The type N Karlhede bound is sharp

We present a family of four-dimensional Lorentzian manifolds whose invariant classification requires the seventh covariant derivative of the curvature tensor. The spacetimes in questions are null radiation, type N solutions on an anti-de Sitter background. The large order of the bound is due to the fact that these spacetimes are properly $CH_2$, i.e., curvature homogeneous of order 2 but non-homogeneous. This means that tetrad components of $R, \nabla R, \nabla^{(2)}R$ are constant, and that essential coordinates first appear as components of $\nabla^{(3)}R$. Covariant derivatives of orders 4,5,6 yield one additional invariant each, and $\nabla^{(7)}R$ is needed for invariant classification. Thus, our class proves that the bound of 7 on the order of the covariant derivative, first established by Karlhede, is sharp. Our finding corrects an outstanding assertion that invariant classification of four-dimensional Lorentzian manifolds requires at most $\nabla^{(6)}R$.Comment: 7 pages, typos corrected, added citation and acknowledgemen

Spin-orbit induced mixed-spin ground state in RRNiO3_3 perovskites probed by XAS: new insight into the metal to insulator transition

We report on a Ni L$_{2,3}$ edges x-ray absorption spectroscopy (XAS) study in $R$NiO$_3$ perovskites. These compounds exhibit a metal to insulator ($MI$) transition as temperature decreases. The L$_{3}$ edge presents a clear splitting in the insulating state, associated to a less hybridized ground state. Using charge transfer multiplet calculations, we establish the importance of the crystal field and 3d spin-orbit coupling to create a mixed-spin ground state. We explain the $MI$ transition in $R$NiO$_3$ perovskites in terms of modifications in the Ni$^{3+}$ crystal field splitting that induces a spin transition from an essentially low-spin (LS) to a mixed-spin state.Comment: 4 pages, 4 figures, accepted as PRB - Rapid Comm. Dez. 200

Resposta do milho verde a lâminas de irrigação.

No Meio-Norte do Brasil, a cultura do milho irrigado direcionado para a comercialização de espigas verdes possui uma grande importância sócio-econômica, permitindo o uso de mão-de-obra familiar, movimentando o comércio e a indústria caseira. Nesse contexto, foi proposto este trabalho com o objetivo de avaliar diferentes lâminas de irrigação sobre os componentes de produção e a produtividade de espiga verde do milho (híbrido simples) BRS 1030. O experimento foi conduzido na Embrapa Meio-Norte, em Teresina, Piauí, de setembro a novembro de 2009. O delineamento experimental foi de blocos ao acaso com quatro repetições. Foram avaliadas cinco lâminas de irrigação, com base em frações da evapotranspiração de referência (25, 50, 75, 100 e 125% da ETo), estimada pelo método de Penman-Monteith. As análises de regressão para as produtividades ajustaram-se a equações polinomiais quadráticas e lineares para os componentes de produção. As máximas produtividades de espigas verdes com palha (13.652,9 kg ha-1) e de espiga verde sem palha (7.709,4 kg ha-1) foram estimadas com a lâmina de irrigação 304,39 mm, respectivamente. Os maiores valores de comprimento (31,4 cm e 21,6 cm), diâmetro (5,62 cm e 4,37 cm) de espigas empalhadas e despalhadas e a melhor relação espiga sem palha/com palha (0,57) foram obtidos com a lâmina de irrigação 340,57 mm.CONBEA 2013

Equilibrium onions?

We demonstrate the possibility of a stable equilibrium multi-lamellar ("onion") phase in pure lamellar systems (no excess solvent) due to a sufficiently negative Gaussian curvature modulus. The onion phase is stabilized by non-linear elastic moduli coupled to a polydisperse size distribution (Apollonian packing) to allow space-filling without appreciable elastic distortion. This model is compared to experiments on copolymer-decorated lamellar surfactant systems, with reasonable qualitative agreement

Cell migration and chimerism after whole‐organ transplantation: The basis of graft acceptance

Improvements in the prevention or control of rejection of the kidney and liver have been largely interchangeable (1, 2) and then applicable, with very little modification, to thoracic and other organs. However, the mechanism by which anti rejection treatment permits any of these grafts to be “accepted” has been an immunological enigma (3, 4). We have proposed recently that the exchange of migratory leukocytes between the transplant and the recipient with consequent long-term cellular chimerism in both is the basis for acceptance of all whole-organ allografts and xenografts (5). Although such chimerism was demonstrated only a few months ago, the observations have increased our insight into transplantation immunology and have encouraged the development of alternative therapeutic strategies (6)

Anharmonic double-phonon excitations in the interacting boson model

Double-$\gamma$ vibrations in deformed nuclei are analyzed in the context of the interacting boson model. A simple extension of the original version of the model towards higher-order interactions is required to explain the observed anharmonicities of nuclear vibrations. The influence of three- and four-body interactions on the moments of inertia of ground- and $\gamma$-bands, and on the relative position of single-$\gamma$ and double-$\gamma$ bands is studied in detail. As an example of a realistic calculation, spectra and transitions of the highly $\gamma$-anharmonic nuclei $^{164}$Dy, $^{166}$Er, and $^{168}$Er are interpreted in this approach.Comment: 38 pages, TeX (ReVTeX). 15 ps figures. Submitted to Phys. Rev.

Eficiência do uso da água e produtividade de espiga verde de milho sob diferentes lâminas de irrigação.

A eficiência do uso da água (EUA), a qual é a relação entre a produtividade e o volume de água utilizado pela cultura durante todo o seu ciclo, fornece um modo simples de avaliar se o rendimento está sendo limitada pelo suprimento de água ou por outros fatores. O objetivo deste trabalho foi avaliar diferentes lâminas de irrigação sobre a produtividade e a eficiência do uso da água em milho verde, cultivar BRS 1030.CONBEA 2013

Plant breeding with marker-assisted selection in Brazil.

Over the past three decades, molecular marker studies reachedextraordinary advances, especially for sequencing and bioinformatics techniques.Marker-assisted selectionbecamepart of the breeding program routines of important seed companies, in order to accelerate and optimize the cultivar developing processes. Private seed companies increasingly use marker-assisted selection, especially for the species of great importance to the seed market, e.g. corn, soybean, cotton, and sunflower. In the Brazilian public institutions few breeding programs use it efficiently.The possible reasons are: lack of know-how, lack of appropriate laboratories, few validated markers, high cost, and lack of urgency in obtaining cultivars. In this article we analyze the use and the constraints of marker-assisted selection in plant breeding programs of Brazilian public institute