Arun Majumdar, who has been one of the Department of Energy's most visible officials since becoming the first director of the Advanced Research Projects Agency-Energy three years ago, will leave the administration next month, the agency said today. It's the first leadership transition for ARPA-E, which Majumdar helped to build from the advice of a 2006 report by the National Academy of Sciences and the directions of the America COMPETES Act, a piece of research legislation that Congress passed in 2007.