When rain and melting snows flow over a city's streets, parking lots and sidewalks, that runoff picks up all kinds of pollutants residues of petroleum and pesticides, soaps and solvents, as well as pet and wildlife waste.

VOA: standard.2010.08.04

Molecules are produced here and they flow directly over, usually by diffusion, to the neighboring molecule.

这里产生的分子,通常是以扩散的方式,直接到达临近的分子

耶鲁公开课 - 生物医学工程探索课程节选