<p>In this paper, we investigate the properties of spreading speeds of the following Fisher-KPP equation in almost periodic media: <Equation ID="Equ42"> <EquationSource Format="TEX">\(\begin{aligned} \left\{ \begin{aligned} u_t(t,x)=\mathcal {M}u(t,x)+f(x,u(t,x)),\ t&gt;0, x\in \mathbb {R},\\ u(0,x)\ge 0,\ u(0,\cdot )\ne 0\ \text {with compact support,}\\ \end{aligned} \right. \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mfenced open="{"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <msub> <mi>u</mi> <mi>t</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo>,</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <mi mathvariant="script">M</mi> <mi>u</mi> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo>,</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>+</mo> <mi>f</mi> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo>,</mo> <mi>u</mi> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo>,</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">)</mo> </mrow> <mo>,</mo> <mspace width="4pt" /> <mi>t</mi> <mo>&gt;</mo> <mn>0</mn> <mo>,</mo> <mi>x</mi> <mo>∈</mo> <mi mathvariant="double-struck">R</mi> <mo>,</mo> </mrow> </mtd> </mtr> <mtr> <mtd columnalign="right"> <mrow> <mrow /> <mi>u</mi> <mo stretchy="false">(</mo> <mn>0</mn> <mo>,</mo> <mi>x</mi> <mo stretchy="false">)</mo> <mo>≥</mo> <mn>0</mn> <mo>,</mo> <mspace width="4pt" /> <mi>u</mi> <mo stretchy="false">(</mo> <mn>0</mn> <mo>,</mo> <mo>·</mo> <mo stretchy="false">)</mo> <mo>≠</mo> <mn>0</mn> <mspace width="4pt" /> <mtext>with compact support,</mtext> </mrow> </mtd> </mtr> <mtr> <mtd columnalign="right"> <mrow /> </mtd> </mtr> </mtable> </mrow> </mfenced> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>where either <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\mathcal {M}u(t,x)=\mathcal {M}^ru(t,x):=\partial _x(a(x)\partial _{x}u(t,x))+b(x)\partial _{x}u(t,x)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">M</mi> <mi>u</mi> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo>,</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msup> <mrow> <mi mathvariant="script">M</mi> </mrow> <mi>r</mi> </msup> <mi>u</mi> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo>,</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>:</mo> <mo>=</mo> <msub> <mi>∂</mi> <mi>x</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>a</mi> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <msub> <mi>∂</mi> <mi>x</mi> </msub> <mi>u</mi> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo>,</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">)</mo> </mrow> <mo>+</mo> <mi>b</mi> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <msub> <mi>∂</mi> <mi>x</mi> </msub> <mi>u</mi> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo>,</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, which represents the random dispersal, or <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\mathcal {M}u(t,x)=\mathcal {M}^nu(t,x):=\int _{\mathbb {R}}\big (u(t,x-y)-u(t,x)\big )d\mu (y)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">M</mi> <mi>u</mi> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo>,</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msup> <mrow> <mi mathvariant="script">M</mi> </mrow> <mi>n</mi> </msup> <mi>u</mi> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo>,</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>:</mo> <mo>=</mo> <msub> <mo>∫</mo> <mi mathvariant="double-struck">R</mi> </msub> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">(</mo> </mrow> <mi>u</mi> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo>,</mo> <mi>x</mi> <mo>-</mo> <mi>y</mi> <mo stretchy="false">)</mo> </mrow> <mo>-</mo> <mi>u</mi> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo>,</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mrow> <mo maxsize="1.2em" minsize="1.2em" stretchy="true">)</mo> </mrow> <mi>d</mi> <mi>μ</mi> <mrow> <mo stretchy="false">(</mo> <mi>y</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, which represents the nonlocal dispersal. With the existence of the spreading speeds <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\omega ^\pm \)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>ω</mi> <mo>±</mo> </msup> </math></EquationSource> </InlineEquation> in the positive and negative directions of the equation at hand, we 1. give a sufficient and necessary condition for <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\omega ^+=\omega ^-\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>ω</mi> <mo>+</mo> </msup> <mo>=</mo> <msup> <mi>ω</mi> <mo>-</mo> </msup> </mrow> </math></EquationSource> </InlineEquation>, which means that the propagation of the solution is symmetric when <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\mathcal {M}=\mathcal {M}^r\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">M</mi> <mo>=</mo> <msup> <mrow> <mi mathvariant="script">M</mi> </mrow> <mi>r</mi> </msup> </mrow> </math></EquationSource> </InlineEquation>; 2. illustrate that the condition above is a sufficient but not necessary one when <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\mathcal {M}=\mathcal {M}^n\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">M</mi> <mo>=</mo> <msup> <mrow> <mi mathvariant="script">M</mi> </mrow> <mi>n</mi> </msup> </mrow> </math></EquationSource> </InlineEquation>; 3. give some other sufficient conditions for <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\omega ^+=\omega ^-\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>ω</mi> <mo>+</mo> </msup> <mo>=</mo> <msup> <mi>ω</mi> <mo>-</mo> </msup> </mrow> </math></EquationSource> </InlineEquation> when <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(\mathcal {M}=\mathcal {M}^n.\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">M</mi> <mo>=</mo> <msup> <mrow> <mi mathvariant="script">M</mi> </mrow> <mi>n</mi> </msup> <mo>.</mo> </mrow> </math></EquationSource> </InlineEquation></p>

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Symmetry of propagation of Fisher-KPP equations: random dispersal v.s. nonlocal dispersal

  • Tao Zhou

摘要

In this paper, we investigate the properties of spreading speeds of the following Fisher-KPP equation in almost periodic media: \(\begin{aligned} \left\{ \begin{aligned} u_t(t,x)=\mathcal {M}u(t,x)+f(x,u(t,x)),\ t>0, x\in \mathbb {R},\\ u(0,x)\ge 0,\ u(0,\cdot )\ne 0\ \text {with compact support,}\\ \end{aligned} \right. \end{aligned}\) u t ( t , x ) = M u ( t , x ) + f ( x , u ( t , x ) ) , t > 0 , x R , u ( 0 , x ) 0 , u ( 0 , · ) 0 with compact support, where either \(\mathcal {M}u(t,x)=\mathcal {M}^ru(t,x):=\partial _x(a(x)\partial _{x}u(t,x))+b(x)\partial _{x}u(t,x)\) M u ( t , x ) = M r u ( t , x ) : = x ( a ( x ) x u ( t , x ) ) + b ( x ) x u ( t , x ) , which represents the random dispersal, or \(\mathcal {M}u(t,x)=\mathcal {M}^nu(t,x):=\int _{\mathbb {R}}\big (u(t,x-y)-u(t,x)\big )d\mu (y)\) M u ( t , x ) = M n u ( t , x ) : = R ( u ( t , x - y ) - u ( t , x ) ) d μ ( y ) , which represents the nonlocal dispersal. With the existence of the spreading speeds \(\omega ^\pm \) ω ± in the positive and negative directions of the equation at hand, we 1. give a sufficient and necessary condition for \(\omega ^+=\omega ^-\) ω + = ω - , which means that the propagation of the solution is symmetric when \(\mathcal {M}=\mathcal {M}^r\) M = M r ; 2. illustrate that the condition above is a sufficient but not necessary one when \(\mathcal {M}=\mathcal {M}^n\) M = M n ; 3. give some other sufficient conditions for \(\omega ^+=\omega ^-\) ω + = ω - when \(\mathcal {M}=\mathcal {M}^n.\) M = M n .