// popup functions
function open_popup (ref, url, width, height, scroll, resizable) {
  window.open(url,
              ref,
              "menubar=no, " +
              "toolbar=no, " +
              "status=no, " +
              "location=no" + 
              ((width) ? (", width=" + width) : "") + 
              ((height) ? (", height=" + height) : "") +
              ((scroll) ? ", scrollbars=yes " : ", scrollbars=no") +
              ((resizable) ? ", resizable=yes " : ", resizable=no") 
             );
}