合作的

METHODS: We performed a cross-sectional observational study.

我们进行了一个横断面观察性研究。

Investigation results indicate that the period of oscillation of granula sharply increases with the decrease of the ratio of density between two kinds of particles.

研究结果表明，颗粒振荡周期随两种颗粒密度比的减少而急剧增加。