function abrir_popup(theURL,w,h,sc) { 
 
    var winName=""; 
    anchop=window.screen.width; 
    altop=window.screen.height;

    var l=(anchop - w)/2; 
    var t=(altop - h)/2;
    
    var windowprops ="top=" + t + ",left= " + l + ",toolbar=no,location=no,status=no,menubar=no,scrollbars=" + sc + ",resizable=yes,width=" + w + ",height=" + h;

    var ventana=window.open(theURL,winName,windowprops);  
    ventana.focus();
   
}