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HindawiPublishingCorporationAdvancesinDifferenceEquationsVolume2010,ArticleID727486,27 pages doi:10.1155/2010/727486 Research Article Existence of Solutions for a Class of Damped Vibration Problems on Time Scales Yongkun Li and Jianwen Zhou Department of Mathematics, Yunnan University, Kunming, Yunnan 650091, China Correspondence should be addressed to Yongkun Li, yklie@ynu.edu.cn Received 3 June 2010; Revised 20 November 2010; Accepted 24 November 2010 Academic Editor: Kanishka Perera Copyright q 2010 Y. Li and J. Zhou. 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. We present a recent approach via variational methods and critical point theory t o obtain the existence of solutions for a class of damped vibration problems on time scale , u Δ 2 t wtu Δ σt ∇Fσt,uσt, Δ-a.e. t ∈ 0,T κ , u0 − uT0,u Δ 0 − u Δ T0, where u Δ t denotes the delta or Hilger derivative of u at t, u Δ 2 tu Δ Δ t, σ is the forward jump operator, T is a positive constant, w ∈R 0,T , , e w T, 01, and F : 0,T × N → . By establishing a proper variational setting, three existence results are obtained. Finally, three examples are presented to illustrate the feasibility and effectiveness of our results. 1. Introduction Consider the damped vibration problem on time-scale u Δ 2 t w t u Δ σ t ∇F σ t ,u σ t , Δ-a.e.t∈ 0,T κ , u 0 − u T 0,u Δ 0 − u Δ T 0, 1.1 where u Δ t denotes the delta or Hilger derivative of u at t, u Δ 2 tu Δ Δ t, σ is the forward jump operator, T is a positive constant, w ∈R 0,T , , e w T, 01, and F : 0,T × N → satisfies the following assumption. A Ft, x is Δ-measurable in t for every x ∈ N and continuously differentiable in x for t ∈ 0,T and there exist a ∈ C , ,b∈ L 1 Δ 0,T , such that | F t, x | ≤ a | x | b t , | ∇F t, x | ≤ a | x | b t 1.2 for all x ∈ N and t ∈ 0,T ,where∇Ft, x denotes the gradient of Ft, x in x. 2AdvancesinDifference Equations Problem 1.1 covers the second-order damped vibration problem for when ¨u t w t ˙u t ∇F t, u t , a.e.t∈ 0,T , u 0 − u T 0, ˙u 0 − ˙u T 0, 1.3 as well as the second-order discrete damped vibration problem for when , T ≥ 2 Δ 2 t w t Δu t 1 ∇F t 1,u t 1 ,t∈ 0,T − 1 ∩ , u 0 − u T 0, Δu 0 − Δu T 0. 1.4 The calculus of time-scales was initiated by Stefan Hilger in his Ph.D. thesis in 1988 in order to create a theory that can unify discrete and continuous analysis. A time-scale is an arbitrary nonempty closed subset of the real numbers, which has the topology inherited from the real numbers with the standard topology. The two most popular examples are and . The time-scales calculus has a tremendous potential for applications in some mathematical models of real processes and phenomena studied in physics, chemical technology, population dynamics, biotechnology and economics, neural networks, and social sciences see 1. For example, it can model insect populations that are continuous while in season and may follow a difference scheme with variable step-size, die out in winter, while their eggs are incubating or dormant, and then hatch in a new season, giving rise to a nonoverlapping population. In recent years, dynamic equations on time-scales have received much attention. We refer the reader to the books 2–7 and the papers 8–15.Inthiscentury,someauthors have begun to discuss the existence of solutions of boundary value problems on time-scales see 16–22. There have been many approaches to study the existence and the multiplicity of solutions for differential equations on time-scales, such as methods of lower and upper solutions, fixed-point theory, and coincidence degree theory. In 14, the authors have used the fixed-point theorem of strict-set-contraction to study the existence of positive periodic solutions for functional differential equations with impulse effects on time-scales. However, the study of the existence and the multiplicity of solutions for differential equations on time- scales using variational method has received considerably less attention see, e.g., 19, 23. Variational method is, to the best of our knowledge, novel and it may open a new approach to deal with nonlinear problems on time-scales. When wt ≡ 0, 1.1 is the second-order Hamiltonian system on time-scale u Δ 2 t ∇F σ t ,u σ t , Δ-a.e.t∈ 0,T κ , u 0 − u T 0,u Δ 0 − u Δ T 0. 1.5 Zhou and Li in 23 studied the existence of solutions for 1.5 by critical point theory on the Sobolevs spaces on time-scales that they established. When wt / ≡0, to the best of our knowledge, the existence of solutions for problems 1.1 have not been studied yet. Our purpose of this paper is to study the variational structure of problem 1.1 in an appropriate space of functions a nd the existence of solutions for problem 1.1 by some critical point theorems. AdvancesinDifferenceEquations 3 This paper is organized as follows. In Section 2, we present some fundamental definitions and results from the calculus on time-scales and Sobolev’s spaces on time-scales. In Section 3, we make a variational structure of 1.1. From this variational structure, we can reduce the problem of finding solutions of problem 1.1 to one of seeking the critical points of a corresponding functional. Section 4 is the existence of solutions. Section 5 is the conclusion of this paper. 2. Preliminaries and Statements In this section, we present some basic definitions and results from the calculus on time-scales and Sobolev’s spaces on time-scales that will be required below. We first briefly recall some basic definitions and results concerning time-scales. Further general details can be found in 3–5, 7, 10, 13. Through this paper, we assume that 0 ,T ∈ . We start by the definitions of the forward and backward jump operators. Definition 2.1 see 3,Definition1.1.Let be a time-scale, for t ∈ ,theforwardjump operator σ : → is defined by σ t inf { s ∈ ,s>t } , ∀t ∈ , 2.1 while the backward jump operator ρ : → is defined by ρ t sup { s ∈ ,s<t } , ∀t ∈ 2.2 supplemented by inf ∅ sup and sup ∅ inf ,where∅ denotes the empty set.Apoint t ∈ is called right scattered, left scattered, if σt >t, ρt <thold, respectively. Points that are right scattered and left scattered at the same time are called isolated. Also, if t<sup and σtt,thent is called right-dense, and if t>inf and ρtt,thent is called left dense. Points that are right-dense and left dense at the same time are called dense. The set κ which is derived from the time-scale as follows: if has a left scattered maximum m,the κ −{m},otherwise, κ . Finally, the graininess function μ : → 0, ∞ is defined by μ t σ t − t. 2.3 When a, b ∈ , a<b,wedenotetheintervalsa, b , a, b ,anda, b in by a, b a, b ∩ , a, b a, b ∩ , a, b a, b ∩ , 2.4 respectively. Note that a, b κ a, b if b is left dense and a, b κ a, b a, ρb if b is left scattered. We denote a, b κ 2 a, b κ κ , therefore a, b κ 2 a, b if b is left dense and a, b κ 2 a, ρb κ if b is left scattered. 4AdvancesinDifference Equations Definition 2.2 see 3, Definition 1.10. Assume that f : → is a function and let t ∈ κ . Then we define f Δ t to be the number provided it exists with the property that given any >0, there is a neighbor hood U of t i.e., U t − δ, t δ ∩ for some δ>0 such that f σ t − f s − f Δ t σ t − s ≤ | σ t − s | ∀s ∈ U. 2.5 We call f Δ t the delta or Hilger derivative of f at t. The function f is delta or Hilger differentiable on κ provided f Δ t exists for all t ∈ κ . The function f Δ : κ → is then called the delta derivative of f on κ . Definition 2.3 see 23,Definition2.3. Assume that f : → N is a function, ft f 1 t,f 2 t, ,f N t and let t ∈ κ . T hen we define f Δ tf 1 Δ t,f 2 Δ t, ,f N Δ t provided it exists.Wecallf Δ t the delta or Hilger derivative of f at t. The function f is delta or Hilger differentiable provided f Δ t exists for all t ∈ κ . The function f Δ : κ → N is then called the delta derivative of f on κ . Definition 2.4 see 3,Definition2.7.Forafunctionf : → we will talk about the second derivative f Δ 2 provided f Δ is differentiable on κ 2 κ κ with derivative f Δ 2 f Δ Δ : κ 2 → . Definition 2.5 see 23,Definition2.5.Forafunctionf : → N we will talk about the second derivative f Δ 2 provided f Δ is differentiable on κ 2 κ κ with derivative f Δ 2 f Δ Δ : κ 2 → N . Definition 2.6 see 23,Definition2.6.Afunctionf : → N is called rd-continuous provided it is continuous at right-dense points in and its left sided limits exist finite at left dense points in . Definition 2.7 see 3, Definition 2.25. Wewesaythatafunctionw : → is regressive provided 1 μ t w t / 0 ∀t ∈ κ 2.6 holds. The set of all regressive and rd-continuous functions w : → is denoted by R R R , , R , w ∈R:1 μ t w t > 0 ∀t ∈ . 2.7 Definition 2.8 see 7, Definition 8.2.18.Ifw ∈Rand t 0 ∈ , then the unique solution of the initial value problem y Δ w t y, y t 0 1 2.8 is called the exponential function and denoted by e w ·,t 0 . The exponential function has some important properties. AdvancesinDifferenceEquations 5 Lemma 2.9 see 3, Theorem 2.36. If w ∈R,then e 0 t, s ≡ 1,e w t, t ≡ 1. 2.9 Throughout this paper, we will use the following notations: C rd C rd , N f : −→ N : f is rd-continuous , C 1 rd C 1 rd , N f : −→ N : f is differentiable on κ and f Δ ∈ C rd κ , C 1 T,rd 0,T , N f ∈ C 1 rd 0,T , N : f 0 f T . 2.10 The Δ-measure m Δ and Δ-integration are defined as those in 10. Definition 2.10 see 23,Definition2.7. Assume that f : → N is a function, ft f 1 t,f 2 t, ,f N t and let A be a Δ-measurable subset of . f is integrable on A if and only if f i i 1, 2, ,N areintegrableonA,and A f t Δt A f 1 t Δt, A f 2 t Δt, , A f N t Δt . 2.11 Definition 2.11 see 13,Definition2.3.LetB ⊂ . B is called Δ-null set if m Δ B0. Say that a property P holds Δ-almost everywhere Δ-a.e. on B,orforΔ-almost all Δ-a.a. t ∈ B if there is a Δ-null set E 0 ⊂ B such that P holds for all t ∈ B \ E 0 . For p ∈ , p ≥ 1, we set the space L p Δ 0,T , N u : 0,T −→ N : 0,T f t p Δt<∞ 2.12 with the norm f L p Δ 0,T f t p Δt 1/p . 2.13 We have the following lemma. Lemma 2.12 see 23,Theorem2.1. Let p ∈ be such that p ≥ 1. Then the space L p Δ 0,T , N is a Banach space together with the norm · L p Δ .Moreover,L 2 Δ a, b , N is a Hilbert space together with the inner product given for every f, g ∈ L p Δ a, b , N × L p Δ a, b , N by f, g L 2 Δ a,b f t ,g t Δt, 2.14 where ·, · denotes the inner product in N . 6AdvancesinDifference Equations As we know from general theory of Sobolev spaces, another important class of functions is just the absolutely continuous functions on time-scales. Definition 2.13 see 13,Definition2.9.Afunctionf : a, b → is said to be absolutely continuous on a, b i.e., f ∈ ACa, b , , if for every >0, there exists δ>0such that if {a k ,b k } n k1 is a finite pairwise disjoint family of subintervals of a, b satisfying n k1 b k − a k <δ,then n k1 |fb k −fa k | <. Definition 2.14 see 23, Definition 2.11.Afunctionf : a, b → N ,ftf 1 t, f 2 t, , f N t. We say that f is absolutely continuous on a, b i.e., f ∈ ACa, b , N ,iffor every >0, there exists δ>0suchthatif{a k ,b k } n k1 is a finite pairwise disjoint family of subintervals of a, b satisfying n k1 b k − a k <δ,then n k1 |fb k −fa k | <. Absolutely continuous functions have the following properties. Lemma 2.15 see 23,Theorem2.2. A function f : a, b → N is absolutely continuous on a, b ifandonlyiff is delta differentiable Δ-a.e. on a, b and f t f a a,t f Δ s Δs, ∀t ∈ a, b . 2.15 Lemma 2.16 see 23,Theorem2.3. Assume that functions f, g : a, b → N are absolutely continuous on a, b .Thenfg is absolutely continuous on a, b and the following equality is valid: a,b f Δ t ,g t f σ t ,g Δ t Δt f b ,g b − f a ,g a a,b f t ,g Δ t f Δ t ,g σ t Δt. 2.16 Now, we recall the definition and properties of the Sobolev space on 0,T in 23. For the sake of convenience, in the sequel, we will let u σ tuσt. Definition 2.17 see 23, Definition 2.12.Letp ∈ be such that p ≥ 1andu : 0,T → N . We say that u ∈ W 1,p Δ,T 0,T , N if and only if u ∈ L p Δ 0,T , N and there exists g : 0,T κ → N such that g ∈ L p Δ 0,T , N and 0,T u t ,φ Δ t Δt − 0,T g t ,φ σ t Δt, ∀φ ∈ C 1 T,rd 0,T , N . 2.17 For p ∈ ,p ≥ 1, we denote V 1,p Δ,T 0,T , N x ∈ AC 0,T , N : x Δ ∈ L p Δ 0,T , N ,x 0 x T . 2.18 Remark 2.18 see 23,Remark2.2. V 1,p Δ,T 0,T , N ⊂ W 1,p Δ,T 0,T , N is true for every p ∈ with p ≥ 1. AdvancesinDifferenceEquations 7 Lemma 2.19 see 23,Theorem2.5. Suppose that u ∈ W 1,p Δ,T 0,T , N for some p ∈ with p ≥ 1,andthat2.17 holds for g ∈ L p Δ 0,T , N . Then, there exists a unique f unction x ∈ V 1,p Δ,T 0,T , N such that the equalities x u, x Δ g Δ-a.e. on 0,T 2.19 are satisfied and 0,T g t Δt 0. 2.20 Lemma 2.20 see 3, Theorem 1.16. Assume that f : → is a function and let t ∈ κ .Then, one has the following. i If f is differentiable at t,thenf is continuous at t. ii If f is differentiable at t,then f σ t f t μ t f Δ t . 2.21 By identifying u ∈ W 1,p Δ,T 0,T , N with its absolutely continuous representative x ∈ V 1,p Δ,T 0,T , N for which 2.19 holds, the set W 1,p Δ,T 0,T , N can be endowed with the structure of Banach space. Theorem 2.21. Assume p ∈ and p ≥ 1. The set W 1,p Δ,T 0,T , N is a Banach space together with the norm defined as u W 1,p Δ,T 0,T | u σ t | p Δt 0,T u Δ t p Δt 1/p ∀u ∈ W 1,p Δ,T 0,T , N . 2.22 Moreover, the set H 1 Δ,T W 1,2 Δ,T 0,T , N is a Hilbert space together with the inner product u, v H 1 Δ,T 0,T u σ t ,v σ t Δt 0,T u Δ t ,v Δ t Δt ∀u, v ∈ H 1 Δ,T . 2.23 Proof. Let {u n } n∈ be a Cauchy sequence in W 1,p Δ,T 0,T , N .Thatis,{u n } n∈ ⊂ L p Δ 0,T , N and there exist g n : 0,T κ → N such that {g n } n∈ ⊂ L p Δ 0,T , N and 0,T u n t ,φ Δ t Δt − 0,T g n t ,φ σ t Δt, ∀φ ∈ C 1 T,rd 0,T , N . 2.24 Thus, by Lemma 2.19,thereexists{x n } n∈ ⊂ V 1,p Δ,T 0,T , N such that x n u n ,x Δ n g n Δ-a.e. on 0,T . 2.25 8AdvancesinDifference Equations Combining 2.24 and 2.25,weobtain 0,T x n t ,φ Δ t Δt − 0,T x Δ n t ,φ σ t Δt, ∀φ ∈ C 1 T,rd 0,T , N . 2.26 Since {u n } n∈ is a Cauchy sequence in W 1,p Δ,T 0,T , N ,by2.22, one has 0,T | u σ n t − u σ m t | 2 Δt −→ 0 m, n −→ ∞ , 2.27 0,T u Δ n t − u Δ m t 2 Δt −→ 0 m, n −→ ∞ . 2.28 It follows from Lemma 2.20, 2.27,and2.28 that 0,T | u n t − u m t | 2 Δt 0,T u σ n t − u σ m t − μ t u Δ n t − u Δ m t 2 Δt ≤ 2 0,T | u σ n t − u σ m t | 2 Δt 2 σ T 2 0,T u Δ n t − u Δ m t 2 Δt −→ 0 m, n∞ . 2.29 By Lemma 2.12, 2.28 and 2.29,thereexistu, g ∈ L p Δ 0,T , N such that u n − u L p Δ −→ 0 n −→ ∞ , u Δ n − g L p Δ −→ 0 n −→ ∞ . 2.30 From 2.26 and 2.30, one has 0,T u t ,φ Δ t Δt − 0,T g t ,φ σ t Δt, ∀φ ∈ C 1 T,rd 0,T , N . 2.31 AdvancesinDifferenceEquations 9 From 2.31,weconcludethatu ∈ W 1,p Δ,T 0,T , N . Moreover, by Lemma 2.20 and 2.30, one has 0,T | u σ n t − u σ t | 2 Δt 0,T u n t − u t μ t u Δ n t − u Δ t 2 Δt 0,T u n t − u t μ t u Δ n t − g t 2 Δt ≤ 2 0,T | u n t − u t | 2 Δt 2 σ T 2 0,T u Δ n t − g t 2 Δt −→ 0 n −→ ∞ . 2.32 Thereby, it follows from Remark 2.18, 2.30, 2.32,andLemma 2.19 that there exists x ∈ V 1,p Δ,T 0,T , N ⊂ W 1,p Δ,T 0,T , N such that u n − x W 1,p Δ,T −→ 0 n −→ ∞ . 2.33 Obviously, the set H 1 Δ,T is a Hilbert space together with the inner product u, v H 1 Δ,T 0,T u σ t ,v σ t Δt 0,T u Δ t ,v Δ t Δt ∀u, v ∈ H 1 Δ,T . 2.34 We will derive some properties of the Banach space W 1,p Δ,T 0,T , N . Lemma 2.22 see 10,TheoremA.2. Let f : a, b → be a continuous function on a, b which is delta differentiable on a, b . Then there exist ξ, τ ∈ a, b such that f Δ τ ≤ f b − f a b −a ≤ f Δ ξ . 2.35 Theorem 2.23. There exists K Kp > 0 such that the inequality u ∞ ≤ K u W 1,p Δ,T 2.36 holds for all u ∈ W 1,p Δ,T 0,T , N ,whereu ∞ max t∈0,T |ut|. Moreover, if 0,T utΔt 0,then u ∞ ≤ K u Δ L p Δ . 2.37 10 AdvancesinDifferenceEquations Proof. Going to t he components of u, we can assume that N 1. If u ∈ W 1,p Δ,T 0,T , , by Lemma 2.19, Ut 0,t usΔs is absolutely continuous on a, b . It follows from Lemma 2.22 that there exists ζ ∈ a, b such that u ζ ≤ U T − U 0 T 1 T 0,T u s Δs. 2.38 Hence, for t ∈ a, b ,usingLemma 2.15, 2.38,andH ¨ older’s inequality, one has that | u t | u ζ ζ,t u Δ s Δs ≤ | u ζ | 0,T u Δ s Δs ≤ 1 T 0,T u s Δs T 1/q 0,T u Δ s p Δs 1/p , 2.39 where 1/p 1/q 1. If 0,T utΔt 0, by 2.39,weobtain2.37. In the general case, for t ∈ a, b ,byLemma 2.20 and H ¨ older’s inequality, we get | u t | ≤ 1 T 0,T u s Δs T 1/q 0,T u Δ s p Δs 1/p ≤ 1 T 0,T | u s | Δs T 1/q 0,T u Δ s p Δs 1/p 1 T 0,T u σ s − μ s u Δ s Δs T 1/q 0,T u Δ s p Δs 1/p 1 T 0,T | u σ s | Δs 1 T σ T 0,T u Δ s Δs T 1/q 0,T u Δ s p Δs 1/p ≤ T −1/p 0,T | u σ s | p Δs 1/p T −1/p σ T 0,T u Δ s p Δs 1/p T 1/q 0,T u Δ s p Δs 1/p ≤ T −1/p T −1/p σ T T 1/q u W 1,p Δ,T . 2.40 From 2.40, 2.36 holds. Remark 2.24. It follows from Theorem 2.23 that W 1,p Δ,T 0,T , N is continuously immersed into C0 ,T , N with the norm · ∞ . [...].. .Advances inDifferenceEquations 11 WΔ,T 0, T Ì, ÊN converges weakly to u in , then {uk }k∈Æ converges strongly in C 0, T Ì, ÊN to u Theorem 2.25 If the sequence {uk }k∈Æ WΔ,T 0, T Ì, ÊN 1,p 1,p ⊂ Proof Since uk u in WΔ,T 0, T Ì, ÊN , {uk }k∈Æ is bounded in WΔ,T 0, T Ì, ÊN and, u in C 0, T Ì, ÊN For hence, in C 0, T Ì, ÊN It follows from Remark 2.24 that... problem 1.1 to one of seeking the critical points of a corresponding functional 14 AdvancesinDifferenceEquations 1,2 WΔ,T 0, T Ì, ÊN with the inner product 1 By Theorem 2.21, the space HΔ,T u, v 1 HΔ,T 0,T Ì uσ t , vσ t Δt Ì 0,T uΔ t , vΔ t Δt 3.1 and the induced norm u is Hilbert space Since w ∈ R 2 |u t | Δt 1 HΔ,T 0,T σ Ì Δ u t Ì 0,T 2 1/2 Δt 3.2 0, T Ì, Ê , by Theorem 2.44 in 3 , one has that ∀t... Reh´ k, “Half-linear dynamic equations, ” in Nonlinear Analysis and Applications: to V Lakshmikantham on His 80th Birthday Vol 1, 2, pp 1–57, Kluwer Academic Publishers, Dordrecht, The Netherlands, 2003 Advances inDifferenceEquations27 7 R P Agarwal, M Bohner, and W.-T Li, Nonoscillation and Oscillation: Theory for Functional Differential Equations, vol 267 of Monographs and Textbooks in Pure and Applied... Combining 4.32 and 4.34 , there exists C17 > 0 such that ϕ uk ≥ 2 ew t, 0 F σ t , 0,T Ì uk Δt − C17 2 4.35 1 Therefore, by 4.35 and iv , {uk } is bounded Hence {uk } is bounded in HΔ,T by 1 Theorem 2.23 and 4.31 By Lemma 3.8 and Theorem 3.4, ϕ has a minimum point on HΔ,T , which is a critical point of ϕ Hence, problem 1.1 has at least one solution which minimizes the function ϕ 26 Advances in Difference. .. Netherlands, 1996 3 M Bohner and A Peterson, Dynamic Equations on Time Scales: An Introduction with Applications, Birkh¨ user, Boston, Mass, USA, 2001 a 4 R P Agarwal and D O’Regan, In nite Interval Problems for Differential Difference and Integral Equations, Kluwer Academic Publishers, Dordrecht, The Netherlands, 2001 5 M Bohner and A Peterso, Eds., Advances in Dynamic Equations on Time Scales, Birkh¨ user, Boston,... mapping from WΔ,T 0, T Ì, ÊN into L1 0, T Ì, Δ ÊN × Lq 0, T Ì, ÊN defined by Δ 1,p u −→ Dx L ·, uσ , uΔ , Dy L ·, uσ , uΔ 2.53 is continuous, so that Φ is continuous from WΔ,T 0, T Ì, ÊN into WΔ,T 0, T Ì, ÊN 1,p 1,p ∗ 3 Variational Setting In this section, in order to apply the critical point theory, we make a variational structure From this variational structure, we can reduce the problem of finding... 0,T Ì Δ-a.e 0 on 0, T , Ì κ 3.14 3.15 16 Advances in Difference Equations By 3.14 , one has ew t, 0 xΔ t 2 w t ew t, 0 xΔ σ t ew t, 0 ∇F σ t , uσ t Δ-a.e on 0, T Ì κ 3.16 Combining 3.14 , 3.15 , 3.16 , and Lemma 2.19, we obtain xΔ t w t xΔ σ t 2 ∇F σ t , uσ t x 0 −x T Δ-a.e xΔ 0 − xΔ T 0, on 0, T , Ì κ 3.17 0 1,2 1 We identify u ∈ HΔ,T with its absolutely continuous representative x ∈ VΔ,T 0, T Ì, ÊN... Results in Mathematics, vol 35, no 1-2, pp 3–22, 1999 9 D R Anderson, “Eigenvalue intervals for a second-order mixed-conditions problem on time scales,” International Journal of Differential Equations, vol 7, pp 97–104, 2002 10 G Sh Guseinov, “Integration on time scales,” Journal of Mathematical Analysis and Applications, vol 285, no 1, pp 107– 127, 2003 11 M Bohner and G Sh Guseinov, “Improper integrals... constant C12 It follows from 4.13 and iii that {|un |} is bounded 1 Hence {un } is bounded in HΔ,T by 4.10 and 4.11 Therefore, there exists a subsequence of {un } for simplicity denoted again by {un } such that un u 1 in HΔ,T 4.14 By Theorem 2.25, one has un −→ u in C 0, T Ì, ÊN 4.15 22 Advances in Difference Equations On the other hand, one has ϕ un − ϕ u , un − u 0,T 2 ew t, 0 uΔ t − uΔ t n Ì Δt... that M1 min ew t, 0 , M2 ≤ u ≤ M2 u t∈ 0,T Ì max ew t, 0 t∈ 0,T Ì 3.7 1 ∀u ∈ HΔ,T 3.8 Hence, one has M1 u 1 HΔ,T Consequently, the norm · and · 1 HΔ,T 1 HΔ,T , are equivalent Advances in Difference Equations 15 1 Consider the functional ϕ : HΔ,T → 1 2 ϕ u ew t, 0 uΔ t 0,T Ê defined by 2 Ì Δt ew t, 0 F σ t , uσ t Δt 0,T 3.9 Ì We have the following facts 1 Theorem 3.2 The functional ϕ is continuously . Hindawi Publishing Corporation Advances in Difference Equations Volume 2010, Article ID 7274 86, 27 pages doi:10.1155/2010/ 7274 86 Research Article Existence of Solutions. continuous while in season and may follow a difference scheme with variable step-size, die out in winter, while their eggs are incubating or dormant, and then hatch in a new season, giving rise to. on 0,T . 2.25 8AdvancesinDifference Equations Combining 2.24 and 2.25,weobtain 0,T x n t ,φ Δ t Δt − 0,T x Δ n t ,φ σ t Δt, ∀φ ∈ C 1 T,rd 0,T , N . 2.26 Since