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(ε−1), 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(ε−1), 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 αβs≠0. 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
{∂t′ni+∂x′(nivi)=0,(1.1a)mini(∂t′vi+vi∂x′vi)=−∂x′pi−nie∂x′ϕ+μ∂2x′vi,(1.1b)0=e∂x′ϕ−KTene∂x′ne,(1.1c)∂2x′ϕ=4πe(ne−ni),(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=t′⋅cs/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+v∂xv+∂xΦ−νLcs1n∂2xv=0,(1.2b)∂xΦ=1ne∂xne,(1.2c)λ2DL2∂2xΦ=ne−n,(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=ni−n0; we have that n−1=Δnn0≪1; taking Δnn0=ε≪1, 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+v∂xv+∂xΦ−βεn∂2xv=0,(1.3b)ne−n=αε∂2xΦ,(1.3c)∂xΦ=1ne∂xne.(1.3d) |
By applying the following Gardner-Morikawa transformation [29] to (1.3),
x→x−λ0t, t→εt, | (1.4) |
we obtain the following parameterized system:
{ε∂tn−λ0∂xn+∂x(nv)=0,(1.5a)ε∂tv−λ0∂xv+v∂xv+∂xΦ−βεn∂2xv=0,(1.5b)ne−n=αε∂2xΦ,(1.5c)∂xΦ=1ne∂xne,(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
{−λ0∂xn(1)+∂xv(1)=0,(1.7a)−λ0∂xv(1)+1ne∂xn(1)e=0,(1.7b)n(1)e−n(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)−λ0∂xn(2)+∂x(v(2)+n(1)v(1))=0,(1.9a)∂tv(1)−λ0∂xv(2)+v(1)∂xv(1)+1ne∂xn(2)e−βn∂2xv(1)=0,(1.9b)n(2)e−n(1)=αne∂2xn(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)e∂xn(1)e+α2λ30∂3xn(1)e−β2n∂2xn(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)e−αλ20∂2xn(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)−λ0∂xn(3)+∂x(v(3)+n(1)v(2)+n(2)v(1))=0,(1.12a)∂tv(2)−λ0∂xv(3)+v(1)∂xv(2)+v(2)∂xv(1)+1ne∂xn(3)e−βn∂2xv(2)=0,(1.12b)n(3)e−n(3)=−αn2e(∂xn(1)e)2+αne∂2xn(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+3λ02∂x(n(1)en(2)e)+α2λ30∂3xn(2)e−β2n∂2xn(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+3λ02∂x(n(1)en(k)e)+α2λ30∂3xn(k)e−β2n∂2xn(k)e=G(k−1),k≥3, | (1.14) |
where G(k−1) only depends on n(1)e,…,n(k−1)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/L2≫ν/Lcs) or the Burgers equation (λ2D/L2≪ν/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 s1≥2 be a sufficiently large integer. Then for any given initial data n(1)0∈Hs1(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 k≥2 and sk≤s1−3(k−1) 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 ε→0. Suppose that (n(k),v(k),n(k)e), 1≤k≤4 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 1≤k≤4 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
{∂tN−λ0−vε∂xN+nε∂xV+∂x˜nV+∂x˜vN+εR1=0,(1.16a)∂tV−λ0−vε∂xV+1neε∂xNe+∂x˜vV−βn∂2xV+εR2=0,(1.16b)Ne−N=αεne∂2xNe−2αn2eε2∂x˜ne∂xNe+εR3,(1.16c) |
where
{R1=∂xn(4)+∂x(n(2)v(4)+n(3)v(3)+n(4)v(3))+ε∂x(n(3)v(4)+n(4)v(3))+ε2∂x(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))+ε2∂x(v(3)v(4))−βn∂xv(3)−βnε∂xv(4),R3=n(4)−n(4)e−2αn2e(∂xn(1)e∂xn(2)e)−αn2eε(2∂xn(3)e∂xn(1)e+∂xn(2)e∂xn(2)e)−2αn2eε2(∂xn(4)e∂xn(1)e+∂xn(3)e∂xn(2)e)+αne(∂2xn(3)e+ε∂2xn(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)e‖Hδ) and C=C(‖n(i)e‖Hδ,√ε‖Ne‖Hs) such that ‖R1,R2‖Hs≤C(‖n(i)e‖Hδ) and
‖R3‖Hs≤C(‖n(i)e‖Hδ,ε‖Ne‖Hs)‖Ne‖Hs, s=1,2,…, | (1.18) |
‖∂TR3‖Hs≤C(‖ne(i)‖Hδ,ε‖Ne‖Hs)‖∂TNe‖Hs, s=1,2,…, | (1.19) |
where δ=max{2,s−1}; 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 si≥2 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+ε2‖∂4xNe‖2L2}≤Cτ(1+‖(N0,V0,Ne0)‖2H2+ε‖(∂3xV0,∂3xNe0)‖2L2+ε2‖∂4xNe0‖2L2). | (1.22) |
From (1.22), we obtain the uniform H2-norm of the remainder (N,V,Ne) on ε, and it satisfies
sup[0,ε−1τ]‖((n−1)/ε(ne−1)/εv/ε)−BKdV‖H2≤Cε | (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=‖V‖2H2+‖Ne‖2H2+ε‖∂3xV‖2+ε‖∂3xNe‖2++ε2‖∂4xNe‖2. | (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],
‖N‖2H2,‖|(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,β≥0 such that
|∂αn(i)e∂βNeR3|≤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 α≥0 be an integer. There exist some constants 0<ε1<1 and C1=C1(ε˜C) such that for every 0<ε<ε1,
C−11‖∂αxN‖2≤‖∂αxNe‖2+ε‖∂α+1xNe‖2+ε2‖∂α+2xNe‖2≤C1‖∂αxN‖2. | (2.3) |
Proof. When α=0, taking the inner product of (1.16c) with Ne, we have
‖Ne‖2+εαne‖∂xNe‖2=∫NNe−εα∫∂x(1ne)∂xNeNe−ε22αn2e∫∂x˜ne∂xNeNe+ε∫R3Ne, | (2.4) |
where α is a constant and 12<ne<32; therefore, there exists a constant C such that
εαne‖∂xNe‖2≥Cε‖∂xNe‖2, | (2.5) |
so the left of (2.5) is larger than ‖Ne‖2+ε‖∂xNe‖2.
Due to the fact that
|∂x(1ne)|≤C(ε|∂x˜ne|+ε3|∂xNe|), | (2.6) |
combined with Young's inequality, we get
|−εα∫∂x(1ne)∂xNeNe|≤18‖Ne‖2+Cε2‖∂xNe‖2+Cε4˜C‖∂xNe‖2. | (2.7) |
Due to the fact that ˜ne is bounded in L∞, by the Hölder inequality, we have
|−ε22αn2e∫∂x˜ne∂xNeNe|≤18‖Ne‖2+Cε2‖∂xNe‖2. | (2.8) |
From Lemma 1.1, it holds that ε<ε1, which is sufficiently small such that
ε∫R3Ne≤14‖Ne‖2. | (2.9) |
Therefore, by the Hölder inequality, we have
‖Ne‖2+ε‖∂xNe‖2≤C‖N‖2. | (2.10) |
Taking the inner product of (1.16c) with ε∂2xNe, we have
ε‖∂xNe‖2+ε2αne‖∂2xNe‖2=ε32αn2e∫∂x˜ne∂xNe∂2xNe−ε∫N∂2xNe−ε2∫R3∂2xNe; | (2.11) |
by the Hölder inequality, the result is as follows
ε‖∂xNe‖2+ε2‖∂2xNe‖2≤C‖N‖2. | (2.12) |
Then, applying the L2-norm of (1.16c), we obtain some C such that
‖N‖2≤‖Ne‖2+ε2‖∂2xNe‖2+ε4‖∂xNe‖2. | (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 ε∂α+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 α≥0 be an integer. There exist some constants C and C1=C1(ε˜C) such that
ε‖∂tN‖2≤C(‖Ne‖2H1+‖V‖2H1+ε‖∂2xNe‖2+ε2‖∂3xNe‖2)+Cε | (2.14) |
and
‖ε∂txN‖2≤C1(‖Ne‖2H2+‖V‖2H2+ε‖∂3xNe‖2+ε2‖∂4xNe‖2)+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
||ε∂tN||2≤C(||∂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
||ε∂txN||2≤C(||V||2H2+||N||2H2)+Cε6∫|∂xV|2|∂xN|2+Cε4. | (2.17) |
By the Sobolev embedding inequality, we have
Cε6‖∂xV‖2L∞||∂xN||2≤Cε6||V||2H2+||N||2H1≤C(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 α≥0 be an integer. There exist some constants C1=C1(ε˜C) and ε1>0 such that for any 0<ε<ε1,
ε‖∂t∂α+1xNe‖2+‖∂t∂αxNe‖2≤C‖∂t∂αxN‖2+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
‖∂tNe‖2+εαne∫|∂txNe|2=∫∂tN∂tNe+αε∫∂t(1ne)∂2xNe∂tNe−αε∫∂x(1ne)∂t∂xNe∂tNe−2αε2∫∂t(1n2e)∂x˜ne∂xNe∂tNe−∫(2αn2eε2∂t∂x˜ne∂xNe)∂tNe−∫(2αn2eε2∂x˜ne∂t∂xNe)∂tNe+∫ε∂tR3∂tNe=:7∑i=1Ai, | (2.20) |
where α is a constant and 1/2<ne<3/2, so there exists a constant C such that εαne∫|∂txNe|2≥Cε∫|∂txNe|2; therefore, the left of (2.20) is greater than or equal to C(‖∂tNe‖2+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=∫∂tN∂tNe≤γ‖∂tNe‖2+Cγ‖∂tN‖2. | (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
A2≤Cε2∫(|∂t˜ne|+ε2|∂tNe|)∂2xNe∂tNe≤C1(||∂tNe||2+ε2‖∂2xNe‖2)+C1,A3≤Cε2∫(|∂x˜ne|+ε2|∂xNe|)∂t∂xNe∂tNe≤C1(||∂tNe||2+ε‖∂xtNe‖2)+C1, | (2.23) |
and
A4≤Cε3∫(|∂t˜ne|+ε2|∂tNe|)∂x˜ne∂xNe∂tNe≤C1(||∂tNe||2+ε‖∂xNe‖2)+C1. | (2.24) |
Similar to A2, by the Hölder inequality, we obtain
A5,6,7≤C1(||∂tNe||2+ε‖∂xtNe‖2)+C1. | (2.25) |
Therefore, we have
||∂tNe||2+ε||∂xtNe||2≤C||∂tN||2+C1. | (2.26) |
When α=1, we take ∂xt of (1.16c); then, taking the inner product with ε∂xtNe, we have
ε‖∂xtNe‖2+αε2ne∫|∂t∂2xNe|2=ε∫∂xtN∂xtNe+ε∫∂xt(αεne)∂2xNe∂xtNe−ε∫∂x(αεne)∂t∂2xNe∂xtNe−ε∫∂xt(2αn2e)ε2∂x˜ne∂xNe∂xtNe−ε∫(2αn2eε2∂xt∂x˜ne∂xNe)∂xtNe−ε∫∂xt(2αn2eε2∂x˜ne∂xt∂xNe)∂xtNe+ε∫ε∂xtR3∂xtNe=:7∑i=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
B1≤γε‖∂xtNe‖2+Cγ‖∂xtN‖2. | (2.28) |
Using (2.1), by the Hölder inequality and Sobolev embedding inequality, we have
B2≤Cε3(|∂xt˜ne|+ε2|∂xtNe|)∂2xNe∂xtNe≤C1(ε||∂xtNe||2+ε2‖∂t∂2xNe‖2)+C1 | (2.29) |
and
B3≤Cε3∫(|∂x˜ne|+ε2|∂xNe|)∂t∂2xNe∂xtNe≤C1(ε||∂xtNe||2+ε2‖∂t∂2xNe‖2)+C1. | (2.30) |
Similar to the process for B2, by the Sobolev embedding inequality, we have
B4,5,6,7≤C1(ε||∂xtNe||2+ε2‖∂t∂2xNe‖2)+C1; | (2.31) |
therefore, we have
ε||∂tNe||2+ε2||∂xtNe||2≤C||∂xtN||2+C1. | (2.32) |
We can give by the similar process for the case of α≥2.
Proposition 2.1. Let (N,V,Ne) be a solution to (1.16) and κ=0,1,2; then,
12ddt‖∂κxV‖2+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
12ddt‖∂κxV‖2−λ0ε∫∂κ+1xV∂κxV+∫∂κx((˜v+ε2V)∂xV)∂κxV+∫∂κx(∂x˜vV)∂κxV−∫∂κx(βn∂2xV)∂κxV+∫∂κx(εR2)∂κxV=∫∂κ−1x(1ne∂xNe)∂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(˜v∂xV)∂κxV+∫∂κx(ε2V∂xV)∂κxV; |
for the first part, integration by parts gives
∫∂κx(˜v∂xV)∂κxV=−12∫∂x˜v∂κxV∂κxV+∑0≤γ≤κ−1Cγκ∫∂κ−γx˜v∂γ+1xV∂κxV≤C‖V‖2H2, |
where, when κ=0, there is no such "summation" term. Regarding the second part, after integration by parts, for 0≤κ≤2, we have
ε2∫∂κx(V∂xV)∂κxV=−ε22∫∂xV∂κxV∂κxV+∑0≤γ≤κ−1Cγκε2∫∂κ−γxV∂γ+1xV∂κxV≤Cε2‖∂xV‖H1‖V‖2Hκ. |
For the fourth therm, similar to the first term,
∫∂κx(∂x˜vV)∂κxV=∫(∂x˜v∂κxV)∂κxV+∑0≤γ≤κ−1Cγκ∫∂κ+1−γx(˜v)∂γxV∂κxV≤C‖V‖2H2. |
For the fifth therm, similar to the first term, integration by parts gives
−∫∂κx(βn∂2xV)∂κxV=∫∂x(βn)∂κ+1xV∂κxV+∫βn∂κ+1xV∂κ+1xV−∑0≤γ≤κ−1Cγκ∫∂κ−γx(βn)∂γ+2xV∂κxV≤C(ε‖∂x˜n+ε3∂xN‖L∞)(‖∂κ+1xV‖2+‖∂κxV‖2)+C‖∂κ+1xV‖2. |
By Lemma (1.1), we have
∫∂κx(εR2)∂κxV≤Cε‖V‖2Hκ. |
Now, we estimate the right side of (2.34) for 0<κ≤2; taking ∂κx of (1.16a), we have
∂κ+1xVε=1n(λ0−vε∂κ+1xN−∂t∂κxN−∑0≤γ≤κ−1Cγκ∂κ−γx(˜v+ε2V)∂γ+1xN−(nε)∂κ+1xV−∑0≤γ≤κ−1Cγκ∂κ−γx(nε)∂γ+1xV−∂κx(∂x˜nV)−∂κx(∂x˜vN)−ε∂κxR1)=:8∑i=1Di |
Incorporating this into the right side of (2.34), we have
8∑i=1Ii=8∑i=1∫∂κ−1x(1ne∂xNe)Di. | (2.35) |
We first estimate the term for 3≤i≤8; for the term I3, by the Hölder inequality and Sobolev embedding inequality, we have
I3=−∑0≤γ≤κ−1Cγκ∫∂κ−1x(1ne∂xNe)1n∂κ−γx˜v∂γ+1xN−∑0≤γ≤κ−1Cγκε2∫∂κ−1x(1ne∂xNe)1n∂κ−γxV∂γ+1xN≤C(‖N‖2H2+‖Ne‖2H2)+C1(1+ε2‖N‖2H2+ε2‖V‖2H2)ε‖Ne‖H3. |
Similar to I3, simple calculation gives
I4=∫∂κ−1x(1ne∂xNe)1n(˜n+ε2N)∂κ+1xV≤C(‖V‖2H2+‖Ne‖2H2)+C1(1+ε2‖N‖2H2+ε2‖V‖2H2)ε‖Ne‖H3, |
and
I5=−∑0≤γ≤κ−1Cγκ∫∂κ−1x(1ne∂xNe)1n(∂κ−γxn+ε2∂κ−γxNe)∂γ+1xV≤C(‖V‖2H2+‖Ne‖2H2)+Cε2‖∂κxNe‖L∞‖Ne‖2H2‖V‖2H2. |
By Lemma (1.1), with a similar calculation to that for I3, we obtain
I6+I7+I8≤C(‖V‖2H2+‖N‖2H2+‖Ne‖2H2). |
Lemma 2.4. Let (N,V,Ne) be a solution to (1.16); we have
I1≤C1(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=∫∂κ−1x(1ne∂xNe)1nλ0−vε∂κ+1xN+∑0<γ≤2Cγκ∫∂κ−1x(1ne∂xNe)1n∂κ−γx(λ0−vε)∂γ+1xN=:I11+I12. |
Taking ∂κ+1x of(1.16c), we have
∂κ+1xN=∂κ+1xNe−∂κ+1x(αεne∂2xNe)+∂κ+1x(2αn2eε2∂x˜ne∂xNe)−ε∂κ+1xR3; |
inserting it into I11 gives
I11=∫∂κ−1x(1ne∂xNe)1nλ0−vε(∂κ+1xNe−∂κ+1x(αεne∂2xNe)+∂κ+1x(2αn2eε2∂x˜ne∂xNe)−ε∂κ+1xR3)=:4∑i=1I11i. |
Regarding estimate of I111, by commutator estimation and Sobolev embedding, we obtain
I111=∫∂κ−1x(1ne∂xNe)1nλ0−vε∂κ+1xNe≤C1ε(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(1ne∂xNe)1nλ0−vε∂κx(αεne∂2xNe)+∫∂κ−1x(1ne∂xNe)∂x(1nλ0−vε)∂κx(αεne∂2xNe)≤C1ε(1+ε2‖|(N,V,Ne)|‖2ε)(ε||Ne||2Hκ+2). |
The estimate of I13 is similar to that of I12:
I113≤C1(1+ε2‖|(N,V,Ne)|‖2ε)(ε||Ne||2Hκ+1). |
By Lemma 1.1, we have
I114≤C‖∂κxNe‖2. |
With a similar estimate to I11, for 0<γ≤2, we obtain
I12≤C1(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
I2≤−12ddt∫1nne|∂κxNe|2−12ddt∫αεnn2e|∂κ+1xNe|2+C1(1+ε2‖|(V,Ne)|‖2ε)(1+‖|(V,Ne)|‖2ε), | (2.37) |
where I2 is defined in (2.35).
Proof. Taking ∂t∂κx of (1.16c), we have
∂t∂κxN=∂t∂κxNe−∂t∂κx(αεne∂2xNe)+∂t∂κx(2αn2eε2∂x˜ne∂xNe)−ε∂t∂κxR3; |
inserting it into I2 gives
I2=−∫∂κ−1x(1ne∂xNe)1n(∂t∂κxNe−∂t∂κx(αεne∂2xNe)+∂t∂κx(2αn2eε2∂x˜ne∂xNe)−ε∂t∂κxR3)=:4∑i=1I2i. |
Regarding the estimate of I21, through integration by parts, we obtain
I21=−12ddt∫1nne|∂κxNe|2+12∫∂t(1nne)|∂κxNe|2−Cγκ−1∫∂κ−1−γx(1nne)∂γ+1xNe1n∂t∂κxNe, |
where the second term on the right-hand side is bounded as follows
12∫∂t(1nne)|∂κxNe|2≤C1(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
|−Cγκ−1∫∂κ−1−γx(1nne)∂γ+1xNe1n∂t∂κxNe|≤Cε(ε‖∂t∂κxNe‖2+ε‖∂κ+1xNe‖2)(ε2‖Ne‖H1+ε2‖N‖H1); |
therefore, we have
I21=−12ddt∫1nne|∂κxNe|2+C1(1+ε2‖|(V,Ne)|‖2ε)(ε||Ne||2Hκ). | (2.38) |
For the estimate of I22, we have the following decomposition:
I22=∫∂κ−1x(1ne∂xNe)1nαεne∂t∂κ+2xNe+∫∂κ−1x(1ne∂xNe)1n∂t(αεne)∂κ+2xNe+∑0<γ≤κ−1Cγκ∫∂κ−1x(1ne∂xNe)1n∂t∂κ−γx(αεne)∂γ+2xNe+∑0<γ≤κ−1Cγκ∫∂κ−1x(1ne∂xNe)1n∂κ−γx(αεne)∂t∂γ+2xNe=:4∑i=1I22i. |
For the term I221, through integration by parts, and by using the Hölder inequality and Sobolev embedding inequality, we have
I221=−12ddt∫αεnn2e|∂κ+1xNe|2+12∫∂t(αεnn2e)|∂κ+1xNe|2−Cγκ∫∂κ−γx(1ne)∂κ+1xNeαεnne∂t∂κ+1xNe−∫∂κ−1x(1ne∂xNe)∂x(1nαεne)∂t∂κ+1xNe≤−12ddt∫αεnn2e|∂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
I222≤Cε2(‖∂κxNe‖2+‖∂κ+2xNe‖2)+Cε4‖∂κxNe‖L∞(‖∂tNe‖2+‖∂κ+2xNe‖2). |
For the term I223, by the Hölder inequality and Sobolev embedding inequality, we have
I223≤C1(1+ε2‖|(V,Ne)|‖2ε)(ε||Ne||2Hκ). |
Therefore, we have the estimate
I22≤−12ddt∫αεnn2e|∂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
I23≤Cε2(||∂κxNe||2+ε||∂κ+1xNe||2)+Cε5||∂κxNe||L∞‖∂tNe‖2+C(ε2||∂κxNe||2+‖ε∂t∂κ+1xNe‖2). | (2.40) |
Regarding the estimate of I24, by Lemma 1.1, we have
I24≤Cε‖∂κxNe‖2. | (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(ε‖∂3xV‖2)+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 ε∂3xV, we have
12ddt(ε‖∂3xV‖2)−∫λ0ε∂4xVε∂3xV+∫1ε∂3x(v∂xV)ε∂3xV+∫∂3x(∂x˜vV)ε∂3xV−∫∂3x(βn∂2xV)ε∂3xV+∫ε∂3xR2ε∂3xV=∫∂2x(1ne∂xNe)∂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
∫1ε∂3x(v∂xV)ε∂3xV=12∫ε∂x(˜v+ε2V)|∂3xV|2+∫ε∂2x(˜v+ε2V)∂2xV∂3xV+∫ε∂3x(˜v+ε2V)∂xV∂3xV≤C(1+ε2‖∂xV‖L∞+ε2‖∂2xV‖L∞+ε2‖∂xV‖L∞)(ε‖∂2xV‖2+ε‖∂3xV‖2)≤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)ε∂3xV≤Cε(1+‖V‖2H3). |
Regarding the estimate for the fifth term, we have the following decomposition:
∫∂3x(βn∂2xV)ε∂3xV=βε∫1n∂5xV∂3xV+βε∫∂x(1n)∂4xV∂3xV+βε∫∂2x(1n)∂3xV∂3xV+βε∫∂3x(1n)∂2xV∂3xV=:E1+E2+E3+E4. |
Integration by parts twice yields
E1=β2ε∫∂2x(1n)|∂3xV|2−βε∫1n|∂4xV|2≤Cε||∂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=β2ε∫∂2x(1n)∂3xV∂3xV≤Cε2(1+ε(||∂2xN||2+ε||∂3xV||2))||∂3xV||2. |
Similarly, through integration by parts, and by using the Sobolev embedding inequality, we have
E4=−βε∫∂2x(1n)|∂3xV|2−βε∫∂2x(1n)∂2xV∂4xV≤Cε2(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
∫ε∂3xR2ε∂3xV≤Cε2(1+‖V‖2H3). |
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
6∑i=1∫∂2x(1ne∂xNe)1n(∂3x((λ0−v)∂xN)−ε∂t∂3xN−2∑γ=1Cγ3∂3−γxn∂γ+1xV−ε∂3x(∂x˜nV)−ε∂3x(˜vN)−ε2∂3xR1)=:6∑i=1˜Ii. |
We first give the estimate of ˜Ii for 3≤i≤6. For ˜I3, we have the following decomposition:
˜I3=−3∑γ=1Cγ3∫∂2x(1ne∂xNe)1n∂γxε˜n∂4−γxV−3∑γ=1Cγ3∫∂2x(1ne∂xNe)1n∂γxε3N∂4−γxV=:˜I31+˜I32. |
Regarding the estimate for ˜I31, by the Hölder inequality and Sobolev embedding, we have
˜I31=−3∑γ=1Cγ3ε∫(1ne∂3xNe)1n∂γx˜n∂4−γxV−3∑γ=1Cγ3ε∫∂x(1ne)1n∂2xNe∂γx˜n∂4−γxV−3∑γ=1Cγ3ε∫∂2x(1ne)1n∂xNe∂γx˜n∂4−γxV≤C(ε2‖∂3xNe‖2+ε2‖V‖2H3+ε2‖∂xNe‖2)(‖∂xNe‖L∞+‖∂2xNe‖L∞). |
Regarding the estimate for ˜I32, through integration by parts, and by using the Hölder inequality and Sobolev embedding, we have
˜I32≤C1(1+‖|(V,Ne)|‖2ε)‖|(V,Ne)|‖2ε. |
Via a similar calculation process, we have
˜I4,5≤C(1+ε3‖∂2xNe‖L∞)(ε‖Ne‖2H3+ε‖V‖2H3). |
By Lemma 1.1, we have
˜I6≤Cε(ε2‖Ne‖2H3). |
Lemma 2.6. Let (N,V,Ne) be a solution to (1.16); we have
˜I1≤C1(1+ε2‖|(V,Ne)|‖2ε)(1+‖|(V,Ne)|‖2ε). | (2.44) |
Proof. We have the following decomposition:
˜I1=∫∂2x(1ne∂xNe)λ0−vn∂4xN−∫∂2x(1ne∂xNe)1n∂x(ε˜v+ε3V)∂3xN−∫∂2x(1ne∂xNe)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(1ne∂xNe)λ0−vn(∂4xNe−∂4x(αεne∂2xNe)+∂4x(2αn2eε2∂x˜ne∂xNe)−ε∂4xR3)=:4∑i=1˜I11i |
Regarding the estimate for ˜I111, by the Hölder inequality and Sobolev embedding, we have
˜I111≤C1(1+ε2‖|(V,Ne)|‖2ε)(1+‖|(V,Ne)|‖2ε), |
where we used the fact that
|∂x(λ0−vn)|≤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
˜I112,3≤C1(1+ε2‖|(V,Ne)|‖2ε)(1+‖|(V,Ne)|‖2ε). |
By Lemma 1.1, we have
˜I114≤Cε(ε‖∂3xNe‖2+ε‖∂2xNe‖2+ε‖∂xNe‖2). |
Therefore, we have
˜I11≤C1(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(1ne∂xNe)1n∂x(ε˜v+ε3V)∂2xN+∫∂2x(1ne∂xNe)∂x(1n)∂x(ε˜v+ε3V)∂2xN+∫∂2x(1ne∂xNe)1n∂2x(ε˜v+ε3V)∂2xN≤C1(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
˜I13≤C1(1+ε2‖|(V,Ne)|‖2ε)(1+‖|(V,Ne)|‖2ε). |
Lemma 2.7. Let (N,V,Ne) be a solution to (1.16); we have
˜I2≤−12ddt∫εnne|∂3xNe|2−12ddt∫αε2n2en|∂4xNe|2++C1(1+ε2‖|(V,Ne)|‖2ε)(1+‖|(V,Ne)|‖2ε). | (2.45) |
Proof. Taking ∂t∂3x of (1.16c), and then inserting the result in ˜I2, we have
˜I2=−∫∂2x(1ne∂xNe)εn(∂t∂3xNe−∂t∂3x(αεne∂2xNe)+∂t∂3x(2αn2eε2∂x˜ne∂xNe)−ε∂t∂3xR3)=:4∑i=1˜I2i. |
Regarding the estimate for ˜I21, through integration by parts, we have
˜I21=−12ddt∫εnne|∂3xNe|2+12∫∂t(εnne)|∂3xNe|2−∫∂x(1ne)∂2xNeεn∂t∂3xNe−∫∂2x(1ne)∂xNeεn∂t∂3xNe=:−12ddt∫εnne|∂3xNe|2+3∑i=1˜I21i. |
For ˜I211, by using the Hölder inequality and Sobolev embedding, we have
˜I211≤Cε(1+ε2‖∂tN‖L∞+ε2‖∂tNe‖L∞)(ε||∂3xNe||2). |
For ˜I212, through integration by parts, by using the Hölder inequality and Sobolev embedding, we have
˜I212=∫∂2x(1ne)∂2xNeεn∂t∂2xNe+∫∂x(1ne)∂3xNeεn∂t∂2xNe+∫∂x(1ne)∂2xNe∂x(εn)∂t∂2xNe≤Cε(1+ε3‖∂2xN‖L∞+ε‖∂xN‖L∞+ε‖∂xNe‖L∞)(‖∂2xNe‖2+ε‖∂3xNe‖2+ε‖∂t∂2xNe‖2). |
For ˜I213, it is similar to ˜I212:
˜I213=∫∂3x(1ne)∂xNeεn∂t∂2xNe+∫∂2x(1ne)∂2xNeεn∂t∂2xNe+∫∂2x(1ne)∂xNe∂x(εn)∂t∂2xNe≤Cε(1+ε2‖∂3xNe‖L∞+ε2‖∂2xNe‖L∞+ε‖∂xN‖L∞)(ε‖∂t∂2xNe‖2+‖∂xNe‖2+‖∂2xNe‖2). |
Therefore, we have
˜I21≤−12ddt∫εnne|∂3xNe|2+C1(1+ε2‖|(V,Ne)|‖2ε)(1+‖|(V,Ne)|‖2ε). |
Regarding the estimate for ˜I22, we have the following decomposition:
˜I22=−∫εnen∂4xNe∂t∂2x(αεne∂2xNe)−∫∂x(εnen)∂3xNe∂t∂2x(αεne∂2xNe)+∫∂x(1ne)∂2xNeεn∂t∂3x(αεne∂2xNe)+∫∂2x(1ne)∂xNeεn∂t∂3x(αεne∂2xNe)=:4∑i=1˜I22i. |
For the term ˜I221, through integration by parts, we have
˜I221=−12ddt∫αε2n2en|∂4xNe|2+12∫∂t(αε2n2en)|∂4xNe|2−∫εnen∂4xNe∂t(αεne)∂4xNe−∫εnen∂4xNe∂t∂x(αεne)∂3xNe−∫εnen∂4xNe∂x(αεne)∂t∂3xNe−∫εnen∂4xNe∂t∂2x(αεne)∂2xNe−∫εnen∂4xNe∂2x(αεne)∂t∂2xNe=:−12ddt∫αε2n2en|∂4xNe|2+6∑i=1˜I221i. |
By using the Hölder inequality and Sobolev embedding, we have
˜I2211,2,3≤Cε(1+ε2||∂tNe||2+ε2||∂tN||2+ε2||∂t∂xNe||L∞+ε3||∂xNe||L∞)(ε2||∂4xNe||2+ε||∂3xNe||2). |
Regarding the term ˜I224, due to the term ∂t∂3xNe, 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=−∫εn∂4xNe∂x(1ne)∂t∂x(αεne∂2xNe−Ne)+∫εn∂4xNe∂x(1ne)∂t∂xNe+∫εn∂4xNe∂x(1ne)(∂x∂t(αεne)∂2xNe+∂t(αεne)∂3xNe+∂x(αεne)∂t∂2xNe); |
by using (1.16c), we have
αεne∂2xNe−Ne=2αn2eε2∂x˜ne∂xNe−εR3−N. |
Inserting it into ˜I2214, and using the Hölder inequality and Sobolev embedding, we have
˜I2214=−∫εn∂4xNe∂x(1ne)∂t∂x(2αn2eε2∂x˜ne∂xNe−εR3−N)+∫εn∂4xNe∂x(1ne)(∂x∂t(αεne)∂2xNe+∂t(αεne)∂3xNe+∂x(αεne)∂t∂2xNe)+∫εn∂4xNe∂x(1ne)∂t∂xNe≤C1(1+ε2‖|(V,Ne)|‖2ε)(1+‖|(V,Ne)|‖2ε). |
Regarding the terms ˜I2215 and ˜I2216, by using the Hölder inequality, we obtain
˜I2215+˜I2216≤C(1+ε2‖∂2xNe‖L∞)(ε2‖∂4xNe‖2+ε‖∂2xNe‖2+ε‖∂t∂2xNe‖2). |
Therefore, we have
˜I221≤−12ddt∫αε2n2en|∂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
˜I222≤C1(1+ε2‖|(V,Ne)|‖2ε)(1+‖|(V,Ne)|‖2ε)−αε2∫∂x(1nen)1ne∂3xNe∂t∂4xNe+F1, |
where we note that
F1=:−αε2∫∂x(1nen)1ne∂3xNe∂t∂4xNe. |
The difficulty is that the term ∂t∂4xNe cannot be controlled in terms of ‖|(V,Ne)|‖ε; we can use (1.16c) to complete this estimate. Simple calculation gives
F1==−ε∫∂x(1nen)∂3xNe∂t∂2x(αεne∂2xNe−Ne)−ε∫∂x(1nen)∂3xNe∂t∂2xNe+ε∫∂x(1nen)∂3xNe(∂t∂2x(αεne)∂2xNe+∂2x(αεne)∂t∂2xNe+∂t∂x(αεne)∂3xNe+∂x(αεne)∂t∂3xNe+∂t(αεne)∂4xNe); |
by using (1.16c), through integration by parts, by using the Hölder inequality and Sobolev embedding, we have
F1=−ε∫∂x(1nen)∂3xNe∂t∂2x(2αn2eε2∂x˜ne∂xNe−εR3−N)−ε∫∂x(1nen)∂3xNe∂t∂2xNe+ε∫∂x(1nen)∂3xNe(∂t∂2x(αεne)∂2xNe+∂2x(αεne)∂t∂2xNe+∂t∂x(αεne)∂3xNe+∂x(αεne)∂t∂3xNe+∂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=−αε2∫∂2x(1ne)∂2xNe1n∂t∂2x(1ne∂2xNe)−αε2∫∂x(1ne)∂3xNe1n∂t∂2x(1ne∂2xNe)−αε2∫∂2x(1ne)∂2xNe∂x(1n)∂t∂2x(1ne∂2xNe)≤C1(1+ε2‖|(V,Ne)|‖2ε)(1+‖|(V,Ne)|‖2ε)+F2, |
where we note that
F2=:−αε2∫∂x(1ne)∂3xNe1n1ne∂t∂4xNe; |
by using (1.16c), we have
F2=−ε∫∂x(1ne)∂3xNe1nαεne∂t∂2xNe(2αn2eε2∂x˜ne∂xNe−εR3−N)−ε∫∂x(1ne)∂3xNe1n∂t∂2xNe+ε∫∂x(1ne)∂3xNe1n(∂t∂2x(αεne)∂2xNe+∂2x(αεne)∂t∂2xNe+∂t∂x(αεne)∂3xNe+∂t∂x(αεne)∂t∂3xNe+∂t(αεne)∂4xNe)≤C1(1+ε2‖|(V,Ne)|‖2ε)(1+‖|(V,Ne)|‖2ε); |
therefore, we have
˜I223≤C1(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
˜I224≤C1(1+ε2‖|(V,Ne)|‖2ε)(1+‖|(V,Ne)|‖2ε)+F3, |
where we note that
F3=:αε2∫∂4x(1ne)∂xNe1n1ne∂t∂3xNe; |
by using (1.16c) we have
F3=ε∫∂4x(1ne)∂xNe1n∂t∂x(2αn2eε2∂x˜ne∂xNe−εR3−N)+ε∫∂4x(1ne)∂xNe1n∂t∂2xNe≤C1(1+ε2‖|(V,Ne)|‖2ε)(1+‖|(V,Ne)|‖2ε). |
Therefore, we have
˜I22≤−12ddt∫αε2n2en|∂4xNe|2+C1(1+ε2‖|(V,Ne)|‖2ε)(1+‖|(V,Ne)|‖2ε). |
Regarding the estimate for ˜I23, similar to ˜I22, we have
˜I23≤C1(1+ε2‖|(V,Ne)|‖2ε)(1+‖|(V,Ne)|‖2ε). |
By Lemma 1.1, we have
˜I24≤Cε(ε‖∂3xNe‖2+ε2‖∂2xNe‖2+ε2‖∂xNe‖2). |
Combining these estimates, we complete this lemma.
Proof of Theorem 1.3. Combining Propositions 2.1 and 2.2, we have
12ddt(‖V‖2H2+ε‖∂3xV‖2)+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)|‖2ε≤C‖|(V,Ne)(0)|‖2ε+∫t0C1(1+‖|(V,Ne)|‖2ε)(1+‖|(V,Ne)|‖2ε)ds≤C‖|(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 C∗1=c(1) and C2>Csupε<1‖|(V,Ne)(0)|‖2ε. For any arbitrarily given τ>0, we choose ˜C such that ˜C>e4C′1τ(1+C2)(1+C′1). Then there exists ε0>0 such that ε˜C≤1 for all ε<ε0; we have
sup0≤t≤τ‖|(V,Ne)(t)|‖2ε<˜C/2. |
By Lemma 2.1, we have
sup0≤t≤τ‖|(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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