[lemma=oxygen] □
[lemma=oxygen] [□]
[lemma=oxygen] □ □
A good example would be when NASA discovered that the crew would run out of oxygen and be overcome by carbon dioxide before they got back to earth . <br /> <br /> Like the human process of breathing in oxygen and exhaling carbon dioxide , Shewanella oneidensis has the ability to inhale certain metals and compounds , which may be toxic to humans , and exhale these metals in an altered , non-toxic state . Hydrogen is pumped through the stack , reacting with oxygen and picking up and removing water vapor on the way . They are used to fire the solid rocket hold-down posts , liquid oxygen and liquid hydrogen tail service mast and external tank vent arm system pyros at liftoff and the space shuttle main engine hydrogen gas burn system prior to engine ignition . Draeger et al ., using density-functional and quantum Monte Carlo calculations , have demonstrated that the optical gap is significantly reduced by the presence of oxygen and fluorine atoms on the surface . When a purge is initiated by opening the purge valves , the oxygen and hydrogen systems become open-loop systems ; and increased flows allow the reactants to circulate through the stack , pick up the contaminants and blow them out overboard through the purge lines and vents .