(Indeed, we may look at this expression is as at the difference between the total energy flow density, \(\mathbf{j}_{\varepsilon} = \int \varepsilon \mathbf{v}wd^3p\), and the product of the average e...(Indeed, we may look at this expression is as at the difference between the total energy flow density, \(\mathbf{j}_{\varepsilon} = \int \varepsilon \mathbf{v}wd^3p\), and the product of the average energy needed to add a particle to the system \((\mu )\) by the particle flow density, \(\mathbf{j}_n = \int \mathbf{v}wd^3p \equiv \mathbf{j}/q\).) 64 Again, at equilibrium \((w = w_0)\) the heat flow vanishes, so that \(w\) in Equation (\ref{104}) may be replaced with its perturbation \(\tilde{w}\…