def electrokinetic2(row):
    """
    notes:  1) zeta potentials are in mV. if in V, remove the 1e3
            2) relative dialectric is for water, if this is not true,
            make a column and change the function.
    references:
            (1) You-Im Chang and Hsun-Chih Chan.
            "Correlation equation for predicting filter coefficient under
            unfavorable deposition conditions".
            AIChE journal, 54(5):1235–1253, 2008.

            (2) Rajagopalan, R. & Kim, J. S.
            "Adsorption of brownian particles in the presence of potential
            barriers: effect of different modes of double-layer interaction".
            Journal of Colloid and Interface Science 83, 428–448 (1981).
    :param row:
    :return: 2nd electrokinetic parameter
    """

    zp = row.enm_zeta_potential / 1e3  # particle zeta potential
    zc = row.collector_zeta_potential / 1e3  # collector zeta potential
    numerator = 2 * (zp / zc)
    denominator = 1 + (zp / zc) ** 2
    return numerator / denominator