<正>分析了多缸发动机正常振动时激振源的平衡性，以及发动机在车架上的振动形式。试验结果表明，个别气缸功率变化时可能发生变化的激振源主要是反倒力矩；由于功率不平衡，各缸本应相互抵消的各非主谐次的反倒力矩，很多谐次都出现且互相助长，导致总的反倒力矩平衡性恶化，致使发动机振动加剧。

Aluminum(A1) toxicity is a limiting factor for agriculture in acidic soils where it results in an inhibition of root growth, drought intolerance, nutrient deficiencies and other physiological and biochemical changes in plants. Soybean is highly nutritious being particularly rich in protein content and useful for soil improvement. In present study,the seedlings of 7 soybean cultivars were grown in solution with or without 2 mmol/L A1 stress in a randomized complete block design experiment for 2 weeks, to evaluate the differential responses of soybean genotypes to AI stress on seedling growth. Results showed that epicotyl length,seedling height, root length, fresh and dry weights, and chlorophyll content were decreased for the cultivars tested under A1 stress. There was no uniform response of the cultivars to A1 stress in seedling growth. However,seven cultivars seem to be categorized as 3 groups,based on the relative root growth data as follows. Nannong 73-935 and Dahuangdou were the most tolerant (15% reduction) and Nannong 87C-38 and Williams were the most sensitive(37%～39% reduction); 1138-2, Hongyin No. 1 and Kefeng No. 1 (23%～27% reduction) showed intermediate response under A1 stress.