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991.
Measurement of penetration force using a Hall-current-sensor 总被引:1,自引:0,他引:1
Due to the evident influence of the penetration velocity on the measurement of cone index (CI), diverse motor-operated penetrometers have been designed to keep the velocity with a constant. In this paper, an attractive method to determine the penetration force for a motor-operated penetrometer was presented. Unlike other conventional methods employing various force sensors, this method used a Hall-current-sensor to dynamically measure the operating current of a permanent magnet dc-motor. For the proposed method, both a theoretical analysis related the operating current of the dc-motor to the penetration force and the measurement principle of the Hall-current-sensor were addressed. A soil column with three-layer water contents was used in the laboratory test. The experimental results confirm that the operating current of the dc-motor was a determinate indictor for estimating the penetration force. 相似文献
992.
993.
By the way of experiment and analysis of two "one story and one bay" reinforced concrete frames, namely a "beam with weaker column" frame and a "column with equally strong beam" frame, the features of internal force redistribution are investigated and an elementary comparison about bending moment redistribution of three kinds of frames namely the "column with weaker beam", "beam with weaker column" and "column with equally strong beam" is given. Through this comparison, the objective existence of such "three kinds of frame" is proven, the moment redistribution is different for each frame and for the moment modulation, the elastic moment diagram and the difference of the internal force redistribution in different frames should be considered together. 相似文献
994.
Zhou Jiyue Zeng Qingyu 《保鲜与加工》1991,(3)
Through the static tests of five two-span continuous beams with a relatively small steel ratio, the regularity of redistribution of internal forces of continuous beams with moment modulation is studied, and the moment modulation influence on cracking and deflection of continuous reinforced concrete beams under service loads is analyzed in detail. The conclusions obtained may be used as reference materials for drafting of design code considering redistribution of internal forces. 相似文献
995.
Hayo M. G. van der Werf 《Euphytica》2004,140(1-2):13-23
Summary Life Cycle Assessment (LCA) was used to assess the environmental impacts of field production of fibre hemp and seven other crops in France. The production of 1 ha of hemp yielded a eutrophication potential of 20.5 kg PO4-equivalents, a global warming potential of 2330 kg CO2-equivalents, an acidification potential of 9.8 kg SO2-equivalents, a terrestrial ecotoxicity potential of 2.3 kg 1,4-dichlorobenzene-equivalents, an energy use of 11.4 GJ, and a land use of 1.02 ha.year. A comparison of hemp (low impacts), wheat (intermediate impacts) and sugar beet (high impacts) revealed that the crops were similar for the relative contributions of emitted substances and resources used to impacts, and for the relative contribution of processes to impacts. A reduction of the impacts of hemp production should focus on eutrophication, and consider the reduction of climate change, acidification and energy use as secondary objectives. Given this objective, the overall environmental effect of the substitution of mineral fertiliser by pig slurry is negative. The introduction of reduced tillage is of interest, as it decreases energy use, acidification and climate change. Measures leading to a reduction in NO3 leaching are highly interesting, as they strongly decrease eutrophication. Implications for hemp breeding are discussed. 相似文献
996.
对改善手扶拖拉机运输机组的性能进行了分析和探讨,并对目前手扶拖拉机运输机组所存在的问题提出了改进性意见,通过分析对比各种方案,认为变牵引型为驱动型的拖斗驱动方式能够很好地提高手扶拖拉机的综合利用率,增加其附着性能以及安全性能。 相似文献
997.
农业规划环境影响评价的理论探讨 总被引:3,自引:0,他引:3
农业在我国国民经济中占有举足轻重的作用,农业规划环境影响评价是保障农业可持续发展的重要技术手段。本文以战略环评的理论为依据,综合探讨农业规划环境影响评价的目的意义、基本原则、技术方法和指标体系。 相似文献
998.
近年来,我国农业环境污染问题日益严重和突出,尤其是农业环境污染事故的频繁发生。本文分析了我国农业环境污染的现状、成因、环境影响评价和农业环境的关系,提出了针对农业环境保护现状而进行环境影响评价的重要性等,旨在为农业环境保护和环境影响评价提供可借鉴的发展方向。 相似文献
999.
规模化畜禽养殖场环境影响评价与实例研究 总被引:1,自引:0,他引:1
以天津某大型种猪场为例,从污染源与污染物、评价标准与评价因子、预测模式与环境保护措施等方面探讨了规模化畜禽养殖场环境影响评价过程. 相似文献
1000.