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

Possible chiral phase transition in two-dimensional solid 3^3He

We study a spin system with two- and four-spin exchange interactions on the triangular lattice, which is a possible model for the nuclear magnetism of solid $^3$He layers. It is found that a novel spin structure with scalar chiral order appears if the four-spin interaction is dominant. Ground-state properties are studied using the spin-wave approximation. A phase transition concerning the scalar chirality occurs at a finite temperature, even though the dimensionality of the system is two and the interaction has isotropic spin symmetry. Critical properties of this transition are studied with Monte Carlo simulations in the classical limit.Comment: 4 pages, Revtex, 4 figures, to appear in Phys.Rev.Let

Predicting Thermoelectric Power Plants Diesel/Heavy Fuel Oil Engine Fuel Consumption Using Univariate Forecasting and XGBoost Machine Learning Models

Monitoring and controlling thermoelectric power plants (TPPs) operational parameters have become essential to ensure system reliability, especially in emergencies. Due to system complexity, operating parameters control is often performed based on technical know-how and simplified analytical models that can result in limited observations. An alternative to this task is using time series forecasting methods that seek to generalize system characteristics based on past information. However, the analysis of these techniques on large diesel/HFO engines used in Brazilian power plants under the dispatch regime has not yet been well-explored. Therefore, given the complex characteristics of engine fuel consumption during power generation, this work aimed to investigate patterns generalization abilities when linear and nonlinear univariate forecasting models are used on a representative database related to an engine-driven generator used in a TPP located in Pernambuco, Brazil. Fuel consumption predictions based on artificial neural networks were directly compared to XGBoost regressor adaptation to perform this task as an alternative with lower computational cost. AR and ARIMA linear models were applied as a benchmark, and the PSO optimizer was used as an alternative during model adjustment. In summary, it was possible to observe that AR and ARIMA-PSO had similar performances in operations and lower error distributions during full-load power output with normal error frequency distribution of −0.03 ± 3.55 and 0.03 ± 3.78 kg/h, respectively. Despite their similarities, ARIMA-PSO achieved better adherence in capturing load adjustment periods. On the other hand, the nonlinear approaches NAR and XGBoost showed significantly better performance, achieving mean absolute error reductions of 42.37% and 30.30%, respectively, when compared with the best linear model. XGBoost modeling was 8.7 times computationally faster than NAR during training. The nonlinear models were better at capturing disturbances related to fuel consumption ramp, shut-down, and sudden fluctuations steps, despite being inferior in forecasting at full-load, especially XGBoost due to its high sensitivity with slight fuel consumption variations

O perfil da indústria de laticínios na Zona da Mata e Campo das Vertentes de Minas Gerais.

Cenário econômico mundial; Cenário econômico brasileiro; Cenário macroeconômico regional: Zona da Mata e Campo das Vertentes; Evolução do setor lácteo brasileiro.bitstream/item/132488/1/Livro-O-perfil-da-industria-de-laticinios.pd

Concentração de ânions no perfil de solo tratado sucessivamente com lodo de esgoto.

Resumo: Uma das preocupações quanto ao uso agrícola de lodo de esgoto é a lixiviação de ânions no perfil do solo, principalmente o nitrato, que podem atingir o lençol freático e contaminar as coleções hídricas após aplicações sucessivas do resíduo. O objetivo foi avaliar a concentração de nitrato, nitrito e sulfato no perfil do solo de 1 a 5 metros de profundidade após seis aplicações anuais de doses superestimadas de lodo de esgoto, seguidas de dez anos de cultivo sem adição do resíduo em poço escavado em uma área experimental. Observaram-se o acúmulo de sulfato até 2 metros de profundidade e as maiores concentrações de nitrato a 4 e 5 metros de profundidade, indicando maior movimentação deste ânion em relação aos demais. Abstract: One concern about using sewage sludge in agriculture is the leaching of anions through the soil profile, particularly nitrate, which could contaminate groundwater after successive residue applications. IN this study, anions concentrations were evaluated through the soil profile (1 to 5 m of depth) after six annual applications of superdoses of sewage sludge followed by 10 years of cultivation without adding the residue using a well excavated at an experimental area. Sulfate accumulation was observed until 2m of depth and mayor nitrate concentrations at 4 and 5m of depth, indicating more intense leaching of this anion

Balanço hidrológico da microbacia do córrego lageado, Município de Uberaba-MG, para o ano de 2012.

O manejo integrado em microbacia hidrográfica implementa uma nova maneira de se planejar e usar os recursos naturais, indo de encontro ao desenvolvimento sustentável. A compreensão do balanço hídrico, mesmo que de forma simplificada, é importante para o entendimento dos processos de degradação e conservação dos recursos naturais relacionados ao uso do solo e da água. Dentro deste contexto, o presente estudo teve por objetivo fazer o balanço hídrico da microbacia do córrego Lageado, situada no município de Uberaba, MG, para o ano de 2012. A escolha desta microbacia para este trabalho baseou-se na sua importância como terceiro maior manancial pertencente à APA (Área de Proteção Ambiental) do rio Uberaba e por estar parcialmente dentro do perímetro urbano. Nas últimas décadas, esta microbacia hidrográfica passou por intensas transformações relacionadas ao uso e à ocupação do solo

Relação entre polimorfismos no gene da leptina, ganho de peso e concentração sérica de leptina em bovinos de corte.

O objetivo do trabalho é estabelecer a relação de polimorfismos no gene da leptina com a quantidade de leptina sérica e ganho de peso durante o confinamento, visando a utilização de dados obtidos em programas de seleção animal. Os bovinos confinados utilizados na pesquisa serão provenientes da Fazenda Tuju Puitan. Serão objetos da pesquisa 100 animais com idade média de 12 meses

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