DEVELOPMENT OF A TRIAXIAL FORCE PLATFORM FOR THE MEASUREMENT OF FORCE AT A BICYCLE PEDAL

The main purpose of this work is to present the methodology used to develop a triaxial force platform for the use at a pedal bicycle; this platform is based on the flexion of beams where strain gages are bonded for the measurements of force components FX, FY and FZ, as well as the force moments MX and MY. The theoretical analysis of this force platform was realized by the Finite Element method, with the simulation of 384 combinations of static loads (force and moments) at different directions. Deformation data numerically obtained is related to the position were sensors will be placed. Output signals obtained were numerically organized and graphically analyzed, in order to show the mathematical relation between force and strain, which is used to generate a "calibration matrix", free of mechanical coupling which usually appears in multiaxis systems. At last, a test was made, simulating an input load, and the output signal obtained was practically equal

Materiais cerâmicos avançados: determinação de kic de sinterizados de alumina

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Materiais cerâmicos avançados: obtenção de sinterizados de alumina de alta densidade

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Ingestive behavior of Angus yearling steers in natural grassland subjected to fertilization and over sown of temperate species

The objective was to evaluate the ingestive behavior of Angus yearling steers grazing natural grasslands of Southern Brazil, submitted or not to the application of fertilizers: NG= natural grassland; FNG= fertilized natural grassland, and FONG= fertilized natural grassland improved with the over sown of temperate forage species. Three Angus yearling steers and a variable number of put-and-take animals were used per experimental unit, to maintain a forage allowance of 13 kg of dry matter/100 kg of body weight. Ingestive behavior of tester animals was visually assessed in four seasons of the year through instantaneous records of activity every ten minutes during the daytime period. There was no effect of pasture treatments on ingestive behavior. An interaction between seasons and periods of the day was observed for daily grazing and rumination time (P <0.05). The grazing activities were clustered at the beginning and the end of the day in summer, autumn and winter, while in spring it was similar in the 1 st three quarters of the day, with higher activity in the period close to sunset. The animals spent more time grazing in the spring despite the better quality of forage in this season. Regardless of the season, longer residence and grazing time were found in water foci areas. We conclude that grazing time on natural pastures is influenced by forage mass and forage allowance, and bite rate is influenced by the chemical composition of the sward

Aplicação de força no pedal em prova de ciclismo 40 km contra-relógio simulada: estudo preliminar

O objetivo deste estudo foi analisar o comportamento das forças aplicadas no pedal durante uma prova de ciclismo 40 km contra-relógio simulada. Avaliou-se um triatleta de nível internacional utilizando-se uma bicicleta modelo estrada acoplada a um ciclossimulador eletromagnético. O protocolo consistiu em completar 40 km no menor tempo possível, utilizando estratégia de livre escolha, incluindo cadência e relação de marchas preferida. Utilizou-se um pedal direito instrumentado com "strain gauges" capaz de mensurar as componentes normal e tangencial da força aplicada no mesmo. Foi possível calcular a força efetiva (componente perpendicular ao pé-de-vela, chamada de FE), a partir das forças registradas pelo pedal. Durante todo o teste, monitorou-se o consumo de oxigênio (VO2), freqüência cardíaca (FC), potência e velocidade. Durante a prova simulada observou-se um aumento do esforço do triatleta a partir da análise do comportamento do VO2 e da FC, bem como pelo aumento da potência e da velocidade. A magnitude das forças normal e tangencial ao pedal apresentou redução no decorrer da prova, enquanto que a FE aumentou durante a fase de recuperação. Provavelmente o triatleta mudou o direcionamento das forças ao longo do teste na tentativa de otimizar as mesmas, influenciando dessa forma a técnica de pedalada. A estratégia adotada pelo triatleta parece ter contribuído para aumentar a efetividade da pedalada.The purpose of this study was to analyze the pedal forces during a simulated cycling 40 km time-trial. One experienced triathlete was evaluated using a road bike mounted on a magnetic cycle simulator. The self-preferred cadence and gear was adopted to complete the 40 km in less time possible. The right regular pedal was replaced by an instrumented pedal to record the normal and tangential components of force applied on it. The effective force (perpendicular component to the crank) was calculated from normal and tangential forces. Oxygen uptake, heart rate, power output and speed were registered. During the time-trial the triathlete.s effort increased and this influenced the oxygen uptake and heart rate. The forces magnitude showed a little decreased by the end of the test while the effective force increased on the second half of the recovery phase. Probably the triathlete changed the direction of the forces during the 40 km trial to try to optimize the application of force thus influencing the pedaling technique. The strategy adopted by the triathlete caused a positive change in the pedaling effectiveness

Desempenho de novilhas de corte dos 14 aos 18 meses de idade em pastagem nativa sob diferentes ofertas de forragem na Depressão Central

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Ecosystems services from natural grasslands: ¿it's possible to enhance them with more productivity?

Grazing intensity is the key component of the interrelations between plants and their environment in pastoral ecosystems. In this way, the natural structural and floristic heterogeneity that is a response to soil variability can be modified by grazing. But the degree of such alterations must to be controlled in order to maintain ecosystems services and at same time to offers an adequate nutritional environment to the herbivores. In this paper we summarize some results from a series of experiments conducted in natural pastures from south Brazil, to demonstrate how grazing control can modified structural pasture characteristics, enhancing animal performance, soil quality, water infiltration, and producing a meat with particular fatty acids composition