1. a Department of Mechanical Engineering , University of Colorado , 427 UCB, Boulder, CO, 80309, USA
2. b Dipartimento di Ingegneria Aerospaziale e Meccanica , Seconda Universitá di Napoli , I 81031, Aversa, Italy
3. c Northwest Research Associates, Inc., CORA Division , 3380 Mitchell Lane, Boulder, CO, 80301, USA
4. d Department of Mathematics & Statistics , McMaster University , Hamilton, ON, L8S 4K1, Canada