• ETRI Journal
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• 제35권4호
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• pp.632-637
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• 2013

In this paper, we propose a superjunction trench gate MOSFET (SJ TGMOSFET) fabricated through a simple p-pillar forming process using deep trench and boron silicate glass doping process technology to reduce the process complexity. Throughout the various boron doping experiments, as well as the process simulations, we optimize the process conditions related with the p-pillar depth, lateral boron doping concentration, and diffusion temperature. Compared with a conventional TGMOSFET, the potential of the SJ TGMOSFET is more uniformly distributed and widely spread in the bulk region of the n-drift layer due to the trenched p-pillar. The measured breakdown voltage of the SJ TGMOSFET is at least 28% more than that of a conventional device.

• 천문학회보
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• 제37권2호
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• pp.118.2-118.2
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• 2012

In particle-in-cell (PIC) simulation studies related to ion-ion two-stream instability, a reduced ion-to-electron mass ratio is often employed to save computation time. But it was not clearly verified how electrons dynamics are coupled with the slower evolution of ion-ion interactions under the external electric field. We have studied the ion beam driven instability using a 1D electrostatic PIC code by comparing different rescaling of parameter with real ion mass from the reference simulation with reduced ion mass. As the external electric field is stronger, the excited unstable mode range was more sensitively affected by the system size with the real mass ratio than the reduced ion mass. The results show that the reduced mass ratio should be used cautiously in PIC code as the electron dynamics can modify the ion instabilities. Additionally we found the formation of electron flat-top distribution in the final saturation stage. Simulation results show that in the early phase electrostatic solitary waves are quasi-periodically formed, but later they are fully dissipated resulting in heated, flat-top distributions. New electron beam components are occasionally formed. These are a consequence of the interaction with solitary wave structures. We parametrically investigate the development of electron phase space distributions for various drift speeds of ion beams and temperature ratios between ions and electrons

• Nuclear Engineering and Technology
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• 제40권5호
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• pp.429-438
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• 2008

The objective of the present study is the depth and layout optimizations of a single layer, high level radioactive waste repository in a discontinuous rock mass with special joint set arrangements. A single layer repository model, considering variations in the repository depths, pitches, and tunnel spacings, is used to analyze the thermomechanical interaction behavior. It is assumed that the repository is constructed in saturated granite with joints; the PWR spent fuel in a disposal canister is installed in a deposition drift which is then sealed with compacted bentonite; and the backfill material is filled in the repository tunnel. The decay heat generated by the high level radioactive wastes governs the thermomechanical behavior of the near field rock mass of the repository. The temperature and displacement behavior of the repository is influenced more by the pitch variations than the tunnel spacing and repository depth. However, the stress behavior is influenced more by the repository depth variations than the pitch and tunnel spacing. For the final selection of the tunnel spacing, pitch, and repository depth, other aspects such as the nuclide migration through a groundwater flow path, construction costs, operation costs, and so on should be considered.

• 한국진공학회지
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• 제9권3호
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• pp.242-248
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• 2000

고주파 스퍼터링 방법으로 증착조건을 변화시키면서 BST 박막을 제작하였다. 증착온도가 높을수록, Ar/O$_2$비가 적을수록 우수한 전기적 특성을 보였다. 누설전류 전도기구를 분석하기 위해 Schottky모델과 modified-Schottky모델을 도입하였다. BST 박막의 누설전류 전도기구는 기존의 Schottky모델이 아니라 modified-Schottky 모델을 따른다는 것을 알았다. Modified-Schottky 모델을 사용하여 광학유전상수 $\varepsilon$=4.9, 이동도 $\mu$=0.019 $\textrm{cm}^2$/V-s, 그리고 장벽높이 $\phi_b$ =0.79 eV를 구하였다.

• Current Optics and Photonics
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• 제5권4호
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• pp.384-390
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• 2021

This paper presents a wide-range tunable wavelength-locking technology based on optoelectronic oscillation (OEO) loops for optical fiber sensors and microwave photonics applications, explains the theoretical fundamentals of the design, and demonstrates a method for locking the relative wavelength differences between a leader semiconductor laser and its follower lasers. The input of the OEO loop in the proposed scheme (the relative wavelength difference) determines the radio-frequency (RF) signal frequency of the oscillation output, which is quantized into an injection current signal for feedback to control the wavelength drift of follower lasers so that they follow the wavelength change of the leader laser. The results from a 10-hour continuous experiment in a field environment show that the wavelength-locking accuracy reached ±0.38 GHz with an Allan deviation of 6.1 pm over 2 hours, and the wavelength jitter between the leader and follower lasers was suppressed within 0.01 nm, even though the test equipment was not isolated from vibrations and the temperature was not controlled. Moreover, the tunable range of wavelength locking was maintained from 10 to 17 nm for nonideal electrical devices with limited bandwidth.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권4호
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• pp.1193-1215
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• 2021

The measurement of the key product quality index plays an important role in improving the production efficiency and ensuring the safety of the enterprise. Since the actual working conditions and parameters will inevitably change to some extent with time, such as drift of working point, wear of equipment and temperature change, etc., these will lead to the degradation of the quality variable prediction model. To deal with this problem, the selective integrated moving windows based principal component regression (SIMV-PCR) is proposed in this study. In the algorithm of traditional moving window, only the latest local process information is used, and the global process information will not be enough. In order to make full use of the process information contained in the past windows, a set of local models with differences are selected through hypothesis testing theory. The significance levels of both T - test and χ² - test are used to judge whether there is identity between two local models. Then the models are integrated by Bayesian quality estimation to improve the accuracy of quality variable prediction. The effectiveness of the proposed adaptive soft measurement method is verified by a numerical example and a practical industrial process.

• International Journal of Advanced Culture Technology
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• 제10권3호
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• pp.295-306
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• 2022

The NOx removal performance of the SCR process depends on various factors such as catalytic factors (catalyst composition, shape, space velocity, etc.), temperature and flow rate distribution of the exhaust gas. Among them, the uniformity of the flow flowing into the catalyst bed plays the most important role. In this study, the flow characteristics in the SCR reactor in the design stage were simulated using a three-dimensional numerical analysis technique to confirm the uniformity of the airflow. Due to the limitation of the installation space, the shape of the inlet duct was compared with the two types of inlet duct shape because there were many curved sections of the inlet duct and the duct size margin was not large. The effect of inlet duct shape, guide vane or mixer installation, and venturi shape change on SCR reactor internal flow, airflow uniformity, and space utilization rate of ammonia concentration were studied. It was found that the uniformity of the airflow reaching the catalyst layer was greatly improved when an inlet duct with a shape that could suppress drift was applied and guide vanes were installed in the curved part of the inlet duct to properly distribute the process gas. In addition, the space utilization rate was greatly improved when the duct at the rear of the nozzle was applied as a venturi type rather than a mixer for uniform distribution of ammonia gas.

• 대기
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• 제26권1호
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• pp.35-45
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• 2016

Initialization of the global seasonal forecast system is as much important as the quality of the embedded climate model for the climate prediction in sub-seasonal time scale. Recent studies have emphasized the important role of soil moisture initialization, suggesting a significant increase in the prediction skill particularly in the mid-latitude land area where the influence of sea surface temperature in the tropics is less crucial and the potential predictability is supplemented by land-atmosphere interaction. This study developed a new soil moisture initialization method applicable to the KMA operational seasonal forecasting system. The method includes first the long-term integration of the offline land surface model driven by observed atmospheric forcing and precipitation. This soil moisture reanalysis is given for the initial state in the ensemble seasonal forecasts through a simple anomaly initialization technique to avoid the simulation drift caused by the systematic model bias. To evaluate the impact of the soil moisture initialization, two sets of long-term, 10-member ensemble experiment runs have been conducted for 1996~2009. As a result, the soil moisture initialization improves the prediction skill of surface air temperature significantly at the zero to one month forecast lead (up to ~60 days forecast lead), although the skill increase in precipitation is less significant. This study suggests that improvements of the prediction in the sub-seasonal timescale require the improvement in the quality of initial data as well as the adequate treatment of the model systematic bias.

• 전기전자학회논문지
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• 제11권4호
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• pp.272-278
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• 2007

본 논문에서는 최근 고출력 및 고온 분야의 반도체 분야에 널리 이용되고 있는 AlGaN/GaN 고 전자 이동도 트랜지스터 (High Electron Mobility Transistor, HEMT) 에 대해 DC (direct current) 특성과 열 특성을 기판을 달리하며 시뮬레이션을 수행하였다. 일반적으로 HEMT 소자의 전자 이동도 및 열전도 특성은 기판의 영향이 그 특성을 크게 좌우한다. 이러한 문제점으로 인해 GaN 기반의 HEMT 소자의 기판에 대한 연구가 활발히 진행되고 있다. 따라서, 일반적인 Drift-Diffusion 모델과 열 모델을 이용하여 Si, sapphire, SiC (silicon carbide)으로 각각 기판을 변화시키며 시뮬레이션을 하였다. 열 모델 시뮬레이션은 온도를 각각 300, 400, 500K로 변화시키며 그 결과를 비교, 해석 하였다. 전류-전압 (I-V) 특성을 T= 300 K, $V_{GS}$=1 V의 조건에서 시뮬레이션 한 결과, 드레인 포화전류 ($I_{D,max}$)의 값과 sapphire 기판은 189 mA/mm, SiC 기판은 293 mA/mm, Si 기판은 258 mA/mm 를 나타내었다. 또한 T= 500 K에서 최대 전달컨덕턴스($G_{m,max}$)는 각각 38, 50, 31 mS/mm 를 나타내었다.

• 한국산림과학회지
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• 제94권4호통권161호
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• pp.209-213
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• 2005

희귀수종 들쭉나무(Vaccinium uliginosum L.)의 유전자원 보존을 위한 분자유전학적 정보를 제공하고자 한라산 및 설악산 정상부에 국소적으로 분포하고 있는 2개 집단을 대상으로 I-SSR 표지자 분석을 수행하였다. 증폭된 I-SSR 산물은 총 68개였고, 유전다양성은 한라산 집단이 0.539로 설악산 집단(0.401) 보다 높았으며, 동일한 표지자로 분석된 타 희귀수종에 비해 상대적으로 높은 유전적 다양성을 보였다. AMOVA 분석 결과 전체 유전변이 중 66.5%가 각 집단 내 개체 간에 공통적으로 존재하며, 33.5%는 집단간 유전적 차이에 기인하는 것으로 추정되어 분석된 두 집단 간에 매우 높은 유전적 분화가 관찰되었다. 지리적으로 격리된 이들 집단 간의 높은 유전적 이질성은 두 집단이 각각 별개의 조상집단으로부터 유래되었을 가능성과 빙하기 이후 급격한 환경변화와 지리적 격리 등으로 인해 각 집단이 유전적 부동과정을 거치며 유전적 이질성이 증가하였을 가능성 등에 의해 설명될 수 있을 것으로 생각된다.