Plant germplasm resources is the material foundation and key point for agricultural production, crop breeding and bioengineering. China is one of the centers for the origin of the cultivated plants worldwide, as well ...Plant germplasm resources is the material foundation and key point for agricultural production, crop breeding and bioengineering. China is one of the centers for the origin of the cultivated plants worldwide, as well as one of the countries with most abundant plant resources and the highest biodiversity. Strengthening research in the conservation and utilization of plant germplasm resources is of significant value and importance. In this study, the present status of conservation, utilization, and existing problems of plant germplasm resources in China and around the world were reviewed; further, through analyzing measures taken by global countries for plant germplasm resources protection, countermeasures for plant germplasm resources conservation in China were also presented from three aspects, namely, collection and conservation, information network construction and national legislation and policies.展开更多
直流输电系统的内过电压主要通过金属氧化物避雷器(metal oxide arrester,MOA)加以限制,避雷器在内过电压下的保护特性对确定设备的操作冲击绝缘水平具有重要意义。根据±1 100 k V主回路接线、避雷器配置、交直流系统参数等,建立...直流输电系统的内过电压主要通过金属氧化物避雷器(metal oxide arrester,MOA)加以限制,避雷器在内过电压下的保护特性对确定设备的操作冲击绝缘水平具有重要意义。根据±1 100 k V主回路接线、避雷器配置、交直流系统参数等,建立了±1 100 k V系统内过电压计算模型。对避雷器电压和电流波形进行仿真,对避雷器电流的波头时间进行统计。统计结果为:内过电压下通过避雷器电流的波头时间均不小于100μs,大于标准操作冲击电流的波头时间30μs,需要对较缓电流波头下避雷器的保护特性进行研究。为加以对比,对波形为316/814μs、30/60μs、8/20μs和1/4μs电流下的避雷器伏秒特性和伏安特性进行了试验研究。结果表明,同样电流下,1/4μs的伏安特性曲线高于8/20μs、30/60μs和316/814μs的曲线,而后三者的伏安特性曲线则区别不大;8/20μs、30/60μs和316/814μs的伏安特性相比,在0.1~1 k A电流范围内,30/60μs的伏安特性曲线比8/20μs和316/814μs的伏安特性曲线稍高。由于避雷器操作冲击电流的波头时间均不小于100μs,内过电压下避雷器取30/60μs电流波形下的伏安曲线是合适的,且是稍微偏严的。最后试验测试了避雷器电阻片在30/60μs操作冲击电流下的伏安特性。展开更多
基金Supported by the Beijing Nova Program(2008B37)the Major Research Program of Beijing Municipal Commission of Science and Technology(D131100000413001)+2 种基金National Key Technologies R&D Program(2012BAK26B03)the Special Fund for Construction of Scientific and Technological Innovation Ability of Beijing Academy of Agriculture and Forestry Sciencesthe Special Research Fund for the Youth of Beijing Academy of Agriculture and Forestry Sciences(QNJJ201211)~~
文摘Plant germplasm resources is the material foundation and key point for agricultural production, crop breeding and bioengineering. China is one of the centers for the origin of the cultivated plants worldwide, as well as one of the countries with most abundant plant resources and the highest biodiversity. Strengthening research in the conservation and utilization of plant germplasm resources is of significant value and importance. In this study, the present status of conservation, utilization, and existing problems of plant germplasm resources in China and around the world were reviewed; further, through analyzing measures taken by global countries for plant germplasm resources protection, countermeasures for plant germplasm resources conservation in China were also presented from three aspects, namely, collection and conservation, information network construction and national legislation and policies.
文摘直流输电系统的内过电压主要通过金属氧化物避雷器(metal oxide arrester,MOA)加以限制,避雷器在内过电压下的保护特性对确定设备的操作冲击绝缘水平具有重要意义。根据±1 100 k V主回路接线、避雷器配置、交直流系统参数等,建立了±1 100 k V系统内过电压计算模型。对避雷器电压和电流波形进行仿真,对避雷器电流的波头时间进行统计。统计结果为:内过电压下通过避雷器电流的波头时间均不小于100μs,大于标准操作冲击电流的波头时间30μs,需要对较缓电流波头下避雷器的保护特性进行研究。为加以对比,对波形为316/814μs、30/60μs、8/20μs和1/4μs电流下的避雷器伏秒特性和伏安特性进行了试验研究。结果表明,同样电流下,1/4μs的伏安特性曲线高于8/20μs、30/60μs和316/814μs的曲线,而后三者的伏安特性曲线则区别不大;8/20μs、30/60μs和316/814μs的伏安特性相比,在0.1~1 k A电流范围内,30/60μs的伏安特性曲线比8/20μs和316/814μs的伏安特性曲线稍高。由于避雷器操作冲击电流的波头时间均不小于100μs,内过电压下避雷器取30/60μs电流波形下的伏安曲线是合适的,且是稍微偏严的。最后试验测试了避雷器电阻片在30/60μs操作冲击电流下的伏安特性。