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RETRACTED ARTICLE: Levin’s type boundary behaviors for functions harmonic and admitting certain lower bounds
Boundary Value Problems volume 2015, Article number: 159 (2015)
Abstract
In this paper, we prove Levin’s type boundary behaviors for functions harmonic and admitting certain lower bounds, which extend Pan, Qiao and Deng’s inequalities for analytic functions in a half-space.
1 Introduction and results
Let R and \({\mathbf{R}}_{+}\) be the set of all real numbers and the set of all positive real numbers, respectively. We denote by \({\mathbf{R}}^{n}\) (\(n\geq2\)) the n-dimensional Euclidean space. A point in \({\mathbf{R}}^{n}\) is denoted by \(P=(X,x_{n})\), \(X=(x_{1},x_{2},\ldots,x_{n-1})\). The Euclidean distance between two points P and Q in \({\mathbf{R}}^{n}\) is denoted by \(|P-Q|\). Also \(|P-O|\) with the origin O of \({\mathbf{R}}^{n}\) is simply denoted by \(|P|\). The boundary and the closure of a set S in \({\mathbf{R}}^{n}\) are denoted by ∂S and S̅, respectively.
We introduce a system of spherical coordinates \((r,\Theta)\), \(\Theta=(\theta_{1},\theta_{2},\ldots,\theta_{n-1})\), in \({\mathbf{R}}^{n}\) which are related to Cartesian coordinates \((x_{1},x_{2},\ldots,x_{n-1},x_{n})\) by \(x_{n}=r\cos\theta_{1}\).
The unit sphere and the upper half-unit sphere in \({\mathbf{R}}^{n}\) are denoted by \({\mathbf{S}}^{n-1}\) and \({\mathbf{S}}^{n-1}_{+}\), respectively. For simplicity, a point \((1,\Theta)\) on \({\mathbf{S}}^{n-1}\) and the set \(\{\Theta; (1,\Theta)\in\Omega\}\) for a set Ω, \(\Omega\subset{\mathbf{S}}^{n-1}\), are often identified with Θ and Ω, respectively. For two sets \(\Xi\subset{\mathbf{R}}_{+}\) and \(\Omega\subset{\mathbf{S}}^{n-1}\), the set \(\{(r,\Theta)\in{\mathbf{R}}^{n}; r\in\Xi,(1,\Theta)\in\Omega\}\) in \({\mathbf{R}}^{n}\) is simply denoted by \(\Xi\times\Omega\). In particular, the half-space \({\mathbf{R}}_{+}\times{\mathbf{S}}^{n-1}_{+}=\{(X,x_{n})\in{\mathbf{R}}^{n}; x_{n}>0\}\) will be denoted by \({T}_{n}\).
For \(P\in{\mathbf{R}}^{n}\) and \(r>0\), let \(B(P,r)\) denote the open ball with center at P and radius r in \({\mathbf{R}}^{n}\). \(S_{r}=\partial{B(O,r)}\). By \(C_{n}(\Omega)\), we denote the set \({\mathbf{R}}_{+}\times\Omega\) in \({\mathbf{R}}^{n}\) with the domain Ω on \({\mathbf{S}}^{n-1}\). We call it a cone. Then \(T_{n}\) is a special cone obtained by putting \(\Omega={\mathbf{S}}^{n-1}_{+}\). We denote the sets \(I\times\Omega\) and \(I\times\partial{\Omega}\) with an interval on R by \(C_{n}(\Omega;I)\) and \(S_{n}(\Omega;I)\). By \(S_{n}(\Omega; r)\) we denote \(C_{n}(\Omega)\cap S_{r}\). By \(S_{n}(\Omega)\) we denote \(S_{n}(\Omega; (0,+\infty))\) which is \(\partial{C_{n}(\Omega)}-\{O\}\).
We use the standard notations \(u^{+}=\max\{u,0\}\) and \(u^{-}=-\min\{u,0\}\). Further, we denote by \(w_{n}\) the surface area \(2\pi^{n/2}\{\Gamma(n/2)\}^{-1}\) of \({\mathbf{S}}^{n-1}\), by \({\partial}/{\partial n_{Q}}\) the differentiation at Q along the inward normal into \(C_{n}(\Omega)\), by \(dS_{r}\) the \((n-1)\)-dimensional volume elements induced by the Euclidean metric on \(S_{r}\) and by dw the elements of the Euclidean volume in \({\mathbf{R}}^{n}\).
Let Ω be a domain on \({\mathbf{S}}^{n-1}\) with smooth boundary. Consider the Dirichlet problem
where \(\Lambda_{n}\) is the spherical part of the Laplace operator
We denote the least positive eigenvalue of this boundary value problem by λ and the normalized positive eigenfunction corresponding to λ by \(\varphi(\Theta)\),
In order to ensure the existence of λ and smooth \(\varphi(\Theta)\), we put a rather strong assumption on Ω: if \(n\geq3\), then Ω is a \(C^{2,\alpha}\)-domain (\(0<\alpha<1\)) on \({\mathbf{S}}^{n-1}\) surrounded by a finite number of mutually disjoint closed hypersurfaces for the definition of \(C^{2,\alpha}\)-domain. Then \(\varphi\in C^{2}(\overline{\Omega})\) and \({\partial\varphi}/{\partial n}>0\) on ∂Ω (here and below, \({\partial}/{\partial n}\) denotes differentiation along the interior normal).
We note that each function \(r^{\aleph^{\pm}}\varphi(\Theta)\) is harmonic in \(C_{n}(\Omega)\), belongs to the class \(C^{2}(C_{n}(\Omega )\backslash\{O\})\) and vanishes on \(S_{n}(\Omega)\), where
In the sequel, for the sake of brevity, we shall write χ instead of \(\aleph^{+}-\aleph^{-}\). If \(\Omega={\mathbf{S}}^{n-1}_{+}\), then \(\aleph^{+}=1\), \(\aleph^{-}=1-n\) and \(\varphi(\Theta)=(2n w_{n}^{-1})^{1/2}\cos\theta_{1}\).
Let \(G_{\Omega}(P,Q)\) (\(P=(r,\Theta), Q=(t,\Phi)\in C_{n}(\Omega)\)) be the Green function of \(C_{n}(\Omega)\). Then the ordinary Poisson kernel relative to \(C_{n}(\Omega)\) is defined by
where \(Q\in S_{n}(\Omega)\), \(c_{n}= 2\pi\) if \(n=2\) and \(c_{n}= (n-2)w_{n}\) if \(n\geq3\).
The estimate we deal with has a long history which can be traced back to Levin’s type boundary behaviors for functions harmonic from below (see, for example, Levin [1], p.209).
Theorem A
Let \(A_{1}\)be a constant, \(u(z)\) (\(|z|=R\)) be harmonic on \(T_{2}\)and continuous on \({\partial T}_{2}\). Suppose that
and
Then
where \(z=Re^{i\alpha}\in{T}_{2}\)and \(A_{2}\)is a constant independent of \(A_{1}\), R, αand the function \(u(z)\).
Recently, Pan et al. [2] considered Theorem A in the n-dimensional case and obtained the following result.
Theorem B
Let \(A_{3}\)be a constant, \(u(P)\) (\(|P|=R\)) be harmonic on \(T_{n}\)and continuous on \(\overline{T}_{n}\). If
and
then
where \(P\in T_{n}\)and \(A_{4}\)is a constant independent of \(A_{3}\), R, \(\theta_{1}\)and the function \(u(P)\).
Now we have the following.
Theorem 1
LetKbe a constant, \(u(P)\) (\(P=(R,\Theta)\)) be harmonic on \(C_{n}(\Omega)\)and continuous on ̅. If
and
then
where \(P\in C_{n}(\Omega)\), \(\rho(R)\)is nondecreasing in \([1,+\infty)\)andMis a constant independent ofK, R, \(\varphi(\theta)\)and the function \(u(P)\).
By taking \(\rho(R)\equiv\rho\), we obtain the following corollary, which generalizes Theorem B to the conical case.
Corollary
LetKbe a constant, \(u(P)\) (\(P=(R,\Theta)\)) be harmonic on \(C_{n}(\Omega)\)and continuous on ̅. If
and
then
where \(P\in C_{n}(\Omega)\), Mis a constant independent ofK, R, \(\varphi(\theta)\)and the function \(u(P)\).
Remark
(see [2])
From corollary, we know that conditions (1.1) and (1.2) may be replaced with weaker conditions
and
respectively.
2 Lemma
Throughout this paper, let M denote various constants independent of the variables in question, which may be different from line to line.
Lemma 1
for any \(P=(r,\Theta)\in C_{n}(\Omega)\)and any \(Q=(t,\Phi)\in S_{n}(\Omega)\)satisfying \(0<\frac{t}{r}\leq\frac{4}{5}\);
for any \(P=(r,\Theta)\in C_{n}(\Omega)\)and any \(Q=(t,\Phi)\in S_{n}(\Omega; (\frac{4}{5}r,\frac{5}{4}r))\).
Let \(G_{\Omega,R}(P,Q)\)be the Green function of \(C_{n}(\Omega,(0,R))\). Then
where \(P=(r,\Theta)\in C_{n}(\Omega)\)and \(Q=(R,\Phi)\in S_{n}(\Omega;R)\).
3 Proof of theorem
Applied Carleman’s formula (see [6–8]) to \(u=u^{+}-u^{-}\) gives
It immediately follows from (1.3) that
and
Notice that
Hence from (3.1), (3.2), (3.3) and (3.4) we have
and
And (3.6) gives
Thus
By the Riesz decomposition theorem (see [7]), for any \(P=(r,\Theta)\in C_{n}(\Omega;(0,R))\), we have
Now we distinguish three cases.
Case 1. \(P=(r,\Theta)\in C_{n}(\Omega;(\frac {5}{4},\infty))\) and \(R=\frac{5}{4}r\).
Since \(-u(x)\leq u^{-}(x)\), we obtain
from (3.8), where
Then from (2.1) and (3.7) we have
and
By (2.2), we consider the inequality
where
and
We first have
from (3.7). Next, we shall estimate \(I_{32}(P)\). Take a sufficiently small positive number k such that
for any \(P=(r,\Theta)\in\Pi(k)\), where
and divide \(C_{n}(\Omega)\) into two sets \(\Pi(k)\) and \(C_{n}(\Omega)-\Pi(k)\).
If \(P=(r,\Theta)\in C_{n}(\Omega)-\Pi(k)\), then there exists a positive \(k'\) such that \(|P-Q|\geq{k}'r\) for any \(Q\in S_{n}(\Omega)\), and hence
which is similar to the estimate of \(I_{31}(P)\).
We shall consider the case \(P=(r,\Theta)\in\Pi(k)\). Now put
where
Since
we have
where \(i(P)\) is a positive integer satisfying \(2^{i(P)-1}\delta(P)\leq\frac{r}{2}<2^{i(P)}\delta(P)\).
Since \(r\varphi(\Theta)\leq M\delta(P)\) (\(P=(r,\Theta)\in C_{n}(\Omega)\)), similar to the estimate of \(I_{31}(P)\) we obtain
for \(i=0,1,2,\ldots,i(P)\).
So
From (3.12), (3.13), (3.14) and (3.15) we see that
On the other hand, we have from (2.3) and (3.5) that
We thus obtain from (3.10), (3.11), (3.16) and (3.17) that
Case 2. \(P=(r,\Theta)\in C_{n}(\Omega;(\frac{4}{5},\frac{5}{4}])\) and \(R=\frac{5}{4}r\).
Equation (3.8) gives that \(-u(P)= I_{1}(P)+I_{5}(P)+I_{4}(P)\), where \(I_{1}(P)\) and \(I_{4}(P)\) are defined in Case 1 and
Similar to the estimate of \(I_{3}(P)\) in Case 1 we have
which together with (3.10) and (3.17) gives (3.18).
Case 3. \(P=(r,\Theta)\in C_{n}(\Omega;(0,\frac{4}{5}])\).
It is evident from (1.4) that we have \(-u\leq K\), which also gives (3.18).
From (3.18) we finally have
which is the conclusion of Theorem 1.
Change history
14 April 2020
A Correction to this paper has been published: https://doi.org/10.1186/s13661-020-01376-7
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Acknowledgements
This paper was written while the corresponding author was at the Department of Mathematics of the University of Ioannina, as a visiting professor.
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The authors read and approved the final manuscript.
The Editors-in-Chief have retracted this article because it significantly overlaps with a previously published article by Pang et al. The article also shows evidence of authorship manipulation. The identity of the corresponding author could not be verified; the University of Ioannina have confirmed that Mohamed Vetro has not been affiliated with their institution. The authors have not responded to correspondence regarding this retraction.
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Li, Z., Vetro, M. RETRACTED ARTICLE: Levin’s type boundary behaviors for functions harmonic and admitting certain lower bounds. Bound Value Probl 2015, 159 (2015). https://doi.org/10.1186/s13661-015-0421-6
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DOI: https://doi.org/10.1186/s13661-015-0421-6