  We investigate the global pulsation properties of DBV white dwarf models that
include both the double-layered envelope structure expected from time-dependent
diffusion calculations, as well as a non-uniform C/O core expected from prior
nuclear burning. We compare these models to otherwise identical models
containing a pure C core to determine whether the addition of core structure
leads to any significant improvement. Our double-layered envelope model fit to
GD 358 that includes an adjustable C/O core is significantly better than our
pure C core fit (7sigma improvement). We find a comparable improvement from
fits to a second DBV star, CBS 114, though the values of the derived parameters
may be more difficult to reconcile with stellar evolution theory. We find that
our models are systematically cooler by 1,900 K relative to the similar models
of Fontaine & Brassard (2002). Although a fit to their model reproduces the
mass and envelope structure almost exactly, we are unable to reproduce the
absolute quality of their fit to GD 358. Differences between the constitutive
physics employed by the two models may account for both the temperature offset
and the period residuals.
