Words are common, yet incomplete means of acknowledging a person's gratefulness, to people who had helped us. But still better ways are yet to be invented for expressing our sincere appreciation of the same. Our special vote of thanks to our colleagues. It gives us immense pleasure to recall the timely help, encouragement and discussion extended by them. We would like to say thanks to our friends for their advice and readiness to share their knowledge. This account would be incomplete without the mentioning of our family members, who have supported us during tough periods of our lives. They have provided moral support and encouragement whenever we needed. The successful completion of this work involves help from many people directly or indirectly. We thank them all. Last, but definitely not the least, we express our reverence to almighty for giving us the strength, confidence and moral boost for successful completion of this book.