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# The BV solution of the parabolic equation with degeneracy on the boundary

Huashui Zhan
• Corresponding author
• School of Applied Mathematics, Xiamen University of Technology, Xiamen 361024, China,
• Email:
/ Shuping Chen
• School of Applied Mathematics, Xiamen University of Technology, Xiamen 361024, China,
• Email:
Published Online: 2016-05-10 | DOI: https://doi.org/10.1515/math-2016-0025

## Abstract

Consider a parabolic equation which is degenerate on the boundary. By the degeneracy, to assure the well-posedness of the solutions, only a partial boundary condition is generally necessary. When 1 ≤ α < p – 1, the existence of the local BV solution is proved. By choosing some kinds of test functions, the stability of the solutions based on a partial boundary condition is established.

MSC 2010: 35L65; 35L85; 35R35

## 1 Introduction and the main results

Yin-Wang [1] first studied the equation

$ut=div(ρα|∇u|p−2∇u), (x,t)∈QT=Ω×(0,T).$(1)

where Ω is a bounded domain in RN with appropriately smooth boundary, ρ(x) = dist(x, ∂Ω), p > 1, α > 0. An obvious character of the equation is that, the diffusion coefficient depends on the distance to the boundary. Since the diffusion coefficient vanishes on the boundary, it seems that there is no heat flux across the boundary. However, Yin-Wang [1] showed that the fact might not coincide with what we image. In fact, the exponent α, which characterizes the vanishing ratio of the diffusion coefficient near the boundary, does determine the behavior of the heat transfer near the boundary. One may refer to [1] for the details.

In our paper, we will consider the following equation

$ut=div(ρα|∇u|p−2∇u)+∑i=1N∂bi(u)∂xi, (x,t)∈QT.$(2)

The convection term ${\sum }_{i=1}^{N}\frac{\partial {b}_{i}\left(u\right)}{\partial {x}_{i}}$ not only brings the difference on operational skills, but more essentially, it makes the nature of boundary condition change. The equation (2) had been originally studied by the authors in [2, 3]. Instead of the whole boundary condition

$u(x,t)=0, (x,t)∈∂Ω×(0,T),$(3)

only a partial boundary condition

$u(x,t)=0, (x,t)∈Σp×(0,T),$(4)

matching equation (2) is considered. Here, denoting {ni (x)} as the unit inner normal vector of ∂Ω, when ${{b}^{\prime }}_{i}\left(0\right){n}_{i}\left(x\right)<0,\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\forall x\in \partial \text{Ω}$, then Σp = ∂Ω. But generally, it is just a portion of ∂Ω. However, we don’t need to pay too much attention to its explicit formula, we only need to remember it is just a subset of ∂Ω. Certainly, the initial value is always necessary,

$u(x,0)=u0(x).$(5)

In [2, 3], we said a bounded domain Ω has the integral non-singularity, if the constants α, p, satisfy

$∫Ωρ−2αp−2dx⩽c.$

We assumed that there are constants β, c such that

$|bi(s)|⩽c|s|1+β, |b′i(s)|⩽c|s|β.$(6)

If p > 2, we had obtained the existence of the solution of equation (2) with the initial boundary values (4)(5), and if Σp = ∂Ω, we also had obtained the stability of the weak solutions. In our paper, we will promote the existence of the solution without the condition (6) but limiting that α ≥ 1. The most innovation of our paper is that the stability of the weak solutions can be obtained only based on the partial boundary condition (4). Comparing with the case of that Σp = ∂Ω in [2, 3] or Σp = ∅ in [1] (when αp – 1), how to obtain the stability of the weak solutions only based on the partial boundary condition (4) seems very difficult.

Let us give the basic definitions and the main results as following.

Definition 1.1: A function u(x, t) is said to be a local BV solution of equation (2) with the initial value (5), if $u∈BV(QTλ)∩L∞(QT),ρα|∇u|p∈L1(QT),$and for any function $\phi \in {C}_{0}^{\infty }\left({Q}_{T}\right)$, the following integral equivalence holds $∬QT(−uφt+ρα|∇u|p−2∇u⋅∇φ+∑i=1Nbi(u)⋅φxi)dxdt=0.$(7)The initial value is satisfied in the sense of $limt→0∫Ω|u(x,t)−u0(x)|dx=0.$(8)Here, Q = {(x, t) ∈ QT : ρ(x) = dist(x, ∂Ω) > λ} for small enough λ > 0.

Definition 1.2: A function u(x, t) is said to be a local BV solution of equation (2) with the initial boundary values (4)(5), if u satisfies Definition 1.1, and it satisfies the partial boundary condition (4) in the sense of the trace.

Definition 1.3: If u is a local BV solution of equation (2), satisfies that $|u(x,t)|≤cρ(x), |∇u|≤cρ−α(x),$(9)when x is near ∂Ω, then we say u is a regular solution.

Remark 1.4: If bi(s) ≡ 0, we had proved that the solution of equation (1) is regular in [4].

Theorem 1.5: Let 1 < p, 1 ≤ α < p – 1, bi(s) ∈ C2(R1). If $u0(x)∈C0∞(Ω),$(10)then equation (2) with initial boundary values (4)(5) has a local BV solution u, and utL(QT).

Theorem 1.6: Let α < p – 1, u and v be two local BV solutions of equation (1) with the same partial homogeneous boundary value $u|Σp×(0,T)=0=υ|Σp×(0,T),$(11)and with the different initial values u(x, 0) = v(x, 0) respectively. If bi(s) is a Lipschitz function, and moreover $|∇u|≤cρ−α(x), |∇υ|≤cρ−α(x)$(12)then $∫Ω|u(x,t)−v(x,t)|dx⩽∫Ω|u0−v0|dx+c∫Σ′p|u−v|dΣ+lim supn→∞∫Σ′pgn(u−v)|u−v|dΣ, ∀t∈[0,T).$(13)Here, n > 0 is a nature number, the details of the definition and the properties of the function gn(s) is in Section 3, in particular, |gn(s)s| ≤ c.

Theorem 1.7: Let αp – 1, and u, v be two local BV solutions of (1) with the initial values u0(x), v0(x) respectively. If u and v are regular, and $|bi(u)−bi(v)|≤c|u−v|α+2,$(14)then $∫Ω|u(x,t)−v(x,t)|2dx≤c∫Ω|u0−v0|2dx,a.e.t∈(0,T).$(15)The most important character of Theorem 1.7 is in that we obtain the stability (15) without any boundary value condition. However, since the solutions considered in the theorem are regular, we can easily obtain the conclusion (15) in a similar way as in [1]. So we omit the details of the proof of the theorem in our paper.

Recently, the author has been interested in the initial-boundary value problem of the following strongly degenerate parabolic equation

$∂u∂t=∂∂xi(aij(u,x,t)∂u∂xj)+∂bi(u,x,t)∂xi,(x,t)∈QT.$(16)

The stability of the solutions based on a partial boundary condition (4) has been established in [57] et. al. Actually, many mathematicians have been interested in the problem, and have obtained many important results of the the stability of the solutions based on a partial boundary condition, one may see the Refs. [811]. Unlike the equation (16), to the best knowledge of the authors, considering the parabolic equation related to the p-Laplacian, our paper is the first one to study the stability of the solutions based on a partial boundary condition (4). Of course, whether the condition (12) in Theorem 1.6 and the assumption that u, v are regular in Theorem 1.7 are necessary or not? This is a very interesting problem to be studied in the future. Some other related references, one can refer to Refs. [1216]. The paper is arranged as following. In Section 1, we have introduced the problem and given the main results of the paper. In Section 2, we prove the existence of the local BV solution. In Section 3, only based on a partial boundary condition, we prove the Theorem 1.6.

## 2 The localBV solution

To study equation (2), we consider the following regularized problem

$uεt−div(ρεα(|∇uε|2+ε)p−22∇uε)−∑i=1N∂bi(uε)∂xi=0,(x,t)∈QT,$(17)$uε(x,t)=0, (x,t)∈∂Ω×(0,T),$(18)$uε(x,0)=u0(x), x∈Ω.$(19)

where ρ = ρ * δ + , > 0, δ is the mollifier as usual. It is well-known that the above problem has a unique classical solution [17, 18]. Hence, for any $\phi \in {C}_{0}^{\infty }\left({Q}_{T}\right)$, u satisfies

$∬QT(−uεφt+ρεα|∇uε|p−2∇uε⋅∇φ+∑i=1Nbi(uε)⋅φxi)dxdt=0.$(20)

Lemma 2.1: If ${u}_{0}\in {C}_{0}^{\infty }\left(\text{Ω}\right),\text{\hspace{0.17em}}\alpha \ge 1$, then the solution u of the initial boundary value problem (17)(19) converges locally in BV(QT), and its limit function u is the local BV solution of equation (2) with the initial value (5).Proof. By the maximum principle, there is a constant c only dependent on ‖u0L(Ω) but independent on ε, such that $‖uε‖L∞(QT)⩽c.$(21)Multiplying (17) by uε and integrating it over QT, we have $12∫Ωuε2dx+∬QTρεα(|∇uε|2+ε)p−22|∇uε|2dxdt+∬QTuε∑i=1N∂bi(uε)∂xidxdt=12∫Ωu02dx.$By the fact $∬QTuε∑i=1N∂bi(uε)∂xidxdt=−∑i=1N∂uε∂xibi(uε)dxdt=−∑i=1N∫Ω∂∂xi∫0uεbi(s)dsdt=0,$then $12∫Ωuε2dx+∬QTρεα(|∇uε|2+ε)p−22|∇uε|2dxdt⩽c.$(22)For small enough λ > 0, let Ωλ = {x ∈ Ω : dist(x, ∂Ω) > λ}. Since p > 1, by (22), $∫0T∫Ωλ|∇uε|dxdt≤c(∫0T∫Ωλ|∇uε|pdxdt)1p≤c(λ).$(23)Differentiating (17) with t, and denoting w = ut, then $∂w∂t=(p−2)ρεα(|∇uε|2+ε)p−42uxkuxiwxkxi+ρεα(|∇uε|2+ε)p−22wxixi+(p−2)∇ρεα⋅∇uε(|∇uε|2+ε)p−42uxkwxk+∇ρεα(|∇uε|2+ε)p−22⋅∇w +(p−2)(p−4)ρεα(|∇uε|2+ε)p−62uxjuxixjuxiwxkuxk+(p−2)ρεα(|∇uε|2+ε)p−42(uxiuxixkwxk+uxkuxkxiwxi+uxkuxixiwxk) +bi″(u)uxiw+bi′(u)wxi,$rewriting it as $∂w∂t=aij∂2w∂xi∂xj+∑i=1Nfi(x,t,w)wxi+bi″(u)uxiw,$where $aij=ρεα(|∇uε|2+ε)p−22(δij+(p−2)(|∇uε|2+ε)−1uxiuxj).fi(x,t,w)=(p−2)∇ρεα⋅∇uε(|∇uε|2+ε)p−42uxi+(|∇uε|2+ε)p−22(ρεα)xi +(p−2)(p−4)ρεα(|∇uε|2+ε)p−62uxjuxkxjuxkuxi+(p−2)ρεα(|∇uε|2+ε)p−42(uxkuxkxi+uxiuxixk+uxiuxkxk)+b′i(u),$Clearly, w satisfies that $w(x,t)=0,(x,t)∈∂Ω×[0,T),w(x,0)=div(ρεα(|∇u0|2+ε)p−22∇u0)+∂bi(u0)∂xi,x∈Ω.$Denoting that $a=(|∇uε|2+ε)p−22,$then $min{p−1,1}a|ξ|2≤aijξiξj≤max{p−1,1}a|ξ|2.$By the maximum principle, due to α ≥ 1, we have $supΩ×(0,T)|uεt|≤supΩ|div(ρεα(|∇u0|2+ε)p−22+∂bi(u0)∂xi|≤c.$(24)By (23)(24), we know that uεBV(QTλ), and $∫0T∫Ωλ|∇uε|dxdt≤c, ∫0T∫Ωλ|uεt|dxdt≤c.$(25)Then by Kolmogoroff’s theorem, there exists a subsequence (still denoted as uε) of uε, which is strongly convergent to uBV(QTλ). In particular, by the arbitrary of λ, uεu a.e. in QT.Hence, by (22), (25), there exists a function u and n dimensional vector function $\stackrel{\to }{\zeta }=\left({\zeta }_{1},\cdots ,{\zeta }_{n}\right)$ satisfying that $u∈BV(QTλ)∩L∞(QT), |ζ→|∈Lpp−1(QT),$and $uε⇀*u, in L∞(QT),∇uε⇀∇u in Llocp(QT),ρεα|∇uε|p−2∇uε⇀ζ→ in Lpp−1(QT).$In order to prove u satisfies equation (2), we notice that for any function $\phi \in {C}_{0}^{\infty }\left({Q}_{T}\right)$, $∬QT(−uεφt+ρεα(|∇uε|2+ε)p−22∇uε⋅∇φ+∑i=1Nbi(uε)⋅φxi)dxdt=0.$(26)and uεu is almost everywhere convergent, so bi(uε) → bi(u) is true. Then $∬QT(∂u∂tφ+ς→⋅∇φ+∑i=1Nbi(u)⋅φxi)dxdt=0.$(27)Now, if we can prove that $∬QTρα|∇u|p−2∇u⋅∇φdxdt=∬QTζ→⋅∇φdxdt.$(28)for any function $\phi \in {C}_{0}^{\infty }\left({Q}_{T}\right)$, then u satisfies equation (2).Let $0⩽\psi \in {C}_{0}^{\infty }\left({Q}_{T}\right)$ and ψ = 1in suppφ. Let vBV(QTλ) ∩ L(QT), ρα|∇v|pL1(QT). It is well-known that $∬QTψρεα(|∇uε|p−2∇uε−|∇v|p−2∇v)⋅(∇uε−∇v)dxdt⩾0.$(29)By choosing φ = ψu in (26), we can obtain $∬QTψρεα(|∇uε|2+ε)p−22|∇uε|2dxdt=12∬QTψtuε2dxdt−∬QTρεαuε(|∇uε|2+ε)p−22∇uε⋅vψdxdt −∑i=1N∬QTbi(uε)(uεxiψ+uεψxi)dxdt.$(30)Noticing that when p ≥ 2, $(|∇uε|2+ε)p−22|∇uε|2≥|∇uε|p,(|∇uε|2+ε)p−22|∇uε|≤(|∇uε|p−1+1),$and when 1 < p < 2, $(|∇uε|2+ε)p−22|∇uε|2≥(|∇uε|2+ε)p2−εp2,(|∇uε|2+ε)p−22|∇uε|≤(|∇uε|2+ε)p−12,$(31)then in both cases, by (29), we have $12∬QTψtuε2dxdt−∬QTρεαuε(|∇uε|2+ε)p−22∇uε⋅∇ψdxdt−∑i=1N∬QTbi(uε)(uεxiψ+uεψxi)dxdt +εp2c(Ω)−∬QTρεαψ|∇uε|p−2∇uε∇vdxdt−∬QTρεαψ|∇v|p−2∇(uε−v)dxdt≥0.$(32)Thus $12∬QTψtuε2dxdt−∬QTρεαuε(|∇uε|2+ε)p−22∇uε⋅∇ψdxdt−∑i=1N∬QTbi(uε)(uεxiψ+uεψxi)dxdt +εp2c(Ω)−∬QTρεαψ|∇uε|p−2∇uε∇vdxdt−∬QTψρα|∇v|p−2∇v⋅(∇uε−∇v)dxdt +∬QTψ(ρα−ρεα)|∇v|p−2∇v⋅(∇uε−∇v)dxdt⩾0.$(33)Noticing $|∬QTψ(ρα−ρεα)|∇v|p−2∇v⋅(∇uε−∇v)dxdt|⩽sup(x,t)∈QT|ψ(ρα−ρεα)|ρα∬QTρα|∇v|p−1|∇uε−∇v|dxdt⩽sup(x,t)∈QT|ψ(ρα−ρεα)|ρα(∬QTρα|∇v|pdxdt+∬QTρα|∇v|p−1|∇uε|dxdt)$(34)and $(|∇uε|2+ε)p−22∇uε=|∇uε|p−2∇uε+p−22ε∫01(|∇uε|2+εs)p−42ds∇uε$then $limε→0∬QTp−22ε∫01(|∇uε|2+εs)p−42ds∇uε∇ψuεdxdt=0.$(35)By Hölder inequality, there holds $∬QTρα|∇v|p−1|∇uε|dxdt⩽(∬QT(ρm|∇v|p−1)sdxdt)1/s⋅(∬QT(ρn|∇uε|)pdxdt)1/p,$where $m=\frac{\alpha \left(p-1\right)}{p},\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}n=\frac{\alpha }{p},\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}s=\frac{p}{p-1}$. Due to ρα|∇|p, ρα|∇|pL1(QT), then $∬QTρα|∇v|pdxdt+∬QTρα|∇v|p−1|∇uε|dxdt⩽c.$Let ε → 0 in (33). It converges to 0.Thus, we have $12∬QTψtu2dxdt−∬QTuζ→⋅∇ψdxdt−∑i=1N∬QTbi(u)(uxiψ+uψxi)dxdt−∬QTψζ→⋅∇vdxdt−∬QTψρα|∇v|p−2∇v⋅(∇uε−∇v)dxdt⩾0.$Let v = ψu in (2), we get $∬QTψζ→⋅∇udxdt−12∬QTu2ψtdxdt+∬QTuζ→⋅∇ψdxdt+∑i=1N∬QTbi(u)(uxiψ+uψxi)dxdt=0.$Thus $∬QTψ(ζ→−ρα|∇v|p−2∇v)⋅(∇u−∇v)dxdt⩾0.$(36)Let v = u – λφ, λ > 0, $\phi \in {C}_{0}^{\infty }\left({Q}_{T}\right)$, then $∬QTψ(ζ→−ρα|∇(u−λφ)|p−2∇(u−λφ))⋅∇φdxdt⩾0,$If λ → 0, then $∬QTψ(ζ→−ρα|∇u|p−2∇u)⋅∇φdxdt⩾0.$Moreover, if λ < 0, similarly we can get $∬QTψ(ζ→−ρα|∇u|p−2∇u)⋅∇φdxdt⩽0.$Thus $∬QTψ(ζ→−ρα|∇u|p−2∇u)⋅∇φdxdt=0,$Noticing that ψ = 1 on suppφ, (28) holds. At the same time, we can prove (5) as in [19], we omit the details here. The lemma is proved. □

Corollary 2.2: If ${u}_{0}\in {C}_{0}^{\infty }\left(\text{Ω}\right)$, α ≥ 1 there exists a local BV solution u of equation (2) with the initial value (5), such that utL(QT).

Lemma 2.3: If α < p – 1, u is a weak solution of equation (1) (also equation (2)) with the initial value (5). Then u has trace on the boundary ∂Ω.

Lemma 2.3 had been proved in [1, 2]. Clearly, Theorem 1.5 is the directly corollary of Lemma 2.12.3.

Remark 2.4: The condition α ≥ 1 is only used to prove that |u∊t| ≤ c, which implies that ${\int }_{{Q}_{T\lambda }}|{u}_{\epsilon t}|dxdt\le c$. Maybe one can prove the later conclusion directly. ${u}_{0}\in {C}_{0}^{\infty }\left(\text{Ω}\right)$ is the simplest condition, but it is not the most general condition. However, we mainly concern with how the degeneracy of diffusion coefficient ρα affects the boundary value condition.

## 3 The stability when α < p – 1

Proof of Theorem 1.6. For a small positive constant λ > 0, let $Ωλ={x∈Ω:ρ(x)=dist(x,∂Ω)>λ},$

and let $ϕ(x)={ 1, if x∈Ω2λ,1λ(ρ(x)−λ), x∈Ωλ\Ω2λ 0,if x∈Ω\Ωλ.$(37)

For any given positive integer n, let gn(s) be an odd function, and $gn(s)={1,s>1n,n2s2e1−n2s2,0≤s⩽1n.$(38)

Clearly, $limn→0gn(s)=sgn(s),s∈(−∞,+∞),$(39)

and $0≤g′n(s)≤cs, 0(40)

where c is independent of n.

By a process of limit, we can choose gn(ϕ(uv) as the test function, then $∫Ωgn(ϕ(u−v))∂(u−v)∂tdx+∫Ωρα(|∇u|p−2∇u−|∇v|p−2∇v⋅ϕ∇(u−v)g′ndx+∫Ωρα(∇u)|p−2∇u−|∇v|p−2∇v)⋅∇ϕ(u−v)g′ndx+∑i=1N∫Ω(bi(u)−bi(v))⋅(u−v)xig′nϕdx+∑i=1N∫Ω(bi(u)−bi(v))⋅(u−v)g′ndx=0.$(41)

Thus $limn→∞limλ→0∫Ωgn(ϕ(u−v))∂(u−v)∂tdx=ddt‖u−v‖1,$(42) $∫Ωρα(|∇u|p−2∇u−|∇v|p−2∇v)⋅∇(u−v)g′nϕ(x)dx≥0.$(43)

By L’Hospital rule, $limλ→0∫Ωλ\Ω2λg′n(ϕ(u−v))(u−v)dxλ=limλ→0∫λ2λ∫ρ=ζg′n(ϕ(u−v))(u−v)dΣdζλ=limλ→0∫ρ=2λg′n(u−v)(u−v)dΣ=∫∂Ωg′n(2(u−v))(u−v)dΣ=∫Σ′pg′n(u−v)(u−v)dΣ.$(44)

Since we assume that ρ|∇u|p < ∞, ρ|∇v|p < ∞, we have $limλ→0|∫Ωρα(|∇u|p−2∇u−|∇v|p−2∇v)⋅∇ϕ(u−v)g′n(ϕ(u−v))dx|=limλ→0|∫Ωλ\Ω2λρα(|∇u|p−2∇u−|∇v|p−2∇v)⋅∇ϕ(u−v)g′n(ϕ(u−v))dx|≤climλ→0|∫Ωλ\Ω2λg′n(ϕ(u−v))(u−v)dxλ=∫∑′pg′n(u−v)(u−v)dΣ.$(45)

While, $|∫Ω(bi(u)−bi(v))g′n(ϕ(u−v))(u−v)ϕxi(x)dx|≤∫Ωλ∖Ω2λ|bi(u)−bi(v)||u−v|gn′(ϕ(u−v))cλdx.$(46)

By |bi(u) – bi(v)| ≤ c|uv|, and by (40), according to the definition of the trace, we have $limλ→0⁡|∫Ω(bi(u)−bi(v))gn′(ϕ(u−v))(u−v)ϕxi(x)dx|≤limλ→0⁡∫Ωλ∖Ω2λ|u−v|2g′n(ϕ(u−v))cλdx=∫∂Ω|u−v|2gn′((u−v))d∑≤c∫∂Ω|u−v|dΣ=c∫∑′p|u−v|dΣ.$(47)

Moreover, $limλ→0⁡|∫Ω(bi(u)−bi(v))gn′(ϕ(u−v))(u−v)xiϕ(x)dx|=|∫{x∈Ω:|u−v|<1n}[bi(u)−bi(v)]gn′(u−v)(u−v)xidx⩽c∫{x∈Ω:|u−v|<1n}|bi(u)−bi(v)u−v||(u−v)xi|dx=c∫{x∈Ω:|u−v|<1n}|ρ−αpbi(u)−bi(v)u−v||ραp(u−v)xi|dx⩽c[∫{x∈Ω:|u−v|<1n}(|ρ−αpbi(u)−bi(v)u−v|)pp−1dx]pp−1⋅[∫{x∈Ω:|u−v|<1n}|ρα∇(u−v)|pdx]1p.$(48)

Since α < p – 1, $∫{x∈Ω:|u−v|<1n}(|ρ−αpbi(u)−bi(v)u−v|)pp−1dx⩽c∫Ωρ−αp−1dx⩽c.$(49)

In (47), let n → ∞. If {x ∈ Ω : |uv| = 0} is a set with 0measure, then $limn→∞∫{x∈Ω:|u−v|<1n}ρ−αp−1dx=∫{x∈Ω:|u−v|=0}ρ−αp−1dx=0.$(50)

If the set {x ∈ Ω : |uv| = 0} has a positive measure, then, $limn→∞∫{x∈Ω:|u−v|<1n}ρα|∇(u−v)|pdx=∫{x∈Ω:|u−v|=0}ρα|∇(u−v)|pdx=0.$(51)

Therefore, in both cases, we have $limn→∞limλ→0⁡∫Ω(bi(u)−bi(v))gn′(ϕ(u−v))(u−v)xiϕ(x)dx=0.$(52)

Now, after letting λ → 0, let n → ∞ in (41). Then $ddt‖u−v‖1⩽c∫Σ′p|u−v|dΣ+lim supn→∞∫Σ′pgn(u−v)|u−v|dΣ.$

It implies that $∫Ω|u(x,t)−v(x,t)|dx⩽∫Ω|u0−v0|dx+c∫Σ′p|u−v|dΣ+lim supn→∞∫Σ′pgn(u−v)|u−v|dΣ, ∀t∈[0,T).$

Theorem 1.6 is proved.

## Acknowledgement

The paper is supported by NSF of China (no.11371297, 11302184), Natural Science Foundation of Fujian province (no: 2015J01592), supported by Science Foundation of Xiamen University of Technology, China (no:XYK201448).

## References

• 1

Yin J., Wang Ch., Properties of the boundary flux of a singular diffusion process., Chin. Ann. Math., 2004, 25B(2), 175-182.

• 2

Zhan H., Yuan H., A diffusion convection equation with degeneracy on the boundary (in Chinese), Journal of Jilin University (Science Edition), 2015, 53(3), 353-358.

• 3

Zhan H., The boundary value condition of an evolutionary p.x/-Laplacian equation, Boundary Value Problems, 2015, 112, DOI: 10.1186/s13661-015-0377-6. [Crossref]

• 4

Zhan H. and Xie Q., The boundary degeneracy of a singular diffusion equation, Journal of inequalities and applications, 2014, 284, DOI: 10.1186/1029-242x-2014-284. [Crossref]

• 5

Zhan H., The solutions of a hyperbolic-parabolic mixed type equation on half-space domain, J. Of Differential Equations, 2015, 259, 1449-1481.

• 6

Zhan H., Homogeneous Dirichlet condition of an anisotropic degenerate parabolic equation, Boundary value problems, 2015, 22, DOI: 10.1186/s13661-015-0283-y. [Crossref]

• 7

Zhan H., The boundary degeneracy theory of a strongly degenerate parabolic equation, Boundary value problems, 2016, 2016, 2, DOI: 10.1186/s13661-015-0516-0. [Crossref]

• 8

Wu Z. and Zhao J., The first boundary value problem for quasilinear degenerate parabolic equations of second order in several variables, Chin. Ann. of Math., 1983, (1) 4B, 57-76.

• 9

Wu Z. and Zhao J., Some general results on the first boundary value problem for quasilinear degenerate parabolic equations, Chin. Ann. of Math., 1983, (3) 4B, 319-328.

• 10

Kobayasi K, Ohwa H., Uniqueness and existence for anisotropic degenerate parabolic equations with boundary conditions on a bounded rectangle, J. of Diff. Equ.. 2012, 252, 137-167.

• 11

Li Y., Wang Q., Homogeneous Dirichlet problems for quasilinear anisotropic degenerate parabolic-hyperbolic equations, J. of Diff. Equ., 2012. 252, 4719-4741.

• 12

Wang J., Gao W., Su M., Periodic solutions of non-Newtonian polytropic filtration equations with nonlinear sources, Applied Mathematics and Computation, 2010, 216, 1996-2009.

• 13

Ye H., Yin J., Propagation profile for a non-Newtonian polytropic filtration equation with orientated convection J. Math. Anal. Appl., 2015, 421, 1225-1237.

• 14

Lee K., Petrosyan A. and Vazquez J. L., Large time geometric properties of solutions of the evolution p-Laplacian equation. J. Diff. Equ., 2006, 229, 389-411.

• 15

Wang J., Wang Z. Yin J., A class of degenerate diffusion equations with mixed boundary conditions, J. Math. Anal. Appl., 2004, 298, 589-603.

• 16

Yin J. and Wang Ch., Evolutionary weighted p-Laplacian with boundary degeneracy, J. Diff. Equ., 2007, 237, 421-445.

• 17

Gu L., Second order parabolic partial differential equations (in chinese), The Publishing Company of Xiamen University, 2002.

• 18

Taylor Michael E., Partial differential equations III, Springer-Verlag, 1999.

• 19

Zhan H., The solution of convection-diffusion equation. Chinese Annals of Mathematics, 2013, 34(2), 235-256.

• 20

Zhan H., A new kind of solutions of degenerate parabolic equations with unbounded convection term, Open Math., 2015, 13, 283-297.

Accepted: 2016-04-09

Published Online: 2016-05-10

Published in Print: 2016-01-01

Citation Information: Open Mathematics, ISSN (Online) 2391-5455, Export Citation