• Applied Chemistry for Engineering
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• v.9 no.4
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• pp.574-578
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• 1998

Electrochemical Ion Exchang(EIX) electrode containing Amberlite IRP-64 as a cation ion exchange resin and Stylene-Buthylene-Rubber(SBR) as a binder was fabricated by the compressed diecasting method. The adsorption and elution characteristics in copper sulfate solution were investigated at the various electrode potentials and electrolyte pHs. In the adsorption process, it was found that the maximum adsorption rate of copper was obtained at -1800 mV and the ratio of adsorption was 92% during 90 min. In the elution process, the elution rate of copper was increased in proportion to anodic potential in the present experimental range and the ratio of elution was 88% during 50 mins at 3600 mV. The adsorption and elution processes were significantly affected by the variation of local pH in the vicinity of electrochemical ion exchange electrode. The higher performances of adsorption and elution were elution were obtained at basic and acidic eletrolytes.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.2
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• pp.303-307
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• 2006

In this paper, we have designed the p-type metal-oxide semiconductor field-effect transistor(pMOSFET) for SiGe devices with gate lengths of $0.9{\mu}m$ and $0.1{\mu}m$using the TCAD simulators. The electrical characteristics of devices have been investigated over the temperatures of 300 and 77K. We have used the two carrier transfer models(hydrodynamic model and drift-diffusion model). We how that the drain current is higher in the hydrodynamic model than the drift-diffusion model. When the gate length is $0.9{\mu}m$, the threshold voltage shows -0.97V and -1.15V for 300K and 77K, respectively. The threshold voltage is, however, nearly same at $0.1{\mu}m$ for 300K and 77K.

• Journal of Korean Society of Water and Wastewater
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• v.24 no.1
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• pp.93-101
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• 2010

Reverse osmosis (RO) membranes have been widely used for desalination as well as water and wastewater treatment facilities. Cleaning process is important to maintain stable operation as well as prevention of membrane fouling. Purpose of this research is to analyze electrostatistic and chemical characteristics after cleaning of RO membrane against $SiO_2$ scale. Four RO membranes of polyamide are used and examined about effect of chemical cleaning. EDTA (ethylene diamine tetraacetic acid) and SDS (sodium dodecil sulfate) and NaOH are applied for cleaning process after operation in synthetic water. Then, cleaning was performed with chemicals such concentration as 6hr, 12hr and 24hr, respectively. As a result, transmittances of FT-IR of four membranes are compared at each cleaning concentration. Ta/Tv shows difference of chemical composition between new membrane and cleaning membrane after cleaning. Type B of RO membrane is turned out to be most vulnerable to cleaning among four membranes. In terms of zeta potential, new membrane has -16 mV to +6 mV on pH while scaled membrane has -18 mV to 2 mV. However, it changed -23mV to 0.9 mV after cleaning. In comparison with existing salt rejection of RO membranes after cleaning, the rejection of the membranes goes down 0.7% maximum. Though cleaning changes the characteristics of membrane surface, it does not greatly affect salt rejection. pH is a critical factor to flux change in PA (polyamide) membrane.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.154-154
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• 2017

Ti-6Al-4V alloys are widely used as metal-lic biomaterials in dentistry and orthopedics due to its excellent biocompatibility and me-chanical properties. However, because of low biological activity, it is difficult to form bone growth directly on the surface of titanium implants. For this reason, surface treatment of plasma electrolytic oxidation(PEO) was used for dental implants. To enhance bioac-tivity on the surface, strontium(Sr) and sili-con(Si) ions can be added to PEO treated sur-face in the electrolyte containing these ions. The presence of Sr in the coating enhances osteoblast activity and differentiation, where-as it inhibits osteoclast production and prolif-eration. And Si has been found to be essen-tial for normal bone, cartilage growth, and development. In this study, electrochemical characteristics of Ca, P, Sr, and Si ions from PEO-treated Ti-6Al-4V alloy surface was re-searched using various experimental instruments. DC power is used and Ti-6Al-4V al-loy was subjected to a voltage of 280 V for 3 minutes in the electrolyte containing 5, 10, 20M% Sr ion and 5M% Si ion. The morphol-ogies of PEO-treated Ti-6Al-4V alloy by electrochemical anodization were examined by field-emission scanning electron micro-scopes (FE-SEM), energy dispersive x-ray spectroscopy (EDS), x-ray diffraction (XRD) and corrosion analysis using AC impedance and potentiodynamic polarization test in 0.9% NaCl solution at similar body tempera-ture using a potentiostat with a scan rate of 1.67mV/s and potential range from -1500mV to + 2000mV.

• Journal of Electrical Engineering and Technology
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• v.10 no.3
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• pp.935-943
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• 2015

Permanent magnetic actuators (P.M.A.s) are widely used to drive medium-voltage-class vacuum circuit breakers (V.C.B.s). In this paper, a method for design optimization of a P.M.A. for V.C.B.s is discussed. An optimal design process employing the response surface method (R.S.M.) is proposed. In order to calculate electromagnetic and mechanical dynamic characteristics, an initial P.M.A. model is subjected to numerical analysis using finite element analysis (F.E.A.), which is validated by comparing the calculated dynamic characteristics of the initial P.M.A. model with no-load test results. Using tables of mixed orthogonal arrays and the R.S.M., the initial P.M.A. model is optimized to minimize the weight of the permanent magnet (P.M.) and to improve the dynamic characteristics. Finally, the dynamic characteristics of the optimally designed P.M.A. are compared to those of the initially designed P.M.A.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.30A no.10
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• pp.33-40
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• 1993

A reflection type 16x8 S-SEED array from LP(Low Pressure)-MODVD-grown GaAs/AlGaAs extremely shallow quantum well(ESQW) structures, with 4% Al fraction, has been fabricated. Its intrinsic region consists of 50 pairs of alternating 100.angs. GaAs and 100.angs. $Al_{0.04}$Ga$_{0.96}$As layers. A multilayer reflector stack of $Al_{0.04}$/Ga$_{0.96}$ As(599$\AA$)/AlAs(723$\AA$) was incorporated for the reflection plane below the p-i-n structures. The device processing after the MOCVD growth includes the mesa etching, isolation etching, insulator deposition, p & n metallization, and AR(Anti-Reflection) coating. For switching characteristics of the S-SEED in the form of p-i-n ESQW diode, the maximum optical negative resistance was observed at 856nm. Reflectance measurements showed a change from 15.6% to 43.3% for +0.9V to -6V bias. The maximum contrast ration of the S-SEED array was 2.0 and all the 128 devices showed optical bistability with contrast ratios over 2.4 at 5V reverse bias.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.7
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• pp.1229-1234
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• 2008

In this work, ultra high-voltage (17 - 50 kV AC), reliable 80 pF mica capacitors for partial discharge system application were investigated. Mica was used as the dielectric of the capacitors. Using the conservative design rule, over 3 individual $50\;{\mu}m$ thick mica sheets with a size of 30mm{\times}35mm were used with lead foils to form a parallel capacitor element and 20 mica sheets were interleaved with lead foils to form a series stack of parallel capacitor element to meet the requirements of the capacitors. The dimensions of the fabricated 80 pF capacitors for 17 kV AC and 50 kV AC were $90\;mm{\times}90\;mm$ and $95\;mm{\times}180\;mm$, respectively. The high-frequency characteristics of the capacitance (C) and dissipation factor (D) of the developed capacitors were measured using a capacitance meter. The developed capacitors exhibited C of 79.5 - 87.5 pF, had D of 0.001% over the frequency ranges of 150 kHz to 50 MHz, had a self-resonant frequency of 65 MHz, and showed results comparable to those measured for the capacitors prepared recently by $Adwel^{Tm}$. The developed capacitors also showed excellent characteristics for thermal shock test and temperature cycling test.

• Speech Sciences
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• v.5 no.2
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• pp.139-159
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• 1999

The purposes of this study are two-folds: to find out the acoustic features of Korean stops in various utterance positions and their influence on the neighbouring segments. Korean stops($/p,\;p',\;p^{h};\;t,\;t',\;t^{h};\;k,\;k',\;k^{h}/$) are examined from CV, $V_1CV_2,\;V_1NCV_2,\;V_1LCV_2$ sequences. Three speakers (two male and one female speakers of Seoul dialect) served as subjects for the present study. VOT, closure duration of the target stops and duration of the neighbouring segments were measured from acoustic data. The results can be summarized as follows. First, stops show different temporal aspects depending on their place of articulation as well as their voice types. Velar stops tend to have shorter closure duration and longer VOT due to relatively slower movement of the articulator (i.e. tongue body) and higher supraglottal air pressure during the closure, respectively. Second, temporal aspects of the neighbouring segments appear to be influenced by the voice type of stop. The preceding segment tends to be longer when a stop has shorter duration. On the other hand, the following segment tends to be shorter, when a stop has longer VOT.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.5
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• pp.711-716
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• 2012

To assess the insulation deterioration of stator windings, diagnostic and AC breakdown tests were performed on the eleven high voltage (HV) motors rated at 6kV. After completing the diagnostic tests, the AC overvoltage test was performed by gradually increasing the voltage applied to the stator windings until electrical insulation failure occurred, to obtain the breakdown voltage. Stator winding of motors 1, 3, and 8 failed at above rated voltage at 14 kV, 13.8kV, and 16.4kV, respectively. The breakdown voltage of three motors was higher than expected for good quality windings in 6kV motors. Based on deterioration evaluation criteria, the stator winding insulation of eleven HV motors are confirmed to be in good condition. The turning point of the current, $P_{i2}$, in the AC current vs. voltage characteristics occurred between 5kV and 6kV, and the breakdown voltage was low between 13.8kV and 16.4kV. There was a strong correlation between the breakdown voltage and various electrical characteristics in diagnostic tests including Pi2.

• Korean Journal of Environmental Biology
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• v.23 no.3 s.59
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• pp.221-227
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• 2005

The effects of light and $CO_2$ on the electrophysiological characteristics of guard cells in the intact leaf and isolated epidermis have been investigated. Fast hyperpolarization of guard cell apoplastic PD in the intact leaf was recorded reaching up to around 7 mV and 20 mV in response to light and $CO_2$. Whenever the experiments were attempted with isolated epidermis, there was no response to light and $CO_2$. In order to determine the influence of the mesophyll cells, the apoplastic PD of guard cells in isolated epidermis was measured in the presence of the mesophyll supernatant or the control medium. The apoplastic PD in isolated epidermis was hyperpolarized to -7mV, changing from -22mV to -29mV at 40 min. But, when isolated epidermis was incubated with the supernatant from mesophyll cells incubated in the light, the apoplastic PD in isolated epidermis was hyperpolarized to -19 mV, changing from -22 mV to -40.5 mV. $CO_2$ also caused a change of 0.1 to 0.3 pH unit in the intact leaf. However, this change was absent in isolated epidermis. A vibrating probe was used to detect the change in electrical currents at the surface of excised intact leaves and isolated epidermis. The reading of excised intact leaves in the dark was $0.5\muA\;cm^{-2},$ remaining steady until illuminated. Light increased the current on the surface of excised leaves to about $0.8\muA\;cm^{-2},$. However, light had no effect in the current on the surface of isolated epidermis. Apoplastic pH changes across the stomatal complex in response to light and dark were measured both in the intact leaves and isolated epidermis over the same time period using pH micro-electrodes. The guard cell wall of intact leaf was acidified to 2.5 pH unit, falling from pH 7.5 to pH 5.0 in the first 10 min. in the light. At the same time the guard cell wall pH of isolated epidermis fell from pH 7.5 to pH 7.0 at 10 min. The guard cell wall pH of isolated epidermis incubated in the mesophyll supernatant fell from pH 7.6 to pH 6.7 at 10 min. Likewise, It could be imagined that an electrical signal, chemicals and hormones propagated from the mesophyll in response to light and $CO_2$ could control a fast stomatal response.