• 대한핵의학회:학술대회논문집
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• 대한핵의학회 2002년도 제23차 연수교육
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• pp.70-76
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• 2002

• Journal of Electrical Engineering and Technology
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• 제10권5호
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• pp.1950-1957
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• 2015

Modern wind generators (WGs) are forced or encouraged to participate in frequency control in the form of inertial and/or primary control to improve the frequency stability of power systems. To participate in primary control, WGs should perform deloaded operation that maintains reserve power using speed and/or pitch-angle control. This paper proposes an optimization formulation that allocates the required reserve to WGs to maximize the kinetic energy (KE) stored in a wind power plant (WPP). The proposed optimization formulation considers the rotor speed margin of each WG to the maximum speed limit, which is different from each other because of the wake effects in a WPP. As a result, the proposed formulation allows a WG with a lower rotor speed to retain more KE in the WPP. The performance of the proposed formulation was investigated in a 100-MW WPP consisting of 20 units of 5-MW permanent magnet synchronous generators using an EMTP-RV simulator. The results show that the proposed formulation retains the maximum amount of KE with the same reserve and successfully increases the frequency nadir in a power system by releasing the stored KE in a WPP in the case of a disturbance.

• 한국전산유체공학회지
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• 제22권1호
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• pp.15-25
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• 2017

Swirl flow is often found in proximal coronary arteries, because the aortic valves can induce swirl flows in the coronary artery due to vortex formation. In addition, the curvature and tortuosity of arterial configurations can also produce swirl flows. The present study was performed to investigate fractional flow reserve alterations in a post-stenotic distal part due to the presence of pre-stenotic swirl flow by computational fluid dynamics analysis for virtual stenotic models by quantifying fractional flow reserve(FFR). Simplified stenotic coronary models were divided into those with and without pre-stenotic swirl flow. Various degrees of virtual stenosis were grouped into three grades: mild, moderate, and severe, with degree of stenosis of 0 ~ 40%, 50 ~ 60%, and 70 ~ 90%, respectively. In this study, three-dimensional computational hemodynamic simulations were performed under hyperemic conditions in virtual stenotic coronary models by coupling with a zero-dimensional lumped parameter model. The results showed that the influence of pre-stenotic swirl inflow is dominant on FFR alteration in mild stenosis, whereas stenosis is dominant on FFR alteration in moderate/severe stenosis. The decrease in FFR caused by swirl flow is more significant in mild stenosis than moderate/severe stenosis. Biomechanical modeling is useful for clinicians to provide insight for medical intervention strategies. This hemodynamic-based parameter study could play a critical role in the development of a non-invasive imaging-based strategy-support system for percutaneous transluminal angioplasty in cases of mild/moderate stenosis.

• Journal of the Korean Data and Information Science Society
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• 제27권1호
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• pp.75-89
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• 2016

본 논문에서는 국민연금과 주요국 공적연금에서 사용되는 재정평가지표들을 고찰해 보고 국민연금 재정계산 시 보완 및 적용 가능한 재정평가지표로 수정적립배율, 보험료충당률, 기금충당률을 제안하였다. 수정적립배율은 평가시점에 보유한 적립기금으로 장래 지출을 감당할 수 있는 제도유지 기간을 측정하며 기금의 적립 수준에 대한 의미 있는 해석을 가능하게 한다. 보험료충당률과 기금충당률은 국민연금의 지출 재원을 보험료수입과 적립기금으로 구분하여 재원에 따른 지출 충당 비율을 측정한 지표이다. 평가기간 동안의 재정상태를 요약하여 나타내며 재원의 적절성에 대한 정보를 제공해 준다. 다양한 재정평가지표의 활용은 재정상태 평가에 대한 신뢰도를 높이고 이해를 돕는데 기여할 것이다.

• 한국경제지리학회지
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• 제19권2호
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• pp.300-312
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• 2016

전남 순천시에 있는 순천만습지와 순천만국가정원은 2013순천만국제정원박람회 개최 이후 우리나라의 대표적인 생태관광지로 각광을 받고 있다. 이 연구는 순천만습지와 순천만국가정원을 관람한 방문객의 관광행태를 분석한 것이다. 순천만습지와 순천만국가정원은 봄보다는 가을에 집중하였고 10월이 1위를 차지하였다. 관광객 거주지는 광주 전남지역이 상대적으로 많았으며, 20~40대의 젊은 연령층(72.6%)이 다수를 차지하였다. 숙박보다 1일 관광객 비중(75.2%)이 많았으며, 자연경관 감상과 가족여행이 주요 관광동기였다. 관광정보는 인터넷을 주로 이용하였고, 가을철에 공원을 재방문하기를 선호하였으며, 순천만습지에 대한 선호도(71.1%)가 높았다. 관광만족도는 전체적으로 매우 높았으며, 춘계 관광객의 만족도가 가장 높았다. 관광객의 1인당 평균 소비지출금액은 5~10만 원(30%)이 다수를 차지하였으며, 순천지역에서 소비하는 지출액은 그렇게 많지 않았다.

• Journal of Electrical Engineering and Technology
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• 제13권2호
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• pp.648-658
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• 2018

Regarding the fact that wind power forecast accuracy is gradually improved as time is approaching, this paper proposes a two-stage rolling dispatch approach based on model predictive control (MPC), which contains an intra-day rolling optimal scheme and a real-time rolling base point tracing scheme. The scheduled output of the intra-day rolling scheme is set as the reference output, and the real-time rolling scheme is based on MPC which includes the leading rolling optimization and lagging feedback correction strategy. On the basis of the latest measured thermal unit output feedback, the closed-loop optimization is formed to correct the power deviation timely, making the unit output smoother, thus reducing the costs of power adjustment and promoting wind power accommodation. We adopt chance constraint to describe forecasts uncertainty. Then for reflecting the increasing prediction precision as well as the power dispatcher's rising expected satisfaction degree with reliable system operation, we set the confidence level of reserve constraints at different timescales as the incremental vector. The expectation of up/down reserve shortage is proposed to assess the adequacy of the upward/downward reserve. The studies executed on the modified IEEE RTS system demonstrate the effectiveness of the proposed approach.

• 한국항공우주학회지
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• 제45권5호
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• pp.386-392
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• 2017

본 논문에서는 700 km 고도의 태양동기궤도 진입을 목표로 하는 3단형 위성발사체에 있어서, 여러 오차 요인들로 인한 성능 오차를 보상하면서 목표 궤도에 정확히 투입시키는데 필요한 비행성능여유에 대해서 살펴보았다. 우선 궤도 투입 오차에 영향을 끼치는 다양한 오차 요인들과 각 오차 요인의 분산을 정의하였다. 이를 토대로 각 오차 요인의 영향을 독립적으로 고려할 수 있는 장점이 있는 민감도 분석을 ${\pm}3{\sigma}$ 분산 조건에 대해서 수행하였다. 여기에 여러 오차 요인에 의한 영향을 종합적으로 고려할 수 있는 Monte Carlo 분석 방법을 적용해서도 요구 추진제를 계산하였다. 결과적으로 두 방법을 통해 얻어진 비행성능여유를 비교했으며, 유사한 수치가 도출됨을 확인하였다.

• 전기학회논문지
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• 제63권10호
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• pp.1328-1336
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• 2014

This paper proposes Power System Health Index(PSHI) newly. The paper describes several kind of power system health indices based on two main categories, which are adequacy and security. In adequacy, four kinds of health indices of Frequency, Voltage, Reserve(Operating Reserve Power and Frequency Regulation Reserve Power) and Overload of lines and transformers are proposed. In security, four kinds of health indices of Voltage(154kV, 345kV and 765kV), Overload of lines and transformers, Power flow constraint among areas and SPS are proposed. All indices are mapped with three domains, which are indicated as Health, Margin and Risk, defined with expert interview. While domains of health, margin and risk is defined similar with the conventional well being analysis of power system. The criterion of the domains is proposed using an interview with expert operators and practical reliability codes in Korea. The several kinds of health index functions, which are linear ratio, piecewise linear ration and reverse ratio function etc. are developed in this paper. It will be expected that the developed health indices can help operators to control power system more successfully and also prevent power system from accident as like as black out in future because operator can make a decision immediately based on more easily visual information of system conditions from too much indices acquisition of complex power system.

• Pediatric Gastroenterology, Hepatology & Nutrition
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• 제22권6호
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• pp.527-535
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• 2019

Purpose: There is increasing prevalence of psychiatric disorders among inflammatory bowel Disease (IBD) population. Further, presence of psychiatric disorders has been shown as an independent predictor of quality of life among patients with IBD. We intended to explore the prevalence of various psychiatric disorders among pediatric and young adult population with IBD as a population-based analysis. Methods: We did a retrospective case control analysis using a deidentified cloud-based database including health care data across 26 health care networks comprising of more than 360 hospitals across USA. Data collected across different hospitals were classified and stored according to Systematized Nomenclature of Medicine-Clinical Terms. We preidentified 10 psychiatric disorders and the queried the database for the presence of at least one of the ten psychiatric disorders among IBD patients between 5 and 24 years of age and compared with controls. Results: Total of 11,316,450 patients in the age group between 5 and 24 years and the number of patients with a diagnosis of IBD, Crohn's disease or ulcerative colitis were 58,020. The prevalence of psychiatric disorders was 21.6% among IBD mainly comprising of depression and anxiety disorder. Multiple logistic regression analysis showed, IBD is 5 times more likely associated with psychiatric disorders than controls, p<0.001). We showed a steady increasing trend in the incidence of psychiatric disorders among IBD patients (2% in 2006 to 15% in 2017). Conclusion: Largest population-based analysis demonstrated an increased prevalence of psychiatric disorders among IBD patients. Our study emphasizes the need for psychological and mental health services to be incorporated as a part of the routine IBD clinic.

• Journal of Forest and Environmental Science
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• 제35권3호
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• pp.205-211
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• 2019

The objective of this research was to assess the amount of carbon stock of coarse woody debris (CWD) in Bombo-Lumene Reserve. Data on lying CWD was collected on 35 circular sampling plots using Line Intersect Sampling (LIS) method. A total of 230 samples CWD (${\geq}10cm$ diameter) were inventoried. The mean carbon stocks of CWD was $29.48Mg\;C\;ha^{-1}$, ranging from 4.32 to $73.54Mg\;C\;ha^{-1}$. The CWD carbon stocks displayed a wide range of variation in decay states. The allocation of CWD among the decay class of all the CWD samples reveals that the most important classes were class 1 and class 3 with 323.66 and $321.96Mg\;C\;ha^{-1}$, followed by class 4 with 264.56 and the last one was class 2 with $121.72Mg\;C\;ha^{-1}$. The results suggested that the dead wood component is important in carbon sequestration and should be taken into consideration for quantification of carbon stocks not only in Bombo-Lumene Reserve, but in all forest ecosystems in the Democratic Republic of Congo.