• Journal of the Korean Ceramic Society
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• v.48 no.4
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• pp.263-268
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• 2011

ZnO hexagonal rods grown in aqueous solution can be changed into a tubular shape by two-step aging in the course of the growing process. In the first step, hexagonal ZnO rods is grown by aging at $90^{\circ}C$ under a highly supersaturated aqueous solution giving rise to a fast precipitation rate. Meanwhile, during the second step aging at $60^{\circ}C$ in the same aqueous solution, the hexagonal polar face (001) having higher surface energy than (010) side planes dissolves to minimize surface energy. Hence the flat (001) face changes to a craterlike face and the hexagonal rod length of ZnO decreases at an initial-stage of this step aging. The formation of the (101) wedge-type faces is ascribed to the resultant of competitive reactions between the dissolution of polar face minimizing the surface energy which is a dominant reaction at the initial stage and the precipitation reaction dissipating supersaturation. At a later stage of the second-step the reaction rates of these two processes in the aqueous solution become similar and the overall reaction is terminated.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.7
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• pp.549-554
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• 2009

Al thin films were synthesized on TiN/Si substrate by MOCVD using N-methylpyrrolidine alane (MPA) precursor. Effects of substrate temperature, reaction pressure on the deposition rate, surface roughness and electrical resistivity were investigated. The early stage of Al thin film formation was analyzed by in-situ surface reflectivity measurement with a laser and photometer apparatus. From the Arrhenius plot of deposition rate vs. substrate temperature, it was found that the activation energy of surface reaction was 91.1kJ/mole, and the transition temperature from surface-reaction-limited region to mass-transfer-limited region was about $150^{\circ}C$. The growth rate increased with the reaction pressure, and average growth rates of $200{\sim}1,200nm/min$ were observed at various experimental conditions. Surface roughness of the film increased with the film thickness. The electrical resistivity of Al film was about $4{\mu}{\Omega}{\cdot}cm$ in the case of optimum condition, and it was close to the value of the bulk Al, $2.7{\mu}{\Omega}{\cdot}cm$.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.18 no.4
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• pp.30-37
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• 2010

This paper deals with attitude determination and parameter estimation problems for a lunar module. For this we first derive equations of motion for the lunar module by considering allocation locations (configurations) of reaction thruster and a reaction wheel assembly. The lunar module is assumed as a rigid body. In order to include the effect of fuel sloshing on the dynamics of the lunar module, we model it as a spherical pendulum for a simple analysis. For estimating angular rates and moment of inertia of the module, we employ an extended Kalman filter and the least mean square algorithms, respectively. Finally we construct a dynamical model for the lunar module by combining all these elements.

• Journal of the Korean Applied Science and Technology
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• v.21 no.1
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• pp.45-50
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• 2004

The effects of reaction temperature and flow rate of reactants on the methane conversion, product selectivity, product ratio, and carbon deposition were investigated with 13wt% Ni/MgO catalyst. Reaction temperatures were changed from 600 to $850^{\circ}C$, and reactants flow rates were changed from 100 to 200 mL/mim. There were no significant changes in the methane conversion observed in the range of temperatures used. It is possibly stemmed from the nearly total exhaustion of oxygen introduced. The selectiveties of hydrogen and carbon monoxide did not largely depend on the reaction temperature. The selectivities of hydrogen and carbon monoxide were 96 and 90%, respectively. Carbon deposition observed was the smallest at $750^{\circ}C$ and the largest at $850^{\circ}C$. It is found that the proper reaction temperature is $750^{\circ}C$. The best reactant flow rate was 150 ml/min.

• Journal of the Korean Chemical Society
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• v.41 no.3
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• pp.157-165
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• 1997

The transesterification reaction could be used to the technical production as it forms an in-situ compatibilizer during the processing of polymer blends. Thus, TR-4,6(poly(tetramethylene-4,4'-terephthaloyldioxydibenzoate-co-hexametylene-4,4'-terephthaloyldioxydibenzoate), one of thermotropic liquid crystalline polymers was synthesized and was blended with PBT(polybutylene terephthalate), one of engineering plastics, to study the transesterification reaction. The transesterification reactions between two components, TR-4,6 and PBT, were monitored by IR, DSC and $^{13}C-NMR$ and analyzed by a statistical treatment method. Also, the reaction rates and the sequence distributions of repeating unit were (calculated and) invesitigated.

• Journal of the Korean Electrochemical Society
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• v.15 no.3
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• pp.165-171
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• 2012

Here is implemented MATLAB program to analyze the characteristic curves of cyclic voltammetry which involves the multi-electron electrode reaction considered as key processes in electrochemical systems. For the electrochemical mass-transfer system, Fick's concentration equation subject to semi-infinite diffusion model for the boundary condition was discretized and solved by the explicit finite difference method. The resulting concentration values were converted into currents at each node by using Butler-Volmer equation. Based on the good agreement between the present numerical solution and the existing experimental results, effects of kinetic constants and CV scan rates on the reaction mechanism in multi-electron transfer processes were investigated effectively.

• Bulletin of the Korean Chemical Society
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• v.24 no.2
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• pp.205-208
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• 2003

Laser-induced Raman spectroscopy has been utilized to demonstrate its feasibility for studying the kinetics of imine formation in chloroform solvent. The imine formation, by the nucleophilic addition of primary amine to the carbonyl group of ketone, has been monitored at ten minute intervals for eight hours. The intensity of the C=O stretching mode at 1684 $cm^{-1}$ was measured to determine the rate constant of the reaction. In order to correct the sample-to-sample fluctuations in Raman peak area, this peak was normalized to the C-Cl bending peak at 666 $cm^{-1}$. By the peak area change during the course of reaction, the second order rates at three different temperatures have been determined. The substituent effects on the π conjugations of imine product have also been investigated. On the basis of Raman frequency shifts, the delocalization properties of the aromatic system modified by substitution of a hydrogen atom with -Cl and $-CH_3O$ groups could be clearly understood.

• Korean Journal of Applied Biomechanics
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• v.21 no.1
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• pp.9-16
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• 2011

The purpose of this study is to analyze the effects of both various shoe types and bare feet on ground reaction force while walking. Ten first-year female university students were selected. A force platform(Kistler, Germany) was used to measure ground reaction force. Six types of shoe were tested: flip flops, canvas shoes, running shoes, elevated forefoot walking shoes, elevated midfoot walking shoes, and five-toed shoes. The control group was barefooted. Only vertical passive/active ground reaction force variables were analyzed. The statistical analysis was carried out using the SAS 9.1.2 package, specifically ANOVA, and Tukey for the post hoc. The five-toed shoe had the highest maximum passive force value; while the running shoe had the lowest. The first active loading rate for running shoes was the highest; meanwhile, bare feet, the five-toed shoe, and the elevated fore foot walking shoe was the lowest. Although barefoot movement or movement in five toed shoes increases impact, it also allows for full movement of the foot. This in turn allows the foot arch to work properly, fully flexing along three arches(transverse, lateral, medial), facilitating braking force and initiating forward movement as the tendons, ligaments, and muscles of the arch flex back into shape. In contrast movement in padded shoes have a tendency to pound their feet into the ground. This pounding action can result in greater foot instability, which would account for the higher loading rates for the first active peak for padded shoes.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.09a
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• pp.187-190
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• 2002

Reductive dechlorination of endosulfans was studied with zero valent metals (ZVMs) and bimetals in aqueous batch reactors. The effect of surfactants was evaluated. Endosulfan was successfully dechlorinated with zero valent iron. However, a bimetal, palladium coated iron (Pd/Fe) showed a highly enhanced reactivity for both endosulfan I and II indicating palladium act as a dechlorination catalyst on the iron. The effect of surfactants on degradation with ZVM has been very controvertible. Variable concentration of a nonionic surfactant, Triton X-100 and an anionic surfactant, SDS were added into the reactor with ZVM. The reaction rates of endosulfan were increased with both surfactants. In the case of Triton X-100, the reaction rate was increased with the increasing surfactant concentration up to 400 mg/L. Addition of small amount of surfactant under the CMC, the reaction rate was increased. However, the enhancing effect was diminished when a higher concentration of surfactant (1,000 mg/L) was used. Current study implicate that the surfactant adsorbed on the metal surface might increase the surface concentration of endosulfan resulting in the increased reaction rate. However, partitioning of endosulfan into the micelle formed at the high concentration of surfactant diminish the enhancing effect by reducing the contact chance between target compound and the metal surface.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.09a
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• pp.87-90
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• 2003

This research examines the feasibility of using laboratory-synthesized nano scale zero-valent iron particles to remove arsenic from aqueous phase. Batch experiments were performed to determine arsenic sorption rates as a function of the nano scale zero-valent iron solution concentration. Rapid adsorption of arsenic was achieved with the nano scale zero-valent iron. Typically 1 mg $L^{-1}$ arsenic (III) was adsorbed by 5 g $L^{-1}$ nano scale zero-valent iron below the 0.01 g $L^{-1}$ concentration within 7min. The kinetics of the arsenic sorption followed pseudo-first-order reaction kinetics. Observed reaction rate constants ( $K_{obs}$) varied between 11.4 to 129.0 $h^{-1}$ with respect to different concentrations of nano scale zero-valent iron. A variety of analytical techniques were used to study the reaction products including HGAAS (hydride generator atomic adsorption spectrophotometer), SEM (scanning electron microscopy) and TEM (transmission electron microscopy). Our experimental results suggest novel method for efficient removal of arsenic Iron groundwater.r.