• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.3
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• pp.275-284
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• 2004

This paper discusses how to control the compensation voltages in dynamic voltage restorers (DVR). On analyzing the power circuit of a DVR system, control limitations and control targets are presented for the voltage compensation in DVRs. Based on the preceded power stage analysis, a novel controller for the compensation voltages of DVRs is proposed by a feed forward control scheme. This paper discusses also the time delay problems in the control system of DVRs. Digitally controlled DVR systems normally have control delay at amount of one sampling time of the control system and a half of the switching period of the DVR inverter. The control delay in digital controllers increases the dimension of the system transfer function one degree higher, which makes the control system more complicate and more unstable. This paper proposes a guide line to design the control gain, appropriate output filter parameters and inverter switching frequency for DVRs with digital controllers. Proposed theory is verified by an experimental DVR system with a full digital controller.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.10
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• pp.95-102
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• 2003

The buffering is a promising solution to resolve the contention problem in optical network. we study the packet loss probability and the dimensioning of optical buffer using a Fiber Delay Line for variable length packet. In this paper, we study the relation between the granularity and the loss of FDL buffer in Single-Stage FDL buffer and propose the Single-Bundle Multi-Stage FDL buffer. The Multi-Stage FDL buffer is too early yet to apply to the current backbone network, considering the current technology in view of costs. but we assume that the above restriction will be resolved in these days. The appropriate number of delay and pass line for a dimensioning is based on a amount of occupied time by packets. Once more another multi-stage FDL buffer is proposed, Split-Bundle multi-stage FDL buffer. The Split-Bundle ms-FDL buffer is more feasible for a FDL buffer structure, considering not only a size of switching matrix but also a bulk of switching element. its feasibility will be demonstrated from a loss probability.

• The KIPS Transactions:PartC
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• v.9C no.6
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• pp.847-856
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• 2002

Cellular network applications are growing drastically and this requires a fast and efficient transport method between the base station and the mobile switching center. One possible solution is to use ATM links. The low data rate and small-sized packets in the typical cellular applications imply that significant amount of link bandwidth would be wasted, if this small sized packet is carried by one ATM cell. For efficient operation for such cellular and low bit rate applications, a new type of ATM Adaptation Layer, AAL Type 2, has been proposed. In this paper, the principles of AAL Type 2 are briefly described along with the introduction of other alternatives which have formed the basis for this new AAL. The result from the simulation to study the performance of the AAL Type 2 is discussed from the view point of packet delay and ATM cell use efficiency. Due to the variable size of packets in this application, the fairness issue in serving variable sized packets is also discussed along with the effect of fair queueing algorithm implemented at AAL Type 2.

• The KIPS Transactions:PartC
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• v.10C no.2
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• pp.185-190
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• 2003

Bluetooth communication is based on piconet, which is composed by one master and maximum seven slaves. Several piconets can be interconnected via an inter-piconet Bluetooth unit called a bridge unit to form a Bluetooth scatternet. This bridge node can make its presence in each piconet by switching. This switching must be carefully scheduled so that slot wastage and, hence, packet delays are minimized. In this paper, we introduce an efficient inter-piconet scheduling scheme based on sniff mode. This scheme tries to minimize the wastage of slots by having the bridge unit sniff with its peering masters with time limits and communicate with its slaves in remaining slots. The sniff time limits are determined adaptively based on the amount of traffic in each piconet. Simulation results show this scheme outperforms round-robin scheme based on sniff intervals of equal lengths.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.6
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• pp.578-586
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• 2005

Recently, due to the launch of digital broadcasting service, the demand of Flat Panel Display (FPD) is sharply rising. Among them, the PDP is expected to be one of the most promising digital displays of next generation because of its large screen size, high resolution, thinness and board field of view. Meanwhile, the PDP uses ADS (Address Display-period Separation) scheme which divide one subfield into address and sustaining period to express the grey scale of images. Since the output of sustaining power module Is mostly used for sustaining period, the load of the sustaining power module can be considered as a pulsating load. Due to this particular load condition, if the wide ZVS range of the power switches is not guaranteed, the hard switching causes large amount of switching loss and serious thermal problem in power module. In this paper, a high efficiency power conversion circuit for 60' PDP sustaining power module which achieves wide ZVS range with the help of additional ZVS tank is proposed. According to the various gating methods, the different operations of the proposed converter are presented. And, to confirm the properties of the proposed converter, an experimental prototype of 900W power converter is constructed md tested. As a result, more than $92\%$ of high efficiency is obtained at $10\%$ load condition, and the ZVS operation is achieved from full load to $10\%$ load condition.

• Journal of Internet Computing and Services
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• v.16 no.4
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• pp.1-11
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• 2015

This study uses the contingent valuation method to estimate the switching cost for adopting the MVNO service. The findings are as follows.: First, Willingness To Switch(WTS) increases as users' using pattern and perceived degree of MVNO service, but satisfaction with current service provider does not play a significant role in predicting Switching Cost. This means that as amount of money users can save exceeds a certain level, users decide to willingly change their service provider to MVNO regardless of their level of satisfaction with current service provider. Second, there are differences in WTS among service subscribers in SKT, KT and LGU+. It means that there will be a difference in the tendency to switch to MVNO among subscribers of service providers. This study suggest the following mangerial perspective to effectively promote the MVNO and boost the MVNO market for activation of mobile data services.: First, MVNOs are better off applying differentiated pricing scheme at attractive rates than using a differentiation of service product and quality. Second, regulators should consider how to implement an MVNO regulatory policy when there is an asymmetric customer loyalty among MNOs. This research will be used to set the MVNO's pricing strategy and to build up a successful regulatory policies.

• Clinical and Experimental Reproductive Medicine
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• v.43 no.1
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• pp.44-50
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• 2016

Objective: This study was performed to assess our clinical experience with single-port access (SPA) laparoscopic cystectomy and myomectomy and the surgical outcomes of those procedures at our institution. Methods: The authors evaluated the surgical outcomes of SPA laparoscopic cystectomy in 293 patients and SPA laparoscopic myomectomy in 246 patients. The surgical outcomes comprised operation time, the amount of blood loss during the operation, the change in hemoglobin (before and after the operation), the change in hematocrit (before and after the operation), switching to the multi-port access method, complications, transfusions, and the duration of the postoperative hospital stay. Results: The Pearson correlation coefficient and the Spearman correlation coefficient between the operation time and the amount of blood loss were 0.312 and 0.321 for SPA laparoscopic cystectomy, respectively, and 0.706 and 0.674 for SPA laparoscopic myomectomy, respectively. The drops in hemoglobin and hematocrit were $1.33{\pm}0.78g/dL$ and $4.14%{\pm}2.45%$, respectively, in SPA laparoscopic cystectomy, while the corresponding figures were $1.34{\pm}1.13g/dL$ and $4.17%{\pm}3.24%$ in SPA laparoscopic myomectomy, respectively. Conclusion: This study reported the surgical outcomes of SPA laparoscopic cystectomy and myomectomy and compared them to previously published findings on traditional laparoscopic cystectomy and myomectomy. No significant differences were found in the surgical outcomes between SPA and traditional laparoscopic cystectomy and myomectomy.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.6
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• pp.1081-1086
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• 2023

The rapid growth and increasing complexity of modern networks have highlighted the limitations of traditional network architectures. The emergence of SDN (Software-Defined Network) in response to these challenges has changed the existing network environment. The SDN separates the control unit and the data unit, and adjusts the network operation using a centralized controller. However, this structure has also recently caused a huge amount of traffic due to the rapid spread of numerous Internet of Things (IoT) devices, which has not only slowed the transmission speed of the network but also made it difficult to ensure quality of service (QoS). Therefore, this paper proposes a method of load distribution by switching the IP and any server (processor) from the existing data processing scheduling technique, RR (Round-Robin), to mapping when a large amount of data flows in from a specific IP, that is, server overload and data loss.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.3
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• pp.107-112
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• 2015

A smart phone and the number of wireless terminals are mobile-to the nature of the AP mobility are many call transfer between wireless terminals and AP (Access Point). Each wireless terminal that is the call processing process for each is relatively large to cause the wireless traffic, and a factor that inhibits the efficient use of the radio band on the AP. In this paper, we use the power intensity threshold and threshold timer of the AP received by the mobile station to reduce the amount of switching traffic between the AP's cause and traffic generation factors between the wireless device and the AP that can effectively utilize the radio traffic from the AP the measures proposed. The proposed method and the conventional method is improved by simulation to handle the amount of radio traffic from the AP it was confirmed that it is possible to effectively utilize the whole of the radio band.

• Journal of the Korean Institute of Telematics and Electronics
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• v.14 no.3
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• pp.25-31
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• 1977

Fe V spinels were prepared by sintering the well-ground stoichiometric mixtures of Fe O and V O at 1,10$0^{\circ}C$ under H -CO atmosphere. The activation energy for electrical conduction decreases with increasing amount of iron. The tendency of activation energy depending on the amount of iron contained clarifies that the electrical condction of the spinel is mainly due to electron hopping between Fe and Fe ions at B sites. In the experiment for negative resistance characteristics, the threshold voltage (Vth) for the samples is related to ambient temperature, thickness and raising rate of applied voltage. Vth decreases as temperature increases while Vth increases linearly with thickness and Vth increases linearly with the raising rate of applied voltage in semi-logarithmic scale. These results lead to a conclusion that current paths mainly formed by thermal breakdown are ascribed to the negative resistance phenomena. Applying this property, these vanadium iron spinels may be used for switching elements.