[ Diff(x[1], t) = (-x[1]) + k[4]*x[2]^2/(k[3]^2 + x[2]^2), Diff(x[2], t) = (-k[5])*x[2] + 1/(1 + x[1]^2)*(k[1] + (k[7] + (k[8] - k[7])*t^2/(k[6]^2 + t^2))*x[2]^2/(1 + x[2]^2)) ]