Any device would also need to be packaged in a way that made it practical - on the scale of an ultrasound scanner, for example.

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Building on the craze for corporate jets--more than 550 are expected to be sold worldwide this year--manufacturers are busily exploring how to create a practical and affordable small-scale model that can let executives fly privately in excess of the sound barrier.

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As the world's largest democracy, India knows a great deal about large scale elections - and their practical difficulties.

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Raised by a family of successful farming entrepreneurs, Jose understands by way of practical experience how growing a business to scale has the power to transform families and communities.

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Fees are charged by the square foot and are on a sliding scale that takes into account the finish and any practical challenges, such as scaffolding, travel or tight work spaces (as, say, on a yacht).

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Touching on immigration in Europe, he said Britain would give "practical help and advice" to its neighbours in order to avoid a "full scale immigration crisis" and a "complete reversal" of the 1985 Schengen Agreement, which phased out border checks across the continent.

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Certainly, greenhouse gas emissions are not the only consideration to be borne in mind in choosing a particular biofuel, and there is the matter of production-costs and the feasibility of making the fuel on the large scale, if any significant substitution for petroleum-derived fuels is to prove practical.

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