WASHINGTON -- Post-9/11 security rules aimed at stopping terrorists from entering America are keeping artists, musicians and others out as well, renowned cellist Yo Yo Ma told a congressional committee Tuesday. With a growing number of foreign artists canceling their U.S. performances -- last week Britain's Halle Orchestra called off its American tour citing prohibitive visa fees and requirements -- Ma said America is in danger of losing meaningful cultural exchanges. "Bringing foreign musicians to this country and sending our performers to visit them is crucial," Ma, a U.S. citizen born in France to Chinese parents, told the House Government...