1-d granular gas with little dissipation in 0-g : A comment on "Resonance oscillations in Granular gases"

It is demonstrated that recent results on 1d granular gas in a container with a vibrating piston, which was modelled by a shock wave propagation, can be understood with a modelling using ideas coming from the "thermodynamics of a single particle". Defining e as the square root of the energetic-restitution coefficient of a single collision, and N as the total number of grains, the mean loss during a round trip of the momentum is calculated in the limit N(1-e)<<1. It is also demonstrated that the system cannot propagate sound waves nor shock waves in the limit of N(1-e)<<1 and that hydrodynamics equations cannot be defined when N(1-e)<<1. Pacs # : 5.40 ; 45.70 ; 62.20 ; 83.70.Fn