• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.5
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• pp.241-245
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• 2013

Granular bamboo-derived active carbons (AC) were impregnated (or coated) with $TiO_2$ nano crystalline powders. The photocatalytic activity of the $TiO_2$-impregnated active carbons ($TiO_2$/AC) were determined on the basis of the degradation rate of methylene-blue aqueous solution under UV irradiation. The active compounds of $TiO_2$ were impregnated onto the AC under moderate hydrothermal conditions (${\leq}200^{\circ}C$, pH 11). The mean size of $TiO_2$ particles calculated from BET surface area were found to be as 50 nm. The $TiO_2$ precipitates were coated on the cavities or pores on the surfaces of highly activated carbons. Since the hydrothermal process led to a lowering of the on-set temperature of the anatase-to-rutile transition of $TiO_2$ as low as $200^{\circ}C$, $TiO_2$ crystallites of a pure anatase or a mixed form with rutile were successfully coated on the AC depending on the synthesis temperatures.

• Journal of the korean academy of Pediatric Dentistry
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• v.35 no.4
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• pp.662-670
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• 2008

The purpose of this in vitro study was to evaluate the effect of fluoride containing adhesive film on prevention of enamel demineralization. Eighty bovine enamel blocks were divided randomly into 4 groups of 25: (1) APF gel applied ; (2) CavityShield$^{TM}$ applied; (3) 3% fluoride film applied; (4) 5% fluoride film applied; Early caries lesions were produced by placing each specimen into demineralization solution at pH 4.0 for 72 hours. Then lesion of the surface microhardness were measured by the Vicke's hardness test and the lesions depth were measured by polarizing light microscope. The results of the present study are as follows: 1. Difference of microhardness value ($M{\pm}SD$) between control and experimental side was the highest in group II, followed by group IV, III, I but, no significant difference was between group II, III and IV. 2. Difference of mean lesion depth ($M{\pm}SD$) between control and experimental side was the highest in group II, followed by group III, IV and I but no significant difference was between group III and IV. The results of the present study indicate that the fluoride film application is more effective than APF gel and is similar to fluoride varnish application for prevention of dental caries.

• Journal of the Korean Ceramic Society
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• v.39 no.5
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• pp.460-466
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• 2002

Titanium oxide film was deposited on the commercially pure titanium (cp-Ti) by thermal oxidation method for its medical application. The cp-Ti disks were cleaned and then heat-treated at the temperatures of 500, 550, 600, 650, and 700${\circ}C$, respectively, for 10 min in air or Ar. To test the ability of calcium phosphate formation, the specimens were immersed in the Eagle's minimum essential medium solution at 36.5${\circ}C$ for 15 days. The morphology and chemical composition of the surfaces before and after soaking were analyzed by using FE-SEM and EDS. The in-vitro formation of carbonated calcium phosphate on the thin films containing nano-sized $TiO_2$ crystals was identified.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.1
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• pp.18-21
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• 2017

In this study, spherical monodispersed cerium-doped yttrium aluminum garnet (YAG : $Ce^{3+}$) phosphor particles were synthesized via homogeneous precipitation method using the mixed solution of yttrium nitrate, cerium nitrate, aluminum nitrate, ammonium aluminum sulfate, and urea as a precipitant. During the process of precursors of monodispersed YAG : $Ce^{3+}$, aluminum ions which form spherical aluminum compounds precipitated first and yttrium compounds precipitated onto the surface of the existing spherical aluminum compounds. Drying process using lyophilization could obtain monodispered spherical YAG : $Ce^{3+}$ particles compare to using oven. The thermal calcination process of YAG : $Ce^{3+}$ precursors under the temperature of $1200^{\circ}C$ for 6 h was enough to obtain 400~500 nm sized YAG particles with pure YAG phase.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.3
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• pp.479-485
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• 2006

The double gate(DG) MOSFET is a promising candidate to further extend the CMOS scaling and provide better control of short channel effect(SCE). DGMOSFETs, having ultra thin undoped Si channel for SCEs control, ale being validated for sub-20nm scaling. A novel analytical transport model for the subthreshold mode of DGMOSFETs is proposed in this paper. The model enables analysis of short channel effect such as the subthreshold swing(SS), the threshold voltage roil-off$({\Delta}V_{th})$ and the drain induced barrier lowering(DIBL). The proposed model includes the effects of thermionic emission and quantum tunneling of carriers through the source-drain barrier. An approximative solution of the 2D Poisson equation is used for the distribution of electric potential, and Wentzel-Kramers-Brillouin approximation is used for the tunneling probability. The new model is used to investigate the subthreshold characteristics of a double gate MOSFET having the gate length in the nanometer range $(5-20{\sim}nm)$ with ultra thin gate oxide and channel thickness. The model is verified by comparing the subthreshold swing and the threshold voltage roll-off with 2D numerical simulations. The proposed model is used to design contours for gate length, channel thickness, and gate oxide thickness.

• Korean Journal of Materials Research
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• v.20 no.12
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• pp.669-675
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• 2010

One of the greatest challenges for our society is providing powerful electrochemical energy conversion and storage devices. Rechargeable lithium-ion batteries and fuel cells are among the most promising candidates in terms of energy and power density. As the starting material, $TiCl_4{\cdot}YCl_3$ solution and dispersing agent (HCP) were mixed and synthesized using ammonia as the precipitation agent, in order to prepare the nano size Y doped spherical $TiO_2$ precursor. Then, the $Li_4Ti_5O_{12}$ was synthesized using solid state reaction method through the stoichiometric mixture of Y doped spherical $TiO_2$ precursor and LiOH. The Ti mole increased the concentration of the spherical particle size due to the addition of HPC with a similar particle size distribution in a well in which $Li_4Ti_5O_{12}$ spherical particles could be obtained. The optimal synthesis conditions and the molar ratio of the Ti 0.05 mol reaction at $50^{\circ}C$ for 30 minutes and at $850^{\circ}C$ for 6 hours heat treatment time were optimized. $Li_4Ti_5O_{12}$ was prepared by the above conditions as a working electrode after generating the Coin cell; then, electrochemical properties were evaluated when the voltage range of 1.5V was flat, the initial capacity was 141 mAh/g, and cycle retention rate was 86%; also, redox reactions between 1.5 and 1.7V, which arose from the insertion and deintercalation of 0.005 mole of Y doping is not a case of doping because the C-rate characteristics were significantly better.

• Journal of the Mineralogical Society of Korea
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• v.19 no.2 s.48
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• pp.81-88
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• 2006

The Yttria Partially Stabilized Zirconia powder was prepared by spontaneous precipitation method using $ZrOCl_2{\cdot}8H_O-YCl_33{\cdot}6H_2O$ solution as a starting materials. The optimal experimental conditions such as concentration and pH of starting solutions, the amounts of stabilizer $Y_2O_3$ used, and sintered temperature were carefully studied. The best condition for synthesizing $ZrO_2$ was experimentally selected and applied throughout this study for the preparation of the 3 mole% $Y_2O_3$ partially stabilized zirconia, 3YSZ. The physical properties of 3YSZ was examined by XRD, Raman, DT A, and SEM. The structural transition from pure monoclinic high temperature $ZrO_2$ to tetragonal room temperature 3YSZ was made possible by the added amount of $Y_2O_3$ in the $ZrO_2+Y_2O_3$ system. All Raman Spectrum band appeared in the lower wave numbers rather than in higher wave numbers as structure changes from monoclinic to tetragonal.

• Korean Journal of Clinical Laboratory Science
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• v.49 no.4
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• pp.323-328
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• 2017

Angiogenesis is a process including members of the angiogenic factors. In particular, fibroblast growth factor 2 (FGF2) is considered the most potent angiogenic factor because it promotes cell proliferation and tube formation. A recent study reported that fucoidan derived from marine plant potentiated FGF-2 induced tube formation in human endothelial cells. On the other hand, the molecular mechanisms involved in the angiogenic activity of fucoidan and FGF2 are unknown. In this study, a fucoidan treatment promoted angiogenesis induced by FGF2. The effects of fucoidan on FGF2-induced angiogenesis were confirmed by a proliferation assay using a CellTiter96 Aqueous One solution after a treatment with fucoidan and FGF2. The tube formation and wound healing assay for the angiogenic activity were also confirmed. Reverse transcription PCR showed a change in the mRNA of vascular endothelial growth factor-A (VEGF-A), intercellular adhesion molecule-1 (ICAM-1), matrix metallopeptidase9 (MMP9), and the signal transducer and activator of transcription3 (STAT3). In summary, the Fucoidan/FGF2 treatment induced an increase in cell proliferation, improved the tube formation and wound healing activity, and altered the STAT3, VEGF-A, ICAM-1, and MMP9 mRNA expression levels. Further research will be needed to provide a scientific explanation in terms of cell-signaling and confirm the present findings.

• Applied Chemistry for Engineering
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• v.23 no.5
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• pp.467-473
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• 2012

Coenzyme Q10 (CoQ10) is a natural lipid cofactor with antioxidant and anti-aging properties as cosmetic and food ingredients, involved in cellular energy metabolism. Here, nano-emulsions with CoQ10 were fabricated with lecithin, ethanol, oil, and sorbitan monostearate (Arlacel 60), as major components. Phase inversion emulsion method with ultrasonicator was utilized in producing CoQ10 solution, and stabilization effects from lecithin and ethanol and other diverse perturbation factors were evaluated over time. Physical properties of the emulsion were characterized such as its size, surface charges by zeta-potential, and the overall structures. Optimal concentrations of CoQ10 and Arlacel 60 were 0.8% and 3%, respectively, for producing the smallest sizes of nanoemersions in a 100 nm diameter with best morphology. No notable changes in the size were observed over 7 days from Ostwald ripening, when the concentration of Arlacel 60 was higher than 2%. Even after 270 days at room temperature, the size of nanoemulsions maintained as 115 nm in diameter, revealing only a 10% increase with high degrees of long termed stability and substantiality. In addition, changes in the surface potential occurred possible due to the flocculation effect on the nanoparticles.

• Economic and Environmental Geology
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• v.50 no.6
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• pp.545-554
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• 2017

Birnessite is one of the dominant Mn (oxyhydr)oxide phases commonly found in soil and deep ocean environments. It typically occurs as nano-sized and poorly crystalline aggregates in the natural environment. It is well known that birnessite participates in a wide variety of bio/geochemical reactions as a reactive mineral phase with structural defects, cation vacancies, and mixed valences of structural Mn. These various bio/geochemical reactions control not only the fate and transport of inorganic and organic substances in the environment, but also the formation of diverse Mn (oxyhydr)oxides through birnessite transformation. This review assessed and discussed about the phase transformation of birnessite under a wide range of environmental conditions and about the potential geochemical factors controlling the corresponding reactions in the literature. Birnessite transformation to other types of Mn (oxyhydr)oxides were affected by dissolved Mn(II), dissolved oxygen, solution pH, and co-existing cation (i.e., $Mg^{2+}$). However, there still have been many issues to be unraveled on the complex bio/geochemical processes involved in the phase transformation of birnessite. Future work on the detail mechanisms of birnessite transformation should be further investigated.