它们可以滑过使它们减速的涡流，然后通过“推开”涡流获得额外的推力。
They can glide past eddies that would slow them down and then gain extra thrust by "pushing off" the eddies.
它们甚至比以往的交通环道（如曼哈顿市区建于上世纪的哥伦布环道）更加高效和安全（现代设计包括使靠近环形路的车辆减速的系统，以及禁止行人进入环形的中心区域）。
(Modern designs include mechanisms for slowing traffic down as it nears the roundabouts, for example, and do not allow pedestrians onto the centre of the circle).
减速使新介质获得不同的折射率。
The deceleration gives the new medium a different refractive index.
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