然而，当在实验室的恒定条件下观察硅藻时，它们仍然表现出周期性的行为，继续按计划挖掘几个星期。

However, when diatoms are observed under constant conditions in a laboratory, they still display periodic behavior, continuing to burrow on schedule for several weeks.

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但是，在这些条件下，这些物理量，如果我们考察自由能的变化,例如在恒定的温度和压强下，我们仍然可以计算。

Whereas under these conditions, these quantities, if you look at free energy change, for example at constant temperature and pressure, H you can still calculate H.

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而它们中的一些保持恒定不变，因变量按某种自然的方式变化，从而维持约束条件。

Some of them are held fixed, and then some dependent variable does whatever it must so that the constraint keeps holding.

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Now, you know with constant volume, H now it's not going to be delta H that's U straightforward to measure, it's going to be dealt u, all right.

好，现在你们知道在体积恒定的条件下，我们得到的不是Δ,我们直接测量到的是Δ,好，但这基本上也是一样的。

麻省理工公开课 - 热力学与动力学课程节选

You just change volume to pressure and basically you're looking at enthalpy under a constant -- anything that's done at a constant volume path with energy, there's the same thing happening under constant pressure path for enthalpy.

可以看到这就是把体积换成了压强,一般我们都是在一种恒定状态下,考虑焓的，任何在恒容条件下,能伴随能量变化的东西，也在恒压条件下伴随焓同样地变化,所以你可以经常。

麻省理工公开课 - 热力学与动力学课程节选

There's our condition for equilibrium at constant temperature and pressure.

这就是我们在,恒定温度和压强下的平衡条件。

麻省理工公开课 - 热力学与动力学课程节选