  We investigate the concept of molecular-sized outward-swinging gate, which
allows for entropy decrease in an isolated system. The theoretical analysis,
the Monte Carlo simulation, and the direct solution of governing equations all
suggest that under the condition of local nonchaoticity, the probability of
particle crossing is asymmetric. It is demonstrated by an experiment on a
nanoporous membrane one-sidedly surface-grafted with bendable organic chains.
Remarkably, through the membrane, gas spontaneously and repeatedly flows from
the low-pressure side to the high-pressure side. While this phenomenon seems
counterintuitive, it is compatible with the principle of maximum entropy. The
locally nonchaotic gate interrupts the probability distribution of the local
microstates, and imposes additional constraints on the global microstates, so
that entropy reaches a nonequilibrium maximum. Such a mechanism is
fundamentally different from Maxwell's demon and Feynman's ratchet, and is
consistent with microscopic reversibility. It implies that useful work may be
produced in a cycle from a single thermal reservoir. A generalized form of the
second law of thermodynamics is proposed.
