具有密度依赖的生育脉冲单种群阶段结构模型

给出具有密度依赖生育脉冲单种群阶段结构数学模型．通过研究其频闪映射所确定的离散动力系统,获得了具有生育脉冲的系统存在周期解及其稳定的阈值,当系统的参数超过阈值,存在一系列的分支并最终走向混沌,这说明生育脉冲使系统动力学行为变得非常复杂,提供了一个自然的周期,而使系统从倍周期分支到混沌．     

具瞬时脉冲接种与非瞬时脉冲接种效应的一类新的SIR传染病模型研究

本文研究了瞬时脉冲接种与非瞬时脉冲接种效应的SIR传染病模型的问题.利用频闪映射和Floquet定理以及脉冲微分方程理论的方法,获得了模型无病周期解的存在性和疫苗接种的控制阈值的结果,推广了瞬时脉冲接种率与非瞬时脉冲接种区间长度对疾病灭绝起着重要作用的结论,为实际传染病控制提供了可靠的策略支持.     

污染喀斯特环境下具瞬时与非瞬时脉冲效应的单种群动力学模型

建立污染喀斯特环境下具瞬时与非瞬时脉冲效应的单种群动力学模型.利用脉冲微分方程理论,得到系统种群持续生存的控制阈值.研究结果表明瞬时脉冲收获量与非瞬时脉冲收获区间长度对于系统种群持久起着重要作用,结论为现实的生物资源管理提供了可靠的策略支持.     

基于四种改进阈值的小波去噪方法

本文提出了四种改进的阈值函数,并且在理论上证明了这四种改进的阈值函数对脉冲噪声都是有效的.仿真实验显示:无论是信噪比还是最小平方误差,改进的软阈值函数比其它三种改进的阈值函数的效果都要好一些.     

具有饱和接触率和垂直传染的SIRS传染病模型分岔分析

研究了一类具有饱和发生率、脉冲生育、脉冲接种和垂直传染的SIRS传染病模型的复杂动力学行为,首先构造了一个庞卡莱映射,然后利用映射的不动点及其特征值,得到了系统无病周期解的存在和稳定的条件,接着详细讨论了系统的跨临界分岔、超临界分岔和倍周期分岔现象,最后给出了能很好验证理论分析的数值结果.     

一种基于脉冲噪声的新型迭代滤波算法

在局部极值噪声检测和迭代中值滤波的基础上,基于图像结构和脉冲噪声的特征分析,有效结合局部极值检测和幅度差阈值、梯度差阈值的检测方法,提出了一种基于噪声检测的迭代脉冲噪声滤除算法.并通过仿真实验和算法评价,验证了该算法不仅能够达到很好的去噪效果,而且在保留图像细节信息方面也取得了一定的成效.     

一般脉冲系统的Melnikov函数构造方法及其应用

利用摄动法给出了一般脉冲系统Melnikov函数构造方法,得到脉冲信号作用下一般非线性系统Melnikov方法.为考察方法的有效性,将方法应用到脉冲信号作用下Duffing系统的混沌预测中去,通过方法得到脉冲信号作用下Duffing系统出现混沌的阈值曲线,数值实验结果验证理论结果的正确性.     

具常数输入及饱和发生率的脉冲接种SIQRS传染病模型

研究了具有常数输入及饱和发生率的脉冲接种SIQRS传染病模型,得到了疾病消除与否的阈值R_0=1.证明了当R_01时,系统存在全局渐近稳定的无病周期解;当R_01时,系统一致持久.     

自起振被动锁模掺Er3+光纤环形腔孤子激光器的实验研究 *

讨论了自起振掺Er³⁺光纤环形腔激光器产生飞秒光脉冲的机制及实验研究结果 .采用976nm半导体激光作为泵浦源 ,利用光纤的非线性偏振旋转效应 ,在掺Er³⁺光纤环形腔激光器中产生可饱和吸收体从而产生自幅度调制锁模机制 ,得到了完全自起振、稳定的锁模光脉冲 .输出最短光脉冲宽度 269 fs ,中心波长1.531 μm ,脉冲重复率21.37MHz ,激光器两个输出端输出的平均功率分别为0.25mW和0.08mW ,最低维持稳定锁模的阈值泵浦功率15mW .在高功率泵浦下 ,光纤激光器产生了稳定的高阶谐波锁模光脉冲 ,还研究了不同腔长、不同泵浦激光功率下锁模光脉冲宽度的变化等 .     

具有Beddington-DeAnglis功能反应和脉冲输入的恒化器模型

本文研究具有周期脉冲输入营养基和Beddington-DeAnglis功能反应捕食一食饵系统．通过分析营养基和食饵的子系统，获得系统的边界周期解．对边界周期解稳定性的分析，得到了捕食者侵入的阈值．     

A real-time methodology for minimizing mean flowtime in FMSs with routing flexibility: Threshold-based alternate routing

This paper presents an efficient continuous real-time routing strategy, namely threshold-based alternate routing (TAR), to minimize mean flowtime of parts in a FMS with routing flexibility. TAR routes parts to alternate machines instead of their primary machines when the benefit in terms of waiting time obtained from routing to an alternate machine exceeds a pre-determined threshold value. This study proposes that the threshold value for each manufacturing system is unique and presents a methodology for determining its unique value. The threshold concept and the performance of TAR in minimizing mean flowtime are tested with extensive experimentation, involving intricate experimental design. TAR provides very significant improvements in system performance measures compared to other real-time rerouting methods and shows that the threshold value is unique and dependent on system parameters for each manufacturing system. The relationship between the threshold value and system parameters has also been determined.     

Computing Approximating Automata for a Class of Hybrid Systems

This paper presents a new algorithm for generating finite-state automata models of hybrid systems in which the continuous-state dynamics can be switched when the continuous-state trajectory generates threshold events. The automata state transitions correspond to threshold events and the automata states correspond to portions of the threshold surfaces in the continuous state space. The hybrid system dynamics are approximated by the automata models in the sense that the languages of threshold event sequences generated by the automata contain the threshold event language for the hybrid system. Properties of the algorithm for constructing and refining the approximating automata are demonstrated and the application of approximating automata for system verification is illustrated for a switching controller for an inverted pendulum. Relationships to other approaches to hybrid system synthesis and verification are also discussed.     

Threshold dynamics for an HIV model in periodic environments

In this paper, we investigate an HIV model incorporating the effect of an ARV regimen. Since drug concentration varies during dose intervals, which results in periodic variation of the drug efficacy, our model is then a periodic time-dependent system. We get a threshold value between the extinction and the uniform persistence of the disease by applying the persistence theory. Our main results show that the disease goes to extinction if the threshold value is less than unity, whilst the disease persists if the threshold value is larger than unity. We also prove that there exists a positive periodic solution which is globally asymptotically stable. The threshold dynamics is in agreement with that for the system with constant coefficients, which extends the classic results for the corresponding autonomous model.     

Threshold of damped critical non-linear Schrödinger equation with fourth-order dispersion

This article is concerned with a damped critical non-linear Schrödinger equation with fourth-order dispersion which models propagation of fibre arrays in non-linear Kerr media. We analyse the effect of the damping force on the solution for the system and prove that there exists a threshold value of the damping parameter for global existence and blowup of the system. Furthermore, we estimate the threshold value.     

Existence of quasi-stationary states at the long range threshold

In this paper the lifetime of quasi-stationary states (QSS) in the α–HMF model are investigated at the long range threshold (α equals to one). It is found that QSS exist and have a diverging lifetime with system size which scales logaritmically with the number of constituents. This contrast to the exhibited power law below the long range threshold (α smaller than one) and the observed finite lifetime beyond. Also even beyond this long range threshold the long range nature of the system is displayed, namely the existence of a phase transition. As a consequence of our findings the definition of a long range system is discussed.     

Performance analysis and optimization of cognitive radio networks with retransmission control

In usual cognitive radio networks with buffer settings, secondary user packets that are interrupted by primary user packets will return to the SU buffer for later retransmission. But this may increase the average delay of the SU packets. In this paper, we propose a novel spectrum sharing strategy (SSS) to dynamically control the retransmission of the SU packets by introducing a returning threshold and a returning probability. This will simultaneously guarantee the Quality of Service for the SUs. In this SSS, when the transmission of an SU packet is interrupted, if the number of SU packets already in SU buffer reaches a returning threshold that is set in advance as a system parameter, an interrupted SU packet is admitted to return to the SU buffer with a dynamic returning probability. This returning probability is inversely proportional to the total number of packets in the system. Based on the SSS with retransmission control proposed in this paper, we build a discrete-time preemptive priority queueing model to comply with digital nature of modern networks. Accordingly, by presenting and analyzing a two-dimensional discrete-time Markov chain that represents the system state transition, we obtain the steady-state distribution of the system and then provide the formulas for several system performance measures. Moreover, with numerical results, we show the influence of the returning threshold on different performance measures. Finally, by building a net benefit function, we optimize the system performance for the returning threshold to balance different system performance measures.     

Threshold behaviour of a stochastic SIR model

In this paper, we investigate the threshold behaviour of a susceptible-infected-recovered (SIR) epidemic model with stochastic perturbation. When the noise is small, we show that the threshold determines the extinction and persistence of the epidemic. Compared with the corresponding deterministic system, this value is affected by white noise, which is less than the basic reproduction number of the deterministic system. On the other hand, we obtain that the large noise will also suppress the epidemic to prevail, which never happens in the deterministic system. These results are illustrated by computer simulations.     

Evaluating correct classification probability for weighted voting classifiers with plurality voting

Weighted voting classifiers (WVCs) consist of N units that each provide individual classification decisions. The entire system output is based on tallying the weighted votes for each decision and choosing the winning one (plurality voting) or one which has the total weight of supporting votes greater than some specified threshold (threshold voting). Each individual unit may abstain from voting. The entire system may also abstain from voting if no decision is ultimately winning. Existing methods of evaluating the correct classification probability (CCP) of WVCs can be applied to limited special cases of these systems (threshold voting) and impose some restrictions on their parameters. In this paper a method is suggested which allows the CCP of WVCs with both plurality and threshold voting to be exactly evaluated without imposing constraints on unit weights. The method is based on using the modified universal generating function technique.     

Optimal control of a production-inventory system with customer impatience

We consider the control of a production-inventory system with impatient customers. We show that the optimal policy can be described using two thresholds: a production base-stock level that determines when production takes place and an admission threshold that determines when orders should be accepted. We describe an algorithm for computing the performance of the system for any choice of base-stock level and admission threshold. In a numerical study, we compare the performance of the optimal policy against several other policies.