Agricultural productivity in 41 Sub-Saharan Africa (SSA) countries from 1960 to 1999 is examined by estimating a semi-nonparametric Fourier production frontier. Over the four decades the estimated rate of productivity change was 0.83% per year, although the average rate from 1985-99 was a strong 1.90% per year. Former UK colonies exhibited significantly higher productivity gains than others, while Liberia and countries that had been colonies of Portugal or Belgium exhibited net reductions in productivity. We measure a significant reduction in productivity during political conflicts and wars, and a significant increase in productivity among those countries with higher levels of political rights and civil liberties.
Rubber components are widely used in many fields because of their superior elastic properties. Fatigue failures, commonly encountered in rubber components, however, remain a critical issue. In this study, the effect of strain ratio R on the fatigue life of filled natural rubbers used in automotive mounts is investigated experimentally and numerically. A uniaxial tension/compression fatigue experiment was conducted on dumb‐bell cylindrical rubber specimens subject to loads representing different R ratios. The experimental fatigue data are used to formulate two preliminary fatigue models based on peak strain and strain amplitude as the damage parameters. The deficiencies of these two models in predicting fatigue life over a wide range of R ratios are discussed, and an alternative life prediction model is proposed. The proposed model incorporates the effect of R ratio using an equivalent strain amplitude. It is shown that the proposed model could effectively predict fatigue life over a wide range of R ratios with an improved accuracy.
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