• 한국분말재료학회지
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• 제22권2호
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• pp.129-133
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• 2015

Porous W with controlled pore structure was fabricated by thermal decomposition and hydrogen reduction process of PMMA beads and $WO_3$ powder compacts. The PMMA sizes of 8 and $50{\mu}m$ were used as pore forming agent for fabricating the porous W. The $WO_3$ powder compacts with 20 and 70 vol% PMMA were prepared by uniaxial pressing and sintered for 2 h at $1200^{\circ}C$ in hydrogen atmosphere. TGA analysis revealed that the PMMA was decomposed at about $400^{\circ}C$ and $WO_3$ was reduced to metallic W at $800^{\circ}C$. Large pores in the sintered specimens were formed by thermal decomposition of spherical PMMA, and their size was increased with increase in PMMA size and the amount of PMMA addition. Also the pore shape was changed from spherical to irregular form with increasing PMMA contents due to the agglomeration of PMMA in the powder mixing process.

• 대한기계학회논문집A
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• 제36권10호
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• pp.1221-1226
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• 2012

핫 스탬핑은 오스테나이트 변태 온도 이상에서 프레스 성형 후 급속히 냉각되는 고강도 부품을 제조하는 성형 방법이다. 매우 적은 양의 보론 성분을 가지고 있는 보론강은 핫 스탬핑에 사용되는 재료 중의 하나이다. 본 연구의 목적은 열처리 조건에 따르는 기계적 성질과 에릭슨 커핑 시험에 의하여 성형성을 조사하는 것이다. 다양한 온도에서 다이��칭은 대기 시간을 달리하여 실시하였다. 1173 K-0s에서 ��칭 후 TWB는 1203 MPa의 인장 강도를 얻었다. 이것은 모재 인장강도(1,522 MPA)의 79 %이다. 금형 온도(298, 523, 673 K)에 따른 보론강 TWB의 성형성은 차이가 크지 않았다. 그러나 성형 속도가 증가함에 따라 성형성이 감소하는 것을 확인할 수 있었다.

• 한국물환경학회지
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• 제22권3호
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• pp.513-520
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• 2006

The effect of chlorination on disinfection byproducts (DBPs) production from bloom-forming freshwater algae including 7 strains of cyanobacteria and 6 strains of diatoms was investigated. The release and degradation of hepatotoxin (microcystins) by the chlorination on Microcystis under differential condition of the chlorination time and dose were also investigated. The disinfection byproducts formation potentials (DBPFP) of cyanobacterial species and diatoms were ranged from 0.017 to $0.070{\mu}mol\;DBPs/mg$ C and from 0.129 to $0.708{\mu}mol\;DBPs/mg$ C respectively. Among three major groups of DBPs, haloacetonitrils (HANs) was major product in most test strains except Aphanizomenon sp. and Oscillatoria sp. Haloacetic acids (HAAs) was less than 5 % of total DBPs. Chloroform and dichloroacetonitril (DCAN) were dominant compounds in trihalomethanes (THMs) and HANs respectively. After 4 hours chlorination of toxic Microcystis aeruginosa under the dose range of 0.5 to $10mg\;Cl_2/L$, the concentration of intracellular microcystins decreased, but dissolved dissolved microcystins concentration increased with the treatment of more than $3mg\;Cl_2/L$. However the total amount of microcystins was almost constant even at $10mg\;Cl_2/L$ of chlorination. To conclude, our results indicate that the chlorination causes algal cell lysis and release of intracellular microcystins in the intact form to surrounding waters.

• 한국분말재료학회지
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• 제31권1호
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• pp.50-56
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• 2024

We report the effect of plastic deformation on the thermoelectric properties of n-type Bi₂Te_2.5Se_0.5 compounds. N-type Bi₂Te_2.5Se_0.5 powders are synthesized by an oxide-reduction process and consolidated via spark-plasma sintering. To explore the effect of plastic deformation on the thermoelectric properties, the sintered bodies are subjected to uniaxial pressure to induce a controlled amount of compressive strains (-0.2, -0.3, and -0.4). The shaping temperature is set using a thermochemical analyzer, and the plastic deformation effect is assessed without altering the material composition through differential scanning calorimetry. This strategy is crucial because the conventional hot-forging process can often lead to alterations in material composition due to the high volatility of chalcogen elements. With increasing compressive strain, the (00l) planes become aligned in the direction perpendicular to the pressure axis. Furthermore, an increase in the carrier concentration is observed upon compressive plastic deformation, i.e., the donor-like effect of the plastic deformation in n-type Bi₂Te_2.5Se_0.5 compounds. Owing to the increased electrical conductivity through the preferred orientation and the donor-like effect, an improved ZT is achieved in n-type Bi₂Te_2.5Se_0.5 through the compressive-forming process.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.106-109
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• 2005

Springback is a common phenomenon in sheet metal forming, caused by the elastic recovery of the internal stresses after removal of the tooling. Recently, advanced high strength steels (AHSS) such as TRIP and DP are finding acceptance in the automotive industry because their superior strength to weight ratio can lead to improved fuel efficiency and assessed crashworthiness of vehicles. The major troubles of the automotive structural members stamped with high strength steel sheets are the tendency of the large amount of springback due to the high yield strength and the tensile strength. The amount of springback is mainly influenced by the type of the yield function and anisotropic model induced by rolling. The discrepancy of the deep drawn product comparing the data of from the product design induced by springback must be compensated at the tool design stage in order to guarantee its function and assembly with other parts. The methodology of compensation of the low shape accuracy induced by large amount of springback is developed by the expert engineer in the industry. Recently, the numerical analysis is introduced in order to predict the amount of springback and to improve the shape accuracy prior to tryout stage of press working. In this paper, the tendency of springback is evaluated with respect to the blank material. The stamping process is analyzed fur the front side member formed with AHSS sheets such as TRIP60 and DP60. The analysis procedure fully covers the binderwrap, stamping, trimming and springback process with the commercial elasto-plastic finite element code LS-DYNA3D.

• 한국콘텐츠학회논문지
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• 제21권7호
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• pp.171-180
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• 2021

대중매체에 노출된 장소는 잠재여행객에게 호기심과 기대를 형성하여 행동을 유도하며 대중매체를 통해 반복적으로 노출된 장소는 시청자에게 영향을 미친다. TV 프로그램 중에서 가장 큰 파급력을 지닌 장르는 드라마이고, 드라마와는 다른 특성의 몰입을 제공하는 리얼리티프로그램은 시청자의 여행지 선정에 영향을 준다. 관광지처럼 시장에서 평가되지 못하는 대상의 가치추정에 주로 이용되는 것이 가상가치평가법(CVM)이다. 본 연구는 CVM을 활용하여 드라마와 여행예능프로그램을 대상으로 촬영지의 경제적 가치평가를 실시 한 후 두 프로그램 촬영지의 연구결과를 비교분석 하였다. 드라마와 여행예능 프로그램 촬영지 지불의사측정을 위해 선형로짓과 로그로짓분석을 실시하였으며 지불가능금액을 도츨하였다. 연구결론은 드라마와 여행예능 프로그램 촬영지를 방문하는데 필요한 여행비용이 증가할수록 방문의사는 감소하였다. 드라마와 여행예능 프로그램 촬영지 방문시에 지불가능한 금액이 일반 당일여행 평균소비금액보다 높았으며 드라마가 여행예능프로그램 촬영지 방문보다 지불가능한 금액이 모두 높았다.

• 인간식물환경학회지
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• 제24권3호
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• pp.267-275
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• 2021

Background and objective: Particulate matter (PM) has a fatal effect on health. There have been many studies on the use of plants such as trees and shrubs as eco-friendly and sustainable biofilter for the removal of PM. In forming more green space, ground cover plants play an important role in multi-layered planting. This study was conducted to investigate the ability of plants to reduce PM, targeting Korean native ground cover plants with high availability in urban green spaces. Methods: For 4 species of Asteraceae, 4 species of Liliaceae, and 3 species of Rosaceae, one species of plants at a time were placed in an acrylic chamber (800 × 800 × 1000 mm, L × W × H) modeling an indoor space. After the injection of PM, the amount of PM remaining in the chamber over time was investigated. Results: For all three types of PM (PM10, PM2.5, PM1), significant difference occurred in the amount of PM remaining between plant species after 1 hour in the Liliaceae chamber, 3 hours in the Asteraceae chamber, and 5 hours in the Rosaceae chamber. With Liliaceae, the leaf area and the amount of PM remaining in the chamber showed a negative (-) correlation. With the Asteraceae and Rosaceae, there was a weak negative correlation between the leaf area and the amount of PM remaining in the chamber. Conclusion: When using ground cover plants as a biofilter to remove PM, it is considered effective to select a species with a large total leaf area, especially for Liliaceae.

• 한국자동차공학회논문집
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• 제13권3호
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• pp.64-73
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• 2005

This paper is concerned with the simulation-based parameter determination for the tool design in the stamping process of the complicated auto-body member. The CAE procedure of the stamping process is proposed so that troubles such as wrinkle, springback and excess metal be eliminated with changing parameters such as the blank size, the restraining force of the draw-bead and the embossing shape in the die face. The selected indicators of failure during forming are wrinkling. the amount of spring after unloading of the tool, the amount of excess metal developed .The proposed analysis scheme is applied to the tool and process parameter design for the front side member of a RV car. The simulation results show that the scheme can produce sound product from the viewpoint of thickness distribution, the contact condition between tools and the blank, the shape accuracy and so on.

• 한국물환경학회지
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• 제23권3호
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• pp.314-318
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• 2007

The feasibility of the employment of waste oyster shell as an adsorbent for fluoride ion has been tested by considering the effect ionic condition on the adsorption of fluoride ion on oyster shell. The adsorption capacity of oyster shell for fluoride ion was found not to be significantly influenced by the ionic strength of aqueous environment. The existence of complexing agent such as nitrilotriacetic acid in wastewater decreased the adsorbed amount of fluoride ion by forming a stable complex of $CaT^-$ and the adsorption reaction of fluoride ion on oyster shell was examined to be endothermic. The coexisting heavy metal ionic adsorbate in wastewater hindered the adsorption of fluoride ion, however, its adsorbed amount was increased as the particulate size of adsorbent was decreased. Finally, a serial adsorption column test has been conducted for a practical application of adsorption process and the breakthrough of the column adsorption was observed in 22 hours under the experimental condition.

• 대기
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• 제15권3호
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• pp.179-186
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• 2005

Due to several difficulties, a number of Automatic Weather Systems (AWS) operated by Korea Meteorological Administration (KMA) are located on the rooftop so that the forming of standard observation environment to obtain the accuracy is needed. Therefore, the air temperature of AWSs on the synthetic lawn and the concrete of the rooftop is compared with the standard observation temperature. The hourly mean temperature is obtained by monthly and hourly mean value and the difference of temperature is calculated according to the location, the weather phenomenon, and cloud amount. The maximum and the minimum temperatures are compared by the conditions, such as cloud amount, the existence of precipitation or not. Consequently, the temperature on the synthetic lawn is higher than it on the concrete so that it is difficult to obtain same effect from ASOS, on the contrary the installation of AWS on the synthetic lawn seem to be inadequate due to heat or cold source of the building.