• International Journal of Computer Science & Network Security
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• 제22권1호
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• pp.189-198
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• 2022

As the number of people using the Internet increases, a new application known as the Internet of Things (IoT) has been emerged. Internet of Things makes it easier for machines and objects to exchange, compute, and coordinate information autonomously without human interference. It is a tool for attaching intelligence to a variety of contemporary objects in houses, hospitals, buildings, vehicles, and even cities. As a new emerging technology, the focus in current IoT surveys does not shed the light on deep understanding for IoT fundamentals, architectures, challenges, and solutions. For this reason, the objective of this paper is to introduce specifications for IoT definitions, characteristics, functional blocks, and different architectures as a cement for better understanding. Additionally, we present current documented IoT challenges, with the existing available solution for each challenge.

• Ocean Systems Engineering
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• 제14권1호
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• pp.85-99
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• 2024

Ocean surface currents have an essential role in the Earth's climate system and significantly impact the marine ecosystem, weather patterns, and human activities. However, predicting ocean surface currents remains challenging due to the complexity and variability of the oceanic processes involved. This review article provides an overview of the current research status, challenges, and opportunities in the prediction of ocean surface currents. We discuss the various observational and modelling approaches used to study ocean surface currents, including satellite remote sensing, in situ measurements, and numerical models. We also highlight the major challenges facing the prediction of ocean surface currents, such as data assimilation, model-observation integration, and the representation of sub-grid scale processes. In this article, we suggest that future research should focus on developing advanced modeling techniques, such as machine learning, and the integration of multiple observational platforms to improve the accuracy and skill of ocean surface current predictions. We also emphasize the need to address the limitations of observing instruments, such as delays in receiving data, versioning errors, missing data, and undocumented data processing techniques. Improving data availability and quality will be essential for enhancing the accuracy of predictions. The future research should focus on developing methods for effective bias correction, a series of data preprocessing procedures, and utilizing combined models and xAI models to incorporate data from various sources. Advancements in predicting ocean surface currents will benefit various applications such as maritime operations, climate studies, and ecosystem management.

• Smart Structures and Systems
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• 제15권2호
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• pp.283-297
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• 2015

Jacket-type offshore structures are always exposed to severe environmental conditions such as salt, high speed of current, wave, and wind compared with other onshore structures. In spite of the importance of maintaining the structural integrity for an offshore structure, there are few cases to apply a structural health monitoring (SHM) system in practice. The impedance-based SHM is a kind of local SHM techniques and to date, numerous techniques and algorithms have been proposed for local SHM of real-scale structures. However, it still requires a significant challenge for practical applications to compensate unknown environmental effects and to extract only damage features from impedance signals. In this study, the impedance-based SHM was carried out on a 1/20-scaled model of an Uldolmok current power plant structure in Korea under changes in temperature and transverse loadings. Principal component analysis (PCA)-based approach was applied with a conventional damage index to eliminate environmental changes by removing principal components sensitive to them. Experimental results showed that the proposed approach is an effective tool for long-term SHM under significant environmental changes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권3호
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• pp.1441-1461
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• 2017

Nowadays, Dynamic Adaptive Streaming over HTTP (DASH) has become very popular in streaming multimedia contents. In DASH, a client estimates current network bandwidth and then determines an appropriate video quality with bitrate matching the estimated bandwidth. Thus, estimating accurately the available bandwidth is a significant premise in the quality of video streaming, especially when network traffic fluctuates substantially. To cope with this challenge, researchers have presented various filters to estimate network bandwidth adaptively. However, experiment results show that current schemes either adapt slowly to network changes or adapt fast but are very sensitive to delay jitter and produce sharply changed estimation. This paper presents a novel bandwidth estimation scheme based on Moving Average Convergence Divergence (MACD). We applied an MACD indicator and its two thresholds to classifying network states into stable state and agile state, based on the network state different filters are applied to estimate network bandwidth. In the paper, we studied the performance of various MACD indicators and the threshold values on bandwidth estimation. Then we used a DASH proxy-based environment to compare the performance of the presented scheme with current well-known schemes. The simulation results illustrate that the MACD-based bandwidth estimation scheme performs superior to existing schemes both in the speed of adaptively to network changes and in stability in bandwidth estimation.

• 보건행정학회지
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• 제24권1호
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• pp.4-12
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• 2014

Background: The purpose of this study is to investigate current status and investigation of government agencies, communities, corporates, hospitals, non-governmental organization, non-profit organization, and so on which performed Corporate Social Responsibility to global health issues. Methods: This paper focuses on analyzing definition and principle of public-private partnership (PPP), types of PPP, challenge of PPP through delphi survey and interview which need to be discussed by professional groups such as private groups, universities and researches, government decision makers, corporates, and hospitals for successful PPP. Results: Based on this analysis on global health issues of 237 groups, the results were shown that main global health issues of many hospitals were aids of the developing countries (48%). Main program was activities of overseas volunteers (30%) and most 152 groups (42%) supported Asia. Also, this paper gives a definition of PPP that is the growth together in PPPs as a way of fulfilling public tasks in partnership between the state administration and private enterprises to apply both strengths behind transparency, accountability. Conclusion: In conclusion, from the results of analysis, we suggest as prior setting of global issues for both demand and supply side and are served as the effective way by PPP on global health issues. Moreover, this study will be expanded on the sections of findings, multiple researches, discussion, and policy recommendations.

• 한국국방경영분석학회지
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• 제26권2호
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• pp.101-119
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• 2000

US DoD designated the High LEvel Architecture (HLA) as the standard technical architecture for all military simulation since 1996. HLA will supercede the current Distributed Interactive Simulation(DIS) and Aggregated LEvel Simulation Protocol(ALSP) methods by no funds for developing/modifying non-HLA compliant simulations. The new architecture specifies Rules which define relationships among federation components, an Objects Model Template which species the form which simulation elements are described, and an Interface Specification which describes the way simulations interact during operations. HLA is named as standard architecture in NATO, Australia and many other militaries. Also, it will be IEEE standard in the near future. It goes without saying that ROK military whose simulation models are almost from US must be prepared in areas such as ROK-US combined exercise, training, weapon system acquisition, interface models with C4I system, OPLAN analysis, operations, and os on. In this paper, we propose several effective alternatives and issues for ROK Defense Modeling and Simulation under the transition of new HLA architecture. Those include secure the kernel of new simulation technology and develop our own conceptual model, RTI software, prototype federation for each service and aggregated one. In order to challenge the new simulation architecture effectively, we should innovate our current defense modeling and simulation infrastructure such s manpower, organization, budget, research environment, relationships among academia and industry, and many others.

• Journal of Power Electronics
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• 제16권6호
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• pp.2129-2138
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• 2016

The full-bridge inverter, widely used for single-phase photovoltaic grid-connected applications, presents a leakage current issue. Therefore, an AC bypass branch is introduced to overcome this challenge. Nevertheless, existing modulation strategies entail drawbacks that should be addressed. One is the zero-crossing distortion (ZCD) of the AC current caused by neglecting the AC filter inductor voltage. Another is that the system cannot deliver reactive power because the AC bypass branch switches at the power frequency. To address these problems, this work proposes an optimized hybrid modulation strategy. To reduce ZCD, the phase angle of the inverter output voltage reference is shifted, thereby compensating for the neglected leading angle. To generate the reactive power, the interval of the negative power output is calculated using the power factor. In addition, the freewheeling switch is kept on when power is flowing into the grid and commutates at a high frequency when power is fed back to the DC side. In this manner, the dead-time insertion in the high-frequency switching area is minimized. Finally, the performances of the proposed modulation strategy and traditional strategies are compared on a universal prototype inverter. Experimental results validate the theoretical analysis.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 센서 박막재료 반도체 세라믹
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• pp.71-74
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• 2003

Photoconductor for direct detection fiat-panel imager present a great materials challenge, since their requirement include high X-ray absorption, ionization and charge collection, low leakage current and large area deposition, CdTe is practical material. We report studies of detector sensitivity, That is an CdTe with $5{\mu}m$ thickness on glass. That is hybrid layer of depositting ZnS:AgCl phosphor with $100{\mu}m$ on CdTe. The leakage current of hybrid is similar to it of a-Se, but photocurrent is larger than a-Se. Both of them have high spatial resolution, but hybrid has higher sensitivity than a-Se at comparable bias voltage.

• Nuclear Engineering and Technology
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• 제37권1호
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• pp.79-90
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• 2005

In this paper are reviewed the current status of nuclear fuel management and reactor operational aid tools. In addition, we indicate deficiencies in current capabilities and what future research is judged warranted. For the nuclear fuel management review the focus is on light water reactors and the utilization of stochastic optimization methods applied to the lattice, fuel bundle, core loading pattern, and for BWRs the control rod pattern/core flow design decision making problems. Significant progress in addressing separately each of these design problems on a single cycle basis is noted; however, the outstanding challenge of addressing the integrated design problem over multiple cycles under conditions of uncertainty remains to be addressed. For the reactor operational aid tools review the focus is on core simulators, used to both process core instrumentation signals and as an operator aid to predict future core behaviors under various operational strategies. After briefly reviewing the current status of capabilities, a more in depth review of adaptive core simulation capabilities, where core simulator input data are adjusted within their known uncertainties to improved agreement between prediction and measurement, is presented. This is done in support of the belief that further development of adaptive core simulation capabilities is required to further significantly advance the utility of core simulators in support of reactor operational aid tools.

• ETRI Journal
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• 제45권3호
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• pp.519-533
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• 2023

This paper implements a simultaneous solar and thermal energy harvesting system, as a hybrid energy harvesting (HEH) system, to convert ambient light into electrical energy through photovoltaic (PV) cells and heat absorbed in the body of PV cells. Indeed, a solar panel equipped with serially connected thermoelectric generators not only converts the incoming light into electricity but also takes advantage of heat emanating from the light. In a conventional HEH system, the diode block is used to provide the path for the input source with the highest value. In this scheme, at each time, only one source can be handled to generate its output, while other sources are blocked. To handle this challenge of combining resources in HEH systems, this paper proposes a method for collecting all incoming energies and conveying its summation to the load via the current mirror cells in an approach similar to the maximum power point tracking. This technique is implemented using off-the-shelf components. The measurement results show that the proposed method is a realistic approach for supplying electrical energy to wireless sensor nodes and low-power electronics.