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Research article

Bio-active compounds, their antioxidant activities, and the physicochemical and pasting properties of both pigmented and non-pigmented fermented de-husked rice flour

  • Received: 23 August 2020 Accepted: 09 November 2020 Published: 01 December 2020
  • The aim of this study was to determine the effect of both the Solid State Fermentation (SSF) technique and the use of Rhizopus oligosporus on the physicochemical changes of fermented de-husked rice flour. Three varieties of de-husked rice, i.e., Mentik Wangi Susu (non-pigmented), red Cempo Merah, and black Jowo Melik (pigmented) were fermented using Rhizopus oligosporus. Fermentation was performed at room temperature with a fermentation time of 0, 24, 48, and 72 hours. The analyzed parameters were proximate composition, bio-active compounds, and pasting profile. The results showed an increase in flour pasting profile, ash, protein, and fat content after the fermentation. The total availability of the total phenolic content (TPC) and antioxidant capacity were also increased. The highest TPC (0.37 mg GAE/g) and antioxidant capacity (1.43 mg TEAC/g) were obtained in the Jowo Melik variety at 72 hours of fermentation. In contrast, anthocyanin and carbohydrate contents decreased as fermentation time increased. The highest anthocyanin content of 0.53 mg/g (after 24-hour fermentation) was obtained in the Jowo Melik variety. In conclusion, 72-hour-fermented black rice flour (Jowo Melik) has a higher potential to be developed as a functional food.

    Citation: Budi Suarti, Sukarno, Ardiansyah, Slamet Budijanto. Bio-active compounds, their antioxidant activities, and the physicochemical and pasting properties of both pigmented and non-pigmented fermented de-husked rice flour[J]. AIMS Agriculture and Food, 2021, 6(1): 49-64. doi: 10.3934/agrfood.2021004

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  • The aim of this study was to determine the effect of both the Solid State Fermentation (SSF) technique and the use of Rhizopus oligosporus on the physicochemical changes of fermented de-husked rice flour. Three varieties of de-husked rice, i.e., Mentik Wangi Susu (non-pigmented), red Cempo Merah, and black Jowo Melik (pigmented) were fermented using Rhizopus oligosporus. Fermentation was performed at room temperature with a fermentation time of 0, 24, 48, and 72 hours. The analyzed parameters were proximate composition, bio-active compounds, and pasting profile. The results showed an increase in flour pasting profile, ash, protein, and fat content after the fermentation. The total availability of the total phenolic content (TPC) and antioxidant capacity were also increased. The highest TPC (0.37 mg GAE/g) and antioxidant capacity (1.43 mg TEAC/g) were obtained in the Jowo Melik variety at 72 hours of fermentation. In contrast, anthocyanin and carbohydrate contents decreased as fermentation time increased. The highest anthocyanin content of 0.53 mg/g (after 24-hour fermentation) was obtained in the Jowo Melik variety. In conclusion, 72-hour-fermented black rice flour (Jowo Melik) has a higher potential to be developed as a functional food.


    The 3D incompressible resistive Hall-Magnetohydrodynamics system (Hall-MHD in short) is the following system of PDEs for (u,p,B):

    ut+uuBB+pμΔu=0, (1a)
    Bt+uBBu+curl((curlB)×B)νΔB=0, (1b)
    divu=0,divB=0, (1c)

    where u=(u1,u2,u3) is the plasma velocity field, p is the pressure, and B=(B1,B2,B3) is the magnetic field. μ and ν are the viscosity and the resistivity constants, respectively. The Hall-MHD is important in describing many physical phenomena [2,17,19,23,26,27,33]. In particular, the Hall MHD explains magnetic reconnection on the Sun which is very important role in acceleration plasma by converting magnetic energy into bulk kinetic energy.

    The Hall-MHD recently has been studied intensively. The Hall-MHD can be derived from either two fluids model or kinetic models in a mathematically rigorous way [1]. Global weak solution, local classical solution, global solution for small data, and decay rates are established in [4,5,6]. There have been many follow-up results of these papers; see [7,8,12,13,14,15,16,18,29,30,31,32,34,35] and references therein.

    We note that the Hall term curl((curlB)×B) is dominant in mathematical analysis of (1) and so we only consider the Hall equations ((u,p)=0 in (1)). Also motivated by [7], we consider the Hall equation with fractional Laplacian:

    Bt+curl((curlB)×B)+ΛβB=0,divB=0, (2)

    where we take ν=1 for simplicity. (2) is locally well-posed [7] when β>1. But, we do not know whether (2) is locally well-posed when β=1:

    Bt+curl((curlB)×B)+ΛB=0,divB=0. (3)

    However, we can show the existence of solutions globally in time if initial data is sufficiently small.

    Theorem 1.1. Let B0Hk with k>52 and divB0=0. There exists a constant ϵ0>0 such that if B0Hkϵ0, there exists a unique global-in-time solution of (3) satisfying

    B(t)2Hk+(1Cϵ0)t0Λ12B(s)2HkdsB02Hkforallt>0.

    Moreover, B decays in time

    ΛlB(t)L2C0(1+t)l,0<lk, (4)

    where C0 depends on B0Hk which is expressed in (27) explicitly.

    Remark 1. The decay rate (4) is consistent with the decay rates of the linear part of (3).

    Remark 2. After this work was completed, the referee pointed out that the same result is proved in [37,Theorem 1.1]. Compared to the proof in [37] where they use the Littlewood-Paley decomposition, we use the standard energy energy estimates and classical commutator estimates.

    As one of a minimal modification of (3) to show the existence of unique local in time solutions, we now take a logarithmic correction of (3):

    Bt+curl((curlB)×B)+ln(2+Λ)ΛB=0, (5)

    where the Fourier symbol of ln(2+Λ)Λ is ln(2+|ξ|)|ξ|.

    Theorem 1.2. Let B0Hk with k>52 and divB0=0. There exists T=T(B0Hk)>0 such that there exists a unique local-in-time solution of (5) satisfying

    B(t)Hkln(1eB0HkCt),0<t<T=exp(B0Hk)C. (6)

    In this paper, we also deal with 2D models closely related to the 212 dimensional (3). If we take B of the form

    B(t,x,y)=(ψy(t,x,y),ψx(t,x,y),Z(t,x,y)), (7)

    we can rewrite (3) as

    ψt+Λψ=[ψ,Z], (8a)
    Zt+ΛZ=[Δψ,ψ], (8b)

    where [f,g]=fg=fxgyfygx. (7) is used to show a finite-time collapse to a current sheet [3,20,21,24] and is used in [10] to study regularity of stationary weak solutions.

    Although (8) is defined in 2D and has nice cancellation properties (18), the local well-posedness seems unreachable. But, suppose that we redistribute the power of the fractional Laplacians in (8) in such a way that (8b) has the full Laplacian and (8a) is inviscid:

    ψt=[ψ,Z],ZtΔZ=[Δψ,ψ]. (9)

    (9) has no direct link to (2), but we may interpret (9) as the 212 dimensional model of the Hall equations where only B3 has the full Laplacian in (2). In this case, we can show that (9) is locally well-posed. Let

    E(t)=ψ(t)2H4+Z(t)2H3,E0=ψ02H4+Z02H3. (10)

    Theorem 1.3. There exists T=T(E0)>0 such that there exists a unique solution of (9) satisfying

    E(t)E011CtE0forall 0<tT<1CE0.

    Moreover, we have the following blow-up criterion:

    E(t)+t0Z(s)2H2ds<t0(2Z(s)L+2ψ(s)2L)ds<.

    Since there is no dissipative effect in the equation of ψ in (9), we only have the local in tim result in Theorem 1.3. Among the possible conditions for the global existence, we find that adding a damping term to the equation of ψ works. More precisely, we deal with the following

    ψt+ψ=[ψ,Z],ZtΔZ=[Δψ,ψ]. (11)

    In this case, we can show the existence of global in time solutions with small initial data having regularity one higher than the regularity in Theorem 1.3. Moreover, we can find decay rates of ψ by using the structure of equation of ψ which is a damped transport equation, and this is also the reason why the same method cannot be applied to Z. Let

    F(t)=ψ(t)2H5+Z(t)2H4,F0=ψ02H5+Z02H4,N1(t)=ψ(t)2H4+Z(t)2H4.

    Theorem 1.4. There exists a constant ϵ0>0 such that if F0ϵ0, there exists a unique global-in-time solution of (11) satisfying

    F(t)+(1Cϵ0)t0N1(s)dsF0forallt>0.

    Moreover, ψ decays exponentially in time

    ψ(t)L2ψ0L2et,Λkψ(t)L2Fk180ψ05k4L2e(5k)(1Cϵ0)4t

    with 1k<5.

    As another way to redistribute the derivatives in (8), we also deal with

    ψtΔψ=[ψ,Z],Zt=[Δψ,ψ]. (12)

    Let E(t) and E0 be defined as before (10).

    Theorem 1.5. There exists T>0, which is depending on E0, such that there exists a unique solution of (12) satisfying

    E(t)E01CtE0forall 0<tT<1CE0.

    Moreover, we have the following blow-up criterion

    E(t)+t0ψ2H4ds<t02ψ2Lds.

    We now add a damping term to the equation of Z in (12):

    ψtΔψ=[ψ,Z],Zt+Z=[Δψ,ψ]. (13)

    In this case, we can use the same regularity used in Theorem 1.5 because the dissipative effect in ψ helps to control Δψ in the equation of Z. Let N2(t)=ψ(t)2H5+Z(t)2H3.

    Theorem 1.6. There exists a constant ϵ0>0 such that if E0ϵ0, there exists a unique global-in-time solution of (13) satisfying

    E(t)+(1Cϵ0)t0N2(s)dsE0forallt>0.

    Remark 3. Compared to Theorem 1.3, we only need one term in the blow-up criterion in Theorem 1.5 which is due to the dissipative effect in the equation of ψ. Compared to Theorem 1.4, the proof of Theorem 1.6 is simpler, but we are not able to derive decay rates of ψ and Z.

    All constants will be denoted by C and we follow the convention that such constants can vary from expression to expression and even between two occurrences within the same expression. And repeated indices are summed over.

    The fractional Laplacian Λβ=(Δ)β has the Fourier transform representation

    ^Λβf(ξ)=|ξ|βˆf(ξ).

    For s>0, Hs is a energy space equipped with

    fHs=fL2+f˙Hs,f˙Hs=ΛsfL2.

    In the energy spaces, we have the following interpolations: for s0<s<s1

    f˙Hsfθ˙Hs0f1θ˙Hs1,s=θs0+(1θ)s1. (14)

    We begin with two inequalities in 3D:

    fLCfHs,s>32, (15a)
    fLpCf˙Hs,1p=12s3. (15b)

    We also provide the following inequalities in 2D

    fL4Cf12L2f12L2,fLCf12L2Δf12L2

    which will be used repeatedly in the proof of Theorem 1.3, Theorem 1.4, Theorem 1.5, and Theorem 1.6. We also recall

    2fL2=ΔfL2

    which holds in any dimension.

    We finally provide the Kato-Ponce commutator cstimate [22]

    [Λk,f]gL2=Λk(fg)fΛkgL2CfLΛk1gL2+CgLΛkfL2 (16)

    and the fractional Leibniz rule [11]: for 1p< and pi,qi1,

    Λs(fg)LpCΛsfLp1gLq1+CfLp2ΛsgLq2,1p=1p1+1q1=1p2+1q2. (17)

    We recall the commutator [f,g]=fg=fxgyfygx. Then, the commutator has the following properties:

    Δ[f,g]=[Δf,g]+[f,Δg]+2[fx,gx]+2[fy,gy], (18a)
    f[f,g]=0, (18b)
    f[g,h]=g[h,f]. (18c)

    We recall (3):

    Bt+curl((curlB)×B)+ΛB=0. (19)

    We first approximate (19) by putting ϵΔB to the right-hand side of (19):

    Bt+curl((curlB)×B)+ΛB=ϵΔB. (20)

    We then mollify (20) as follows

    tB(ϵ)+curl(Jϵ(curlJϵB(ϵ))×JϵB(ϵ))+ΛJ2ϵB(ϵ)=ϵJ2ϵΔB(ϵ),B(ϵ)0=JϵB0, (21)

    where Jϵ is the standard mollifier described in [25,Chapter 3.2]. Then, as proved in [4,Proposition 3.1], there exists a unique global-in-time solution {B(ϵ)} of (21). Since the bounds in Section 3.1.2 are independent of ϵ>0, we can pass to the limit in a subsequence and show the existence of smooth solutions globally in time when B0Hk, k>52, is sufficiently small as in [37,Section 3.2].

    We begin with the L2 bound:

    12ddtB2L2+Λ12B2L2=0. (22)

    We now take Λk to (19) and take the inner product of the resulting equation with ΛkB. Then,

    12ddtΛkB2L2+Λ12+kB2L2=Λkcurl((curlB)×B)ΛkB=([Λ12+k,B]×curlB)Λk12curlB[Λ12+k,B]×curlBL2Λ12+kBL2.

    By (16) and (15a) with k>52,

    [Λ12+k,B]×curlBL2CBLΛk12curlBL2CBHkΛ12+kB2L2. (23)

    So, we obtain

    ddtΛkB2L2+Λ12+kB2L2CBHkΛ12+kB2L2. (24)

    By (22) and (24),

    ddtB2Hk+Λ12B2HkCBHkΛ12+kB2L2.

    If B0Hk=ϵ0 is sufficiently small, we can derive a uniform bound

    B(t)2Hk+(1Cϵ0)t0Λ12B(s)2HkdsB02Hkforallt>0. (25)

    Let B1 and B2 be two solutions of (19). Then, B=B1B2 satisfies

    Bt+ΛB+curl((curlB1)×B)curl((curlB)×B2)=0 (26)

    with B0=0. We take the inner product of (26) with B. By (17) with k>52,

    12ddtB2L2+Λ12B2L2=(curl((curlB1)×B))B=Λ12(((curlB1)×B))Λ12curlBCB1LΛ12B2L2+CΛ12B1L6BL3Λ12BL2CB1LΛ12B2L2+CΛ52B1L2Λ12B2L2CB1HkΛ12B2L2,

    where we use (15b) to control L6 and L3 terms. If Cϵ0<1, (25) implies B=0 in L2 which gives the uniqueness of a solution.

    By (14), it is enough to derive the decay rate with k=l to show (4). Since

    ΛkB2k+1kL2B1kL2Λ12+kB2L2B01kL2Λ12+kB2L2

    by (14) and (22), we create the following ODE from (24)

    ddtΛkB2L2+1Cϵ0B01kL2ΛkB2k+1kL20.

    By solving this ODE, we find the following decay rate

    ΛkB(t)L2((2k)kB0L2ΛkB0L2)(2kB01kL2+(1Cϵ0)ΛkB01kL2t)k. (27)

    We recall (5):

    Bt+curl((curlB)×B)+ln(2+Λ)ΛB=0,

    The the uniqueness part of Theorem 1.2 is the same as that of Theorem 1.1 and we only derive a priori bounds. Let

    ln(2+Λ)Λsf2L2=(ln(2+|ξ|))|ξ|2s|ˆf(ξ)|2dξ.

    We begin with the L2 bound:

    12ddtB2L2+ln(2+Λ)Λ12B2L2=0. (28)

    Following the computations in the proof of Theorem 1.1, we also have

    ddtΛkB2L2+ln(2+Λ)Λ12+kB2L2CBHkΛ12+kB2L2. (29)

    For each NN, we have

    Λ12+kB2L2=|ξ|2N|ξ|2k+1|ˆB(ξ)|2dξ+|ξ|2N|ξ|2k+1|ˆB(ξ)|2dξ2N|ξ|2N|ξ|2k|ˆB(ξ)|2dξ+1ln(2+2N)|ξ|2Nln(2+|ξ|)|ξ|2k+1|ˆB(ξ)|2dξ2NΛkB2L2+1ln(2+2N)ln(2+Λ)Λ12+kB2L2.

    So, (29) is replaced by

    ddtΛkB2L2+ln(2+Λ)Λ12+kB2L2C2NΛkB2L2BHk+CBHkln(2+2N)ln(2+Λ)Λ12+kB2L2.

    We now choose N>0 such that

    12ln(2+2N)<CBHk<ln(2+2N)

    and so NBHk. Then, (29) is reduced to

    ddtΛkB2L2Cexp(BHk)BHkΛkBL2. (30)

    By (28) and (30), we obtain

    ddtB2HkCexp(BHk)B2Hk

    and so we have

    ddtBHkCexp(BHk)BHkCexp(BHk).

    By solving this ODE, we can derive (6).

    We recall (9):

    ψt=[ψ,Z], (31a)
    ZtΔZ=[Δψ,ψ]. (31b)

    We first approximate (31a) by putting ϵΔψ to the right-hand side and mollify the resulting equations as (21). Then, we have

    tψ(ϵ)=Jϵ[Jϵψ(ϵ),JϵZ(ϵ)]+ϵJ2ϵΔψ(ϵ),tZ(ϵ)ΔJ2ϵZ(ϵ)=Jϵ[ΔJϵψ(ϵ),Jϵψ(ϵ)] (32)

    with ψ(ϵ)0=Jϵψ0 and Z(ϵ)0=JϵZ0. Since (32) is defined in R2, the proof of the existence of a unique global-in-time solution of (32) is relatively easier than the one to (21). Moreover, the bounds in Section 4.1.2 are independent of ϵ>0 and so we can pass to the limit in a subsequence and show the existence of smooth solutions locally in time when ψ0H4 and Z0H3.

    We first note that

    12ddtψ2L2=ψ[ψ,Z]=0. (33)

    We next multiply (31a) by Δψ, (31b) by Z, and integrate over R2. By (18c),

    12ddt(ψ2L2+Z2L2)+Z2L2=(Δψ[ψ,Z]+Z[Δψ,ψ])=0. (34)

    We also multiply (31a) by Δ4ψ, (31b) by Δ3Z and integrate over R2. Then,

    12ddt(Δ2ψ2L2+ΔZ2L2)+Δ2Z2L2=Δ4ψ[ψ,Z]Δ3Z[Δψ,ψ]=R. (35)

    We now compute the right-hand side of (35). By (18a), (18b), and (18c),

    R=2Δ2ψ[Δψ,ΔZ]+4Δ2ψ[ψx,ΔZx]+4Δ2ψ[ψy,ΔZy]+4Δ2ψ[Δψx,Zx]+4Δ2ψ[Δψy,Zy]+4Δ2ψ[ψxx,Zxx]+8Δ2ψ[ψxy,Zxy]+4Δ2ψ[ψyy,Zyy]2Δ2Z[Δψx,ψx]2Δ2Z[Δψy,ψy]. (36)

    So, we find that the number of derivatives acting on (ψ,ψ,Z) are (4,4,2), (3,4,3), and (4,2,4) up to multiplicative constants. Hence,

    ddt(Δ2ψ2L2+ΔZ2L2)+Δ2Z2L2C|4ψ||4ψ||2Z|+C|3ψ||4ψ||3Z|+C|4ψ||2ψ||4Z|CΔ2ψ2L22ZL+C3ψL4Δ2ψL23ZL4+CΔ2ψL22ψLΔ2ZL2CΔ2ψ2L22ZL+CΔ2ψ32L2Δψ12L2Δ2ZL2+CΔ2ψL22ψLΔ2ZL2CE2+14Δ2Z2L2+δ2Z2LCE2+12Δ2Z2L2+14Z2L2,

    where we use

    2Z2LCΔZL2Δ2ZL2CZ23L2Δ2Z43L2CZ2L2+CΔ2Z2L2

    with δ satisfying 4Cδ=1. So, we have

    ddt(Δ2ψ2L2+ΔZ2L2)+Δ2Z2L2CE2+12Z2L2. (37)

    By (33), (34), and (37), we derive ECE2 from which we deduce

    E(t)E01CtE0forall 0<tT<1CE0. (38)

    Let (ψ1,Z1) and (ψ2,Z2) be two solutions of (31) and let ψ=ψ1ψ2 and Z=Z1Z2. Then, (ψ,Z) satisfies the following equations:

    ψt=[ψ,Z1]+[ψ2,Z],ZtΔZ=[Δψ,ψ1]+[Δψ2,ψ]

    with ψ(0,x)=Z(0,x)=0. For these equations, we have

    12ddt(ψ2L2+Z2L2)+Z2L2=Δψ[ψ,Z1]Δψ[ψ2,Z]+Z[Δψ,ψ1]+Z[Δψ2,ψ]=(I)+(II)+(III)+(IV).

    The first term is bounded using the definition of [f,g] and divZ1=0:

    (I)=(Z1ψ)Δψ=(lZ1ψ)lψC2Z1Lψ2L2.

    We next bound (II)+(III) as

    (II)+(III)=Z[Δψ,ψ]C2ψLψL2ZL2C(2ψ12L+2ψ22L)ψ2L2+14Z2L2.

    The last term is bounded as

    (IV)C2ψ2LψL2ZL2C2ψ22Lψ2L2+14Z2L2.

    So, we have

    ddt(ψ2L2+Z2L2)C(2Z1L+2ψ12L+2ψ22L)(ψ2L2+Z2L2). (39)

    By (38), 2ψ12L+2ψ22L is integrable in time. Integrating (34) and (35) in time, we have

    t0(Z(s)2L2+Δ2Z(s)2L2)ds<for0<tT2

    which gives the integrability of the first term in the parentheses on the right-hand side of (39). By repeating the same argument one more time, we have the uniqueness up to T.

    Let

    B(s)=2Z(s)L+2ψ(s)2L.

    We first deal with

    12ddt(Δψ2L2+Z2L2)+ΔZ2L2=Δ2ψ[ψ,Z]ΔZ[Δψ,ψ]=2Δψ[ψx,Zx]+2Δψ[ψy,Zy]C2ZLΔψ2L2

    and so we have

    ddt(Δψ2L2+Z2L2)+ΔZ2L2C2ZLΔψ2L2.

    This implies

    Δψ(t)2L+Z(t)2L2+t0ΔZ(s)2L2ds<t02Z(s)Lds<. (40)

    We also deal with

    12ddt(Δψ2L2+ΔZ2L2)+ΔZ2L2=Δ3ψ[ψ,Z]+Δ2Z[Δψ,ψ]=Δ2ψ[Δψ,Z]2Δ2ψ([ψx,Zx]+[ψy,Zy])2Δψ([ψx,ΔZx]+[ψy,ΔZy])=(I)+(II)+(III).

    As in Section 4.1.3,

    (I)=(ZΔψ)ΔψC2ZLΔψ2L2. (41)

    We next estimate (II)+(III):

    (II)+(III)=4Δψ([Δψy,Zy]+[ψy,ΔZy]+[ψxy,Zxy]+[ψyy,Zyy])C|2Z||3ψ|2+C|2ψ||3ψ||3Z|C2ZLΔψ2L2+C2ψ2LΔψ2L2+12ΔZ2L2. (42)

    By (41) and (42), we have

    ddt(Δψ2L2+ΔZ2L2)+ΔZ2L2C(2ZL+2ψ2L)Δψ2L2

    which implies

    Δψ(t)2L2+ΔZ(t)2L2+t0ΔZ(s)2L2ds<t0B(s)ds<. (43)

    We finally deal with

    12ddt(Δ2ψ2L2+ΔZ2L2)+Δ2Z2L2=Δ4ψ[ψ,Z]Δ3Z[Δψ,ψ]=R

    with the same R in (36). So, we have

    12ddt(Δ2ψ2L2+ΔZ2L2)+Δ2Z2L2C2ZLΔ2ψ2L2+C2ψLΔ2ZL2Δ2ψL2+CΔZL4ΔψL4Δ2ψL2C(2ZL+2ψ2L+ΔZ32L2Δψ32L2)Δ2ψ2L2+12Δ2Z2L2

    which gives

    ddt(Δ2ψ2L2+ΔZ2L2)+Δ2Z2L2C(B(s)+ΔZ32L2Δψ32L2)Δ2ψ2L2. (44)

    By (40) and (43), (44) implies

    Δ2ψ(t)2L2+ΔZ(t)2L2+t0Δ2Z(s)2L2ds<t0B(s)ds<.

    We recall (11):

    ψt+ψ=[ψ,Z],ZtΔZ=[Δψ,ψ]

    Since the uniqueness is already proved in Section 4.1.3 even without the damping term, we only focus on the a priori bounds and the decay rates.

    We first have

    12ddtψ2L2+ψ2L2=0,12ddt(ψ2L2+Z2L2)+ψ2L2+Z2L2=0. (45)

    We now consider the highest order part:

    12ddt(Δ2ψ2L2+Δ2Z2L2)+Δ2ψ2L2+Δ2Z2L2=Δ5ψ[ψ,Z]+Δ4Z[Δψ,ψ].

    We compute the right-hand side of this. By (18a), (18b), and (18c),

    Δ5ψ[ψ,Z]+Δ4Z[Δψ,ψ]=2Δ3Z[Δψx,ψx]+2Δ3Z[Δψy,ψy]+2Δ2Z[Δ2ψx,ψx]+2Δ2Z[Δ2ψy,ψy]+2ΔZ[Δ2ψx,Δψx]+2ΔZ[Δ2ψy,Δψy]Δ3ψ[Δψ,ΔZ]2Δ3ψ[Δψx,Zx]2Δ3ψ[Δψy,Zy]2Δ3ψ[ψx,ΔZx]2Δ3ψ[ψy,ΔZy]2Δ4ψ[ψx,Zx]2Δ4ψ[ψy,Zy]Δ3ψ[Δ2ψ,Z]. (46)

    We now count the number of derivatives hitting on (Z,ψ,ψ) using the integration by parts and (18b) and (18c) up to multiplicative constants. Except for the last integral, we have

    (6,2,4)(5,2,5), (5,3,4)(4,2,6)(5,5,2), (4,3,5)(2,2,8)(3,2,7)(4,2,6), (3,3,6)(5,5,2), (4,3,5)(2,4,6)(2,5,5), (3,4,5).

    The last integral is

    (ZΔ2ψ)Δ3ψ=(lZΔ2ψ)lΔ2ψ

    and so this gives (2,5,5). So, the combinations of the numbers of derivatives taken on (Z,ψ,ψ) are

    (2,5,5), (3,4,5), (4,3,5), (5,2,5), (5,3,4).

    The first and the fourth cases are bounded by

    C2ZLΔ2ψ2L2C2Z2LΔ2ψ2L2+16Δ2ψ2L2,C2ψLΔ2Z2L2C2ψLΔ2Z2L2+14Δ2Z2L2.

    The second case is bounded by

    C3ZL44ψL4Δ2ψL2CΔZ12L2Δ2Z12L2Δ2ψ12L2Δ2ψ32L2CΔZ2L2Δ2ψ2L2Δ2Z2L2+16Δ2ψ2L2.

    The third case is bounded by

    \begin{split} &C\left\|\nabla^{4}Z\right\|_{L^{4}}\left\|\nabla^{3}\psi\right\|_{L^{4}}\left\|\nabla\Delta^{2}\psi\right\|_{L^{2}}\leq C\left\|\Delta^{2}Z\right\|^{\frac{1}{2}}_{L^{2}}\left\|\nabla\Delta^{2}Z\right\|^{\frac{1}{2}}_{L^{2}} \left\|\Delta \psi\right\|^{\frac{1}{2}}_{L^{2}}\left\|\nabla\Delta^{2}\psi\right\|^{\frac{3}{2}}_{L^{2}}\\ & \leq C\left\|\Delta \psi\right\|^{2}_{L^{2}}\left\|\Delta^{2}Z\right\|^{2}_{L^{2}}\left\|\nabla\Delta^{2}Z\right\|^{2}_{L^{2}} +\frac{1}{6}\left\|\nabla\Delta^{2}\psi\right\|^{2}_{L^{2}}. \end{split}

    The last one is bounded by

    \begin{split} &C\left\|\nabla^{3}\psi\right\|_{L^{4}}\left\|\nabla^{4}\psi\right\|_{L^{4}}\left\|\nabla\Delta^{2}Z\right\|_{L^{2}}\leq C\left\|\nabla\Delta \psi\right\|^{\frac{1}{2}}_{L^{2}}\left\|\Delta^{2}\psi\right\|_{L^{2}}\left\|\nabla\Delta^{2}\psi\right\|^{\frac{1}{2}}_{L^{2}}\left\|\nabla\Delta^{2}Z\right\|_{L^{2}}\\ & \leq C\left\|\nabla \Delta \psi\right\|_{L^{2}}\left\|\nabla \Delta^{2}\psi\right\|_{L^{2}}\left\|\nabla\Delta^{2}Z\right\|_{L^{2}} \leq C\left\|\nabla \Delta \psi\right\|^{2}_{L^{2}}\left\|\nabla \Delta^{2}\psi\right\|^{2}_{L^{2}} +\frac{1}{4}\left\|\nabla\Delta^{2}Z\right\|^{2}_{L^{2}}. \end{split}

    So, we obtain

    \begin{equation} \begin{split} &\frac{d}{dt} \left(\left\|\nabla \Delta^{2}\psi\right\|^{2}_{L^{2}}+\left\|\Delta^{2} Z\right\|^{2}_{L^{2}} \right)+\left\|\nabla\Delta^{2}\psi\right\|^{2}_{L^{2}} +\left\|\nabla\Delta^{2} Z\right\|^{2}_{L^{2}}\\ & \leq C\left\|\nabla^{2}Z\right\|^{2}_{L^{\infty}}\left\|\nabla \Delta^{2}\psi\right\|^{2}_{L^{2}}+ C\left\|\nabla^{2}\psi\right\|^{2}_{L^{\infty}}\left\|\nabla \Delta^{2}Z\right\|^{2}_{L^{2}}+C\left\|\nabla \Delta \psi\right\|^{2}_{L^{2}}\left\|\nabla \Delta^{2}\psi\right\|^{2}_{L^{2}}\\ &+C\left\|\Delta Z\right\|^{2}_{L^{2}}\left\|\Delta^{2}\psi\right\|^{2}_{L^{2}}\left\|\nabla\Delta^{2}Z\right\|^{2}_{L^{2}}+C\left\|\Delta \psi\right\|^{2}_{L^{2}}\left\|\Delta^{2}Z\right\|^{2}_{L^{2}}\left\|\nabla\Delta^{2}Z\right\|^{2}_{L^{2}} \end{split} \end{equation} (47)

    By (45) and (47),

    \mathcal{F}'(t)+\mathcal{N}_{1}(t)\leq C \left(\mathcal{F}(t)+\mathcal{F}^{2}(t)\right)\mathcal{N}_{1}(t).

    So, if \mathcal{F}_{0} = \epsilon_{0} is sufficiently small, we obtain

    \label{A priori damping dd} \mathcal{F}(t)+(1-C \epsilon_{0})\int^{t}_{0}\mathcal{N}_{1}(s)ds\leq \mathcal{F}_{0} \quad {{\rm{for}} \;{\rm{all}} \;t > 0 .}

    From (45), \left\|\psi(t)\right\|_{L^{2}}\leq \left\|\psi_{0}\right\|_{L^{2}} e^{-t} . Since

    \begin{split} \frac{1}{2}\frac{d}{dt}\left\|\nabla \psi\right\|^{2}_{L^{2}}+\left\|\nabla \psi\right\|^{2}_{L^{2}}& = -\int \Delta \psi[\psi, Z] = \int \left(\nabla^{\perp}Z\cdot \nabla \psi\right)\Delta \psi\\ & = -\int \left(\partial_{l}\nabla^{\perp}Z\cdot \nabla \psi\right)\partial_{l} \psi\\ &\leq \left\|\nabla^{2}Z\right\|_{L^{\infty}}\left\|\nabla \psi\right\|^{2}_{L^{2}} \leq C\epsilon_{0}\left\|\nabla \psi\right\|^{2}_{L^{2}}, \end{split}

    we have

    \left\|\nabla \psi(t)\right\|_{L^{2}}\leq \left\|\nabla \psi_{0}\right\|_{L^{2}} e^{-(1-C\epsilon_{0})t}.

    By using (14), we also obtain

    \left\|\Lambda^{k}\psi(t)\right\|_{L^{2}}\leq \mathcal{F}^{\frac{k-1}{8}}_{0}\left\|\nabla \psi_{0}\right\|^{\frac{5-k}{4}}_{L^{2}} e^{-\frac{(5-k)(1-C\epsilon_{0})}{4}t}, \quad 1\leq k < 5.

    We recall (12):

    \psi_{t}-\Delta \psi = [\psi, Z], \quad Z_{t} = [\Delta \psi, \psi].

    By applying the same approximation and mollification methods in Section 4.1.1, we can show the existence of smooth solutions locally in time when \psi_{0}\in H^{4} and Z_{0}\in H^{3} .

    We first have

    \begin{equation} \begin{split} &\frac{1}{2}\frac{d}{dt}\left\|\psi\right\|^{2}_{L^{2}}+\left\|\nabla \psi\right\|^{2}_{L^{2}} = 0, \\ & \frac{1}{2}\frac{d}{dt} \left(\left\|\nabla \psi\right\|^{2}_{L^{2}}+\left\|Z\right\|^{2}_{L^{2}}\right) + \left\|\Delta \psi\right\|^{2}_{L^{2}} = 0. \end{split} \end{equation} (48)

    We next deal with

    \frac{1}{2}\frac{d}{dt} \left(\left\|\Delta^{2}\psi\right\|^{2}_{L^{2}}+\left\|\nabla\Delta Z\right\|^{2}_{L^{2}} \right) +\left\|\nabla \Delta^{2} \psi\right\|^{2}_{L^{2}} = \int \Delta^{4} \psi [\psi, Z] -\int\Delta^{3} Z[\Delta \psi, \psi] = \mathcal{R}

    with the same \mathcal{R} in (36). In this case, we choose the the number of derivatives acting on (\psi, \psi, Z) different from Section 4.1.2, which are given by (3, 5, 2) , (2, 5, 3) , and (4, 4, 2) after several integration by parts. Hence, we have

    \begin{equation*} \begin{split} & \frac{d}{dt} \left(\left\|\Delta^{2}\psi\right\|^{2}_{L^{2}}+\left\|\nabla\Delta Z\right\|^{2}_{L^{2}} \right) +\left\|\nabla\Delta^{2} \psi\right\|^{2}_{L^{2}}\\ & \leq C \left\|\nabla^{2} Z\right\|_{L^{2}}\left\|\Delta^{2}\psi\right\|^{2}_{L^{4}} + C\left\|\nabla \Delta Z\right\|_{L^{2}} \left\|\nabla^{2}\psi\right\|_{L^{\infty}} \left\|\nabla \Delta^{2} \psi\right\|_{L^{2}}+\\ & C\left\|\Delta Z\right\|_{L^{4}}\left\|\nabla^{3}\psi\right\|_{L^{4}} \left\|\nabla \Delta^{2}\psi\right\|_{L^{2}} \\ &\leq C \mathcal{E}^{2}_{1}+\frac{1}{2}\left\|\nabla \Delta^{2} \psi\right\|^{2}_{L^{2}} \end{split} \end{equation*}

    and so we have the following bound

    \begin{eqnarray} \frac{d}{dt} \left(\left\|\Delta^{2}\psi\right\|^{2}_{L^{2}}+\left\|\nabla\Delta Z\right\|^{2}_{L^{2}} \right) +\left\|\nabla \Delta^{2} \psi\right\|^{2}_{L^{2}} \leq C \mathcal{E}^{2}. \end{eqnarray} (49)

    By (48) and (49), we derive \mathcal{E}' \leq C \mathcal{E}^{2} from which we deduce

    \begin{eqnarray} \mathcal{E}(t)\leq \frac{\mathcal{E}_{0}}{1-Ct\mathcal{E}_{0}} \quad {{\rm{for}}\; {\rm{all}}} \;\ 0 < t\leq T_{\ast} < \frac{1}{C \mathcal{E}_{0}}. \end{eqnarray} (50)

    Let (\psi_{1}, Z_{1}) and (\psi_{2}, Z_{2}) be two solutions and let \psi = \psi_{1}-\psi_{2} and Z = Z_{1}-Z_{2} . As in Section 4.1.3

    \begin{equation*} \begin{split} &\frac{1}{2}\frac{d}{dt}\left(\left\|\nabla \psi\right\|^{2}_{L^{2}}+ \|Z\|^{2}_{L^{2}}\right)+ \left\|\Delta \psi\right\|^{2}_{L^{2}}\\ & = -\int \Delta \psi [\psi, Z_{1}]-\int \Delta \psi [\psi_{2}, Z]+\int Z [\Delta\psi, \psi_{1}]+\int Z[\Delta\psi_{2}, \psi]\\ & = \text{(I)+(II)+(III)+(IV)}. \end{split} \end{equation*}

    The first term three terms are bounded as

    \begin{split} \text{(I)}&\leq \left\|\nabla Z_{1}\right\|_{L^{\infty}}\left\|\nabla \psi\right\|_{L^{2}}\left\|\Delta \psi\right\|_{L^{2}} \leq C\left\|\nabla Z_{1}\right\|^{2}_{L^{\infty}}\left\|\nabla \psi\right\|^{2}_{L^{2}}+\frac{1}{3}\left\|\Delta \psi\right\|^{2}_{L^{2}}, \\ \text{(II)+(III)}& = -\int Z[\Delta \psi, \psi]\leq C \left\|\nabla Z\right\|_{L^{\infty}}\left\|\nabla \psi\right\|_{L^{2}}\left\|\Delta \psi\right\|_{L^{2}} \\ &\leq C \left(\left\|\nabla Z_{1}\right\|^{2}_{L^{\infty}}+\left\|\nabla Z_{2}\right\|^{2}_{L^{\infty}}\right)\left\|\nabla \psi\right\|^{2}_{L^{2}}+\frac{1}{3}\left\|\Delta \psi\right\|^{2}_{L^{2}} \end{split}

    The last term is bounded as

    \begin{split} \text{(IV)}&\leq C \left\|\nabla^{3}\psi_{2}\right\|_{L^{4}}\left\|\nabla \psi\right\|_{L^{4}}\left\|Z\right\|_{L^{2}} \leq C \left\|\nabla^{3}\psi_{2}\right\|_{L^{4}}\left\|\nabla \psi\right\|^{\frac{1}{2}}_{L^{2}}\left\|\Delta \psi\right\|^{\frac{1}{2}}_{L^{2}}\left\|Z\right\|_{L^{2}} \\ & \leq C \left\|\nabla^{3}\psi_{2}\right\|^{\frac{4}{3}}_{L^{4}}\left\|\nabla \psi\right\|^{\frac{2}{3}}_{L^{2}}\left\|Z\right\|^{\frac{4}{3}}_{L^{2}} +\frac{1}{3}\left\|\Delta \psi\right\|^{2}_{L^{2}} \leq C \left\|\nabla^{3}\psi_{2}\right\|^{4}_{L^{4}}\left\|\nabla \psi\right\|^{2}_{L^{2}}\\ &+ C \left\|Z\right\|^{2}_{L^{2}} +\frac{1}{3}\left\|\Delta \psi\right\|^{2}_{L^{2}}\\ & \leq C \left\|\nabla\Delta \psi_{2}\right\|^{2}_{L^{2}}\left\|\Delta^{2}\psi_{2}\right\|^{2}_{L^{2}} \left\|\nabla \psi\right\|^{2}_{L^{2}}+ C \left\|Z\right\|^{2}_{L^{2}} +\frac{1}{3}\left\|\Delta \psi\right\|^{2}_{L^{2}}. \end{split}

    So, we have

    \begin{split} &\frac{d}{dt}\left(\left\|\nabla \psi\right\|^{2}_{L^{2}}+ \|Z\|^{2}_{L^{2}}\right)\\&\leq C\left(\left\|\nabla Z_{1}\right\|^{2}_{L^{\infty}}+\left\|\nabla Z_{2}\right\|^{2}_{L^{\infty}} +\left\|\nabla\Delta \psi_{2}\right\|^{2}_{L^{2}}\left\|\Delta^{2}\psi_{2}\right\|^{2}_{L^{2}}\right)\left(\left\|\nabla \psi\right\|^{2}_{L^{2}}+ \|Z\|^{2}_{L^{2}}\right). \end{split}

    By (50), the terms in the parentheses are integrable up to \frac{T_{\ast}}{2} . By repeating the same argument one more time, we have the uniqueness up to T_{\ast} .

    To derive the blow-up criterion, we first bound

    \begin{split} &\frac{1}{2}\frac{d}{dt} \left(\left\|\Delta\psi\right\|^{2}_{L^{2}}+\left\|\nabla Z\right\|^{2}_{L^{2}} \right) +\left\| \nabla \Delta \psi\right\|^{2}_{L^{2}} = \int \Delta^{2} \psi [\psi, Z] -\int\Delta Z[\Delta \psi, \psi]\\ & = 2\int \Delta \psi[\psi_{x}, Z_{x}]+2\int \Delta \psi[\psi_{y}, Z_{y}]\leq C \left\|\nabla^{2}\psi\right\|_{L^{\infty}}\left\|\nabla Z\right\|_{L^{2}}\left\|\nabla \Delta \psi\right\|_{L^{2}}\\ &\leq C \left\|\nabla^{2}\psi\right\|^{2}_{L^{\infty}}\left\|\nabla Z\right\|^{2}_{L^{2}}+\frac{1}{2}\left\|\nabla \Delta \psi\right\|^{2}_{L^{2}} \end{split}

    and so we have

    \frac{d}{dt} \left(\left\|\Delta\psi\right\|^{2}_{L^{2}}+\left\|\nabla Z\right\|^{2}_{L^{2}} \right) +\left\| \nabla \Delta \psi\right\|^{2}_{L^{2}} \leq C \left\|\nabla^{2}\psi\right\|^{2}_{L^{\infty}}\left\|\nabla Z\right\|^{2}_{L^{2}}.

    This implies

    \begin{eqnarray} \begin{split} &\left\|\Delta \psi(t)\right\|^{2}_{L^{}}+ \left\|\nabla Z(t)\right\|^{2}_{L^{2}}+\int^{t}_{0}\left\| \nabla \Delta \psi(s)\right\|^{2}_{L^{2}} ds < \infty\\& \iff \int^{t}_{0}\left\|\nabla^{2}\psi(s)\right\|^{2}_{L^{\infty}}ds < \infty \end{split} \end{eqnarray} (51)

    We also take

    \begin{split} &\frac{1}{2}\frac{d}{dt} \left(\left\|\nabla \Delta\psi\right\|^{2}_{L^{2}}+\left\|\Delta Z\right\|^{2}_{L^{2}} \right) +\left\| \Delta^{2} \psi\right\|^{2}_{L^{2}} = -\int \Delta^{3} \psi [\psi, Z] +\int\Delta^{2} Z[\Delta \psi, \psi]\\ & = -\int \Delta^{2}\psi [\Delta \psi, Z] -2\int \Delta^{2}\psi \left([\psi_{x}, Z_{x}]+[\psi_{y}, Z_{y}]\right) \\&\qquad- 2\int \Delta\psi \left([\psi_{x}, \Delta Z_{x}]+[\psi_{y}, \Delta Z_{y}]\right)\\ & = \text{(I)+(II)+(III)}. \end{split}

    By using the computation in (41),

    \begin{split} \text{(I)}& = \int \left(\nabla \nabla^{\perp}Z\cdot \nabla \Delta \psi\right)\cdot \nabla \Delta\psi \leq C\left\|\nabla^{2}Z\right\|_{L^{2}} \left\|\nabla^{3}\psi \right\|^{2}_{L^{4}} \\ &\leq C\left\|\nabla^{2}Z\right\|^{2}_{L^{2}} \left\|\nabla\Delta \psi \right\|^{2}_{L^{2}}+\frac{1}{6}\left\|\Delta^{2}\psi \right\|^{2}_{L^{2}}. \end{split}

    We next estimate \text{(II)}+\text{(III)} using (42):

    \begin{equation*} \begin{split} \text{(II)}+\text{(III)}&\leq C\int \left|\nabla^{2}Z\right| \left|\nabla^{3}\psi \right|^{2}+C\int \left|\nabla^{2}\psi \right| \left|\nabla^{4}\psi \right|\left|\nabla^{2}Z\right|\\ &\leq C\left\|\Delta Z\right\|^{2}_{L^{2}} \left\|\nabla\Delta \psi \right\|^{2}_{L^{2}}+C\left\|\nabla^{2}\psi\right\|^{2}_{L^{\infty}} \left\|\Delta Z \right\|^{2}_{L^{2}}+\frac{1}{3}\left\|\Delta^{2}\psi \right\|^{2}_{L^{2}} \end{split} \end{equation*}

    So, we have

    \begin{eqnarray} \begin{split} &\frac{d}{dt}\left(\left\|\nabla \Delta \psi\right\|^{2}_{L^{2}}+\left\|\Delta Z\right\|^{2}_{L^{2}}\right) +\left\|\Delta^{2} \psi\right\|^{2}_{L^{2}}\\&\leq C\left(\left\|\nabla\Delta \psi \right\|^{2}_{L^{2}}+\left\|\nabla^{2}\psi\right\|^{2}_{L^{\infty}}\right)\left\|\Delta Z\right\|^{2}_{L^{2}}. \end{split} \end{eqnarray} (52)

    By (51), (52) implies

    \begin{eqnarray} \begin{split} &\left\|\nabla \Delta \psi(t)\right\|^{2}_{L^{2}}+\left\|\Delta Z(t)\right\|^{2}_{L^{2}}+\int \left\|\Delta^{2} \psi(s)\right\|^{2}_{L^{2}}ds < \infty \\ &\iff \int^{t}_{0}\left\|\nabla^{2}\psi(s)\right\|^{2}_{L^{\infty}}ds < \infty. \end{split} \end{eqnarray} (53)

    We finally deal with

    \frac{1}{2}\frac{d}{dt} \left(\left\|\Delta^{2}\psi\right\|^{2}_{L^{2}}+\left\|\nabla\Delta Z\right\|^{2}_{L^{2}} \right) +\left\|\nabla \Delta^{2} \psi\right\|^{2}_{L^{2}} = \int \Delta^{4} \psi [\psi, Z] -\int\Delta^{3} Z[\Delta \psi, \psi]

    where we count the number of derivatives acting on (\psi, \psi, Z) in (46) as (3, 5, 2) , (2, 5, 3) , and (4, 4, 2) . Then, we obtain

    \begin{equation*} \begin{split} &\frac{1}{2} \frac{d}{dt} \left(\left\|\Delta^{2}\psi\right\|^{2}_{L^{2}}+\left\|\nabla\Delta Z\right\|^{2}_{L^{2}} \right) +\left\|\nabla\Delta^{2} \psi\right\|^{2}_{L^{2}}\\ & \leq C\left\|\Delta Z\right\|^{2}_{L^{2}}\left\|\Delta^{2}\psi\right\|^{2}_{L^{2}}\\&\qquad+ C\left\|\nabla^{2}\psi\right\|^{2}_{L^{\infty}}\left\|\nabla \Delta Z\right\|^{2}_{L^{2}} +C\left\|\Delta Z\right\|^{2}_{L^{4}}\left\|\nabla^{3}\psi\right\|^{2}_{L^{4}}+\frac{1}{2}\left\|\nabla \Delta^{2} \psi\right\|^{2}_{L^{2}}\\ &\leq C\left\|\Delta Z\right\|^{2}_{L^{2}}\left\|\Delta^{2}\psi\right\|^{2}_{L^{2}}+ C\left\|\nabla^{2}\psi\right\|^{2}_{L^{\infty}}\left\|\nabla \Delta Z\right\|^{2}_{L^{2}} +C\left\|\Delta Z\right\|^{2}_{L^{2}}\left\|\nabla\Delta Z\right\|^{2}_{L^{2}}\\ &+C\left\|\nabla \Delta \psi\right\|^{2}_{L^{2}}\left\|\Delta^{2}\psi\right\|^{2}_{L^{2}}+\frac{1}{2}\left\|\nabla \Delta^{2} \psi\right\|^{2}_{L^{2}} \end{split} \end{equation*}

    and so we have

    \begin{equation} \begin{split} &\frac{d}{dt} \left(\left\|\Delta^{2}\psi\right\|^{2}_{L^{2}}+\left\|\nabla\Delta Z\right\|^{2}_{L^{2}} \right) +\left\|\nabla\Delta^{2} \psi\right\|^{2}_{L^{2}}\\ &\leq C\left(\left\|\nabla^{2}\psi\right\|^{2}_{L^{\infty}}+\left\|\Delta Z\right\|^{2}_{L^{2}}\right)\left\|\nabla \Delta Z\right\|^{2}_{L^{2}} +C\left(\left\|\nabla \Delta \psi\right\|^{2}_{L^{2}}+\left\|\Delta Z\right\|^{2}_{L^{2}}\right)\left\|\Delta^{2}\psi\right\|^{2}_{L^{2}} \end{split} \end{equation} (54)

    By (51) and (53), (54) implies

    \label{BW 5}\begin{split} &\left\|\Delta^{2} \psi(t)\right\|^{2}_{L^{2}}+\left\|\nabla \Delta Z(t)\right\|^{2}_{L^{2}}+\int^{t}_{0} \left\|\nabla\Delta^{2} \psi(s)\right\|^{2}_{L^{2}}ds < \infty\\& \iff \int^{t}_{0}\left\|\nabla^{2}\psi(s)\right\|^{2}_{L^{\infty}}ds < \infty. \end{split}

    We recall (13):

    \psi_{t}-\Delta \psi = [\psi, Z], \quad Z_{t}+Z = [\Delta \psi, \psi].

    Since the uniqueness is already proved in Section 5.1.2 even without the damping term, we only focus on the a priori bounds.

    We first have

    \begin{equation} \begin{split} &\frac{1}{2}\frac{d}{dt}\left\|\psi\right\|^{2}_{L^{2}}+\left\|\nabla \psi\right\|^{2}_{L^{2}} = 0, \\ & \frac{1}{2}\frac{d}{dt} \left(\left\|\nabla \psi\right\|^{2}_{L^{2}}+\left\|Z\right\|^{2}_{L^{2}}\right) + \left\|\Delta \psi\right\|^{2}_{L^{2}}+\left\|Z\right\|^{2}_{L^{2}} = 0. \end{split} \end{equation} (55)

    We also have

    \begin{split} \frac{1}{2}\frac{d}{dt} \left(\left\|\Delta^{2}\psi\right\|^{2}_{L^{2}}+\left\|\nabla\Delta Z\right\|^{2}_{L^{2}} \right) &+\left\|\nabla \Delta^{2} \psi\right\|^{2}_{L^{2}}+\left\|\nabla\Delta Z\right\|^{2}_{L^{2}} \\ & = \int \Delta^{4} \psi [\psi, Z] -\int\Delta^{3} Z[\Delta \psi, \psi] = \mathcal{R} \end{split}

    with the same \mathcal{R} in (36). In this case, we also choose the the number of derivatives acting on (\psi, \psi, Z) as (3, 5, 2) , (2, 5, 3) , and (4, 4, 2) . Hence,

    \begin{equation*} \begin{split} & \frac{d}{dt} \left(\left\|\Delta^{2}\psi\right\|^{2}_{L^{2}}+\left\|\nabla\Delta Z\right\|^{2}_{L^{2}} \right) +\left\|\nabla\Delta^{2} \psi\right\|^{2}_{L^{2}} +\left\|\nabla\Delta Z\right\|^{2}_{L^{2}}\\ & \leq C \left\|\nabla^{2} Z\right\|_{L^{2}}\left\|\Delta^{2}\psi\right\|^{2}_{L^{4}} + C\left\|\nabla \Delta Z\right\|_{L^{2}} \left\|\nabla^{2}\psi\right\|_{L^{\infty}} \left\|\nabla \Delta^{2} \psi\right\|_{L^{2}}\\ &+ C\left\|\Delta Z\right\|_{L^{4}}\left\|\nabla^{3}\psi\right\|_{L^{4}} \left\|\nabla \Delta^{2}\psi\right\|_{L^{2}} \\ & \leq C \left\|\nabla Z\right\|^{\frac{1}{2}}_{L^{2}}\left\|\nabla\Delta Z\right\|^{\frac{1}{2}}_{L^{2}} \left\|\nabla \Delta\psi\right\|^{\frac{1}{2}}_{L^{2}}\left\|\nabla \Delta^{2}\psi\right\|^{\frac{3}{2}}_{L^{2}}+C\left\|\nabla \Delta Z\right\|_{L^{2}} \left\|\nabla^{2}\psi\right\|_{L^{\infty}} \left\|\nabla \Delta^{2} \psi\right\|_{L^{2}}\\ &+ C\left\|\Delta Z\right\|^{\frac{1}{2}}_{L^{2}}\left\|\nabla\Delta Z\right\|^{\frac{1}{2}}_{L^{2}} \left\|\Delta\psi\right\|^{\frac{1}{2}}_{L^{2}} \left\|\nabla \Delta^{2}\psi\right\|^{\frac{3}{2}}_{L^{2}}\\ & \leq C\left(\left\|\nabla Z\right\|^{2}_{L^{2}}\left\|\nabla \Delta\psi\right\|^{2}_{L^{2}}+\left\|\Delta Z\right\|^{2}_{L^{2}}\left\|\Delta\psi\right\|^{2}_{L^{2}}+\left\|\nabla^{2}\psi\right\|^{2}_{L^{\infty}}\right)\left\|\nabla\Delta Z\right\|^{2}_{L^{2}}\\&\qquad +\frac{1}{2} \left\|\nabla \Delta^{2} \psi\right\|_{L^{2}}. \end{split} \end{equation*}

    So, we obtain

    \begin{equation} \begin{split} &\frac{d}{dt} \left(\left\|\Delta^{2}\psi\right\|^{2}_{L^{2}}+\left\|\nabla\Delta Z\right\|^{2}_{L^{2}} \right) +\left\|\nabla\Delta^{2} \psi\right\|^{2}_{L^{2}} +\left\|\nabla\Delta Z\right\|^{2}_{L^{2}}\\ & \leq C\left(\left\|\nabla Z\right\|^{2}_{L^{2}}\left\|\nabla \Delta\psi\right\|^{2}_{L^{2}}+\left\|\Delta Z\right\|^{2}_{L^{2}}\left\|\Delta\psi\right\|^{2}_{L^{2}}+\left\|\nabla^{2}\psi\right\|^{2}_{L^{\infty}}\right)\left\|\nabla\Delta Z\right\|^{2}_{L^{2}} \end{split} \end{equation} (56)

    By (55) and (56),

    \mathcal{E}'(t)+\mathcal{N}_{2}(t)\leq C \left(\mathcal{E}(t)+\mathcal{E}^{2}(t)\right)\mathcal{N}_{2}(t).

    So, if \mathcal{E}_{0} = \epsilon_{0} is sufficiently small, we obtain

    \mathcal{E}(t)+(1-C \epsilon_{0})\int^{t}_{0}\mathcal{N}_{2}(s)ds\leq \mathcal{E}_{0} \quad {\rm{for}}\; {\rm{all}}\; t > 0 .

    H.B. was supported by NRF-2018R1D1A1B07049015. H. B. acknowledges the Referee for his/her valuable comments that highly improve the manuscript.



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