“…Under certain assumptions, these models can be described by stochastic differential equations, and results that include the existence and uniqueness of nonequilibirum steady states have been shown [3], as have exponential convergence and other statistical properties [16,17]; see also [1]. A second group consists of results for Hamiltonian models similar to those in [4], with additional assumptions or special features to make the problem more tractable (as noted earlier, Hamiltonian models are much harder), they include: [2,20], which prove ergodicity of the invariant measure assuming existence; [9], which proves existence and uniqueness for a model in which all energy exchanges are exclusively with 'thermostats' (or heat baths); and, [21], which treats a model with special geometry. A third group of results we know of consists of [10] and variants of this model [11,15].…”