\begin{acknowledgements}
\addchaptertocentry{\acknowledgementname} % Add the acknowledgements to the table of contents

\begin{center}
\begin{quotation}
~~~~~~~``A timely benefit, -though thing of little worth,\\
~~~~~~~The gift itself, -in excellence transcends the earth.''\\
~~~~~~~~~~~~~~~~~~~~~~\medskip ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~- Thirukkural (102)
\end{quotation}
\end{center}
It has been an incredible journey that brought me to the completion of this dissertation. I am deeply indebted to everyone who shared an important path in my journey to this point. It is their support and inspiration that made this adventure both pleasant and fruitful.

First and foremost, I thank my research supervisor Prof. M. Daniel for giving freedom, guidance and support. I admire the way he approaches the research problem from both physical and mathematical point of view. Also, I am amazed about his planning, punctuality, positive attitude and patiently correcting and offering suggestions on anything, whether it is a letter or manuscript or thesis (including this one!). Throughout the years, I have learned a lot from him on both professional and personal level. Thank You Sir!

I am forever thankful to my collaborator and my senior Dr. P. Sabareesan, Assistant Professor, SASTRA University, Thanjavur for being with me throughout my research work. I extend my thanks for his moral support, enthusiastic words, guidance and advice filled with care. Thank You Anna!

It is a great pleasure to thank my co-guide Dr. M. Senthilvelan, Assistant Professor, Centre for Nonlinear Dynamics, Bharathidasan University for his constant support and advice. I wonder about his obsession with Mathematics.

I am very much thankful to my doctoral committee member Prof. K. Thamilmaran, Head, Centre for Nonlinear Dynamics, Bharathidasan University for periodically appraising the progress of my research work. I extend my thanks for his continuous help, support and kind words. 

Also, I am happy to thank the other doctoral committee member Prof. S. Rajasekar, Head \& Chair, School of Physics, Bharathidasan University for periodically monitoring the progress of my research work and asking critical and interesting questions which challenges me to dig deeper.

I am grateful to Prof. M. Lakshmanan, Professor of Eminence \& NASI Senior Scientist, Centre for Nonlinear Dynamics, Bharathidasan University for his support, encouragement and insightful questions that motivated me to learn more.

It is my great pleasure to thank Prof. S. Dhanuskodi, Prof. S. Arumugam, Prof. K. Jeganathan, Dr.~P.~Muruganandam, Dr.
R. Ramesh Babu, Dr. T. C. Sabari Girisun and Dr. L.C.~Nehru, Faculty Members, School of Physics, Bharathidasan University for their support, questions and comments during the doctoral research committee meetings and the departmental seminars.

I extend my thanks to Dr. B. Jeyapragash and Dr. M. Surulinathi, Faculty Members, Department of Library
and Information Science, Bharathidasan University for their help, support and constant encouragement.

I thank my research group members Dr. M. Vanitha, Dr. A. Arul Gnanam, Mr.~R.~Arun, Mr. D. Giridharan and Mr. K. Prabakaran for the fruitful discussions and their help \& support.

My special thanks to my friend Mr. P. A. Praveen, Research Scholar, School of Physics, Bharathidasan University for illustrations of our models in this thesis and for many interesting discussions on a wide range of topics ranging from latex to latest literature books. 

I express my sincere thanks to Dr. R. Jothimurugan and Mr. K. Suresh for their assistance in numerical programming \& computer, Mr. S. Stalin for his help in analytical calculations, and Mr. N. Ananth and Mr.~T.~Sriraman for their technical support. Apart from the academic support, each one helped me in many ways and gave their continuous support and encouragement. I extend my thanks to Ms.~R.~Parameshwari for her help in the procedure of INSPIRE Fellowship procedure from scratch till end and her encouraging words.

I am grateful in acknowledging the Department of Science and Technology (DST), Govt. of India for the financial support in the form of DST-INSPIRE Fellowship. It is one of the motivating factors to join for Ph.D.

I extend my thanks to the organizers of 2016 - Joint MMM-Intermag Conference held at the Hilton San Diego Bayfront Hotel in
San Diego, California, United States for providing a Student Travel Grant for participating in the Conference.

I wish to thank the University Library and University Informatics Centre authorities for providing the wonderful learning facilities.

I express my thanks to Mrs. S. Sumathi and all the non-teaching staff members of the School of Physics and Administrative Office, Bharathidasan University for their support in the administrative process.

I thank the Management of Dr. SNS Rajalakshmi College of Arts and Science (Autonomous), Coimbatore for providing facilities during the writing of my thesis.

My friends and classmates have been a continuous fountain of support and companionship. I thank Mr. K. Manikandan, Mr.~M.~Vadivel, Dr.~S.~Sadhasivam, Mr. S. Raja, Mr.~M.~Gopalakrishnan, Mr. S. Sabarathinam and Mr. C. Murugesan for their care, help, support and being with me throughout the period of my Ph.D. Work.

I wish to thank my fellow scholars in our department, Dr. Ajey Kumar Tiwari, Dr. S. P. Prabakaran, Dr. R. Mohandoss, Dr. D. Mohan Radheep, Dr. S. Esakkimuthu, Dr. M. Kanagaraj, Dr. R. Suresh, Dr. V. Chithika Ruby, Dr. R. Durga Devi, Dr. P. S. Swathy, Dr. U. Devarajan, Mr. B. Subash, Mr. R. Gopal, Ms. S. Amreetha, Ms. P. Rajeshwari, Sr. Nisha Francis, Mr. K. Karthik, Mr. P. Senthilkumar, Mr. K. Manikandan, Mr. M. Manikandan, Mrs. P. V. Bhuvaneswari, Mrs. T. Indira Gandhi, Mr. M. Sukumar, Mr. P. Velusamy, Mr. K. Arjunan, Mr. P. Mega Varna Ezhilarasu, Mr. S. Leo Kingston, Mr. D. Premraj, Mrs. K. Abirami, Ms. S. Rajamani, Mrs. L. Mohanasubha, Ms. S. Karthiga, Ms. K. Premalatha, Ms. S. Bhuvaneswari, Mr. R. Ravishankar,  Mr. P. Justin Jesuraj, Mr. V. Rajiv, Mr. P. Dharmaraj, Mr. S. Gopalakrishnan, Mr. N. Anbarasan, Mr. K. Manikandan, Mr. C. Saravanan, Mr. C. Jeganathan, Mr. M. Saravanan, Ms. N. Priyadarshani and Mr. R. Bharthasaradhi for their support and making the period of my Ph.D. an enjoyable one. 

During my time at Bharathidasan University, I have had the opportunity to make a number of good friends, and I wish to thank them all for the many hours of fun, I had enjoyed with them. These people include Dr. V. Ramalingam, Mr. D. Chellapillai, Mr. R. Thiyagu, Mr. Abhishek Raj, Dr. S. Ananth, Mr. N. Annamalai, Mr. S. Anbalagan, Mr. D. Mahamuni, Mr. A.Murugadas, Mr. B. S. Karthikeyan, Mr. A. William James, Mr. R. Vijayakumar, Mr. K. Varunkumar, Mr. S. Sampathkumar, Dr. C. Sivaprakasam, Mr. R. Ramachandran and Dr. C. R. G. Siva.

Also, I thank my friends Mr. E. Siva, Dr.~C.~Jeevarathinam, Mr.~S.~Udhayakumar, Ms. A. Bhuvaneshwari, Ms. S. Mathuri, Mrs. G. Ponmalar, Mr. G. Kalaiselvan, Mr. J. B. Sudharshan, Mr. P. Sakthivinayagam, Mr. D. Felix Irudhayaraj, Mr. S. Senthilkumar, Mr. R. Rajeshwaran, Mr. H. Bhoomeeswaran,  Ms. R. Sangeetha Devi and  Ms. S. Latha for their support and encouragement.

I am deeply grateful to my wonderful roommates Mr. J. Sivakumar, Mr. T. Mathimani, Mr. K. Boopathi, Mr. R. G.
Bharadvaj, Dr. M. Logeshwaran, Dr. M. Ayyanar, Mr.~S.~L.~Dinesh and Mr. S. Rakesh for making my hostel days pleasant and memorable one.

I thank Mr. N. Prakash and Mr. C. Puravi for their hospitality during my academic visits to Chennai and their kind help. I extend my thanks to Mr. P. Prabakaran for his help, support and continuous encouragement.

I am deeply indebted to my father Mr. P. Devarasu, my mother Mrs. D. Vijayalakshmi, my aunt Mrs. T. Logambal and my dear brothers Mr. D. Dineskumar \& Mr. P. Senthilkumar for their unconditional love, care, unfailing support and being with me throughout my journey. 

Finally, I thank the people of my village (Iluppaiyur) for their affection and support in all possible ways.

Over the years, I have learned an incredible amount from all of you. Thank You All!
\\[0.5cm]
\noindent{Tiruchirappalli}\\
\noindent{September 2016 \hfill \sc \bfseries D. Aravinthan}

\end{acknowledgements}
