We are concerned with the following nonlinear secondorder threepoint boundary value problem on time scales , , , , where with and . A new representation of Green's function for the corresponding linear boundary value problem is obtained and some existence criteria of at least one positive solution for the above nonlinear boundary value problem are established by using the iterative method.
1. Introduction
Let be a time scale, that is, is an arbitrary nonempty closed subset of . For each interval of we define For more details on time scales, one can refer to [1–5]. Recently, threepoint boundary value problems (BVPs for short) for secondorder dynamic equations on time scales have received much attention. For example, in 2002, Anderson [6] studied the following secondorder threepoint BVP on time scales:
where , , and . Some existence results of at least one positive solution and of at least three positive solutions were established by using the wellknown Krasnoselskii and LeggettWilliams fixed point theorems. In 2003, Kaufmann [7] applied the Krasnoselskii fixed point theorem to obtain the existence of multiple positive solutions to the BVP (1.1). For some other related results, one can refer to [8–10] and references therein.
In this paper, we are concerned with the existence of at least one positive solution for the following secondorder threepoint BVP on time scales:
Throughout this paper, we always assume that with , , and
It is interesting that the method used in this paper is completely different from that in [6, 7, 9, 10], that is, a new representation of Green's function for the corresponding linear BVP is obtained and some existence criteria of at least one positive solution to the BVP (1.2) are established by using the iterative method.
For the function , we impose the following hypotheses:
(H1) is continuous;
(H2)for fixed , is monotone increasing on ;
(H3)there exists such that
Remark 1.1.
If (H3) is satisfied, then
2. Main Results
Lemma 2.1.
The BVP (1.2) is equivalent to the integral equation
where
is called the Green's function for the corresponding linear BVP, here
is the Green's function for the BVP:
Proof.
Let be a solution of the BVP:
Then, it is easy to know that
Now, if is a solution of the BVP (1.2), then it can be expressed by
which together with the boundary conditions in (1.2) and (2.6) implies that
On the other hand, if satisfies (2.1), then it is easy to verify that is a solution of the BVP (1.2).
Lemma 2.2.
For any one has
Proof.
Since it is obvious from the expression of that
we know that (2.9) is fulfilled.
Our main result is the following theorem.
Theorem 2.3.
Assume that (H1)–(H3) are satisfied. Then, the BVP (1.2) has at least one positive solution . Furthermore, there exist such that
Proof.
Let
Define an operator :
Then it is obvious that fixed points of the operator in are positive solutions of the BVP (1.2).
First, in view of (H2), it is easy to know that is increasing.
Next, we may assert that , which implies that for any , there exist positive constants and such that
In fact, for any , there exist such that
which together with (H2), (H3), and Remark 1.1 implies that
By Lemma 2.2 and (2.16), for any , we have
If we let
then it follows from (2.17) and (2.18) that
which shows that .
Now, for any fixed , we denote
and let
where
Then, it is easy to know from (2.20), (2.21), (2.22), (2.23), (2.24), (H3), and Remark 1.1 that
Moreover, if we let , then it follows from (2.22), (2.23), (2.24), and (H3) by induction that
which together with (2.25) implies that for any positive integers and ,
Therefore, there exists a such that and converge uniformly to on and
Since is increasing, in view of (2.28), we have
So,
which shows that is a positive solution of the BVP (1.2). Furthermore, since , there exist such that
Acknowledgment
This work is supported by the National Natural Science Foundation of China (10801068).
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