Display of the non-zero Lyapunov exponent for different types of models. First, the non-zero Lyapunov exponent is given regarding the exponential law for the reductant input function r( t) with respect to the adjustable parameter α (top figure) and the logistic decay function with respect to the adjustable parameter κ (middle figure). The bottom figure depicts the non-zero Lyapunov exponent as function of the strength of Gaussian noise concerning the exponential law for the reductant input function by assuming α = 1.4, 2.6, and 3.4 (solid, dotted, and dashed lines, respectively).