- Meiqiang Feng
^{1}, - Xuemei Zhang
^{2, 3}Email author and - Weigao Ge
^{3}

**2009**:219251

**DOI: **10.1155/2009/219251

© Meiqiang Feng et al. 2009

**Received: **1 December 2008

**Accepted: **10 June 2009

**Published: **19 July 2009

## Abstract

By constructing an available integral operator and combining Krasnosel'skii-Zabreiko fixed point theorem with properties of Green's function, this paper shows the existence of multiple positive solutions for a class of *m*-point second-order Sturm-Liouville-like boundary value problems on time scales with polynomial nonlinearity. The results significantly extend and improve many known results for both the continuous case and more general time scales. We illustrate our results by one example, which cannot be handled using the existing results.

## 1. Introduction

Recently, there have been many papers working on the existence of positive solutions to boundary value problems for differential equations on time scales; see, for example, [1–20]. This has been mainly due to its unification of the theory of differential and difference equations. An introduction to this unification is given in [11, 12, 18, 19]. Now, this study is still a new area of fairly theoretical exploration in mathematics. However, it has led to several important applications, for example, in the study of insect population models, neural networks, heat transfer, and epidemic models; see, for example, [10, 11]. For some other excellent results and applications of the case that boundary value problems on time scales to a variety of problems from Khan et al. [21], Agarose et al. [22], Wang [23], Sun [24], Feng et al. [25], Feng et al. [26] and Feng et al. [27].

*m*-point nonlinear dynamic equation on time scales with polynomial nonlinearity:

By means of fixed point index theory in a cone, the author established the existence of two nonnegative solutions for problem (1.5).

As far as we know, there is no paper to study the existence of multiple positive solutions to problem (1.1) on time scales with polynomial nonlinearity. The objective of the present paper is to fill this gap. On the other hand, many difficulties occur when we study BVPs on time scales. For example, basic tools from calculus such as Fermat's theorem, Rolle's theorem and the intermediate value theorem may not necessarily hold. So it is interesting and important to discuss the problem (1.1). The purpose of this paper is to prove that the problem (1.1) possesses at least two positive solutions. Moreover, the methods used in this paper are different from [6, 28] and the results obtained in this paper generalize some results in [6, 28] to some degree.

The time scale related notations adopted in this paper can be found, if not explained specifically, in almost all literature related to time scales. The readers who are unfamiliar with this area can consult for example [11, 12, 18, 19] for details.

For convenience, we list the following well-known definitions.

Definition 1.1.

A time scale is a nonempty closed subset of .

Definition 1.2.

Define the forward (backward) jump operator at for at for by for all .

We assume throughout that has the topology that it inherits from the standard topology on and say is right-scattered, left-scattered, right-dense and left-dense if and , respectively. Finally, we introduce the sets and . which are derived from the time scale as follows. If has a left-scattered maximum , then , otherwise . If has a right-scattered minimum , then , .

Definition 1.3.

Definition 1.4.

for all . Call the nabla derivative of at the point .

If then . If then is the forward difference operator while is the backward difference operator.

Definition 1.5.

A function is called rd-continuous provided it is continuous at all right dense points of and its left sided limit exists (finite) at left dense . We let denote the set of rd-continuous functions .

Definition 1.6.

is called ld-continuous provided it is continuous at all left and its right sided limit exists (finite) at right dense . We let denote the set of ld-continuous .

Definition 1.7.

Definition 1.8.

## 2. Preliminaries

In this section, we provide some necessary background. In particular, we state some properties of Green's function associated with problem (1.1), and we then state a fixed-point theorem which is crucial to prove our main results.

The basic space used in this paper is . It is well known that is a Banach space with the norm defined by . Let be a cone of , , where .

respectively.

Lemma 2.1 (see [6]).

From Lemma 2.1 and the definition of , we can prove that has the following properties.

Proposition 2.2.

In fact, from Lemma 2.1, we have for Therefore (2.5) holds.

Proposition 2.3.

Proof.

In fact, from Lemma 2.1, we obtain for So .

On the other hand, from Lemma 2.1, we know that for . This together with implies that for . Hence is nondecreasing on , is nonincreasing on . So (2.6) holds.

Proposition 2.4.

Proof.

Therefore (2.7) holds.

Lemma 2.5 (see [6]).

The following lemma is crucial to prove our main results.

## 3. Main Results

In this section, we apply Lemma 2.6 to establish the existence of at least two positive solutions for BVP (1.1).

The following assumptions will stand throughout this paper.

where and are defined in (1.4), respectively.

for and given in (2.2) and (2.12), respectively.

If holds, then we can show that have the following properties.

Proposition 3.1.

Proof.

Then from (1.2)–(1.4) and , we obtain Therefore,

On the other hand, since

Proposition 3.2.

Proof.

The proof is similar to that of Proposition 3.1. So we omit it.

By (2.14), it is well known that the problem (1.1) has a positive solution if and only if is a fixed point of .

Lemma 3.3.

Suppose that (1.2)–(1.4) and - hold. Then and is completely continuous.

Proof.

On the other hand, for , by (3.9),(3.10) and (2.7), we obtain

Next by standard methods and the Ascoli-Arzela theorem one can prove that is completely continuous. So it is omitted.

Theorem 3.4.

where and are defined in (3.3), (3.7) and in Proposition 3.1, respectively.

Proof.

Let be the cone preserving, completely continuous operator that was defined by (3.9).

Let , where . Choosing and satisfy

Now we prove that

In fact, if there exists such that , then for , we have

Therefore , that is, , which is a contradiction. Hence (3.14) holds.

Next, turning to (3.15). If there exists such that , then for , we have

Therefore , that is, , which is a contradiction. Hence (3.15) holds.

It remains to prove

In fact, if there exists such that , then for , we have

which is a contradiction, where are defined by (2.17). Hence (3.18) holds. From Lemma 2.6, (3.14), (3.15) and (3.18) yield that the problem (1.1) has at least two solutions and . The proof is complete.

## 4. Example

Example 4.1.

To illustrate how our main results can be used in practice we present an example.

Let . Take in (1.1). Now we consider the following three point boundary value problem

Finally, we prove that

Therefore, the conditions of Theorem 3.4 hold. Hence problem (4.1) has at least two positive solutions.

Remark 4.2.

Example 4.1 implies that there is a large number of functions that satisfy the conditions of Theorem 3.4. In addition, the conditions of Theorem 3.4 are also easy to check.

## Declarations

### Acknowledgments

This work is sponsored by the National Natural Science Foundation of China (10671012) and the Scientific Creative Platform Foundation of Beijing Municipal Commission of Education (PXM2008-014224-067420). The authors thank the referee for his careful reading of the manuscript and useful suggestions.

## Authors’ Affiliations

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