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Nahm, Choon-Woo The Korean Ceramic Society 2014 한국세라믹학회지 Vol.51 No.6
The microstructure, nonlinear properties, and impulse clamping characteristics of Pr/Co/Cr/Al co-doped zinc oxide ceramics were investigated with various contents of $Er_2O_3$. Increasing $Er_2O_3$ content increased the density of the sintered pellets from 5.69 to $5.83g/cm^3$, and decreased the average grain size from 10.6 to $6.5{\mu}m$. With increased $Er_2O_3$ content, the breakdown field increased from 2318 to 4205 V/cm, and the nonlinear coefficient increased from 19.4 to 40.2. The clamp characteristics were improved with the increase of the content of $Er_2O_3$. The varistors doped with 2.0 mol% exhibited the best clamp characteristics, in which the clamp voltage ratio was 1.40-1.73 at 1-50 A in an impulse current.
Microstructure and Electrical Properties of ZPCCYT Varistor Ceramics
Nahm, Choon-Woo,Lee, Sun-Kwon The Korean Institute of Electrical and Electronic 2012 Transactions on Electrical and Electronic Material Vol.13 No.5
The Microstructure and nonlinear electrical properties of the ZPCCYT (ZnO-$Pr_6O_{11}$-CoO-$Cr_2O_3$-$Y_2O_3$-$Tb_4O_7$) varistors were investigated for different amounts of $Tb_4O_7$. The addition of $Tb_4O_7$ has a significant effect on microstructure and electrical properties. Analysis of the microstructure indicated that the ceramics consisted of ZnO grain as a main phase and a few secondary phases as a mix of $Pr_6O_{11}$, $Y_2O_3$, and $Tb_4O_7$. As the amount of $Tb_4O_7$ increased, the sintered densities of pellets increased from $\rho$ = 5.70 to $5.78g/cm^3$ and the average grain size decreased from d = 4.8 to $3.6{\mu}m$. The increase in the amount of $Tb_4O_7$ increased from $E_B$ = 7,473 to 10,035 V/cm and from ${\alpha}$ = 39.7 to 52.2. In particular, it was found that the ceramics modified with 1.0 mol% in the amount of $Tb_4O_7$ are suited for the varistors for high voltage in the light of a high sintered density and a high voltage gradient.
Electrical Properties of ZPCCT-based Varistor Ceramics
Nahm, Choon-Woo The Korean Institute of Electrical and Electronic 2007 Transactions on Electrical and Electronic Material Vol.8 No.3
The microstructure and electrical properties of Zn-Pr-Co-Cr-Tb oxide-based varistors were investigated for different $Tb_4O_7$ amounts. As the $Tb_4O_7$ amount increased, the average grain size decreased from 7.7 to $4.8{\mu}m$ and the sintered density increased from 5.73 to $5.84g/cm^3$. As the $Tb_4O_7$ amount increased, the varistor voltage increased from 280.9 to 715.8V/mm and the nonlinear coefficient increased from 26.4 to 44.4. It is assumed that these varistors can be applied for high power with compact size.
Nahm, Choon-Woo The Korean Institute of Electrical and Electronic 2006 Transactions on Electrical and Electronic Material Vol.7 No.4
The microstructure, electrical and dielectric properties, and stability against DC accelerated aging stress of the varistors, which are composed of quaternary system $ZnO-Pr_6O_{11}CoO-Cr_2O_3-based$ ceramics, were investigated for different $La_2O_3$ contents. The increase of $La_2O_3$ content led to more densified ceramics, whereas abruptly decreased the nonlinear properties by incorporating beyond 1.0mol%. The highest nonlinearity was obtained from 0.5mol% $La_2O_3$, with the nonlinear coefficient of 81.6 and the leakage current of $0.1{\mu}A$. The varistors doped with 0.5mol% $La_2O_3$ exhibited high stability, in which the variation rates of breakdown voltage, nonlinear coefficient, leakage current, dielectric constant, and dissipation factor were -1.1%, -3.7%, +100%, +1.4%, and +8.2%, respectively, for stressing state of $0.95V_{1mA}/150^{\circ}C/24h$.
Survey on the Treatment of Postherpetic Neuralgia in Korea: Multicenter Study of 1,414 Patients
Nahm, Francis Sahngun,Kim, Sang Hun,Kim, Hong Soon,Shin, Jin Woo,Yoo, Sie Hyeon,Yoon, Myung Ha,Lee, Doo Ik,Lee, Youn Woo,Lee, Jun Hak,Jeon, Young Hoon,Jo, Dae Hyun The Korean Pain Society 2013 The Korean Journal of Pain Vol.26 No.1
Background: Postherpetic neuralgia (PHN) is a serious complication resulting from herpes zoster infections, and it can impair the quality of life. In order to relieve pain from PHN, various treatments, including pharmacological and interventional methods have been used. However, little information on the recommendations for the interventional treatment of PHN, along with a lack of nation-wide surveys on the current status of PHN treatment exists. This multicenter study is the first survey on the treatment status of PHN in Korea. Methods: Retrospective chart reviews were conducted on the entire patients who visited the pain clinics of 11 teaching hospitals from January to December of 2011. Co-morbid disease, affected site of PHN, routes to pain clinic visits, parenteral/topical medications for treatment, drugs used for nerve block, types and frequency of nerve blocks were investigated. Results: A total of 1,414 patients' medical records were reviewed. The most commonly affected site was the thoracic area. The anticonvulsants and interlaminar epidural blocks were the most frequently used pharmacological and interventional methods for PHN treatment. For the interval of epidural block, intervals of 5 or more-weeks were the most popular. The proportion of PHN patients who get information from the mass media or the internet was only 0.8%.The incidence of suspected zoster sine herpete was only 0.1%. Conclusions: The treatment methods for PHN vary among hospitals. The establishment of treatment recommendation for PHN treatment is necessary. In addition, public relations activities are required in order to inform the patients of PHN treatments by pain clinicians.
Influence of Dy Doping on Electrical Properties and dc Aging Behaviors of Zn-Pr-Co-Cr System
Nahm, Choon-Woo The Korean Institute of Electrical and Electronic 2007 Transactions on Electrical and Electronic Material Vol.8 No.6
The electrical properties and dc aging behavior for specified stress state of system, which is composed of quaternary Zn-Pr-Co-Cr, were investigated for different $Dy_2O_3$ addition doping level. As $Dy_2O_3$ doping level increased, the density decreased in the range of 5.51-4.90 $g/cm^3$, reaching maximum at 0.5 mol% and the average ZnO grain size decreased in the range of 17.7-6.0 ${\mu}m$. The incorporation of $Dy_2O_3$ significantly improved the non-ohmic properties, above 30 in non-ohmic coefficient, compared with that of undoped samples. The samples with the best performance of non-ohmic properties were obtained for $Dy_2O_3$ doping level of 1.0 mol%, with 49 in non-ohmic coefficient and 2.6 ${\mu}A/cm^2$ in leakage current. The samples with the highest stability were obtained for $Dy_2O_3$ doping level of 0.5 mol%.
Estimation of Sales Elasticity of R&D by Average median Derivative
Nahm, Joon-Woo 서강대학교 경제학연구원 2002 시장경제연구 Vol.31 No.2
This paper examines the R&D expenditure-sales profiles at firm level and derives estimates of the sales elasticity using Korean manufacturing firms' data. Usually the data sets on R&D expenditure typically include a few observations with very large expenditures and have a huge mass at zero amount, distribution-oriented estimation methods such as nonparametric quantile regression, are more suitable to analyze the R&D data. Since the shape of the R&D expenditure-sales profile is unknown, we use nonparametric quantile regression estimation method. This method also allows the construction of robust measures for sales elasticity by average median derivative estimation.