• 열처리공학회지
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• 제21권3호
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• pp.137-143
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• 2008

Effect of quenching medium on the mechanical properties of ductil iron GCD 50 has been investigated using ADI treated specimens. The specimens have been austenitized at $900^{\circ}C$ for 2 hours, followed by controlled cooling to $800^{\circ}C$ under the cooling rate of $0.05^{\circ}C/sec$, then austempered at $380^{\circ}C$, $330^{\circ}C$, $280^{\circ}C$ and $230^{\circ}C$ for 1 hour. The specimens treated in the salt of 5% water were found to have higher tensile strength than that of the normal salt bath. Elongation and impact energy increased in proportion to the increase of retained austenite volume fraction. The increase of cooling rate of the salt by the addition of 5% water to the salt resulted in the increase of retained austenite volume fraction and the formation of fine bainitic ferrite.

• 한국재료학회지
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• 제19권6호
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• pp.305-312
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• 2009

The effects of Quenching and Partitioning (Q&P) and Annealed Martensite (AM) heat treatment on the microstructure and tensile properties were investigated for 0.24C-0.5Si-1.5Mn-1Al steels. The Q&P steels were annealed at a single phase ($\gamma$) or a dual phase (${\gamma}+{\alpha}$), followed by quenching to a temperature between $M_s$ and $M_f$. Then, enriching carbon was conducted to stabilize the austenite through the partitioning, followed by water quenching. The AM steels were intercritically annealed at a dual phase (${\gamma}+{\alpha}$) temperature and austempered at $M_s$ and $M_s{\pm}50^{\circ}C$, followed by cooling in oil quenching. The dual phase Q&P steels showed lower tensile strength and yieldyield strength than those of the single phase Q&P steels, and tThe elongation for the dual phase Q&P steel was partitioning 100s higher than that of that for the single phase Q&P steels as the partitioning time was less than 100s up to partitioning 100s. For AM steels, the tensile/yield strength decreased and the total elongation increased as the austempering temperature increased. The stability of the retained austenite controlled the elongation for Q&P steels and the volume fraction of the retained austenite controlled the elongation for AM steels.

• 한국해양학회지
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• 제3권2호
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• pp.47-54
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• 1968

Monthly mean values for EDTA hardness in the Han River water were determined for March 1966 through May 1967. The hardness was retained a range of 22-59 mg/L the maximum value of 59 mg/L was approached in the months of mid-winter, indicating a seasonal variation. The annual ranges of Ca and Mg were 3.7-9.1 mg/L, 1.5-10.4 mg/L, respectively. The annual range of Mg:Ca ratio was 0.18-2.60. And the hardness correlated closely with Mg volume. In Korea, fortunately, most river waters are not yet suffering from damaging pollution. We must try to establish our water quality criteria based on scientific data, and make research recommendations for the following water uses; public water supplies, aquatic life and wildlife, industry, recreation and aesthetics.

• 지질공학
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• 제13권1호
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• pp.51-65
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• 2003

불포화대에서 저밀도 비수용성유체의 이동과 분포를 모의하기 위하여 STOMP(Subsurface Transport over Multiple Phase) 시뮬레이터를 이용하였다. 균질한 매질에서의 저밀도 비수용성유체의 이동은 조립질 매질에서 빠르고, 세립질 매질에서는 불포화대에 더 많이 잔류한다. 조립질 매질 내에 세립질층이 존재할 경우, 이 층이 지하수면으로부터 멀수록 저밀도 비수용성유체가 불포화대에 더 많이 잔류된다. 조립질 매질에 세립질 또는 더 조립질인 매질이 렌즈 상으로 존재하는 경우에는 저밀도 비수용성유체가 이들 렌즈를 통과하지 못한다. 불균질한 렌즈가 존재할 때의 저밀도 비수용성유체의 분포를 초기조건으로, 지하수면의 변동에 따른 저밀도 비수용성유체의 이동을 모의하였다. 지하수위의 변동에 따라 불포화대에 잔류되어 있던 저밀도 비수용성유체의 수직방향 이동이 증가되었다. 특히, 지하수면의 하강 시 저밀도 비수용성유체가 조립질 렌즈를 통해 이동하나, 세립질 렌즈를 통해서는 이동하지 못한다. 일련의 수치실험의 결과로부터 유류 등의 저밀도 비수용성유체의 오염분포는 매질의 불균질성 그리고 지하수위 변동과 같은 수리지질학특성에 의해 크게 영향을 받을 수 있음을 알 수 있다.

• 한국식품영양과학회지
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• 제26권6호
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• pp.1013-1020
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• 1997

To elicit the effect of fermentation on food quality of the watery Chinese cabbage pickles without fish sauce and red pepper paste(Baik-kimchi), changes in physicochemical properties and microstructure of fiber components were studied. Better water holding capacity(WHC) was showed in Baik-kimchi fermented at $25^{\circ}C$ than that of Baik-kimchi fermented at 5$^{\circ}C$. WHC measured at pH 2 and 6 were ranged from 10.18 to 16.79g/g dried sample for Baik-kimchi fermented at $25^{\circ}C$ and 6.51~14.58g/g dried sample for sample for samples at 5$^{\circ}C$, respectively. The higher WHC was resulted in pH controlled freeze-dried sample to pH 6 than that measured in pH 2 sample. The settling volume(SV) and oil adsorption capacity(OAC) increased with fermentation period and kept the same value for a little while, but slightly decreased in the over ripening period. Baik-kimchi fermented at $25^{\circ}C$ exhibited more shrunk microstructure of parenchyma cell and xylem than those of Baik-kimchi fermented at 5$^{\circ}C$. The appearance of SDF of the both Baik-kimchi ripened at 5$^{\circ}C$ and $25^{\circ}C$ could give granular shape, whereas the overripened Baik-kimchi had smooth surface of SDF. On the other hand, the IDF retained the original shape during fermentation.

• Environmental Engineering Research
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• 제23권2호
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• pp.195-204
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• 2018

A pilot scale study was conducted on a down-flow hanging sponge (DHS) reactor installed at a sewage treatment plant in Banda Aceh, Indonesia for treatment of desludging septic tank wastewater. Raw wastewater with an average biochemical oxygen demand (BOD) and total suspended solids of 139 mg/L and 191 mg/L, respectively, was pumped into the reactor. Two different hydraulic retention times (HRTs, 3 h and 4 h) were investigated, equivalent to organic loadings of 1.11 and $0.78kg\;BOD/m^3/d$, respectively. The average BOD concentration in the final effluent was 46 and 26 mg/L at HRTs of 3 and 4 h, respectively. The concentration of retained sludge along the reactor height was 10.2-18.7 g VSS/L-sponge, and the sludge activities were 0.24-0.32 and 0.04-0.40 mg/g VSS/h for heterotrophs and nitrification, respectively. Values of water hold-up volume, dispersion coefficient, and number of tank in-series found from tracer studies of clean sponge and biomass-loaded sponge confirmed that growth of retained sludge on the sponge module improved hydraulic performance of the reactor. Adoption of the DHS reactor by this Indonesian sewage treatment plant would enhance the role of the current desludging septic tank wastewater treatment system.

• 대한지하수환경학회지
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• 제4권3호
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• pp.144-152
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• 1997

본 연구에서는 비포화흐름을 해석하는데 있어 기초자료가 되는 물보유함수를 추정하기 위하여 SUS, KUS 등 두가지 국내토양에 대한 물보유함수를 체적기압판추출장치를 이용하여 측정하였다. 체적기 압판추출장치를 사용할 때 압력을 점차적으로 증가하면서 흙시료로 배출되는 물의 양을 정확히 측정한다. 또한 압력이 점차적으로 줄어들 때 흙에 유입되는 물의 양을 정확히 측정한다. 실험결과 젖음 또는 마름과정에 따라 물보유함수가 차이가 나는 이력현상이 발생하였다. 대표적인 물보유함수인 Gardner식, Brooks-Corey식 그리고 van Genuchten식의 실측치에 대한 매개변수 추정을 통하여 그 물리적 의미와 각 토양시료별 매개변수 값을 구하였다. 그 결과 Gardner식, Brooks-Corey 그리고 van Genuchten의 매개변수는 공기유입값과 토양의 입경 크기에 관계 되는 변수임을 알 수 있었다. 결론적으로 van Genuchten식이 측정된 실험자료를 가장 정확하게 모의함을 알 수 있었다.

• 한국식품저장유통학회지
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• 제30권4호
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• pp.602-616
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• 2023

Fifteen types of rice collected from Kurdistan region-Iraq were investigated by principal component analysis (PCA) in terms of physical properties and cooking characteristics. The dimensions of evaluated grains correspond to 5.05-8.75 mm for length, 1.54-2.47 mm for width, and 1.37-1.95 for thickness. The equivalent diameter was in the range of 5.23-10.03 mm, and the area took 13.30-28.25 mm². The sphericity analysis values varied from 0.32 to 0.56, the aspect ratio from 0.17 to 0.39, and the volume of the grain was measured in the range from 4.48 to 17.74 mm³, hectoliter weight values were 730-820 kg/m³, and true density from 0.6 to 0.96 g/cm³. The broken grain ratio was 1.5-18.3%, thousand kernel weight corresponded to 15.88 to 22.42 g. The water uptake ratios for 30 min of soaking were increased at 60℃ compared to 30 and 45℃. The PCA was used to study the correlation of the most effective factors. Results of PCA showed that the first (PC1) and second (PC2) components retained 63.4% and 34.8% of the total variance, which PC1 was mostly related to hectoliter, broken ratio, and moisture content characteristics while PC2 was mostly concerned with hardness and true density. For cooking properties, the PC1 and PC2 retained 88.5% and 9.3% of the total variance, respectively. PC1 was mostly related to viscosity, spring value, and hardness after cooking, while PC2 was mostly concerned with spring value, hardness before cooking, and hardness after cooking.

• 한국해양공학회지
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• 제2권2호
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• pp.87-95
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• 1988

This paper is studied to know corrowive wear characteristics of austempered ductile cast ironin corrosive environments against mating SM45C hardened two test pieces in distilled water and NaCl aqueous solution. The corrosive wear mechanism was investigated by scanning electron microscopy and retained austenite volume fraction was investigated by X-ray diffractometer. The experimental result show that the corrosive wear characteristics depend largely on the $\textrm{Fe(OH)}_{3}$which is influenced by the critical sliding distance $L_{cr}$ and $L_{cr}$ shorted with increasing NaCl concentration. It was found that the carbides in matrix have a significant effect on their corrosive wear resisance and the fine acicular bainite showed corrosive wear resistance stronger than that of the coarse acicular and platelet bainite. From above results the model of corrosive wear mechanism in corrosive environments is proposed.

• 대한환경공학회지
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• 제27권12호
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• pp.1311-1320
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• 2005

본 연구에서는 pilot 규모의 활성탄 공정을 운전하면서 입상활성탄(granular activated carbon: GAC) 단계에서부터 생물활성탄(biological activated carbon: BAC) 단계로 전환되고 난 후 까지 활성탄 재질별로 유기물 제거능과 미생물 군집특성을 함께 조사하였다. 활성탄 재질별 유기물 흡착능은 석탄계 재질의 활성탄이 가장 우수하였고, bed volume 20,000 이후부터는 3가지 활성탄들이 정성상태에 도달하였다. 부착세균의 생체량과 생산력 또한 석탄계 재질 활성탄에서 가장 높은 것으로 나타났으며, heterotrophic plate count(HPC), eubacteria(EUB), 4,6-diamidino-2-phenylindole(DAPI) 및 생산력은 각각 $0.95{\times}10^7{\sim}52.4{\times}10^7$ CFU/g, $3.8{\times}10^8{\sim}134.2{\times}10^8$ cell/g, $7.0{\times}10^8{\sim}250.2{\times}10^8$ cell/g 및 $1.2{\sim}3.4\;mg{\cdot}C/m^3{\cdot}h$의 범위로 나타났다. 그리고 부착세균의 생체량과 생산력은 모두 bed volume 20,000 이후부터 증가하는 경향을 보였다. 활성탄 재질별 부착세균 생체량과 세균 생산력에 대한 동화가능한 유기탄소(assimilable organic carbon: AOC) 제거율과의 상관성 평가에서는 석탄계 재질 활성탄이 가장 양호한 상관성을 보였으며, 항목별로는 세균 생산력에 대한 상관성이 상대적으로 높은 것으로 나타났다. Fluorescent in situ hybridization(FISH)에 의한 세균군집 구조 조사결과, bed volume 20,000까지는 모든 활성탄에서 $\alpha$ 그룹($\alpha$-proteobacteria)과 other bacteria가 우점하였고, bed volume 20,000 이상에서는 석탄계 재질 환성탄에서는 $\beta$ 그룹($\beta$-proteobacteria)과 $\gamma$ 그룹($\gamma$-proteobacteria)의 우점비율이 상승하였으나, 야자계와 목탄계에서는 $\alpha,\;\beta$ 및 $\gamma$ 그룹의 우점비율이 상승하는 것으로 조사되었다.