最近一个周期中，M82的重力增强了M81周围密度波的脉动，导致M81的旋臂更浓密。

Last go-round, M82's gravity likely raised density waves rippling around M81, resulting in the richness of M81's spiral arms.

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由此产生的聚落地图显示，公元500年至公元850年，科潘古城崩溃时，城市周围农村人口的分布和密度发生了巨大变化。

The resulting settlement maps show how the distribution and density of the rural population around the city changed dramatically between AD 500 and 850, when copán collapsed.

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另一种理论是，板块下沉部分的密度大于周围较热的地幔，将板块的其余部分拉在后面。

An alternative theory is that the sinking part of the plate, which is denser than the hotter surrounding mantle, pulls the rest of the plate after it.

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And if we go ahead and square that, then what we get is a probability density, and specifically it's the probability of finding an electron in a certain small defined volume away from the nucleus.

我们得到的是，一个概率密度，它是，在核子周围，某个很小的,特定区域,找到电子的概率,所以它是概率密度。

麻省理工公开课 - 化学原理课程节选