Mr Loh said in a statement that the hospital had put her on "maximum artificial ventilation support, optimal antibiotic doses as well as stimulants which maximise her body's capability to fight infections".

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Though it was intended as a temporary shelter, its amenities were impressive: some 600 above-ground doors from which someone can enter the underground city from, 15, 000 ventilation ducts to provide fresh air, as well as multiple wineries, cellars and a complex network of passages, tunnels, and corridors.

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Helsinki Airport, for example, has cut its carbon dioxide emissions by nearly 2, 500 tonnes compared to 2011, by making heating, ventilation and lighting more energy-efficient, as well as using electrically-operated vehicles.

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But the authors are persuasive that some things can be done just as well with less fuel or material: drip irrigation, for example, superwindows, innovative cooling and ventilation systems, integrated fish management, and economic incentives that reward efficiency rather than waste.

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