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Choon‑W. Nahm 한국세라믹학회 2020 한국세라믹학회지 Vol.57 No.1
This study elucidates the effect of sintering temperature on the nonlinearity and surge degradation characteristics of Mn3O4/ Nb2O5/Er2O3–doped ZnO–V2O5-based varistors. With increasing sintering temperature, the average grain size increased from 6.3 to 16.6 μm and the ceramic density decreased from 5.51 to 5.41 g/cm3. The highest nonlinearity (α1 = 45.6) was obtained when the sintering temperature reached 900 °C. The sample sintered at 900 °C exhibited the best clamp characteristics, where the clamp voltage ratio was 1.84–2.44 at a surge current of 1–25 A. By contrast, the sample sintered at 925 °C exhibited the highest electrical stability, where ΔE 1 mA/cm2E 1 mA/cm2 = −10.6% , Δ1∕1 = −37.2% and ΔJL/JL = 10.2% after applying a surge current of 200 A.
Nahm, Choon-W. The Korean Ceramic Society 2019 한국세라믹학회지 Vol.56 No.1
The varistor properties and stability against dc-accelerated stress of $V_2O_5-Mn_3O_4-Co_3O_4-Dy_2O_3-Nb_2O_5-Bi_2O_3$ (VMCDNB)-doped zinc oxide ceramics sintered at $850-925^{\circ}C$ were investigated. Increasing the sintering temperature increased the average grain size from 4.6 to 8.7 mm and decreased the density of the sintered pellet density from 5.54 to $5.42g/cm^3$. The breakdown field decreased from 5919 to 1465 V/cm because of the increase in the average grain size. Zinc oxide ceramics sintered at $875^{\circ}C$ showed the highest nonlinear coefficient (43.6) and the highest potential barrier height (0.96 eV). Zinc oxide ceramics sintered at $850^{\circ}C$ showed the highest stability: the variation rate of the breakdown field was -2.0% and the variation rate of the nonlinear coefficient was -23.3%, after application of the specified stress (applied voltage/temperature/time).
Kim, Seung-Hyun,Choi, Jeong-Hee,Holloway, J. W.,Suh, Chang-Hee,Nahm, Dong-Ho,Ha, Eun-Ho,Park, Choon-Sik,Park, Hae-Sim The Korean Academy of Medical Sciences 2005 JOURNAL OF KOREAN MEDICAL SCIENCE Vol.20 No.6
<P>The pathogenesis of aspirin (acetylsalicylic acid, ASA)-intolerant urticaria (AIU) is still poorly understood but it has recently been suggested that it is associated with the overproduction of leukotriene (LT). This is supported by evidence that cyclooxygenase 2 inhibitor is given safely to patients with AIU. The present study was designed to investigate the role of genetic polymorphism of LT related genes in the pathogenesis of AIU via a case-control study. We screened single nucleotide polymorphisms (SNPs) in genes encoding enzymes involved in leukotriene synthesis in the Korean population with AIU (n=101), ASA-intolerant asthma (AIA, n=95) and normal healthy controls (n=123). Genotype was determined by primer extension reactions using the SNapShot ddNTP primer extension kit. Among 8 SNPs of four LT related genes, the polymorphism of <I>ALOX5</I> at positions of -1708 G>A showed significant difference in genotype frequency between AIU and AIA (<I>p</I>=0.01). Furthermore, there were significant differences observed in the frequencies of two ALOX5 haplotypes between the AIU group and AIA group (<I>p</I><0.05). However, there were no differences in allele, genotype, or haplotype frequencies of ALOX5 between the AIU group and the normal control group. These results suggested that ALOX5 has a differing contribution in two major clinical pathogenesis related to ASA-sensitivity.</P>