2,924 research outputs found
Enhancement of the ferromagnetic order of graphite after sulphuric acid treatment
We have studied the changes in the ferromagnetic behavior of graphite powder
and graphite flakes after treatment with diluted sulphuric acid. We show that
this kind of acid treatment enhances substantially the ferromagnetic
magnetization of virgin graphite micrometer size powder as well as in graphite
flakes. The anisotropic magnetoresistance (AMR) amplitude at 300 K measured in
a micrometer size thin graphite flake after acid treatment reaches values
comparable to polycrystalline cobalt.Comment: 3.2 pages, 4 figure
The direct evaluation of attosecond chirp from a streaking measurement
We derive an analytical expression, from classical electron trajectories in a
laser field, that relates the breadth of a streaked photoelectron spectrum to
the group-delay dispersion of an isolated attosecond pulse. Based on this
analytical expression, we introduce a simple, efficient and robust procedure to
instantly extract the attosecond pulse's chirp from the streaking measurement.Comment: 4 figure
Integrating Pastures into the Traditional Slash-and-Burn Cycle in Northeastern Pará, Brazil
A project to test possibilities to integrate pastures into the traditional slash-and-burn cycle of small farmers in the Bragantina region in northeastern Pará, Brazil, is presented. Whereas in practice the traditional grass-only pasture is managed separately from the crop/fallow cycle, two options for integration are tested: a Brachiaria humidicola pasture enriched with two bushy and one herbaceous legume, Cratylia argentea, Chamaecrista rotundifolia and Arachis pintoi, and a B. humidicola pasture allowing a controlled regrowth of secondary vegetation ( Capoeira ). The regeneration performance of these pastures for a subsequent cropping period is compared with plots of undisturbed regrowth of Capoeira concerning soil chemical and physical properties, botanical composition and biomass accumulation. To evaluate comparative pasture productivity and animal performance, a traditional grass-only pasture is included in the comparisons. The results will show if these alternative pastures lead to an ecologically more appropriate management concept for grasslands in the humid tropics
Experiences with legumes as part of a ley pasture in a low input farming system of North-Eastern Pará, Brazil.
Anomalous Periodicity of the Current-Phase Relationship of Grain-Boundary Josephson Junctions in High-Tc Superconductors
The current-phase relation (CPR) for asymmetric 45 degree Josephson junctions
between two d-wave superconductors has been predicted to exhibit an anomalous
periodicity. We have used the single-junction interferometer to investigate the
CPR for this kind of junctions in YBCO thin films. Half-fluxon periodicity has
been experimentally found, providing a novel source of evidence for the d-wave
symmetry of the pairing state of the cuprates.Comment: 4 pages, 5 figure
Caracterização e avaliação da pastagem do rebanho de agricultores familiares do nordeste paraense.
No Nordeste Paraense alguns agricultores familiares têm implantado pequenas áreas de pastagens e manejado pequenos rebanhos com o objetivo de aplicar eventuais ganhos obtidos com os cultivos, criando uma poupança a ser utilizada nas necessidades futuras da famÃlia ou da propriedade. Há indÃcios de problemas nas pastagens e no rebanho que limitam tanto a produção e a sustentabilidade da pecuária, como comprometem os cultivos agrÃcolas que realmente sustentam a propriedade. Este estudo tratou de identificar as principais limitações e propor alternativas de manejo que sejam econômica e ecologicamente mais sustentáveis. Na primeira fase do estudo, numa amostra ao acaso de 38 propriedades, descreveu-se o manejo da pastagem e do rebanho, e na segunda, numa amostra menor, de doze propriedades e por um perÃodo de 29 meses, avaliou-se o potencial desses dois componentes. As propriedades estudadas desenvolvem uma pecuária de baixa produtividade. Devido à baixa fertilidade do solo e o deficiente manejo, as pastagens não suprem os alimentos necessários ao rebanho, tanto em quantidade como em qualidade. Também foram identificadas deficiências no manejo do rebanho, próprias de sistemas extensivos. Contudo, as limitações podem ser solucionadas com práticas amplamente conhecidas de manejo da pastagem (como formação, manutenção e manejo) e do rebanho (reprodução, manejo de bezerros e sanidade em geral). Novos modelos de exploração também foram sugeridos
Cattle impact on secondary vegetation proposed as component for smallholder pastures in the Eastern Amazon, Brazil - vegetation development and composition after 42 months of grazing.
Experiences with Establishing Legumes as Part of a Ley Pasture in a Low-Input Farming System of the Eastern Amazon, Brazil
In the Eastern Amazon extensive pasture management by smallholders can result in degradation of grassland, leading to unproductive and abandoned agricultural areas (Dias-Filho, 2003). To avoid long and costly restoration of those areas, ley-systems with alternating cropping and pasture phases might offer a promising solution. The inclusion of N-fixing legumes is seen as a suitable method to improve soil fertility during the pasture phase. As mono-cultures seem not to be appropriate, given the phytodiverse climax vegetation in the humid tropics, a combination of various shrub and herbaceous legume species is proposed. Thus, this paper tests a grass-legume mixture to replace the fallow phase in the slash-and-burn agriculture practised by smallholders
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