Damped/dissipative collision

As, however, the frequency of exciton-phonon or exciton-impurity collisions, giving rise to the scattering of waves and dissipation, is small compared to the frequencies wp(k), then the expression (7.29) can also be used in the presence of damping, but the energies p(k) must be considered as complex... 

Restitution coefficient e decides the damping coefficient t) as shown in Eq. (5). As the value of e gets smaller, more euer dissipates when collision occurs. However, the restitution coefficient is not a material property it depends primarily on the size, shape, and impact velocities of the colliding bodies as pointed out by Mishra [9]. Tn Fig. 9., it seems that the collapse of a part of the bed, discussed briefly above, occurs higher up when e is high. 

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