一类中立型时滞系统周期运动的近似解

对一类中立型时滞系统在临界状态小扰动下的平衡点进行了稳定性分析,同时讨论了该系统在非线性扰动下的周期运动的近似解及稳定性.     

柔性约束下压杆的一些稳定和不稳定的临界状态

研究了一端固定、一端弹簧约束滑动固定的压杆在Euler临界载荷作用下的稳定性.将系统的势能表示为转角的泛函,将扰动量展开成Fourier级数,将势能的二阶变分表示成一个二次型,得到在临界状态下势能的二阶变分半正定,并求得临界载荷与屈曲模态.进一步研究临界状态下高阶变分的正定性,包括四阶和六阶变分的正定性.结果表明,与刚性约束不同的是,柔性约束压杆临界状态的稳定性与约束的刚度有关,有稳定与不稳定之分,并给出了临界状态是稳定和不稳定的情况下柔性约束相对刚度的范围.     

噪声和生存环境对捕食生态系统的影响

建立了可以描述自然生物生存环境复杂度的捕食生态系统的随机模型,并基于实验得到的系统参数研究了生存环境复杂程度和随机激励强度对两个物种的稳态概率分布,以及系统由非临界状态到临界状态的平均首次穿越时间的影响．在弱扰动假设下应用Stratonovich-Khasminskii随机平均原理分别得到了两个物种的稳态概率密度函数并采用Monte-Carlo对原系统模拟来验证理论求解的正确性．利用Pontryagin方程得到了系统由非临界状态到临界状态的平均首次穿越时间表达式.研究表明:1)生存环境越简单的生态系统越容易受到随机因素的影响;2)随机干扰强度越大生态系统越不稳定;3)系统的平均首次穿越时间随生存环境复杂度提高而变长;4)作用在食物自然生长率的随机激励对系统的平均首次穿越时间影响较大．     

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于一个具有历史相依临界状态的可维修n中取k:G系统, 论文给出了当系统平稳时它的可用度, 一个循环中的平均工作时间和平均失效时间. 并且和不具有年龄相依临界状态的可维修n中取k:G系统进行了比较.     

二维渗流最低水平开穿透的宽度

在二维渗流中,设rn是矩形[O,n]2的最低水平开穿透,令ξn=max｛y：（xy）∈rn｝．本文证明了在临界状态p＝pc时,存在常数0＜C1＜C2＜1,当n充分大时有存在,而在上临界状态p＞pc时,有存在］＝0.     

四阶抛物型方程在加权空间下临界状态的小初值问题

研究了一类四阶抛物型方程在加权的L~P空间下的小初值问题.应用Sobolev嵌入定理、Fourier分解和象征算子及压缩映射等方法,证明出了此类四阶抛物型方程在临界状态σ=4/n时,小初值解的存在唯一性和最优衰减估计,从而为图像处理奠定了理论基础.     

利用中介算子计算最小特征值的上、下界

1 引言 微分算子的最小特征值λ_1常被用来分析一些临界状态,如承重杆件的临界压力、振动现象中的临界频率。常见的Rayleigh-Riese法只能给出λ_1的上估计,然而更重要的是下估计,因为只有下估计才能给出避开临界状态的安全范围。 Euler幂法可以同时给出λ_1的上、下估计。它最初被用来计算Bessel函效的零点,最近被成功地用来计算常微分算子的最小特征值(见[3]、[4])。其基础是Euler不等式:     

一类具有临界状态的Athreya—Karlin BPRE.灭种概率的渐近行为

当随机环境为一有限状态平遍成Ｍａｒｋｏｖ链时，本文证明了总存在常数ｃ１，ｃ２〉０，使得一类含有临界状态的上临界Ａｔｈｒｅｙａ－Ｋａｒｌｉｎ ＢＰＲＥ随初始众数Ｋ无限增大时相应的灭种概率ｑｋ的负对数的变化恒介于ｃ１ｌｏｇｋ与ｃ２ｋ之间。     

含有界面裂纹的粘弹性层合板应变能释放率的计算

将裂纹扩展所对应的能量释放率定义为同一时刻,同样载荷条件下两种状态的能量之差.一是裂纹长度为a时,系统内能,第二状态是指裂纹长度为a+Δa时系统内能.这样,所定义的能量释放率相当于在无限短时间内,裂纹从a扩展到a+Δa所释放的能量.通过计算发现,对于给定的加载历史,应变能释放率是时间的函数,它的最大值相对应于层间开裂临界状态.在William工作的基础上,根据经典梁的理论求得双悬臂梁结构的应变能释放率的显函表达式.     

二维渗流中的最短开穿透

在二维边渗流模型中，设／ｒｎ／＝ｍｉｎ（／ｒ／：ｒ是正方形「０，ｎ」＾２的开穿透），这里／ｒ／表示ｒ的长度，本文证明了在上临界状态有ｌｉｍＥ／ｒｎ／／ｎ＝λ，在临界状态时，我们对Ｅ／ｎ／给出了上界，并对一个ｒｎｒｎ给出了Ｅ／ｒｎ／的下界。     

基于关键链改进搜索的遗传算法求解分布式多项目调度

针对基于多代理系统求解分布式多项目调度问题的不足, 开发了一种适应性的遗传算法ccm_GA。ccm_GA的独特性体现为两点:第一, 修正的串行调度过程分两个阶段分别消除全局资源和本地资源冲突; 第二, 在满足两类资源约束的调度方案中, 识别出关键链并改变关键活动在活动序列编码中的位置以增加解的多样性从而提高搜索效率。设计并实施大规模数值实验测试算法性能, 与现有文献中的六种算法作对比, 结果表明:ccm_GA在50%的算例集上获得的测试指标都好于六种算法, 且对于资源约束越紧的算例集, ccm_GA的求解效果越好。     

中国建筑产业链两阶段综合效率、纯技术效率、规模效率及其影响因素

目前从建筑产业链角度对建筑产业效率问题的研究并不多。据此,本研究通过梳理相关文献,识别出建筑产业链的两个关键环节:工程咨询阶段和工程施工阶段;根据筛选的建筑产业链投入、产出指标,利用链式关联网络DEA模型测算2014~2015年中国各省份建筑产业链两阶段的综合效率、纯技术效率与规模效率;利用Tobit模型确定影响三种效率的关键因素,以此实现对建筑产业链两阶段生产资源的优化与整合,更期待为客观度量产业链两阶段生产效率的研究提供新思路与方法。研究发现,综合效率普遍偏低且各省份之间差距较大,其主要原因是纯技术效率偏低且省份之间差异大;三种效率的主要影响因素及其作用程度不尽相同。在此基础上提出相应的对策建议以促进中国建筑业生产效率的提高。     

Structure of multi-criteria decision-making

Multi-criteria decision-making (MCDM) is presented as an eight-stage process of shaping information that satisfies the following criteria. The information should be accessible, differentiable, abstractable, understandable, verifiable, measurable, refinable and usable. For some stages, the decision-advisor should emphasize doing the stage convincingly by carrying out first its technical aspects, then relating to the context of the problem, and finally by taking into account the particular situation of the decision. For others, the decision-advisor should emphasize evincing information from the decision-maker first by relating to the situation of the decision, then seeing it in its context, and finally in its technical aspects. Methods for supporting the first four stages are shown to be personal construct theory for accessing the information, grounded theory for differentiating clusters of constructs, critical realism for abstracting their real meaning, and Nomology to understand how they fit into the criteria tree. An illustration is given.     

弹性介质中受轴向冲击载荷作用的圆柱壳的屈曲临界载荷计算分析

建立并求解了弹性介质中圆柱壳的径向位移控制方程,考虑边界条件及相容条件,得到了应力波传播及反射过程中圆柱壳的动力屈曲分叉条件.通过计算得到了不同时间段屈曲临界载荷与应力波波阵面到达圆柱壳的位置、弹性介质的刚度、壳体未嵌入弹性介质部分的长度与总长之比的关系.数值计算结果表明,弹性介质中的圆柱壳发生轴对称屈曲和非轴对称屈曲趋势一致;嵌入弹性介质部分越深、弹性介质刚度越大圆柱壳越难屈曲;屈曲临界载荷随着弹性介质刚度的增大经历了增长缓慢、增长迅速以及增长较慢3个阶段;应力波反射前波阵面通过分界面后,屈曲仅发生在应力波传播区域,反射波波阵面通过分界面前,临界载荷较小时屈曲先发生在反射端部,随着轴向阶数增大,屈曲覆盖整个圆柱壳区域,反射波波阵面通过分界面后,壳体发生的屈曲始终覆盖整个圆柱壳区域.     

Progressive hedging innovations for a class of stochastic mixed-integer resource allocation problems

Numerous planning problems can be formulated as multi-stage stochastic programs and many possess key discrete (integer) decision variables in one or more of the stages. Progressive hedging (PH) is a scenario-based decomposition technique that can be leveraged to solve such problems. Originally devised for problems possessing only continuous variables, PH has been successfully applied as a heuristic to solve multi-stage stochastic programs with integer variables. However, a variety of critical issues arise in practice when implementing PH for the discrete case, especially in the context of very difficult or large-scale mixed-integer problems. Failure to address these issues properly results in either non-convergence of the heuristic or unacceptably long run-times. We investigate these issues and describe algorithmic innovations in the context of a broad class of scenario-based resource allocation problem in which decision variables represent resources available at a cost and constraints enforce the need for sufficient combinations of resources. The necessity and efficacy of our techniques is empirically assessed on a two-stage stochastic network flow problem with integer variables in both stages.     

Supply chain scheduling: Sequence coordination

A critical issue in supply chain management is coordinating the decisions made by decision makers at different stages, for example a supplier and one or several manufacturers. We model this issue by assuming that both the supplier and each manufacturer have an ideal schedule, determined by their own costs and constraints. An interchange cost is incurred by the supplier or a manufacturer whenever the relative order of two jobs in its actual schedule is different from that in its ideal schedule. An intermediate storage buffer is available to resequence the jobs between the two stages. We consider the problems of finding an optimal supplier's schedule, an optimal manufacturer's schedule, and optimal schedules for both. The objective functions we consider are the minimization of total interchange cost, and of total interchange plus buffer storage cost. We describe efficient algorithms for all the supplier's and manufacturers’ problems, as well as for a special case of the joint scheduling problem. The running time of these algorithms is polynomial in both the number of jobs and the number of manufacturers. Finally, we identify conditions under which cooperation between the supplier and a manufacturer reduces their total cost.     

An integrated approach for supplier selection in multi-item/multi-supplier environment

One of the important stages in supply chain management which regards all the activities from the purchasing of raw material to final delivery of the product is the supplier selection process. Since it is the first stage of the supply chain management, it is a critical process affecting the consecutive stages. It is simply desired to select the best supplier for a specific product. But since there are a lot of criteria and alternatives to be considered, numerous decision making models have been proposed to provide a solution to this problem. Within this study, an integrated approach including fuzzy Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) and a mixed integer linear programming model is developed to select the best supplier in a multi-item/multi-supplier environment. The importance value of each supplier with respect to each product is obtained via fuzzy TOPSIS in the first stage. Then in the second stage, these values are used as an input in the mathematical model which determines the suppliers and the quantities of products to be provided from the related suppliers. So as to validate the proposed methodology, an application is performed in air filter sector.     

Mathematical modeling of the first phase of morphogenesis of mechanoreceptors in <Emphasis Type="Italic">D. melanogaster</Emphasis>

The mechanoreceptors (in particular, macrochaetes) of drosophila pass three stages in its development (morphogenesis) whose genetic support is described in terms of gene networks. The key object of the gene networks of macrochaete morphogenesis is the achaete-scute (AS-C) complex of genes. Each mechanoreceptor develops from one parent cell distinguished by high concentration of the AS-C protein. The activity of this complex, which ensures the protein concentration critical for initiating morphogenesis, is determined by the central regulatory contour which includes a system of interactions among certain objects of the networks (genes and their products).     

Experimental investigation of low cycle fatigue of metallized polyethylene terephthalate films

Conclusion The destruction of the coating of a loaded metallized film is a process that includes the stages of formation of point defects, formation and development of a network of cracks. In proportion to the increase of the load or of the number of load cycles the density of the network of cracks increases. When an element of the network has attained the critical dimension, crumbling ceases. Measurement of the light transmission is an effective method of investigating the damage to metallized films, even if they are opaque in the undamaged state.Translated from Mekhanika Kompozitnykh Materialov, No. 6, pp. 787–795, November, 1992.