• Journal of the Korean Ceramic Society
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• v.32 no.1
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• pp.51-56
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• 1995

Variation of sintered density of BaTiO3 powder calcined at 120$0^{\circ}C$ and 135$0^{\circ}C$ was investigated with respect to the grain growth behavior. It was found that BaTiO3 powder, which was calcined at 120$0^{\circ}C$, showed abnormal grain growth behavior during sintering process. At initial stage of sintering process, the densification rate of specimen was accelerated with rapid grain growth caused by the abnormal grain growth. But with the increase of sintering time, abnormally grown grain met each other and the density of specimen decreased drastically due to coalescence of pores located in triple junction. On the contrary, BaTiO3 powder calcined at 135$0^{\circ}C$ showed normal grain growth behavior and gradually densified with the increase of sintering time.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.100-100
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• 2010

Because of power consumption increase, global wanning, and limitation of installation, not only high reliability and interruption capability but also compact and light power apparatuses are needed. To improve the insulation performance, the high E field concentration phenomena was considered. Breakdown mechanism in vacuum is different from that in other insulation materials. therefore, It is necessary to understand the electric field distribution and insulation characteristics. This paper discusses the simulation and LI(light impulse) test of the shield of outside vacuum interrupter As a result, FEM simulation and LI test show that improve distribution of electrical field and equi-potential line. due to external shield. in this case, outside shield induced electric field of triple junction point.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.1181-1182
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• 2015

본 논문에서는 초고압 가스절연개폐장치(GIS, Gas Insulated Switchgear) 내 고체 절연물인 스페이서에서 삼중점의 전계를 완화하기 위한 쉴드링 설계 방법과 그에 따른 효과를 분석하였다. 이를 위해 420kV GIS 스페이서를 축대칭 모델로 단순화하여 전계해석을 수행하였으며, 쉴드링 직경에 따른 삼중점 전계세기 변화를 확인하였다. 또한 쉴드링과 스페이서 계면 사이의 최소 이격거리를 계산하여 쉴드링의 최적 직경을 구하였다. 추가적으로, 새로운 설계 기법인 Double 쉴드링 기법을 소개하고 기존의 쉴드링이 하나인 경우와 비교 분석하여 그 효과를 확인하였다.

• Proceedings of the KIEE Conference
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• 1990.07a
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• pp.289-292
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• 1990

This study is to develope a spacer having almost uniform field distribution along the profile by controlling the high electric field in tensification at earthed part, especially triple junction in the spacer-electrode-gas boundary interface. Based on the extensive field calculation using CSM, a model spacer has been manufactured and tested. The test results show that the breakdown strength of the spacer is almost same as that of SF6 gas itself without spacer.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07a
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• pp.342-344
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• 2005

We have simulated a symmetric dual-gate TFT which has triple floating n+ channel to improve the on-current of the dual-gate TFT. We achieved a low hole concentration at the source and channel junction causes the improvement the potential barrier so that we observed the reduction of the kink-effect. In this paper, we observed the reduction of the kink-effect compared with the conventional single-gate TFT and the improvement of the on-current compared with the conventional dual-gate TFT.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.584-587
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• 2006

An energy generating greenhouse based on fluoropolymer envelope and fresnel lens is proposed. The outstanding properties of the fluoropolymer films make them very suitable for large scale solar applications. Extremely high optical transmission over the whole solar spectrum, combined with mechanical strength, and durability allows us to design a highly optimized greenhouses for both plant growing and energy generation. Systems such as photovoltaic triple junction cells are especially attractive since they have up to 35% efficiency with much less cell material when the sun beam is focused with concentrators such as fresnel lenses. Cooling such devices will enhance the efficiency and provide useful thermal energy that could be further utilized for various applications depending on the local demands. This article introduces the basic ideas and principles of the energy generating greenhouses as a first step towards the actual deployment of such systems under Korean environment.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.12
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• pp.1019-1025
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• 2021

In nearly all space environments, the solar cell degradation is dominated by protons[1]. Even through a GEO orbit lines in the electron radiation belts, the protons emitted from any solar event will still dominate the degradation[1]. Since COMS launch on June 26 2010, the proton events with the fluence of more than approximately 30 times the average level of perennial observations were observed between January 23 - 29 2012 and March 07 - 14 2012[16]. This paper studies the solar cell degradation by solar proton events in January and March 2012 for the open circuit voltage(Voc) of a witness cell and the short circuit current(Isc) of a section connected to a shunt switch. To evaluate the performance of solar cell, the flight data of voltage and current are corrected to the temperature, the Earth-Sun distance and the Sun angle and then compare with the solar cell characteristics at BOL. The Voc voltage dropped about 23.6mV compare after the March 2012 proton events to before the January 2012 proton events. The Voc voltage dropped less than 1% at BOL, which is 2575mV. The Isc current decreased negligible, as expected, in the March 2012 proton events.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.428-429
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• 2011

Recently, we performed ab initio total energy calculation and tight-binding molecular dynamics (TBMD) simulation to study structures and the reconstruction of native defects in graphene. In the previous study, we predicted by TBMD simulation that a double vacancy in graphene is reconstructed into a 555-777 composed of triple pentagons and triple heptagons [1]. The structural change from pentagon-octagon-pentagon (5-8-5) to 555-777 has been confirmed by recent experiments [2,3] and the detail of the reconstruction process is carefully studied by ab initio calculation. Pentagon-heptagon (5-7) pairs are also found to play an important role in the reconstruction of vacancy in graphene and single wall carbon nanotube [4]. In the TBMD simulation of graphene nanoribbon (GNR), we found the evaporation of carbon atoms from both the zigzag and armchair edges is preceded by the formation of heptagon rings, which serve as a gateway for carbon atoms to escape. In the simulation for a GNR armchair-zigzag-armchair junction, carbon atoms are evaporated row-by-row from the outermost row of the zigzag edge [5], which is in excellent agreement with recent experiments [2, 6]. We also present the recent results on the formation and development of dislocation in graphene. It is found that the coalescence of 5-7 pairs with vacancy defects develops dislocation in graphene and induces the separation of two 5-7 pairs. Our TBMD simulations also show that adatoms are ejected and evaporated from graphene surface due to large strain around 5-7 pairs. It is observed that an adatom wanders on the graphene surface and helps non-hexagonal rings change into stable hexagonal rings before its evaporation.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.147.2-148
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• 2016

Light management technology is very important for thin film solar cells, which can reduce optical reflection from the surface of thin film solar cells or enhance optical path, increasing the absorption of the incident solar light. Using proper light trapping structures in hydrogenated amorphous silicon (a-Si:H) solar cells, the thickness of absorber layers can be reduced. Instead, the internal electric field in the absorber can be strengthened, which helps to collect photon generated carriers very effectively and to reduce light-induced loss under long-term light exposure. In this work, we introduced a chemical etching technology to make honey-comb textures on glass substrates and analyzed the optical properties for the textured surface such as transmission, reflection and scattering effects. Using ray optics and finite difference time domain method (FDTD) we represented the behaviors of light waves near the etched surfaces of the glass substrates and discussed to obtain haze parameters for the different honey-comb structures. The simulation results showed that high haze values were maintained up to the long wavelength range over 700 nm, and with the proper design of the honey-comb structure, reflection or transmission of the glass substrates can be enhanced, which will be very useful for the multi-junction (tandem or triple junction) thin film a-Si:H solar cells.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.9
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• pp.10-17
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• 2007

It opens a new horizon on spintronics for the potential application of MTJ as a universal logic element, to employ the magneto-logic in substitution for the transistor-based logic device. The magneto-logic based on the MTJ element shows many potential advantages, such as high density, and nonvolatility. Moreover, the MTJ element has programmability and can therefore realize the full logic functions just by changing the input signals. This magneto-logic using MTJ elements can embody the reconfigurable circuit to overcome the rigid architecture. The established magneto-logic element has been designed and fabricated on a triple-layer MTJ. We present a novel magneto-logic structure that consists of a single layer MTJ and a current driver, which requires less processing steps with enhanced functional flexibility and uniformity. A 4-bit gray counter is designed to verify the magneto-logic functionality of the proposed single-layer MTJ and the simulation results are presented with the HSPICE macro-model of MTJ that we have developed.