Thank you very much for your answer, but I would simulate something like this http://www.google.com.mx/imgres?imgurl=http://esdocs.org/pars_docs/refs/55/54876/54876_html_29ed05e5.jpg&imgrefurl=http://esdocs.org/docs/index-54876.html?page%3D3&h=360&w=664&tbnid=SDzOGl3fofR7DM:&zoom=1&docid=ee-xhb93OWVPeM&ei=4g8kVa7pPMSjgwSpi4S4Bw&tbm=isch&ved=0CG8QMyg7MDs