1,114 research outputs found

    Distribuição do carbono orgânico em Latossolo sob manejo da adubação fosfatada em plantio direto no Cerrado.

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    O objetivo deste trabalho foi avaliar a distribuição vertical e horizontal do carbono orgânico do solo (CO) sob cinco manejos da adubação fosfatada, no sistema plantio direto. O experimento foi instalado sob Latossolo Vermelho, cultivado durante oito anos com soja ou milho, com milheto como planta de cobertura na entressafra. As parcelas foram submetidas aos tratamentos: aplicação de superfosfato triplo a lanço e no sulco, fosfato natural reativo a lanço e no sulco, e ausência de adição de fertilizante fosfatado (testemunha). A adição anual dos adubos fosfatados, na dose de 80 kg ha‑1 de P2O5, foi realizada em solo inicialmente com baixo teor de fósforo disponível. Amostras foram coletadas perpendicularmente à linha de plantio, em sete pontos distanciados a 12,5 cm, e cinco camadas: 0?2,5, 2,5?5,0, 5,0?10, 10?20 e 20?30 cm. O conteúdo e a distribuição do CO são afetados pela adubação fosfatada, tanto vertical quanto horizontalmente, com os maiores conteúdos observados nos tratamentos com adubos fosfatados. Em comparação com a testemunha, o superfosfato triplo apresentou maior conteúdo de CO até a camada de 5,0?10 cm, e o fosfato natural reativo até 10?20 cm. A aplicação de fósforo em sulcos proporciona maior volume de solo com teores adequados de CO, em comparação à aplicação a lanço

    Noether symmetries for two-dimensional charged particle motion

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    We find the Noether point symmetries for non-relativistic two-dimensional charged particle motion. These symmetries are composed of a quasi-invariance transformation, a time-dependent rotation and a time-dependent spatial translation. The associated electromagnetic field satisfy a system of first-order linear partial differential equations. This system is solved exactly, yielding three classes of electromagnetic fields compatible with Noether point symmetries. The corresponding Noether invariants are derived and interpreted

    Long-term in vivo imaging of fibrillar tau in the retina of P301S transgenic mice.

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    Tauopathies are widespread neurodegenerative disorders characterised by the intracellular accumulation of hyperphosphorylated tau. Especially in Alzheimer's disease, pathological alterations in the retina are discussed as potential biomarkers to improve early diagnosis of the disease. Using mice expressing human mutant P301S tau, we demonstrate for the first time a straightforward optical approach for the in vivo detection of fibrillar tau in the retina. Longitudinal examinations of individual animals revealed the fate of single cells containing fibrillar tau and the progression of tau pathology over several months. This technique is most suitable to monitor therapeutic interventions aimed at reducing the accumulation of fibrillar tau. In order to evaluate if this approach can be translated to human diagnosis, we tried to detect fibrillar protein aggregates in the post-mortem retinas of patients that had suffered from Alzheimer's disease or Progressive Supranuclear Palsy. Even though we could detect hyperphosphorylated tau, we did not observe any fibrillar tau or Aß aggregates. In contradiction to previous studies, our observations do not support the notion that Aβ or tau in the retina are of diagnostic value in Alzheimer's disease

    On the linearization of the generalized Ermakov systems

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    A linearization procedure is proposed for Ermakov systems with frequency depending on dynamic variables. The procedure applies to a wide class of generalized Ermakov systems which are linearizable in a manner similar to that applicable to usual Ermakov systems. The Kepler--Ermakov systems belong into this category but others, more generic, systems are also included

    Anisotropic Bose-Einstein condensates and completely integrable dynamical systems

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    A Gaussian ansatz for the wave function of two-dimensional harmonically trapped anisotropic Bose-Einstein condensates is shown to lead, via a variational procedure, to a coupled system of two second-order, nonlinear ordinary differential equations. This dynamical system is shown to be in the general class of Ermakov systems. Complete integrability of the resulting Ermakov system is proven. Using the exact solution, collapse of the condensate is analyzed in detail. Time-dependence of the trapping potential is allowed

    Lie symmetries for two-dimensional charged particle motion

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    We find the Lie point symmetries for non-relativistic two-dimensional charged particle motion. These symmetries comprise a quasi-invariance transformation, a time-dependent rotation, a time-dependent spatial translation and a dilation. The associated electromagnetic fields satisfy a system of first-order linear partial differential equations. This system is solved exactly, yielding four classes of electromagnetic fields compatible with Lie point symmetries

    Generalized Hamiltonian structures for Ermakov systems

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    We construct Poisson structures for Ermakov systems, using the Ermakov invariant as the Hamiltonian. Two classes of Poisson structures are obtained, one of them degenerate, in which case we derive the Casimir functions. In some situations, the existence of Casimir functions can give rise to superintegrable Ermakov systems. Finally, we characterize the cases where linearization of the equations of motion is possible
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