6000系铝合金晶间腐蚀研究进展

介绍了与晶界直接相关的铝合金腐蚀类型,概述了合金元素和稀土元素对6000系铝合金晶间腐蚀的影响,重点介绍了热处理条件对6000系铝合金晶间腐蚀敏感性的影响．大量实验显示,热处理影响腐蚀模式,且晶间腐蚀向点蚀的转变与固溶处理温度、冷却速度,以及随后的人工时效温度和时效时间等诸多因素有关,发现经适当条件热处理的6000系铝合金可免受局部腐蚀影响．展望了铝合金晶间腐蚀研究的发展方向．     

低周反复荷载下弯剪破坏钢筋混凝土柱的变形性能

为研究地震作用下弯剪破坏钢筋混凝土(RC)柱的变形性能,对24根不同剪跨比、轴压比及配箍率的RC柱进行了低周反复试验.分析了剪跨比、轴压比和配箍率对柱滞回曲线、骨架曲线及变形能力的影响,研究了RC柱的地震破坏模式以及不同破坏模式下柱的弯曲位移、剪切位移及滑移位移在总水平位移中所占比例和变化规律.结果表明,反复荷载下RC柱会发生弯曲、剪切及弯剪3种典型破坏.当剪跨比较小、轴压比较大且配箍率较小时,RC柱易发生弯剪破坏或剪切破坏,试件的耗能能力和延性较差,表现为滞回环面积和极限位移较小.当RC柱发生弯剪或剪切破坏时,弯曲位移在总水平位移中所占比例较小,剪切位移所占比例较大,钢筋拔出产生的滑移位移所占比例约为30%~40%.     

考虑再生粗骨料随机分布的混凝土氯离子扩散细观数值模拟

考虑粗骨料分布的随机性及氯离子结合的非线性对氯离子扩散性的影响,对再生混凝土中氯离子扩散进行数值建模与细观仿真分析,并将数值模拟结果与已有试验数据进行对比;通过改变老硬化砂浆扩散系数、新硬化砂浆扩散系数、老界面过渡区扩散系数及浸泡时间,对比研究了不同情况下再生混凝土中氯离子的扩散特性.结果表明:数值模拟结果与试验结果接近;再生混凝土中氯离子沿扩散深度方向呈波浪式下降;随着扩散系数的增大及浸泡时间的增长,氯离子扩散速度加快;随着再生粗骨料取代率的增加,氯离子扩散速度也增加;相同扩散深度处,不同随机骨料模型中氯离子含量最大值接近,说明所采用的随机骨料模型模拟结果具有较好的稳定性.     

证券市场中大股东“掏空”策略的演化博弈分析及调控

随着所有权从分散走向集中,大股东的行为在公司治理问题中的地位日益重要。针对此种情况,笔者从公司治理角度对大股东行为问题的现实背景进行分析,在此基础上通过建立演化博弈模型从有限理性的角度分析大、小股东博弈双方的演化稳定策略（ESS）,并且在博弈矩阵中引入监管力度因子,说明各参数变化对均衡结果的影响,从而为规范证券市场中大股东的行为提供决策参考。     

基于DSP的混沌语音加密

基于语音加密的特殊性,利用可逆二维Arnold变换和改进的Logistic映射进行了混沌加密算法研究,并以TMS320VC5509A为中央处理器提出了语音加密的系统方案,实现了语音的加密和解密.首先介绍了数据加密技术基本原理和方法,然后详细给出了混沌加密系统的软硬件设计方案,并通过DSP芯片实现了混沌语音加密和解密.最后对语音信号进行了模拟仿真和测试,加解密前后的信号和频谱取得了较好的一致性,证实了该混沌语音加密算法的可行性.     

冻融循环作用后钢筋混凝土柱的偏心受压性能

为了研究冻融循环作用对钢筋混凝土柱偏心受压性能的影响,对经历0,75,100,125,150次冻融循环作用后的立方体试块进行了抗压强度试验,并设计制作了30根钢筋混凝土柱,将其经历0,75,100,125,150次冻融循环作用后进行偏心受压静力试验.分析了混凝土相对抗压强度、质量损失率、相对动弹性模量与冻融循环次数的关系,研究了冻融循环次数、轴向力偏心距对钢筋混凝土柱偏心受压性能的影响.研究结果表明,随着冻融循环次数的增加,试验柱的开裂荷载和极限荷载都逐渐减小,极限变形逐渐增大,部分试件由大偏心受压破坏转变为小偏心受压破坏.现行混凝土结构设计规范关于钢筋混凝土偏心受压柱极限承载力的计算理论适用于冻融循环作用后的钢筋混凝土柱.     

Starch grain evidence reveals early pottery function cooking plant foods in North China

Early pottery sherds excavated in northern China date back to more than 11,000 cal a BP, and are presumed to have been used as cooking vessels. There has been, however, no direct evidence to demonstrate this function. Here we report ancient starch grains recovered from carbonized residues adhering to the bases of flat- bottomed vessels excavated from the Zhuannian site dating more than 10,000 cal a BP in the North China Plain. This evidence demonstrates that early pottery was being used to cook cereal grains, particularly millets, and acorns. Because millets were in the process of domestication at thistime, we propose that pottery invention in northern China may have been related to early farming activities.     

Climatic significance of n-alkanes and their compound-specific dD values from lake surface sediments on the Southwestern Tibetan Plateau

The content and hydrogen isotope ratios of n-alkanes extracted from recent lake surface sediments sampled from nine lakes in three different climate zones on the Southwestern Tibetan Plateau were analyzed.Values were compared with n-alkanes in plants from lake drainages,and dD values of meteoric water,lake water,and mean annual precipitation.The results showed that n-C23was predominantly derived from aquatic plants,and n-C27–n-C33from terrestrial higher plants.The average carbon chain length of n-C27–n-C33(ACL27–33)was positively correlated with the mean annual precipitation.dD values of the long-chain n-alkanes n-C29and n-C31of terrestrial origin(varying between-214%and-169%,and-226%and-185%,respectively)were inversely correlated with mean annual precipitation;but in accordance with the average annual variations in dD(OIPC),dD values of n-C31were strongly related to the dD values of growing season meteoric water(R2=0.74).The large difference between dD values of n-C23of aquatic origin and n-C31(an average of about 27%)demonstrates the enrichment of the lake water dD compared to precipitation,caused by strong evaporation in the semiarid–arid areas of the southwestern Tibetan Plateau.Average value of en C25 31=p(-95%)is evidently higher than the value observed in European wet regions(-128%);besides,en C31(about-116%)is constant along the study transect(SD=9),which indicates that n-C31is a useful proxy for the environment.     

Engineering acid dew temperature: the limitation for flue gas heat recovery

In order to study how deep we can reduce the temperature of exhaust flue gas, an experiment focusing on the combined influence of ash deposition and acid condensation on the heat transfer characteristics of the heat exchanger was carried out in a 300-MW boiler unit. An annular tube was inserted into the flue gas duct between the air preheater and the electrostatic precipitator. The water with given temperature firstly entered the inner tube and then flowed into the outer tube at the end of the inner tube. It is found that heat transfer performance drops sharply at fixed temperature range under given coal quality. The turning temperature is defined as the engineering acid dew temperature （EADT）. When the inlet water temperature is under the EADT, ash sticks to the tube and is difficult to blow off, and thus the flow resistance rises. Furthermore, the corrosion can be observed obviously. From the point of economy and reliability, EADT is the limitation for flue gas heat recovery. The EADT is at least 30 ℃ lower than ADT calculated by traditional empirical and theoretical equations.     

Isolation and characterization of rl（t）, a gene that controls leaf rolling in rice

Moderate leaf rolling is one of the most important morphological traits in rice breeding for plant ideotype. Previous studies have shown that the rl（t） gene has a high breeding potential for developing hybrid-rice varieties with an ideal ideotype, because it leads to an appropriate leaf rolling index （LRI） of about 30 % in the heterozygous state, and had a positive effect on grain yield. In this study, we isolated rl（t） and performed a preliminary investigation of its function in regulating leaf rolling in rice. DNA sequencing identified a single base change （G to T） in the finely mapped region （11 kb） containing rl（t）, and this is located in 3′-untranslated region （3′-UTR） of the only predicted gene, Roc5 （Rice outermost cell-specific）. The expression level of Roc5 is significantly higher in the rl（t） mutant than in the wild-type. Using RNAi and overexpression analysis, we found that the expression level of Roc5 correlated with LRI and leaf bulliform area, and wasalso associated with leaf abaxial or adaxial rolling. These results confirmed that Roc5 controls leaf rolling in a dosagedependent manner. Bioinformatics analysis revealed a conserved 17-nt sequence （called the GU-rich element） in the 3′-UTR of HD-GL2 （Homeodomain-Glabra2） family genes including Roc5. Based on the model of this element in regulating mRNA stability in mammals, we speculate that the single nucleotide change in this element accounts for the higher expression level of Roc5 in the rl（t） mutant compared to the wild-type, which ultimately leads to adaxial rolling of the leaf. This discovery further enhances our knowledge of the molecular mechanisms underlying leaf rolling in rice.