• Korean Journal of Food Science and Technology
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• v.51 no.4
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• pp.404-409
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• 2019

This study was performed to determine the optimum conditions for the production of gaseous chlorine dioxide ($ClO_2$) from aqueous $ClO_2$ (HCl+$NaClO_2$). When 1 N HCl was reacted with various concentrations of $NaClO_2$ (50,000-500,000 mg/mL), the highest concentration (695 mg/L) of gaseous $ClO_2$ was obtained from the aqueous $ClO_2$ containing $100,000{\mu}g/mL$ $NaClO_2$. Next, the effects of relative humidity (RH; 43, 85, and 100%) and temperature (4, 12, and $25^{\circ}C$) on the production of gaseous $ClO_2$ were investigated. It was observed that the concentration of gaseous $ClO_2$ was increased as RH was decreased, or the temperature was increased. Finally, it was confirmed that the amount of gaseous $ClO_2$ was highly correlated ($R^2=0.9546-0.9992$) with the volume of aqueous $ClO_2$. The results of this study provide useful information for designing a sanitization program using gaseous $ClO_2$ under various environmental conditions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.4
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• pp.137-145
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• 1984

Tests for the physical and chemical properties on the dispersive soils from the 3 selected sites in the northeast region of Thailand were carried out in the field and laboratory. In oder to find out the relationship between c1ay contents and dispersivity of the soil, some specimens are artificially mixed with a certain amount of clay in the laboratory and tested by means of pinhole tests. The artificial soils are dispersed in pinhole tests regardless of their clay contents. Chemical properties on the soil saturation extract and reservoir water are also determined by means of sodium adsorption ratio (SA,R), exchangeable sodium percentage (ESP) and pH. The dispersive soils in the region have ranges of 1.8~6.7 SAR, 1.4~7.9 ESP and 5.4~9.0 pH value. Namely, the dispersive soils studied have somewhat higher SAR, ESP and pH value than those of ordinary soil.

• Journal of the Korean School Mathematics Society
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• v.23 no.1
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• pp.89-109
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• 2020

This study aims to improve teacher education by analyzing the causes and backgrounds of which pre-service mathematics teachers experience learning difficulties on the topic of discrete mathematics. To this end, we conducted a questionnaire and an evaluation on the topic of discrete mathematics, and the obtained data were analyzed. The results show that (1) pre-service mathematics teachers need to share their perceptions of the need for discrete mathematics education; (2) a review of the adequacy of the discrete mathematical content and its credits are required; (3) the causes of their learning difficulties need to be looked at from a different perspective than the learning factors. And two implications were obtained. First, it is necessary to study the systematicity and sequence of content elements of discrete mathematics in the aspect of its continuity of curriculum of secondary school and university. Second, it is required consideration for adjusting the ratio of discrete mathematics to secondary teachers' employment examination.

• The Korean Journal of Mycology
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• v.19 no.4
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• pp.285-291
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• 1991

Sulfur dioxide discharged from the factories in Yeochun industrial complex severely damaged to the growth of oyster mushrooms. The continuous monitoring indicated that high concentration of sulfur dioxide was repeatedly detected in Kwang-Yang and Seung-Ju. The first injury symptoms on the mushroom fruit bodies were observed a day later when sulfur dioxide was detected over 300 ppb. Under the high concentration of sulfur dioxide exposure, the young fruit bodies showed blight and sudden death and the mature fruit bodies turned to blue-brown and frequently progressed to blight. The symptoms at Spring cropping were more severe than those at Autumn cropping. The severity was associated with the frequency of sulfur dioxide monitored. However, sulfur content in the mushroom fruit bodies and culture media did not show clear differences between the injured mushroom from Yeochun industrial complex areas and normal ones from no damaged areas.

• Computational Structural Engineering
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• v.10 no.2
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• pp.255-263
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• 1997

The optimum design of most structural systems used in practice requires considering design variables as discrete quantities. The present paper shows that the linear approximation method is very effective as a tool for the discrete optimum designs of unsymmetric composite laminates. The formulated design problem is subjected to a multiple in-plane loading condition due to shear and axial forces, bending and twisting moments, which is controlled by maximum strain criterion for each of the plys of a composite laminate. As an initial approach, the process of continuous variable optimization by FDM is required only once in operating discrete optimization. The nonlinear discrete optimization problem that has the discrete and continuous variables is transformed into the mixed integer programming problem by SLDP. In numerical examples, the discrete optimum solutions for the unsymmetric composite laminates consisted of six plys according to rotated stacking sequence were found, and then compared the results with the nonlinear branch and bound method to verify the efficiency of present method.

• Journal of the Korean Society of Food Science and Nutrition
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• v.38 no.5
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• pp.601-604
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• 2009

This study was conducted to examine the effect of aqueous chlorine dioxide treatment as a washing method on removal of pesticide residues. Three pesticides of chlorpyrifos, diazinon, and metalaxyl, which are commonly used in vegetable crops, were treated with 10, 50, and 100 ppm of aqueous chlorine dioxide and decomposition of the pesticides was determined using gas chromatography. Three pesticides used in this study were decomposed by aqueous chlorine dioxide treatment and removal rate was proportional to treatment time as well as concentration of aqueous chlorine dioxide. In particular, 100 ppm of aqueous chlorine dioxide treatment decreased the pesticides efficiently. In addition, lettuce was treated by dipping in distilled water and 100 ppm aqueous chlorine dioxide, respectively, and was compared regarding removal efficiency of the pesticides. The results revealed that washing with 100 ppm aqueous chlorine dioxide for 10 min was the most effective for removing the pesticides. These results suggest that aqueous chlorine dioxide can be used as a washing method of fresh produce to remove the residual of pesticides.

• Journal of the Korea Society for Simulation
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• v.19 no.2
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• pp.17-28
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• 2010

Since a homing torpedo system consists of various subsystems, organic interactions of which dictate the performance of the torpedo system, it is necessary to estimate the effects of individual subsystems in order to obtain an optimized design of the overall system. This paper attempts to gain some insight into the detection mechanism of a torpedo run, and analyze the relative importance of various parameters of a torpedo system. A database for the analysis was generated using a simulation model based on the combined discrete event and discrete time architecture. Multiple search schemes, including the snake-search method, were applied to the torpedo model, and some parameters of the torpedo were found to be stochastic. We then analyzed the effectiveness of torpedo’s detection capability according to the torpedo speed, the target speed, and the maximum detection range.

• Ceramist
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• v.18 no.2
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• pp.78-85
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• 2015

이산화티탄 나노튜브와 같이 방향성을 가지고 성장한 반도체는 염료감응 태양전지의 새로운 박막구조로서 많은 관심을 받고 있다. 감응형 태양전지의 전력 생산에 필요한 빛 흡수, 전하주입, 전하운반체수송 등이 박막에서 이루어진다는 점에서 박막은 태양전지의 광전효율을 결정하는 중요한 요소이다. 특히 이산화티탄 나노튜브가 가지는 물리적, 전기적, 광학적 특성을 조절함으로써 이산화티탄 나노입자를 이용한 태양전지의 광전효율을 빠르게 따라잡을 수 있었다. 본고에서는 이산화티탄 나노튜브의 구조와 합성에 대해 검토하고 나노입자와 나노튜브 각각의 구조가 감응형 태양전지에서 빛의 수집과 전하 수집에 주는 영향에 대해 논의하고자 한다. 뿐만 아니라 나노튜브의 구조적, 전기적 특성에 따른 태양전지 제작과정의 차이를 알아본다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.6
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• pp.1089-1098
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• 1992

This paper concerns a discrete time control of noncolocated flexible mechanical systems by using time delay relation. A stability criterion of closed-loop system is derived in discrete time domain and a graphic method is developed for designing controllers. Based on this method, a derivative controller is designed for a simply supported uniform beam in the cases of colocation without time delay and of noncolocation with time delay. Some simulation results show the effectiveness of the suggested control.

• The Journal of the Korea institute of electronic communication sciences
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• v.5 no.3
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• pp.233-238
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• 2010

In this paper, we have proposed discrete ray tracing method (DRTM) for numerical analysis of characteristics of electromagnetic propagation along 2D random rough surfaces. The point of the present method is to discretize not only rough surface but also ray tracing. The former helps saving computer memories and the latter does simplifying ray searching algorithm resulting in saving computation time. Numerical calculations are carried out for 2D random rough surfaces, and electric field distributions are shown to check the effectiveness of the proposed DRTM.