碳化钒析出对X80管线钢焊接热影响区韧性的影响

通过Gleeble-3500热模拟机对钒(V)含量分别为0.06%和0.02%的X80管线钢进行了峰值温度为1350℃和750℃的焊接热模拟试验,利用硬度计和光学显微镜(OM)分别分析了焊接热模拟试样硬度和试样中马氏体-奥氏体岛状组织(M-A)的数量、尺寸和形貌。利用透射电镜(TEM)对母材、粗晶区和部分相变区中粒子析出进行了表征。结果表明,与0.02%含V量X80管线钢相比,0.06%含V量的X80管线钢由于V含量较高,在受到多道次焊接热循环影响时,部分相变区有较大量碳化钒(VC)粒子析出,明显阻碍位错运动,使其强度明显提高的同时脆性增大、塑性变形难以进行,导致其焊接热影响区韧性下降。     

Modeling of an industrial scale hydrodynamic cavitation multiphase reactor for Prileschajew epoxidation

The hydrodynamic cavitation multiphase reactor (HCMR) is emerging as a promising alternative for the intensification of liquid–liquid heterogeneous reactions, but research on HCMR modeling is lacking. In this article, an HCMR model was developed using Prileschajew epoxidation as the model system. First, based on experimental measurements of oil/water two-phase flow downstream of hydrodynamic cavitation devices, semiempirical correlations were proposed to describe the droplet size and droplet size distribution (DSD) as functions of flow conditions and geometry parameters. Then, with boundary conditions calculated by the DSD correlation, a droplet dynamics simulation in a reaction tank was performed by computational fluid dynamics coupled with population balance model to obtain the two-phase interfacial area. Finally, the acquired reactor model was substituted into an overall kinetic model, to simulate the epoxidation reaction in HCMR. Model predictions were verified by experimental results measured on an industrial scale HCMR.     

MOOC Learner’s Final Grade Prediction Based on an Improved Random Forests Method

Massive Open Online Course (MOOC) has become a popular way of online learning used across the world by millions of people. Meanwhile, a vast amount of information has been collected from the MOOC learners and institutions. Based on the educational data, a lot of researches have been investigated for the prediction of the MOOC learner’s final grade. However, there are still two problems in this research field. The first problem is how to select the most proper features to improve the prediction accuracy, and the second problem is how to use or modify the data mining algorithms for a better analysis of the MOOC data. In order to solve these two problems, an improved random forests method is proposed in this paper. First, a hybrid indicator is defined to measure the importance of the features, and a rule is further established for the feature selection; then, a Clustering-Synthetic Minority Over-sampling Technique (SMOTE) is embedded into the traditional random forests algorithm to solve the class imbalance problem. In experiment part, we verify the performance of the proposed method by using the Canvas Network Person-Course (CNPC) dataset. Furthermore, four well-known prediction methods have been applied for comparison, where the superiority of our method has been proved.     

一种新的电磁轨道炮电感梯度计算方法

针对现有文献对速度趋肤效应影响下的电磁轨道炮电感梯度研究不足的问题,从毕奥-萨伐尔定律出发,提出一种新的电感梯度计算方法。指出文献给出的4种电感梯度计算方法的缺点与不足,将轨道中电流假设为均匀分布于轨道的内表面及上、下表面,采用文中方法与文献给出4种计算方法对电感梯度进行分析,并将其计算值与ANSYS仿真及实验得到的电感梯度值进行对比。结果表明:该方法与文献给出4种计算方法所得计算值的变化趋势较为一致,但方法得到的电感梯度值较为接近,具有形式简单、计算准确的优点。     

回望生命的光辉——北川地震遗址博物馆及震灾纪念地规划的思考

介绍了中国城市规划设计研究院第一时间进入北川县城开展"北川地震遗址博物馆及震灾纪念地规划研究"的工作情况,并特别就北川地震遗址的重要价值分析、定位研究、规划原则和功能区划、以及保护与展示的主要构思做了扼要的阐述。强调应重点保护好救灾纪念地、典型地表灾害遗迹和典型建筑结构灾害遗迹,将县城范围作为地震遗址保护区加以整体保护,并围绕北川中学遗址规划抗震救灾纪念区。规划应将对生命的纪念作为主题,让所有人面对这座废墟时,感受到的不只是对死亡的无奈,更是生命的力量。     

高层建筑考虑施工过程的徐变收缩分析

基于现有的试验技术条件 ,高层及大跨度民用建筑的徐变收缩分析还只能参照桥梁结构中比较成熟的徐变系数方法进行。根据考虑延迟弹性的混凝土线性徐变老化理论 ,引用桥梁结构中徐变系数的概念 ,推导了利用徐变系数对高层建筑进行考虑施工过程的徐变收缩分析的有限元公式 ,并编制了相应程序 ,对框架和框支剪力墙结构分别选取算例进行了全过程的弹性和徐变收缩分析。结果表明工程设计人员应当考虑到施工过程和徐变收缩因素对高层建筑变形和内力的影响。     

公园城市,城市建设的新模式

我们今天的对话安排了三个议题,每个议题有三到四位专家做引导性发言和主题讨论,然后请与会的其他的专家做评论和建议,再和听众做一些互动,2018年2月习近平总书记在成都视察,提出了建设公园城市这个概念,之后成都市组织了国内外机构参与的"公园城市理论与规划方法"的8个专题研究。     

冬瓜山铜矿磨矿提质增效降耗的应用研究

介绍了通过改变磨机球荷尺寸组成,提高安徽铜陵冬瓜山铜矿选矿厂磨矿质量和磨机利用系数,降低磨矿球耗的方法。根据冬瓜山铜矿的矿石力学性质和磨矿条件,利用球径半理论公式精确计算合理的补装球荷尺寸组成,即m(Ф60)∶m(Ф40)=45∶55。工业试验结果表明,采用新的补装球荷后,磨矿细度(-0.074 mm)和中间可选粒级(-0.15+0.01 mm)含量分别提高了7.60和5.76个百分点,不合格粗粒级(+0.15 mm)含量和过细粒级(-0.01 mm)含量分别减少了2.90和2.86个百分点。磨机利用效率提高了9.8%,球耗降低了10.52%。球径半理论公式因计算方便、效果显著,具有很好的应用及推广价值。     

Growth and degradation in the Orient’s ‘Las Vegas’: issues of environment in Macau

This paper argues that the rapid growth of gambling‐related tourism and urban construction in Macau has given rise to serious environmental degradation. The major environmental issues include air quality, water supply, solid waste disposal, noise prevention, heritage conservation and environmental management. The author suggests that the government in Macau should refocus this city’s development direction and commit itself to sustainable development. At the policy‐making level, there are such urgent issues as integration of environmental, economic and urban planning with community participation in decision‐making; enhancement of environmental legislation and institutions; implementing vital measures to control of the numbers of visitors; developing a mass transport system; and protecting the city’s cultural heritage.