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Twitter may be one of the world's fastest-growing social media tools, but the question of how the 140-character micro-blogging site could turn tweets into dollar signs has gone unanswered since its launch in 2006. Until now. The San Francisco-based company…

VOLCANIC ASH GROUNDS FLIGHTS | A giant cloud of ash from a glacial volcano in Iceland grounded hundreds of flights across northern Europe on Thursday. Jim Lehrer gets a report from Independent Television News about when air traffic might resume.

SENATE BRACES FOR FINANCIAL REFORM FIGHT | President Obama made a case for overhauling the nation's financial system today, in an attempt to win action on a Senate reform bill. For perspective on the prospects of a Senate bill, Jeffrey…

NUCLEAR SECURITY SUMMIT | Jeffrey Brown reports on the second day of the nuclear security summit in Washington, where President Obama called for new safeguards against nuclear terrorism. NEGOTIATING NUCLEAR ARMS REDUCTIONS | For perspective on the nuclear security summit…