• Journal of the Korean Ceramic Society
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• v.39 no.8
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• pp.801-806
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• 2002

The decomposition and/or conversion of carbon dioxide to carbon have been studied using oxygen-deficient ferrites for the reduction of $CO_2$ emission to the atmosphere. In this work, the homogeneous precipitation method using urea decomposition was employed to induce in situ precipitation of Ni ferrite($Ni_{0.4}Fe_{2.6}O_4$) on the porous ceramic fiber support (50 mm diameter${\times}$10 mm thickness). Effects of ferrite loading conditions on the CO2 decomposition efficiency were discussed in this paper. Removal of residual chloride ions and urea by solvent exchange from the porous media after ferrite deposition apparently helps to form spinel ferrite, but does not increase the efficiency of $CO_2$ decomposition. Porous ceramic fiber composites containing 20 wt% (1g) ferrite samples showed 100% efficiency for $CO_2$decomposition during the first three minutes, but the efficiency decreased rapidly after the elapsed time of ten minutes. The characteristic reduction time for the $CO_2$ decomposition efficiency was estimated as about 3∼7 min.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.6 no.2
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• pp.63-70
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• 2001

Changes in concentrations of dissolved oxygen, ammonia, nitrate, pH, Fe and Mn were monitored from the laboratory incubation of an benthic chamber. The extent of sedimentary organic carbon and nitrogen decomposition was quantified by applying the concentration data to the chemical reaction equations of early diagenesis. The patterns of the concentration changes, observed during the 237 hr long incubation experiment, made it possible to divide the entire experiment period into four characteristic sub-periods (0-9 hr, 9-45 hr, 45-141hr, 141-237 hr). C/N ratio, estimated for each sub-period, was 6.63, 1.49, 0.81 and 0.02, respectively. This sequential decrease in C/N ratio suggests that during the incubation experiment dissolved nitrogen species diffuse more out of the sediment than dissolved carbon species. Greater diffusion of nitrogen indicates the preferential decomposition of organic nitrogen during early diagenesis of sedimentary organic matter. Comparison of the concentration data (sedimentary organic carbon and nitrogen, porewater organic carbon and ammonia)between the sediment pre and post incubation also indicates the preferential decomposition of nitrogen during early diagenesis of sedimentary organic matter.

• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2257-2262
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• 2014

$C_{60}$ is widely investigated because of its unique structure. But its applications in solid propellant seem to be relatively neglected. $C_{60}$ has more outstanding features than carbon black which is widely used as a catalyst ingredient of solid propellant. To combine the advantages of fullerene and lead salts, another good composite in propellant catalysts, we synthesized a kind of fullerene phenylalanine lead salt (FPL) and explored its thermal performances by differential thermal analysis (DTA) and thermogravimetry analysis (TGA). The results show it undergoes four exothermic processes started from 408 K. Combined TGA and X-ray diffractometer (XRD), the decomposition mechanism of FPL was derived by TG-IR and comparing IR spectra of FPL and its residues after burned to $327^{\circ}C$, $376^{\circ}C$ and $424^{\circ}C$, respectively. Effect of FPL on the decomposition characteristic of hexogen (RDX), a type of explosive in propellant, has been investigated using DTA at different heating rate, which shows the decomposition temperatures of the explosive are all reduced by more than 20 K. The corresponding activation energy ($E_a$) is decreased by $30kJ{\cdot}mol^{-1}$. So FPL has potential application as a combustion catalyst in solid propellant.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.4
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• pp.359-366
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• 2010

For the application of Lamb wave to structural health monitoring(SHM), understanding its physical characteristic and interaction between Lamb wave and defect of the host structure is an important issue. In this study, reflected, transmitted and mode converted Lamb waves at discontinuity of a plate structure were simulated and the amplitude ratios are calculated theoretically using Modal decomposition method. The predicted results were verified comparing with finite element method(FEM) and experimental results simulating attached PZTs. The result shows that the theoretical prediction is close to the FEM and the experimental verification. Moreover, quantitative estimation method was suggested using amplitude ratio of Lamb wave at discontinuity.

• Journal of the Korean Mathematical Society
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• v.50 no.5
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• pp.945-957
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• 2013

In this paper we consider a Riemann problem, in particular, the case of the presence of the semi-hyperbolic patches arising from a transonic shock in simple waves interaction. Under this circumstance, we construct global solutions of the two-dimensional Riemann problem of the pressure gradient system. We approach the problem as a Goursat boundary value problem and a mixed initial-boundary value problem, where one of the boundaries is the transonic shock.

• The Pure and Applied Mathematics
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• v.11 no.1
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• pp.1-14
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• 2004

Due to the development of computer network and mobile communications, the security in image data and other related source are very important as in saving or transferring the commercial documents, medical data, and every private picture. Nonetheless, the conventional encryption algorithms are usually focusing on the word message. These methods are too complicated or complex in the respect of image data because they have much more amounts of information to represent. In this sense, we proposed an efficient secret symmetric stream type encryption algorithm which is based on Boolean matrix operation and the characteristic of image data.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2010.04a
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• pp.610-611
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• 2010

• The Journal of the Acoustical Society of Korea
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• v.16 no.3E
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• pp.7-13
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• 1997

This paper addresses traffic prediction issues on MPEG. A new adaptive traffic prediction scheme is proposed using MPEG picture characteristic that picture traffic depends on the coding mode of that picture, that is, I, P, and B mode. Our prediction scheme, which is based n picture decomposition (PD) and the cross-correlation of the different types of pictures, has better performance in predicting bursty MPEG traffic than that of the first-order autoregressive (AR) prediction scheme. Our simulation results show that the performance is further improved about 15% by utilizing the cross-correlations between pictures.

• Journal of the Korean Ceramic Society
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• v.29 no.4
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• pp.253-258
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• 1992

ZnO varistors were prepared by the organochemical method which used citric acid and ethylene glycol as gelling agents. The microstructure of the sintered specimens exhibited small grains, uniform grain size distribution, and few intragranular pores. Thermal decomposition of the organic resin formed during the powder preparation process was completed around 450$^{\circ}C$. No significant changes were observed in microstructure and current voltage characteristic with respect to calcination temperatures. A major advantage of the organochemical method used in this experiment is a possible uniform mixing of trace amounts of dopants. Therefore, this powder preparation method seems promising in investigating the effect of Li or In ion, which is added in ppm level to ZnO varistors, on the pulse respose characteristic.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.2356-2361
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• 2005

In this paper, we present a complete isotropy analysis of a caster wheeled omnidirectional mobile robot(COMR) with nonredundant/redundant actuation. The motivation of this work is that the omnidirectional mobility loses significance in motion control unless the isotropy characteristics is maintained well. First, with the characteristic length introduced, the kinematic model of a COMR is obtained based on the orthogonal decomposition of the wheel velocities. Second, a general form of the isotropy conditions of a COMR is given in terms of physically meaningful vector quantities which describe the wheel configurations. Third, for all possible nonredundant and redundant actuation sets, the algebraic expressions of the isotropy conditions are derived to completely identify the isotropic configurations of a COMR. Fourth, the number of the isotropic configurations and the characteristic length required for the isotropy are discussed.