Approved:

Acknowledgements I am most grateful to my advisor, Professor Benjamin Goldberg, not only for his guiding me through the doctoral study but also for his continued support in various aspects. His deep involvement have been invaluable during the preparation of this thesis. I would like to thank Professor Edmond Schonberg and Professor Anindya Banerjee for being on my thesis committee. Their comments are precious and very helpful for this thesis. I appreciate Professor Robert Paige for showing me some important work in this area. I would like to thank Professor Malcolm Harrison of NYU GriÆn Project, and Professor Ajit Kambil of NYU EDGAR Project. Their leadership of the research projects made it very pleasant to work with them. Much of the motivation of this dissertation came from the experience of working in both projects. I would like to thank my oÆcemate Madhu Nayakkankuppam. The talks an