The salt of the seawater draws the fresh water across the membrane, leading to a build-up of pressure which forces water through the turbine, generating electricity.

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He said there had been a build-up of pressure, which was relieved when some fluid was removed through a small opening in the skull.

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However, an inquest held into his death in February 2011 found that he died after his bowel burst due to a build-up of pressure in it - not because of any problems caused by a surgical instrument.

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Continued pressure requires continued build-up of military forces, but this clearly cannot go on for ever.

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"The nature of the bowling determines that if we can build up pressure on the two batsmen who are out there hopefully that can cause wickets to fall, " said Finn.

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Powered by a CO2 cartridge that can pretty much reach anywhere in the arena depending on how much pressure you allow to build up between launches (members of the squad told me they're not allowed to aim for the lights), it's basically a surface-to-air missile.

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And governments and companies will probably take advantage of any drop in the oil price to build up stocks, thereby putting upward pressure on the price.

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