function popup(address, window_name, sizex, sizey)
{
   var posx = (screen.width / 2) - (sizex / 2);
   var posy = (screen.height / 2) - (sizey / 2);
   void window.open(address, window_name , 'toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=yes,resizable=no,copyhistory=no,width=' + sizex + ',height=' + sizey + ',left=' + posx + ',top=' + posy);
}