Double-core evolution and the formation of neutron-star binaries with compact companions

We present the results of a systematic exploration of an alternative evolutionary scenario to form double neutron-star binaries, first proposed by Brown (1995), which does not involve a neutron star passing through a common envelope. In this scenario, the initial binary components have very similar masses, and both components have left the main sequence before they evolve into contact; preferably the primary has already developed a CO core. We have performed population synthesis simulations to study the formation of double neutron star binaries via this channel and to predict the orbital properties and system velocities of such systems. We obtain a merger rate for DNSs in this channel in the range of 0.1 - 12/Myr. These rates are still subject to substantial uncertainties such as the modelling of the contact phase.Comment: MNRAS, accepte

Influência da percentagem de armadura convencional no comportamento à flexão de vigas reforçadas com sistemas de CFRP

Com o objectivo de avaliar a contribuição dos laminados de fibras de carbono (CFRP) no comportamento do betão armado fendilhado foi efectuada uma campanha de ensaios experimentais em vigas. A influência da relação entre a percentagem de laminados e de armadura convencional no comportamento das vigas foi investigada. Neste trabalho os ensaios efectuados são descritos e os resultados obtidos são analisados

Metodologia com base em imagens binárias obtidas com limiar fixo para classificação de plantas de milho atacadas por Spodoptera frugiperda.

Na agricultura os diagnósticos visuais são muito utilizados para tomada de decisão por parte do produtor. Acredita-se que os sistemas de visão artificial apresentam um grande potencial de utilização, especialmente na área de agricultura de precisão. Um passo muito importante no processamento de imagens é a segmentação dos objetivos de interesse e uma das técnicas mais empregadas para geração de imagens binárias é a limiarização. O objetivo deste trabalho foi propor e avaliar uma metodologia para criação de imagens binárias utilizando um limiar fixo a partir de imagens processadas pelo indice do excesso de verde normalizado. Foram utilizados imagens de plantas atacadas e não atacadas pela lagarta do cartucho obtidas em três intensidades de iluminação. As imagens criadas com o limiar fixo foram comparadas com as imagens criadas pelo metodo interativo de limiarização e apresentaram exatidão global superior a 99% em 720 imagens. As imagens binárias do limiar fixo permitiram a classificação das plantas como atacadas e não atacadas com exatidão acima de 95%

Avaliação de parâmetros de textura para classificação de plantas daninhas em imagens digitais.

As plantas daninhas podem causar danos, qualitativos e quantitativos, às culturas de valor agronômico. A agricultura de precisão, utilizando-se de técnicas de visão artificial, possibilita a análise do local de produção através de imagens digitais que, processadas fornecerão informações para tomada de decisão, possibilitando a otimização de recursos, garantindo maiores lucros e menos impactos ambienttais. Neste trabalho foram selecionados e avaliados 9 parâmetros da matriz de co-ocorrência de imagens digitais monocromáticas de plantas daninhas de folha larga e estreita, coletadas 25 dias após a emergência. Dos nove parâmetros testados, cinco apresentaram resultados satisfatórios individualmente para separação das plantas: Momento angular (f1), valor medio (f2). momento da diferença inversa (f6), entropia (f7) e medida de correlação A (f10). A combinação dos parâmetros f2, f6, f7 e f10 apresentaram o melhor resultado dois a dois

Steel fibre reinforced self-compacting concrete for lightweight and durable pedestrian bridges : creep behaviour

In recent years, pedestrian bridges built from composites materials have notably increased. This growth is related to the durability problems of traditional materials, as well as the need for fastest construction times. In this context, fiber reinforced concrete (FRC) becomes an important material in this type of structures, since the ductility, high post-cracking tensile strength, high compressive stiffness and strength of FRC can be combined with the benefits derived from the use of FRP profiles to obtain high performance structural systems. In addition, FRC exhibits a durable behaviour since, in general, does not have corrosion problems. In this paper a 12 m length single span pedestrian bridge composed by a Steel Fiber Reinforced Self-Compacting Concrete (SFRSCC) deck and two Glass Fiber Reinforced Polymer (GFRP) pultruded I shape profiles was designed. The SFRSCC deck has a constant thickness of 40 mm and 2000 mm wide and a content of hooked ends steel fibers in its mixture, which ensures the necessary strength and ductility for the acting loads. The high post-cracking tensile strength of the SFRSCC allowed the use of pre-stressed solutions in the bridge structural system, which caused an upward deflection and, consequently, tensile stresses in the SFRSCC deck. Two prototypes of this structural system were built and monitored in order to assess their long-term deformational behavior when subjected to a loading configuration correspondent to the load combination for the deflection serviceability limit states. The main results are presented and discussed

Influence of fatigue and aggressive exposure on GFRP girder to SFRSCC deck all-adhesive connection

To assess the influence of fatigue loading and environmental conditions on the bond behavior between glass fiber reinforced polymer (GFRP) systems and steel fiber reinforced self-compacting concrete (SFRSCC) that are adhesively bonded, an experimental program composed of push-out tests was carried out. The following three scenarios were selected for the environmental conditions: natural conditions; wet-dry cycles; and temperature cycles. Half of the specimens were submitted to monotonic loading up to failure, and the other half were submitted to a fatigue load configuration of 1-million cycles and then subjected to a monotonic loading up to failure. The results have shown that for the investigated environmental conditions the GFRP-SFRSCC push-out specimens never failed up to 1 million cycles. However, temperature cycles caused a considerable reduction on the stiffness and load carrying capacity in the specimens submitted to fatigue loading, while wet-dry cycles did not modify significantly the maximum shear stress transfer in the investigated connection. This paper describes in detail the experimental program, presenting and discussing the relevant results.AD

Development of a pedestrian bridge with GFRP profiles and fibre reinforced self-compacting concrete deck

In recent years, the number of pedestrian bridges built from composites materials has notably increased. The combination of fiber reinforced polymers (FRP) profiles with fiber reinforced concrete (FRC) elements is being adopted in this type of structures, since the ductility, high post-cracking tensile strength, compressive stiffness and strength of FRC can be combined with the benefits derived from the use of FRP’s profiles to obtain high performance structural systems. In the context of the present work a 12 m long single span pedestrian bridge with two composite Iprofiles was designed. In terms of deflection requirements imposed by serviceability limit states, the influence of the height and thickness of GFRP (Glass Fiber Reinforced Polymer) profiles, as well as the addition of a thin layer of prestressed carbon fiber sheet in the bottom flange of the GFRP profile was evaluated. Using software based on the finite element method, the structural behavior of the developed structural systems was analyzed. Furthermore, two prototypes of this structural system were built and monitored in order to assess their long-term deformational behavior when subjected to a loading configuration correspondent to the load combination for the deflection serviceability limit states. The main results obtained are presented and discussed.This work is part of the research project QREN number 3456, PONTALUMIS- Development of a prototype of a pedestrian bridge in GFRP-ECC concept, involving the Company ALTO - Perfis Pultrudidos, Lda., the ISISE/University of Minho and the ICIST/Technical University of Lisbon. The first and fourth authors wish to acknowledge the research grants under this project. The authors also wish to acknowledge the Civitest Company for the conception and development of the steel fiber reinforced self-compacting concrete used in this work, and to Secil, S&P Clever Reinforcement Iberica Lda. and Hilti Portugal - Productos e Servicos Lda. for the supplied materials and technical support

Influence of fatigue loading and environmental conditions on the bond behavior between GFRP systems and SFRSCC substrate

To assess the influence of fatigue loading and environmental conditions on the bond behavior between glass fiber reinforced polymer (GFRP) systems and steel fiber reinforced self-compacting concrete (SFRSCC) that are adhesively bonded, an experimental program composed of push-out tests was carried out. The following three scenarios were selected for the environmental conditions: natural conditions; wet-dry cycles; and temperature cycles. Half of the specimens were submitted to monotonic loading up to failure, and the other half were submitted to a fatigue load configuration of 1 -million cycles and then subjected to a monotonic loading up to failure. The results have shown that for the investigated environmental conditions the GFRP-SFRSCC push-out specimens never failed up to 1 million cycles. However, temperature cycles caused a considerable reduction on the stiffness and load carrying capacity in the specimens submitted to fatigue loading, while wet-dry cycles did not modify significantly the maximum shear stress transfer in the investigated connection. This paper describes in detail the experimental program, presenting and discussing the relevant results

Identificação de plantas atacadas pela lagarta Elasmo (Elasmopalpus lignosellus) em imagens digitais de plantas de milho.

A crescente demanda por técnica para minimização de custos, otimização de mão de obra e redução da contaminação do meio ambiente em sistemas de produção agrícola, vem abrindo portas para a implantação da tecnologia de Agricultura de Precisão. A lagarta (Elasmopalpus lignosellus) é uma praga que ataca a planta de milho no início de seu desenvolvimento ocasionando redução na população, com reflexos na produtividade da cultura. O desenvolvimento de um sistema de visão artificial pode ser uma boa alternativa para manejo e controle da praga de maneira localizada. O objetivo deste trabalho foi elaborar um algoritmo de processamento de imagens para identificação de plantas de milho atacadas pela lagarta elasmo utilizando redes neurais artificiais, associado à limiarização interativa e índices espectrais. Os resultados preliminares da avaliação do algoritmo proposto, com 100% de acerto utilizando 5 imagens de plantas atacadas e 5 de plantas não atacadas, mostram-se promissores

Homeostasis of common bean populations with different genetic structures.

Eight lines of common bean, a mixture in equal proportions (MP) and the F2 generation of the multiple hybrids (MH) between them were analyzed to verify whether they differ in homeostasis and phenotypic plasticity. The experiments were conducted in 20 environments (seasons and locations) from November 2004 to December 2005, in Alto Paranaíba and the south of Minas Gerais state. Based on the mean yield of the environments the stability was evaluated by the ecovalence values (Wi 2). To estimate the repeatability of the stability parameters the 20 environments were separated in two groups of 10, simulating 1000 possibilities. The MH and MP were the most stable. Nevertheless, high stability was also identified in some pure lines. The repeatability of mean grain yield (rk 2=0.73) was higher than Wi 2 (rk 2=0.18). The chances of success of selection for the smallest contribution to the G x E interaction are small