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讨论一种典型的采样控制系统──直接数字控制(DDC)系统(简称数控系统)在S域和P域的分析设计方法。根据采样控制系统理论,从数控系统在Z平面的稳定性判据出发,利用tustin变换(P变换),通过Z平面、S平面和P平面之间的映像关系,导出数控系统在S域和P域的稳定性判据,进而提出了数控系统在S域和P域的分析设计方法,并详细说明了这两种设计方法的具体方法与步骤。 相似文献
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We have discovered > 10(8) microbial cells/cm3 attached to clay grains in the bottom 13 m of the GISP2 (Greenland Ice Sheet Project) ice core. Their concentration correlates with huge excesses of CO2 and CH4. We show that Fe-reducing bacteria produce most of the excess CO2 and methanogenic archaea produce the excess CH4. The number of attached cells per clay grain is proportional to grain perimeter rather than to area, which implies that nutrients are accessed at grain edges. We conclude that Fe-reducing microbes immobilized on clay surfaces metabolize via "shuttle" molecules that transport electrons to grain edges, where they reduce Fe(III) ions at edges to Fe(II) while organic acid ions are oxidized to CO2. Driven by the concentration gradient, electrons on Fe(II) ions at grain edges "hop" to Fe(III) ions inward in the same edges and oxidize them. The original Fe(III) ions can then attach new electrons from shuttle molecules at the edges. Our mechanism explains how Fe-reducers can reduce essentially all Fe(III) in clay minerals. We estimate that the Fe(III) in clay grains in the GISP2 silty ice can sustain Fe-reducing bacteria at the ambient temperature of -9 degrees C for approximately 10(6) years. F420 autofluorescence imaging shows that > 2.4% of the cells are methanogens, which account for the excess methane. 相似文献
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卫星有效载荷的地位和作用 总被引:2,自引:0,他引:2
1 有效载荷的慨念有效载荷是是指空间航天系统中能直接产生满足人类文明进步和社会日渐繁荣需求的输出的仪器、设备或装置等物质性有效载荷和执行航天任务的人及其装备组成的航天员系统。广义说来 ,对运载器 ,其所运送的空间飞行器 (载人的或不载人的 )是其有效载荷。文章不讨论这一意义上的有效载荷。狭义说来 ,狭义范围的航天器 (空间飞行器 )包括航天器平台和有效载荷。航天器上用于保证与支持有效载荷工作的仪器设备和系统称为航天器的服务与支持系统 ,包括热控制 ,姿态与轨道控制 ,遥测与遥控 ,能源 ,天线 ,数据管理等。航天器服务与… 相似文献
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