And since ultrasound travels in a tight line akin to laser light, the emergent tones are audible only in a narrow, cylindrical path from source to ear.

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For two centuries, America's free market has not only been the source of dazzling ideas and path-breaking products, it has also been the greatest force for prosperity the world has ever known.

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This unusually long potentiometer shaft allows the signal path between the audio source and the potentiometer to be kept very short, thus preventing possible interference of the signal.

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When one views a web page or Twitter post, what she actually reads is not the original material, but what her computer says the page or tweet is supposed to look like, after the data to form it is transmitted through many routers, servers, and other network devices along the path from the its original source.

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Because as those structures come down, YOU as your own source comes forward, and helps direct your path.

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"Hard to see a path for us without Iowa, " one source said.

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When the fight against al Qaeda and our efforts in Afghanistan needed new focus, Bob Gates helped us devise the strategy that has finally put al Qaeda on a path to defeat and ensures that Afghanistan never again becomes a source for attacks against our nation.

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