V. Kavitha,M. Mallika Arjunan ∗ C. Ravichandran 1 Department of Mathematics, Karunya University, Karunya Nagar,Coimbatore-641 114, Tamil Nadu, India Department of Mathematics, Karunya University, Karunya Nagar,Coimbatore641 114, Tamil Nadu, India Department of Mathematics, Karunya University, Karunya Nagar,Coimbatore641 114, Tamil Nadu, India (Received 27 Sepember 2011 , accepted 17 April 2012)