Almost periodic oscillations of suspended string under quasiperiodic linear force

We shall be concerned with the behavior of a suspended string to which a time-periodic or time-quasiperiodic outer force works. We shall deal with IBVP for a linear equation of a suspended string, and show that every solution is almost periodic in time. The result shall be shown under the assumptions that the basic periods (the period), the length of the string and the zero points of the Bessel functions of the first kind satisfy the Diophantine type number-theoretic condition and the forcing term is smooth. In order to deal with the problems we shall develop some well-matched function spaces and solve the eigenvalue problem for suspended string operator.     

Global smooth solutions of IBVP to nonlinear equation of suspended string

We shall consider IBVP to a nonlinear equation of suspended string with uniform density to which a nonlinear time-independent outer force works. The nonlinear term is smooth but not monotone. We shall show that IBVP has a unique time-global smooth solution. The regularity of the solutions shall be also studied.     

Time periodic solutions of the diffusive Nicholson blowflies equation with delay

This paper is concerned with the Nicholson blowflies equation with nonlinear diffusion and time delay subject to the homogeneous Dirichlet boundary condition in a bounded domain. We establish the existence of nontrivial periodic solutions of the time-periodic problem under general conditions by constructing a coupled upper–lower solution pair and by applying the Schauder fixed point theorem. The attractivity of the periodic solutions is also discussed by using the monotone iteration method.     

Multiplicity of Positive Periodic Solutions to Second Order Singular Dynamical Systems

The existence and multiplicity of non-collision periodic solutions for second order singular dynamical systems are discussed in this paper. Using the Green’s function of linear differential equation, we consider general singularity and do not need any kind of strong force condition. The proof relies on a nonlinear alternative principle of Leray–Schauder and a fixed point theorem in cones.     

On existence of periodic solutions for gradient systems with applications

In this paper we prove the existence of periodic solutions for gradient systems in finite and infinite dimensional spaces. The techniques of the proofs are based on the application of a global inverse functions theorem, the Schäefer fixed point theorem and the Faedou–Galerkin method. We apply our results in order to solve nonlinear reaction–diffusion equations with Dirichlet and Neumann boundary conditions.     

Generalized 1D Jörgens theorem

We study the Cauchy problem for a 1D nonlinear wave equation on R. The nonlinearity can depend on the unknown function and its first order spatial derivative. Using the fixed point theorem we prove the existence of a classical solution. Moreover, the existence of periodic and almost periodic solutions are shown.     

Existence results of periodic solutions for third‐order nonlinear singular differential equation

Using Green's function for third‐order differential equation and some fixed‐point theorems, i.e., Leray‐Schauder alternative principle and Schauder's fixed point theorem, we establish three new existence results of periodic solutions for nonlinear third‐order singular differential equation, which extend and improve significantly existing results in the literature.     

奇异一阶周期系统正解的存在性

主要研究了具有奇异一阶周期系统正解的存在性,证明了一阶周期系统在点(x,y)=(0,0)处具有奇异性时,在一些合理的条件下,此问题正解的存在性.证明主要依赖非线性Leray-Schauder抉择定理和Krasnoselskii锥不动点定理,同时在证明过程中格林函数也起了非常重要的作用.     

Doubly periodic solutions of a coupled nonlinear telegraph system with weak singularities

In this paper, a weak force condition enables the achievement of new existence criteria for positive doubly periodic solutions of a nonlinear telegraph system through a basic application of Schauder’s fixed point theorem. A weak singularity will be useful to our proofs.     

The antipodal mapping theorem and difference equations in Banach spaces†

We employ the Borsuk–Krasnoselskii antipodal theorem to prove a new fixed point theorem in ordered Banach spaces. Then, the applicability of the result is shown by presenting sufficient conditions for the existence of solutions to initial value problems for first-order difference equations in Banach spaces. To prove that result we shall employ set valued analysis techniques.     

Existence of a time periodic solution for the compressible Euler equation with a time periodic outer force

We are concerned with a time periodic supersonic flow through a bounded interval. This motion is described by the compressible Euler equation with a time periodic outer force. Our goal in this paper is to prove the existence of a time periodic solution. Although this is a fundamental problem for other equations, it has not been received much attention for the system of conservation laws until now.When we prove the existence of the time periodic solution, we face with two problems. One is to prove that initial data and the corresponding solutions after one period are contained in the same bounded set. To overcome this, we employ the generalized invariant region, which depends on the space variables. This enable us to investigate the behavior of solutions in detail. Second is to construct a continuous map. We apply a fixed point theorem to the map from initial data to solutions after one period. Then, the map needs to be continuous. To construct this, we introduce the modified Lax–Friedrichs scheme, which has a recurrence formula consisting of discretized approximate solutions. The formula yields the desired map. Moreover, the invariant region grantees that it maps a compact convex set to itself. In virtue of the fixed point theorem, we can prove a existence of a fixed point, which represents a time periodic solution. Finally, we apply the compensated compactness framework to prove the convergence of our approximate solutions.     

The time-periodic solution for a 2D dissipative Klein-Gordon equation

In this paper, we study a 2D dissipative Klein-Gordon equation with periodic boundary condition. The existence and uniqueness of a time-periodic solution is proved by the Galerkin method and Leray-Schauder fixed point theorem.     

Banach空间一类非线性积分微分方程解的存在性

本文利用Ｍ?ｎｃｈ不动点定理研究了Ｅａｎａｃｈ空间中一类非线性积分微分方程解的存在性,给出的结论改进、推广了［１－２］中的结果．     

偏距离空间上四个映射的公共不动点的存在性与唯一性

该文证明了偏距离空间上满足广义非线性压缩型的四个映射的公共不动点定理.最后,举例说明了该文压缩条件确实改进了目前一些文献中压缩条件.     

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.     

Multiplicity results of fourth-order singular nonlinear differential equation with a parameter

In this paper, we investigate a class of fourth-order singular nonlinear differential equation with superlinearity or sublinearity assumptions at infinity for an appropriately chosen parameter. By applications of Green''s function and the Krasnoselskii fixed point theorem, sufficient conditions for the existence of positive periodic solutions are established.     

Multiplicity results of positive solutions for fourth‐order nonlinear differential equation with singularity

By application of Green's function and some fixed‐point theorems, that is, Leray–Schauder alternative principle and Schauder's fixed‐point theorem, we establish two new existence results of positive periodic solutions for nonlinear fourth‐order singular differential equation, which extend and improve significantly existing results in the literature. Copyright © 2015 John Wiley & Sons, Ltd.     

电报方程双周期解的极大值原理与强正性估计及应用

本文讨论非线性电报方程u_(tt)-u_(xx)+cu_t=F(t,x,u),(t,x)∈R~2时空双2π周期解的存在性。改进了Ortega与Robles-Perez关于线性电报方程双周期解的极大值原理,应用新获得的极大值原理,推广了相应的上下解定理,并且加强了极大值原理的结论,建立了线性方程解的强正性估计,利用这个强正性估计及锥上的不动点定理获得了超线性电报方程及奇异电报方程正双周期解的存在性。     

Formation of singularities for wave equations including the nonlinear vibrating string

Under very general assumptions, the authors prove that smooth solutions of quasilinear wave equations with small-amplitude periodic initial data always develop singularities in the second derivatives in finite time. One consequence of these results is the fact that all solutions of the classical nonlinear vibrating string equation satisfying either Dirichlet or Neumann boundary conditions and with sufficiently small nontriviai initial data necessarily develop singularities. In particular, there are no nontrivial smooth small-amplitude time-periodic solutions.     

非自治时滞微分方程正周期解的存在性

应用Krasnoselskii锥映射不动点定理，研究了具一般时滞非线性非自治Logistic方程的ω-周期解的存在性，获得了存在正周期解的充分条件．