• Applied Chemistry for Engineering
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• v.30 no.6
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• pp.698-706
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• 2019

Over the last few decades, there have been a lot of efforts to develop soft actuators, which can be external stimuli-responsive and applied to the human body. In order to fabricate medical soft actuators with a dynamic precision control, the 3D crosslinked poly(acrylic acid) (PAAc)/poly(vinyl alcohol) (PVA)/poly(ethylene glycol) (PEG) hydrogels were synthesized in this study by using a radiation technique without noxious chemical additives or initiators. After irradiation, all hydrogels showed high gel fraction over 75% and the ATR-FTIR spectra indicated that PAAc/PVA/PEG hydrogels were successfully synthesized. In addition, the gel fraction, equilibrium water content, and compressive strength were measured to determine the change in physical properties of PAAc/PVA/PEG hydrogels according to the irradiation dose and content ratio of constituents. As the irradiation dose and amount of poly(ethylene glycol) diacrylate (PEGDA) increased, the PAAc/PVA/PEG hydrogels showed a high crosslinking density and mechanical strength. It was also confirmed that PAAc/PVA/PEG hydrogels responded to electrical stimulation even at a low voltage of 3 V. The bending behavior of hydrogels under an electric field can be controlled by changing the crosslinking density, ionic group content, applied voltage, and ionic strength of swelling solution.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.1
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• pp.9-17
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• 2017

$K_2Ti_6O_{13}$ whisker have been synthesized by hydrothermal process at low temperature and pressure condition. The average length of the synthesized $K_2Ti_6O_{13}$ whisker was about in the range of 300 nm to $1.5{\mu}m$. The average diameter of the synthesized $K_2Ti_6O_{13}$ whisker was 15 nm to 60 nm. The aspect ratio of the synthesized $K_2Ti_6O_{13}$ whisker was below 12. The average length and diameter of the synthesized $K_2Ti_6O_{13}$ whisker can be controlled by reaction temperature and time, KOH molar ratio. $K_2Ti_6O_{13}$ whisker was synthesized from more than $210^{\circ}C$ and 4 h at reaction temperature and time. The length of the whisker is increased with increasing reaction temperature. Characterization of the synthesized $K_2Ti_6O_{13}$ whisker was carried out using the XRD and FE-SEM.

• Microbiology and Biotechnology Letters
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• v.24 no.1
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• pp.44-49
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• 1996

By using the ${\beta}$-tyrosinase of Citrobacter freundii KCT2006, which was cloned and overexpressed in Escherichia coli, 3,4-dihydroxy phenyl-L-alanine (L-DOPA) was synthesized efficiently from pyrocatechol, sodium pyruvate, and ammonium acetate. Optimal temperature and pH for the reaction were determined to be about 18$^{\circ}C$ and 8.5, respectively. The effects of substrate concentrations were also examined at different concentrations of ammonium acetate, sodium pyruvate, and pyrocatechol. Ammoniumacetate and sodium pyruvate increased the reaction rate until the concentrations reached to 300mM and 50mM, respectively. Although pyrocatechol showed the optimal concentration at 20mM, it was controlled between 20mM and 50mM to avoid the depletion of substrate during the enzymatic synthesis. Meanwhile the synthetic rate was improved about 20% when ethanol was included in the reaction solution. Based on above results, a reaction medium for the productin of L-DOPA was prepared and incubated with 1 unit/ml of ${\beta}$-tyrosinase. Pyrocatechol and sodium pyruvate was added to the reaction solutin intermittently to avoid the substrate depletion during the enzymatic reaction. After 24 hour of reaction, 31.6g/l of L-DOPA was accumulated in the reaction solution as soluble and precipitated ones and the conversion yield was about 85.2%.

• Restorative Dentistry and Endodontics
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• v.25 no.4
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• pp.509-526
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• 2000

It is known that injuries to the dentin have a corresponding inflammatory effect on the pulp and these inflammatory effects frequently result in pulpal pathoses due to progressive degradation of pulpal connective tissue. It was supposed that the tissue degradation in different inflammatory process was controlled by proteinase activity and antiproteinase activity. Therefore, the purpose of this study was to examine the pulp and periapical pathoses in terms of the activities of proteinase and proteinase inhibitor, 37 pulpal tissues were divided by clinical diagnostic criteria into normal pulp, acute inflamed pulp, and chronic inflamed pulp, and then those groups were subdivided by histopathological findings into 5 pulpal pathoses groups, i.e. normal pulp (P1, n=8), chronic pulpitis with fibrotic change (P2, n=2), chronic pulpitis with dystrophic calcification (P3, n=11), chronic pulpitis with pulp abscess (P4, n=7), acute pulpitis with necrotic change (P5, n=4), 26 periapical tissues were also divided by ordinary histopathological findings into 3 periapical pathoses group, i.e., granuloma (A1, n=17), cyst (A2, n=2) and abscess (A3, n=7). The activities of proteinases (cathepsin G, MMP-3) and proteinase inhibitors (${\alpha}1$-AT, TIMP-1 and, SLPI) were evaluated by RT-PCR and immunohistochemical methods. The results were as follows. 1. Generally, the intensity of immunohistochemical staining of proteinases and proteinase inhibitors increased in P2 and P5 groups compared to P1 group. 2. The immunohistochemical stain of proteinases and proteinase inhibitors was intensely detected in P2 group, showing low inflammatory reaction and low tissue degradation, but it was reduced in P3 and P4 groups, showing severe tissue degradation. 3. The distribution of proteinases and proteinase inhibitors in pulpal pathoses was consistently presented by immunohistochemical staining, while the expression of proteinase and/or proteinase inhibitors mRNAs in pulpal pathoses was occasionally detected by RT-PCR methods. 4. RT-PCR of proteinase and proteinase inhibitors was usually positive in P2, showing rare tissue degradation, but it was almost negative in P3 and P4, showing severe tissue degradation. 5. We presume that the reason why the level of proteinase and proteinase inhibitors was so sparse in RT-PCR method is due to the abrupt decrease of mRNA synthesis or degradation of synthesized mRNA of proteinase and/or proteinase inhibitors depend on the inflammatory reaction and/or on the degradation of pulp tissues(P3, P4). 6. Pulpal pathoses groups showed significant lower RT-PCR detection of proteinases and proteinase inhibitors than the periapical pathoses group(p<0.05), and there is no significant difference among the periapical pathoses groups(p>0.05).

• Journal of Life Science
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• v.23 no.8
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• pp.1064-1072
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• 2013

Circadian rhythm is controlled by hormonal oscillations governing the physiology of all living organisms. In mammals, the main function of the pineal gland is to transform the circadian rhythm generated in the hypothalamic suprachiasmatic nucleus into rhythmic signals of circulating melatonin characterized by a largely nocturnal increase that closely reflects the duration of night time. The pineal gland has lost direct photosensitivity, but responds to light via multi-synaptic pathways that include a subset of retinal ganglion cells. Rhythmic control is achieved through a tight coupling between environmental lighting and arylalkylamine-N-acetyltransferase (AANAT) expression, which is the rhythm-controlling enzyme in melatonin synthesis. Previous studies on the nocturnal expression of AANAT protein have described transcriptional, post-transcriptional, and post-translational regulatory mechanisms. Molecular mechanisms for dependent AANAT expression provide novel aspects for melatonin's circadian rhythmicity. Extensive animal research has linked pineal melatonin for the expression of seasonal rhythmicity in many mammalian species to the modulation of circadian rhythms and to sleep regulation. It has value in treating various circadian rhythm disorders, such as jet lag or shift-work sleep disorders. Melatonin, also, in a broad range of effects with a significant regulation influences many of the body's physiological functions. In addition, this hormone is known to influence reproductive, cardiovascular, and immunological regulation as well as psychiatric disorders.

• Applied Chemistry for Engineering
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• v.21 no.5
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• pp.537-541
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• 2010

Pt-Sn with various ratios was supported on carbon black after pretreatment in an acidic solution by a reduction method. The Pt/Sn ratio was controlled by varying the concentration of each component in the solution, and the influence of the composition on the electrocatalytic activities was investigated. The crystallinity of the synthesized materials was investigated by XRD (X-ray Diffraction), and the oxidation states of both the platinum and tin were determined by XPS (X-ray Photoelectron Spectroscopy). SEM (Scanning Electron Microscopy)-EDS (Energy Dispersive Spectroscopy) was utilized to examine the morphology and composition of the synthesized electrode, and the particle size of the Pt-Sn was analyzed by TEM (Transmission Electron Microscopy). The electrocatalytic activity for oxygen reduction was evaluated in a 0.5 M $H_2SO_4$ solution using a rotating disk electrode system. The activity and stability were found to be strongly dependent on the electrode composition (Pt/Sn ratio). The catalytic activity and stability for methanol oxidation were also measured using cyclic voltammetry (CV) in a mixture of 0.5 M $H_2SO_4$ and 0.5 M $CH_3OH$ aqueous solution. The addition of proper amount of Sn was found to significantly improve both catalytic activity and stability for methanol oxidation.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.120-120
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• 2011

Graphene is a carbon based material and it has great potential of being utilized in various fields such as electronics, optics, and mechanics. In order to develop graphene-based logic systems, graphene field-effect transistor (GFET) has been extensively explored. GFET requires supporting devices, such as volatile memory, to function in an embedded logic system. As far as we understand, graphene has not been studied for volatile memory application, although several graphene non-volatile memories (GNVMs) have been reported. However, we think that these GNVM are unable to serve the logic system properly due to the very slow program/read speed. In this study, a GVM based on the GFET structure and using an engineered graphene channel is proposed. By manipulating the deposition condition, charge traps are introduced to graphene channel, which store charges temporarily, so as to enable volatile data storage for GFET. The proposed GVM shows satisfying performance in fast program/erase (P/E) and read speed. Moreover, this GVM has good compatibility with GFET in device fabrication process. This GVM can be designed to be dynamic random access memory (DRAM) in serving the logic systems application. We demonstrated GVM with the structure of FET. By manipulating the graphene synthesis process, we could engineer the charge trap density of graphene layer. In the range that our measurement system can support, we achieved a high performance of GVM in refresh (>10 ${\mu}s$) and retention time (~100 s). Because of high speed, when compared with other graphene based memory devices, GVM proposed in this study can be a strong contender for future electrical system applications.

• Korean Journal of Materials Research
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• v.13 no.9
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• pp.572-580
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• 2003

Synthesizing behavior and microstructural evolution of $CaZrO_3$and $m-ZrO_2$in a thermal reaction process of $ZrSiO_4$-$xCaCO_3$mixtures, where x is 7 and 19, were investigated to determine the addition amount of CaO in CaO:$ZrO_2$:$SiO_2$ternary composition. CaZrO$_3$-Ca$_2$SiO$_4$precursor prepared by the mixture of $ZrSiO_4$and CaCO$_3$in aqueous suspending media was controlled to the acidic (pH=4.0) condition with HCI solution to enhance the thermal reaction. The addition amount of dispersant into the $ZrSiO_4$-$xCaCO_3$slip increased with increasing mole ratio of $CaCO_3$, which was associated with the viscosity of slip. Decarbonation reaction was activated with an increase of the addition amount of $CaCO_3$, showing different final temperatures in $ZrSiO_4$-$7CaCO_3$and $ZrSiO_4$-$19CaCO_3$mixtures as about 980 and 116$0^{\circ}C$, respectively, for finishing decarbonation reaction. The grain morphology was changed to spherical shape for all samples with an increase of sintering temperature. The grain size and phase composition of the synthesized composites depended on the mixture ratio of Zrsi04 and CacO3 powders, indicating that the main crystals were m-ZrO2 ($\leq$3 $\mu\textrm{m}$) and $CaZrO_3$ ($\leq$ 7 $\mu\textrm{m}$) in $ZrSiO_4$$>-7CaCO_3$and $ZrSiO_4$-$19CaCO_3$mixtures, respectively.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.62-62
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• 2018

Pt is still considered as one of the most active electrocatalysts for ORR in alkaline fuel cells. However, the high cost and scarcity of Pt hamper the widespread commercialization of fuel cells. As a strong candidate for the replacement of Pt catalyst, silver (Ag) has been extensively studied due to its high activity, abundance, and low cost. Ag is more stable than Pt in the pH range of 8~14 as the equilibrium potential of Ag/Ag+ being ${\approx}200mV$ higher than that of Pt/PtO. However, Ag is the overall catalytic activity of Ag for oxygen reduction reaction(ORR) is still not comparable to Pt catalyst since the surface Ag atoms are approximately 10 times less active than Pt atoms. Therefore, further enhancement in the ORR activity of Ag catalysts is necessary to be competitive with current cutting-edge Pt-based catalysts. We demonstrate the architectural design of Ag catalysts, synthesized using plasma discharge in liquid phase, for enhanced ORR kinetics in alkaline media. An attractive feature of this work is that the plasma status controlled via electric-field could form the Ag nanowires or dendrites without any chemical agents. The plasma reactor was made of a Teflon vessel with an inner diameter of 80 mm and a height of 80 mm, where a pair of tungsten(W) electrodes with a diameter of 2 mm was placed horizontally. The stock solutions were made by dissolving the 5-mM AgNO3 in DI water. For the synthesis of Agnanowires, the electricfield of 3.6kVcm-1 in a 200-ml AgNO3 aqueous solution was applied across the electrodes using a bipolar pulsed power supply(Kurita, Seisakusyo Co. Ltd). The repetition rate and pulse width were fixed at 30kHz and 2.0 us, respectively. The plasma discharge was carried out for a fixed reaction time of 60 min. In case of Ag nanodendrites, the electric field of 32kVcm-1 in a 200-ml AgNO3 aqueous solution was applied and other conditions were identical to the plasma discharge in water in terms of electrode configuration, repetition rate and discharge time. Using SEM and STEM, morphology of Ag nanowires and dendrites were investigated. With 3.6 kV/cm, Ag nanowire was obtained, while Ag dendrite was constructed with 32 kV/cm. The average diameter and legth of Ag nanowireses were 50 nm and 3.5 um, and thoes values of Ag dendrites were 40 nm and 3.0 um. As a results of XPS analysis, the surface defects in the Ag nanowires facilitated O2 incorporation into the surface region via the interaction between the oxygen and the electron cloud of the adjacent Ag atoms. The catalytic activity of Ag for oxygen reduction reaction(ORR) showed that the catalytic ORR activity of Ag nanowires are much better than Ag nanodendrites, and electron transfer number of Ag nanowires is similar to that of Pt (${\approx}4$).

• Applied Chemistry for Engineering
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• v.5 no.4
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• pp.698-705
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• 1994

The basic medium oil modified alkyd resin was synthesized from linseed oil fatty acid(LOFA), phthalic anhydride(PAA), maleic anhydride(MA) and trimethylol propane(TMP) by condensation polymerization at $230^{\circ}C$. MA/TMPTA modified water-reducible alkyd resins were synthesized with TMPTA graft copolymerization onto the basic resin at $180^{\circ}C$. Acid value of the resin was controlled by the addition amount of MA and N,N-dimethylethanol amine(DMEA) was used as a neutralizing agent to prepare of the water-reducible alkyd resin. The effect of TMPTA on the graft copolymerization of the resin was studied by measuring molecular weight glass transition temperature(Tg), viscosity, graft efficiency, and gel contents of melanin cured film. Heat resistance, UV resistance and water resistance of cured film of MA/TMPTA modified resin was compared to those of TMA/TMPTA modified alkyd resin. The molecular weight, viscosity gel contents and graft efficiency of water reducible alkyd resin were increased according to the TMPTA graft copolymerization, but Tg was decreased. The viscosity was lower when the solid contents reached 40% than that of 30% content and also and also became lower with the extent of neutralization ratio, The heat resistance, UV resistance and water resistance of the MA/TMPTA modified alkyd resis were better than those of TMA/TMPTA modified alkyd resin but the storage stability of the TMA/TMPTA alkyd resis was better than that of MA/TMPTA modified alkyd resin.