一类竞争扩散系统的定态分歧与稳定性

本文研究一类竞争扩散系统,在方程所描述的模型中,两个相互竞争的物种栖息在同一有界区域内,相互制约的项是Holling-Tanner型的,在齐次Dirichlet边界条件下,应用谱分析和分歧理论的方法,研究了非负定态解的分歧及其稳定性。     

具有饱和项的互惠系统的分歧与稳定性

运用谱分析和分歧理论的方法,在齐次Dirichlet边界条件下,对具有饱和项的互惠系统的非负定态解的分歧及其稳定性进行研究.一方面,分别以生长率作为分歧参数,讨论了发自半平凡解的分歧;另一方面,以两物种的生长率作为分歧参数,利用Liapunov-Schmidt过程,研究了在二重特征值处的分歧;同时判定了这些分歧解的稳定性.     

具有饱和与竞争项的捕食系统的全局分歧及稳定性

利用比较原理,分歧理论,特征值线性扰动理论,主要研究了一类具有饱和与竞争反应项的捕食-食饵系统在Dirichlet边界条件下的平衡态分歧解.首先给出了一个先验估计和局部分歧解存在的充分条件.然后对局部分歧解进行了全局延拓,得到了该系统平衡态的全局分歧解及其走向.最后讨论了局部分歧解的稳定性.     

带Ivlev反应项的捕食模型的全局分歧

在Dirichlet边界条件下研究一类带Ivlev反应项的捕食模型.利用谱分析和分歧理论的方法,证明了发自半平凡解的局部分歧正解的存在性,同时运用线性特征值扰动理论给出局部分歧解的稳定性.最后将局部分歧延拓为全局分歧,从而得到正解存在的充分条件.     

关于非线性方程的分歧问题

本文讨论非线性方程的分歧问题,给出了分歧点的一个充分条件,并研究分歧解的线性化稳定性。     

关于非线性方程的分歧问题

本文讨论非线性方程的分歧问题,给出了分歧点的一个充分条件,并研究分歧解的线性化稳定性。     

一类带Michaelis-Menten收获项的Holling-Ⅳ型捕食-食饵模型的定性分析

本文对一类带Michaelis-Menten收获项的Holling-Ⅳ型捕食-食饵模型进行了定性分析.首先,利用极值原理和线性稳定性理论,得到了平衡态方程解的先验估计和正常数解的局部渐近稳定性;然后,借助分歧理论,给出了以d2为分歧参数,平衡态方程在正常数解U_1处的局部分歧,证明了在一定条件下,(d_2~j,U_1)处产生的局部分歧可以延拓成全局分歧.     

双营养物的非均匀Chemostat模型解的性质

本文讨论双营养物的非均匀Chemostat模型解的性质.通过运用极值原理,上下解方法以及分歧理论得到了正平衡解的存在性,运用稳定性理论证明了正平衡解的稳定性.     

含两时滞捕食-被捕食系统的稳定性及分歧

本文研究一类含两相异时滞的捕食－被捕食系统的稳定性及分歧。首先，我们讨论两相异时滞对系统唯一正平衡点的稳定性的影响，通过对系数与时滞有关的特征方程的分析，建立了一种稳定性判别性。其次，将一个时滞看成分歧参数，而另一个看作固定参数，我们证明了该系统具有HOPF分歧特性。最后，我们讨论了分歧解的稳定性。     

一类交叉扩散系统的定态解的分歧分析及稳定性

利用Liapunov-Schmidt方法证明了一类交叉扩散系统的发自平凡解的非平凡正定态解的存在性,并利用谱分析方法得到关于这个分歧解的稳定性的一个条件。     

Stability radius of linear parameter-varying systems and applications

In this paper, we present a unifying approach to the problems of computing of stability radii of positive linear systems. First, we study stability radii of linear time-invariant parameter-varying differential systems. A formula for the complex stability radius under multi perturbations is given. Then, under hypotheses of positivity of the system matrices, we prove that the complex, real and positive stability radii of the system under multi perturbations (or affine perturbations) coincide and they are computed via simple formulae. As applications, we consider problems of computing of (strong) stability radii of linear time-invariant time-delay differential systems and computing of stability radii of positive linear functional differential equations under multi perturbations and affine perturbations. We show that for a class of positive linear time-delay differential systems, the stability radii of the system under multi perturbations (or affine perturbations) are equal to the strong stability radii. Next, we prove that the stability radii of a positive linear functional differential equation under multi perturbations (or affine perturbations) are equal to those of the associated linear time-invariant parameter-varying differential system. In particular, we get back some explicit formulas for these stability radii which are given recently in [P.H.A. Ngoc, Strong stability radii of positive linear time-delay systems, Internat. J. Robust Nonlinear Control 15 (2005) 459-472; P.H.A. Ngoc, N.K. Son, Stability radii of positive linear functional differential equations under multi perturbations, SIAM J. Control Optim. 43 (2005) 2278-2295]. Finally, we give two examples to illustrate the obtained results.     

Stability,stabilization and duality for linear time-varying systems

In this article, we study stability properties of linear continuous time-varying systems. Based on a time-varying version of the Lyapunov stability theorem, we obtain stabilizability, stability and duality properties of associated systems.     

On the pathwise exponential stability of non–linear stochastic partial differential equations

Sufficient conditions to get exponential stability for the sample paths (with probability one) of a non–linear monotone stochastic Partial Differential Equation are proved. In fact, we improve a stability criterion established in Chow [3] since, under the same hypotheses, we get pathwise exponential stability instead of stability of sample paths     

Generalizations of a theorem of Rolewicz

The aim of this article is to give a unified treatment for the theorems of Rolewicz and Neerven type for uniform exponential stability of evolution families. We obtain necessary and sufficient conditions for uniform exponential stability of evolution families, generalizing a stability theorem due to Rolewicz and we present a new proof for the Rolewicz theorem, based on the theory of Banach function spaces. Finally, we apply our results and we deduce a generalization for a classical stability theorem due to Przyluski and Rolewicz.     

Chain prolongation and chain stability

In this article we introduce chain prolongation, with which we define the concept of chain stability that takes an intermediate position between absolute stability and asymptotic stability. Two characterizations of chain stability are given, in terms of a Lyapunov function and a fundamental system of neighborhoods. As a matter of fact, a positively invariant compact set is chain stable if and only if it is a quasi-attracting set.     

带跳随机微分方程的Euler-Maruyama方法的几乎处处指数稳定性和矩稳定性

本文首先研究了一维带跳随机微分方程的指数稳定性,并证明Euler-Maruyama(EM)方法保持了解析解的稳定性.其次,研究了多维带跳随机微分方程的稳定性,证明若系数满足全局Lipchitz条件,则EM方法能够很好地保持解析解的几乎处处指数稳定性、均方指数稳定性.最后,给出算例来支持所得结论的正确性.     

Stability results involving time-averaged Lyapunov function derivatives

The stability results which comprise the Direct Method of Lyapunov involve the existence of auxiliary functions (Lyapunov functions) endowed with certain definiteness properties. Although the Direct Method is very general and powerful, it has some limitations: there are dynamical systems with known stability properties for which there do not exist Lyapunov functions which satisfy the hypotheses of a Lyapunov stability theorem.In the present paper we identify a scalar switched dynamical system whose equilibrium (at the origin) has known stability properties (e.g., uniform asymptotic stability) and we prove that there does not exist a Lyapunov function which satisfies any one of the Lyapunov stability theorems (e.g., the Lyapunov theorem for uniform asymptotic stability). Using this example as motivation, we establish stability results which eliminated some of the limitations of the Direct Method alluded to. These results involve time-averaged Lyapunov function derivatives (TALFD’s). We show that these results are amenable to the analysis of the same dynamical systems for which the Direct Method fails. Furthermore, and more importantly, we prove that the stability results involving TALFD’s are less conservative than the results which comprise the Direct Method (which henceforth, we refer to as the classical Lyapunov stability results).While we confine our presentation to continuous finite-dimensional dynamical systems, the results presented herein can readily be extended to arbitrary continuous dynamical systems defined on metric spaces. Furthermore, with appropriate modifications, stability results involving TALFD’s can be generalized to discontinuous dynamical systems (DDS).     

Robustness of strong stability of semigroups

In this paper we study the preservation of strong stability of strongly continuous semigroups on Hilbert spaces. In particular, we study a situation where the generator of the semigroup has a finite number of spectral points on the imaginary axis and the norm of its resolvent operator is polynomially bounded near these points. We characterize classes of perturbations preserving the strong stability of the semigroup. In addition, we improve recent results on preservation of polynomial stability of a semigroup under perturbations of its generator. Theoretic results are illustrated with an example where we consider the preservation of the strong stability of a multiplication semigroup.