function open_popup(w, h, url, titolo, resizable, scrollbars)
{
		 var winl  = (screen.width - w) /2;
		 var wint  = (screen.height - h) /2;
		 winprops  = "width=" + w + ",height=" + h + ",top=" + wint + ",left=" + winl;
		 winprops += ",resizable=" + resizable + ",scrollbars=" + scrollbars ;

		 window.open(url, titolo, winprops);
}