• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.77.1-77.1
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• 2010

Durability problems of gas diffusion layer(GDL) is one of the important issues for accomplishing commercialization of proton exchange membrane fuel cell(PEMFC). GDL is strongly related to the performance of PEMFC because one of the main function of GDL is to work as a path of fuel, air and water. When the GDL is degraded, it causes water balance problems such as the flooding phenomenon. Thus, investigating the durability characteristics of the GDL is important and understanding the GDL degradation process is needed. In this study, the GDLs are degraded by carbon corrosion stress method which is the electrochemical degradation mode. To determine the effects of carbon corrosion of the GDL, 1.45 V of potential is imposed for 96 hours. In this manner, in the previous research, the structure between the substrate and the MPL is weaken. Further investigations are needed to clarify this phenomenon. Therefore, in this study, the carbon corrosion stress method is carried out with GDLs which have various MPL penetration levels and the effects of the MPL penetration level on the characteristics change of the GDL are analyzed. The changes in characteristics are measured with various properties of GDL such as weight, thickness and static contact angle. The degraded GDL shows loss of their properties.

• The Journal of Asian Finance, Economics and Business
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• 제7권12호
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• pp.565-576
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• 2020

This study examines factors of unemployment and career path challenges commonly faced by youth in the East Coast of Peninsular Malaysia. The study employed a quantitative approach which involved a total of 1,083 youths in Kelantan, Pahang and Terengganu selected at random. Descriptive and multiple regression analysis (OLS) methods were used to analyze demographic distribution of youth in determining factors influencing unemployment among them. The results reveal that the majority of youth respondents in the East Coast states of Malaysia are still unemployed and actively seeking employment. Demographic profiles are based on the survey results, youths seeking employment with 36 per cent distribution in Kelantan, 34 per cent in Pahang, and 30 per cent in Terengganu. Majority of the respondents were youths aged 20 to 24 years with a 40.9 percent percentage. The findings show that there are differences in factors affecting youth unemployment in the three states of East Coast, Malaysia. For Kelantan (age, experience, work mobility, marital status), Pahang (experience, marital status) and Terengganu (experience, gender, marital status, training). This study suggests that youths should be wise in preparing for their career by choosing the right career as well as doing side jobs to gain experience before they pursue for a real job.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권5호
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• pp.1036-1057
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• 2013

Wireless body area network (WBAN) is a promising candidate for future health monitoring system. Nevertheless, the path to mature solutions is still facing a lot of challenges that need to be overcome. Energy efficient scheduling is one of these challenges given the scarcity of available energy of biosensors and the lack of portability. Therefore, researchers from academia, industry and health sectors are working together to realize practical solutions for these challenges. The main difficulty in WBAN is the uncertainty in the state of the monitored system. Intelligent learning approaches such as a Markov Decision Process (MDP) were proposed to tackle this issue. A Markov Decision Process (MDP) is a form of Markov Chain in which the transition matrix depends on the action taken by the decision maker (agent) at each time step. The agent receives a reward, which depends on the action and the state. The goal is to find a function, called a policy, which specifies which action to take in each state, so as to maximize some utility functions (e.g., the mean or expected discounted sum) of the sequence of rewards. A partially Observable Markov Decision Processes (POMDP) is a generalization of Markov decision processes that allows for the incomplete information regarding the state of the system. In this case, the state is not visible to the agent. This has many applications in operations research and artificial intelligence. Due to incomplete knowledge of the system, this uncertainty makes formulating and solving POMDP models mathematically complex and computationally expensive. Limited progress has been made in terms of applying POMPD to real applications. In this paper, we surveyed the existing methods and algorithms for solving POMDP in the general domain and in particular in Wireless body area network (WBAN). In addition, the papers discussed recent real implementation of POMDP on practical problems of WBAN. We believe that this work will provide valuable insights for the newcomers who would like to pursue related research in the domain of WBAN.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권5호
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• pp.1146-1165
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• 2013

Collaborative awareness between persons with various smart multimedia devices is a new trend in the Internet of Things (IoT). Because of the mobility, randomness, and complexity of persons, it is difficult to achieve complete data awareness and data transmission in IoT. Therefore, research must be conducted on mobile-aware service models. In this work, we first discuss and quantify the social relationships of mobile nodes from multiple perspectives based on a summary of social characteristics. We then define various decision factors (DFs). Next, we construct a directed and weighted community by analyzing the activity patterns of mobile nodes. Finally, a mobile-aware service routing algorithm (MSRA) is proposed to determine appropriate service nodes through a trusted chain and optimal path tree. The simulation results indicate that the model has superior dynamic adaptability and service discovery efficiency compared to the existing models. The mobile-aware service model could be used to improve date acquisition techniques and the quality of mobile-aware service in the IoT.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.147.2-148
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• 2016

Light management technology is very important for thin film solar cells, which can reduce optical reflection from the surface of thin film solar cells or enhance optical path, increasing the absorption of the incident solar light. Using proper light trapping structures in hydrogenated amorphous silicon (a-Si:H) solar cells, the thickness of absorber layers can be reduced. Instead, the internal electric field in the absorber can be strengthened, which helps to collect photon generated carriers very effectively and to reduce light-induced loss under long-term light exposure. In this work, we introduced a chemical etching technology to make honey-comb textures on glass substrates and analyzed the optical properties for the textured surface such as transmission, reflection and scattering effects. Using ray optics and finite difference time domain method (FDTD) we represented the behaviors of light waves near the etched surfaces of the glass substrates and discussed to obtain haze parameters for the different honey-comb structures. The simulation results showed that high haze values were maintained up to the long wavelength range over 700 nm, and with the proper design of the honey-comb structure, reflection or transmission of the glass substrates can be enhanced, which will be very useful for the multi-junction (tandem or triple junction) thin film a-Si:H solar cells.

• Journal of Power Electronics
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• 제17권2호
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• pp.432-441
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• 2017

Grid voltage feedforward is extensively used for controlling grid-connected converters. However, the conventional voltage feedforward control reduces the stability margins of the converter connected to a high-impedance grid. The effect mechanism of voltage feedforward on the grid-connected converter control under high-inductive conditions of the grid impedance is clearly explained in this study using the equivalent transformations of control block diagrams. Results show that the delay produced by the digital control is the root cause of this effect. An improved voltage feedforward strategy, in which a bandpass filter (BPF) is introduced into the feedforward path, is proposed to strengthen the converter's robust stability against grid impedance variations. The selection method of the BPF's bandwidth is also provided considering the tradeoff between the response speed to the grid voltage sag and the system's robust stability. The converter can work stably over a wide range of the grid impedance through the proposed approach. Simulation and experimental results fully verify the effectiveness of the BPF-based voltage feedforward strategy.

• 한국조경학회지
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• 제34권4호
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• pp.61-68
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• 2006

A park will soon be developed in an area of Gwangjang-dong, Gwangjin-gu. The place has been a patch of green space for years, isolated by driveways and apartment complexes and abandoned. This article describes plans to infuse the abandoned green space with history, ecology, culture, and sports. The facilities that are to be constructed in and around the green space are positioned to take into account the path of the sun and the location of the curvilinear green space axis. The cultural space is planned as a centerpiece of the park, linked with the sports facilities. The overall framework is arranged in harmony with nearby elementary schools, parks, public facilities, athletic facilities, parking lots, and apartment complexes. The themed circulation route was constructed according to the environmental conditions and the spatial plan. In addition, the historical space is planned to work in close conjunction with the cultural space, and the streets and pedestrian pathways have characters of their own. The established contour lines will be carefully preserved, and an ecological pond will. The facilities, such as the outdoor performance stage, the outdoor art gallery, the Monument of Wind represented by a sail, and the pedestrian bridge in memory of Acha-sansung, are positioned for spatial balance and to provide a nexus. The bamboo forest, designed to foster the experience of sound effects, the architectural thematic plants, and the ecological pond are positioned to connect to each other around the greenspace axis. The main facilities are the outdoor theater, the bamboo forest, the Acha-sansung bridge, the Monument of Wind, the ecological pond, the four-season flower garden, parking lots, playgrounds, circulatory athletic pathways, and the tennis court.

• 항공우주기술
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• 제9권2호
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• pp.185-192
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• 2010

75톤급 터보펌프를 대상으로 한 속도복합형 터빈과 설계회전수를 50% 증가시킨 30톤급 터보펌프 터빈 적용을 위한을 압력복합형 터빈 설계를 수행하였다. 속도복합형 터빈의 경우 1차원설계-유동해석-1차원설계의 반복적인 설계과정을 통해 원형노즐을 적용한 2열 초음속 충동터빈의 특성을 파악하였으며 최종적으로 기본형인 1열 충동형 터빈 대비 비출력 23.1% 향상, 무게 5% 감소된 ver. 14h 모델을 완성하였다. 압력복합형 터빈은 에너지 회수 비율, 2단 노즐 출구각, 2단 노즐 누설유량, 단별 출력 비율 등의 새로운 인자의 고려하여 각 변수의 성능에 미치는 영향을 검토하였으며 1차원 해석 기준 비출력이 36%가 증대되고 무게는 51% 감소한 터빈을 설계하였다. 압력복합형 터빈의 높은 성능을 위해서는 1단 및 2단 노즐의 형상설계가 매우 중요할 것으로 판단되며 유동해석을 통해 최적화할 예정이다.

• 한국건설관리학회:학술대회논문집
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• 한국건설관리학회 2008년도 정기학술발표대회 논문집
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• pp.222-226
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• 2008

건설산업은 불확실성이 높은 산업으로 이에 따른 비용효용성 향상 및 경쟁력 강화를 위한 연구가 다각적으로 진행되어 왔다. 린 건설의 대표적인 요소기술인 라스트플래너 시스템은 기존의 상의하달식 의사결정체계를 개선한 하의상달식 접근방식으로서, 모든 참여주체가 함께 중 단기 공정계획을 검토 시행하는 체계이다. 이와 같은 린 건설은 최근 들어 건설프로젝트에서 주도적인 역할을 하고 있는 발주자의 적극적인 참여와 전체 생애주기를 총괄할 수 있는 리더역량을 요구하는 방향으로 논의가 전개되고 있다. 그러나 발주자가 참여하는 린 건설이 성공하기 위해서는 건설주체 상호간에 요구하는 니즈(needs)수준과 이를 개선하기 위한 전략들이 우선적으로 고려되어야 한다. 본 연구에서는 건설 시공과정에서의 참여주체 니즈 요소를 규명 분석하고, 중점관리항목과 이들 항목들의 개선가능성을 도출하는 방법, 그리고 이를 기반으로 한 발주자 참여형 린 건설 협업 모델을 제시하였다.

• 한국의학물리학회지:의학물리
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• 제14권1호
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• pp.1-7
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• 2003

본 연구에서는 팬텀에 인가된 강한 자기장에서 전자선에 대한 선량분포 계산을 위하여 EGS4 제어코드를 개발하였다. 이를 위하여 먼저 자기장에서 전자의 운동을 고찰하고 전자의 방향변화에 관한 수학적 결과를 EGS4 제어코드에 삽입하였다. 개발된 코드를 이용하여 6 MeV 전자선에 대하여 세로자기장 1-3T가 인가된 물팬텀 속에서 팬슬빔 전자들의 경로를 계산하였고 0.6-1 T가 인가된 물팬텀 속에서 직경 1cm의 조사면의 깊이선량율과 빔측면도를 계산하였다. 전자의 경로추적 계산결과 3 T의 자기장에서 전자들의 측면변위가 현저히 감소하는 것으로 나타났다. 직경 1 cm 전자선에 대한 깊이선량율은 비정근처에서 자기장의 세기에 따라 미소한 증가를 보였으며, 반음영은 1 T에서 약 0.15 cm 감소가 나타났다. 선량분포의 변화에 관한 계산결과들은 모두 이론적 해석이 가능하였으며 이로부터 본 계산코드의 신뢰성을 평가할 수 있었다.