Going through this three years journey would not have been possible without the help and support of friends and colleagues on both sides of the Mediterranean. A special thank goes to Yang, Julie, Baisi, Henri, Fanny who kindly accepted me in their office and with whom I share a good meal and a good laugh. All my gratitude goes to Ramla, Manel, Manel, Maissa, Ryma, Abir, Fattoum who made me feel at home when missing Tunisia and for their good friendship inside and outside the University. Life would not have been possible without the support of my family, my sisters Fatma, Amina, Hanen, my brother Mohamed, my nephews Abdou, Doudi and Maymou who bring me much joy and happiness in my life. Finally, I would like to dedicate this thesis to my parents Wassila and Abdelkarim for their love, confidence, parayers and support throughout my studies and life.