First of all, I want to thank Mr. Wang. Teacher Wang has given me a lot of help in my study and life, from the beginning of the thesis to the end and polishing of the thesis, all of which are soaked with the teacher's great efforts. Teacher Wang's profound knowledge, rigorous academic attitude and innovative scientific research attitude infected me and made me learn the thinking method of analyzing and solving problems. Teacher Wang gave me the enlightenment of life, which made me learn a lot about how to behave. What's more, Mr. Wang's diligent working attitude and approachable attitude towards life are also worthy of my lifelong study. Once again, I would like to express my heartfelt thanks to Mr. Wang! Finally, I would like to thank my classmates and all my friends for their concern and support.