def gamma(oxamide_fraction):
    """Ratio of specific heats vs. oxamide content model.

    Returns:
        gamma: Exhaust gas ratio of specific heats [units: dimensionless].
    """
    # oxamide_fraction = cas.fmax(oxamide_fraction, 0)

    coefs = [1.238, 0.216, -0.351]
    return coefs[0] + coefs[1] * oxamide_fraction + coefs[2] * oxamide_fraction ** 2