function obrir(url) {
	LeftPosition = (screen.width) ? (screen.width - 790) / 2 : 0;
	TopPosition = (screen.height) ? (screen.height - 580) / 2 : 0;
	window.open (url,'','width=790,height=580,scrollbars=yes,statusbar=no,toolbar=no,mainbar=no,left='+LeftPosition+',top='+TopPosition+'');
}