Determination of Total Vector Error of the Phasor Measurement Unit (PMU) Using the Phase Angle Error of a Constant Amplitude Voltage Signal

This paper investigates the effect of the Phase Angle Error of a Constant Amplitude Voltage signal in determining the Total Vector Error (TVE) of the Phasor Measurement Unit (PMU) using MATLAB/Simulink. The phase angle error is measured as a function of time in microseconds at four points on the IEEE 14-bus system. When the 1 pps Global Positioning System (GPS) signal to the PMU is lost, sampling of voltage signals on the power grid is done at different rates as it is a function of time. The relationship between the PMU measured signal phase angle and the sampling rate is established by injecting a constant amplitude signal at two different points on the grid. In the simulation, 64 cycles per second is used as the reference while 24 cycles per second is used to represent the fault condition. Results show that a change in the sampling rate from 64 bps to 24 bps in the PMUs resulted in phase angle error in the voltage signals measured by the PMU at four VI Measurement points. The phase angle error measurement that was determined as a time function was used to determine the TVE. Results show that (TVE) was more than 1% in all the cases.

Predicting Net Cross-Shore Total Load Transport: A Phase-Averaging, Quasi-Steady Approach Incorporating Undertow Contribution

Wave shapes that induce velocity skewness and acceleration asymmetry are usually responsible for onshore sediment transport, whereas undertow and bottom slope effect normally contribute to offshore sediment transport. By incorporating these counteracting driving forces in a phase-averaged manner, the theoretically-based quasi-steady formula of Wang （2007） is modified to predict the magnitude and direction of net cross-shore total load transport under the coaction of wave and current. The predictions show an excellent agreement with the measurement data on medium and fine sand collected by Dohmen-Janssen and Hanes （2002） and Schretlen （2012） in a full-scale wave flume at the Coastal Research Centre in Hannover, Germany. The modified formula can predict the net onshore transport of fine sand in sheet flows. In particular, it can predict the net offshore transport of medium sand in rippled beds through enlarged bed roughness, as well as the net offshore transport of fine-to-coarse sand in sheet flows with the aid of a new criterion to judge the occurrence of net offshore transport.

Low-complexity fractional phase estimation for totally blind channel estimation

To remove the scalar ambiguity in conventional blind channel estimation algorithms, totally blind channel estimation （TBCE） is proposed by using multiple constellations. To estimate the unknown scalar, its phase is decomposed into a fractional phase and an integer phase. However, the maximum-likelihood （ML） algorithm for the fractional phase does not have closed-form solutions and suffers from high computational complexity. By ex- ploring the structures of widely used constellations, this paper proposes a low-complexity fractional phase estimation algorithm which requires no exhaustive search. Analytical expressions of the asymptotic mean squared error （MSE） are also derived. The theo- retical analysis and simulation results indicate that the proposed fractional phase estimation algorithm exhibits almost the same performance as the ML algorithm but with significantly reduced computational burden.

Preparation of single-phase ammonium dimolybdate by combination process

A novel method for the preparation of single-phase ammonium dimolybdate with industrial ammonium molybdate was studied. Various in- fluential factors were evaluated in the paper, including reaction temperature, reaction time, initial molybdenum concentration, initial NH_3 /Mo molar ratio, and stirring speed. Under the optimum experimental conditions, the crystallization rate of product is 85.23%. The X-ray diffraction (XRD) analysis and chemical analysis show that the product is single-phase ammonium dimolybdate, and no impurity phases exist. The scanning electronic microscope (SEM) image reveals uniform particle size, good particle dispersion, and no agglomeration between particles. Meanwhile, the final pH value of acidification was investigated. The total molybdenum recovery can reach up to 99.40%, and the main phases of acidification product are the same as those of raw material with the final pH value of 1.5. This determines that the acidification product can be used as a raw material to produce single-phase ammonium dimolybdate.

Capacitance Sensor for Nondestructive Determination of Total Oil Content in Peanut Kernels

In this work, attempts were made to estimate the total oil content (TOC) in single peanut kernels, using the CI meter (Chari’s Impedance meter, described below). Mature peanut kernels of selected varieties with a range of oil contents from 47% to 61% were placed one at a time, between the parallel-plate electrodes of the CI meter, and the impedance (Z) and phase angle (q) of the system were measured, and capacitance, C was computed at 1, 5 and 9 MHz. After the measurements, the TOC of each kernel was determined by Soxhlet method. Using the known TOC values, and the corresponding C, Z and q values, initially on a calibration group of kernels, calibration equations were developed. Using the model coefficients from the calibration, the TOCs of kernel samples of 31 diverse peanut genotypes grown in different environments in Australia were determined. The method predicted the TOC values of peanut kernels of 31 peanut genotypes, within 2% of the Soxhlet values, with an R2 of 0.87 (P 0.001).

A Forecasting Model of Vector Similarity in Phase Space for Flood and Drought over the Huanghe-Huaihe-Haihe Plain in China

To represent well the characteristics of temporal and spatial distributions, chart of 3-dekad moving total precipitation is proposed in this paper first. Then this kind of chart is expanded in terms of Chebyshev polynomial at irregular grids, and the quantitative representation of precipitation is got. Finally the Chebyshev coefficients are forecasted by using the forecasting method of vector similarity in phase space proposed by Zhou (1992). Using above mentioned procedures temporal and spatial distributions of precipitation over the Huanghe-- Huaihe-- H aihe Plain in China are forecasted.

在役螺栓超声三维成像监测数据的智能化分析方法

螺栓是一种常见的机械连接件,一旦失效,可能会导致设备损坏、结构崩塌,甚至危及人身安全。因此,在役螺栓的监测一直受到广泛关注。将相控阵超声全聚焦技术应用于螺栓在役监测,开发了专用系统和阵列探头,实现了三维成像可视化监测,改变了螺栓监测数据单一的现状。针对大量三维图像化数据处理的关键问题,提出了智能化分析方法,对比分析了决策树、支持向量机和神经网络算法的适用性,最终开发了基于决策树算法的智能分析评价软件模块并取得了较好的检测效果。

楔块耦合的碳纤维增强复合材料褶皱缺陷全聚焦成像

褶皱是碳纤维增强复合材料中最主要的缺陷类型之一,当使用超声相控阵对复合材料薄板进行检测时,由于采集系统非线性效应和电子串扰等干扰会引发盲区现象,掩盖了薄板内的褶皱信息。为削弱盲区影响,考虑在相控阵与复合材料薄板(小于10 mm)之间增加楔块,提出楔块耦合的最短路径射线追踪全聚焦方法。基于费马原理与斯涅耳定律,建立楔块耦合的多层介质超声波传播模型;制备含褶皱缺陷的碳纤维增强复合材料试样,搭建超声相控阵数据采集系统,采集全矩阵数据;将楔块耦合的最短路径射线追踪全聚焦方法和传统全聚焦方法的成像效果进行对比。结果表明,基于楔块耦合的最短路径射线追踪全聚焦方法能减小试样表面盲区深度,修正声时偏差,削弱盲区影响,恢复出试样内的褶皱缺陷。相比传统全聚焦方法,纤维褶皱长度、褶皱顶部高度、褶皱角度这3个参数表征的精准程度分别提高了5.9%、4.1%、4.2%。该文为碳纤维增强复合材料薄板褶皱缺陷的检测提供了新思路。

相控阵超声相位相干成像(PCI)检测原理及应用

为了了解相控阵超声相位相干成像(PCI)检测技术在工业无损检测应用中的效果及特点,详细介绍了相控阵超声全聚焦成像与相位相干成像(PCI)检测技术的基本原理,从原理上分析了PCI检测技术与全聚焦成像检测技术的差异性。通过试验测试了PCI检测技术对点状缺陷、面状缺陷与体积状缺陷的检测特点及效果,根据得到的检测效果,展示了PCI检测技术对于不同类型缺陷的检测优势与不足,以推动该技术在工业无损检测中的正确应用。

基于北斗GEO卫星观测的桂林地区TEC空间梯度研究

小尺度的总电子含量(TEC)梯度异常会显著影响区域电离层模型以及地基增强系统(GBAS)的精度。因此,为了提高区域电离层模型的准确性和GBAS导航定位的精度,深入研究小尺度的TEC空间梯度显得尤为重要。为了研究中小尺度的空间梯度,利用2019—2022年间桂林地区全球卫星导航系统(GNSS)接收机的北斗地球静止轨道(GEO)卫星数据,对中国低纬地区(23°N 107.9°~113.1°E)电离层的TEC空间梯度进行研究分析。根据3颗北斗GEO卫星对地形成的3个相邻穿刺点(从西至东,依次编号为C02,C03,C01)的TEC观测值,构成C02-C03与C03-C01两个约为300 km尺度区域(107.9°~110.3°E,110.3°~113.1°E)的TEC梯度观测。统计结果显示,C02-C03区域的空间梯度基本为西向;而C03-C01区域的空间梯度在1~4月与9~12月为东向,5~8月为西向。这表明2个相邻区域的空间梯度在季节变化上存在差异,揭示了中小尺度空间梯度具有显著的局地效应。此外,地方时差并非空间梯度事件的主要原因。在太阳活动高年,背景TEC较高,空间梯度事件更易发生。梯度事件发生率的半年变化是TEC半年异常的体现。空间梯度事件在不同地磁条件下的发生率相似。

应用于斜楔块的子孔径虚拟源全聚焦成像

楔块斜入射检测工艺下,楔块会进一步降低全聚焦成像的缺陷检测能力。尤其是在检测大深度缺陷和粗晶材料时,全聚焦图像会因为缺陷回波幅值下降,导致缺陷图像的信噪比较低。为了提高入射能量,提出了应用于斜楔块的子孔径虚拟源全聚焦成像技术。研究结果表明:该技术通过延时控制子孔径阵元激励形成虚拟源发射,显著增加了射入到被检构件中的声能。在横向L值为20∼40 mm探头移动区间内,17∼38 mm深度范围内Φ3边钻孔幅值较黄铜全聚焦图像提高4.58∼7.12 dB;当钢制试块为被检对象时,在横向L值为30∼40 mm探头移动区间内,40∼65 mm深度范围内Φ1边钻孔幅值较全聚焦图像提高0.63∼2.35 dB。因此在该技术应用于楔块斜入射检测工艺下的粗晶材料检测,具有较好的检测效果。

酶解-超声辅助双水相法提取泡桐花总黄酮工艺优化及体外抗氧化能力研究

试验旨在探究酶解-超声辅助双水相法提取泡桐花总黄酮的最佳工艺参数,评价其体外抗氧化活性。采用单因素试验和响应面法优化泡桐花总黄酮的提取工艺,并对比几种不同的提取方法,测定总黄酮对DPPH自由基、OH自由基和ABTS自由基的清除率。结果表明:最优提取工艺条件:(NH4)2SO4质量分数20%、乙醇质量分数33%、超声温度60℃、液料比23∶1 m L/g,总黄酮的实际提取率为7.62%,与理论值7.59%的相对偏差为0.40%。不同提取方法比对,酶解-超声法提取率最高。泡桐花黄酮能够有效清除DPPH自由基、OH自由基和ABTS自由基,最高清除率分别为78.1%、86.2%和83.3%,可为其开发为天然饲料添加剂应用在动物生产领域提供科学参考。

超声波-微波辅助双水相提取桑葚总黄酮工艺优化

以桑葚果实为原料,采用超声波-微波辅助乙醇-硫酸铵双水相提取总黄酮.采用单因素实验考察乙醇质量分数、硫酸铵质量分数、提取时间、微波功率、液料比等因素对总黄酮得率的影响,并以响应面分析法优化实验,确定总黄酮最佳提取工艺条件.实验结果表明:实验过程中超声波始终保持50 W,当乙醇质量分数为25%、硫酸铵质量分数为20%、提取时间为6.1 min、微波功率为300 W及液料比为27∶1(mL/g)时,桑葚中黄酮类化合物的提取得率最高,为17.44 mg/g.

基于改进YoloX算法的HDPE管接头TFM相控阵超声图谱缺陷识别

针对高密度聚乙烯(High Density Polyethylene,HDPE)管热熔接头相控阵超声检测时存在的图谱判读效率低、人员经验要求高等问题,文章提出一种基于改进YoloX算法的热熔接头全聚焦(Total Focusing Method,TFM)相控阵超声图谱缺陷(以孔洞为例)智能识别方法。在YoloX的加强特征提取网络中引入卷积注意力机制模块,提高模型对缺陷信息的关注度,使用CIoU损失函数计算回归损失,以提升模型的定位精度,降低漏检率。通过TFM相控阵超声检测实验,采集原始缺陷图谱,并在完成图像增强后创建数据集。采用迁移学习策略进行训练,加快模型收敛速度。结果表明:该方法对缺陷的识别精度达98.18%,检测平均速度达23.92帧·s^(-1),检测精度相较于原YoloX模型提升了2.57个百分点且对小目标缺陷有更好的检测效果。文中方法可以识别出TFM相控阵超声图谱中的缺陷,为热熔接头的精确检测提供技术支撑。

一起220 kV线路开关双跳动作分析及处理

针对某变电站进行220 kV线路II的开关非全相试验,220 kV线路I出现单相跳闸、延时重合和三相跳闸现象。对事故原因进行分析,经过现场检查发现,与站内两组直流系统的接地以及混电有很大关联。消除直流接地点和混电点后,220 kV线路I的开关不再误动作,电网恢复稳定运行。

钛焊缝的对置串列PCI与脉冲回波TFM组合检测

随着近年来PCI技术及TFM技术的发展与应用,与FMC及PWI所对应的数据处理方式已日渐丰富,从原先优化定性的辅助工具逐步转变为可用于实际检测的整套先进技术。针对钛焊缝检测中PCI技术与TFM技术的组合使用开展了相关分析,进行了二者与FMC和PWI配合使用的不同结合方式的对比试验。结果表明,采用PWI-TFM与对置串列PWI/FMC-PCI组合检测方式,能够优化钛焊缝检测效率与成像质量。

超声辅助双水相提取无花果总黄酮的工艺优化及其理化性质分析

采用响应面法优化超声辅助双水相法提取无花果总黄酮的工艺,并对其稳定性和体外抗氧化性进行研究。结果表明:提取无花果总黄酮的最佳双水相体系为质量分数25.2%聚乙二醇1000-质量分数为28.3%硫酸铵;最佳提取工艺为超声温度45℃、超声功率70 W、料液比1∶32(g/mL)、提取时间30 min,在此条件下无花果总黄酮得率为0.83%±0.01%。无花果总黄酮在温度<70℃、pH 6~8、还原剂质量分数<0.024%作用下稳定性好,其在储存和生产中应避免接触金属离子Fe^(3+)、Ba^(2+)、Ca^(2+),食品添加剂(葡萄糖和蔗糖)对其稳定性基本无影响。在一定质量浓度范围内,无花果总黄酮对DPPH自由基、ABTS自由基、羟基自由基、超氧阴离子自由基的最高清除率分别达到97.81%、96.74%、73.54%、59.45%。

骨碎补总黄酮双水相提取工艺优化及抗氧化活性研究

试验旨在优化超声辅助PEG400-(NH_(4))_(2)SO_(4)双水相体系提取骨碎补中总黄酮的工艺,并对骨碎补中总黄酮的抗氧化活性进行评价。在单因素试验的基础上,以(NH_(4))_(2)SO_(4)质量分数、PEG400质量分数、超声功率以及超声时间为自变量,以骨碎补中总黄酮得率为因变量,采取响应面法优化骨碎补中总黄酮的提取工艺。以维生素C为阳性对照,分别测定骨碎补总黄酮对1,1-二苯基-2-苦基肼自由基(1,1-Diphenyl-2-picryl-hydrazyl radical,DPPH·)、羟基自由基(Hydroxyl radical,·OH)的清除能力和铁还原力。结果表明:骨碎补中总黄酮的最佳提取工艺为PEG400质量分数19%,(NH_(4))_(2)SO_(4)质量分数19%,超声功率180 W,超声时间40 min,该条件下骨碎补总黄酮得率为183.29 mg/g,与理论预测值接近。抗氧化活性分析表明,在一定的浓度范围内,骨碎补总黄酮对DPPH·、·OH的清除能力和铁还原力随浓度的增加不断增强并趋于稳定。以PEG400-(NH_(4))_(2)SO_(4)双水相体系提取骨碎补中总黄酮的方法可行,且最佳工艺条件可靠。

超声波辅助双水相萃取鼠曲草总黄酮及抗氧化活性研究

本研究以鼠曲草为原料,鼠曲草总黄酮得率为指标,探究超声波辅助双水相萃取鼠曲草总黄酮的最佳工艺路线。利用523双水相试验法,以鼠曲草总黄酮得率为指标,探究双水相最佳组成体系。结果表明,其最佳体系组成为质量分数为16%的磷酸氢二钾,质量分数为30%的乙醇,与乙醇和热水浸提两类传统提取法相比,双水相法具有更好的提取效果,提取率提升了1~2倍。以鼠曲草黄酮得率为响应指标,通过响应面优化超声波辅助双水相萃取体系,得到最优超声波条件参数为超声功率420W、提取时间23 min,超声温度50℃,与常规室温双水相萃取比,其提取率提升了34%左右。测定总抗氧化能力试验结果表明,超声波辅助双水相的黄酮提取物总抗氧化能力约为水提物和乙醇提取物的2倍,乙醇提取物的1.8倍。综上所述,本试验优化构建的超声波辅助双水相萃取法对鼠曲草黄酮具有更高的提取效率,同时能使其提取物保有更强的抗氧化活性。

超声辅助双水相艾叶总黄酮提取工艺及其抗氧化活性研究

以总黄酮提取率为指标,通过超声辅助双水相法结合单因素和响应面法试验优化提取艾叶总黄酮的工艺条件,并在此基础上进行其体外抗氧化活性研究。结果表明,艾叶总黄酮最佳提取条件为聚乙二醇(PEG)400质量分数为24%、提取温度为60℃、提取功率为70 W、提取时间为50 min,在此条件下对建立的数学模型进行试验验证,验证结果为预测值为17.23%,实际值为17.25%。艾叶总黄酮对DPPH、ABTS、羟基自由基的清除率分别达89.68%、99.74%、99.99%,说明艾叶总黄酮具有良好的抗氧化活性。试验表明:该方法操作简便,总黄酮提取率高,适用于艾叶总黄酮的提取。