• Journal of Korean Society for Atmospheric Environment
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• v.25 no.2
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• pp.154-166
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• 2009

In this study, 1-hour integrated $PM_{2.5}$ mass and chemical composition concentrations were monitored at the St. Louis-Midwest Supersite in Illinois. Time-resolved samples were collected one week in each of June 2001 (22 June to 28 June), November 2001 (7 November to 13 November), and March 2002 (19 March to 25 March). A total of 427 samples were collected by CAMM (continuous ambient mass monitor) and 15 compounds were analyzed by AAS, PILS (particle-into-liquid sampler), and TOT (thermal optical transmittance) method. PMF was applied to identify the sources and apportion the $PM_{2.5}$ mass to each source for highly time resolved data. In addition, the nonparametric regression (NPR) was applied to identify the predominant directions of local sources relative to wind direction. Also, this study performed compare the NPR analysis and location of actual local point sources at the St. Louis area. The PMF modeling identified nine sources and the average mass was apportioned to gasoline vehicle, road dust, zinc smelter, copper production, secondary sulfate, diesel emission, secondary nitrate, iron+steel, and lead smelter, respectively. These results suggested that this study results will be help for $PM_{2.5}$ source apportionment studies at similar metropolitan area, establish $PM_{2.5}$ standard, and establish effective emissions reduction strategies in Korea.

• The korean journal of orthodontics
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• v.42 no.3
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• pp.129-137
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• 2012

Objective: The purpose of this study was to evaluate the surface roughness (SR) of 2 types of orthodontic archwires made by 4 different manufacturers. Methods: This in vitro experimental study was conducted on 35 specimens of 7 different orthodontic archwires, namely, 1 nickel-titanium (NiTi) archwire each from the manufacturers American Orthodontics, OrthoTechnology, All-Star Orthodontics, and Smart Technology, and 1 stainless steel (SS) archwire each from the manufacturers American Orthodontics, OrthoTechnology, and All-Star Orthodontics. Aft er analyzing the composition of each wire by energy-dispersive X-ray analysis, the SR of each wire was determined by scanning electron microscopy (SEM) and surface profilometry. Data were analyzed using the Kruskal-Wallis and Mann-Whitney U tests (${\alpha}$ < 0.05). Results: The average SR of NiTi wires manufactured by Smart Technology, American Orthodontics, OrthoTechnology, and All-Star Orthodontics were $1,289{\pm}915A^{\circ}$, $1,378{\pm}372A^{\circ}$, $2,444{\pm}369A^{\circ}$, and $5,242{\pm}2,832A^{\circ}$, respectively. The average SR of SS wires manufactured by All-Star Orthodontics, OrthoTechnology, and American Orthodontics were $710{\pm}210A^{\circ}$, $1,831{\pm}1,156A^{\circ}$, and $4,018{\pm}2,214A^{\circ}$, respectively. Similar to the results of profilometry, the SEM images showed more defects and cracks on the SS wire made by American Orthodontics and the NiTi wire made by All-Star Orthodontics than others. Conclusions: The NiTi wire manufactured by All-Star Orthodontics and the SS wire made by American Orthodontics were the roughest wires.

• Journal of the East Asian Society of Dietary Life
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• v.5 no.2
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• pp.39-48
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• 1995

The effects of storage containers and storage temperatures on Kimchi quality were investigated. The results were summarized as follows : 1. Pabix, poly ethylene-back+plastic container, tupper-ware were much better than crock, stainless steel, and plastic container in keeping a Kimchi. However, there was no significant differences between containers in the sensory test for Kimchi. 2. Kimchi stored at 18$\pm$2$^{\circ}C$ was the most delicious, which revealed pH 4.30, acidity 0.45-0.50%, and salt concentration 3.10wt% in the 4th days after storage whereas sensory score for Kimchi quality was very low in the 12th days after storage. 3. pH in Kimchi stored at 5$^{\circ}C$ after fermentation at 18$\pm$2$^{\circ}C$ was slowly decreased as compared to the Kimchi stored at 18$\pm$2$^{\circ}C$, but texture score of Kimchi stored at -5$^{\circ}C$ or -8$0^{\circ}C$ after fermentation at 18$\pm$2$^{\circ}C$, but texture score of Kimchi stored at -5$^{\circ}C$ or -8$0^{\circ}C$ were compared to that of the Kimchi stored at 18$\pm$2$^{\circ}C$ after fermentation. 5. In the group of Kimchi stored at 1$0^{\circ}C$, immediately after picking it took 48days until the best conditions which were pH 4.30 and acidity 0.45-0.50% were matched. 6. The most promising method in keeping good taste and good quality of Kimchi was to store Kimchi at 5$^{\circ}C$ after 4days fermentation at 18$\pm$2$^{\circ}C$. And, for long period preservation of Kimchi, it took would be effective to store at -8$0^{\circ}C$ after fermentation at 18$\pm$2$^{\circ}C$.

• Journal of the Korean Society of Industry Convergence
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• v.7 no.4
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• pp.399-405
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• 2004

Currently, the use of carbon steel in a high temperature environment, such atomic reactor, increases. Test piece was heated in electric furnace and the prescribed temperature was controlled within ${\pm}1^{\circ}C$. Debris that falls apart from cracked section due to friction is accumulated inside. Then, as it causes fretting corrosion (formation of oxide layer), it contributes to crack closure.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.1023-1028
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• 2003

The structure of Tower Palace III Sports Center building was designed as concrete Filled Steel Tube(CFT) Column and the filled-in concrete was designed as high compressive strength of 500kgf/$m_2$. The self compacting concrete(SCC, non-vibrating concrete) with 65$\pm$5cm flow must be applied to this case for filling the CFT by injecting the concrete from the column bottom. Laboratory tests and pilot productions of batcher plant were performed for optimum mix design and the full scale Mock-Up test was performed to check the appicability of the construction method. As a result, we observed that good quality SCC and the pressure change of concrete pump normally used domestically. Based on these results, we have constructed 20-40m height CFT columns successfully.

• Journal of Powder Materials
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• v.1 no.2
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• pp.190-197
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• 1994

The densification behavior during a sintering of M2 and T15 grade high speed steel powder compacts was reported. Sintered densities over 98% theoretical were achieved by a liquid phase sintering in vacuum for both grades. The optimum sintering temperature range where full densification could be achieved without excessive carbide coarsening and incipient melting was much narrower in M2 than in T15 grade. The sintering response was mainly affected by the type of carbides present. The primary carbides in M2 were identified as $M_6C$ type whereas those in T15 were MC type which provides wider sintering range. The addition of elemental carbon up to 0.3% lowered the optimum sintering temperature for both grades, but had little effect on expanding the sintering range and sintered structure.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.841-843
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• 2006

In high-performance cold work applications, tool failure depends on the predominating loading conditions. Typical failure mechanisms are a combination of abrasive wear, adhesive wear, plastic deformation, cracking and edge crumbling. In this paper we demonstrate how the microstructure of tool steels can be positively influenced by modifying the alloying system and the production route to meet the demands of the different loading situations which occur during operation. The investigation was focused on ductility, fatigue strength and wear resistance. Theoretical considerations were confirmed by practical tests.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.411-412
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• 2006

A high nitrogen PM tool steel has shown to have an excellent galling resistance due to the introduction of a high amount of a low friction phase predominantly consisting of VN. Tool making and heat treatment are according to standard procedures. An increase of tool life of more than two times compared to ordinary tool steels is found. Furthermore, the new low friction tool steel shows a potential for sintered parts with higher densities through the applica bility of increased compaction pressure or minimized lubricant amount.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.389-390
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• 2006

Selective surface densification is a tool for improving the mechanical properties of PM steels, such that the requirements for highly loaded gears can be matched. This paper describes the manufacturing and the properties of a helical P/M gear. The gear performance was evaluated on a 3-shaft back to back test rig, on a load bearing test rig and on a sound test bench. The results of these tests are presented and compared to data obtained from solid steel gear with identical geometry and surface quality. This comparison indicates that P/M gears have a load bearing capacity and noise level which are both well comparable to solid steel gears.

• Journal of the Korean institute of surface engineering
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• v.29 no.2
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• pp.132-139
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• 1996

Experiments on the automatic control of NaOH concentration and on the spraying condition of NaOH solution in the alkaline degreasing process of a continuous hot-dip galvanizing line have been carried out in order to improve degreasing performance of a galvanizing sheet steel using laboratory degreasing and galvanizing simulators. The concentration of NaOH for the good degreasing has been determined to be 6.0% and more and this concentration has been able to be automatically well controlled within $\pm$0.1% by employing a solution electrical conductivity meter under a flow injection analysis condition rather than by employing a sodium ion selective electrode in the degreasing simulator. Frequent blocking of the spraying nozzles of the solution has been reduced considerably by the set-up and periodical operation of an automatic valve system in the nozzle system. By applying this automatic valve system and by automatic controlling the NaOH concentration and other ordinary variables in the degreasing process, the degreasing performance has been increased from the conventional 76% to the new 85%.