有保护区的海洋渔业资源的临界稳定性分析

考虑一类渔业资源储量-捕捞力度模型,首先,本文运用中心流形定理确定系统的不动点在发生Flip分叉时的临界稳定性,然后,根据规范型理论确定系统的不动点在发生Neimark-Sacker分叉时的临界稳定性,最后,通过数值模拟验证了结论.     

具有初始缺陷弹性板的稳定性分析

本文以Marguerre方程为基础,用奇异性理论研究了初始挠度缺陷以及横向载荷对弹性板屈曲后分叉解的影响。借助于普适开折的原理,在单特征值局部邻域内将该问题的失稳分析转化为三次代数方程的讨论,从而确定出分叉解的性态。同时绘出了在不同参数下的分叉解文,讨论了几何缺陷和横向载荷对特征值的影响。     

有积分算子的非线性发展方程的空间周期分叉解及其稳定性*

本文研究比较一般的有积分算子的非线性发展方程的空间周期分叉解及稳定性问题。首先分别研究分叉解存在的必要条件和充分条件,然后用算子半群方法分析平衡解的稳定性,并讨论了稳定性交换原则。最后研究一个应用例子,对有指数型积分算子的情形得到具体结果。     

随机时滞神经网络系统指数稳定性的新判定准则(英文)

本文主要研究了一类随机时滞神经网络的稳定性条件.利用随机分析技巧和不动点原理,建立了一个关于随机时滞神经网络指数稳定性判定的新的准则.     

一类具有时滞的金融系统的稳定性

首先建立了一类具有时滞的金融模型,该模型以累计利润额为关键因素,接着以τ为参考元素研究了该模型的稳定性及Hopf分叉.发现当τ变化时,该系统的稳定性会发生变化,该模型会在某一确定值处出现Hopf分叉.最后用中心流形定理和规范型方法研究分叉周期解的稳定性.     

多自由度非线性振动系统的多频分叉

本文研究自治和非自治多目由度非线性振动系统当其线化系统有多个特征值同时经过虚轴时产生的多频分叉问题,提出了用于分析多频分叉问题的平均摄动解法,得到了在共振和非共振情形的多频分叉渐近摄动解和稳定性判据,我们还将本文方法用在分析机车轮对动力系统的Hopf分叉中和Van der PolDuffing耦合非线性振子的双频分叉中。     

扰动非线性Schr(o)dinger方程组的动力性态

研究具周期边界条件的扰动非线性Schrodinger方程组的动力性态,首先,在常值平面上用线性算子的谱对扰动和未扰动系统进行动力性态分析,然后利用奇异扰动理论和不动点原理证明局部不变流形的存在性.     

一类具时滞SIR传染病模型的动力行为

分析传染病模型的稳定性,并考虑到已感染者对易感染者的作用的时滞影响.文中首先在R_01时,构造一个Lyapunov泛函,证明了无病平衡点的全局渐近稳定性.当R_01时,证明了正平衡点的局部渐近稳定性和持久性.     

一类离散生态经济系统稳定性与分支研究

本文研究了一个离散生态经济模型的稳定性和分支问题.利用离散奇异系统理论,中心流形定理及Neimark-Sacker分支理论,得到了系统关于不动点的稳定性和Neimark-Sacker分支的有关结果,并与相应的连续模型进行对比分析.推广了文献[5]的结果.     

具有时空时滞的非局部扩散SIR模型的行波解

针对种群中的染病个体在疾病潜伏期内具有自由移动和传染疾病的现象,研究了一个具有时空时滞的非局部扩散SIR模型的行波解问题.利用基本再生数和最小波速判定行波解是否存在.首先,通过在有界区域上构造一个初始函数的不变锥,利用Schauder不动点定理证明在该锥上存在不动点,然后通过取极限的方法得到行波解的存在性.其次,利用双边Laplace(拉普拉斯)变换法证明了行波解的不存在性.由于行波解的最小传播速度对控制疾病传播具有重要的指导意义,最后讨论了非局部扩散、时滞等因素对最小波速的影响.     

A MODEL OF TROPICAL MARINE RESERVE‐FISHERY LINKAGES

ABSTRACT. The excessive and unsustainable exploitation of our marine resources has led to the promotion of marine reserves as a fisheries management tool. Marine reserves, areas in which fishing is restricted or prohibited, can offer opportunities for the recovery of exploited stock and fishery enhancement. In this paper we examine the contribution of fully protected tropical marine reserves to fishery enhancement by modeling marine reserve‐fishery linkages. The consequences of reserve establishment on the long‐run equilibrium fish biomass and fishery catch levels are evaluated. In contrast to earlier models this study highlights the roles of both adult (and juvenile) fish migration and larval dispersal between the reserve and fishing grounds by employing a spawner‐recruit model. Uniform larval dispersal, uniform larval retention and complete larval retention combined with zero, moderate and high fish migration scenarios are analyzed in turn. The numerical simulations are based on Mombasa Marine National Park, Kenya, a fully protected coral reef marine reserve comprising approximately 30% of former fishing grounds. Simulation results suggest that the establishment of a fully protected marine reserve will always lead to an increase in total fish biomass. If the fishery is moderately to heavily exploited, total fishery catch will be greater with the reserve in all scenarios of fish and larval movement. If the fishery faces low levels of exploitation, catches can be optimized without a reserve but with controlled fishing effort. With high fish migration from the reserve, catches are optimized with the reserve. The optimal area of the marine reserve depends on the exploitation rate in the neighboring fishing grounds. For example, if exploitation is maintained at 40%, the ‘optimal’ reserve size would be 10%. If the rate increases to 50%, then the reserve needs to be 30% of the management area in order to maximize catches. However, even in lower exploitation fisheries (below 40%), a small reserve (up to 20%) provides significantly higher gains in fish biomass than losses in catch. Marine reserves are a valuable fisheries management tool. To achieve maximum fishery benefits they should be complemented by fishing effort controls.     

Influence of prey reserve in a prey–predator fishery

The excessive and unsustainable exploitation of marine resources has to led to the promotion of marine reserve as a fisheries management tool. In this paper we study a prey–predator system in a two-patch environment: one accessible to both prey and predators (patch 1) and the other one being a refuge for the prey (patch 2). The prey refuge (patch 2) constitutes a reserve zone of prey and fishing is not permitted, while the unreserved zone area is an open-access fishery zone. The existence of possible steady states, along with their local and global stability, is discussed. We then examine the possibilities of the existence of bionomic equilibrium. An optimal harvesting policy is given using Pontryagin’s maximum principle.     

Stability Analysis for Discrete Biological Models Using Algebraic Methods

This paper is concerned with stability analysis of biological networks modeled as discrete and finite dynamical systems. We show how to use algebraic methods based on quantifier elimination, real solution classification and discriminant varieties to detect steady states and to analyze their stability and bifurcations for discrete dynamical systems. For finite dynamical systems, methods based on Gr?bner bases and triangular sets are applied to detect steady states. The feasibility of our approach is demonstrated by the analysis of stability and bifurcations of several discrete biological models using implementations of algebraic methods.     

Bifurcation from periodic solutions with spatiotemporal symmetry, including resonances and mode interactions

We study local bifurcation in equivariant dynamical systems from periodic solutions with a mixture of spatial and spatiotemporal symmetries.In previous work, we focused primarily on codimension one bifurcations. In this paper, we show that the techniques used in the codimension one analysis can be extended to understand also higher codimension bifurcations, including resonant bifurcations and mode interactions. In particular, we present a general reduction scheme by which we relate bifurcations from periodic solutions to bifurcations from fixed points of twisted equivariant diffeomorphisms, which in turn are linked via normal form theory to bifurcations from equilibria of equivariant vector fields.We also obtain a general theory for bifurcation from relative periodic solutions and we show how to incorporate time-reversal symmetries into our framework.     

Optimal harvesting of a Gompertz population model with a marine protected area and interval‐value biological parameters

To protect fishery populations on the verge of extinction and sustain the biodiversity of the marine ecosystem, marine protected areas (MPA) are established to provide a refuge for fishery resource. However, the influence of current harvesting policies on the MPA is still unclear, and precise information of the biological parameters has yet to be conducted. In this paper, we consider a bioeconomic Gompertz population model with interval‐value biological parameters in a 2‐patch environment: a free fishing zone (open‐access) and a protected zone (MPA) where fishing is strictly prohibited. First, the existence of the equilibrium is proved, and by virtue of Bendixson‐dulac Theorem, the global stability of the nontrivial steady state is obtained. Then, the optimal harvesting policy is established by using Pontryagin's maximum principle. Finally, the results are illustrated with the help of some numerical examples. Our results show that the current harvesting policy is advantageous to the protection efficiency of an MPA on local fish populations.     

Bifurcations of hyperbolic fixed points for explicit Runge-Kutta methods

Discretization of autonomous ordinary differential equationsby numerical methods might, for certain step sizes, generatesolution sequences not corresponding to the underlying flow—so-called‘spurious solutions’ or ‘ghost solutions’.In this paper we explain this phenomenon for the case of explicitRunge-Kutta methods by application of bifurcation theory fordiscrete dynamical systems. An important tool in our analysisis the domain of absolute stability, resulting from the applicationof the method to a linear test problem. We show that hyperbolicfixed points of the (nonlinear) differential equation are inheritedby the difference scheme induced by the numerical method whilethe stability type of these inherited genuine fixed points iscompletely determined by the method's domain of absolute stability.We prove that, for small step sizes, the inherited fixed pointsexhibit the correct stability type, and we compute the correspondinglimit step size. Moreover, we show in which way the bifurcationsoccurring at the limit step size are connected to the valuesof the stability function on the boundary of the domain of absolutestability, where we pay special attention to bifurcations leadingto spurious solutions. In order to explain a certain kind ofspurious fixed points which are not connected to the set ofgenuine fixed points, we interprete the domain of absolute stabilityas a Mandeibrot set and generalize this approach to nonlinearproblems.     

A two-patch model for the optimal management of a fishing resource considering a marine protected area

In this work, we propose and analyze a model related with the management optimization of a renewable resource in aquatic environment composed of two different patches. Spatial distribution of each subpopulation is assumed: one is developed in a marine protected area (MPA) or a marine reserve and the other is located in a zone where fishing with open access may be effected.It is generally assumed that there may be migration between both areas, but in this work we will consider that the flux goes.When a fishing ban in the protected area is established it becomes a marine reserve, which can also be assumed as a refuge for the captured species. In this case, the marine reserve is the source and the exploitation area is a sink.The behavior of the renewable resource is modeled by a deterministic continuous time system. To establish the optimal harvesting policy, we will maximize the present value J of a continuous time stream of revenues, given by a cost functional indicating the net economic revenue to the fishermen, the perceived rent. Using Pontragyn’s Maximum Principle we will obtain the Hamiltonian function to determine the optimal policies.     

EXOGENOUS SHOCKS AND MARINE RESERVES

Abstract The impact on the value of a fishery from exogenous shocks is investigated. Part of the habitat is protected by a marine reserve, while the remaining fishery is managed by optimal, total allowable catch quotas. Shocks of different, spatial nature and with different probability distributions are investigated. The results suggest that reserves are of minor interest as a management tool when shocks affect the stock uniformly. Reserves may substantially enhance the value of the fishery when shocks are nonuniformly spatially distributed.     

A dynamic Stackelberg duopoly model with different strategies

In this paper, a duopoly Stackelberg model of competition on output is formulated. The firms announce plan products sequentially in planning phase and act simultaneously in production phase. For the duopoly Stackelberg model, a nonlinear dynamical system which describes the time evolution with different strategies is analyzed. We present results on existence, stability and local bifurcations of the equilibrium points. Numerical simulations demonstrate that the system with varying model parameters may drive to chaos and the loss of stability may be caused by period doubling bifurcations. It is also shown that the state variables feedback and parameter variation method can be used to keep the system from instability and chaos.     

Stability criteria for a nonlinear nonautonomous system with delays

This paper further develops a method, originally introduced by Mori et al., for proving local stability of steady states in linear systems of delay differential equations. A nonlinear nonautonomous system of delay differential equations with several delays is considered. Explicit delay-independent sufficient conditions for global attractivity of the solutions with an extremely simple form are provided. The above-mentioned conditions make the stability test quite practical. We illustrate application of this test to the Hopfield neural network models. The results obtained were also applied to a new marine protected areas model with delay that describes the ecological linkage between the reserve and fishing ground.