• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.5
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• pp.37-46
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• 2013

The gas jet from a coaxial porous injector for two-phase flows is discharged radially from the porous surface, which encloses the center liquid jet. Several hot-firing test using ethanol/nitrous oxide propellants was conducted to analyze the effect of oxidizer/fuel ratio on the combustion performance, and the uncertainty analysis was performed for the results. The characteristic velocity was affected by oxidizer/fuel ratio similarly with the results of CEA calculation except that the maximum characteristic velocity was appeared in the stoichiometric ratio. The characteristic velocity efficiency was increased as the oxidizer/fuel ratio increases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.4
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• pp.431-438
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• 2011

Flame lift-off conditions determine the operating conditions of burners. It is known that a flame can be lifted when the Schmidt number (Sc), which is the ratio of the dynamic viscosity to the mass diffusivity, is greater than unity. In this study, the flame lift-off characteristics of non-premixed flames of propane (Sc > 1) and methane (Sc < 1) in a coaxial outer air tube were experimentally compared. The experimental results indicated that stable lifted flames could be obtained even when Sc < 1 in a confined air tube. On the basis of the results of a simple numerical analysis, it was confirmed that a new flame stabilization mechanism exists in the tube. A velocity field is preferentially developed upstream of the flame, and it results in a new stabilization condition. This result can be very useful in explaining the stabilization of the flames of ordinary burners in which a flame is produced in a confined space.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.3
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• pp.221-228
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• 2013

An experimental study was carried out to investigate the effects of the injection timing on the spray and combustion characteristics in a spray-guided direct-injection spark-ignition (DISI) engine under lean stratified operation. An in-cylinder pressure analysis, exhaust emissions measurement, and visualization of the spray and combustion were employed in this study. The combustion in a stratified DISI engine was found to have both lean premixed and diffusion controlled flame combustion characteristics. The injection timing condition corresponding to the stratified mixture characteristics was verified to be a dominant factor for these flame characteristics. For the early injection timing, a non-luminous blue flame and low combustion efficiency were observed as a result of the lean homogeneous mixture formation. On the other hand, a luminous sooting flame was shown at the late injection timing because of an under-mixed mixture formation. In addition, the smoke emission and incomplete combustion products were increased at the late injection timing as a result of the increased locally rich area. On the other hand, the NOx emissions decreased and IMEP increased as the injection timing retarded. The combustion phasing produced by the injection timing was verified as the reason for this observation.

• Proceedings of the Korean Society of Organic Agriculture Conference
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• 2009.12a
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• pp.286-286
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• 2009

벼 유기재배시 토양양분공급용으로 이용되고 있는 유기자재(금수강산골드)를 대조로 하고 식물성유기 자재(쌀겨팰렛), 동물성유기자재, 식물성과 동물성이 혼합된 유기자재를 질소 성분량(7kg/10a)을 기준으로 하여 이앙 20일전에 전량 기비로 시비하고 경운한 다음 동진1호를 시험품종으로 하여 2년연속 유기 자재와 벼를 재배하면서 일어나는 토양의 이화학적 특성과 벼 생육 및 특성의 변화를 시기별로 조사하였다. 시험 전 토양의 화학성은 전반적으로 유기물은 높고 인산함량은 매우 낮은 조건의 토양이었다. 관행유기자재(금수강산골드)는 20일경에 50% 무기화율을 보였으나, 식물성자재 40~60일경, 동물성자재와 혼합자재(식물성+동물성)는 60~80일경에 47~52% 무기화 정도를 나타내 식물성 자재의 무기화 속도가약 20일정도 빨랐다. 토양 중의 유기물 잔존함량은 식물성자재 > 혼합자재 > 동물성자재 > 관행 순이었으며, 토양 중의 전 질소 잔존함량의 경우 관행유기자재는 처리초기부터 빠르게 감소하는 특성을 보이나, 식물성자재와 혼합 자재는 시비초기와 거의 비슷한 수준을 유지하였고, 동물성 자재는 서서히 감소되는 경향이었다. 토양 물리성은 액상과 공극율 다소 증가되는 경향이었으며 식물성과 혼합유기자재처리구가 컸으며, 토양 유효 입단 형성력에 있어서도 유사한 경향이었다. 벼 수량 특성은 관행유기자재보다 1년차에는 3~9%의 낮았으나, 2년 연속처리를 할 경우 관행유기자재를 처리할 때와 동일한 생산성을 기대할 수 있었다. PME와 $\beta$-Glucosidase의 효소활성은 관행유기자재 < 식물성자재 < 동물성자재 < 혼합유기자재의 순으로 높은 경향을 볼 수 있었다.

• Nuclear Engineering and Technology
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• v.19 no.2
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• pp.122-129
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• 1987

Experiments and numerical analysis have been performed to investigate the effect of preoxidation by oxidizing Zircaloy-4 specimens at a higher temperature after a period of exposure at a lower temperature. The oxidation experiments were performed between $700^{\circ}C$ and 85$0^{\circ}C$ after Preoxidation at $650^{\circ}C$ in a steam and water mixture for 600 seconds and 1,800 seconds. As the thickness of preoxidized layer increased, the oxidation rate of preoxidized specimens at higher temperature became lower than that of as-received claddings. A transition region of oxidation rate exist in the preoxidized specimens, and the region disappeared rapidly as the oxidation temperature increased. This effect appeared more clearly at lower temperatures. According to the results of numerical analysis performed in this study, the growth rate of oxide layer thickness and weight gains were similarly affected by the thickness of preoxidized layer.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.101-102
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• 2014

Rising oil price and environmental problems are causing automotive industry to increase fuel efficiency. Improved fuel efficiency in gasoline engine was made possible by development of DISI gasoline engine. Since fuel is injected inside cylinder directly, in-cylinder temperature can be reduced than multi-port injection engine and this leads to increased compression ratio. However, engine performance is largely dependent on mixture formation process due to in-cylinder fuel injection. Especially for spray guided and air guided DISI gasoline engine, injection direction is important factor to mixture preparation. It is because interaction between intake flow and spray affect fuel-air mixture. Hence, in this study, mixture formation characteristics were analyzed by varying injection direction using KIVA 3V release2 code. Residual gas was considered for assuming combustion. Therefore, initial condition for in-cylinder temperature was set equal to the end state of exhaust stroke of combustion cycle. Since angle between intake air flow direction and spray direction affects fluid flow and evaporation field, mixture distribution was affected by fuel injection direction dominantly.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.9-12
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• 2010

This paper discusses experimental data for the assessment of flow discharging characteristics of double swirl coaxial injectors operating at fuel-rich conditions. Combustion tests employing liquid oxygen and kerosene (Jet A-1) were conducted and a discharge coefficient was utilized for defining flow characteristics. A mass flow rate, a pressure, and a temperature were measured to estimate discharge coefficients. Fuel injectors revealed a fixed value of a discharge coefficient regardless of matched LOx injector design, chamber pressure, and mixture ratio. However, oxidizer injectors showed varying discharging coefficients depending on chamber pressure and mixture ratio. Flame structure variations seem to affect flow discharging characteristics of the oxidizer side.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.5
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• pp.811-816
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• 2019

This paper first proposes a technique to separate clean speech signals and mixed noise signals by using an independent vector analysis algorithm of frequency band for 4 channel speech source signals with a noise. An improved output speech signal from the proposed independent vector analysis algorithm is obtained by using the cross-correlation between the signal outputs from the frequency domain delay-sum beamforming and the output signals separated from the proposed independent vector analysis algorithm. In the experiments, the proposed algorithm improves the maximum SNRs of 10.90dB and the segmental SNRs of 10.02dB compared with the frequency domain delay-sum beamforming algorithm for the input mixed noise speeches with 0dB and -5dB SNRs including white noise, respectively. Therefore, it can be seen from this experiment and consideration that the speech quality of this proposed algorithm is improved compared to the frequency domain delay-sum beamforming algorithm.

• Korean Journal of Food Science and Technology
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• v.31 no.5
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• pp.1171-1177
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• 1999

The changes on microstucture of recombinated gels with different ratio of amylose(A) and amylopectin(AP) which were isolated from nonwaxy rice starch were investigated by scanning electron microscope(SEM) and X-ray diffractometer. As the concentration of amylose was above 3%(1.08% of soluble amylose) in the amylose suspension, gel matrix became like a three-dimensional network. The microstructure of amylose gels showed a network including macroporous structure, but the higher the ratio of amylopectin content were, the firmer network were formed. In case of A/AP mixed gels(15%) with different amylose/amylopectin percent ratios ; 0/5, 5/10, 10/5, 15/0%, as the storage time of gels and the percent ratio of amylose content were increased, network was formed harder with thick films. While X-ray diffractograms of waxy rice starch which contained 100% amylopectin showed A type, those of purified amylose and amylopectin showed V type and amorphous patterns, respectively. Amylose(3%) gels added $2{\sim}3%$ amylopectin and A/AP mixed gels(15%) showed peak at $2{\theta}\;=\;17.0^{\circ}$which were shown B type crystallinity similar af retrograded starches. Also as the percent ratio of amylose content in mixed gels was increased, peak intensity wat increased.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2018.04a
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• pp.22-22
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• 2018

실고사리[Lygodium japonicum (Thunb.) Sw.]는 국내 자생하는 덩굴성 양치식물로 유인재배가 용이하여 실내 외 조경 및 관상소재로 활용이 가능하다. 한방에서는 전초를 해금사초, 포자를 해금사, 뿌리와 지하경을 해금사근이라 약재로 사용한다. 본 연구는 관상 및 약재로 이용이 가능한 실고사리의 대량생산을 위한 기내 외 번식방법을 개발하고자 수행되었다. 식물재료는 경상북도 의성군 일대에서 성체를 수집하여 청주의 일반하우스에 식재하여 성숙한 포자를 채취하였다. 포자를 기내 발아시켜 전엽체를 획득한 다음 8주 간격으로 계대하면서 연구의 재료를 확보하였다. 전엽체의 증식과 생육에 적합한 배지를 비교 하고자, 1/4, 1/2, 1, 2MS배지와 Knop배지를 조성하여 배양하였다. 배양방법은 전엽체 300mg을 메스로 균일하게 다져서 배양하는 방법을 이용하였으며, 배양환경은 온도($25{\pm}1.0^{\circ}C$), 광도($30{\pm}1.0{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$), 광주기(16/8h light/dark)로 조절되었다. 연구결과, 모든 처리구의 생체중은 초기접종량 보다 11배 이상 증가하였고, 그 중 1MS배지에서는 전엽체의 생체중이 7.3g으로 가장 많이 증가하였다. 뿐만 아니라, 형태형성도 우수하여 모두 정상적인 전엽체의 형태인 하트형으로 발달이 유도되었다. 전엽체로부터 포자체 형성을 유도하고자, 원예상토, 피트모스, 펄라이트 및 마사토의 혼합비율을 5종류로 달리하여 사각분($7.5{\times}7.5{\times}7.5cm$)에 혼합토양을 충진하였다. 전엽체 1g과 증류수 25mL를 핸드블랜더로 10초간 분쇄하여 사각분의 토양표면에 균일하게 분주하는 방법을 사용하였다. 이후 온도($25{\pm}1.0^{\circ}C$), 광도($43{\pm}2.0{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$), 광주기(16/8h light/dark), 습도($72{\pm}2.0%$)를 유지하면서 10주간 재배되었다. 연구결과, 원예상토 단용, 원예상토와 펄라이트 및 마사토가 2:1(v:v)로 혼합된 토양에서 각 498.0, 402.5, 482.5개의 포자체가 형성되어 사각분 면적대비 7.16개($cm^2$)가 생산되었다. 한편 포자체의 생육은 원예상토와 펄라이트가 2:1(v:v)로 혼합된 토양에서 생체중, 엽장, 엽폭, 근장 및 SPAD value 등이 우수하였다.