• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.10
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• pp.125-132
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• 2019

Because the water exposed to shock waves caused by an underwater explosion cannot withstand the appreciable tension induced by the change in both pressure and velocity, the surrounding water is cavitated. This cavitating water changes the transferring circumstance of the shock loading. Three phenomena contribute to hull-plate damage; initial shock loading and its interaction with the hull plate, local cavitation, and local cavitation closure then shock reloading. Because the main concern of this paper is local cavitation due to a near-field underwater explosion, the water surface and the waves reflected from the sea bottom were not considered. A set of governing equations for the structure and the fluid were derived. A simple one-dimensional infinite plate problem was considered to verify this uncoupled solution approach compared with the analytic solution, which is well known in this area of interest. The uncoupled solution approach herein would be useful for obtaining a relatively high level of accuracy despite its simplicity and high computational efficiency compared to the conventional coupled method. This paper will help improve the understanding of fluid-structure interaction phenomena and provide a schematic explanation of the practical problem.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.5
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• pp.605-617
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• 2021

The recovery of the sedimentary environment around a fallowing shellfish farm during its rest period after 20 years of long-running operation, was explored in Tongyeong Bay of Korea. Seasonal survey on macrobenthos community was conducted from July 2016 to September 2018 at five stations, which included the fallowing shellfish farm after 20-year operation (FF), a newly installed shellfish farm (NF), a shellfish farm for comparison around the closed shellfish farm (CF), and control stations with no farming activities (Con1, Con2). The total number of species and the density of macrobenthos were higher at the shellfish farm stations than the non-shellfish farm station, and their seasonal changes were significant. The dominant species at the shellfish farm stations was Capitella capitata while Paraprionospio patiens was dominant at the non-shellfish farm stations. The two dominant species were potential organic contamination indicators usually inhabiting the areas with dense organic matter. This suggests that the overall survey area was highly polluted with organic matters. Multivariate analysis showed that the macrobenthic community of CF changed to a level similar to that of Con1 immediately after the investigation, but not to a state above the Con1 level. Furthermore, the changes in NF were not significant when compared to those in CF.

• Journal of Wetlands Research
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• v.23 no.2
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• pp.189-200
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• 2021

To improve the water quality of agricultural reservoirs, constructed wetlands are applied in many places. These are technologies that establish ecosystems and important design factors include water depth distribution, inflow and outflow, water flow distribution, hydraulic residence time, water quality treatment efficiency, aspect ratio, and the distribution of open water and covered water surfaces. For high efficiency during the operation of a constructed wetland, the design needs to be optimized and this requires consideration of the different types and length of the intake dam as well as the type and connection of wetland cells. Therefore, this study was conducted to investigate and suggest factors that needs to be considered during the design and for efficient operation measures through field surveys of 23 constructed wetlands that have been established and operated in agricultural reservoirs. Results of the field investigation shows that several sites were being operated improperly due to the malfunctioning or failure of the water level sensors, sedimentation in the intake dam, and clogging of the mechanical sluice frames. In addition, it was found that as the length of the inlet channel increases, the ecological disconnection between the intake dam upstream and the wetland outlet downstream also increases and was identified as a problem. Most of the wetlands are composed of 2 to 5 cells which can result to poor hydraulic efficiency and difficulty in management if they are too large. Moreover, it was found that the flow through a small wetland can be inadequate when there are too many cells due to excessive amounts of headloss.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.233-233
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• 2020

최근 우리나라의 2030년 10GW의 농촌 태양광 보급목표 달성을 위해 전국적으로 분포하고 있는 저수지 및 댐 등의 공유 수면을 활용한 수상태양광 설치가 적극 검토되고 있다. 수상태양광 사업의 증가와 함께 수상태양광 설치 및 운영이 환경적 측면에서 논쟁이 대두되고 있으나 수상태양광 발전시설이 호소 수생태계에 미치는 영향을 판단할 수 있는 장기적인 조사나 과학적 연구가 부족한 실정이다. 본 연구에서는 저수지에 설치되어 있는 수상태양광 발전시설에 의한 수생태계에 미치는 영향을 파악하기 위해 수상태양광이 운영되고 있는 2개소의 저수지를 대상으로 식물플랑크톤, 동물플랑크톤, 저서성 대형무척추동물, 어류 군집조사를 2개년(2017~2018년) 동안 실시하여 각각의 종풍부도 및 종다양도 지수를 분석하였다. 1차년도에는 수상태양광 패널 설치지역 및 패널로부터 200~250m로 이격거리를 유지하면서 총 6지점을 조사하였으며, 2차년도에는 수상태양광 패널 하부(영향권) 3지점과 패널로부터 약 250m 이격된 2지점(비영향권)을 대상으로 총 6회의 조사를 수행하였다. 식물성플랑크톤, 동물성플랑크톤, 저서 대형무척추동물, 어류 군집에 대한 종풍부도와 종다양성에 대한 분석결과, 종풍부도 및 종다양도는 발전시설 영향권 지역과 비영향권 지역간에 통계학적으로 유의미한 차이는 없는 것으로 나타났다. 종풍부도는 수상태양광 패널로부터 이격거리가 멀어질수록(열린수역으로 향할수록) 감소하는 수치를 보이다가 저수지 수변부에 가까워지면 높아지는 경향을 나타났다. 종다양도 역시 종풍부도 결과와 유사하게 수상태양광 패널 지역으로부터 이격거리가 증가함에 따라(열린수역으로 향할수록) 지수가 감소하다가 저수지 수변부에 가까울수록 높아지는 결과를 보였다. 이러한 결과는 동식물성 플랑크톤과 저서생물 및 어류 군집의 종풍부도, 종다양도가 수상태양광의 영향권과 비영향권간에 큰 차이를 없음을 나타내고 있으며, 일부 분류군의 경우 열린 수면보다 수상태양광 설비에 의한 반 폐쇄수역에서 종풍부도와 종다양도가 오히려 높게 나타났다. 그러나 본 연구결과는 설치된 수상태양광 패널이 전체 수면의 5% 미만에 해당하는 소규모 시설이므로 본 연구결과를 일반화해서 해석하기에는 한계가 있다. 넓은 수면적에 설치되어 있는 대규모 시설 및 20년 이상 장기간 운영되는 수상태양광 발전시설을 대상으로 지속적인 모니터링 및 누적된 환경영향 평가가 필요할 것으로 판단된다.

• Sleep Medicine and Psychophysiology
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• v.19 no.2
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• pp.68-76
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• 2012

Objectives: Sleep disorders cause changes of autonomic nervous system (ANS) which affect cardiovascular system. Primary insomnia (PI) makes acceleration of sympathetic nervous system (SNS) tone by sleep deficiency and arousal. Obstructive sleep apnea syndrome (OSAS) sets off SNS by frequent arousals and hypoxemias during sleep. We aimed to compare the changes of heart rate variability (HRV) indices induced by insomnia or sleep apnea to analyze for ANS how much to be affected by PI or OSAS. Methods: Total 315 subjects carried out nocturnal polysomnography (NPSG) were categorized into 4 groups - PI, mild, moderate and severe OSAS. Severity of OSAS was determined by apnea-hypopnea index (AHI). Then we selected 110 subjects considering age, sex and valance of each group's size [Group 1 : PI (mean age=$41.50{\pm}13.16$ yrs, AHI <5, n=20), Group 2 : mild OSAS (mean age=$43.67{\pm}12.11$ yrs, AHI 5-15, n=30), Group 3 : moderate OSAS (mean age $44.93{\pm}12.38$ yrs, AHI 16-30, n=30), Group 4 : severe OSAS (mean age=$45.87{\pm}12.44$ yrs, AHI >30, n=30)]. Comparison of HRV indices among the four groups was performed with ANCOVA (adjusted for age and body mass index) and Sidak post-hoc test. Results: We found statistically significant differences in HRV indices between severe OSAS group and the other groups (PI, mild OSAS and moderate OSAS). And there were no significant differences in HRV indices among PI, mild and moderate OSAS group. In HRV indices of PI and severe OSAS group showing the most prominent difference in the group comparisons, average RR interval were $991.1{\pm}27.1$ and $875.8{\pm}22.0$ ms (p=0.016), standard deviation of NN interval (SDNN) was $85.4{\pm}6.6$ and $112.8{\pm}5.4$ ms (p=0.022), SDNN index was $57.5{\pm}5.2$ and $87.6{\pm}4.2$ (p<0.001), total power was $11,893.5{\pm}1,359.9$ and $18,097.0{\pm}1,107.2ms^2$(p=0.008), very low frequency (VLF) was $7,534.8{\pm}1,120.1$ and $11,883.8{\pm}912.0ms^2$ (p=0.035), low frequency (LF) was $2,724.2{\pm}327.8$ and $4,351.6{\pm}266.9ms^2$(p=0.003). Conclusions: VLF and LF which were correlated with SNS tone showed more increased differences between severe OSAS group and PI group than other group comparisons. We could suggest that severe OSAS group was more influential to increased SNS activity than PI group.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.16 no.4
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• pp.224-232
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• 2004

Sedimentation changes related with bottom shear stress attenuation at JangHang channel in the Keum River Estuary, where several huge coastal constructions including an estuarine dam have been conducted for last 2 decades, were evaluated for 7 cases to figure out passage hindrance through the channel by a hydrodynamic model using hind-casting technique from 1988 to 2000 at every 2 years interval. Due to the construction of Keum River Estuary Dam, the maximum bottom shear stress rapidly lessened to $0.2-0.6N/m^2$ compared to$1-2N/m^2$ in natural status. Especially it marks below the critical shear stress of $0.4N/m^2$ resulting in severe siltation in the channel just after the closing of dam gates in 1994. It is concluded that the dam may block the tidal energy propagation to upstream and directly results in sedimentation environment in front of dam site. It is also revealed that at least 20% of passage hindrance of small fishing boats through the channel could be counted due to sedimentation by analysis of predicted mean spring tides.

• Management & Information Systems Review
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• v.29 no.4
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• pp.89-108
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• 2010

Social Network Service(SNS) indicates the service to promote mutual friendship built in online focused on social relation between people. While a demand and concern of the service gets higher now more than ever, there are a lack of the approach in aspect of both technology and service still. 'Facebook' is the most famous in the world and the biggest in user number among various social network service. We investigate the key factors of 'Facebook' based on the side of approach both technology and service. We observe the behavior of users who have rich experience on using the social network service to find it. The result of this study reveals that an asynchronous method related to the technology drive to improve a sociality in social media. Furthermore, we find that openness connected with the technology force to intent the closed attribute in service through user observation. It is the unique qualities social media holds. The successful social network service can be expected if social media are developed to concern these factors.

• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.4
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• pp.371-388
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• 2003

The tunnels that longer than 2km which have been recently constructed have serious noise problems resulting from the friction of vehicle wheels and pavement. In special, concrete pavement inside tunnels with a closed characteristic increases discomfort due to the traffic noise and the dust of pavement pollutes the air in tunnels. Therefore, it is urgent that we find out ways to cope with. This study purported to reduce noise inside tunnels covers the investigation of various pavement surface treatment methods adapted in developed countries, the analysis of the effect in noise reduction and construction methods and cases. The surface treatment method for silent pavement in tunnels reduced noise to 5dB (A)~10dB (A). Aggregate treatment method is evaluated the most appropriate method in that, related with other surface treatment method, it reduces noise and improves skid resistance. It is necessary for us to introduce equipments and design and rearrange of specification for the development of the silent pavement method in Korea.

• The korean journal of orthodontics
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• v.33 no.1 s.96
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• pp.21-29
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• 2003

Recent developments in software technology have made it possible to create a virtual three-dimensional model of the dental arches from digitally scanned casts of a patient's dentition. This modelmay then be manipulated with software to produce stages of tooth movement from the initial malocclusion to the final desired occlusion. A sterolithograghic model is made for each stage of tooth movement which is the basis for construction of a series of clear and thin overlay appliances. These appliances are worn full time by the patient to move the teeth according to the programmed stages of movement. Malocclusions involving mild to moderate crowding and space closure have been proven to be successfully treated with this appliance. Experience with this appliance has demonstrated excellent patient compliance with less discomfort, improved esthetics and oral hygiene control, when compared with fixed orthodontic appliances. Orthodontic treatment with this appliance is a potentially useful alternative approach to fixed appliances for treatment of a variety of malocclusions in patients with fully erupted permanent teeth.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2001.11a
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• pp.67-68
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• 2001

제지공장은 에너지 다소비 업종이며 고도의 장치산업이기 때문에 초지 설비의 효과적 운영을 통한 생산성 극대화가 경제성과 직결되어 었다. 또한 24시간 연속생산을 하는 초지 설비로 소비자가 선호하는 품질의 종이를 생산하기 위해서는 공정의 안정성 이 매우 중요하다. 이는 공정의 불안정화는 생산제품의 품질 변화를 유발함으로써 균일 성을 저하시키는 악영향을 미치기 때문이다. 제지 공정의 안정화를 저해하는 인자에는 지절, 지종 변화, 조업중단, 조업재개 둥과 공정의 특성상 수반되는 돌발사태 등이 있을 수 있다. 이들 인자 가운데 가장 심각하게 공정의 안정성을 악화시키는 것은 지절의 발 생이라 할 수 있다. 지절이 발생되면 생산성 저하 등의 여러 문제점이 발생하기도 하지 만 다량의 파지가 발생되기 때문에 공정 안정성 면에서 볼 때에도 부득이하게 생성된 다량의 파지를 공정에 재투입하기 위해 재해리해야하므로 많은 양의 백수가 소모되며 이에 따라 예기치 않은 공정 백수의 사용으로 전체 백수계에 갑작스런 변동이 생기게 된다. 백수가 파지의 해리에 사용됨에 따라 공정 내에는 추가적인 청수가 공급되어야 하므로 전체적으로는 청수의 사용량도 늘어난다. 또한 증가된 파지의 재사용도 대부분 의 공장에서 broke chest의 용량이 한정되어 있으므로 이의 적절한 컨트롤은 중요하다. 더욱이 점차 공정이 고폐쇄화됨에 따라 공정 컨트롤에 대한 여유가 적으므로 백수와 공정의 관리는 점차 어려워지고 있다. 공정 시율레이션은 현존하는 공정을 수학적으로 모델화하여 이를 컴퓨터 하드 왜어를 이용해 실제 공장에서 일어나는 상황을 모사하는 것이다. 이러한 공정 모사는 새로운 공장을 설계하기 전에 타당성 조사와 여러 가지 사례조사를 실시할 때, 기존 공 장의 개조나 증설 또는 기존 공장의 운전조건을 실제로 변경하기 전에도 미리 모사를 함으로써 실제 시험 운전을 하는 경우 보다 많은 비용과 시간을 절약할 수 있다. 본 연 구는 백상지 생산 공정 설계도면을 참고하여 상용 시율레이터로 시율레이션 모델을 구 축하고 이를 기반으로 지절 상황을 모사하였으며, 지절 후의 공정 불안정화 상황을 파 악하였다. 또한 이러한 상황의 대책을 강구하기 위해 다양한 공정 조절 방안을 시율레이션 모댈에 적용하여 그 결과를 해석하였다.