It follows that every reversible adiabatic process is one of constant entropy, and may be described as isentropic.

可见可逆绝热过程都是熵不变的过程，可以把这种过程叫做等熵过程。

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Let's hang on for a little while longer to a set of conditions where we will maintain constant entropy, namely constant entropy and pressure.

我们先继续考虑，保持熵不变的情况，即保持熵和压强不变。

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The entropy density is constant ahead of the shock.

冲击波前方的熵密度是恒定的。

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Let's hang on for a little while longer to a set of conditions where we will maintain constant entropy, namely constant entropy and pressure.

我们先继续考虑,保持熵不变的情况，即保持熵和压强不变。

麻省理工公开课 - 热力学与动力学课程节选

Now, we can immediately see what du/dV at constant entropy is.

我们能够很容易看出,恒定熵的条件下du/dV的数值。

麻省理工公开课 - 热力学与动力学课程节选

In other words, the order of taking the derivatives with respect to pressure and temperature doesn't matter And what this will show is that dS/dp dS/dp at constant temperature, here we saw how entropy varies with volume, this is going to show us how it varies with pressure.

换句话说,对温度和压强的求导顺序无关紧要,结果会表明,恒定温度下的，对应我们上面看到的，熵如何随着体积变化，这个式子告诉我们，熵如何随着压强变化。

麻省理工公开课 - 热力学与动力学课程节选