• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.12
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• pp.639-647
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• 2001

We present an integrated optical microswitch, composed of silicon waveguides, gold-coaled silicon micromirrors, and electrostatic contact actuators, for applications to the optical signal transceivers. For a low switching voltage, we modify the conventional curled electrode microactuator into a electrostatic microactuator with touch-down beams. We fabricate the silicon waveguides and the electrostatically actuated micromirrors using the ICP etching process of SOI wafers. We observe the single mode wave propagation through the silicon waveguide with the measured micromirror loss of $4.18\pm0.25dB$. We analyze major source of the micromirror loss, thereby presenting guidelines for low-loss micromirror designs. From the fabricated microswitch, we measure the switching voltage of 31.74V at the resonant frequency of 6.89kHz. Compared to the conventional microactuator, the present contact microactuator achieves 77.4% reduction of the switching voltage. We also discuss a feasible method to reduce the switching voltage to 10V level by using the electrode insulation layers having the residual stress less than 30MPa.

• Korean Journal of Family Social Work
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• no.56
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• pp.69-104
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• 2017

This research aims to understand in depth and contextually of the grandchildren 's growth with their grandparents. The data were collected through in-depth interviews with observation and documents and analyzed using life history approach. The life history method was based on Mandelbaum(1973)'s framework including 'life dimensions', 'turning points', and 'adaptations'. After the analysis, central themes in each domain emerge as follows; 'social prejudice', 'growing poverty', 'a painstaking smile', 'more polite and honest', and 'being alone' in life dimensions, 'parentless children', 'a painful memory, outcast', and 'going to college' in turning points, and 'a willing person, parents', 'a blessed person', 'self-reliance and scale of economic life', and 'diligence and inborn cheerfulness' in adaptations, respectively. Based on these results, several intervention strategies and implications for healthy growth of grandchildren.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.5
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• pp.418-425
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• 2019

A piezoelectric ceramic fiber composite (PCFC) was successfully fabricated using $0.69Pb(Zr_{0.47}Ti_{0.53})O_3-0.31[Pb(Zn_{0.4}Ni_{0.6})_{1/3}Nb_{2/3}]O_3$ (PZT-PZNN) for use in small-scale wind energy harvesters. The PCFC was formed using an epoxy matrix material and an array of Ag/Pd-coated PZT-PZNN piezo-ceramic fibers sandwiched by Cu interdigitated electrode patterned polyethylene terephthalate film. The energy harvesting performance was evaluated in a custom-made wind tunnel while varying the wind speed and resistive load with two types of flutter wind energy harvesters. One had a five-PCFC array vertically clamped with a supporting acrylic rod while the other used the same structure but with a five-PCFC cantilever array. Stainless steel (thickness: $50{\mu}m$) was attached onto one side of the PCFC to form the PZT-PZNN cantilever. The output power, in general, increased with an increase in the wind speed from 2 m/s to 10 m/s for both energy harvesters. The highest output power of $15.1{\mu}W$ at $14k{\Omega}$ was obtained at a wind speed of 10 m/s for the flutter wind energy harvester with the PZT-PZNN cantilever array. The results presented here reveal the strong potential for wind energy harvester applications to supply sustainable power to various IoT micro-devices.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.14 no.1
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• pp.63-68
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• 2009

Among various microscopic organisms producing photobiological hydrogen, cyanobacteria have long been recognized as the promising biological agents for hydrogen economy in 21 century. For photobiological production of hydrogen energy, marine unicellular $N_2$-fixing cyanobacteria have been evaluated as an ideal subgroup of Cyanophyceae. To develope the hydrogen production technology using unicellular $N_2$-fixing cyanobacteria, 3 important factors are pre-requisite: 1) isolation of the best strain from marine natural environment, 2) exploration on the strain-specific optimal conditions for the photobiological hydrogen production, and finally 3) application of the molecular genetic tools to improve the natural ability of the strain to produce hydrogen. Here we reviewed the recent research & development to commercialize photobiological hydrogen production technology, and suggest that intensive R&D during next 10-15 years should be imperative for the future Korean initiatives in the field of the photobiological hydrogen production technology using photosynthetic marine unicellular cyanobacterial strains.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.3
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• pp.187-195
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• 2024

This paper presents two-dimensional boundary value problems of the stress-based gradient elasticity within the smoothed finite element method (S-FEM) framework. Gradient elasticity is introduced to address the limitations of classical elasticity, particularly its struggle to capture size-dependent mechanical behavior at the micro/nano scale. The Ru-Aifantis theorem is employed to overcome the challenges of high-order differential equations in gradient elasticity. This theorem effectively splits the original equation into two solvable second-order differential equations, enabling its incorporation into the S-FEM framework. The present method utilizes a staggered scheme to solve the boundary value problems. This approach efficiently separates the calculation of the local displacement field (obtained over each smoothing domain) from the non-local stress field (computed element-wise). A series of numerical tests are conducted to investigate the influence of the internal length scale, a key parameter in gradient elasticity. The results demonstrate the effectiveness of the proposed approach in smoothing stress concentrations typically observed at crack tips and dislocation lines.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2019.04a
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• pp.25-25
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• 2019

1953년 7월 27일 정전협정 이후 한반도를 가로지르는 DMZ (Demilitarized zone: 비무장지대)가 설정되었다. DMZ에 출입은 군사정전위원회의 허가가 있어야 가능하기에 군사시설 및 군작전지역을 포함하여 DMZ 및 민간인통제선 이북은 민간인 접근의 제한으로, 단절된 공간으로 변모하였다. DMZ는 우리나라의 대표적인 동고서저의 지형 및 다양한 생태환경을 두루 갖추고 있어 중요한 생태적 요충지로 평가받고 있다. 산림지역은 민간인통제지역까지 합치면 40여개의 산지가 분포하고 있으며, 하천은 크게 15개의 크고 작은 하천이 위치하고 있다. 남방한계선 수계를 따라 일부지역들은 하천 배후습지, 묵논습지 등 습원형태로도 많이 발견되고 있다. 이런 습원지역들은 대부분 미확인 지뢰지대로 접근이 제한적인 만큼 지난 세월의 흔적들을 고스란히 담고 있다. 1965년 한국자연보존연구회는 30여명의 국내학자를 동원하여 서울에서 가까운 DMZ 인접지역에 대한 예비적인 학술조사를 실시하였으며, 이를 계기로 1966년 10월부터 1968년 9월까지 2년간에 걸쳐 한국자연보존위원회 34명의 국내학자와 미국 스미소니언연구소(Smithsonian Institution) H. K. Buechner 박사를 대표로 5명의 국외학자가 공동으로 종합적인 학술조사를 수행하였다. 이는 DMZ 연구의 시작을 알렸으며, 이후 남북관계나 시대여건에 맞추어 간헐적으로 다양한 조사 및 연구들이 이어져오고 있다. 2015년부터 2018년까지 DMZ 철책주변 현장조사를 통해 확인된 식물현황은 964분류군이다. 군시설로 인해 식물서식환경이 제한적인 상황이지만 척박한 환경에 적응하고 있는 식물은 다양하다. DMZ와 맞닿아 있는 7개 지역에 대한 식물현황은 철원 638분류군, 연천 631분류군, 양구 525분류군 순으로 나타났다. 대부분 중동부 지역에 높은 식물종수가 나타났으며, 서부와 동부의 식물들이 고르게 나타나는 결과로 보인다. 큰잎쓴풀, 봉래꼬리풀 등 희귀식물도 있는 반면, 잠재적으로 생태계에 영향을 줄 수 있는 침입외래식물도 다수 포함되어 있어서, 지속적인 모니터링 및 관리가 필요하다. 그 중에서도 양구지역에 새롭게 발견된 Macleaya cordata (Willd.) R.Br.(양귀비과)는 독성이 포함된 식물이며, 인제에서 2014년에 발견된 미역취아재비는 DMZ일원에 제한적으로 분포하는 종이였으나 현재 연천에서 발견되는 등 확산에 대한 관리방안이 필요하다.

• Journal of Conservation Science
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• v.37 no.6
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• pp.723-737
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• 2021

This study analyzed the composition and structure of materials with Buddhist paper scriptures excavated from architectural sites in 'Sum Tolgoi' of the 17^th century and carried out conservation treatment base on the result of the analysis. The scriptures were covered in dust and foreign sub stances, and were so crumpled that it was impossible to identify the form. The damage, loss, and discoloration have been identified. Buddhist scriptures written in Tibetan used indigo and ink sticks on paper as a result of UV-Vis analysis, and ink sticks as black character materials from scriptures written ancient Mongolian. SEM-EDS and Micro-XRF analyses revealed that the outlines were drawn with red lines using a mix of Minium (Pb₃O₄) and Cinnabar (HgS), or Cinnabar (HgS) alone, and the contents of the scriptures were written with silver paint. Silver chloride (AgCl) and Calcium (Ca) were identified in the silver paint component of the characters, while Calcium and Orpiment (As₂S₃) were identified in the yellow lines. Concerning the paper ground, Buddhist scriptures written in ancient Mongolian were characterized by herbal plant fiber and bast fiber, and those written in Tibetan, by bast fiber. Radiocarbon dating indicates that the paper for the scriptures was produced between the 15^th and 17^th centuries. Conservation treatment of the scriptures was carried out based on the experiment on the production of pre-coated paper and how to coat that to prevent the second damage due to the deformation and fragility of the excavated paper. The scriptures were preserved and mounted, and a neutral box was made to identify the contents of the scriptures recorded on both sides after the treatment. This conservation treatment is the result of a study that applied new conservation treatment materials and methods according to the principle of conservation treatment reversibility.

• Journal of the Korean Society for Nondestructive Testing
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• v.15 no.4
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• pp.549-560
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• 1996

The purpose of this study is to investigate the usefulness of small punch(SP) test using miniaturized specimens as a method for fracture strength evaluation of CANDU pressure tube embrittled by hydrogen. According to the test results, the fracture strength evaluation as a function of hydrogen concentration at $-196^{\circ}C$ was much better than that at room temperature, as the difference of SP fracture energy(Esp) with hydrogen concentration was more significant at $-196^{\circ}C$ than at room temperature for the hydrogen concentration up to 300ppm-H. It was also observed that the peak of average AE energy, the cumulative average AE energy and the cumulative average AE energy per equivalent fracture, strain increased with the increase of hydrogen concentration. From the results of load-displacement behaviors, Esp behaviors, macro- and micro-SEM fractographs and AE test it has been concluded that the SP test method using miniaturized specimen($10mm{\times}10mm{\times}0.5mm$) will be a useful test method to evaluate the fracture strength for CANDU pressure tube embrittled by hydrogen.

• Journal of Environmental Impact Assessment
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• v.29 no.5
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• pp.307-322
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• 2020

This study was conducted to obtain information relevant to resolving problems related to artificially introduced plants in ecological restoration projects. We investigated artificially introduced plants and plants growing naturally from its surroundings in the active restoration sites of the Ecosystem Conservation Fund Return Project (ECFRP) of the Ministry of Environment and the Civilian Control Zone Forest Restoration Project (CCZFRP) of the Korea Forest Service. We also analyzed the characteristics of native, exotic, and cultivated plants in addition to their Raunkiaer's life forms. Furthermore, we compared the planted areas and inhabited areas, as well as the characteristics of the habitats of native plants among the planted plants. We found that among the plants planted in the ECFRP, 50.4% were native, 6.8% were exotic, and 42.9% were cultivated. Meanwhile, in the CCZFRP, 78.6% were native, 21.4% were exotic. We also noted that many native plants were found in the planted areas that were far from their habitats. In addition, we identified many native plants that were planted in areas judged to have characteristics different from that of their natural habitat. In the case of Raunkiaer's life forms, the planted plants showed high ratios of megaphanerophytes (MM) and microphanerophytes (N), while the invasive plants showed high ratios of therophytes (Th) and hemicryptophytes (H). When restoring the ecosystem, the ratio of planting native plants should be higher than that of exotic or cultivated plants. Moreover, the habitats and ecological characteristics should be considered when selecting native plants to enhance the effect of ecological restoration.

• Conservation Science in Museum
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• v.15
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• pp.78-95
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• 2014

To examine the materials, production techniques, and key features of Goryeo wooden lacquerwares, scientific analysis was conducted on six relevant lacquerware items. All of the items, except for a lacquered bowl ^{duksu 4123}, were found to have been made by first covering the surface of the wood with cloth and then varnishing with lacquer. The wooden frames of flower-shaped lacquered case and pine leaves shape lacquered case were made by wrapping thin wood around either the lid or bottom panel. In most cases, microscopic analysis revealed a lower layer of lacquer mixed with bone ash and bone dust, followed by an upper varnish layer of lacquer. SEM-EDS analysis and μ-XRF ^{Micro-X-ray Fluorescence} analysis showed that vermilion lacquer mixed with cinnabar was used on the surface. A lid decorated with a dot pattern was made by first varnishing the surface with yellow lacquer mixed with orpiment, and then irregular dot pattern with a mixture of black lacquer and soot. The vermilion lacquer used to varnish the side of the lacquered bowls was composed of lacquer mixed with cinnabar and minium ^{Red Lead}.