function openpopup(size_x, size_y, url)
{
	var def = "scrollbars=yes,toolbar=no,locationbar=no,menubar=no,personalbar=no,statusbar=no,width=" + size_x + ",height=" + size_y;
  
  popup_t = window.open(url , "blank", def);
	popup_t.moveTo(screen.width/2 - size_x/2, screen.height/2 - size_y/2);
}