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2 Acknowledgements I would like to acknowledge the guidance received from my thesis advi-sor Kedar Damle. I am deeply grateful to all my colleagues and teachers for their invaluable help. Finally, I would like to thank my family members and friends for their support and encouragement. 1 Declaration This thesis is a presentation of my original research work. Wherever contributions of others are involved, every effort is made to indicate this clearly, with due reference to the literature, and acknowledgement of col-laborative research and discussions. In my capacity as supervisor of the candidate's thesis, I certify that the above statements are true to the best of my knowledge.