12,143 research outputs found
The balance between sustainability dimensions: ecological base familiar smallholders' case from Coagrosol/Brazil .
This report shows some initial results about the research project entitled GlobalOrg, on a Brazilian case study, investigating the sustainability of tropical fruit organic farming in a global food chains perspective. It was performed an analysis about the production strategies of certified units of a familiar smalholders cooperative from Itápolis-SP-Brazil. In this analysis it was verified the application of sustainability principles recommended by the ecological based agriculture, focused on the agrobiodiversity, material recycling and the social-economic aspects from the agroecology conversion process. The research occurs through the complementarities provided by a combination of sociological and agronomic research methods, it means, qualitative interviews and questionnaire application with semi-structured questions. What was concluded is that the establishment of an economic relationship between the cooperative and a fair-trade international entity stimulates an interesting growing in the production diversity and also stimulates the application of different principles of ecological based agriculture. It indicates an important balance between the sustainability dimensions and demonstrates a visible attitude change in the natural resource exploration in this region
Spin-glass behaviour on random lattices
The ground-state phase diagram of an Ising spin-glass model on a random graph
with an arbitrary fraction of ferromagnetic interactions is analysed in the
presence of an external field. Using the replica method, and performing an
analysis of stability of the replica-symmetric solution, it is shown that
, correponding to an unbiased spin glass, is a singular point in the
phase diagram, separating a region with a spin-glass phase () from a
region with spin-glass, ferromagnetic, mixed, and paramagnetic phases
()
Diluted antiferromagnet in a ferromagnetic enviroment
The question of robustness of a network under random ``attacks'' is treated
in the framework of critical phenomena. The persistence of spontaneous
magnetization of a ferromagnetic system to the random inclusion of
antiferromagnetic interactions is investigated. After examing the static
properties of the quenched version (in respect to the random antiferromagnetic
interactions) of the model, the persistence of the magnetization is analysed
also in the annealed approximation, and the difference in the results are
discussed
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
Characterization of the Intra-Unit-Cell magnetic order in Bi2Sr2CaCu2O8+d
As in YBa2Cu3O6+x and HgBa2CuO8+d, the pseudo-gap state in Bi2Sr2CaCu2O8+d is
characterized by the existence of an intra-unit-cell magnetic order revealed by
polarized neutron scattering technique. We report here a supplementary set of
polarized neutron scattering measurements for which the direction of the
magnetic moment is determined and the magnetic intensity is calibrated in
absolute units. The new data allow a close comparison between bilayer systems
YBa2Cu3O6+x and Bi2Sr2CaCu2O8+d and rise important questions concerning the
range of the magnetic correlations and the role of disorder around optimal
doping.Comment: 12 pages, 8 figures, submitted to physical review
Irrigação e fertirrigação na cultura do abacaxi.
Necessidades hídricas; Salinidade e o cultivo do abacaxi; Resposta da planta à irrigação; Métodos de irrigação; Irrigação localizada; Irrigação por aspersão; Monitoramento da irrigação; Fertirrigação
MODELING AND ANALYSIS OF AN ELECTRIC VEHICLE USING PAMVEC
Electric vehicles are considered a key technology to reduce fossil fuel consumption, emissions and energy consumption. However, Electric Vehicles require larger battery packs to reach acceptable range levels. The development of new batteries with higher specific energy could reduce the mass and the cost of Electric Vehicles and increase their driving range. This work analyzes the influence of battery specific energy on battery pack mass, energy consumption and the cost per kilometer of a Tesla Model S Electric Vehicle. The energy consumption and the cost per kilometer calculated were 0.221 kWh/km (22.1 kWh/100 km) and 0.024 US$/km respectively
Proposta metodológica para avaliação da efetividade das políticas sociais para agricultores familiares do Estado de Goiás.
O objetivo principal desse artigo é realizar uma revisão bibliográfica e uma proposta metodológica para avaliar as efetividades sociais das políticas públicas para os agricultores familiares do estado de Goiás. Os programas escolhidos pelas suas representatividades sociais e econômicas para o campo e especificamente para a agricultura familiar, sujeito deste trabalho, são o Programa Nacional da Alimentação Escolar (PNAE), o Programas de Aquisição de Alimentos (PAA) da Agricultura Familiar. Também será abordado o Programa Bolsa Família, que não se trata da temática da segurança alimentar, mas que é um programa social de grande inserção no meio rural, especificamente para os agricultores familiares, e com a hipótese que tem efeitos significativos em elementos de segurança alimentar dos agricultores familiares do território em questão
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