电解还原法处理含铬废水

采用电解还原方法模拟工业含铬废水的处理。试验以普通铁极板作阴阳极,在直流电的作用下,铁阳极溶解生成的Fe2 和硫酸亚铁中的Fe2 把废水中的六价铬离子还原成三价铬离子;随着氢离子阴极放电使废水pH值逐渐升高,Cr3 和Fe3 便形成氢氧化铬及氢氧化铁沉淀,同时氢氧化铁有凝聚作用,能促进氢氧化铬的迅速沉淀。在实验最佳条件下,废水初始含铬浓度在600mg/L及600mg/L以下、反应pH=3、加入FeSO4的量1.20g(Fe2 与Cr2O72 比例1∶1)、反应时间40min、换极周期10min、电流密度0.085A/cm2,出水浓度达到0.57mg/L,去除率为94%。出水浓度达到国家排放标准。     

形如1/2(a2n+1)的孤立数

设a是正整数,13≤a≤31,证明了1/2(a2n+1)(2(|)a)都是孤立数,这里n是任意的正整数.     

一类改进的HIV病理模型的全局稳定性

将治愈率引入经典的HIV病理模型,构建一个改进的HIV病理模型.证明了改进模型中无病平衡点的全局稳定性,给出染病平衡点全局稳定性的参数域,并进行了相关的数值模拟,进而发现当染病平衡点不稳定时模型存在周期解.研究结果表明:提高治愈率是有效控制HIV感染的重要途径.     

基于FPGA的交流伺服系统电流环带宽扩展

在电流环的数学模型基础上,分析了电流环带宽与电流环路延时的关系,比较了几种典型电流环时序下产生的延时,对电流采样和PWM占空比更新时序进行了改进,并在FPGA中得到了具体的验证和实现.实验结果表明:这种改进的电流环时序克服了原有电流环时序的问题,能在不改变功率器件开关频率和不损失输出电压能力的基础上减小电流环路延时,从而提高电流环带宽,改善电流环和速度环的控制性能.     

On a dynamic mixture GARCH model

This paper proposes a new mixture GARCH model with a dynamic mixture proportion. The mixture Gaussian distribution of the error can vary from time to time. The Bayesian Information Criterion and the EM algorithm are used to estimate the number of parameters as well as the model parameters and their standard errors. The new model is applied to the S&P500 Index and Hang Seng Index and compared with GARCH models with Gaussian error and Student's t error. The result shows that the IGARCH effect in these index returns could be the result of the mixture of one stationary volatility component with another non‐stationary volatility component. The VaR based on the new model performs better than traditional GARCH‐based VaRs, especially in unstable stock markets. Copyright © 2008 John Wiley & Sons, Ltd.     

论《鲁宾逊漂流记》中反文学生态中心主义思想

《鲁宾逊漂流记》一直是国内外学者的研究经典，学者们从人物形象、叙事技巧、神话原型、殖民和后殖民主义等多个角度对之进行阐释和评价，但《鲁宾逊漂流记》却深刻地体现了反文学生态中心主义思想。该文运用生态文学批评理论，重新解读《鲁宾逊漂流记》。     

Magnetoresistance of the thin film ferromagnetic nanoconstrictions

The magnetoresistance and I-V characteristics at different temperatures of the thin film ferromagnetic nanoconstrictions of variable width (from 20 to 250 nm) and 10 nm thicknesses, fabricated by electron beam lithography and vacuum thin film deposition are compared. The magnetoresistance and resistance of the thin film ferromagnetic nanoconstrictions are not related to the width of the nanoconstrictions. Instead the resistance of the local nano-region in the middle of the thin film ferromagnetic nanoconstriction has only a minor role compared to that of the two microscale thin film ferromagnetic electrodes, which contribute the majority of the measured resistance. The magnetoresistances of the thin film ferromagnetic nanoconstrictions and a 0.2 cm × 0.8 cm thin ferromagnetic film deposited under the same conditions were also compared; the thin film ferromagnetic nanoconstrictions have higher magnetoresistances than the thin ferromagnetic film, which implies that the measured magnetoresistance of the thin film ferromagnetic nanoconstrictions comes mainly from the local nano-region in their centers. In conclusion, the measured magnetoresistance of the whole sample is similar to the anisotropic magnetoresistance, because the resistance of the two microscale thin film ferromagnetic electrodes is much higher than that of the local nano-region in the middle of the samples. Comparing the experimental results for the thin film ferromagnetic nanoconstrictions and the thin ferromagnetic film reveals that the magnetoresistance of the local nano-region in the middle of the sample is much higher than that of the two microscale thin film ferromagnetic electrodes attached to it.     

Chiral pyrrolidine-azole conjugates: Simple and efficient asymmetric organocatalysts for Michael addition to nitrostyrenes

Simple pyrrolidine-azole conjugates have been synthesized and found to be efficient catalysts for asymmetric Michael addition to nitrostyrenes. The identified optimal catalysts, pyrrolidine-azoles 2, 8 and 13, could catalyze the asymmetric Michael addition of a range of Michael donors and nitrostyrenes in high yields (up to 99%) and excellent stereoselectivities (up to 99:1 dr and 97% ee).     

广告用语中语用预设特征的应用

本文从语用预设的三个主要特征：可撤销性,共知性和隐蔽性的角度分析广告语言,以及这些特征如何使广告语言具有吸引力和说服力。除了这三个相对显著的特征,语用预设还会结合其他一些特点,如主观性,单向性和合适性,来达到广告预期效果。根据可撤销性,可以将广告分为语用预设可撤销类型和不可撤消类型,还可以根据语用预设在共同性和隐蔽性上的不同侧重分为两类。另外,本文将共同性与文化语境,隐蔽性与情景语境结合起来,从语用预设各个特点的角度对广告用语的特点进行了较整体性的研究。     

论目标设置训练对网球练习者击球准确率和自我控制能力的影响

通过教学实验法和问卷测试,对目标设置训练对网球专选班学生正反手抽击球准确率和自我控制能力的影响,以及自我控制能力各结构要素与正反手抽击球动作准确性的相关性等问题进行研究.