Pullback Exponential Attractor for Second Order Nonautonomous Lattice System
Abstract
We first present some sufficient conditions for the existence of a pullback exponential attractor for continuous process on the product space of the weighted spaces of infinite sequences. Then we prove the existence and continuity of a pullback exponential attractor for second order lattice system with time-dependent coupled coefficients in the weighted space of infinite sequences. Moreover, we obtain the upper bound of fractal dimension and attracting rate for the attractor.
1. Introduction
2. Preliminaries
In this section, we present some sufficient conditions for the existence of a pullback exponential attractor for a continuous process on the product space of m weighted space of infinite sequences.
Consider a two-parameter continuous process on E: W(t, τ) : E → E, t ≥ τ ∈ ℝ, satisfying the following: W(τ, τ) = I, for all τ ∈ ℝ; W(t, r)W(r, τ) = W(t, τ), −∞ < τ ≤ r ≤ t < ∞; (t, τ, φτ) → W(t, τ)φτ is continuous for −∞ < τ ≤ t < ∞.
Definition 1. A family {ℳ(t)} t ∈ℝ of subsets of is called a pullback exponential attractor for the continuous process {W(t, τ)} t≥τ, if
- (i)
each ℳ(t) (t ∈ ℝ) is a compact set of and its fractal dimension is uniformly bounded in t; that is, supt ∈ℝdimfℳ(t) < ∞;
- (ii)
it is positively invariant; that is, W(t, τ)ℳ(τ) ⊂ ℳ(t) for all −∞ < τ ≤ t < ∞;
- (iii)
there exist an exponent α > 0 and two positive-valued functions Q, 𝒯 : ℝ+ → ℝ+ such that for any bounded set
()
As a direct consequence of Theorem 2 of [20], we have the following theorem.
Theorem 2. Let {W(t, τ)} t≥τ be a continuous process in . Assume that there exists a uniformly bounded absorbing set for {W(t, τ)} t≥τ: for any bounded set , there exists a constant TB ≥ 0 such that W(t, τ)B⊆B0 for all t ≥ τ + TB, τ ∈ ℝ. For any t ∈ ℝ, set . If
-
(A1) there exist and such that, for every τ ∈ ℝ, any t ∈ [0, T*], and φτ, ψτ ∈ X(τ),
() -
(A2) there exist a positive constant γ ∈ [0, 1/2) and a (2N + 1)m-dimensional bounded projection such that, for every τ ∈ ℝ and φτ, ψτ ∈ X(τ),
()
3. Pullback Exponential Attractor for Second Order Nonautonomous Lattice System
- (P0)
0 < ρ(i) ≤ M0, ρi = ρ(i) ≤ c0ρ (i ± 1), i ∈ ℤ, for some positive constants M0 and c0.
- (H1)
There exist two positive constants and such that
() - (H2)
Let η(t) = {sup|ηi,j(t)| : i ∈ ℤ, j = −q ⋯ q} < ∞ (q ∈ ℕ) satisfy the following:
- (H2a)
in t;
- (H2b)
there exists a continuous positive valued function Q : ℝ+ → ℝ+ such that
()where is a positive constant; - (H2c)
there exist I0 ∈ ℕ and η0 > 0 such that
()
- (H2a)
- (H3)
For all i ∈ ℤ, let fi satisfy the following:
- (H3a)
fi(x, t) is differentiable in x and continuous in t;
- (H3b)
for any i ∈ ℤ, fi(0, t) = 0, supx,t ∈ℝ | fi(x, t)| ≤ βi(t);
- (H3c)
there exist functions Γ ∈ C(ℝ+ × ℝ, ℝ+) and such that
()
- (H3a)
- (H4)
g(t) = (gi(t)) i ∈ℤ ∈ G, β(t) = (βi(t)) i ∈ℤ ∈ G, where
()
Definition 3. The function φ : [τ, τ + T) → E (T > 0) is called a mild solution of the following lattice differential equations:
Theorem 4. Assume that (P0) and (H1)–(H4) hold. Then for any fixed τ ∈ ℝ and any initial data φ(τ) = (uτ, vτ) ∈ E, problem (19) admits a unique mild solution φ(·, τ; φτ) ∈ C([τ, +∞), E) with φ(τ, τ; φτ) = φτ and φ(·, τ; φτ) being continuous in φτ ∈ E, and the mapping
Proof. Let
Theorem 5. Assume that (P0) and (H1)–(H4) hold. There exists a uniform bounded closed absorbing ball B0 = B0(0, r0) ⊂ E of {U(t, τ)} t≥τ centered at 0 with radius r0 (independent of τ, t) such that, for any bounded subset B ⊂ E, there exists TB ≥ 0 yielding U(t + τ, τ)B⊆B0 for all t ≥ TB.
Proof. Let be a mild solution of (19), t ≥ τ. Since the set of continuous functions is dense in , by (H2a), there exist sequences of continuous functions , m ∈ ℕ, such that
Consider the following lattice differential equations:
Lemma 6. Assume that (P0) and (H1)–(H4) hold. For any ε > 0, there exist and I(ε, B0) ∈ ℕ such that, for t ≥ T(ε, B0), the mild solution U(τ + t, t)φτ = φ(τ + t, τ; φτ) = (ui(τ + t, τ; uτ), vi(τ + t, τ; vτ)) i ∈ℤ ∈ E of system (19) with φτ ∈ B0 ⊂ E satisfies
Proof. Let ξ ∈ C1(R+, R) be a smooth increasing function which satisfies
Theorem 7. Assume that (P0) and (H1)–(H4) hold.
- (a)
There exists a continuous positive value function Lt in t such that, for every τ ∈ ℝ,
() - (b)
There exist positive constants T* > 0, γ ∈ [0, 1/2), and a 2(2N + 1)-dimensional orthogonal projection PN : E → EN (N ∈ ℤ), such that, for every τ ∈ ℝ and φτ, ψτ ∈ Y(τ),
() - (c)
For each fixed t ∈ ℝ, .
Proof. For any τ ∈ ℝ, initial data φτ = (uτ, vτ), ψτ = (xτ, yτ). Let φ(t) = U(t, τ)φτ, ψ(t) = U(t, τ)ψτ, and ϕ(t) = φ(t) − ψ(t) = (ϕi(t)) i ∈ℤ; then, φ(t), ψ(t), ϕ(t) ∈ C([τ, +∞), E).
(a) For any t ≥ τ, let φm(t), ψm(t) be two solutions of (29) with initial data φτ, ψτ and set ϕm(t) = φm(t) − ψm(t), and then ϕm(t) ∈ C([τ, +∞), E)∩C1((τ, +∞), E) satisfies
Taking the inner product (·, ·) E of (69) with ϕm, we have
(b) For i ∈ ℤ, let and , where ξ is as in (52) and M > I0 + q. Taking the inner product of (69) with ωm in E, we have that, for t ≥ τ,
(c) It follows from the following estimate:
As a direct consequence of Theorem 2, Theorem 4, Theorem 5, Theorem 7, and Theorem 3.1 of [15], we have the following result.
Theorem 8. Assume that (P0) and (H1)–(H4) hold. The process {U(t, τ)} t≥τ associated with (19) possesses a pullback exponential attractor {𝒜(t)} t ∈ℝ with the following properties:
- (i)
for any t ∈ ℝ, 𝒜(t)⊆Y(t)⊆B0;
- (ii)
;
- (iii)
and for any bounded set B ⊂ E, dh(U(t, τ)Y(τ), , −∞ < τ + TB < t ≤ +∞;
- (iv)
limt→τdh(𝒜(t), 𝒜(τ)) = 0;
Remark 9. It should be pointed out that, for some special cases, (H2) and (27) can be removed. For example, if the coupled linear operator A(t) ≡ A in (10) is a constant operator A satisfying −A = D*D = DD*, where , for all (constant), − m0 ⩽ j ⩽ m0, and D* is the adjoint of D. A simple example of such an operator A is (Au) i = ui−1 + ui+1 − 2ui and (Du) i = ui+1 − ui. Choose a positive weight function ρ : ℤ → ℝ+ satisfying the properties (P0) and |ρ(i ± 1) − ρ(i)| ≤ bρ(i), for all i ∈ ℤ for some small b ≥ 0. Two examples of such weight functions are ρ(i) = 1/(1 + κ2i2) q, q > 1/2, and ρ(i) = e−κ|i|, i ∈ ℤ, with κ > 0 being a parameter. If the number b satisfies
Conflict of Interests
The authors declare that there is no conflict of interests regarding the publication of this paper.
Acknowledgments
This work is supported by the National Natural Science Foundation of China under Grant no. 11071165, 11326114 and Zhejiang Normal University (ZC304011068).