  Experimental data from Maxwell's demon experiments on granular gas are
revisited. It is shown that the transition nature changes from critical to
sub-critical via a tri-critical point when frequency of vibration is increased
continuously. So (i) the transition is not hyper-critical as asserted
previously, but (ii) the fluctuations amplitude is spontaneously reinforced at
the tri-critical point compared to the one at other frequencies. So, (iii) this
analysis still contradicts a recent study which asserts that the bifurcation is
always critical, and that fluctuations shall depend on the number of grains
only. Beside, (iv) it is proposed a way to build an experiment, based on some
modification of the "Maxwell's demon in granular gas" set up, which undergoes a
hyper-critical bifurcation, with the use of some controlled feed-back of the
flows. This last idea can be generalised and used in other domains where
bifurcation theory applies, i.e. physics, chemistry, population dynamics,
economy, to improve regulation, but generating hyper- fluctuations. Finally it
is shown that the dynamical result is sensitive to the very-details of the
regulation.
