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

Estudo sobre a mosca-dos-chifres (Haemotobia irritans) em bovinos nelorados no Pantanal.

O Pantanal representa uma das regiões mais importantes do pais em termos de Pecuária de corte, com um rebanho estimado em cerca de 3,8 milhões de cabeças (Cadavid Garcia, 1986). Desde sua chegada a região em 1991 (Barros, 1992), a mosca-dos-chifres (Haematobia irritans) tem gerado uma significativa apreensão a classe produtora. A ocorrência inicial de níveis de infestação considerados prejudiciais e a crescente demanda por um programa de controle evidenciaram a necessidade de estudos na região. Desde 1993, pesquisas vem sendo desenvolvidas visando definir as épocas, níveis e duracao das infestações nos bovinos, com o objetivo de avaliar a magnitude do problema e propor um programa de controle adequado ao Pantanal. Paralelamente, tendo em vista a dificuldade de se estimar o nível de infestação nos bovinos, esta sendo verificada a viabilidade de se utilizar o comportamento dos animais como um indicador prático do nível de infestação do rebanho, possibilitando uma melhor avaliação e decisão, por parte do produtor, quanto a necessidade de tratamento.bitstream/item/63602/1/CPAP-PESQ.-AND.-14-95.pd

Tratamento parcial do rebanho: revisão sobre sua utilização no controle da mosca-dos-chifres.

Métodos e estratégias alternativas de controle da mosca-dos-chifres são cada vez mais necessários para reduzir custos e impactos causados pelo controle químico. Entretanto, tais opções estão ainda em estudo, apresentam restrições à sua efetiva adoção ou demonstram limitada eficiência quando aplicadas isoladamente. Assim, visando reduzir o problema da resistência e da contaminação, além dos gastos com o controle, o tratamento de uma parcela do rebanho constitui uma estratégia alternativa de controle parasitário, a qual tem sido utilizada de forma empírica por alguns produtores. Este artigo apresenta uma abrangente revisão sobre esta estratégia, chamada de tratamento parcial do rebanho ou de tratamento seletivo, e sua possível utilização no controle da mosca-dos-chifres. São discutidos prós e contras, à luz do conhecimento atual, de modo a subsidiar reflexões e decisões sobre sua adoção no controle parasitário.bitstream/CPAP-2009-09/56783/1/DOC96.pdfFormato eletrônico

Aspectos do controle da mosca-dos-chifres e manejo de resistência.

A mosca-dos-chifres é uma praga relativamente recente na bovinocultura brasileira, introduzida na região Centro-Oeste há pouco mais de uma década. Desde então, seu controle tem sido dependente do uso de produtos inseticidas, o que tem sido realizado, de modo geral, de forma abusiva e indiscriminada em todo o país. Ao longo dos anos, o controle químico deste e de outros ectoparasitas tem levado à seleção de populações resistentes, reduzindo a eficácia dos produtos, mantendo perdas na produtividade e encarecendo os custos do manejo sanitário e, em última análise, da produção.bitstream/CPAP/55970/1/DOC77.pdfFormato Eletrônic

Resistência da mosca-dos-chifres a inseticidas: um problema à pecuária.

bitstream/CPAP/56440/1/ADM025.pdfFormato eletrônico

An integrated approach for analysing and assessing the performance of virtual learning groups

Collaborative distance learning involves a variety of elements and factors that have to be considered and measured in order to analyse and assess group and individual performance more effectively and objectively. This paper presents an approach that integrates qualitative, social network analysis (SNA) and quantitative techniques for evaluating online collaborative learning interactions. Integration of various different data sources, tools and techniques provides a more complete and robust framework for group modelling and guarantees a more efficient evaluation of group effectiveness and individual competence. Our research relies on the analysis of a real, long-term, complex collaborative experience, which is initially evaluated in terms of principled criteria and a basic qualitative process. At the end of the experience, the coded student interactions are further analysed through the SNA technique to assess participatory aspects, identify the most effective groups and the most prominent actors. Finally, the approach is contrasted and completed through a statistical technique which sheds more light on the results obtained that far. The proposal draws a well-founded line toward the development of a principled framework for the monitoring and analysis of group interaction and group scaffolding which can be considered a major issue towards the actual application of the CSCL proposals to real classrooms.Peer ReviewedPostprint (author's final draft

Polymer based nanocomposites: synthetic strategies for hybrid materials

Associating the well known advantages of hybrid materials to the wide potential of nanomaterials, the new and featuring class of polymer nanocomposites turned into one of the most intensively researched areas. This review highlights recent developments in the field of the synthesis of polymer based nanocomposites. Important issues related to the surface modification of fillers, in order to promote the compatibility between the inorganic/organic components, are also reported. The enhancement of the physical properties and the potential applications of polymer nanocomposites are considered in typical examples, given for each synthetic method describe

Indirect assessment of the contribution of NSM CFRP laminates for the shear strengthening of RC beams

Near Surface Mounted (NSM) strengthening technique has received increasing attention within the scientific and technical communities due to the positive indicators that this technique can provide in terms of strengthening performance. The NSM is especially effective for the shear strengthening of RC beams due to the ease of its application and the possibility of installing the Fibre Reinforced Polymer (FRP) elements in the most appropriate locations for the optimization of their contribution in terms of shear resistance. Furthermore, the FRP elements are protected against acts of vandalism and do not change the geometric configuration of the strengthened components since they are installed into thin slits opened on the concrete cover. Although either circular or rectangular FRP bars are used, recent research shows that the latter (herein designated as laminates) are more effective and easier to install. Research carried out in the area of NSM for the shear strengthening of RC beams reveals that the percentage, inclination and spacing of FRP laminates have a considerable influence on the effectiveness of this technique. The percentage of existent internal stirrups, the relative position of stirrups and FRP laminates and concrete strength class are also important aspects for the performance of the NSM technique. To estimate the influence of these parameters, a new test setup is proposed and an experimental program has been planned. The test setup is similar to the indirect tensile test (Brazilian test). The experimental program consists of 27 cylindrical concrete specimens of 180 mm thickness and 600 mm diameter, grouped in series for evaluating the influence of the aforementioned parameters. The test setup is detailed, and the results of the first series are presented and discussed.Fundação para a Ciência e a Tecnologia (FCT) - POCTI/ECM/59033/2004