PREVISIBILIDADE DE MERCADOS: UM ESTUDO COMPARATIVO ENTRE BOVESPA E S&P500

Este estudo tem por objetivo comparar a previsibilidade do mercado de capitais brasileiro e americano, através do uso de redes neurais Group Method of Data Handling (GMDH) em uma aproximação indutiva do retorno mensal do índice Ibovespa e do S&P500. Inicialmente, foi realizada uma revisão teórica sobre o tema de redes neurais e, após, procurou-se a desmistificação do conceito de redes neurais, prejudicada pelo efeito “caixa preta” que impede o conhecimento dos métodos de processamento e decisão de uma rede neural, bem como seus efeitos. Os resultados das redes demonstram uma maior previsibilidade para o mercado brasileiro

Estudo das transformações de fase no sistema Fe-N induzidas por bombardeamento iônico

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Estudo das transformações de fase no sistema Fe-N induzidas por bombardeamento iônico

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Low-temperature iron-nitride phase transformations induced by ion bombardment

We show that for the Fe–N system the combined use of ion irradiation and thermal annealing can lower the temperature for a given phase transformation. By Ar bombarding N-implanted Fe samples at 250 and 300 °C, we have induced the є-Fe2N→є-Fe2 + x N + є-Fe3.2N and the є-Fe2N→e-Fe3N +Y'-Fe4N phase transformations, respectively. These temperatures are 50 °C lower than the ones needed to produce the same transformations by thermal annealing

Optical and structural properties of Si nanocrystals produced by Si hot implantation

It was already demonstrated that Si hot implantation followed by high-temperature annealing induces the formation of Si nanocrystals Si NCs which when excited in a linear excitation regime present two photoluminescence PL bands at 780 and 1000 nm . We have undertaken the present work in order to investigate three features: First, to determine the origin of each band. With this aim we have changed the implantation fluence and the high-temperature annealing time. Second, to investigate the influence of the postannealing atmosphere on the PL recovering process after bombarding the Si NCs. Third, we have annealed the as-produced Si NCs in a forming gas FG atmosphere in order to observe the PL behavior of each band. The results have shown that the 780 nm PL band has its origin in radiative interfacial states, while the 1000 nm one is due to quantum size effects. From the experiments we have concluded that the PL recovery after the Si NCs irradiation strongly depends on the type of postannealing atmosphere. Finally, it was found that the FG treatment strongly affects the line shape of the PL spectrum