• 전기학회논문지P
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• 제66권2호
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• pp.63-68
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• 2017

This paper proposes a new non-isolated DC conversion circuit topology of the voltage source coupled inductor series resonant high-frequency PFM controlled boost chopper type DC-DC power converter using two in one IGBT power module, which can efficiently operate under a principle of zero current soft switching for wide output regulation voltage setting ranges and wide fluctuation of the input DC side voltage as well as the load variation ranges. Its steady state operating principle and the output voltage regulation characteristics in the open-loop-based output voltage control scheme without PI controller loop are described and evaluated from theoretical and experimented viewpoints. Finally, in this paper the computer-aided simulation steady-state analysis and the experimental results are presented in order to prove the effectiveness and the validity of voltage regulation characteristics of the proposed series resonant zero current soft switching boost chopper type DC-DC power converter circuit using IGBTs which is based on simple pulse frequency modulation strategy more than, 20kHz.

• Wind and Structures
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• 제13권3호
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• pp.235-256
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• 2010

The aeroelastic stability of bridge decks equipped with multiple tuned mass dampers is studied. The problem is attacked in the time domain, by representing self-excited loads with the aid of aerodynamic indicial functions approximated by truncated series of exponential filters. This approach allows to reduce the aeroelastic stability analysis in the form of a direct eigenvalue problem, by introducing an additional state variable for each exponential term adopted in the approximation of indicial functions. A general probabilistic framework for the optimal robust design of multiple tuned mass dampers is proposed, in which all possible sources of uncertainties can be accounted for. For the purposes of this study, the method is also simplified in a form which requires a lower computational effort and it is then applied to a general case study in order to analyze the control effectiveness of regular and irregular multiple tuned mass dampers. A special care is devoted to mistuning effects caused by random variations of the target frequency. Regular multiple tuned mass dampers are seen to improve both control effectiveness and robustness with respect to single tuned mass dampers. However, those devices exhibit an asymmetric behavior with respect to frequency mistuning, which may weaken their feasibility for technical applications. In order to overcome this drawback, an irregular multiple tuned mass damper is conceived which is based on unequal mass distribution. The optimal design of this device is finally pursued via a full domain search, which evidences a remarkable robustness against frequency mistuning, in the sense of the simplified design approach.

• Journal of Power Electronics
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• 제18권2호
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• pp.482-491
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• 2018

The practical design methodology of a three-phase dual active bridge (3ph-DAB) converter applied to low voltage direct current (LVDC) applications is proposed by using a mathematical model based on the steady-state operation. An analysis of the small-signal model (SSM) is important for the design of a proper controller to improve the stability and dynamics of the converter. The proposed lead-lag controller for the 3ph-DAB converter is designed with a simplified SSM analysis including an equivalent series resistor (ESR) for the output capacitor. The proposed controller can compensate the effects of the ESR zero of the output capacitor in the control-to-output voltage transfer function that can cause high-frequency noises. In addition, the performance of the power converter can be improved by using a controller designed by a SSM analysis without additional cost. The accuracy of the simplified SSM including the ESR zero of the output capacitor is verified by simulation software (PSIM). The design methodology of the 3ph-DAB converter and the performance of the proposed controller are verified by experimental results obtained with a 5-kW prototype 3ph-DAB converter.

• Carbon letters
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• 제6권1호
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• pp.41-46
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• 2005

Plasma carbon blacks of 20~30 nm diameter were synthesized by direct decomposition of natural gas using a hybrid plasma torch system with 50 kW direct current and 4 MHz of radio frequency. The insulating rector which inside diameter of 400 mm and length of 1500 mm, respectively was kept at 300~$400^{\circ}C$ during the preparation. The ultimate analysis of plasma carbon blacks reveals that the raw plasma carbon blacks contains a large quantity of volatile which is mainly consist of hydrogen. Therefore devolatilization of raw plasma carbon blacks were carried out at $900^{\circ}C$ for one hour under nitrogen atmosphere. The devolatilization leads to the decrease in electrical resistivity and surface oxygen functional groups of plasma carbon black significantly. In order to investigate the plasma carbon as a catalyst support, devolatilized plasma black at $900^{\circ}C$ (DPB) supported PtAu catalyst was synthesized by sodium boronhydride reduction method. Electrochemical measurements and direct formic acid fuel cell test indicated that catalytic activity of DPB supported PtAu catalyst for formic acid oxidation was similar to that of Vulcan XC-72 of commercial carbon black supported one.

• 한국정보과학회논문지:데이타베이스
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• 제31권2호
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• pp.91-98
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• 2004

DHP 연관 규칙 탐사 알고리즘은 후보 빈발 항목 집합들에 대한 계수를 유지하기 위한 해쉬트리의 크기를 가능한 한 줄이기 위하여, 독립된 직접 해쉬 테이블을 미리 준비해 놓았다가 후보 빈발 항목 집합을 생성할 때 적용함으로써 전지 효과를 얻는다. 이 때 직접 해쉬 테이블의 크기가 클수록 전지효과는 커지며, 특히 길이 2인 후보 빈발 항목 집합을 생성하는 단계에서의 전지 효과는 알고리즘 전체의 성능을 좌우할 만큼 큰 영향을 발휘한다. 따라서 급속도로 보편화되고 있는 대용량 주기억장치 시스템 추세에 따라 단계 2에서의 직접 해쉬 테이블 크기의 극단적인 증가에 대한 시도가 이루어지고 있으며, 이러한 것 중의 하나가 완전 해쉬 테이블이다. 그러나 단계 2에서의 완전 해쉬 테이블을 사용할 경우, 이를 단순히 기존 DHP 알고리즘에 적용하여 버켓 크기(｜H$_2$｜)만을 재 설정하는 것 보다, DHP 알고리즘 자체를 조금 변경했을 때 약 20% 이상의 추가 성능 이득을 얻을 수 있음이 밝혀졌다. 이 논문에서는 단계 2에서의 완전 해쉬 테이블의 타당성을 조명해 본 후, 그 특성을 충분히 활용하도록 DHP를 개선한 PHP 알고리즘을 제안하며 그 결과를 실험적 환경에서 검증한다.

• 대한간호학회지
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• 제33권1호
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• pp.122-129
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• 2003

Purpose: The purpose of this study is to examine the difference of direct nursing activity and patient outcomes as mortality rate, complication rate, readmission rate and length of stay related to graded fee of nursing management for inpatient. Method: The subjects of this study were 44 general hospitals with more than 500 beds. Data totaled to 86,044 claims provided to inpatients in Jan. 2001 requested by an electronic data interchange from a Health Insurance Review Agency. The data was analyzed by SPSS win(ver.10.0) and statistical methods used were frequency, one-way ANOVA, $X^2$-Test and regression. Result: Synthetic judgment through performance index and 95% confidence interval, direct nursing activity showed to provided adequate quality of nursing care on 2nd, 3rd, 4th and 6th nursing degree. Also, patient outcomes showed difference by graded fee of nursing management for inpatient. Mortality rate of 2nd was the lowest with P.I. 67.9, 3rd, 5th, 6th, 4th in order. In case of complication rate, 2nd, 3rd and 4th were lower than other nursing degree. Readmission rate of 4th and 5th was the lowest. Length of stay of 2nd was the shortest with P.I. 88.3, 3rd, 4th, 5th, 4th, 6th in order. Conclusion: The findings from this study showed that, the higher nurse-to-patient ratio, the greater amount of direct nursing care activity for the patient. Also, the more direct nursing activities influenced a lower mortality rate, complication rate and readmission rate, shorter length of stay.

• 간호행정학회지
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• 제8권3호
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• pp.475-488
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• 2002

Purpose : The purpose of this study is to establish a basis of patient classification in the ICU by selecting the determination critical indicator of special nursing activities that show high interrilation with daily total nursing care time. Method : This study is composed of the six steps. The first step is the listing direct nursing activities in the ICU. The last step is the determination indicator of each group were selected on the basis of their relationship to the daily total nursing care time of each patient classification group and each nursing activity. Result : Result shows that: 1. direct nursing activities in the ICU are 149 items of 13 territories. 2. the average time and frequency for each direct nursing activities 3. total direct nursing care time of 42 patients in ICU for 2 days. According to the results of the Cluster analysis, the first group is 10 people, the second group is 13 people, the third group is 16 people, the fourth group is 3 people. 4. Determination critical indicator is the item that is r>0.6(p<0.05) of Pearson Correlation between each patient daily total nursing care time and 149 items of nursing activities. The nursing activities selected were as follows: 2 items in the first group, 17 items in the second group. 16 items in the third group, 8 items in the fourth group. Conclusion : This study can help future studies which measure nursing activities standard time or assigns value to nursing activities time.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2006년도 공동학술대회 논문집
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• pp.17-22
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• 2006

Shear modulus is directly linked to material's stiffness and is one of the most critical engineering parameters. Seismically, shear-wave velocity (Vs) is its best indicator. Although methods like refraction, down-hole, and cross-hole shear-wave surveys can be used, they are generally known to be tougher than any other seismic methods in field operation, data analysis, and overall cost. On the other hand, surface waves, commonly known as ground roll, are always generated in all seismic surveys with the strongest energy, and their propagation velocities are mainly determined by Vs of the medium. Furthermore, sampling depth of a particular frequency component of surface waves is in direct proportion to its wavelength and this property makes the surface wave velocity frequency dependent, i.e., dispersive. The multichannel analysis of surface waves (MASW) method tries to utilize this dispersion property of surface waves for the purpose of Vs profiling in 1-D (depth) or 2-D (depth and surface location) format. The active MASW method generates surface waves actively by using an impact source like sledgehammer, whereas the passive method utilizes those generated passively by cultural (e.g., traffic) or natural (e.g., thunder and tidal motion) activities. Investigation depth is usually shallower than 30 m with the active method, whereas it can reach a few hundred meters with the passive method. Overall procedures with both methods are briefly described.

• Nuclear Engineering and Technology
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• 제53권2호
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• pp.498-508
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• 2021

Micro reactors are increasingly being considered for utilization as distributed power sources. Hence, the probabilistic safety assessment (PSA) of a direct supercritical-CO₂-cooled fast reactor, called micro modular reactor (MMR), was performed in this study; this reactor was developed using innovative design concepts. It adopted a modular design and passive safety systems to minimize site constraints. As the MMR is in its conceptual design phase, design weaknesses and valuable safety insights could be identified during PSA. Level 1 internal event PSA was carried out involving literature survey, system characterization, identification of initiating events, transient analyses, development of event trees and fault trees, and quantification. The initiating events and scenarios significantly contributing to core damage frequency (CDF) were determined to identify design weaknesses in MMR. The most significant initiating event category contributing to CDF was the transients with the power conversion system initially available category, owing to its relatively high occurrence frequency. Further, an importance analysis revealed that the safety of MMR can be significantly improved by improving the reliability of reactor trip and passive decay heat removal system operation. The findings presented in this paper are expected to contribute toward future applications of PSA for assessing unconventional nuclear reactors in their conceptual design phases.

• 한국치위생학회지
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• 제18권3호
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• pp.281-293
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• 2018

Objectives: This study was conducted to identify the requirements for the clinical dental tasks in the dental hygienists using the frequency of dental hygienists' tasks in the Korean dental clinics, and to provide them with the core competencies for achieving these. Methods: This study was based on evaluation of a self-reported survey. The dental hygienists were investigated upon classification of their tasks into direct and assistant performances, and the dentists were investigated by the competency level of the dental hygienists. The data from 481 clinical dental hygienists and 67 dentists were used for final analysis in this study, excluding the subjects who provided incomplete or inappropriate responses to the survey. The collected data were analyzed by frequency analysis. Results: The clinical dental core competency tasks of the dental hygienists were divided into 4 tasks for common dentistry, 4 for periodontics, 5 for conservative dentistry, 5 for pediatric dentistry, 5 for dental prosthodontics, and 3 for dental orthodontics. Clinical dental core competency tasks of the dental hygienists were performed more frequently of tasks performance than 8.0, and dentists required competence level was similar to that of most dental hygienists clinical dental core competencies. Conclusions: It is necessary to check whether the curricula of the universities include the competencies for the students enough to perform the corresponding tasks and the core competencies need to be reflected in the curricula. The clinical dental core competencies need to be agreed by dental hygienists, and it is necessary to be organized as the evaluation guide of the institute of dental hygiene education and evaluation and utilized as the national examination.