Carbon dispersed iron-manganese catalyst for light olefin synthesis from CO hydrogenation

High performance iron-manganese catalysts dispersed with carbon to produce light olefins from CO hydrogenation were prepared by sol-gel method using citric acid as precursor. The effects of carbon content on the bulk structure, the water gas shift reaction, the chain propagation ability and the activity and selectivity of the catalysts were investigated. The results showed that the catalysts were gradually reduced during the decomposition of the precursor when calcined under pure N₂. The formation of iron-manganese mixed crystallites was favored and stabilized because of the enhanced interaction of iron and manganese with increasing carbon content. During the subsequent CO hydrogenation reaction, all the catalysts showed high activity and olefin selectivity. With increasing carbon content, the water gas shift (WGS) reaction was restrained and the chain propagation ability was inhibited. Catalysts with higher carbon content showed much lighter hydrocarbon products; however, the selectivity of CH₄ was almost unchanged. This work was presented at the 7 ^th Korea-China Workshop on Clean Energy Technology held at Taiyuan, Shanxi, China, June 26–28, 2008.     

ZrB2-SiC复相陶瓷的制备及其力学性能研究

以ZrB2和SiC粉为原料,采用Si3N4球为球磨介质,通过热压烧结制备了ZrB2-SiC复相陶瓷.并对ZrB2-SiC复相陶瓷进行了相对密度、力学性能检测和微观结构分析.结果表明:随着ZrB2球磨时间和SiC含量的增加,该复相陶瓷相对密度先增加后略有降低,ZrB2最佳球磨时间为8小时,SiC最佳含量为20vol.%.ZrB2+20vol.%SiC复相陶瓷的相对密度达到98.3%,抗弯强度达到631±4MPa,断裂韧性达到5.4±0.2 MPa·m1/2.随着球磨时间的增加,ZrB2+20vol.%SiC复相陶瓷的断裂方式由穿晶断裂向沿晶断裂转变.     

浸没式双轴旋转厌氧膜生物反应器的污泥特性研究

研究了新型浸没式双轴旋转厌氧膜生物反应器(SDRAnMBR)处理模拟啤酒废水的污泥特性.结果表明,SDRAnMBR的污泥活性高,旋转剪切力没有对厌氧颗粒污泥的性质造成破坏并具有性能良好的絮体;而且能有效减轻污泥浓度、EPS、污泥粘度,污泥颗粒粒径的变化对膜污染的影响,使之能在较高的MLSS(18～19.5 g·L-1),较高的EPS浓度(50.9～63.9 mg·gMLSS-1)、较小的污泥颗粒粒径(4.00～36.54μm)和较大的污泥粘度(6.6～7.5mPa·s-1)时稳定运行.SDRAnMBR中由膜旋转形成的三相旋转流和厌氧颗粒污泥的协同作用,使SDRAnMBR具有性能良好的活性污泥,同时强化了膜组件的抗污染性能.     

速度·活力·梦想——浅谈高速铁路客运枢纽影响下城市地区的发展策略

借鉴外国的成功经验,结合我国实际情况,寻找合适的高速铁路客运枢纽影响下城市地区发展策略,已经成为城市规划与设计研究的当务之急。该文简要分析了日本东京新宿和法国里尔两个成功案例,总结了若干发展策略,希望能引起大家进一步的关注、研究和讨论。     

Visibility, air quality and daily mortality in Shanghai, China

This study was designed to assess the association between visibility and air quality, and to determine whether the variations in daily mortality were associated with fluctuations in visibility levels in Shanghai, China. Mortality data were extracted from the death certificates, provided by Shanghai Municipal Center of Disease Control and Prevention, and visibility data were obtained from Shanghai Municipal Bureau of Meteorology. Air quality data (PM₁₀, PM_2.5, PM_10-2.5, SO₂, NO₂ and O₃) were obtained from Shanghai Environmental Monitoring Center. Generalized additive model (GAM) with penalized splines was used to analyze the mortality, visibility, air pollution, and covariate data. Among various pollutants, PM_2.5 showed strongest correlation with visibility. Visibility, together with humidity, was found appropriate in predicting PM_2.5 (R-squared: 0.64) and PM₁₀ (R-squared: 0.62). Decreased visibility was significantly associated with elevated death rates from all causes and from cardiovascular disease in Shanghai; one inter-quartile range (8 km) decrease in visibility corresponded to 2.17% (95%CI: 0.46%, 3.85%), 3.36% (95%CI: 0.96%, 5.70%), and 3.02% (95%CI: − 1.32%, 7.17%) increase of total, cardiovascular and respiratory mortality, respectively. The effect estimates using predicted PM_2.5 and PM₁₀ concentrations were similar to those assessed using actual concentrations. This is the first study in Mainland China assessing the association between visibility and adverse health outcomes. Our findings suggest the possibility of using visibility as a surrogate of air quality in health research in developing countries where air pollution data might be scarce and not routinely monitored.     

用于空域扫描的表面离散化边界方程法

表面离散化边界方程法可以独立计算物体表面任意点处的电流密度,而所需求逆的矩阵阶数远小于矩量法.文中将它与渐近波形估计相结合实现了空域内的快速扫描,从而避免了许多重复计算.与矩量法相比,新方法降低了所需求逆矩阵的阶数,减小了存储需求,缩短了计算时间,提高了计算效率且易于并行计算.文中还将该方法成功运用到电大尺寸物体的散射问题中.计算表明对于尺寸越大的物体,新方法的优势就越明显.     

用雪崩三极管电路生成高压负脉冲技术研究

雪崩效应因为能在极短时间内输出极大电流,常被用来设计高压脉冲电路。分析了利用雪崩三极管电路生成高压正脉冲的实现方案,并提出了改进的设计,接着分析了脉冲输出过程中负载回路的电流流向,通过改变信号输出点,设计了输出高压负脉冲的电路。电路输出的脉冲幅度达到了-200V,前沿约3.2ns。与相似结构的正脉冲电路相比,性能略有降低。同时对性能下降的原因进行了分析。     

协同系统中预编码技术的发展

协同系统与多人多出系统具有相似性,在协同系统中引入预编码技术是方便可行的.本文从本地和虚拟天线阵的构成方式及系统拓扑等角度出发,对协同系统中的预编码技术进行了分类整理,总结了其研究现状.     

The red-light running behavior of electric bike riders and cyclists at urban intersections in China: An observational study

Electric bikes and regular bicycles play an important role in the urban transportation system of China. Red-light running is a type of highly dangerous behavior of two-wheeled riders. The main purpose of this study was to investigate the rate, associated factors, and behavior characteristics of two-wheelers’ red-light running in China. A field observational study was conducted using two synchronized video cameras at three signalized intersections in Beijing. A total of 451 two-wheelers facing a red light (222 e-bike riders and 229 cyclists) were observed and analyzed. The results showed that 56% of the two-wheelers crossed the intersection against a red light. Age was found to be a significant variable for predicting red-light runners, with the young and middle-aged riders being more likely than the old ones to run against a red light. The logistic regression analysis also indicated that the probability of a rider running a red light was higher when she or he was alone, when there were fewer riders waiting, and when there were riders already crossing on red. Further analysis of crossing behavior revealed that the majority of red-light running occurred in the early and late stages of a red-light cycle. Two-wheelers’ crossing behavior was categorized into three distinct types: law-obeying (44%), risk-taking (31%) and opportunistic (25%). Males were more likely to act in a risk-taking manner than females, and so were the young and middle-aged riders than the old ones. These findings provide valuable insights in understanding two-wheelers’ red-light running behaviors, and their implications in improving road safety were discussed.     

Ce-La-Mn超细粒子的制备、表征及催化性能研究

以碳酸铈、氧化镧和硝酸锰为主要原料,采用"溶胶-凝胶"法结合"超临界流体干燥"技术获取Ce-La-Mn气凝胶,在850℃热处理制备Ce-La-Mn混合氧化物,并采用TG-DTA、XRD、FT-IR和TEM进行表征,用"2CO+2NO=2CO2+N2"特征反应测试超细粒子的催化活性,考察超临界流体干燥技术与铈掺杂对超细Ce-La-Mn混合氧化物的结构、形貌和催化活性的影响。结果显示:经260℃超临界流体干燥得到的Ce-La-Mn气凝胶为分散性好的棕色絮状粉末,由大量直径小于10nm的球型颗粒组成,晶相为CeO2、MnO、La5O7NO3和La(OH)2NO3;经850℃热处理得到的Ce-La-Mn混合氧化物的粒径约为20nm,晶相为LaMnO3+λ、La2O3和CeO2;铈掺杂增加了LaMnO3+λ晶格中氧空缺数量,改善了催化的气氛条件,提高了Ce-La-Mn混合氧化物的催化活性。