function popup(url, largura, altura) {
    popupOpen = window.open(url,"popup","toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=no,resizable=no,copyhistory=no,width="+largura+",height="+altura+",left="+(window.screen.width-largura)/2+", top="+(window.screen.height-altura)/2);
    popupOpen.focus();
}