Furthermore, equations (6) have a minus sign in front of \varvec{\nabla }_{\!\varvec{x}}\varphi while in (42) there is a plus sign; this flip in sign just reflects the change of charge in the gravitational attractive and electrically repulsive case. Finally, observe that equations (...
can reproduce increasing, decreasing or non-monotone and convex up or down dependences of lateral strain and Poisson's ratio on time and it can provide existence of minimum, maximum or inflection points and sign changes from minus to plus and vice versa and asymptotic stabilization at large ...
For anisotropic systems Poisson’s ratio changes with the direction of measurement and may take any value between minus and plus infinity [18]. A relatively recently discovered group of materials for which Poisson’s ratio takes negative values [19], the so-called auxetics [20], has become th...