Liénard方程极限环的存在唯一性定理

本文研究 Lienard方程 x+f(x)x+g(x)=0.建立了方程(1)存在极限环或极限环唯一的若干充分条件,改进了文[2-6]等的结果。     

Thirty million year deep-sea records in the South China Sea

In the spring of 1999 the Ocean Drilling Program (ODP) Leg 184 Shipboard Party cored 17 holes at 6 deep water sites in the northern and southern parts of the South China Sea (SCS). Chinese scientists actively participated in the entire process of this first deep-sea drilling leg off China, from proposal to post-cruise studies. More than 30 categories of analyses have been conducted post-cruise in various Chinese laboratories on a large number of core samples, and the total number of analyses exceeded 60 thousand.The major scientific achievements of the Leg 184 studies are briefly reported in three successive papers, with the first one presented here dealing with deep-sea stratigraphy and evolution of climate cycles. This ODP leg has established the best deep-sea stratigraphic sequences in the Western Pacific: the 23-Ma isotope sequence from the Dong-Sha area is unique worldwide because of its continuity; the last 5-Ma sequence from the Nansha area represents one of the best 4 ODP sites worldwide with the highest time-resolution for that time interval, and the sequences of physical properties enable a decadal-scale time resolution. All these together have provided for the first time high-quality marine records for paleoenvi-ronmental studies in the Asian-Pacific region. This new set of stratigraphic records has revealed changes in climate cyclicity over the last 20 Ma with the fluctuating power of the 100 ka, 400 ka, 2000 ka eccentricity cycles, indicating the evolving response of the climate system to orbital forcing along with the growth of the Antarctic and Northern Hemisphere ice sheets.     

一类两种群食饵-捕食者系统极限环的存在性

研究了一类具有Ivlev型功能反应的两种群食饵-捕食者系统的极限环的存在性和唯一性．应用微分方程的稳定性理论对该系统的正奇点进行分析，得到了该系统存在极限环的一个充分条件及该系统存在唯一极限环的一个充分条件．     

一类捕食者-被捕食者种群模型的Hopf分支问题

利用常微分方程的定性理论,讨论了2个种群具有非线性密度制约的捕食-被捕食者系统:(dx)/(dx)=b0x(b1 b2x-b3x2)-b4xy,(dy)/(dt)=-cy (ax-βy)y的平衡点和极限环的问题,证明了当系统的参数有如下关系时a2=(2k-1) (1-2a1-2k)/(x4),系统存在Hopf分支.同时证明了由Hopf分支所产生的周期解的稳定性.     

细菌培养模型极限环的唯一性

分析了一类细菌培养模型,证明了在一定参数范围内极限环是唯一的。     

Working Within Organizational Cycles—A More Suitable Way to Manage Action Research Projects in Large Organizations?

This article proposes that action research projects in a large business context may need to fit within organizational funding and political cycles. It outlines some of the problems that may occur in attempting to implement an action research project in a large organization. It gives a case study of such a project that aimed to introduce a systemic human resource strategy to bring about organizational cultural change. Part way through the completion of the project the cycle changed, funds were cut, and the project was abolished, although significant portions of it had been implemented and other parts were later reestablished. The article establishes a link to punctuated equilibrium theory in exploring the political and funding cycles that influenced the decision to cut funding. It considers whether this could have been foreseen, and gives some recommendations for future action research projects.     

HOPF分叉定理在非线性振荡电路中的应用

利用李雅普诺夫函数推导的HOPF分叉定理时域型式中的综合参数－曲率系数a0和其二维系统中的局部型式来分析二阶自治非线性电路中的振荡问题。通过列出电路的状态方程计算其雅可比矩阵共轭复数特征值和求出曲率系数，并判别系统是否具有稳定的极限环来判断电路是否会出现自激振荡，从而为电子线路的振荡分析提供一种新的分析方法。     

插电式混合动力汽车能耗及其影响因素分析

通过建立插电式混合动力汽车(plug-in hybrid electric vehicle,PHEV)的前向仿真模型,对其能耗进行仿真,并分析PHEV能耗的使用影响因素.基于Modelica物理建模语言,搭建PHEV整车动力传动及纵向动力学模型,并在标准测试工况下仿真整车各部分能耗变化.针对影响PHEV能耗的使用因素,重点仿真分析表征行驶工况的平均车速和驾驶激进性对电量消耗(charge deplete,CD)阶段电耗和电量保持(charge sustain,CS)阶段油耗的影响规律.通过分析不同车速与驾驶激进性下各部分能耗以及动力部件工作效率的影响,揭示了行驶工况对能耗影响规律的内在机理.     

严酷水环境下胶-混凝土界面黏结性能

为了研究胶-混凝土界面黏结性能在严酷水环境下的劣化规律,设计了胶-混凝土黏结试件在泡淡水、泡淡水与持续荷载耦合以及冻融循环3种环境下的劣化试验。试验方案同时考虑了2种混凝土强度和2种界面胶黏剂,共制作了100个试件。在劣化处理后,对试件进行四点弯曲试验,实测了不同劣化时长下试件的破坏荷载、破坏形态和荷载-位移曲线。在此基础上,分析了胶-混凝土界面黏结性能的劣化规律。试验结果表明:淡水环境对胶-混凝土界面的影响可忽略不计;淡水与持续荷载耦合环境的劣化作用较为明显,42 d后试件的最大承载力的下降可达41.2%;冻融循环的劣化作用在循环次数25次时不明显,但当循环次数达到50次后,试件最大承载力的下降可达28.3%;各种劣化环境下试件的破坏形态均为胶-混凝土混合破坏;荷载-位移曲线表明胶-混凝土混合破坏属于脆性破坏。     

Entransy dissipation and irreversibility of some thermodynamic processes

The relationship between entransy dissipation and the irreversibility of some thermodynamic processes, such as heat transfer, work-heat conversion, free expansion, isothermal diffusion etc., are analyzed in this paper. The results show that there is entropy generation but no entransy dissipation in irreversible work-heat conversion, free expansion and isothermal diffusion. Therefore, entransy dissipation cannot be used to describe the irreversibility of these processes. Both entropy generation and entransy dissipation exist in heat transfer process, which indicates that the entransy dissipation can be used to describe the irreversibility of heat transfer processes. Furthermore, the irreversibility of endoreversible cycles is analyzed. As all the irreversibility in endoreversible cycles is attributed to heat transfer between the heat sources and the working medium, entransy dissipation can be used to describe the irreversibility of this kind of cycles. To verify this conclusion, numerical examples of the endoreversible Carnot cycle are discussed.