Realistic signals are made by summing sine waves of lots of frequencies, so that after some finite number of wavelengths they interfere destructively and you get a signal of finite width and duration.

现实中的信号由各种频率的正弦波组成，因此，在有限的波长数后，它们会干涉相消，你就得到一个有限宽度和有限延续的信号。

youdao

If you compare the s orbital with the bottom lobe, these have a different sign so they're going to destructively interfere.

如果你们比较s轨道和下面这叶，它们正负号相反，所以它们相消干涉。

youdao

If you compare the s orbital with the bottom lobe, these have a different sign so they're going to destructively interfere.

如果你们比较s轨道和下面这叶，它们正负号相反,所以它们相消干涉。

麻省理工公开课 - 化学原理课程节选

see people with them, and what happens here is it's supposed to be those noise cancellation headphones. All they do is they take in the ambient noise that's around it, and there's actually battery in the headphones, that then produces waves that are going to destructively interfere with that ambient noise.

我从来没有用过这个,但你会看到有人带他们,它们可以作为消噪音耳机,它们所做的就是采入,周围的随机噪声，耳机里面是，有电池的，然后它能产生和,随机噪声相干相消的声波。

麻省理工公开课 - 化学原理课程节选