var popupwin = null;
        function popup(loc) {
          var myspecs = "'menubar=0,status=1,resizable=1,location=0,titlebar=1,toolbar=0,scrollbars=1,width=500,height=450'";
          if (popupwin == null || popupwin.closed) {
            popupwin = window.open (loc, 'popupwin', myspecs);
          } else {
            popupwin.focus();
            popupwin.location.href = loc;
          }
        }