\section*{Acknowledgments}
I would like to acknowledge the efforts and input of my supervisor, Prof.~XXX~YYY, and all my colleagues of the XXXX Lab (XLAB) who were of great help during my research. In particular my thanks go to XXX YYYYY, AAAAAA BBBBB and LLLLL DDDDDDD who collaborated on the main parts of my research work. I would like to thank also Dr.~XXXXX XXXXXX for his kind support and hospitality during my stay at XXXXXXX.