Hindawi Publishing Corporation Boundary Value Problems Volume 2008, Article ID 585378, 14 pages doi:10.1155/2008/585378 Research Article Antiperiodic Boundary Value Problems for Second-Order Impulsive Ordinary Differential Equations Chuanzhi Bai Department of Mathematics, Huaiyin Teachers College, Huaian, Jiangsu 223300, China Correspondence should be addressed to Chuanzhi Bai, czbai8@sohu.com Received 23 July 2008; Accepted 23 November 2008 Recommended by Raul F. Manasevich We consider a second-order ordinary differential equation with antiperiodic boundary conditions and impulses. By using Schaefer’s fixed-point theorem, some existence results are obtained. Copyright q 2008 Chuanzhi Bai. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1. Introduction Impulsive differential equations, which arise in biology, physics, population dynamics, economics, and so forth, are a basic tool to study evolution processes that are subjected to abrupt in their states see 1–4. Many literatures have been published about existence of solutions for first-order and second-order impulsive ordinary differential equations with boundary conditions 5–19, which are important for complementing the theory of impulsive equations. In recent years, the solvability of the antiperiodic boundary value problems of first-order and second-order differential equations were studied by many authors, for example, we refer to 20–32 and the references therein. It should be noted that antiperiodic boundary value problems appear in physics in a variety of situations 33, 34. Recently, the existence results were extended to antiperiodic boundary value problems for first-order impulsive differential equations 35, 36. Very recently, Wang and Shen 37 investigated the antiperiodic boundary value problem for a class of second-order differential equations by using Schauder’s fixed point theorem and the lower and upper solutions method. Inspired by 35–37, in this paper, we investigate the antiperiodic boundary value problem for second-order impulsive nonlinear differential equations of the form u t f t, ut 0, t ∈ J0 J \ {t1 , . . . , tm }, Δu tk Ik utk , k 1, . . . , m, 2 Boundary Value Problems Δu tk Ik∗ utk , u0 uT 0, k 1, . . . , m, u 0 u T 0, 1.1 where J 0, T , 0 < t1 < t2 < · · · < tm < T , f : 0, T × R → R is continuous on t, x ∈ J0 × R, ftk , x : limt → tk ft, x, ft−k , x : limt → t−k ft, x exist, ft−k , x ftk , x; Δutk utk − ut−k , Δu tk u tk − u t−k ; Ik , Ik∗ ∈ CR, R. To the best of the authors knowledge, no one has studied the existence of solutions for impulsive antiperiodic boundary value problem 1. The following Schaefer’s fixed-point theorem is fundamental in the proof of our main results. Lemma 1.1 see 38 Schaefer. Let E be a normed linear space with H : E → E a compact operator. If the set S : x ∈ E | x λHx, for some λ ∈ 0, 1 1.2 is bounded, then H has at least one fixed point. The paper is formulated as follows. In Section 2, some definitions and lemmas are given. In Section 3, we obtain two new existence theorems by using Schaefer’s fixed point theorem. In Section 4, an illustrative example is given to demonstrate the effectiveness of the obtained results. 2. Preliminaries In order to define the concept of solution for 1, we introduce the following spaces of functions: P CJ {u : J → R : u is continuous for any t ∈ J0 , utk , ut−k exist, and ut−k utk , k 1, . . . , m}, P C1 J {u : J → R : u is continuously differentiable for any t ∈ J0 , u tk , u t−k exist, and u t−k u tk , k 1, . . . , m}. P CJ and P C1 J are Banach space with the norms uP C sup|ut|, t∈J uP C1 max uP C , u P C . 2.1 A solution to the impulsive BVP 1 is a function u ∈ P C1 J ∩ C2 J0 that satisfies 1 for each t ∈ J. Consider the following impulsive BVP with λ > 0 −u t λ2 ut σt, t ∈ J0 , Δu tk Ik utk , k 1, . . . , m, Δu tk Ik∗ utk , k 1, . . . , m, u0 uT 0, where σ ∈ P CJ. u 0 u T 0, 2.2 Chuanzhi Bai 3 For convenience, we set Ik Ik utk , Ik∗ Ik∗ utk . Lemma 2.1. u ∈ P C1 J ∩ C2 J0 is a solution of 2.2 if and only if u ∈ P C1 J is a solution of the impulsive integral equation ut T Gt, sσsds 0 m G t, tk − Ik∗ W t, tk Ik , 2.3 k1 where ⎧ −λt−s eλt−s e ⎪ ⎪ ⎪ − , 0 ≤ s < t ≤ T, 1 ⎨ 1 e−λT 1 eλT Gt, s 2λ ⎪ ⎪ eλT t−s e−λT t−s ⎪ ⎩ − , 0 ≤ t ≤ s ≤ T, 1 eλT 1 e−λT ⎧ −λt−s eλt−s e ⎪ ⎪ ⎪ , 0 ≤ s < t ≤ T, ⎨ 1 1 e−λT 1 eλT Wt, s ⎪ eλT t−s e−λT t−s 2⎪ ⎪ ⎩− − , 0 ≤ t ≤ s ≤ T. 1 eλT 1 e−λT 2.4 Proof. If u ∈ P C1 J ∩ C2 J0 is a solution of 2.2, setting vt u t λut, 2.5 then, by the first equation of 2.2 we have v t − λvt −σt, t / tk . 2.6 Multiplying 2.6 by e−λt and integrating on 0, t1 and t1 , t t1 < t ≤ t2 , respectively, we get e−λt1 v t−1 − v0 − e −λt vt − e −λt1 v t1 − t t1 σse−λs ds, 0 2.7 σse −λs ds, t1 < t ≤ t2 . t1 So t −λs −λt1 vt e v0 − e σsds e Δv t1 , λt t1 < t ≤ t2 . 2.8 0 In the same way, we can obtain that vt e λt v0 − t e 0 −λs σsds e 0<tk <t −λtk Ik∗ λIk , t ∈ J, 2.9 4 Boundary Value Problems where v0 u 0 λu0. Integrating 2.5, we have ut e −λt u0 t vse ds λs 0 e λtk Ik , t ∈ J. 2.10 0<tk <t By 2.9, we get t 2λt 2λt 1 v0 e − 1 − vse ds e − e2λs σse−λs ds 2λ 0 0 −λtk ∗ 2λt 2λtk e −e e Ik λIk . t λs 2.11 0<tk <t Substituting 2.11 into 2.10, we obtain 1 ut λu0 − u 0 e−λt u 0 λu0 eλt 2λ t −λt−s − eλt−s σsds eλt−tk Ik∗ λIk e 0 − e −λt−tk 0<tk <t Ik∗ − λIk 2.12 0<tk <t , t ∈ J, 1 u t − λu0 − u 0 e−λt u 0 λu0 eλt 2 t −λt−s − eλt−s σsds eλt−tk Ik∗ λIk e 0 e 0<tk <t −λt−tk Ik∗ − λIk 2.13 0<tk <t , t ∈ J. In view of u0 uT 0 and u 0 u T 0, we have T 1 λT −s λT −tk ∗ e σsds − e u 0 λu0 Ik λIk , 1 eλT 0 0<tk <T T 1 −λT −s −λT −tk ∗ − e λu0 − u 0 σsds e Ik − λIk . 1 e−λT 0 0<tk <T 2.14 Substituting 2.14 into 2.12, by routine calculation, we can get 2.3. Conversely, if u is a solution of 2.3, then direct differentiation of 2.3 gives −u t σt−λ2 ut, t / tk . Moreover, we obtain Δu|ttk Ik utk , Δu |ttk Ik∗ utk , u0uT 0 and u 0 u T 0. Hence, u ∈ P C1 J ∩ C2 J0 is a solution of 2.2. Chuanzhi Bai 5 Remark 2.2. We call Gt, s above the Green function for the following homogeneous BVP: −u t λ2 ut 0, t ∈ J, 2.15 u 0 u T 0. u0 uT 0, Define a mapping A : P C1 J → P C1 J by Aut T 0 m Gt, s f s, us λ2 us ds G t, tk − Ik∗ W t, tk Ik , t ∈ 0, T . k1 2.16 In view of Lemma 2.1, we easily see that u is a fixed point of operator A if and only if u is a solution to the impulsive boundary value problem 1. It is easy to check that Gt, s ≤ eλT − 1 , 2λ 1 eλT Wt, s ≤ 1 . 2 2.17 Lemma 2.3. If u ∈ P C1 J and u0 uT 0, then uP C 1 ≤ 2 T m u sds Δu tk . 0 2.18 k1 Proof. Since u ∈ P C1 J, we have ut u0 Δu tk t u sds. 2.19 0 0<tk <t Set t T , we obtain from u0 uT 0 that 1 u0 − 2 m k1 Δu tk T u sds . 2.20 0 Substituting 2.20 into 2.19, we get T t 1 1 ut u sds − u sds Δu tk − Δu tk 2 2 0<tk <t 0 t t≤tk T t 1 1 u sds u sds Δu tk Δu tk ≤ 2 2 0<tk <t 0 t t≤tk T m 1 u sds Δu tk . 2 0 k1 The proof is complete. 2.21 6 Boundary Value Problems 3. Main results In this section, we study the existence of solutions for BVP 1. For this purpose we assume that there exist constants 0 < η < 1, functions a, b, h ∈ CJ, 0, ∞, and nonnegative constants αk , βk , γk , δk k 1, 2, . . . , m such that H1 |ft, u| ≤ at|u| bt|u|η ht, and H2 |Ik u| ≤ αk |u| βk , |Ik∗ u| ≤ γk |u| δk , k 1, . . . , m hold. Remark 3.1. H1 means that the nonlinearity growths at most linearly in u, H2 implies that the impulses are at most linear. For convenience, let 3 p1 2 T atdt λ T 2 0 3 2 p2 3 p3 2 T γi , i1 T 3.1 btdt, 0 htdt 0 m m δi . i1 Theorem 3.2. Suppose that conditions (H1 and (H2 are satisfied. Further assume that T q1 4 holds, where q1 solution. T 0 atdt m m m T q1 m αi α2 < 1, 2 i1 4 i1 i i1 p1 αi 3.2 γi and p1 as in 3.1. Then, BVP 1 has at least one Proof. It is easy to check by Arzela-Ascoli theorem that the operator A is completely continuous. Assume that u is a solution of the equation u μAu, μ ∈ 0, 1. 3.3 Then, u t μAu t μ − f t, ut − λ2 ut λ2 Aut −μf t, ut − λ2 μ − 1ut, −utu t μutf t, ut λ2 μ − 1u2 t ≤ μutf t, ut . 3.4 3.5 Chuanzhi Bai 7 Integrating 3.4 from 0 to T , we get that T u T − u 0 u tdt 0 m Ii∗ −μ T f t, ut dt − λ2 μ − 1 T 0 i1 utdt 0 m Ii∗ . 3.6 i1 In view of u 0 u T 0, we obtain by 3.6 that 1 u 0 ≤ 2 T 2 f t, ut dt λ 2 0 T m utdt 1 I ∗ . 2 i1 i 0 3.7 Integrating 3.4 from 0 to t, we obtain that u t − u 0 t Ii∗ 0<ti <t u sds 0 −μ t f s, us ds − λ2 μ − 1 t 0 usds 0 Ii∗ . 3.8 0<ti <t From 3.7 and 3.8, we have u t ≤ u 0 T f s, us ds λ2 T 0 T m usds I ∗ i 0 i1 T m η 3 3 atut btut ht dt λ2 utdt γi uP C δi 2 2 0 0 i1 T T T m 3 3 3 η uP C atdt uP C btdt htdt λ2 T uP C ≤ γi uP C δi , 2 2 2 i1 0 0 0 3.9 ≤ 3 2 that is, u P C 3 ≤ 2 T atdt λ T 2 0 m γi i1 3 uP C 2 T 0 η btdtuP C 3 2 T htdt 0 m 3 δi . 2 i1 3.10 Thus, η u P C ≤ p1 uP C p2 uP C p3 , 3.11 where p1 , p2 , p3 are as in 3.1. Integrating 3.5 from 0 to T , we get that − T 0 utu tdt ≤ μ T utft, utdt. 0 3.12 8 Boundary Value Problems In view of u0 uT 0 and u 0 u T 0, we have T T utu tdt 0 utd u t 0 t1 utd u t 0 tu t|t01 − t1 0 t2 2 u t dt utu t|tt21 − · · · utu t|Ttn − utd u t tn t1 T utd u t · · · T t2 2 u t dt t1 2 u t dt tn u t1 − 0 u t1 − 0 − u0u 0 u t2 − 0 u t2 − 0 − u t1 0 u t1 0 T 2 · · · uT u T − u tn 0 u tn 0 − u t dt 0 u t1 − 0 u t1 − 0 − u t1 0 u t1 0 T 2 · · · u tn − 0 u tn − 0 − u tn 0 u tn 0 − u t dt 0 u t1 − 0 u t1 − 0 − u t1 − 0 u t1 0 u t1 − 0 u t1 0 − u t1 0 u t1 0 · · · u tn − 0 u tn − 0 − u tn − 0 u tn 0 T 2 u tn − 0 u tn 0 − u tn 0 u tn 0 − u t dt 0 −ut1 − 0I1∗ − u t1 0I1 − · · · − utn − 0In∗ − u tn 0In − T 0 u t dt. 2 3.13 Substituting 3.13 into 3.12, we obtain by H2 , H3 , and 3.11 that T 0 2 T utf t, ut dt − u t1 − 0 I1∗ 0 − u t1 0 I1 − · · · − u tn − 0 In∗ − u tn 0 In T m m ≤ μ utf t, ut dt uP C Ii∗ u P C Ii u t dt ≤ μ ≤ T 0 i1 0 uP C m m γi uP C δi u P C αi uP C βi i1 ≤ u2P C i1 1η atu2 t btut htut dt m i1 T 0 1η atdt uP C γi u2P C m i1 T 0 i1 btdt uP C T htdt 0 m η δi uP C p1 uP C p2 uP C p3 αi uP C βi . i1 3.14 Chuanzhi Bai 9 Thus, T 2 1η η u t dt ≤ q1 u2P C q2 uP C q3 uP C q4 uP C q5 , 0 3.15 where q1 T atdt 0 q2 T m p1 αi γi , i1 btdt p2 m 0 q3 T htdt 0 q4 p2 αi , i1 m p1 βi p3 αi δi , 3.16 i1 m βi , i1 q5 p3 m βi . i1 By Lemma 2.3 and 3.15, we have u2P C 1 ≤ 4 T 0 u tdt 2 1 2 T m u tdt |Ii | 1 4 0 i1 m |Ii | 2 i1 √ T 1/2 m m 2 T T 2 m ≤ |Ii | |Ii |2 u t dt u t dt 4 0 2 4 0 i1 i1 T T 1η η q1 u2P C q2 uP C q3 uP C q4 uP C q5 4 √ 1/2 T 1η η q1 u2P C q2 uP C q3 uP C q4 uP C q5 2 m m m 2 × αi uP C βi αi u2P C 2αi βi uP C βi2 4 i1 i1 m m T q1 T q1 m 2 αi α u2P C · · · . 4 2 i1 4 i1 i ≤ 3.17 It follows from the above inequality and 3.2 that there exists M1 > 0 such that uP C ≤ M1 . Hence, we get by 3.11 that η u P C ≤ a1 M1 a2 M1 a3 : M2 . 3.18 10 Boundary Value Problems Thus, uP C1 ≤ max{M1 , M2 }. It follows from Lemma 1.1 that BVP 1 has at least one solution. The proof is complete. Theorem 3.3. Assume that (H2 holds. Suppose that there exist a continuous and nondecreasing function ψ : 0, ∞ → 0, ∞ and a nonnegative function c ∈ CJ with ft, u λ2 u ≤ ctψ|u|, t ∈ J, u ∈ R. 3.19 Moreover suppose that ψu <L u→∞ u lim sup 3.20 holds, where L : 1− m m eλT − 1 /2λ 1 eλT i1 γi − 1/2 i1 αi > 0. λT T csds e − 1 /2λ 1 eλT 0 3.21 Then, BVP 1 has at least one solution. Proof. From 3.20, there exist 0 < ε < L and M > 0 such that ψv ≤ L − εv, v ≥ M. 3.22 Thus, there exists K > 0 such that ψv ≤ L − εv K, v ≥ 0. 3.23 Assume that u is a solution of the equation u μAu, μ ∈ 0, 1. 3.24 Then, we have by 3.19, 2.17, and 3.23 that m T ∗ ut μ Gt, s fs, us λ2 us ds G t, tk − Ik W t, tk Ik 0 k1 eλT − 1 ≤ 2λ 1 eλT T 0 csψ|u|ds m m 1 eλT − 1 u δ γ αi uP C βi . i P C i λT 2 2λ 1 e i1 i1 3.25 Chuanzhi Bai 11 Thus, we have uP C T eλT − 1 ≤ csds L − εuP C K λT 2λ 1 e 0 m m m m eλT − 1 1 eλT − 1 1 u γ α δ βi , i i P C i 2 i1 2 i1 2λ 1 eλT i1 2λ 1 eλT i1 3.26 that is, eλT − 1 ε 2λ 1 eλT T csdsuP C 0 eλT − 1 ≤ K 2λ 1 eλT T csds 0 m m eλT − 1 1 δ βi , i 2 i1 2λ 1 eλT i1 3.27 which implies that there exists M3 > 0 such that uP C ≤ M3 . By 3.7, 3.8, and 3.23, we get 3 u t ≤ 2 ≤ 3 2 3 ≤ 2 ≤ 3 2 T fs, usds 3 λ2 2 0 T T |us|ds 0 fs, us λ2 usds 3λ2 0 T 0 T T 0 csψ |us| ds 3λ2 T m 3 I ∗ 2 i1 i |us|ds m 3 I ∗ 2 i1 i m 3 |us|ds γi uP C δi 2 i1 0 3.28 m 3 csds LuP C K 3λ2 T uP C γi uP C δi , 2 0 i1 which implies that m m 3L T 3 3K T 3 csds 3λ2 T γi uP C csds δi 2 0 2 i1 2 0 2 i1 T m m 3 3K T 3 2 ≤ γi M3 csds δi : M4 . L csds 2λ T 2 2 0 2 i1 0 i1 u P C ≤ 3.29 Hence, uP C1 ≤ max{M3 , M4 }. It follows from Lemma 1.1 that BVP 1 has at least one solution. The proof is complete. 4. Example In this section, we give an example to illustrate the effectiveness of our results. 12 Boundary Value Problems Example 4.1. Consider the problem 1 1 u t utcos2 t et u1/2 t 1 tan t 0, π 2 1 1 Δu t1 sin u t1 , 3 4 u0 uT 0, π π \ , t ∈ 0, 2 3 1 1 Δu t1 u t1 , 2 3 t1 π , 3 4.1 u 0 u T 0, Let ft, u 1/πu cos2 t 1/2et u1/2 1 tan t, I1 u 1/3 sin u 1/4, I1∗ u 1/2u 1/3, T π/2, J 0, π/2. It is easy to show that ft, u ≤ at|u| bt|u|1/2 ht, 4.2 where at 1/πcos2 t, bt 1/2et , ht 1 tan t. And I1 u ≤ 1 |u| 1 , 3 4 ∗ 1 I u ≤ |u| 1 . 1 2 3 4.3 Thus, H1 and H2 hold. Obviously, α1 1/3, β1 1/4, γ1 1/2, δ1 1/3, and m 1. Let λ2 1/4π, we have T m 3 1 1 1 3 3 2 , p1 atdt 2λ T γi 2 2 4 4 2 2 0 i1 T m 1 3 1 1 5 q1 atdt p1 αi γi · . 4 2 3 2 4 0 i1 4.4 Therefore, T q1 4 m m T q1 m αi α2 0.7522 < 1, 2 i1 4 i1 i 4.5 which implies that 3.2 holds. So, all the conditions of Theorem 3.2 are satisfied. By Theorem 3.2, antiperiod boundary value problem 4.1 has at least one solution. Acknowledgments The author would like to thank the referees for their valuable suggestions and comments. This project is supported by the National Natural Science Foundation of China 10771212 and the Natural Science Foundation of Jiangsu Education Office 06KJB110010. References 1 V. Lakshmikantham, D. D. Baı̆nov, and P. S. 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