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Electrical resistivity-temperature characteristics enhancement of insulating cross-linked polyethylene composites by incorporating positive temperature coefficient particles with different Curie temperatures

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High Voltage 2023年第1期8卷 1-11页

作者： Guimin Jiang Yuanxiang Zhou Chenyuan Teng Yunxiao Zhang Xin Huang Lei Xue Luming Zhou The Wind Solar Storage Division of State Key Laboratory of Control and Simulation of Power System and Generation Equipment Xinjiang UniversityUrumqiChina State Key Laboratory of Power System and Generation Equipment Department of Electrical EngineeringTsinghua UniversityBeijingChina College of Information Engineering Zhejiang University of TechnologyHangzhouChina School of Electronics and Computer Science University of SouthamptonSouthamptonUK

Incorporating positive temperature coefficient(PTC)ceramic particles into polymers provides a prospective alternative solution for suppressing severe electric field distortions caused by negative temperature coefficient(NTC)of electrical resistivity within polymer insulation in high voltage direct current cable.The effect of the Curie temperature of PTC particles on the inhibition of the NTC effect of cross-linked polyethylene(XLPE)is investigated in this study.Positive temperature coefficient particles with varied Curie temperatures are surface-modified and melt blending with XLPE.The modified particles are dispersed on averagely in the matrix.The electrical resistivity,space charge behaviour,and direct current(DC)electrical breakdown strength of the samples are investigated at different temperatures,exploring the effect of the Curie temperature of PTC particles on suppressing the NTC effect of XLPE.It is demonstrated that the reduction in Curie temperature can further suppress the NTC effect of XLPE,enhance the DC strength at elevated temperatures,and inhibit the internal space charge accumulation.The reduction in the Curie temperatures means that the initiation of the PTC effect advances,exhibiting a higher potential barrier and inhibiting the NTC effect more effectively.This work may give a reference for improving the temperature stability of DC properties for XLPE cable insulation.

关键词： coefficient resistivity insulation

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Frequency-angle two-dimensional reflection coefficient modeling based on terahertz channel measurement

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Frontiers of Information Technology & Electronic Engineering 2023年第4期24卷 626-632页

作者： Zhaowei CHANG Jianhua ZHANG Pan TANG Lei TIAN Li YU Guangyi LIU Liang XIA State Key Laboratory of Networking and Switching Technology Beijing University of Posts and TelecommunicationsBeijing 100876China China Mobile Research Institute Beijing 100053China

Terahertz(THz)channel propagation characteristics are vital for the design,evaluation,and optimization of THz communication systems.Moreover,reflection plays a significant role in channel propagation.In this correspon... 详细信息

关键词： channel reflection coefficient

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New correlation features for dissolved gas analysis based transformer fault diagnosis based on the maximal information coefficient

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High Voltage 2022年第2期7卷 302-313页

作者： Yongliang Liang Zhongyi Zhang Ke‐Jun Li Yu‐Chuan Li School of Electrical Engineering Shandong UniversityJinanChina Department of Electrical&Electronic Engineering Imperial College LondonSouth Kensington CampusLondonUK

Online monitoring of gases dissolved in transformer oil is widely applied.Improving the performance of dissolved gas analysis(DGA)‐based fault diagnosis methods by exploring new features of time‐series data has become an appealing topic.In this study,a new type of correlation features between characteristic gases was extracted from time‐series data based on the maximal information coefficient(MIC),and a fuzzy inference system was established.After the introduction of the principle of the MIC and a method for calculating the MIC‐based correlation features,the dominant symptom features that can be used to classify fault types were extracted through the receiver operating characteristic curve.Then,fuzzy rules were learnt,and a fuzzy inference system was designed.In addition,to improve the feasibility of the method,the Newton interpolation method was used for adaptation to the existing sampling cycle.The diagnostic results of the test data show that the proposed method has excellent per-formance and outperforms some prevailing traditional rule‐based methods as well as some artificial intelligent methods.The results also show that by exploring new cor-relation features from time‐series data based on the MIC,the performance of DGA‐based methods can be improved.

关键词： fault diagnosis coefficient

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Tomography of the dynamic stress coefficient for stress wave prediction in sedimentary rock layer under the mining additional stress

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International Journal of Mining Science and Technology 2021年第4期31卷 653-663页

作者： Wenlong Shen Guocang Shi Yungang Wang Jianbiao Bai Ruifeng Zhang Xiangyu Wang Henan Key Laboratory for Green and Efficient Mining&Comprehensive Utilization of Mineral Resources School of Energy Science and EngineeringHenan Polytechnic UniversityJiaozuo 454000China Key Laboratory of Deep Coal Resource Mining Ministry of Education State Key Laboratory of Coal Resources and Safe MiningChina University of Mining and TechnologyXuzhou 221116China Collaborative Innovation Center of Coal Work Safety and Clean High Efficiency Utilization Jiaozuo 454000China

In this study,the tomography of dynamic stress coefficient(TDSC)was established based on a mechanical model of stress wave propagation in bedding planes and a mathematical model of the stress wave attenuation in rock masses.The reliability of the TDSC was verified by a linear bedding plane model and field monitoring.Generally,the TDSC in the dynamic stress propagation of bedding planes increases with the following conditions:(1)the increase of the normal stiffness of the bedding plane,(2)the increase of the incident angle of the stress wave,(3)the decrease of the incident frequency of the stress wave,or(4)the growth of three ratios(the ratios of rock densities,elastic moduli,and the Poisson’s ratios)of rocks on either side of bedding planes.The additional stress weakens TDSC linearly and slowly during the stress wave propagation in bedding planes,and the weakening effect increases with the growth of the three ratios.Besides,the TDSC decreases exponentially in the rock mass as propagation distance increases.In a field case,the TDSC decreases significantly as vertical and horizontal distances increase and its wave range increases as vertical distance increases in the sedimentary rock layers.

关键词： Tomography of the dynamic stress coefficient Stress wave attenuation Mining additional stress Sedimentary rock layer

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Fast correlation coefficient estimation algorithm for HBase-based massive time series data

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Frontiers of Computer Science 2019年第4期13卷 864-878页

作者： Wen LIU Tuqian ZHANG Yanming SHEN Peng WANG Department of Electrical and Information Engineering Xinjiang Institute of Engineering Urumqi 830091 China School of Computer Science and Technology Dalian University of Technology Dalian 116024 China School of Computer Science Fudan University Shanghai 201203 China

In recent years, the rapid development of Internet of Things and sensor networks makes the time series data experiencing explosive growth. OpenTSDB and other emerging systems begin to use Hadoop, HBase to store massive time series data, and how to use these platforms to query and mine time series data has become a current research hotspor. As a typical time series distance measurement method, correlation coefficient is widely used in various applications. However, it requires a large amount of I/O and network transmission to compute the correlation coefficient of long time sequence on HBase in real time, and therefore cannot be applied to interactive query. To address this problem, in this paper, we present two methods to estimate the correlation coefficients of two sequences on HBase. We first propose a fast estimation algorithm for the upper and lower bounds of correlation coefficient, named as DCE. In order to further reduce the cost of I/O, we extend the DCE algorithm, and propose the ADCE algorithm, which can estimate the correlation coefficient quickly with an iterative manner. Experiments show that the algorithms proposed in this paper can quickly calculate the correlation coefficient of the long time series.

关键词： time series HBase correlation coefficient fast estimation

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Improvement of the electrical resistivity of epoxy resin at elevated temperature by adding a positive temperature coefficient BaTiO3-based compound

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Plasma Science and Technology 2020年第4期22卷 15-23页

作者：滕陈源周文俊周远翔张灵张云霄周仲柳李文鹏 School of Electrical Engineering and Automation Wuhan UniversityWuhan 430072People's Republic of China China State Key Laboratory of Power System and Generation Equipment Department of Electrical EngineeringTsinghua UniversityBeijing 100084People's Republic of China School of Electrical Engineering Xinjiang UniversityUrumqi 830047People's Republic of China State Key Laboratory of Advanced Power Transmission Technology Global Energy Interconnection Research Institute CorporationBeijing 102211People’s Republic of China

The DC electrical resistivity-temperature characteristic is an important property for insulating materials to operate at a high stress level.In order to improve the DC electrical resistivity at elevated temperature in a targeted way,a positive temperature coefficient(PTC)material(Ba Ti O3-based compound(BT60))was selected as the filler in this paper,whose electrical resistivity has a PTC effect when the temperature exceeds its Curie temperature.The BT60 was treated with hydrogen peroxide and(3-Aminopropyl)triethoxysilane.Epoxy composites with different loadings of BT60 fillers(0 wt%,0.5 wt%,and 2 wt%of epoxy)were prepared,denoted as EP-0,EP-0.5,and EP-2.It was shown that BT60 was able to maintain the DC breakdown strength when its loading was less than 2 wt%of epoxy.As the temperature exceeds 60°C,BT60 will compensate for the negative temperature coefficient effect of epoxy resin to some extent.The electrical resistivity of EP-2 was improved by 55%compared with that of neat epoxy at 90°C.It was found that the potential barrier at the grain boundary of BT60 and the deep traps in the interface between BT60 and the epoxy resin hinder the migration of carriers and thus increase the electrical resistivity of epoxy composite.

关键词： epoxy resin positive temperature coefficient barium titanate based compounds resistivity-temperature characteristics traps

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coefficient Estimates for a Class of m-fold Symmetric Bi-univalent Function Defined by Subordination

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Communications in Mathematical Research 2019年第1期35卷 57-64页

作者： Guo Dong Tang Huo Ao En Xiong Liang-peng Ji You-qing Foundation Department Chuzhou Vocational and Technical CollegeChuzhouAnhui239000 School of Mathematics and Statistics Chifeng UniversityChifengInner Mongolia024000 School of Mathematics and Statistics Wuhan UniversityWuhan430072 不详

In this paper, we investigate the coefficient estimates of a class of m-fold bi-univalent function de?ned by subordination. The results presented in this paper improve or generalize the recent works of other authors.

关键词： analytic function univalent function coefficient estimate m-fold symmetric bi-univalent function subordination

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Quantitative effects of phase transition on solute partition coefficient,inclusion precipitation, and microsegregation for high-sulfur steel solidification

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Journal of Materials Science & Technology 2019年第10期35卷 2383-2395页

作者： Lintao Gui Mujun Long Shixin Wu Zhihua Dong Dengfu Chen Yunwei Huang Huamei Duan Levente Vitos State Key Laboratory of Coal Mine Disaster Dynamics and Control College of Materials Science and EngineeringChongqing UniversityChongqing400044China Department of Materials Science and Engineering KTH Royal Institute of TechnologyStockholm10044Sweden Chongqing Key Laboratory of Vanadium-Titanium Metallurgy and New Materials Chongqing UniversityChongqing400044China

Segregation and inclusion precipitation are the common behaviours of steel solidification, which are resulted from the redistribution and diffusion of the solute elements at the solid-liquid interface. The effect of the phase transition of high-sulfur free-cutting steel is quantified in the present work for the solute partition coefficient(ki), inclusion precipitation, and microsegregation by establishing a coupling model of microsegregation and inclusion precipitation, wherein the quantified dependencies of ki in terms of temperature, phase and carbon(C) content were applied. Results showed that the solidification temperature range and phase transition of high-sulfur steel that under different solidification paths and C contents were quite different, leading to differences in ki and eventually in microsegregation. kC,kP, and kS were mainly affected by phase composition and kSi was primarily by temperature, while kMn depended on both phase composition and temperature during solidification. Increasing the C content within the interval 0.07-0.48 wt%, the ‘proportion of the δ phase maintained temperature region during solidification’(Pδ), kave Pand kave S(kiave, the average value of the ki across the whole stages of solidification)decreased monotonically, whereas kave Cincreased linearly. The peritectic reaction impacted on the phase composition and ki, leading to the change in microsegregation. Such effect of the peritectic reaction was more significant at the last stage of solidification. When the Pδ was between 75% and 100%(corresponding to 0.07-0.16 wt% C), the solidification path resulted in a greater effect on the microsegregation of solutes C, P, and S because of the peritectic reaction. The microsegregation of solutes Mn and S were comprehensively influenced by kMn, kS and Mn S precipitation as well. The studies would help reveal the solute redistribution at the solid-liquid interface, and improve the segregation of high-sulfur steel by controlling the solidification and precipitation in practice.

关键词： Phase transition Microsegregation Solute partition coefficient Inclusion precipitation High-sulfur steel

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Silicon saturation coefficient changes in hydrogarnets during the Bayer process with lime addition

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Chinese Journal of Chemical Engineering 2019年第8期27卷 1965-1972页

作者： Guozhi Lü Ting’an Zhang Xiaofeng Zhu Chaozhen Zheng Yanxiu Wang Weiguang Zhang Zimu Zhang Key Laboratory of Ecological Metallurgy of Multi-metal Intergrown Ores of Ministry of Education School of Metallurgy Northeastern University

The relationship between the silicon saturation coefficient of hydrogarnets and Bayer reaction parameters was studied. The peak position, crystal plane spacing, and cell edge length of typical hydrogarnet patterns were calculated to find the key factors influencing the relationship. The results showed that the crystal face(420) is the optimal garnet growth direction during hydration and crystal growth along the faces(521) and(611) were not affected significantly by the varying experimental conditions. The reaction temperature significantly influenced the silicon saturation coefficient of hydrogarnets. The silicon saturation coefficient of hydrogarnets increased from 0.2 to about 1.0 in the temperature range of 30–270 °C and a rapid expansion process was observed in the temperature range of 120–150 °C. Moreover, the reaction time, alumina concentration, and C/S were shown to be less important factors. Averaging the results obtained by the 3 methods was shown suitable for calculating the SiO2 saturation coefficient of hydrogarnets. The calculated results of the Al2O3 and SiO2 contents matched the actual ones. However, the actual SiO2 content was about10 % less than the calculated one for SiO2 saturation coefficients higher than 1.

关键词： Hydrogarnet Saturation coefficient Peak position Crystal plane spacing Cell edge length

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Histogram analysis of apparent diffusion coefficient predicts response to radiofrequency ablation in hepatocellular carcinoma

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Chinese Journal of Cancer Research 2019年第2期31卷 366-374页

作者： Xiaohong Ma Han Ouyang Shuang Wang Meng Wang Chunwu Zhou Xinming Zhao Department of Diagnostic Radiology National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital Chinese Academy of Medical Sciences Peking Union Medical College Department of Epidemiology National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital Chinese Academy of Medical Sciences Peking Union Medical College

Objective: The aim of this study was to predict tumor progression in patients with hepatocellular carcinoma(HCC) treated with radiofrequency ablation(RFA) using histogram analysis of apparent diffusion coefficients(ADC).Methods: Breath-hold diffusion weighted imaging(DWI) was performed in 64 patients(33 progressive and 31 stable) with biopsy-proven HCC prior to RFA. All patients had pre-treatment magnetic resonance imaging(MRI)and follow-up computed tomography(CT) or MRI. The ADC values(ADC_(10), ADC_(30_, ADC_(median) and ADC_(max))were obtained from the histogram's 10 th, 30 th, 50 th and 100 th percentiles. The ratios of ADC_(10), ADC_(30_,ADCmedian and ADCmax to the mean non-lesion area-ADC(RADC_(10), RADC_(30_, RADC_(median), and RADC_(max)) were calculated. The two patient groups were compared. Key predictive factors for survival were determined using the univariate and multivariate analysis of the Cox model. The Kaplan-Meier survival analysis was performed, and pairs of survival curves based on the key factors were compared using the log-rank test.Results: The ADC_(30_, ADCmedian, ADCmax, RADC_(30_, RADC_(median), and RADC_(max) were significantly larger in the progressive group than in the stable group(P<0.05). The median progression-free survival(PFS) was 22.9 months for all patients. The mean PFS for the stable and progressive groups were 47.7±1.3 and 9.8±1.3 months,respectively. Univariate analysis indicated that RADC_(10), RADC_(30_, and RADC_(median) were significantly correlated with the PFS [hazard ratio(HR)=31.02, 43.84, and 44.29, respectively, P<0.05 for all]. Multivariate analysis showed that RADCmedian was the only independent predictor of tumor progression(P=0.04). And the cutoff value of RADC_(median) was 0.71.Conclusions: Pre-RFA ADC histogram analysis might serve as a useful biomarker for predicting tumor progression and survival in patients with HCC treated with RFA.

关键词： Diffusion-weighted imaging apparent diffusion coefficient histogram analysis hepatocellular carcinoma radiofrequency ablation survival time

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