Teresa Radice

Refinable functions, functionals, and iterated function systems

Invariant measures of iterated function systems and refinable functions are mathematical tools of vast usage, that, although usually considered in different contexts, are deeply linked. We outline these links, in particular with respect to existence and regularity of these objects.

Divergence forms of the

Ihe central theme rnnning through our investigation la the on-Laplacian operator in the plane. Upon multiplication by a suitable funetion we express it in divergence form, this allows os to speak of weak no-harmonir funetion jo 4/1,2 lo every no-harmonir function u we associate its conjogate funetion e. We focus our attention to Ihe first order Beltrami type equation for h u + iv.

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Abstract The present paper arose from recent studies of energy-minimal deformations of planar domains. We are concerned with the Dirichlet energy. In general the minimal mappings need not be homeomorphisms. In fact, a part of the domain near its boundary may collapse into the boundary of the target domain. In mathematical models of nonlinear elasticity this is interpreted as interpenetration of matter. We call such occurrence the Nitsche phenomenon, after Nitsche’s remarkable conjecture (now a theorem) about existence of harmonic homeomorphisms between annuli. Indeed the round annuli proved to be perfect choices to grasp the nuances of the problem. Several papers are devoted to a study of deformations of annuli. Because of rotational symmetry it seems likely that the Dirichlet energy-minimal deformations are radial maps. That is why we confine ourselves to radial minimal mappings. The novelty lies in the presence of a weight in the Dirichlet integral. We observe the Nitsche phenomenon in this case as well, see our main results Theorem 1.4 and Theorem 1.7. However, the arguments require further considerations and new ingredients. One must overcome the inherent difficulties arising from discontinuity of the weight. The Lagrange–Euler equation is unavailable, because the outer variation violates the principle of none interpenetration of matter. Inner variation, on the other hand, leads to an equation that involves the derivative of the weight. But our weight function is only measurable which is the main challenge of the present paper.