Spin-Driven Nematic Instability of the Multi-Orbital Hubbard Model: Application to Iron-Based Superconductors

Nematic order resulting from the partial melting of density-waves has been proposed as the mechanism to explain nematicity in iron-based superconductors. An outstanding question, however, is whether the microscopic electronic model for these systems -- the multi-orbital Hubbard model -- displays such an ordered state as its leading instability. In contrast to usual electronic instabilities, such as magnetic and charge order, this fluctuation-driven phenomenon cannot be captured by the standard RPA method. Here, by including fluctuations beyond RPA in the multi-orbital Hubbard model, we derive its nematic susceptibility and contrast it with its ferro-orbital order susceptibility, showing that its leading instability is the spin-driven nematic phase. Our results also demonstrate the primary role played by the $d_{xy}$ orbital in driving the nematic transition, and reveal that high-energy magnetic fluctuations are essential to stabilize nematic order in the absence of magnetic order.Comment: 8 pages, 6 figure

Elastic properties of carbon nanotubes and their heterojunctions

Comprehensive studies on the modelling and numerical simulation of the mechanical behaviour under tension, bending and torsion of single-walled carbon nanotubes and their heterojunctions are performed. It is proposed to deduce the mechanical properties of the carbon nanotubes heterojunctions from the knowledge of the mechanical properties of the single-walled carbon nanotubes, which are their constituent key unit

Automatic identification of gait events using an instrumented sock

Background: textile-based transducers are an emerging technology in which piezo-resistive properties of materials are used to measure an applied strain. By incorporating these sensors into a sock, this technology offers the potential to detect critical events during the stance phase of the gait cycle. This could prove useful in several applications, such as functional electrical stimulation (FES) systems to assist gait. Methods: we investigated the output of a knitted resistive strain sensor during walking and sought to determine the degree of similarity between the sensor output and the ankle angle in the sagittal plane. In addition, we investigated whether it would be possible to predict three key gait events, heel strike, heel lift and toe off, with a relatively straight-forward algorithm. This worked by predicting gait events to occur at fixed time offsets from specific peaks in the sensor signal. Results: our results showed that, for all subjects, the sensor output exhibited the same general characteristics as the ankle joint angle. However, there were large between-subjects differences in the degree of similarity between the two curves. Despite this variability, it was possible to accurately predict gait events using a simple algorithm. This algorithm displayed high levels of trial-to-trial repeatability. Conclusions: this study demonstrates the potential of using textile-based transducers in future devices that provide active gait assistance

Dinâmica do nitrogênio no solo em áreas de cerrado e de pastagens cultivadas no Pantanal Sul Mato-Grossense.

Um estudo foi conduzido em fazenda do Pantanal Sul Mato-Grossense, visando avaliar as alteracoes nas taxas de mineralizacao de N e nitrificacao liquidas no solo, em consequencia do desmatamento e implantacao de pastagens cultivadas. Foram tomadas dez amostras de solo compostas, em seis epocas a partir da semeadura da graminea, analisados os teores de amonia e nitrato, e calculadas as taxas de mineralizacao e nitrificacao. Os resultados mostraram que o desmatamento e implantacao de pastagem provocou alteracoes significativas na dinamica do nitrogenio do solo, com conteudos menores de amonia e maiores de nitrato, e menores taxas de mineralizacao e nitrificacao liquidas no solo das areas sob pastagem em relacao ao solo das areas sob cerrado nativo.bitstream/item/37440/1/BP13.pd

Características químicas do solo em área de pastagem nativa recém queimada no Pantanal arenoso, MS.

Estudou-se as alterações nas características químicas do solo sob pastagem nativa, no Pantanal Mato-Grossense, 15 dias após a queima. Foram demarcadas parcelas de 100x40m em área de savana gramíneo-lenhosa onde predominava o capim-carona (Elyonurus muticus), sobre podzol hidromórfico. Foram coletadas 10 amostras de solo compostas, em transectos, antes e 15 dias após a queima, realizada no início de setembro de 1995. As amostras foram tomadas nas seguintes profundidades: 0-5, 5-10, 10-20 e 20-40cm. Foram determinados o pH, a capacidade de troca de cátions (T), a soma de bases trocáveis (S), a porcentagem de saturação em bases (V) e o conteúdo de fósforo assimilável da área nas duas épocas. Os resultados obtidos mostraram que a queima inicialmente elevou significativamente (P<0,05) o pH e o valor de T, independente da profundidade. Para os terores de S e V os incrementos foram significativos (P<0,05) nas camadas 0-5, 5-10 e 10-20cm. O conteúdo de fósforo assimilável somente sofreu aumento significativo (P<0,05) na camada 0-5cm. Esses aumentos foram atribuídos ao efeito fertilizador das cinzas depositadas na superfície do solo após a queima.bitstream/item/37416/1/BP36.pd

Cálculo dos estoques de carbono do solo sob diferentes condições de manejo.

A conversão de ecossistemas naturais para uso agrícola pode exercer uma grande influência no destino do carbono (C) estocado nos solos. Mudanças no uso da terra alteram os processos biogeoquímicos do solo, com reflexos no estoque de C e no fluxo de gases entre o solo e a atmosfera.bitstream/CPAP-2009-09/56775/1/COT69.pdfFormato eletrônico