1. Asst. Prof., Dept. of Soil and Water Sci., P.O. Box 34, Al-Khod 123, Sultan Qaboos Univ., Sultanate of Oman. E-mail: anvar@squ.edu.om
2. Assoc. Prof., Inst. Math. Mech., Kazan Univ., Univ. Str., 17, Kazan, 420008, Russia. E-mail: Yurii.Obnosov@ksu.ru