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Uniform Attractor for the Partly Dissipative Nonautonomous Lattice Systems
Advances in Difference Equations volume 2009, Article number: 916316 (2009)
Abstract
The existence of uniform attractor in is proved for the partly dissipative nonautonomous lattice systems with a new class of external terms belonging to , which are locally asymptotic smallness and translation bounded but not translation compact in . It is also showed that the family of processes corresponding to nonautonomous lattice systems with external terms belonging to weak topological space possesses uniform attractor, which is identified with the original one. The upper semicontinuity of uniform attractor is also studied.
1. Introduction
This paper is concerned with the longtime behavior of the following nonautonomous lattice systems:
with initial conditions
where is the integer lattice; is a nonlinear function satisfying ; is a positive selfadjoint linear operator; belong to certain metric space, which will be given in the following.
Lattice dynamical systems occur in a wide variety of applications, where the spatial structure has a discrete character, for example, chemical reaction theory, electrical engineering, material science, laser, cellular neural networks with applications to image processing and pattern recognition; see [1–4]. Thus, a great interest in the study of infinite lattice systems has been raising. Lattice differential equations can be considered as a spatial or temporal discrete analogue of corresponding partial differential equations on unbounded domains. It is well known that the longtime behavior of solutions of partial differential equations on unbounded domains raises some difficulty, such as wellposedness and lack of compactness of Sobolev embeddings for obtaining existence of global attractors. Authors in [5–7] consider the autonomous partial equations on unbounded domain in weighted spaces, using the decaying of weights at infinity to get the compactness of solution semigroup. In [8–10], asymptotic compactness of the solutions is used to obtain existence of global compact attractors for autonomous system on unbounded domain. Authors in [11] consider them in locally uniform space. For nonautonomous partial differential equations on bounded domain, many studies on the existence of uniform attractor have been done, for example [12–14].
For lattice dynamical systems, standard theory of ordinary differential equations can be applied to get the wellposedness of it. "Tail ends" estimate method is usually used to get asymptotic compactness of autonomous infinitedimensional lattice, and by this the existence of global compact attractor is obtained; see [15–17]. Authors in [18, 19] also prove that the uniform smallness of solutions of autonomous infinite lattice systems for large space and time variables is sufficient and necessary conditions for asymptotic compactness of it. Recently, "tail ends" method is extended to nonautonomous infinite lattice systems; see [20–22]. The traveling wave solutions of lattice differential equations are studied in [23–25]. In [18, 26, 27], the existence of global attractors of autonomous infinite lattice systems is obtained in weighted spaces, which do not exclude traveling wave.
In this paper, we investigate the existence of uniform attractor for nonautonomous lattice systems (1.1)–(1.3). The external term in [20] is supposed to belong to and to be almost periodic function. By BochnerAmerio criterion, the set of this external term's translation is precompact in . Based on ideas of [28], authors in [14] introduce uniformly limit compactness, and prove that the family of weakly continuous processes with respect to (w.r.t.) certain symbol space possesses compact uniform attractors if the process has a bounded uniform absorbing set and is uniformly limit compact. Motivated by this, we will prove that the process corresponding to problem (1.1)–(1.3) with external terms being locally asymptotic smallness (see Definition 4.5) possesses a compact uniform attractor in , which coincides with uniform attractor of the family of processes with external terms belonging to weak closure of translation set of locally asymptotic smallness function in . We also show that locally asymptotic functions are translation bounded in , but not translation compact (tr.c.) in . Since the locally asymptotic smallness functions are not necessary to be translation compact in , compared with [20], the conditions on external terms of (1.1)–(1.3) can be relaxed in this paper.
This paper is organized as follows. In Section 2, we give some preliminaries and present our main result. In Section 3, the existence of a family of processes for (1.1)–(1.3) is obtained. We also show that the family of processes possesses a uniformly (w.r.t ) absorbing set. In Section 4, we prove the existence of uniform attractor. In Section 5, the upper semicontinuity of uniform attractor will be studied.
2. Main Result
In this section, we describe our main result. Denote by the Hilbert space defined by
with the inner product and norm given by
For , we endow with the inner and norm as. For
Denote by the space of function with values in that locally 2power integrable in the Bochner sense, that is,
It is equipped with the local 2power mean convergence topology. Then, is a metrizable space. Let be a space of functions from such that
Denote by the space endow with the local weak convergence topology.
For each sequence define linear operators on by
Then
For convenience, initial value problem (1.1)–(1.3) can be written as
with initial conditions
where , .
In the following, we give some assumption on nonlinear function , and :
There exists a positivevalue continuous function such that
There exist positive constants such that
Let the external term belong to , it follows from the standard theory of ordinary differential equations that there exists a unique local solution for problem (2.8)–(2.10) if (H _{ 1 })–(H _{ 3 }) hold. For a fixed external term , take the symbol space , the set contains all translations of in . Take the the closure of in . Denote by the translation semigroup, for all or , , . It is evident that is continuous on in the topology of and on in the topology of , respectively,
In Section 3, we will show that for every and , , problem (2.8)–(2.10) has a unique global solution Thus, there exists a family of processes from to . In order to obtain the uniform attractor of the family of processes, we suppose the external term is locally asymptotic smallness (see Definition 4.5). Let be a Banach space which the processes acting in, for a given symbol space , the uniform (w.r.t. ) limit set of is defined by
The first result of this paper is stated in the following, which will be proved in Section 4.
Theorem 2 A.
Assume that be locally asymptotic smallness and hold. Then the process corresponding to problems (2.8)–(2.10) with external term possesses compact uniform attractor in which coincides with uniform (w.r.t. attractor for the family of processes , , that is,
where is the uniform absorbing set in , and is kernel of the process . The uniform attractor uniformly attracts the bounded set in .
We also consider finitedimensional approximation to the infinitedimensional systems (1.2)(1.3) on finite lattices. For every positive integer , let , consider the following ordinary equations with initial data in :
In Section 5, we will show that the finitedimensional approximation systems possess a uniform attractor in , and these uniform attractors are upper semicontinuous when . More precisely, we have the following theorem.
Theorem 2 B.
Assume that and hold. Then for every positive integer , systems (2.17) possess compact uniform attractor . Further, is upper semicontinuous to as , that is,
where
3. Processes and Uniform Absorbing Set
In this section, we show that the process can be defined and there exists a bounded uniform absorbing set for the family of processes.
Lemma 3.1.
Assume that and hold. Let , and . Then the solution of (2.8)–(2.10) satisfies
where , .
Proof.
Taking the inner product of (2.8) with in , by we get
Similarly, taking the inner product of (2.9) with in , we get
Note that
Summing up (3.2) and (3.3), from (3.4), we get
Thus, by ,
Since , from [12, Proposition V.4.2.], we have
From (3.6)(3.7), applying Gronwall's inequality of generalization (see [12, Lemma II.1.3]), we get (3.1). The proof is completed.
It follows from Lemma 3.1 that the solution of problem (2.8)–(2.10) is defined for all . Therefore, there exists a family processes acting in the space , , , , where is the solution of (2.8)–(2.10), and the time symbol belongs to and , respectively. The family of processes satisfies multiplicative properties:
Furthermore, the following translation identity holds:
The kernel of the processes consists of all bounded complete trajectories of the process , that is,
denotes the kernel section at a times moment :
Lemma 3.1 also shows that the family of processes possesses a uniform absorbing set in .
Lemma 3.2.
Assume that and hold. Let . Then, there exists a bounded uniform absorbing set in for the family of processes , that is, for any bounded set , there exists ,
Proof.
Let , from (3.1) we have
where
Let . The proof is completed.
4. Uniform Attractor
In this section, we establish the existence of uniform attractor for the nonautonomous lattice systems (2.8)–(2.10). Let be a Banach space, and let be a subset of some Banach space.
Definition 4.1.
is said to be weakly continuous, if for any , the mapping is weakly continuous from to .
A family of processes , is said to be uniformlylimit compact if for any and bounded set , the set is bounded for every and is precompact set as . We need the following result in [14].
Theorem 4.2.
Let be the weak closure of . Assume that , is weakly continuous, and

(i)
has a bounded uniformly (w.r.t. ) absorbing set ,

(ii)
is uniformly (w.r.t. ) limit compact.
Then the families of processes , , possess, respectively, compact uniform (w.r.t. , , resp.) attractors and satisfying
Furthermore, is nonempty for all .
Let be a Banach space and , denote the space of functions , with values in that are locally power integral in the Bochner sense, it is equipped with the local power mean convergence topology. Recall the Propositions in [12].
Proposition 4.3.
A set is precompact in if and only if the set is precompact in for every segment . Here, denotes the restriction of the set to the segment .
Proposition 4.4.
A function is tr.c. in if and only if

(i)
for any the set is precompact in ;

(ii)
there exists a function , such that
(42)
Now, one introduces a class of function.
Definition 4.5.
A function is said to be locally asymptotic smallness if for any , there exists positive integer such that
Denote by the set of all locally asymptotic smallness functions in . It is easy to see that . The next examples show that there exist functions in but not in , and a function belongs to is not necessary a tr.c. function in .
Example 4.6.
Let ,
For every , ,
Thus,
and . However, for every positive integer , and for any positive ,
Therefore, .
Example 4.7.
,
for ,
Here, denote the positive integer set.
For every positive integer , , and for ,
which implies that
Therefore, . Note that for any ,
From Proposition 4.4, is not translation compact in .
Remark 4.8.
Example 4.7 shows that a locally asymptotic function is not necessary translation compact in .
In the following, we give some properties of locally asymptotic smallness function.
Lemma 4.9.
is a closed subspace of .
Proof.
Let such that
Then, for any , there exists positive integer such that for every ,
Since , there exist such that for all ,
Let , we get that
Therefore, . This completes the proof.
Lemma 4.10.
Every translation compact function in is locally asymptotic smallness.
Proof.
Since is tr.c. in , we get that is precompact in . By Proposition 4.3, we get that is precompact in . Thus, for any , there exists finite number such that for every , there exist some , , such that
For the given above, implies that there exists positive integer such that
Therefore,
which implies is locally asymptotic smallness. This completes the proof.
We now establish the uniform estimates on the tails of solutions of (2.8)–(2.10) as .
Lemma 4.11.
Assume that hold and is locally asymptotic smallness. Then for any , there exist positive integer and such that if , , satisfies
Proof.
Choose a smooth function such that for , and
and there exists a constant such that for . Let be a suitable large positive integer, . Taking the inner product of (2.8) with and (2.9) with in , we have
From , we have
where is same as in Lemma 3.1
as in (3.10)
Summing up (4.22), from (4.23)–(4.25) we get
Thus,
We now estimate the integral term on the righthand side of (4.27).
Similarly,
Since is locally asymptotic smallness, from (4.27)–(4.29) we get that for any , if , there exist and sufficient large positive integer such that
The proof is completed.
Lemma 4.12.
Assume that hold, let , . If in and weakly in , then for any ,
Proof.
Let , . Since is bounded in , by Lemma 3.2, we get that
Therefore, for all , ,
Note that is the solution of (2.8) and (2.9) with time symbol , it follow from (4.32) that
In the following, we show that . By the fact that is the solution of (2.8) and (2.9), for any , we get that
Note that weakly in . Let in (4.35), by (4.34) we get that is the solution of (2.8) and (2.9) with the initial data . By the unique solvability of problem (2.8)–(2.10), we get that . This completes the proof.
Proof of Theorem A.
From Lemmas 3.2, 4.11 and 4.12, and Theorem 4.2, we get the results.
5. Upper Semicontinuity of Attractors
In this section, we present the approximation to the uniform attractor obtained in Theory A by the uniform attractor of following finitedimensional lattice systems in :
with the initial data
and the periodic boundary conditions
Similar to systems (2.8)–(2.10), under the assumption , the approximation systems (5.1)–(5.2) with possess a unique solution , which continuously depends on initial data. Therefore, we can associate a family of processes which satisfy similar properties (3.8)–(3.9). Similar to Lemma 3.2, we have the following result.
Lemma 5.1.
Assume that , and hold. Let . Then, there exists a bounded uniform absorbing set for the family of processes , that is, for any bounded set , there exists , for ,
In particular, is independent of and .
Since (5.1) is finitedimensional systems, it is easy to know that under the assumption of Lemma 5.1, the family of processes , is uniformly (w.r.t. ) limit compact. Similar to Lemma 4.12, if in , weakly in , then for any , ,
Lemma 5.2.
Assume that and hold. Then the process corresponding to problems (5.1)(5.2) with external term possesses compact uniform (w.r.t. ) attractor in which coincides with uniform (w.r.t. attractor for the family of processes , , that is,
where is the uniform absorbing set in , and is kernel of the process . The uniform attractor uniformly attracts the bounded set in .
Proof of Theorem B.
If , it follows from Lemma 5.2 that there exist and a bounded complete solution such that
Since , there exist and a subsequence of , which is still denote by , such that
From Lemma 5.1, we get that
which imply that
Thus,
Let be a sequence of compact intervals of such that and . From (5.9) and (5.11), using Ascoli's theorem, we get that for each , there exists a subsequence of (still denoted by ) and such that
Proceeding as in the proof of Lemma 4.11, we get that the weak convergence is actually strong convergence, and therefore is precompact in for each . Then we infer that there exists a subsequence of and such that converges to . Using Ascoli's theorem again, we get, by induction, that there is a subsequence of such that converges to in , where is an extension of to . Finally, taking a diagonal subsequence in the usual way, we find that there exist a subsequence of and such that for any compact interval
From (5.9) we get that
Next, we show that is the solution of (2.8)–(2.10). It follows from (5.10) that
For fixed , let . Since is the solution of (5.1)–(5.2) with , we have
Thus, for each , we have
Letting , by (5.8), (5.13), (5.15) and (5.17) we find that satisfies
Since is arbitrary, we note that (5.18) are valid for all . From (5.14) we find that is a bounded complete solution of (2.8)–(2.10). Therefore, . By (5.13) we get that
The proof is complete.
Remark 5.3.
All the result of this paper is valid for the systems in [20, 21].
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Acknowledgments
The authors are extremely grateful to the anonymous reviewers for their suggestion, and with their help, the version has been improved. This research was supported by the NNSF of China Grant no. 10871059
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Li, X., Lv, H. Uniform Attractor for the Partly Dissipative Nonautonomous Lattice Systems. Adv Differ Equ 2009, 916316 (2009). https://doi.org/10.1155/2009/916316
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Keywords
 Global Attractor
 Unbounded Domain
 Cellular Neural Network
 Time Symbol
 Asymptotic Compactness