Neil Johnson, a University of Miami physicist, developed this mathematical formula to predict insurgent attacks in war zones. Courtesy of Neil Johnson hide caption

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A woman at the protest holds a photograph of missing male relatives. Isra' al Rubei'i/NPR hide caption

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The party of Shiite cleric Muqtada al-Sadr holds 40 out of 325 seats in Iraq's Parliament. Karim Kadim/AP hide caption

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Baghdad's traffic, choked by hundreds of checkpoints, slows to a crawl while security forces inspect vehicles for weapons and explosives. Lynsey Addario/National Geographic hide caption

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Iraqi demonstrators shout slogans during a weekly protest against corruption, unemployment and poor public services in the war-torn country at Baghdad's Tahrir Square on July 8. Mahmoud Othman, a Kurdish member of Parliament, says it's the Iraqi people who are losing out as a political stalemate continues. Ali al-Saadi/AFP/Getty Images hide caption

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Secretary of Defense Leon Panetta sits with Gen. Lloyd Austin, the top U.S. commander in Iraq, as they fly in a Black Hawk helicopter over Baghdad on Monday. Paul J. Richards/AP hide caption

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Air conditioners keep tents cool on a U.S. military base in Iraq. The tents have been treated with polyurethane foam to increase energy efficiency. Courtesy Steven Anderson hide caption

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Army Spc. Christopher B. Fishbeck of Buena Park, Calif., poses for a photo on a rooftop during his tour of duty in Iraq. Courtsey of Fishbeck's Family hide caption

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