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Research article

The Burgers-KdV limit in one-dimensional plasma with viscous dissipation: A study of dispersion and dissipation effects

  • Received: 07 October 2023 Revised: 28 November 2023 Accepted: 28 November 2023 Published: 07 December 2023
  • MSC : 35Q53, 35Q35

  • The Burgers-KdV equation as a highly nonlinear model, is commonly used in weakly nonlinear analysis to describe small but finite amplitude ion-acoustic waves. In this study, we demonstrate that by considering viscous dissipation, we can derive the Burgers-KdV limit from a one-dimensional plasma system by using the Gardner-Morikawa transformation. This transformation allows us to obtain both homogeneous and inhomogeneous Burgers-KdV equations, which incorporate dissipative and dispersive terms, for the ionic acoustic system. To analyze the remaining system, we employ the energy method in Sobolev spaces to estimate its behavior. As a result, we are able to capture the Burgers-KdV dynamics over a time interval of order O(ε1), where ε represents a small parameter.

    Citation: Rong Rong, Hui Liu. The Burgers-KdV limit in one-dimensional plasma with viscous dissipation: A study of dispersion and dissipation effects[J]. AIMS Mathematics, 2024, 9(1): 1248-1272. doi: 10.3934/math.2024062

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  • The Burgers-KdV equation as a highly nonlinear model, is commonly used in weakly nonlinear analysis to describe small but finite amplitude ion-acoustic waves. In this study, we demonstrate that by considering viscous dissipation, we can derive the Burgers-KdV limit from a one-dimensional plasma system by using the Gardner-Morikawa transformation. This transformation allows us to obtain both homogeneous and inhomogeneous Burgers-KdV equations, which incorporate dissipative and dispersive terms, for the ionic acoustic system. To analyze the remaining system, we employ the energy method in Sobolev spaces to estimate its behavior. As a result, we are able to capture the Burgers-KdV dynamics over a time interval of order O(ε1), where ε represents a small parameter.



    Recently, highly nonlinear models have attracted the focus of many scientists due to their ability to provide more meaningful insights into physical phenomena with memory effects [1]. The Burgers-Korteweg-de Vries (Burgers-KdV) equation has gained attention for the purpose of modeling various natural phenomena, such as the propagation of undular bores in shallow water, the flow of liquids containing gas bubbles and the propagation of waves in elastic tubes filled with viscous fluids [2,3,4,5]. This equation has attracted physicists, engineers and applied mathematicians from different disciplines who are interested in studying these phenomena. In the field of weak nonlinearity, the Burgers-KdV equation (or KdV equation) is commonly used to describe dispersion waves of finite but small magnitude, and it is not limited to waves in bubble streams. On the other hand, the nonlinear Schrödinger equation (or Ginzburg-Landau equation) is a widely used nonlinear wave equation (or nonlinear evolution equation) for cases involving strong dispersion.

    Yatabe et al. [6] employed a multi-scale method to derive two KdV-Burgers equations that incorporate a drag force correction term. They verified that the time evolution of wave dissipation, caused by the drag force, differs from that caused by acoustic radiation. From a mathematical perspective, there exists a close relationship between the Burgers equation (s=0) [7] and the KdV equation (β=0) [8]. The standard Burgers-KdV equation is given by

    ut+αuux+βuxx+suxxx=0,

    where the real constants α, β and s satisfy that αβs0. The nonexistence of a spectral solution for this equation presents a challenge in studying its integrability. Currently, there is no effective analytical method available to solve this type of equation.

    Indeed, there have been numerous studies on the Burgers-KdV equation, addressing various aspects such as the existence, uniqueness, well-posedness, stability and solution properties [9,10,11,12,13,14,15]. Many physical processes can be perturbed by external factors, and the nature of these perturbations can vary across different problems. In recent years, investigating the limit problem with viscous dissipation has received significant attention.

    Significant progress has been made in understanding the Burgers-KdV equation. Luc and Francis [16] showed that the Burgers-KdV equations are globally well-posed. They established the low regularity of solutions through the use of an algebraic inequality and an a priori estimate. Dlotko [17] proved the local and global solvability in H2(R) of the Cauchy problem for the generalized KdV-Burgers equation by using the parabolic regularization technique. Wang et al. [18] obtained an approximate solution to the KdV-Burgers equation with boundary conditions by employing the Adomian decomposition method. Feng and Knobel [19] obtained traveling wave solutions from a KdV-Burgers-type equation with higher-order nonlinearities. Zhao and colleagues [20,21,22] introduced some localized wave solutions of the high-dimensional integrable systems for the nonlinear mathematical physics. These are just a few examples of the extensive research findings in this area.

    Recently, there has been significant interest in the asymptotic connection between ionic dynamical systems and hydrodynamic models. The Euler-Poisson system has been used to derive various nonlinear dispersive equations through the use of reduced perturbation methods, including the KdV equation [23], Kadomtsev-Petviashvili equation [24], Zakharov-Kuznetsov equation [25,26], Burgers equation [27] and Schrödinger equation [28]. However, directly applying this method to nonlinear systems involving both dissipative and dispersive effects can be challenging. Based on the literature mentioned, this paper focuses on the question of whether the Burgers-KdV system can converge to a similar solution. The reduced perturbation method is not directly applicable when both dispersion and dissipation are present.

    When regardless of the magnetic field, we consider the one-dimensional plasma with viscous dissipation [29,30], the two-fluid system describing ionic sound waves is reduced to

    {tni+x(nivi)=0,(1.1a)mini(tvi+vixvi)=xpiniexϕ+μ2xvi,(1.1b)0=exϕKTenexne,(1.1c)2xϕ=4πe(neni),(1.1d)

    where ϕ is the perturbed potential, μ is interpreted as the equivalent viscosity coefficient and ni and vi represent the density and velocity, respectively.

    Standardize the physical quantities in (1.1) as follows:

    x=x/L,t=tcs/L,v=vi/cs,Φ=eϕ/KTe,n=ni/n0,ne=ne/n0,

    where L is the characteristic scale of fluctuation, cs=KTemi denotes the ion-acoustic velocity, K is the Boltzmann constant and n0 is the undisturbed density.

    When ignoring the influence of the ion pressure term, the dimensionless equations can be simplified to

    {tn+x(nv)=0,(1.2a)tv+vxv+xΦνLcs1n2xv=0,(1.2b)xΦ=1nexne,(1.2c)λ2DL22xΦ=nen,(1.2d)

    where ν=μmin0 represents the equivalent kinematic viscosity coefficient and λD=KTe/4πn0e2 is the Debye length.

    Assuming a finite small quantity of density perturbation, let Δn=nin0; we have that n1=Δnn01; taking Δnn0=ε1, let λD/L2=αε and ν/Lcs=βε; this is what the weak dispersion and viscosity require. The quantity ε is a quantity that describes the strength of the nonlinearity. When both the weak dispersion and the weak dissipative effect are equivalent to ε, we can obtain the Burgers-KdV equation via the perturbation method. The system (1.1a) can be rewritten as follows:

    {tn+x(nv)=0,(1.3a)tv+vxv+xΦβεn2xv=0,(1.3b)nen=αε2xΦ,(1.3c)xΦ=1nexne.(1.3d)

    By applying the following Gardner-Morikawa transformation [29] to (1.3),

    xxλ0t,  tεt, (1.4)

    we obtain the following parameterized system:

    {εtnλ0xn+x(nv)=0,(1.5a)εtvλ0xv+vxv+xΦβεn2xv=0,(1.5b)nen=αε2xΦ,(1.5c)xΦ=1nexne,(1.5d)

    where the small quantity ε is also the amplitude of initial disturbance and λ0 is the velocity parameter.

    Assume that the variables have the following expansions:

    {n=1+εn(1)+ε2n(2)+ε3n(3)+ε4n(4)+,(1.6a)ne=1+εn(1)e+ε2n(2)e+ε3n(3)e+ε4n(4)e+,(1.6b)v=εv(1)+ε2v(2)+ε3v(3)+ε4v(4)+;(1.6c)

    we then incorporate (1.6) into system (1.5), terminating each expansion at different orders of magnitude ε.

    At the order of O(ε), we have

    {λ0xn(1)+xv(1)=0,(1.7a)λ0xv(1)+1nexn(1)e=0,(1.7b)n(1)en(1)=0;(1.7c)

    a simpler calculation gives

    {v(1)=λ0n(1)=λ0n(1)e,(1.8a)λ20ne=1.(1.8b)

    At the order of O(ε2), we have

    {tn(1)λ0xn(2)+x(v(2)+n(1)v(1))=0,(1.9a)tv(1)λ0xv(2)+v(1)xv(1)+1nexn(2)eβn2xv(1)=0,(1.9b)n(2)en(1)=αne2xn(1)e.(1.9c)

    Taking x of (1.9c), multiplying (1.9a) by λ0 and then putting them into (1.9b), we obtain the homogeneous Burgers-KdV equation for n(1)e:

    tn(1)e+3λ02n(1)exn(1)e+α2λ303xn(1)eβ2n2xn(1)e=0, (1.10)

    where we applied (1.8). Note that system (1.10) and (1.9) are self contained for (n(1),v(1),ϕ(1)).

    From (1.9), we can express (n(2),v(2)) in the following form:

    {v(2)=λ0n(2)e+f(1),(1.11a)n(2)=n(2)eαλ202xn(1)e,(1.11b)

    where we have used (1.8b) and the function f(1) only depends on n(1)e and its derivatives.

    At the order of O(ε3), we have

    {tn(2)λ0xn(3)+x(v(3)+n(1)v(2)+n(2)v(1))=0,(1.12a)tv(2)λ0xv(3)+v(1)xv(2)+v(2)xv(1)+1nexn(3)eβn2xv(2)=0,(1.12b)n(3)en(3)=αn2e(xn(1)e)2+αne2xn(2)e.(1.12c)

    Taking x of (1.12c), multiplying (1.12a) by λ0 and then putting them into (1.12b), we obtain the inhomogeneous Burgers-KdV equation for n(2)e:

    tn(2)e+3λ02x(n(1)en(2)e)+α2λ303xn(2)eβ2n2xn(2)e=G(1), (1.13)

    where we have applied (1.11) and G(1) depends only on n(1)e and its derivatives.

    At the order of O(εk+1), we can get the linearized inhomogeneous Burgers-KdV equation for n(k)e:

    tn(k)e+3λ02x(n(1)en(k)e)+α2λ303xn(k)eβ2n2xn(k)e=G(k1),k3, (1.14)

    where G(k1) only depends on n(1)e,,n(k1)e, which can all be determined from the preceding k-1 steps. The system (1.14) is also self-contained and only depends on n(k)e.

    Equations (1.10), (1.13) and (1.14) contain both third derivative terms and second derivative terms which arise from the interplay of dispersion and dissipation in the system. Finding a general Gardner-Morikawa transformation that keeps the equation unchanged is not possible in this case. This implies that the general reduced perturbation method fails to preserve the original form of the equation. Therefore we assumed that the magnitudes of the dispersion and dissipation terms are at the same level.

    Remark 1.1. If the magnitudes of dispersion and dissipation terms are not on the same order, the approximate evolution equation may be reduced to either the KdV equation (λ2D/L2ν/Lcs) or the Burgers equation (λ2D/L2ν/Lcs) respectively. These reduced equations capture the dominant behavior of the system when either dispersion or dissipation is significantly stronger than the other.

    Remark 1.2. Through qualitative analysis, (1.10), (1.13) and (1.14) can be likened to a nonlinear oscillator equation with a damping term, which can be solved in the form of an oscillating shock wave by applying qualitative analysis for sufficiently large damping. On the contrary, when the damping is small enough, the soliton-mode solution with slow attenuation of amplitude can be obtained.

    Theorem 1.1. Let s12 be a sufficiently large integer. Then for any given initial data n(1)0Hs1(R), there exists τ>0 such that the initial value problem (1.8) and (1.10) has the unique solution

    (n(1),v(1),n(1)e)L(τ,τ;Hs1(R))

    with initial data (n(1)e0,λ0n(1)e0,n(1)e0). Moreover, we can extend the solution to any time interval [τ,τ] by the conservation of the Burgers-KdV equation [30,31].

    Theorem 1.2. Let k2 and sks13(k1) be sufficiently large integers. Then, for any τ>0 and any given initial data (n(k)0,v(k)0,n(k)e0)Hsk(R), the initial value problem of (1.14) with initial data (n(k)0,v(k)0,n(k)e0) has the unique solution

    (n(k),v(k),n(k)e)L(τ,τ;Hsk(R)).

    Next, we will give a strict proof to show that n(1)e converges to a solution of the Burgers-KdV equation as ε0. Suppose that (n(k),v(k),n(k)e), 1k4 are sufficiently smooth. Let (n,v,ne) be a solution of (1.5) and have the following expansions:

    {n=1+εn(1)+ε2n(2)+ε3n(3)+ε4n(4)+ε3N,(1.15a)ne=1+εn(1)e+ε2n(2)e+ε3n(3)e+ε4n(4)e+ε3Ne,(1.15b)v=εv(1)+ε2v(2)+ε3v(3)+ε4v(4)+ε3V,(1.15c)

    where (n(k),v(k),n(k)e) for 1k4 satisfies (1.8), (1.10) and (1.13) respectively, and (N,V,Ne) is the remainder.

    Just for the sake of calculation, we denote

    ˜n=n(1)+εn(2)+ε2n(3)+ε3n(4),˜ne=n(1)e+εn(2)e+ε2n(3)e+ε3n(4)e,˜v=v(1)+εv(2)+ε2v(3)+ε3v(4).

    Putting (1.15) into the scaled system (1.5), a simper calculation gives the remainder system, as follows

    {tNλ0vεxN+nεxV+x˜nV+x˜vN+εR1=0,(1.16a)tVλ0vεxV+1neεxNe+x˜vVβn2xV+εR2=0,(1.16b)NeN=αεne2xNe2αn2eε2x˜nexNe+εR3,(1.16c)

    where

    {R1=xn(4)+x(n(2)v(4)+n(3)v(3)+n(4)v(3))+εx(n(3)v(4)+n(4)v(3))+ε2x(n(4)v(4)),R2=tv(4)+(v(1)xv(4)+v(2)xv(3)+v(3)xv(2)+v(4)xv(1))+ε(v(2)xv(4)+v(3)xv(3)+v(3)xv(2))+ε2x(v(3)v(4))βnxv(3)βnεxv(4),R3=n(4)n(4)e2αn2e(xn(1)exn(2)e)αn2eε(2xn(3)exn(1)e+xn(2)exn(2)e)2αn2eε2(xn(4)exn(1)e+xn(3)exn(2)e)+αne(2xn(3)e+ε2xn(4)e). (1.17)

    Next, we give some basic estimates for the remainder term R3.

    Lemma 1.1. For the s=1,2, integers, there exists some constant C=C(n(i)eHδ) and C=C(n(i)eHδ,εNeHs) such that R1,R2HsC(n(i)eHδ) and

    R3HsC(n(i)eHδ,εNeHs)NeHs,  s=1,2,, (1.18)
    TR3HsC(ne(i)Hδ,εNeHs)TNeHs,  s=1,2,, (1.19)

    where δ=max{2,s1}; due to the fact that Hs is an algebra, the proof of Lemma 1.1 is obvious; also, the constant C is nondecreasing.

    The main results are given as follows:

    Theorem 1.3. Let si2 in Theorems 1.1 and 1.2 be sufficiently large and (n(1),v(1),n(1)e)Hs1 be a solution constructed in Theorem 1.1 for the Burgers-KdV equation with initial data (n(1)0,v(1)0,n(1)e0) in Hs1 satisfying (1.8). Let (n(i),v(i),n(i)e)Hsi(i=2,3,4) be a solution of (1.14), as constructed in Theorem 1.2 with initial data (n(i)0,v(i)0,n(i)e0) in Hsi. Let (Nε0,Vε0,Nεe0)Hs and assume the following:

    {n0=1+εn(1)0+ε2n(2)0+ε3n(3)0+ε4n(4)0+ε3N0,ne0=1+εn(1)e0+ε2n(2)e0+ε3n(3)e0+ε4n(4)e0+ε3Ne0,v0=εv(1)0+ε2v(2)0+ε3v(3)0+ε4v(4)0+ε3V0. (1.20)

    Then, for any τ>0, there exists ε0>0 such that, if 0<ε<ε0, the solution of the system (1.5) with initial data (n0,v0,ne0) can be expressed as follows:

    {n=1+εn(1)+ε2n(2)+ε3n(3)+ε4n(4)+ε3N,ne=1+εn(1)e+ε2n(2)e+ε3n(3)e+ε4n(4)e+ε3Ne,v=εv(1)+ε2v(2)+ε3v(3)+ε4v(4)+ε3V, (1.21)

    such that, for all 0<ε<ε0,

    sup[0,τ]{(N,V,Ne)2H2+ε(3xV,3xNe)2L2+ε24xNe2L2}Cτ(1+(N0,V0,Ne0)2H2+ε(3xV0,3xNe0)2L2+ε24xNe02L2). (1.22)

    From (1.22), we obtain the uniform H2-norm of the remainder (N,V,Ne) on ε, and it satisfies

    sup[0,ε1τ]((n1)/ε(ne1)/εv/ε)BKdVH2Cε (1.23)

    where C is independent of ε and BKdV denotes the Burgers-KdV equation.

    In order to give the proof of Theorem1.3, we define the following weighted norm:

    |(V,Ne)|2ε=V2H2+Ne2H2+ε3xV2+ε3xNe2++ε24xNe2. (1.24)

    In this section, we will give the uniform estimates of the system (1.16) and show that (1.16) has smooth solutions for significantly small τε>0, as dependent on ε>0. Let ˜C be a constant that is independent of ε. By the classical theorem, we know that there exists τε>0 such that on [0,τε],

    N2H2,|(V,Ne)(t)|2ε˜C. (2.1)

    Note that n is bounded, i.e., 1/2<n<3/2, and |v|<1/2 for ε<ε1. There exists some constant C1=C1(ε˜C) for any α,β0 such that

    |αn(i)eβNeR3|C1=C1(ε˜C), (2.2)

    where C1 is chosen to be nondecreasing in its argument.

    Next, we will give some lemmas to show the relation between N and Ne.

    Lemma 2.1. Let (N,V,Ne) be a solution to (1.16) and α0 be an integer. There exist some constants 0<ε1<1 and C1=C1(ε˜C) such that for every 0<ε<ε1,

    C11αxN2αxNe2+εα+1xNe2+ε2α+2xNe2C1αxN2. (2.3)

    Proof. When α=0, taking the inner product of (1.16c) with Ne, we have

    Ne2+εαnexNe2=NNeεαx(1ne)xNeNeε22αn2ex˜nexNeNe+εR3Ne, (2.4)

    where α is a constant and 12<ne<32; therefore, there exists a constant C such that

    εαnexNe2CεxNe2, (2.5)

    so the left of (2.5) is larger than Ne2+εxNe2.

    Due to the fact that

    |x(1ne)|C(ε|x˜ne|+ε3|xNe|), (2.6)

    combined with Young's inequality, we get

    |εαx(1ne)xNeNe|18Ne2+Cε2xNe2+Cε4˜CxNe2. (2.7)

    Due to the fact that ˜ne is bounded in L, by the Hölder inequality, we have

    |ε22αn2ex˜nexNeNe|18Ne2+Cε2xNe2. (2.8)

    From Lemma 1.1, it holds that ε<ε1, which is sufficiently small such that

    εR3Ne14Ne2. (2.9)

    Therefore, by the Hölder inequality, we have

    Ne2+εxNe2CN2. (2.10)

    Taking the inner product of (1.16c) with ε2xNe, we have

    εxNe2+ε2αne2xNe2=ε32αn2ex˜nexNe2xNeεN2xNeε2R32xNe; (2.11)

    by the Hölder inequality, the result is as follows

    εxNe2+ε22xNe2CN2. (2.12)

    Then, applying the L2-norm of (1.16c), we obtain some C such that

    N2Ne2+ε22xNe2+ε4xNe2. (2.13)

    Putting (2.10), (2.12) and (2.13) together, we obtain (2.3) for α=0.

    For the higher-order cases, we can differentiate (1.16c) with respect to α, take the inner product with αxNe and εα+2xNe and then perform the same procedure as for the case α=0; we can complete this lemma.

    Lemma 2.2. Let (N,V,Ne) be a solution to (1.16) and α0 be an integer. There exist some constants C and C1=C1(ε˜C) such that

    εtN2C(Ne2H1+V2H1+ε2xNe2+ε23xNe2)+Cε (2.14)

    and

    εtxN2C1(Ne2H2+V2H2+ε3xNe2+ε24xNe2)+Cε. (2.15)

    Proof. Due to the fact that 1/2<n<3/2 and |v|<1/2, taking the L2-norm of (1.16a) gives

    ||εtN||2C(||xN||2+||xV||2)+Cε2(ε2+||N||2+||V||2). (2.16)

    By using Lemma 2.1 with α=1, we have (2.14).

    Then, taking x of (1.16a), we obtain

    ||εtxN||2C(||V||2H2+||N||2H2)+Cε6|xV|2|xN|2+Cε4. (2.17)

    By the Sobolev embedding inequality, we have

    Cε6xV2L||xN||2Cε6||V||2H2+||N||2H1C(ε˜C)||V||2H2; (2.18)

    then by Lemma 2.1, we complete this lemma.

    Lemma 2.3. Let (N,V,Ne) be a solution to (1.16) and α0 be an integer. There exist some constants C1=C1(ε˜C) and ε1>0 such that for any 0<ε<ε1,

    εtα+1xNe2+tαxNe2CtαxN2+C1. (2.19)

    Proof. For the case of α=0, taking t of (1.16c) and then taking the inner product with tNe, we have

    tNe2+εαne|txNe|2=tNtNe+αεt(1ne)2xNetNeαεx(1ne)txNetNe2αε2t(1n2e)x˜nexNetNe(2αn2eε2tx˜nexNe)tNe(2αn2eε2x˜netxNe)tNe+εtR3tNe=:7i=1Ai, (2.20)

    where α is a constant and 1/2<ne<3/2, so there exists a constant C such that εαne|txNe|2Cε|txNe|2; therefore, the left of (2.20) is greater than or equal to C(tNe2+ε|txNe|2). Now, we estimate the right of (2.20). For A1, for any small γ>0, by Young's inequality, we have

    A1=tNtNeγtNe2+CγtN2. (2.21)

    Due to the fact that

    |t(1ne)|,|t(1n2e)|C(ε|t˜ne|+ε3|tNe|),|x(1ne)|C(ε|x˜ne|+ε3|xNe|), (2.22)

    by the Hölder inequality and Sobolev embedding inequality, we obtain

    A2Cε2(|t˜ne|+ε2|tNe|)2xNetNeC1(||tNe||2+ε22xNe2)+C1,A3Cε2(|x˜ne|+ε2|xNe|)txNetNeC1(||tNe||2+εxtNe2)+C1, (2.23)

    and

    A4Cε3(|t˜ne|+ε2|tNe|)x˜nexNetNeC1(||tNe||2+εxNe2)+C1. (2.24)

    Similar to A2, by the Hölder inequality, we obtain

    A5,6,7C1(||tNe||2+εxtNe2)+C1. (2.25)

    Therefore, we have

    ||tNe||2+ε||xtNe||2C||tN||2+C1. (2.26)

    When α=1, we take xt of (1.16c); then, taking the inner product with εxtNe, we have

    εxtNe2+αε2ne|t2xNe|2=εxtNxtNe+εxt(αεne)2xNextNeεx(αεne)t2xNextNeεxt(2αn2e)ε2x˜nexNextNeε(2αn2eε2xtx˜nexNe)xtNeεxt(2αn2eε2x˜nextxNe)xtNe+εεxtR3xtNe=:7i=1Bi

    Due to the fact that

    |xt(1ne)|,|xt(1n2e)|C(ε|xt˜ne|+ε3|xtNe|), (2.27)

    for arbitrary γ>0, by Young's inequality, we obtain

    B1γεxtNe2+CγxtN2. (2.28)

    Using (2.1), by the Hölder inequality and Sobolev embedding inequality, we have

    B2Cε3(|xt˜ne|+ε2|xtNe|)2xNextNeC1(ε||xtNe||2+ε2t2xNe2)+C1 (2.29)

    and

    B3Cε3(|x˜ne|+ε2|xNe|)t2xNextNeC1(ε||xtNe||2+ε2t2xNe2)+C1. (2.30)

    Similar to the process for B2, by the Sobolev embedding inequality, we have

    B4,5,6,7C1(ε||xtNe||2+ε2t2xNe2)+C1; (2.31)

    therefore, we have

    ε||tNe||2+ε2||xtNe||2C||xtN||2+C1. (2.32)

    We can give by the similar process for the case of α2.

    Proposition 2.1. Let (N,V,Ne) be a solution to (1.16) and κ=0,1,2; then,

    12ddtκxV2+12ddt(1nne|κxNe|2+αεnn2e|κ+1xNe|2)C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε). (2.33)

    Proof. We take κx of (1.16b) and the inner product of κxV. Integrating by parts yields

    12ddtκxV2λ0εκ+1xVκxV+κx((˜v+ε2V)xV)κxV+κx(x˜vV)κxVκx(βn2xV)κxV+κx(εR2)κxV=κ1x(1nexNe)κ+1xVε. (2.34)

    The second term vanishes by integration by parts. The third term can be divided into two parts as follows

    κx((˜v+ε2V)xV)κxV=κx(˜vxV)κxV+κx(ε2VxV)κxV;

    for the first part, integration by parts gives

    κx(˜vxV)κxV=12x˜vκxVκxV+0γκ1Cγκκγx˜vγ+1xVκxVCV2H2,

    where, when κ=0, there is no such "summation" term. Regarding the second part, after integration by parts, for 0κ2, we have

    ε2κx(VxV)κxV=ε22xVκxVκxV+0γκ1Cγκε2κγxVγ+1xVκxVCε2xVH1V2Hκ.

    For the fourth therm, similar to the first term,

    κx(x˜vV)κxV=(x˜vκxV)κxV+0γκ1Cγκκ+1γx(˜v)γxVκxVCV2H2.

    For the fifth therm, similar to the first term, integration by parts gives

    κx(βn2xV)κxV=x(βn)κ+1xVκxV+βnκ+1xVκ+1xV0γκ1Cγκκγx(βn)γ+2xVκxVC(εx˜n+ε3xNL)(κ+1xV2+κxV2)+Cκ+1xV2.

    By Lemma (1.1), we have

    κx(εR2)κxVCεV2Hκ.

    Now, we estimate the right side of (2.34) for 0<κ2; taking κx of (1.16a), we have

    κ+1xVε=1n(λ0vεκ+1xNtκxN0γκ1Cγκκγx(˜v+ε2V)γ+1xN(nε)κ+1xV0γκ1Cγκκγx(nε)γ+1xVκx(x˜nV)κx(x˜vN)εκxR1)=:8i=1Di

    Incorporating this into the right side of (2.34), we have

    8i=1Ii=8i=1κ1x(1nexNe)Di. (2.35)

    We first estimate the term for 3i8; for the term I3, by the Hölder inequality and Sobolev embedding inequality, we have

    I3=0γκ1Cγκκ1x(1nexNe)1nκγx˜vγ+1xN0γκ1Cγκε2κ1x(1nexNe)1nκγxVγ+1xNC(N2H2+Ne2H2)+C1(1+ε2N2H2+ε2V2H2)εNeH3.

    Similar to I3, simple calculation gives

    I4=κ1x(1nexNe)1n(˜n+ε2N)κ+1xVC(V2H2+Ne2H2)+C1(1+ε2N2H2+ε2V2H2)εNeH3,

    and

    I5=0γκ1Cγκκ1x(1nexNe)1n(κγxn+ε2κγxNe)γ+1xVC(V2H2+Ne2H2)+Cε2κxNeLNe2H2V2H2.

    By Lemma (1.1), with a similar calculation to that for I3, we obtain

    I6+I7+I8C(V2H2+N2H2+Ne2H2).

    Lemma 2.4. Let (N,V,Ne) be a solution to (1.16); we have

    I1C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε), (2.36)

    where I1 is defined in (2.35).

    Proof. For the first term I1, by using a simpler calculation, we can decompose it into two parts:

    I1=κ1x(1nexNe)1nλ0vεκ+1xN+0<γ2Cγκκ1x(1nexNe)1nκγx(λ0vε)γ+1xN=:I11+I12.

    Taking κ+1x of(1.16c), we have

    κ+1xN=κ+1xNeκ+1x(αεne2xNe)+κ+1x(2αn2eε2x˜nexNe)εκ+1xR3;

    inserting it into I11 gives

    I11=κ1x(1nexNe)1nλ0vε(κ+1xNeκ+1x(αεne2xNe)+κ+1x(2αn2eε2x˜nexNe)εκ+1xR3)=:4i=1I11i.

    Regarding estimate of I111, by commutator estimation and Sobolev embedding, we obtain

    I111=κ1x(1nexNe)1nλ0vεκ+1xNeC1ε(1+ε2|(N,V,Ne)|2ε)|(N,V,Ne)|2ε.

    Regarding estimate of I12, by performing integration by parts twice, commutator estimation and Sobolev embedding, we have

    I112=κx(1nexNe)1nλ0vεκx(αεne2xNe)+κ1x(1nexNe)x(1nλ0vε)κx(αεne2xNe)C1ε(1+ε2|(N,V,Ne)|2ε)(ε||Ne||2Hκ+2).

    The estimate of I13 is similar to that of I12:

    I113C1(1+ε2|(N,V,Ne)|2ε)(ε||Ne||2Hκ+1).

    By Lemma 1.1, we have

    I114CκxNe2.

    With a similar estimate to I11, for 0<γ2, we obtain

    I12C1(1+ε2|(N,V,Ne)|2ε)(ε||Ne||2Hκ+1).

    Combining the estimate of I11 and I12, we can get (2.36).

    Lemma 2.5. Let (N,V,Ne) be a solution to (1.16); then, the following inequality holds

    I212ddt1nne|κxNe|212ddtαεnn2e|κ+1xNe|2+C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε), (2.37)

    where I2 is defined in (2.35).

    Proof. Taking tκx of (1.16c), we have

    tκxN=tκxNetκx(αεne2xNe)+tκx(2αn2eε2x˜nexNe)εtκxR3;

    inserting it into I2 gives

    I2=κ1x(1nexNe)1n(tκxNetκx(αεne2xNe)+tκx(2αn2eε2x˜nexNe)εtκxR3)=:4i=1I2i.

    Regarding the estimate of I21, through integration by parts, we obtain

    I21=12ddt1nne|κxNe|2+12t(1nne)|κxNe|2Cγκ1κ1γx(1nne)γ+1xNe1ntκxNe,

    where the second term on the right-hand side is bounded as follows

    12t(1nne)|κxNe|2C1(1+ε2|(V,Ne)|2ε)(ε||Ne||2Hκ),

    where we have used the fact that

    |t(1nne)|C(ε(|t˜n|+|t~ne|)+ε3(|tN|+|tNe|));

    for the third term, by the Hölder inequality and Sobolev embedding inequality, we have

    |Cγκ1κ1γx(1nne)γ+1xNe1ntκxNe|Cε(εtκxNe2+εκ+1xNe2)(ε2NeH1+ε2NH1);

    therefore, we have

    I21=12ddt1nne|κxNe|2+C1(1+ε2|(V,Ne)|2ε)(ε||Ne||2Hκ). (2.38)

    For the estimate of I22, we have the following decomposition:

    I22=κ1x(1nexNe)1nαεnetκ+2xNe+κ1x(1nexNe)1nt(αεne)κ+2xNe+0<γκ1Cγκκ1x(1nexNe)1ntκγx(αεne)γ+2xNe+0<γκ1Cγκκ1x(1nexNe)1nκγx(αεne)tγ+2xNe=:4i=1I22i.

    For the term I221, through integration by parts, and by using the Hölder inequality and Sobolev embedding inequality, we have

    I221=12ddtαεnn2e|κ+1xNe|2+12t(αεnn2e)|κ+1xNe|2Cγκκγx(1ne)κ+1xNeαεnnetκ+1xNeκ1x(1nexNe)x(1nαεne)tκ+1xNe12ddtαεnn2e|κ+1xNe|2+C1(1+ε2|(V,Ne)|2ε)(ε||Ne||2Hκ),

    where we used the fact that

    |t(αεnn2e)|Cε2(1+ε2(|tN|+|tNe|)),|x(αεnne)|Cε2(1+ε2(|xN|+|xNe|)).

    For the term I222, by the Hölder inequality and Sobolev embedding inequality, we have

    I222Cε2(κxNe2+κ+2xNe2)+Cε4κxNeL(tNe2+κ+2xNe2).

    For the term I223, by the Hölder inequality and Sobolev embedding inequality, we have

    I223C1(1+ε2|(V,Ne)|2ε)(ε||Ne||2Hκ).

    Therefore, we have the estimate

    I2212ddtαεnn2e|κ+1xNe|2+C1(1+ε2|(V,Ne)|2ε)(ε||Ne||2Hκ). (2.39)

    For the estimate of I23, by the Hölder inequality and Sobolev embedding inequality, we have

    I23Cε2(||κxNe||2+ε||κ+1xNe||2)+Cε5||κxNe||LtNe2+C(ε2||κxNe||2+εtκ+1xNe2). (2.40)

    Regarding the estimate of I24, by Lemma 1.1, we have

    I24CεκxNe2. (2.41)

    Combining (2.38), (2.39), (2.40) and (2.41), we complete this lemma.

    Proposition 2.2. Let (N,V,Ne) be a solution to (1.16); then,

    12ddt(ε3xV2)+12ddt(εnne|3xNe|2+αε2n2en|4xNe|2)C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε). (2.42)

    Proof. Taking 3x of (1.16b) and then taking the inner product with ε3xV, we have

    12ddt(ε3xV2)λ0ε4xVε3xV+1ε3x(vxV)ε3xV+3x(x˜vV)ε3xV3x(βn2xV)ε3xV+ε3xR2ε3xV=2x(1nexNe)4xV. (2.43)

    Estimate the left-hand side of (2.43). The second term vanishes by integration by parts. For the third term, by the Hölder inequality and Sobolev embedding inequality, we get

    1ε3x(vxV)ε3xV=12εx(˜v+ε2V)|3xV|2+ε2x(˜v+ε2V)2xV3xV+ε3x(˜v+ε2V)xV3xVC(1+ε2xVL+ε22xVL+ε2xVL)(ε2xV2+ε3xV2)C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε).

    Regarding the estimate for the fourth term, similar to the third term, we have

    3x(x˜vV)ε3xVCε(1+V2H3).

    Regarding the estimate for the fifth term, we have the following decomposition:

    3x(βn2xV)ε3xV=βε1n5xV3xV+βεx(1n)4xV3xV+βε2x(1n)3xV3xV+βε3x(1n)2xV3xV=:E1+E2+E3+E4.

    Integration by parts twice yields

    E1=β2ε2x(1n)|3xV|2βε1n|4xV|2Cε||4xV||2+Cε2||3xV||2+Cε3||3xV||L(||2xN||2+ε||3xV||2).

    Through by parts, and by using the Sobolev embedding inequality, we have

    E2+E3=β2ε2x(1n)3xV3xVCε2(1+ε(||2xN||2+ε||3xV||2))||3xV||2.

    Similarly, through integration by parts, and by using the Sobolev embedding inequality, we have

    E4=βε2x(1n)|3xV|2βε2x(1n)2xV4xVCε2(1+ε(||2xN||2+ε||3xV||2))||3xV||2+Cε2||4xV||2+Cε2||2xV||L(||2xN||2+ε2||4xV||2).

    For the last term, by Lemma 1.1, we have

    ε3xR2ε3xVCε2(1+V2H3).

    Estimate the right-hand side of (2.43). Taking 3x of (1.16a) and inserting it into the right-hand side of (2.43) gives

    6i=12x(1nexNe)1n(3x((λ0v)xN)εt3xN2γ=1Cγ33γxnγ+1xVε3x(x˜nV)ε3x(˜vN)ε23xR1)=:6i=1˜Ii.

    We first give the estimate of ˜Ii for 3i6. For ˜I3, we have the following decomposition:

    ˜I3=3γ=1Cγ32x(1nexNe)1nγxε˜n4γxV3γ=1Cγ32x(1nexNe)1nγxε3N4γxV=:˜I31+˜I32.

    Regarding the estimate for ˜I31, by the Hölder inequality and Sobolev embedding, we have

    ˜I31=3γ=1Cγ3ε(1ne3xNe)1nγx˜n4γxV3γ=1Cγ3εx(1ne)1n2xNeγx˜n4γxV3γ=1Cγ3ε2x(1ne)1nxNeγx˜n4γxVC(ε23xNe2+ε2V2H3+ε2xNe2)(xNeL+2xNeL).

    Regarding the estimate for ˜I32, through integration by parts, and by using the Hölder inequality and Sobolev embedding, we have

    ˜I32C1(1+|(V,Ne)|2ε)|(V,Ne)|2ε.

    Via a similar calculation process, we have

    ˜I4,5C(1+ε32xNeL)(εNe2H3+εV2H3).

    By Lemma 1.1, we have

    ˜I6Cε(ε2Ne2H3).

    Lemma 2.6. Let (N,V,Ne) be a solution to (1.16); we have

    ˜I1C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε). (2.44)

    Proof. We have the following decomposition:

    ˜I1=2x(1nexNe)λ0vn4xN2x(1nexNe)1nx(ε˜v+ε3V)3xN2x(1nexNe)1n[3x(ε˜v+ε3V)xN+2x(ε˜v+ε3V)2xN]=:˜I11+˜I12+˜I13

    Regarding the estimate for ˜I11, taking 4x of (1.16c) and inserting it into ˜I11, we have

    ˜I11=2x(1nexNe)λ0vn(4xNe4x(αεne2xNe)+4x(2αn2eε2x˜nexNe)ε4xR3)=:4i=1˜I11i

    Regarding the estimate for ˜I111, by the Hölder inequality and Sobolev embedding, we have

    ˜I111C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε),

    where we used the fact that

    |x(λ0vn)|Cε(1+ε2|xN|+ε2|xV|+ε2|xNe|).

    Regarding the estimate for ˜I112 and ˜I113, through integration by parts, using the Hölder inequality and Sobolev embedding, we have

    ˜I112,3C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε).

    By Lemma 1.1, we have

    ˜I114Cε(ε3xNe2+ε2xNe2+εxNe2).

    Therefore, we have

    ˜I11C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε).

    Regarding the estimate for ˜I12, through integration by parts, and by using the the Hölder inequality and Sobolev embedding, we have

    ˜I12=3x(1nexNe)1nx(ε˜v+ε3V)2xN+2x(1nexNe)x(1n)x(ε˜v+ε3V)2xN+2x(1nexNe)1n2x(ε˜v+ε3V)2xNC1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε).

    Regarding the estimate for ˜I13, through integration by parts, and by using the Hölder inequality and Sobolev embedding, we have

    ˜I13C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε).

    Lemma 2.7. Let (N,V,Ne) be a solution to (1.16); we have

    ˜I212ddtεnne|3xNe|212ddtαε2n2en|4xNe|2++C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε). (2.45)

    Proof. Taking t3x of (1.16c), and then inserting the result in ˜I2, we have

    ˜I2=2x(1nexNe)εn(t3xNet3x(αεne2xNe)+t3x(2αn2eε2x˜nexNe)εt3xR3)=:4i=1˜I2i.

    Regarding the estimate for ˜I21, through integration by parts, we have

    ˜I21=12ddtεnne|3xNe|2+12t(εnne)|3xNe|2x(1ne)2xNeεnt3xNe2x(1ne)xNeεnt3xNe=:12ddtεnne|3xNe|2+3i=1˜I21i.

    For ˜I211, by using the Hölder inequality and Sobolev embedding, we have

    ˜I211Cε(1+ε2tNL+ε2tNeL)(ε||3xNe||2).

    For ˜I212, through integration by parts, by using the Hölder inequality and Sobolev embedding, we have

    ˜I212=2x(1ne)2xNeεnt2xNe+x(1ne)3xNeεnt2xNe+x(1ne)2xNex(εn)t2xNeCε(1+ε32xNL+εxNL+εxNeL)(2xNe2+ε3xNe2+εt2xNe2).

    For ˜I213, it is similar to ˜I212:

    ˜I213=3x(1ne)xNeεnt2xNe+2x(1ne)2xNeεnt2xNe+2x(1ne)xNex(εn)t2xNeCε(1+ε23xNeL+ε22xNeL+εxNL)(εt2xNe2+xNe2+2xNe2).

    Therefore, we have

    ˜I2112ddtεnne|3xNe|2+C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε).

    Regarding the estimate for ˜I22, we have the following decomposition:

    ˜I22=εnen4xNet2x(αεne2xNe)x(εnen)3xNet2x(αεne2xNe)+x(1ne)2xNeεnt3x(αεne2xNe)+2x(1ne)xNeεnt3x(αεne2xNe)=:4i=1˜I22i.

    For the term ˜I221, through integration by parts, we have

    ˜I221=12ddtαε2n2en|4xNe|2+12t(αε2n2en)|4xNe|2εnen4xNet(αεne)4xNeεnen4xNetx(αεne)3xNeεnen4xNex(αεne)t3xNeεnen4xNet2x(αεne)2xNeεnen4xNe2x(αεne)t2xNe=:12ddtαε2n2en|4xNe|2+6i=1˜I221i.

    By using the Hölder inequality and Sobolev embedding, we have

    ˜I2211,2,3Cε(1+ε2||tNe||2+ε2||tN||2+ε2||txNe||L+ε3||xNe||L)(ε2||4xNe||2+ε||3xNe||2).

    Regarding the term ˜I224, due to the term t3xNe, even if we raise the Sobolev order or the expansion order, it cannot be controlled in terms of |(V,Ne)|ε, the essential reason is related to Lemmas 2.2 and 2.3. But, by observing its features, we can use (1.16c) to complete this estimate. Simple calculation gives

    ˜I2214=εn4xNex(1ne)tx(αεne2xNeNe)+εn4xNex(1ne)txNe+εn4xNex(1ne)(xt(αεne)2xNe+t(αεne)3xNe+x(αεne)t2xNe);

    by using (1.16c), we have

    αεne2xNeNe=2αn2eε2x˜nexNeεR3N.

    Inserting it into ˜I2214, and using the Hölder inequality and Sobolev embedding, we have

    ˜I2214=εn4xNex(1ne)tx(2αn2eε2x˜nexNeεR3N)+εn4xNex(1ne)(xt(αεne)2xNe+t(αεne)3xNe+x(αεne)t2xNe)+εn4xNex(1ne)txNeC1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε).

    Regarding the terms ˜I2215 and ˜I2216, by using the Hölder inequality, we obtain

    ˜I2215+˜I2216C(1+ε22xNeL)(ε24xNe2+ε2xNe2+εt2xNe2).

    Therefore, we have

    ˜I22112ddtαε2n2en|4xNe|2+C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε).

    Regarding the estimate of ˜I222, by using the Hölder inequality and Sobolev embedding, we have

    ˜I222C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε)αε2x(1nen)1ne3xNet4xNe+F1,

    where we note that

    F1=:αε2x(1nen)1ne3xNet4xNe.

    The difficulty is that the term t4xNe cannot be controlled in terms of |(V,Ne)|ε; we can use (1.16c) to complete this estimate. Simple calculation gives

    F1==εx(1nen)3xNet2x(αεne2xNeNe)εx(1nen)3xNet2xNe+εx(1nen)3xNe(t2x(αεne)2xNe+2x(αεne)t2xNe+tx(αεne)3xNe+x(αεne)t3xNe+t(αεne)4xNe);

    by using (1.16c), through integration by parts, by using the Hölder inequality and Sobolev embedding, we have

    F1=εx(1nen)3xNet2x(2αn2eε2x˜nexNeεR3N)εx(1nen)3xNet2xNe+εx(1nen)3xNe(t2x(αεne)2xNe+2x(αεne)t2xNe+tx(αεne)3xNe+x(αεne)t3xNe+t(αεne)4xNe)C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε).

    Regarding the estimate of ˜I223, through integration by parts, and by using the Hölder inequality and Sobolev embedding, we have

    ˜I223=αε22x(1ne)2xNe1nt2x(1ne2xNe)αε2x(1ne)3xNe1nt2x(1ne2xNe)αε22x(1ne)2xNex(1n)t2x(1ne2xNe)C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε)+F2,

    where we note that

    F2=:αε2x(1ne)3xNe1n1net4xNe;

    by using (1.16c), we have

    F2=εx(1ne)3xNe1nαεnet2xNe(2αn2eε2x˜nexNeεR3N)εx(1ne)3xNe1nt2xNe+εx(1ne)3xNe1n(t2x(αεne)2xNe+2x(αεne)t2xNe+tx(αεne)3xNe+tx(αεne)t3xNe+t(αεne)4xNe)C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε);

    therefore, we have

    ˜I223C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε).

    Regarding the estimate of ˜I224, through integration by parts, and by using the Hölder inequality and Sobolev embedding, we have

    ˜I224C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε)+F3,

    where we note that

    F3=:αε24x(1ne)xNe1n1net3xNe;

    by using (1.16c) we have

    F3=ε4x(1ne)xNe1ntx(2αn2eε2x˜nexNeεR3N)+ε4x(1ne)xNe1nt2xNeC1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε).

    Therefore, we have

    ˜I2212ddtαε2n2en|4xNe|2+C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε).

    Regarding the estimate for ˜I23, similar to ˜I22, we have

    ˜I23C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε).

    By Lemma 1.1, we have

    ˜I24Cε(ε3xNe2+ε22xNe2+ε2xNe2).

    Combining these estimates, we complete this lemma.

    Proof of Theorem 1.3. Combining Propositions 2.1 and 2.2, we have

    12ddt(V2H2+ε3xV2)+12ddt((1nne|Ne|2+αεnn2e|xNe|2)+(1nne|xNe|2+αεnn2e|2xNe|2)+(1nne|2xNe|2+αεnn2e|3xNe|2)+(εnne|3xNe|2+αε2n2en|4xNe|2))C1(1+ε2|(V,Ne)|2ε)(1+|(V,Ne)|2ε). (3.1)

    Integrating the inequality over (0,t) yields

    |(V,Ne)(t)|2εC|(V,Ne)(0)|2ε+t0C1(1+|(V,Ne)|2ε)(1+|(V,Ne)|2ε)dsC|(V,Ne)(0)|2ε+t0C1(1+ε˜C)(1+|(V,Ne)|2ε)ds,

    where C is an absolute constant.

    Since C1 is nondecreasing and depends on |(V,Ne)|2ε through ε|(V,Ne)|2ε, let C1=c(1) and C2>Csupε<1|(V,Ne)(0)|2ε. For any arbitrarily given τ>0, we choose ˜C such that ˜C>e4C1τ(1+C2)(1+C1). Then there exists ε0>0 such that ε˜C1 for all ε<ε0; we have

    sup0tτ|(V,Ne)(t)|2ε<˜C/2.

    By Lemma 2.1, we have

    sup0tτ|(N)(t)|2H2˜C/2.

    By the Grönwall inequality, we complete the proof of Theorem 1.3.

    The authors declare that they have not used artificial intelligence tools in the creation of this article.

    The author (R. Rong) was supported by Xiamen Institute of Technology High-level Talents Research Launch Project (No. YKJ22050R) and Fujian Province Young and Middle-aged Teacher Education Research Project (No. JAT220337). The author (H. Liu) was supported by the National Natural Science Foundation of China (Nos. 12271293, 11901342) and Natural Science Foundation of Shandong Province (No. ZR2023MA002).

    All authors declare no conflict of interest that may influence the publication of this paper.



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