• Journal of Mechanical Science and Technology
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• 제15권9호
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• pp.1292-1301
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• 2001

The mean-line method using empirical models is the most practical method of predicting off-design performance. To gain insight into the empirical models, the influence of empirical models on the performance prediction results is investigated. We found that, in the two-zone model, the secondary flow mass fraction has a considerable effect at high mass flow-rates on the performance prediction curves. In the TEIS model, the first element changes the slope of the performance curves as well as the stable operating range. The second element makes the performance curves move up and down as it increases or decreases. It is also discovered that the slip factor affects pressure ratio, but it has little effect on efficiency. Finally, this study reveals that the skin friction coefficient has significant effect on both the pressure ratio curve and the efficiency curve. These results show the limitations of the present empirical models, and more resonable empirical models are reeded.

• 대한지리학회지
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• 제50권2호
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• pp.165-183
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• 2015

15세기 이래로 인간의 토지이용으로 인한 토양유실은 그 어느 때보다 급격하게 증가하였다. 그러나 '현재와 같은 토양유실이 계속되면 언제까지 토양이 유지될 수 있는가?'라는 물음에 우리는 정작 답할 수 없었다. 이는 토양생성률을 정량화하는 것이 쉽지 않았기 때문이다. 최근 우주선유발 동위원소를 이용하여 토양생성률을 정량화하는 기법이 등장하였고 국내에도 이를 적용한 시도가 있었다. 본 연구는 우주선유발 동위원소를 이용한 토양생성률 및 토양생성함수 도출 원리를 소개하고, 국내 토양생성률 연구결과를 20세기 이후의 토양유실률 자료와 비교 분석하여 토양의 지속가능기간을 예측해보았다. 대관령 고원에서 추정한 인류세 이전의 토양생성률은 평균 $0.05[mm\;yr^{-1}]$으로 밝혀졌으며, 20세기 후반 인간의 토지이용이 집약적으로 나타나는 농경지에서의 토양유실률은 이에 비해 많게는 60배나 상회하였다. 현재의 토지이용이 유지될 경우, 대하천 상류지역 농경지의 표층토양은 빠르면 수십 년내 사라질 것으로 예측된다.

• 대한기계학회논문집B
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• 제36권6호
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• pp.593-600
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• 2012

대형 선박의 추진용 디젤엔진에서 버려지는 배기가스의 열을 회수하기 위한 랭킨사이클이 적용된 발전시스템에 대하여 R245fa 및 water의 작동유체에 따른 그 엑서지 특성을 분석하였다. 그 이론적인 계산 결과로, R245fa에 대하여 터빈입구의 압력이 증가할수록 엑서지 효율 및 시스템의 엑서지 효율이 증가하였고, 엑서지 파괴율은 주로 응축기 및 증발기에서 상대적으로 높게 나타났다. 그리고 질량유량의 증가에 따라 시스템의 엑서지 효율이 증가하는 특성을 보였다. Water의 경우에, 증발기에서의 엑서지 파괴율은 R245fa의 경우와 유사하게 나타났지만, 터빈입구의 압력 및 질량유량 비율의 변동에 대하여 열원에 대한 엑서지 손실률이 가장 큰 폭으로 변동하였다.

• Journal of Ecology and Environment
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• 제43권4호
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• pp.376-384
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• 2019

Background: Nutrient release during litter decomposition was investigated in Vitex doniana, Terminalia avecinioides, Sarcocephallus latifolius, and Parinari curatellifolius in Makurdi, Benue State Nigeria (January 10 to March 10 and from June 10 to August 10, 2016). Leaf decomposition was measured as loss in mass of litter over time using the decay model W_t/W₀ = e-^{kd t}, while $Kd=-{\frac{1}{t}}In({\frac{Wt}{W0}})$ was used to evaluate decomposition rate. Time taken for half of litter to decompose was measured using T₅₀ = ln ²/k; while nutrient accumulation index was evaluated as $NAI=(\frac{{\omega}t\;Xt}{{\omega}oXo})$. Results: Average mass of litter remaining after exposure ranged from 96.15 g, (V. doniana) to 78.11 g, (S. lafolius) in dry (November to March) and wet (April to October) seasons. Decomposition rate was averagely faster in the wet season (0.0030) than in the dry season (0.0022) with P. curatellifolius (0.0028) and T. avecinioides (0.0039) having the fastest decomposition rates in dry and wet seasons. Mean residence time (days) ranged from 929 to 356, while the time (days) for half the original mass to decompose ranged from 622 to 201 (dry and wet seasons). ANOVA revealed highly significant differences (p < 0.01) in decomposition rates and exposure time (days) and a significant interaction (p < 0.05) between species and exposure time in both seasons. Conclusion: Slow decomposition in the plant leaves implied carbon retention in the ecosystem and slow release of CO₂ back to the atmosphere, while nitrogen was mineralized in both seasons. The plants therefore showed effectiveness in nutrient cycling and support productivity in the ecosystem.

• 한국지하수토양환경학회지:지하수토양환경
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• 제13권6호
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• pp.40-49
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• 2008

평평한 fractures에서 공극을 가진 모암으로의 NAPL 확산을 수치적인 방법으로 해석하였다. 2D와 3D에 대한 일회성 디스크 소스와 3D 연속 디스크소스에 대한 모델은 Caralaw and Jaeger(1959)의 이론을 바탕으로 개발하였다. 3D 연속 디스크소스에 대해 공극모암으로 확산되는 NAPL의 총량을 계산할 수 없기 때문에 확산이 반구형으로 이루어진다고 가정하여 등농도선의 합을 이용하여 공극모암으로 확산되는 NAPL의 총량을 계산하였다. 수치적 계산에 따르면 2D 대비 3D의 경우에 NAPL 손실 시간이 현저히 빠른 것으로 나타났으며, 디스크 소스의 중심점에서 normalized된 농도는 일회성 디스크 소스는 시간에 따라 감소하고, 연속 디스크 소스는 증가하는 것으로 나타났으며, 시간과 공간에 따라 확산율은 감소하는 것으로 나타났다. 그리고 NAPL의 mass 손실은 1에 도달하지 못하였으며, 이는 연속 디스크 소스를 semi-infinite로 가정하고 적분했기 때문이다. 확산에 의해 사라지는 시간은 소스의 크기 및 모암 공극률 크기 증가에 비례해서 지수함수적으로 증가하고, 반면 NAPL의 용해성이 증가하면 감소하는 것으로 나타났다.

• 대한한의정보학회지
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• 제11권1호
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• pp.52-57
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• 2005

Objectives : Recurrent pregnancy loss occurs in approximately 0.5-3% of women. There are many studies concerning immunological factor recently. Therefore, aim of this study is to examine the latest trend of researches concerning recurrent pregnancy loss, and controlled experiment on animals about antiphospholipid antibody. Method : We referred Pubmed site by using searching word of 'recurrent pregnancy loss' (Limits : 2000.1-2004.3, animal) Results and conclusions : 1. We searched 29 papers. Immunological factor : 18 ( about antiphospholipid antibody : 10 ), Chromosomal abnormality : 6, The others : 5 2. In five papers about controlled experiment on animals, (1) Materials : 8-12 weeks old mice / 11.5-day old-rat embryos / New Zealand rabbit (2) Inductions : inject intraperitoneally with human IgG containing antiphospholipid antibodies / culture in a solution of 1 ml medium which contained IgG purified from sera of women / inject intradermally with cardiolipin (3) Treatments : inject intraperitoneally with complement component before / culture in a solution of 1 ml medium which contained IgG purified from sera of women with SLE and RPL or from healthy women / inject intradermally with TFX, 0.9% NaCl (4) Measurements : weight fetuses and placentas, calculate frequency of fetal resorption / after culture, examine the embryos / examine platelet counts, APTT and numbers of live and dead newborns, resorbed fetuses, body mass, newborn viability and survival rates.

• 한국환경생태학회지
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• 제24권3호
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• pp.279-285
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• 2010

본 연구는 중금속이 낙엽의 분해에 미치는 영향을 알아보기 위하여 충남 청양의 폐금광의 광미에 분포하는 쑥(Artemisia princeps var. orientalis)과 쇠뜨기(Equisetum arvense)를 이용하여 실험하였다. 광미는 높은 중금속 함량과 낮은 유기물 함량을 가지고 있었다. 광미의 중금속 함량은 대조구 토양에 비해 비소(As)는 약 13배, 카드뮴(Cd)은 약 28배 높은 것으로 나타났다. 또한 크롬(Cr), 니켈(Ni) 및 아연(Zn)은 약 3배에서 6배 높게 측정되었다. 광미와 대조구 토양에서 채집한 식물체내의 중금속 함량은 광미에서 채집한 식물에서 현저히 높게 나타났으며, 쑥 잎의 경우 As는 약 23배, Cd은 25배 높게 나타났으며, 쇠뜨기 지상부의 경우 As는 58배, Cd은 11배 높은 것으로 나타났다. 대조구에서 분해 결과 중금속 농도가 높은 쑥의 잎과 대조구에서 채취한 잎이 각각 50.4%, 65.7%가 분해되었다. 또한 광미에서 진행된 분해 결과 쑥의 잎은 폐광지역에서 채취한 잎과 대조구에서 채취한 잎이 각각 31.6%, 57.5%가 분해되었다. 쑥의 줄기의 분해결과도 잎의 분해율과 비슷한 양상을 나타내었다. 쇠뜨기의 지상부의 분해는 대조구에서 분해된 결과 광미에서 채집된 쇠뜨기와 대조구에서 채집한 쇠뜨기가 각각 77.8%와 89.3%가 분해되었으며, 광미지역에서 분해 결과 각각 67.6%와 82.1%가 분해된 것으로 나타났다. 따라서 광미에서 생육하는 식물체의 중금속의 함량이 높을수록 분해가 느린 것으로 나타났으며, 이는 중금속이 낙엽의 분해에 영향을 미친 것이라고 판단된다.

• Journal of Biosystems Engineering
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• 제6권1호
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• pp.83-92
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• 1981

A simulation model of natural air drying to predict the changes of the grain moisture content and dry matter loss of rough rice was developed by the application of mass diffusion theory. A series of simulated drying tests was conducted using the 10 year weather data (1970-1979) obtained from Cheongju, Chuncheon, Daegu, Daejeon, Jeonju, Jinju and Suweon in Korea. System performance factors treated in this study were initial moisture content, airflow rate, bin diameter and grain depth. The results obtained in this study are summarized as follows: 1) The simulation model used in this study was validated with actual experimental results and was applicable to the natural air drying of rough rice. 2) Minimum airflow rates for safe drying were determined for different initial moisture contents and regional weather conditions as shown in Table 6. 3) Equations for estimating drying time and dry matter loss in terms of airflow rate and initial moisture content were derived in the form of an exponential function. 4) These results show that the natural air drying system of rough rice is feasible in Korea even for the poorest drying condition.

• Journal of Forest and Environmental Science
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• 제26권1호
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• pp.17-23
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• 2010

The present study was conducted to quantify wood and leaf litter decomposition and nutrient release of a dominant tree species, Tectona grandis Linn. F. in a tropical dry deciduous forest of Rajasthan, Western India. The mean relative decomposition rate was maximum in the wet summer and minimum during dry summer. Rainfall and its associated variables exhibited greater control over litter decomposition than temperature. The concentrations of N and P increased in decomposing litter with increasing retrieval days. Mass loss was negatively correlated with N and P concentrations. The monthly weight loss was significantly correlated (P < 0.05) with soil moisture and rainfall in both wood and leaf litter. Tectona grandis was found to be most suitable tree species for plantation programmes in dry tropical regions as it has high litter deposition and decomposition rates and thus it has advantages in degraded soil restoration and sustainable land management.

• Journal of Forest and Environmental Science
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• 제38권1호
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• pp.48-54
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• 2022

This study was conducted to examine litter inputs and litter decomposition rates following thinning, which is among the most important forest management activities that enhance the beneficial functions in Korean forests. Litter inputs and litter decomposition rates following a 2-year elapse from thinning in Pinus densiflora and following a 7-year elapse from thinning in Quercus variabilis stands were measured for 2 years from 16 sites in three regions (Sancheong-gun, Uiryeong-gun, and Jinju-si) in Gyeongsangnam-do, Korea. Annual needle litter inputs in P. densiflora stands were significantly decreased following thinning, whereas annual broadleaved leaf litter inputs in Q. variabilis stands were not significantly different between thinned and unthinned treatments. The annual mean total litter inputs in both tree species were significantly lower in the thinned (P. densiflora: 3,653 kg ha^-1 year^-1; Q. variabilis: 4,963 kg ha^-1 year^-1) compared to the unthinned stands (P. densiflora: 5,138 kg ha^-1 year^-1; Q. variabilis: 5,997 kg ha^-1 year^-1) during the study period. The mass loss rates from decomposing needle litter in P. densiflora stands were significantly lower (p<0.05) in the thinned stands than in the unthinned stands for two sampling dates of the eight included in the study, whereas the decomposition rates from decomposing leaf litter in Q. variabilis stands were not affected by thinning. The results indicate that thinning effects on total litter inputs remained clear following a 2-year elapse from thinning in P. densiflora stands and following a 7-year elapse from thinning in Q. variabilis stands.