Template-directed synthesis of nitrogen- and sulfur-codoped carbon nanowire aerogels with enhanced electrocatalytic performance for oxygen reduction

Heteroatom doping,precise composition control,and rational morphology design are efficient strategies for producing novel nanocatalysts for the oxygen reduction reaction (ORR) in fuel cells.Herein,a cost-effective approach to synthesize nitrogen-and sulfur-codoped carbon nanowire aerogels using a hard templating method is proposed.The aerogels prepared using a combination of hydrothermal treatment and carbonization exhibit good catalytic activity for the ORR in alkaline solution.At the optimal annealing temperature and mass ratio between the nitrogen and sulfur precursors,the resultant aerogels show comparable electrocatalytic activity to that of a commercial Pt/C catalyst for the ORR.Importantly,the optimized catalyst shows much better long-term stability and satisfactory tolerance for the methanol crossover effect.These codoped aerogels are expected to have potential applications in fuel cells.     

Analyses of the fatigue crack propagation process and stress ratio effects using the two parameter method

In situ SEM observations (Zhang JZ. A shear band decohesion model for small fatigue crack growth in an ultra-fine grain aluminium alloy. Eng Fract Mech 2000;65:665–81; Zhang JZ, Meng ZX. Direct high resolution in-site SEM observations of very small fatigue crack growth in the ultra fine grain aluminium alloy IN 9052. Script Mater 2004;50:825–28; Halliday MD, Poole P, Bowen P. New perspective on slip band decohesion as unifying fracture event during fatigue crack growth in both small and long cracks. Mater Sci Technol 1999;15:382–90) have revealed that fatigue crack propagation in aluminium alloys is caused by the shear band decohesion around the crack tip. The formation and cracking of the shear band is mainly caused by the plasticity generated in the loading part of a load cycle. This shear band decohesion process has been observed to occur in a continuous way over the time period during the loading part of a cycle. Based on this observation, in this study, a new parameter has been introduced to describe fatigue crack propagation rate. This new parameter, da/dS, defines the fatigue crack propagation rate with the change of the applied stress at any moment of a stress cycle. The relationship between this new parameter and the conventional da/dN parameter which describes fatigue crack propagation rate per stress cycle is given.Using this new parameter, it is proven that two loading parameters are necessary in order to accurately describe fatigue crack propagation rate per stress cycle, da/dN. An analysis is performed and a general fatigue crack propagation model is developed. This model has the ability to describe the four general type of fatigue crack propagation behaviours summarised by Vasudevan and Sadananda (Vasudevan AK, Sadananda K. Fatigue crack growth in advanced materials. In: Fatigue 96, Proceedings of the sixth international conference on fatigue and fatigue threshold, vol. 1. Oxford: Pergamon Press; 1996. p. 473–8).     

两步动态编程识别连续单词的算法实现

传统的DTW算法大多用来识别孤立单词,并已极具实用价值,但是这种方法不适用于连续单词的识别。利用两步动态编程算法解决了连续单词的识别问题。两步动态编程算法首先把每个参考模型与测试串的一部分匹配,然后根据获得两者间最小距离的次序将参考模型个体拼接起来当作辨识解。给出了两步动态编程算法的基本实现方法,并进行了实验验证。     

Physical insights regarding design and performance of independent-gate FinFETs

Important physical insights regarding the design and performance of independent-gate FinFETs, e.g., the MIGFET , are gained from measured data and predictions from our process/physics-based double-gate (DG) MOSFET model (UFDG) in Spice3. Inversion charge-centroid shifting, modulated by gate biases as well as by quantum-confinement and short-channel effects, underlies the sensitivity of the MIGFET (front-gate) threshold voltage to the back-gate bias. MIGFET design and operation-mode options are examined for optimizing circuit applications. Further, novel design of a single-device RF mixer and a double-balanced counterpart using MIGFETs is studied with UFDG/Spice3. Reasonably good MIGFET mixers, with regard to conversion gain and linearity with small-size/low-voltage/low-power requirements, can be achieved with optimal biases on the two gates and good design of the MIGFET structure.     

DSL系统中双绞线电缆的测试和分析

本文系统提出了DSL系统中双绞线电缆的测试方法和数据处理方法,包括双绞线传递函数和近端、远端串音传递函数,进行了实际的测量并给出了相应的测试结果.在此基础上用最小二乘法对测试结果进行了数据处理,给出了实验室环境下测得的双绞线近端串音耦合系数和远端串音耦合系数,为我国DSL传输线路的研究提供了第一手数据.结果显示,测试和数据处理结果与相关的国际标准非常近似,这从一定程度上说明本论文提出的双绞线电缆的测试方法和数据处理方法具有可行性和可靠性.     

Effects of Indium Doping on the Properties of Cd1-xMnxTe Crystals

通过近红外和红外透过谱表征,确定出掺铟后碲锰镉晶体透过率迅速下降,这是晶格吸收和自由载流子吸收共同作用的结果;而光致发光谱的分析结果表明,掺杂后施主-受主对峰增加,受主束缚激子峰减弱,且随着In含量的增加,受主束缚激子峰消失,只剩下施主-受主对峰。这一系列变化是因为替代的In原子作为施主补偿了Cd空位的缘故。拉曼光谱的测量显示,In掺杂导致"类CdTe"的纵向光学声子峰减弱;而磁学的测试结果则说明In的引入几乎不引起碲锰镉晶体磁化强度的变化。     

极罕遇地震作用下PC隔震结构侧向倒塌可靠度分析

为研究极罕遇地震作用下PC隔震结构的抗侧向倒塌能力,同时考虑地震动与结构参数的不确定性,利用MIDAS建立PC隔震结构与现浇隔震结构的随机有限元模型进行弹塑性时程分析,对比两类结构在不同类型极罕遇地震作用下的损伤指数,并以损伤指数作为性能指标,利用二次四阶矩法计算PC隔震结构与现浇隔震结构的失效概率,对两类结构的抗侧向...     

数字地图的安全保护在档案管理信息系统中的实现方法

数字地图是测绘单位的宝贵财富，具有巨大的可重复利用价值，是保密资料，特别是全面实行数字作业以来，形成的数字地图由于具有易复制、易携带、易更改重用和易大范围泄密等特性，单纯的磁盘文件式管理存在着巨大的安全隐患．介绍了一种在测绘档案管理信息系统的开发中，通过数据库和压缩技术的应用，全面实现数字地图安全高效管理的方法。     

On cutting temperatures in high and ultrahigh-speed machining

Since Dr. Carl Salomon proposed the well-known hypothesis on cutting temperatures in 1931, the debate on the hypothesis has never stopped. It shows that ev     

ISO14000标准在我国基本建设领域的具体适用

ISO14000标准要求实施从产品开发设计、加工制造、流通、使用、报废处理到再生利用全过程的产品生命周期评定制度。实施ISO14000标准,对保护环境资源和推动可持续发展均具有重要意义。虽然我国《建筑法》对ISO14000标准有所反映,但是仍然存在法律体系庞杂、制度不配套,标准不统一、缺乏可操作性等缺陷。为了落实ISO14000标准,我们应该在科学发展观的指导下,在基本建设领域建立环境管理手册、新闻披露制度和市场清除、绿色认证和绿色标志以及环境保护公众参与制度。