• International Journal of Air-Conditioning and Refrigeration
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• 제16권4호
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• pp.117-123
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• 2008

The present study is directed at flow and heat transfer of $CO_2$ and oil mixtures in a circular tube. PAG and POE oils are considered in this study. Flow characteristics of $CO_2$ and oil mixtures have been investigated by flow visualization. Pressure drop has been measured in the range of operating mass flow rate from 0.1 to 0.4 kg/min in a circular tube. Heat transfer characteristics of $CO_2$/oil mixtures have been investigated using a counterflow heat exchanger. In case of pure liquid $CO_2$ as well as $CO_2$ and POE mixtures, flow are seen to be uniform so that $CO_2$ and POE oil are still miscible even at flowing state. However, it is found that $CO_2$ and PAG are not miscible. Pressure drop of $CO_2$/PAG mixtures are much higher than that of $CO_2$/POE mixtures as well as pure $CO_2$ at a fixed mass flow rate. As the concentration of POE oil is increased from 0 to 5 wt%, pressure drop is increased. However, heat transfer rate and heat transfer coefficient of $CO_2$/POE mixtures are much higher than that of $CO_2$/PAG mixtures. The f-factor correlation and Nusselt number correlation for $CO_2$/POE oil mixtures are suggested in this paper.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권12호
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• pp.599-606
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• 2001

In this paper, the ac breakdown characteristics of pure Ar, Kr and $N_2$ gas with gas pressure range of 58.8-137.3[kPa] under uniform and non-uniform fields were investigated, and the measured values were compared with those In Ar/$N_2$ and Kr/$N_2$ gas mixtures with pressure varying. Summarizing the experimental results, the breakdown voltages of Pure $N_2$gas, under uniform and non-uniform fields, were increased about 4.8 and 1.1 times than those of pure Ar gas, and about 4.4 and 1.2 times than those of pure Kr gas, and the ac breakdown voltage increased with the pressure increasing. The breakdown voltages of Ar/$N_2$ gas mixtures were decreased with decreasing the mixture ratio of Pure $N_2$ gas. In case of Ar(85%)/$N_2$ (15%) and Ar(70%)/$N_2$ (30%) gas mixtures comparing to the pure Ar gas, the breakdown voltages under uniform field were increased about 1.8 and 2.2 times, and under non-uniform field were increased about 1.1 and 1.3 times at the pressure of 101.3[kPa]. Also, in case of Kr(85%)/$N_2$ (15%) and Kr(70%)/$N_2$ (30%) gas mixtures comparing to the pure Kr gas, the breakdown voltages under uniform field were increased about 1.7 and 2.0 times, and under non-uniform field were increased about 1.0 and 1.2 times. Corona inception voltage of Kr(70%)/$N_2$(30%) gas mixtures under non-uniform fields were increased about 1.28 times than those of Ar(70%)/$N_2$ (30%) gas mixtures. In case of practical incandescent lamps, luminous and lifetime of Kr(70%)/$N_2$ (30%) gas mixtures were increased about 1.15 and 1.21 times than those of Ar(70%)/$N_2$ (30%) gas mixtures.

• Bulletin of the Korean Chemical Society
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• 제23권7호
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• pp.953-956
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• 2002

Excess molar volumes (Vm E ) of binary liquid mixtures: xC6H5CH3 + (1-x1)CH3CN or + (1-x1)C6H5NO2, or + (1-x1)C2H5NO2 have been determined as a function of mole fraction of C6H5CH3 (x) at a temperature of 303.15 K over a entire range of composition. The densities of the binary liquid mixtures were determined by pycnometrically. The VmE values of the mixtures have been found to be negative over the whole composition in order of C6H5CH3 + C6H5NO2, < C6H5CH3 + CH3CN, and < C6H5CH3 + C2H5NO2. The negative magnitude of VmE suggests the presence of intermolecular interaction in the three binary liquid mixtures.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2001년도 학술대회논문집
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• pp.187-191
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• 2001

In this paper, the ac breakdown characteristics of Ar/$N_2$and Kr/$N_2$gas mixtures with gas pressure range of 58.8~137.3[kPa] under uniform and non-uniform fields were investigated. Summarizing the experimental results, the breakdown voltages of Ar/$N_2$ gas mixtures were decreased with decreasing the mixture ratio of pure $N_2$gas. In case of Ar(85%)/$N_2$(15%) and Ar(70%)/$N_2$(30%) gas mixtures comparing to the pure Ar gas, the breakdown voltages under uniform field were increased about 1.8 and 2.2 times, and under non-uniform field were increased about 1.1 and 1.3 times at the pressure of 101.3[kPa]. Also, in case of Kr(85%)/$N_2$(15%) and Kr(70%)/$N_2$(30%) gas mixtures comparing to the pure Kr gas, the breakdown voltages under uniform field were increased about 1.7 and 2.0 times, and under non-uniform field were increased about 1.0 and 1.2 times.

• 한국농공학회논문집
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• 제55권2호
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• pp.65-75
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• 2013

In this study, the engineering characteristics of volcanic ash-cement soil mixtures and zeolite-cement soil mixtures are investigated by using unconfined compression test, freezing-thawing test, SEM and XRD analysis. The samples were mixed with volcanic ash from Mt. Baekdusan or porous zeolite, and cement as the ratios of 3.5:1, 4.0:1, 4.5:1, 5.0:1 with and without metakaolin. It is confirmed that compressive strength degraded with increasing of the amount of volcanic ash or zeolite, and increased with addition of metakaolin as a binder. Moreover, test results suggested that the mixtures provided sufficient freezing-thawing resistance. In addition, ettringite as a product of cement hydration was detected by SEM and XRD, and that possibly contributes to the strength of the mixtures.

• 한국농공학회지
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• 제39권6호
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• pp.99-110
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• 1997

The study was conducted in order to investigate the basic geotechnical properties of sand-bentonite mixtures with the various bentonite contents. The results obtained are as follows : 1. Optimum moisture content of sand-bentonite mixtures was approximately 17.10~18.52% corresponding to the maximum dry density of 1.58~1 .64gf/$cm^3$. As the bentonite contents and curing peroid increased, both the maximum dry density and optimum moisture content of sand-bentonite mixtures increased. 2. The unconfined compressive strength of sand-bentonite mixtures increased as the increase of bentonite content, but it did not change along the curing period. 3. The sand-bentonite mixtures ruptured at 8~15% of the axial strain and the maxi-mum shearing stress was about O.7Okgf/$cm^2$. 4. According to the increase of bentonite content, the cohesion intercept and internal friction of the sand-bentonite mixtures increased slightly in the shear test, while the cohesion intercept increased largely, and the internal friction angle decreased largely in the triaxial test. 5. Both the initial void ratio and swelling of the sand-bentonite mixtures were very low with respect to the consolidation pressure increase. 6. The swelling and shrinkage of sand-bentonite mixtures increased slightly according to the increment of bentonite content.

• Journal of Ginseng Research
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• 제5권1호
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• pp.8-23
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• 1981

Color is one of the most important quality factors of red ginseng (Hong-sam) which is processed from fresh ginseng (Panax ginseng C. A. Meyer). Therefore, a study of characteristics of browning mixtures of aqueous fresh ginseng extracts, factors which accelerate the browning of the aqueous extracts, and the antioxidant activity of the browning mixtures may contribute to the improvement of the color and other quality of red ginseng and other ginseng products such as ginseng extracts. In the present study, factors which affect the Maillard-type browning reaction of aqueous extracts of fresh ginseng roots were investigated firstly by adding various concentrations (0.001-0.5M) of arginine or glucose solutions, by varying the browning reaction temperatures and durations. Secondly, some characteristics such as brown color intensity, amounts of water-soluble and ether-soluble extracts, amounts of non-dialyzable materials, pH, viscosity, and reactivity with 2,2'- diphenyl -1 - picrylhydrazyl and antioxidant activity of the browning mixtures of the aqueous fresh ginseng extracts with small amounts of 0.1 M arginine, 0.1 M glucose, and distilled water at various browning temperatures and reaction time were studied. The results of the present study are as follows. 1. Color intensity (absorbance at 470 nm) of the browning mixtures was increased by adding various concentrations of arginine solution to the fresh ginseng extract, but the addition of the same amount of glucose solution did not increase the color intensity. 2 The amounts of water- or ether-soluble extracts, amounts of non-dialyzable materials were slightly greater in case of the browning mixtures of the fresh ginseng extract with 0.1M arginine solution than in case of the browning mixtures of the fresh ginseng extract with the same amount of 0.1 M glucose solution. In the process of the browning reaction, the pH of the browning mixtures of the fresh ginseng extract with 0.1 M arginine solution decreased slightly, while that of the browning mixtures with 0. 1 M glucose solution was almost constant. 3. The color intensity (absorbance at 470 nm) of the browning mixtures of the fresh ginseng extract with 0.1 M arginine or 0.1 M glucose solutions did not correlate well with the reducing power or the antioxidant power of the browning mixtures. The antioxidant activity of 90% ethanol extracts from the earlier stages of the browning mixtures of the fresh ginseng extract with the arginine solution was almost comparable to that of the 90% ethanol extracts from the later stages of the corresponding browning mixtures. The browning mixtures of only the fresh ginseng extract or of the fresh ginseng extract with the glucose solution showed considerable antioxidant activity, although both showed less brown color intensity than the fresh ginseng extract with he arginine solution.

• 한국초지조사료학회지
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• 제25권3호
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• pp.185-190
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• 2005

본 연구는 2000년 7월부터 12월까지 충남대학교 생명과학대학 내 부속 환경조절축사에서 수행하였다. 공시된 혼파유형별 목초는 관행 혼파초지(orchardgrass 50+tall fescue 20+perennial ryegrass 10+ Kentucky bluegrass 10+white clover $10\%$), 다초종 혼파초지(orchardgrass 40+tall fescue 20+perennial ryegrass 10+Kentucky bluegrass 10+redtop 10+alfalfa 5+red clover $5\%$) 및 단순 혼파초지(orchardgrass 80+red clover $20\%$)의 3처리를 두어 1999년 9월 7일 경운초지조성 방법에 의해 조성된 기존초지에서 수확한 1번초(4월 20일)를 재래산양에 급여하여 목초의 이용성을 비교 분석하였다. 얻어진 결과는 다음과 같다. 건물섭취량은 다초종 혼파초지(30.2g/BWkg/day)가 관행(26.5g/BWkg/day)이나 단순 혼파초지(26.9/BWkg/day)에 비하여 다소 높은 결과를 보였으나 유의적인 차이는 없었다(p>0.05). 건물소화율과 세포내용물질(cellular constituents)의 소화율은 다초종 혼파초지가 관행이나 단순 혼파초지에 비하여 높은 결과를 보였으나 (p<0.05), NDF와 ADF 소화율은 혼파유형간에 유의적인 차이가 인정되지 않았다(p>0.05). 외관상 생물가는 다초종 혼파초지$(55.1\%)$가 관행 $(54.0\%)$이나 단순 혼파초지$(53.3\%)$에 비하여 높은 편이었으나 유의적인 차이는 인정되지 않았다.(p>0.05). 외관상 대사에너지 축적률은 다초종 혼파초지$(60.2\%)$가 관행$(56.9\%)$이나 단순 혼파초지$(55.9\%)$에 비하여 높았다(p<0.05). 이상의 결과로 보아, 재래산양에 의한 초지 유형별 목초의 질소 및 에너지의 이용성은 대체적으로 다초종 혼파초지가 다른 혼파유형에 비하여 개선되는 결과를 보였다.

• Journal of Animal Science and Technology
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• 제46권4호
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• pp.701-706
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• 2004

본 연구는 2001년 3월부터 2001년 12월까지 충남대학교 농업생명과학대학내 부속 초지시험포장에서 하번초형 혼파초지 {Turf type mixtures: Kentucky bluegrass(Newport) 40%+tall fescue(Rebell Jr.) 20%+perennial ryegrass(Palmer II) 10%+redtop(Barricuda) 10%+red fescue(Salem) 10%+creeping bentgrass(Crenshaw) 10%}에서 수확한 1번초(4월 24일)의 목초와 상번초형 혼파초지 {tall type mixtures:orchardgrass(Potomac) 40%+tall fescue(Fawn) 20%+Festulolium braunii(Paulita) 10%+perennial ryegrass(Feveille) 10%+timothy(Climax) 10%+red clover(Kenblue) 5%+alfalfa(Vemal) 5%}에서 수확한 1번초(4월 24일)를 공시하였다. 시험축은 한국재래산양을 8두를 공시하여 건물소화율, 건물섭취량, 질소 및 에너지 이용성을 비교 분석하였으며, 얻어진 결과는 다음과 같다. 1) 건물섭취량은 하번초형 초지(28.9g/BW,kg/day)가 상번초형 초지(26.2g/BW,kg/day)에 비하여 다소 높은 편이었으나 유의적인 차이는 없었다. 세포내용물질(cellular constituents)의 소화율은 하번초형 초지가 높은 편이었으나(P<0.05), DM, NDF 및 ADF 소화율은 두 초지간에 유의적인 차이가 인정되지 않았다. 2) 외관상 생물가는 하번초형 초지(56.7%)가 상번초형 초지(56.4%)보다 높은 편이었으나 유의적인 차이는 인정되지 않았다. 3) 외관상 대사에너지 축적률은 하번초형 초지(58.3%)가 상번초형 초지(57.9%)보다 높은 편이었으나 유의적인 차이는 인정되지 않았다. 이상의 결과로 보아, 재래산양에 의한 하번 초형 목초의 이용성은 상번초형 초지에서 생산된 목초와 비교할 때 큰 차이가 없는 것으로 나타나 조사료원으로 이용가능성은 충분하다고 하겠다.

• 한국환경보건학회지
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• 제29권3호
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• pp.28-34
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• 2003

This study was performed to compare the effects of chaff and sawdust as bulking materials on temperature, pH, weight and volume reduction and salinity in aerobic composting of food wastes. Volume ratios of food wastes to chaff in reactor of Control, Ch-l, Ch-2, Ch-3 and Ch-4 were 4:0, 4:1, 4:2, 4:3 and 4:4, respectively. Volume ratios of food wastes to sawdust in reactor of Control, Sd-l, Sd-2, Sd-3 and Sd-4 were 4:0, 4:1, 4:2, 4:3 and 4:4, respectively. Reactors were operated for 24 days with 1 hour stirring by 1 rpm and 2 hours aeration per day. The lowering of the volume ratio of food wastes to chaff and sawdust resulted in the reaction at higher reaction temperature and the elongation of the high temperature reaction period. The lowering of the volume ratio of food wastes to chaff and sawdust resulted in faster pH increase. In the volume ratio of 4:3 and 4:4, pH increased faster in food-chaff mixtures than in food-sawdust mixtures. The lowering of the volume ratio of food wastes to chaff and sawdust resulted in faster steady state in the weight reduction rate and the volume reduction rate. The weight reduction rates of chaff mixtures were higher than those of sawdust mixtures, but the volume reduction rates of sawdust mixtures were more higher than those of chaff mixtures. Salinity increased as composting reaction proceeded, due to reduction in mass weight. The final salinity of Control was 2.79%, and the final range of salinities of chaff and sawdust mixtures were 2.18∼2.37% and 1.86∼2.05%, respectively.