• Journal of Science Education
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• v.33 no.2
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• pp.353-364
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• 2009

The purpose of this study was to develop 'the problem situations' for the Problem Based Learning(PBL) and to examine it's effects on the science achievement and the attitude towards science learning. Also the students' perception on the PBL model was examined. The topics of the problem situations developed were 'the future energy for reducing the green house effect' and 'the Indonesian forest fire and the El Nino'. The coaching strategies for the PBL were designed and implemented to 10th grade high school students in the science classes, the results are follows; First, the science achievement of the group of PBL is significantly higher than those of group of traditional teaching. Second, the scores of the test of attitude toward science learning of the group of PBL is significantly higher than those of group of traditional teaching. Third, the students' perception of the PBL was positive. Many students have interests and motivations in PBL, some students have difficulties in learning on the PBL. In the students' personal reflection notes the step of a problem statement is the hardest one of the PBL model. Therefore, this study suggests that developing the problem situations based on real context is of great importance for implementing a problem based learning model continuously.

• Korean Journal of Medicinal Crop Science
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• v.4 no.3
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• pp.187-192
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• 1996

This study was investigated to know about the stages of flower bud development and the effects of natural and artificial cold treatment on flowering of herbaceous peony. Developing buds of Paeonja lactㅑflora Pall. var. Taebaek were observed since Jun. 17 and peony plants were forced since Nov. 27 in the green house with two weeks interval, and other plants were forced after cold treatment in $5^{\circ}C$ for 1, 2, 4, 6weeks. Differentiation of vegetable part in peony buds was started in early June, and floral part was differentiated in September and their differentiation was continued to shooting in early spring. Buds of peony were sprouted and flowered when it was forced on Dec. 4. Days to shooting were decreased with delay of forcing time from early to late of December, significantly. Two weeks for cold treatment were enough to break dormancy of peony and days to shooting of the cold treated were significantly shorter than the untreated in the same forcing times

• Korean Journal of Occupational Health Nursing
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• v.7 no.2
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• pp.177-185
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• 1998

The purposes of this study were to investigate the effects of farming in greenhouses with respect to subjective fatigue symptoms among farmers and the degree of symptoms. The study compared 176 green-house farmers with 216 open field farmers using a subjective fatigue symptoms rating scale developed by the Industrial Research Institute of Fatigue, Japanese Association for industrial Hygiene. 1. With respect to complaint rates of the subjective fatigue symptoms, the results indicated that greenhouse farmers have, in order of severity, high degrees of low back pain, difficulty in collecting thoughts, and apt to forget. 2. With respect to cumulative scores of fatigue symptoms, the results indicated that both groups of farmers exhibited a lack of attentiveness and a high degree of dullness and sleepiness(category I), body projection of fatigue(category II), and difficulty in concentration(category III). 3. With respect to general characteristics, it was found that the degrees of subjective fatigue symptoms were found to be higher among females, people with lower educational levels, and the elderly, regardless of the group. 4. With respect to work related factors, farmers with more years of experiences were found to have higher degrees of subjective fatigue symptoms, except for open field farmers with less than nine years experience. Both groups of farmers were found to have high degrees of subjective fatigue symptoms when working less than eight hours a day and less than six months a year. 5. With respect to health habits, for people who get less than eight hours of sleep per day exhibited higher fatigue scores than people who get more than eight hours. People who do not smoke and drink also exhibited higher fatigue scores than people who smoke and drink. 6. The results of multiple regression showed that the risk factors related to the subjective fatigue symptoms of farmers in the greenhouse group were ages, levels of education, sex and for the comparison group, were sex. years of farming, and hours of sleep. The R-square were 12.5% in the greenhouse group and 12.1% in the comparison son group. The differences between the greenhouse and open field farmers in the degrees of fatigue symptoms were found not to be statistically significant even if the working conditions of the greenhouse farmers were poor. This may be attributed to non-work related factors, i.e., social, economical, and psychological factors among greenhouse farmers.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.1
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• pp.19-26
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• 2010

A PEMFC(proton exchange membrane fuel cell) is a good candidate for residential power generation to be coped with the shortage of fossil fuel and green house gas emission. The attractive benefit of the PEMFC is to produce electric power as well as hot water for home usage. The thermal management of PEMFC for RPG is to utilize the heat of PEMFC so that the PEMFC can be operated at its optimal efficiency. In this study, thermal management system of PEMFC stack is modeled to understand the dynamic response during load change. The thermal management system of PEMFC for RPGFC is composed of two cooling circuits, one for controling the fuel cell temperature and the other for heating up the water for home usage. The different operating strategy is applied for each cooling circuit considering the duty of those two circuits. Even though the capacity of PEMFC system (1kW) is enough to supply hot domestic water for residence, heat-up of reservior takes some hours. Therefore, in this study, time schedule of the simulation reflects the heat-up process. Dynamic responses and operating strategies of the PEMFC system are investigated during load changes.

• Korean Journal of Environmental Agriculture
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• v.15 no.2
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• pp.217-222
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• 1996

A green-house experiment was conducted to know the performance of Chinese cabbage and radish applied with simulated acid rain(SAR) on the leaf and/or soil. The pHs of SAR and normal water were 2.7 and 6.0, respectively. The pHs of SAR and normal water applied on leaf/soil were 6.0/6.0, 6.0/2.7, 2.7/6.0, and 2.7/2.7 and they were applied fifteen times at the two- or three-day intervals with 10mm at a time. Leaf application of SAR caused brown spots in both crops, while no such symptoms were observed in soil application. SAR applied on the leaf or soil increased chlorophyll content significantly in Chinese cabbage, but slightly in radish. Leaf or soil application of SAR did not affect N, P, and K concentrations in both crops. The sulfur content in radish leaf increased by leaf or soil application of SAR, while in the root it increased by soil application only. Yield of Chinese cabbage was not affected by SAR, while both leaf and root yields of radish were significantly reduced by leaf application of SAR compared with soil application.

• Korean Journal of Environmental Agriculture
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• v.15 no.4
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• pp.419-424
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• 1996

A green house experiment was conducted to investigate the performance of Chinese cabbage and radish and changes in soil chemical properties after application of different amounts of simulated acid rain (SAR). About 10mm of normal water (pH 6.0), 5mm of SAR followed by 5mm of normal water, and 10mm of SAR were applied 24 times at the two-day intervals. The results obtained are summarized as follows : 1. Visible symptoms were dark brown, red brown, or grey brown leaf spots, reduced leaf size, or some times wrinked leaves in both crops. The visible symptoms started after the third application of SAR. The degree of damages was greater as the amounts and the number of times of SAR application increased. 2. Chlorophyll contents of SAR applied leaves decreased as the amounts of SAR application increased. 3. As the amounts of SAR increased, length, diameter, and fresh weight of Chinese cabbage heads and radish roots decreased. 4. In both crops sulfur content increased, while calcium content decreased as the amounts of SAR increased. Contents of N, P, K, and Mg were not significnatly affected by the amounts of SAR. 5. SAR decreased soil pH and exchangeable cations (Ca, Mg, K), while increased soil sulfur content.

• Korean Journal of Soil Science and Fertilizer
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• v.43 no.5
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• pp.610-615
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• 2010

This study was conducted to evaluate fertigation effects of pig slurry (PS) and chemical fertilizer (CF) in tomato by analyzing the growth and yield, nutrient content and uptake, nutrient use efficiency, and soil characteristics in greenhouse cultivation. The treatments compared were; no-fertilizer, two different levels of PS (26 mg $L^{-1}$ and 52 mg $L^{-1}$), and a control treatment of chemical fertilizer. There was no significant difference in growth and yield between PS and CF treatments. however, yield reduction was observed in PS 26 mg $L^{-1}$ treatment. The N-utilization efficiency in CF treatment was similar to that of PS 52 mg $L^{-1}$ treatment. Nutrient utilization efficiency decreased in order of potassium (K), nitrogen (N), phosphate (P) with 29.2~43.3% in K, 15.8~36.7% in N, and 3.0~6.3% in P. In soil chemical characteristics, soil pH in PS treatment was higher than in CF treatment. In contrast, nitrate content in soil was higher in CF treatment than in PS treatment. The content of exchangeable K in soil was higher in PS and CF 52 mg $L^{-1}$ treatments. There was no significant difference in exchangeable Ca and Mg among those treatments. Therefore, it can be concluded that chemical fertilizers can be substituted by PS based on soil chemical analysis in tomato fertigation culture.

• Korean Journal of Soil Science and Fertilizer
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• v.41 no.6
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• pp.408-414
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• 2008

Importance of climate change and its impact on agriculture and environment has increased with the rise Green House Gases (GHGs) concentration in the atmosphere. To slow down the speed of climate change many efforts have been applied in industrial sectors to reduce GHGs emission and to enhance carbon storage. In agricultural sector, many researches have been performed on GHGs emission reduction, but few on the role of carbon sink. In this study, we investigated carbon balance and soil carbon storage in agricultural field in the barley-red pepper and barley-soybean cropping system. With the system for automatic measuring of carbon dioxide, net ecosystem production(NEP) was estimated to be $6.3ton\;CO_2\;ha-1$ for N-P-K chemical fertilizer treatment plot and $10.6ton\;CO_2\;ha^{-1}$ for N-P-K chemical fertilizer with swine manure treatment plot in the barley-soybean rotation cropping. In the barley-red pepper rotation cropping, it was $12.0ton\;CO_2\;ha^{-1}$ for N-P-K chemical fertilizer treatment plot and $13.2ton\;CO_2\;ha^{-1}$ for N-P-K chemical fertilizer with swine manure treatment plot. Soil carbon storage rate was estimated to be $0.7ton\;C\;ha^{-1}$ for the barley-soybean cropping system and $0.5ton\;C\;ha^{-1}$ for barley-pepper cropping system. In appeared that agricultural lands may contribute to the greenhouse effect as a potential carbon sink preserving carbon into soil.

• Korean Journal of Soil Science and Fertilizer
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• v.50 no.2
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• pp.81-92
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• 2017

Recently, agricultural lands have decreased sharply, which was caused by huge housing site, urbanization, land consolidation, and road construction etc. In particular, Yangju city near Seoul city has the most severe land use change in Korea. Therefore, we analyzed changes of land use, soil properties, and soil information in order to provide the basic soil information and soil management practices in this city. The area of crop cultivated land in Korea (2015) reduced by 12,090 ha compared to ones from the previous year (2014). The paddy field decreased by 25,421 ha but, upland field increased by 13,331 ha. One of the reasons for the reduction of the paddy field was converting paddy field to upland (20,916 ha) > others (3,056) > building (2,571) > public facilities (847) > idle land (217). But, reasons for increase of upland field were switching paddy to upland (20,916 ha) > land developed (634). The main reason of converting paddy field to upland was changing from rice to more profitable speciality crops or pulses. The cropland area (paddy fields, upland, orchard) of Yangju city reduced by 1,412 ha (2015/2014). The ratio of cropland area in each city reduced by 22.9% dramatically compared 2015 to 1999. The paddy fields located in alluvial plains in Yangju city were changed into upland or green house. The drainage classes of soil have been deteriorated because the flows of water were intercepted by road construction and other disturbance to water flows. In particular, paddy fields have been changed to not only upland, orchard, greenhouse cultivation but also to fallow and soil dressing on paddy in Yangju city. To analyze result of soil survey of Yangju city, 858 soil codes (soil phases) were used and the area was 105.17ha. The number of soil series increased from 60 to 65, and that of soil phase increased from 105 to 124. The largest increased area was Noegog soil series. 125.7ha of Neogog soil series was incorporated from the existing Sachon, Yecheon and Eungog soil series. The soil suitability class of paddy field in Ogjung huge housing site of Yangju city was the 4th grade for 32.6% of the area. The soil suitability classes of upland were 2nd and 3rd grade for 72.4% of the area. Farm land with high quality should be conserved by related law.

• Journal of the Korean Wood Science and Technology
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• v.42 no.1
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• pp.1-12
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• 2014

This study carried out life cycle assessment for evaluating environmental impacts of timber Arch-Truss bridge by using domestic Pinus rigida Miller glued-laminated timber throughout life cycle such as extraction, manufacturing, transportation, construction, use, dismantlement, transportation of waste, disposal and recycling. The life cycle GHG (GreenHouse Gas) emissions of the target bridge are 192.56 ton $CO_2$ eq. in 50 years. Especially, the life cycle GHG emissions of concrete used in the target bridge are 82.84 ton $CO_2$ eq. which accounts for 53.02% of the GWP (Global Warming Potential) in extraction and manufacturing stages. The target bridge is constructed of $116.57m^3$ of domestic Pinus rigida Miller glued-laminated timber and used timber has stored 104.72 ton $CO_2$. If an effect of carbon storage in timber is applied to the total GHG emissions of the target bridge, the GHG emissions can be reduced by 54.38%. In the case of substitution effect, if domestic Pinus rigida Miller glued-laminated timber replaces steel manufactures used in other bridge which has the same structure and life span as the target bridge, the GHG emissions in extraction and manufacturing stages can be reduced by 10.26% to 23.91%.