So what I'm saying here is we are specializing to a limited class of motion where the particle has a definite acceleration, a.

我在这里想说的是,我们正在专门讨论一类问题,这些问题中,质点都有一个确定的加速度a

耶鲁公开课 - 基础物理课程节选

The Alpha Magnetic Spectrometer was designed to search for dark matter by collecting high energy radiation known as cosmic rays, and then sort through it looking for a certain class of particle believed to be created after two bits of dark matter collide in space and destroy each other.

FORBES: Experiment May Have Found Dark Matter, The Key To A Cosmic Mystery