Equivalent Mohr–Coulomb and generalized Hoek–Brown strength parameters for supported axisymmetric tunnels in plastic or brittle rock

The evaluation of equivalent Mohr–Coulomb (M–C) strength parameters to the prototype Hoek–Brown (H–B) ones for tunnels has been tackled in different ways for many years. The extension of the H–B criterion to the generalized one has made the challenge even greater. Most of the latest methods did not account for the effect of the support pressure and none gave formulae for equivalent parameters of supported or brittle rock. Here, an almost exact explicit solution for the evaluation of the critical pressure, of a tunnel in a rock mass satisfying the generalized H–B criterion, is initially investigated. Then, formulae are derived for the evaluation of equivalent parameters, of either elastoplastic or elastic–brittle plastic rock. They are based either on a best fitting procedure of the two envelopes or on the equation of selected responses of the models. Supported tunnels in equivalent M–C rock masses are then validated against those excavated in the prototype H–B rock masses.     

影响弹簧支承式推力轴承性能的几个因素

本文对弹簧支承式推力轴承进行了三维热弹流研究,发现变形量对轴承性能有很大影响,为此,着重分析了决定轴承变形和油膜形状分布的几个因素对轴承性能影响情况,研究表明,弹簧布置方式,轴瓦厚度和型面形状能严重改变轴承性能,在进行轴承设计时必须对上述因素进行了优化,并提出了一些优化建议。     

Nuclear Magnetic Resonance of Physisorbed 129Xe Used as a Probe to Investigate Porous Solids

Xenon is an inert gas with a large electronic environment that makes it sensitive to any interaction, even physical. In the case of ¹²⁹Xe isotope (spin 1/2), the resulting electronic perturbation is directly transmitted to the nucleus and, therefore, affects the nuclear magnetic resonance chemical shift. In this review, we report exhaustively up to 1996 the many applications of this technique in both fundamental and applied research in the fields of microporous and mesoporous solids.     

Degradation of organic pollutants in water by photochemical reactors

The degradation of glycolic acid in aqueous media was performed by homogeneous photochemical and heterogeneous photocatalytic processes using different kinds of chemical reactors. The efficiency of the degradation processes was evaluated by measuring both the reactant conversion and the decrease of the total organic carbon (TOC) of the solution. The best results were obtained by using a continuous reactor with a fixed supported photocatalyst.     

基于电流内环的一种逆变器控制策略研究

比较了几种电流内环控制的方法,提出了基于电感电流反馈的SPWM电流控制型双环控制策略。针对输出电压对电流环的交叉反馈作用,通过采用电容电压解耦方法,削弱了电容电压对内环的影响;针对负载电流扰动对电压外环的影响,采用负载电流前馈补偿方法,很大程度上增加了系统对负载电流扰动的抑制能力;针对电压外环的PI调节器存在的相位滞后,提出了基准电容电流前馈补偿方法,理论上达到输出电压与基准正弦给定的零相差。通过仿真和实验,证实了本控制方案的可行性和优越性。     

基于DSP的高压巡线机器人伺服控制系统

在分析和研究高压巡线机器人原控制器的基础上,设计了一种基于DSP 的全数字化控制器。该控制器采用主从式多处理器工作模式,用6 个DSP 对机器人12 个关节的无刷直流电机进行伺服控制,采用高速CAN 总线实现上位机和下位机的通讯。与原控制器相比,该控制器具有较高的集成度和优良的性价比,便于降低成本,减少机电系统体积。试验表明,该控制器性能稳定可靠,可满足机器人多轴控制的需要。     

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.     

超限框支高层抗震墙建筑结构抗震设计

结合工程实例,对超限框支结构设计原则进行简要论述。通过对设计探索过程的剖析,我们试图阐明:对于较为复杂的结构体系,在缺乏较为明确或常规的规范依据情况下,需要回归到结构设计最基本的原理上。先期针对结构不同部位、不同受力状态,分别设定出在小震、中震、大震作用下不同的抗震设防目标,并根据目标期望,进行有目的的结构分析,并取得相对应的、可靠的内力值。这样,才更能够最真实的反应出结构状态,从而确保结构安全。     

A durable ruthenium catalyst for the NaBH4 hydrolysis

Ru-active carbon (Ru/C) catalysts are prepared by impregnation reduction method for hydrogen generation via hydrolysis of alkaline sodium borohydride (NaBH₄) solution. The corresponding activity and durability of the prepared catalysts are tested in an immobile bed reactor. The variation of hydrogen generation rate with the increasing of flux and concentration of NaBH₄ solution is measured. The durability of the catalysts prepared under various reductive pH values and reductants is tested by using different concentrations of NaBH₄ solution (10 & 15 wt%). It is found that the durability of catalyst in 15 wt% NaBH₄ solution is longer than that in 10 wt% NaBH₄ solution. The deactivation of Ru/C catalysts is considered as the comprehensive effect of three factors: the loss of Ru, the deposition of byproducts on the catalyst surface and the aggregation of Ru particles.     

Co-production of hydrogen and multi-wall carbon nanotubes from ethanol decomposition over Fe/Al2O3 catalysts

The co-production of hydrogen and carbon nanotubes (CNTs) from the decomposition of ethanol over Fe/Al₂O₃ at different temperatures and feeding rates of ethanol was investigated systematically. The results indicated that Fe/Al₂O₃ was a quite active catalyst for the co-production of hydrogen and CNTs and that its activity and stability depended strongly on the Fe loading. Among all catalysts tested, 10 mol% Fe/Al₂O₃ was the most effective catalyst based on the ratio of hydrogen production, the total H₂ yield, and the quality of the CNTs formed. The efficiency of hydrogen production from ethanol decomposition over 10 mol% Fe/Al₂O₃ reached a maximum of 80% at 800 °C and the yield of CNTs with well-oriented growth and uniform diameter was 141%. In addition, the reaction of hydrogen and CNTs co-produced from ethanol decomposition was proposed.