Hindawi Publishing Corporation Journal of Applied Mathematics Volume 2012, Article ID 693163, 12 pages doi:10.1155/2012/693163 Research Article Exponential Stability for a Class of Stochastic Reaction-Diffusion Hopfield Neural Networks with Delays Xiao Liang1 and Linshan Wang2 1 2 College of Information Science and Engineering, Ocean University of China, Qingdao 266100, China Department of Mathematics, Ocean University of China, Qingdao 266100, China Correspondence should be addressed to Linshan Wang, wangls@ouc.edu.cn Received 7 August 2011; Accepted 28 November 2011 Academic Editor: Jitao Sun Copyright q 2012 X. Liang and L. Wang. 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. This paper studies the asymptotic behavior for a class of delayed reaction-diffusion Hopfield neural networks driven by finite-dimensional Wiener processes. Some new sufficient conditions are established to guarantee the mean square exponential stability of this system by using Poincaré’s inequality and stochastic analysis technique. The proof of the almost surely exponential stability for this system is carried out by using the Burkholder-Davis-Gundy inequality, the Chebyshev inequality and the Borel-Cantelli lemma. Finally, an example is given to illustrate the effectiveness of the proposed approach, and the simulation is also given by using the Matlab. 1. Introduction Recently, the dynamics of Hopfield neural networks with reaction-diffusion terms have been deeply investigated because their various generations have been widely used in some practical engineering problems such as pattern recognition, associate memory, and combinatorial optimization see 1–3. However, under closer scrutiny, that a more realistic model would include some of the past states of the system, and theory of functional differential equations systems has been extensively developed 4, 5, meanwhile many authors have considered the asymptotic behavior of the neural networks with delays 6– 9. In fact random perturbation is unavoidable in any situation 3, 10; if we include some environment noise in these systems, we can obtain a more perfect model of this situation 2 Journal of Applied Mathematics 3, 11–16. So, this paper is devoted to the exponential stability of the following delayed reaction-diffusion Hopfield neural networks driven by finite-dimensional Wiener processes: ⎛ l ∂ dui t, x ⎝ ∂x j j1 ∂ui ∂ν m ∂ui Dij x ∂xj − ai ui n ⎞ cij fj uj t − r, x ⎠dt j1 gij ui t − r, xdWj , j1 0, 1.1 t ≥ 0, ∂O ui θ, x φi θ, x, x ∈ O ∈ Rl , θ ∈ −r, 0, i 1, 2, . . . , n. There are n neural network units in this system and ui t, x denote the potential of the cell i at t and x. ai are positive constants and denote the rate with which the ith unit will reset its potential to the resting state in isolation when it is disconnected from the network and external inputs at t, and cij are the output connection weights from the jth neuron to the ith neuron. fj are the active functions of the neural network. r is the time delay of a neuron. O denotes an open bounded and connected subset of Rl with a sufficient regular boundary ∂O, ν is the unit outward normal on ∂O, ∂ui /∂ν ∇ui , νRl , and gij are noise intensities. Initial data φi are F0 -measurable and bounded functions, almost surely. We denote Ω, F, P a complete probability space with filtration {Ft }t≥0 satisfying the usual conditions see 10. Wi t, i 1, 2, . . . , m, are scale standard Brownian motions defined on Ω, F, P. For convenience, we rewrite system 1.1 in the vector form: du ∇ · Dx ◦ ∇u − Au Cfut − r dt Gut − rdW, ∂ut, x 0, t ≥ 0, ∂ν 1.2 ∂O u0, x φx, where C cij n×n , u u1 , u2 , . . . , un T , ∇u ∇u1 , . . . , ∇un T , W W1 , W2 , . . . , Wm T , fu f1 u1 , f2 u2 , . . . , fn un T , A Diaga1 , a2 , . . . , an , φ φ1 , φ2 , . . . , φn T , Gu gij ui n×m , D Dij n×l , and D ◦ ∇u Dij ∂ui /∂xj n×l is the Hadamard product of matrix D and ∇u; for the definition of divergence operator ∇ · u, we refer to 2, 3. 2. Preliminaries and Notations In this paper, we introduce the following Hilbert spaces H L2 O, V H 1 O, according to 17–19, V ⊂ H H ⊂ V , where H , V denote the dual of the space H, V , respectively, the injection is continuous, and the embedding is compact. · , ||| · ||| represent the norm in H, V , respectively. U L2 On is the space of vector-valued Lebesgue measurable functions on O, which is a Banach space under the norm uU ni1 ui x2 1/2 . C C−r, 0, U is the Banach space of all continuous functions from −r, 0 to U, when equipped with the sup-norm φC sup−r≤s≤0 φU . Journal of Applied Mathematics 3 With any continuous Ft -adapted U-valued stochastic process ut : Ω → U, t ≥ −r, we associate a continuous Ft -adapted C-valued stochastic process ut : Ω → C, t > 0, by setting ut s, xω ut s, xω, s ∈ −r, 0, x ∈ O. CFb 0 denote the space of all bounded continuous processes φ : −r, 0 × Ω → U such that φθ, · is F0 -measurable for each θ ∈ −r, 0 and EφC < ∞. LK is the set of all linear bounded operators from K into K; when equipped with the operator norm, it becomes a Banach space. In this paper, we assume the following. H1 fi and Gij are Lipschitz continuous with positive Lipschitz constants k1 , k2 such that |fi u − fi v| ≤ k1 |u − v| and |Gij u − Gij v| ≤ k2 |u − v|, ∀u, v ∈ R, and fi 0 0, gij 0 0. H2 There exists α > 0 such that Dij x ≥ α/l. H3 Let η 2αβ2 2k3 − nk12 σ 2 er − mk22 er − 2 > 0, k3 min{ai }, σ max{|cij |}. Remark 2.1. We can infer from H1 that system 1.1 has an equilibrium ut, x, ω 0. Let us define the linear operator as follows: A : ΠA ∈ U −→ U, Au ∇ · Dx ◦ ∇u, 2.1 and ΠA {u ∈ H 2 On , ∂u/∂ν|∂O 0}. Lemma 2.2 Poincaré’s inequality. Let O be a bounded domain in Rl and φ belong to a collection of twice differentiable functions defined on O into R; then φ ≤ β−1 φ , 2.2 where the constant β depends on the size of O. Lemma 2.3. Let us consider the equation du Au, t ≥ 0, dt u0 φ. 2.3 For every φ ∈ U, let ut Stφ denote the solution of 2.3; then St is a contraction map in U. Proof. Now we take the inner product of 2.3 with ut in U; by employing the Gaussian theorem and condition H2, we get that Au, u ≤ −α|u|2H 1 On , ·, · is the inner product in U, |u|2H 1 On denote the norm of H 1 On see 3, which means 1 d ut2U α|ut|2H 1 On ≤ 0. 2 dt 2.4 4 Journal of Applied Mathematics Thanks to the Poincaré inequality, one obtains d ut2U 2αβ2 ut2U ≤ 0. dt 2.5 2 Multiplying e2αβ t in both sides of the inequality, we have d 2αβ2 t e ut2U ≤ 0. dt 2.6 Integrating the above inequality from 0 to t, we obtain 2 2 ut2U ≤ e−2αβ t φU . 2.7 By the definition of T tLU , we have T tLU ≤ 1. Definition 2.4 see 20–22. A stochastic process ut : −r, ∞ × Ω → U is called a global mild solution of 1.1 if i ut is adapted to Ft ii ut is measurable with ut Stφ − t St − sA ds 0 ut φ ∈ CFb 0 , ∞ 0 t ut2U dt < ∞ almost surely and St − sfus − rds 0 t St − sGus − rdW, 0 2.8 t ∈ −r, 0, for all t ∈ −r, ∞ with probability one. Definition 2.5. Equation 1.1 is said to be almost surely exponentially stable if, for any solution ut, x, ω with initial data φ ∈ CFb 0 , there exists a positive constant λ such that lim sup ln ut C ≤ −λ, ut ∈ C, almost surely. t−→∞ 2.9 Definition 2.6. System 1.1 is said to be exponentially stable in the mean square sense if there exist positive constants κ and α such that, for any solution ut, x, ω with the initial condition φ ∈ CFb 0 , one has Eut2C ≤ κe−αt−t0 , t ≥ t0 , ut ∈ C. 2.10 3. Main Result Theorem 3.1. Suppose conditions H1–H3 hold; then 1.1 is exponentially stable in the mean square sense. Journal of Applied Mathematics 5 Proof. Let u be the mild solution of 1.1; thanks to the Itô formula, we observe that ⎞⎞ ⎛ ⎛ l n ∂ ∂u i λt 2 λt 2 λt ⎝ 2ui ⎝ Dij − ai ui cij fj uj t − r ⎠⎠dt d e ui λe ui dt e ∂xi ∂xj 3.1 j1 j1 eλt Gi GTi dt 2eλt ui Gi dW, Gi Gi1 , Gi2 , . . . , Gim , where λ is a positive constant that will be defined below. Then, by integration between 0 and t, we find that ⎛ ⎞ t l ∂ ∂u i ⎠ds − 2 eλs ai u2 ds Dij eλt u2i t φi 02 λeλs u2i ds 2 eλs ⎝ui i ∂xj ∂xj 0 0 0 j1 t t t n λs λs T 2 e ui cij fj uj s − r ds e Gi Gi ds 2 eλs ui Gi dW. t t 0 0 j1 3.2 0 Integrating the above equation over O, by virtue of Fubini’s theorem, we prove that 2 eλt u2i 2 φi 0 λ −2 t t λs 0 e O λs 0 O e λs O 0 e t u2i dx ds ai u2i dx ds Gi GTi dx ds 2 e λs 0 t e λs 0 2 t t e O λs 0 O ui l ∂ 2ui ∂x j O j1 n ∂ui Dij ∂xj dx ds cij fj uj s − r dx ds 3.3 j1 ui Gi dx dW. Taking the expectation on both sides of the last equation, by means of 3, 10, 16 t 2E 0 O eλs ui Gi dx dW 0. 3.4 Then, by Fubini’s theorem, we have t t l 2 2 ∂ ∂ui 2 λs 2 λs Dij dx ds e Eui E φi 0 λ e Eui dx ds 2E e ui ∂xj ∂xj 0 0 O O j1 t t n − 2 eλs ai Eu2i dx ds 2E eλs ui cij fj uj s − r dx ds λt O 0 E t 0 0 eλs O Gi GTi dx ds I1 I 2 I 3 I 4 I 5 I 6 . O j1 3.5 6 Journal of Applied Mathematics We observe that 2 2 I1 Eφi 0 ≤ sup Eφi θ , θ∈−r,0 t I2 λ 0 O eλs Eu2i dx ds λ t eλs Eui 2 ds. 3.6 3.7 0 From the Neumann boundary condition, by means of Green’s formula and H2 see 3, 6, 7, we know ⎛ ⎞ l ∂ ∂u i ⎠dx ds Dij I3 2E eλs ⎝ui ∂x ∂x j j 0 O j1 2 t l ∂ui λs −2E e Dij dx ds ∂xj 0 O j1 t t 2 λs 2 ≤ −2α e E|ui | ds ≤ −2αβ eλs Eui 2 ds. t 0 3.8 0 Then, by using the positiveness of ai , one gets the relation I4 −2 t O 0 e λs ai Eu2i dx ds ≤ −2k3 t eλs Eui 2 ds, 3.9 0 where k3 min{a1 , a2 , . . . , an } > 0. By using the Young inequality as well as condition H1, we have that I5 2E t O 0 eλs ui j1 2 ⎞ n ⎟ ⎜ ≤ eλs ⎝E|ui |2 E cij fj ⎠dx ds j1 0 O ⎛ ⎞ t n 2 2 λs ⎝ 2 ≤ E|ui | σ e Efj uj s − r ⎠dx ds t O 0 t ≤ O 0 t ≤ 0 ⎛ n cij fj dx ds ⎛ 3.10 j1 ⎞ n 2 eλs ⎝E|ui |2 σ 2 k12 Euj s − r ⎠dx ds j1 eλs Eui 2 σ 2 k12 Eus − r2U ds, where σ max |cij |, and I6 t 0 O e λs EGi GTi dx ds ≤ mk22 t 0 eλs Eui s − r2 ds. 3.11 Journal of Applied Mathematics 7 We infer from 3.6–3.11 that t 2 eλt Eui t2 ≤ sup Eφi θ − 2αβ2 2k3 − 1 − λ θ∈−r,0 σ 2 k12 t e ut − λs 0 r2U ds mk22 t eλs Eui 2 ds 0 3.12 2 e Eui s − r ds. λs 0 Adding 3.12 from i 1 to i n, we obtain e λt Eu2U 2 ≤ EφC − 2αβ2 2k3 − 1 − λ nk12 σ 2 mk22 t t 0 e Eus − λs 0 eλs Eu2U ds 3.13 r2U ds, due to t e Eus − λs 0 r2U ds ≤e λr t ≤ e2λr −r 0 eλs Eus2U ds −r 2 EφsU ds eλr 2 ≤ re2λr EφC eλr t 0 t 0 eλs Eus2U ds 3.14 eλs Eus2U ds; we induce from the previous equations that e λt Eu2U ≤ −c1 t 0 eλs Eu2U ds c2 , 3.15 where c1 2αβ2 2k3 − 1 − nk12 σ 2 eλr − mk22 eλr − λ and c2 1 mk22 re2λr nk12 σ 2 re2λr Eφ2C ; so we choose λ 1 such that c1 η > 0. By using the classical Gronwall inequality we see that eλt Eu2U ≤ c2 e−ηt ; 3.16 Eu2U ≤ c2 e−η1t . 3.17 in other words, we get So, for t θ ≥ t/2 ≥ 0, we also have Eut θ2U ≤ c2 e−η1tθ , ≤ c2 e −κt , η1 , θ ∈ −r, 0, κ 2 3.18 8 Journal of Applied Mathematics and we can conclude that Eut 2C ≤ c2 e−κt . 3.19 Theorem 3.2. If the system 1.1 satisfies hypotheses H1–H3, then it is almost surely exponentially stable. Proof. Let ut be the mild solution of 1.1. By Definition 2.4 as well as the inequality ni1 ai 2 ≤ n ni1 a2i , ai ∈ R, we have E sup ut2U ≤ 4 sup St − N 1uN2U N≤t≤N1 N≤t≤N1 2 t 4 sup −ASt − su ds N−1 N≤t≤N1 U 2 t 4 sup St − sCfus − rds N≤t≤N1 N−1 U 2 t 4 sup St − sGus − rdW N−1 N≤t≤N1 3.20 U I1 I2 I3 I4 . Using the contraction of the map St and the result of Theorem 3.1, we find I1 4 sup ESt − N 1uN − 12U N≤t≤N1 ≤ 4 sup EuN−1 2C ≤ 4c2 e−κN−1 . 3.21 N≤t≤N1 By the Hölder inequality, we obtain 2 t I2 4 sup E −ASt − su ds N−1 N≤t≤N1 U t ≤ 4 sup t − N 1 E−ASt − su2U ds N≤t≤N1 ≤ 8 sup N≤t≤N1 ≤ 8k42 N1 N−1 N−1 3.22 EAu2U ds Eu2U ds ≤ 8k42 N−1 N1 ≤ 8k42 c2 N−1 t N1 N−1 Eus 2C ds e−κs ds ≤ 8k42 ρ1 e−κN−1 , where ρ1 c2 /κ, k4 max{a1 , a2 , . . . , an }. Journal of Applied Mathematics 9 By virtue of Theorem 3.1, Hölder inequality, and H1, we have 2 t I3 4 sup E St − sCfus − rds N−1 N≤t≤N1 U t 2 Cfus − r ds ≤ 4 sup t − N 1E N≤t≤N1 ≤ 8σ 2 sup E t N−1 N≤t≤N1 ≤ 8k12 σ 2 ≤ 8k12 c2 N1 N−1 N1 N−1 U N−1 fus − r2 ds U Eus − r2U ds ≤ 8k12 σ 2 3.23 N1 N−1 Eus 2C ds e−κs ds ≤ 8k12 ρ1 e−κN−1 . Then, by the Burkholder-Davis-Gundy inequality see 18, 22, there exists c3 such that 2 t I4 4 sup E St − sGus − rdW N−1 N≤t≤N1 U t ≤ 4c3 sup E St − sGus − rI2U ds N−1 N≤t≤N1 ≤ 4c3 k22 t sup ≤ 4c3 k22 c2 N1 N−1 Eus − N−1 N≤t≤N1 r2U ds ≤ 4c3 k22 N1 N−1 3.24 Eus 2C ds e−κs ds ≤ 4c3 k22 ρ1 e−κN−1 , where I 1, 1, . . . , 1T is an m-dimensional vector. We can deduce from 3.21–3.24 that E sup ut2U ≤ ρ2 e−κN−1 , N≤t≤N1 3.25 where ρ2 4c2 8k42 8k12 4c3 k22 ρ1 . Thus, for any positive constants εN , thanks to the Chebyshev inequality we have that P sup utU > εN N≤t≤N1 1 sup Eut2U 2 εN N≤t≤N1 1 ≤ 2 ρ2 e−κN−1 . εN ≤ 3.26 10 Journal of Applied Mathematics Frequence of u2 Frequence of u1 u 1 1 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 v 0 0 −0.2 −0.2 −0.4 −0.4 −0.6 −0.6 −0.8 −0.8 −1 −1 0 0.5 1 0 0.5 t 1 t a b Figure 1 Due to the Borel-Cantelli lemma, we see that lim sup t−→∞ ln ut2U ≤ −κ, t almost surely. 3.27 This completes the proof of the theorem. 4. Simulation Consider two-dimensional stochastic reaction-diffusion recurrent neural networks with delay as follows: du1 t, x 10Δu1 − 7u1 1.3 tanhu1 t − 1, xdt u1 t − 1, xdW, du2 t, x 10Δu2 − 7u2 tanhu1 t − 1, x − tanhu2 t − 1, xdt u2 t − 1, xdW ∂ui t, 0 ∂ui t, 20 0, t ≥ 0, ∂x ∂x u1 θ, x cos0.2πx, u2 θ, x cos0.1πx, x ∈ 0, 20, θ ∈ −1, 0. 4.1 Δ is the Laplace operator. We have β ≥ 1/20, α ≥ 10, k1 1, k2 1, k3 7, σ 1.3, n 2, and η > 0; by Theorems 3.1 and 3.2, this system is mean square exponentially stable as well as almost surely exponentially stable. The results can be shown in Figures 1, 2 and 3. Journal of Applied Mathematics 11 Simulation of u1 1 0.5 u1 0 −0.5 −1 30 150 20 x 100 10 50 0 0 t Figure 2 Simulation of u2 1 0.5 u2 0 −0.5 −1 30 150 20 x 100 10 50 0 0 t Figure 3 We use the forward Euler method to simulate this example 23–25. We choose the time step Δt 0.01 and space step Δx 1, and δ Δt/Δx2 0.01. Acknowledgment The authors wish to thank the referees for their suggestions and comments. We are also indebted to the editors for their help. This work was supported by the National Natural Science Foundation of China no. 11171374, Natural Science Foundation of Shandong Province no. ZR2011AZ001. 12 Journal of Applied Mathematics References 1 X. X. Liao and Y. L. Gao, “Stability of Hopfield neural networks with reactiondiffusion terms,” Acta Electronica Sinica, vol. 28, pp. 78–82, 2000. 2 L. S. Wang and D. Xu, “Global exponential stability of Hopfield reaction-diffusion neural networks with time-varying delays,” Science in China F, vol. 46, no. 6, pp. 466–474, 2003. 3 L. S. Wang and Y. F. Wang, “Stochastic exponential stability of the delayed reaction diffusion interval neural networks with Markovian jumpling parameters,” Physics Letters A, vol. 356, pp. 346–352, 2008. 4 J. K. Hale and V. S. M. Lunel, Introduction to Functional-Differential Equations, vol. 99 of Applied Mathematical Sciences, Springer, Berlin, Germany, 1993. 5 S.-E. A. Mohammed, Stochastic Functional Differential Equations, vol. 99 of Research Notes in Mathematics, Pitman, London, UK, 1984. 6 L. S. Wang and Y. Y. Gao, “Global exponential robust stability of reactiondiffusion interval neural networks with time varying delays,” Physics Letters A, vol. 305, pp. 343–348, 2006. 7 L. S. Wang, R. Zhang, and Y. Wang, “Global exponential stability of reaction-diffusion cellular neural networks with S-type distributed time delays,” Nonlinear Analysis: Real World Applications, vol. 10, no. 2, pp. 1101–1113, 2009. 8 H. Y. Zhao and G. L. Wang, “Existence of periodic oscillatory solution of reactiondiffusion neural networks with delays,” Physics Letters A, vol. 343, pp. 372–382, 2005. 9 J. G. Lu and L. J. Lu, “Global exponential stability and periodicity of reaction-diffusion recurrent neural networks with distributed delays and Dirichlet boundary conditions,” Chaos, Solitons and Fractals, vol. 39, no. 4, pp. 1538–1549, 2009. 10 X. Mao, Stochastic Differential Equations and Applications, Horwood, 1997. 11 J. Sun and L. Wan, “Convergence dynamics of stochastic reaction-diffusion recurrent neural networks with delays,” International Journal of Bifurcation and Chaos in Applied Sciences and Engineering, vol. 15, no. 7, pp. 2131–2144, 2005. 12 M. Itoh and L. O. Chua, “Complexity of reaction-diffusion CNN,” International Journal of Bifurcation and Chaos in Applied Sciences and Engineering, vol. 16, no. 9, pp. 2499–2527, 2006. 13 X. Lou and B. Cui, “New criteria on global exponential stability of BAM neural networks with distributed delays and reaction-diffusion terms,” International Journal of Neural Systems, vol. 17, pp. 43–52, 2007. 14 Q. Song and Z. Wang, “Dynamical behaviors of fuzzy reaction-diffusion periodic cellular neural networks with variable coefficients and delays,” Applied Mathematical Modelling, vol. 33, no. 9, pp. 3533–3545, 2009. 15 Q. Song, J. Cao, and Z. Zhao, “Periodic solutions and its exponential stability of reaction-diffusion reccurent neural networks with distributed time delays,” Nonlinear Analysis B, vol. 8, pp. 345–361, 2007. 16 K. Liu, “Lyapunov functionals and asymptotic stability of stochastic delay evolution equations,” Stochastics and Stochastics Reports, vol. 63, no. 1-2, pp. 1–26, 1998. 17 R. Temam, Infinite-Dimensional Dynamical Systems in Mechanics and Physics, vol. 68 of Applied Mathematical Sciences, Springer, New York, NY, USA, 1988. 18 G. Da Prato and J. Zabczyk, Stochastic Equations in Infinite Dimensions, vol. 44 of Encyclopedia of Mathematics and its Applications, Cambridge University Press, Cambridge, UK, 1992. 19 I. Chueshov, Introduction to the Theory of Infinite-Dimensional Dissipative Systems, Acta Kharkov, 2002. 20 R. Jahanipur, “Stochastic functional evolution equations with monotone nonlinearity: existence and stability of the mild solutions,” Journal of Differential Equations, vol. 248, no. 5, pp. 1230–1255, 2010. 21 T. Taniguchi, “Almost sure exponential stability for stochastic partial functional-differential equations,” Stochastic Analysis and Applications, vol. 16, no. 5, pp. 965–975, 1998. 22 T. Caraballo, K. Liu, and A. Truman, “Stochastic functional partial differential equations: existence, uniqueness and asymptotic decay property,” Proceedings the Royal Society of London A, vol. 456, no. 1999, pp. 1775–1802, 2000. 23 M. Kamrani and S. M. Hosseini, “The role of coefficients of a general SPDE on the stability and convergence of a finite difference method,” Journal of Computational and Applied Mathematics, vol. 234, no. 5, pp. 1426–1434, 2010. 24 D. J. Higham, “Mean-square and asymptotic stability of the stochastic theta method,” SIAM Journal on Numerical Analysis, vol. 38, no. 3, pp. 753–769, 2000. 25 P. E. Kloeden and E. Platen, Numerical Solution of Stochastic Differential Equations, vol. 23, Springer, Berlin, Germany, 3rd edition, 1999. Advances in Operations Research Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 Advances in Decision Sciences Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 Mathematical Problems in Engineering Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 Journal of Algebra Hindawi Publishing Corporation http://www.hindawi.com Probability and Statistics Volume 2014 The Scientific World Journal Hindawi Publishing Corporation http://www.hindawi.com Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 International Journal of Differential Equations Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 Volume 2014 Submit your manuscripts at http://www.hindawi.com International Journal of Advances in Combinatorics Hindawi Publishing Corporation http://www.hindawi.com Mathematical Physics Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 Journal of Complex Analysis Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 International Journal of Mathematics and Mathematical Sciences Journal of Hindawi Publishing Corporation http://www.hindawi.com Stochastic Analysis Abstract and Applied Analysis Hindawi Publishing Corporation http://www.hindawi.com Hindawi Publishing Corporation http://www.hindawi.com International Journal of Mathematics Volume 2014 Volume 2014 Discrete Dynamics in Nature and Society Volume 2014 Volume 2014 Journal of Journal of Discrete Mathematics Journal of Volume 2014 Hindawi Publishing Corporation http://www.hindawi.com Applied Mathematics Journal of Function Spaces Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 Optimization Hindawi Publishing Corporation http://www.hindawi.com Volume 2014 Hindawi Publishing Corporation http://www.hindawi.com Volume 2014