165 resultados para Rigidez


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Objectives: Epidemiological studies have shown a relationship between long-term use of proton pump inhibitors and bone metabolism. However, this relationship has not yet become established. The aim of the present study was to analyze the mechanical properties and bone mineral density (BMD) of rats that were subjected to long-term omeprazole use. Methods: Fifty wistar rats weighing between 200 and 240 g were divided equally into five groups: OMP300 (omeprazole intake at a dose of 300 moL/kg/day); OMP200 (200 moL/ kg/day); OMP40 (40 moL/kg/day); OMP10 (10 moL/kg/day); and Cont (control group; intake of dilution vehicle). The solutions were administered for 90 consecutive days. After the rats had been sacrificed, their BMD, the mechanical properties of the dissected femurs and their serum Ca++ levels were analyzed. Results: The BMD of the OMP300 group was lower than that of the controls (p = 0.006). There was no difference in comparing the OMP200, OMP40 and OMP10 groups with the controls. The maximum strength and rigidity of the femur did not differ in the experimental groups in comparison with the controls. The OMP300 group had a statistically lower serum Ca++ concentration than that of the controls (p = 0.049), but the other groups did not show any difference in relation to the controls. Conclusion: Daily intake of 300moL/kg/day of omeprazole decreased the BMD of the femur, but without changes to the rigidity and strength of the femur in adult rats. © 2

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During clinical routine, the orthodontist uses several materials, which include metallic alloys in the form of metallic wires. However, it is necessary that the professional has some knowledge of the properties of those wires. Different types of wires are commercially available: stainless steel wires, chrome-cobalt wires, nickel-titanium wires and beta-titanium wires. Among the nickel-titanium wires, there are three subdivisions: a conventional alloy and two superelastic alloys. The superelasticity, associated to the effect of form memory, is a property used in orthodontics to initiate the dental movement in the first phase of the orthodontic treatment. This property is considered to be biologically compatible with the effective dental movement. These wires are available at the market in different transformation temperatures, and they offer the best adaptation in the groove of the bracket, simplicity and a faster treatment. However, they present little formability, and they don’t accept solder. They are also more onerous than other wires. Moreover, the low rigidity of these wires doesn’t allow them to be used for the retraction of the anterior teeth or closing of spaces. Therefore, the coherent use of superelastic orthodontic wires is recommended, accompanied by a detailed diagnosis and planning, so the result will be an efficient orthodontic correction, accomplished in a shorter period of time.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Modelos escritos através dos conceitos da Mecânica do Dano no Contínuo representam atualmente uma alternativa consistente para a simulação numérica do comportamento de estruturas constituídas por materiais quase frágeis, onde a perda de rigidez em função da fissuração crescente é o fator preponderante da resposta não-linear de seus elementos estruturais. No entanto, modelos de dano apresentam forte dependência de parâmetros internos usados para descrever os critérios e evolução das variáveis de dano, que devem ser calibrados adequadamente para uma resposta mecânica coerente da estrutura. Neste contexto, o artigo mostra um estudo sobre a calibração de parâmetros do modelo de dano de Mazars e sua aplicação na análise numérica de vigas e pórticos planos em concreto armado. O Método dos Mínimos Quadrados é adotado para resolver o problema, em conjunto com a técnica de Gauss-Newton. Em virtude da ausência de resultados experimentais para diversas classes de resistência do concreto, como referência para o processo de calibração, são adotados alguns modelos constitutivos teóricos tanto à tração quanto à compressão. Esse processo de calibração de parâmetros é incorporado a um modelo mecânico em elementos finitos para análise de barras em concreto armado, com a consideração conjunta dos mecanismos complementares de resistência ao cisalhamento, como efeito de pino, armadura transversal e engrenamento de agregados. Uma lei constitutiva exponencial para o decaimento da resistência à tração do concreto é proposta com o objetivo de simular o comportamento do tipo tension softening do material. Testes de simulação envolvendo o modelo proposto foram realizados, comparando-se com resultados experimentais e numéricos mostrando a boa precisão e capacidade de obtenção de cargas últimas em estruturas de barras em concreto armado.

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This study aimed to investigate the influence of storage time (0, 48 hours) of Pinus elliottii pieces and the tests to obtaining modulus of elasticity (static bending and transversal vibration) in glued laminated timber beams, produced with resorcinol based adhesive and 0.8 MPa compaction pressure. After pieces were properly prepared, part of them was used in immediate three manufacturing glulam beams, tested after adhesive cure, and part stored for 48 hours under a roof with a temperature of 25°C and relative humidity of 60% for subsequent manufacturing and testing three other glulam beams. Results of analysis of variance (ANOVA) revealed that the storage period was significant influence in modulus of elasticity obtained in static bending test (8% reduction from 0 to 48 hours). This not occurred with modulus of elasticity obtained by transversal vibration test (no significant influence). ANOVA results showed equivalence of means in both test procedures. New researches ire needed to better understand the investigated phenomenon, using new wood species, other storage conditions and a great number of samples.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Pós-graduação em Agronomia (Energia na Agricultura) - FCA

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Pós-graduação em Cirurgia Veterinária - FCAV

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Pós-graduação em Engenharia Mecânica - FEIS

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In this work, we discuss the procedures adopted for the design of built-up columns (laced and battened columns). Built-up columns are widely used in steel construction generally when the compression forces are relatively low and the column buckling lengths are large. They are commonly used in industrial buildings, for example, as posts for cladding, or as columns supporting a crane girder. Unlike columns with full section, in the case of built-up columns, it is necessary to evaluate the shear stiffness. In fact, the shear strength leads to a significant reduction of the critical load. In the context of this work, the components of the columns (chords, diagonals, posts, etc.) are formed by cold-formed members. In order to systematize and rationalize the verification of the built-up columns, this work aim to develop a computer program based on the standards NBR 14762, NBR 6355 and Eurocode 3, basically the considerations of the part EN 1993-1-1