环区原理的一个推论及其应用

本文给出环区原理在三维空间中的一个推论,它证明了满足三个条件的空间系统就满足环区原理的条件,从而存在周期轨道。利用这个推论,又得到两个有关构作空间极限环的定理。     

Cellular responses to mild heat stress

Since its discovery in 1962 by Ritossa, the heat shock response has been extensively studied by a number of investigators to understand the molecular mechanism underlying the cellular response to heat stress. The most well characterized heat shock response is induction of the heat shock proteins that function as molecular chaperones and exert cell cycle regulatory and anti-apoptotic activities. While most investigators have focused their studies on the toxic effects of heat stress in organisms such as severe heat stress-induced cell cycle arrest and apoptosis, the cellular response to fever-ranged mild heat stress has been rather underestimated. However, the cellular response to mild heat stress is likely to be more important in a physiological sense than that to severe heat stress because the body temperature of homeothermic animals increases by only 1–2°C during febrile diseases. Here we provide information that mild heat stress does have some beneficial role in organisms via positively regulating cell proliferation and differentiation, and immune response in mammalian cells.Received 14 May 2004; received after revision 2 August 2004; accepted 16 August 2004     

风险投资能筛选并培育优质企业吗?——基于中国创业板的模糊断点回归分析

风险投资（venture capital，简称VC）能否筛选出优质企业进行投资并促进被投企业的业绩改善，是判断新兴市场国家风险投资行业是否成熟的一个重要标志.对于这一问题，针对国内市场的研究匮乏.本文以中国创业板上市企业为研究样本，研究VC能否筛选出优质企业以及能否为被投企业带来业绩改善，并进一步探讨其作用机制.研究发现：1）基于逻辑回归，VC未必能筛选出优质的企业，表现为企业业绩变量回归系数不显著；2）基于模糊断点回归进行内生性调整后，VC能够促进被投企业的发展，对被投企业的业绩改善有正向作用；3）从经营效益和创新角度研究VC影响企业业绩的潜在机制发现：一方面，VC降低了被投企业的销售成本率，提高了企业的经营效益；另一方面，VC的进入为被投企业带来行业经验和资源等，促进被投企业技术或商业模式的创新，从而有助于改善企业的经营业绩.本文实证结果表明国内VC具有"增值"作用，能够创造经济价值，但不具有"筛选"作用，揭示了VC对被投企业业绩的影响及潜在作用机制，为VC能促进被投企业的发展提供了新的实证参考.研究结果对于企业、风险投资机构和政策制定者具有借鉴意义和参考价值.     

A Study on the Economic Dislocation in Dynamic input-Output Model

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Fitting of growth curves over time when the data are obtained from a single realization

This paper focuses on the general problem of forecasting the maximum value of a time series which by the nature of the data must approach an asymptotic value. Examples of such series include the growth of organisms, the concentration of a chemical reagent during a reaction occurring over time or the amount of a fossil fuel resource which has been discovered or produced as a function of time. The approach taken below differs from the usual models for this type of data in that it assumes that an unobserved time series is actually driving the process, and that the observed data series is a function of the unobserved process. In the case of fossil fuels the unobserved series might be a measure of the exploratory drilling, the number of production days in a given time period or even the amount of fiscal resources devoted to exploratory activities. A maximum likelihood method is developed for estimating the parameters of the process, especially the maximum S, and the covariance structure of the estimators is developed. The methodology is illustrated on an example of oil production. Finally, methods are developed for forecasting the data into the near future.     

Logistic生产函数

在对经典Cobb-Douglass生产函数讨论的基础上,根据实际经济运行,给出了一个新的生产函数——Logistic生产函数,研究了新生产函数的性质,并应用动力系统理论对其进行了动态分析,导出了此经济系统的多重定态,得出经济发展具有阶段性的结论.还分析了技术进步和教育在系统演化中的作用.     

一个生物化学反应的振荡现象

本文讨论生物化学反应中的一类模型:运用定性分析方法及Hopf分枝理论,对系统(?)进行研究,得到了系统(?)的极限环存在性及不存在性条件.最后对所得结果给出了实际解释.     

一类以拋物线为特殊积分曲线的二次系统存在极限环的必要条件

本文将一类以抛物线为特殊积分曲线的二次系统分成四种情形来研究,分别给出了存在极限环的必要条件和易于判别极限环不存在的充分条件。     

考虑承压水影响的基坑抗隆起稳定性上限分析

考虑基坑底部的承压水作用效应,假定Prandtl土体滑移破坏形式,采用极限分析的上限定理建立了基坑抗隆起稳定性分析方法及其验算公式,讨论了承压水头大小、不透水层厚度以及挡土墙插入深度等因素对于基坑抗隆起稳定性的影响.工程实例的计算结果表明,坑底承压水对于基坑抗隆起稳定性的影响不可忽视,承压水头越大,基坑抗隆起稳定性安全系数越低.将本算法与传统算法的结果进行了对比,该方法能够体现出承压水对软土基坑稳定性所产生的风险.