Systems whose potential energies consists of pieces that scale as  , together with pieces that scale as  , show no violent relaxation to Virial equilibrium, but may pulsate at considerable amplitude for ever. Despite this pulsation these systems form lattices when the non-pulsational energy is low, and these disintegrate as that energy is increased. The quasi specific heats show the expected halving as the solid' is gradually replaced by the gas of independent particles. The forms of the lattices are described here for   while they become hexagonal close packed for large N. In the larger N limit, a shell structure is formed. Their large N behaviour is analogous to a   polytropic gas with a quasi-gravity such that every element of fluid attracts every other in proportion to their separation. To cite this article: C. Pichon, D. Lynden-Bell, C. R. Physique 7 (2006).

Les systèmes dont lʼénergie potentielle est constituée dʼune composante en   et dʼune composante en   ne presentent pas de relaxation violente vers lʼéquilibre du viriel mais vont osciller fortement indéfiniment. En dépit de ces pulsations, de tels systèmes forment un réseau quand lʼénergie non oscillatoire reste faible, et se désintegrent si elle augmente. Leurs quasi chaleur spécifique est divisée par deux quand le gaz de particules indépendantes remplace la phase solide. La forme du crystal est décrite ici pour  . Dans la limite des grands N le réseau se stratifie en coquilles suivant un motif hexagonal compact. Pour citer cet article : C. Pichon, D. Lynden-Bell, C. R. Physique 7 (2006).