acknowledgements

　　mydeepestgratitudegoesfirstandforemosttoprofessoraaa,mysupervisor,,thisthesiscouldnothavereacheditspresentform.

　　second,iwouldliketoexpressmyheartfeltgratitudetoprofessoraaa,:professordddd,professorssss,whohaveinstructedandhelpedmealotinthepasttwoyears.