We would like to thank Kathleen Pagliaro who believed in this project and helped us in every possible way to realize it. Also, we thank Christina E. Linda, our project editor, for her help and assistance. In addition, we thank Andromache Spanou for carefully reading drafts of the text and suggesting improvements and corrections. Also, we thank Athanasios Margaris and Basil K. Papadopoulos for reading parts of the book and making comments and suggestions.