SK单组分刮涂聚脲及其工程应用

水工建筑物混凝土常常出现渗漏、裂缝、冻融剥蚀、冻胀、冲磨空蚀以及伸缩缝漏水等病害。为了及时消除病害,需要采用有效的修补材料及可靠的技术。文中介绍了水工建筑物混凝土表面防护的一种柔性高性能防护涂料及其使用方法,SK单组分刮涂聚脲具有抗拉强度高、伸长率大、与混凝土粘接强、抗冲磨和防渗效果好、耐老化、施工工艺简单等特点,适用于处理混凝土伸缩缝、裂缝、大面积防渗及有抗冲磨要求的泄洪建筑物等水利水电工程。通过在大量工程中应用,取得了较显著的效果。     

Passivating Defects of Perovskite Solar Cells with Functional Donor-Acceptor–Donor Type Hole Transporting Materials

In this study, a series of donor–acceptor–donor (D-A-D) type small molecules based on the fluorene and diphenylethenyl enamine units, which are distinguished by different acceptors, as holetransporting materials (HTMs) for perovskite solar cells is presented. The incorporation of the malononitrile acceptor units is found to be beneficial for not only carrier transportation but also defects passivation via Pb–N interactions. The highest power conversion efficiency of over 22% is achieved on cells based on V1359, which is higher than that of spiro-OMeTAD under identical conditions. This st shows that HTMs prepared via simplified synthetic routes are not only a low-cost alternative to spiro-OMeTAD but also outperform in efficiency and stability state-of-art materials obtained via expensive cross-coupling methods.     

Synthesis of Pt nanocrystals with different shapes using the same protocol to optimize their catalytic activity toward oxygen reduction

Engineering the shape and thus surface structure of Pt nanocrystals is an effective strategy for optimizing their catalytic activities toward various reactions. However, different protocols are typically used to produce Pt nanocrystals with distinctive shapes, making it difficult to directly compare their catalytic activities owing to the complication of surface contamination. Here we demonstrate that Pt nanocrystals with a variety of shapes, including those enclosed with low- or high-index facets, can be synthesized using the same protocol by simply adjusting the concentration of reducing agent and/or the reaction time. Specifically, when the reducing agent was used at a relatively low concentration, Pt truncated cubes, cuboctahedrons, truncated octahedrons, and octahedrons were produced sequentially upon the increase in reaction time. When 67% more reducing agent was used, Pt cubes and concave cubes were obtained consecutively as the reaction time was prolonged. Our quantitative analysis suggests that the diversity of shape and difference in size can be resulted from the difference in reduction kinetics. In evaluating their structure–activity relationship for oxygen reduction, it was established that the high-index facets on Pt concave cubes possessed a specific activity of 6.3 and 1.3 times greater than those of Pt cubes and octahedrons exposed by {1?0?0} and {1?1?1} facets, respectively. This work not only offers a general method for the synthesis of Pt nanocrystals having diverse shapes and thus different types of facets but also highlights the significance of reduction kinetics in controlling the structure evolution of other metal nanocrystals.     

Modeling of interfacial intermetallic compounds in the application of very fine lead-free solder interconnections

Intermetallic compounds (IMCs) are formed between lead-free solders and base metals during soldering processes. The morphology as well as the amount of the IMCs, in particular the interfacial IMCs, are important to mechanical performance of the solder joints in their service environment. This is especially the case in state-of-art ultrafine-pitch wafer-level packaging, in which solder joints could become as small as 50 μm in diameter or even less. However, research addressing growth kinetics of the IMCs in the existing literature has concentrated on fitting experimental data onto a simple parabolic growth equation, which cannot account for all the complicated physics involved in the process of IMC formation. There are a few models based on Fick’s diffusion equations in the literature, which assume the growing IMC interface is planar. A combined thermodynamic–kinetic model has been derived from the relationships amongst some thermodynamic parameters; however, this model is only one dimension (1-D) in nature. 2-D models have also been proposed, e.g. an implicit boundary tracking method, and a phase field model. This paper reviews the modeling techniques in the literature for both the growth kinetics and morphology of the interfacial IMCs, under the context of lead-free soldering in very fine interconnections. The advantages and disadvantages of each method are discussed. Possible solutions to include the geometrical features of micro solder joints in the modeling of growth kinetics of interfacial IMC are presented.     

A data mining proxy approach for efficient frequent itemset mining

Data mining has attracted a lot of research efforts during the past decade. However, little work has been reported on the efficiency of supporting a large number of users who issue different data mining queries periodically when there are new needs and when data is updated. Our work is motivated by the fact that the pattern-growth method is one of the most efficient methods for frequent pattern mining which constructs an initial tree and mines frequent patterns on top of the tree. In this paper, we present a data mining proxy approach that can reduce the I/O costs to construct an initial tree by utilizing the trees that have already been resident in memory. The tree we construct is the smallest for a given data mining query. In addition, our proxy approach can also reduce CPU cost in mining patterns, because the cost of mining relies on the sizes of trees. The focus of the work is to construct an initial tree efficiently. We propose three tree operations to construct a tree. With a unique coding scheme, we can efficiently project subtrees from on-disk trees or in-memory trees. Our performance study indicated that the data mining proxy significantly reduces the I/O cost to construct trees and CPU cost to mine patterns over the trees constructed.     

钢桁架连梁-联肢剪力墙耗能机理及抗震性能试验研究

对设置全钢桁架连梁和设置钢筋混凝土、钢桁架混合连梁的双层联肢剪力墙平面结构进行了拟动力试验和低周反复荷载试验,研究了不同工况地震波作用下剪力墙的时程响应,以及其破坏机理、承载力、滞回延性性能、耗能机理、刚度及强度退化机理。试验结果表明：全部设置钢桁架连梁的剪力墙的刚度分布合理,耗能机理及刚度强度退化机理符合联肢剪力墙抗震设计的要求。大震时,在保证较高耗能能力的同时能够维持较高的承载力和刚度,持续约束墙肢,抗震性能优于混凝土连梁联肢剪力墙体系,是一种较理想的连梁设置方案。     

基于区域电价之差的输电线路的成本效益分析模型

电力工业体制的改革使输电线路规划的外部环境发生了明显的变化,要求对规划理念和理论进行根本性的转变。为了适应市场化条件下的输电线路的规划,可以从技术经济的角度,综合考虑多种不确定因素,用成本-效益分析的方法来评价输电线路扩展的可行性。文中以区域电价之差作为项目的收益,不仅充分利用了市场提供的电价信息,符合市场化改革的方向,而且避免了预测项目现金流的复杂的计算,具有计算简便的优点。通过引入弹性概念,给出了输电线路容量与区域电价之差之间的数量关系模型,通过分析,说明市场条件下区域电价与输电容量存在着非常敏感的负相关关系。通过算例分析表明,该方法是可行的、有效的,可以作为传统输电项目扩展规划可行性分析的一个重要的补充方法。     

一种有效的空间域视频传输差错掩盖算法

针对易错信道中传输视频图像容易发生差错而导致图像块丢失的现象，提出一种有效的空间域差错掩盖算法．根据周围正确解码块中的边缘信息把丢失块分成平滑块和边缘块两类．对于不舍有边缘的丢失块用简单的线性插值进行恢复；对含有边缘的丢失块先用基于梯度的自适应预测（GAP）法获得丢失块的初始值，然后用最大后验概率方法对初始值进行优化．实验结果表明该算法能够获得优越的图像质量，同时计算复杂度低，适用于视频图像的实时性传输．