Gravity, however, causes density waves to move out through the galaxy which in turn triggers the formation of 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。
This paper presents an analysis of the characteristics and laws of formation of 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。
Further investigation on the propagation of elastic waves along a fluid-filled borehole in slow formation is studied in the paper.
木文对低速地层裸眼井中弹性波的传播问题作了进一步研究。
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