• Journal of Korean Society for Atmospheric Environment
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• v.33 no.1
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• pp.64-74
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• 2017

In this study, we have analyzed relationship between the measured Water Soluble Organic Carbon (WSOC) concentrations and the estimated aerosol water content of $PM_{10}$ (particulate matter with an aerodynamic diameter of less than or equal to $10{\mu}m$) for the period between September 2006 and August 2007 at Seoul, Korea. Water content of $PM_{10}$ was estimated by using a gas/particle equilibrium model, Simulating composition of Atmospheric Particles at Equilibrium 2 (SCAPE2). The WSOC concentrations showed low correlation with Elemental Carbon (EC), but Water Insoluble Organic Carbon (WISOC) were highly correlated with EC. It seemed that hydrophilic groups were produced by secondary formation rather than primary formation. As with the previous studies, WSOC showed good correlation with secondary ions ($NO_3{^-}$, $SO_4{^{2-}}$, $NH_4{^+}$), especially WSOC was highly correlated with $NO_3{^-}$ that is a secondary ion formed by photochemical oxidation from more local sources than $SO_4{^{2-}}$. No apparent correlation between the measured WSOC and estimated water content was observed. However, WSOC showed good correlation with estimated water content when it was assumed that relative humidity was higher than the deliquescence relative humidity of the system. In conclusion, WSOC is correlated with water content by hygroscopic ions and it is expected that nitrate play an important role among the water content and WSOC.

• Journal of The Korean Association For Science Education
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• v.25 no.2
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• pp.146-161
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• 2005

This case study searched two secondary school science teachers' faiths on experiments in science classes. For this study, scaled questionnaires, open-ended questionnaires, structured and semi-structured interviews were conducted. Classroom activities were observed, and instructional plans and materials were collected. In addition, students of the two teachers' classes were interviewed with respect to their thoughts on the lessons. Data sources were analyzed inductively. The triangulation and the member checking guaranteed the validity of this study. As the results, the teachers' faiths on experiments were related to the constructivism, but the faiths were not in accord with their classroom practices. From these results, it was concluded that the teachers' misjudgments about the students' inquiry levels and unfit reorganizations of the experimental activities were the causes of the gap between the teachers' faiths on experiments and classroom practices.

• Journal of Korean Society of Water and Wastewater
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• v.17 no.4
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• pp.542-549
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• 2003

In the present study, the feasibility of $UV/H_2O_2$ systems was investigated using low and medium-pressure lamps on biologically treated wastewater effluents for secondary effluent reclamation. Two types of UV lamps were used as the light sources (a 39-W low-pressure mercury lamp and a 350-W medium-pressure mercury lamp). The results from these UV systems showed that the removal of organic compounds could be achieved in the contact time of longer than 30min (i.e., low UV doses). Efficiencies of color removal and disinfection were far better than those of organic matters measured as TOC, DOC and $TCOD_{cr}$. In the low-pressure lamp UV system, it has been found that DOC and color removals were 60.9 and 86.2% with 50mg/L of $H_2O_2$ and contact times of 30 minute, respectively. Whereas, with the medium-pressure lamp UV system, TOC, DOC and color removal were 27.1, 5.6 and 95% with 14.3mg/L of $H_2O_2$ and 14 minute of contact times, respectively. Both systems could be applied for the reclamation of secondary effluent treated with biological treatment processes.

• Journal of the Korean Solar Energy Society
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• v.40 no.5
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• pp.23-34
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• 2020

Concentrator photovoltaic (CPV) system consists of high-quality complex optical elements, mechanical devices, and electronics components and can have the advantages of high integration and high-efficiency energy sources. III-V compound semiconductor cells have proven performance based on high reliability in the aerospace field, but have characteristics that require absolute support of the balance of systems (BOS) such as solar position trackers, receivers with heat sinks, and housing instruments. To determine the optimum parameters of secondary optical elements (SOEs) design for CPV systems, we designed three types of CPV modules, classified as non-SOEs type, reflective mirror type, and CPC lens type. We measured the I-V and P-V characteristics of the prototype CPV modules with the angle of inclination varying from 0° to 12° and with a 500-magnification Fresnel lens. The experimental results assumed misalignment of the solar position tracker or module design of pinpoint accuracy. As a result, at the 0° tilt angle, the CPC lens produced lower power due to the quartz transmittance ratio compared to that by other SOEs. However, for tilt angles greater than 3°, the CPC lens type module achieved high efficiency and stability. This study is expected to help design high-performance CPV systems.

• Korean Journal of Weed Science
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• v.15 no.2
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• pp.154-159
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• 1995

Water extracts from Polygonum aviculare and Salix koreansis markedly inhibited the germination of lettuce and rice seeds, indicating the presence of biologically active substances. The biochemical substances such as salicylic and+vanillic acid, tannic acid + gallic acid, p-coumaric acid, p-cressol, sinapic acid and catechol etc. belonging to phenolic compounds were detected in the cultured cells, suggesting that the secondary metabolites can be synthesized in plant cell and tissue culture. In addition, fatty acid like linolenic acid and organic acid such as oxalic acid were presented in the highest amount, 3.7 mg/g and 14.288 mg/g, respectively, which seem to be related to exhibiting phytotoxicity of P. aviculare. Petroleum ether extract exhibited another potential relating to inhibitory effect which needs further investigation. Calli from two plant sources were easily introduced by uses of 1.0 mg/l of 2.4-D and 0.1 to 0.2 mg/l of BAP in MS basal medium which can be implemented for a large scale production through cell culture.

• Journal of Power Electronics
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• v.19 no.2
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• pp.403-412
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• 2019

Aiming at the problems of large dv/dt and di/dt in traditional single-ended converters and high electromagnetic interference (EMI) noise levels, a single-ended isolated converter using the secondary resonance technique is proposed in this paper. In the proposed converter, the voltage stress of the main power switch can be reduced and the voltage across the output diode is clamped to the output voltage when compared to the conventional flyback converter. In addition, the peak current stress through the main power switch can be decreased and zero current switching (ZCS) of the output diode can be achieved through the resonance technique. Moreover, the EMI noise coupling path and an equivalent model of the proposed converter topology are presented through the operational principle of the proposed converter. Analysis results indicate that the common mode (CM) EMI noise and the differential mode (DM) EMI noise of such a converter are deduced since the frequency spectra of the equivalent controlled voltage sources and controlled current source are decreased when compared with the traditional flyback converter. Furthermore, appropriate parameter selection of the resonant circuit network can increase the equivalent impedance in the EMI coupling path in the low frequency range, which further reduces the common mode interference. Finally, a simulation model and a 60W experimental prototype of the proposed converter are built and tested. Experimental results verify the theoretical analysis.

• Journal of Surface Science and Engineering
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• v.55 no.1
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• pp.32-37
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• 2022

In a carbon-zero social atmospher, research is underway to reduce the use of fossil fuels. Interest in cleaner energy sources and their storage system is growing, and among them, research on effective energy storage is being actively conducted. Energy storage system(ESS) can be divided into secondary batteries, fuel cells, and capacitors, and the superiority of energy density of secondary batteries has a dominent influence on the ESS market. However, as problems with secondary batteries, charge/discharge speed, safety, and deterioration of electrodes are being highlighted. In this study, an electrode for supercapacitor with superior charge/discharge speed and specific capacitance is manufactured. The manufactured spinel nickel cobalt electrodes had specific capacitances of 1018.8 F/g, 690.8 F/g, and 475.1 F/g at 1 A/g in 1 M KOH electrolyte, and shows a performance retention rate of 77.48%, 63.30%, and 58.16% after 2000cycles at 7 A/g.

• Korean Journal of Environmental Agriculture
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• v.15 no.4
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• pp.506-519
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• 1996

The water quality in the rural areas is degrading due to a variety of causes such as the increase of the urban sewage and industrial wastes, the disposal of solid wastes, the growth of livestock waste, the growth of leisure facilities, the establishment of agricultural industry estates and etc. The water pollutants are scarce while the effluent is increasing from wide scattered sources. The technology specifically designed for the rural wastes water treatment plant needs to be implemented with improvement of agricultural water quality. 1. An integrated management measures against water pollution sources. The prevention of water pollution is the best measures in the environmental pollution. Hence, the most effective measures needs to be against the sources. Small-scale water treatment plants needs to be constructed in each village in the rural areas. As for the industrial effluent, the effluent discharge needs to be strictly monitored. Government subsidy for the establishment of treatment plant for livestock wastes is necessary. 2. The establishment of national-wide network for agricultural water quality. The network for agricultural water quality have been operated to conserve the agricultural water quality, and to develop management policies by the assessment of water pollution in the rural areas. The results of agricultural water quality network indicates that the water quality is degrading not only around urban areas but also in the distant rural areas, and the water quality at the pumping stations and weirs is worse than that of reservoirs. 3. The legal, systematic, and technical approaches for the agricultural water quality management. The actions currently implemented for the improvement of agricultural water quality involve temporary measures such as the improvement of irrigation facilities. These contingency measures are not effective in the long-term, and sometimes bring secondary pollution. Therefore, integrated measures covering the whole water environment such as the flow, quality, river morphology, aquatic ecosystem, and the surrounding environment, need be invented and implemented. Besides, the legal, systematic, and technical frameworks for the management are not fully established so far. The technology for the treatment of rural water pollution should be refined afterwards, and the research for the development of rural waste water treatment plant should be carried out.

• Asian Journal of Atmospheric Environment
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• v.11 no.3
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• pp.165-175
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• 2017

In Japan, the primary carbonaceous particles emitted from motor vehicles and waste incinerators have been reduced due to strict regulations against exhaust gas. However, the relative contribution of carbonaceous particles derived from plants and biomass has been increasing. Accordingly, compositional analysis of carbonaceous particles has become increasingly important to determine the sources and types of particles produced. To reveal the sources of the organic particles contained in particulate matter with diameters of ${\leq}2.5{\mu}m$ ($PM_{2.5}$) and the processes involved in their generation, we analyzed molecular marker compounds (2-methyltetrols, cis-pinonic acid, and levoglucosan) derived from the plants and biomass in the $PM_{2.5}$ collected during daytime- and nighttime-sampling periods in summer (July and August) and autumn (November) in Kazo, which is in the northern area of Saitama prefecture, Japan. We also measured $^{14}C$ carbonaceous concentrations in the same $PM_{2.5}$ samples. The concentrations of 2-methyltetrols were higher in the summer than in the autumn. Because the deciduous period overlaps with this decrease in the levels of 2-methyltetrols, we considered the emission source to broad-leaved trees. In contrast, the emission source of the cis-pinonic acid precursor was considered to be conifers, because its concentration remained almost constant throughout the year. The concentration of levoglucosan was considerably increased in the autumn due to frequent biomass open burning. The ratio of plant-derived carbon to total carbon, obtained by measuring of $^{14}C$, in summer $PM_{2.5}$ sample was higher in the nighttime, and could be influenced by anthropogenic sources during the daytime.

• Asian Journal of Atmospheric Environment
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• v.12 no.1
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• pp.59-66
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• 2018

This study aims to evaluate the performance of the Air Quality Model (AQM) for the seasonal and spatial distribution of the $NH_3$ concentration in the atmosphere. To obtain observational data for the model validation, observations based on biweekly sampling have been conducted using passive samplers since April 2015 at multiple monitoring sites in the Tokyo metropolitan area. AQM, built based on WRF/CMAQ, was applied to predict the $NH_3$ concentration observed from April 2015 to March 2016. The simulation domain includes the Kanto region, which is the most densely populated area in Japan. Because the area also contains large amount of livestock, especially in its northern part, the density of the $NH_3$ emissions derived from human activities and agriculture there are estimated to be the highest in Japan. In the model validation, the model overestimated the observed $NH_3$ concentration in the summer season and underestimated it in the winter season. In particular, the overestimation in the summer was remarkable at a rural site (Komae) in Tokyo. It was found that the overestimation at Komae was caused by the transportation of $NH_3$ emitted in the northern part of the Kanto region during the night. It is suggested that the emission input used in this study overestimated the $NH_3$ emission from human sources around the Tokyo suburbs and agricultural sources in the northern part of the Kanto region in the summer season. In addition, the current emission inventories might overestimate the difference of the agricultural $NH_3$ emissions among seasons. Because the overestimation of $NH_3$ in the summer causes an overestimation of $NO_3{^-}$ in $PM_{2.5}$ in the AQM simulation, further investigation is necessary for the seasonal variation in the $NH_3$ emissions.