Magnetization plateau in a two-dimensional multiple-spin exchange model

We study a multiple-spin exchange model on a triangular lattice, which is a possible model for low-density solid 3He films. Due to strong competitions between ferromagnetic three-spin exchange and antiferromagnetic four-spin one, the ground states are highly degenerate in the classical limit. At least 2^{L/2}-fold degeneracy exists on the L*L triangular lattice except for the SO(3) symmetry. In the magnetization process, we found a plateau at m/m_{sat}=1/2, in which the ground state is "uuud state" (a collinear state with four sublattices). The 1/2-plateau appears due to the strong four-spin exchange interaction. This plateau survives against both quantum and thermal fluctuations. Under a magnetic field which realizes the "uuud" ordered state, a phase transition occurs at a finite temperature. We predict that low-density solid 3He thin films may show the 1/2-plateau in the magnetization process. Experimental observation of the plateau will verify strength of the four-spin exchange. It is also discussed that this magnetization plateau can be understood as an insulating-conducting transition in a particle picture.Comment: 10 pages, RevTeX, 12 figures, added a reference and corrected typos, to be published in Phys.Rev.B (01 APR 99

Regressão linear para predição do estado nutricional de bananeiras tipo prata.

A avaliação do estado nutricional de bananeiras é fundamental para recomendação de adubação e manejo da cultura. Diversos métodos analíticos são utilizados, mas a segurança dos dados e a demora para a obtenção dos resultados dificulta a tomada de decisão que favorece o aparecimento de sintomas de deficiência e consequente queda de produtividade da lavoura

High-resolution abundance analysis of red giants in the metal-poor bulge globular cluster HP~1

The globular cluster HP~1 is projected at only 3.33 degrees from the Galactic center. Together with its distance, this makes it one of the most central globular clusters in the Milky Way. It has a blue horizontal branch (BHB) and a metallicity of [Fe/H]~-1.0. This means that it probably is one of the oldest objects in the Galaxy. Abundance ratios can reveal the nucleosynthesis pattern of the first stars as well as the early chemical enrichment and early formation of stellar populations. High-resolution spectra obtained for six stars were analyzed to derive the abundances of the light elements C, N, O, Na, and Al, the alpha-elements Mg, Si, Ca, and Ti, and the heavy elements Sr, Y , Zr, Ba, La, and Eu.} High-resolution spectra of six red giants that are confirmed members of the bulge globular cluster HP~1 were obtained with the 8m VLT UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVES configuration. The spectroscopic parameter derivation was based on the excitation and ionization equilibrium of FeI and FeII. We confirm a mean metallicity of [Fe/H] = -1.06~0.10, by adding the two stars that were previously analyzed in HP~1. The alpha-elements O and Mg are enhanced by about +0.3<[O,Mg/Fe]<+0.5 dex, Si is moderately enhanced with +0.15<[Si/Fe]<+0.35dex, while Ca and Ti show lower values of -0.04<[Ca,Ti/Fe]<+0.28dex. The r-element Eu is also enhanced with [Eu/Fe]~+0.4, which together with O and Mg is indicative of early enrichment by type II supernovae. Na and Al are low, but it is unclear if Na-O are anticorrelated. The heavy elements are moderately enhanced, with -0.20<[La/Fe]<+0.43dex and 0.0<[Ba/Fe]<+0.75~dex, which is compatible with r-process formation. The spread in Y, Zr, Ba, and La abundances, on the other hand, appears to be compatible with the spinstar scenario or other additional mechanisms such as the weak r-process.Comment: 15 pages, 8 figures In press in Astronomy & Astrophysics (2016

Diversidade genética entre progênies de maracujazeiro amarelo baseado em características morfo agronômicas.

O estudo da diversidade genética é básico para subsidiar a escolha de genitores e trabalhos de seleção e melhoramento. Este trabalho foi realizado no Departamento de Fitotecnia da Universidade Federal de Viçosa. Avaliouse a diversidade genética entre 34 famílias de meios-irmãos e 3 cultivares de maracujazeiro amarelo. O delineamento experimental foi em blocos casualizados, com 37 tratamentos, três repetições e quatro plantas por parcela. As características avaliadas foram: altura da planta e diâmetro do caule aos 60 dias após o transplantio, diâmetro do caule no início da produção, vigor, severidade de verrugose e produção por parcela. Os dados foram submetidos à análise de variância e as médias comparadas pelo método de Dunnett. Para o estudo da diversidade genética, foram estimadas as distâncias de Mahalanobis (D2) entre progênies, bem como realizadas análises de agrupamento de Tocher e das Variáveis Canônicas. Por meio da análise de variância, verificou-se efeito dos tratamentos em todas as variáveis, evidenciando a existência de variabilidade genética entre as progênies e cultivares avaliados. Houve concordância na formação dos grupos de similaridade por meio dos diferentes métodos de análise multivariada. Os grupos de tratamentos divergentes entre si e superiores foram: Grupo I - 2, 3, 6 e 15; Grupo II - 14; e Grupo III - 25

Plataforma web para sistemas de informação geoespacial (SIG): aplicações no projeto GeoDegrade.

O projeto ?Desenvolvimento de geotecnologias para identificação e monitoramento de níveis de degradação em pastagens - GeoDegrade? tem como objetivo principal desenvolver metodologias para a identificação e o monitoramento de níveis de degradação em pastagens dos biomas Amazônia, Cerrado e Mata Atlântica (Nogueira et al, 2013). O presente documento tem como objetivo a demonstrar o potencial do repositório digital GeoInfo no gerenciamento e compartilhamento de informações geoespaciais do projeto Geodegrade

Spin-1/2 Heisenberg-Antiferromagnet on the Kagome Lattice: High Temperature Expansion and Exact Diagonalisation Studies

For the spin-$\frac{1}{2}$ Heisenberg antiferromagnet on the Kagom\'e lattice we calculate the high temperature series for the specific heat and the structure factor. A comparison of the series with exact diagonalisation studies shows that the specific heat has further structure at lower temperature in addition to a high temperature peak at $T\approx 2/3$. At $T=0.25$ the structure factor agrees quite well with results for the ground state of a finite cluster with 36 sites. At this temperature the structure factor is less than two times its $T=\infty$ value and depends only weakly on the wavevector $\bf q$, indicating the absence of magnetic order and a correlation length of less than one lattice spacing. The uniform susceptibility has a maximum at $T\approx 1/6$ and vanishes exponentially for lower temperatures.Comment: 15 pages + 5 figures, revtex, 26.04.9

Genetic variations in the leptin gene associated with growth and carcass traits in Nellore cattle.

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