全封闭大功率永磁牵引电机的温度场数值计算

为研究全封闭大功率永磁牵引电机额定工况下的稳态温度场,以一台额定功率为815 kW的永磁同步牵引电机为研究对象,依据成型绕组槽部导热模型,建立了整机三维温度场共轭传热计算模型。考虑旋转磁化、冲压过程和磁密高阶谐波对定子铁耗的影响,以及水套-定子铁心间接触热阻抗对电机温升的影响,采用Fluent软件对电机额定工况下的稳态流场与温度场求解,使用电阻法和埋置检温计法（ETD）测得电机在额定工况下绕组的平均温升、铁心测点和绕组端部测点局部温升,绝对误差分别为-3.7 K、-0.3 K和7.6 K。进一步分析了电机水路和内风路流场分布特性、水套-定子铁心间接触间隙对绕组平均温升的影响以及槽内绕组附近的温升分布情况,最后提出了该类电机冷却系统设计优化方向。     

纳米Cr颗粒对Ni-Mo复合镀层性能的影响

为了研究纳米Cr颗粒对Ni-Mo复合镀层性能的影响,采用脉冲电沉积方法制备具有不同Cr含量的Ni-Mo复合镀层.利用扫描电子显微镜和X射线衍射仪分别观察和分析复合镀层的组织形貌及结构.采用电化学测试和X射线光电子能谱研究复合镀层的析氢性能和耐蚀性能.结果表明:随着镀液中纳米Cr颗粒含量的增加,镀层晶粒得到细化,析氢过电位增大,复合镀层析氢性能得到提高;当镀液中纳米Cr颗粒含量为20 g/L时,复合镀层表面钝化膜中MoO₃含量较高,且可与Cr产生协同效应,因而复合镀层具有较好的耐蚀性能;但随着镀液中纳米Cr颗粒含量的进一步增加,复合镀层中沉积的Cr元素含量降低,复合镀层的析氢性能和耐蚀性能均降低.因此,当镀液中纳米Cr颗粒含量为20 g/L时,复合镀层具有较好的析氢性能和耐蚀性能.     

电缆化配电系统高频谐振频移方法

为解决电缆化配电网高频谐振问题,提出了一种基于配电网阻抗重构的高频谐振频移方法。首先,分析了电缆化配电网高次谐波源与高频谐振的产生机理。其次,给出了电缆化配电网阻抗重构的高频谐振频移方法,并比较不同无源阻抗重构后的频移及谐振峰抑制效果。然后,结合实际工程案例,利用系统函数绘出伯德图与根轨迹评价该方法对高频谐振治理效果以及系统稳定性的影响,验证了基于电缆化配电网阻抗重构的高频谐振频移方法的有效性,最后研究了无源阻抗参数变化对配电网高频谐振的影响。     

采用VSG策略的MMC阻抗建模及并网稳定性分析

随着分布式能源并网的增多,局部电网逐渐呈现出弱电网特性,虚拟同步发电机（VSG）控制由于可以模拟同步发电机的特性,能够为弱电网提供惯性和阻尼支撑。本文采用谐波线性化方法对采用VSG控制策略的模块化多电平换流器(MMC)进行阻抗建模。所得到的阻抗模型在低频段主要呈容性,在高频段主要呈感性,在复杂电力系统中,可能会与电网阻抗存在谐振点。分析了VSG主要控制参数对MMC阻抗的影响,发现有功-频率下垂系数、阻尼系数和虚拟转动惯量主要影响50Hz附近的阻抗。根据阻抗稳定性判据对MMC并网系统进行稳定性分析,发现并网系统在高频段有振荡的风险。     

Real-Time Monitoring the Effect of Cytopathic Hypoxia on Retinal Pigment Epithelial Barrier Functionality Using Electric Cell-Substrate Impedance Sensing (ECIS) Biosensor Technology

Disruption of retinal pigment epithelial (RPE barrier integrity is a hallmark feature of various retinal blinding diseases, including diabetic macular edema and age-related macular degeneration, but the underlying causes and pathophysiology are not completely well-defined. One of the most conserved phenomena in biology is the progressive decline in mitochondrial function with aging leading to cytopathic hypoxia, where cells are unable to use oxygen for energy production. Therefore, this study aimed to thoroughly investigate the role of cytopathic hypoxia in compromising the barrier functionality of RPE cells. We used Electric Cell-Substrate Impedance Sensing (ECIS) system to monitor precisely in real time the barrier integrity of RPE cell line (ARPE-19) after treatment with various concentrations of cytopathic hypoxia-inducing agent, Cobalt(II) chloride (CoCl₂). We further investigated how the resistance across ARPE-19 cells changes across three separate parameters: R_b (the electrical resistance between ARPE-19 cells), α (the resistance between the ARPE-19 and its substrate), and C_m (the capacitance of the ARPE-19 cell membrane). The viability of the ARPE-19 cells and mitochondrial bioenergetics were quantified with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay and seahorse technology, respectively. ECIS measurement showed that CoCl₂ reduced the total impedance of ARPE-19 cells in a dose dependent manner across all tested frequencies. Specifically, the ECIS program’s modelling demonstrated that CoCl₂ affected R_b as it begins to drastically decrease earlier than α or C_m, although ARPE-19 cells’ viability was not compromised. Using seahorse technology, all three concentrations of CoCl₂ significantly impaired basal, maximal, and ATP-linked respirations of ARPE-19 cells but did not affect proton leak and non-mitochondrial bioenergetic. Concordantly, the expression of a major paracellular tight junction protein (ZO-1) was reduced significantly with CoCl_2-treatment in a dose-dependent manner. Our data demonstrate that the ARPE-19 cells have distinct dielectric properties in response to cytopathic hypoxia in which disruption of barrier integrity between ARPE-19 cells precedes any changes in cells’ viability, cell-substrate contacts, and cell membrane permeability. Such differences can be used in screening of selective agents that improve the assembly of RPE tight junction without compromising other RPE barrier parameters.     

An experimental evaluation of the effects of ripple current generated by the power conditioning stage on a proton exchange membrane fuel cell stack

In this article, an impedance model of the proton exchange membrane fuel cell stack (PEMFCS) is proposed. The proposed study employs an equivalent circuit of the PEMFCS derived by the frequency response analysis technique. An equivalent circuit for the PEMFCS is developed to evaluate the effects of ripple currents generated by the power-conditioning unit. The calculated results are then verified by means of experiments using a commercially available PEMFCS. The relationship between ripple current and fuel cell performance, such as power loss and fuel consumption, is investigated. Experimental results show that the ripple current can contribute up to a 6% reduction in the available output power. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory, S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.     

TiAl基合金与陶瓷界面反应的研究

借助电子探针微区分析仪、维氏显微硬度计、光学和电子显微镜对TiAl合金与Al2O3,ZrO2以及经CaO稳定的ZrO23种陶瓷型壳的界面反应进行了研究分析。结果表明，这3种材料的化学稳定性依次升高，而经CaO稳定的ZrO2型壳与TiAl反应层的厚度仅为50μm,故可望用作钛铝合金精密铸造型壳面层材料。     

LiFePO4基正极材料容量的温度敏感特性及交流阻抗谱研究

采用原位碳包覆法制备了锂离子二次电池用LiFePO4／C复合正极材料。考察了环境温度对LiFePO4/C电池容量的影响，得到容量与绝对温度之间符合Arrhenius关系。运用交流阻抗谱分析了温度与电池电化学特性的关系，并对电极基于电荷和质量传递控制过程给出了一种新的模拟等效电路，通过Zview拟合软件得到了各个模拟元件的数值及变化趋势，从而定量地解释LiFePO4／C复合电极容量与温度的关系。     

Synthesis of LaF3 superfine powder by microwave heating method

LaF3 superfine powder was synthesized from La(CH3COO)3 and NH4 F by microwave heating method,using ethanol or pure water as dispersants respectively. The results of XRD and SEM indicate that the superfine powder has high purity, regular particle shape and narrow distribution of granularity. The granularity of the best sample is in the range of 100 -200 nm. The influence of different dispersants on the crystal degree and microstructure was discussed. After the superfine powder was formed into a slice at pressure of 25 - 60 MPa, its electrochemical impedance spectroscopy was tested by electrochemical impedance spectroscopy (EIS) measurement. The result shows that the grain refining of LaF3 powder increases its ionic conductivity. Compared with traditional preparation methods of LaF3 powder, the advantages of microwave heating method were summarized.     

Synthesis and electrochemical properties of Th-doped LiMn2O4 powders for lithium-ion batteries

To improve the cycle performance of eco-friendly and cost-effective spinel LiMN2O4 as the Li secondary batteries, the Th-doped LiThxMn1-xO4 spinel powers were synthesized by solid-state method. The starting materials, Li2CO3,MnO2 and Th(NO3)4·4H2O, were mixed uniformly using a traditional ball milling, which resulted in a uniform particle size distribution in the mixed powers. Tests of X-ray diffraction, SEM, impedance spectra and charge-discharge were carried out for LiThxMn1-xO4 cathode materials. Results show that the synthesized LiTh0.01Mn1.99O4 material exhibits standard spinel structure, regular particle morphology and excellent property of charge-discharge for big current. The capacity retention of the material modified by doping Th is more than 85.1% of the first discharge specific capacity of 111.5 mAh·g -1 after 20 cycles at the current rate 1C, while the pristine LiMN2O4 is only 57% of the first discharge specific capacity of 110.2 mAh·g-1 after the same cycles at the same current rate.