327 research outputs found
Impactos do sistema de plantio direto com cobertura vegetal (SPDCV) sobre a dinamica da agua, do nitrogenio mineral e do carbono do solo do cerrado brasileiro
Impacts des systèmes de culture en semis direct avec couverture végétale (SCV) sur la dynamique de l'eau, de l'azote minéral et du carbone du sol dans les cerrados brésiliens
Dans les conditions tropicales humides des cerrados brésiliens, de nouveaux systèmes de culture étaient nécessaires pour assurer une production agricole durable. Des systèmes en semis direct avec couverture végétale (SCV) ont été mis au point en incorporant des plantes de couverture avant ou après la culture commerciale. Depuis 1999, différentes études ont été réalisées dans le cadre d'un projet de recherche franco-brésilien. Elles ont permis de quantifier les effets de ces SCV sur les dynamiques de l'eau, de l'azote et du carbone en particulier. Il a été ainsi confirmé que les SCV permettent de diminuer le ruissellement et donc l'érosion qui lui est liée. De même, les SCV permettent une fourniture en azote supérieure pour la plante commerciale. L'eau et l'azote non valorisées par cette culture peuvent l'être par la plante de couverture additionnelle, de même que l'eau et l'azote mis à disposition en dehors de ce cycle commercial. Les importantes restitutions de phytomasse de ces nouveaux systèmes à plusieurs plantes dans l'année aboutissent à un bilan de carbone positif et une augmentation des taux de matière organique des sols. (Résumé d'auteur
A p-Spin Interaction Ashkin-Teller Spin-Glass Model
A p-spin interaction Ashkin-Teller spin glass, with three independent
Gaussian probability distributions for the exchange interactions, is studied by
means of the replica method. A simple phase diagram is obtained within the
replica-symmetric approximation, presenting an instability of the paramagnetic
solution at low temperatures. The replica-symmetry-breaking procedure is
implemented and a rich phase diagram is obtained; besides the paramagnetic
phase, three distinct spin-glass phases appear. Three first-order critical
frontiers are found and they all meet at a triple point; among such lines, two
of them present discontinuities in the order parameters, but no latent heat,
whereas the other one exhibits both discontinuities in the order parameters and
a finite latent heat.Comment: 17 pages, 2 figures, submitted to Physica
Fine-tuning of defensive behaviors in the dorsal periaqueductal gray by atypical neurotransmitters
This paper presents an up-to-date review of the evidence indicating that atypical neurotransmitters such as nitric oxide (NO) and endocannabinoids (eCBs) play an important role in the regulation of aversive responses in the periaqueductal gray (PAG). Among the results supporting this role, several studies have shown that inhibitors of neuronal NO synthase or cannabinoid receptor type 1 (CB1) receptor agonists cause clear anxiolytic responses when injected into this region. The nitrergic and eCB systems can regulate the activity of classical neurotransmitters such as glutamate and γ-aminobutyric acid (GABA) that control PAG activity. We propose that they exert a ‘fine-tuning’ regulatory control of defensive responses in this area. This control, however, is probably complex, which may explain the usually bell-shaped dose-response curves observed with drugs that act on NO- or CB1-mediated neurotransmission. Even if the mechanisms responsible for this complex interaction are still poorly understood, they are beginning to be recognized. For example, activation of transient receptor potential vanilloid type-1 channel (TRPV1) receptors by anandamide seems to counteract the anxiolytic effects induced by CB1 receptor activation caused by this compound. Further studies, however, are needed to identify other mechanisms responsible for this fine-tuning effect
Desempenho produtivo e econômico de três grupos genéticos de bovinos recriados a pasto com suplementação e terminados em confinamento
Radioisótopo e modelagem matemática na avaliação da suplementação de fitase em dietas para suínos em crescimento
Preliminary results on organization on the court, physical and technical performance of Brazilian professional futsal players: comparison between friendly pre-season and official match
Response of Epidendrum Ibaguense (orchidaceae) to the application of lime rates to the pot
Influência da estratificação térmica no volume útil e no comportamento hidrodinâmico de lagoa de estabilização: determinação experimental e teórica
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