基于不同化学还原法制备的Au/XC-72及其对L-CySH的催化氧化反应研究

本文采用乙二醇还原法、抗坏血酸还原法、柠檬酸三钠还原法及硼氢化钠还原法合成胶体金溶液,并将其负载于XC-72上制备Au/XC-72催化剂。X射线衍射(XRD)表明四种方法制备的催化剂均具有明显的Au特征衍射峰,且硼氢化钠还原法制备的Au衍射峰最平缓。透射电子显微镜(TEM)表明硼氢化钠还原法制备的金纳米颗粒(Au NPs)粒径最小,在XC-72表面分布均匀,其他三种方法制备的AuNPs粒径较大,且发生不同程度的团聚。利用制备的催化剂(Au/XC-72)修饰玻碳电极(GCE)并用于L-半胱氨酸(L-CySH)的电催化氧化机制研究,结果显示硼氢化钠还原法制备的Au/XC-72在pH为2时对L-CySH的催化氧化较其它三种方法制备的材料表现出最优的活性,且在1m M～10m M的范围内呈现线性关系,表明L-CySH在Au/XC-72上的氧化反应的速率是受扩散过程控制的。电催化活性高粒径小的Au/XC-72修饰GCE构建的传感器具有广泛的实际应用价值。     

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 72B线材在绕簧过程中发生了断裂现象。利用金相显微镜对断口附近的金相组织、非金属夹杂物和表面形貌等进行了分析。结果表明：钢丝表面有损伤，且损伤部位出现横向裂纹和形变马氏体，这是导致绕簧过程中发生断裂的主要原因。针对断裂产生的原因，提出具体的改进措施。     

Fundamentals of hydrogen storage processes over Ru/SiO2 and Ru/Vulcan

Hydrogen adsorption and desorption over Ru/SiO₂ and Ru/Vulcan are investigated in terms of hydrogen storage and release characteristics by both dynamic and static experiments. Ru particle dispersions as a function of metal loading were determined by HR-TEM and volumetric chemisorption experiments. Vulcan was more accommodating for spillover hydrogen than SiO₂. High Ru dispersions, i.e., small particle sizes, favored the amount of hydrogen spillover to Vulcan, as revealed by temperature programmed desorption (TPD) of hydrogen. TPD of hydrogen under He flow experiments over Ru/SiO₂ and Ru/Vulcan materials revealed a low temperature process (up to 200 °C) attributed to desorption of weakly bound hydrogen from Ru metal surface. A high temperature process (above 450 °C) was attributed to diffusion of hydrogen from the support to the Ru particle and desorption at the Ru sites. Hydrogen adsorbs strongly on Ru metal, as indicated by the initial heats of H₂ adsorption measured as 100 kJ/mol over 1 wt% Ru/Vulcan by adsorption calorimetry. At higher coverages, heat of adsorption of hydrogen was measured as 10 kJ/mol. Low heat of adsorption of hydrogen at high coverages indicate multilayer weak adsorption of hydrogen over the storage material, which can desorb at lower temperatures.     

基于8XC552 I2C总线结构的多主串行通信的设计与实现

介绍了I^2C总线的特点，重点给出了基于Philips公司内嵌I^2C总线结构微控制器80C552多主双向串行通信的设计与实现方法。     

A design method for flaming fire detection

The scientific basis of a design method for the detection of flaming fires is reviewed. The equations required to calculate detector spacings are included and the selection of appropriate design input parameters is discussed. Limitations of the method and areas for further research are identified. The design method has been implemented and proposed for inclusion in NFPA Standard 72E-1984 as Appendix C by the 72E-M Committee. Center for Fire Safety Studies Worcester Polytechnic Institute     

用XC4000系列芯片设计同步FIFO存储器

本文描述基于双口RAM的同步FIFO存储器设计。双口RAM是采用可编程逻辑XC4000系列器件中的双口RAM,同步FIFO设计使用公共读/写时钟信号。     

基于CAN总线网络技术的温室控制系统设计

对温室控制系统的特点进行了研究,从低成本和可靠性以及技术优势的角度出发,提出了基于CAN总线网络技术的温室控制系统设计,介绍了P8XC591单片机的特点,分析了系统软硬件的设计     

FANUC0i与华中HNC-21／22T系统的G72、G73指令应用的区别

通过对比分析G72、G73指令在FANUC0i系统和华中HNC-21／22T系统的数控车床上编程格式、编程要求和指令执行过程,得出G72、G73指令在2种系统上应用时,编程格式、编程要求和指令执行过程的异同,并使用G72、G73指令编程,在上述数控车床上进行了加工验证,验证结果表明,本文所做的分析和结论完全符合实际情况,可以作为在实际中使用这2种数控系统功能指令的参考依据。     

The Influence of Pt Loading,Support and Nafion Content on the Performance of Direct Methanol Fuel Cells: Examined on the Example of the Cathode

Nano‐sized Pt colloids were prepared using the polyol method and supported on Ketjen black EC 600J (KB), Vulcan XC‐72 (VC) and high surface area graphite 300 (HG). The effects of the Nafion ionomer content, and the Pt loading of the cathode catalyst layer as well as the Pt loading on the support on the performance of direct methanol fuel cells (DMFCs), were studied. The membrane electrode assemblies (MEAs) were analysed using current–voltage curves, cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and adsorbed CO stripping voltammetry. Optimum Nafion to carbon (N/C) ratios (N/C being defined as the weight ratio of the Nafion ionomer to the carbon) were determined. The optimum N/C ratios were found to depend on the support as follows, 1.4, 0.7 and 0.5 for Pt/KB, Pt/VC and Pt/HG, respectively and to be independent of the Pt/C loading range of 20–80 wt% tested in this work. The highest DMFC performances, as well as the highest electrochemical active surface areas, and improved gas diffusivities, were achieved using these ratios. For the catalysts prepared in this work, the average Pt crystallite size was found to decrease with increasing surface area of the support for a particular Pt loading. MEAs made using KB as support and the optimal N/C ratio of 1.4 showed the best performances, i.e. higher than the VC and HG supports for any N/C ratio. The highest DMFC performance was observed using 60 wt% Pt on KB cathode electrodes of 1 mg Pt cm^–2 loading and an N/C value of 1.4. For all three supports studied, the 60 wt% Pt on carbon loading resulted in the best DMFC performance. This may be linked to the Pt particle size and catalyst preparation method used in this work. In comparison to literature results, high DMFC performances were achieved using relatively ‘low' Pt and Ru loadings. For example, a maximum power density of >100 mW cm^–2 at 60 °C was observed using a 1 mg Pt cm^–2 cathode loading and a 2 mg PtRu cm^–2 anode loading.     

雷达天线运动参数的自动测量

为了自动测量某型雷达天线运动参数(天线俯仰运动范围、方位扇扫范围、方位扇扫速度、天线圆扫速度等),该文搭建了由工业控制计算机、PXI模块化仪器和自动测试软件组成的自动测试系统(ATS).该系统利用PXI-6704数模变换器发送天线运动控制指令,运用FPGA XC3090A测量天线运动参数,通过PXI-8420串行总线模块回传给工控机,并给出了运动参数的计算方法和误差分析.实际应用表明,该方法提高了自动检测水平和测量结果的准确性、实时性,不仅为雷达设备的自动测试提供了通用的设计方法,而且可为其他电子设备自动测试系统的组建提供有益的借鉴.