中立型时滞差分方程的振性与正解存在性

本文研究了一类中立型时滞差分方程的振动性和正解存在性，获得了该方程所有解振动的“Sharp”条件及存在正解的一个充分条件．     

基于线性耦合下混沌系统的同步条件

将混沌同步问题用精确的数学语言给予描述，通过数学分析将其转化为微分方程组的稳定性问题.以Lorenz系统族的Chen氏系统作为典型系统，在线性耦合下分析系统参数，得到了系统达到同步时的充分条件，且在理论上加以证明.结合该条件，提出了一种确定耦合系数的方法.最后用仿真实验验证了该方法的正确性，并验证了在不同耦合方式和参考系统的情况下定理的有效性. 关键词： 混沌同步 耦合 稳定性     

荧光光纤温度传感器激励光源的选择

本文分析计算了荧光光纤温度传感器的温敏元件——GsAlAs/GaAs双异质结半导体材料的荧光辐射效率与激励光波长的关系。讨论了温度测量范围及温敏元件GaAlAs层铝含量对激励光源的限制,在0～200℃测温范围内,若采用LED作激励光源,其峰值波长应在0.70～0.76μm之间选择。     

Investigation of sulfonated poly(ether ether ketone sulfone)/heteropolyacid composite membranes for high temperature fuel cell applications

The sulfonated poly(ether ether ketone sulfone) (SPEEKS)/heteropolyacid (HPA) composite membranes with different HPA content in SPEEKS copolymers matrix with different degree of sulfonation (DS) were investigated for high temperature proton exchange membrane fuel cells. Composite membranes were characterized by Fourier transfer infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). FTIR band shifts suggested that the sulfonic acid groups on the copolymer backbone strongly interact with HPA particles. SEM pictures showed that the HPA particles were uniformly distributed throughout the SPEEKS membranes matrix and particle sizes decreased with the increment of copolymers' DS. The holes were not found in SPEEKS‐4/HPA30 (consisting of 70% SPEEKS copolymers with DS = 0.8 and 30% HPA) composite membrane after composite membranes were treated with boiling water for 24 h. Thermal stabilities of the composite membranes were better than those of pure sulfonated copolymers membranes. Although the composite membranes possessed lower water uptake, it exhibited higher proton conductivity for SPEEKS‐4/HPA30 especially at high temperature (above 100 °C). Its proton conductivity linearly increased from 0.068 S/cm at 25 °C to 0.095 S/cm at 120 °C, which was higher than 0.06 S/cm of Nafion 117. In contrast, proton conductivity of pure SPEEKS‐4 membrane only increased from 0.062 S/cm at 25 °C to 0.078 S/cm at 80 °C. At 120 °C, proton conductivity decreased to poor 0.073 S/cm. The result indicated that composite membranes exhibited high proton conductivity at high temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1967–1978, 2006     

Discrete-time GI/Geo/1 queue with multiple working vacations

Consider the discrete time GI/Geo/1 queue with working vacations under EAS and LAS schemes. The server takes the original work at the lower rate rather than completely stopping during the vacation period. Using the matrix-geometric solution method, we obtain the steady-state distribution of the number of customers in the system and present the stochastic decomposition property of the queue length. Furthermore, we find and verify the closed property of conditional probability for negative binomial distributions. Using such property, we obtain the specific expression for the steady-state distribution of the waiting time and explain its two conditional stochastic decomposition structures. Finally, two special models are presented.      

Model and empirical study on some collaboration networks

In this paper we present an empirical study of a few practical systems described by cooperation networks, and propose a model to understand the results obtained. We study four non-social systems, which are the Bus Route Networks of Beijing and Yangzhou, the Travel Route Network of China, Huai-Yang recipes of Chinese cooked food, and a social system, which is the Collaboration Network of Hollywood Actors. In order to explain the results related to the degree distribution, act-degree distribution and act-size distribution (especially about the degree distribution, which may be better fitted using a stretched exponential distribution (SED)), we suggest a simple model to show a possible evolutionary mechanism for the emergence of such networks. The analytic and numerical results obtained from the model are in good agreement with the empirical results.     

A Convenient Method for the Stereoselective Synthesis of 7αHydroxycholesterol

7-Hydroxyderivativesofcholesteroldisplayawidevarietyofbiologicalactivities'-',mostofwhicharerelatedtothephysiologicalcontrolofcholesterolbiosynthesisandantitumoractivity.Inearlyreports',the7-hydroxycholesterolswerepreparedbythesequenceofacetylation,allylicchromicoxidation,andhydridereduction.Generally,theproductisamixtureof7a-and76-epimerswhichisdifficulttobeseparated.V.Kumaretal5improvedthisprocedurebyusingstereospecificreducingreagentsinsteadofthesimplehydride.7a-and7o-epimerscouldbeobtained…     

经济增长与宏观经济运行模型

对国民经济进行宏观调控，如同经济增长问题一样是一个永恒问题，对宏观调控的基本内容，手段，方法，国内外学者已进行了较多的规范性讨论，尤其是在数理分析方面，也已有许多具有普遍意义的成果，但是，要把那些成果转化为“生产力”从而变成清晰的，简明的，可操作的手段和方法，尚需人们不断的探索，本文通过对国民经济运行过程中若干宏观经济变量之间的数量关系分析，并以此建立了的国民经济宏观数量模型，就是尝试性的探索。     

添加助剂的钙钛矿型氧化物NdMO_3上的甲烷氧化偶联——Ⅱ.15% Li_2O/NdMO_3(M=Cr、Mn、Fe、Co、Ni)上的OCM反应研究

在添加了15%Li_2O的NdMO_3(M=Cr、Mn、Fe、Co、Ni)上进行了甲烷氧化偶联(OCM)反应研究.通过改变反应气中CH_4:O_2浓度比,在氧化态和“脱氧态”催化剂上的CH_4脉冲反应,探讨了表面吸附氧和晶格氧在OCM反应中的作用以及NdMO_3中不同金属离子(M)对OCM反应活性的影响等.     

WAVELET TRANSFORM IN FRACTAL IMAGE ENCODING

This paper presents some results of the relation between wavelet transform and fractal transform. The wavelet transform of the attractor of fractal transform posseses translational and scale invariance. So we speed the fractal image encoding by testing the invariance of the wavelet transform appropriate for image encoding. The classfication scheme of range blocks by wavelet transform is given in this paper.