• East Asian mathematical journal
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• 제33권4호
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• pp.333-351
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• 2017

Schools are expected to ultimately moderate the difference of inequality issues among social groups and reduce the achievement gaps. This study investigates this expectation, in particular, how students' mathematics achievements are influenced by their parents' education at the individual level and by collective responsibility for teaching at the school level as well as the interaction of the two. Using a two-level hierarchical linear model, this study indicates that a school collective responsibility has a larger positive effect on students' mathematics achievement when their parents' education level is high. This means that school's collective responsibility accelerates inequity in students' mathematics achievement. Knowing that collective responsibility has less of an effect on students whose parents' education is not high, researchers, schools, and school districts should continue to search for school effects that have more of a positive impact on the relationship between mathematics achievement for students whose parents' education is not high in order to have more equitable results for all students.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 학술대회 논문집 전문대학교육위원
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• pp.125-130
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• 2002

This paper examines the application of high voltage static var compensator(SVC) with cascade multilevel inverter which employs H~bridge inverter(HBI). The SVC system is modeled using the d-q transform which calculates the instantaneous reactive power. This model is used to design a controller and analyze the SVC system. From the mathematical model of the system, the design procedures of the circuit parameters Land C are presented in this thesis. To meet the specific total harmonic distortion(THD) and ripple factor of the capacitor voltage, the circuit parameters Land C are designed. Simulated and experimental results are also presented and discussed to validate the proposed schemes.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 춘계학술발표회논문집(1)
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• pp.340-345
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• 1996

Because of limited resources of time and information processing capability during abnormal situation, diagnosis is difficult tasks in nuclear power plant (NPP) operators. Moreover since minimizing of adverse consequences according to process abnormalities is vital for the safety of NPP, introducing of diagnosis support systems have particularly emphasized. However, considerable works to develop effective diagnostic support system are not sufficiently fulfilled because of the complexity of NPP is one of the major problems. To cope with this complexity, a lot of model-based diagnosis support systems have considered and implemented worldwide. In this paper, as a prior step to development of model-based diagnosis support systems, primary side of pressurized water reactor is functionally modeled by multilevel flow modeling (MFM) concept. MFM is suitable for complex system modeling and for diagnosis of abnormalities. Furthermore, knowledge-based diagnosis process, of NPP operator could be supported because this diagnosis strategy can represent operator's one.

• Journal of Power Electronics
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• 제18권2호
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• pp.467-481
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• 2018

Modular multilevel converter (MMC)-based high-voltage direct current (HVDC) presents attractive technical advantages and contributes to enhanced system operation and reduced oscillation damping in dynamic MMC-HVDC systems. We propose an advanced small-signal multi-terminal MMC-HVDC based on dynamic phasors and state space for power system stability analysis to enhance computational accuracy and reduce simulation time. In accordance with active and passive network control strategies for multi-terminal MMC-HVDC, the matchable small-signal stability models containing high harmonics and dynamics of internal variables are conducted, and a related theoretical derivation is carried out. The proposed advanced small-signal model is then compared with electromagnetic-transient and traditional small-signal state-space models by adopting a typical multi-terminal MMC-HVDC network with offshore wind generation. Simulation indicates that the advanced small-signal model can successfully follow the electromechanical transient response with small errors and can predict the damped oscillations. The validity and applicability of the proposed model are effectively confirmed.

• 전력전자학회논문지
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• 제23권5호
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• pp.359-365
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• 2018

This study introduces a model predictive control method for controlling a cascaded flying capacitor multilevel rectifier used as an AC-DC rectifier of a solid-state transformer for DC distribution systems. The proposed method reduces the number of states that need to be considered in model predictive control by separately controlling input current, output DC link voltage, and flying capacitor voltage. Thus, calculation time is shortened to facilitate the level expansion of the cascaded flying capacitor multilevel rectifier. The selection of weighting factors did not present difficulties because the weighting factors in the cost function of the conventional model predictive control are not used. The effectiveness of the proposed method is verified through computer simulation using powersim and experiment.

• 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.

• Asian Pacific Journal of Cancer Prevention
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• 제16권14호
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• pp.5787-5792
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• 2015

Background: Reported age standardized incidence rates for esophageal cancer in Iran are 0.88 and 6.15 for females and males, at fifth and the eighth ranks, respectively, of cancers overall. The present study aimed to map relative risk using more realistic and less problematic methods than common estimators. Materials and Methods: In this ecological investigation, the studied population consisted of all esophageal cancer patients in Iran from 2005 to 2007. The Bayesian multilevel space-time model with three levels of county, province, and time was used to measure the relative risk of esophageal cancer. Analyses were conducted using R package INLA. Results: The total number of registered patients was 7,160. According to the results, the three-level model with adjustment for risk factors of physical activity and smoking had the best fit among all models. The overall temporal trend was significantly increasing. At county level, Ahar, Marand, Salmas, Bojnoord, Saghez, Sarakhs, Shahroud and Torbatejam had the highest relative risks. Physical activity was found to have significant direct association with risk of developing esophageal cancer. Conclusions: Given to great variation across geographical areas, many different factors affect the incidence of esophageal cancer. Conducting further studies at the individual level in areas with high incidence could provide more detailed information on risk factors of esophageal cancer.

• 지역연구
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• 제36권1호
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• pp.69-88
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• 2020

최근 지역에 거주하는 구성원이 다양한 사회적 배경을 갖는 정도를 의미하는 사회적 다양성 논의가 확산되고 있다. 기존 연구들은 사회적 다양성이 사회적 신뢰, 사회자본 등 삶의 질과 높은 상관관계를 형성하는 개념들과 긍정적 영향관계가 있음을 제시한다. 사회적 다양성의 대칭적 개념인 사회적 분리가 주민의 삶에 미치는 부정적인 영향력이 사회 이슈임을 고려할 때 사회적 다양성과 삶의 질에 대한 직접적이고 심층적인 논의가 필요하다. 본 연구는 지역의 사회적 다양성이 개인의 삶의 질에 미치는 영향력을 다수준모형을 활용하여 분석하였다. 또한 기존 연구 결과에 기초해 전체표본에 대한 분석과 더불어 소득계층을 구분한 분석을 추가적으로 진행하였다. 그 결과, 투입된 다섯 개의 사회적 다양성 지표 중 주민 직업 유형의 다양성을 측정한 직업다양성이 삶의 질에 긍정적인 영향을 미치는 것으로 나타났다. 반면 소득다양성의 경우에는 동질성이 높을수록 삶의 질이 높아지는 것으로 나타났다. 이와 같은 분석은 이후 도시정책의 방향 설정에 유용한 정책적 함의를 제공할 것으로 기대한다.

• 대한건축학회논문집:계획계
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• 제35권8호
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• pp.101-109
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• 2019

Korea's transportation paradigm is shifting from a vehicle-oriented transportation plan to a pedestrian-friendly environment that emphasizes walking safety. However, the level of pedestrian traffic accidents in Korea is still high and serious. The purpose of this study is to investigate factors affecting the severity of pedestrians traffic accidents using the multilevel logistic regression model based on 2015-2017 pedestrian accidents data provided by the Traffic Accident Analysis System(TAAS). The main results of the multilevel logistic regression model showed that 89% of pedestrian traffic accidents in Seoul were explained by individual characteristics such as drivers and pedestrians, and 11% were explained by neighborhood environmental characteristics. The results are as follows : In the individual characteristics such as pedestrians and drivers, the older the pedestrians and the drivers, the higher the traffic accident severity. The severity of traffic accidents was high when the pedestrians were female and the drivers were male. In the case of accident types, traffic accidents were more serious in the cases of heavy vehicles, inclement weather, and occurring at intersections and crosswalks. The results of the neighborhood environmental characteristics are as follows. The intersection density and the crosswalk density tended to reduce the severity of traffic accidents. On the other hand, the traffic light density and the school zones were founded to related to the higher level of traffic accident severity. This study suggests that both individual and neighborhood environmental characteristics should be considered together to prevent and reduce the severity of pedestrian traffic accidents.

• 한국측량학회지
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• 제25권6_1호
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• pp.565-574
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• 2007

Because of most current cadastral systems maintain 2D geometric descriptions of parcels linked to administrative records, the system may not reflect current tendency to use space above and under the surface. The land has been used in multi-levels, e.g. constructions of multi-used complex buildings, subways and infrastructure above/under the ground. This cadastre situation of multilevel use of lands cannot be defined as cadastre objects (2D parcel-based) in the cadastre systems. This trend has requested a new system in which right to land is clearly and indisputably recorded because a right of ownership on a parcel relates to a space in 3D, not any more relates to 2D surface area. Therefore, this article proposes a 3D spatial data model to represent geometrical and topological data of 3D (property) situation on multilevel uses of lands in 3D cadastre systems, and a conceptual 3D cadastral model in Korea to design a conceptual schema for a 3D cadastre. Lastly, this paper presents the results of an experimental implementation of the 3D Cadastre to perform topological analyses based on 3D Network Data Model to identify spatial neighbors.