Entanglement versus Quantum Discord in Two Coupled Double Quantum Dots

We study the dynamics of quantum correlations of two coupled double quantum dots containing two excess electrons. The dissipation is included through the contact with an oscillator bath. We solve the Redfield master equation in order to determine the dynamics of the quantum discord and the entanglement of formation. Based on our results, we find that the quantum discord is more resistant to dissipation than the entanglement of formation for such a system. We observe that this characteristic is related to whether the oscillator bath is common to both qubits or not and to the form of the interaction Hamiltonian. Moreover, our results show that the quantum discord might be finite even for higher temperatures in the asymptotic limit.Comment: 14 pages, 8 figures (new version is the final version to appear in NJP

Fertilidade do solo em sistemas agroflorestais.

Discussão sobre o tema desenvolvimento sustentável ocupa grande espaço na sociedade devido ao declínio na qualidade de vida no meio rural e urbano. A perda de qualidade de vida associa-se à intensa degradação dos recursos naturais atrelada à modernização da agricultura e ao aumento populacional das cidades. A agricultura é função da interação de fatores socioambientais e naturais, englobando dimensões sociais, culturais, políticas e econômicas. O desafio para uma agricultura sustentável passa pelo ajuste das relações socioeconômicas que governam o que é produzido, como é produzido e para quem é produzido. Isto necessita de uma abordagem que integra os princípios agronômicos, ecológicos e socioeconômicos à compreensão e avaliação do efeito das tecnologias sobre os sistemas agrícolas e a sociedade como um todo.Palestra

Structural characteristics of soil humic acids in coffee-cultivation systems: 13C NMR and analytical pyrolysis.

Structural characterization of soil organic matter is still poorly understood in Brazilian agroecosystems. We aimed to identify the qualitative changes of soil humic acids as influenced by agroforestry- and full sun-coffee systems in the Atlantic Coastal Rainforest domain. The study was carried out in the Zona da Mata located in the state of Minas Gerais, Brazil. The specific studied sites were:agroforestry-coffee (AGF), Full sun coffee (FSC) and Native forest (NF) which was selected and used to determine the native or steady state condition of soil. Soil humic acids were extracted by using basic-acid medium, purified, and freeze-dried to a solid state to perform 13C NMR and analytical pyrolysis analyses. 13C NMR assignment of soil HAs from FSC system suggests an intensification of the process of humification of HAs structure. The higher aromaticity index of HAs from FSC compared to the AGF system confirmed this result. The relative abundance in each specific pyrolitic group was similar among the different land use, with exception to the higher amounts of lignin-like and lipids compounds in AGF compared to FSC system, and the higher abundance of N-compounds in FSC (37,0%) than in AGF (21,5%) system. Combining 13C NMR with Pyrolysis is an interesting tool to the study of structural features of HAs. Despite of the discrepancies, both techniques indicated that studied AGF systems favor the genesis of soil HAs with lower degree of humification when compared to FSC system, as a result of the influence of organic residues (fresh and old) from trees.pdf 1519-

Avaliação dos impactos econômico, social e ambiental do uso da alfafa em sistemas de produção de leite.

Foram avaliados os impactos econômico, social e ambiental do uso da alfafa na produção de leite. Compararam-se dois sistemas de produção: a) confinamento com fornecimento de silagem de milho (seca) e pastejo rotacionado de forrageira tropical (chuvas); b) pastejo rotacionado de alfafa e suplementação com silagem de milho (seca), e pastejo rotacionado de alfafa e de forrageira tropical (chuvas). Utilizou-se a metodologia do sistema Ambitec, composto por indicadores sociais e ambientais agrupados em planilhas eletrônicas. Na análise econômica calculou-se o custo operacional efetivo (COE), do custo operacional total (COT), do custo total de produção (CT) e do lucro operacional (LO). Utilizou-se a análise de probabilidade para avaliar o risco econômico da adoção da tecnologia, por meio de uma função de lucro operacional. Os coeficientes técnicos utilizados foram fornecidos por pesquisadores da Embrapa Pecuária Sudeste, com dados da unidade de demonstração da tecnologia, e por técnicos extensionistas e produtores rurais, com dados de propriedades dos Estados do PR e de SP. A tecnologia teve índice de 1,76 para o impacto social e índice de 0,43 para o impacto ambiental. O uso da alfafa reduziu em 40% o consumo de silagem de milho na estação seca e possibilitou a redução de 8% no teor de proteína bruta do concentrado, sem prejuízo da produção média das vacas em lactação (25 L/vaca.dia em ambos os sistemas). A introdução da alfafa na dieta (20% do consumo de matéria seca) reduziu em 9% e 7% o COE e o COT de produção de leite, respectivamente. Na análise de risco, o sistema sem alfafa teve LO de R$/L 0,26 (19,2$/L 0,26)

Photon Orbital Angular Momentum and Mass in a Plasma Vortex

We analyse the Anderson-Higgs mechanism of photon mass acquisition in a plasma and study the contribution to the mass from the orbital angular momentum acquired by a beam of photons when it crosses a spatially structured charge distribution. To this end we apply Proca-Maxwell equations in a static plasma with a particular spatial distribution of free charges, notably a plasma vortex, that is able to impose orbital angular momentum (OAM) onto light. In addition to the mass acquisition of the conventional Anderson-Higgs mechanism, we find that the photon acquires an additional mass from the OAM and that this mass reduces the Proca photon mass.Comment: Four pages, no figures. Error corrections, improved notation, refined derivation

Calibration and validation of models for short-term decomposition and N mineralization.

Insight of nutrient release patterns associated with the decomposition of plant residues is important for their effective use as a green manure in food production systems. Thus, this study aimed to evaluate the ability of the Century, APSIM and NDICEA simulation models for predicting the decomposition and N mineralization of crop residues in the tropical Atlantic forest biome, Brazil. The simulation models were calibrated based on actual decomposition and N mineralization rates of three types of crop residues with different chemical and biochemical composition. The models were also validated for different pedo-climatic conditions and crop residues conditions. In general, the accuracy of decomposition and N mineralization improved after calibration. Overall RMSE values for the decomposition and N mineralization of the crop materials varied from 7.4 to 64.6 % before models calibration compared to 3.7 to 16.3 % after calibration. Therefore, adequate calibration of the models is indispensable for use them under humid tropical conditions. The NDICEA model generally outperformed the other models. However, the decomposition and N mineralization was not very accurate during the first 30 days of incubation, especially for easily decomposable crop residues. An additional model variable may be required to capture initial microbiological growth as affected by the moisture dynamics of the residues, as is the case in surface residues decomposition model

Pressure and chemical substitution effects in the local atomic structure of BaFe2As2

The effects of K and Co substitutions and quasi-hydrostatic applied pressure (P<9 GPa) in the local atomic structure of BaFe2As2, Ba(Fe{0.937}Co{0.063})2As2 and Ba{0.85}K{0.15}Fe2As2 superconductors were investigated by extended x-ray absorption fine structure (EXAFS) measurements in the As K absorption edge. The As-Fe bond length is found to be slightly reduced (<~ 0.01 Angstroms) by both Co and K substitutions, without any observable increment in the corresponding Debye Waller factor. Also, this bond is shown to be compressible (k = 3.3(3)x10^{-3} GPa^{-1}). The observed contractions of As-Fe bond under pressure and chemical substitutions are likely related with a reduction of the local Fe magnetic moments, and should be an important tuning parameter in the phase diagrams of the Fe-based superconductors.Comment: 7 pages, 6 figure