function PopupCentrata(pagina) {
   var w = 550;
   var h = 650;
   var l = Math.floor((screen.width-w)/2);
   var t = Math.floor((screen.height-h)/2);
      window.open(pagina, "popup", "scrollbars=yes, status=no, menubar=no, toolbar=no, width=" + w + ",height=" + h + ",top=" + t + ",left=" + l);
 }