UC San Diego

We investigate the concept of locally nonchaotic barrier. They are analyzed theoretically and numerically. Inside the barrier, the particle-particle interaction is negligible and thus, the particle movement tends to be nonchaotic. Across the barrier, the distribution of particle number density may not reach thermodynamics equilibrium. Globally, the system steady state may be inherently nonequilibrium.

Two “toy models” are examined. The first model features an outside-swinging molecular-sized gate that interacts with gas particles one at a time; it can be viewed as an entropy barrier. The second model is an energy barrier, much narrower than the nominal particle mean free path. They are examined theoretically, numerically, and experimentally. The basic concept is compatible with the fundamental principle of maximum entropy, i.e., the most probable state is the one with the highest entropy. As additional constraints are imposed on local microstates, the probability density of global microstates is affected. Hence, entropy reaches a nonequilibrium maximum that is less than the equilibrium maximum. Such a mechanism is fundamentally different from Maxwell's demon or Feynman's ratchet.