Submitted by Sandro Camargo (sandro.camargo@unipampa.edu.br) on 2015-05-09T22:33:43Z No. of bitstreams: 1 126110043.pdf: 2117805 bytes, checksum: f107c883cc20c40fff355188fc0e7df6 (MD5) / Made available in DSpace on 2015-05-09T22:33:44Z (GMT). No. of bitstreams: 1 126110043.pdf: 2117805 bytes, checksum: f107c883cc20c40fff355188fc0e7df6 (MD5) Previous issue date: 2014-08-20 / Atualmente as técnicas não lineares de modulação de potência aplicadas ao aquecimento resistivo de água, principalmente em redes elétricas mal projetadas, podem gerar vários problemas no ambiente onde estão instaladas. É o caso dos chuveiros eletrônicos que, dependendo da técnica utilizada para executar o processo de modulação de potência, podem ocasionar efeitos indesejáveis na rede elétrica e ambiente. Um exemplo típico é o Controle por Ciclos Inteiros, foco deste trabalho, que apresenta baixa probabilidade de geração de harmônicas e interferência eletromagnética (IEM). Em contrapartida, é praticamente inevitável o surgimento de flicker na rede elétrica decorrente de sua utilização, principalmente devido às altas potências dos equipamentos de aquecimento resistivo, agravadas pelos longos intervalos entre condução e não condução de corrente. Considerando que a geração de flicker é a principal desvantagem proveniente do Controle por Ciclos Inteiros, o presente trabalho tem por objetivo propor outras técnicas a fim de atenuar este efeito indesejável e, ao mesmo tempo, possibilitar a utilização de vários níveis de potência. / Currently the non-linear power modulation techniques applied to resistive water heating, mainly on not properly designed electric installations, can generate various problems in the environment where they are present. This is the case of electronic showers that depending on the power modulation technique may result in undesirable effects in the power grid and environment. A typical example is the zero-crossing AC power control, focus of this work, which has low probability of generating harmonics and electromagnetic interference (EMI). On the other hand, it is almost inevitable the emergence of Flicker on the power grid resulting from its use, mainly due to high electrical power consumed by heating equipment, compounded by long conducting and non-conducting power intervals. Whereas the flicker generated is the main drawback from the zero-crossing power control, this work aims to propose other techniques to reduce this undesirable effect allowing several output power levels.

La stimulation transcrânienne par courant alternatif (tACS) est une technique de stimulation non invasive du cerveau qui est d’un intérêt croissant, entre autres pour ses effets sur les ondes cérébrales intrinsèques. Par opposition à la stimulation transcranienne par courant direct (tDCS), la tACS permet l’administration d’un courant sinusoïdal ajusté à la fréquence endogène individuelle d’un individu. Les oscillations cérébrales constituant la bande de fréquence alpha (8-12 Hz) sont parmi les plus étudiées en raison de leurs associations variées avec les fonctions et états cérébraux. Un nombre important d’études ont montré l’efficacité de la tACS de diverses façons pour augmenter la puissance de l’activité EEG dans la bande de fréquence alphal’onde alpha. Cependant, l’hétérogénéité des paramètres de stimulation, particulièrement l’intensité, rend l’implémentation de nouveaux protocoles ardue. En effet, il n’y a actuellement aucun consensus sur les paramètres optimaux de stimulation pour moduler l’activité EEG dans la bande de fréquence alphal’onde alpha. Ce projet a pour but de documenter l’impact différentiel de contrôler les caractéristiques de stimulation tACS, soit l’intensité, la fréquence et le site (antérieur ou postérieur) de stimulation. À cette fin, 20 participants en santé ont pris part à notre étude, chacun soumis à 4 conditions de stimulation tACS, échelonnées sur 2 jours (2 blocs par jour). Pour chaque condition expérimentale, la stimulation tACS a été administrée de façon continue via 2 électrodes pendant 20 minutes. Deux conditions actives de tACS ont été réalisées aux sites PO7-PO8 (Système International EEG 10-10), l’une à Fréquence Alpha Individuelle (IAF) et l’autre à Fréquence Theta Individuelle (ITF), qui ont été prédéterminées par une session EEG, au repos et les yeux ouverts, de 5 minutes a priori. Deux conditions de stimulation ont été effectuées avec les électrodes de stimulation positionnées aux sites F3F4 (Système International EEG 10-20), à IAF ou à intensité SHAM (montée de courant 15 secondes seulement). L’intensité de stimulation a été ajustée en respectant le degré de confort de chaque participant, selon une échelle standardisée de désagréabilité (≤ 40 sur 100), et ne pouvait excéder 6 mA. La seconde séance journalière était exécutée 180 minutes après la première séance de tACS. Afin d’évaluer les niveaux de fatigue, les participants ont eu à réaliser une tâche psychomotrice de vigilance (PVT) durant la tACS. Toutes les conditions ont été contrebalancées. Les résultats suggèrent que la tACS ajustée à IAF a été plus efficace que les conditions ITF et SHAM afin d’augmenter la puissance alpha. Pour les deux sites de stimulation IAF tACS, l’augmentation de puissance spectrale la plus importante a été obtenue en tACS antérieure; par contre cette augmentation est distale et spécifique aux générateurs alpha, en pariéto-occipital. Pour ce qui est du montage tACS postérieur, l’augmentation alpha est observée pour les deux régions cérébrales, frontale et postérieure, tout en démontrant un effet d’augmentation préférentiel sur la puissance alpha, versus les autres bandes de fréquence theta et beta. Cette étude propose une évidence préliminaire que la tACS ajustée à IAF à plus hautes intensités est bien tolérée et démontre que l’optimisation de la technique peut avoir un impact prometteur dans le domaine. / Transcranial alternating current stimulation (tACS) is a non-invasive brain stimulation technique increasingly used for its modulating effect on intrinsic brain oscillations. In comparison to transcranial direct current stimulation (tDCS), tACS allows the administration of a sinusoidal current adjusted to one’s endogenous measured frequency. Oscillations within the alpha band range (8-12 Hz) are among the most studied, given their various associations with brain functions and states. A number of studies have proven to be effective in increasing alpha power using tACS through diverse methods. However, the heterogeneity of stimulation parameters, notably the intensity, makes it difficult to implement new tACS protocol. Indeed, there is currently no consensus on optimal stimulation parameters to modulate the alpha rhythm. The current project aimed to document the differential impact of controlling for key tACS stimulation characteristics, namely the stimulation intensity, the stimulation frequency and the stimulation site (anterior or posterior). To this end, we conducted a study, in which 20 healthy participants underwent four different tACS conditions conducted over two non-consecutive days (2 blocks per day). In each experimental condition, tACS stimulation was continuously delivered via two electrodes for a total duration of 20 minutes. Two active tACS conditions were administered at electrode sites PO7-PO8 (10-10 International System) at either the Individual’s Alpha Frequency (IAF) or at the Individual’s Theta Frequency (ITF), which were a priori determined via a 5-minute pre-stimulation EEG recording with eyes open at rest. Two stimulation conditions were performed with stimulating electrodes positioned over F3-F4 electrode sites, at IAF or sham intensity (ramp-up of 15 seconds). The stimulation intensity was set according to the participant’s own rating of unpleasantness on a standardized unpleasantness scale (≤ 40 out of 100) and could not exceed 6 mA. The second tACS condition was administered 180 minutes after the first tACS condition. To assess for fatigue levels, participants were asked to perform a psychomotor vigilance task (PVT) during tACS. All conditions were counterbalanced. Results suggest that alpha tACS stimulation adjusted to IAF was effective in increasing alpha power. Of the two stimulating sites, anterior alpha tACS stimulation induced greatest increases in alpha power, maximal when set to IAF, although specific to alpha generators’ site. Posterior alpha tACS stimulation showed overall increase both over frontal and posterior brain areas. These effects persisted at the 60-minute recording for the anterior tACS only. The current pilot study provides preliminary evidence that posterior tACS stimulation adjusted to IAF at higher intensities is well tolerated and shows potential as an effective brain stimulation technique to increase posterior alpha power.

This biomedical engineering thesis explores the opportunities and challenges of 2D+t contrast echocardiography for left ventricle functional analysis, both clinically and within a computer vision atlas-based deformable template model framework. A database was created for the experiments in this thesis, with 21 studies of contrast Dobutamine Stress Echo, in all 4 principal planes. The database includes clinical variables, human expert hand-traced myocardial contours and visual scoring. First the problem is studied from a clinical perspective. Quantification of endocardial global and local function using standard measures shows expected values and agreement with human expert visual scoring, but the results are less reliable for myocardial thickening. Next, the problem of segmenting the endocardium with a computer is posed in a standard landmark and atlas-based deformable template model framework. The underlying assumption is that these models can emulate human experts in terms of integrating previous knowledge about the anatomy and physiology with three sources of information from the image: texture, geometry and kinetics. Probabilistic atlases of contrast echocardiography are computed, while noting from histograms at selected anatomical locations that modelling texture with just mean intensity values may be too naive. Intensity analysis together with the clinical results above suggest that lack of external boundary definition may preclude this imaging technique for appropriate measuring of myocardial thickening, while endocardial boundary definition is appropriate for evaluation of wall motion. Geometry is presented in a Principal Component Analysis (PCA) context, highlighting issues about Gaussianity, the correlation and covariance matrices with respect to physiology, and analysing different measures of dimensionality. A popular extension of deformable models ---Active Appearance Models (AAMs)--- is then studied in depth. Contrary to common wisdom, it is contended that using a PCA texture space instead of a fixed atlas is detrimental to segmentation, and that PCA models are not convenient for texture modelling. To integrate kinetics, a novel spatio-temporal model of cardiac contours is proposed. The new explicit model does not require frame interpolation, and it is compared to previous implicit models in terms of approximation error when the shape vector changes from frame to frame or remains constant throughout the cardiac cycle. Finally, the 2D+t atlas-based deformable model segmentation problem is formulated and solved with a gradient descent approach. Experiments using the similarity transformation suggest that segmentation of the whole cardiac volume outperforms segmentation of individual frames. A relatively new approach ---the inverse compositional algorithm--- is shown to decrease running times of the classic Lucas-Kanade algorithm by a factor of 20 to 25, to values that are within real-time processing reach.