Cities ability reducing earthquake disasters is a complex system involving numerous factors, moreover the re-search on evaluating cities ability reducing earthquake disasters relates to multi-subject, such as earthqua...Cities ability reducing earthquake disasters is a complex system involving numerous factors, moreover the re-search on evaluating cities ability reducing earthquake disasters relates to multi-subject, such as earthquake sci-ence, social science, economical science and so on. In this paper, firstly, the conception of cities ability reducing earthquake disasters is presented, and the ability could be evaluated with three basic elements the possible seis-mic casualty and economic loss during the future earthquakes that are likely to occur in the city and its surround-ings and time required for recovery after earthquake; based upon these three basic elements, a framework, which consists of six main components, for evaluating citys ability reducing earthquake disasters is proposed; then the statistical relations between the index system and the ratio of seismic casualty, the ratio of economic loss and re-covery time are gained utilizing the cities prediction results of earthquake disasters which were made during the ninth five-year plan; at last, the method defining the comprehensive index of cities ability reducing earthquake disasters is presented. Thus the relatively comprehensive theory frame is set up. The frame can evaluate cities ability reducing earthquake disasters absolutely and quantitatively and consequently instruct the decision-making on reducing cities earthquake disasters loss.展开更多
A new coaxial pulsed plasma thruster （PPT） laboratory model is designed and employed in this study. A Teflon sleeve is connected with the anode, which is shaped as a nozzle, and a cathode is mounted in the cavity of...A new coaxial pulsed plasma thruster （PPT） laboratory model is designed and employed in this study. A Teflon sleeve is connected with the anode, which is shaped as a nozzle, and a cathode is mounted in the cavity of the Teflon sleeve and kept in close contact with it. A thread is then designed in the internal surface of the Teflon sleeve, and because of the strong field strength of the cathode triple junction （CTJ）, vacuum flashover occurs and a plasma jet is acquired behind the anode. The electric field distribution of the designed coaxial PPT laboratory model is simulated by MAXWELL 3D simulation software, and the plasma density and thrust are measured by a Langnmir probe and a piezoelectric thin-film sensor, respectively. Through a series of comparative experiments, we discuss the impact of optimal designs, such as the thread and the nozzle-shaped anode, on the discharge characteristics of the coaxial PPT. The experimental and simulation results indicate that the designed coaxial PPT laboratory model presents better discharge characteristics in view of its higher plasma density and greater thrust.展开更多
There are hundreds of villages in the western mountainous area of Beijing,of which quite a few have a profound history and form the settlement culture in the western part of Beijing.Taking dozens of ancient villages i...There are hundreds of villages in the western mountainous area of Beijing,of which quite a few have a profound history and form the settlement culture in the western part of Beijing.Taking dozens of ancient villages in Mentougou District as the research sample,the village space as the research object,based on ASTER GDEM database and quantitative analysis tools such as Global Mapper and ArcGIS,this study analyzed from the perspectives of altitude,topography,slope direction,and building density distribution,made a quantitative study on the spatial distribution and plane structure of ancient villages so that the law of village space with the characteristics of western Beijing was summarized to supplement and improve the relevant achievements in the research field of ancient villages in western Beijing.展开更多
文摘Cities ability reducing earthquake disasters is a complex system involving numerous factors, moreover the re-search on evaluating cities ability reducing earthquake disasters relates to multi-subject, such as earthquake sci-ence, social science, economical science and so on. In this paper, firstly, the conception of cities ability reducing earthquake disasters is presented, and the ability could be evaluated with three basic elements the possible seis-mic casualty and economic loss during the future earthquakes that are likely to occur in the city and its surround-ings and time required for recovery after earthquake; based upon these three basic elements, a framework, which consists of six main components, for evaluating citys ability reducing earthquake disasters is proposed; then the statistical relations between the index system and the ratio of seismic casualty, the ratio of economic loss and re-covery time are gained utilizing the cities prediction results of earthquake disasters which were made during the ninth five-year plan; at last, the method defining the comprehensive index of cities ability reducing earthquake disasters is presented. Thus the relatively comprehensive theory frame is set up. The frame can evaluate cities ability reducing earthquake disasters absolutely and quantitatively and consequently instruct the decision-making on reducing cities earthquake disasters loss.
文摘A new coaxial pulsed plasma thruster （PPT） laboratory model is designed and employed in this study. A Teflon sleeve is connected with the anode, which is shaped as a nozzle, and a cathode is mounted in the cavity of the Teflon sleeve and kept in close contact with it. A thread is then designed in the internal surface of the Teflon sleeve, and because of the strong field strength of the cathode triple junction （CTJ）, vacuum flashover occurs and a plasma jet is acquired behind the anode. The electric field distribution of the designed coaxial PPT laboratory model is simulated by MAXWELL 3D simulation software, and the plasma density and thrust are measured by a Langnmir probe and a piezoelectric thin-film sensor, respectively. Through a series of comparative experiments, we discuss the impact of optimal designs, such as the thread and the nozzle-shaped anode, on the discharge characteristics of the coaxial PPT. The experimental and simulation results indicate that the designed coaxial PPT laboratory model presents better discharge characteristics in view of its higher plasma density and greater thrust.
基金Sponsored by National Natural Science Fund of China(51608007)Young Top-notch Talent Cultivation Project of North China University of Technology(2018)
文摘There are hundreds of villages in the western mountainous area of Beijing,of which quite a few have a profound history and form the settlement culture in the western part of Beijing.Taking dozens of ancient villages in Mentougou District as the research sample,the village space as the research object,based on ASTER GDEM database and quantitative analysis tools such as Global Mapper and ArcGIS,this study analyzed from the perspectives of altitude,topography,slope direction,and building density distribution,made a quantitative study on the spatial distribution and plane structure of ancient villages so that the law of village space with the characteristics of western Beijing was summarized to supplement and improve the relevant achievements in the research field of ancient villages in western Beijing.
