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();
            }
        });