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. 2008 Apr 30;3(4):e2052. doi: 10.1371/journal.pone.0002052

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This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.

This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration, which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.

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Top left: distribution of singular values. The first component accounts for 74.4% of variance. Top right: The first right singular vector (temporal component). Bottom: The most negative and most positive projections of specific words onto the first component. Most positive words are increasing in frequency; most negative words are decreasing.