• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.351-352
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• 2016

Since anti-islanding scheme of grid-connected inverter is a key function of standards compliance, unintentional islanding results in safety hazards, reliability, and many other issues. Therefore, many anti-islanding schemes have been researched, however, existing anti-islanding schemes show poor power quality and non-detection zone issues. Besides, most of them have problems which deteriorate performance of islanding detection under parallel-operation. Therefore, this paper proposes a new anti-islanding scheme that has both negligible power quality degradation, no non-detection zone and precise islanding detection under parallel-operation. Finally, both simulation and experimental results validate the proposed scheme.

• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.411-416
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• 1991

Operation simulation is a key factor to evaluate investment and operation in a power utility. Probabilistic production simulation is of major concern. With pumped-storage plant, production simulation is not an easy task, because its economy should fully be exploited. In addition, usual operation interval is a week rather than a day. Most existing models are based on approximate production simulation such as adopting simple priority orders of generations. This study is based on the more elaborate model developed by authors. Further, a policy of weekly coordination is established based on the Maximum Principle. Chronological load curve instead of usual load duration curve is used and the accuracy in simulation is enhahced. Resulting economics are compared. Deviation between these two toad curve is shown.

• Journal of Communications and Networks
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• v.12 no.5
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• pp.480-491
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• 2010

Along with the wide acceptance of IEEE 802.11 wireless local area network (WLAN), new applications such as Internet protocol (IP) telephony over WLAN are fast emerging today. For battery-powered IP phone devices, the life time extension is a key concern for the market acceptance while today's 802.11 is not optimized for snch an operation. In this paper, we propose a novel idle mode operation, which comprises paging, idle handoff, and delayed handoff. Under the idle mode operation, a mobile host(MH) without any active session does not need to perform handoff within a predefined paging area (PA). Only when it enters a new PA, an idle handoff is performed. The proposed idle mode allows an MH without traffic to extend its life time. We develop a new analytical model in order to comparatively evaluate our proposed scheme. The numerical resnlts demonstrate that the proposed scheme outperforms the existing schemes with respect to power consumption.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.615-619
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• 2009

This paper is investigated to variation of wave power generation operation rate, operating capacity and output with the wave conditions represented by wave height-period window. By the use of the long-term wave data from 1979 to 2002 which is provided by Korea Ocean Research & Development Institute(KORDI), we calculated the monthly variation of significant wave height(Hs), zero-up crossing period(Tz) and distribution of wave appearance rate. And using the same wave data, it was charted the Hs-Tz and wave-energy scatter diagrams.

• ETRI Journal
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• v.25 no.5
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• pp.315-320
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• 2003

Elliptic curve cryptography (ECC) offers the highest security per bit among the known public key cryptosystems. The operation of ECC is based on the arithmetic of the finite field. This paper presents the design of a 193-bit finite field multiplier and an inversion unit based on a normal basis representation in which the inversion and the square operation units are easy to implement. This scalable multiplier can be constructed in a variable structure depending on the performance area trade-off. We implement it using Verilog HDL and a 0.35 ${\mu}m$ CMOS cell library and verify the operation by simulation.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.2 s.179
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• pp.65-72
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• 2006

Downcoiler is one of the major facilities in hot strip mill operation. The key to good coiling is having good equipment, modem control systems, excellent maintenance and an understanding of coiling process. Therefore, this study aims to develop a program that is useful for calculating machine design parameters and simulating coiling process. In this study, the pinching and coiling mechanism of the downcoiler was thoroughly studied and some of operational factors and their effects on the coiling process were investigated. The software was developed to estimate engineering parameters for coiler component design and to determine optimal setting values for successful coiling operation. In order to check the accuracy and usefulness of the developed software, the simulation of the downcoiler in $\#2$ Hot Strip Mill in Pohang Works was performed. The simulation results suggested that the set-up value for unit tension could be lowered. Test coiling operation by using the lowered set-up value for unit tension resulted in much more successful coiling in the aspect of strip quality and power consumption.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.51-54
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• 2010

Physical characteristics of liquid and gaseous oxygen and the detailed ignition characteristics of oxygen system were introduced. Compatible and non-compatible materials for oxygen were discussed. To ensure the safety operation of the oxygen system, one of the most important point, cleaning, was reviewed. To design the gaseous and liquid oxygen system, key points were introduced. To safe operation, the operating procedure and considerations were introduced.

• Journal of the military operations research society of Korea
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• v.16 no.2
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• pp.1-13
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• 1990

The life of an equipment depends upon its operating characteristics and physical environment factors. This paper presents the economic life length of 2 1/2 ton truck considering the operation terrains. For this specific research, the operation terrains are categorized into seacoast area, mountain area and plain area. To compute the life length, the method of equivalent annual cost is employed. The sample vehicles from each corresponding area are randomly selected from those vehicles whose ages exceed 9 years. This research finds the following results : (1) The life length operated at seacoast area is 9.75 years, (2) The life length operated at mountain area is 11.25 years, (3) The life length operated at plain area is 14 years. This research argues that the key factor such as characteristics of operating enviroment for allocation of operating and maintaining cost should be considered.

• Journal of IKEEE
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• v.22 no.4
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• pp.1019-1024
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• 2018

In this paper, we suggest a combined cost function to find out the optimal operation of an envelope tracking system, and evaluated its performance with Quadrature Amplitude Modulation (QAM) waveform, with which envelope tracking coefficients for the peak drain efficiency and the bandwidth of power amplifiers are determined. Based on the classical envelope tracking theory, the operation of the supply modulator, which is a key part of the envelope tracking process, is modeled and analyzed mathematically. Then characteristics of the modulator by setting envelope shaping function as a cubic polynomial and sweeping the coefficients of this function was analyzed. By sweeping the coefficients, efficiency and bandwidth at each condition with 64-QAM signal was used to obtain optimal point of the supply modulator. Compared to the conventional shaping functions, the optimized function showed the bandwidth reduction by 12.7 percent point while the efficiency was maintained.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.5
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• pp.107-112
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• 2020

Recently, unstructured data is rapidly being produced based on web-based services. NoSQL systems and key value stores that process unstructured data as key and value pairs are widely used in various applications. In this paper, a study was conducted on a skip list used for in-memory data management in an LSM-tree based key value store. The skip list used in the key value store is an insertion-based skip list that does not allow overwriting and processes all changes only by inserting. This behavior can support Multi-Version Concurrency Control (MVCC), which can simultaneously process multiple read/write requests through snapshot isolation. However, since duplicate keys exist in the skip list, the performance significantly degrades due to unnecessary node visits during a list traverse. In particular, serious overhead occurs when a range query or scan operation that collectively searches a specific range of data occurs. This paper proposes a newly designed Stride SkipList to reduce this overhead. The stride skip list additionally maintains an indexing pointer for the last node of the same key to avoid unnecessary node visits. The proposed scheme is implemented using RocksDB's in-memory component, and the performance evaluation shows that the performance of SCAN operation improves by up to 350 times compared to the existing skip list for various workloads.