Influence of slopes of sigmoid function on dynamic behaviors of the model, showing r_g with respect to r_s for C₃ = 10 (a) and C₃ = 20 (c), [(b) and (d)] frequency distribution diagrams, curves of frequency with respect to r_s and r_g for C₃ = 10 (e) 10 and C₃ = 20 (f). Other parameters remain the default values as listed in Table 1, and (g) effect factor K of the parameters r_s and r_g on generating limit cycle oscillation.