It is also pretty clear that for some after the foundation of the polis, there were no city walls.

而且很明显,在城邦建立起来之后的相当长的一段时间内,都没有城墙

耶鲁公开课 - 古希腊历史简介课程节选

So, municipal privileges-- walls were put up for a variety of reasons around towns. Plague, for example.

在那些有特权的地方,人们因为各种理由修建围墙,例如瘟疫

耶鲁公开课 - 欧洲文明课程节选

You're taking the air inside of the pump and you're compressing it. You're doing it so fast that there's not enough time for heat to come out of the gas that's inside the pump towards the walls of the pump.

你把空气吸进气筒里并且压缩它,你的动作很快以至于,没有足够的时间让热量,从气筒里面跑出来,传递到气筒壁上。

麻省理工公开课 - 热力学与动力学课程节选