<p>We consider second order elliptic equations in divergence form <Equation ID="Equ47"> <MediaObject> <ImageObject Color="BlackWhite" FileRef="208_2025_3126_Article_Equ47.gif" Format="GIF" Height="48" Rendition="HTML" Resolution="72" Type="Linedraw" Width="327" /> </MediaObject> <EquationSource Format="TEX">\(\begin{aligned} \sum _{i=1}^{n}\frac{\partial }{\partial x_{i}}a^{i}\left( x,u,Du\right) =b\left( x,u,Du\right) ,\;\;\;\;\;x\in \Omega , \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <munderover> <mo>∑</mo> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>n</mi> </munderover> <mfrac> <mi>∂</mi> <mrow> <mi>∂</mi> <msub> <mi>x</mi> <mi>i</mi> </msub> </mrow> </mfrac> <msup> <mi>a</mi> <mi>i</mi> </msup> <mfenced close=")" open="("> <mi>x</mi> <mo>,</mo> <mi>u</mi> <mo>,</mo> <mi>D</mi> <mi>u</mi> </mfenced> <mo>=</mo> <mi>b</mi> <mfenced close=")" open="("> <mi>x</mi> <mo>,</mo> <mi>u</mi> <mo>,</mo> <mi>D</mi> <mi>u</mi> </mfenced> <mo>,</mo> <mspace width="0.277778em" /> <mspace width="0.277778em" /> <mspace width="0.277778em" /> <mspace width="0.277778em" /> <mspace width="0.277778em" /> <mi>x</mi> <mo>∈</mo> <mi mathvariant="normal">Ω</mi> <mo>,</mo> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>where <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="208_2025_3126_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="13" /> </InlineMediaObject> <EquationSource Format="TEX">\(\Omega \)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="normal">Ω</mi> </math></EquationSource> </InlineEquation> is a bounded open set in <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="208_2025_3126_Article_IEq2.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="20" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathbb {R}^{n}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mi mathvariant="double-struck">R</mi> </mrow> <mi>n</mi> </msup> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="208_2025_3126_Article_IEq3.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="74" /> </InlineMediaObject> <EquationSource Format="TEX">\(u:\Omega \rightarrow \mathbb {R}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>u</mi> <mo>:</mo> <mi mathvariant="normal">Ω</mi> <mo stretchy="false">→</mo> <mi mathvariant="double-struck">R</mi> </mrow> </math></EquationSource> </InlineEquation>. Our aim is to give conditions on the vector field <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="208_2025_3126_Article_IEq4.gif" Format="GIF" Height="25" Rendition="HTML" Resolution="72" Type="Linedraw" Width="252" /> </InlineMediaObject> <EquationSource Format="TEX">\( a\left( x,u,Du\right) =\left( a^{i}\left( x,u,Du\right) \right) _{i=1,\ldots ,n}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>a</mi> <mfenced close=")" open="("> <mi>x</mi> <mo>,</mo> <mi>u</mi> <mo>,</mo> <mi>D</mi> <mi>u</mi> </mfenced> <mo>=</mo> <msub> <mfenced close=")" open="("> <msup> <mi>a</mi> <mi>i</mi> </msup> <mfenced close=")" open="("> <mi>x</mi> <mo>,</mo> <mi>u</mi> <mo>,</mo> <mi>D</mi> <mi>u</mi> </mfenced> </mfenced> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mo>…</mo> <mo>,</mo> <mi>n</mi> </mrow> </msub> </mrow> </math></EquationSource> </InlineEquation> and on the right hand side <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="208_2025_3126_Article_IEq5.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="82" /> </InlineMediaObject> <EquationSource Format="TEX">\(b\left( x,u,Du\right) \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>b</mi> <mfenced close=")" open="("> <mi>x</mi> <mo>,</mo> <mi>u</mi> <mo>,</mo> <mi>D</mi> <mi>u</mi> </mfenced> </mrow> </math></EquationSource> </InlineEquation> in order to obtain the <i>global boundedness</i> in <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="208_2025_3126_Article_IEq6.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="13" /> </InlineMediaObject> <EquationSource Format="TEX">\(\overline{\Omega }\)</EquationSource> <EquationSource Format="MATHML"><math> <mover> <mi mathvariant="normal">Ω</mi> <mo>¯</mo> </mover> </math></EquationSource> </InlineEquation> of weak solutions <i>u</i> to the Dirichlet problem associated to the previous differential equation, when a boundary condition <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="208_2025_3126_Article_IEq7.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="121" /> </InlineMediaObject> <EquationSource Format="TEX">\(u=u_{0}\in L^{\infty }\left( \Omega \right) \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>u</mi> <mo>=</mo> <msub> <mi>u</mi> <mn>0</mn> </msub> <mo>∈</mo> <msup> <mi>L</mi> <mi>∞</mi> </msup> <mfenced close=")" open="("> <mi mathvariant="normal">Ω</mi> </mfenced> </mrow> </math></EquationSource> </InlineEquation> has been fixed on <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="208_2025_3126_Article_IEq8.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="23" /> </InlineMediaObject> <EquationSource Format="TEX">\(\partial \Omega \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>∂</mi> <mi mathvariant="normal">Ω</mi> </mrow> </math></EquationSource> </InlineEquation>. We do not assume <i>structure conditions</i> on the vector field <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="208_2025_3126_Article_IEq9.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="84" /> </InlineMediaObject> <EquationSource Format="TEX">\(a\left( x,u,Du\right) \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>a</mi> <mfenced close=")" open="("> <mi>x</mi> <mo>,</mo> <mi>u</mi> <mo>,</mo> <mi>D</mi> <mi>u</mi> </mfenced> </mrow> </math></EquationSource> </InlineEquation>, nor <i>sign assumptions</i> on <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="208_2025_3126_Article_IEq5.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="82" /> </InlineMediaObject> <EquationSource Format="TEX">\(b\left( x,u,Du\right) \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>b</mi> <mfenced close=")" open="("> <mi>x</mi> <mo>,</mo> <mi>u</mi> <mo>,</mo> <mi>D</mi> <mi>u</mi> </mfenced> </mrow> </math></EquationSource> </InlineEquation>; we only consider <i> ellipticity</i> and <i>growth conditions</i> on <i>a</i> and <i>b</i>. A main novelty with respect to the literature about this subject is that we assume <i>general </i><InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="208_2025_3126_Article_IEq11.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="43" /> </InlineMediaObject> <EquationSource Format="TEX">\(p,q-\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>p</mi> <mo>,</mo> <mi>q</mi> <mo>-</mo> </mrow> </math></EquationSource> </InlineEquation><i>growth conditions</i> for the principal part of the differential equation; however <i>we do not need an upper bound for the ratio</i> <InlineEquation ID="IEq12"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="208_2025_3126_Article_IEq12.gif" Format="GIF" Height="23" Rendition="HTML" Resolution="72" Type="Linedraw" Width="10" /> </InlineMediaObject> <EquationSource Format="TEX">\(\frac{q}{p}\)</EquationSource> <EquationSource Format="MATHML"><math> <mfrac> <mi>q</mi> <mi>p</mi> </mfrac> </math></EquationSource> </InlineEquation>, but nothing more than <InlineEquation ID="IEq13"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="208_2025_3126_Article_IEq13.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="73" /> </InlineMediaObject> <EquationSource Format="TEX">\(1\le p\le q\,\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>1</mn> <mo>≤</mo> <mi>p</mi> <mo>≤</mo> <mi>q</mi> <mspace width="0.166667em" /> </mrow> </math></EquationSource> </InlineEquation>.</p>

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Global boundedness of weak solutions to a class of nonuniformly elliptic equations

  • Giovanni Cupini,
  • Paolo Marcellini

摘要

We consider second order elliptic equations in divergence form \(\begin{aligned} \sum _{i=1}^{n}\frac{\partial }{\partial x_{i}}a^{i}\left( x,u,Du\right) =b\left( x,u,Du\right) ,\;\;\;\;\;x\in \Omega , \end{aligned}\) i = 1 n x i a i x , u , D u = b x , u , D u , x Ω , where \(\Omega \) Ω is a bounded open set in \(\mathbb {R}^{n}\) R n and \(u:\Omega \rightarrow \mathbb {R}\) u : Ω R . Our aim is to give conditions on the vector field \( a\left( x,u,Du\right) =\left( a^{i}\left( x,u,Du\right) \right) _{i=1,\ldots ,n}\) a x , u , D u = a i x , u , D u i = 1 , , n and on the right hand side \(b\left( x,u,Du\right) \) b x , u , D u in order to obtain the global boundedness in \(\overline{\Omega }\) Ω ¯ of weak solutions u to the Dirichlet problem associated to the previous differential equation, when a boundary condition \(u=u_{0}\in L^{\infty }\left( \Omega \right) \) u = u 0 L Ω has been fixed on \(\partial \Omega \) Ω . We do not assume structure conditions on the vector field \(a\left( x,u,Du\right) \) a x , u , D u , nor sign assumptions on \(b\left( x,u,Du\right) \) b x , u , D u ; we only consider ellipticity and growth conditions on a and b. A main novelty with respect to the literature about this subject is that we assume general \(p,q-\) p , q - growth conditions for the principal part of the differential equation; however we do not need an upper bound for the ratio \(\frac{q}{p}\) q p , but nothing more than \(1\le p\le q\,\) 1 p q .