Effect of fretting amplitudes on fretting wear behavior of steel wires in coal mines

Given that fretting wear causes failure in steel wires, we carried out tangential fretting wear tests of steel wires on a self-made fretting wear test rig under contact loads of 9 and 29 N and fretting amplitudes ranging from 5 to 180 μm. We observed morphologies of fretted steel wire surfaces on an S-3000N scanning electron microscope in order to analyze fretting wear mecha-nisms. The results show that the fretting regime of steel wires transforms from partial slip regime into mixed fretting regime and gross slip regime with an increase in fretting amplitudes under a given contact load. In partial slip regime, the friction coefficient has a relatively low value. Four stages can be defined in mixed fretting and gross slip regimes. The fretting wear of steel wires in-creases obviously with increases in fretting amplitudes. Fretting scars present a typical morphology of annularity, showing slight damage in partial slip regime. However, wear clearly increases in mixed fretting regime where wear mechanism is a combination of plastic deformation, abrasive wear and oxidative wear. In gross slip regime, more severe degradation is present than in the other regimes. The main fretting wear mechanisms of steel wires are abrasive wear, surface fatigue and friction oxidation.     

混凝土受压构件的力学行为及设计计算

受压构件是混凝土结构课程的主要内容之一,包括轴心受压构件和偏心受压构件.通过轴心受压构件的学习,主要让学习者加深对钢筋与混凝土共同受力时的力学行为的认识;而偏心受压构件的受力状态较复杂,特别是小偏心受压学习起来有一定难度.而一般教材中对有些问题的认识存在偏颇,有些问题没有交代清楚.主要针对轴心受压构件的应力重分布、大小偏心受压的判别条件及其应用、小偏心受压的不同受力状态及其计算方法等问题作了一些较深入的探讨,以期与同行交流,同时希望对"混凝土结构"的学习有所帮助.     

厌氧活性污泥PCR-DGGE图谱的优化

针对特种污泥PCR-DGGE图谱的优化一直是微生物分子生态学研究的重点.在反硝化抑制硫酸盐还原菌的研究中,研究厌氧硫酸盐还原污泥和反硝化污泥DNA的提取方法,应用通用引物958F/1401R扩增16S rDNA序列,探讨不同的退火温度对DGGE指纹图谱多样性影响,同时采用时间进程法对DGGE图谱进行优化.结果表明,采用PBS洗涤污泥和超声震荡有利于硫酸盐还原污泥DNA提取;采用958F/1401R为引物时,扩增片段大约500 bp,不同的退火温度对DGGE指纹图谱的多样性影响不显著;采用时间进程法可以很好地再现不同电泳阶段对样品的分离效果,最佳变性剂梯度为40%～60%,在130 V电压下,最佳电泳时间为5 h.     

海刺参组织蛋白酶L基因的克隆、重组表达及活性鉴定

通过RT-PCR和RACE PCR技术,从海刺参(Stichopus japonicus)肠中克隆得到编码组织蛋白酶L(SjCL)基因,其中全长cDNA 1 287 bp,5′非编码区(UTR)202 bp,3′UTR 87 bp,开放阅读框(ORF)999 bp,编码332个氨基酸(aa),包括组织蛋白酶L成熟肽316 aa和信号肽16 aa,分子质量预测为35.3 ku。用SjCL序列与相似物种海胆、海葵等进行对比,可知SjCL具有组织蛋白酶L所特有的氨基酸保守区域ERFNIN和GNFD,以及由Cys 139,His 278和Asn 299残基组成的保守活性位点。将编码SjCL基因克隆进原核表达载体pET32a(+)中,构建重组质粒pET32a(+)-SjCL,转化至大肠杆菌BL21(DE3)pLysS感受态细胞,再进行诱导表达、亲和纯化和透析复性,得到了纯化且具有活性的重组SjCL。酶活力检测结果表明,重组SjCL对组织蛋白酶L特异性底物Z-Phe-Arg-Nmec具有较高活性,而对组织蛋白酶B特异性底物Z-Arg-Arg-Nmec无活性。本实验对SjCL的cDNA序列进行了生物信息学分析并通过基因工程...     

基于数值模拟的袋式除尘器清灰性能影响探讨

脉冲清灰是袋式除尘器的过滤再生循环过程,相关的流场分布特性直接影响其清灰性能。针对清灰过程喷吹时间短、速度变化快的特点,建立相应的质量通量方程及非稳态流场模型。通过改变喷嘴结构及喷吹控制参数,采用数值模拟方法获得各种条件下的压力、速度分布云图。实际应用表明：基于数值模拟探讨影响清灰效果的因素及其规律,可为袋式除尘器喷吹清灰的优化设计提供重要参考。     

HP nonlinear guidance law design based on smooth sliding mode control

To eliminate the perturbation of interceptor detection induced by aerodynamic heating,the head pursuit (HP) guidance law for three-dimensional interception was presented. The guidance law positioned the interceptor ahead of the target on its flight trajectory,and the speed of interceptor was required to be lower than that of the target. On the basis of a novel head pursuit three-dimensional guidance model,a nonlinear guidance law was developed based on smooth sliding mode control theory. At the same time,a special observer was designed to estimate the target acceleration,and a numerical example on maneuvering ballistic target interception verified the effectiveness of the presented guidance law.     

Synchronization and channel estimation for MIMO OFDM wireless LAN systems

A new preamble structure is designed for wireless LAN based on MIMO OFDM systems, which can be used for both synchronization and channel estimation. Modulatable orthogonal polyphase sequence is utilized in training symbol design regarding its correlation properties. The time synchronization and channel estimation are achieved by measuring the correlation between the received training sequence and the locally generated training sequence. Repeated training symbols are used to get carrier frequency offset (CFO) estimation. It is shown from the analysis that the accuracy of frequency synchronization is close to the Cramér-Rao lower bound. The training sequences are optimal for channel estimation based on the minimum mean square error (MMSE).     

新型燃煤烟气汞吸附剂的评价研究

利用汞蒸气发生器产生的单质汞,与压缩空气组成模拟烟气,在吸附剂评价实验台上进行吸附剂脱汞实验,研究不同吸附剂对单质汞的脱除效率．实验结果表明,活性炭对汞的吸附效率在60％左右,未改性的燃煤飞灰吸附效率在10％～20％,改性后的燃煤飞灰比表面积有很大程度的提高,吸附效率可以达到25％,与活性炭吸附效率相比仍有不小的差距．     

非线性部分最小二乘方法的研究与应用

该文将部分最小二乘算法与径向基函数神经网络相结合,给出了一种非线性部分最小二乘建模方法,可以更加有效地处理过程非线性和数据共线性等复杂特性,提高模型的精度和推广能力。该方法在确定径向基函数神经网络的隐节点时,采用了一种改进型的k-均值聚类算法来自动确定最优的聚类区数。对煤气化炉合成气组分浓度软测量建模的应用结果表明,采用该方法建立的软测量模型在模型精度和推广能力等方面明显优于二次型多项式部分最小二乘方法建立的模型,并且计算精度满足工业生产的实际要求。     

3D Simulation Research on Urea-SCR DeNO<em>x Catalyst for Diesel Engine

In order to reduce oxides of nitrogen (NOx) emanated from a diesel eng ine, a comprehensive urea selective catalyst reduction (SCR) DeNOx catalys t was modeled in which numerical simulations were used as a complementary tool f or the experimental investigations to make the design decisions, and hence short en the development process. In this approach, relevant conversion reactions were studied in 1D model, and the parameters obtained in this way were transferred t o 3D simulations. According to the results ...