Modern microwave methods in solid state inorganic materials chemistry: from fundamentals to manufacturing

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Integration of Gravitational Torques in Cerebellar Pathways Allows for the Dynamic Inverse Computation of Vertical Pointing Movements of a Robot Arm

Several authors suggested that gravitational forces are centrally represented in the brain for planning, control and sensorimotor predictions of movements. Furthermore, some studies proposed that the cerebellum computes the inverse dynamics (internal inverse model) whereas others suggested that it computes sensorimotor predictions (internal forward model).This study proposes a model of cerebellar pathways deduced from both biological and physical constraints. The model learns the dynamic inverse computation of the effect of gravitational torques from its sensorimotor predictions without calculating an explicit inverse computation. By using supervised learning, this model learns to control an anthropomorphic robot arm actuated by two antagonists McKibben artificial muscles. This was achieved by using internal parallel feedback loops containing neural networks which anticipate the sensorimotor consequences of the neural commands. The artificial neural networks architecture was similar to the large-scale connectivity of the cerebellar cortex. Movements in the sagittal plane were performed during three sessions combining different initial positions, amplitudes and directions of movements to vary the effects of the gravitational torques applied to the robotic arm. The results show that this model acquired an internal representation of the gravitational effects during vertical arm pointing movements.This is consistent with the proposal that the cerebellar cortex contains an internal representation of gravitational torques which is encoded through a learning process. Furthermore, this model suggests that the cerebellum performs the inverse dynamics computation based on sensorimotor predictions. This highlights the importance of sensorimotor predictions of gravitational torques acting on upper limb movements performed in the gravitational field

Influência do Y2O3 na sinterização rápida de mulita comercial Influence of Y2O3 on rapid sintering of commercial mullite

A mulita tem se tornado um material forte candidato para uso como cerâmica avançada e funcional. Nesse sentido, muito interesse tem sido devotado no estudo de aditivos de sinterização. Assim, este trabalho tem por objetivo analisar a influência do Y2O3 na queima rápida de mulita comercial. Pó de mulita comercial foi dopado com 0,5, 1,0 e 2,0% de Y2O3 prensado isostaticamente e submetida a ciclos de sinterização rápida a 1600 ºC. Foi determinada a densidade dos corpos sinterizados e executada sua análise por difração de raios X e microscopia eletrônica. A sinterização rápida da mulita gera corpos com baixa densidade, enquanto a adição de Y2O3 possibilita atingir elevadas densificações nos corpos mulíticos. O aumento do teor de Y2O3 não provoca alterações significativas na distribuição de tamanho de grão da mulita quando de sua sinterização rápida. Elevadas taxas de aquecimento permitem a obtenção de microestruturas com distribuições de tamanho de grão mais estreitas.<br>Mullite has become a strong candidate material for advanced structural and functional ceramics. Much interest has recently focused on sintering aids for mullite. The aim of this work was to evaluate Y2O3 influence on rapid sintering of commercial mullite. Mullite powder was doped with Y2O3, pressed under a cold isostatic pressure and fast sintered at 1600 ºC. Sintered mullite was characterized by density determination, X ray diffraction and electronic microscopy. Rapid sintering produces low density mullite bodies, however, Y2O3 addition significantly increase the densification of fast fired doped bodies. Rise of Y2O3 content do not alter the grain size distribution of rapid sintered mullite. High heating rates produce microstructures with narrower grain size distributions