function janela(url, larg, alt) {
            var w = larg //largura da janela
            var h = alt //altura da janela
            var u = url //url da página à ser aberta
            var winl = (screen.width - w) / 2;
            var wint = (screen.height - h) / 2;
            window.open(u, 'ampliar', 'width=' + w + ',height=' + h + ',top=' + wint + ',left=' + winl + ',toolbar=no,location=no,directories=no,status=no,menubar=no,resizeable=yes,scrollbars=yes')
        }