Comparação da eficiência de fontes de fósforo na produção de arroz de terras altas.

O arroz de terras altas é importante componente dos sistemas de produção na região do Cerrado do Brasil. A deficiência de fósforo é um dos fatores limitantes na produção das culturas nessa região. Foi conduzido um ensaio em casa de vegetação com o objetivo de avaliar fontes de fósforo na produção de arroz de terras altas. Foram utilizadas seis fontes de P, i. e. Superfosfato simples (SFS), superfosfato simples policote (SFSP), superfosfato triplo (SFT), superfosfato triplo policote SFTP), fosfato monoamômico (FMA) e fosfato monoamômicopolicote (FMAP). As doses de P utilizados foram 50, 100, 200 e 400 mg kg-1 + testemunha. Houve resposta significativa e quadrática à aplicação de fontes de P na produção de grãos. Baseado na produção máxima, as fontes de P foram classificadas na ordem de fosfato monoamômicopolicote> superfosfato simples = fosfato monoamômico>superfosfatosimples policote > superfosfato triplo > superfosfato triplo policote

On the search for the chiral anomaly in Weyl semimetals: The negative longitudinal magnetoresistance

Recently, the existence of massless chiral (Weyl) fermions has been postulated in a class of semi-metals with a non-trivial energy dispersion.These materials are now commonly dubbed Weyl semi-metals (WSM).One predicted property of Weyl fermions is the chiral or Adler-Bell-Jackiw anomaly, a chirality imbalance in the presence of parallel magnetic and electric fields. In WSM, it is expected to induce a negative longitudinal magnetoresistance (NMR), the chiral magnetic effect.Here, we present experimental evidence that the observation of the chiral magnetic effect can be hindered by an effect called "current jetting". This effect also leads to a strong apparent NMR, but it is characterized by a highly non-uniform current distribution inside the sample. It appears in materials possessing a large field-induced anisotropy of the resistivity tensor, such as almost compensated high-mobility semimetals due to the orbital effect.In case of a non-homogeneous current injection, the potential distribution is strongly distorted in the sample.As a consequence, an experimentally measured potential difference is not proportional to the intrinsic resistance.Our results on the MR of the WSM candidate materials NbP, NbAs, TaAs, TaP exhibit distinct signatures of an inhomogeneous current distribution, such as a field-induced "zero resistance' and a strong dependence of the `measured resistance" on the position, shape, and type of the voltage and current contacts on the sample. A misalignment between the current and the magnetic-field directions can even induce a "negative resistance". Finite-element simulations of the potential distribution inside the sample, using typical resistance anisotropies, are in good agreement with the experimental findings. Our study demonstrates that great care must be taken before interpreting measurements of a NMR as evidence for the chiral anomaly in putative Weyl semimetals.Comment: 13 pages, 6 figure

Seleção de híbridos e acessos de tomate para resistência a Fusarium oxysporum f. sp. lycopersici raça 3.

bitstream/CNPH-2010/36465/1/bpd-62.pd

Influence of the external pressure on the quantum correlations of molecular magnets

The study of quantum correlations in solid state systems is a large avenue for research and their detection and manipulation are an actual challenge to overcome. In this context, we show by using first-principles calculations on the prototype material KNaCuSi$_{4}$O$_{10}$ that the degree of quantum correlations in this spin cluster system can be managed by external hydrostatic pressure. Our results open the doors for research in detection and manipulation of quantum correlations in magnetic systems with promising applications in quantum information science