• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.11
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• pp.1840-1847
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• 2016

The surface of nanosilica and microsilica was modified in order to develop a high voltage insulation material for outdoor application. The modified silicas were well dispersed in an aliphatic cyclic epoxy resin. Dielectric properties were studied for 8 kinds of specimens: 1 kind of neat epoxy, 3 kinds of epoxy/microsilica composites, and 4 kinds of epoxy/microsilica/nanosilica composites. Complex dielectric constants were measured in the range of 10-2~1.2 Hz at room temperature.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1288-1300
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• 1994

Mathematical modeling and numerical calculation on the flow and thermal characteristics induced by fire in a partial enclosure are performed. The solution procedures include the Shvab-Zeldovich approximation for the physical transport equations, low Reynolds number k-.epsilon. model for the turbulent fluid flow and Discrete Ordinate method(DOM) to calculate the radiative heat transfer. PMMA(Polymethylmethacrylate) is adopted as a solid fuel. Two different cases are considered : combustions with and without gas radiation occuring in a open cavity for variable pyrolyzing location of PMMA. When the fire source is located at the left-wall, the flow region of flame gas is limited at the left-wall and ceiling and recirculation region of inlet gas is formulated at neat the floor. In case of neglecting the radiative heat transfer, more large flame size and higher temperature is predicted. It is essential to consider the radiative heat transfer for analysis of fire phenomenon.

• Journal of Mechanical Science and Technology
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• v.18 no.4
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• pp.709-717
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• 2004

Biodiesel has great potential as an alternative fuel for diesel engines that would reduce air pollution. It is a domestically produced, renewable fuel that can be manufactured from fresh or used vegetable oils, or from animal fats. In this study, a biodiesel fuel derived from rice bran oil was tested as an alternative fuel for agricultural diesel engines. The emissions were characterized for both neat and blended biodiesel fuels, and for conventional diesel fuel. Since this biodiesel fuel contained 11 % oxygen, it strongly influenced the combustion process. The use of biodiesel fuel resulted in lower carbon monoxide, carbon dioxide, and smoke emissions, without any increase in nitrous oxide emissions. The study demonstrated that biodiesel fuel could be effectively used as a renewable and environmentally innocuous fuel for agricultural diesel engines.

• Asian Journal of Turfgrass Science
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• v.9 no.2
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• pp.137-157
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• 1995

Some indices of species of the Arundinella hirta communities in Cheolwon area were studied and the following results were obtained. The vegetational date was analyzed from six grass stands selected with the distance away from the DMZ in Cheolwon area. Species diversity was higher in the stand away from the DMZ than in that neat to it. All six stands are not considered to be free of disturbance. Species composition of the stands might be related to the degree of disturbance. It can be said that the destruction of the vegetation by periodical fire or cutting simplifies the species composition. In the rear district the human inter ference is supposed to be more frequent. But it is supposed to be slight in near the DMZ and that the degree of disturbance is not so destructive. This could be the explanation of high diversity in these stands.

• Bulletin of the Korean Mathematical Society
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• v.52 no.5
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• pp.1549-1557
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• 2015

Characterizations of closed subgroups in abelian groups have been generalized to modules in essentially dierent ways; they are in general inequivalent. Here we consider the relations between these generalizations over commutative rings, and we characterize the commutative rings over which they coincide. These are exactly the commutative noetherian distributive rings. We also give a characterization of c-injective modules over commutative noetherian distributive rings. For a noetherian distributive ring R, we prove that, (1) direct product of simple R-modules is c-injective; (2) an R-module D is c-injective if and only if it is isomorphic to a direct summand of a direct product of simple R-modules and injective R-modules.

• Elastomers and Composites
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• v.31 no.1
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• pp.13-22
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• 1996

In order to Improve the fracture toughness of epoxy resin system, liquid chloroprene rubber(LCR) and liquid butadiene rubber (LBR) which have hydroxy group were used in the brittle epoxy system. Mechanical and toughness characterization of the modified epoxy resins were investigated as a function of liquid rubbers content. Epoxy resins modified with both of the liquid rubbers showed complete phase-separation microstructure : In all of the LCR content, it was observed that the domain size of LCR dispersed in the epoxy matrix ranging from $2{\mu}m\;to\;5{\mu}m$. It was found that fracture toughness, $K_{ic}$, of the modified LCR system was enhanced continuously as increasing LCR content. However around 10phr of LBR system showed maximum fracture toughness. Specifically, when BPA add to the modified LCR system, thermal and mechanical properties increased than neat epoxy. At the same time, fracture toughness was enhanced.

• Hwankyungkyoyuk
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• v.14 no.2
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• pp.51-67
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• 2001

In this study we developed a framework to evaluate environmental education programs through lived experience in nature and the framework was applied to a neat case,'2001 Green Camp'. The framework consists of 4 items; goals and objectives, instructional planning, teaching and learning, methods and learning operation and environment. Learning outcomes such as changes to the levels of knowledge, attitude, participation and environmental sensitivity are not included in the evaluation framework but evaluated through direct questions to students. Two researchers observed and evaluated programs with the framework. This study reflected various perspectives of researchers, teachers, students and staff members.

• YAKHAK HOEJI
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• v.34 no.2
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• pp.133-138
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• 1990

The reaction of 2-aminobenzamide with phthalic acid anhydride In dioxane produced a bicyclic product 2,8-dioxoisoindole(1,2,a) quinazoline (I) in addition to hydrolysis product 2(2-Carboxyphenyl)-1,2-2H-quinazoline-4-one (II). The yields were 64% and 30% respectively. On the other hand, the same reaction in DMF afforded compound (I) and 2(2N-dimethyl carbamyl phenyl)-1,4-2H-quinazoline-4-one (III) in 30% and 60% yield respectively. The compound III was also obtained by the reaction of compound II with dimethylamine. However the reaction of 2-aminobenzamide with neat succinic acid anhydride gave only bicyclic product 2,8-oxopyrrolidine (2,1,a)-1,4-2H-quinazoline (IV) in 93%.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.16-20
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• 2003

As the preliminary works for the preparation of exfoliated nanocomposites by reactive extrusion (REX) the modified anionic polymerization proceeded in a flask using an $\varepsilon$-caprolactam, catalyst, initiator, and clay. Polymerization methods were classified with a variation of the clay adding time. Intercalations mechanism of clay layers was investigated by measuring the WAXD peaks of clay with polymerization. In the preparation of nanocomposites, the molecular weight of nylon 6 was affected by the clay content. From the mechanical property measurement, improved properties were obtained in comparison to the neat nylon 6, and these properties were also affected by the molecular weight.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.6
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• pp.1474-1482
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• 1994

In order to study the influence of a circular inclusion on a stress field neat a crack tip, mutual interference of a crack and the circular inclusion is analyzed by using the two dimensional boundary element method program made for the analysis of a bimaterial inclusion. The stress intensity factor of an inclusion which has small stiffness is a little greater than that of large stiffness in the near-by crack tip, and similar values tends to appear for distant crack tips. A line crack shows the repetition phenomena which caused by stress mutual interference depending on the radius and stiffness of an inclusion, and the repetition phenomena becoms weak in the inclusion which has large stiffness. Stress mutual interference shows repetition phenomena after extension of a line crack by the length of the radius of the inclusion which has small stiffness.