• Proceedings of the Korea Technology Innovation Society Conference
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• 2000.05a
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• pp.74-88
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• 2000

본 연구는 폐열 활용을 보다 실질적으로 적용하기 위한 사건 단계로서 에너지 요소기술들을 폐열활용을 위해 필요한 용도별, 성상별 등과 같은 요인들을 고려한 분석과 함께 이에 따른 체계도를 구축하였다. 또한, 이들 기술들을 이용하여 수요처에 알맞는 적용 시스템들을 구성하기 위해 폐열활용 요소기술의 접목을 통한 시스템의 최적화를 구현하고자 하였으며 이에 따라 폐열발생처별 특성과 이에 가능한 시스템을 선정하고 요소기술을 적용할 시스템 모형의 대안들을 제시하였다. 특히, 기술체계도와 요소기술의 시스템 분석을 통하여 폐열활용의 기본틀을 제시하였으며, 폐열 활용의 종합적인 이용 방법과 함께 적용처별로 시스템 대안을 제시하였다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2012.07a
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• pp.188-191
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• 2012

단일 주파수 방송 시스템에서 이레이저 현상이 생길 경우 기존의 공간 다중화 기법은 큰 성능 저하가 발생한다. 이에 본 논문에서는 라이시안 이레이저 페이딩 채널 환경에서 기존의 $2{\times}2$ 공간 다중화 기법에 직교 선부호기를 직렬 연접한 공간 다중화 기법의 성능을 분석하고, 수신 SER 성능을 최대화하는 선부호기 최적화를 수행한다. 전산 실험 결과, Rician 이레이저 페이딩 채널 환경에서 최적의 선부호화 공간 다중화 기법은 수신단에서 성상 모호성을 줄여 기존의 공간 다중화 기법에 비하여 우수한 성능 향상을 보였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.8A
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• pp.1133-1140
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• 1999

In order to provide high-speed wide-band multimedia services via Low earth(LEO) mobile satellire, power and bandwidth efficient digital transmission technique should to employed. This paper analyzes the performance of Trellis-soded 16QAM and 8PSK-2AM which can transmit twice as much inforemation as QPSK in nonlinearly amplified LEO mobile satellite channel. In the analysis the nonlinear mobile satellite channel is modelled by Rician fading channel amplified by Fujitsu's GaAs FET HPA. Our simulation result shows that 8PSK-2AM is less sensitive to the satellite channel nonlinear distortion and its BER performance is better than that of 16QAM. The BER performance of 8PSK-2AM is further improved by optimizing its signal constellation. Accocordingly it is found that Trellis-coded 8PSK-2AM could provide multimedia services such as Satellite Internet, DBS, DAB and ISDB more efficiently in the power and bandwidth limited mobile satellite channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.4C
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• pp.362-369
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• 2007

APSK (Amplitude Phase Shift Keying) digital modulation is characterized by the circular positioning of the transmission symbols in the constellation diagram. Due to such structural characteristics, the peak-to-average power ratio of the APSK modulation is lower than that of the QAM (Quadrature Amplitude Modulation), and the amount of performance degradation over nonlinear channels can be mitigated. The APSK modulation scheme has recently been adopted as satellite communication system standards including the DVB-S2 (Digital Video Broadcasting - Satellite, Version 2). In this paper, a BER (Bit Error Rate) upper bound approximation formula is derived using the channel model with the output power saturation characteristics, and its accuracy is demonstrated. Using the derived formula, the input power level that minimizes the BER is determined. The optimized performance based on the radii ratio of the 16APSK constellation and the channel saturation level is also presented.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.1
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• pp.24-31
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• 2007

DVB-T (Digital Video Broadcasting-Terrestrial) is an important multimedia broadcasting technology capable of high data-rate transmission and adopted by Europe. OFDM (Orthogonal Frequency Division Multiplexing) is the backbone technique employed in DVB-T to support multimedia services that have various bandwidths. Unfortunately, an OFDM signal has a large PAPR (Peak-to-Average Power Ratio). In this paper, we investigate the performance of a simple PAPR reduction scheme for the DVB-T system, which requires no change of a receiver structure or no additional information transmission. The approach we employed is clipping in the time and frequency domains. The time-domain clipping is carried out with a predetermined clipping level while the frequency-domain clipping is done within EVM (Error Vector Magnitude). This approach is suboptimal with lower computational complexity compared to the optimal method. The simulation results demonstrate that the proposed one is getting more effective at lower modulation levels and with more allowed constellation error.

• Reproductive and Developmental Biology
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• v.31 no.3
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• pp.175-179
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• 2007

The objective of this study was to investigate the effect of thawing temperature on the sperm viability and acrosomal morphology for semen storage of miniature pig by the 0.5ml straw method. In this present study, sperm viability (SYBR-14/PI staining), membrane integrity (Hypoosmotic Swelling Test), acrosome intactness, intensity and capacitation status (chlorotetracycline staining) in frozen miniature pig sperm were evaluated after thawing at 37, 50 and $70^{\circ}C$ for 5, 10 and 45 sec, respectively. Interestingly, the results indicated that sperm thawed at $70^{\circ}C$ for 5 sec significantly (p<0.05) increased sperm viability, but lower the percentage of AR (acrosome reacted spermatozoa) pattern compared to sperm thawed at $37^{\circ}C$ for 45 sec and $50^{\circ}C$ for 10 sec. In terms of thawing condition, high temperature for a short time using the 0.5ml straw was improved cryosurvival of miniature pig semen. Therefore, appropriate thawing method for cryopreservation of miniature pig is required for increasing post-thawing viability.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.8
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• pp.781-788
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• 2008

This study shows how to find out optimum co-substrate conditions and continuous operating parameters for maximum acidification of three different organic wastes - livestock wastewater, sewage sludge and food waste. Design of experiments and statistical analysis were revealed as appropriate optimization schemes in this study. Analyses of data obtained from batch tests demonstrated the optimum substrate mixing ratio, which was determined by maximum total volatile fatty acids(TVFA) increase and soluble chemical oxygen demand(SCOD) increase simultaneously. Suggested optimum mixing ratio of livestock wastewater, sewage sludge and food waste was 0.4 : 1.0 : 1.1 based on COD, respectively. Response surface methodology(RSM) contributed to find out optimum operating parameter - hydraulic retention time(HRT) and substrate concentration - for the semi-continuous acidogenic fermentation of mixed organic wastes. The optimum condition for maximum TVFA increase was 2 days of HRT and 29,237 mg COD/L. Empirical equations obtained through regression analysis could predict that TVFA increase would be 73%. To confirm the validity of the statistical experimental strategies, a confirmation experiment was conducted under the obtained optimum conditions, and relative error between theoretical and experimental results was within 4%. This result reflects that using statistical and RSM technique can be effectively used for the optimization of real waste treatment processes.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.143-153
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• 2018

Environmental regulations, which are discussed through the International Maritime Organization, focus on two aspects: the economic supply of fuel oil and, ultimately, securing next-generation energy sources. At present, there are limitations in relation to the basic quality of fuel oil and the direct relation through basic quality when applied to ships and traps in relation to environmental regulations, and the standard for the basic quality of fuel oil is generally used. There are many cases where the composition is very complicated, and the interpretation and analysis of basic quality deviate from the range of the basic standard. In other words, it is difficult to classify and apply the problem when analyzing it in connection with fuel quality and ship operations. In this paper are various factors for the basic quality of fuel oil, and a proposed possibility for the scope of the standard.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.4
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• pp.281-286
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• 2021

The International Maritime Organization recently proposed a policy to establish a preemptive response strategy for exhaust gas pollution on board ships according to the recent strengthening of the sulfur content regulations. Discussions on improving the fuel oil quality and reducing emissions are also ongoing. Fuel oil quality information, which is one of the main concerns internationally, is increasing as the sulfur content standard is being applied from the current 3.5% to 0.5% by 2020. From the perspective of shipping companies and recipients, the essential quality of fuel oil is also requested for domestic and international fuel oil information, basic properties, correlation information between characteristics for application of solid ships and ships. The current standard for the basic quality of fuel oil is generally used, but the nature and composition of the fuel oil are very complex, and the interpretation of the basic quality is complicated because there are many cases outside the scope of the basic standard. Various factors were analyzed for the basic quality of fuel oil in terms of the basic quality of fuel oil, optimization of operation in ships, and fuel efficiency in ships. Moreover, the possibility of applying the standard according to the dilution was suggested.

• Journal of the Korean Magnetics Society
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• v.12 no.2
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• pp.57-63
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• 2002

In order to increase the magnetic properties of a Nd-Fe-B sintered magnet, the general factors including particle size and its distribution, volume fraction of Nd$_2$Fe$_{14}$B phase, degree of alignment of Nd$_2$Fe$_{14}$B grain, oxygen content and grain size etc. should be optimized by controlling the composition of Nd-Fe-B alloy as well as the manufacturing process. In this study, fabrication of the Nd-Fe-B sintered magnet was carried out in a laboratory scale by controlling the composition of Nd-Fe-B alloy and the manufacturing process. The optimum milling condition was found by investigating the milling media, milling time and ball size. The addition of FeGa was effective to increase the coercivity of the Nd-Fe-B sintered magnet. A remanence of 14.4 kG, a coercivity of 9.4 kOe and a maximum energy product of 47 MGOe were obtained from the sintered magnet.