Non-additive entropy: Reason and conclusions
  In this work the non-additive entropy is examined. It appears in isolated particle systems composed of few components. Therefore, the mixing of isolated particle systems S=S1+S2 has been studied. Two cases are considered T1=T2 and T1\leqT2, where T1,T2 are the initial temperatures of the system S1 and S2 respectively. The concept of similar systems containing interacting particles is introduced. These systems are defined by a common temperature and an identical time evolution process, i.e. the approach to the same thermodynamic equilibrium. The main results are: 1) The properties of the similar particle systems yield the non-additive entropy and free energy. The Gibbs Paradox is not a paradox. 2) The relation between the initial temperatures T1 and T2 governs the mixing process. 3) In the two cases T1=T2, T1\leqT2 mixing of the systems S1, S2 results in a uniform union system S=S1+S2. The systems S, S1, S2 are similar one to the other. 4) The mixing process is independent of the extensive quantities (volume, particle number, energy) and of the particle type. Only the mean energy plays an important role in the mixing of the systems S1, S2. 5) Mixing in the case T1\leqT2 is in essence a thermalization process, but mixing in the case T1=T2 is not a thermodynamic process. 6)Mixing is an irreversible process. Keywords: Entropy; Similar systems of interacting particles; Mixing of systems; Thermal equilibrium 
Miriam Lemanska
physics.gen-ph