• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.5
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• pp.218-227
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• 2021

A thick film NTC thermistor for low temperature co-firing was manufactured by printing and sintering a paste prepared using NTC powder of Mn_1.5Ni_0.4Co_0.9Cu_0.4O₄ composition, lead free frit, and RuO₂ on a 96 % alumina substrate. The effect of frit and RuO₂ on the electrical properties of thick film NTC thermistor was studied. The resistance of the thick film NTC thermistor was higher than that of the bulk phase sintered at the same temperature, but it was found that the negative resistance temperature characteristic appeared more clearly and linearly in the resistance - temperature characteristic. On the other hand, the area resistance decreased as the sintering temperature increased, and the area resistance increased as the amount of frit added increased. The B constant of the thick film NTC thermistor was 3000 K or higher. Among them, it was found that the B constant of the thick film NTC thermistor made of paste with 5 wt% of frit added and sintered at 900℃ showed the highest B constant. Also, it can be seen that the area resistance decreased with the addition of RuO₂, and the change in the area resistance decrease of the thick film NTC thermistor obtained by sintering the paste containing 5 wt% of RuO₂ at 900℃ is the most obvious.

• Journal of the Korean Geographical Society
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• v.49 no.1
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• pp.32-44
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• 2014

This study aimed to analyze the characteristic of the distribution of minimum temperature during January in the central region of South Korea and to investigate causes for the occurrence of extreme minimum temperature in Cheorwon. January temperature distribution data which were collected from 25 weather stations in central area from 1991 to 2010 were investigated, and the difference of temperature between Cheorwon and the other stations in central region, such as Chuncheon, Hongcheon, Bonghwa, Daegwallyoung, Wonju and Jecheon were analyzed by the type of atmospheric pressure system. Daily mean temperature and mean of daily minimum temperature appear to be low at Cheorwon and at the sites in high altitudes, but the frequency of extreme cold wave such as below $-15^{\circ}C$ is also noticeable in Cheorwon. When the Siberian High has expanded and migratory anticyclone has moved onto the north of the Korean Peninsula, the temperature at Cheorwon is relatively low. Furthermore it shows a lesser difference between Cheorwon and the compared stations when the migratory anticyclone affected the area, even at basin like Bonghwa, Jecheon more lower than Cheorwon.

• Proceedings of the Korean Society of Crop Science Conference
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• 2022.10a
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• pp.124-124
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• 2022

Wheat (Triticum aestivum L.) is the major staple foods and is in increasing demand in the world. The elevated temperature due to changes in climate and environmental conditions is a major factor affecting wheat development and grain quality. The optimal temperature range for winter wheat is between 15~25℃, it is necessary to study the physiological characteristic of wheat according to the elevated temperature. This study presents the effect of elevated temperature on the yield and quality of two Korean bread wheat (Baekkang and Jokyoung) in a temperature gradient tunnel (TGT). Two bread wheat cultivars were grown in TGT at four different temperature conditions, i.e. TO control (near ambient temperature), T1 control+1℃, T2 control+2℃, T3 control+3℃. The period from sowing to heading stage has accelerated, while the growth properties including culm length, spike length and number of spike, have not changed by elevated temperature. On the contrary, the number of grains per spike and grain yield was reduced under T3 condition compared with that of control condition. In addition, the. The grain filling rate and grain maturity also accelerated by elevated temperature (T3). The elevating temperature has led to increasing protein and gluten contents, whereas causing reduction of total starch contents. These results are consistent with reduced expression of starch synthesis genes and increased gliadin synthesis or gluten metabolism genes during late grain filling period. Taken together, our results suggest that the elevated temperature (T3) leads to reduction in grain yield regulating number of grains/spike, whereas increasing the gluten content by regulating the expression of starch and gliadin-related genes or gluten metabolism process genes expression. Our results should be provide a useful physiological information for the heat stress response of wheat.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2471-2475
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• 2007

Clathrate compound is the material that host in hydrogen bond forms cage and guest is included into it and combined. Crystallization of hydrate is generated at higher temperature than that of ice from pure water. And physical properties according to temperature are stable and congruent melting phenomenon is occurred without phase separation. But clathrate compound still had supercooling problem occurred in the course of phase change and supercooling should be minimized because it affects efficiency of equipment very much. Therefore, various studies on additives to restrain this or heat storage methods are needed. In this study was investigated the cooling characteristics of the TMA-water clathrate compound including TMA (Tri-methyl-amine, $(CH_3)_3N)$ of 20${\sim}$25 wt% as a low temperature latent heat storage material. And ethanol$(CH_3CH_2OH)$ was added and its cooling characteristics were studied experimentally to restrain supercooling of TMA-water clathrate compound.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.467-469
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• 2009

In this study, fatigue samples were prepared from cylinder head parts that are actually used in domestic (A) and foreign (B) automobiles; high-temperature, high-cycle, and low-cycle fatigue characteristics were then evaluated and compared. A study on the correlation between the microstructural factor and high temperature fatigue characteristic was attempted. The chemical compositions of the heat resistant aluminum alloys above represented A356 (A) and A319 (B), respectively. The result of the tensile strength test on material B at $250^{\circ}C$ was higher by 30.8MPa compared to material A. On the other hand, elongation was 8.5% higher for material A. At $130{\circ}C$, material B exhibited high fatigue life given high cycle fatigue under high stress, whereas material A showed high fatigue life when stress was lowered. With regard to the low-cycle fatigue result ($250^{\circ}C$) showing higher fatigue life as ductility is increased, material A demonstrated higher fatigue life. Through the observation of the differences in microstructure and the fatigue fracture surface, an attempt to explain the high-temperature fatigue deformation behavior of the materials was made.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.80.2-80.2
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• 2010

The development of high temperature-proton exchange fuel cell (HT-PEFC) is a key in solving the problem of carbon monoxide poisoning of the platinum at anode as well as water management in PEFCs operated below $90^{\circ}C$. In order to overcome these main issues, PEFCs must be operated at high temperature above $120^{\circ}C$. Ionic liquids are available for HT-PEFC due to exhibiting non-volatility and thermal stability. Ionic liquids are however leached out from polymeric matrix resulting in the increase of gas permeability. In this study, we have prepared and characterized the composite membranes with the ionic liquids consisting of 1-(4-vinylbenzyl)-3-butyl imidazolium chloride immobilized by the cross-linkers in pore-filling membrane to prevent to be leached out from the membrane. We confirmed that cross-linked ionic liquids were not leached out from the composite membranes through the various characteristic analyses. It was also verified that the prepared membranes are thermally stable from the result of TG analysis. The pore-filling membranes with the immobilized ionic liquids have a high proton conductivity over $10^{-2}$ S/cm at high temperature (> $120^{\circ}C$).

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.64 no.4
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• pp.236-240
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• 2015

Natural ester has a higher biodegradability, flash and fire points, and a greater permittivity compared to conventional mineral oils. However, natural ester also has a higher pour point, viscosity, and water content. These characteristics hamper circulation and the electrical properties of oil-filled transformer. Thus, this paper applied electromagnetic-thermal-flow coupled analysis method to predict temperature distribution inside 154kV single phase power transformer using natural ester. It modeled in the actual appearance for the tank and winding of the power transformer to improve the accuracy of analysis and applied heat flow analysis that considered hydromechanics and heat transfer at the same time. It calculated the power loss, the main cause of temperature rise, from winding and core with electromagnetic analysis then used for the heat source for the heat flow analysis. It then compared the reasonability of result of measurement analysis based on the result acquired from temperature rise test using FBG sensor on the power transformer.

• Journal of Powder Materials
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• v.16 no.2
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• pp.104-109
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• 2009

Niobium powder was made from potassium heptafluoroniobite ($K_2NbF_7$) as the raw material using sodium (Na) as a reducing agent based on the hunter process. The apparatus for the experiment was designed and built specifically for the present study. The niobium particle size greatly increased as the reduction temperature increased from $710^{\circ}C$ to $800^{\circ}C$. The particle size was fairly uniform, varying from $0.09{\mu}m$ to $0.4{\mu}m$ depending on the reduction temperatures. The niobium powder morphology and particle size are very sensitive to a reaction temperature in the metallothermic reduction process. The yield of niobium powder increased from 55% to 80% with a increasing a reaction temperature.

• Journal of Powder Materials
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• v.9 no.5
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• pp.315-321
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• 2002

Pure tantalum powder has been produced by combining Na as a reducing agent, $K_2TaF_{7}$ as feed material, KCl and KF as a diluent in a stainless steel(SUS) bomb, using the method of metallothermic reduction. The present study investigated the effect of the amount of the diluent and reaction temperature on the characteristics of tantalum powder in the production process. The temperature applied in this study $850^{\circ}C$ and the amount of the additional reductant from +5% of the theoretical amount used for the reduction of the entire $K_2TaF_{7}$. The results showed that as the amount of the diluent increased, the reaction temperature became lower because the diluent prevented a temperature rise. Also, according to the mixture ratio of the feed materials and the diluent changed from 1 : 0.25 to 1 : 2, the particle size decreased from $5\mutextrm{m}$ to $1\mutextrm{m}$ and a particle size distribution which is below 325 mesh in fined powder increases from 71% to 83%. The average size of Tantalum powder, $2-4\mutextrm{m}$, was close to that of the commercial powders($2-5\mutextrm{m}$). Also under this condition, impurities contained in the powder were within the range allowed for the commercial Ta powders.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.1014-1017
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• 2001

In recent years, The tantalum nitride(TaN) thin-film has been developed for the electronic resistor and capacitor. In this papers, The effect of thermal annealing in the temperature range of 300∼700$^{\circ}C$ on the sheet resistor properties and microistructure of tantalum nitride(TaN) thin-film deposited by RF sputtering was studied. XRD(X-ray diffractometer) and AFM were used to observe electrical properties and microstructrue of the TaN film and sheet resistance. The TCR properties of the TaN films were discussed in terms of annealing temperature, ratio of nitrogen, crystallization and thin films surface morphology due to annealing temperature. The leakage current of the TaN thin film annealed 400 $^{\circ}C$ was stabilized in the study. How its was found that the sheet resistance in the polycrystalline TaN thin film decreased with increasing the annealing temperature above 600 $^{\circ}C$ after sudden peak upen 400 $^{\circ}C$.