def dr_hill_zero_background(x, theta, eta, kappa):
    """dr hill zero background
 
    Parameters
    ----------
    x: int
    theta: float
    eta: float
    kappa: float

    Returns
    -------
    float
        (theta* x**eta) / (kappa**eta + x**eta)
    """
    return (theta* x**eta) / (kappa**eta + x**eta)