Effects of High Salt Concentration and Residue on Copper and Aluminum Corrosion

Traditional researches on metal corrosion under salt solutions deposit conditions are usually carried out by visual, electron microscopic observations and simple electrochemical measurement via a traditional one-piece electrode. These techniques have difficulties in measuring localized corrosion that frequently occur in inhomogeneous media. This paper reports the results from the experiments using specially shaped coupons and a relatively new method of measuring heterogeneous electrochemical processes, namely, the wire beam electrode(WBE). Preliminary results from copper and aluminum corrosion in highly concentrated sodium chloride solutions with and without solid deposits show that the method is useful in simulating and studying corrosion especially localized corrosion in pipelines.     

带有锥形孔的复合变幅杆设计及动态分析

在超声振动拉丝加工过程中,为了实现线材的顺利拉拔,需要应用带有锥形孔的复合变幅杆。为此,本文基于等效四端网络与传输矩阵法,建立了带锥形孔圆锥变幅杆的传输矩阵,推导出带锥形孔圆锥过渡复合变幅杆的频率方程的一般公式。根据推导出的频率方程,应用区间搜索法和牛顿迭代法获取了准确的数值解,实现了该复合变幅杆的纵向振动。之后,应用有限元软件Ansys对设计出的复合变幅杆分别进行模态分析和动力学特性分析,获得了各段不同长度下复合变幅杆谐振频率、放大系数以及最大应力值的变化规律。最后,对制造出的复合变幅杆进行阻抗与振动性能测试,结果表明其频率准确,且振幅比较稳定。     

非均匀钹式换能器平面阵指向性特性研究

针对钹式基阵工作频率低、布阵紧凑导致阵元之间互干扰严重、指向性能退化的现象,本文在均匀平面基阵的基础上提出强度可调节的非均匀平面基阵,建立了基阵指向性能的数学模型,通过数值计算的方法分析阵元间距和中心阵元声强度变化对基阵指向性能的影响。研究给出了主瓣宽度、旁瓣个数、栅瓣个数随阵元间距的变化规律,总结了在各种工作频率下,基阵可用的最大阵元间距。研究结果表明:中心阵元强度增大时,基阵的总体指向性稍有降低。所以当通过调整阵元间距和强度来优化基阵指向性能时,应综合考虑它们对基阵其它性能的影响,以获得最佳的总体性能。     

传声器阵列声压级在线校准*

在户外环境中对某一目标噪声源进行声压级测量时,由于单个传声器不能在多声源干扰情况下有效监测目标信号,为了有效抑制非目标信号的干扰,通常利用传声器阵列进行波束形成从而对目标信号进行增强。MEMS传声器阵列由于体积小,价格低等优点而得到广泛使用,为了解决在户外进行噪声监测时,MEMS然而MEMS传声器阵列器件的工艺误差和灵敏度退化问题会导致波束形成滤波器的性能下降存在由器件工艺误差和老化所导致的声压级测量不准确问题,从而影响声压级的测量结果。为了解决这一问题,本文介绍了一种通过比较补偿参考传声器与传声器阵列之间的测量声压级之偏差进行从而实时在线校准的方法。该方法利用TDOA多声源定位方法在时频点上对实时采集的信号对所采集的信号在时频点上挑选有效目标信号进行有效挑选,并利用参考传声器的标准频响特性去修正阵列的声压级测量误差值。为了验证方法的可行性,本文通过实验比较了不同环境噪声干扰下的测量声压级差与无干扰条件下的测量声压级差的一致性,结果证明该校准方法在具有较好高的精确性和鲁棒性,并且可推广于任意一种阵型的传声器阵列声源定位装置噪声监测装置。     

Simulation of Dynamic Light Scattering Signals of Ultrafine Particles

In order to conveniently obtain dynamic light scattering (DLS) signal, a simulation method of DLS signal is proposed in this paper. This method regards the light intensity fluctuation of DLS as a stationary random process. According to autocorrelation function (ACF) of DLS signal, the stationary random process of DLS can be generated by auto‐regressive (AR) model. Signal simulations of several kinds of distribution particles and comparison of simulations and experiment prove that AR model can be used for DLS signal simulation. Moreover, by analyzing effect of simulation parameters on simulation precision, we obtained the relationship between simulation parameters and simulation precision. Finally, application of simulation signal verifies the effectiveness and convenience of this simulation method.     

Functionalized carbon nanotube/polyacrylonitrile composite nanofibers: fabrication and properties

The functionalized multi‐walled carbon nanotubes (f‐MWCNTs) were obtained by Friedel–Crafts acylation, which introduced aromatic amine groups onto the sidewall. And the grafted yield was adjusted by controlling the concentration of the catalyst. The composite solutions containing f‐MWCNTs and polyacrylonitrile (PAN) were then prepared by in‐situ or ex‐situ solution polymerization. The resulting solutions were electrospun into composite nanofibers. In the in‐situ polymerization, morphological observation revealed that f‐MWCNTs was uniformly dispersed along the axes of the nanofibers and increased interfacial adhesion between f‐MWCNTs and PAN. Furthermore, two kinds of f‐MWCNTs/PAN composite nanofibers had a higher degree of crystallization and a larger crystal size than PAN nanofibers had, so the specific tensile strengths and modulus of the composite nanofibers were enhanced. And the thermal stability of f‐MWCNTs/PAN from in‐situ method was higher than that of ex‐situ system. When the f‐MWCNTs content was less than 1 wt%, the specific tensile strengths and modulus of nanofibers were enhanced with increase in the amounts of f‐MWCNTs, and f‐MWCNTs/PAN of in‐situ system provided better mechanical properties than that of ex‐situ system. Copyright © 2010 John Wiley & Sons, Ltd.     

微尺度圆管内气体流量的实验测量

以氮气和氦气为工作介质,研究了微尺度(φ=17.6μm,17.9μm)圆管内压力驱动的气体流动,测量了在不同进出口压力下的流量,并与计算值进行了比较.结果表明,即使对于极低Mach数(M=0.003～0.03)流动,其可压缩性仍十分明显,它来源于微尺度效应.在本文的实验参数下,Kundsen数范围为3×10-3～7×10-3,表面滑移不明显,稀薄气体效应可以忽略.     

锡青铜基自润滑材料的摩擦学特性研究

采用粉末冶金自由烧结工艺制备出锡青铜基自润滑复合材料,对该类复合材料的力学性能与摩擦磨损特性进行了研究,从固体润滑剂角度就其室温与450℃自润滑机理进行了分析与探讨。研究结果表明,该类材料在室温至450℃温度范围内具有良好的机械性能与磨擦磨损特性。XRD分析结果显示：在室温下磨损表面形成的含石墨、Pb和SnO2的复合膜是其具有润滑性能的主要原因;在高温下则由石墨、Pb2O3和CuO组成的复合膜起主要润滑作用。     

模糊处理变结构神经网络日负荷预测方法研究

对于受不确定因素影响的日电力负荷,首次提出了基于模糊分类规则的变结构神经网络负荷预测模型,考虑从两方面改进预测精度,一个方面是通过模糊分类规则,使过去的负荷数据分为不同气候特征,选用同类特征数据进行预测,另一方面是通过神经网络变结构优化,确定最优网络和最优拟合逼近,从而得到最优的预测结果,这种新方法同时考虑了天气因素的影响和神经网络的最优确定,因此,较大提高了日负荷预测的精度。     

全空间上半线性椭圆方程的正解

采用域扩线技巧与广义Mountain-Pass引理相结合的方法,给出了全空间上方程－Δu mu=u^p-1u的正确的存在性和光滑性。