Exponential Ordering for Neutral Functional Differential Equations With Non-Autonomous Linear D-Operator

We study neutral functional differential equations with stable linear non-autonomous $D$-operator. The operator of convolution $\widehat{D}$ transforms $BU$ into $BU$. We show that, if $D$ is stable, then $\widehat{D}$ is invertible and, besides, $\widehat{D}$ and ${\widehat{D}}^{-1}$ are uniformly continuous for the compact-open topology on bounded sets. We introduce a new transformed exponential order and, under convenient assumptions, we deduce the 1-covering property of minimal sets. These conclusions are applied to describe the amount of material in a class of compartmental systems extensively studied in the literature.