Manufacturing accuracy, especially position accuracy of fastener holes, directly affects service life and security of aircraft. The traditional modification has poor robustness, while the modification based on laser t...Manufacturing accuracy, especially position accuracy of fastener holes, directly affects service life and security of aircraft. The traditional modification has poor robustness, while the modification based on laser tracker costs too much. To improve the relative position accuracy of aircraft assembly drilling, and ensure the hole-edge distance requirement, a method was presented to modify the coordinates of drilling holes. Based on online inspecting two positions of pre-assembly holes and their theoretical coordinates, the spatial coordinate transformation matrix of modification could be calculated. Thus the straight drilling holes could be modified. The method improves relative position accuracy of drilling on simple structure effectively. And it reduces the requirement of absolute position accuracy and the cost of position modification. And the process technician also can use this method to decide the position accuracy of different pre-assembly holes based on the accuracy requirement of assembly holes.展开更多
Social Network Analysis,Statistical Analysis,Content Analysis and other research methods were used to research online learning communities at Capital Normal University,Beijing.Analysis of the two online courses result...Social Network Analysis,Statistical Analysis,Content Analysis and other research methods were used to research online learning communities at Capital Normal University,Beijing.Analysis of the two online courses resulted in the following conclusions:(1)Social networks of the two online courses form typical core-periphery structures;(2)Social networks of the two online courses contain“structural holes,”where some actors position themselves to become potential opinion-leaders within their social networks;(3)Actors,variously positioned within a core-periphery structure,show quite significant differences in terms of knowledge building;(4)Taking“structural holes”into account,there exist considerable differences in knowledge building between opinion-leaders and non opinion-leaders;(5)Actors in the“core”and“structural hole”positions have very different characteristics in terms of knowledge building.These actors in particular play important roles in online learning communities,impacting on the level of the constructed knowledge.展开更多
文摘Manufacturing accuracy, especially position accuracy of fastener holes, directly affects service life and security of aircraft. The traditional modification has poor robustness, while the modification based on laser tracker costs too much. To improve the relative position accuracy of aircraft assembly drilling, and ensure the hole-edge distance requirement, a method was presented to modify the coordinates of drilling holes. Based on online inspecting two positions of pre-assembly holes and their theoretical coordinates, the spatial coordinate transformation matrix of modification could be calculated. Thus the straight drilling holes could be modified. The method improves relative position accuracy of drilling on simple structure effectively. And it reduces the requirement of absolute position accuracy and the cost of position modification. And the process technician also can use this method to decide the position accuracy of different pre-assembly holes based on the accuracy requirement of assembly holes.
文摘Social Network Analysis,Statistical Analysis,Content Analysis and other research methods were used to research online learning communities at Capital Normal University,Beijing.Analysis of the two online courses resulted in the following conclusions:(1)Social networks of the two online courses form typical core-periphery structures;(2)Social networks of the two online courses contain“structural holes,”where some actors position themselves to become potential opinion-leaders within their social networks;(3)Actors,variously positioned within a core-periphery structure,show quite significant differences in terms of knowledge building;(4)Taking“structural holes”into account,there exist considerable differences in knowledge building between opinion-leaders and non opinion-leaders;(5)Actors in the“core”and“structural hole”positions have very different characteristics in terms of knowledge building.These actors in particular play important roles in online learning communities,impacting on the level of the constructed knowledge.