Aspects of Sobolev-type inequalities (Q2759120)

The book provides a very nice illustration of various aspects of Sobolev type inequalities when considered over complete (non-compact) Riemannian manifolds that simply do not emerge in \(\mathbb{R}^n\).NEWLINENEWLINENEWLINEIn fact, as a start the author begins with a clear presentation of the familiar Sobolev inequalities in \(\mathbb{R}^n\), in a spirit that already ancitipates their (possible) extension to manifolds. This point of view is extended to the subsequent discussion on the role of Sobolev inequalities in Moser's iteration scheme when deriving Harnack's inequality for (positive) solutions of elliptic operators over \(\mathbb{R}^n\). NEWLINENEWLINENEWLINEThe author then returns to discuss Sobolev type inequalities over manifolds, their weak and/or equivalent forms and how they reveal geometrical properties to be satisfied by the underlying Riemannian manifold. Such a discussion motivates the introduction of `local' versions for such inequalities as to relax the requirements on the class of manifolds to be considered.NEWLINENEWLINENEWLINEBeside interesting other applications, the author concludes by discussing the impact of Sobolev inequalities on parabolic equations on manifolds. There, the validity of certain inequalities of Sobolev type is strictly related to the growth properties of the corresponding heath-kernel and (via Moser's scheme) on the validity of Harnack type inequalities.NEWLINENEWLINENEWLINEThe book is very well written and organized. It contains so many comments and explanations that both experts and non-experts on the subject may enjoy reading it.