• 전력전자학회논문지
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• 제25권5호
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• pp.395-403
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• 2020

This study presents a stable start-up strategy for v/f scalar-controlled permanent magnet synchronous motors (PMSMs). The v/f-controlled PMSMs easily lose synchronism under low-speed conditions if an insufficient stator voltage is applied to the machine due to errors in measured motor parameters and inverter nonlinearity, such as inverter dead time and on-state voltage drop. The proposed method adopts the I/f control method to ensure a stable start at low speeds and then switches to the v/f control method at medium speeds. A smooth transition method from I/f control to v/f control is proposed to minimize the oscillation of the stator current and rotor speed during transition. Moreover, the stability of the I/f and v/f control methods is analyzed using a small-signal model. Simulation and experimental results are provided to verify the performance of the proposed control strategy.

• Water Engineering Research
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• 제7권1호
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• pp.21-28
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• 2006

The scouring process is complex and subject to many factors. Recently, experiments for real-time bridge scour monitoring have been active as means for a more reliable scour prediction. Riverbed materials are an important factor in bridge scouring; therefore, an accurate estimation of riverbed material is critical in predicting a scour. As a part of this approach, an ultrasonic sensor, which can not only detect river bottom during floods but can also be installed lose to the underwater structures, was developed. This sensor is able to map the river bottom using an ultrasonic waves with the characteristics of the returning wave, reflected from an object or bottom ground. The reflected wave is unique according to the situations, or materials below. Therefore, it would be possible to identify the consisting materials of a riverbed if we could reveal each characteristic in the received signals. In this study, a preliminary experiment was performed in the laboratory to identify and classify received signals, which is unique to each material. The analysis of this experiment gives the graph, which makes it possible to identify materials of the river bottom through the ultrasonic signals. The proposed graph was verified through a comparison with the actual field data measured in river.

• 한국정보과학회논문지:컴퓨팅의 실제 및 레터
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• 제6권6호
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• pp.601-607
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• 2000

컴포넌트의 런타임 갱신은 컴포넌트를 사용하는 프로그램을 종료하지 않고, 기존에 사용하는 컴포넌트를 그 내부가 새로 변경된 컴포넌트로 교환하는 기술이다. 최근 소프트웨어 개발에서는 기존 컴포넌트를 재활용하여 새로운 소프트웨어를 개발하는 추세이다. 그러나 컴포넌트가 시간 측면에서 연속적인 서비스를 제공해야하는 소프트웨어에 사용될 때 컴포넌트를 새롭게 기능이 바뀐 것으로 변경하려면 기존 소프트웨어를 종료해야한다. 이 경우 기존 소프트웨어의 서비스를 제공받는 사용자는 서비스를 다시 요구해야 되며 때로는 자신이 사용하는 정보를 손실하는 경우도 발생한다. 따라서, 본 논문에서는 기존 컴포넌트 갱신 방법의 문제점을 해결하기 위하여 소프트웨어를 종료하지 않고 그 소프트웨어를 구성하는 컴포넌트를 새로운 컴포넌트로 갱신하기 위한 방법을 제시한다.

• 한국재난정보학회 논문집
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• 제8권2호
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• pp.108-118
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• 2012

현재 TBM공법의 적용은 1985년 이래로 점진적으로 증가되고 있는 추세에 있다. 이 연구는 암반터널에서 탁월한 굴진실적을 갖고 있는 TBM공법의 이해와 운영발전을 위해서 TBM공법을 적용한 시공 사례의 시간손실과 TBM 굴진장의 상관관계를 분석하였다. 그리고 분석 결과를 기 분석된 국내, 미국, 일본의 현장 결과치와 비교 분석하여 TBM 굴진에 영향을 주는 요인을 분석하였고, 그 분석결과에 따른 운영개선방안을 제시하였다. 따라서 이 연구에서 제시한 개선방안은 향후 기본계획수립단계에서 TBM공법 적용 시 개략적인 지표로 활용할 수 있을 것으로 사료된다.

• 아시안잔디학회지
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• 제11권4호
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• pp.303-309
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• 1997

The investigation was cycle of aluminum of surface soil elements in dynamic grassland ecosystems at a steady state in a Zoysia japonica and a Miscanthus sinensis ecosystem in Mt. Kwanak, Korea. Average amounts of total storage for aluminum in Z japonica and M. sinensis grasslands were 8,426mg /$m^2$ and 7,849mg /$m^2$ respectively. Decay constants estimated on the base of experimental and mathematical model, were 0.04 in Z japonica grassland, and 0.08 in M. sinensis grassland. Half time to decay aluminum of litter soils were 17.33 years in Z japonica grass-land, and 8.66 years in Al. sinensis grassland. 95% decay times in Z japonica, and in M. sinensis grassland were 75.0 years and 35.0 years respectively. Needed times to lose almost all of elements in Z japonica and M. sinensis grassland were 125.0 years, and 62.50 years respectively. The metals were losed more rapidly in M. sinensis than in Z japonica grassland. The cycle of aluminum was investigated to be related with soil acidity. Key words: Cycle of aluminum, Zoysia japonica. Miscanthus sinensis, Mt. Kwanak, Decay constants, Soil acidity.

• Journal of Korea Trade
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• 제25권4호
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• pp.128-145
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• 2021

Purpose - The main purpose of this study is thus to investigate the contingent effect of imitation strategies on firm performance in transition economies such as China, focusing on pure and creative imitation. Design/methodology - We conducted a survey targeting department heads of each company who have more than 10 years work experiences. We assessed that the ability to gain trust and to access information from high-ranking informants would be greater if the firms were from the same country - Korea - as the lead researcher. A total of 200 highly reliable samples were obtained, which could effectively explain the nine variables set in the study. Relevant hypotheses were tested using a hierarchical linear model (HLM). Findings - The findings suggest that SMEs' technology level also had a positive impact on performance. Firms with better technology had a positive impact on performance, irrespective of pure or creative imitation. This reflects the cases where many Korean SMEs entering China without high technology level lose their competitiveness due to Chinese firms' technology catch-up within a short period of time. Originality/value - SMEs that lack technology and know-how need to focus on pure imitation strategies. It is possible that SMEs can perform creative imitation, but it seems difficult under the current circumstances. Therefore, SMEs with limitations in technology and know-how should maintain their competitive advantage for a while, by maintaining their pure imitation strategy.

• 천문학회지
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• 제54권2호
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• pp.71-88
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• 2021

We use N-body/hydrodynamic simulations to study the evolution of the spin of a Milky Way-like galaxy through interactions. We perform a controlled experiment of co-planar galaxy-galaxy encounters and study the evolution of disk spins of interacting galaxies. Specifically, we consider cases where the late-type target galaxy encounters an equally massive companion galaxy, which has either a late or an early-type morphology, with a closest approach distance of about 50 kpc, in prograde or retrograde sense. By examining the time change of the circular velocity of the disk material of the target galaxy from each case, we find that the target galaxy tends to lose the spin through prograde collisions but hardly through retrograde collisions, regardless of the companion galaxy type. The decrease of the spin results mainly from the deflection of the orbit of the disk material by tidal disruption. Although there is some disk material which gains the circular velocity through hydrodynamic as well as gravitational interactions or by transferring material from the companion galaxy, it turns out that the amount of the material is generally insufficient to increase the overall galactic spin under the conditions we set. We find that the spin angular momentum of the target galaxy disk decreases by 15-20% after a prograde collision. We conclude that the accumulated effects of galaxy-galaxy interactions will play an important role in determining the total angular momentum of late-type galaxies.

• ETRI Journal
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• 제41권4호
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• pp.473-482
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• 2019

High availability and reliability have been considered promising requirements for the support of seamless network services such as real-time video streaming, gaming, and virtual and augmented reality. Increased availability can be achieved within a local area network with the use of the virtual router redundancy protocol that utilizes backup routers to provide a backup path in the case of a master router failure. However, the network may still lose a large number of packets during a failover owing to a late failure detections and lazy responses. To achieve an efficient failover, we propose the implementation of fast detection with virtual router redundancy protocol (FDVRRP) in which the backup router quickly detects a link failure and immediately serves as the master router. We implemented the FDVRRP using open neutralized network operating system (OpenN2OS), which is an open-source-based network operating system. Based on the failover performance test of OpenN2OS, we verified that the FDVRRP exhibits a very fast failure detection and a failover with low-overhead packets.

• 한국식생활문화학회지
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• 제37권2호
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• pp.109-118
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• 2022

This study was undertaken to compare meal skipping, snacking, and weight perceptions between students on-campus living alone and off-campus living with parents, in an urban college in the United States. The self-report survey was completed by 219 college students (on-campus=100, off-campus=119) between April and May 2012. Two-thirds (67%) of the respondents skipped at least one meal in the past week, and most participants showed strong desires to lose weight despite their normal/under-weight status. Significant differences between the two groups were obtained for the reason to skip a meal and the type of snack consumed. Compared to on-campus students, significantly higher values were obtained for off-campus students for choosing 'no time to prepare' as a meal skipping reason for lunch and dinner, and 'sweets' as a preferred snack. In addition to the group comparison, multiple regression results indicate that the body mass index (BMI) positively correlates with meal skipping and snacking frequencies. Younger students and female students were determined to have a higher frequency of meal skipping and morning snacking. Future research is required to study the dietary factors associated with living arrangements, to help college students develop healthy eating habits.

• 대한조선학회논문집
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• 제59권1호
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• pp.29-38
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• 2022

In offshore installations, fires cause the structure to lose its rigidity and it leads to structural integrity and stability problems. The Passive Fire Protection (PFP) system slows the transfer rate of fire heat and helps prevent the collapse of structures and fatality. Especially, intumescent epoxy coating is widely used in the offshore industry, and not only is the material cost expensive, but it also takes a lot of time and cost for construction. Several studies have been conducted on the efficient application and optimal design of the PFP system. However, the mechanical properties and the strength of the PFP material have not been considered. In addition, researches on the correlation between the thickness of PFP and the structural behavior were insufficient. Therefore, this study aims to analyze the thermal and mechanical effects of the PFP on the structure when it is applied to the structural member. In particular, it is intended to resolve the change in strength characteristics of the structural members as the thickness of the PFP increases.