As the expansion device of amplitude, horn is used to focus energy and enlarge the mechanical vibration of the particledisplacement or velocity.
变幅杆作为振幅扩大装置，主要作用是把能量集中，将机械振动的质点位移或速度放大。
2
Arbilrary particledisplacement is required to be solved and applied in engineering calculation and dynamic analyses for gantry structure, but formula of this kind is still lacking at present.
门架结构工程计算和动态分析中均需求解和应用门架任意点的位移，但目前尚缺乏这种位移公式。
3
The universal formulae of the fringe visibility, film resolution requirement and maximum allowable displacement of a particle are given.