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排序方式: 共有127条查询结果,搜索用时 62 毫秒
81.
In this paper, we study the relationship between exponential dichotomy and quadratic Lyapunov function for the linear equation x△=A(t)x on time scales. Moreover, for the nonlinear perturbed equation x△= A(t)x + f(t, x) we give the instability of the zero solution when f is sufficiently small. 相似文献
82.
Zhenjie Liu 《逼近论及其应用》2009,(4):369-380
This paper investigates the existence of periodic solutions of a three-species food-chain diffusive system with Beddington-DeAngelis functional responses and time delays in a two-patch environment on time scales. By using a continuation theorem based on coincidence degree theory, we obtain sufficient criteria for the existence of periodic solutions for the system. Moreover, when the time scale T is chosen as R or Z, the existence of the periodic solutions of the corresponding continuous and discrete models follows. Therefore, the method is unified to provide the existence of the desired solutions for continuous differential equations and discrete difference equations. 相似文献
83.
84.
In this paper, competitive neural networks with time-varying and distributed delays are investigated. By utilizing Lyapunov functional methods, the global exponential stability of periodic solutions of the neural networks is discussed on time scales. In addition, an example is given to illustrate the effectiveness of the theoretical results. 相似文献
85.
86.
On the horizontal distribution of algal-bloom in Chaohu Lake and its formation process 总被引:2,自引:0,他引:2
Based on the remote sensing images of algae, the present work analyzes the horizontal distribution characteristics of algal blooms in Chaohu Lake, China, which also reveals the frequency of algal blooms under different wind directions. Further, an unstructured-grid, three-dimensional finite-volume coastal ocean model (FVCOM) is applied to investigate the wind-induced currents and the transport pro- cess to explain the reason why algal blooms occur at the detected places. We first deduce the primary distribution of biomass from overlaid satellite images, and explain the formation mechanism by analyzing the pollution sources, and simulating the flow field and transportation process under prevailing wind over Chaohu Lake. And then, we consider the adjustment action of the wind on the corresponding day and develop a two-time scale approach to describe the whole formation process of algae horizontal distribution in Chaohu Lake. That is, on the longer time scale, i.e., during bloom season, prevailing wind determines the primary distribution of biomass by inducing the characteristic flow field; on the shorter time scale, i.e., on the day when bloom occurs, the wind force adjusts the primary distribution of biomass to form the final distribution of algal bloom. 相似文献
87.
齿轮副中的齿距偏差等短周期误差使系统出现复杂的周期运动, 影响齿轮传动的平稳性. 将该类复杂周期运动定义为近周期运动, 采用多时间尺度Poincaré映射截面对其进行辨识. 为研究齿轮副的近周期运动, 引入含齿距偏差的直齿轮副非线性动力学模型, 并计入齿侧间隙与时变重合度等参数. 采用变步长4阶Runge-Kutta法数值求解动力学方程, 由所提出的辨识方法分析不同参数影响下系统的近周期运动. 根据改进胞映射法计算系统的吸引域, 结合多初值分岔图、吸引域图与分岔树状图等研究了系统随扭矩与啮合频率变化的多稳态近周期运动. 研究结果表明, 齿轮副中的短周期误差导致系统的周期运动变复杂, 在微观时间尺度内, 系统的Poincaré映射点数呈现为点簇形式, 系统的点簇数与实际运动周期数为宏观时间尺度的Poincaré映射点数. 短周期误差导致系统在微观时间尺度内的吸引子数量增多, 使系统运动转迁过程变复杂. 合理的参数范围及初值范围可提高齿轮传动的平稳性. 该辨识与分析方法可为非线性系统中的近周期运动研究奠定理论基础. 相似文献
88.
In this paper, we axe interested in the existence of three positive solutions to a BVP for p-Laplacian impulsive functional dynamic equations on a time scale. Using the five-functional fixed theory, we establish a Banach space and an appropriate operator. In this paper, we combine the delta-nabla p-Laplacian BVP with impulsive functional dynamic equations, and obtain some new sufficient conditions for the existence of three positive solutions to the BVP, and our result here generalizes the previous related results. 相似文献
89.
This paper deals with the boundedness of the solutions of the following dynamic equations(r(t)x△(t))△+a(t)f(xσ(t))+b(t)g(xσ(t))=0and(r(t)x△(t))△+a(t)xσ(t)+b(t)f(x(t-τ(t)))=e(t)on a time scale T.By using the Bellman integral inequality,we establish some suffcient conditions for boundedness of solutions of the above equations.Our results not only unify the boundedness results for differential and difference equations but are also new for the q-difference equations. 相似文献
90.
预混火焰界面的RM(Richtmyer-Meshkov)不稳定现象在自然界和工程实践中十分常见,但目前关于反应性RM不稳定的研究主要集中于均匀介质的情况,而实际中的预混气体往往是非均匀的,因此开展非均匀介质中火焰界面演化和混合特性的研究十分必要。采用带单步化学反应的Navier-Stokes方程和高精度数值格式,研究了预混火焰界面在入射激波及反射激波作用下的RM不稳定过程,考察了化学反应活性以及介质非均匀性对RM不稳定过程中火焰界面混合特性的变化规律的影响。结果表明,在入射激波作用后的阶段,在均匀介质中的火焰界面形态呈现典型的"钉-帽-泡"结构,化学反应活性越强,界面的"泡"结构和"钉-帽"结构增长越快;而在非均匀介质中,火焰界面形态则呈现"钉-钉"结构,界面在流向速度差的诱导下被更大程度地拉伸。在第一次反射激波作用后的阶段,混合区的增长速率不依赖于反应活性和均匀性,仅与流动特性有关。时间尺度的研究表明,大尺度流动是反应性RM不稳定的主导因素,其次是化学反应,最后是小尺度混合,化学反应的强化会抑制大尺度流动,非均匀性会强化大尺度流动。 相似文献