First of all, I would like to thank to my teacher Tiberiu Apostol who gave me the chance to finish my studies at the University of Trento, Italy. And of course, this wouldn't have been possible without his support during the 5 years spent back home, at the Polytechnic University of Bucharest.
Every thesis has it's supervisors, and in my case they were Paolo Baggio and Marco Ragazzi. These teachers from the University of Trento, Italy helped me with this project by giving me their suggestions and all the answers I needed.
The teachers Marco Baratieri, Maurizio Grisante and Elena Cristina Rada made my stay in Italy as pleasant as possible and helped me every time I was stuck with the project.
I would like to thank also to my parents and friends who wanted only the best for me. Thank you for all your help during the last 5 years and especially during the last 4 months.