def fuller_diffusivity(target, molecular_weight='pore.molecular_weight',
    molar_diffusion_volume='pore.molar_diffusion_volume', temperature=
    'pore.temperature', pressure='pore.pressure'):
    """
    Estimates the diffusion coeffient of both species in a binary gas
    mixture using the Fuller correlation

    Parameters
    ----------
    target : OpenPNM Mixture Object
        The object for which these values are being calculated.  This
        controls the length of the calculated array, and also provides
        access to other necessary thermofluid properties.
    molecular_weight : string
        Dictionary key containing the molecular weight of each species.  The
        default is 'pore.molecular_weight'
    molar_diffusion_volume : string
        Dictionary key containing the molar diffusion volume of each species.
        This is used by the Fuller correlation.  The default is
        'pore.molar_diffusion_volume'
    temperature : string
        Dictionary key contain the temperature of the mixture.  The default
        is 'pore.temperature'
    pressure : string
        Dictionary key contain the pressure of the mixture.  The default
        is 'pore.pressure'

    Returns
    -------
    Dij : dict containing ND-arrys
        The dict contains one array for each component, containing the
        diffusion coefficient of that component at each location.
    """
    species_A, species_B = target.components.values()
    T = target[temperature]
    P = target[pressure]
    MA = species_A[molecular_weight]
    MB = species_B[molecular_weight]
    vA = species_A[molar_diffusion_volume]
    vB = species_B[molar_diffusion_volume]
    MAB = 1000.0 * 2 * (1.0 / MA + 1.0 / MB) ** -1
    P = P * 1e-05
    value = 0.00143 * T ** 1.75 / (P * MAB ** 0.5 * (vA ** (1.0 / 3) + vB **
        (1.0 / 3)) ** 2) * 0.0001
    return value
