Over the next week, Khan Academy will be adding other tutorials and materials to its computer science platform.

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Since its privatisation Vale, which the government often berates for not adding value to the raw materials it exports, has transformed itself from a medium-sized conglomerate to one of the world's biggest mining companies.

ECONOMIST: Brazil's presidential campaign

"They're linked together with all kinds of wires, " he said of the materials in the apartment, adding that, as someone who wasn't a bomb expert, it was unlike anything he had seen before.

WSJ: Shooting Suspect Built Arsenal by Mail Order, Police Say

China, of course, needs raw materials for its own value-adding industries: hence the fears of some Latin American trade unionists, and industrialists, that a closer relationship with the Chinese will simply help them to compete in the world market in manufactures.

ECONOMIST: China and Latin America

Other gases can be targeted by adding metal atoms to the tubes' walls or wrapping other materials around them.

BBC: MIT pencil 'draws' gas sensors onto paper

The 787 is made from light and strong composite materials that allow higher cabin pressure and humidity, adding to passengers' comfort.

ECONOMIST: Airbus��s jumbo-sized problem threatens the firm��s future