I would like to express my gratitude to my wonderful friends in Groningen. In particular, I want to thank Lennart Stangenberg, my paranymph, lunchmate and former officemate. Finding someone who shares so many of my interests is fantastic. I enjoy all our lunch talks about sports, culture, current affairs and environmental issues. I also value all the help he has offered me in my daily life. I am thankful to Dr. Meng Han and Ziwei Rao for your continuing inspiration and encouragement. I also want to thank other former and current officemates, Jhordano