Hyperbolicity criterion for periodic solutions of functional-differential equations with several delays

In this paper, a hyperbolicity criterion for periodic solutions of nonlinear functional-differential equations is constructed in terms of zeros of the characteristic function. In the earlier papers in this area, necessary and sufficient conditions were different from each other. Moreover, it was assumed that if the period of the investigated solution is irrational, then that solution admits a rational approximation. In this paper, we obtain necessary and sufficient conditions of the hyperbolicity. It is proved (and the proof is constructive) that a rational approximation exists for any irrational period. All the results are obtained for the case of several rational delays. __________ Translated from Sovremennaya Matematika. Fundamental’nye Napravleniya (Contemporary Mathematics. Fundamental Directions), Vol. 21, Proceedings of the Seminar on Differential and Functional Differential Equations Supervised by A. Skubachevskii (Peoples’ Friendship University of Russia), 2007.     

Positive periodic solutions for neutral functional differential equations with distributed delays and feedback control

By using a fixed point theorem of strict-set-contraction, some criteria are established for the existence of positive periodic solutions of neutral functional differential equations with distributed delays and feedback control.     

First order ordinary differential equations with several periodic solutions

The method of upper and lower solutions and convexity arguments are used to prove sharp results for the existence and multiplicity of periodic solutions for first order ordinary differential equations depending upon a parameter.Dedicated to Professor H. W. Knobloch for his sixtieth birthday     

Linearized stability in periodic functional differential equations with state-dependent delays

In this paper, we study stability of periodic solutions of a class of nonlinear functional differential equations (FDEs) with state-dependent delays using the method of linearization. We show that a periodic solution of the nonlinear FDE is exponentially stable, if the zero solution of an associated linear periodic linear homogeneous FDE is exponentially stable.     

Positive periodic solutions of functional differential equations

We consider the existence, multiplicity and nonexistence of positive ω-periodic solutions for the periodic equation x′(t)=a(t)g(x)x(t)−λb(t)f(x(t−τ(t))), where are ω-periodic, , , f,g∈C([0,∞),[0,∞)), and f(u)>0 for u>0, g(x) is bounded, τ(t) is a continuous ω-periodic function. Define , , i₀=number of zeros in the set and i_∞=number of infinities in the set . We show that the equation has i₀ or i_∞ positive ω-periodic solution(s) for sufficiently large or small λ>0, respectively.     

Generic periodic solutions of functional differential equations

Consider the class of retarded functional differential equations

$\text{x(t) = f(x}{}_{\mathrm{t}}\text{)}$

, (1) where x_t(θ) = x(t + θ), ?1 ? θ ? 0, so x_t?C = C([?1, 0], Rⁿ), and $\text{f∈}\textcolor{red}{}\text{=C}{}^{\mathrm{r}}\text{(C,R}{}^{\mathrm{n}}\text{)}$. Let 2 ? r ? ∞ and give $\text{X}$ the appropriate (Whitney) topology. Then the set of $\text{f∈}\textcolor{red}{}$ such that all fixed points and all periodic solutions of (¹) are hyperbolic is residual in

.     

Almost periodic solutions of neutral functional differential equations

We study a nonlinear neutral functional differential equation. Applying the properties of almost periodic function and exponential dichotomy of linear system as well as Krasnoselskii’s fixed point theorem, we establish the conditions for the existence of almost periodic solution of the equations.     

Positive periodic solutions of impulsive functional differential equations

We study the existence and nonexistence of positive periodic solutions of a non-autonomous functional differential equation with impulses. The equations we study may be of delay, advance or mixed type functional differential equations and the impulses may cause the existence of positive periodic solutions. The methods employed are fixed-point index theorem, Leray-Schauder degree, and upper and lower solutions. The results obtained are new, and some examples are given to illustrate our main results.     

Stability of solutions to differential equations with several variable delays. I

We consider a class of scalar linear differential equations with several variable delays and constant coefficients. A family of equations of the class is defined by coefficients and maximum admissible values of delays. We obtain conditions that are necessary and sufficient for the stability of solutions to all equations of the family. It is ascertained that the conditions are determined entirely by properties of the solution to the initial problem for an autonomous equation that belongs to the family. Some alternatives of required conditions are obtained in the form of estimates for solutions to autonomous equations in a finite interval.     

Positive periodic solutions of first-order functional differential equations with parameter

We prove the existence and multiplicity of positive T$T$-periodic solution(s) for T$T$-periodic equation x^′(t)=h(t,x)−λb(t)f(x(t−τ(t)))$x^{\prime }\left(t\right)=h(t,x)-\lambda b\left(t\right)f\left(x(t-\tau \left(t\right))\right)$ by Krasnoselskii fixed point theorem, where f(x)$f\left(x\right)$ may be singular at x=0$x=0$. Our results improve some recent results in previous literature.     

On periodic solutions of functional differential equations with infinite delay

In this paper,using Mawhin's continuation theorem in the theory of coincidence degree,we first prove the general existence theorem of periodic solutions for F.D.Es with infinite delay:dx(t)/dt=f(t,x_t),x(t)∈R~n,which is an extension of Mawhin's existence theorem of periodic solutions of F.D.Es with finite delay.Second,as an application of it,we obtain the existence theorem of positive periodic solutions of the Lotka-Volterra equations:dx(t)/dt=x(t)(a-kx(t)-by(t)),dy(t)/dt=-cy(t)+d integral from n=0 to +∞ x(t-s)y(t-s)dμ(s)+p(t).     

Stability of solutions to differential equations with several variable delays. III

We consider a class of scalar linear differential equations with several variable delays and constant coefficients. We treat the coefficients and maximum admissible values of delays as parameters that define a family of equations of the considered class. Using the necessary and sufficient stability conditions established in preceding papers, we obtain an analytic form and a geometric interpretation of boundaries of stability domains for families of equations with a small number of independent parameters.     

Stability of solutions to differential equations with several variable delays. II

We consider a class of scalar linear differential equations with several variable delays and constant coefficients. We treat coefficients and maximum admissible values of delays as parameters that define a family of equations from the class under consideration. We study domains in the parameter space, where fundamental solutions of all equations of the family are uniformly or exponentially stable and have a fixed sign. We establish explicit necessary and sufficient conditions for the stability and sign-definiteness of the equations family.     

Three periodic solutions of nonlinear neutral functional differential equations

In this paper, a type of nonlinear neutral functional differential equations are considered. Some results on the existence of three positive periodic solutions are obtained by using the Leggett–Williams fixed point theorem.     

Asymptotically almost periodic solutions of stochastic functional differential equations

In this paper, we investigate a class of stochastic functional differential equations of the form

dx(t)=(Ax(t)+F(t,x(t),x_t))dt+G(t,x(t),x_t)°dW(t).     

Two periodic solutions of second-order neutral functional differential equations

In this paper, we consider a type of second-order neutral functional differential equations. We obtain some existence results of multiplicity and nonexistence of positive periodic solutions. Our approach is based on a fixed point theorem in cones.