Partial regularity for doubly nonlinear parabolic systems of the first type

We study solutions ${\bf v}$ of the parabolic system of PDE $$\partial_t\left(D\psi({\bf v})\right)=\text{div}DF(D{\bf v}).$$ Here $\psi$ and $F$ are convex functions, and this is a model equation for more general doubly nonlinear evolutions that arise in the study of phase transitions in materials. We show that if ${\bf v}$ is a weak solution, then $D{\bf v}$ is locally H\"older continuous except for possibly on a lower dimensional subset of the domain of ${\bf v}$. Our proof is based on compactness properties of solutions, two integral identities and a fractional time derivative estimate for $D{\bf v}$.