Phase transition or Maxwell's demon in Granular gas?

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Dynamics of vibro-fluidised granular gas is investigated experimentally using the transfer of grains from a compartment through a horizontal slit at a given height h. It is demonstrated that the transfer rate j varies linearly with the grain number N in the box when N remains small; however j(N) becomes strongly non linear as soon as the number n of layers is larger than 0.3; dj/dN becomes negative for n>0.4.It is found also that the maximum of j(N) increases slightly with the acceleration af of the vibration which excites the granular gas. Using dynamical system theory, dynamics equations are written, and a critical bifurcation is found, which explains the existence of a condensation and of a phase transition. This explains how the pseudo " Maxwell's demon" works in granular gases. This experiments contradicts recent modeling. Pacs #: 5.40; 45.70; 62.20; 83.70.Fn