192 research outputs found
A new model for gravitational potential perturbations in disks of spiral galaxies. An application to our Galaxy
We propose a new, more realistic, description of the perturbed gravitational
potential of spiral galaxies, with spiral arms having Gaussian-shaped groove
profiles. We investigate the stable stellar orbits in galactic disks, using the
new perturbed potential. The influence of the bulge mass on the stellar orbits
in the inner regions of a disk is also investigated. The new description offers
the advantage of easy control of the parameters of the Gaussian profile of its
potential. We find a range of values for the perturbation amplitude from 400 to
800 km^2 s^{-2} kpc^{-1} which implies a maximum ratio of the tangential force
to the axisymmetric force between 3% and 6%, approximately. Good
self-consistency of arm shapes is obtained between the Inner Lindblad resonance
(ILR) and the 4:1 resonance. Near the 4:1 resonance the response density starts
to deviate from the imposed logarithmic spiral form. This creates bifurcations
that appear as short arms. Therefore the deviation from a perfect logarithmic
spiral in galaxies can be understood as a natural effect of the 4:1 resonance.
Beyond the 4:1 resonance we find closed orbits which have similarities with the
arms observed in our Galaxy. In regions near the center, in the presence of a
massive bulge, elongated stellar orbits appear naturally, without imposing any
bar-shaped potential, but only extending the spiral perturbation a little
inward of the ILR. This suggests that a bar is formed with a half-size around 3
kpc by a mechanism similar to that of the spiral arms. The potential energy
perturbation that we adopted represents an important step in the direction of
self-consistency, compared to previous sine function descriptions of the
potential. Our model produces a realistic description of the spiral structure,
able to explain several details that were not yet understood.Comment: 12 pag., 11 fig. Accepted for publication in A&A, 2012 December 1
Convergent adaptations: bitter manioc cultivation systems in fertile anthropogenic dark earths and floodplain soils in central Amazonia
Shifting cultivation in the humid tropics is incredibly diverse, yet research tends to focus on one type: long-fallow shifting cultivation. While it is a typical adaptation to the highly-weathered nutrient-poor soils of the Amazonian terra firme, fertile environments in the region offer opportunities for agricultural intensification. We hypothesized that Amazonian people have developed divergent bitter manioc cultivation systems as adaptations to the properties of different soils. We compared bitter manioc cultivation in two nutrient-rich and two nutrient-poor soils, along the middle Madeira River in Central Amazonia. We interviewed 249 farmers in 6 localities, sampled their manioc fields, and carried out genetic analysis of bitter manioc landraces. While cultivation in the two richer soils at different localities was characterized by fast-maturing, low-starch manioc landraces, with shorter cropping periods and shorter fallows, the predominant manioc landraces in these soils were generally not genetically similar. Rather, predominant landraces in each of these two fertile soils have emerged from separate selective trajectories which produced landraces that converged for fast-maturing low-starch traits adapted to intensified swidden systems in fertile soils. This contrasts with the more extensive cultivation systems found in the two poorer soils at different localities, characterized by the prevalence of slow-maturing high-starch landraces, longer cropping periods and longer fallows, typical of previous studies. Farmers plant different assemblages of bitter manioc landraces in different soils and the most popular landraces were shown to exhibit significantly different yields when planted in different soils. Farmers have selected different sets of landraces with different perceived agronomic characteristics, along with different fallow lengths, as adaptations to the specific properties of each agroecological micro-environment. These findings open up new avenues for research and debate concerning the origins, evolution, history and contemporary cultivation of bitter manioc in Amazonia and beyond
Doenças do pequizeiro.
O pequizeiro (Caryocar spp.) é uma árvore frutífera nativa dos biomas Cerrado, Caatinga, Mata Atlântica, Amazônia e Pantanal. Seus frutos são muito apreciados como alimento, mas eles também produzem ácidos graxos, que podem ser utilizados na fabricação de biocombustíveis, temperos e cos- méticos. A maior parte dos frutos comercializados ainda vem de atividades extrativistas. Quando cresce em seu ambiente natural não modificado, o pequizeiro con- vive em equilíbrio com patógenos e pragas coevoluídas. No entanto, esse equilíbrio pode estar em processo de rompimento devido aos desmatamen- tos, às queimadas frequentes, à introdução de organismos e plantas exóti- cas e atividades extrativistas predatórias, que provocam danos físicos e defi- ciências nutricionais nos pequizeiros nativos. Acredita-se que o rompimento desse equilíbrio natural vem aumentando a predisposição dos pequizeiros nativos ao ataque de várias doenças e pragas. A alta incidência de doenças em pequizeiros nativos vem preocupando agricultores, ambientalistas, extra- tivistas e outros povos que têm o pequi como fonte de renda. Essas doenças são ameaças futuras à implantação de cultivos comerciais em larga escala. Em geral, as doenças que causam a morte ou seca das árvores ou de seus galhos são as mais importantes em termos de expressão econômica. Há, também, as doenças que atacam folhas, ramos novos e frutos, que provocam queda e depreciações na qualidade dos frutos e desfolhamentos. Nesta pu- blicação, são listadas as principais doenças do pequizeiro e seus possíveis agentes etiológicos, além de medidas de controle disponíveis até o momento. Ressaltamos que inspeções sanitárias realizadas pela Embrapa, que gera- ram parte das informações relatadas neste trabalho, foram realizadas antes de 2000. Sebastiã
Mapeamento de QTL (quantitative trait loci) associados à resistência do maracujá-doce à bacteriose.
Epidural administration of ropivacaine and its effects on the pharmacodynamics of rocuronium: Randomized controlled trial. Interaction between ropivacaine and rocuronium
Potentiation of neuromuscular blocking agents by local anesthetics has been described in various clinical and experimental studies. This study assessed the influence of epidural ropivacaine on pharmacodynamic characteristics of rocuronium.Design: This was a prospective randomized clinical trial at the women's hospital, an university tertiary hospital in Brazil. Sixty-two patients underwent elective abdominal surgeries requiring general anesthesia.Intervention: Patients were distributed into two groups: Group 1 (general anesthesia and epidural anesthesia) and Group 2 (general anesthesia). In Group 1, 0.2% ropivacaine at a dose of 40 mg (20 ml) was associated with 2 mg (2 ml) of morphine in a single epidural injection. The following parameters were assessed: clinical duration (DC25) and time for recovery of the train-of-four (TOF) 0.9 ratio (T4/T1 = 90%) after an initial 0.6 mg/kg dose of rocuronium. The primary outcomes were DC25and TOF 0.9 ratio (T4/T1 = 90%). Secondary outcomes were total propofol and remifentanil consumption.Results: Values were presented as median and interquartile range. The results for DC25and TOF 0.9 of rocuronium were, respectively, 41.5 35.0-55.0 (25.0-63.0) in Group 1 and 44.0 37.0-51.0 (20.0-67.0) in Group 2 (P = 0.88); 88.0 67.0-99.0 (43.0-137.0) in Group 1; and 80.0 71.0-86.0 (38.0-155.0) in Group 2 (P = 0.83). There was no significant difference between the groups, in terms of pharmacodynamic characteristics of rocuronium. Propofol consumption did not show any difference between the groups. However, remifentanil consumption was significantly lower in Group 1 (P < 0.01).Conclusion: Epidural ropivacaine, in the dose studied, did not prolong the duration of rocuronium-induced neuromuscular blockade.Trial Registry Number: ReBEC (ref: RBR-7cyp6t)141636
Características físicas e químicas de oito genótipos de Passiflora maliformis Linn. cultivados no Distrito Federal.
Parâmetros de irrigação durante o período seco em plantas jovens de dendê cultivadas no Cerrado.
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