• 한국산업융합학회 논문집
• /
• 제23권1호
• /
• pp.65-71
• /
• 2020

Recently, interest in the DC transmission is rapidly increasing worldwide. In many countries and leading companies are prior to the aggressive development of HVDC technology and application. Especially, VSC-HVDC system has been widely applied to transfer power at long distance between power plant and power consumption area. Therefore in this paper, we analyzed the benefit-cost of VSC-HVDC system which has more advantages than existing transmission system. The proposed system is MMC(Modular Multilevel Converter) VSC-HVDC system that have stability of Power Grid, interconnect Large-scale New Power Generation Plants by prevents Blackout. And MMC VSC-HVDC system Reduced the loss importing foreign systems. And the benefits were calculated in four stages, and the costs were applied to the actual project. By evaluating the various avoidance costs compared to the benefit-cost, it was confirmed that MMC VSC-HVDC system was advantageous in system stability and economic and social benefits.

• Current Optics and Photonics
• /
• 제2권6호
• /
• pp.532-539
• /
• 2018

Multiple LED arrays can be utilized in visible-light communication (VLC) to improve communication efficiency, while maintaining smart illumination functionality through dimming control. This paper proposes a modulation scheme called "Spatial Intensity Modulation" (SIM), where the effective number of turned-on LEDs is employed for data modulation and dimming control in VLC systems. Unlike the conventional pulse-amplitude modulation (PAM), symbol intensity levels are not determined by the amplitude levels of a VLC signal from each LED, but by counting the number of turned-on LEDs, illuminating with a single amplitude level. Because the intensity of a SIM symbol and the target dimming level are determined solely in the spatial domain, the problems of conventional PAM-based VLC and related MIMO VLC schemes, such as unstable dimming control, non uniform illumination functionality, and burdens of channel prediction, can be solved. By varying the number and formation of turned-on LEDs around the target dimming level in time, the proposed SIM scheme guarantees homogeneous illumination over a target area. An analysis of the dimming capacity, which is the achievable communication rate under the target dimming level in VLC, is provided by deriving the turn-on probability to maximize the entropy of the SIM-based VLC system. In addition, a practical design of dimmable SIM scheme applying the multilevel inverse source coding (MISC) method is proposed. The simulation results under a range of parameters provide baseline data to verify the performance of the proposed dimmable SIM scheme and applications in real systems.

• Journal of Preventive Medicine and Public Health
• /
• 제48권1호
• /
• pp.18-27
• /
• 2015

Objectives: Civic participation, that which directly influences important decisions in our personal lives, is considered necessary for developing a society. We hypothesized that civic participation might be related to self-rated health status. Methods: We constructed a multi-level analysis using data from the World Value Survey (44 countries, n=50 859). Results: People who participated in voting and voluntary social activities tended to report better subjective health than those who did not vote or participate in social activities, after controlling for socio-demographic factors at the individual level. A negative association with unconventional political activity and subjective health was found, but this effect disappeared in a subset analysis of only the 18 Organization for Economic Cooperation and Development (OECD) countries. Moreover, social participation and unconventional political participation had a statistically significant contextual association with subjective health status, but this relationship was not consistent throughout the analysis. In the analysis of the 44 countries, social participation was of borderline significance, while in the subset analysis of the OECD countries unconventional political participation was a stronger contextual determinant of subjective health. The democratic index was a significant factor in determining self-rated health in both analyses, while public health expenditure was a significant factor in analysis of 18 countries. Conclusions: Our investigation suggests that civic participation, including unconventional political activity at the contextual level, might be a significant determinant of health status of a country.

• 산업노동연구
• /
• 제23권2호
• /
• pp.169-193
• /
• 2017

본 연구는 우리나라에서 동학적 고용안정성을 진단하기 위해서 고용유지율에 영향을 미치는 결정요인을 분석하였다. 고용유지 결정요인 분석을 위해서 사업체 패널자료와 고용보험 이력자료를 연계하고, 다층적 위계적 자료 분석에 적절한 다층 분석모형을 활용하여 결정요인을 분석하였다. 분석결과, 우리나라에서 고용안정성이 매우 낮은 것은 임금수준이 낮고 비정규직 활용수준이 높은 주변부 부문이 광범위하게 존재하기 때문으로 추정된다. 또한 우리나라의 고용구조는 고용과 실업이 반복되는 단기간 고용이 상당한 영역을 차지하면서 전반적으로 고용안정성이 약한 것으로 평가된다. 이러한 사실은 기업이나 개인적 차원에서 숙련향상 및 숙련형성기회가 제한되면서 지속적인 성장 제약요인으로 작용할 가능성이 높으며, 이에 대한 적극적 대응책으로 고용구조의 질적 개선노력이 요구된다.

• Journal of Preventive Medicine and Public Health
• /
• 제45권2호
• /
• pp.90-97
• /
• 2012

Objectives: While there have been many quantitative studies on the public's attitude towards mental illnesses, it is hard to find quantitative study which focused on the contextual effect on the public's attitude. The purpose of this study was to identify factors that affect the public's beliefs and attitudes including contextual effects. Methods: We analyzed survey on the public's beliefs and attitudes towards mental illness in Korea with multi-level analysis. We analyzed the public's beliefs and attitudes in terms of prejudice as an intermediate outcome and social distance as a final outcome. Then, we focused on the associations of factors, which were individual and regional socioeconomic factors, familiarity, and knowledge based on the comparison of the intermediate and final outcomes. Results: Prejudice was not explained by regional variables but was only correlated with individual factors. Prejudice increased with age and decreased by high education level. However, social distance controlling for prejudice increased in females, in people with a high education level, and in regions with a high education level and a high proportion of the old. Therefore, social distance without controlling for prejudice increased in females, in the elderly, in highly educated people, and in regions with a high education and aged community. Conclusions: The result of the multi-level analysis for the regional variables suggests that social distance for mental illness are not only determined by individual factors but also influenced by the surroundings so that it could be tackled sufficiently with appropriate considering of the relevant regional context with individual characteristics.

• 한국콘텐츠학회논문지
• /
• 제17권8호
• /
• pp.186-195
• /
• 2017

본 연구는 부모의 학대와 청소년의 삶의 만족도와의 관계에서 또래애착, 자아존중감의 매개효과를 검증함을 목적으로 한다. 이를 위하여 층화다단계집락표집에 의해 표본으로 선정된 한국아동 청소년 패널 조사의 초4패널 6차년도 자료 중 중학교 3학년 1,823명의 자료를 분석하였다. 수집된 자료는 SPSS WIN 21.0 프로그램을 이용하였고, 빈도분석, 기술통계량분석, 상관분석, 경로분석, sobel test를 하였다. 분석한 결과는 첫째, 부모의 학대가 청소년의 삶의 만족도에 유의미한 부적영향을 주었다. 둘째, 부모의 학대와 청소년의 삶의 만족도와의 관계에서 또래애착은 부분매개 효과를 나타냈다. 셋째, 부모의 학대와 청소년의 삶의 만족도와의 관계에서 자아존중감은 완전매개 효과를 나타냈다. 이러한 결과를 토대로 하여 또래애착, 자아존중감 향상방안을 제시하였다. 후속 연구자는 청소년의 삶의 만족도를 향상시킬 수 있는 다양한 환경적 요인을 추가하는 연구가 필요하다.

• 전기전자학회논문지
• /
• 제23권4호
• /
• pp.1218-1223
• /
• 2019

HVDC 시스템에서 풀-브리지 서브 모듈 구조는 하프브리지 서브 모듈에 비해 부품 수가 증가하지만 100 % 여유율 확보가 가능하여 고장률을 크게 줄일 수 있다. 그러나 풀-브리지 서브 모듈은 여유율 보장과 암(arm) 단락 방지를 위한 데드 타임(dead-time)을 확보하기 위해 복잡한 제어 알고리즘이 필요하다. 이 문제를 해결하기 위해 풀-브리지 서브 모듈과 동일한 부품 수와 100 % 여유율을 갖는 병렬 하프브리지 구성의 고장률을 분석한다. 기존의 부품 고장 분석에 고장나무분석 방법을 적용하여 서브 모듈의 동작 위험을 반영함으로써 서브 모듈의 수명주기를 보다 정확하게 예측할 수 있다. 병렬 하프브리지 서브모듈의 타당성 검증을 위해 FTA 기반 분석 방법과 기존의 PCA 기반 방법으로 분석된 고장률을 비교한다.

• 해양환경안전학회지
• /
• 제25권6호
• /
• pp.802-808
• /
• 2019

직류전동기는 속도제어가 간단하고, 출력 토크특성이 우수한 장점으로 윈치나 카고 펌프 모터 등으로 선박에서 많이 사용되었으며, 전기추진선박이 도입된 초기에는 선박용 추진전동기로도 적용되었다. 하지만 브러시와 정류기와 같은 기계적 정류장치의 단점으로 인해 최근에는 직류전동기와 전기적인 특성은 매우 유사하지만 기계적인 정류장치를 설치하지 않고 반도체 소자를 이용한 전자적인 정류장치를 사용하는 브러시리스 직류전동기의 사용이 증가하고 있다. 기존의 브러시리스 직류전동기를 구동하기 위한 인버터 시스템은 2상여자방식을 사용하므로 역기전력파형이 사다리꼴모양으로 되며, 이로인해 전류가 흐르는 권선이 바뀌는 상전류 전환 구간에서 고조파와 토크리플이 발생하게 된다. 이러한 고조파와 토크리플을 저감하기 위한 다양한 방안이 연구되어 발표되었으며, 본 연구에서는 전력분석프로그램을 이용하여 브러시리스 직류전동기의 구동회로에 비례적분 속도전류제어기 알고리즘을 구현한 Cascaded H-Bridge 멀티레벨 인버터를 적용하였다. 모델링한 브러시리스 직류전동기의 시뮬레이션을 통해 제안하는 전동기의 구동방식을 적용하는 경우에 기존의 구동방식에 비해 전동기 입력측 전압파형 개선과 고조파 및 토크리플이 현저히 저감되는 결과를 확인할 수 있었다.

• Asian Pacific Journal of Cancer Prevention
• /
• 제14권10호
• /
• pp.6019-6023
• /
• 2013

Lung cancer, one of the leading causes of cancer-related deaths, usually appears as solitary pulmonary nodules (SPNs) which are hard to diagnose using the naked eye. In this paper, curvelet-based textural features and clinical parameters are used with three prediction models [a multilevel model, a least absolute shrinkage and selection operator (LASSO) regression method, and a support vector machine (SVM)] to improve the diagnosis of benign and malignant SPNs. Dimensionality reduction of the original curvelet-based textural features was achieved using principal component analysis. In addition, non-conditional logistical regression was used to find clinical predictors among demographic parameters and morphological features. The results showed that, combined with 11 clinical predictors, the accuracy rates using 12 principal components were higher than those using the original curvelet-based textural features. To evaluate the models, 10-fold cross validation and back substitution were applied. The results obtained, respectively, were 0.8549 and 0.9221 for the LASSO method, 0.9443 and 0.9831 for SVM, and 0.8722 and 0.9722 for the multilevel model. All in all, it was found that using curvelet-based textural features after dimensionality reduction and using clinical predictors, the highest accuracy rate was achieved with SVM. The method may be used as an auxiliary tool to differentiate between benign and malignant SPNs in CT images.

• Asian Pacific Journal of Cancer Prevention
• /
• 제14권9호
• /
• pp.5325-5329
• /
• 2013

Objectives: Although there are many reports about the risk of breast cancer, few have reported clinical factors including history of breast-related or other diseases that affect the prevalence of breast cancer. This study explores these risk factors for breast cancer cases reported in Beijing in 2009. Materials and Methods: Data were derived from a Beijing breast cancer screening performed in 2009, of 568,000 women, from 16 districts of Beijing, all aged between 40 and 60 years. In this study, multilevel statistical modeling was used to identify clinical factors that affect the prevalence of breast cancer and to provide more reliable evidence for clinical diagnostics by using screening data. Results and Conclusion: Those women who had organ transplants, compared with those with none, were associated with breast cancer with an odds ratio (OR)=65.352 [95% confidence interval (CI): 8.488-503.165] and those with solid breast mass compared with none had OR=1.384 (95% CI: 1.022-1.873). Malignant tendency was strongly associated with increased risk of breast cancer, OR=207.999(95% CI: 151.950-284.721). The risk of breast cancer increased with age, $OR_1$=2.759 (95% CI: 1.837-4.144, 56-60 vs. 40-45), $OR_2$=2.047 (95% CI: 1.394-3.077, 51-55 vs. 40-45), $OR_3$=1.668 (95% CI: 1.145-2.431). Normal results of B ultrasonic examination show a lower risk among participants, OR= 0.136 (95% CI: 0.085-0.218). Those women with ductal papilloma compared with none were associated with breast cancer, OR=6.524 (95% CI: 1.871-22.746). Therefore, this study suggests that clinical doctors should pay attention to these high-risk factors.