唐钢“40000”空分设备冷箱总体布置几点体会

结合唐钢“40000”空分冷箱总体设计,简述了在大型空分冷箱总体设计中应考虑的问题,尤其对于带卧式主冷的空分冷箱进行合理的布置,可降低成本,同时可确保整套空分装置运行的安全性和可靠性.     

基于高速A／D卡的全波形采集超声自动检测系统

设计了一种全波形采集超声自动检测系统,实现了A,B,C 3种扫描方式且具有记录被检材料上所有检测点超声A扫描波形的功能,支持材料超声检测、评价技术研究.该系统由高速A/D卡、超声检测仪、自动扫描器、运动控制系统和CSCAN软件等组成,作为核心部件的高速A/D卡选用PCI-9820型,负责从超声检测仪采集A扫描波形信号.自动扫描过程中,A/D卡与超声检测仪、运动控制系统之间通过硬件信号实现同步,使A扫描波形数据的采集与被检材料上声传播的渡越时间、预定测量点位置相对应,采集得到的A扫描波形数据通过A/D卡的板载SDRAM及DMA功能异步传输至计算机内存,并由CSCAN软件进一步实现数据压缩、滤波、存储以及不同方式成像等处理.测试结果证明,该系统运行速度快,成像精度高且性能稳定. 更多还原     

Hydrothermal Transformation of Dried Grass into Graphitic Carbon‐Based High Performance Electrocatalyst for Oxygen Reduction Reaction

In this work, we present a low cost and environmentally benign hydrothermal method using dried grass as the sole starting material without any synthetic chemicals to directly produce high quality nitrogen‐doped carbon nanodot/nanosheet aggregates (N‐CNAs), achieving a high yield of 25.2%. The fabricated N‐CNAs possess an N/C atomic ratio of 3.41%, consist of three typed of doped N at a ratio of 2.6 (pyridinic):1.7 (pyrrolic):1 (graphitic). The experimental results reveal that for oxygen reduction reaction (ORR), the performance of N‐CNAs, in terms of electrocatalytic activity, stability and resistance to crossover effects, is better or comparable to the commercial Pt/C electrocatalyst. The theoretical studies further indicate that the doped pyridinic‐N plays a key role for N‐CNAs' excellent four‐electron ORR electrocatalytic activity.     

Speed limit reduction in urban areas: A before–after study using Bayesian generalized mixed linear models

In fall 2009, a new speed limit of 40 km/h was introduced on local streets in Montreal (previous speed limit: 50 km/h). This paper proposes a methodology to efficiently estimate the effect of such reduction on speeding behaviors. We employ a full Bayes before–after approach, which overcomes the limitations of the empirical Bayes method. The proposed methodology allows for the analysis of speed data using hourly observations. Therefore, the entire daily profile of speed is considered. Furthermore, it accounts for the entire distribution of speed in contrast to the traditional approach of considering only a point estimate such as 85th percentile speed. Different reference speeds were used to examine variations in the treatment effectiveness in terms of speeding rate and frequency. In addition to comparing rates of vehicles exceeding reference speeds of 40 km/h and 50 km/h (speeding), we verified how the implemented treatment affected “excessive speeding” behaviors (exceeding 80 km/h). To model operating speeds, two Bayesian generalized mixed linear models were utilized. These models have the advantage of addressing the heterogeneity problem in observations and efficiently capturing potential intra-site correlations. A variety of site characteristics, temporal variables, and environmental factors were considered. The analyses indicated that variables such as lane width and night hour had an increasing effect on speeding. Conversely, roadside parking had a decreasing effect on speeding. One-way and lane width had an increasing effect on excessive speeding, whereas evening hour had a decreasing effect. This study concluded that although the treatment was effective with respect to speed references of 40 km/h and 50 km/h, its effectiveness was not significant with respect to excessive speeding-which carries a great risk to pedestrians and cyclists in urban areas. Therefore, caution must be taken in drawing conclusions about the effectiveness of speed limit reduction. This study also points out the importance of using a comparison group to capture underlying trends caused by unknown factors.     

Novel computational methods for high‐dimensional stochastic sensitivity analysis

This paper presents three new computational methods for calculating design sensitivities of statistical moments and reliability of high‐dimensional complex systems subject to random input. The first method represents a novel integration of the polynomial dimensional decomposition (PDD) of a multivariate stochastic response function and score functions. Applied to the statistical moments, the method provides mean‐square convergent analytical expressions of design sensitivities of the first two moments of a stochastic response. The second and third methods, relevant to probability distribution or reliability analysis, exploit two distinct combinations built on PDD: the PDD‐saddlepoint approximation (SPA) or PDD‐SPA method, entailing SPA and score functions; and the PDD‐Monte Carlo simulation (MCS) or PDD‐MCS method, utilizing the embedded MCS of the PDD approximation and score functions. For all three methods developed, the statistical moments or failure probabilities and their design sensitivities are both determined concurrently from a single stochastic analysis or simulation. Numerical examples, including a 100‐dimensional mathematical problem, indicate that the new methods developed provide not only theoretically convergent or accurate design sensitivities, but also computationally efficient solutions. A practical example involving robust design optimization of a three‐hole bracket illustrates the usefulness of the proposed methods. Copyright © 2014 John Wiley & Sons, Ltd.