A categorical approach to integration.
Let be a standard probability space. We say that a sub-σ-algebra of decomposes μ in an ergodic way if any regular conditional probability with respect to andμ satisfies, for μ-almost every x∈X, . In this case the equality , gives us an integral decomposition in “-ergodic” components. For any sub-σ-algebra of , we denote by the smallest sub-σ-algebra of containing and the collection of all setsAin satisfyingμ(A)=0. We say that isμ-complete if . Let be a non-empty family...
We characterize the autonomous, divergence-free vector fields on the plane such that the Cauchy problem for the continuity equation admits a unique bounded solution (in the weak sense) for every bounded initial datum; the characterization is given in terms of a property of Sard type for the potential associated to . As a corollary we obtain uniqueness under the assumption that the curl of is a measure. This result can be extended to certain non-autonomous vector fields with bounded divergence....
Given two positive Daniell integrals I and J, with J absolutely continuous with respect to I, we find sufficient conditions in order to obtain an exact Radon-Nikodym derivative f of J with respect to I. The procedure of obtaining f is constructive.
We study some problems of optimal distribution of masses, and we show that they can be characterized by a suitable Monge-Kantorovich equation. In the case of scalar state functions, we show the equivalence with a mass transport problem, emphasizing its geometrical approach through geodesics. The case of elasticity, where the state function is vector valued, is also considered. In both cases some examples are presented.