• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.6
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• pp.35-40
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• 2020

The ballast layers play a key role in distributing and supporting a trainload. On the other hand, it settles down by dynamic train loading due to large void ratios. Consequently, it requires continuous maintenance. In this paper, ballast layers mixed with three types of specially shaped artificial ballast (AB) (Rectangular, Tetrapod, Hexagonal) were modeled by using a two dimensional DEM (Discrete Element Method). Repeated loading tests were performed to evaluate the settlement behavior of the ballast layers. The smallest settlement was observed in the case of the ballast layer mixed with Tetrapod AB than in other cases, according to an analysis of the force transfer routes. In addition, contact force analysis showed that the Tetrapod AB, which has a concave shape, could easily make small and multi-channel force-transfer routes. This means that the stress in the ballast layer by the train loading transferred through the sleeper uniformly was distributed well by the AB. Therefore, the settlement of the ballast layer mixed with the concave-shaped Tetrapod AB could be reduced effectively under a repeated train loading. The effects of a decrease in settlement of the ballast layer highlight the possibility of a maintenance-free ballasted track.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.12
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• pp.8306-8313
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• 2015

Open-type current sensors have been commonly used for DC motor controller, AC variable controller and Uninterruptible Power Supply. Recently they have begun to be used more widely, as the growth of renewable energy and smart-grid in power system. Considering most of the open-type current sensors are imported, developing the core technology needed to produce open-type current sensors is required. This paper describes the development and test results of open-type current sensors. Design of C type magnetic core, selection and test of a Hall sensor, design of current source circuit and signal conditioning circuit are described. 100A class DIP(Dual In-line Package) type and SMD(Surface Mount Devide) type open-type current sensors was made and tested. Test results show that the developed open-type current sensor satisfies the accuracy requirement of 2% and linearity requirement of 2% at 100 A of DC and AC current of 60Hz. Temperature compensation was carried out by using a temperature compensation circuit with NTC(Negative Temperature Coefficient) thermistor and the effect of the temperature compensation are described.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.38 no.4
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• pp.304-311
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• 1993

To find out suitable crops and their rotation years with rice for paddy-upland rotation, continuous rice cropping and rice with 1, 2 and 3 years cropping of upland crops(soybean, maize and job's tears) were tested for four years from 1989 to 1992. Rice yield, when averaged over rotation years for each crop, was increased ranging from 7% to 12% when compared with that of continuous rice cropping. With every crop, rice yield of 2 year upland rotation was higher than that of 1 year upland rotation, but rice quality seemed to deteriorate in paddy-upland rotation. When considering yields of the upland crops, 1 year rotation was the best condition for soybean and job's tears, with 3 years rotation being the best for maize. In paddy-upland rotation, number of weed species and its occurrence rates were reduced in paddy and upland condition and the reduction rates in paddy condition were higher than those in upland condition. Physical properties of soil were improved in paddy-upland rotation and airphase seemed to increase with increasing upland period.

• International Journal of Highway Engineering
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• v.10 no.2
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• pp.1-13
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• 2008

This study presents a case study of condition evaluation of various asphalt pavement sections to estimate performance lives. The pavement surface conditions including cracking and rutting are first evaluated using a automatic pavement analyzer, ARAN. HPCI(Highway Pavement Condition Index) values are estimated using the pavement surface distress data. It is observed from the pavement distress survey that the major distress type of the sections is top-down cracking. The modulus value of each pavement layer is back-calculated from the defection data obtained from a FWD(Falling Weight Deflectometer) and compared with the laboratory measured dynamic modulus values. Remaining lives of the various pavement sections are estimated based on a mechanistic-empirical approach and AAHTO 1993 design guide. The structural capacities of the all pavement sections based on the two approaches are strong enough to maintain the pavement sections for the rest of design life. Since the major distress type is top-down cracking, the remaining lives of the pavement sections are estimated based on HPCI and existing performance database of highway pavements. To evaluate the causes of premature pavement distress, various material properties, such as air void, asphalt binder content, aggregate gradation, dynamic modulus and fatigue resistance, are measured from the field cores. It is impossible to accurately estimate the binder contents of field samples using the ignition method. It is concluded from the laboratory tests that the premature top down cracking is mainly due to insufficient compaction and inadequate aggregate gradation.

• Journal of the Korea Concrete Institute
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• v.16 no.3 s.81
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• pp.407-414
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• 2004

The purpose of this study is to evaluate the ability to resist chloride ions penetration of the concrete structure under marine environment in south-east asia especially. In this study, high strength concrete(HSC) with various combination of ordinary portland cement(OPC), blast-furnace slag(SG) and silica fume(SF) are cured 23 and $35^{\circ}C$ considering the site weather, and are cured in water for 3, 7 or 56 days respectively. And to investigate the fundamental properties and the resistance of chloride penetration of various HSC, setting time, slump flow, compressive strength, void and ASTM C 1202 test were conducted. Test results show that the compressive strength of HSC is similar regardless of SG replacement ratio and total charge passed of chloride is the smallest at 40% replacement of SG. The compressive strength of G4FS HSC is, besides, outstandingly high at early age compare with other HSC, but the compressive strength of G4F HSC, which is vary according to curing temperature and condition, most high at the age after 7 days. Total passed charge of HSC get larger in the order G4FS

• Journal of the Korea Concrete Institute
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• v.27 no.4
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• pp.443-450
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• 2015

This paper presents an investigation of the mechanical and microstructural properties of Class F fly ash based geopolymer containing sodium sulfate as an additive. Sodium sulfate was used as an chemical additive at the dosage levels of 0, 2, 4, and 6wt% of fly ash. Sodium hydroxide and sodium silicate solutions were used to activate fly ash. The compressive strengths of geopolymer pastes were measured at the age of 28 days. The microstructures of the geopolymer pastes were examined using XRD, MIP and SEM tests. The additions of 2wt% and 4wt% sodium sulfate produced geopolymers with high strength, while increasing the dosage of levels to 6% resulted in almost no changes in strength, comparing with the control geopolymer. The optimum increase in strength was obtained with the addition of 4wt% sodium sulfate. As the amount of sodium sulfate is increased, no additional crystalline phase was detected and no change of amorphous phase indicated despite the change in the strength development. The increase in the strength was due to the change of pore size distribution in samples. As addition of sodium sulfate altered the morphologies of reactive productions and Si/Al ratios of the reaction products, the strengths were thus affected. It was found that the strengths of geopolymer were larger for lower Si/Al ratios of reaction products formed in samples. The optimal amount of sodium sulfate in the fly ash based geopolymer helps to improve mechanical properties of the geopolymer, on the other hand, the high percentage of sodium sulfate could exist as an impurity in the geopolymer and hinder the geopolymer reaction.

• Korean Journal of Soil Science and Fertilizer
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• v.32 no.3
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• pp.254-260
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• 1999

This experiment was carried out to evaluate the effect of improvement of soil physical property such as deep plowing and chiseling and diagnostic application of N, P, K fetilizers. Latex Coated Urea(LCU), compost, sillicate for increasing yielding and enchancing N-use efficiency in puddled-soil drill seeding of Rice. The soil physical properties, such as bulk density, hardness and porosity were increased by deep plowing and chiseling, as well as chemical propeties were highly enhanced soil productivity due to increase the content of organic matter, available $P_2O_5$ and K as compare with control. The amount of $NH_4-N$ in soil was highly increased by diagnostic fertilization and chiseling, while recovery rate of V fertilizer was the highest at LCU 80% applied with chiseling. The rice yield increased by 23% under the diagnositic application of LCU 80% applied base with chiseling.

• Korean Journal of Soil Science and Fertilizer
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• v.16 no.2
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• pp.92-97
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• 1983

This experiment was designed to establish the soil physical improvement practice to increase the rice yields at fine textured fluvio-marine paddy field. After chiseling and trenching the paddy soil, the rice growth and soil physical properties were investigated for 4 years. The results are summarize as follows; 1. The soil physical properties, such as bulk density, hardness, porosity and permeability were prominently improved by trenching and chiseling. 2. There were significant relationships among the soil physical properties, root developments and rice yields. 3. The increasing rates of rice yields by soil physical improvement were about 10%, which is better than 5% of drainage effects. 4. The effects of trenching and chiseling on rice yields were continued to fourth year. Even if trenching effects was better than chiseling the chiseling was considered as a useful treatment for its simple working practice by using a heavy machine. 5. In case of trenching, straw application were increased the rice yields.

• Korean Journal of Medicinal Crop Science
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• v.15 no.3
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• pp.177-182
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• 2007

This study was conducted to produce high quality ginseng seedlings by improvement of the physical properties of nursery soil. In order to select optimum nursery conditions, nursery types were treated with the yangiik nursery and semi-yangiik nursery. Soil conditioners were treated with two different materials of puffed rice husks and perlite. This experiments were tested at Gyunggido Agricultural Research and Extention Services, Hwaseng, from 2003 to 2004. Soil permeability was better at the plot of yangiik nursery than that of semi-yangjik nursery, and was better at plot of puffed rice husks than that of perlite. Soil porosity was improved 2.2% at plot of yangjiik nursery compare at that of semi-yangjik nursery, and was improved 2.0% at plot of puffed rice husks compared to control. There was no difference in the number of ginseng plants per kan among treatments. Root length was longer at plot of yangjik nursery than that of semi-yangjik nursery. More available ginseng plants per kan were obtained from the plot of yangjik nursery by more 252 seedlings than that of semi-yangjik nursery, but there was no significant difference between soil conditioners. The number of available seedlings per kan produced from yangjik nursery was 21.7% higher than those produced by semi-yangjik nursery. The number of available seedlings per kan produced from plot of puffed rice husks was 16.3% higher than that of control.

• The Korean Journal of Mycology
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• v.36 no.1
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• pp.26-30
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• 2008

This study was carried out to develop artificial culture method of Grifola frondosa in polypropylene bag. To find out the favorable substrate formulation of G. frondosa, physicochemical conditions were investigated. The T2 formulation (55 : 25 : 12 : 8) mixing ratio of oak sawdust, oak chip, dried bean-curd refuse and wheat bran showed the shortest time to complete the crop cycle and the highest yield (weight of fresh mushrooms harvested at maturity). Those physicochemical conditions were pH 4.3, 2.4% crude fat contents, 54.1% total carbon, 1.42% total nitrogen, 38.1 C/N ratio, 75.5% porosity and $0.21\;g/cm^3$ bulk density. Among the physicochemical factors, pH, crude fat and total nitrogen may affect mushroom yield. Therefore, development of favorable substrate would be benefit to increase production efficiency of G. frondosa, mushrooms and be commercial potential.