var order_by;
function change_order(set_order_by)
{
  order_by = set_order_by;
  load_topic_list();
}

function load_topic_list()
{
  $("forum_topic_content").innerHTML = loadingImg();
  var url = webLink +'index/loadTopicList';
  var req = new Ajax.Request(url,{
      method: 'post',
      parameters: {order_by : order_by},
      onSuccess: function(response){
                 var json = response.responseText.evalJSON();
                 $("forum_topic_content").innerHTML = json.HTML;
      }
    }
   );
}