• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 추계학술대회 논문집
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• pp.100-105
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• 2003

25Cr-20Ni series strainless steel have an excellent high temperature strength, high oxidation and high corrosion resistance. However, further improvement can be creep strength by work hardening prior creep. In the present study, the effect of prestraining at room temperature on the creep behavior of a Class M(STS310S) and a Class A(STS310J1TB) alloy containing precipitates have been examined. Prestraining was carried out at room temperature and range of prestrain was $0.5{\sim}2.5$ % at STS310J1TB and $2.0{\sim}7.0$ % at STS310S. Creep behavior and creep rate of pre-strained specimens were compared with that of virgin specimens. Room temperature prestraining produced the creep life that is longer than that of a virgin specimen both for STS310J1TB and STS310S when creep test carried out at the temperature lower than recrystallization temperature. The reason for this improvement of creep life was ascribable to the interaction between dislocations and precipitates in addition to the dislocation-dislocation interaction in STS310J1TB and the dislocation-dislocation interaction in STS310S. The beneficial effect of prestraining in STS310J1TB was larger than that of STS310S.

• 한국유체기계학회 논문집
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• 제19권6호
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• pp.50-54
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• 2016

The performance of a scroll expander is the most important factor for the efficiency of small scale Organic Rankine cycle waste heat power generation systems. In this research, a scroll compressor was purchased and operated in reverse to function as a scroll expander. With air as a working fluid, a series of performance test were conducted on this expander by varying the inlet and outlet pressure. Secondly, We have tested through 2000 to 3500 rpm rotational speed to find the maximum power and efficiency of the expander. And last, It was observed in the initial experiments that the design of the expander's orbiting scroll wrap partially blocked the fluid intake which may have caused unnecessary flow resistance. To verify this theory, a small part of the scroll wrap was removed and the performance test was redone. It was observed that the lower back pressure assure the higher efficiency and power of expander and the rotational speed that shows maximum adiabetic efficiency of scroll expander is 69% at 2500 rpm. And by modified wrap of the scroll, we could get volume flow rate for 13% to 19% and power for 5% to 18% increased. But the maximum efficiency of the modified scroll was decreased 8%.

• 전자공학회논문지
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• 제50권12호
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• pp.56-62
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• 2013

우리는 MOSFET Layout 단계에서 Multiplier 구성을 통한 Common centroid layout 방식을 사용한 무선 전력 전송 용 CMOS 정류회로를 제안한다. 제안하는 정류회로는 기존의 다이오드를 사용하지 않은 Cross-coupled MOSFET 정류회로로 13.56 MHz에서 동작한다. 전력 소모를 최소화하고, 높은 주파수까지 동작하기 위하여 Full bridge 정류회로에서 효율을 높이기 위한 비교기를 제거하였다. Layout 단계에서 Multiplier 구성을 통한 Common centroid layout 방식은 Chip-layout 상에서 MOSFER의 Finger에 의해 길어진 연결 선로에 존재하는 기생 직렬 저항과 병렬 Capacitor에 의해 발생하는 시간 지연을 줄이기 위해 고안되어, 천이 시간을 줄여 Cross-coupled 구조의 On-상태에서 Off-상태, 혹은 그 반대의 상태 변화를 빠르게 한다. 이는 빠른 상태 변화 시간으로 인해 전력 변환 효율을 증가시킨다. 본 정류회로는 $0.11{\mu}m$ CMOS 공정으로 제작되었으며, 전력 변환 효율은 최대 86.4%로 측정되었으며, 600 MHz 이상까지 높은 전력 변환 효율을 가지며, 이는 현재 발표된 것 중, Cross-coupled 구성을 기반으로 한 정류회로 중 가장 높은 성능을 가진다.

• 한국전산유체공학회지
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• 제21권2호
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• pp.112-119
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• 2016

NEXTSat-1 is the next-generation small-size artificial satellite system planed by the Satellite Technology Research Center(SatTReC) in Korea Advanced Institute of Science and Technology(KAIST). For the control of attitude and transition of the orbit, the system has adopted a RHM(Resisto-jet Head Module), which has a very simple geometry with a reasonable efficiency. An axisymmetric model is devised with two coil-resistance heaters using xenon(Xe) gas, and the minimum required specific impulse is 60 seconds under the thrust more than 30 milli-Newton. To design the module, seven basic parameters should be decided: the nozzle shape, the power distribution of heater, the pressure drop of filter, the diameter of nozzle throat, the slant length and the angle of nozzle, and the size of reservoir, etc. After quasi one-dimensional analysis, a theoretical value of specific impulse is calculated, and the optima of parameters are found out from the baseline with a series of multi-physical numerical simulations based on the compressible Navier-Stokes equations for gas and the heat conduction energy equation for solid. A commercial code, COMSOL Multiphysics is used for the computation with a FEM (finite element method) based numerical scheme. The final values of design parameters indicate 5.8% better performance than those of baseline design after the verification with all the tuned parameters. The present method should be effective to reduce the time cost of trial and error in the development of RHM, the thruster of NEXTSat-1.

• 대한토목학회논문집
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• 제38권3호
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• pp.377-385
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• 2018

튜브 내부의 공기저항을 최소화해 운송체의 빠른 이동을 가능하게 해주는 초고속 진공튜브 시스템(Super-speed vacuum tube system)은 고효율 친환경성으로 인해 차세대 운송시스템으로 주목받고 있다. 초고속 진공튜브 시스템은 외부에 비해 튜브 내부의 압력을 매우 낮게 유지할 필요가 있으므로 기밀성의 확보가 무엇보다 중요한 설계 요건이라 할 수 있다. 본 연구에서는 균열의 발생이 진공튜브 구조물 내부의 압력 변화에 어떠한 영향을 미치는지 고찰하기 위해 일련의 콘크리트 튜브 구조물에 대해 균열에 따른 내부 압력의 변화를 측정하는 실험을 실시하였다. 실험결과 균열의 길이 또는 균열폭에 대한 정보만으로는 시스템의 기밀성에 영향을 주는 균열의 성질을 표현하기에 부족한 것으로 나타났으며, 반면에 발생된 구조물의 변위와 등가투기계수와의 관계는 상대적으로 높은 상관관계를 가지는 것으로 나타났다. 이와 같은 실험 결과를 바탕으로 설계 단계에서 시스템의 기밀성을 예측하기 위한 향후 연구방향을 제시하였다.

• Journal of Plant Biotechnology
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• 제2권2호
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• pp.55-60
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• 2000

Experiments initiated 30 years ago to obtain selectable markers have led to a series of studies of Trp biosynthesis and anthranilate synthase (AS) the control enzyme using largely plant tissue cultures since they have experimental properties that can be readily exploited. Enzymological and compound feeding studies provided evidence that AS is the control point in the Trp biosynthesis branch and that altering the AS feedback control by the selection of mutants resistant to the Trp analog 5-methyl-tryptophan (5MT) can lead to the overproduction of this important amino acid. Plants regenerated from these Trp overproducing lines of most species also had high free Trp levels but Nicotiana tabaum (tobacco) plants expressed the feedback altered AS only in cultured cells and not in the regenerated plants. further tests by transient and stable expression of the cloned promoter for the naturally occurring tobacco feedback-insensitive AS, denoted ASA2, confirmed the tissue culture specific nature of the expression control. The 5MT caused by the expression of a feedback-insensitive AS from tobacco has been used to select protoplast fusion hybrids with several species since the resistance is expressed dominantly. Recently the ASA2 gene has been used successfully as a selectable marker to select transformed Astragalus sinicus and Glycine max hairy roots induced by Agrobactetium rhizogenes. These results show that the ASA2y-subunit can interact with the y-subunit of another species to form active feedback-insensitive enzyme that may be useful for selecting transformed cells. Plastid DNA transformation of tobacco has also effectively expressed ASA2 in the compartment in which Trp biosynthesis is localized in the cell.

• 한국세라믹학회지
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• 제48권4호
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• pp.328-333
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• 2011

The influence of Al-doped ZnO (AZO) thin films degraded under high temperature and damp heat on the performance deterioration of Cu(In,Ga)$Se_2$ (CIGS) solar cells was investigated. CIGS solar cells with AZO/CdS/CIGS/Mo structure were prepared on glass substrate and exposed to high temperature ($85^{\circ}C$) and damp heat ($85^{\circ}C$/85% RH) for 1000 h. As-prepared CIGS solar cells had 64.91% in fill factor (FF) and 12.04% in conversion efficiency. After exposed to high temperature, CIGS solar cell had 59.14% in FF and 9.78% in efficiency, while after exposed to damp heat, it had 54.00% in FF and 8.78% in efficiency. AZO thin films in the deteriorated CIGS solar cells showed increases in resistivity up to 3.1 times and 4.4 times compared to their initial resistivity after 1000 h of high temperature and damp heat exposure, respectively. These results can be explained by the decreases in carrier concentration and mobility due to diffusion or adsorption of oxygen and moisture in AZO thin films. It can be inferred that decreases in FF and conversion efficiency were caused by an increase in series resistance, which resulted from an increase in resistivity of AZO thin films degraded under high temperature and damp heat.

• 한국산학기술학회논문지
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• 제12권3호
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• pp.1479-1487
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• 2011

모바일 IT기기 등의 전자부품 분야에서 다기능, 고용량 메모리를 가능하게 하는 패키지의 중요성이 점차 증대되고 있다. 이러한 목적으로 여러개의 칩을 하나의 패키지에 실장하여 다기능, 고용량을 구현하는 Multi Chip Package(MCP)가 활용되고 있다. 이러한 MCP에서 칩과 칩간 접합 혹은 칩과 지지부재(substrate)간 접합을 구현하기위해 에폭시계 필름형 접착제가 사용되고 있다. 에폭시, 아민, 머캡탄, 아이소시아네이트 등의 유기 반응기를 가진 실란커플링제를 적용하여 에폭시계 필름형 접착제에 대한 점착성과 신뢰성을 확인하였다. 결과로부터 에폭시계 반응기를 가진 실란커플링제를 적용한 시료의 점착성과 필특성이 가장 뛰어났으며, 내습 테스트에서 계면파괴가 억제되어 가장 좋은 신뢰성을 나타내었다.

• 한국인쇄학회지
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• 제28권1호
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• pp.15-24
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• 2010

Photovoltaic solar cells are all in the incident because they are not converted into electrical energy, high-efficiency solar cells in order to reduce the loss of elements must be. Significant factor in the loss of solar cells, optical loss and electrical loss can be divided into. Optical losses occur when the sun will be joined on the surface of the reflection, the shadow loss due to electrodes, and the losses are in the solar wavelengths. Commercialization is currently the most common solar cells on the front of the light incident on the electrode is formed. Therefore, the shadow caused by the electrode to cover the dead area of the sun, due to factors that hinder the absorption of sunlight which is shadowing them and conversion efficiency of solar cells is the inhibition factor. These barriers to eliminate the electrode linewidth reduces the shadowing to reduce, but simply of the electrode line width is reduced electrode area by reducing the series resistance elevates this because to improve the electrode Aspect ratio(height/width) to increase Ag development of paste is required. In this study, aspect ratio of screen-printing method to increase the electrode Ag paste composition of the binder for the characterization of rheology in the shadow of the electrode by reducing the optical loss of the photoelectric conversion efficiency of solar cells to boost the performance measures was. Properties and printability of the paste, the binder resin sintered characteristics that affect the thermal properties are excellent with a good screen printability acrylic resin, ethyl cellulose, using a resin were evaluated. Prepared paste rheology properties, was formed to evaluate the electrode conductivity and aspect ratio.

• KCI Concrete Journal
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• 제14권1호
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• pp.51-60
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• 2002

Strengthening of existing concrete structures is a major concern in recent years as the number of degraded structures increases. The purpose of this paper is to investigate the static and fatigue behavior of reinforced concrete (RC) beams strengthened with steel plates. To this end, a comprehensive test program has been set up and many series of strengthened beams have been tested. The major test variables include the plate thickness, adhesive thickness, and the shear-span to depth ratio. The test results indicate that the separation of plates is the dominant failure mechanism even for the full-span-length strengthened beams with steel plate. The theoretical ultimate load capacities for strengthened beams based on the full composite action of concrete beam and steel plate are found to be larger than the actual measured load capacities. The strengthened beams exhibit more dominant shear cracking as the shear-span to depth ratio decreases. The ultimate capacity of strengthened beams increases slightly with the increase of adhesive thickness, which may be caused by the late initiation of plate separation in the beams with thicker adhesive. A realistic concept of ductility for plate-strengthened beams is proposed in this study. It is seen that the strengthened beams show relatively low ductility compared with unstrengthened beams. The present study indicates that the strengthened beams exhibit much higher fatigue resistance than the unstrengthened beams. The increase of deflections of strengthened beams according to the number of load cycles is much smaller than that of unstrengthened beams. The present study provides very useful results for the realistic application of plate-strengthening method in reinforced concrete structures.