• 대한기계학회논문집B
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• 제29권5호
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• pp.633-642
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• 2005

Nucleate pool boiling experiments for R11 under a constant wall temperature condition were carried out. A microscale heater array was used for the heating and the measurement of high temporal and spatial resolution by the Wheatstone bridge circuit. Very sensitive heat flow rate data were obtained by the control for the surface condition with high time resolution. The measured heat flow rate shows a discernable peak at the initial growth stage and reaches an almost constant value. In the thermal growth region, bubble shows a growth proportional to $t^{\frac{1}{5}}$. The bubble growth behavior is analyzed with a dimensionless parameter to compare with the previous results in the same scale. As the wall superheat increases, the departure diameter and the departure time increase, and the waiting time decreases. But the asymptotic growth rate is not affected by the wall superheat change. The effect of the wall superheat is resolved into the suggested growth equation. Dimensionless parameters of time and bubble radius characterize the thermal growth behavior well, irrespective of wall condition. The comparison between the result of this study and the previous results shows a good agreement at the thermal growth region. The quantitative analysis for the heat transfer mechanism is conducted with the measured heat flow rate behavior and the bubble growth behavior. The required heat flow rate for the volume change of the observed bubble is about twice as much as the instantaneous heat flow rate supplied from the wall.

• Nuclear Engineering and Technology
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• 제27권4호
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• pp.503-517
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• 1995

강제대류 천이비등 열유속을 보다 실제 적으로 예측하기 위한 역학적 모델을 개발하였다. 이 모델은 가열된 벽면 근처를 어떤 기포기둥(Vapor Blanket)이 통과할 때 일어나는 다단계 비등과정 즉, 임계 기포기둥의 형성, 기포기둥밑의 미소액막(Macrolayer)의 기화 및 고갈, 그리고 얇은 기체막에서 일어나는 불안정한 막비등과정에 기초하였다. 핵비등이탈점 (DNB )과 막비등이탈점 (DFB)사이의 천이비등 곡선상의 열유속은 임계 기포기둥이 주어진 벽면을 통과할 동안 상기한 각 비등과정의 지속 시간비(Time Fraction)를 각 비등열유속에 곱한 후 그것을 합하여 정량화하였다. 이 모델의 예측치를 현재까지 발표된 문헌들에 나타난 실험치와 비교한 결과, 본 모델은 저건도 및 10 bar 근처의 고압조건의 실험치를 잘예측하는 것으로 나타났다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2022년도 춘계학술대회
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• pp.275-276
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• 2022

해상교통관제사는 항로폭이 협소한 항만에서 선박 충돌사고 예방을 위해 one-way로 항해하도록 선박의 입·출항 대기 지시를 한다. 현재 해상교통관제사의 입·출항대기 지시는 과학적이고 통계적인 데이터를 기반으로 하지 않고 해상교통관제사의 개인 역량에 따라 편차가 크다. 이에 따라 본 연구에서는 항만에서의 선박 입·출항 대기 지시를 위한 정확한 이동 시간을 예측하기 위해 선박 및 기상 데이터를 수집하여 1d-합성곱신경망 모델을 구축하였다. 제안한 모델이 다른 앙상블 기계학습 모델보다 4.5% 이상 개선된 것을 확인하였다. 본 연구를 통해 다양한 상황에서도 선박 입·출항 소요시간 예측이 가능하여 해상교통관제사는 선박에게 정확한 정보 제공 및 대기지시 판단에 도움이 될 것으로 기대된다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.1722-1729
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• 2011

This paper presents an optimization model for revising train timetable based on an existing timetable to improve transfer time at each station. The transfer time consists of walking and waiting time. The model is formulated as a mixed integer programming. The objective function is to minimize the transfer time from one train to another train at each station. To reflect real situations, range of revising departure time is considered as major condition in the model. To validate the effectiveness of the model, rudimentary computational results are included, and the results are analyzed in terms of transfer time.

• 한국철도학회논문집
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• 제17권4호
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• pp.313-319
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• 2014

여객 증편열차 운영은 수송력 보강이나 관광열차 운행을 위해 증편된다. 화물열차의 경우는 철도화물수요를 위해 주로 증편된다. 기존 연구들에서는 증편열차 스케줄 작성을 위해 추가 열차의 운행시각을 지정한 후에 운행가능성을 판단한다. 그러나 국내에서 이러한 방법의 경우 추가열차의 증편이 불가능한 경우가 많다. 왜냐하면 한국철도 네트워크는 운행밀도가 높고 여러 차종이 있기 때문이다. 특히 화물열차의 경우 여객열차와의 경합이 발생할 때마다 지연이 증가되거나 운행이 불가능하다. 본 논문에서는 출발시각이 지정된 요청열차 스케줄과 시간범위 내에 운행 가능한 스케줄을 찾을 수 있는 열차 증편모형을 제시한다. 제시된 모형은 혼합정수 계획법으로 모델링하고 열 생성기법을 사용하였다.

• 대한전자공학회논문지TC
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• 제45권12호
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• pp.74-82
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• 2008

본 논문에서는 다중 체인구조를 이용한 P2P 기반 IPTV 시스템을 제안한다. 제안하는 시스템은 P2P 네트워크의 특징인 peer의 빈번한 가입과 탈퇴 상황에서 단순한 과정으로 네트워크를 재구성하는 장점이 있다. 인터넷과는 달리 ISP가 관리하는 IPTV 환경은 전송회선의 속도와 안정성이 일정수준으로 보장되어 있다. 따라서 IPTV 환경에서의 P2P 네트워크는 단순성 측면을 우선적으로 고려해야 한다. 기존에 제안되어있는 단일 체인구조는 단순성을 강조하였으나 같은 채널을 시청하는 peer의 개수가 증가하면 체인의 끝 부분에 연결되어 있는 peer는 상당한 delay가 발생한다. 제안하는 시스템은 이러한 delay 문제를 해결하기 위하여 체인을 여러 개의 레벨로 분리하고 각 레벨은 다시 span으로 나누었다. 레벨과 span으로 분리를 하였지만 기본적인 구조는 체인구조이므로 peer가 join 하거나 departure 할 경우에 단순한 네트워크의 재구성 과정을 제공한다. 수치적인 해석을 통해 본 논문에서 제안한 다중 체인구조를 이용한 P2P 시스템이 단일 체인구조 방식에 비해 delay 및 신뢰도 성능이 우수하다는 것을 보여준다.

• Journal of Chest Surgery
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• 제55권6호
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• pp.452-461
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• 2022

Background: Extracorporeal membrane oxygenation (ECMO) can be used in patients with refractory cardiogenic shock or respiratory failure. In South Korea, the need for transporting ECMO patients is increasing. Nonetheless, information on urgent transportation and its outcomes is scant. Methods: In this retrospective review of 5 years of experience in ECMO transportation at a single center, the clinical outcomes of transported patients were compared with those of in-hospital patients. The effects of transportation and the relationship between insertion-departure time and survival were also analyzed. Results: There were 323 cases of in-hospital ECMO (in-hospital group) and 29 cases transferred to Hallym University Sacred Heart Hospital without adverse events (mobile group). The median transportation time was 95 minutes (interquartile range [IQR], 36.5-119.5 minutes), whereas the median transportation distance was 115 km (IQR, 15-115 km). Transportation itself was not an independent risk factor for 28-day mortality (odds ratio [OR], 0.818; IQR, 0.381-1.755; p=0.605), long-term mortality (OR, 1.099; IQR, 0.680-1.777; p=0.700), and failure of ECMO weaning (OR, 1.003; IQR, 0.467-2.152; p=0.995) or survival to discharge (OR, 0.732; IQR, 0.337-1.586; p=0.429). After adjustment for covariates, no significant difference in the ECMO insertion-departure time was found between the survival and mortality groups (p=0.435). Conclusion: The outcomes of urgent transportation, with active involvement of the ECMO center before ECMO insertion and adherence to the transport protocol, were comparable to those of in-hospital ECMO patients.

• 가정과삶의질연구
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• 제33권6호
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• pp.15-33
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• 2015

The present study conducted ethnography of a welfare facility for single-father families. The participants were 13 single-fathers living in a welfare facility. To explore life within the welfare facility, the qualitative research method of ethnography was used with Spradley's developmental research sequence (DRS). The major results of this study were as follows. The first theme was 'finding a way to overcome the crisis: the facility is a lifeline.' For fathers, choosing to enter a facility meant enduring a social stigma, but the decision was made with the hope of achieving successful parenting and economic independence amidst pressing difficulties. The category of living in the facility was represented by the theme 'build the family: preparing for independence through living in a welfare facility.' The fathers achieved psychological recovery through the decrease in parenting stress, improvements in their economic situation brought by living in a facility, and used this time as the foundation to gain independence and build a stable life. The event of departure from the facility was seen as 'incomplete preparation for departure' by the single fathers. The fathers with infants or younger children admitted to being anxious about leaving the facility, which involved the burden of raising the children on their own. There are practical and policy-related implications based on the results of this study.

• 한국경영과학회지
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• 제27권4호
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• pp.185-205
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• 2002

In this study, we consider infinite supply of raw materials and backlogged demands as given two boundary conditions. And we need not make any specific assumptions about the inter-arrival of external demand and service time distributions. Under these situations, the ultimate objective of this study is to prove the variability propagation principle in a pull serial line and is to measure it in terms of the first two moments of the inter-departure process subject to number of cards in each cell. Two preparations are required to achieve this objective : The one is to derive a true lower bound of variance of the inter-departure process. The other is to establish a constrained discrete minimax problem for the no backorder (backlogging) probabilities in each cell. We may get some fundamental results necessary to a completion for the proof through the necessary and sufficient conditions for existence of optimal solution of a constrained discrete minimax problem and the implicit function theorem. finally, we propose a numeric model to measure the variability propagation principle. Numeric examples show the validity and applicability of our study.

• 한국도로학회논문집
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• 제20권1호
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• pp.137-146
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• 2018

PURPOSES : This study aims to analyze how the installation of advanced warning devices affects individual drivers' driving behaviors with operating record data collected from 100 vehicles. METHODS : With collected data, the changes in individual drivers' driving behaviors, such as Forward Collision Warning (FCW) and Lane Departure Warning (LDW), were investigated with respect to the cumulative distance traveled and driving time. For the analysis, operating record data collected from 100 vehicles for seven months were used. RESULTS : The results showed that individual drivers' driving behaviors could be categorized into six different types. In addition, most of the drivers showed unstable warning patterns in the initial stage after installation of an advanced warning device. Approximately 40% of vehicles equipped with advanced warning systems were found to have positive effects, indicating that the frequencies of both FCW and LDW had been continuously decreasing after installation of the system. CONCLUSIONS : The warning device might be helpful for making drivers' driving behaviors safer. Driving behaviors during the initial stage of the system installation, which might be regarded as an adaptation phase, were found to be very unstable compared with normal situations, indicating that adequate education and training should be provided to all the drivers to prevent operator disruption at the initial installation of the system.