Maxwell's demon is the little guy who opens an atomic door to a container to let atoms fly in, but shuts it before an atom flies out, thus increasing the internal pressure. Suppose the walls of a container had several small cone-shaped holes built into it. The inside hole might be pretty small, maybe 1->several atom's widths and it would taper outward so that the outside wall's opening was larger. The slope/incline of the cone would be whatever works best for my example. It would be more likely for an atom to enter the larger outside hole than exit through the smaller inside one. If atoms that entered the cone were likely enough to continue through the inner hole instead of eventually deflecting back out the way they came, it might be possible to build up internal pressure. What do you think?