조재영 Cho Jae Young , 구자웅 Koo Ja Woong , 손재권 Son Jae Gwon

DOI: JKWST Vol.48(No.3) 3-8, 2006

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The fractions of nitrogen were investigated in the soils of reclaimed and natural tidelands of southwest coastal area of Korea. The content of total-N varied to ranged form 619 to 5,534 mg/kg dry weight with a mean value of 1,857 mg/kg. The order of different fractions of nitrogen was as follows: Acid non-extractable-N > uncounted-N > acid extractable-N > ammonia-N > nitrate-N. The content of ammonia-N, acid extractable-N, and acid non-extractable-N showed highly negative correlations with pH. The content of acid extractable-N and ammonia-N showed highly positive correlation with clay content.

이용직 Lee Yong-jig , 김선주 Kim Sun Joo , 김필식 Kim Phil-shik , 주욱종 Joo Uk Jong , 양용석 Yang Yong Seok

DOI: JKWST Vol.48(No.3) 11-20, 2006

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In this study, the actual water management were investigated and analyzed on site for effective use of the paddy irrigation water. And this study is tried to analyze the difference between simulated irrigation water according to current design method and actual water supply in experimental reservoirs. The reservoirs in Idong, Yongdeok and Misan, which are managed by Korea Rural Community & Agriculture Corporation, were selected fur field investigation. The purpose of this study is to suggest an improved method for irrigation water calculation through quantitative and periodical analysis considering the difference between design and actual field condition.

황세운 Hwang Sye Woon , 장태일 Jang Taeil , 박승우 Park Seung Woo , 강문성 Kang Moon Seong

DOI: JKWST Vol.48(No.3) 23-34, 2006

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This study reviews the applicability of the GWLF (Generalized Watershed Loading Function) model, which is based on a loading function that requires only a relatively small amount of data, in a small agricultural watershed. The hydrological data was collected from 1996 to 2004 for a study area based on the HP#6 upper stream reservoir small watershed area. This data was then used to calibrate and verify the model. A simulation based on the model yielded R²values of 0.47~0.89. This is considered to have high applicability when compared to the simulation and the observed results, which yielded relatively high values of R² for SS (Suspended Solid), TN (Total Nitrogen), and TP (Total Phosphorus) of 0.58, 0.47 and 0.62, respectively. This study provides a useful approach fur researchers selecting appropriate models to use the insufficient measuring data for rural watersheds.

김선주 Sun Joo Kim , 김형중 Hyung Jung Kim , 김필식 Phil Shik Kim , 지용근 Yong Geun Jee , 양용석 Yong Seok Yang

DOI: JKWST Vol.48(No.3) 35-45, 2006

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Fallow paddy areas have been increased due to the import of cheap agricultural product, and the unbalance between farming cost and rice price since 1990. In domestic, rice production control that decrease paddy field area has been introduced for the control of rice demand and supply and stabilization of rice price since 2003. Because of the desire of paddy field's owner to create benefit by using paddy for other object, fallow paddy would be continuously increased. In the other aspect, many people in the world is suffering from hunger because of the shortage of food. In case of Korea, continuous drought and flood damages will be potential concern of stable food supply. From this viewpoint, the increasing fallow paddy area needs to be protected from the devastation by weed breeding for the re-cultivation. In this study, fallow paddy managed with the shallow pools and shallows was selected fur monitoring and analyzing of water quality and plant body change. As the results, the managed fallow paddy found to be effective in the purification of water quality and the control of plant growth.

양용석 Yang Yong Seok , 김선주 Kim Sun Joo , 김필식 Kim Phil-shik , 지용근 Jee Yong Geum

DOI: JKWST Vol.48(No.3) 49-59, 2006

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The purpose of this study is to provide basic materials for working out differentiated marketing strategies appropriate to the visitors and potential visitors of rural tourism for the sustainable development of rural tourism. The study was conducted through a questionnaire survey fur 500 adults aged 18-year-old or older residing in downtown Seoul, and the characteristics of the visitors and potential visitors of the rural tour were analyzed through frequency analysis and logistic analysis. The analysis results are summarized as follow. In many cases, they obtained information on the rural tourism chiefly through mass media and decided their participation after listening to the stories of nearby people or visitors. The survey showed that the estimated necessary expenses of the potential visitors were more than actual ones of the visitors. It was analyzed that the reception attitude of residents was a factor to have the most significant effect on the participation of rural tourism, while necessary budget for potential visitors.

홍성구 Hong Seong Gu

DOI: JKWST Vol.48(No.3) 63-71, 2006

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A downdraft gasifier was made of stainless steel for biomass gasification. Internal reactor had a 300 mm diameter and 8 air intakes. Three thermocouples were installed to measure the temperature inside the reactor. Three different biomass fuels were provided in the experiments to find out the effects of fuel conditions on gasification processes; charcoals, woodchips, and mixture of woodchip and charcoals. Two different experiments were conducted for charcoal experiments, small and larger sizes of charcoal fuels. It took about 10 minutes after ignition to generate combustible producer gas when charcoal was fed, but 20 or more minutes for woodchips. When the gasification was stabilized, the highest temperature was observed just below the combustion zone. The air flow rate for woodchip experiment was provided at 25% of a stoichiometric requirement of combustion, which was within the range of typical air flow rate for woody biomass gasification. Carbon monoxide concentrations were also within the values reported in the previous studies, ranging 20 to 30% depending on fuel types. It could be seen that fuel size and heating value were very important parameters in biomass gasification. These parameters should be taken into account in operating and designing biomass gasifiers.

홍성구 Hong Seong Gu

DOI: JKWST Vol.48(No.3) 73-82, 2006

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Wind energy is one of the promising renewable energies that could provide electricity and other mechanical power. Wind energy market is dramatically growing in many European countries, but wind power is only 0.2% of the total renewable energy uses that is only about 2% of the primary energy consumption in Korea. It is widely accepted that wind resources fur power generation are only limited in some areas including coastal regions and mountainous areas in Gangwon province in Korea, particularly in terms of large scale wind power developments. In this study, wind velocity data were analyzed with respect to the potential utilization. The data provided from National Weather Service were used for the analysis. In addition, field wind data were also collected and analyzed for the comparison between the national data. The comparison showed that there were significant differences between the experimental station and the national station that are about 5km away. Annual average wind speed at the experimental station was less than 2 m/s, which is not enough fur wind power generation. It seemed that the topographic condition resulted in a significant difference in wind speed. When 600 W and 2.5 kW wind turbines were used, annual power productions were only 186 kWh and 598 kWh, respectively. When the average wind speed is lower, wind pumping is an alternative use of wind. At the experimental station, the average pumping rate of 3㎥/h at the head of 3 m was expected at a 2.5 m rotor under the conditions that efficiencies of the rotor and the pump were 40% and 80%, respectively. It did not seem that the wind pumping was not applicable at the station either. A higher wind speed was required to install the wind machines. Meanwhile, wind pumping would be applicable in conditions with lower pumping heads. Other applications were introduced far further wind energy utilization, including wind powered ventilation and friction heat generation in greenhouses.

곽계환 Kae-hwan Kwak , 황해성 Hae-sung Hwang , 성배경 Bai-kyung Sung , 장화섭 Hwa-sup Jang

DOI: JKWST Vol.48(No.3) 85-94, 2006

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Practially useful method of steel fiber for construction work is presented in this study. The most important purpose of this study is to develop a model which can predict mechanical behavior of the structure according to aspect ratio and volume fraction of steel fiber. Experiments on compressive strength, elastic modulus, and splitting strength were performed with self-made cylindrical specimens of variable aspect ratios and volume fractions. The experiment showed that compressive strength was not in direct proportion to volume fraction which doesn't seem to have great influence over compressive strength. However, splitting strength showed almost direct proportion to aspect ratio and volume fraction. Improvement of optimal efficiency was confirmed when the aspect ratio was 70. Experiments on flexural strength, fracture energy, and characteristic length were carried out with self-manufactured beams with notch. As a result, increases of flexural strength, fracture energy, and characteristic length according to increase of volume fraction tend to be prominent when aspect ratio is 70. The steel fiber improves concrete to be more ductile and tough. Moreover, regression analysis was the performed and predictable model was developed after determining variables. With comparison and analysis of suggested estimated values and measured data, reliance of the model was verified.

조재원 Cho Jae Won , 김진수 Kim Jin Soo , 오광영 Oh Kwang Young , 오승영 Oh Seung Young

DOI: JKWST Vol.48(No.3) 97-106, 2006

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The pollutant concentrations at experimental paddy plots with three (excessive, standard, reduced) different fertilization rates were investigated during 2001-2002 irrigation seasons. Mean concentrations of pollutants in ponded water were not significantly different among three experimental plots, but the T-N concentrations in percolated water significantly depended on fertilization rates. The T-N, T-P and COD_Cr, concentrations in ponded water during early irrigation season (late May to mid-June) were much higher than those during later irrigation season likely due to fertilization and low uptake by young rice crops. The T-N concentrations decreased but the concentrations of T-P and COD_Cr, increased three days after tillering fertilization. The removal rates of T-N by paddy plots were 0.13-0.16g/㎡ㆍd for an excessive fertilization plot, 0.08-0.25 g/㎡ㆍd for a standard fertilization plot, and 0.03-0.34 g/㎡ㆍd for a reduced fertilization plot three days after tillering fertilization. On the other hand, T-P and COD_Cr, were released three days after tillering fertilization.