1. Vibration and Acoustics Laboratories, Mechanical Engineering Dept., Virginia Polytechnic Institute & State University, Blacksburg, VA 24061-0238.; G.A. U.S., Mechanical Engineering Department, Universite de Sherbrooke, Sherbrooke (Quebec), Canada JIK 2R1
2. G.A. U.S., Mechanical Engineering Department, Universite de Sherbrooke, Sherbrooke (Quebec), Canada JIK 2R1
3. Vibration and Acoustics Laboratories, Mechanical Engineering Department, Virginia Polytechnic Institute & State University, Blacksburg, VA, 24061-0238