• 자원환경지질
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• 제21권1호
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• pp.97-106
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• 1988

The purpose of this study is to collect basic data which are prerequisite for quantitative analysis of coal logging data. The study involves laboratory measurements of physical properties such as seismic velocities (P,S-waves), resitivity and density of domestic and imported foreign coals. The relationships between these properties were analyzed by using cross-plots. Correlation between the physical properties of coal and the results of chemical analysis (calorie, fixed carbon, ash, moisture, volatile matter and sulfur contents) was also studied to obtain ideas about coal quality analysis using logging data. Summarized results are as follows: 1. $V_P$ is exponentialy related to $V_S$. And the average value of $V_P$ is about l.8 times as large as $V_S$. 2. Since coal has very low density compared with surrounding sedimentary rocks, density logging is appeared to be the best method for identifying coal seams and evaluating their qualities. 3. For the case of domestic coals, the ash contents and calorie show a perfect inverse relationship. Since the density increases as increase of ash content with a well-defined functional form, the ash content of domestic coals can be estimated by density measurements. 4. Because of low ash content, low density and high resistivity, foreign coals and domestic lignites are easily distinguished from domestic coals.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.50.1-50.1
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• 2010

결정질 실리콘 태양전지의 원가에서 Wafer는 60~70%의 매우 높은 비중을 차지하고 있다. 많은 연구들이 원가 절감을 위하여 Wafer의 두께를 감소시키는 것에 집중하고 있다. 그러나 Wafer 두께의 감소는 태양전지의 효율 감소와 공정 진행 중에 파손율이 상승하는 등의 문제가 발생한다. 이에 본 논문에서는 결정질 태양전지 구조 중에서 24.7% 이상의 최고 변환 효율을 갖는 PERL(Passivated Emitter, Rear Locally diffuse) 구조를 대상으로 wafer 두께 감소에 따른 변환 효율 감소의 원인과 해결 방안을 제시하고자 한다. Simulation으로 확인한 결과 370 um 두께의 wafer에서 24.2 %의 효율은 50 um 두께의 wafer에서는 20.8 %로 감소함을 확인할 수 있었다. 얇아진 wafer에서 감소한 효율을 개선하기 위하여 후면 recombination velocity, 후면 fixed charge density, 후면 산화막 두께 등을 다양화하여, 각각의 경우에 대한 cell의 효율 변화를 살펴보았다. 그 결과 후면 recombination velocity, 후면 fixed charge density, 후면 산화막 두께를 최적화 하여, 각각 2.8 %p, 1.5 %p, 2.8 %p의 효율 개선 효과를 얻었다. 위 세 가지 효과를 동시에 적용하면 50 um wafer에서 370 um wafer 효율의 결과와 근접한 24.2 %의 효율을 얻을 수 있었다. 향후에는 위의 결과를 바탕으로 실제 실험을 통하여 확인할 계획이다.

• 센서학회지
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• 제29권5호
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• pp.348-353
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• 2020

This paper presents an adaptive method to avoid obstacles in various environmental settings, using a two-dimensional (2D) LiDAR sensor for mobile robots. While the conventional reaction based smooth nearness diagram (SND) algorithms use a fixed safety distance criterion, the proposed algorithm autonomously changes the safety criterion considering the obstacle density around a robot. The fixed safety criterion for the whole SND obstacle avoidance process can induce inefficient motion controls in terms of the travel distance and action smoothness. We applied a multinomial logistic regression algorithm, softmax regression, to classify 2D LiDAR point clouds into seven obstacle structure classes. The trained model was used to recognize a current obstacle density situation using newly obtained 2D LiDAR data. Through the classification, the robot adaptively modifies the safety distance criterion according to the change in its environment. We experimentally verified that the motion controls generated by the proposed adaptive algorithm were smoother and more efficient compared to those of the conventional SND algorithms.

• 대한전자공학회논문지
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• 제16권1호
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• pp.26-32
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• 1979

실리콘의 dry oxidation과 wet oxidation공정의 특성을 실험적으로 조사하였다. 산화온도는1,100℃, 1.150℃, 1.200℃를 사용하였고, 산소의 유량은 0.2 liter/min으로 부터 2.8 liter/min까지 변화시켰다. 산화막의 두께를 측정하여 0.1μ ∼ 1.0μ 을 성장시키는데 필요한 온도, 시간, 산소의 유량을 도표로 나타냈다. 산화막의 특성을 조사하기 위하여 유전 상수 절연파괴 전압, fixed surface charge density (Qss/q), mobile ciarge densify (Q /q)를 측정하였다. 측정 결과로부터 산화막이 MOS transistor에도 적합한 양질이라는 결론을 얻었다.

• 한국분말재료학회지
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• 제1권2호
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• pp.153-158
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• 1994

The effect of the role of alloyed components on the densification of two kind of high speed steel (mixed and prealloyed powder), which were sintered at 1403~ 1573 K for 7.2 ks in vacuum, was investigated. The results obtained were as follows. (1) Without the presence of Vanadium (V), the relative density of sintered compacts (Ds) could not reached the density of 100% regardless of the. elements in the compacts. (2) The addition of V up to 2 mass% did not result In the complete densification when the carbon content was fixed at 2% in the compact. (3) With the fixed amount of V of 7%, Ds decreased with the increase of the carbon content. (4) The addition of mixed fine powder to the prealloyed powder in the range of 20 to 40% provided the complete densification and carbide panicles of 1~2 $\mu\textrm{m}$ through the solid phase sintering. (5) The V element played important role in controlling the complete or incomplete densification of the sintered compacts in the alloyed component because of its formation of stable oxide and carbide as well as the low equilibrium pressure of CO gas.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 C
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• pp.1243-1245
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• 1994

SiN films were deposited in $Si_2H_6$(99.9%), $NH_3$(99.99%) gas mixture with carrier gas $N_2$ on Si substrate by ArF Excimer Laser CVD. SiN film deposition conditions that are substrate temperature and Laser average power were varied in order to investigate the dependence of SiN film on the condition. A post-deposition anneal was performed to examine variation of fixed charge density in the films. The deposition rate was increased as the substrate temperature and Laser power were increased during film deposition. The refractive index was increased with increasing substrate temperature, but it didn't have the dependence on Laser power. The fixed charge density was decreased when a post-deposition anneal was performed.

• 한국통신학회논문지
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• 제27권10A호
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• pp.1000-1010
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• 2002

Partial response maximum likelihood (PRML)과 fixed-delay tree search with decision feedback (FDTS/DF)은 기록 재생 시스템에서 준최적 성능을 보이는 정보열 검출 기법 (sequence detection)으로 알려져 있다. 그러나, 정보열 검출 기법 고유의 metric 연산은 심각한 하드웨어 복잡도를 유발한다. 본 논문은 정보열 검출 기법의 복잡도 문제를 극복하기 위한 대안을 제시한다. 제안된 저 복잡도 기법들은 검출 과정에서 덧셈 및 곱셈의 수를 최소화하여 고속 프로세스 및 저 복잡도 하드웨어 구현에 적합하다. 결정 궤환 드화 깁버 (decision feedback equalization; DFE)을 결합하여 ${\tau}$=2 FDTS/DF와 동일한 성능을 보이며, 기록 밀도 S>5.6에서 PR(1111)ML의 성능을 능가함이 모의 실험을 통해 보여진다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2017년도 추계학술대회
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• pp.181-182
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• 2017

In the battery system, an isolated converter is used for the stability of the system when controlling the charge and discharge of the battery. A fixed frequency LLC converter which is a type of isolated converter, has the advantage of high efficiency and power density with zero voltage switching at high frequency. Therefore, in this paper, the operation analysis, design and experimental verification of the LLC resonant converter with high efficiency and high power density for the ESS system were conducted.

• 대한기계학회논문집
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• 제19권2호
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• pp.548-558
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• 1995

An experimental investigation has been conducted to study the spray and combustion characteristics using the air-assisted twin fluid atomizer. Axial mean and fluctuating velocity components as well as drop-size distributions in non-reaction spray were measured with a nonintrusive phase doppler technique. Droplet number density distributions were also visualized using high speed CCD camera. Locations of spray and flame boundaries are obtained by direct photographic method. It is confirmed that at the fixed fuel flow rate, the increase of the atomizing air flow causes improvements on both spray and combustion characteristics under stable flame conditions. Internal group combustion modes where flame is located inside the spray boundary are observed to exist in the upstream region of higher droplet number density.

• 한국세라믹학회지
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• 제28권11호
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• pp.908-916
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• 1991

The characteristics of the carbonized and calcined products made from coal tar pitch coke and coal tar pitch, were investigated in the aspect of the manufacture of isotropic graphite with high density. The mesophase from the pitch was rapidly formed at higher heat-treatment temperature between 410$^{\circ}C$ and 450$^{\circ}C$, where the insolubes in the pitch accelerated the rate of nucleation and growth of the mesophase. The benzene insolubles and the quinoline insolubes were increased as the heat treatment temperature and the heat-treatment time increased. The ratio of benzene insolubles and quinoline solubles (BI/QS) was decreased as the heat-treatment temperature was higher and maintained to be nearly constant regardless of heat-treatment time at fixed heat treatment temperature. The bulk density of the calcined carbon was linearly proportional to the ratio of quinoline solubes to volatile matter in the green coke. Anisotropic ratio of electrical resistance was measured to be between 0.98 and 1.10.