• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.30 no.3
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• pp.21-29
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• 2016

In this paper, optical tracking and analysis was carried out to find the optical properties with respect to various geometric design parameters of collimator lens which is very efficient when collect the light. As a result, a whole, ellipse incident part can obtain a high light efficiency and a narrow beam angle, and angled cylinder incident part is confirmed to obtain high efficiency and a narrow beam angle at a certain height or more. When Transmission part have a specific surface which can reflect the light in forward direction, a good optical properties was confirmed.

• Journal of Ceramic Processing Research
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• v.20 no.6
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• pp.603-608
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• 2019

In this study, the multilayered thin films of (Ba,Sr)TiO3/K(Ta,Nb)O3 were fabricated by the sol-gel and spin coating methods, and their structural and electrical properties were investigated. The specimen showed polycrystalline X-ray diffraction (XRD) characteristics with a tetragonal structure. The average grain size and film thickness for one coating were about 30~40nm and 60nm, respectively. The phase transition temperature of specimen was lower than 10 ℃. The dielectric constant and loss at 20 ℃ of the specimen coated six times were 1,231 and 0.69, respectively. The rate of change in dielectric constant at an applied direct current (DC) voltage of the six times coated thin films was 17.3%/V. The electrocaloric effect was the highest around the temperature at which the remanent polarization rapidly changed. When an electric field of 660kV/cm was applied to the triply coated thin films, the highest electrocaloric property of 4.41 ℃ was observed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.2
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• pp.103-118
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• 2022

With the recent increase in demand for electronic devices, multi-layer ceramic capacitors (MLCCs) have become the most important core component. In particular, the next-generation MLCC with extremely high reliability is required for the 4^th industrial revolution and electric vehicle applications. Therefore, it is necessary to develop dielectric ceramic materials with high dielectric properties and reliability. During the decades, electrical properties of BaTiO₃ based dielectric ceramics, which have been widely used in MLCC industrial field, have been improved by microstructure and defect chemistry control. However, electrical properties of BaTiO₃ have reached their limits, and new types of dielectric materials have been widely studied. Based on these backgrounds, this report presents the recent development trends of BaTiO₃-based dielectric materials for the next-generation MLCCs, and suggests promising candidates to replace BaTiO₃ ceramics.

• Journal of the Korean Society of Industry Convergence
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• v.22 no.5
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• pp.475-481
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• 2019

The paradigm of convergence R&D is shifting from the convergence of technologies to the convergence of solutions to solve the complex problems of scientific and social development. On the other hand, it is prevalent that there is a lack of convergence in our research field. Although Korea has invested heavily in fusion research and development, Korea has mainly focused on the application and development of technology, so failed to plan convergence R&D in line with the new paradigm. Therefore, in this study, we searched for convergence R&D area that is being done to solve social problems, and tried to make use of data-driven objective methods. For this purpose, we used the investment information of global R&D projects that had no retrospective properties and derived the convergence R&D area related to coastal flooding.

• Composites Research
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• v.29 no.6
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• pp.408-413
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• 2016

Commonly-used polymers are manufactured as versatile forms. Furthermore, continuous polymer fibers are recently manufactured using nylon or aramid fiber. One of common epoxy was also used to make polymer fibers. Bisphenol-A type was used as base epoxy whereas amine and anhydride were used as hardeners. Epoxy fibers was cured by stepping up the temperature to maintain the shape of epoxy fiber. Surface energy was measured to confirm the degree of interfacial adhesion by modified static contact angle method. After mechanical properties were measured via fiber tensile test, the evaluation of fiber fracture was proceeded. Tensile strength of epoxy fiber using amine type hardener was higher as 138 MPa than anhydride case as 70 MPa. Fractured surface exhibited different failure patterns at the cross-section.

• Korean Journal of Mathematics
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• v.18 no.3
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• pp.229-241
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• 2010

In this paper, we introduce the Denjoy-Pettis integral of fuzzy mappings in Banach spaces and obtain some properties of the Denjoy-Pettis integral of fuzzy mappings and the convergence theorems for Denjoy-Pettis integrable fuzzy mappings.

• Korean Journal of Mathematics
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• v.10 no.1
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• pp.25-28
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• 2002

We introduce the notion of $s{\gamma}$-sets, and we investigate some properties of $s{\gamma}$-sets. In particular, we characterize the $s{\gamma}$-closure by terms of supra-convergence of filters.

• Communications of the Korean Mathematical Society
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• v.18 no.1
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• pp.87-94
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• 2003

We use geometric properties of Gromov-Hausdorff-convergence to present a way to construct rough but natural invariants of metric geometry.

• Kyungpook Mathematical Journal
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• v.52 no.2
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• pp.137-147
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• 2012

In this paper we introduce some new double sequence spaces via ideal convergence and an Orlicz function in $n$-normed spaces and examine some properties of the resulting spaces.

• Journal of the Chungcheong Mathematical Society
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• v.27 no.4
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• pp.753-762
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• 2014

A three-step sextic simple-root finder is constructed with the use of weighting functions of derivative-to-derivative ratios. Their convergence and computational properties are investigated along with concrete numerical examples to verify the theoretical analysis.