• Clean Technology
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• v.24 no.3
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• pp.183-189
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• 2018

Hollow carbon spheres (HCS) and carbon spheres (CS) were prepared by a hydrothermal reaction and they were introduced as a substrate for the deposition of $MnO_2$ nanoparticles. The $MnO_2$ nanoparticles were deposited on the carbon surface by a chemical redox deposition method. After deposition, the $MnO_2$ nanoparticles were uniformally distributed on the carbon surface in a slit-shape, and sparse $MnO_2$ slits appeared on the HCS surface. The $MnO_2-HCS$ showed an initial specific capacitance of $164.1F\;g^{-1}$ at scan rate of $20mv\;s^{-1}$, and after 1,000 cycles, the specific capacitance was maintained to $141.3F\;g^{-1}$. The capacity retention of $MnO_2-HCS$ and $MnO_2-CS$ were calculated to 86% and 78% in the cycle performance test up to 1,000 cycles, respectively. $MnO_2-HCS$ showed a good cycle stability due to the mesoporous hollow structure which can cause a faster diffusion of the electrolyte and can easily adsorb and desorb $Na^+$ ions on the surface of the electrode.

• Polymer(Korea)
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• v.30 no.6
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• pp.556-562
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• 2006

Quarternized poly(4-vinyl pyridine)s have been prepared by the reaction of poly (4-vinyl pyridine)s (Mw=50 kg/mol and 200 kg/mol) and alkylating agents varying the carbon numbers of the alkyl groups (m):dimethyl sulfate (m=1) as well as bromoalkane (m= 5, 8, 12, 16, and 22) was used as an alkylating agent. The degree of alkylation was determined by using an elemental analysis and NMR spectroscopy. As a result, polyelectrolytes were obtained by the almost full alkylation of poly (4-vinyl pyridine)s. The critical aggregation concentration (CAC) was determined by measuring the change of turbidity occurred by addition of sodium dodecyl sulfate (SDS) into aqueous solution of quarternized poly-(4-vinyl pyridine)s, and the dependence of molecular weight of polymer, the length of N-alkyl group and concentration of NaCl upon CAC was investigated. As a result, as the molecular weight or the length of alkyl group was increased, less amount of SDS Gould induce the aggregation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.6
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• pp.1283-1293
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• 2014

In ubiquitous environment, data are changing rapidly and new data is coming as times passes. And sometimes all of the past data will be lost if there is not sufficient space in memory. Therefore, there is a need to make rules and combine it with new data not to lose all the past data or to deal with large amounts of data. In making decision trees and extracting rules, the weight of each of rules is generally determined by the total number of the class at leaf. The computational problem of finding a minimum finite state acceptor compatible with given data is NP-hard. We assume that rules extracted are not correct and may have the loss of some information. Because of this precondition. this paper presents a new approach for refining rules. It controls their weight of rules of previous knowledge or data. In solving rule refinement, this paper tries to make a variety of rules with pruning method with majority and minority properties, control weight of each of rules and observe the change of performances. In this paper, the decision tree classifier with extended data expression having static weight is used for this proposed study. Experiments show that performances conducted with a new policy of refining rules may get better.

• Korean Chemical Engineering Research
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• v.56 no.5
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• pp.718-724
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• 2018

In this study, the $Ni_{0.9}Co_{0.05}Ti_{0.05}(OH)_2$ precursor was prepared by the concentration gradient co-precipitation method. In order to overcome the structural change due to oxygen desorption in the cathode active material with high nickel content, the physical and electrochemical analysis of the cathode active material according to the calcination temperature were investigated. Physical properties of $Li_{1.05}Ni_{0.9}Co_{0.05}Ti_{0.05}O_2$ were analyzed by FE-SEM, XRD and TGA. The electrochemical performance of the coin cell using a cathode active material and $LiPF_6$(EC:EMC=1:2 vol%) electrolyte was evaluated by the initial charge/discharge efficiency, cycle retention, and rate capabilities. As a result, the initial capacity and initial efficiency of cathode materials were excellent with 244.5~247.9 mAh/g and 84.2~85.8% at the calcination temperature range of $750{\sim}760^{\circ}C$. Also, the capacity retention exhibited high stability of 97.8~99.1% after 50cycles.

• Korean Chemical Engineering Research
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• v.44 no.2
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• pp.160-165
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• 2006

A Pd-Cu-Ni alloyed hydrogen membrane has fabricated on porous nickel support formed by nickel powder. Porous nickel support made by sintering shows a strong resistance to hydrogen embrittlement and thermal fatigue. Plasma surface modification treatment is introduced as pre-treatment process instead of conventional HCl wet activation. Nickel was electroplated to a thickness of $2{\mu}m$ in order in to fill micropores at the nickel support surface. Palladium and copper were deposited at thicknesses of $4{\mu}m$ and $0.5{\mu}m$, respectively, on the nickel coated support by DC sputtering process. Subsequently, copper reflow at $700^{\circ}C$ was performed for an hour in $H_2$ ambient. And, as a result PdCu-Ni composite membrane has a pinhole-free and extremely dense microstructure, having a good adhesion to the porous nickel support and infinite hydrogen selectivity in $H_2/N_2$ mixtures.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.5
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• pp.221-226
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• 2010

Quartz crystal microbalance (QCM) gas sensor to detect methyl mercaptan ($CH_3SH$) gas was fabricated by depositing $TiO_2$ nanoparticles and polyelectrolyte on the electrode of QCM. The $TiO_2$/poly(sodium 4-styrenesulfonate) (PSS) thin film fabricated by a layer-by-layer self-assembly (LBL-SA) method showed a high surface area and increased the sensitivity of gas sensor. When the QCM sensors coated with triethanolamine (TEA) or ($TiO_2$/PSS) were exposed to methyl mercaptan gas (1.0 ppm), the frequency shifts of QCM with TEA casting film and $TiO_2$/PSS thin film were ca. 9 Hz and ca. 24 Hz, respectively. As the bilayer number of ($TiO_2$/PSS) increased, the frequency shift of QCM sensor with ($TiO_2$/PSS) thin film was gradually increased. In addition, the frequency shift of QCM sensor was gradually increased as the concentration of methyl mercaptan gas increased from 0.5 ppm to 2.0 ppm. In this study, the surface morphology and sensor property of QCM sensor coated with ($TiO_2$/PSS) thin film were measured.

• Clean Technology
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• v.18 no.4
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• pp.426-431
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• 2012

Carbon-rich coal can be utilized as a fuel for direct carbon fuel cell (DCFC). However, left-behind ash after the electrochemical oxidation may hinder the electrochemical reactions. In this study, we produced ash-free coal (AFC) by thermal extraction and then tested it as a fuel for DCFC. DCFC was built based on solid oxide electrolyte and the electrochemical performance of AFC mixed with $K_2CO_3$ was compared with AFC only. Significantly enhanced power density was found by catalytic steam gasification of AFC. However, an increase of the power density by catalytic pyrolysis was negligible. This result indicated that a catalyst activated the steam gasification reactions, producing much more $H_2$ and thus increasing the power density, compared to AFC only. Results of a quantitative analysis showed much improved kinetics in AFC with $K_2CO_3$ in agreement with DCFC results. A secondary phase of potassium on yttria-stabilized zirconia (YSZ) surface was observed after the cell operation. This probably caused poor long-term behavior of AFC with $K_2CO_3$. A thin YSZ (30 ${\mu}m$ thick) was found to be higher in the power density than 0.9 mm of YSZ.

• Journal of the Korean Chemical Society
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• v.42 no.4
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• pp.422-431
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• 1998

Tridentate Schiff base ligands such as $SIPH_2,\;SIPCH_2,\;HNIPH_2,\;and\; HNIPCH_2$ were prepared by the reaction of salicylaldehyde and 2-hydroxy-l-naphthaldehyde with 2-aminophenol and 2-amino-p-cresol. The structures and properties of ligands and their Co(II) complexes were investigated by elemental analysis, $^1H$NMR, IR, UV-visible spectra, and thermogravimetric analysis. The molar ratio of Schiff base to the metal of complexes was found to be 1:1. Co(II) complexes were contemplated to be hexa-coordinated octahedral configuration containing three water molecules. The redox process of ligands and complexes in DMSO solution containing 0.1 M TBAP as a supporting electrolyte were investigated by cyclic voltammetry with glassy carbon electrode. The redox process of the tridentate Schiff base ligands was totally irreversible. The redox process of Co(II) complexes were irreversible and one electron processes by two steps in diffusion controlled reaction. The reduction potential of the Co(II) complexes was shifted to the positive direction in the order [Co(Ⅱ)$(HNIPC)(H_2O)_3$]>[Co(Ⅱ)$(HNIP)(H_2O)_3$]>[Co(II)$(SIPC)(H_2O)_3$]>[Co(Ⅱ)$(SIP)(H_2O)_3], and their dependence on ligands were not so high.

• Polymer(Korea)
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• v.33 no.4
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• pp.377-383
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• 2009

Ionic polymer-metal composite (IPMC) actuator generates bending actuation via ion/water flux to the cathode side under an electric field. Polyelectrolytes in IPMC should possess high water-retention capability, proton conductivity, and Young's modulus. In this study. for endowing IPMCs with these properties, Nafion-alumina composite membranes containing $\alpha$- or $\gamma$-aluminas of $4{\sim}8$ wt% were prepared. Mechanical moduli of Nafion-alumina composite membranes were $7{\sim}3$ MPa higher than that of Nafion, with the slight decrease in proton conductivity. At DC 3 V. the actuation performance of the Nafion-$\alpha$-alumina (8 wt%)-IPMC was superior to that of the typical Nafion-IPMC. exhibiting 2.7 times the displacement with an enhanced blocking force. The enhanced actuation performance with the Nafion-$\alpha$-alumina composite membranes was attributed to the higher proton conductivity, the elevated ion/water flux, and the lower interfacial electric resistance of platinum electrodes and membrane, compared with those containing $\gamma$-alumina.

• The Journal of Natural Sciences
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• v.6 no.1
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• pp.5-39
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• 1993

The Blue-green algae collected from whole coasts of Korea were investigated morphotaxonomically in order to list up Korean marine Cyanophyta and clarify their taxnomic position. As a result, 36 species, 20 genus, 6 families belonging to 3 orders were identified. Among these, 14 species were recorded for the first time in Korea. They are Chroococcus minutus (K$\"{u}$tzing) N$\"{a}$geli, Merismopedia punctata Meyen, Microcystis ichtyoblabe K$\"{u}$zing, Dermocarpa leibleiniae (Reinsch) Born. et Thur., Hydrocoleum confluens (Setchell et Gardner) Drouet, Lyngbya sordida (Zanard.) Gomont, Phormidium forveolarum (Mont.) Gomont, Phormidium hansgieri Schmidle, Skujaella hildebrandtii (Gomont.) de Toni, Sphaeronema lithophila (Ercegovic) Umezaki, Spirulina tenerrima K$\"{u}$tzing, Hormothamnion enteromorphoides Grunow, Michrochaete aeruginea Batters, Michrochaete grisea Thuret ex Born. et flah.. Using the phase contrast microscope and the Nomarski interference micrope, we made photomicrographs of minute blue green algae. The cellular inclusions especially PHB(poly-$\SS$-hydroxy-butyrate) granules of the blue-green algae identified were investigated. The species clearly characteriged to have PHB granule were Lyngbya confervoides, L. semiplena, Phormidium corium, Sirocoleum kurzii, Hormothamnion enteromorphoides and Calothrix crustacea. These result would be fundamental data for estabilishing phylogenetic system of blue-green algae based on physio-biochemical characteristics in future.