  In an effort to explore the differences between rare-earth-based and
uranium-based heavy Fermion (HF) compounds that reflect the underlying
difference between local 4$f$ moments and itinerant 5$f$ moments we analyze
scaling laws that relate the low temperature neutron spectra of the primary
("Kondo-esque") spin fluctuation to the specific heat and susceptibility. While
the scaling appears to work very well for the rare earth intermediate valence
compounds, for a number of key uranium compounds the scaling laws fail badly.
There are two main reasons for this failure. First, the presence of
antiferromagnetic (AF) fluctuations, which contribute significantly to the
specific heat, alters the scaling ratios. Second, the scaling laws require
knowledge of the high temperature moment degeneracy, which is often
undetermined for itinerant 5$f$ electrons. By making plausible corrections for
both effects, better scaling ratios are obtained for some uranium compounds. We
point out that while both the uranium HF compounds and the rare earth
intermediate valence (IV) compounds have spin fluctuation characteristic
energies of order 5 - 25 meV, they differ in that the AF fluctuations that are
usually seen in the U compounds are never seen in the rare earth IV compounds.
This suggests that the 5f itineracy increases the f-f exchange relative to the
rare earth case.
