• Journal of the Korean Ceramic Society
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• v.39 no.1
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• pp.68-73
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• 2002

The dielectric properties and synthesis of $LaAlO_3$ ceramics from mixtures of $La_2O_3-Al_2O_3$ (LAO) and $La_2O_3-Al(OH)_3$(LAH) via grinding process were investigated. The single phase $LaA1O_3$of LAO and LAH powders were formed at $1300^{\circ}C$ and $1000^{\circ}C$, respectively. A non-reacted $La_2O_3$ existing in calcined powder was changed to La(OH)$_3$by moisture in the air, and their samples were worse than those of the samples made from a $LaA1O_3$single phase powder. The densities of LAO samples sintered at 150$0^{\circ}C$ for 4 h and LAH samples sintered at $1400^{\circ}C$ for 4 h were 97.3% and 98.3% of theory density, respectively. Grains of LAH sample showed uniformity and their sizes were 0.75 ${\mu}{\textrm}{m}$, and LAO samples showed non-uniformity and their sizes were 4-5 ${\mu}{\textrm}{m}$. Dielectric constant of LAO and LAH samples were the same value (≒22), however dielectric loss of LAH sample (0.0003) were lower than that of LAO sample(0.001)due to grain size.

• Journal of the Korean earth science society
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• v.38 no.7
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• pp.496-510
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• 2017

This study presents a new nationwide quantitative precipitation estimation (QPE) based on the hybrid surface rainfall (HSR) technique using the weather radar network of Korea Meteorological Administration (KMA). This new nationwide HSR is characterized by the synthesis of reflectivity at the hybrid surface that is not affected by ground clutter, beam blockage, non-meteorological echoes, and bright band. The nationwide HSR is classified into static (STATIC) and dynamic HSR (DYNAMIC) mosaic depending on employing a quality control process, which is based on the fuzzy logic approach for single-polarization radar and the spatial texture technique for dual-polarization radar. The STATIC and DYNAMIC were evaluated by comparing with official and operational radar rainfall mosaic (MOSAIC) of KMA for 10 rainfall events from May to October 2014. The correlation coefficients within the block region of STATIC, DYNAMIC and MOSAIC are 0.52, 0.78, and 0.69, respectively, and their mean relative errors are 34.08, 30.08, and 40.71%.

• Journal of the korean academy of Pediatric Dentistry
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• v.24 no.1
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• pp.204-219
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• 1997

The use of fluoride is one of the most effective methods for caries prevention. Fluoridation of public water supply has been recognized, for many years, as an effective way to reduce dental caries. The fluoride supplement has been recommended when the natural fluoride was unavailable or below the optimal range. However the mechanism of caries prevention by fluoride has not yet been clarified and it is well known that an overdose of fluoride results inacute and chronic toxicity, especially dental fluorosis. Fluoride mouthrinsing solution is widely used in dentistry due to its effectiveness in carrying anticariogenic action. Understanding the effects of fluoride mouthrinsing solution on human gingival fibroblasts will provide the safety rationale for its use during the caries preventive therapy. The purpose of this study was to evaluate the cytotoxic effect of fluoride mouthrinsing solution on the human gingival fibroblast in vitro. The human gingival fibroblasts were cultured from healthy gingiva on the extracted deciduous teeth of children. Cells were inoculated into a 24-well plate with $1{\times}10^4cells/well$ of medium at $37^{\circ}C$, 100% humidity, 5% $CO_2$ incubator for 24 hours. And the cells were counted by using the hemocytometer at each designed study. Human gingival fibroblasts were cultured in growth medium after one minute application range of 0.02%-0.2% NaF solution and 0.1% $SnF_2$ solution. The cells used in this study were between fifth to eighth passage number. The cell morphology was examined by inverted microscope and cell proliferation was measured by incorporating $[^3H]$-thymidine into DNA. DNA synthesis by human gingival fibroblasts was assessed by $[^3H]$-thymidine uptake assays while the cell activity was measured by MTT assay. Each concentrated fluoride mouthrinsing solution was estimated for its biocompatability with fibroblasts by the tissue culture technique. The results of this study were as follows : 1. It was observed that at 0.05%, 0.2% NaF mouthrinsing solution the cytoplasmic processes became globular. When 0.1% $SnF_2$ mouthrinsing solution was applied, the cytoplasmic process and cell morphology were disappeared. 2. DNA synthetic activity was reduced regardless of the concentration of the fluoride mouthrinsing solution. However, the result is statistically insignificant except 0.1% $SnF_2$ mouthrinsing solution(p<0.05). 3. Our results indicate that 0.02%, 0.05% concentrations of NaF mouthrinsing solution caused minimal cytotoxicity. But 0.2% NaF and 0.1% $SnF_2$ concentration were a significant difference between the cell activity in the experimental group and control group (p<0.05). 4. After appling 0.05% & 0.02% NaF fluoride mouthrinsing solution, cell activity was restored to the control groups level according to incubating time. The results suggest that direct exposure to fluoride solution inhibits gingival fibroblast activity. Therefore, for the most effective use of fluoride use, lowering the concentration of fluoride mouthrinsing is advisable because it maintains biocompatability and free ion in the oral fluid.

• Tuberculosis and Respiratory Diseases
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• v.70 no.2
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• pp.113-124
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• 2011

Background: Macrophages are one of the most important inflammatory cells in innate immunity. PU.1 is a macrophage-specific transcription factor. Ubiquitins are the ultimate regulator of eukaryotic transcription. The ubiquitination process for PU.1 is unknown. This study investigated the lipopolysaccharide (LPS)-induced activation of PU.1 and its relation to ubiquitins in the macrophages. Methods: Raw264.7 cells, the primary cultured alveolar, pulmonary, and bone marrow derived macrophages were used. The Raw264.7 cells were treated with MG-132, $NH_4Cl$, lactacytin and LPS. Nitric oxide and prostaglandin D2 and E2 were measured. Immunoprecipitation and Western blots were used to check ubiquitination of PU.1. Results: The PU.1 ubiquitination increased after LPS ($1{\mu}g$/mL) treatment for 4 hours on Raw264.7 cells. The ubiquitination of PU.1 by LPS was increased by MG-132 or $NH_4Cl$ pretreatment. Two hours of LPS treatment on macrophages, PU.1 activation was not induced nor increased with the inhibition of proteasomes and/or lysosomes. The ubiquitination of PU.1 was increased in LPS-treated Raw264.7 cells at 12- and at 24 hours. LPS-treated cells increased nitric oxide production, which was diminished by MG-132 or $NH_4Cl$. LPS increased the production of $PGE_2$ in the alveolar and peritoneal macrophages of wild type mice; however, $PGE_2$ was blocked or diminished in Rac2 null mice. Pretreatment of lactacystin increased $PGE_2$, however it decreased the $PGD_2$ level in the macrophages derived from the bone marrow of B57/BL6 mice. Conclusion: LPS treatment in the macrophages ubiquitinates PU.1. Ubiquitination of PU.1 may be involved in synthesis of nitric oxide and prostaglandins.

• Journal of the Korean Electrochemical Society
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• v.7 no.3
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• pp.131-137
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• 2004

Sol-gel method which provides better electrochemical and physiochemical properties compared to the solid-state method was used to synthesize the material of $LiFe_yMn_{2-y}O_4$. Fe was substituted to increase the structural stability so that the effects of the substitution amount and sintering temperature were analyzed. XRD was used for the structural analysis of produced material, which in turn, showed the same cubic spinel structure as $LiMn_2O_4$ despite the substitution of $Fe^{3+}$. During the synthesis of $LiFe_yMn_{2-y}O_4$, as the sintering temperature and the doping amount of Fe(y=0.05, 0.1, 0.2)were increased, grain growth proceeded which in turn, showed a high crystalline and a large grain size, certain morphology with narrow specific surface area and large pore volume distribution was observed. In order to examine the ability for the practical use of the battery, charge-discharge tests were undertaken. When the substitution amount of $Fe^{3+}\;into\;LiMn_2O_4$ increased, the initial discharge capacity showed a tendency to decrease within the region of $3.0\~4.2V$ but when charge-discharge processes were repeated, other capacity maintenance properties turned out to be outstanding. In addition, when the sintering temperature was $800\~850^{\circ}C$, the initial capacity was small but showed very stable cycle performance. According to EVS(electrochemical voltage spectroscopy) test, $LiFe_yMn_{2-y}O_4(y=0,\;0.05,\;0.1,\;0.2)$ showed two plateau region and the typical peaks of manganese spinel structure when the substitution amount of $Fe^{3+}$ increased, the peak value at about 4.15V during the charge-discharge process showed a tendency to decrease. From the previous results, the local distortion due to the biphase within the region near 4.15V during the lithium extraction gave a phase transition to a more suitable single phase. When the transition was derived, the discharge capacity decreased. However the cycle performance showed an outstanding result.

• Journal of the Korean Electrochemical Society
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• v.23 no.1
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• pp.11-17
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• 2020

The Prussian blue analogues of Fe₂(CN)₆ and Na_xFe₂(CN)₆ are prepared by precipitation method and evaluated the electrochemical characteristics as positive electrode materials for lithium-ion batteries (LIBs) because of their low cost. Fe₂(CN)₆ shows a low reversible capacity of 34.6 mAh g^-1, whereas sodium-containing Na_xFe₂(CN)₆ exhibits a reversible capacity of 107.5 mAh g^-1 when the discharge process proceeds first. When charging is first carried out to remove sodium in the structure, the reversible capacity of 114.1 mAh g^-1 is achieved and the cycle performance is further improved. In addition, Na_x-Fe₂(CN)₆ is synthesized at 0℃, room temperature (RT), and 60℃, respectively. Regardless of the synthesis temperature, Na_xFe₂(CN)₆ shows similar initial reversible capacity, but the crystallite size is formed smaller and improved cycle performance when synthetic temperature is lower. The sample synthesized at 0℃ shows a reversible capacity of 86.4 mAh g^-1 at the 120^th cycle and maintains 76.8% of the initial capacity.

• Journal of the Korean Chemical Society
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• v.43 no.1
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• pp.28-42
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• 1999

Polysilanes with sterically bulky substituents, -[2-( $R^1R^2$-phenyl)propyl]Si[$R^3$]-, such as poly(2-phenylpropyl)(n-hexyl)silane [$R^1=R^2$=H, $R^3$=n-hexyl] were prepared by Wurtz-type coupling reactions with Na using a sonochemical method. The high-intensity ultrasound provided the formation of high quality Na dispersion in toluene and its active surface which was important for the synthesis of polysilanes in Wurtz-type coupling reaction was freshly and continuously regenerated during the process. The polysilanes products were mixtures of high molecular weight polymers with $\={M}_W$ of ∼$10^6$ and low molecular weight polymers with $\={M}_W$ of ∼$10^3$. It was found that the formation of high molecular weight polymerr was greatly influenced by the substituents $R^3$, directly attached to Si. On the contrary, changes on substituents ($R^1, R^2$) gave no influences at all. Overall yields for polysilanes were 75-99% in general but high molecular weight polysilanes were obtained as a major product when substituent $R^3$ is n-hexyl group and low molecular weight polysilanes were obtained as a major product when substituent $R^3$ is cyclohexyl and 2-phenylethyl groups. Effects of reaction conditions to polysilane yields were investigated.

• Journal of Hydrogen and New Energy
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• v.10 no.1
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• pp.27-40
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• 1999

By hydrogen induced planetary ball milling process, $Mg_2NiH_x$ hydrogen absorbing materials were successfully alloyed mechanically at room temperature, using pure Mg and Ni chips. The Mg & Ni chips were mixed by 45:55 weight ratio and Mechanical Alloying(M.A.) was carried out : the hydrogen pressure induced in the jar was varied from 1 to 20 bars and the M.A. times were 24 and 48 hours. The XRD results revealed that the homogeneous $Mg_2NiH_x$ was incresed with the hydrogen pressure increasing, and that $MgH_x$ was detected by unalloyed Ni chips. The shape and size of the mechanically alloyed particles didn't depend on the induced hydrogen pressure. The results of TGA showed that the hydrogen quantities of $Mg_2NiH_x$ has 1.1~3.9 wt%.

• KSBB Journal
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• v.25 no.4
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• pp.337-343
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• 2010

It has been well known that organic solvents like t-butanol and n-hexane can protect lipases from the inhibition by short-chain alcohols in the enzymatic transesterification. However, use of the organic solvents should be minimized considering their negative effects on environment and human health. Therefore, use of the greener solvents has been pursued in various are as including the enzymatic biotranformation. In this study, the liquid carbon dioxide ($LCO_2$) was employed as an alternative media for the enzymatic transesterification of canola oil. The conversion in the $LCO_2$ was comparable with those in organic solvents and the supercritical carbon dioxide, and under optimum conditions, the value reached 99.7%. It is expected that this method can provide a new type of biodiesel production process with higher energy efficiency and lower environmental impact.

• Economic and Environmental Geology
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• v.45 no.5
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• pp.589-597
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• 2012

Recently, an understanding of new sources of liquid hydrocarbons such as bioethanol is economically very important. Bioethanol is actually ethyl alcohol or also referred to as ethanol, identical to drinking alcohol by its composition. There are mainly two ways of producing ethanol, namely by synthesis of hydrocarbons and from biomass. Only the second approach deserves the terminology 'bioethanol'. The present dissertation is also designed with purpose of developing the energy-saving process for the separation of bioethanol. The world population is expected to grow past 8 billion by 2030 which are almost 60% in Asia Pacific. History has shown that energy use rises much faster than population expands. World wide demand for energy will increase significantly during the next 15 years driven by population growth and the transition of emerging markets into the global economy. In developing nations, a smaller increment in GDP per capita yields a higher increment in energy consumption compared to developed countries. In this study, we analised total 2,454 dissertations for the bioethanol during the 2001~2012 periods by the programs of 'web of science' and 'recently developped program by Korea Institute of Science Technology Information'.