Radon is a natural radioactive gas that occurs at higher than normal levels in certain parts of the U.S..
氡是一种天然的放射性气体，在美国某些地区浓度高于平均水平。
If there is a bulk mixing of the layers of gas in the tube by mechanical stirring or because of a density gradient, mass transfer occurs primarily by the mechanism of forced or natural convection.
如果是受到机械式的搅拌或者是密度梯度发生了变化而使得管中有大量的分层的气体，那么传递就主要通过强制对流或自然对流而发生。
Leakage, a serious problem, often occurs in the exhausted underground natural gas storage built around the city during its running period, which results in less actual reserves than that of account.
利用城市附近枯竭气藏建立的用于调峰的地下储气库，在运行过程中常发生渗漏，导致地下储气库的实际存气量低于帐面上的存气量。
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