• Journal of the Korean Applied Science and Technology
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• v.30 no.3
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• pp.423-430
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• 2013

Carbon coils could be synthesized using $C_2H_2/H_2$ as source gases and $SF_6$ as an incorporated additive gas under thermal chemical vapor deposition (CVD) system. Prior to the carbon coils deposition reaction, two kinds of samples having different combination of Ni catalyst and substrate were employed, namely, a commercially-made $Al_2O_3$ ceramic boat with Ni powders and a commercially-made $Al_2O_3$ substrate with Ni layer. By using a commercially-made $Al_2O_3$ ceramic boat, the synthesis of carbon coils could be enhanced as much as 10 times higher than that of $Al_2O_3$ substrate. Furthermore, the dominant formation of the microsized carbon coils could be obtained by using $Al_2O_3$ ceramic boat. The surface roughness of the supporting substrate of $Al_2O_3$ ceramic boat was understood to be associated with the large scale synthesis of carbon coils as well as the dominant formation of the larger-sized, namely the microsized carbon coils.

• Journal of Powder Materials
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• v.27 no.5
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• pp.394-400
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• 2020

Molybdenum trioxide (MoO₃) is used in various applications including sensors, photocatalysts, and batteries owing to its excellent ionic conductivity and thermal properties. It can also be used as a precursor in the hydrogen reduction process to obtain molybdenum metals. Control of the parameters governing the MoO₃ synthesis process is extremely important because the size and shape of MoO₃ in the reduction process affect the shape, size, and crystallization of Mo metal. In this study, we fabricated MoO₃ nanoparticles using a solution combustion synthesis (SCS) method that utilizes an organic additive, thereby controlling their morphology. The nucleation behavior and particle morphology were confirmed using ultraviolet-visible spectroscopy (UV-vis) and field emission scanning electron microscopy (FE-SEM). The concentration of the precursor (ammonium heptamolybdate tetrahydrate) was adjusted to be 0.1, 0.2, and 0.4 M. Depending on this concentration, different nucleation rates were obtained, thereby resulting in different particle morphologies.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.9
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• pp.1428-1435
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• 1989

In this paper we propose a new algorithm which extracts spatial arrangement information of texture elements in structural textures. In the proposed algorithm, by the use of projection information in several directions obtained from the texture image we can get two directions which determine the texture structure and the parallelogram grid which isolates texture elements. The isolated texture elements are analyzed and used to synthesize texture images. Computer simulation shows that the proposed method can extract proper spatial structure of the texture element even when the texture image is highly corrupted by additive noise.

• The Journal of the Acoustical Society of Korea
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• v.15 no.2E
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• pp.24-32
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• 1996

A rigorous theory for modeling, analysis, optimum nonseparable filter bank in multidimensional M-band quantized subband codec are developed in this paper. Each pdf-optimized quantizer is modeled by a nonlinear gain-plus-additive uncorrelated noise and embedded into the subband structure. We then decompose the analysis/synthesis filter banks into their polyphase components and shift the down-and up-samplers to the right and left of the analysis/synthesis polyphase matrices respectively. Focusing on the slow clock rate signal between the samplers, we derive the exact expression for the output mean square quantization error by using spatial-invariant analysis. We show that this error can be represented by two uncorrelated components : a distortion component due to the quantizer gain, and a random noise component due to fictitious uncorrelated noise at the uantizer. This mean square error is then minimized subject to perfect reconstruction (PR) constraints and the total bit allocation for the entire filter bank. The algorithm gives filter coefficients and subband bit allocations. Numerical design example for the optimum nonseparable orthonormal filter bank is given with a quincunx subsampling lattice.

• Journal of the Korean Applied Science and Technology
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• v.26 no.4
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• pp.385-393
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• 2009

Different types magnesium hydroxide groups have been obtained using the hydrothermal precipitation technique from magnesium sulfate and calcium carbonate solution. The Mg atom coordinated around O atom of ${SO_4}^{2-}$ in another layer to form a multi-layer structure crystal. The influence of synthesis parameters on the morphological characteristics and size of magnesium hydroxide groups precipitated in aqueous were investigated such as different of additive and pH. Magnesium hydroxide groups were decomposed gradually and converted finally to MgO particles after heated in air temperature up to $1050^{\circ}C$. The particle size and it's distribution morphology, crystal phase and thermal behavior of the samples were characterized through XRD, SEM, EDS, and TG/DTA.

• Journal of the Korean Ceramic Society
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• v.22 no.5
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• pp.35-42
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• 1985

$eta$-Sialon powders were prepared by reduction-nitridation from mixture of Wando pyrophyllite and graphite as a reducing agent at 135$0^{\circ}C$ in 80% $N_2$-20% $H_2$ atmosphere. As the reaction products $Si_2ON_2$, $\beta$-$Si_3N_4$ a--$Si_3N_4$ and $\beta$-SiC were observed. Additive agents of MgO, CaO, $Y_2O_3$ were used for promoting the reduction and nitridiation aeaction. The present study was conducted to investigate the effects of silica-carbon ratio ($SiO_2$/C=weight ratio), raction time gas flow rate pellet size and powder packing on synthesis of $\beta$-Sialon from Wando pyropyllite.

• Macromolecular Research
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• v.16 no.7
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• pp.620-625
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• 2008

A novel nitrogen-phosphorus compound, diphenyl piperazine-1,4-diylbis(methylphosphinate)(DPPMP) was synthesized via a two step reaction and its flame retarding efficiency as a single component additive was investigated. The success of synthesis was confirmed by FTIR and $^1H$ and $^{31}P$ NMR analysis. The product was mixed with polycarbonate (PC), poly(butylene terephtalate) (PBT), ethylene-vinyl-acetate copolymer (EVA), and acrylonitrile-butadiene-styrene copolymer (ABS). The flame-retarding efficiency was evaluated using the limiting oxygen index (LOI) and the UL-94 vertical test methods. The addition of DPPMP enhanced the flame retardancy of the polymers and the V-0 ratings were obtained for the polymers examined in this study at a loading of 7-30 wt%. The gas-phase flame retardancy mode of action was suggested for this material from the thermogrametry experiment results.

• Journal of Biomedical Engineering Research
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• v.15 no.2
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• pp.195-200
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• 1994

To develop an artificial bone substitute that is gradually degraded and replaced by the regenerated natural bone, the authors designed a composite that consists consisted of calcium phosphate and collagen according to the natural bone's main composition. The crystallinity of the synthesized apatite was shown to depend on the synthesis temperature. Carbonate apatite synthesized at $58{\circ}C$ demonstrated crystallinity very similar to that of the natural bone. By sintering the apatite over $700{\circ}C$ in vacuum, porous carbonate apatite could be obtained, and the pore extent was controllable according to the additive hydrogenperoxide volume.

• BMB Reports
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• v.40 no.2
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• pp.156-162
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• 2007

Two lysis-defective but DNA synthesis non-defective temperature-sensitive (ts) mutants of mycobacteriophage L1, L1G23ts23 and L1G25ts889 were found to be defective also in phage-specific RNA synthesis in the late period of their growth at 42$^{\circ}C$each to the extent of 50% of that at 32$^{\circ}C$The double mutant, L1G23ts23G25ts889 showed the ts defect in phage RNA synthesis that was nearly additive of those shown individually by the two single-mutant parents. Both G23 and G25 were shown to start functioning sometimes between 30 and 45 min after infection but the former gene might be dispensable after 45 min, while the latter was not. Northern analysis also shows that at 42$^{\circ}C$>, L1G23ts23 affects RNA synthesis more strongly than L1G25ts889 from L1 DNA segments that serve as the template for late gene transcription. Among the 21 virion and 12 non-virion late proteins synthesized by L1, L1G23ts23 is defective in the synthesis of at least 9 virion and all of non-virion proteins at 42$^{\circ}C$>. In contrast, L1G25ts889 is completely defective in synthesis of all the 33 late proteins. Possible roles of G23 and G25 in the positive regulation of transcription of different sets of late genes of L1 have been discussed.

• Journal of Powder Materials
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• v.20 no.5
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• pp.332-337
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• 2013

Recently, self-propagating high-temperature synthesis (SHS), related to metallic and ceramic powder interactions, has attracted huge interest from more and more researchers, because it can provide an attractive, energy-efficient approach to the synthesis of simple and complex materials. The adiabatic temperature $T_{ad}$ and apparent activation energy analysis of different thermit systems plays an important role in thermodynamic studies on combustion synthesis. After establishing and verifying a mathematic calculation program for predicting adiabatic temperatures, based on the thermodynamic theory of combustion synthesis systems, the adiabatic temperatures of the NiO/Al aluminothermic system during self-propagating high-temperature synthesis were investigated. The effect of a diluting agent additive fraction on combustion velocity was studied. According to the simulation and experimental results, the apparent activation energy was estimated using the Arrhenius diagram of $ln(v/T_{ad}){\sim}/T_{ad}$ based on the combustion equation given by Merzhanov et al. When the temperature exceeds the boiling point of aluminum (2,790 K), the apparent activation energy of the NiO/Al aluminothermic system is $64{\pm}14$ kJ/mol. In contrast, below 2,790 K, the apparent activation energy is $189{\pm}15$ kJ/mol. The process of combustion contributed to the mass-transference of aluminum reactant of the burning compacts. The reliability of the simulation results was experimentally verified.