[ Diff(x[1], t) = (1*k[9]*k[1]*(1 + piecewise(And(t > 10, t < 150), 13/5, 0) + k[5]*(x[2]/k[6])^4/(1 + (x[2]/k[6])^4)) + (-1)*k[9]*k[2]*x[1]*k[8])/k[9],
  Diff(x[2], t) = (1*k[9]*k[3]*x[1]*k[8] + (-1)*k[9]*k[4]*x[2]*k[8])/k[9] ]