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Journal of Rare Earths 2014年第1期32卷 29-36页

作者： choon-w.nahm Semiconductor Ceramics Laboratory Department of Electrical Engineering Dongeui University

The effect of sintering temperature on microstructure, electrical properties, and pulse aging behavior of （V2O5-Mn3O4-Er2O3）-doped zinc oxide varistor ceramics was systematically studied. when the sintering temperature increased, the average grain size increased from 6.1 to 8.7μm and the sintered density decreased from 5.52 to 5.43 g/cm3. The breakdown field decreased from 3856 to 922 V/cm with an increase in the sintering temperature up to 900 °C, whereas a further increase to 2352 V/cm at 925 °C. The nonlinear coefficient increased pronouncedly from 4.6 to 30.0 with an increase in the sintering temperature. The varistor ceramics sintered at 850 °C exhibited the best clamping characteristics, with the clamp voltage ratio of the range of 2.22-2.88 for pulse current of 1-25 A. The varistor ceramics sintered at 925 °C exhibited the strongest stability, with %ΔE1 mA/cm2=-8.8% after applying the multi-pulse current of 25 A.

关键词： ceramics sintering electrical properties pulse aging behavior varistors rare earths

Sintering effect on ageing behavior of rare earths (Pr_6O_(11)-Er_2O_3-Y_2O_3 )-doped ZnO varistor ceramics

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Journal of Rare Earths 2012年第10期30卷 1028-1033页

作者： choon-woo nahm Semiconductor Ceramics Laboratory Department of Electrical Engineering Dongeui University

The electrical properties and ageing behavior of the rare earths （Pr6O11-Er2O3-Y2O3）-doped ZnO varistor ceramics were systematically investigated at sintering temperature range of 1335-1350°C. with an increase in the sintering temperature, the sintered density increased from 5.41 to 5.64g/cm3 and the average grain size increased from 5.8 to 7.9μm. The varistor properties and ageing behavior were significantly affected by small sintering temperature range of 1335-1350°C. The breakdown field noticeably decreased from 5767 to 3628V/cm with an increase in the sintering temperature. The varistor ceramics exhibited the highest nonlinear coefficient （43.2） at the sintering temperature of 1340°C. The varistor ceramics sintered at 1350°C exhibited a surprisingly excellent stability by exhibiting 0.3% in the variation rate of the breakdown field and 0.3% in the variation rate of the nonlinear coefficient for ageing stress of 0.95 E1mA/150°C/24 h.

关键词： sintering rare earths nonlinear properties ageing varistors

Nonlinear behavior of Tb_4O_7-modified ZnO-Pr_6O_(11)-based ceramics with high breakdown field

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Journal of Rare Earths 2013年第3期31卷 276-280页

作者： choon-woo nahm Semiconductor Ceramics Laboratory Department of Electrical EngineeringDongeui UniversityBusan 614-714Korea

The effect of Tb407 on electrical behavior of the ZnO-Pr6Oll-based varistor ceramics was investigated. Microstructural analysis indicated that the addition of Tb407 decreased average grain size from 3.6 to 3.2 and increased the sintered density from 5.58 to 5.68 g/cm3. As the amount ofTb407 increased, the breakdown field increased from 9393 to 12437 V/cm and the nonlinear coefficient increased from 50 to 65. The varistor ceramics added with 0.5 mol.% in the amount of Tb407 exhibited an excellent stability by exhibiting 0. 1% in the variation rate of the breakdown field, 0% in the variation rate of the nonlinear coefficient, and 8.8% in the variation rate of the leakage current density for DC-accelerated aging stress of 0.85 E1 mA/115 ℃/24 h.

关键词： doping ZnO breakdown field electrical properties varistor ceramics rare earths

Microstructure, electrical and dielectric properties, and aging behavior of ZPCCA varistor ceramics with Er_2O_3 doping

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Journal of Rare Earths 2015年第4期33卷 403-410页

作者： nahm choonwoo Semiconductor Ceramics Laboratory Department of Electrical Engineering Dongeui University

The microstructure, electrical and dielectric properties, and DC-accelerated aging of the ZPCCA （ZnO-Pr6O11-CoO- Cr203-A1203） ceramics were investigated with various contents of Er203. The ceramic phases consisted of a bulk phase of ZnO grains, and a minor secondary phase of mixture of Pr6O11 and Er203. The increase of the content of doped Er203 increased the densities of sintered pellet from 5.66 to 5.85 g/cm3, and decreased the average grain size from 9.6 to 6.3 μm. with the increase of the content of doped Er203, the breakdown field increased from 2390 to 4530 V/cm, and the nonlinear coefficient increased from 28.4 to 39.1. The sample doped with 0.25 mol.% Er203 exhibited the strongest electrical stability; variation rates for the breakdown field measured at 1.0 mA/cm2, and for the non-ohmic coefficient were -3.4% and -23,8%, respectively, after application of a stress of 0.95 Eu/125 ℃/24 h.

关键词： microstructure Er203 electrical properties aging behavior varistor ceramics rare earths

Effect of sintering temperature on microstructure and varistor properties of Zn-V-O-based ceramics incorporated with Mn-Nb-Tb

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Transactions of Nonferrous Metals Society of China 2015年第12期25卷 4040-4045页

作者： C.w.nahm Semiconductor Ceramics Laboratory Department of Electrical Engineering Dongeui University

The effect of sintering temperature on microstructure and varistor properties of Zn-V-O-based ceramics incorporated with Mn-Nb-Tb was investigated. The results showed that the increase of sintering temperature in the range from 875 to 950 °C decreased the densities of sintered pellets in the range of 5.55 to 5.45 g/cm3 and increased the average grain size in the range of 4.1 to 8.8 ？m. The breakdown field decreased noticeably from 7443 to 1064 V/cm with increasing sintering temperature from 875 to 950 °C. The varistor ceramics sintered at 900 ？C exhibited nonlinear properties, with 49.4 in the nonlinear coefficient and 0.21 m A/cm2 in the leakage current density. The dielectric constant increased greatly from 440.1 to 2197.2 with increasing sintering temperature from 875 to 950 °C; however, the dissipation factor exhibited a fluctuation between 0.237 and 0.5. These ceramic compositions and sintering conditions can be applied to the development of advanced multiplayer varistors with silver as an inner electrode.

关键词： Zn-V-O-based ceramics Mn-Nb-Tb sintering varistor properties dielectric characteristics varistor

Effect of small changes in sintering temperature on varistor properties and degradation behavior of V-Mn-Nb-Gd co-doped zinc oxide ceramics

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Transactions of Nonferrous Metals Society of China 2015年第4期25卷 1176-1184页

作者： C.w.nahm Semiconductor Ceramics Laboratory Department of Electrical Engineering Dongeui UniversityBusan 614-714 Korea

The effect of small changes in sintering temperature on microstructure, electrical properties, dielectric characteristics, and degradation behavior of V-Mn-Nb-Gd co-doped zinc oxide ceramics was investigated. with the increase of sintering temperature, the densities of the sintered pellets decreased from 5.54 to 5.42 g/cm3 and the average grain size increased from 4.1 to 11.7 μm. The breakdown field(E1 m A) decreased noticeably from 7138 to 920 V/cm with the increase of sintering temperature. The varistor ceramics sintered at 900 ℃ exhibited excellent nonohmic properties, which were 66 for the nonohmic coefficient and 77 μA/cm2 for the leakage current density. Concerning stability, the varistors sintered at 900 ℃ exhibited the strongest accelerated degradation characteristics, with ΔE1 mA =-9.2% for DC accelerated degradation stress of 0.85 E1 m A at 85 °C for 24 h.

关键词： ZnO-V2O5-based ceramics sintering electrical properties degradation behavior varistor

Optimal Operation of Turbo Blowers Serially Connected Using Inlet Vanes

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Journal of Thermal Science 2011年第1期20卷 26-31页

作者： choon-Man Jang Plant Research Division Korea Institute of Construction Technology1190 IIsanseo-GuGoyang-Si411-712Korea

Optimal operation of the turbo blowers having an inlet vane has been studied to understand the blowers' operating *** analyze three-dimensional flow field in the turbo blowers serially connected,general analysis code,CFX,is introduced in the present *** turbulence model is employed to estimate the eddy *** the numerical analysis,it is found that the flow rates of the turbo blowers can be controlled at the vane angle between 90 (full open condition) degrees and 60 degrees effectively,because pressure loss rapidly increases below 60 degree of a vane *** also has almost the same values from 90 degrees to 60 degrees of a vane *** is noted that the distorted inlet velocity generated in the small vane angle makes performance deterioration of the turbo blowers due to the local leading edge separation and the following non-uniform blade loading.

关键词： Turbo Blower Inlet Vane Refuse Collection System Efficiency Numerical Simulation

Characteristics analysis and library development for piezoelectric transformer to drive a ballast for a 35 w class fluorescent lamp using PSPICE modeling

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Journal of Central South University 2016年第1期23卷 169-180页

作者： KIM Young-choon Division of Mechanical and Automotive Engineering College of Engineering Kongju National University

PSPICE model driven by an electric equivalent circuit of a piezoelectric circuit is presented. In order to confirm this model to be effective, an independent model of cold cathode fluorescent lamp(CCFL) driving circuit is used to conduct simulations, leading to a precise modeling. A library is configured through modeling and its accuracy is verified through simulations for widely used and representative lamps such as CCFL, fluorescent lamps, HID lamps, and electrodeless fluorescent lamps. On the basis of experiments, a lamp simulation is also performed using PSPICE, which allows us to take advantage of the lamp library easily. Also, PSPICE model driven by an electric equivalent circuit of a piezoelectric transformer is presented. In order to confirm this model to be effective, an independent model of CCFL driving circuit is used to conduct simulations, leading to a precise modeling. In addition, a new type of electronic ballast is proposed, which allows 35 w-class(T5-class) fluorescent lamp to work. This system is built by a rectifier which has improved power factor and half-bridge series resonant inverter. Also, with size of 27.5 mm high, 27.5 mm wide and 2.5 mm thick, the produced piezoelectric transformer has a high step-up ratio, through which it is possible for the electric ballast circuit to be lighter, smaller and more efficient. After the produced ballast is used to drive the fluorescent lamp for 25 min, it yields 0.95 in power factor correction, 86% in efficiency, 35.07 w in output voltage and 20.5 °C in temperature increase while meeting the characteristics of the 35 w-class fluorescent lamp.

关键词： PSPICE 35 w-class cold cathode fluorescent lamp (CCFL) fluorescent lamp library

The IOSS Chaos Synchronization Method

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Chinese Physics Letters 2011年第1期28卷 32-35页

作者： choon Ki Ahn Faculty of the Department of Automotive Engineering Seoul National University of Science&Technology172 Gongneung 2-dongNowon-guSeoul 139-743Korea

A new synchronization method, called the input/output-to-state stable synchronization (IOSSS) method, is proposed for a general class of chaotic systems with external disturbance. By introducing Lyapunov stability theory and linear matrix inequality (LMI) for the first time, the IOSSS controller is shown to not only guarantee the synchronization of the chaotic systems, but also reduce the effect of external disturbance. The proposed IOSSS controller can be obtained by solving the LMI, which can easily be done using standard numerical packages. A numerical example is given to demonstrate the availability of the proposed method.

关键词： method chaotic inequality

A novel method for clustering cellular data to improve classification

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Neural Regeneration Research 2025年第9期20卷 2697-2705页

作者： Diek w.wheeler Giorgio A.Ascoli Center for Neural Informatics Structures&PlasticityKrasnow Institute for Advanced Study Bioengineering Department Volgenau School of Engineering George Mason University FairfaxVAUSA

Many fields,such as neuroscience,are experiencing the vast prolife ration of cellular data,underscoring the need fo r organizing and interpreting large datasets.A popular approach partitions data into manageable subsets via hierarchical clustering,but objective methods to determine the appropriate classification granularity are *** recently introduced a technique to systematically identify when to stop subdividing clusters based on the fundamental principle that cells must differ more between than within *** we present the corresponding protocol to classify cellular datasets by combining datadriven unsupervised hierarchical clustering with statistical *** general-purpose functions are applicable to any cellular dataset that can be organized as two-dimensional matrices of numerical values,including molecula r,physiological,and anatomical *** demonstrate the protocol using cellular data from the Janelia MouseLight project to chara cterize morphological aspects of neurons.

关键词： cellular data clustering dendrogram data classification Levene's one-tailed statistical test unsupervised hierarchical clustering