The us has lost predator observation planes to hostile fire before , but rarely , if ever , over iraq 美国空军在伊拉克上空被击落的事件以前几乎没有发生过
2.
It can give vector of stress , and break factor and direction vector of tensive crack and shearing crack in the special observation planes ( for examples , in a stratal surface which is fluctuant in depth ) 软件可视化包括：空间应力矢量(大小和方向) 、裂缝性态(张裂缝和剪裂缝发育程度及其方向矢量)在特定观察面(如沿起伏的地层面)上的展示。
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Abstract : in this paper ， a ray - optics analysis is performed to investigate the asymmetry of dual beam scanning field produced by a rotating polygon . some basic equations of dual beam scan are derived ， such as ， the position vector for the incident point ， the scalar expression for reflected ray ， scan pattern on observation plane ect . the far - field asymmetry of the scanning field has been discussed 文摘:应用几何光学理论研究了多光束转镜扫描场的非对称性，导出多光束扫描入射点位置矢量、反射线标量表达式、观察面上的扫描轨迹方程，并研究了扫描远场的非对称性。
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