Gradient potential estimates for elliptic obstacle problems

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Abstract

In this paper, we consider the solutions of the non-homogeneous quasilinear elliptic obstacle problems involving measure data. At first we prove the existence of approximable solutions to these problems. Then we establish pointwise and oscillation estimates for the gradients of solutions via the nonlinear Wolff potentials, and these yield results on C1,α-regularity of solutions.

Section snippets

Introduction and main results

The obstacle problems discussed in this paper are related to the following quasilinear equation:div(a(|Du|)Du)=μinΩ where ΩRn,n2 is a bounded open set and μ is a Radon measure defined on Ω with finite total mass. Moreover we assume that μ(Rn\Ω)=0 and a:(0,)(0,)C1(0,) satisfies0ia=:inft>0ta(t)a(t)supt>0ta(t)a(t)=:sa<. The obstacle condition that we impose on the solution is of the form uψ a.e. on Ω, where ψW1,G(Ω)W2,1(Ω) is a given function with div[a(|Dψ|)Dψ]L1(Ω) and G is

Preliminaries

In this section, we introduce some notions and results which will be used in this paper. Firstly, we denote by m any number in the natural number set N, it is easily verified thatf(f)ΩL2(Ω)=mincRmfcL2(Ω) for any measurable set ΩRn and every function f:ΩRm such that fL2(Ω). If q[1,], we havef(f)ΩLq(Ω)2mincRmfcLq(Ω).

Definition 2.1

A Young function B is called an N-function if0<B(t)<+fort>0 andlimt+B(t)t=limt0tB(t)=+. The Young conjugate B of a Young function B is defined asB=sups

Existence result

In this section we shall prove the existence result for the obstacle problems with measure data. Let's start with the following lemma, which will be useful for Lemma 3.2.

Lemma 3.1

Let ΩR be a bounded domain. Assume that 2+ian, hT01,G(Ω) satisfiesΩ{|h|k}|Dh|2+iadxMk+M2+ia1+ia for k>0, and fixed constants M>0. Then we haveΩ|h|1+αdxc1M1+α1+ia,Ω|Dh|1+βdxc2M1+β1+ia, where 0<α<min{1,nia+2+ian2ia},0<β<min{1,nia+1n1},c1=c1(Ω,n,ia,α),c2=c2(Ω,n,ia,β).

Proof

We first assume that M=1, the inequality (3.1)

Comparison estimates

This section is devoted to compare the solutions of obstacle problems to the solutions of elliptic equations. Therefore we can obtain a similar excess decay estimate for solutions of obstacle problems with measure data.

Firstly, we shall prove the comparison estimate between the solutions of elliptic obstacle problems with measure data and the solutions of the corresponding homogeneous obstacle problems.

Lemma 4.1

Under the assumption (1.2), let B2R(x0)Ω,fL1(BR(x0))(W1,G(BR(x0))) and the map uW1,G(BR(

Gradient estimates by potentials

In this section, we first prove a pointwise estimate of fractional operator by precise iteration methods, and therefore allow to get L-bounds. We thus obtain pointwise and oscillation estimates for the gradients of solutions by means of the sharp maximal function estimates.

Proof of Theorem 1.7

We choose a geometric sequence Ri whose spread H>1 will be a certain function of the fixed quantities n,ia,sa, and will be determined later. More precisely we defineBi:=B(x,RHi)=B(x,Ri),fori=0,1,2,...,Aˆi:=RiαBi|Du(Du)Bi|

Acknowledgments

The authors are supported by the National Natural Science Foundation of China (NNSF Grant No.12071229 and No.11671414). The authors would like to express their gratitude to the anonymous reviewers for their constructive comments and suggestions that improved the last version of the manuscript.

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