1. Postdoctoral Res. Assoc., School of Aerosp. and Mech. Engrg., Univ. of Oklahoma, 865 Asp Ave., Rm. 212, Norman, OK 73019-1052. E-mail: huanzeng@hotmail.com
2. Perkinson Chair, School of Aerosp. and Mech. Engrg., Univ. of Oklahoma, 865 Asp Ave., Rm. 212, Norman, OK 73019-1052. E-mail: cbert@ou.edu