Hi all, I am studyng the "ding-a-ling" model for the Heat transfer in a 1D chain. Particularly, from this article: http://polymer.chph.ras.ru/asavin/teplopr/mb97pre.pdf I need help with the equation (1), I don't know specifically what the "hard-point core" interaction means. I was thinking that is related to infinite barriers of potential but not sure. Also, I would like to get help with the equation (4), I was thinking that is related to equation (1) meaning that there is a collision whenever this condition is satisfied, and therefore the barrier of potential is infinite but I don't know, it's very weird that the collision is related to the size of lattice. Really, I would appreciate your help. Thanks in advance.