584 research outputs found

    Viscoelastic properties of green wood across the grain measured by harmonic tests in the range of 0\degree C to 95\degree C. Hardwood vs. softwood and normal wood vs. reaction wood

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    The viscoelastic properties of wood have been investigated with a dynamic mechanical analyser (DMA) specifically conceived for wooden materials, the WAVET device (environmental vibration analyser for wood). Measurements were carried out on four wood species in the temperature range of 0\degree C to 100\degree C at frequencies varying between 5 mHz and 10 Hz. Wood samples were tested in water-saturated conditions, in radial and tangential directions. As expected, the radial direction always revealed a higher storage modulus than the tangential direction. Great differences were also observed in the loss factor. The tan\delta peak and the internal friction are higher in tangential direction than in radial direction. This behaviour is attributed to the fact that anatomical elements act depending on the direction. Viscoelastic behaviour of reaction wood differs from that of normal or opposite wood. Compression wood of spruce, which has higher lignin content, is denser and stiffer in transverse directions than normal wood, and has lower softening temperature (Tg). In tension wood, the G-layer is weakly attached to the rest of the wall layers. This may explain why the storage modulus and the softening temperature of tension wood are lower than those for the opposite wood. In this work, we also point out that the time-temperature equivalence fits only around the transition region, i.e. between Tg and Tg + 30\degree C. Apart from these regions, the wood response combines the effect of all constitutive polymers, so that the equivalence is not valid anymore

    A step towards standardising accelerated corrosion tests on laboratory reinforced concrete specimens

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    Natural steel corrosion of reinforced concrete (RC) structures is a slow process which researchers find necessary to accelerate in laboratory tests to obtain needed damage in a short time. Regrettably, there is no standard procedure for accelerating steel corrosion in RC specimens. Researchers therefore continue to use various techniques to accelerate it. Unfortunately, structural damage and rate of steel corrosion are dependent on the accelerated corrosion technique used. Despite that, results obtained by researchers are applied by structural engineers and asset managers to in-service structures. This paper reviews previous techniques used to accelerate steel corrosion. Where possible it proposes standard procedures to accelerate steel corrosion. In other instances it points out needed further research. One of the procedures recommended in the paper is to contaminate selected faces of RC specimens with chlorides, as opposed to immersing samples in NaCl solution or adding chlorides to concrete mixes. It is also recommended to allow specimens to sufficiently dry during steel corrosion so as to promote steel corrosion

    Chondroblastoma of the proximal tibia

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    O ensino de lógica na sala de aula de matemática: uma proposta

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    This research is part of the Mathematics Education area and proposes the inclusion of the study of Logic in mathematics classes. It aimed to investigate the production of a set of tasks on concepts of Logic, formulated for the insertion and study of this content in the mathematics classroom of the ninth grade of elementary school. This work is characterized as a qualitative research approach, developed with field research, with two participating students from a class of ninth grade of elementary school in the public school system in the city of Juiz de Fora, Minas Gerais. The theoretical framework adopted in this research was the Model of the Semantic Fields, proposed by Romulo Campos Lins (1999, 2012), from which it was possible to analyze the speeches of students through their production of meanings on the proposed tasks. The analysis of the speeches and records of the students is evidence of the potential of introducing Logic in the mathematics classroom, through tasks that stimulate logical thinking. The educational product resulting from this research consists of a teaching proposal for mathematics teachers in the ninth grade of elementary school and / or high school consisting of a set of tasks addressing concepts of logic and themes related to it.Esta pesquisa faz parte da área de Educação Matemática e tem como proposta a inserção do estudo da Lógica nas aulas de matemática. Ela teve como objetivo investigar a produção de um conjunto de tarefas sobreconceitos deLógica,formuladopara a inserção e o estudo deste conteúdona sala de aula de matemática donono ano do Ensino Fundamental. Este trabalho caracteriza-se como uma abordagem qualitativa de investigação, desenvolvida com uma pesquisa de campo, com dois participantes estudantes de uma turma de nono ano do Ensino Fundamental da rede públicade ensinoda cidade de Juiz de Fora,Minas Gerais. O referencial teórico adotado nessa pesquisa foi o Modelo dos Campos Semânticos,proposto por Romulo Campos Lins (1999, 2012), a partir do qual foi possível analisar as falas de estudantes através de suas produções de significados sobre as tarefas propostas. A análise das falas e registros dos discentes são evidências da potencialidade da introdução da Lógica na sala de aula de matemáticaatravés de tarefas que estimulem o pensamento lógico. O produto educacional resultante desta pesquisa é composto por uma proposta de ensino para professores de matemática donono ano doEnsino Fundamental e/ou Ensino Médio constituído por um conjunto de tarefas abordando conceitos de Lógica etemas ligados a ela

    Inflammatory myofibroblastic tumor

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