• Bulletin of the Korean Chemical Society
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• v.24 no.4
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• pp.446-452
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• 2003

Some new nanohybrid materials have been synthesized by intercalating the oxotitanium(IV) meso-tetrakis(4- sulfonatophenyl) porphyrin$(O=Ti^{(IV)} TSPP)$ into the Zn/Al layered double hydroxides (LDHs), and their structures and photophysical properties have been investigated by various laser spectroscopic techniques. According to the XRD pattern of the synthesized nanohybrid materials, the macrocycle plane of $O=Ti^{(IV)}$ TSPP are grafted perpendicular to the LDH layers. The $O=Ti^{(IV)}$ TSPP-intercalated LDH exhibits band broadening of the absorption spectrum and a blue shift of Q-band as compared to that observed in solution. Resonance Raman spectral measurements demonstrate that the positively charged LDHs give rise to a slight decrease of the electronic density of the porphyrin ring accompanying a small change of the electronic distribution of the $O=Ti^{(IV)}$ TSPP. Consequently the LDH environment affects the energies of the two highest occupied molecular orbitals (HOMOs) of the $O=Ti^{(IV)}$) TSPP, $a_{1u}$ and $a_{2u}$, producing a mixed orbital character. Being consistent with these electronic structural changes of $O=Ti^{(IV)}$ TSPP in LDH, both the fluorescence spectral change and the fsdiffuse reflectance transient measurements imply that the photoexcitation of the $O=Ti^{(IV)}$ TSPP intercalated into LDH undergoes fast relaxation to the O=Ti(IV) $TSPP^+-LDH^- $charge transfer (CT) state within a few picoseconds, followed by a photoinduced electron transfer between the O=Ti(IV) TSPP and LDHs with a rate constant greater than %1×10^{10}S^{-1}$. No evidence is found for back electron transfer. In conclusion, the $O=Ti^{(IV)}$ TSPP intercalated LDH seems to be a possible candidate for an artificial reaction center for an efficient solar energy conversion system.

• Resources Recycling
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• v.28 no.6
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• pp.96-105
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• 2019

Automobile shredder residue (ASR) is the final waste produced when end-of-life vehicles (ELVs) are shredded. ASR can be separated using mineral-processing operations such as comminution, air classification, magnetic separation, and/or electrostatic separation. In this work, trajectory analyses of conductors (copper) and non-conductors (glass) in the ASR have been carried out using induction electrostatic separator for predicting or improving the ASR-separation efficiency. From results of trajectory analysis for conductors, the trajectories of copper wire by observation versus simulation for coarse particles of 0.5 and 0.25 mm showed consistent congruity. The observed 0.06 mm fine-particles trajectory was deflected toward the (-) attractive electrode owing to the charge-density effects due to the particle characteristics and relative humidity. In the case of non-conductors, the actual trajectory of dielectric glass deflected toward the (-) electrode, showing characteristics similar to those of conductive particles. The analyses of stereoscopic microscope and SEM & EDS found heterologous materials (fine ferrous particles and conductive organics) on the glass surface. This demonstrates the glass decreasing separation efficiency for non-ferrous metals during electrostatic separation for the recycling of ASR. Future work will require a pretreatment process for eliminating impurities from the glass and advanced trajectory-simulation processes.

• Journal of the Korean Applied Science and Technology
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• v.34 no.2
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• pp.280-288
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• 2017

Nanocarbon base materials such as, graphene and graphene hybrid with high electrochemical performances have great deal of attention to investigate flexible, stretchable display and wearable electronics in order to develop portable and high efficient energy storage devices. Battery, fuel cell and supercapacitor are able to achieve those properties for flexible, stretchable and wearable electronics, especially the supercapacitor is a promise energy storage device due to their remarkable properties including high power and energy density, environment friendly, fast charge-discharge and high stability. In this study, we have fabricated flexible supercapacitor composed of graphene/conductive polymer composite which could improve its electrochemical performance. As a result, specific capacitance value of the flexible supercapacitor (unbent) was $198.5F\;g^{-1}$ which decreased to $128.3F\;g^{-1}$ (65% retention) after $500^{th}$ bending cycle.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.5
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• pp.329-337
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• 2001

It has been known that the leakage current in the low field region consists of the dielectric relaxation current and intrinsic leakage current, which cause the charge loss in dynamic random access memory (DRAM) storage capacitor using (Ba,Sr)TiO$_{3}$ (BST) thin film. Especially, the dielectric relaxation current should be seriously considered since its magnitude is much larger than that of the intrinsic leakage current in giga-bit DRAM operation voltage (~IY). In this study, thermally stimulated current (TSC) measurement was at first applied to investigate the activation energy of traps and relative evaluation of the density of traps according to process change. And, through comparing TSC to early methods of I-V or I-t measurement and analyzing, we identify the origin of the dielectric relaxation current and investigate the reliability of TSC measurement. First, the polarization condition such as electric field, time, temperature and heating rate was investigated for reliable TSC measurement. From the TSC measurement, the energy level of traps in the BST thin film has been investigated and evaluated to be 0.20($\pm$0.01) eV and 0.45($\pm$0.02) eV. Based on the TSC measurement results before and after rapid thermal annealing (RTA) process, oxygen vacancy is concluded to be the origin of the traps. TSC characteristics with thermal annealing in the MIM BST capacitor have shown the same trends with the current-voltage (I-V) and current-time (I-t) characteristics. This means that the TSC measurement is one of the effective methods to characterize the traps in the BST thin film.

• Journal of the Korean Vacuum Society
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• v.14 no.2
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• pp.91-96
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• 2005

The silicon-on-insulator (SOI) wafer fabrication technique has been developed by using ion-cut process, based on proton implantation and wafer bonding techniques. It has been shown by SRIM simulation that 65keV proton implantation is required for a SOI wafer (200nm SOI, 400nm BOX) fabrication. In order to investigate the optimum proton dose and primary annealing condition for wafer splitting, the surface morphologic change has been observed such as blistering and flaking. As a result, effective dose is found to be in the $6\~9\times10^{16}\;H^+/cm^2$ range, and the annealing at $550^{\circ}C$ for 30 minutes is expected to be optimum for wafer splitting. Direct wafer bonding is performed by joining two wafers together after creating hydrophilic surfaces by a modified RCA cleaning, and IR inspection is followed to ensure a void free bonding. The wafer splitting was accomplished by annealing at the predetermined optimum condition, and high temperature annealing was then performed at $1,100^{\circ}C$ for 60 minutes to stabilize the bonding interface. TEM observation revealed no detectable defect at the SOI structure, and the interface trap charge density at the upper interface of the BOX was measured to be low enough to keep 'thermal' quality.

• Journal of the Korean Electrochemical Society
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• v.15 no.2
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• pp.95-100
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• 2012

$LiFePO_4$ is an attractive cathode material due to its low cost, good cyclability and safety. But it has low ionic conductivity and working voltage impose a limitation on its application for commercial products. In order to solve these problems, the iron($Fe^{2+}$)site in $LiFePO_4$ can be substituted with other transition metal ions such as $Mn^{2+}$ in pursuance of increase the working voltage. Also, reducing the size of electrode materials to nanometer scale can improve the power density because of a larger electrode-electrolyte contact area and shorter diffusion lengths for Li ions in crystals. Therefore, we chose electrospinning as a general method to prepare $Li[Fe_{0.9}Mn_{0.1}]PO_4$ to increase the surface area. Also, there have been very a few reports on the synthesis of cathode materials by electrospinning method for Lithium ion batteries. The morphology and nanostructure of the obtained $Li[Fe_{0.9}Mn_{0.1}]PO_4$ nanofibers were characterized using scanning electron microscopy(SEM). X-ray diffraction(XRD) measurements were also carried out in order to determine the structure of $Li[Fe_{0.9}Mn_{0.1}]PO_4$ nanofibers. Electrochemical properties of $Li[Fe_{0.9}Mn_{0.1}]PO_4$ were investigated with charge/discharge measurements, electrochemical impedance spectroscopy measurements(EIS).

• Journal of the Korean Electrochemical Society
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• v.20 no.2
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• pp.34-40
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• 2017

Electric double layer capacitors (EDLC: electric double layer capacitors) have drew attention as an energy storage device for the next generation because of their outstanding power capability and durability. But their usage is somewhat limited due to low energy density over secondary batteries. One of methods to improve the energy of EDLC is expanding the voltage window of cell operation by increasing the charge cut-off voltage. In this study, $SBP-BF_4$ (spirobipyrrolidinium tetrafluoroborate), $TEA-BF_4$ (tetraethylammonium tetraflouroborate) and $EMI-BF_4$ (1-ethyl-3-methylimidazolium tetrafluoroborate) in AN (acetonitrile) were selected to evaluate the possibility of application at high voltage environment. The LSV (linear sweep voltammetry) measurements showed that the 1.5M SBP-BF4/AN electrolyte was stable over a wide potential window and showed the best electrochemical performance compared to other combinations of electrolytes at high voltage environments (over 3.0 V). Furthermore, TMSP (tris(trimethylsilyl) phosphite) was applied to 1.5M SBP-BF4/AN in order to maintain stable performance at high voltage for the long period of time. The electrolyte with TMSP additive showed the capacity retention of 93% after 10,000 cycles at 3.3 V.

• Journal of the Korean Chemical Society
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• v.42 no.1
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• pp.84-91
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• 1998

Random copolymers of N-isopropyl acrylamide (NIPAAm) and acrylic acid (AAc) which exhibit temperature- and pH-responsive behavior were synthesized by free-radical polymerization. The copolymers were characterized by means of FT-IR spectrometry and titration. The influence of polyelectrolyte on the lower critical solution temperature (LCST) of pH/temperature-sensitive polymers was investigated in the pH range of 2-12. The LCSTs of PNIPAAm/water in poly(NIPAAm-co-AAc) were determined by cloud-point measurements. A polyelectrolyte complex was prepared by mixing poly(NIPAAm-co-AAc) with poly(allylamine) (PAA) or poly(L-lysine) (PLL) solutions as anionic and cationic polyelectrolytes, respectively. Back titration was performed to determine the content of AAc and to study the effect of comonomer ionization on the LCST. The LCSTs of PNIPAAm/water in the copolymers were strongly affected by pH, presence of polyelectrolyte, AAc content, and charge density on the polymer. The polyelectrolyte complexes were formed at neutral condition. The influence of more hydrophobic PLL as polyelectrolyte on the cloud-point of PNIPAAm/water in the copolymer was stronger than that of poly(allylamine) (PAA).

• Molecular & Cellular Toxicology
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• v.4 no.2
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• pp.157-163
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• 2008

Formation of ${\beta}$-amyloid $(A{\beta})$ fibrils has been identified as one of the major characteristics of Alzheimer's disease (AD). Inhibition of $A{\beta}$ fibril formation in the CNS would be attractive therapeutic targets for the treatment of AD. Several small compounds that inhibit amyloid formation or amyloid neurotoxicity in vitro have been known. Citrate has surfactant function effect because of its molecular structure having high anionic charge density, in addition to the well-known antibacterial and antioxidant properties. Therefore, we hypothesized that citrate might have the inhibitory effect against $A{\beta}$ fibril formation in vitro and have the protective effect against $A{\beta}$-induced neurotoxicity in PC12 cells. We examined the effect of citrate against the formation of $A{\beta}$ fibrils by measuring the intensity of fluorescence in thioflavin-T (Th-T) assay of between $A{\beta}_{25-35}$ groups treated with citrate and the control with $A{\beta}_{25-35}$ alone. The neuroprotective effect of citrate against $A{\beta}$-induced toxicity in PC12 cells was investigated using the WST-1 assay. Fluorescence spectroscopy showed that citrate inhibited dose-dependently the formation of $A{\beta}$ fibrils from ${\beta}$-amyloid peptides. The inhibition percentages of $A{\beta}$ fibril formation by citrate (1, 2.5, and 5 mM) were 31%, 60%, and 68% at 7 days, respectively in thioflavin-T (Th-T) assay. WST-1 assay revealed that the toxic effect of $A{\beta}_{25-35}$ was reduced, in a dose-dependent manner to citrate. The percentages of neuroprotection by citrate (1, 2.5, and 5 mM) against $A{\beta}-induced$ toxicity were 19%, 31 %, and 34%, respectively. We report that citrate inhibits the formation of $A{\beta}$ fibrils in vitro and has neuroprotective effect against $A{\beta}$-induced toxicity in PC12 cells. Neuroprotective effects of citrate against $A{\beta}$ might be, to some extent, attributable to its inhibition of $A{\beta}$ fibril formation. Although the mechanism of anti-amyloidogenic activity is not clear, the possible mechanism is that citrate might have two effects, salting-in and surfactant effects. These results suggest that citrate could be of potential therapeutic value in Alzheimer's disease.

• Journal of the Korean Ceramic Society
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• v.42 no.4
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• pp.251-259
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• 2005

In order to characterize the influence of the reaction-site density on the cathodic polarization property of LSCF, we chose the porosity of LSCF as a main controlling variable, which is supposed to be closely related with active sites for the cathode reaction. To control the porosity of cathodes, we changed the mixing ratio of fine and coarse LSCF powders. The porosity and pore perimeter of cathodes were quantitatively analyzed by image analysis. The electrochemical half cell test for the cathodic polarization was performed via 3-probe AC-impedance spectroscopy. According to the investigation, the reduction of oxygen at LSCF cathode was mainly controlled by following two rate determining steps; i) surface diffusion and/or ionic conduction of ionized oxygen through bulk LSCF phase, ii) charge transfer of oxygen ion at cathode/electrolyte interface. Moreover, the overall cathode polarization was diminished as the cathode porosity increased due to the increase of the active reaction sites in cathode layer.