• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.132.1-132.1
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• 2013

현재 고품위GaN 박막 성장은 사파이어 기판이 주로 사용되며, 사파이어 기판 상에 저온에서 질화물 완충층을 선성장한 후 고온에서 GaN 박막을 성장하는 2단계 공정법을 일반적으로 택하고 있다. 본 연구에서는 새롭게 주목받고 있는 신소재인 그래핀을 본 실험실에서 기개발한 확산이용형성법을 이용하여 사파이어 기판에 직접 코팅하여 이를 완충층으로 사용한 후, MOCVD를 이용하여 저온 완충 층의 성장없이 고온에서 직접 성장한 GaN 박막에 관한 연구를 진행하였다. 매우 얇은 두께인 ~0.6 nm의 그래핀을 완충층으로 도입함으로써 GaN의 성장모드가 3차원 모드에서 2차원 모드로 바뀜을 확인 할 수 있었고, 그래핀 완충층의 두께가 점점 두꺼워짐에 따라 고온 성장한 GaN 박막의 구조적, 광학적 특성이 향상되어 기존의 2단계 성장법으로 얻은GaN 박막의 특성에 비견할 만큼 향상됨을 확인할 수 있었다. 그래핀상에 성장한 GaN 박막과 2단계 성장법으로 성장한 GaN 박막 상에 동일한 InGaN/GaN 다중양자우물구조를 형성하여 유사한 내부양자효율을 얻을 수 있게 되어, 그래핀을 완충 층으로 한 GaN 박막의 광전 소자에의 응용가능성을 확인 할 수 있었다.

• Journal of the Korean Applied Science and Technology
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• v.35 no.4
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• pp.1088-1095
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• 2018

In this study, reduced graphene oxide/polyaniline composite was fabricated tomaximize their advantages with electrochemical performances and use as a electrodematerial for supercapcaitor. Polyaniline as an electrode material was synthesized bychemical polymerization of aniline monomer and reduced graphene oxide wasintroduced to prepare composite with polyaniline without any pre-treatment. Thereduced graphene oxide, polyaniline and their composite electrodes were fabricatedon gold coated PET(polyethylene terephthalate) substrate through spray coatingmethod which can also apply to industrial scale. we have also prepared reducedgraphene oxide and polyaniline single material electrode to compare theirelectrochemical properties with reduced graphene oxide/polyaniline composite electrode. We have analyzed and compared electrochemical properties of eachelectrodes by using cyclic voltammetry(CV), galvanostaticcharge-discharge(GCD) and electrochemical impedancespectroscopy(EIS) at same condition. As a result, reduced graphene oxide /polyaniline composite electrode showed higher capacitance value more thanpolyaniline and reduced graphene oxide electrode, respectively. Internal resistanceof reduce graphene oxide/polyaniline composite electrode was 24% and 58% lessthan polaniline and reduced graphene oxide electrode respectively. These resultsconsidered that reduced graphene oxide/polyaniline composite electrode has potential ability and enable to apply flexible energy storage and wearable devices.

• Journal of Advanced Navigation Technology
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• v.24 no.4
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• pp.245-250
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• 2020

Currently, unmanned military vehicles under development in Korea have more devices to carry out various missions, and interface cables between them are also increasing. In addition, due to a small space problem inside the unmanned vehicle, devices are required to be miniaturized and integrated. For two reasons, connectors also need to be selected, which makes them vulnerable to noise due to the closer distance between the pins. In this paper, we analyzed how much the magnetic field produced by noise at the connector pin where cable twist is released affects the surrounding pin and presented the guide for optimal pin placement. First, the effect of magnetic field is greater than the crosstalk between pin and pin. Second, the magnetic field on both sides between + and - is strong when approaching one step with noise source. Third, the magnetic field strength is improved when setting the ground pin as the ground pin between the noise and the original signal when approaching the A noise source and the two steps. Fourth, in the case of a differential mode communication, the optimal placement area of the sensitive signal was presented according to positions Tx± and Rx±.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.1
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• pp.203-211
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• 1994

An experiment was carried out to evaluate the heat transfer and pressure drop performances of the smooth tube and two augmented tubes using R-113 under horizontal condensation condition. The augmented tubes are a spirally-twisted tube and an internally-finned tube. The test tube is 13.88 mm in diameter and 3.2 m long. Five different inlet pressure of 0.13, 0.16, 0.18, 0.21 and 0.23 MPa were employed and the mass flux was varied from 80 to 265 $kg/m^{2}s.$ The results showed that the overall heat transfer coefficient for the spirally-twisted tube and internally-finned tube were enhanced by 30-85% and 130-180%, respectively, over that for the smooth tube. The increase in total pressure drop for the spirally-twisted tube and internally-finned tube were reached up to 250-350% and 1100-1600%, respectively, over that for the smooth tube. Correlations were proposed for predicting the condensation heat transfer coefficient for the smooth tube and two augmented tubes.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.3
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• pp.31-39
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• 2011

The flowfield in a solid rocket motor was simulated at the wall-injection test model, which has a fin-slot grain and submerged nozzle, and visualized by a smoke-wire. The high speed CCD camera captured the visualized images around the nozzle inlet through the grain center port. The vortical tube structure and circumferential flow patterns at the nozzle throat were visualized. The radial momentum transfer caused by the shear-interactions of slot-outlet flow, fin-base flow and grain port flow from upstream worked as the source of these phenomena.

• Solar Energy
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• v.11 no.1
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• pp.78-86
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• 1991

Heat transfer characteristics of a rotating heat pipe have been studied numerically and experimentally with using water-ethanol mixture as working fluid. And triangular fins are attached inside the rotating heat pipe. Experimental results generally agreed with numerical results. According to increasing rpm and vapour pressure of the rotating heat pipe, the heat transfer rate increased. And also according to decreasing the concentration of ethanol, the heat transfer rate increased. In the case of using the pure ethanol as working fluid, the heat transfer rate was about 80% of using distilled water. The heat transfer rate and operating temperature difference of the rotating heat pipe was much influenced by ethanol concentration, and the optimum ethanol concentration was 0.2.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.225-227
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• 2011

The geometrically sub-scaled wall-injection test model was employed to visualize interactions of internal flow of a solid rocket motor equipped fin/slot grain and submerged nozzle. Symmetric vortex and circumferential flow patterns were visualized.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.12
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• pp.1084-1096
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• 2016

This paper presents method of design and analysis of a high-speed serial interface connector with a data rate of 12.5 Gbps. A high-speed serial interface connector is composed of various material and complex structures. It is very difficult to match the impedance of each discontinuous portion of connector. Therefore, this paper proposes the structure of a connector line that be simplified a connector. In the structure of proposed connector line, this research presents a method for extracting R, L, C and G parameters, analyzing the differential mode impedance, and minimizing the impedance discontinuity using time domain transmissometry and time domain reflectometry. This paper applies the proposed methods in the connector line to the high-speed serial interface connector. The proposed high-speed serial interface connector, which consists of forty-four pins, is analyzed signal transmission characteristics by changing the width and spacing of the four pins. According to the analysis result, as the width of the ground pin increases, the impedance decreases slightly. And as the distance between the ground pin and the signal pin increases, the impedance increases. In addition, as the width of the signal pin increases, the impedance decreases. And as the distance between the signal pin and the signal pin increases, the impedance decreases. The impedance characteristic of initial connector presents ranges from 96 to $139{\Omega}$. Impedance characteristic after applying the structure of proposed connector is shown as a value between 92.6 to $107.5{\Omega}$. This value satisfies the design objective $100{\Omega}{\pm}10%$.

• Journal of Korean Society of Steel Construction
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• v.12 no.4 s.47
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• pp.437-443
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• 2000

In order to clarify the behavior of beam-to-concrete filled steel tube column under cyclic loading condition, experimental studies were carried out on shear connections. Test parameters of this study are the width-to-thickness ratio and the effect on beams with or without slab and diaphragm. Test results show that the moment-rotation relationships of connections without slab are in the range of AISC regulation of pinned connections and the rotation capacity of connection is dependent upon the width-to-thickness ratio of the column.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.50-57
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• 2017

In the injection molding process, a core that builds a space for a product is installed at the internal place in the mold and fabricated as the frame of the mold. In this make up, the fabricating partial form of the mold at a pin is a core pin. The core pin is finer because an injection mold produces miniaturization and integration. On the other hand, when the core is manufactured using the existing centerless grinder, it generates vibrations because of the lack of a fixed zig for a micro size workpiece. For this reason, an existing centerless grinder without a micron size fixed zig, makes a defective product due to vibration and deformation. In this study, a compact grinding system that can be installed using an existing centerless grinder was fabricated to make a micro size core pin. Using the compact grinding system, grinding experiment for core pin was carried out. The performance of the system was confirmed by measuring the surface roughness, roundness, and cylindricity.