Harnack不等式

在最高项系数无界的条件下讨论了二阶椭圆型微分方程弱解的局部极大值原理及Ｈａｒｎａｃｋ不等式．     

Nonlocal Harnack inequalities

We state and prove a general Harnack inequality for minimizers of nonlocal, possibly degenerate, integro-differential operators, whose model is the fractional p-Laplacian.     

Extended Harnack inequalities with exceptional sets and a boundary Harnack principle

Harnack’s inequality is one of the most fundamental inequalities for positive harmonic functions and has been extended to positive solutions of general elliptic equations and parabolic equations. This article gives a different generalization; namely, we generalize Harnack chains rather than equations. More precisely, we allow a small exceptional set and yet obtain a similar Harnack inequality. The size of an exceptional set is measured by capacity. The results are new even for classical harmonic functions. Our extended Harnack inequality includes information about the boundary behavior of positive harmonic functions. It yields a boundary Harnack principle for a very nasty domain whose boundary is given locally by the graph of a function with modulus of continuity worse than Hölder continuity.     

Remarks on differential Harnack inequalities

In this paper, we give a generalization of (global and local) differential Harnack inequalities for heat equations obtained by Li and Xu [J.F. Li, X.J. Xu, Differential Harnack inequalities on Riemannian manifolds I: linear heat equation, Adv. Math. 226 (5) (2011) 4456–4491] and Baudoin and Garofalo [F. Baudoin, N. Garofalo, Perelman’s entropy and doubling property on Riemannian manifolds, J. Geom. Anal. 21 (2011) 1119–1131]. From this we can derive new Harnack inequalities and new lower bounds for the associated heat kernel. Also we provide some new entropy formulas with monotonicity.     

Harnack estimate for the H~k-flow

We obtain the Harnack estimate of the solution to H~k-flow in Euclidean space R~(n 1),for k>0.By using this estimate,we get some corollaries about the translation soliton.     

Stability of parabolic Harnack inequalities

Let be a graph with weights for which a parabolic Harnack inequality holds with space-time scaling exponent . Suppose is another set of weights that are comparable to . We prove that this parabolic Harnack inequality also holds for with the weights . We also give stable necessary and sufficient conditions for this parabolic Harnack inequality to hold.

     

流形上的微分Harnack 估计

In the thesis, we study the differential Harnack estimate for the heat equation of the Hodge Laplacian deformation of (p, p)-forms on both fixed and evolving (by Kähler-Ricci flow) Kähler manifolds, which generalize the known differential Harnack estimates for (1, 1)-forms. On a Kähler manifold, we define a new curvature cone C_p and prove that the cone is invariant under Kähler-Ricci flow and that the cone ensures the preservation of the nonnegativity of the solutions to Hodge Laplacian heat equation. After identifying the curvature conditions, we prove the sharp differential Harnack estimates for the positive solution to the Hodge Laplacian heat equation. We also prove a nonlinear version coupled with the Kähler-Ricci flow after obtaining some interpolating matrix differential Harnack type estimates for curvature operators between Hamilton’s and Cao’s matrix Harnack estimates. Similarly, we define another new curvature cone, which is invariant under Ricci flow, and prove another interpolating matrix differential Harnack estimates for curvature operators on Riemannian manifolds.     

Harnack Inequalities for Jump Processes

We consider a class of pure jump Markov processes in R ^d whose jump kernels are comparable to those of symmetric stable processes. We establish a Harnack inequality for nonnegative functions that are harmonic with respect to these processes. We also establish regularity for the solutions to certain integral equations.     

Harnack inequalities for evolving hypersurfaces

This work was carried out while the author was supported by an Australian Postgraduate Research Award and an ANUTECH scholarship     

Zur Erinnerung an Axel Harnack

Ohne Zusammenfassung     

Dimension-Free Harnack Inequality and its Applications

This paper presents a self-contained account concerning a dimension-free Harnack inequality and its applications. This new type of inequality not only implies heat kernel bounds as the classical Li-Yau’s Harnack inequality did, but also provides a direct way to describe various dimension-free properties of finite and infinite-dimensional diffusion semigroups. The author starts with a standard weighted Laplace operator on a Riemannian manifold with curvature bounded from below, and then move further to the unbounded below curvature case and its infinite-dimensional settings.     

A Harnack inequality for Dirichlet eigenvalues

We prove a Harnack inequality for Dirichlet eigenfunctions of abelian homogeneous graphs and their convex subgraphs. We derive lower bounds for Dirichlet eigenvalues using the Harnack inequality. We also consider a randomization problem in connection with combinatorial games using Dirichlet eigenvalues. © 2000 John Wiley & Sons, Inc. J Graph Theory 34: 247–257, 2000     

Dimension-Independent Harnack Inequalities for Subordinated Semigroups

Dimension-independent Harnack inequalities are derived for a class of subordinate semigroups. In particular, for a diffusion satisfying the Bakry-Emery curvature condition, the subordinate semigroup with power α satisfies a dimension-free Harnack inequality provided \(\alpha \in \left(\frac{1}{2},1 \right)\), and it satisfies the log-Harnack inequality for all α?∈?(0, 1). Some infinite-dimensional examples are also presented.     

Degenerate parabolic equations and Harnack inequality

Sunto Viene risolto il problema di Cauchy Dirichlet relativo all'operatore parabolico degenere u/t–/x_i(a_ij(x, t) u/x_j), in opportune ipotesi di integrabilità per gli autovalori di a_ij(x, t). Vengono inoltre forniti controesempi circa l'impossibilità di risultati di regolarità per le soluzioni deboli mostrando in tal modo che operatori parabolici degeneri hanno un comportamento radicalmente differente da quello dei corrispondenti operatori ellittici degeneri.

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Both the authors were supported in part by a grant of the italian C.N.R.     

Harnack inequalities for Yamabe type equations

We give some a priori estimates of type sup×inf on Riemannian manifolds for Yamabe and prescribed curvature type equations. An application of those results is the uniqueness result for Δu+?u=uN−1 with ? small enough.     

Some Remarks on the Elliptic Harnack Inequality

Three short results are given concerning the elliptic Harnackinequality, in the context of random walks on graphs. The firstis that the elliptic Harnack inequality implies polynomial growthof the number of points in balls, and the second that the ellipticHarnack inequality is equivalent to an annulus-type Harnackinequality for Green's functions. The third result uses thelamplighter group to give a counter-example concerning the relationof coupling with the elliptic Harnack inequality. 2000 MathematicsSubject Classification 31B05 (primary), 60J35, 31C25 (secondary).     

Harnack estimate for a semilinear parabolic equation

We study the Cauchy problem of a semilinear parabolic equation. We construct an appropriate Harnack quantity and get a differential Harnack inequality. Using this inequality, we prove the finite-time blow-up of the positive solutions and recover a classical Harnack inequality. We also obtain a result of Liouville type for the elliptic equation.