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History of a viation The history of aviation has extended over more than two thousand years from the earliest attempts in kites and gliders to powered heavier-than-air, supersonic and hypersonic flight. The first form of man-made flying objects was kites. The earliest known record of kite flying is from around 200 BC in China, when a general flew a kite over enemy territory to calculate the length of tunnel required to enter the region. In 6th century, Yuan Huangtou (,北魏王族) , a Chinese prince, survived by tying himself to the kite. With the efforts to analyze the atmosphere in the 17th and 18th centuries, gases such as hydrogen were discovered which in turn led to the invention of hydrogen balloons. Various theories in mechanics by physicists during the same period of time, notably fluid dynamics and Newton ’ s laws of motion, led to the foundation of modern aerodynamics. Tethered balloons filled with hot air were used in the first half of the 19th century and saw considerable action in several mid-century wars, most notably the American Civil War, where balloons provided observation during the Battle of Petersburg. Experiments with gliders provided the groundwork for heavier-than-air craft, and by the early 20th century advances in engine technology and aerodynamics made controlled, powered flight possible for the first time.
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【单选题】车站自动广播分固定广播和非固定广播,固定广播主要是_______,播放的优先级最高。( )
A.
列车到站开关门广播
B.
扶梯安全广播
C.
客流控制广播
D.
三品广播
【判断题】一个数据库只能有一个事务日志文件ldf( )。
A.
正确
B.
错误
【判断题】运行设备应建有检查、维护、故障及大修记录。()
A.
正确
B.
错误
【单选题】信号系统应能实现下列控制:控制中心自动控制;车站自动控制;车站人工控制和()。
A.
自动控制
B.
车站自动控制
C.
控制中心自动控制
D.
控制中心自动控制时的人工介入控制
【单选题】在安装电路是,安装顺序下列哪个?
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先接主电路,后接控制电路
B.
先接控制电路,后接主电路
C.
先接电源线
D.
自下而上接线
【多选题】设备管理中应当建立并保存相应设备()记录。
A.
采购
B.
确认
C.
操作
D.
维护
【简答题】按照齿轮两轴线的相对位置,齿轮传动可以分为两轴线 、两轴线 和两轴线 三种。
【判断题】在采用振冲加固或挤密碎石桩加固后桩间土的实测标贯值仍低于相应临界值时,可以简单地判为液化土。
A.
正确
B.
错误
【简答题】按照齿轮两轴线的相对位置,齿轮传动可以分为两轴线 齿轮传动、两轴线 齿轮传动和两轴线 齿轮传动三种。
【判断题】采用振冲或挤密碎石桩加固后桩间土的实测标准贯入锤击数低于相应临界值时,即可判定为液化。
A.
正确
B.
错误
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