Até recentemente, o projeto dos tratores agrícolas centrava-se na maximização da eficiência do trator, em detrimento do fator humano. No entanto, devido ao aumento no rigor das normas de segurança de trabalho, há tendência para a melhoria das condições de ergonomia e segurança do operador, visando a melhorar as condições de trabalho, diminuir o nível
ABSTRACT RESUMOde fadiga ao qual este está exposto, diminuir o risco de acidentes e aumentar a produtividade e qualidade do trabalho (Alves 2009). O operador necessita não apenas de conforto, mas sentir-se em ambiente seguro, no seu posto de operação, sendo que o estresse pode afetar o desempenho e a eficiência do trabalho humano, aumentando a fadiga e o desconforto. Outro fator desfavorável, e que está em constante aumento de intensidade, é 1. Trabalho recebido em maio/2010 e aceito para publicação em jan./2011 (n° registro: PAT 9741/
The composite materials using polyhydroxybutyrate as matrix and hydroxyapatite as reinforcement (PHB/HA) were produced by molding, using pressing at 100 MPa and 165 °C for 30 min. The amount of filler was varied from 0 to 20 wt% to evaluate the effect of the HA particles on mechanical properties and the bioactivity of the composites. The increase of the HA amount reduced the compressive strength of the composites nearly 20% while bending strength reduced nearly 30%. However, the bioactivity after 14 days immersion in SBF was improved with the increase of HA amount, with formation of apatite layer on the surface of the PHB/HA composite. Keywords: polyhydroxybutyrate, hydroxyapatite, composite, biomaterials.
Resumo
Materiais compósitos com matriz de poli-hidroxibutirato e material de reforço de hidroxiapatita (PHB
During handling operations, many problems that reduce the quality of vegetables may occur. Mechanical injuries are the leading cause of postharvest losses for the pumpkin, and can take place at any point of the production chain. This study aimed at evaluating the pumpkin fruits behavior, during their ripening stages, on the values of maximum compression force for fixed deformations, and determining the proportional deformability modulus of the fruits under compression at the repose position. Fruits were harvested at 15, 30, 40, 50 and 60 days after flowering and uniaxially compressed between two parallel plates. The results allowed to conclude that both the required compression force and the proportional deformability modulus increased during the maturation course, reaching a maximum force of 1,778 N and a maximum deformation modulus of 164 MPa, after 30 days. After this period, both the maximum force and the modulus values decreased, reaching 1,514.8 N of maximum force and a modulus of 132.09 MPa, after 60 days of ripening. Over the course of a longer maturation time, the fruit firmness increased, therefore requiring an increase in the maximum load to achieve greater deformation. The ideal period for harvest and transport of 'Jacarezinho' pumpkin fruits was set from 30 to 40 days after anthesis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.