16,437 research outputs found
Magnetic phases evolution in the LaMn1-xFexO3+y system
We have investigated the crystal structure and magnetic properties for
polycrystalline samples of LaMn1-xFexO3+y, in the whole range x=0.0 to x=1.0,
prepared by solid state reaction in air. All samples show the ORT-2
orthorhombic structure that suppresses the Jahn-Teller distortion, thus
favoring a ferromagnetic (FM) superexchange (SE) interaction between
Mn^{3+}-O-Mn^{3+}. For x=0.0 the oxygen excess (y ~ 0.09) produces vacancies in
the La and Mn sites and generates a fraction around 18% of Mn^{4+} ions and 82%
of the usual Mn^{3+} ions, with possible double exchange interaction between
them. The Fe doping in this system is known to produce only stable Fe^{3+}
ions. We find an evolution from a fairly strong FM phase with a Curie
temperature T_{C} ~ 160 K, for x=0.0, to an antiferromagnetic (AFM) phase with
T_{N} = 790 K, for x=1.0, accompanied by clear signatures of a cluster-glass
behavior. For intermediate Fe contents a mixed-phase state occurs, with a
gradual decrease (increase) of the FM (AFM) phase, accompanied by a systematic
transition broadening for 0.2 < x < 0.7. A model based on the expected exchange
interaction among the various magnetic-ion types, accounts very well for the
saturation-magnetization dependence on Fe doping.Comment: 27 pages, 9 figure
On Matrix Superpotential and Three-Component Normal Modes
We consider the supersymmetric quantum mechanics (SUSY QM) with three-
component normal modes for the Bogomol'nyi-Prasad-Sommerfield (BPS) states. An
explicit form of the SUSY QM matrix superpotential is presented and the
corresponding three-component bosonic zero-mode eigenfunction is investigated.Comment: 17 pages, no figure. Paper accepted for publication in Journal of
Physics A: Mathematical and Theoretica
On Useful Conformal Tranformations In General Relativity
Local conformal transformations are known as a useful tool in various
applications of the gravitational theory, especially in cosmology. We describe
some new aspects of these transformations, in particular using them for
derivation of Einstein equations for the cosmological and Schwarzschild
metrics. Furthermore, the conformal transformation is applied for the
dimensional reduction of the Gauss-Bonnet topological invariant in to the
spaces of lower dimensions.Comment: 17 pages, LaTeX. The paper is intended mainly for pedagogical
purposes and represents a collection of exercises concerning local conformal
transformations and dimensional reduction. To be published in "Gravitation
and Cosmology
Métodos para produção de mudas de jatobá (Hymenaea courbaril Linnaues) e colubrina (Colubrina glandulosa Perk) em condições de viveiro na Amazônia.
O objetivo deste trabalho é produzir mudas de Hymenaea courbaril e Colubrina glandulosa em diferentes recipientes além de avaliar os parâmetros de crescimento, para poder se estabelecer um protocolo de produção para mudas de boa qualidade com baixo custo e em menor tempo no viveiro
Phenolic compounds and organic acids evaluation on red grapes used for winemaking in the Northeast of Brazil.
Monitoring maturation to determine harvest time is very important to determine the enological potential and the quality characteristics and typicality of the wines (Borghezan et al., 2011). Considering that there is no cold weather in the São Francisco Valley, it is possible to scale and production of two harvests per year. This study aimed to determine the chemical composition of the ?Syrah? and ?Tempranillo? grapes, during maturation. Sixty plants were used for each cultivar, divided into three blocks
Quantum state tomography of photons polarization and path degrees of freedom
Quantum state tomography (QST), the process through which the density matrix
of a quantum system is characterized from measurements of specific observables,
is a fundamental pillar in the fields of quantum information and computation.
We propose a simple QST method to reconstruct the density matrix of two qubits
encoded in the polarization and path degrees of freedom of a single photon,
which can be realized with a single linear-optical setup. We demonstrate that
the density matrix can be fully described in terms of the one-point Stokes
parameters related to the two possibles paths of the photon, together with a
quantum version of the two-point Stokes parameters introduced here.Comment: 5 pages, 2 figure
Otimização e validação de método para determinação de ácidos orgânicos em vinhos por cromatografia líquida de alta eficiência.
Reagentes e soluções analíticas; Instrumentação e condição cromatográfica; Estabilidade dos padrões analíticos e da fase móvel; Validação do método; Preparação das amostras de vinho
Crescimento da Bertholletia excelsa, Humb. et Bompl. em Manaus, AM.
Este trabalho teve como objetivo estudar o crescimento e o comportamento silvicultural da castanheira-do-Brasil na região de Manaus, AM
Caracterização de substâncias húmicas extraídas de solo tratado com carvão vegetal (biochar).
As Terras Pretas de Índio (TPI) são solos antropogênicos encontrados na Amazônia, que têm alto teor de carbono (C) orgânico, alta fertilidade e alta capacidade de recuperação. Os TPI possuem estas características devido ao caráter pirogênico do C que neles se encontra, e que se manifestam na alta proporção de estruturas aromáticas policondensadas com grupos funcionais carboxílicos originadas das alterações naturais de biomassa carbonizada adicionada ao solo pelas populações indígenas pré-colombianas
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