• Korean Journal of Materials Research
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• v.20 no.8
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• pp.439-443
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• 2010

Nano sized SiC particles (270 nm) are easily agglomerated in nickel sulfamate electrolytic bath during a composite electrodeposition process. The agglomeration of nano particles in composite coatings can significantly reduce the mechanical properties of the composite coatings. In this study, Ni-SiC nano composite coatings were fabricated using a conventional electrodeposition process with the aid of ultrasound. Nano particles were found to be distributed homogeneously with reduced agglomeration in the ultrasonicated samples. Substantial improvements in mechanical properties were observed in the composite coatings prepared in presence of ultrasound over those without ultrasound. Ni-SiC composite coatings were prepared with variable ultrasonic frequencies ranging from 24 kHz to 78 kHz and ultrasonic powers up to 300 watts. The ultrasonic frequency of 38 kHz with ultrasonic power of 200 watt was revealed to be the best ultrasonic conditions for homogeneous dispersion of nano SiC particles with improved mechanical properties in the composite coatings. The microstructures, phase compositions, and mechanical properties of the composite coatings were observed and evaluated using SEM, XRD, Vickers microhardness, and wear test. The Vickers microhardness of composite coatings under ultrasonic condition was significantly improved as compared to the coatings without ultrasound. The friction coefficient of the composite coating prepared with an ultrasonic condition was also smaller than the pure nickel coatings. A synergistic combination of superior wear resistance and improved microhardness was found in the Ni-SiC composite coatings prepared with ultrasonic conditions.

• Journal of the Korean Society of Safety
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• v.28 no.1
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• pp.12-17
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• 2013

Considering the wind power system and the rotor blades which are composed of much technology, the wind power blade would be the most dangerous part because it revolves at high speed and weighs about dozens of tons, if the accident happens. Therefore, the light weight composite materials have been replacing as substitutional materials. The object of this study is to examine the delamination and damage for CFRP/GFRP hybrid composite that is used for strength improvement of a wind power blade. The influence of the initial crack length and fiber orientation for the interlaminar delamination was exposed for the blade safety. Plain woven CFRP instead of GFRP was inserted into the layer of the box spar for improving the strength and blade life. DCB(Double Cantilever Beam) specimen was used for evaluating fracture toughness and damage evaluation of interlaminar delamination. The material used in the experiment is a commercial material known as CF 3327 EPC in plain woven carbon prepreg(Hankuk Carbon Co.) and UD glass fiber prepreg(Hyundai Fiber Co.). From the results, crack growth rate is not so different according to the variation of the initial crack length. Mode I interlamainar fracture toughness of fiber direction $0^{\circ}$ is higher than that of $45^{\circ}$. Interlaminar fracture has an effect on fiber direction and K decreased with lower value according to increasing initial crack length. Also energy release rate fracture toughness was evaluated because CFRP/GFRP hybrid composite with a different thickness is under the mixed mode loading condition. The interlaminar fracture was almost governed by mode I fracture even though the mixed mode.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.7
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• pp.988-991
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• 2012

The computer simulation was performed to confirm distribution of current and power density according to inner diameter of graphite mold of SPS(Spark Plasma Sintering). When the inner diameters of a graphite mold are varied $10mm{\Phi}$, $20mm{\Phi}$, $30mm{\Phi}$ and $40mm{\Phi}$, the more the inner diameter of graphite mold is decreased, the more the current density of punch section is increased. Because the electrical resistivity of the SiC-$ZrB_2$ specimen section($7.77{\times}10^{-4}{\Omega}{\cdot}cm$) was lower than the electrical resistivity($6.00{\times}10^{-3}{\Omega}{\cdot}cm$) of graphite section, the current density and power density of specimen section was higher than those of graphite section. It is considered that a SiC-$ZrB_2$ composite is sintered by more Joule heat of specimen section than that of mold and punch section. The current and power density distribution of a SiC-$ZrB_2$ composite can be predicted through computer simulation when SPS is conducted, and an electrical resistivity of the SiC-$ZrB_2$ composite is main element of SPS.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.8
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• pp.4142-4159
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• 2019

We have developed composite measures of supercomputer technology, reflecting various factors of supercomputers using Martino's scoring model. CPUs, accelerators, memory, interconnection networks, and power consumption are chosen as factors of the model. The weight values of the factors are derived based on a survey of 129 domestic and international experts. The measured values are then standardized to integrate measurement units of the factors in the model. This model has been applied to 50 supercomputers, and rank correlation analysis was performed using representative measures. As a consequence, the ranking drastically changes except for the 1st and 2nd supercomputers on the TOP500. In addition, the characteristics of memory and interconnection networks influence the ranking, and the results demonstrate that the proposed model has low correlations with HPL and HPCG but a high correlation with Green500. This indicates that power consumption is an important factor that has a significant effect on the measures of supercomputer technology. In addition, it is determined that the differences between the HPL ranking and the proposed model ranking are influenced by power consumption, CPU theoretical peak performance, and main memory bandwidth in order of significance. In conclusion, the composite measures proposed in this study are more suitable for comprehensively describing supercomputer technology than existing performance measures. The findings of this study are expected to support decision making related to management and policy in the procurement and operation of supercomputers.

• 한국초전도학회:학술대회논문집
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• v.14
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• pp.5-5
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• 2004

• JOURNAL OF ELECTRICAL WORLD
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• no.12 s.108
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• pp.18-22
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• 1985

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.1
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• pp.68-72
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• 2012

In this paper, highly linear power amplifier using bandpass filter based on metamaterial and Composite Right- / Left-Handed (CRLH) structure is proposed. The proposed bandpass filter consist of the series capacitor, series microstrip line and the parallel inductor, parallel microstrip line. The insertion loss is minimized at operation frequency and the $2^{nd}$ harmonic is suppressed by the bandpass filter using the CRLH structure. And we improved the Adjacent Channel Leakage Ratio (ACLR) using the characteristic of the proposed bandpass filter. At 2.14 GHz, we have obtained the output power of 38.83 dBm, the $2^{nd}$ harmonic of .61.33 dBc, the $3^{rd}$ IMD of .54.67 dBc, and ACLR of .51.33 dBc at 5 MHz offset, -56.50 dBc at 10 MHz offset, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.2
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• pp.285-292
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• 2001

In this paper, the analysis model of a composite electromagnetic interference environment is proposed, and the composite interference consists of three types, i.e., impulse, sinusoidal, and rectangular type. Also, we have derived the p.d.f of the amplitude of the composite interference. And using a derived p.d.f, we have evaluated the performance of 16QAM (Quadrature Amplitude Modulation) system in a composite electromagnetic interference environment. From the results, it is known that when impulse type interference is weaker than the others, the shape of p.d.f is dominantly governed by the power component ratio of sinusoidal and rectangular type interference. On the other hand, when impulse type interference is stronger, the effect of the other two interference becomes insignificant. Also, It is shown that the smaller both impulsive index (A) and the mean power component ratio ($\Gamma$') in impulse type interference are, the worse the performance of 16QAM system is.

• Journal of the Korean Magnetics Society
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• v.23 no.3
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• pp.83-88
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• 2013

The soft magnetic Fe-Si-Cr flakes with the thickness of about 1 ${\mu}m$ were annealed at 500 and $700^{\circ}C$ for 1 h, and the composite sheets for electromagnetic wave noise absorber available for quasi-microwave band were fabricated by using these annealed flakes and polymer. Further the power loss characteristics of the composite sheets was investigated to clarify the annealing effect on electromagnetic wave absorption properties. The power loss decreased in the frequency range of several GHz when the annealed flakes were used as compared to the sheet using the as-milled FeSiCr alloy flakes. Moreover the sheets using annealed flakes exhibited lower value of real and imaginary part of complex permeability. These inferior electromagnetic wave absorption properties of the composite sheets using annealed alloy flakes were considered to be obtained by the enhanced eddy current effect upon annealing-induced recovery of microstructure and resulted low complex permeability.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.94-100
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• 2002

This paper is concerned with the development, and performance test of LIPCA (Lightweight Piezo-composite Curved Actuator) that is lighter than other conventional piezo-composite type actuators. LIPCA is composed of top fiber composite layers with a high modulus and low CTE (Coefficient of Thermal Expansion), a middle PZT cermaic wafer, and base layers with a high modulus and high CTE. The performance of each actuator was evaluated using an actuator test system consisting of an actuator supporting jig, a high voltage actuating power supplier, and a non-contact laser measuring system. The simply supported condition actuator was excited by the power supplier with 1.0Hz cycle and up to $100\sim400V_{pp}$. The displacement at the center point of actuator was measured with non-contact laser displacement measuring system, It has been shown that the LIPCA-C2 can 34% decrease in mass and 13% increase in displacement compared to THUNDER.