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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;"><a href="http://www.sciencemag.org/content/336/6078/159.summary" target="_blank">http://www.sciencemag.org/content/336/6078/159.summary</a><br>

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<a href="http://www.sciencemag.org/content/336/6078/159.full.pdf" target="_blank">http://www.sciencemag.org/content/336/6078/159.full.pdf</a><br>

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