Next, I investigated whether a steady state of an ORN is stable against fluctuation. Prigogine has reported that a steady state of a nonequilibrium open system in which various flow processes in the near-equilibrium linear region are coupled with each other, where some of them are placed under constant thermodynamic forces, is stable against fluctuation because the entropy production rate of such a system takes a minimum in a steady state. Therefore, I calculated the entropy production rate  in an ORN. The  is expressed in the form of the product of the rate of flow and the thermodynamic force and can be expressed as 𝜎 = 𝜎 1 + 𝜎 2 (3)