jQuery.easing.quart = function (x, t, b, c, d) {
    return -c * ((t=t/d-1)*t*t*t - 1) + b;
};  


$(function () {
    $('#link_pagetop').click(function () {
        $('html,body').animate({ scrollTop: 0 }, 600, 'quart');
    });
});