* This research was sponsored under grant MSM-8552479.Space Center under contract NAS-9-17380 and by NSFThis researchw as sponsoredb y NASA under contractN AS-9-17380a nd NSF under grant MSM-8552479.W e are grateful for the computing resourcesm ade available by the Aeros-cience Branch of the NASA-Johnson SpaceC enter. We are also thankful to Dr. W. Goodrich of NASA-[!text type='JS']JS[!/text]C for his guidance and encouragement.D r. A.K.M.F. Hussain and Dr. R. Pollard of the University of Houston provided valuable comments;