"There's no single impulse, " he said.

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The delicate, single-seat Solar Impulse flies around 40 mph and can't go through clouds.

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The Kindle Store facilitates impulse subscriptions, locks readers to a single seller, and shuts competitors clean out of the process. (In this respect Amazon appears to have learned well the lessons of its sometime rival Apple and its market-dominating iTunes Store.) The larger-format Kindle Amazon will reportedly introduce this week only seems likely to accelerate that process.

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