• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.12
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• pp.2262-2269
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• 2016

In IEEE 802.11 wireless LANs, when a source node with low data rate occupies the channel resource for a long time, network performance degrades. In order to improve performance, the cooperative communication has been proposed. In the previous cooperative communication protocols, relay nodes deliver data packets only for a source node. In this paper, we propose an additional transmission scheme in which relay nodes select an additional source node based on several information and deliver data packets for the original source node and the selected additional source node. The proposed scheme improves performance and provides fairness among source nodes. Performance of the proposed scheme is investigated by simulation. Our results show that the proposed scheme outperforms the previous protocol in terms of fairness index and throughput.

• Journal of KIISE:Databases
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• v.31 no.3
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• pp.320-330
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• 2004

Query languages for XML use paths in a data graph to represent queries. Actually, paths in a data graph are used as a basic constructor of an XML query. User can write more expressive Queries by using Patterns (e.g. regular expressions) for paths. There are many identical paths in a data graph because of the feature of semi-structured data. Current researches for indexing XML utilize identical paths in a data graph, but such an index can grow larger than source data graph and cannot guarantee efficient access path. In this paper we propose a partitioning technique that can partition all the paths in a data graph. We develop an index graph that can find appropriate partitions for a path query efficiently. The size of our index graph can be adjusted regardless of the source data. So, we can significantly improve the cost for index graph traversals. In the performance study, we show our index much faster than other graph based indexes.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.7
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• pp.907-915
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• 2018

With the increase of metal usage in various industries, metal pollution and ecological toxicity in the environmental system have become a significant concern. A geo-statistical index has been widely used to determine contamination level with normalization through a background value. In this study, geo-statistical indexes such as an enrichment factor, accumulation index, and potential ecological risk index were used to assess metal pollution in soil at locations associated with shipbuilding manufacturing industries. Metal contamination, especially of Cu and Pb, was observed in some samples located closer to manufacturing sites. Enrichment factor and accumulation (IGEO) values were indicative of concerning levels of soil contamination in specific samples, and the soil contamination could be induced by anthropogenic sources. In further study, after more detailed sampling for soil and potential pollution sources, high interpretation techniques such as Pb isotope analysis and X-ray analysis will be needed to investigate source identification.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1351-1365
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• 2019

This paper proposes two modified Z-source inverter topologies, namely an embedded L-Z-source inverter (EL-ZSI) and a coupled inductor L-Z source inverter (CL-ZSI). The proposed topologies offer a high voltage gain with a reduced passive component count and reduction in source current ripple when compared to conventional ZSI topologies. Additionally, they prevent overshoot in the dc-link voltage by suppressing heavy inrush currents. This feature reduces the transition time to reach the peak value of the dc-link voltage, and reduces the risk of component failure and overrating due to the inrush current. EL-ZSI and CL-ZSI possess all of the inherent advantages of the conventional L-ZSI topology while eliminating its drawbacks. To verify the effectiveness of the proposed topologies, MATLAB/Simulink models and scaled down laboratory prototypes were constructed. Experiments were performed at a low shoot through duty ratio of 0.1 and a modulation index as high as 0.9 to obtain a peak dc-link voltage of 53 V. This paper demonstrates the superiority of the proposed topologies over conventional ZSI topologies through a detailed comparative analysis. Moreover, experimental results verify that the proposed topologies would be advantageous for renewable energy source applications since they provide voltage gain enhancement, inrush current, dc-link voltage overshoot suppression and a reduction of the peak to peak source current ripple.

• Proceedings of the KIPE Conference
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• 2004.11a
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• pp.64-69
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• 2004

This paper deals with an algorithm for controlling ac output voltage of Z-source inverter using Modified SVPWM (abbreviated as MSVPWM). Unlike the conventional space vector pulse width modulation, MSVPWM has one extra shoot-through zero time $T_{sh}$. During shoot-through zero time, both switches in a leg are conducted simultaneously in order to boost inverter output voltage to any desirable value regardless the line voltage. The algorithm to control linearly the capacitor voltage is suggested to improve the performance of Z-source inverter system. The performance of Z-source inverter using above algorithms is demonstrated in simulation results using PSIM. Index terms-Z-source inverter (ZSI), shoot-through time, three-phase carrier-based PWM, space vector PWM (SVPWM), modified space vector PWM (MSVPWM).

• International Journal of Internet, Broadcasting and Communication
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• v.10 no.2
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• pp.31-38
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• 2018

As the use of open source databases grows, so does need to evaluate, the performance of search queries for these databases. This paper compares the search query performance of SQL-based open source databases with commercial databases through experiments. The targets are MySql, MariaDB, and MS-SQL Server. In this study, the execution time of various types of search queries are measured. Also, search query performance was experimented according to change of index and number of tuples. Experimental results show that SQL-based open source databases have the potential to replace commercial databases when indexes are used and the number of tuples is not very large.

• Journal of Korean Library and Information Science Society
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• v.35 no.3
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• pp.271-291
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• 2004

Such information services source like digital library has been asked information services of atypical multimedia database like image, voice, VOD/AOD. Examined in this study are suggestions such as word-phrase generator, syllable recoverer, morphological analyzer, corrector for voice processing. Suggested voice processing technique transform voice database into tort database, then extract index database from text database. On top of this, the study suggest a information retrieval model to use in extracted index database, voice full-text information retrieval.

• Journal of the Optical Society of Korea
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• v.9 no.2
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• pp.49-53
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• 2005

We report a new configuration of a reflection-type confocal scanning optical microscope system for measuring the refractive index profile of an optical waveguide. Several improvements on the earlier design are proposed; a light emitting diode (LED) at 650 nm wavelength instead of a laser diode (LD) or He-Ne laser is used as a light source for better index precision, and a simple longitudinal linear scanning and curve fitting techniques are adapted instead of a servo control for maintaining an optical confocal arrangement. We have obtained spatial resolution of 700 nm and an index precision of $2\times10^{-4}$. To verify the system's capability, the refractive index profiles of a conventional multimode fiber and a home-made four-mode fiber were examined with our proposed measurement method.

• MALSORI
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• no.53
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• pp.157-169
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• 2005

This paper proposes an efficiently representing method of spatial cues on multichannel spatial audio coding. The Binaural Cue Coding (BCC) method introduced recently represents multichannel audio signals by means of Inter Channel Level Difference (ICLD) or Source Index (SI). We tried to express more efficiently ICLD and SI information based on Inter Channel Correlation in this paper. We adopt different spatial cues according to ICC and propose a compensation method of empty spectrums created by using SI. We performed a MOS test and measuring spectral distortion. The results show that the proposed method can reduce the bitrate of side information without large degradation of the audio quality.

• Journal of Environmental Science International
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• v.33 no.6
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• pp.383-402
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• 2024

Variations in lettuce growth and quality were observed depending on the type of artificial light source. The RGB LED treatment resulted in thick leaf development, leading to higher fresh weight, dry weight, and relative growth rates. Two cultivars, "Tomalin" and "seonpunggold," exhibited increased anthocyanin content and dark red leaf color under conditions of RGB LED treatment. Additionally, they exhibited high chlorophyll content under conditions of RGB LED and RGBFR LED treatments. Particularly, under Red LED treatment, the plants showed elongated leaves with narrow widths, resulting in a higher leaf shape index and a tendency towards leaf curling. Therefore, RGB LED lighting which appropriately blends red, blue, and green lights, is more effective than single lighr sources at improving lettuce growth and quality.