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보건조사연구에서 다변량결측치가 내포된 자료를 효율적으로 분석하기 위한 통계학적 방법
김동기,박은철,손명세,김한중,박형욱,안재형,임종건,송기준,Kim, Dong-Kee,Park, Eun-Cheol,Sohn, Myong-Sei,Kim, Han-Joong,Park, Hyung-Uk,Ahn, Chae-Hyung,Lim, Jong-Gun,Song, Ki-Jun 대한예방의학회 1998 예방의학회지 Vol.31 No.4
Missing observations are common in medical research and health survey research. Several statistical methods to handle the missing data problem have been proposed. The EM algorithm (Expectation-Maximization algorithm) is one of the ways of efficiently handling the missing data problem based on sufficient statistics. In this paper, we developed statistical models and methods for survey data with multivariate missing observations. Especially, we adopted the EM algorithm to handle the multivariate missing observations. We assume that the multivariate observations follow a multivariate normal distribution, where the mean vector and the covariance matrix are primarily of interest. We applied the proposed statistical method to analyze data from a health survey. The data set we used came from a physician survey on Resource-Based Relative Value Scale(RBRVS). In addition to the EM algorithm, we applied the complete case analysis, which uses only completely observed cases, and the available case analysis, which utilizes all available information. The residual and normal probability plots were evaluated to access the assumption of normality. We found that the residual sum of squares from the EM algorithm was smaller than those of the complete-case and the available-case analyses.
김동기,정진호,권영우,Kim Dong-Ki,Jeong Jin-Ho,Kwon Young-Woo 한국전자파학회 2005 한국전자파학회논문지 Vol.16 No.5
본 연구를 통하여 60 GHz근방의 V-band에서 도파관과 MMIC 집적을 위한 도파관-CPW변환 구조가 개발되었다. 수치 해석과 반복적인 실험을 통하여 두 가지 형태의 변환 구조를 제작하였으며, 손실이 적은 수정 기판을 이용하여 광대역 및 저손실 특성을 갖도록 설계하였다 개발된 변환 구조는 재현성이 뛰어나고, 금속 가공의 정밀도가 특성을 크게 변화시키지 않아 기존의 커넥터보다 저 비용으로 제작이 가능하였다. 본 연구를 통해 제안된 두 가지 형태의 도파관-CPW 변환 구조를 back-to-back으로 연결하여 특정한 결과 공진 구간을 제외하고 두 구조 모두 $53\~60 GHz$에서 삽입 손실은 1.9 dB 이하, 반사 손실은 14 dB 이상의 특성을 보였다. In this study, waveguide-to-CPW transitions were developed for integrating waveguide and MMIC at V-band. The finite element method for numerical analysis and repeated experiments were performed to propose two types of waveguide-to-CPW transition. Using quartz substrate, proposed structures were designed for low loss as well as broadband characteristics. These waveguide-to-CPW transitions showed a good reliability and insensitivity to matching precision, and they could be fabricated with lower cost than that of the conventional connectors. Proposed two types of the structure showed insertion loss less than 1.9 dB and return loss better than 14 dB from 53 GHz to 60 GHz except unwanted resonance region, respectively.
혈소판 농축 혈장과 혼합된 자가골 및 이종골 이식재가 치주 조직의 재생에 미치는 효과
김동기,임성빈,정진형,홍기석,Kim, Dong-Gi,Lim, Sung-Bin,Chung, Chin-Hyung,Hong, Ki-Seok 대한치주과학회 2004 Journal of Periodontal & Implant Science Vol.34 No.3
Regeneration of Periodontium with PRP does not only improve regeneration rate and density of bone but have a possibility to estimate faster healing process for soft tissue. And also, autogenous bone and xenogenic bone graft are effective on regeneration of periodontium. The purpose of this study is to evaluate the effectiveness of autogenous bone and xenogenic bone $(BBP^{(R)})$ grafts with the PRP technique on regeneration of periodontium. 52 Generally healthy Pt. who had pocket depth 5mm at any of 6 surfaces of the teeth were in the study at Dept. of Perio. in Dankook Dental Hospital. Open Flap was treated for 18 infra-bony pockets as control group, autogenous bone with PRP was inserted for 25 infrabony pockets as first test group, and $(BBP^{(R)})$ with PRP was inserted for 22 infrabony pockets as 2nd test group. Then evaluation was made after 3 and 6 months 1. There were significant differences between average probing pocket depth and clinical attachment level of 3, 6 months and minimal and maximal attachment level after 6 months each other. 2. There were significant differences in average probing pocket depth of control group and 2nd experimental group between 1 and 6 months. For clinical attachment level and minimal and maximal proving attachment level, there was a significant difference after 6 month of surgery. 3. There was no significant difference between two test groups for average probing depth, clinical attachment level, and minimal and maximal probing attachment level. As the result, PRP with bone graft could be very effective for regeneration of periodontium and there was no difference between xenogenic bone and autogenous bone.
슬롯라인-마이크로스트립 변환을 이용한 고효율 V-band 전력 결합 모듈
김동기,정진호,권영우,Kim Dong-Ki,Jeong Jin-Ho,Kwon Young-Woo 한국전자파학회 2005 한국전자파학회논문지 Vol.16 No.6
Two high-efficiency and high power power-combing modules were developed using slotline-to-microstrip transition at V-band. Power-combining modules incorporating two MMIC power amplifiers demonstrated combining efficiencies higher than $80\%$(maximum $86\%$) with saturated output power of 22.96 dBm and 22.81 dBm, respectively. The measurement of back-to-back connected combiners demonstrated insertion loss less than 1.2 dB with return loss better than 15 dB around 60 GHz, respectively. 본 연구를 통하여 슬롯라인-마이크로스트립 변환을 이용한 고효율 전력 결합 모듈을 개발하였다. 제작된 전력 결합 모듈은 본 논문에서 제안하는 두 가지 형태의 전력 결합기를 이용하여 슬롯라인 중앙에서 도파관을 통해 입사된 전력을 분배하고 전력 증폭기를 거친 후 다시 전력이 결합되도록 하였다. 제작한 결과 58.5 GHz와 60 GHz에서 각각 22.96 dBm, 22.81 dBm의 포화 출력 전력과 $80\%$ 이상의(최대 $86\%$)고효율 전력 결합도를 얻을 수 있었다. 각각의 전력 결합기를 back-to-back으로 연결하여 손실을 측정한 경우 두 가지 형태 모두 60 GHz 근방에서 1.2 dB 내의 우수한 삽입손실을 보였으며 반사 손실은 15 dB 이상의 특성을 보였다.
김동기(Dong Ki Kim),김원태(Won Tae Kim),강신재(Shin Jae Kang),오제하(Jae Ha Oh),송준혁(Joon Hyuk Song) 한국자동차공학회 2008 한국자동차공학회 지부 학술대회 논문집 Vol.2008 No.11
Structures, characteristics and correspodning mechanisms will be correlated with regard to various components in Low Temperature Solid Oxide Fuel Cells. Special emphases are placed on electrolytes (ceria-based), electrodes (of mixed conduction), and the corresponding microstructure, in combination with a novel processing using rapid thermal sintering techniques. Materials design and processing development proposed in this research, aims at contributing to low temperature solid oxide fuel cells using rapid thermal annealing. The current project will establish an effective processing tool for sintering electrolytes and can lead to novel nanoscale microstructure. Furthermore, reliability in solid oxide fuel cells will be significantly enhanced through feed-back with research counterparts. Finally, teamwork study consisting of undergraduate and graduate students will give them a chance of learning , processing, theory and applications in SOFC technology and will help domestic energy industries internationally competitive.
철도노선선정에 영향을 미치는 주요환경항목 정량화에 관한 연구
김동기(Kim Dong-ki),박용걸(Park Yong-Gul),정우성(Jung Woo-Sung) 대한토목학회 2009 대한토목학회논문집 D Vol.29 No.6D
철도는 다른 육상교통수단보다 에너지 효율성이 높은 환경 친화적인 교통수단이다. 예비타당성조사와 철도노선 선정 과정에서 에너지 효율성과 환경에 관한 문제들이 일반적으로 고려되고 있다. 철도노선 선정에서는 지형적인 특성 그리고 시설물의 관리와 운영을 중심으로 선정되고 있다. 철도노선선정에 영향을 미치는 환경관련 문제에 대해서 본 연구는 집중적으로 검토 분석하였다. 본 연구는 철도 및 환경전문가 그리고 철도 노선선정에 관련된 전문가 의견을 검토 분석하여 환경에 영향을 미치는 주요 항목의 가중치를 선정하였다. 환경 친화적인 철도노선을 선정하기 위하여 여러 대안이 비교되어야 하고 각 대안의 평가는 환경성을 검토하여야 한다. 이 문제를 해결하기 위해 본 연구에서는 계층구조를 이용하여 복잡한 문제를 간단하고 객관적으로 결론 내리는데 용이한 AHP 기법을 이용하였다. 이에 따라 전문가에 의한 환경평가항목의 가중치를 기본 값으로 정하고 GUI를 활용한 정량화 시스템을 개발하였다. The energy efficiency and environment-friendly aspect of the railway system would be superior to other on-land transportation systems. In a preliminary feasibility study stage and selection of optimal railway route, the energy efficiency and problems related to environment are usually considered. For the selection of optimal railway route, geographical features and facility of management are generally considered. Environment effect factors for the selection of environment-friendly railway router are focused and studied in this paper. In this study, various analysis of opinion of specialists (railway, environment, transport, urban planning, survey) and the guideline for construction of environment-friendly railway were accomplished. From these results of various analysis, 7 major categories (topography/geology, flora and fauna, Nature Property, air quality, water quality, noise/vibration, visual impact/cultural assets) were extracted, To select environment friendly railway route, many alternatives should be compared optimal route must be selected by a comprehensive assessment considering these 7 categories. To solve this problem, the selected method was AHP which simplifies the complex problems utilizing hierarchy, quantifying qualitative problems through 1: 1 comparison, and extracting objective conclusions by maintaining consistency. As a result, a GUI-based program was developed which provides basic values of weighted parameters of each category defined by specialists, and a quantification of detailed assessment guidelines to ensures consistency.
자동차 연료 펌프용 BLDC 모터의 전자기적인 소음 저감에 관한 연구
김동기(Dong-Ki Kim),이승우(Seung-Woo Lee),윤덕용(Duck-Yong Yoon) 대한전기학회 2019 전기학회논문지 Vol.68 No.2
This paper proposes a driving method in order to reduce the electromagnetic noise of blushless DC motor for fuel pump of vehicles. In recent years, these motors have been widely employed in the electric fuel pumps because of its high-efficiency, high-reliability, compact size, light weight, and simple control method. However, despite the various advantages, brushless DC motors have realistic problems. These problems are acoustic noise and vibration, which are caused by torque ripple and sudden current fluctuation in the stator windings due to the mechanical structures and control methods. If the mechanical structures are redesigned or the control methods are improved, both cogging torque and torque ripple due to commutation can be reduced. Nevertheless, if quasi-square-wave currents are supplied to these motors by conventional methods, the stator windings may generate the electromagnetic noise and vibration within the audio frequency bands. In this paper, a sinusoidal-wave driving method is proposed to suppress the fluctuating currents. The reduction effects on noise and vibration are verified through computer simulations and experiments.
김동기(Dong Ki Kim)(金東基),박수지(Su Sie Park)(朴秀智) 위기관리 이론과 실천 2013 Crisisonomy Vol.9 No.11
본 연구는 중증 장애인이 장애인활동지원서비스에서 경험한 학대와 학대경험에 영향을 미치는 요인에 대하여 분석하였다. 학대경험에 영향을 미치는 요인으로는 이용자 특성으로 인구사회학적 요인과 서비스 이용 요인, 그리고 공급 특성으로 활동보조인 요인, 전담인력요인, 기관요인을 고려하였다. 본 연구는 분석 자료로 보건복지부가 2012년 실시한 활동지원제도 실태조사를 활용하였다. 이 데이터는 활동지원서비스를 이용하고 있는 1급 등록장애인 1000명을 대상으로 하여 전국 91개 국민연금공단 지사에서 수집되었다. 분석 결과 중증 장애인의 학대경험에 영향을 미치는 이용자 특성으로 연령, 학력, 우울, 장애유형, 서비스 이용시간 그리고 공급 특성으로 서비스 제공자인 활동보조인의 성별, 서비스 제공 태도, 기관이 긴급한 경우에 행하는 적절한 대응의 요인이 통계적으로 유의미하게 나타났다. 이러한 분석결과를 바탕으로 결론에서는 정기적인 기관 모니터링, 기관의 보수교육 강화, 서비스 단가의 개선, 기관 전담인력의 수적기준 제시의 필요성 등을 제언하였다. This study analyze a influence of service agency and service consumer characteristics, on the essential standard "safety from mistreatment", in a provision of personal assistance service for disabled. For this purpose is used as a secondary date 「A survey on personal assistance service for disabled」, which is investigated by Ministry of Health and Human Service in 2012. As a results is founded influences of the following, also age, education, physical disability and depression, as service consumers characteristics. On the service provision side, the followings affect on "safety of service consumer from mistreatment", also, thoughtful attitude and gender of service provider, service hours and adequately answer the emergency call, as service agency characteristics. Finally, it suggests a regular monitering of service, reinforcement of education for service provider, improvement of service price, presentation of personal size as implications for a attainment to security of "safety from mistreatment" in a provision of personal assistance service for disabled.