par Brocas, Jean ;George, Claude
Référence Physica, 34, 4, page (515-524)
Publication Publié, 1967
Article révisé par les pairs
Résumé : We stress the differences that exist between the equilibrium semi-invariants and the analogous operators which have been recently introduced out of equilibrium. By an example, we show that these operators, in contrast with their equilibrium analogs, are not the sum of all irreducible Mayer graphs. They are now related to the Husimi operators introduced by Cohen who showed for a different case that the Husimi operators can play the same role out of equilibrium as the irreducible graphs in the equilibrium theory. We study also the relation between the semi-invariant operators and the Ωψ operator appearing in the kinetic equations derived by Prigogine and his coworkers. We show - up to the sixth order in the coupling parameter - that both formalisms give equivalent results for long times but, because of the operator character of Ωψ and the semi-invariants, no trivial relation seems to exist between the quantities involved in the two theories. Another consequence of the fact that semi-invariants are operators - their complicated asymptotic time dependence (0, t1, t2, ..) - is also studied for a simple case. © 1957.