几类凝聚图的轮廓

设Ｇ是个图，｜Ｖ（Ｇ）＝ｎ｜对Ｇ上的任一个标号ｆ：Ｖ（Ｇ）→｛１，…，ｎ｝记，且当ｊ≠ｉ时，Ｇ中有边以ｆ（－１）（ｊ）及ｆ（－１）（ｉ）为两端点｝）．称Ｐ（Ｇ）＝ｍｉｎ｛Ｐ（ｆ）：ｆ是Ｇ上的标号｝为图Ｇ的轮廓．对以Ｗ表示Ｇ中Ｗ的边界．本文证明：ｉ）若Ｇ是凝聚图，ｆ及ｆ是Ｇ上一对互逆标号，则Ｐ（Ｇ）＝Ｐ（ｆ）的充要条件是ｆ为凝聚标号，且此时若Ｇ，Ｈ均是凝聚图，则存在阶梯标号。使得路、回、完全留之间的下列乘积图也是凝聚图，且其轮廓为     

一类摄动系统的Poincaré分叉与极限环

本文利用临界情形的隐函数存在定理讨论了一类摄动系统分支周期解的存在性与稳定性,利用后继函数法讨论了该系统极限环的存在性、唯一性和稳定性。     

平面多项式系统及其相伴系统

引进平面多项式系统的相伴系统的概念 ,分析了多项式系统与其相伴系统之间在极限环不存在性 ,唯一性 ,中心焦点的判定等问题上的相似之处和不同之处 ,提出了几个公开问题 .     

一类Lyness方程的一些性质

本文主要研究下列Lyness方程的性质Xn+1=Xn\(a+b0Xn+b1Xn-1+…+bkXn-k)Xn-k-1,n=0,1,2,…,其中a,b0,b,…,bk∈[0,∞),a+k∑i=0bi＞0,k∈{0,1,2,…}.文中给出了方程(*)严格振动的充分条件,以及环长和环上极值的位置.另外,还得到了方程(*)在特殊情况下分别具有4,5,6周期的必要充分条件.本文的结果改进并推广了一些已知结果.     

机器维修的排序问题

研究了机器维修的排序问题,假设第i台机器的维修起始日期为第αi天(i=1,2,…,n)．n台机器的维修起始日期简记为(α1,α2,…,αn),得到一系列(α1,α2,…,αn)存在的充分或必要条件。     

利用LNG冷(火用)的准零CO2排放循环探析

本文研究利用LNG冷(火用)来完善燃用它的热机性能,既提高了效率,又能回收用LNG燃料热机的唯一主要排放-CO2.这种系统的温度区间横跨大气温度,会有很多新的特点值得探索.作为前期研究,本文建议了两种新循环,分别基于Brayton循环与超临界Rankine循环,且分别适用于LNG超临界及亚临界汽化过程.文中对此两种循环进行了分析计算与讨论,说明建议是可行的,热机效率可达60%以上,且同时基本回收所有燃烧产生的CO2.     

Limit cycles and invariant cylinders for a class of continuous and discontinuous vector field in dimention 2n

The subject of this paper concerns with the bifurcation of limit cycles and invariant cylinders from a global center of a linear differential system in dimension 2n perturbed inside a class of continuous and discontinuous piecewise linear differential systems. Our main results show that at most one limit cycle and at most one invariant cylinder can bifurcate using the expansion of the displacement function up to first order with respect to a small parameter. This upper bound is reached. For proving these results we use the averaging theory in a form where the differentiability of the system is not needed.     

New types of 3-D systems of quadratic differential equations with chaotic dynamics based on Ricker discrete population model

The wide class of 3-D autonomous systems of quadratic differential equations, in each of which either there is a couple of coexisting limit cycles or there is a couple of coexisting chaotic attractors, is found. In the second case the couple consists of either Lorentz-type attractor and another attractor of a new type or two Lorentz-type attractors. It is shown that the chaotic behavior of any system of the indicated class can be described by the Ricker discrete population model: z_i+1 = z_i exp(r − z_i), r > 0, z_i > 0, i = 0, 1, … . The values of parameters, at which in the 3-D system appears either the couple of limit cycles or the couple of chaotic attractors, or only one limit cycle, or only one sphere-shaped chaotic attractor, are indicated. Examples are given.     

摩擦对空气标准Diesel循环功率效率特性的影响

1前言自Novikov（1957），Chambadait1957）和Curzon－Ahlborn（1975）将传热过程引入卡诺热机循环研究，开创有限时间热力学理论后，截止96年9月已有八百余篇有关文献发表，包括专著七部，有关进展见综述文献＞3I。对mesel循环的有限时间热力学分析也已取得了一些进展。Hoffman等N用最优控制理论优化Diesel循环的活塞运动规律，AIZ。nblld等和本文作者将活塞式加热气缸中活塞最优运动规律用到了内燃机循环分析中；Orlov等导出了内燃机的功率效率极限，Klein，Blank等和本文作者问考虑了传热对Diesel循环特性的影响。除了热漏（传热）…     

Pulsed microwave damage trend of bipolar transistor as a function of pulse parameters

In the present paper we conduct a theoretical study of the thermal accumulation effect of a typical bipolar transistor caused by high power pulsed microwave (HPM), and investigate the thermal accumulation effect as a function of pulse repetition frequency (PRF) and duty cycle. A study of the damage mechanism of the device is carried out from the variation analysis of the distribution of the electric field and the current density. The result shows that the accumulation temperature increases with PRF increasing and the threshold for the transistor is about 2 kHz. The response of the peak temperature induced by the injected single pulses indicates that the falling time is much longer than the rising time. Adopting the fitting method, the relationship between the peak temperature and the time during the rising edge and that between the peak temperature and the time during the falling edge are obtained. Moreover, the accumulation temperature decreases with duty cycle increasing for a certain mean power.