• Proceedings of the KIPE Conference
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• 2010.07a
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• pp.295-296
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• 2010

본 논문에서는 고속전철용 추진제어장치의 개발 및 본선 주행시험에 관한 내용을 소개하였다. 고속열차용 추진제어장치는 입력 전류의 고조파를 감소하기 위하여 단상 PWM 컨버터 2대가 병렬로 구성되고 인버터는 3상 인버터 1대로 구성된다. 추진제어장치의 전력회로를 간단히 구성하기 위하여 최대용량(4500V/4200A)의 IGBT 전력소자를 적용하였다. 3상 인버터는 가속시 스위칭 기어현상을 저감하기 위하여 저주파 동기 PWM 기법을 적용하였다. 추진제어장치의 성능을 평가하기 위하여 실제 차량이 운행될 본선에서 속도 300km/h까지 가속시험, 비상제동 시험, 구배기동 시험 등을 실시하였다. 시험을 통하여 제작된 추진제어장치가 성능사양을 만족함을 확인하였다.

• Laser Solutions
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• v.2 no.2
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• pp.27-33
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• 1999

Electron beam was applied on the low carbon steel in order to fabricate Metal/Metal GBM(Graded Boundary Material). Ni sheet was placed on the steel substrate. The electron beam was irradiated on the surface and produced a homogeous alloyed layer. Sequential repetition of electron beam treatments for 4 times resulted in 8mm thick graded layer. To determine each layers property, optical microscopy, XRD, microhardness tester and EDS were used. The residual stress was measured by the low angle x-ray diffraction method. The graded boundary layer was stepwise profile, but Ni content incresed up to 80 wt% and Fe content decreased 20 wt% near surface. Each layers microstructure and hardness varied by different Fe/Ni composition. The compressive residual stress was induced by martensite transformation in the 1st and End layers and the shrinkage cracks were formed in graded layer by rapid cooling.

• Electrical & Electronic Materials
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• v.6 no.4
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• pp.311-317
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• 1993

발열체 소자에 있어서 발열체의 방사스펙트럼과 피가열체의 흡수스펙트럼을 일치시키는 문제는 효과적인 가열을 위하여 매우 중요한 연구과제이다. 본 연구는 재료의 합성기술과 열처리기술을 이용하여 PTC 서머스터의 R-T특성은 그대로 유지시키면서 원적외선 방사특성을 증대시키기 위한 것이다. 이를 위하여 BaTiO$_{3}$+1.67Al$_{2}$O$_{3}$+3.75SiO$_{2}$+1.25TiO$_{2}$을 기본조성으로 하고 여기에 첨가제로서 Sb$_{2}$O$_{3}$와 MnO$_{2}$를 선정하여 이의 첨가량과 소결온도 그리고 소결온도구배를 파라메터로한 시편을 제작하였으며 각 시편의 IR특성과 R-T특성등을 측정 검토한 결과 파장 4.5-14.5[.mu.m]범위에서 방사율 0.8이상의 고효율 원적외선 방사특성을 얻었다.

• Korean Journal of Crystallography
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• v.3 no.1
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• pp.37-43
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• 1992

KTiOP04 is a nonlinear optical crystal which is most widely used for frequency doubling of the radiation of Nd : YAG laser. In the experiment, sin ale crystals of KTiOP04 were grown by TSSG technique using 3K2W04·P2O5 flux. Low temperature gradient furnace suitable for KTP single crystal growth was used. Seed crystal was placed at the surface of the solution for the purpose of better observation of the growing crystals and the possibility of diameter control. Solution included 66.7mol% KTiOP04 for all experiments and its saturation temperature was 1020℃. The conditions of single crystal growth were as follows: cooling rate 0.2℃/h, crystal rotation rate 50rpm, c -axis seed. Using these conditions, single crystals up to 23 ×25×25mm3 have been groan from about 100cc solution. We have also observed a change in the crystal growth habit which resulted in the formation of large (201) faces and small (100) faces. And some crystals have (101) faces.

• Korean Journal of Plant Resources
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• v.32 no.4
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• pp.325-337
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• 2019

This study was conducted to analyze character of distribution of plants by landforms and altitude in Mt. myeonbong. The chemical properties of soil in this study sites were as follows; pH 4.86, organic 52.53 g/kg, $P_2O_5$ 7.57 mg/kg, potassium $0.18cmol^+/kg$, calcium $2.45cmol^+/kg$ and magnesium $0.49cmol^+/kg$. Generalists in the upper layer were analyzed as follows; Quercus mongolica, Pinus densiflora, Quercus variabilis, and specialists; Carpinus cordata, Tilia amurensis, Morus bombycis etc. In the middle layer, generalists were Betula schmidtii, Quercus mongolica, Sorbus alnifolia and specialists; Lindera erythrocarpa, Quercus serrata, Staphylea bumalda etc. Generalist of shrubs; Lindera obtusiloba, Rhododendron mucronulatum, Sorbus alnifolia, and specialists; Morus bombycis, Pinus densiflora, Deutzia glabrata etc. Generalists of herbaceous layer; Rhus tricocarpa, Lespedeza maximowiczii, Polygonatum odoratum var. pluriflorum and specialists; Liparis kumokiri, Davallia mariesii and Chrysosplenium flagelliferum etc.

• Journal of the Korean Society for Marine Environment & Energy
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• v.2 no.1
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• pp.102-112
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• 1999

The purpose of this study is to evaluate the effects of design criteria and environmental conditions of the site of created tidal flats on the structure and function of man-made ecosystem. Seven constructed tidal flats and three natural tidal flats were studied taking the difference in the location (wave height and tidal current), inflow of river water, slope of tidal flat and age after the construction completed into consideration. Parameters studied were physico-chemical and biological characteristics of soils and rate of respiration. The natural tidal flats had higher contents of silt, nitrogen and organic matter compared with the constructed ones. The natural ones had reductive zone below 2cm, whereas the constructed ones had aerobic zone from the surface to below 20cm. The bacterial population in the soil of the constructed tidal flats was one to two orders of magnitude lower than that in the natural ones. Both biomass of macrobenthos and microbial respiration rate, however, were not different significantly between the natural and the constructed tidal flats. There was an exceptional constructed tidal flat with similar physico-chemical and biological characteristics to the natural ones. It is most probable that sufficient conditions to have similar tidal flats to natural ones are the location in enclosed bay or calm coastal area. Thus, to make man-made tidal flats with the same characteristics as those in natural ones, man-made tidal flats should be designed and/or located to enhance the accumulation of silt on tidal flat. It is important to select a place having low water motion for construction of tidal flat.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.532-538
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• 1998

Emerald ($3BeO{\cdot}Al_2O_3{\cdot}6SiO_2:Cr^{3+}$) single crystal was grown by temperature gradient reflux method with using Korean natural beryl. The flux of lithium-molibudenium-vanadium oxide system was made by means of mixing the 2 sort of flux which were differently melted $Mo_3-Li_2O$ and $V_2O_5-Li_2O$ each other. The optimum composition of flux was 3 mole ratio of molibudenium. vanadium oxides to lithium oxide ($(MoO_3+V_2O_5)/Li_2O$), flux additives were substituted more less then 0.2 mole% of $K_2O$ or $Na_2O$ to the $Li_2O$ amount. The melting concentration of mixing beryl material was 3~10% content to the flux, that of $Cr_2O_3$ color dopant was 1% to the beryl amount. In the crystal growing apparatus with temperature gradient in the 3 zone furnace which was separated into the block of melt, growth and return, the solution have got to circulate continuously between $1100^{\circ}C$ and $1000^{\circ}C$ in steady state. When thermal fluctuation was treated to during 2 hrs once on a day at 950~$1000^{\circ}C$ in growth zone, the supersaturation solution was maintained, controled and emerald single crystal can be grown large crystal which was prevented from the nucleation of microcrystallite. The preferencial growth direction of hexagonal columnar emerald single crystal was the c(0001) plane of botton side and vertical to the m(1010) plane of post side.

• Korean Journal of Crystallography
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• v.9 no.1
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• pp.21-29
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• 1998

The rare-earth orthoborate family, RM3(BO3)4 is known to be the most promising material for the microlaser host. To grow LaSc3(BO3)4 single crystal, the phase relation of the system LaBO3-ScBO3 was investigated by DTA method. LaSc(BO3)4 was the unique intermediate compound in the binary system the peritectic reaction point of which was 1495 ±2℃. Owing to the peritectic behavior of the compound, the crystal growth of the rare-earth Sc-borate was carried out by pulling from the melt-soultion of La1+xSc3-x(BO3)4. The optimal conditions for the growth of LaSc3(BO3)4 were determined by traditional CZ method : pulling speed 0.7mm/hr, rotation speed 7-10 rpm under reduction condition. Pt and Ir crucibles could be used for about 8-10 times of growth. The effect of thermal configurations on the temperature distribution was investigated. A special two-coordinate manipulator was made for the precise movement of thermocouples from the melt to the top of the furnace for several thermal configurations. The radial gradient on the melt surface depends strongly on the construction of the afterheater. On the other hand, the axial gradient was mainly propotional to both the opening degree of baffle plate and the mutual positions of crucible and heater.

• Journal of the Korean Electrochemical Society
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• v.13 no.4
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• pp.270-276
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• 2010

Nickel-copper foam electrodes with pore gradient micro framework and nano-ramified wall have been prepared by using an electrochemical deposition process. Growth habit of nickel-copper co-deposits was quite different from that of pure nickel deposit. In particular, the ramified structure of the individual particles was getting clear with chloride ion content in the electrolyte. The ratio of nickel to copper in the deposits decreased with the distance away from the substrate and the more chloride ions in the electrolyte led to the more nickel content throughout the deposits. Compositional analysis for the cross section of a ramified branch, together with tactical selective copper etching, proved that the copper content increased with approaching central region of the cross section. Such a composition gradient actually disappeared after heat treatment. It is anticipated that the pore gradient nickel-copper nanostructured foams presented in this work might be a promising option for the high-performance electrode in functional electrochemical devices.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.770-774
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• 2009

한강하구 일대는 세계최대 규모의 갯벌이 조성되어 해양생태계에서 중요한 역할을 수행하는 곳이다. 육상기원의 퇴적물이 흐름이 완만한 하구 주변부에 퇴적되어 대규모의 갯벌을 생성하여 육상에서 유입되는 많은 유기물이 집중되고 탁도가 높아 대량의 플랑크톤과 같은 일차생산자가 상대적으로 부족한 대신에 담수 유입이 많아 하구와의 거리에 따른 일정한 염분 구배를 가지고 있어 더욱 다양한 환경이 조성되어 있음에도 1980년대 후반부터 각종 매립사업과 한강종합개발사업($1982{\sim}1986$)이 실시되어 한강하구의 습지가 줄어들고, 해안침식, 토사유입, 퇴적, 적조현상, 갯벌 및 해수오염과 같은 결과를 가져왔다. 1990년대에는 한강하구지역에서 퇴적으로 인한 홍수 예방과 건설골재 확보를 위한 준설이 활발히 이루어졌으나, 이로 인한 습지생물 서식처 파괴와 같은 환경영향이 우려되어 현재는 실시하지 않고 있다. 무차별적인 개발계획으로 매년 홍수 때마다 피해를 입는 김포일대, 한강과 임진강 지역의 수위 및 흐름 영향을 살펴보고 향후 대책 수립을 검토해야 한다. 이에 본 연구에서는 한강하구의 유사이송에 의한 수리학적 특성을 분석하기 위해 상류로부터 이송되어온 유사에 대하여 시간적 흐름특성을 통하여 조성된 한강하구의 특징을 분석하였고, 지형변화 분석을 위해 MIKE 21 프로그램의 이동상 해석모듈을 사용하여 지형변화에 따른 한강하구에서의 홍수기 하상변화와 유수 흐름 및 수위등의 변화를 모의하였다. 그 결과 예성강과 한강의 유수흐름은 청주초를 통하여 외해로 유출되고 이 흐름은 대부분 강화도와 교동도 사이의 교동수로로 유출되는 것으로 나타났으며, 염하수로 합류부 및 임진강 합류부에서는 침식 및 퇴적이 활발히 일어나는 것으로 모의되었다. 향후 수리학적 특성변화에 따른 유사의 퇴적 및 세굴에 의한 한강하구 지역의 지형변화를 분석하여, 주변 환경영향에 대한 대책 수립을 검토해야 할 것이다.