Those are low density, so they are very permeable to oxygen.

VOA: special.2011.02.01

So, for example, we have this average level, and then it can go high where we have the peak, or it can go very low. We can also discuss sound waves, so again it's just the periodic variation of some property -- in this case we're talking about density, so we have high density areas and low density areas.

例如这是平均位置，在峰的位置水位高，在谷水位低，我们也可以,讨论声波它也是某种,量的周期变化，在这里我们,讨论的是密度,我们有高密度区和低密度区。

麻省理工公开课 - 化学原理课程节选

You've probably seen agar plates, if you smear a solution that's contaminated with bacteria on it, then that bacteria will grow on this agar rich medium and you'll get many, many copies of the bacteria that you've smeared at low density onto the plate.

你们大概见过琼脂培养基,如果将有细菌的溶液涂抹在培养基上,细菌就会在富含琼脂的培养基上生长,你会得到许多许多细菌,即使你只涂抹了低浓度溶液

耶鲁公开课 - 生物医学工程探索课程节选

You can see down here its affect on cholesterol levels: that the bad fats raise the LDL levels, the low-density lipoproteins levels, that's not good for you.

在下面你可以看到它对胆固醇含量的影响,坏脂肪会提高LDL含量,低密度脂蛋白含量,这是对身体不好的

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选

There are different kinds of cholesterol, and the first cut that people made at this were saying that there are things called HDL and LDL, which is high-density lipoproteins and low-density lipoproteins, the LDL.

胆固醇分为许多种,人们分离胆固醇时,最早得到的馏分是HDL和LDL,HDL即高密度脂蛋白,LDL即低密度脂蛋白

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选