Once the gases are mixed, there's not going to be any further net change in the system.

一旦气体混合,这个系统就不会发生任何净的变化。

麻省理工公开课 - 热力学与动力学课程节选

Now the last thing is that because the neutron has no net charge, we can change neutron number.

现在，最后一件事是,因为中子没有净电子，我们可以改变中子数。

麻省理工公开课 - 固态化学导论课程节选