Nina Uraltseva has made lasting contributions to mathematics with her pioneering work in various directions in analysis and PDEs and the development of elegant and sophisticated analytical techniques. She is most renowned for her early work on linear
and quasilinear equations of elliptic and parabolic type in collaboration with Olga Ladyzhenskaya, which is the category of classics, but her contributions to the other areas such as degenerate and geometric equations, variational inequalities, and free boundaries are equally deep and significant. In this article, we give an overview of Nina Uraltsevas work with some details on selected results.
We study a question arising in inverse scattering theory: given a penetrable obstacle, does there exist an incident wave that does not scatter? We show that every penetrable obstacle with real-analytic boundary admits such an incident wave. At zero f
requency, we use quadrature domains to show that there are also obstacles with inward cusps having this property. In the converse direction, under a nonvanishing condition for the incident wave, we show that there is a dichotomy for boundary points of any penetrable obstacle having this property: either the boundary is regular, or the complement of the obstacle has to be very thin near the point. These facts are proved by invoking results from the theory of free boundary problems.
Given a global 1-homogeneous minimizer $U_0$ to the Alt-Caffarelli energy functional, with $sing(F(U_0)) = {0}$, we provide a foliation of the half-space $R^{n} times [0,+infty)$ with dilations of graphs of global minimizers $underline U leq U_0 leq
bar U$ with analytic free boundaries at distance 1 from the origin.
In this paper we study the following parabolic system begin{equation*} Delta u -partial_t u =|u|^{q-1}u,chi_{{ |u|>0 }}, qquad u = (u^1, cdots , u^m) , end{equation*} with free boundary $partial {|u | >0}$. For $0leq q<1$, we prove optimal
growth rate for solutions $u $ to the above system near free boundary points, and show that in a uniform neighbourhood of any a priori well-behaved free boundary point the free boundary is $C^{1, alpha}$ in space directions and half-Lipschitz in the time direction.
We prove a boundary Harnack principle in Lipschitz domains with small constant for fully nonlinear and $p$-Laplace type equations with a right hand side, as well as for the Laplace equation on nontangentially accessible domains under extra conditions
. The approach is completely new and gives a systematic approach for proving similar results for a variety of equations and geometries.
The objective of this paper is twofold. First we provide the -- to the best knowledge of the authors -- first result on the behavior of the regular part of the free boundary of the obstacle problem close to singularities. We do this using our second
result which is the partial answer to a long standing conjecture and the first partial classification of global solutions of the obstacle problem with unbounded coincidence sets.
We introduce a new boundary Harnack principle in Lipschitz domains for equations with right hand side. Our approach, which uses comparisons and blow-ups, will adapt to more general domains as well as other types of operators. We prove the principle f
or divergence form elliptic equations with lower order terms including zero order terms. The inclusion of a zero order term appears to be new even in the absence of a right hand side.
This is an introduction to The Theme Issue on Free Boundary Problems and Related Topics, which consists of 14 survey/review articles on the topics, of Philosophical Transactions of the Royal Society A: Physical, Mathematical and Engineering Sciences, 373, no. 2050, The Royal Society, 2015.
