• Korean Chemical Engineering Research
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• v.40 no.6
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• pp.729-734
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• 2002

In this study, the polyaniline films of emeraldine base(EB) and lucoemeraldine base(LEB) form chemically doping with poly(sodium-4 styrenesulfonate, PSS) were prepared by casting the mixed solution of chloroform and m-cresol on ITO(indium tin oxide) electrode. By analyzing UV-vis spectra of the mixed solutions, the effects of the secondary doping by m-cresol were obtained. And the conductivity of polyaniline film was increased with increasing m-cresol content. The results suggest that the improvement of conductivity obtained by secondary doping results primarily from interaction of polyaniline and m-cresol. As the results of analyzing cyclic voltammograms, it was known that the redox peak currents of polyaniline electrode prepared from LEB were larger and more reversible than those of polyaniline electrodes prepared from EB. The charge transfer resistances($R_{ct}$) of polyaniline electrodes were reduced with increasing m-cresol content, and LEB/PSS electrodes were smaller than EB/PSS electrodes. This result agrees to the analysis of the redox peak current of cyclic voltammograms. The solution resistance and the capacity of electrical double layer almost unchanged in all prepared polyaniline electrodes. It was confirmed that solution resistance was independent of frequency factor in AC impedance spectra. Also the polyaniline film doping with PSS was revealed pseudo n-type characteristics of conducting polymer.

• Korean Journal of Materials Research
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• v.9 no.11
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• pp.1075-1082
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• 1999

Composite air electrodes of 50/50 vol% LSM- YSZ where LSM =$\textrm{La}_{1-x}\textrm{Sr}_{x}\textrm{MnO}_{3}$(0$\leq$x$\leq$0.5) were prepared by colloidal deposition technique. The electrodes were then examined by scanning electron microscopy (SEM) and studied by ac impedance spectroscopy in order to improve the performance of a solid oxide fuel cell (SOFC). Reproducible impedance spectra were confirmed by using the improved cell, consisting of LSM- YSZ/YSZ/LSM-YSZ. These spectra were a strong function of operating temperature and the stable conditions for the cells were typically reached at $900^{\circ}C$. The typical spectra measured for an air//air cell at $900^{\circ}C$ were composed of two arcs. Addition of YSZ to the LSM electrode led to a pronounced decrease in cathodic resistivity of LSM-YSZ composite electrodes. Polishing the electrolyte surface to eliminate the influences of surface impurities could further reduce cathode resistivity. The cathodic resistivity of the LSM-YSZ electrodes with catalytic interlayer (Ni or Sr) was much smaller than that of LSM-YSZ electrodes without catalytic interlayer. In addition, the cathodic resistivity of the LSM-YSZ electrodes was a strong function of composition of electrode materials, the electrolyte geometry, and applied current.

• Microbiology and Biotechnology Letters
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• v.38 no.4
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• pp.349-361
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• 2010

In this review, the current knowledge of the carbon metabolism and global carbon regulation in Corynebacterium glutamicum are summarized. C. gluamicum has phosphotransferase system (PTS) for the utilization of sucrose, glucose, and fructose. C. glutamicum does not show any preference for glucose when various sugars or organic acids are present with glucose, and thus cometabolizes glucose with other sugars or organic acids. The molecular mechanism of global carbon regulation such as carbon catabolite repression (CCR) in C. glutamicum is quite different to that in Gram-negative or low-GC Gram-positive bacteria. GlxR (glyoxylate bypass regulator) in C. glutamicum is the cyclic AMP receptor protein (CRP) homologue of E. coli. GlxR has been reported to regulate genes involved in not only glyoxylate bypass, but also central carbon metabolism and CCR including glycolysis, gluconeogenesis, and tricarboxylic acid (TCA) cycle. Therefore, GlxR has been suggested as a global transcriptional regulator for the regulation of diverse physiological processes as well as carbon metabolism. Adenylate cyclase of C. glutamicum is a membrane protein belonging to class III adenylate cyclases, thus it could possibly be a sensor for some external signal, thereby modulating cAMP level in response to environmental stimuli. In addition to GlxR, three additional transcriptional regulators like RamB, RamA, and SugR are also involved in regulating the expression of many genes of carbon metabolism. Finally, recent approaches for constructing new pathways for the utilization of new carbon sources, and strategies for enhancing amino acid production through genetic modification of carbon metabolism or regulatory network are described.

• Geophysics and Geophysical Exploration
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• v.13 no.4
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• pp.336-348
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• 2010

The Single-channel seismic survey with the source of bubble pulser and drilling survey was carried out in 2008 and 2009 for the site survey of Daecheon-Wonsando area, which was a proposed area of Korea-China subsea tunnel. The goal of this study is to analyze the depth and characteristics of acoustic basement for the stability assessment and tunnel design in this proposed area through combining drilling data with this single-channel seismic data after detailed processing. For this purpose, among the data processing schemes which are usually applied to multi-channel seismic data, we applied the F-K filtering to eliminate the AC(alternating current) noise and the post-stack depth migration to produce depth section. As a result, we verified that the improved depth section could be obtained from single-channel seismic data, and the distribution and characteristics of basement could be analyzed in survey area through the combined analysis with drilling data. However, we could not interpret the detailed structures, fault and fracture zone, due to the quality of bubble pulser source and single-channel data. We expect that those detailed structures can be analyzed when higher resolution seismic data is provided. Therefore, we recommend some items for future seismic survey of subsea tunnel to obtain the high resolution seismic data.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.5
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• pp.564-570
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• 2007

This study investigated the treatment of liquid waste containing highly concentrated iron(III)-ethylenediaminetetraaceticacid (Fe(III)-EDTA) of 70,000 mg/L by an underwater electrical discharge process using low voltage and high current. When AC voltage is applied to the discharging electrode with the other electrode grounded, the temperature of the liquid waste around the discharging electrode rapidly increases, and at the same time, hydrogen and oxygen gases are formed at the electrode as a result of electrochemical reactions. Ultimately, gases formed by vaporization of water and electrochemical reactions cover the electrode. Since the liquid waste is electrically conductive, it elongates the ground electrode up to the border of the gas layer, where electrical discharge occurs. Without hydrogen peroxide, electrical discharge was able to remove about 50% of Fe(III)-EDTA. As the concentration of hydrogen peroxide added increased, the removal efficiency of Fe(III)-EDTA increased. When the molar ratio of hydrogen peroxide to the initial Fe(III)-EDTA was higher than 24.7, more than 80 g of Fe(III)-EDTA was removed with an energy of 1 kWh. A comparison between tungsten and steel electrodes showed that electrode material did not affect the Fe(III)-EDTA removal. In the present underwater electrical discharge process, the removal of Fe(III)-EDTA was completed within 30 min at molar ratios of hydrogen peroxide to the initial Fe(III)-EDTA higher than 24.7.

• Applied Chemistry for Engineering
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• v.9 no.5
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• pp.734-741
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• 1998

Electrode characteristics were studied in the interface between sample solutions and $K^+$ ion selective PVC membrane electrodes containing neutral carriers, dibenzo-18-crown-6(D18Cr6) and valinomycin(Val). The effect of doping of base electrolytes, the chemical structure and the content of carrier, variation of plasticizer, membrane thickness, and concentration variation of sample solution on the response characteristics of electrode such as the measured Nernstian slope, the detection limit, the linear response range, and potentiometric selectivity coefficients, were studied. In order to synthesize the membrane D18Cr6 and Val as neutral carriers were used, and complex between the carrier and $K^+$ ions were used as active materials. PVC membrane electrodes were made of plasticizers (DBP, DOS, and DBS), the base electrolyte[potassium tetraphenylborate(KTPB)], and solvent(THF). The chemical structure of carrier D18Cr6 was best for electrode and ideal electrode characteristics were appeared especially in case of doping of TPB. The optimum carrier content was about 3.23 wt % in case of D18Cr6 and Val. DBP was best as a plasticizer. As membrane thickness decreased the electrode characteristics was improved. But its characteristics were lowered below the optimum membrane thickness because of the elution of carrier, deterioration of membrane strength, etc. In the case of D18Cr6, the selectivity coefficients by the mixed solution method for the $K^+$ ion were in the order of $NH_4{^+}>Ca^{2+}>Mg^{2+}>Na^+$.

• Bulletin of the Korean Chemical Society
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• v.21 no.11
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• pp.1125-1132
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• 2000

The pH effect of the precursor solution on the preparation of $LiCoO_2$ by a solution phase reaction containing malonic acid was carried out. Layered $LiCoO_2$ powders were obtained with the precursors prepared at the different pHs (4, 7, and 9) and heat-treated at $700^{\circ}C(LiCoO_2-700)$ or $850^{\circ}C(LiCoO_2-850)$ in air. pHs of the media for precursor synthesis affects the charge/discharge and electrochemical properties of the $LiCoO_2electrodes.$ Upon irrespective of pH of the precursor media, X-ray diffraction spectra recorded for $LiCoO_2-850$ powder showed higher peak intensity ratio of I(003)/I(104) than that of $LiCoO_2-700$, since the better crystallization of the former crystallized better. However, $LiCoO_2$ synthesized at pH 4 displayed an abnormal higher intensity ratio of I(003)/I(104) than those synthesized at pH 7 and 9. The surface morphology of the $LiCoO_2-850$ powders was rougher and more irregular than that of $LiCoO_2-700$ made from the precursor synthesized at pH 7 and 9. The $LiCoO_2electrodes$ prepared with the precursors synthesized at pH 7 and 9 showed a better electrochemical and charge/discharge characteristics. From the AC impedance spectroscopic experiments for the electrode made from the precursor prepared in pH 7, the chemical diffusivity of Li ions (DLi+) in $Li0.58CoO_2determined$ was 2.7 ${\times}$10-8 $cm^2s-1$. A cell composed of the $LiCoO_2-700$ cathode prepared in pH 7 with Lithium metal anode reveals an initial discharge specific capacity of 119.8 mAhg-1 at a current density of 10.0 mAg-1 between 3.5 V and 4.3 V. The full-cell composed with $LiCoO_2-700$ cathode prepared in pH 7 and the Mesocarbon Pitch-based Carbon Fiber (MPCF) anode separated by a Cellgard 2400 membrane showed a good cycleability. In addition, it was operated over 100 charge/discharge cycles and displayed an average reversible capacity of nearly 130 mAhg-1.

• Ceramist
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• v.21 no.4
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• pp.378-387
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• 2018

The optimal fabrication conditions for $Gd_{0.1}Ce_{0.9}O_{2-{\delta}}$(GDC) buffer layer and $La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_{3-{\delta}}$ (LSCF) cathode on 1mol% $CeO_2-10mol%\;Sc_2O_3$ stabilized $ZrO_2$ (CeScSZ) electrolyte were investigated for application of IT-SOFCs. GDC buffer layer was used in order to prevent undesired chemical reactions between LSCF and CeScSZ. These experiments were carried out with $5{\times}5cm^2$ anode supported unit cells to investigate the tendencies of electrochemical performance, Microstructure development and interface reaction between LSCF/GDC/CeScSZ along with the variations of GDC buffer layer thickness, sintering temperatures of GDC and LSCF were checked, respectively. Electrochemical performance was analyzed by DC current-voltage measurement and AC impedance spectroscopy. Microstructure and interface reaction were investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Although the interfacial reaction between these materials could not be perfectly inhibited, We found that the cell, in which $6{\mu}m$ GDC interlayer sintered at $1200^{\circ}C$ and LSCF sintered at $1000^{\circ}C$ were applied, showed good interfacial adhesions and effective suppression of Sr, thereby resulting in fairly good performance with power density of $0.71W/cm^2$ at $800^{\circ}C$ and 0.7V.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.186-188
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• 2014

In recent years, domestic as well as LTE wireless network of Wi-Fi and most used. In addition, mobile-intensive services that used mainly in our society makes it easier, SNS, application (APP), and file downloads. As such, the amount of data requested, while living at the time of mobile users will want to be safe from the earliest. And the wireless network communications mortality (3G, 4G (LTE), LTE-A) and Wi-Fi (802.11 n-2.4 G H z z H a c-5, 802.11 G), and users are mainly used in the death 4G (LTE), communication Wi-Fi, 802.11 n-2.4 GHz are used most frequently. As above, use the wireless network in order to safely and quickly developed the technology of the Li-Fi. Li-Fi light (visible light) technology to communicate with, and Wi-Fi (802.11 n-2.4 G z H) 100 times faster, LTE-A 66 times faster. However, the current Li-Fi to commercialise the big issue exists. In this paper, there are a lot of existing problems in the commercialization of Li-Fi being used in Wi-Fi, and a comparative analysis.

• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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• v.8 no.6
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• pp.853-861
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• 2018

This paper proposes the application of harmonic constraints to address the problems caused by abnormal voltage increases when electric railway vehicles are running. The AC line that supplies the train with power during operation is used to provide electricity of 25kV/60 Hz, but gradually the size and frequency of harmonics involved in the line are varied with the technological evolution of the railroad vehicle electrical equipment. An increase in heat losses due to the failure of the instrument transformer (PT), the main circuit device, which is a serious problem with the recent train safety operation, or to the main displacement voltage. When high frequency components are introduced through low frequency Transformers of the main circuit device, the high intensity of the components is caused by the high intensity of the core and the current flow of the parasitic core is increased, thus generating heat. To solve this problem, the recent adjustment of the sequence has applied artificial NOTCH OFF of the power converter. However, the method of receiving and controlling the OFF signal operates by interaction between the ground and the vehicle's devices, thus it is invalid in the event of failure, and an actual accident is occurring. Therefore, the harmonic currents were required to prevent possible flow of harmonics, and conducted a study to prevent accidental occurrence of train accidents and to verify feasibility of the device through the simulations of the train's experimental analysis and the simulations of the train for safe operation.