• Journal of Power Electronics
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• 제17권1호
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• pp.282-293
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• 2017

There exists a strong coupling between real and reactive power owing to the complex impedances in droop based islanded microgrids (MGs). The existing virtual impedance methods consider improvements of the impedance matching for sharing of the voltage controlled power (VCP) (reactive power for Q-V droop, and real power for P-V droop), which yields a 1-DOF (degree of freedom) tunable virtual impedance. However, a weak impedance matching for sharing of the frequency controlled power (FCP) (real power for $P-{\omega}$ droop, and reactive power for $Q-{\omega}$ droop) may result in FCP overshoots and even oscillations during load transients. This in turn results in VCP oscillations due to the strong coupling. In this paper, a 2-DOF tunable adaptive virtual impedance method considering impedance matching for both real and reactive power (IM-PQ) is proposed to improve the power sharing performance of MGs. The dynamic response is promoted by suppressing the coupled power oscillations and power overshoots while realizing accurate power sharing. In addition, the proposed power sharing controller has a better parametric adaptability. The stability and dynamic performances are analyzed with a small-signal state-space model. Simulation and experimental results are presented to investigate the validity of the proposed scheme.

• Journal of Information Technology Applications and Management
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• 제20권4호
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• pp.165-189
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• 2013

The advance of the smart working environment came the expectation that it would innovate and revolutionize the way people work, particularly in a society where smart work is readily available for creating a collaborative and 'connected' business. One of the core infrastructure elements for making smart work a viable option is the smart work center, the promotion of which requires a new form of 'smart work center business model' that can satisfy the purposes of both public services and private businesses. This calls for collaboration between the public and private sectors. Recently a number of businesses have been making significant headway in the creation of a new environment for business support and collaboration by adopting a sharing economy business model in their offices. The so-called 'Coworking Space' is an advanced form of business environment in the emerging 'smart work' era, and comes with the benefits of reduced costs as a result of sharing office space and knowledge sharing through the use of human networks. This paper describes the framework of a 'smart work center business model based on the sharing economy' using a BMC (Business Model Canvas), with an understanding of the characteristics inherent to the smart work center and the sharing economy. It was on the basis of this framework that a smart work center model for business incubation and startup, a private smart work center model for childcare services, and a community marketplace model with a global network were developed.

• 한국멀티미디어학회논문지
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• 제7권2호
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• pp.264-271
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• 2004

인터넷기반의 클러스터 시스템 환경에서 부하공유 알고리즘은 네트워크의 특성 및 노드의 이질성에 따른 부하 불균형에 효과적으로 대처 할 수 있어야 한다. 본 논문에서 제안하는 효율적인 부하공유기법은 Weighted Factoring 알고리즘을 기반으로 스케줄러를 생성하고 여기에 적응할당정책과 개선된 고정 분할 단위 알고리즘을 적용하여 작업을 분배하는 것이다. 본 논문에서 적용한 적응할당정책은 상대적으로 작업속도가 느린 종노드의 작업을 빠른 종노드가 대신 수행하도록 하는 기법이며, 개선된 고정 분할 단위 알고리즘은 종노드의 계산시간과 데이터전송에 필요한 네트워크 통신시간을 겹치도록 하는 것이다. 제안된 알고리즘의 성능 평가를 위한 시스템 환경에서 멀티미디어 응용에 많이 사용되는 행렬의 곱셈 프로그램을 PVM을 통하여 실험한 결과, 본 논문에서 제안한 알고리즘이 NOW 환경에서 우수한 Send, GSS, Weighted Factoring 알고리즘보다 각각 75%, 79%, 그리고 17% 효율적임을 보였다.

• 정보처리학회논문지A
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• 제8A권2호
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• pp.117-124
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• 2001

At NOW (Networks Of Workstations), the load sharing is very important role for improving the performance. The known load sharing strategy is fixed-granularity, variable-granularity and adaptive-granularity. The variable-granularity algorithm is sensitive to the various parameters. But Send algorithm, which implements the fixed-granularity strategy, is robust to task granularity. And the performance difference between Send and variable-granularity algorithm is not substantial. But, in Send algorithm, the computing time and the communication time are not overlapped. Therefore, long latency time at the network has influence on the execution time of the parallel program. In this paper, we propose the preSend algorithm. In the preSend algorithm, the master node can send the data to the slave nodes in advance without the waiting for partial results from the slaves. As the master node sent the next data to the slaves in advance, the slave nodes can process the data without the idle time. As stated above, the preSend algorithm can overlap the computing time and the communication time. Therefore we reduce the influence of the long latency time at the network and the execution time of the parallel program on the NOW. To compare the execution time of two algorithms, we use the $320{\times}320$ matrix multiplication. The comparison results of execution times show that the preSend algorithm has the shorter execution time than the Send algorithm.

• Journal of Communications and Networks
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• 제17권4호
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• pp.394-405
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• 2015

This paper considers a wideband cognitive radio network which can simultaneously sense multiple narrowband channels and thus aggregate the detected available channels for transmission and proposes a novel cognitive radio system that exhibits improved sensing throughput and can save power consumption of secondary user (SU) compared to the conventional cognitive radio system studied so far. More specifically, under the proposed cognitive radio system, we study the problem of designing the optimal sensing time and power allocation strategy, in order to maximize the ergodic throughput of the proposed cognitive radio system under two different schemes, namely the wideband sensing-based spectrum sharing scheme and the wideband opportunistic spectrum access scheme. In our analysis, besides the average interference power constraint at primary user, the average transmit power constraint of SU is also considered for the two schemes and then a subgradient algorithm is developed to obtain the optimal sensing time and the corresponding power allocation strategy. Finally, numerical simulations are presented to verify the performance of the two proposed schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권9호
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• pp.4220-4241
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• 2017

For the downlink energy-harvesting small cell network, this paper proposes an interference management algorithm based on distributed coalitional game. The cooperative interference management problem of the energy-harvesting small cells is modeled as a coalitional game with transfer utility. Based on the energy harvesting strategy of the small cells, the time sharing mode of the small cells in the same coalition is determined, and an optimization model is constructed to maximize the total system rate of the energy-harvesting small cells. Using the distributed algorithm for coalition formation proposed in this paper, the stable coalition structure, optimal time sharing strategy and optimal power distribution are found to maximize the total utility of the small cell system. The performance of the proposed algorithm is discussed and analyzed finally, and it is proved that this algorithm can converge to a stable coalition structure with reasonable complexity. The simulations show that the total system rate of the proposed algorithm is superior to that of the non-cooperative algorithm in the case of dense deployment of small cells, and the proposed algorithm can converge quickly.

• 한국경영과학회지
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• 제36권1호
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• pp.69-84
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• 2011

In this study, based on the principal-agent paradigm, we investigate a joint cost reduction activity in a buyer-supplier supply chain where a buyer motivates its operations department and a supplier to reduce the supply chain's production cost. We construct a benefit-sharing model based on the target cost scheme, a basic philosophy in practice which has not been explored in previous studies. The model also incorporates various supply chain issues such as the cooperation of multiple agents, the opportunity loss, and the degree of strategic relationship between the buyer and the supplier. Based on the analysis of the principal-agent model, we investigate the benefit-sharing rule to control agents' actions, and we also provide important managerial implications into supply chain practices via extensive comparative static analyses.

• 한국데이타베이스학회:학술대회논문집
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• 한국데이타베이스학회 2008년도 연합학회학술대회
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• pp.307-320
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• 2008

본 연구는 관계중심적 지식관의 관점에서 지식공유의 영향 요인을 파악하고, 이 요인들이 실제로 지식공유에 긍정적인 영향을 미쳐서 지식성과활동을 향상 시키는지 알아보고자 한다. 독립변수인 관계적 요인은 신뢰, 개방적 의사소통, 협동으로 설정하였고, 지식공유의 영향을 받는 종속 변수인 지식활동성과는 지식품질과 지식경영사용자만족도로 설정하였다. 본 연구를 통해 조직경쟁력 향상을 위해서는 지식뿐만 아니라 그것을 사용하는 사람 및 주변 환경까지 관리할 필요가 있음을 제안한다.

• Journal of Information Technology Applications and Management
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• 제25권4호
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• pp.171-184
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• 2018

Social media has been integrated into a part of travel industry. Subsequently, it has influenced tourists' travel behavior. Prior studies claim that individuals have different behaviors regarding the use of social media for travel purposes. With lack of studies focusing on age group, the objective of this study is to determine whether there is a difference in the motivation among three generations in using social media for the sake of sharing travel experiences. Finding shows that all generations use social media with similar motivation for travel purposes. They have high motivation in obtaining travel information before the trip and in sharing memorable travel experiences through social media. They also wanted to keep such information as personal document during and after the traveling.

• Journal of Information Technology Applications and Management
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• 제30권2호
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• pp.19-30
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• 2023

This study aims to analyze service improvement and success factors of electric scooter sharing service companies by using text mining after collecting reviews of shared electric scooter service applications among various models of sharing economy. In this study, the factors of satisfaction and dissatisfaction of service users were identified using the term frequency inverse document frequency (TF-IDF) technique, and topics for each keyword were extracted using the Latent Dirichlet Allocation (LDA) Topic Modeling technique. According to the analysis results, the main topics were entertainment, safety, service area, application complaints, use complaints, convenience, and mobility. Using the analysis results of this study, employees and researchers of electric scooter sharing service companies will be able to contribute to the improvement and success of related services.