[ Diff(x[1], t) = k[1]*x[1],
  Diff(x[2], t) = k[2]*x[2]^k[8],
  Diff(x[3], t) = k[3]*x[3]*(1 - x[3]/k[9]),
  Diff(x[4], t) = k[4]*x[4]/(x[4] + k[10]),
  Diff(x[5], t) = k[5]*x[5]/(x[5] + k[11])^(1/3),
  Diff(x[6], t) = k[6]*x[6]*ln(k[12]/(x[6] + k[14])),
  Diff(x[7], t) = k[7]*x[7]^(2/3) - k[13]*x[7] ]