• Analytical Science and Technology
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• v.10 no.3
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• pp.187-195
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• 1997

Chemically modified electrodes(CMEs) for Ag(I) were constructed by incoporating 1,5,9,13-tetrathiacyclohexadecane([16]-ane-$S_4$) with a conventional carbon-paste mixture composed of graphite powder and nujol oil. Ag(I) ion was chemically deposited onto the surface of the modified electrode with [16]-ane-$S_4$ by immersion of the electrode in the acetate buffer solution(pH=4.5) containing $5.0{\times}10^{-4}M$ Ag(I) ion. And then the electrode deposited with Ag(I) was reduced at -0.3V vs. S.C.E. Well-defined stripping voltammetric peaks could be obtained by scanning the potential to the positive direction. The CME surface was regenerated with exposure to 0.1M $HNO_3$ solution and was reused for the determination of Ag(I) ion. When deposition/measurement/regeneration cycles were 10 times, the response could be reproduced with relative standard deviation of 6.08%. In case of differential pulse stripping voltammetry, the calibration curve for Ag(I) was linear over the range of $5.0{\times}10^{-7}{\sim}1.5{\times}10^{-6}M$. And the detection limit was $2.0{\times}10^{-7}M$. Various ions such as Cd(II), Ni(II), Pb(II), Zn(II), Mn(II), Mg(II), EDTA, and oxalate(II) did not influence the determination of Ag(I) ion, except Cu(II) ion.

• Journal of the Korean Chemical Society
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• v.35 no.5
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• pp.545-552
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• 1991

A mercury ion-sensitive carbon-paste electrode (CPE) was constructed with l-sparteine. Mercury (II) ion was chemically deposited by the complexation with l-sparteine onto the CPE. The surface of CPEs was characterized by cyclic voltammetry and anodic stripping voltammetry in an acetate buffer solution, separately. Exposure of CPEs to acid solution could regenerate surface and reuse it for deposition. In 5 deposition/measurement/regeneration cycle, the response was reproducible and in licnear up to $2.0\;{\times}\;10^{-6}$ M with linear sweep voltammetry. In case of using the differential pulse technique, we have obtained the linear response up to $7.0 {\times}10^{-7}$ M with relative standard deviation of ${\pm}5.1$%. The detection limit was $5.0{\times}10^{-7}$ M for 20 minutes of the deposition. We have investigated the interference effect of various metal ions, which are expected to form the complex with ligand. Silver (I) ion of these has interfered with the analysis of Hg (II) ions. However, pretreatment of the silver (I) ion with potassium chloride led to no interference on the analysis of mercury ions in aqueous solution.

• The Journal of the Acoustical Society of Korea
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• v.31 no.1
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• pp.19-28
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• 2012

The time-domain solution from the Kirchhoff integral equation for an exterior problem is not unique at certain eigen-frequencies associated with the fictitious internal modes as happening in frequency-domain analysis. One of the solution methods is the CHIEF (Combined Helmholtz Integral Equation Formulation) approach, which is based on employing additional zero-pressure constraints at some interior points inside the body. Although this method has been widely used in frequency-domain boundary element method due to its simplicity, it was not used in time-domain analysis. In this work, the CHIEF approach is formulated appropriately for time-domain acoustic boundary element method by constraining the unknown surface pressure distribution at the current time, which was obtained by setting the pressure at the interior point to be zero considering the shortest retarded time between boundary nodes and interior point. Sound radiation of a pulsating sphere was used as a test example. By applying the CHIEF method, the low-order fictitious modes could be damped down satisfactorily, thus solving the non-uniqueness problem. However, it was observed that the instability due to high-order fictitious modes, which were beyond the effective frequency, was increased.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.1
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• pp.53-57
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• 2010

The influence of CaO addition on the crystallization temperature, crystal types, and microstructure of L-A-S ($Li_2O-Al_2O_3-SiO_2$) glass-ceramics system fabricated from a coal bottom ash, produced at thermal power plant, was studied. The glass transition and crystallization temperatures were shifted to the higher temperature position with increasing CaO content in a non-isothermal analysis using a DTA. The major crystalline phases of L-A-S glass-ceramics system produced were identified as ${\beta}$-spodumene ($LiAlSi_2O_6$) and eucryptite ($LiAlSiO_4$). The glass-ceramics showed a bulk and surface crystallization behavior at a time. With increasing CaO content, the ${\beta}$-spodumene peak in XRD increased and some CaO-related phases were formed. The surface crystal grown from the exterior to the center in glass-ceramics showed various shapes by amount of CaO added. Some cracks were generated at the glass-ceramics containing CaO above 9 wt% due to the mismatch of thermal expansion coefficients between a ${\beta}$-spodumene and CaO-related crystal phases.

• Journal of Energy Engineering
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• v.28 no.3
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• pp.1-9
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• 2019

A major stress determining the remaining life of the tube in feedwater heater of fossil fuel power plant is hoop stress by the internal pressure. However, thermal stress due to temperature difference across the wall thickness also contributed to reduce the remaining life of the tube. Therefore, thermal loading must be considered even though the contribution of internal pressure loading to the stresses of the tube was known to be much higher than that of the thermal loading. In this study, thermal stress of the tubes in the de-superheating zone was estimated, which was generated due to the temperature difference across the tube thickness. Analytic equations were shown for determining the hoop stress and the radial stress of the tube with uniform thinning and for the temperature across the tube thickness. Accuracy and effectiveness of the analytic equations for the stresses were verified by comparing the results obtained by the analytic equations with those obtained from finite element analysis. Using finite element analysis, the stresses for eccentric thinning were also determined. The effect of heat transfer coefficient on thermal stress was investigated using series of finite element analyses with various values of heat transfer coefficient for both inner and outer surface of the tube. It was shown that the effect of heat transfer coefficient at outer surface was larger than that of heat transfer coefficient at inner surface on the thermal stress of the tube. Also, the hoop stress was larger than the radial stress for both cases of uniformly and eccentrically thinned tubes when the thermal loading was only considered without internal pressure loading.

• Journal of the Korean Society for Advanced Composite Structures
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• v.3 no.1
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• pp.8-15
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• 2012

The initial clamping forces of high strength bolts depending on different faying surface conditions drop within 1,000 hours regardless of loading, any other external force or loosening of the nut. This study is focused on an expectation model for relaxation of high strength bolt, which is confined to creep on coated faying surfaces after initial clamping. The range of this experiment is limited to estimate the relaxation of bolted joints coated by inorganic zinc primer. The candidate bolts were dacro-coated tension control bolts. The parameters of coated thickness for the faying surface were 96, 168,and $226{\mu}m$ respectively. From experiments, it exhibited that the logarithmic function for creep strain was derived due to the parameter of coating thickness. By using the creep strain, subsequently the quantitative model for estimating long term relaxation of high strength bolt can be taken with the elapsed time. The experimental results showed that the relaxation after the initial clamping of high strength bolt rose to a much higher range from 10% to 18% due to creep of the coating as the coating thickness was increased. This study showed that the clamping force reflecting relaxation after the elapse of constant time can be calculated from the initial clamping force of high strength bolt.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.7
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• pp.579-589
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• 2015

This study aims to understand the internal flow and the evaporation characteristics of a deionized water droplet subjected to vertical forced vibrations. To predict and evaluate its resonance frequency, the theories of Lamb, Strani, and Sabetta have been applied. To visualize the precise mode, shape, and internal flow inside a droplet, the experiment utilizes a combination of a high-speed camera, macro lens, and continuous laser. As a result, a water droplet on a hydrophobic surface has its typical shape at each mode, and complicated vortices are observed inside the droplet. In particular, large symmetrical flow streams are generated along the vertical axis at each mode, with a large circulating movement from the bottom to the top and then to the triple contact line along the droplet surface. In addition, a bifurcation-shaped flow pattern is formed at modes 2 and 4, whereas a large ellipsoid-shape flow pattern forms at modes 6 and 8. Mode 4 has the fastest internal flow speed and evaporation rate, followed by modes 8 then 6, with 2 having the slowest of these properties. Each mode has the fastest evaporation rate amongst its neighboring frequencies. Finally, the droplet evaporation under vertical vibration would lead to more rapid evaporation, particularly for mode 4.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.24 no.5
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• pp.345-355
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• 1991

In order to effectively utilize the by-products of sea-food, the utilization of enzyme-modified flounder(Limanda aspera) skin gelatin as an emulsifier was investigated. In the experiment, the gelatin was extracted from the flounder skin with the heat-treatment at $60^{\circ}C$ and in pH 5.0 for 3 hrs with four volumes of distilled water and emulsifiers were enzymatically modified L-leucine alkyl esters$(L-leucine-OC_n$ : n= 2, 4, 6, 8 and 10) to the gelatin$(EMFSG-C_2,\;EMFSG-C_4,\;EMFSG-C_6,\;EMFSG-C_8,\;EMFSG-C_{10})$ for improving the functional properties such as emulsifying activity, emulsifying viscosity, whippability, electric conductivity, critical micelle concentration and interface tension, etc. Also, the functional properties of the L-leucine alkyl ester modified gelatins were compared with those of Tween-60 as reference. Molecular weights of the enzymatically modified flounder skin gelatin(EMFSG) were 20.5kDa. in $EMFSG-C_2.\;19.5 kDa.\;in\;EMFSG-C_4\;and\;16.5kDa.\;in\;EMFSG-C_6,\;EMFSG-C_8$ and $EMFSG-C_{10}$. respectively. Emulsifying activity and emulsifying viscosity in the modified gelatins were risen with increase of carbon number of the introduced L-leucine alkyl esters. Among the modified gelatins, $EMFSG-C_6$ exhibited the highest emulsifying stability and foaming stability, whereas $EMFSG-C_8$ showed the highest whippability. The electric conductivities of the all $EMFSG-C_n$ were linearly risen to critical micelle concentration(CMC) , therefore $EMFSG-C_{10}$ exhibited the lowest CMC value and interface tension, and dense particles in the microscopic observation. In conclusion, the best quality in functional properties was assured on $EMFSG-C_{10}$.

• Journal of KIISE:Computer Systems and Theory
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• v.33 no.3
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• pp.147-156
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• 2006

Physically-based simulation modeling is to simulate the real world by using physical laws such as Newton's second law of motion, while other modelings use only geometric Properties. In this paper, we present a real time simulation of stone skipping by using the physically-based modeling. We also describe interaction of a stone on the surface of water, and focus on calculating the path of the stone and the natural phenomena of water The path is decided by velocity of the stone and drag force from the water The motion is recalculated until the stone is immersing into the water surface. Our simulation provides a natural motion of stone skippings in real time. And the motion of stone skippings are generated by give interactive displays on the PC platforms. The techniques presented can easily be extended to simulate other interactive dynamics systems.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.9
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• pp.938-943
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• 2014

The scattered field by a gap/crack on the PEC surface of a large object having low-observable RCS cannot be negligible, but may not be analyzed by the known high-frequency technique. If the electrical width of the crack is very small, the crack can be modeled by an impedance strip, whose scattering formulation can be analytically obtained based on a low-frequency approximation. The scattering solution is formulated for the 2D strip and TE(Transverse Electric) or TM(Transverse Magnetic) wave incidence, from which a 3D ILDC(Incremental Length Diffraction Coefficients) can be extracted. Using the ILDC formulation, the scattering by any arbitrary shaped crack can be estimated. In this paper, an improved ILDC equations are proposed, which combine the known TE and TM solutions. The improved accuracy of the proposed solution is numerically verified.