• Journal of Powder Materials
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• v.16 no.1
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• pp.16-21
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• 2009

Nanostructured $ReSi_{1.75}$ was synthesized to have high density via rapid and cost effective process named as high-frequency induction heated combustion synthesis(HFIHCS) method. For the process, mechanically activated Re-Si powder was used, which had been prepared by mechanical ball milling of Re and Si powders with mixing ratio of 1:1.75. Both combustion synthesis and densification were accomplished simultaneously by applying electric current and mechanical pressure of 80 MPa during the process. The average grain size, hardness, and fracture toughness of the compound were 210 nm, 1085 $kg/mm^2$ and 4 $MPa{\cdot}m^{1/2}$, respectively. The experimental results show that HFIHCS is a promising process for synthesis of nanostructured $ReSi_{1.75}$ which has a potential for both high temperature and thermo-electric applications.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.7
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• pp.649-656
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• 2002

This paper addresses the phase noise analysis of high-speed DH-PLL(Digital Hybrid Phase-Locked Loops) frequency synthesizer. Because of the additional quantization noise of D/A converter in DH-PLL, the phase noise of DH-PLL is increased than the conventional PLL. Three kinds of noise sources such as reference input, D/A converter, and VCO(Voltage Controlled Oscillator) are considered to analyze the phase noise. It largely depends on the closed loop bandwidth and frequency synthesis division ratio(N) so that we can decide the optimal closed loop bandwidth to minimize the phase noise of DH-PLL. It is shown that the simulation results closely match with the results of analytical approach.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.10
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• pp.1137-1146
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• 2008

OFDM is very effective for the high speed communication system. However, OFDM has the problems of high PAPR and serious ICI, which is different from the single carrier system. Especially, ICI problem caused by phase noise, Doppler effect and frequency offset is main reason for poor performance since it breaks down the orthogonality between subcarriers in OFDM communication system. Therefore, WFMT modulation scheme is studied and the effect of the carrier frequency offset and phase noise is analyzed. WFMT modulation scheme is based on the wavelet theory and complex filter banks for synthesis and analysis of multichannel signal. WFHT modulation scheme keeps on the advantage of filter banks system and can be easily possible for the implementation of filter banks. In this paper, we compare ISI and ICI distortions of the WFMT and OFDM system due to the carrier frequency offset and phase noise. Also, we analyze the PAPR and BER performances in the HPA and ICI situation caused by the Doppler frequency shift and the frequency offset.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.62 no.2
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• pp.87-95
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• 2017

The increase in the frequency of occurrence of abnormal weather could include severe rainfall, which could cause rice submergence during the ripening stage. This experiment was conducted to clarify the effects of submergence during the ripening period on yield and quality of rice. The flooding treatment was conducted at 7 and 14 days after heading. Flooding conditions were created with two conditions, flag leaf exposed and overhead flooding, and each condition was divided into two conditions according to water quality-clear and muddy. Although the yield decrease was more severe at 7 days after heading because of the decrease in the ripening ratio, the head rice ratio was more affected at 14 days after heading because of the increase in the chalky kernel ratio. The maximum quantum yield (Fv/Fm), which indicates the photosynthetic efficiency, did not differ before and after the flooding treatment until flooding continued for 4 days. In addition, stem elongation occurred because of flooding as an avoidance mechanism in japonica rice. This phenomenon was expected to decrease the supply of assimilation products to the spikelet (sink). Overall, it was suggested that additional experiments should be conducted examining the change in the starch synthesis mechanism and transfer of assimilate products resulting from submergence, for development of cultivation techniques corresponding to submergence and breeding of varieties with submergence tolerance characteristics.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.4
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• pp.190-193
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• 2012

Transparent diamond-like carbon (DLC) films were synthesized on glass using radio frequency plasma enhanced chemical vapor deposition method from the gas mixture of $CH_4$, $SiH_4$ and Ar. The pressure, the rf-power, $CH_4/SiH_4/Ar$ ratio, and the deposition time were 0.1Torr, 100W, 20 : 1 : 1, and 20 min, respectively. The optical transmittances of DLC-deposited glass and uncoated glass were compared with each other in the visible light regions. The DLC-deposited glass showed transmittance of approximately 83 % and 95 % as compared to the uncoated glass for the wavelength of 380 nm and 500 nm, respectively. The hardness and roughness of DLC-coated glass have been measured by nanoindentation and AFM, respectively. The DLC-coated glass showed a little less or similar optical transmittance compared to the uncoated glass, while the hardness of DLC-coated glass was 2.5 times higher than that of the uncoated glass. The deposited DLC film had the very smooth surface and was thicker than 150 nm after deposition for 20 min.