A visualization study and Quantitative velocity measurements have been performed in Taylor-Couette flow with a medium-gap (ç= 0.356), over a large range of Taylor numbers (2.1x10(4) < Ta < 1.1x10(11)), with the outer cylinder fixed and the inner cylinder rotating about its axis. Quantitative velocity measurements were carried out using the PHANTOMM flow tagging technique. Two techniques were used for visualization study: the PHANTOMM technique that allowed flow structure visualization from small to moderate Taylor numbers, and the Particle Streak Imaging, PSI (the flow was seeded with neutrally buoyant polystyrene micro spheres) that permitted the flow structure visualization from moderate to high Taylor numbers. The results illustrate the expected three-dimensional features of flow and presence of Taylor cells at low Taylor numbers. Our study examined the interplay between small and large scales present in the flow as well as showed the gradual transition to turbulence with increasing Taylor numbers. Taylor cells were found for Taylor numbers less than 1.13 x 10(10). At low Taylor numbers, the flow in the cells appeared to be a rotational laminar flow with a high degree of coherence. At higher Taylor numbers, the cells aspect became more irregular, and the flow inside them became turbulent. The Görtler instability developed inside Taylor cells and close to the inner cylinder wall. At the highest Taylor numbers, turbulence increased up to the point where no Taylor cells could be detected. For the flow in our study, at Ta = 1.13 x 10(10), the homogenization by turbulence spread across the gap, and the flow structure sharply changed its pattern as a toroidal vortex in helical motion developed in a thin layer on the inner cylinder wall. Instantaneous velocities, average velocities, angular-momentum ratio and spectral density function were computed for all ranges of Taylor numbers in the range studied. These quantitative results show the same conclusions as the ones presented by the visualization stud
The irrigation is a technique developed to supply the hydric needs of the plants. The use of the water should be optimized so that the culture just has enough for its growth, avoiding waste. The objective of this work was to characterize the behavior of capacitive sensors of humidity to monitor the moisture in the soils. In first instance, it was appraised sensors with dielectric built of synthetic pomes stone (Rd = 0,4 and Rd = 0,8) and of soil samples (Rd = 0,8 and Rd = 1,0), being the Rd parameter a geometric factor that relates the distance between the capacitor plates with radius of the plates. For the calibration, the sensors were installed in PVC recipient of cylindrical shape, filled with soil. The set (sensor and soil) was humidified by capillary effect and submitted by a natural drying very slowly. The parameter readings were taken daily, which allowed obtain the curves relating the humidity percentage, expressed in terms of dry weight, with the output voltage fort the sensor. The experiments were performed in sand soil and in dark red latossolo. The obtained results allowed to infer that the behavior of the sensor has a specific feature for each type of soil, being, therefore, necessary to develop a own calibration curve for the sensor, when used in soil with specific characteristic
Resumo: A crise financeira de 2008 resultou em um quadro de taxas de juros de curto prazo próximas de zero e levou vários países a adotarem políticas monetárias não convencionais com a finalidade de estabilizar o sistema financeiro e sustentar o nível da atividade econômica. Embora o objetivo do programa de compra de títulos, denominado como quantitative easing(QE), iniciado pelo Federal Reserve (Banco Central dos Estados Unidos), fosse estimular a atividade econômica interna, seu efeito externalidade foi sentido pelos países emergentes que observaram uma elevação no fluxo de capital externo, um aumento na procura por ativos e uma apreciação da moeda nacional. Dado este contexto, o presente estudo avalia se o QE afetou a volatilidade do índice Ibovespa, do câmbio, do riscopaís, da taxa de juros dos Estados Unidos e do índice de renda fixa. Para tanto, utiliza-se de técnicas de estudos de eventos e modelos autorregressivos e generalizados autorregressivos heteroscedásticos para verificar o comportamento das variáveis consideradas. Os resultados encontrados indicam que o QE alterou a volatilidade dos ativos em alguns períodos analisados e seu início/fim modificou os retornos dos ativos.
Palavras-chave:Quantitative easing.Volatilidade. Ativos financeiros.
Abstract:The financial crisis of 2008 resulted in a short-term interest rates near zero frame and led many countries to adopt unconventional monetary policies in order to stabilize the financial system and sustain the level of economic activity. Although the purpose of the bond-buying program, known as quantitative easing(QE), initiated by the Federal Reserve (Central Bank of the United States) is related only to domestic economic, his externality effect was felt by the emerging countries that had an increase in the flow of foreign capital, increased demand for assets and appreciation of the national currency. Given this context, the objective of this study is to evaluate whether the QE policy affected the volatility of Ibovespa index, exchange rate, country risk, US interest rates and fixed income index. Therefore, it uses the event study and auto regressive models and generalized autoregressive heteroscedastic to check the behavior of the variables considered. The results show that the
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