Acknowledgement

All my thanks is for our father in heaven for his eternal love to us. I would like to thank Eitan, my supervisor, for his many suggestions and constant support during this small research. I am also thankful for the two Lebanese of the team Ahmad and Sara for they have been a support to me, and they encourage me on the road of the research. My companion of the office, Urtzi, was my example in the manner he works. I thank him, because he was gentle and a man of peace. I thank Bala for he helped me in his knowledge, and he was present to listen to me. I thank Tania for she was always smiling, and present in the critical situations. Each day my first good morning was to Florence, I wish to here good days full of graces. It was a pleasure to me to meet Robin. I thank all the persons on the team and specially the chief Philippe, for he guides the team in an intelligent manner