当介质的密度增加时（包含更多的原子），群速度就降低。

When the medium density increases (with more atoms), the slow group velocity decreases.

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科学家发现海马区——一个负责学习和记忆的区域——的灰质密度增加。

Scientists found increases in grey-matter density in the hippocampus—an area responsible for learning and memory.

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不过当涉及到群体的密度增加，运行变得混乱时，对于预测发生的变化往往不能奏效。

But it often fails to predict the changes that happen as a crowd's density increases and its movement becomes chaotic.

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The reason that there is increased electron density here is you can see that these two orbitals come together and constructively interfere.

你们可以看到两个轨道,靠在一起相长叠加,这就是为什么中间的电子态密度增加了。

麻省理工公开课 - 化学原理课程节选

It raises both LDL and HDL this can't be right.

低密度脂蛋白和高密度脂蛋白都增加了,这不对

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