the highest antioxidant activities. The following steps of the work focused on sesame only. The second part of the work aimed to optimize the extraction of total phenolics and lignans from sesame seed cake. Initially, a second-order polynomial model was set up to predict the responses in different temperatures, solid/solvent ratios and ethanol concentrations. The response variables were the concentrations of total phenolics, sesamin, sesaminol triglucoside and antioxidant activity of the extracts. Among the analyzed compounds, ST is presented in the highest quantity in sesame cake. Solid to liquid ratio and ethanol concentration where the most important factors affecting extraction, whereas temperature showed reduced influence. In the third part of this work, the aim was to evaluate alternative methodologies in the extraction of phenolics and proteins. The technologies used were pulsed electric fields (PEF) and high voltage electric discharges (HVED). These methods were used as pre-treatments, prior to diffusion. Result show that PEF and HVED were efficient and increased the extraction yield for phenolic compounds, lignans and proteins from the cake. The use of different percentages of ethanol was also significant in this stage; however, the effect of this parameter was reduced when the electrical treatments were used. In the same way, temperature also showed a smaller influence on the results when the pre-treatments were used. The observed behaviors suggest that the use of PEF and HVED increases extraction efficiency. Finally, the goal of the last part of the work was to improve oil expression from sesame seeds, using the aforementioned technologies. These experiments show a significant effect of both PEF and HVED. It was observed an increase of the amount of oil extracted with the energy input applied to the seeds. When compared both technologies, HVED showed a more expressive effect then PEF.

Les décharges Nanosecondes Répétitives Pulsées (NRP) dans l'air à pression atmosphérique ont de nombreuses applications potentielles. Ces applications dépendent de la nature des décharges NRP. Les décharges NRP spark stabilisent les flammes pauvres, qui émettent moins d’oxydes d’azote. Un chauffage ultrarapide de plusieurs milliers de degrés en une vingtaine de nanosecondes a également été observé dans de telles décharges, ce qui permettrait par exemple la production de nanomatériaux. Les décharges NRP glow ont l'avantage de produire un grand nombre d'espèces actives comme le radical O tout en échauffant très peu le gaz ambiant, ce qui les rend utilisables dans des applications sensibles à la température comme la bio-décontamination. Dans une première partie, nous validons expérimentalement le mécanisme chimique à l'origine du chauffage ultra-rapide grâce à des mesures résolues en temps de la densité absolue de deux états excités du diazote ainsi que des mesures de température du gaz. Dans un deuxième temps, nous montrons expérimentalement l'existence du régime glow à température ambiante, celui-ci n'ayant été observé jusqu’à présent que pour des températures supérieures à 750 K. En effet, nous avons démontré que son existence dépend de nombreux paramètres : température et pression du gaz, tension entre les électrodes, distance inter-électrodes, durée de l’impulsion de tension, rayon de courbure des électrodes. Grâce à une étude expérimentale paramétrique détaillée et à l’analyse des résultats obtenus, nous avons réussi à identifier les conditions permettant d’obtenir le régime NRP glow à température ambiante et un nouveau régime de décharge de type “multi-canal” a été mis en évidence. / Nanosecond Repetitively Pulsed (NRP) discharges in atmospheric pressure air have many potential applications. Spark NRP discharges have applications in plasma assisted combustion. These discharges tend to stabilize lean flames which produce less NOx. Furthermore, an increase of several hundreds of Kelvins in less than 20 ns has been observed following NRP spark discharges, which could be used to create nanomaterials. NRP glow discharges, while creating an important number of actives species such as atomic oxygen, do not heat the ambient gas, which allows them to be used in temperature-sensitive applications such as bio-decontamination. In the first part of this thesis, we validate experimentally the mechanism that was proposed to explain the ultrafast heating observed. Time-resolved measurements of the absolute densities of two excited states of nitrogen and of the gas temperature have been performed with calibrated Optical Emission Spectroscopy. The second part of the thesis deals with the NRP glow regime. We have shown that its existence depends on several parameters, gas temperature and pressure, voltage across the electrodes, inter-electrode distance, pulse duration, radius of curvature of the electrodes. This regime had not been observed for temperatures lower than 750 K so far. Thanks to a detailed parametrical experimental study and the analysis of the obtained results, we have succeeded in identifying the NRP glow regime at ambient temperature and we observe a new type of “multi-channel” glow regime.

Orientador: José Pissolato Filho / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-20T15:35:10Z (GMT). No. of bitstreams: 1 Silva_DaianaAntonioda_M.pdf: 4722111 bytes, checksum: 375d62ec89d5043ee6edb2f08c980d9d (MD5) Previous issue date: 2012 / Resumo: Sistemas de energia elétrica estão constantemente sujeitos à sobretensões classificadas como internas, decorrentes de operações de manobras e chaveamento no próprio sistema; ou sobretensões decorrentes de agentes externos, por exemplo, descargas atmosféricas. Em ambas as situações, para-raios de óxido de zinco (ZnO) tem sido uma solução eficaz, tanto para os transitórios lentos e oscilatórios quanto para os transitórios rápidos e impulsivos. A utilização de para-raios de óxido de zinco com invólucro polimérico nesses casos é relativamente recente, recorrendo a meados dos anos 80. As informações sobre o desempenho elétrico desses dispositivos ao longo de anos de uso ou quando submetidos a condições críticas de operação são escassas e pouco difundidas na literatura técnica disponível. Dessa forma, uma análise criteriosa é proposta para avaliar o desempenho elétrico de para-raios com invólucro de silicone utilizados nos sistemas de distribuição de energia elétrica, em função da degradação físico-química dos mesmos. São realizados, então, 3 meses de ensaio de imersão/envelhecimento das amostras em água com cloreto de sódio à temperatura de 90 °C, visando representar 20 anos de aplicação do dispositivo em campo. A avaliação do desempenho elétrico é realizada através de medições periódicas da corrente de fuga e da tensão residual, enquanto a avaliação físico-química é obtida através da qualificação do invólucro de silicone utilizado nos para-raios por meio da classificação do grau de hidrofobicidade / Abstract: Electric power systems are constantly subjected to internal overvoltages, i.e. resulting from switching and mechanical operations in the system, or then overvoltages resulting from external causes, e.g. atmospheric surges. In both situations, metal-oxide surge arresters have been an efficacious solution for fast and impulsive electromagnetic transients as well as for slow and oscillatory transients. The use of polymeric metal oxide surge arresters, against atmospheric surges as well as for switching operations, is a relatively recent, dating back to the 1980s. However, the information on the electrical performance of these devices throughout the years of use, or when submitted to critical conditions of operation, is scarce and poorly discussed in the available technical literature. Thus, a thorough analysis is proposed to evaluate the electrical performance of surge arresters with silicone housing, commonly applied in the distribution network, as a function of their physical-chemical degradation. In order to represent 20 years of the field device, 3 months of immersion test/aging in water with sodium chloride at a temperature of 90 degrees will be performed. The evaluation will be through periodic measurements of the leakage current and residual voltage. Another objective is to describe the silicone housing used in surge arresters for classifying the degree of hydrophobicity / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

O presente trabalho teve como objetivo estudar diferentes tecnologias na extração de óleo da semente de gergelim e de compostos fenólicos e proteínas da torta de gergelim. Este estudo está dividido em quatro partes. O objetivo da primeira parte do trabalho foi extrair compostos fenólicos de diferentes tortas de nozes e sementes nas mesmas condições e comparar o teor de tais compostos e a atividade antioxidante dos extratos. Nessa fase, foram utilizadas nos experimentos tortas das sementes de girassol, linhaça e gergelim, e das nozes amêndoa, pecã, macadâmia e avelã. O extrato da torta de noz pecã apresentou o maior teor de todos os compostos fenólicos analisados, seguido pelo extrato da torta de semente de girassol e de avelã. Essas amostras também apresentaram as maiores atividades antioxidantes. As etapas seguintes do trabalho focaram-se no gergelim. A segunda parte do trabalho teve como objetivo a otimização da extração, pela metodologia convencional, de fenólicos totais e lignanas da torta de gergelim. Inicialmente, um modelo polinomial de segunda ordem foi utilizado para predição dos resultados, mediante a variação da temperatura, concentração de etanol e razão, sólido/solvente. As variáveis de resposta foram as concentrações de fenólicos totais, de sesamina e de sesaminol triglicosídeo e a atividade antioxidante dos extratos obtidos. Entre os compostos analisados, o sesaminol triglicosídeo está presente em maior quantidade na torta de gergelim. A razão sólido/solvente e a concentração de etanol foram os fatores que mais afetaram a extração, enquanto a temperatura demonstrou uma influência reduzida. Na terceira etapa, o escopo da pesquisa foi a avaliação de metodologias alternativas na extração desses mesmos compostos e, também, de proteínas. As tecnologias usadas foram as de campo elétrico pulsado (CEP) e de descargas elétricas de alta tensão (DEAT). A análise da aplicação de CEP e de DEAT foi realizada usando essas tecnologias como pré-tratamentos ao processo de extração com solvente. Os resultados demonstraram que as técnicas foram eficazes e aumentaram os rendimentos do processo para fenólicos totais, lignanas e proteínas da torta. O uso de diferentes porcentagens de etanol também se mostrou significativo nessa etapa, entretanto, esse efeito foi reduzido quando utilizadas as tecnologias elétricas. Da mesma forma, o efeito da temperatura na etapa difusiva foi menor quando os pré-tratamento foram utilizados. Os comportamentos observados sugerem que a aplicação de CEP e DEAT aumenta a eficiência da extração de compostos de interesse. Por fim, na quarta parte do trabalho, objetivou-se melhorar a eficiência do processo de extração do óleo de gergelim aplicando as tecnologias previamente citadas. Esses experimentos demonstraram um efeito significativo dos tratamentos de CEP e DEAT e um aumento na quantidade de óleo extraído com o aumento da energia aplicada às sementes. O uso de DEAT gerou um aumento maior na quantidade de óleo extraído, se comparado à tecnologia de CEP. / The goal of the present work was to study different technologies in the extraction of oil from sesame seed and phenolic compounds and proteins from sesame cake. This study is divided in four parts. The first part aimed to extract water-soluble compounds from different seed and nut cakes under the same conditions and compare the phenolic content and antioxidant activity of the extracts. For the first portion of the study, seed cakes of sunflower, pumpkin, flaxseed and defatted sesame, and nut cakes of almond, pecan, macadamia and hazelnut were used in the experiments. The extract from pecan nut cake presented the highest amounts of all compounds analyzed, followed by sunflower seed and hazelnut cake extracts. These samples also had the highest antioxidant activities. The following steps of the work focused on sesame only. The second part of the work aimed to optimize the extraction of total phenolics and lignans from sesame seed cake. Initially, a second-order polynomial model was set up to predict the responses in different temperatures, solid/solvent ratios and ethanol concentrations. The response variables were the concentrations of total phenolics, sesamin, sesaminol triglucoside and antioxidant activity of the extracts. Among the analyzed compounds, ST is presented in the highest quantity in sesame cake. Solid to liquid ratio and ethanol concentration where the most important factors affecting extraction, whereas temperature showed reduced influence. In the third part of this work, the aim was to evaluate alternative methodologies in the extraction of phenolics and proteins. The technologies used were pulsed electric fields (PEF) and high voltage electric discharges (HVED). These methods were used as pre-treatments, prior to diffusion. Result show that PEF and HVED were efficient and increased the extraction yield for phenolic compounds, lignans and proteins from the cake. The use of different percentages of ethanol was also significant in this stage; however, the effect of this parameter was reduced when the electrical treatments were used. In the same way, temperature also showed a smaller influence on the results when the pre-treatments were used. The observed behaviors suggest that the use of PEF and HVED increases extraction efficiency. Finally, the goal of the last part of the work was to improve oil expression from sesame seeds, using the aforementioned technologies. These experiments show a significant effect of both PEF and HVED. It was observed an increase of the amount of oil extracted with the energy input applied to the seeds. When compared both technologies, HVED showed a more expressive effect then PEF.

In preparation for the High-Luminosity Large Hadron Collider (HL-LHC) at CERN, the Compact Muon Solenoid (CMS) Detector is undergoing a series of upgrades to its existing infrastructure, and is adding in several completely new subdetector systems. The first of these new systems, called GE1/1, is a series of 144 gas electron multiplier (GEM) detectors, arranged as 36 two-detector "superchambers" in each of the muon endcaps of CMS. These detectors are a subtype of micropattern gas detectors, and consist of three layers of "GEM foils", thin sheets of polyimide coated with 5 um of copper on each side and chemically etched with holes of 50 - 70 um diameter at a pitch of 140 um. These layers are stacked on top of a printed circuit board (PCB) readout and sealed within a gastight volume that is filled with Ar:CO2 70:30, and a high voltage is applied to the foils to create electric fields within the GEM detectors. When a muon enters the detector and ionizes the gas within, the ionized electrons encounter these fields and multiply in Townsend avalanches at each successive foil layer, until they are read out at the readout PCB at a gain of ~10^4. In early 2017, a demonstrator system known as the "slice test" was installed into the negative endcap. Consisting of 10 GEM detectors, the two-year-long slice test served as both a proof of concept for the GE1/1 system and an invaluable learning experience that would permanently impact not only the GE1/1 project, but future GEM systems GE2/1 and ME0 as well. During the slice test, it was observed that readout channels were being lost in the course of operation to such a degree that the operational lifetime of the system was in serious jeopardy. These losses were attributed to damage to the front-end readout ASIC (VFAT) inputs, caused propagating electrical discharges within the detectors, and a dedicated campaign to study the discharges was launched. The results of this study will be presented in this dissertation. A campaign to mitigate these discharges and their resulting damage was launched. In order to protect the sensitive VFAT from damage, several external protection circuits were proposed and thoroughly tested. The results of these tests, which are presented herein, determined that a series of resistors totaling 470 Ohms would be installed on the VFAT hybrid. When coupled with an additional 200 kOhm resistor on the HV filter, this reduced the probability of damage following a discharge from 93% to 3% As GE2/1 and ME0 are not due to be installed for another few years, more complex discharge-prevention measures can be put into place. As such, the following measures have been examined, and results will be discussed herein: A new, larger VFAT hybrid is being manufactured, whose larger surface area can accommodate more robust protection circuits than those considered and used for GE1/1. As well, double-segmented GEM foils, in which both the top and bottom of each foil is segmented into < 100 cm^2 sectors that are separated by resistors, were examined for use in the detectors. These double-segmented foils were found to introduce a cross-talk signal in the detectors that results in false signals being treated as true signals, which causes a saturation of the GEM bandwidth and results in unwanted dead time. These cross-talk signals, as well as the compromises made to reduce the cross-talk while maintaining robust discharge prevention, will be discussed. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

<p dir="ltr"> Conventional RF switching technologies struggle to simultaneously achieve high-power handling, low loss, high isolation, broadband operation, quick reconfiguration, high linearity, and low cost, which are desirable for many applications, including communications, radar, and sensors. Moreover, they require electrical bias networks, which degrade performance and, in many cases, inhibit wideband applications, including DC operation. On the other hand, plasma (photoconductive) switches use an optical bias to generate free charge carriers. Recently these switches have begun to not only rival conventional technologies in terms of performance metrics such as switching speeds and loss but have exceeded what is possible in terms of power handling. This work details the strides made in placing solid-state plasma technologies at the forefront of advanced, high-power switching applications including a novel high-power tuner and an absorptive/reflective SPnT switch. In various form factors, SSP has achieved analog control of loss as low as 0.09 dB and isolation as high as 54 dB, linearity of 68.8 dBm (IP3), 110 GHz instantaneous bandwidth, including DC, switching speeds as low as 3.5 us, 100+ W power handling, and 30+ W hot switching. In addition, comprehensive physics modeling has been developed to enable seamless design validation before fabrication commences. This thesis discusses the achievements and design considerations for creating optimized plasma switches and proposes a path for future applications.</p>

L’épilepsie est une pathologie chronique. Elle se définit par la répétition de manifestations cliniques paroxystiques appelées aussi crises d’épilepsie. Ces crises résultent d’un dysfonctionnement cérébral généralisé ou focalisé dû à une décharge électrique anormale. L’électroencéphalographie (EEG) est la méthode de référence permettant l’enregistrement de l’activité électrique du cerveau. Lors d’une crise d’épilepsie, les signaux EEG prennent une allure sinusoïdale et se caractérisent par une grande intensité. Génératrice de signaux EEG, les populations neuronales se synchronisent pour créer un système dynamique. Les changements d’état des oscillations des signaux EEG, variables au cours de temps, passage d’un état stable à un état instable, reflètent le début d’une crise d’épilepsie.Dans ce cadre, l’objectif de cette thèse est de proposer une nouvelle approche de prédiction de l’avènement d’une crise d’épilepsie et de localisation des générateurs corticaux associés tout en employant un minimum d’électrodes crâniennes. Cette approche permet d’alerter le malade et son entourage afin qu’ils puissent prendre les précautions nécessaires.Pour assurer une détection précoce des prémices de la crise et une localisation précise de ses origines focales éventuelles, nous proposons une méthode fiable basée en premier lieu sur la modélisation autorégressive multivariable des signaux EEG. Cette modélisation génère des coefficients capables de décrire les changements de l’état de ce système dynamique. Une Analyse en Composantes Principales basée sur l’extraction des valeurs propres du système a été utilisée pour calculer un Indice de stabilité. La variation temporelle de cet indice permet de déterminer l’état de stabilité du système avant, pendant et après la crise d’épilepsie et de détecter d’éventuelles anomalies paroxystiques précritiques. Nos principales contributions sont comme suit :- La modélisation autorégressive et l’analyse de la stabilité pour la détection précoce de la survenue des crises d’épilepsie tout en utilisant un nombre minimal d’électrodes EEG crâniennes.La méthodologie proposée comporte quatre phases principales : un prétraitement adapté pour améliorer la qualité du signal, une extraction des paramètres pertinents du modèle autorégressif, un calcul de l’Indice de stabilité et une analyse des périodes de crises.La fiabilité de notre méthode et la pertinence de nos résultats ont a été prouvée en les comparant avec d’autres méthodes rapportées par l’état de l’art et validées sur la même base de données (CHB-MIT).- Meilleur localisation spatiotemporelle des régions des décharges électriques épileptiques sur le cortex, suite à l’amélioration de la résolution surfacique de l’EEG par l'intégration des électrodes virtuellesLes décharges électriques naissent dans des points du cortex cérébral et se propage vers d’autres points du même hémisphère ou d’un autre hémisphère. Le suivi de la propagation de ces décharges permet de contrôler l’état de conscience du malade. Il s’agit de différencier une crise focale d’une crise généralisées qui se manifestent par une altération de conscience. L’étude que nous avons menée consiste à localiser de manière fiable et précise les régions cérébrales impliquées dans la crise et à suivre leurs évolutions au cours du temps. Cette étude comporte trois phases principales :Dans un troisième temps, le suivi de l’évolution spatiotemporelle des décharges épileptiques détectées par les électrodes permet d’évaluer l’état du malade et de prédire d’éventuelles altérations de la conscience. Dans les cas d’un décharge électrique épileptique du lobe fronto-temporale ou de plusieurs régions sur les deux hémisphères, le malade passe par une altération momentanée de conscience / Epilepsy is a chronic pathology defined by the repetition of clinical paroxysmal manifestations called crises. These crises are the result of a generalized or focal brain dysfunction due to an abnormal electrical discharge. The electroencephalography (EEG) is the reference method allowing the recording of the electrical activity of the brain. During an epileptic crisis, EEG signals are of sinusoidal nature and characterized by a high intensity. Generator of the EEG signals, the neuronal populations sync to create a dynamic system. The changes of the oscillations state of the EEG signals, variables over the time, passage of a stable state to an unstable state, reflect the beginning of an epileptic crisis.The conceptual framework of this thesis describes the objective to propose a new approach to predict the occurrence of epileptic crisis and localize the cortical generators associated with the minimum of cranial electrodes. This approach allows alerting the patient and his entourage so that they can take necessary precautions.To ensure early detection of the crisis onset and a precise location of its focuses, we propose a reliable method based firstly on the Multivariate Autoregressive modeling of EEG signals. This modeling generates coefficients capable to describe early changes in the dynamic system state. A Principal Components Analysis based on the extraction of values own of the system has been used to calculate an index of stability. The temporal variation of this index is used to determine the stability of system before, during and after epilepsy and to detect any paroxysmal abnormalities precritical. Our main contributions are as follows:- The Autoregressive Modeling and stability analysis for the early detection occurrence of seizures by using a minimum number of cranial EEG electrodesThe proposed methodology has four main phases: a pretreatment adapted to improve the quality of the signal, an extraction of the relevant parameters of the autoregressive model, a calculation of the stability index and the analysis of crises periods.The reliability of our method and the relevance of our results have been proved by comparing them with other methods reported by the state of the art and validated on the same database (CHB-MIT).- Best spatiotemporal localization of epileptic electric discharge regions on the cortex, following the improvement of the surface resolution of the EEG by the integration of virtual electrodesElectrical discharges are born in the points of the cerebral cortex and propagated to other points in the same hemisphere or of the other hemisphere. The monitoring of the spread of these discharges allows controlling the state of consciousness of the patient. The study that has been conducted is to locate the brain regions involved in the crisis reliably and precisely and monitoring their evolution over time. This study consists of three main phases:In a third phase, the spatiotemporal evolution of the epileptic discharges detected by the electrodes makes it possible to evaluate the patient's condition and to predict possible alterations in consciousness. In the case of an epileptic electric discharge of the fronto-temporal lobe or of several regions on the two hemispheres, the patient passes through a momentary alteration of consciousness

<p>  </p> <p>Electron emission plays a vital role in many modern technologies, from plasma medicine to heavy ion beams for fusion. An accurate theoretical model based upon the physics involved is critical to efficient operation of devices pushing the boundaries of complexity. The interactions between different electron emission mechanisms can severely alter device performance, especially when operating in extreme conditions. This dissertation studies electron emission from the perspectives of increasing geometric and physical mechanism complexities </p> <p>One half of this dissertation derives new relations for space-charge limited emission (SCLE) in non-planar geometries. SCLE is the maximum stable current that may be produced by electron emission before the electric field of the electrons themselves self-limits further emission. In planar devices, this is modeled by the well-established Child-Langmuir (CL) equation. The Langmuir-Blodgett (LB) equations remain the most commonly accepted theory for SCLE for cylindrical and spherical geometries after nearly a century; however, they suffer from being approximations based on a polynomial series expansion fit to a nonlinear differential equation. I derive exact, fully analytic equations for these geometries by using variational calculus to transform the differential equation into a new form that is fully and exactly solvable. This variational approach may be extended to any geometry and offers a full description of the electric field, velocity, and charge density profiles in the diode. </p> <p>SCLE is also an important mechanism for characterizing the operation of devices with an external magnetic field orthogonal to the electric field. This “crossed-field” problem decreases the limiting current as electrons travel longer, curved paths, effectively storing some charge in the gap (moving parallel to the emitter). At a critical magnetic field called the Hull cutoff, electron paths become so tightly curved that the circuit can no longer be completed, a condition called magnetic insulation. Crossed-field SCLE has been accurately modeled in planar devices by Lau and Christenson. Using the variational approach, I replicate their planar results and extend the calculation to cylindrical geometry, a common choice for magnetron devices. Further, I derive additional equations with simplified assumptions that, for the first time, provide an analytic description of experimental results below the Hull cutoff field. Following this I incorporate a series resistor: device resistance (or impedance) changes non-linearly with current and voltage, so I couple Ohm’s Law (OL) to all the models of crossed-field devices. For devices just below the Hull cutoff, I predict analytically and show in simulation novel bi-modal behavior, oscillating between magnetically insulated and non-insulated modes. With crossed-field device assessment, the variational calculus approach to space-charge may be used for numerous applications, including high power microwave sources, relativistic klystron devices, heavy ion beams, Hall thrusters, and plasma processing. </p> <p>The other half of this dissertation derives analytic theories to solve for emission current with three or more electron emission mechanisms simultaneously. In addition to the CL law, SCLE may also occur in neutral, non-vacuum diodes, modeled by the Mott-Gurney (MG) equation. These are the two limiting mechanisms I study; the other major modality of electron emission is direct electron production, the source of current in the device. Electrons are ejected when impelled by high temperature or electric field at the emission surface. These mechanisms are thermionic (or thermal) emission, modeled by the Richardson-Laue-Dushman (RLD) equation, and field emission, modeled by the Fowler-Nordheim (FN) equation, respectively. Additionally, just as I calculated the impedance of devices operating in a crossed-field configuration, all these models can be similarly coupled to OL. I derive models unifying FN, MG, and CL (with an extension linking OL, mentoring an undergraduate) and RLD, FN, and CL. These models are relevant for modern device design, especially as micro- and nano-scale devices seek to eliminate vacuum requirements and as space and military applications require higher temperature tolerances.</p> <p>While multi-physics models, like the ones described above, are important, the single-physics models (FN, RLD, MG, CL, OL) are still valid (and much easier to use) in their respective asymptotic limits. For example, a circuit behaves purely according to OL for very high resistances, according to MG for very high pressures, and so forth. Importantly, when devices operate in transition regions between these asymptotic limits, <em>none </em>of the asymptotic equations match the predictions of multi-physics models. Yet, intersections between the asymptotic equations are easily found, say for a certain set of voltage, gap distance, and pressure, CL=MG. Since both asymptotic equations give the same prediction, we may conclude that both must be inaccurate for those physical parameters! This gives rise to what I term “nexus theory:” solving two or more asymptotic equations simultaneously to rapidly and accurately predict sets of physical parameters at which multi-physics models (specifically, the physics leading to the “nexus point” parameters, points or curves at which nexus conditions are satisfied) are required for accurate device predictions. In fact, I show that multi-physics models are necessary within roughly one to two orders of magnitude from a nexus. In effect, nexus theory provides a simple, powerful tool to determine how complex a model is necessary for a particular device. Both nexus theory and multi-physics results in this dissertation have been successfully used to design devices to operate in specific transition regimes and identify the resulting device behavior.  </p>

<p dir="ltr">Understanding the acceleration of particles responsible for high-energy non-thermal phenomena in astrophysical jets is a ubiquitous pursuit. A possible culprit for non-thermal particle acceleration is turbulence. Specifically in this thesis, I investigate highly magne- tized or relativistic turbulence, where the magnetic energy to enthalpy ratio of the plasma is much greater than one, as a possible high-energy accelerator inside relativistic jets. I do this through three distinct projects. </p><p dir="ltr">My first project [1] (discussed in Section 3) was built upon a recent study of relativistic turbulence from [2], which found that a non-thermal particle equilibrium can be achieved when a plasma is heated via turbulence but allowed to cool radiatively. I extrapolated these results from PIC (Particle-in-Cell) simulations to larger scales and magnetizations, allowing me to encode key microphysical results of PIC simulations into a Fokker-Planck formalism. Combining these results with a single zone model for a blazar jet, I successfully define the underlying particle distribution with the global parameters of the emission region. To test this model, I fit data from 12 sources and successfully constrain key blazar parameters such as magnetization, bulk Lorentz factor, emission region size, and distance from the central engine. </p><p dir="ltr">My second project covers the development and testing of the open-source toolkit Tleco. This code base was used to evolve the Fokker-Planck equation and solve the resultant emission in my first project. Tleco offers efficient algorithms for evolving particle distributions and solving the resultant emission. It is meant to be user-friendly and easily customizable. </p><p dir="ltr">My third project attempts to enhance our understanding of coherent structures in relativistic turbulence. I employ intermittency analysis to establish a link between statistical fluctuations within the plasma and regions of high-energy dissipation. To achieve this, we used first-principle turbulent PIC simulations across a range of magnetizations and fluctuating magnetic field values. By utilizing the statistical fluctuations to determine the fractal dimension of the structures, I then examine their filling fraction and its dependence on magnetization and the fluctuating magnetic field.</p>

Electrical discharges with a variety of different forms (streamers, glow corona, leaders, etc.) broadly exist in nature and in industrial applications. Under certain conditions, one electrical discharge can be transformed into another form. This thesis is aimed to develop and use numerical simulation models in order to provide a better physical understanding of two of such transitions, namely the glow-to-streamer and the streamer-to-leader transitions in air. In the first part, the thesis includes the two-dimensional simulation of the glow-to-streamer transition under a fast changing background electric field. The simulation is performed with a fluid model taking into account electrons. An efficient semi-Lagrangian algorithm is proposed to solve the convection-dominated continuity equations present in the model. The condition required for the glow-to-streamer transition is evaluated and discussed. In order to enable such simulations for configurations with large interelectrode gaps and long simulation times, an efficient simplified model for glow corona discharges and their transition into streamers is also proposed. The second part of the thesis is dedicated to investigate the dynamics of the streamer-to-leader transition in long air gaps at atmospheric pressure. The transition is studied with a one-dimensional thermo-hydrodynamic model and a detailed kinetic scheme for N2/O2/H2O mixtures. In order to evaluate the effect of humidity, the kinetic scheme includes the most important reactions with the H2O molecule and its derivatives. The analysis includes the simulation of the corresponding streamer bursts, dark periods and aborted leaders that may occur prior to the inception of a stable leader. The comparison between the proposed model and the widely-used model of Gallimberti is also presented. / Elektriska urladdningar av olika former (streamers (från engelska), glöd-korona, ledare, etc.) förekommer i stor utsträckning i naturen och i industriella applikationer. Under vissa förhållanden kan en elektrisk urladdning omvandlas till en annan form av elektrisk urladdning. Denna avhandling syftar till att utveckla och använda numeriska simuleringsmodeller för att ge en bättre fysikalisk förståelse av två sådana övergångar, nämligen glöd-till-streamer- och streamer-till-ledar-övergångar, i luft. I den första delen, avhandlas en tvådimensionell simulering av glöd-till-streamer-övergången med ett hastigt föränderligt elektriskt fält i bakgrunden. Simuleringen utförs med en flödesmodell som tar hänsyn till elektronerna. En effektiv semi-Lagrangesk algoritm föreslås för att lösa de konvektionsdominerade kontinuitetsekvationerna i modellen. Vidare utvärderas och diskuteras förutsättningarna för glöd-till-streamer-övergången. För att möjliggöra sådana simuleringar i konfigurationer med stora elektrodavstånd och långa simuleringstider, föreslås också en effektiv och förenklad modell för glöd-korona-urladdningar samt deras övergång till streamers. Den andra delen av avhandlingen är tillägnad att undersöka dynamiken i streamer-till-ledar-övergångar över långa avstånd i luft, under atmosfäriskt tryck. Övergången studeras med en endimensionell termohydrodynamisk modell och en detaljerad kinetisk modell för blandningar av N2/O2/H2O. För att utvärdera effekten av luftfuktighet, innefattar den kinetiska modellen de viktigaste reaktionerna med H2O-molekylen och dess derivat. Analysen innefattar simuleringen av motsvarande streamer-kedjor, mörka perioder och avbrutna ledare som kan förekomma före starten av en stabil ledare. En jämförelse mellan den föreslagna modellen och den allmänt använda modellen av Gallimberti presenteras också. / <p>QC 20170418</p>