Corrosive wear behavior of HVOF-sprayed micro-nano-structured Cr3C2–NiCr cermet coatings under aqueous media

A novel micro-nano-structured Cr₃C₂–NiCr cermet coating was prepared on 316L stainless steel by high-velocity oxygen fuel spraying technology (HVOF). Cermet coatings with different contents of micro-and nano-sized Cr₃C₂ particles as the hard phase and a NiCr alloy matrix as the bonding phase were prepared and characterized in terms of porosity, microhardness, and corrosive wear resistance in a 3.5% NaCl solution and artificial seawater. Compared to nanostructured coatings, micro-nano-structured coatings avoid decarburization and reduce nanoparticle agglomeration during the spray process, and mechanical and electrochemical properties were improved in comparison with those of conventional coatings. The micro-nano-structured Cr₃C₂–NiCr coating rendered low porosity (≤0.34%) and high microhardness (≥1105.0HV_0.3). The coating comprising 50% nano-sized Cr₃C₂ grains exhibited the best corrosive wear resistance owing to its densest microstructure and highest microhardness. Furthermore, compared to static corrosion, the dynamic corrosion of the coatings led to more severe mechanical wear, because corrosion destroyed the coating surface and ions promoted corrosion to invade coatings through the pores during corrosion wear.     

密文策略属性加密中的撤销控制方案

在云环境下使用数据共享功能时，由于云环境的复杂性，需要对数据进行安全保护和访问控制，这就要求使用加密机制。基于密文策略属性的加密（CP-ABE）是当前广泛使用的加密机制，它可以根据用户的属性来设置访问权限，任何具有合格访问权限的用户都可以访问数据。然而云是一个动态环境，有时可能只允许具有访问权限用户中的一部分用户访问数据，这就需要用户权限的撤销机制。然而，在CP-ABE中，访问权撤销或用户撤销是一个冗长且代价高昂的事件。所提出方案根据对CP-ABE流程的改进，在原密文中嵌入了可灵活控制的用户个人秘密，使得用户权限撤销时既不要求使用新访问策略的用户撤销数据，也不要求对数据进行重新加密，大幅减少撤销时的计算成本。与知名CP-ABE撤销方案对比，所提出方案的计算成本更低且具有良好的安全性。     

Astragali Radix-derived nitrogen-doped porous carbon: An efficient electrocatalyst for the oxygen reduction reaction

The development of biomass-derived nitrogen-doped porous carbons (NPCs) for the oxygen reduction reaction (ORR) is important for sustainable energy systems. Herein, NPCs derived from Astragali Radix (AR) via a cost-effective strategy are reported for the first time. The as-prepared AR-950-5 catalyst shows a stacked layer-like structure and porosity. Notably, the optimized AR-950-5 delivers catalytic activity comparable to that of commercial Pt/C (C-Pt/C), with high onset potential, positive half-wave potential and large limiting current density. It also displays superior long-term stability and methanol tolerance for ORR. This work will pave the way for a new approach in the development of highly active and low-cost NPCs for fuel cells.     

寒冷地区某既有办公建筑围护结构优化改造研究

既有公共建筑能耗中,围护结构节能潜力巨大。以兰州某既有办公建筑为例,采用DeST-C软件模拟围护结构不同材料厚度、窗型,得出系列负荷,通过对数据分析、比较,得出如下结论:外墙外保温适宜材料为50mm的挤塑板,最大热负荷节能率为45.66%;屋面适宜保温材料为65mm的挤塑板,最大热负荷节能率为4.25%;外窗各个朝向全部更换玻璃,推荐选用内张膜中空玻璃(双膜),最大热负荷节能率为7.36%;单独更换南向外窗材料,推荐选用真空镀膜复合中空玻璃,最大热负荷节能率为1.78%。     

Superhydrophobic aluminum alloy surface with excellent universality,corrosion resistance,and antifouling performance prepared without prepolishing

It is urgently necessary to seek more simple and effective methods to construct superhydrophobic metal surfaces to improve the corrosion resistance and antifouling performance. Herein, a facile method for fabricating superhydrophobic aluminum alloy surface is developed via boiling water treatment and stearic acid modification. It is noteworthy that no prepolishing on aluminum alloy is required and no caustic reagents and typical equipments are used during the preparation procedure. Therefore, the fabrication method is quite a simple and environment-friendly technique. Both micro- and nano-scaled binary structure forms at the resultant aluminum alloy surface while long alkyl chains are grafted onto the rough aluminum alloy surface chemically. Consequently, the resultant aluminum alloy exhibits outstanding superhydrophobicity. More importantly, the superhydrophobicity has excellent universality, diversity, stability, excellent corrosion resistance, and antifouling performance. The facile preparation, excellent superhydrophobic durability, and outstanding performance are quite in favor of the practical application.     

高能电子成像研究进展

本文通过蒙特卡罗程序EGS模拟研究了电子束与靶的相互作用，对成像束流光学进行了设计，并对束流匹配对空间分辨的影响、超快分束技术和产生横向均匀束技术等进行了模拟研究。实验验证了高能电子成像能达到μm量级的空间分辨，并可实现厚度、密度分辨及明-暗场成像等特点。同时给出了后续实验及研究计划，希望进一步提高高能电子成像性能并拓宽其应用领域。     

基于stackelberg多步博弈的无人机协同搜索路径规划

考虑到现有无人机搜索问题研究中无人机、移动目标仅有一方具有远距离探测能力的设定，已经无法体现出战场环境下双方的博弈关系。针对这一不足，基于stackelberg均衡策略，结合多步预测的思想，提出了stackelberg多步博弈策略，实现了无人机、目标都具有远距离探测能力的博弈搜索。通过建立无人机、目标各自的路径收益函数，使双方能够根据不同时刻的博弈状态选择相对应的函数，实现无人机的动态路径规划。仿真结果表明所提出策略完全适用于该博弈模型，比贪婪策略具有更高的搜索效率，大大提高了目标捕获率。     

单相并联型有源电力滤波器主电路参数耦合关系研究

单相并联型有源电力滤波器(SAPF)主电路参数之间存在一定的耦合关系,这对各参数值的合理选择有较大的影响。通过分析现有单/三相SAPF主电路交流侧电感以及直流侧电压、电容值等参数的计算方法,得到了具体的单相SAPF电路参数解析表达式。针对所得表达式各变量之间的耦合关系,在MATLAB中进行建模优化分析,得出一套完整的参数设计方案。保证在特定负载下补偿后谐波含量低于2%的综合优化目标。仿真和实验过程验证了所选参数的正确性。