• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2005년도 연구개발 발표회 논문집
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• pp.562-565
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• 2005

• 디지털융복합연구
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• 제13권8호
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• pp.59-67
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• 2015

청소년들의 게임 중독이 사회적 문제로 부각되자 청소년들의 게임 이용을 제한하는 다양한 게임 규제 정책들이 도입되기 시작하였다. 그러나 '강제적 셧다운제', '선택적 셧다운제'를 포함하여 논의 중인 기타 게임 규제 정책들이 실제로 실효성이 없다는 지적이 증가하고 있으며, 이론적으로도 그 필요성에 대한 논쟁이 지속되고 있는 상황이다. 따라서 본 연구에서는 청소년들의 게임 규제에 대한 국내외 도입 현황 및 선행 연구 결과들을 고찰하여 이론적 측면의 청소년 게임 규제 정책의 필요성을 재검토한다. 또한 게임 규제 정책 도입 전후의 청소년들의 게임 이용시간 및 패턴을 비교 분석하여 실증적 효과에 대해서도 탐색한다. 연구 결과에 따르면 청소년 게임 규제 정책들의 실제 효과는 미비한 것으로 나타나고 있는데, 이에 대하여 본 연구에서는 법 정책 기술적 측면을 포함한 융합적 접근을 통해 합리적인 개선방안을 제시한다.

• 한국게임학회 논문지
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• 제12권2호
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• pp.63-74
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• 2012

본 논문은 최근에 국내 게임시장에 큰 반향을 일으키고 있는 오픈마켓과 셧다운제의 제도화 과정을 통해 시장에 미치는 영향과 그 의미를 살펴본다. 제도는 사회적 환경과 인식이 반영된 결과물이라는 점에서 오픈마켓과 셧다운제를 이해하는데 핵심 요소이다. 이에 오픈마켓과 셧다 운제의 제도가 추진되는 사회적 환경과 인식의 영향과 그 결과의 방향성을 조망한다. 오픈마켓은 스마트폰의 도입에 따라 이전과 다른 모바일콘텐츠 유통체계의 변화에 대한 기존 국지성 제도와의 합리적이고 미래지향적인 접근을 통해 시장 활성화에 기여했다. 한편 셧다운제는 게임이용과정에서 나타난 문제적 현상에 대한 환경적 구조적 진단 보다는 현상적 형태에 집중함으로써 제도화의 의미가 퇴색하고 오히려 시장에서 부작용을 부추기는 결과를 가져오고 있다. 이러한 상반된 결과의 방향성을 통해 제도화의 중요성을 지적하였고, 오픈마켓과 셧다운제도의 실효성과 제도 및 시장성에 대하여 고찰하였다.

• 한국추진공학회지
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• 제21권4호
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• pp.89-95
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• 2017

본 논문에서 극저온 추진제를 사용하는 액체추진기관의 재순환예냉 시스템 설계의 유연성을 확보하기 위한 연소기 산화제 개폐밸브 재순환예냉 유로의 유량계수 개선 내용을 소개하였다. 밸브의 재순환 예냉 출구 포트 크기와 밸브 내부 유로 형상 변경에 의한 재순환예냉 유로의 유량계수 값을 예측하기 위해서 기존 밸브에서 측정한 재순환예냉 유로의 유량계수 값들을 활용하였으며, 액체질소를 운용유체로 사용하여 측정한 유량계수와 예측값과의 비교를 통해 밸브 내부 형상 변경에 의한 유량계수 개선정도를 확인하였다. 연소기 산화제 개폐밸브의 재순환예냉 유로의 유량계수는 기존 밸브에 비해 2배가량 향상되었으며, 결과적으로 연소기 산화제 개폐밸브에 할당되었던 설계 요구 차압의 75%가량을 재순환예냉 시스템에서 추가적으로 소요될 수 있는 잠재적인 차압과 재순환예냉 시스템의 다른 구성품의 추가 차압으로 활용될 수 있을 것으로 기대된다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 추계학술대회
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• pp.494-497
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• 2006

For commercialization of polymer electrolytemembrane fuel cell (PEMFC), durability of membrane electrode assemblies (MEAs) has to be improved. Especially, long-term stability of MEA is one of the most important issues for frequent shut-down and start-up processes of PEMFC. The degradation of MEA could be attributed to chemical attack of hydrogen peroxide radicals that are formed at high cell voltages without any special treatment to remove residual hydrogen from anode gas channel after shut-down of the fuel cell. In this study, we investigated the long-term stability of MEA under different on/off operation conditions. Residential hydrogen gas was removed from the anode flow channel by purging air or nitrogen. Also, a dummy resistance was applied to the fuel cell to exhaust residential hydrogen at the anode. In these cases, MEA showed much more stable durability. Electrochemical characteristics of the fuel cell were measured byrepeating the on/off cycles with the hydrogen removal processes. Also, degradation of MEA components was examined by SEM, TEM and XRD analyses.

• 동력기계공학회지
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• 제13권6호
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• pp.95-101
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• 2009

The generator for gas turbine power generation consists of the rotor which generates magnetic field, the winding coil which is the path for the field current and the wedge and retaining ring which prevents the radial movement of the coil. Relatively severe deformation was observed at the coil end section during the inspection of the generator for peaking-load operation, and the thermal-electricity and the centrifugal force were evaluated by the simple modeling of the windings to find the cause. But the simulation stress was not sufficient to induce the coil plastic deformation. The analysis result seems to be applicable to the base-load generators which runs continuously without shut down up to a year, but there had been more deformation than simulated for the generator which is started up and shut down frequently. The cause of the coil deformation was the restriction of the expansion and shrinkage. The restriction occurs when the winding coil shrinks, and the stress overwhelms the yield stress and cause the plastic deformation. The deformation is accumulated during the start-ups and shut-downs and the thermal growth occurs. The factors which induce the coil restriction during the expansion and shrinkage should be reduced to prevent the unallowable deformation. The resolutions are cutting off the field current earlier during the generator shut-down, modifying the coil end section to remove the stress concentration and making the insulation plate inserted between the coil end section and the retaining ring have the constant thickness.

• 한국수소및신에너지학회논문집
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• 제23권2호
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• pp.156-161
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• 2012

In case of commercializing of the hydrogen fuel cell vehicle, the suitable emergency response guide is necessary to prepare an accident. In order to suggest the suitable guide for the domestic affairs, the existing external guide about GM, Ford, Honda, and Hyundai was reviewed. The emergency response guides in CAFCP and main FC vehicle makers were included in the analysis. As the results, it was found that the design and make of vehicle for the domestic user are demanded in the emergency response and the guide is made with the shut-down manual picked out for the rescuer and repair man as well as user.

• Wind and Structures
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• 제17권6호
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• pp.671-680
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• 2013

Static aeroelastic is investigated in a wind turbine blade. Imposed to different loadings, the very long and flexible structures of blades experience some changes in its preliminary geometry. This results in variations of aerodynamic loadings. An iterative approach is developed to study the interactions between structure and aerodynamics evaluating variations in induced stresses in presence of aeroelasticity phenomenon for a specific wind turbine blade. A 3D finite element model of the blade is constructed. Aerodynamic loading is applied to the model and deflected shape is extracted. Then, aerodynamic loadings are updated in accordance with the new geometry of the deflected blade. This process is repeated till the convergence is met. Different operational conditions consisting of stand-by, start-up, power production and normal shut-down events are investigated. It is revealed that stress components vary significantly in the event of power production at the rated wind speed; while it is less pronounced for the events of normal shut-down and stand-by.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제30회 추계학술대회
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• pp.179-183
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• 1999

Rubbing occurs when a rotating element comes in contact with a stationary element. In the steam turbines, the rotating element is the rotor while the stationary elements are usually the oil deflectors and packing seals. Rubbing phenomenon may be often obseued on a new or rebuilt machine rather than on a machine that has been operating for several months or years. Rubbing in the turbine has been classified into two modes by the operating conditions: 1) start up or shut down, 2) steady state. At start up or shut down operation, rubbing produces synchronous whirl vibration, which are caused by thermal bow of the shaft due to localized heating on the shaft surface. While subsynchronous whirl vibration is caused by partial rubbing during the steady state operation. In this paper, the two case studies of troubleshooting for excessive vibration caused by rubbing in the actual steam turbines are investigated.

• Journal of Preventive Medicine and Public Health
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• 제53권5호
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• pp.293-301
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• 2020

Objectives: At the beginning of the coronavirus disease 2019 (COVID-19) pandemic, some countries imposed entry bans against Chinese visitors. We sought to identify the effects of border shutdowns on the spread of the COVID-19 outbreak. Methods: We used the synthetic control method to measure the effects of entry bans against Chinese visitors on the cumulative number of confirmed cases using World Health Organization situation reports as the data source. The synthetic control method constructs a synthetic country that did not shut down its borders, but is similar in all other aspects. Results: Six countries that shut down their borders were evaluated. For Australia, the effects of the policy began to appear 4 days after implementation, and the number of COVID-19 cases dropped by 94.4%. The border shutdown policy took around 13.2 days to show positive effects and lowered COVID-19 cases by 91.7% on average by the end of February. Conclusions: The border shutdowns in early February significantly reduced the spread of the virus. Our findings are informative for future planning of public health policies.