<p>We investigate a moving recurrent problem for the nonautonomous dynamical system induced by the Cantor series expansion.To be precise, let <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="91" /> </InlineMediaObject> <EquationSource Format="TEX">\(Q=\{q_{k}\}_{k\geq1}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>Q</mi> <mo>=</mo> <msub> <mrow> <mo stretchy="false">{</mo> <msub> <mi>q</mi> <mi>k</mi> </msub> <mo stretchy="false">}</mo> </mrow> <mrow> <mi>k</mi> <mo>≥</mo> <mn>1</mn> </mrow> </msub> </mrow> </math></EquationSource> </InlineEquation> be a sequence of positive integers with <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="48" /> </InlineMediaObject> <EquationSource Format="TEX">\(q_{k}\geq2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>q</mi> <mi>k</mi> </msub> <mo>≥</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation> for all <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="42" /> </InlineMediaObject> <EquationSource Format="TEX">\(k\geq1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <mo>≥</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>. Put<InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_IEq4.gif" Format="GIF" Height="22" Rendition="HTML" Resolution="72" Type="Linedraw" Width="233" /> </InlineMediaObject> <EquationSource Format="TEX">\(T_{Q}^{n}(x)=q_{1}\cdots q_{n}x-\lfloor q_{1}\cdots q_{n}x\rfloor\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>T</mi> <mrow> <mi>Q</mi> </mrow> <mi>n</mi> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msub> <mi>q</mi> <mn>1</mn> </msub> <mo>⋯</mo> <msub> <mi>q</mi> <mi>n</mi> </msub> <mi>x</mi> <mo>-</mo> <mrow> <mo>⌊</mo> <msub> <mi>q</mi> <mn>1</mn> </msub> <mo>⋯</mo> <msub> <mi>q</mi> <mi>n</mi> </msub> <mi>x</mi> <mo>⌋</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> for each <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_IEq5.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="43" /> </InlineMediaObject> <EquationSource Format="TEX">\(n\geq1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>n</mi> <mo>≥</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>, which gives the <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_IEq6.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="19" /> </InlineMediaObject> <EquationSource Format="TEX">\(Q\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>Q</mi> </math></EquationSource> </InlineEquation>-Cantor series expansion.We focus on the following <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_IEq7.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="62" /> </InlineMediaObject> <EquationSource Format="TEX">\(\{n_{k},r_{k}\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">{</mo> <msub> <mi>n</mi> <mi>k</mi> </msub> <mo>,</mo> <msub> <mi>r</mi> <mi>k</mi> </msub> <mo stretchy="false">}</mo> </mrow> </math></EquationSource> </InlineEquation>-moving recurrent points proposed by Boshernitzan and Glasner:<Equation ID="Equ1"> <MediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_Equ1.gif" Format="GIF" Height="30" Rendition="HTML" Resolution="72" Type="Linedraw" Width="207" /> </MediaObject> <EquationSource Format="TEX">\(\inf_{k\geq1}|T^{n_{k}}_{Q}(x)-T^{n_{k}+r_{k}}_{Q}(x)|=0,\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <munder> <mo movablelimits="true">inf</mo> <mrow> <mi>k</mi> <mo>≥</mo> <mn>1</mn> </mrow> </munder> <mrow> <mo stretchy="false">|</mo> <msubsup> <mi>T</mi> <mi>Q</mi> <msub> <mi>n</mi> <mi>k</mi> </msub> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>-</mo> <msubsup> <mi>T</mi> <mi>Q</mi> <mrow> <msub> <mi>n</mi> <mi>k</mi> </msub> <mo>+</mo> <msub> <mi>r</mi> <mi>k</mi> </msub> </mrow> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">|</mo> </mrow> <mo>=</mo> <mn>0</mn> <mo>,</mo> </mrow> </math></EquationSource> </Equation>where <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_IEq8.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="59" /> </InlineMediaObject> <EquationSource Format="TEX">\(\{n_{k}\}_{k\geq1}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mrow> <mo stretchy="false">{</mo> <msub> <mi>n</mi> <mi>k</mi> </msub> <mo stretchy="false">}</mo> </mrow> <mrow> <mi>k</mi> <mo>≥</mo> <mn>1</mn> </mrow> </msub> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_IEq9.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="56" /> </InlineMediaObject> <EquationSource Format="TEX">\(\{r_{k}\}_{k\geq1}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mrow> <mo stretchy="false">{</mo> <msub> <mi>r</mi> <mi>k</mi> </msub> <mo stretchy="false">}</mo> </mrow> <mrow> <mi>k</mi> <mo>≥</mo> <mn>1</mn> </mrow> </msub> </math></EquationSource> </InlineEquation> are two given sequences of integers. It is proved that when <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_IEq8.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="59" /> </InlineMediaObject> <EquationSource Format="TEX">\(\{n_{k}\}_{k\geq1}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mrow> <mo stretchy="false">{</mo> <msub> <mi>n</mi> <mi>k</mi> </msub> <mo stretchy="false">}</mo> </mrow> <mrow> <mi>k</mi> <mo>≥</mo> <mn>1</mn> </mrow> </msub> </math></EquationSource> </InlineEquation>and <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_IEq9.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="56" /> </InlineMediaObject> <EquationSource Format="TEX">\(\{r_{k}\}_{k\geq1}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mrow> <mo stretchy="false">{</mo> <msub> <mi>r</mi> <mi>k</mi> </msub> <mo stretchy="false">}</mo> </mrow> <mrow> <mi>k</mi> <mo>≥</mo> <mn>1</mn> </mrow> </msub> </math></EquationSource> </InlineEquation> tend to infinity, the set of <InlineEquation ID="IEq12"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_IEq7.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="62" /> </InlineMediaObject> <EquationSource Format="TEX">\(\{n_{k},r_{k}\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">{</mo> <msub> <mi>n</mi> <mi>k</mi> </msub> <mo>,</mo> <msub> <mi>r</mi> <mi>k</mi> </msub> <mo stretchy="false">}</mo> </mrow> </math></EquationSource> </InlineEquation>-moving recurrent points is of full Lebesgue measure. In addition,we study the size of the following quantitative version of <InlineEquation ID="IEq13"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_IEq7.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="62" /> </InlineMediaObject> <EquationSource Format="TEX">\(\{n_{k},r_{k}\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">{</mo> <msub> <mi>n</mi> <mi>k</mi> </msub> <mo>,</mo> <msub> <mi>r</mi> <mi>k</mi> </msub> <mo stretchy="false">}</mo> </mrow> </math></EquationSource> </InlineEquation>-moving recurrent set:<Equation ID="Equ2"> <MediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_Equ2.gif" Format="GIF" Height="25" Rendition="HTML" Resolution="72" Type="Linedraw" Width="517" /> </MediaObject> <EquationSource Format="TEX">\( R(\{n_{k},r_{k}\}):=\big\{x\in [0,1] : |T^{n_{k}}_{Q}(x)-T^{n_{k}+r_{k}}_{Q}(x)|&lt;\varphi(k)~\text{for i.m.}~k\in \mathbb{N}\big\},\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mi>R</mi> <mrow> <mo stretchy="false">(</mo> <mrow> <mo stretchy="false">{</mo> <msub> <mi>n</mi> <mi>k</mi> </msub> <mo>,</mo> <msub> <mi>r</mi> <mi>k</mi> </msub> <mo stretchy="false">}</mo> </mrow> <mo stretchy="false">)</mo> </mrow> <mo>:</mo> <mo>=</mo> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">{</mo> </mrow> <mi>x</mi> <mo>∈</mo> <mrow> <mo stretchy="false">[</mo> <mn>0</mn> <mo>,</mo> <mn>1</mn> <mo stretchy="false">]</mo> </mrow> <mo>:</mo> <mrow> <mo stretchy="false">|</mo> <msubsup> <mi>T</mi> <mi>Q</mi> <msub> <mi>n</mi> <mi>k</mi> </msub> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>-</mo> <msubsup> <mi>T</mi> <mi>Q</mi> <mrow> <msub> <mi>n</mi> <mi>k</mi> </msub> <mo>+</mo> <msub> <mi>r</mi> <mi>k</mi> </msub> </mrow> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">|</mo> </mrow> <mo>&lt;</mo> <mi>φ</mi> <mrow> <mo stretchy="false">(</mo> <mi>k</mi> <mo stretchy="false">)</mo> </mrow> <mspace width="3.33333pt" /> <mtext>for i.m.</mtext> <mspace width="3.33333pt" /> <mi>k</mi> <mo>∈</mo> <mi mathvariant="double-struck">N</mi> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">}</mo> </mrow> <mo>,</mo> </mrow> </math></EquationSource> </Equation>where <InlineEquation ID="IEq14"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_IEq14.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="84" /> </InlineMediaObject> <EquationSource Format="TEX">\(\varphi \colon \mathbb{N}\rightarrow\mathbb{R}^{+}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>φ</mi> <mo lspace="0pt">:</mo> <mi mathvariant="double-struck">N</mi> <mo stretchy="false">→</mo> <msup> <mrow> <mi mathvariant="double-struck">R</mi> </mrow> <mo>+</mo> </msup> </mrow> </math></EquationSource> </InlineEquation> is a positive function and ``i.m.'' stands for ``infinitely many''. It is proved that when <InlineEquation ID="IEq15"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_IEq8.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="59" /> </InlineMediaObject> <EquationSource Format="TEX">\(\{n_{k}\}_{k\geq1}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mrow> <mo stretchy="false">{</mo> <msub> <mi>n</mi> <mi>k</mi> </msub> <mo stretchy="false">}</mo> </mrow> <mrow> <mi>k</mi> <mo>≥</mo> <mn>1</mn> </mrow> </msub> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq16"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_IEq9.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="56" /> </InlineMediaObject> <EquationSource Format="TEX">\(\{r_{k}\}_{k\geq1}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mrow> <mo stretchy="false">{</mo> <msub> <mi>r</mi> <mi>k</mi> </msub> <mo stretchy="false">}</mo> </mrow> <mrow> <mi>k</mi> <mo>≥</mo> <mn>1</mn> </mrow> </msub> </math></EquationSource> </InlineEquation> tend to infinity, theLebesgue measure and Hausdorff measure of <InlineEquation ID="IEq17"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10474_2025_1514_Article_IEq17.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="83" /> </InlineMediaObject> <EquationSource Format="TEX">\(R(\{n_{k},r_{k}\})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>R</mi> <mo stretchy="false">(</mo> <mrow> <mo stretchy="false">{</mo> <msub> <mi>n</mi> <mi>k</mi> </msub> <mo>,</mo> <msub> <mi>r</mi> <mi>k</mi> </msub> <mo stretchy="false">}</mo> </mrow> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> respectively fulfill a dichotomy law according to the convergence or divergence of certain series.</p>

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Moving recurrent problems in the nonautonomous dynamical systems corresponding to Cantor series expansions

  • Z. Shen

摘要

We investigate a moving recurrent problem for the nonautonomous dynamical system induced by the Cantor series expansion.To be precise, let \(Q=\{q_{k}\}_{k\geq1}\) Q = { q k } k 1 be a sequence of positive integers with \(q_{k}\geq2\) q k 2 for all \(k\geq1\) k 1 . Put \(T_{Q}^{n}(x)=q_{1}\cdots q_{n}x-\lfloor q_{1}\cdots q_{n}x\rfloor\) T Q n ( x ) = q 1 q n x - q 1 q n x for each \(n\geq1\) n 1 , which gives the \(Q\) Q -Cantor series expansion.We focus on the following \(\{n_{k},r_{k}\}\) { n k , r k } -moving recurrent points proposed by Boshernitzan and Glasner: \(\inf_{k\geq1}|T^{n_{k}}_{Q}(x)-T^{n_{k}+r_{k}}_{Q}(x)|=0,\) inf k 1 | T Q n k ( x ) - T Q n k + r k ( x ) | = 0 , where \(\{n_{k}\}_{k\geq1}\) { n k } k 1 and \(\{r_{k}\}_{k\geq1}\) { r k } k 1 are two given sequences of integers. It is proved that when \(\{n_{k}\}_{k\geq1}\) { n k } k 1 and \(\{r_{k}\}_{k\geq1}\) { r k } k 1 tend to infinity, the set of \(\{n_{k},r_{k}\}\) { n k , r k } -moving recurrent points is of full Lebesgue measure. In addition,we study the size of the following quantitative version of \(\{n_{k},r_{k}\}\) { n k , r k } -moving recurrent set: \( R(\{n_{k},r_{k}\}):=\big\{x\in [0,1] : |T^{n_{k}}_{Q}(x)-T^{n_{k}+r_{k}}_{Q}(x)|<\varphi(k)~\text{for i.m.}~k\in \mathbb{N}\big\},\) R ( { n k , r k } ) : = { x [ 0 , 1 ] : | T Q n k ( x ) - T Q n k + r k ( x ) | < φ ( k ) for i.m. k N } , where \(\varphi \colon \mathbb{N}\rightarrow\mathbb{R}^{+}\) φ : N R + is a positive function and ``i.m.'' stands for ``infinitely many''. It is proved that when \(\{n_{k}\}_{k\geq1}\) { n k } k 1 and \(\{r_{k}\}_{k\geq1}\) { r k } k 1 tend to infinity, theLebesgue measure and Hausdorff measure of \(R(\{n_{k},r_{k}\})\) R ( { n k , r k } ) respectively fulfill a dichotomy law according to the convergence or divergence of certain series.