• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.11
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• pp.33-38
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• 2004

In this paper, we review a trellis-coded orthogonal frequency division multiplex (TC-OFDM) system, which combines OFDM with trellis-coded modulation, for overcoming the frequency selective and multipath fading of time dispersive channels. We simulate and analyse the BER performance of rate 2/3 trellis coded 8DPSK-OFDM over time dispersive channels. Design of the trellis codes at different carrier numbers of OFDM is discussed. Results show that TC-OFDM system can provide 6 dB coding gain at a BER of 10$^{-3}$ compared with OFDM system without coding.

• Journal of Dental Rehabilitation and Applied Science
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• v.23 no.1
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• pp.79-84
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• 2007

Mineral Trioxide Aggregate(MTA) has been used in Endodontic treatment successfully for more than 10 years. But the high cost of MTA limits its use in endodontics in Korea. Recently many studies have been done to compare MTA and Portland cements. To investigate the chemical constitutions of MTA (Proroot MTA, Tulsa Dental), Gray Portland cement (Lafarge Halla cement), White Portland cement(Union corp), and fast setting cement (SSangyong cement), we performed SEM(scanning electron microscope)(S4700, Hitachi) examination and EDS(Energy dispersive spectrometry)(emax, Horiba) analysis. SEM examination and EDS analysis were committed to and performed in SNU DRI (Seoul National University Dental Research Institute). We found that particles of MTA were relatively round, uniform in size, and compactly packed compared to Portland cements. Chemical constitutions of MTA, GPC, WPC and FSC were similar. It was shown that MTA contains much BiO2 . MTA and WPC showed less heavy metals such as Fe and Mg compared to GPC and FSC. FSC showed remarkably high aluminum content.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.6
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• pp.102-107
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• 2007

A fast response $CO_2$ ($fCO_2$) analyzer for real-time measurement of carbon dioxide concentration during transient states of internal combustion engines has been developed. This analyzer uses non-dispersive infrared absorption (NDIR) technique for measuring $CO_2$ concentration and Kalman filter for removing noise components from output signals. The analyzer has good linearity, repeatability and drift with a response time of 11 ms; it is sufficiently fast to detect $CO_2$ concentration during transient states of internal combustion engines. The $fCO_2$ analyzer was used to measure transient $CO_2$ concentration of exhaust gas of the SI engine with a standard gas analyzer, and the signal of the $fCO_2$ analyzer was compared to that of the standard gas analyzer. The two concentrations were well matched during the steady state, and the $fCO_2$ analyzer could measure the variations of $CO_2$ concentration during the transient state.

• Journal of Environmental Science International
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• v.5 no.3
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• pp.317-327
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• 1996

This study was performed to develop the biological treatment technology of wastewater polluted with heavy metals. Zinc-tolerant microorganism, such as Pseudomonas chlororaphis which possessed the ability to accumulate zinc, was isolated from industrial wastewaters polluted with various heavy metals. The characteristics of zinc accumulation in the cells, recovery of the zinc from the cells accumulating zinc, were investigated. Removal rate of zinc from the solution containing 100 mall of Zinc by zinc-tolerant microorganism was more than 90% at 48 hours after inoiulation of the microorganisms. A large number of the electron-dense granules were found mainly on thIn cell wall and membrane fractions, when determined by transmission electron microscope. Energy dispersive X- ray spectroscopy revealed that the electron-dense granules were zinc complex with the substances binding Heavy metals. The zinc accumulated into cells was not desorbed by distilled water, but more than 80% of the zinc accumulated was desorbed by 0.1M-EDTA. The residues of the cells after combustion at 55$0^{\circ}C$ amounted to about 21% of the dry weight of the cells. EDS analysis showed that the residues were comparatively pure zinc compounds containing more than 79% of zinc.

• Journal of Powder Materials
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• v.19 no.6
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• pp.416-423
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• 2012

This paper introduces an effect of a preparing $ZrO_2$-Ag composite on its mechanical properties and microstructure. In present study, $ZrO_2$-Ag was prepared by reduction-deposition route and wetting dispersive milling method, respectively. Two type of Ag powders (nano Ag and micron Ag size, respectively) were dispersed into $ZrO_2$ powder during wetting dispersive milling in D.I. water. Each sample was sintered at $1450^{\circ}C$ for 2hr in atmosphere, and then several mechanical tests and analysis of microstructure were carried out by bending test, hardness, fracture toughness and fracture surface microstructure. As for microstructure, the Ag coated $ZrO_2$ showed homogeneously dispersed Ag in $ZrO_2$ in where pore defect did not appear. However, $ZrO_2$-nano Ag and $ZrO_2$-micro Ag composite appeared Ag aggregation and its pore defect, which carried out low mechanical property and wide error function value.

• The Journal of Engineering Geology
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• v.27 no.4
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• pp.513-518
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• 2017

Groundroll is a coherent noise showing dispersive behavior in land seismic-reflection records and its rejection has been a stubborn problem in data processing because they severely degrade the continuities and resolution of reflection signals. Conventional processing schemes of attenuating noises are the kind of frequency filtering (i.e., bandpass and f-k) that uses the Fourier transform (FT) along the entire trace in the time domain. To suppress them in this study, 1D wavelet filtering (WT) that can control time-varying frequency properties is tested and performed in the land-based synthetic and field seismic data. The results are compared to the ones from conventional filtering techniques in terms of continuities and resolution of reflection events. This filtering technique enhanced the reflection events by effectively eliminating the dispersive groundroll and random noises with control of time-scale function on wavelet domain.

• Journal of Conservation Science
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• v.35 no.4
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• pp.373-383
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• 2019

We characterized the smelting process and smelting furnace through scanning electron microscopy-energy dispersive spectroscopy, wavelength dispersive X-ray fluorescence, X-ray diffraction, and raman micro-spectroscopy with 13 relics including slags and furnace walls excavated from square-shaped building sites and pits of the Three Kingdoms site at the Ungyo site section I. Our results revealed that the principal components were FeO and SiO₂; and CuO, PbO, and ZnO were contained in small quantities. Furthermore, fayalite, magnetite, augite, copper, and cuprite were found. High contents of FeO or SiO₂ components seem to have been added to form fayalite to remove gangue in the smelting process. The relatively low content of S detected in the copper prills suggests that roasting was performed well. Cristobalite and mullite, which are minerals that indicate high-temperature found in the furnace wall, show that the smelting temperature was higher than 1,250℃. The findings of this study show a high possibility that the Wanju Ungyo site is smelting remains of copper ores, which are nonferrous metals, rather than iron. Various smelting byproducts excavated in this area in the future will help us better understand the copper smelting process that may have been performed since ancient times.

• Geomechanics and Engineering
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• v.7 no.6
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• pp.649-663
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• 2014

In past few years, the use of bacterial calcium carbonate precipitation (biocementation) has become popular as a ground improvement technique for sandy soil. However, this technique was not applied to organic soil. This study focused on bacterial calcium carbonate precipitation and its effect on permeability in organic soil. A special injection system was prepared for inducing bacterial solution to the samples. The bacterial solution supplied to the samples by gravity for 4 days in specific molds designed for this work. Calcite precipitation was observed by monitoring pH value and measuring amount of calcium carbonate. Change in the permeability was measured before and after biocementation. The test results showed that the pH values indicates that the treatment medium is appropriate for calcite precipitation, and amount of precipitated calcium carbonate in organic soil increased about 20% from untreated one. It was also found that the biocementation can be considered as an effective method for reducing permeability of organic soil. The results were supported by Scanning electron microscopy (SEM) analysis and energy-dispersive x-ray (EDX) analysis.

• KSBB Journal
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• v.15 no.1
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• pp.60-65
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• 2000

In order to predict the chromatogram for organic acid in ion chromatography, Langmuir isotherm parameters were obtained by Retention Time Method (RTM) and moment method. Ion chromatography analysis for formic acid was performed and compared with theoretically predicted profiles under isocratic condition. Band profiles were estimated with the equilibrium-dispersive model of chromatography using a PDEsolver Macsyma . The relationship between the characteristics of chromatogram and the variable operating condition in chromatography such as the flow rate, ionic strength and injection volume was studied. Satisfactory agreement was observed between the experimental and the estimated chromatograms with parameters obtained form the moment method.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.67-69
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• 2006

Capacitance and loss values of pentacene MIS capacitors with different thicknesses are measured as a function of frequency for the modeling of the devices. The equivalent circuit for the ideal MIS capacitor is adopted to model the obtained admittance, so the values of $C_i,\;C_d,\;C_b$, and $R_b$ are determined for each pentacene thickness. In the loss curve, broader loss peaks are observed in measurement than the modeling results regardless of the pentacene thickness. By considering the effects of dispersive charge transport in bulk semiconductor, more accurate modeling results are obtained.