• Nuclear Engineering and Technology
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• 제50권4호
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• pp.542-552
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• 2018

Operators face challenges to plan alternative countermeasures when no procedure exists to address the current plant state. A model-based approach is desired to aid operators in acquiring plant resources and deriving response plans. Multilevel flow modeling (MFM) is a functional modeling methodology that can represent intentional knowledge about systems, which is essential in response planning. This article investigates the capabilities of MFM to plan alternatives. It is concluded that MFM has a knowledge capability to represent alternative means that are designed for given ends and a reasoning capability to identify alternative functions that can causally influence the goal achievement. The second capability can be applied to find originally unassociated means to achieve a goal. This is vital in a situation where all designed means have failed. A technique of procedure synthesis can be used to express identified alternatives as a series of operations. A case of station blackout occurring at the boiling water reactor is described. An MFM model of a boiling water reactor is built according to the analysis of goals and functions. The accident situations are defined by the model, and several alternative countermeasures in terms of operating procedures are generated to achieve the goal of core cooling.

• Journal of Power Electronics
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• 제16권5호
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• pp.1706-1715
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• 2016

In this paper, a single phase modified switched-diode topology for both symmetrical and asymmetrical cascaded multilevel inverters is presented. It consists of a Modified Switched-Diode Unit (MSDU) and a Twin Source Two Switch Unit (TSTSU) to produce distinct positive voltage levels according to the operating modes. An additional H-bridge synthesizes a voltage waveform, where the voltage levels of either polarity have less Total Harmonic Distortion (THD). Higher-level inverters can be built by cascading MSDUs. A comparative analysis is done with other topologies. The proposed topology results in reductions in the number of power switches, losses, installation area, voltage stress and converter cost. The Nearest Level Control (NLC) technique is employed to generate the gating signals for the power switches. To verify the performance of the proposed structure, simulation results are carried out by a PSIM under both steady state and dynamic conditions. Experimental results are presented to validate the simulation results.

• Journal of Power Electronics
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• 제16권2호
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• pp.490-497
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• 2016

The analysis of the switch status of each unit module of a cascaded multi-level inverter reveals that the working condition of the switch of a chopper arm causes unnecessary switching under the conventional unipolar sinusoidal pulse width modulation (SPWM). With an increase in the number of cascaded multilevel inverters, the superposition of unnecessary switching gradually occurs. In this work, we propose an improved SPWM strategy to reduce switching in cascaded multilevel inverters. Specifically, we analyze the switch state of the switch tube of a chopper arm of an H-bridge unit. The redundant switch is then removed, thereby reducing the switching frequency. Unlike the conventional unipolar SPWM technique, the improved SPWM method greatly reduces switching without altering the output quality of inverters. The conventional unipolar SPWM technique and the proposed method are applied to a five-level inverter. Simulation results show the superiority of the proposed strategy. Finally, a prototype is built in the laboratory. Experimental results verify the correctness of the proposed modulation strategy.

• Journal of Power Electronics
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• 제16권6호
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• pp.2294-2305
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• 2016

The introduction of a high-voltage direct-current (HVDC) system based on a modular multilevel converter (MMC) for wind farm integration has stimulated studies on methods to control this type of converter. This research article focuses on the control of the AC voltage and circulating current for a wind-farm-side MMC (WFS-MMC). After theoretical analysis, emotional learning (EL) controllers are proposed for the controls. The EL controllers are derived from the learning mechanisms of the amygdala and orbitofrontal cortex which make the WFS-MMC insensitive to variance in system parameters, power change, and fault in the grid. The d-axis and q-axis currents are respectively considered for the d-axis and q-axis voltage controls to improve the performance of AC voltage control. The practicability of the proposed control is verified under various conditions with a point-to-point MMC-HVDC system. Simulation results show that the proposed method is superior to the traditional proportional-integral controller.

• 한국통신학회논문지
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• 제32권3C호
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• pp.216-225
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• 2007

본 논문에서는 대표적인 반복 부호 알고리즘인 터보 부호, LDPC부호 TPC 등 세 가지 알고리즘에 대해 8PSK 이상의 다치 변조 방식 적용을 위해 수신단에서 비트 분리 방법을 제시한다. 수신된 I, Q 심볼만을 이용하여 세 비트 이상의 비트를 분리하기 위한 LLR 방식에 기초를 하여 LLR 방식의 단점인 복잡도를 개선하기 위해 Euclidean, MAX, Sector 방식을 제시하였으며, 세 가지 반복 부호에 대해 최적의 비트 분리 방법을 제시하였다.

• 한국정보처리학회논문지
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• 제4권10호
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• pp.2493-2500
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• 1997

대칭키 관리 시스템에서 계층적 구조를 지닌 다중 사용자 그룹에 대한 새로운 키관리 방안을 제안한다. 제안된 방식은 의사 랜덤치환에 의해 새성되는 트랩도어 일방향 치환을 이용하며, 구현시 시간과 공간적 측면에서 유리하기 때문에, 완전순서 집합과 부분순서가 있는 집합으로 구성되는 다단계 계층적 구조에 사용 가능하다. 또한, 다른 제안 방식과 비교하여 성능을 분석하고, 제안 방식이 키생성 시간과 키저장 크기에서 보다 효율적인 것을 보인다.

• 대한교통학회지
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• 제20권7호
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• pp.79-85
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• 2002

각 개인이 발생하는 통행 행태와 이들 가구 구성원간의 연관관계 및 영향에 대한 이해는 활동기반모형의 궁극적 목표라 할 수 있는 미래의 활동패턴 예측의 가장 기본이 되는 연구사항이라 할 수 있다. 일반적인 회귀 모형의 경우 개인의 활동/통행 패턴을 알아내기 위하여 모집단으로부터 수집되는 개인자료는 가구라는 부분모집단으로 세분화되어 계층적 구조(Hierarchical structure)의 성향을 고려하지 못하고 있어, 그 결과는 편이된 추정치를 낳는다. 따라서, 본 연구에서는 계층적 구조를 갖고 있는 자료를 이용하여 다수준 모형(Multi-Level Model)을 사용하여 개인의 활동/통행 패턴 영향을 규명해내고 활동/통행 패턴의 변화를 가구수준의 변동과 개인수준의 변동으로 나누어 분석하였다. 사용된 자료는 미국 Puget Sound 지역의 Transportation Panel 자료(PSTP)를 이용하였다. 분석 결과 개인의 통행사슬 발생모형에서 가구수준의 변동이 전체변동의 1/4를 차지하고 생계활동 지속시간 모형에서는 전체 변동의 1/8을 차지하는 등의 매우 큰 값을 나타내어 개인의 활동/통행 패턴 분석시 다수준 모형을 통한 분석의 필요성이 대두되었다.

• 한국표면공학회지
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• 제48권5호
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• pp.233-237
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• 2015

In order to investigate the potassium (K) gettering, Al-1%Si/$SiO_2$/PSG multilevel thin films were fabricated. Al-1%Si thin films and $SiO_2$/PSG passivations were deposited by using DC magnetron sputter techniques and APCVD (atmosphere pressure chemical vapor deposition), respectively. Heat treatment was carried out at $300^{\circ}C$ for 5 h in air. SIMS (secondary ion mass spectrometry) depth profiling analysis was used to determine the distribution of K, Al, Si, P, and other elements throughout the $SiO_2$/PSG passivated Al-1%Si thin film interconnections. Potassium peaks were observed throughout the $SiO_2$/PSG passivation layers, and especially the interface gettering at the $SiO_2$/PSG and at the Al-1%Si/$SiO_2$ interfaces was observed. Potassium gettering in Al-1%Si/$SiO_2$/PSG multilevel thin films is considered to be caused by a segregation type of gettering.

• 한국임상수의학회지
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• 제34권2호
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• pp.140-145
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• 2017

The goal of this study was to investigate risk factors associated with porcine reproductive and respiratory syndrome (PRRS) in pig farms in the Republic of Korea using logistic regression and a multilevel model. A cross-sectional study was applied to 305 pig farms with a questionnaire-based interview by veterinarians between March 2014 and February 2015. The questionnaire comprised eight categories: proximity to neighbors, disinfection, visitors, vehicles, insecticides, wild animals, gilts, and feeding. In total, 61 questions in eight categories related to pig farm biosecurity were investigated. Farms were classified as PRRS stable or unstable based on the results of an antibody test and PCR. For univariate analysis, keeping production records with computers (OR = 0.283, 95% CI = 0.056 - 1.425), accredited farm with no use of antibiotics (OR = 0.412, 95% CI = 0.134 - 1.269), reviewing health record of semen prior to purchasing (OR = 0.492, 95% CI = 0.152 - 1.589), complete isolation of runt pigs (OR = 0.264, 95% CI = 0.084 - 0.829), compulsory registering for visitors (OR = 0.424, 95% CI = 0.111 - 1.612), keeping records of insecticide history (OR = 0.406, 95% CI = 0.089 - 1.846), routine on-farm monitoring by veterinarians (OR = 0.314, 95% CI = 0.069 - 1.423), and use of on-farm checklist for biosecurity monitoring (OR = 0.313, 95% CI = 0.063 - 1.553) were found to decrease the probability of PRRS infection. Multivariate and multilevel analysis revealed only two factors, complete isolation of runt pigs (OR = 0.165, 95% CI = 0.045 - 0.602 and OR = 0.208, 95% CI = 0.055 - 0.782) and compulsory registering for visitors (OR = 0.106, 95% CI = 0.017 - 0.655 and OR = 0.119, 95% CI = 0.017 - 0.809) were found to decrease the probability of PRRS infection. The intracluster correlation coefficient of a province for multilevel model was 0.05. The results of this study might facilitate biosecurity measures for individual farms to reduce the probability of PRRS infection.

• 대한토목학회논문집
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• 제34권2호
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• pp.561-571
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• 2014

전라북도내 14개 시 군의 교통사고 자료를 활용하여 고령운전자의 교통사고 피해 심각성을 분석하였다. 교통사고는 1차적으로 개인 및 운전환경 속성과 2차적으로 도시관련 속성에 의해 영향을 받는 2단계 위계적 특성을 갖는 것으로 가정하였다. 위계적 특성을 고려한 피해 심각성에 대한 영향요인을 분석하기 위해 다수준분석모형을 활용하였다. 분석결과로서 65세 이후의 고령운전자는 연령이 증가할수록 교통사고로 인한 피해상황이 심각해짐을 보여주며 안전한 운전방법의 교육과 교통사고를 미연에 방지하기 위한 대안이 필요하다. 음주운전은 고령운전자에게 사고발생시 피해 심각성을 크게 할 경향이 높은데, 사망사고에 있어서 비고령자에 비해 발생비율이 약 3.0배 이상 높았다. 고령운전자는 야간 교통사고 발생빈도가 높은 편이나, 낮 시간대의 교통사고일수록 피해 심각성은 높아졌다. 고령운전자는 비고령자보다 흐린 날씨에서 사고 발생빈도가 높으나, 심각성에서는 맑은 날에 높아짐을 보였다. 습윤상태의 노면이 피해 심각성에 큰 영향을 주고 있는데, 비고령자에 비해서 고령운전자가 중상 및 사망비율도 높은 것으로 분석되었다.