The value of the critical density is very small: it corresponds to roughly 6 hydrogen atoms per cubic meter, an astonishingly good vacuum by terrestrial standards!
临界密度的值非常小：它相当于每立方米约6个氢原子，从地球上的标准来看这简直是真空！
2
Up near the jet stream above New York, the wind power density can reach 16 kilowatts per square meter.
在纽约上空的射流层（对流层顶）附近，风能密度可达16千瓦每平方米。
3
The best ground-based sites have a wind-power density of about a kilometer per square meter of area swept.