A national college fraternity has revoked the charter of the chapter at the University of Nevada, Reno, where an 18-year-old pledge died following a fall down a stairway in October. Lexington Kentucky based Sigma Nu, announced the action against its chapter at UNR this week. The campus student conduct office last month suspended Sigma Nu’s Chapter for 15 years for violating the school’s alcohol policy and conduct codes, after an investigation of allegations of marijuana use and topless dancers at a pledging event. School police declined to press criminal charges.