The bipolar plate of AISI 1045 steel with chromized coatings prepared by low-temperature pack cementation for proton exchange membrane fuel cell

The low-temperature pack chromization, a reforming pack cementation process, is employed to modify AISI 1045 steel for the application of bipolar plates in PEMFC. The process is conducted to yield a coating, containing major Cr-carbides and minor Cr-nitrides, on the substrate in view of enhancing the steel's corrosion resistance and lowering interfacial contact resistance between the bipolar plate and gas diffusion layer. Electrical discharge machining and rolling approach are used as the pretreatment to produce an activated surface on the steel before pack chromization process to reduce operating temperatures and increase deposition rates. The rolled-chromized steel shows the lowest corrosion current density, 3 × 10⁻⁸ A cm⁻², and the smallest interfacial contact resistance, 5.9 mΩ cm², at 140 N cm⁻² among all tested steels. This study clearly states the performance of 1045 carbon steel modified by activated and low-temperature pack chromization processes, which possess the potential to be bipolar plates in the application of PEMFC.     

Characterizations,relationship, and potential sources of outdoor and indoor particulate matter bound polycyclic aromatic hydrocarbons (PAHs) in a community of Tianjin,Northern China

Polycyclic aromatic hydrocarbons (PAHs) are among the most toxic air pollutants in China. However, because there are unsubstantial data on indoor and outdoor particulate PAHs, efforts in assessing inhalation exposure and cancer risk to PAHs are limited in China. This study measured 12 individual PAHs in indoor and outdoor environments at 36 homes during the non‐heating period and heating period in 2009. Indoor PAH concentrations were comparable with outdoor environments in the non‐heating period, but were lower in the heating period. The average indoor/outdoor ratios in both sampling periods were lower than 1, while the ratios in the non‐heating period were higher than those in the heating period. Correlation analysis and coefficient of divergence also verified the difference between indoor and outdoor PAHs, which could be caused by high ventilation in the non‐heating period. To support this conclusion, linear and robust regressions were used to estimate the infiltration factor to compare outdoor PAHs to indoor PAHs. The calculated infiltration factors obtained by the two models were similar in the non‐heating period but varied greatly in the heating period, which may have been caused by the influence of ventilation. Potential sources were distinguished using a diagnostic ratio and a mixture of coal combustion and traffic emission, which are major sources of PAHs.     

变电站电缆防火措施分析与改进

通过分析变电站现有电缆防火措施，提出进一步完善变电站电缆防火措施的方案，可供从事电力防火安全管理的技术人员参考。     

化学发光免疫分析现状

化学发光免疫分析是近年来获得迅速发展的一类重要免疫分析技术,本工作对这一技术的原理、现状和发展趋势作了评述。     

曲柄摇杆式分插机构再现轨迹的优化设计

应用优化设计方法，对再现轨迹的分插机构进行了尺度综合。从工程实际出发，以轨迹误差最小为目标函数，以满足传动角条件及尺寸条件为约束条件，求得了机构最优参数。     

科技成果价值的模糊评判

通过模糊数学方法在科技成果价值模糊综合评判上的运用，解决了因素打分法，投票表决法等方法之不足。通过示例，展示科技成果价值的模糊综合评判，既反映人们认识上的差异性，又反映出事物的本质属性，并为科技成果的商品化、产业化提供科学依据。     

串联系统可靠度优化分配

目前系统可靠度优化分配只考虑系统的成本而忽视了系统的长远利益．针对这一问题，本文建立了系统的长远利益（损失期望）与可靠度间的函数关系，在此基础上提出了既考虑当前成本又考虑长远利益的串联系统可靠度优化分配方法，并给出了具体算例．     

关于南水北调中线工程中建立计算机控制系统策略的思考

本文介绍了南水北调中线工程的概况，并对枢纽站控制室的布置和数据采集与控制系统的策略发表了看法。