Now, the clock says I've run out of time.

哦,我们的时间不多了

耶鲁公开课 - 美国内战与重建课程节选

It's usually shown like a clock is shown here, where time 0, which is at the top here is right at the end of mitosis where you have two new cells that are formed.

通常会用一个类似时钟的图来图示,0时刻,在最上端 为上次有丝分裂终点,代表两个新细胞刚刚形成

耶鲁公开课 - 生物医学工程探索课程节选

First of all, negative time should not bother anybody; t=0 is when I set the clock, I measured time forward, but yesterday would be t = -1 day, right?

首先,负的时间对我们不存在任何干扰,t=0使我们设定的初始时间,我是用顺序计时,所以昨天就可以记为-1天,对吗

耶鲁公开课 - 基础物理课程节选