Volume 13, Issue 1, June 1988, Pages 49-61
Helmy El-Sayed Ibrahim Gad; H. A. El-Seddiek; Mahmoud Moustafa Ali Awad
Volume 12, Issue 1, June 1987, Pages 23-33
Helmy El-Sayed Ibrahim Gad; H. A. El-Seddiek; M. M. Awad