Acknowledgements
S.S. Zaharah gratefully acknowledges the Ministry of Higher
Education Malaysia and Universiti Putra Malaysia for financial support
under academic training scheme of Malaysia Public Higher
Education Institution and study leave during her PhD studies. We
are grateful to A/Prof Dr A.S. Khan and Prof. Dr H. Behboudian for
their critical comments on this manuscript. We acknowledge Mrs. S. Petersen and Mr. I. Iberahim for their technical support.