Gravity, however, causes density waves to move out through the galaxy which in turn triggers the formationof hot, bright young stars, producing the ring that we see in this picture.
引力会使密度波穿透星系，继而形成炽热、耀眼的年轻恒星，产生我们在图片中看到的光环。
2
This paper presents an analysis of the characteristics and laws offormationof pressure waves in guns, based on the ignition process and propellant bed structure.
本文根据点火过程和药床结构，分析膛内压力波形成的特征及其规律。
3
Further investigation on the propagation of elastic waves along a fluid-filled borehole in slow formation is studied in the paper.