  An enhanced Fourier law (EFL) that accounts for quasi-ballistic phonon
transport effects in a formulation entirely in terms of physical observables,
is derived from the Boltzmann transport equation, assuming a gray population of
quasi-ballistic phonon modes. This equation is generalized to an arbitrary
phonon population. Other phonon transport models are analyzed in the context of
the generalized EFL and connections are made between the generalized EFL and
other models, revealing the essential unity of seemingly disparate models
reported in the literature.
