function AbrirPopUp(direccion,nombreventana,ancho,alto,barras) {
  posH = (screen.width - ancho)/2;
  posV = (screen.height - alto)/2;
  window.open(direccion,nombreventana,'scrollbars='+barras+',width='+ancho+',height='+alto+',left='+posH+',top='+posV);
}