86.5GHz下输出功率257mW的 W波段GaN MMIC放大器

我们报道了一个三级W波段GaN MMIC功率放大器。考虑到W波段MMIC的耦合效应,所有的匹配电路和偏置电路都是先进行电路仿真以后,再用3D电磁场仿真软件进行系统的仿真。此MMIC功率放大器在频率为86.5GHz下输出功率能达到257mW,相应的功率附加效率(PAE)为5.4%,相应的功率增益为6.1dB。功率密度为459 mW/mm。另外,此MMIC功率放大器在83 GHz到90 GHz带宽下有100mW以上的输出功率。以上特性都是在漏极电压为12V时测试得到。     

基于去极化电流子谱线的油纸绝缘老化评估

去极化电流能够很好表征油纸绝缘系统介质响应过程.本文对去极化电流内部弛豫特性进行研究,引入子谱线和子谱线能量这两个新特征量,探讨子谱线能量与绝缘老化状况的关系,进而研究子谱线与油纸绝缘成分的对应关系,从而得到油纸绝缘老化的判别方法.研究结果表明子谱线能量对老化变化灵敏,它随绝缘水平的降低而显著增加;绝缘油的状态与小时间常数子谱线相关;绝缘纸的状态与大时间常数子谱线相关.因此,去极化电流子谱线及其能量可重点作为绝缘诊断的判据,其为准确评估油纸绝缘老化状态提供一种可靠有力的分析手段.     

基于PSCAD的三相不平衡治理措施研究

随着农村经济的高速增长,用电量飞速上升,农村配电网建设的长期滞后及用户负荷不均导致低电压现象严重。三相不平衡严重、无功欠补、供电半径较长、导线截面积偏小是低电压问题的主因。本文首先通过低电压问题的成因分析,重点讨论三相不平衡对线路电压的影响。其次针对三相不平衡造成的线路低电压问题,提出采用管理上和技术上的治理措施,解决重载相线路低电压问题。本文最后采用PSCAD/EMTDC仿真软件建立某一农村配电网实际供电模型,通过仿真验证三相不平衡的治理措施,为农村配电网的线路低电压问题提供治理依据。     

电力机车列车供电系统接地研究

详细介绍了列车供电系统多种接地方法,并给出其相应的工作原理图,利用Matlab建立电力机车列车供电系统模型,对每一种接地情况作了闭环仿真分析,通过多方面的仔细研究和论证,并结合现场的高压试验验证,找出了最佳的接地判断解决方案,为列车供电系统的接地判断提供了必要的依据。     

特高压直流入闽全寿命周期费用计算和CVaR分析

为了量化特高压的投资风险,以全寿命周期成本为指导,构建包括一次投资、线路和变压器的运行损耗、运行维护、故障损失及提出了估算公式的报废成本的LCC模型,在对费用分解成设备级、系统级和外部环境成本的基础上,将特高压直流的直流偏磁影响和交流系统故障导致换相失败等故障纳入故障成本估算中,提出了区域级费用概念,建立更为全面的特高压全周期寿命成本模型。分别从品牌价值、销售收入和减少碳排放量的角度分析特高压所带来的社会经济环境综合效益,估算特高压直流系统60年内的投资收益率。采用条件风险价值分析法,与蒙特卡罗模拟法相结合进行求解,量化直流特高压入闽的风险,预测在置信度为95%和99%的特高压直流投资的最大损失,为进一步深化特高压系统投资管理提供了参考依据。提出了满足福建直流特高压入闽的时空方案建议。     

基于RT Thread的便携式健康监测仪的设计

随着社会的发展、生活水平的不断提高,人们对自身健康问题更为重视,而传统的健康监测设备缺乏有效的健康管理功能。为此,介绍了一种便携式健康监测仪的软硬件设计,该设计采用基于Cortex M4内核的32位低功耗处理器作为系统的控制核心,采用RT Thread实时操作系统作为系统的软件平台。系统可实现心率测量、额温测量、计步与能耗监测、健康任务管理等功能。进而通过健康检测—干预方案生成—干预方案执行监测—干预效果评估（健康再检测）的闭环管理模式,不断改善和促进健康。     

An efficient small‐delay faults simulator based on critical path tracing

Testing for small‐delay defects (SDDs) has become an important component of integrated circuit testing. In this paper, an efficient small‐delay fault simulator, a hybrid method combining forward serial simulation and backward critical path tracing simulation for SDDs is proposed, which aims to determine the coverage of small‐delay defects for a given test set fast and accurately. In our proposed method, a unit delay model is employed, and reconvergent sensitization as well as hazard‐based detection is considered. Signal waveforms are expressed by bitmap data forms. In addition to providing an accurate result for fault simulation, the proposed simulator can well assist test generation. Experimental results demonstrate that the proposed simulator can further accelerate the simulation by one or two orders of magnitude compared with previous works. Copyright © 2014 John Wiley & Sons, Ltd.     

Mechanistic insights into the structure‐dependent selectivity of catalytic furfural conversion on platinum catalysts

The effects of surface structures on the selectivity of catalytic furfural conversion over platinum (Pt) catalysts in the presence of hydrogen have been studied using first principles density functional theory (DFT) calculations and microkinetic modeling. Three Pt model surface structures, that is, flat Pt(111), stepped Pt(211), and Pt₅₅ cluster are chosen to represent the terrace, step, and corner sites of Pt nanoparticle. DFT results show that the dominant reaction route (hydrogenation or decarbonylation) in furfural conversion depends strongly on the structures (or reactive sites). Using the size‐dependent site distribution rule, our microkinetic modeling results indicate the decarbonylation route prevails over smaller Pt particles less than 1.4 nm while the hydrogenation is the dominant reaction route over larger Pt catalyst particles at T = 473 K and = 93 kPa. This is in good agreement with the reported experimental observations. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3812–3824, 2015     

Enhanced Ferroelectric Phase Stability and High Temperature Piezoelectricity in PN Ceramics via Multisite Co‐Doping

The tungsten bronze‐type lead metaniobate (PbNb₂O₆, PN) is a promising material for high‐temperature piezoelectric devices, while its application is limited by the difficulty in fabrication. In this study, the microstructure and electrical properties of Ca‐doped PN and Ca, Mn‐co‐doped PN ceramics sintered at different temperatures were investigated. Doping promoted the formation of the originally metastable ferroelectric orthorhombic phase. This might be partly attributed to the increased lattice distortion of the orthorhombic phase in the doped samples compared to that reported for pure PN. However, in single A‐site Ca‐doped PN the ferroelectric orthorhombic structure showed a low stability and started to transform to paraelectric phase far below 300°C, resulting in unstable high temperature piezoelectric properties. Interestingly, such a phase transition was completely depressed by A‐site Ca and multisite Mn‐co‐doping, which also improved the piezoelectric performance (d₃₃ = 71 pC/N) and thermal stability in both structure and piezoelectricity. The better stability and performance of the co‐doped samples were explained by the improved sintering behavior and poling efficiency as well as its ability to occupy different sites in the TTB lattice.     

Use of Cottonseed Meal for Producing Eicosapentaenoic Acid by Pythium irregulare

Cottonseed meal (CSM), a common agricultural by‐product, was used as a nutrient source for the production of eicosapentaenoic acid (EPA) by Pythium irregulare. CSM can support good cell growth performance, as can yeast extract (YE). In terms of the maximum EPA content and EPA yield, CSM is superior to YE. Low concentrations of CSM are beneficial to lipid synthesis, and high concentrations favor the EPA content. Utilizing response surface methodology (RSM) analysis, the optimum contents of glucose and CSM in the fermentation medium were determined to be 40.2 and 16.1 g/l, respectively. After 6 days of fermentation at 25 °C and optimal conditions, the EPA yield and productivity were 245.3 and 40.9 mg/l day, respectively. Particle size of CSM was found to affect the EPA production, and a finely ground CSM (100 mesh) was determined to be best for EPA production. The variation in the fatty acid content of total fatty acid (TFA) indicates that EPA was synthesized through the n‐6 route in P. irregulare and Δ12 desaturase was the key enzyme for EPA biosynthesis. Sodium carbonate was determined to be notably good at removing free gossypol attached to biomass. After fungal biomass from each flask had been harvested from Na₂CO₃‐supplemented medium, 1 % (w/v) Na₂CO₃ solution was used to wash the mycelia three times; free gossypol (FG) was not detected (detection limit 0.0018 %). This work provides a new approach using cottonseed meal to produce EPA through fungal fermentation.