• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.121-121
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• 2010

유기발광소자의 발광 효율을 향상하기 위해 발광층에서 전자와 정공의 효율적인 재결합이 중요하기 때문에 발광층에서 재결합 확률을 높이기 위한 전하의 효율적인 주입과 전송에 대한 연구가 많이 진행되고 있다. 본 연구에서는 전자주입효율을 향상하기 위하여 강한 전자 받게 역할을 하는 플러렌 (C60)과 무기물 절연층인 cesium flouride (CsF) 층을 조합한 무기물 이중 전자주입층을 삽입한 녹색 유기발광소자를 제작하였고, 녹색 유기 발광 소자에 사용하여 발광효율의 변화를 관찰하였다. 큰 쌍극자 모멘트를 갖는 CsF 층은 전기전도성이 좋은 C60 층과 Al 층 사이에 삽입되어 전자의 주입장벽을 낮추어 전자주입 효율을 향상하는 역할을 한다. C60만으로 이루어진 단층 전자 주입층으로 구성된 유기발광 소자는 Al 음극전극과 C60 계면사이에 거칠기가 크기 때문에 누설전류의 크기가 커지며 Al 과 플러렌 C60 의 공유결합 형성으로 인해 전자의 주입이 오히려 저하되는 현상을 보였다. 무기물 절연층인 CsF 층을 C60 과 Al 사이에 삽입한 유기발광소자에서 C60 층은 Cs 원자가 유기물층 내부로 확산되는 것을 감소하였다. 매우 얇은 CsF층을 Al층과 C60층 사이에 삽입함으로써 C60과 Al 사이의 공유결합을 없애고 누설전류를 줄이고 전자주입장벽을 낮추어 전자주입효율이 향상하였다. 전자주입 향상으로 인해 발광층 내에서 전자와 정공간의 비율이 개선되어 유기발광 소자의 발광효율도 증가되고 색안정성이 향상되는 것을 관찰할 수 있었다.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.3
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• pp.120-126
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• 2005

The method of decreasing the ecological risk for the LRE(Liquid Rocket Engine) test is developed, working on the cryogenic oxidizer and the high-boiling fuel(Kerosene). This Method is based on the study that contains a technical solution method and an accident occurrence range for decreasing of accident probability and damage. This paper contains schematic on the all risk circumstance bring to accident, block-diagram for an accident growth process in case of the propellant leakage, technical solution method and risk reduction evaluation method. It will be used to alternative method for the risk reduction of complex technical systems.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.279-279
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• 2011

나노 입자를 이용한 비휘발성 메모리 소자의 전기적 특성 향상을 위하여 일함수가 Si 보다 큰 금속, 금속산화물, 금속 실리사이드 나노입자를 이용한 다양한 형태의 메모리 구조가 제안되어져 왔다.[1] 특히 이와 같은 나노 부유 게이트 구조에서 터널 절연막의 구조를 소자의 동작 속도를 결정하는데 이는 터널링 되어 주입되는 전자의 확률에 의존하기 때문이다. 양자 우물에 국한된 전하가 누설되지 않으면서 주입되는 전자의 터널링 확률을 증가시키기 위하여, dielectric constant 와 barrier height를 고려한 다양한 구조의 터널 절연막의 형태가 제안 되었다.[2-3] 특히 낮은 전계에서도 높은 터널링 확률은 메모리 소자의 동작 속도를 향상시킬 수 있다. 본 연구에서는 n형 Si 기판위에 Si3N4 및 HfAlO를 각각 1.5 nm 및 3 nm 로 atomic layer deposition 방법으로 증착하였으며 3~5 nm 지름을 가지는 $TiSi_2$ 및 $WSi_2$ 나노 입자를 형성한 후 컨트롤 절연막인 $SiO_2$를 ultra-high vacuum sputtering을 사용하여 20 nm 두께로 형성 하였다. 마지막으로 $200{\mu}m$ 지름을 가지는 Al 전극을 200 nm 두께로 형성하여 나노 부유 게이트 커패시터를 제작하였다. 제작된 소자는 Agilent E4980A precision LCR meter 및 HP 4156A precision semiconductor parameter analyzer 를 사용하여 전기용량-전압 및 전류-전압 특성분석을 하여 전하저장 특성 및 제작된 소자의 터널링 특성을 확인 하여 본 연구를 통하여 제작된 나노 부유 게이트 커패시터 구조가 메모리 소자응용이 가능함을 확인하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.23-26
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• 2005

The method of decreasing the ecological risk for the LRE(Liquid Rocket Engine) test is developed, working on the cryogenic oxidizer and the high-boiling fuel(Kerosene). This Method is based on the study that contains a technical solution method and an accident occurrence range for decreasing of accident probability and damage. This paper contains schematic on the all risk circumstance bring to accident, block-diagram for an accident growth process in case of the propellant leakage, evaluation method of safety distance from test stand to residential area. It will be used to alternative method for the risk reduction of complex technical systems.

• Fire Science and Engineering
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• v.18 no.2
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• pp.57-67
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• 2004

The results of the risk assessing on general buses, consisting mainly of diesel-fueled buses, show that the frequency of the instantaneous release is 1.4${\times}$10$^{-3}$ /bus/year, from which the probability of the formation of fireball as a sub event becomes 1.7${\times}$104, and show that the leakage from the CNG-fueled buses is 0.002 event/year. Also, the frequency of gradual release due to a crack is estimated at 3.7${\times}$10$^{-3}$ /buses/year, and a subsequent probability at which this could lead to a jet flame as a sub event is 1.2${\times}$10$^{-3}$ This corresponds to 0.04event/year for the CNG-fueled buses. Dividing all the fired casualties by the running distance of diesel-fueled buses, the risk is 0.091 fire fatalities per 100-million miles. And the total fire risk fur CNG buses is approximately 0.17 per 100-million miles of travel. This means that CNG buses is twice or more dangerous than diesel buses. After all CNG buses are more susceptible to the major fires. In the aspect of the reliability of this study, generic models and the failure data used in assessing the risks of CNG buses are appropriate. However, more accurate physics-based models and databases should be supplemented with this study to provide the better results.

• Journal of the Korean Institute of Intelligent Systems
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• v.11 no.4
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• pp.354-358
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• 2001

This paper presents a fuzzy neural network model which solves the underutilization problem. This fuzzy neural network has both stability and flexibility because it uses the control structure similar to AHT(Adaptive Resonance Theory)-l neural network. And this fuzzy nenral network does not need to initialize weights and is less sensitive to noise than ART-l neural network is. The learning rule of this fuzzy neural network is the modified and fuzzified version of Kohonen learning rule and is based on the fuzzification of leaky competitive leaming and the fuzzification of conditional probability. The similarity measure of vigilance test, which is performed after selecting a winner among output neurons, is the relative distance. This relative distance considers Euclidean distance and the relative location between a datum and the prototypes of clusters. To compare the performance of the proposed fuzzy neural network with that of Kohonen Self-Organizing Feature Map the IRIS data and Gaussian-distributed data are used.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.2
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• pp.138-146
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• 2013

The present paper provides the elastic stress intensity factors(SIFs) of thick-walled cylinder with non-idealized circumferential through-wall cracks. For estimating these elastic SIFs, the systematic three-dimensional(3D) elastic finite element(FE) analyses were performed. In order to consider practical shape of thick-walled cylinder and non-idealized circumferential through-wall crack, the values of thickness of cylinder, reference crack length and crack length ratio were systematically varied. As for loading conditions, axial tension, global bending and internal pressure were considered. In particular, in order to calculate the SIFs of thick-walled cylinder with non-idealized circumferential through-wall crack from those of thick-walled cylinder with idealized circumferential through-wall crack, the correction factor representing the effect of non-idealized crack on the SIFs were proposed in this paper. The present results can be applied to accurately evaluate the rupture probabilities of nuclear piping considering actual crack growth behaviors.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.10
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• pp.783-790
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• 2018

The frequency-hopping technique is one of the spread-spectrum techniques. Frequency hopping is a communication system in which the carrier frequency channel is hopped within the wideband. Therefore, a frequency-hopping system has such advantages as antijamming and low probability of intercept. This system is often used in military communications. Because frequency-hopping signal detection is difficult, it is an important research issue. A novel detection technique is proposed that can improve detection probability. When the received signal is transformed to a frequency domain sample by fast Fourier transform, spectral leakage lowers the detection probability. This problem can be solved by using the Hamming window, and the detection probability can be increased. However, in a frequency-hopping environment, the windowing technique lowers the detection probability. The proposed method solves this weakness. The simulation results show that the proposed detection technique improves the detection probability by as much as 13 %.