玉米种子脱粒过程高速摄影观察分析

为优化差速式玉米种子脱粒机脱粒系统的有关参数,进而降低玉米种子在脱粒过程中的损伤,采用高速摄影方法对单个玉米果穗喂入与脱粒过程进行了观察分析.分析结果表明:果穗在开始喂入阶段,籽粒破碎大;在脱粒起始阶段,果穗撞击强烈,越到后段,撞击越弱;果穗在正常脱粒情况下,脱下籽粒多,籽粒运动轨迹可近似为沿直辊与果穗接触点的切线方向;而果穗非正常脱粒情况下,脱下籽粒少,籽粒运动规律呈杂乱状态,没有一定飞行方向;螺旋辊的转速偏大造成果穗的非正常脱粒加大,果穗的非正常脱粒会影响果穗的脱粒质量和脱粒效率.     

Deforestation trends in the Atlantic Zone of Costa Rica: A case study

In this study we have tried to link a quantitative inventory of deforestation to possible factors driving forest clearing, like accessibility and soil quality. The Study Area covered 395 km² in the Atlantic Zone of Costa Rica. Basic information came from aerial photographs taken in 1952, 1960, 1971 to 73, 1981 and 1984. Photo interpretations were digitized and processed with the help of a monoplotting programme. Three phases in deforestation were distinguished:

• 1 The period before 1960, characterized by a gradual increase in the rate of deforestation, with preferential clearing along rivers and on fertile soils.
• 2 The period 1960-1972. This period shows an increased clearing rate caused by a new centre of colonization, Cariari. Furthermore, banana plantations entered the area and main roads were constructed. Deforestation took place preferentially along roads and on fertile soils.
• 3 In the period 1972-1984 the remaining forest ‘islands’ were cleared at an accelerated rate. This was because only small areas of forest were left by this period. Also between 1972 and 1984 the fertile soils were cleared most rapidly.