jQuery UI dialog 隐藏默认关闭按钮

 var O_dialog = $("#dialog-modal");
         O_dialog.dialog({
             closeOnEscape: false,
             width: 250,
             height: 80,
             resizable: false,
             draggable: false,
             modal: true,
             title: "正在加载，请稍候...",
             //隐藏默认的关闭按钮
             open: function (event, ui) {
                 $(".ui-dialog-titlebar-close", $(this).parent()).hide();
             }
         });