BRIEF-Citigroup expects "improved revenue" in rest of 2014

July 14 (Reuters) - Citigroup Inc chief executive officer Michael Corbat and chief financial officer John Gerspach said on a Monday conference call with analysts: * Corbat: expect "improved revenue" in second half of 2014 * Gerspach: expect net interest margin to stay level through rest of year * Corbat: continue to believe capital plan rejection was not over business model * Corbat and Gerspach: we're still confident we will meet 2015 efficiency target * Corbat and Gerspach: efficiency tar