The main purpose of this book is to present some old and new results in this research field. This book can be divided into two parts. The first part is the first chapter, in which we briefly introduce some basic concepts and results. It can help readers quickly learn about some of the classic research results in this field, as well as understand their research motivation and background. The remaining chapters can be considered as the second part. In these chapters, we will introduce in detail our relevant research results in recent years, which may help readers understand the main research content and motivation in this field today.