“…Such a function, that hereafter will be denoted as shape function, has to satisfy the following property (2) Ω w xs (y)dy = m and has units µg/µm 2 . Obviously, cell activation, and the relative switch between the two mathematical descriptive instances, is possible only if there is a sufficient amount of mass over the support I xs of w xs , i.e., if ρ(t, y) ≥ w xs (y), ∀ y at time t. If this condition is satisfied, the updated cell density is given by (3) ρ(t, y) = ρ(t, y) − w xs (y) ∀ y ∈ Ω, whereas, as already explained, at the same time t, a localized material point "appears" in x s , giving rise to a hybrid description of the system. In this respect, we remark that the activated cell takes places in the barycenter of the shape function and carries the same amount of mass.…”