• Journal of Power Electronics
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• v.16 no.1
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• pp.173-181
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• 2016

In this paper, a new technique for harmonic optimization in cascaded H-bridge 7-level inverters is proposed. The suggested strategy is based on minimizing an objective function which simultaneously optimizes the converter utilization and Total Harmonic Distortion (THD). The Switch Utilization Ratio (SUR) is formulized for both the phase and line-line voltages of a 7-level inverter and is considered in the final objective functions. Based upon the SUR formula, utilization ratio enhancement will reduce the value of feeding DC links, which improves the efficiency and lifetime of the circuit components due to lower voltage stresses and losses. In order to achieve more effective solution in different modulation indices, it is assumed that the DC sources can be altered. Experimental validation is presented based on a three-phase 7-level inverter prototype.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.11
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• pp.3680-3693
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• 2022

The handover procedure of IEEE 802.11 wireless local area networks (WLANs) introduces significant delay, which can degrade the quality of service (QoS) especially for delay-sensitive applications. Although studies have been conducted to support handover in SDN-based WLAN, there is no research to reduce the channel scanning procedure that takes up the most delay time in the handover process. The channel scanning procedure is essential to determine the appropriate access point (AP). To mitigate this problem, this paper proposes a SWITCH: SDN-WLAN integrated handover scheme for QoS-Guaranteed mobile service. In SWITCH, each AP periodically broadcasts beacon frames through different channels in a predetermined order that includes the operating channel information of the AP. This allows mobile stations (MSs) to receive the beacon frames of nearby APs, and therefore they can determine the appropriate APs for handover without the channel scanning procedure. By reporting the information of the newly moved AP to the SDN controller, a flow rule is installed in advance to provide fast handover, and packet loss is reduced by buffering data destined for MS. In addition, the proposed scheme can adaptively operate SWITCH to consider the user location and QoS requirement of flow to save radio resource overhead. Performance evaluation results demonstrate that SWITCH can reduce the handover delays, flow table utilization ratio and radio resource overhead while improving the network throughput.

• The Transactions of the Korea Information Processing Society
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• v.6 no.3
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• pp.742-749
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• 1999

This paper proposes the mechanism of cell buffering in the output buffer of ATM switch for the traffic with the different QOS in the ATM environment. The proposed mechanism, VQS(Variable Queue Sharing) can minimize the cell loss ratio(CLR) of bursty traffic through the sharing of CBR queue, VBR queue, ABR queue to maximize the utilization of queue resource. To evaluate VQS performance, we make simulator using Visual Slam 2.0. We compare the CLP and cell average delay of VQS and HOL, QLT_HOL using the bursty traffic patterns.

• Journal of Institute of Convergence Technology
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• v.4 no.1
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• pp.15-20
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• 2014

Recently, the development of renewable energy sources in Korea has been needed due to climate change. One of powerful alternative energy resources to mitigate emission is to switch conventional fuels to renewable energy, such as bioenergy. In this study, current status of bioenergy conversion technology and its supply in Korea was investigate. Based on theoretical, technical and realizable potential of biomass in Korea, the amount of reduction of green house gases was estimated. The results shown that the contribution of biomass on 2020 reduction target of green house gases emission in power generation was $513,000\;tCO_2/yr$ and utilization ratio of technical potential of biomass was 6.4%. For the effective supply of bioenergy in Korea, more exact estimation of realizable potential of biomass in Korea and stable supply sources are needed.

• Journal of the Korea Computer Industry Society
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• v.3 no.1
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• pp.19-26
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• 2002

This paper propose the queue structure of cell buffering in the output buffer of ATM switch for the traffic with the different QoS. The proposed queue structure can minimize the cell loss ratio of bursty traffic, maximize the queue utilization through the sharing of real-time queue and non-real-time queue. To evaluate the proposed queue structure, we compare the CLP and cell average delay of the proposed queue and fixed queue using the bursty traffic patterns.

• Journal of Korea Port Economic Association
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• v.31 no.4
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• pp.121-132
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• 2015

Yangsan ICD (Inland Container Depot) has played an important role for Busan Port and Korea's port & logistics industries, increasing international logistics competitiveness and containers' transportation competitiveness in Busan region dealing with 1330 thousand TEU in 2005, since its opening in March 2000. However, it is necessary to seek new measures to revitalize Yangsan ICD, since its cargo volume decreased rapidly owing to the opening of Busan New Port and hinterland in 2006. This study constructed an evaluation model using AHP (Analytic Hierarchy Process) and conducted a survey targeting local businesses and persons concerned in Yangsan ICD to seek measures for revitalization. The results suggest that Yangsan ICD needs to switch functions to logistics centers (terminal facilities, logistics warehouse) for revitalization considering its advantage of facility location. Moreover, by extending the utilization period and securing building-to-land ratio, existing and new businesses' stable activity should be guaranteed. Furthermore, utilizing facilities such as the railway station in ICD, an active railway revitalization policy may increase cargo volume. Yangsan ICD should perform its role as an inland logistics depot through the revitalization of railway freight transportation in the national logistics system focusing on road freight transportation.

• Journal of Navigation and Port Research
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• v.47 no.2
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• pp.106-119
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• 2023

Due to global decarbonization movement and tightening of maritime emissions restrictions, the shipping industry is going to switch to alternative fuels. Among candidates of alternative fuel, methanol is promising for decreasing SOx and CO2 emissions, resulting in minimum climate change and meeting the goal of green shipping. In this study, a novel combined system of direct methanol solid oxide fuel cells (SOFC), proton exchange membrane fuel cells (PEMFC), gas turbine (GT), and organic Rankine cycle (ORC) targeted for marine vessels was proposed. The SOFC is the main power generator of the system, whereas the GT and PEMFC could recover waste heat from the SOFC to generate useful power and increase waste heat utilizing efficiency of the system. Thermodynamics model of the combined system and each component were established and analyzed. Energy and exergy efficiencies of subsystems and the entire system were estimated with participation of the first and second laws of thermodynamics. The energy and exergy efficiencies of the overall multigeneration system were estimated to be 76.2% and 30.3%, respectively. The combination of GT and PEMFC increased the energy efficiency by 18.91% compared to the SOFC stand-alone system. By changing the methanol distribution ratio from 0.05 to 0.4, energy and exergy efficiencies decreased by 15.49% and 5.41%, respectively. During the starting up and maneuvering period of vessels, a quick response from the power supply system and propulsion plant is necessary. Utilization of PEMFC coupled with SOFC has remarkable meaning and benefits.