Influence of friction on gear dynamics

Sliding friction between meshing teeth can be a very important of noise and vibration excitation source in geared systems. This study presents a single degree of freedom torsional model for a FZG type C single gear pair. Starting from a base dynamic model with time varying mesh stiffness as the only internal excitation, the influence of additional effects is gradually considered, namely, constant friction coefficients and time varying output torques. In particular, sliding friction is modeled as external and internal linear time varying excitation. On the other hand, time varying output torques are also considered as alternative of constant driven torque. The gears rotational vibrations are calculated by Runge-Kutta method for different combinations of rational speeds, input torques and friction coefficients. The results indicate that dynamic transmission errors calculated from modeling the friction force as external and internal excitation are quite different, especially when contact point moves ahead of pitch point. However the influence of time variations on output torque is very reduced

A História da Alimentação: balizas historiográficas

Os M. pretenderam traçar um quadro da História da Alimentação, não como um novo ramo epistemológico da disciplina, mas como um campo em desenvolvimento de práticas e atividades especializadas, incluindo pesquisa, formação, publicações, associações, encontros acadêmicos, etc. Um breve relato das condições em que tal campo se assentou faz-se preceder de um panorama dos estudos de alimentação e temas correia tos, em geral, segundo cinco abardagens Ia biológica, a econômica, a social, a cultural e a filosófica!, assim como da identificação das contribuições mais relevantes da Antropologia, Arqueologia, Sociologia e Geografia. A fim de comentar a multiforme e volumosa bibliografia histórica, foi ela organizada segundo critérios morfológicos. A seguir, alguns tópicos importantes mereceram tratamento à parte: a fome, o alimento e o domínio religioso, as descobertas européias e a difusão mundial de alimentos, gosto e gastronomia. O artigo se encerra com um rápido balanço crítico da historiografia brasileira sobre o tema

A geometria das rodas cilíndricas de engrenagens exteriores com perfil em evolvente de circulo

O projecto de modernos sistemas de engrenamento, para operarem em regimes de grandes potências e elevadas velocidades, recorre cada vez com maior frequência à Concepção Assistida por Computador apoiada em códigos do Método dos Elementos Finitos e do Método dos Elementos Fronteira. A correcta definição da geometria do perfil dos dentes das rodas é fundamental para a credibilidade dos resultados obtidos. A definição geométrica do perfil dos dentes pode também assumir um papel importante no ensino tecnológico e na formação profissional, nomeadamente, na simulação visual de processos de talhagem por geração e na visualização da configuração dos dentes em função dos seus parâmetros caracterizadores. Neste texto, desenvolve-se um tratamento unificado da geometria do perfil dos dentes de rodas cilíndricas exteriores (dentados recto e helicoidal), que inclui os efeitos da correcção do dentado e da protuberância da cabeça dos dentes da ferramenta de corte. Em complemento, apresentam-se alguns exemplos de aplicação dos conceitos expostos

Clinical validation of the portuguese version of “substance addiction consequences” derived from the nursing outcomes classification

Our aim was to contribute to the clinical validation of “Substance Addiction Consequences” (SAC) derived from the nursing outcomes classification (NOC), and to analyse psychometric properties. To that purpose, we applied a methodological design. The study’s outcome comprises 16 nursing-sensitive indicators, within four different consequence factors: psychological and family; physical and cognitive ability; self-care; economic and work. The psychometric properties were considered good. We concluded that the scale can be used as a valid tool to measure the consequences of substance addiction and to assess the health status as a nursing sensitive outcome. The scale is considered valid to monitor nursing interventions in the clinical setting; being a comprehensive tool it allows the nurse to understand better this complex health problem.N/

The use of broccoli agro-industrial waste in dairy cattle diet for environmental mitigation

Livestock feed production for the intensive dairy industry has a significant environmental impact. This study evaluated the potential to reduce the environmental impacts of milk production in Guanajuato, Mexico, by incorporating broccoli stems (BS), an abundant agro-industrial waste product with high nutritional value, into dairy cattle feed. The potential reduction of environmental impacts from adding BS to cattle diet formulation was estimated using a life cycle assessment and a linear programming model which considered nutritional requirements as constraints. Two scenarios for milk production were considered: an optimized conventional diet and an optimized diet including BS. The results indicated that incorporating BS in cattle feed could reduce greenhouse gas emissions by 118 g CO2 eq kg−1 fat-and-protein corrected milk (FPCM and agricultural land occupation by 0.002 m2a kg−1 FPCM but increased fossil depletion by 4 g oil eq kg−1 FPCM. BS can replace 11.1% of conventional feeds and maximize the incorporation feeds with low environmental impacts in the diet, such as alfalfa hay and maize silage. A sensitivity analysis of the economic allocation showed that the maximum price of BS to remain environmentally viable was 19.28 USD t−1 on a fresh matter basis

Environmental implications of anaerobic digestion for manure management in dairy farms in Mexico: a life cycle perspective

<div><p>The environmental profile of milk production in Mexico was analysed for three manure management scenarios: fertilization (F), anaerobic digestion (AD) and enhanced anaerobic digestion (EAD). The study used the life cycle assessment (LCA) technique, considering a ‘cradle-to-gate’ approach. The assessment model was constructed using SimaPro LCA software, and the life cycle impact assessment was performed according to the ReCiPe method. Dairy farms with AD and EAD scenarios were found to exhibit, respectively, 12% and 27% less greenhouse gas emissions, 58% and 31% less terrestrial acidification, and 3% and 18% less freshwater eutrophication than the F scenario. A different trend was observed in the damage to resource availability indicator, as the F scenario presented 6% and 22% less damage than the EAD and AD scenarios, respectively. The magnitude of environmental damage from milk production in the three dairy manure management scenarios, using a general single score indicator, was 0.118, 0.107 and 0.081 Pt/L of milk for the F, AD and EAD scenarios, respectively. These results indicate that manure management systems with anaerobic digestion can improve the environmental profile of each litre of milk produced.</p></div

The columnar to equiaxed transition of horizontal unsteady-state directionally solidified Al-Si alloys

Experiments were conducted to investigate the influence of thermal parameters on the columnar to equiaxed transition during the horizontal unsteady-state directional solidification of Al-Si alloys. The parameters analyzed include the heat transfer coefficients, growth rates, cooling rates, temperature gradients and composition. A combined theoretical and experimental approach is developed to determine the solidification thermal variables considered. The increasing solute content in Al-Si alloys was not found to affect significantly the experimental position of the CET which occurred for cooling rates in the range between 0.35 and 0.64 K/s for any of three alloy compositions examined. A comparative analysis between the results of this work and those from the literature proposed to analyze the CET during upward vertical solidification of Al-Si alloys is reported and the results have shown that the end of the columnar region during horizontal directional solidification is abbreviated as a result of about six times higher thermal gradient than that verified during upward unidirectional solidification of alloys investigated

V Simposio Ibérico de Riesgos Psicosociales

Conjunto de artigos resultantes de revisão cega por pares dentro da temática dos Riscos Psicossociais e áreas relacionadasinfo:eu-repo/semantics/publishedVersio

Solidification thermal parameters and dendritic growth during the horizontal directional solidification of Al-7wt.%Si alloy

The main purpose of this work is to investigate the influence of thermal parameters such as growth rate (V L) and cooling rate (T R) on the primary dendrite arm spacings (&#955;1) during the horizontal transient directional solidification of Al-7wt.%Si hypoeutectic alloy. The primary dendrite spacings were measured along the length of the samples and correlated with these thermal parameters. The variation of dendrite spacings is expressed as a power law function of V L and T R given by the formulas &#955;1 = 55(V L)-1.1 and &#955;1 = 212 (T R)-0.55, respectively. A comparative study between the results of this work and those from the literature proposed to investigate these dendrite spacings during the upward and downward vertical directional solidification of Al-7wt.%Si alloy is also conducted. Finally, the experimental data are compared with some predictive dendritic models from the literature