In this paper, we are concerned with the following fractional equation:
with the boundary value conditions
where is the standard Caputo derivative with and δ, γ are constants with , . By applying a new fixed point theorem on cone and Krasnoselskii’s fixed point theorem, some existence results of positive solution are obtained.
MSC: 34A08, 34B15, 34B18.
Keywords:fractional differential equations; existence results; fixed point theorem; positive solution
In this paper, we are concerned with the existence of positive solutions for the fractional equation
with the boundary value conditions
where is the standard Caputo derivative with and δ, γ are constants with , .
Differential equations of fractional order have recently proved to be valuable tools in the modeling of many phenomena in various fields of science and engineering. Indeed, we can find numerous applications in viscoelasticity, electrochemistry, control, porous media, electromagnetism, etc. (see [1-5]). There has been a significant development in the study of fractional differential equations and inclusions in recent years, see the monographs of Podlubny , Kilbas et al., Lakshmikantham et al., Samko et al., Diethelm , and the survey by Agarwal et al.. For some recent contributions on fractional differential equations, see [9-25] and the references therein.
On the other hand, it is well known that the fourth-order boundary value problem describes the deformations of an elastic beam in equilibrium state. Owing to its importance in physics, the existence of solutions to this problem has been studied by many authors; see, for example, [26-30] and references therein. Recently, there have been a few papers dealing with the existence of solutions for fractional equations of order .
In , Xu et al. discussed the problem
where and is nonnegative, is the Riemann-Liouville fractional derivative of order α. The existence results of positive solutions are obtained by applying the Leray-Schauder nonlinear alternative theorem.
In , Liang and Zhang studied the following nonlinear fractional boundary value problem:
where , is nondecreasing relative to u, is the Riemann-Liouville fractional derivative of order α. By means of the lower and upper solution method and fixed point theorems, some results on the existence of positive solutions were obtained.
In , Agarwal and Ahmad studied the solvability of the following anti-periodic boundary value problem for a nonlinear fractional differential equation:
where . The existence results were obtained by the nonlinear alternative theorem.
Inspired by above work, the author will be concerned with the boundary value problem (BVP for short in the sequel) (1.1)-(1.2). To the best of our knowledge, no contribution exists concerning the existence of solutions for BVP (1.1)-(1.2). In the present paper, by applying a new fixed point theorem on cone and Krasnoselskii’s fixed point theorem, some existence results of positive solution for BVP (1.1)-(1.2) are obtained. It is worth to point out that the results in this paper are also new even for relative to the corresponding literature with regard to the fourth-order boundary value problem. In addition, the conditions imposed in this paper are easily verified.
The organization of this paper is as follows. In Section 2, we present some necessary definitions and preliminary results that will be used to prove our main results. In Section 3, we put forward and prove our main results. Finally, we give two examples to demonstrate our main results.
In this section, we introduce some preliminary facts which are useful throughout this paper.
Let ℕ be the set of positive integers, ℝ be the set of real numbers, , and . Let . Denote by the Banach space endowed with the norm , where for .
The Riemann-Liouville fractional integral of order of a function is given by
The Riemann-Liouville fractional derivative of order of a function is given by
where , denotes the integer part of α.
The Caputo fractional derivative of order of a function y on is defined via the above Riemann-Liouville derivatives by
Let and . Then
holds on .
Let with , . If and , then
holds on .
For convenience, we first list some hypotheses which will be used throughout this paper.
( ) .
( ) , , .
For , consider the following BVP:
We have the following lemma, which is important in this paper.
Lemma 2.3Let ( ) hold. Then is a solution of BVP (2.1)-(2.2) iff has the expression as follows:
Proof Let be a solution of (2.1)-(2.2). Then by Lemma 2.2, we have
Thus, by the boundary value condition (2.2), we can obtain
From (2.11), we have
Substituting (2.12) into (2.10), we get
So, by (2.13), (2.12), and (2.9), we have
Thus, from (2.8), we have
Hence, from (2.7) together with (2.12)-(2.15), it follows that
by Definition 2.1, we have
Conversely, if u has the expression (2.3), then from the fact that , we can easily verify that
hold for , and u satisfies the boundary condition (2.2).
Again, from (2.16) and Lemma 2.1, we have that , . In addition, noting that , it is easy to see that from (2.19). □
For the forthcoming analysis, we need to introduce some new notations.
Let , and . Denote
It is easy to verify that , and noting that , , .
We also need the following lemma, which will play an important role in obtaining our main results in Section 3.
Lemma 2.4Under the assumption ( ), Green’s function has the following properties:
(1) Gis continuous on ;
(2) , ; , , ;
(3) , ; , , ;
, , ; , , , .
Proof (1) Observing the expression of Green’s function given by (2.4)-(2.6), the conclusion (1) of Lemma 2.4 is obvious.
(2) We first show that , , .
In fact, if , then by (2.5) we have
Owing to the fact that and , we have that . Thus, we immediately obtain that for from (2.20) together with the condition , .
Similarly, we can deduce that
for , and so for .
To summarize, for all with .
Now, since for , and for with , it follows that for all .
(3) The proof is divided into four steps.
Step 1. We show that for .
(i) If , then by (2.5) and the assumption that , , and , we have
(ii) If , then by an argument similar to (2.22), we have
Summing up the above analysis (i)-(ii), we obtain
Step 2. We show that for and .
In fact, if and , then by (2.5) combined with the assumption that , , , we have
where , because .
If with , then by an argument similar to (2.23), we have
So, by (2.23)-(2.24), we have
for , and .
Step 3. Now, we show that
(i) If , then by (2.20) and keeping in mind that , , , it follows that
(ii) If , then by an argument similar to (2.25), from (2.21), we have
Summing up the above analysis (i)-(ii), and noting Step 2 of the proof as before, it follows that
Step 4. It remains to show that
(i) If , then by (2.20) and the fact that , we know that the relations
hold for , with , where , and
Similarly, we can obtain that
The proof is complete. □
Now, we introduce a cone as follows:
It is easy to check that the above set P is a cone in the space , which will be used in the sequel.
We define an operator T on P as follows:
Obviously, under the assumption ( )-( ), the operator T is well defined. Moreover,
where , , , , and , are given by (2.20)-(2.21), respectively.
A function is a positive solution of BVP (1.1)-(1.2) if , , , and u satisfies BVP (1.1)-(1.2).
By Lemma 2.3, it is easy to know that a function is a positive solution of BVP (1.1)-(1.2) iff is a nonzero fixed point of T. So, we can focus on seeking the existence of a nonzero fixed point of T in P.
Finally, for the remainder of this section, we give the following two theorems, which are fundamental in the proof of our main results.
Let X be a Banach space, and let be a cone. Suppose that the functions α, β satisfy the following condition:
(D) are continuous convex functionals satisfying , for , ; for , and for with , where is a constant.
Assume that , , Lare constants with , , and
Set . Suppose that is a completely continuous operator satisfying
( ) , ; , ;
( ) , ;
( ) there is a such that and for all and .
ThenThas at least one fixed point in .
Assume that , are two open subsets ofXwith , and let be a completely continuous operator such that either
(i) , ; , , or
(ii) , ; , .
ThenThas a fixed point in .
3 Main results
We first prove the following lemma to obtain our main results.
Lemma 3.1Suppose that ( )-( ) hold. Then the operatorTdefined by (2.26) mapsPintoP, andTis completely continuous.
Proof It is well known that the norms and are equivalent on . So, we can consider that the Banach space is equipped with the norm in the following proof.
For any , in view of the conclusion (1)-(2) of Lemma 2.4 and the hypotheses ( )-( ), it is easy to see that , , , and , observing (2.26)-(2.27). Moreover, the conclusion (3) of Lemma 2.4 implies that
From (3.1)-(3.2), it follows that , , . Thus,
Similarly, we can obtain
In addition, . Thus, .
Now, we show that the operator T is compact on P.
In fact, let U be an arbitrary bounded set in P. Then there exists a positive number L such that for all , and so such that , for all .
In terms of Lemma 2.4, it follows from (2.26)-(2.27) that
Because the functions and are integrable on I, the formulae (3.3)-(3.4) yield that , , where . So, . That is, TU is uniformly bounded.
On the other hand, for any with , by setting , the formula (2.26) implies that
According to (2.4)-(2.5) and by applying the mean value theorem, we have
Similarly, there is another constant such that
Again, because the function is integrable on I, the absolute continuity of integral of on ensures that there exists a constant such that
So, (3.5) together with (3.6)-(3.8) implies that there exists a constant N such that the inequality
holds for any and with . That is, the set TU is equicontinuous.
Similarly, we can deduce that the set is also equicontinuous in terms of (2.27).
So, as a consequence of the Arzelà-Ascoli theorem, we have that TU is a compact set.
Now, we come to prove the operator T is continuous on P.
Let be an arbitrary sequence in P with . Then there exists an such that
According to the uniform continuity of f on , for an arbitrary number , there is a number such that
for all , whenever .
Thus, in view of Lemma 2.4, from (2.26)-(2.27) and (3.9), it follows that
whenever . That is, T is continuous on P. □
We are now in a position to state and prove the first theorem in the article. Let constants , satisfy , .
Theorem 3.1Suppose that ( )-( ) hold. In addition, there are two constants , with such thatfsatisfies the following condition:
( ) , for ;
, for .
Then BVP (1.1)-(1.2) has at least one positive solutionusatisfying and .
Proof We already know that is completely continuous by Lemma 3.1.
Let , for . It is easy to verify that the functions α, β satisfy the condition (D).
Choose a constant L large enough so that , where , and , . Set , , . Define the function on as , , where , .
Consider the following ancillary BVP:
Obviously, the function is continuous on according to the continuity of f. Thus, by an argument similar to that in Lemma 3.1, the operator given by is also completely continuous on P and maps P into P.
We will prove that T has at least one nonzero fixed point in P by applying Lemma 2.5. The approach is divided into four steps.
Step 1. We first show that
In fact, for any , owing to the condition , we have that , , and so .
On the other hand, applying the mean value theorem, for any , we have that for some . Therefore, we have that from the fact that , because . So,
keeping in mind that , for .
Step 2. Now, we come to verify that the conditions corresponding to ( ) in Lemma 2.5 hold.
For any with , we have that , , , and . Thus, in view of (3.11), we have that , , . So, according to ( ), we have
Thus, from (2.27) and Lemma 2.4, it follows that
Thus, , noting that the assumption . That is, .
For any with , then , , , and . Thus, from (3.11), we obtain
from the condition ( ). Therefore, in view of Lemma 2.4, we have
Thus, , noting that . That is, .
Step 3. We verify that the conditions corresponding to ( ) in Lemma 2.5 hold.
For any , owing to the fact that , , from the meaning of M, we have immediately that
Hence, , and so from the choice of L. Thus, .
Step 4. Finally, take with . Then, by an argument similar to that in Lemma 3.1, we can know that . Moreover, , , and , from (3.11). Thus, , . Again,
for any , .
So, the conditions corresponding to ( ) in Lemma 2.5 hold.
Summing up the above steps 1-4 and applying Lemma 2.5, we obtain that BVP (3.10) has at least one positive solution . That is, . , and so from the fact that and by (3.13). Thus, , , , , and . Hence, , , and so u is a positive solution of BVP (1.1)-(1.2). The proof is complete. □
Now, we state another theorem in this paper. Let us begin with introducing some notations.
Let . Denote with , and with . Put , , where , , , and ( ) are given in Lemma 2.4.
Theorem 3.2Assume that ( )-( ) hold. If , , then BVP (1.1)-(1.2) has at least one positive solution.
Proof As described in the proof of Theorem 3.1, is completely continuous. Again, from , it follows that there exists an such that
holds when with , .
Take . Set . Now, we show that the following relation holds:
In fact, for any , we have that with . Then
Thus, from (3.12), (3.14), it follows that
Hence, (2.26) together with (3.15) implies that
Similarly, we can obtain
Therefore, noting that , from (3.16)-(3.17), we have
So, the relation (3.13) holds.
Now, from , it follows that there exists an such that
whenever with , .
Take . Set . We prove the following relation holds:
In fact, for any , we have and . Thus, , , , and , . So, by (3.18), it follows that
Therefore, from (2.26) and in view of Lemma 2.4, we have
Similarly, we can obtain