This thesis proposes a novel algorithm to optimize multi-modal, nonlinear, black-box objective functions for electric power system design using an electromagnetic transients (EMT) simulator. The algorithm discovers multiple local optimal solutions for a given complex power system, and then generates accurate surrogate models of an objective function around each discovered local optimal solution. These surrogate models represent the local behaviour of the objective function that can be used in the subsequent stages of sensitivity analyses. Using surrogate models instead of intensive transient simulation during sensitivity analysis reduces computational intensity and simulation time. This makes the proposed algorithm particularly suited for optimization of computationally expensive black-box functions. The stages of the algorithm can be implemented independently and hence the computations can be done in parallel. Therefore, the algorithm is implemented in a parallel environment to gain significant speed-up in the design of electric power systems. Comparative studies in terms of objective function evaluation and computation time are provided. Using several multi-modal benchmark objective functions, the superiority of the proposed algorithm compared to other recently developed algorithms is demonstrated. Additionally, the application of the algorithm in the design process of complex electric power system demonstrated through several examples. The case studies show that the parallelized algorithm provides computational savings up to 39 times compared to the conventional sequential approach. / May 2016

This work contributes toward research in the field of lightning performance of High Voltage Direct Current (HVDC) transmission lines, focusing on the impact of the line polarity on the incidence of line faults. Although there has been some recent research into the influence of polarity, there appears to be no confirmed effect that might influence the design of new lines. The research presents an investigation into the lightning performance of the two poles of the Cahora-Bassa HVDC transmission line. In order to compare the performance of the two polarities, the average lightning exposure over an 8-year period was confirmed to be very similar for both lines. Lightning stroke data from the South African Lightning Detection Network was correlated with fault times from the transmission-line protection scheme. The classification of the lightning related faults was used to determine the relative performance of the two poles, particularly in relation to polarity, and to infer if there was any influence of polarity on the lightning attachment process. This investigation for the Cahora-Bassa scheme shows that twenty-three out of twenty-five lightning related faults occurred on the positive pole. The results concur with performance experience on several HVDC lines from China and Canada, which indicate that lightning related faults favour the positive pole by a ratio of between 8:1 and 10:1. This represents a valuable contribution, which substantiates that HVDC line polarity has an influence on the lightning attachment process, and indicates that there is a need to re-examine the lightning shielding design for HVDC transmission lines. / GS2016

Introdução: Climatério é definido como o período de tempo onde ocorre a mudança de vida reprodutiva para não reprodutiva, com extensão de duração variável. Durante esse período e após o estabelecimento da menopausa, é comum o surgimento de diversos sintomas que expressam o esgotamento dos folículos ovarianos. Dentre os sintomas, o mais comumente relatado pelas mulheres são os sintomas vasomotores ou fogachos. Além da Terapia de Reposição Hormonal (TRH), outras medicações como os Inibidores Seletivos da Recaptação da Serotonina (ISRS) têm sido empregadas na tentativa de melhorá-los. Justificativa: TRH não pode ser aplicado a todas as mulheres com sintomas. As medicações não hormonais, apesar de apresentarem melhores respostas que placebo, ainda demonstram pouco impacto clínico na redução dos sintomas vasomotores. Esta lacuna permite avaliar outras alternativas terapêuticas, como a Estimulação Transcraniana por Corrente Direta (ou tDCS, do inglês transcranial direct current stimulation). O racional para estudar o efeito desta técnica neste contexto, é o seu possível efeito modulatório autonômico. O que reforça a escolha desta técnica é o fato de ter eficácia demonstrada em outras patologias como depressão, dor, doença Parkinson dentre outras. A tDCS é um método de neuromodulação transcraniana não invasivo, que se baseia na aplicação de correntes contínuas de baixa intensidade, através de eletrodos colocados sobre o escalpo, de forma simples e indolor. Objetivo: Avaliar o efeito da tDCS (tratamento ativo) comparada ao tDCS-sham (placebo) nos sintomas vasomotores de mulheres na pós- menopausa como objetivo primário; e como objetivo secundário, seus efeitos na qualidade de vida. Método: Ensaio Clínico Randomizado realizado em 30 pacientes pós-menopáusicas com queixa de pelo menos 05 episódios de fogachos/dia. Participantes foram selecionadas no ambulatório de Climatério do Serviço de Ginecologia e Obstetrícia do Hospital de Clínicas de Porto Alegre e via chamamento de jornal. Estas foram randomizadas para um dos grupos: tDCS ou placebo-sham. A intervenção consistiu na aplicação de sessões diárias de estimulação com corrente elétrica de 02 mili Ampere, pelo período de 10 dias consecutivos, à exceção dos finais de semana. Por uma semana anterior à intervenção e por 30 dias após, as participantes registravam o número e intensidade dos fogachos ao dia. Responderam ao Women´s Health Questionaire (WHQ) antes e ao termino da intervenção. Resultados: A média de fogachos/dia se comportou de forma semelhante nos dois grupos havendo uma redução do número de fogachos nas três primeiras semanas após intervenção com retorno ao basal a partir da quarta semana pós-aplicação. No grupo tDCS, se observou uma tendência a uma transferência dos fogachos intensos para leves sugerindo uma melhora clínica. Os resultados, apesar de não apresentarem significância estatística, reforçam a ideia de ampliar a investigação, com maior número de pacientes e com maior tempo de duração além do caráter inovador da pesquisa. / Introduction: Menopause is defined as a period where there is a change from the reproductive stage to a nonreproductive phase, with variable duration. During this period and following the establishment of menopause, there is usually an onset of several symptoms indicating the depletion of ovarian follicles. Among the symptoms, the ones that are more frequently reported by women are vasomotor symptoms or hot flashes. In addition to Hormone Replacement Therapy (HRT), other medications such as Selective Serotonin Reuptake Inhibitors (SSRIs) have been employed to treat them. Justification: HRT may not be applied to all women with symptoms. Non-hormonal medications, despite having better responses than placebo, have still shown little clinical impact on the reduction of vasomotor symptoms. This gap allows other therapeutic alternatives to be considered, such as Transcranial Direct Current Stimulation (tDCS). The rationale for studying the effect of this technique in this context is its possible autonomic modulatory effect. What reinforces the choice of this technique is the efficacy which it has demonstrated in other disorders such as depression, pain, Parkinson's disease, among others. tDCS is a non-invasive transcranial neuromodulation method based on the application of continuous low-intensity currents through electrodes placed to the scalp, in a simple and painless way. Goal: To evaluate the effect of tDCS (active treatment) compared to tDCS-sham (placebo) on vasomotor symptoms in postmenopausal women as a primary endpoint and its effects on quality of life as a secondary endpoint. Method: Randomized Clinical Trial conducted in 30 postmenopausal patients complaining of at least five episodes of hot flashes per day. Participants were selected at the Gynecology and Obstetrics Service Menopause Outpatient Clinic, Hospital de Clínicas de Porto Alegre and via a newspaper call. These were randomized to one of the groups: tDCS or placebo-sham. The intervention consisted of daily sessions in which stimulation was applied with an electric current of 02 milliamperes for 10 consecutive days, except on weekends. Participants recorded the number and intensity of hot flashes per day for one week before and for 30 days after the intervention. They answered the Women’s Health Questionnaire (WHQ) before and after the intervention completion. Results: The mean of hot flashes/day behaved in a similar way in both groups, and there was a reduction in hot flashes in the first three weeks following the intervention with a return to baseline starting in the fourth week after the administration. In the tDCS group, a trend towards a conversion of intensive hot flashes into mild ones was noted, which suggested a clinical improvement. The results, despite not showing statistical significance, supported the idea of extending the investigation with a larger number of patients and longer duration, in addition to the innovating nature of the research.

Satisfaire les besoins en énergie de manière responsable est possible grâce aux énergies renouvelables, notamment éoliennes et solaires. Cependant ces centres de captation d’énergie sont éloignés dans zones de consommation. Le transport de l’énergie via des réseaux HVDC (haute tension courant continu) permet un rendement et une flexibilité avantageuse face au transport HVAC (haute tension courant alternatif). Ceci est rendu possible grâce aux convertisseurs utilisant l’électronique de puissance. Les récents développements sur les semi-conducteurs à large bande interdite, plus particulièrement le carbure de silicium (SiC) offrent la possibilité de concevoir ces convertisseurs plus simples, utilisant des briques technologiques de plus fort calibre (≤ 10 kV). Cependant le packaging, essentiel à leur bon fonctionnement, ne suit pas ces évolutions. Dans cette thèse, nous explorons les technologies actuelles ainsi que les limites physique et normatives liées au packaging haute tension. Des solutions innovantes sont proposées pour concevoir un module de puissance haute tension, impactant que faiblement les paramètres connexes (résistance thermique, isolation électrique et paramètres environnementaux). Les éléments identifiés comme problématiques sont traités individuellement. La problématique des décharges partielles sur les substrats céramiques métallisés est développée et une solution se basant sur les paramètres géométriques a été testée. Le boitier standard type XHP-3 a été étudié et une solution permettant de le faire fonctionner à 10 kV à fort degré de pollution a été développée. / The supply of carbon-free energy is possible with renewable energy. However, windfarms and solar power plants are geographically away from the distribution points. Transporting the energy using the HVDC (High Voltage Direct Current) technology allow for a better yield along the distance and result in a cost effective approach compared to HVAC (High Voltage Alternative Current) lines. Thus, there is a need of high voltage power converters using power electronics. Recent development on wide bandgap semiconductors, especially silicon carbide (SiC) allow a higher blocking voltage (around 10 kV) that would simplify the design of such power electronic converters. On the other hand, the development on packaging technologies needs to follow this trend. In this thesis, an exploration of technological and normative limitation has been done for a high voltage power module design. The main hot spot are clearly identified and innovative solutions are studied to provide a proper response with a low impact on parasitic parameters. Partial Discharges (PD) on ceramic substrates is analyzed and a solution of a high Partial Discharge Inception Voltage (PDIV) is given based on geometrical parameters. The XHP-3 like power modules are studied and a solution allowing a use under 10 kV at a high pollution degree (PD3) is given.

abstract: High Voltage Direct Current (HVDC) Technology has several features that make it particularly attractive for specific transmission applications. Recent years have witnessed an unprecedented growth in the number of the HVDC projects, which demonstrates a heightened interest in the HVDC technology. In parallel, the use of renewable energy sources has dramatically increased. For instance, Kuwait has recently announced a renewable project to be completed in 2035; this project aims to produce 15% of the countrys energy consumption from renewable sources. However, facilities that use renewable sources, such as solar and wind, to provide clean energy, are mostly placed in remote areas, as their installation requires a massive space of free land. Consequently, considerable challenges arise in terms of transmitting power generated from renewable sources of energy in remote areas to urban areas for further consumption. The present thesis investigates different transmission line systems for transmitting bulk energy from renewable sources. Specifically, two systems will be focused on: the high-voltage alternating current (HVAC) system and the high-voltage direct current (HVDC) system. In order to determine the most efficient way of transmitting bulk energy from renewable sources, different aspects of the aforementioned two types of systems are analyzed. Limitations inherent in both HVAC and HVDC systems have been discussed. At present, artificial intelligence plays an important role in power system control and monitoring. Consequently, in this thesis, the fault issue has been analyzed in transmission systems, with a specific consideration of machine learning tools that can help monitor transmission systems by detecting fault locations. These tools, called models, are used to analyze the collected data. In the present thesis, a focus on such models as linear regression (LR), K-nearest neighbors (KNN), linear support vector machine (LSVM) , and adaptive boost (AdaBoost). Finally, the accuracy of each model is evaluated and discussed. The machine learning concept introduced in the present thesis lays down the foundation for future research in this area so that to enable further research on the efficient ways to improve the performance of transmission line components and power systems. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2019

With increasing life expectancy and global population of older adults, preserving cog- nitive function throughout life represents a growing priority. Numerous approaches to cognitive enhancement exist, but few have scientific merit. Among the most preva- lent – and commercialized – approaches are cognitive training (“brain training”) and non-invasive brain stimulation through electric currents applied at the surface of the scalp. The present dissertation describes a collection of work contextualizing the appeal of these cognitive enhancement methods and addressing some of the most pervasive limitations of research in this field thus far. One largely ignored issue in cognitive intervention research pertains to people’s expectations of programs and their relationship with intervention outcomes. In a series of initial studies, we developed and validated the Expectation Assessment Scale (EAS), a tool created to measure as well as prime expectations of outcomes in the context of cognitive enhancement interventions. In our first two studies, we probed expectations of cognitive training or non-invasive brain stimulation in over 1,000 young, middle-aged, and older adults. Ratings on the EAS suggested that older adults may have particularly high expectations of cognitive training, but that expectations can be primed to increase or decrease – at least in hypothetical scenarios. We used these data to assess the psychometric properties of the EAS with item-response theory, and confirmed its internal consistency. Next, we incorporated the EAS into two cognitive enhancement trials, one in- vestigating a computerized cognitive training intervention in nearly 100 older adults and another examining non-invasive brain stimulation in nearly 100 young adults. Both trials had a double-blind balanced-placebo design in which participants were assigned to the intervention or control condition, and then subdivided to receive ei- ther high or low expectation priming (i.e., primed to have high or low expectations of the program’s effectiveness). Although expectation ratings replicated our previous findings, results from these trials suggest little, if any, effect of either expectations or the intervention on performance outcomes. We nevertheless found that participants enjoyed their assigned program and that those who received high expectation prim- ing tended to report a more positive experience. Our findings put into question the effectiveness of such interventions and support the need for more rigorous trials of cognitive enhancement.

Tinnitus is the perception of sound in the absence of an actual sound stimulus. Recent developments have shifted the focus to the central nervous system and the neural correlate of tinnitus. Broadly, tinnitus involves cortical map rearrangement, pathological neural synchrony, and increased spontaneous firing rates. Various cortical regions, such as Heschl’s gyrus in the auditory cortex, have been found to be associated with different aspects of tinnitus, such as perception and loudness. I propose a cortical stimulation mapping study of Heschl’s gyrus using a depth and subdural electrode montage to conduct electrocorticography. This study would provide high-resolution data on abnormal frequency band oscillations characteristic of tinnitus and pinpoint regions where they occur. The validity of the neural synchrony model would also be tested in this study.

Direct current (DC) potential is an objective measure of the functional state of the human organism. It is a sensitive and accurate indicator of short- and long-term adaptations to stress, adaptive capacities, and it is an important marker of athlete readiness. Sleep is posited to be the most efficacious strategy for improving recovery to enhance sport performance, and adequate sleep is considered vital to normal psycho-physiological function. Thus, optimal sleep may enhance the functional state, in turn enhancing an athlete’s adaptability to training stress. However, little is known about the relationship between sleep and DC potential. Therefore, the purpose of this study was to examine the effect of acute (one-night) and extended (two-night) sleep quantity and quality on DC potentials in collegiate American football players. Twenty-four Division 1 American football players (Age: 20.6 ± 1.30 yr; Height: 183.4 ± 6.40 cm; Body mass: 114.40 ± 24.60 kg) wore a wrist-worn actigraphy band seven days per week over the course of 136 days, which spanned the pre-season training camp and competitive season, to measure sleep quantity and quality. DC potential was assessed six days per week using the Omegawave Ltd (Espoo, Finland) athlete monitoring system either 30 minutes upon waking or 75-120 minutes prior to the onset of the football training session. Sleep quantity was stratified into duration categories and sleep quality was stratified within sleep latency, number of awakenings, and sleep efficiency variables. Sleep quantity and quality were evaluated using acute (one night) and extended (rolling average of two consecutive nights) sleep outcomes. Within subject comparisons of DC potential were made across sleep quantity and quality categories using repeated-measures analysis of variance to examine the influence of acute and extended sleep quantity and quality on DC potential outcomes. The level of significance was set at p ≤ 0.025. Statistically significant main effects were identified for acute sleep (F3,16 = 4.68, p < .02, η2p = 0.47) and extended sleep durations (F2,17 = 7.71, p < 0.005, η2p = 0.48). Specifically, for acute sleep durations, there was a 17.1% increase in DC potentials (3.59, p < 0.01, Cohen’s d = 0.52, SE 1.18) for sleep durations ≥ 7 hours to < 9 hours, compared to sleeping < 6. For extended sleep, there was a 20% increase in DC potentials (4.53, p < 0.002, Cohen’s d = 0.68, SE = 1.13) when recording a two-day sleep average of ≥ 7.5 hours and < 9 hours, compared to an extended sleep duration of < 6 hours. A statistically significant main effect was also identified for extended wake episodes (F2,19 = 4.5, p = 0.025, η2p = 0.32). For extended sleep periods with > 4 wake episodes there was a 12% increase in DC potentials (2.57 ± 2.24mV, p < 0.25, Cohen’s d = 0.34) compared to extended sleep periods with 2-3 wake episodes. There was not a significant effect of acute (p ≥ 0.20) sleep quality or extended latency (p > 0.18) and efficiency (p > 0.08) on DC potentials. These findings suggest that sleep quantity affects DC bio-potentials and thus the functional state of the athlete. Specifically, sleep durations between 7.00/7.50 to 9 hours correspond with higher measures of DC potentials compared to lesser durations. Given the effect of sleep quantity on biological markers for training adaptability, practitioners should prioritize sleep in the training process and educate athletes on proper sleep hygiene and sleep quantity to enhance their readiness to train.

Thesis (MSc. (Physics)) --University of Limpopo, 2015 / This study investigated the extent to which learners from rural and peri-urban areas understand what the symbols represent and their roles in simple direct current resistive electrical circuits. The emphasis was on simple direct current resistive electrical circuits that consist of batteries and bulbs. The study was carried out with Grade 12 learners at high school level in the Limpopo Provincial Department of Education. It used both qualitative and quantitative data collection methods to investigate learners’ understanding of direct current resistive electrical circuits at rural and peri-urban schools. It used questionnaires and structured interviews to collect the data so that the results could provide in-depth understanding and generalizability. The results revealed that learners knew the symbols used in direct current resistive circuits, however, when the circuit was populated with a number of known symbols it became complex to such an extent that some learners struggled to identify the symbols. As it appeared, learners could not conceptualize the role played by a battery, conductor, ammeter and voltmeter in direct current resistive electrical circuit. In addition, the study also revealed that learners experience difficulties when translating a real circuit to a schematic circuit. This study suggests that deeper focus has to be directed towards developing leaners’ understanding of the working and role played by each symbol in a schematic circuit. Learners were operating at far lower conceptual basis and thought of conductor as a hollow pipe like material. Results were also compared in terms of geographical location of the school, and findings indicate that the rural school was performing better than peri-urban school. The results highlight a number of the frequently encountered alternative frameworks which learners come across when they are faced with schematic circuit diagrams. Most of the alternative frameworks found are well documented in literature (for example current consumption, difficulty with understanding electric concepts, difficulty with concept differentiation, and no firm alternative frameworks). vi The participants in this study were not exposed to practical work. This suggests the results might be different with learners exposed to practical work. It is therefore recommended that future studies look at the understanding of the role played by individual electrical components with learners who had practical experience with real electrical circuits. Majority of learners in this study could not communicate their scientific conclusions using English, as the English is their second language.

It is well established that cathodal transcranial direct current stimulation (tDCS) can decrease the excitability of the primary motor cortex (M1) in humans. Despite the cortical inhibition caused by cathodal tDCS, it remains unknown how this intervention alters unrestrained dynamic reaching movements qualitatively. Accordingly, we designed this study to examine how cathodal tDCS impacts unrestrained dynamic reaching as measured by qualitative kinematic features and electromyography (EMG). Ten young, healthy adult subjects were recruited to participate in a two day protocol involving repetitively reaching to two different targets (large and small) both before and following cathodal tDCS applied over the contralateral M1 during one session and before and following sham tDCS over the same brain region during another session. We discovered that cathodal tDCS was not able to alter the kinematic features of reaching in these subjects but did degrade the EMG performance, specifically by increasing the amount of co-contraction between muscle pairs. Because co-contraction is an indicator of relatively unskilled performance, these results seem to indicate that cathodal tDCS of M1 preferentially disrupts the learning or execution of highly coordinated muscle firing patterns during dynamic reaching. This work adds to the growing body of knowledge about how tDCS applied over M1 affects our movements. Moreover, it leads us to believe that tDCS can be utilized to assist in rehabilitation of patient populations who suffer from neurological dysfunctions but EMG assessments may need to be included in order to more effectively assess the patient performance.