The Association of American Universities on Monday announced that it had invited Boston University to join its ranks. Membership in the AAU is highly sought by up-and-coming research universities. The last new members was the Georgia Institute of Technology, in 2010. Last year, the AAU lost two members, with Syracuse University leaving voluntarily and the University of Nebraska at Lincoln being kicked out. At that time, AAU leaders said that they didn't want the organization to get too large, and that they wanted to periodically evaluate whether members met the criteria for membership. An AAU spokesman said that no institutions were asked to leave this year.