• Journal of the Korean Ceramic Society
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• v.42 no.11 s.282
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• pp.722-728
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• 2005

A wet-chemical route was utilized to obtain nanosized crystalline goethite ($\alpha$-FeOOH) particle, which was known as an oxidation catalyst in reducing carbon monoxide (CO) and dioxine during incineration. A cost-effective $FeSO_4{\cdot}7H_2O$ was used as starting raw material and a successive process of hydrolysis-oxidation was utilized as synthetic method. The effects of the initial $Fe^{2+}$ concentration, hydrolysis time and oxidation period on the crystalline phase and particle characteristics were systematically investigated by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and BET analyses. It was found that the spindle-shaped crystalline $\alpha$-FeOOH particle with the width of 70 nm and the length of 200 nm could be obtained successfully when the initial concentration of 1.5 M, hydrolysis time of 4h, and oxidation period of 10 h, respectively. In addition, it was observed that the spindle-shaped $\alpha$-FeOOH particle consisted of nano-sized primary crystallites of $30\~50\;nm$, which were de-agglomerated into individual particle and successively re­agglomerated into spherical or irregular-shaped agglomerates beyond certain periods in the hydrolysis and oxidation process.

• Journal of Powder Materials
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• v.25 no.5
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• pp.408-414
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• 2018

This study investigates the microstructure and wear properties of cermet (ceramic + metal) coating materials manufactured using high velocity oxygen fuel (HVOF) process. Three types of HVOF coating layers are formed by depositing WC-12Co, WC-20Cr-7Ni, and Cr3C2-20NiCr (wt.%) powders on S45C steel substrate. The porosities of the coating layers are $1{\pm}0.5%$ for all three specimens. Microstructural analysis confirms the formation of second carbide phases of $W_2C$, $Co_6W_6C$, and $Cr_7C_3$ owing to decarburizing of WC phases on WC-based coating layers. In the case of WC-12Co coating, which has a high ratio of $W_2C$ phase with high brittleness, the interface property between the carbide and the metal binder slightly decreases. In the $Cr_3C_2-20CrNi$ coating layer, decarburizing almost does not occur, but fine cavities exist between the splats. The wear loss occurs in the descending order of $Cr_3C_2-20NiCr$, WC-12Co, and WC-20Cr-7Ni, where WC-20Cr-7Ni achieves the highest wear resistance property. It can be inferred that the ratio of the carbide and the binding properties between carbide-binder and binder-binder in a cermet coating material manufactured with HVOF as the primary factors determine the wear properties of the cermet coating material.

• Korean Journal of Veterinary Service
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• v.34 no.4
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• pp.429-439
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• 2011

This article described the comparison of a quick, easy, cheap, effective, rugged and safe (QuEChERS) sample preparation and the classical method established by National Veterinary Research and Quarantine Service (NVRQS) for the determination of pesticide residues in livestock products using GC-tandem mass spectrometry. The classical method by NVRQS used liquid-liquid partioning followed by evaporizing. The modified QuEChERS entailed extraction of 2 g sample with 15 ml acetonitrile containing 1% acetic acid followed by addition of 6 g anhydrous magnesium sulfate and 1.5 g sodium acetate. After centrifugation, 6 ml of the extract underwent a cleanup step (in a technique known as column-based solid phase extraction) using 400 mg each of $C_{18}$ and primary secondary amine sorbents plus 1,200 mg magnesium sulfate. The quantitation of individual pesticides by both methods was based on tissue standard calibration curves with a correlation coefficient in excess of 0.98 for the 24 pesticides. The detection limits by the classical method were ranged 1.3~5.0 ${\mu}g$/kg, with mean recoveries between 76.2% and 114.3% except aldrin (59.3%) and deltamethrin (63.6%). The detection limits by modified QuEChERS were ranged 0.3~6.2 ${\mu}g$/kg, with mean recoveries between 68.0% and 114.3% except dimethipin (152.6%), chlorfenvinphos (138.1%), 4,4-DDT (61.5%), aldrin (60.4%) and chinomethionate (30.3%).

• Journal of the Korean Ceramic Society
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• v.43 no.10 s.293
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• pp.666-672
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• 2006

GDC20($Ce_{0.8}Gd_{0.2}O_{1.9}$) powder was synthesized by oxalate co-precipitation and milling and its thermal decomposition, phase formation, and sinterability were investigated. As-prepared precipitates were non-crystalline due to the milling process and completely decomposed at 400$^{\circ}C$ The powder calcined at 800$^{\circ}C$ for 2 h contained fine p]sty particles with an average size of 0.69 $\mu$m. Attrition milling of the calcined powder for 2 h had a little milling effect, resulting in a slight decrease in the particle size to 0.45 $\mu$m. The milled powder consisted of small spherical primary particles and some large particles, which had been agglomerated during calcination. Due to the excellent sinterability of the powder, sintering of the powder compacts for 4 h showed relative densities of 78.7% at 1000$^{\circ}C$ and 97.8% at 1300$^{\circ}C$, respectively. Densification was found to almost complete at temperature above 1200$^{\circ}C$ and a dense and homogeneous microstructure was obtained. A rapid grain growth occurred between 1200$^{\circ}C$ and 1300$^{\circ}C$. Grains in 0.1$\sim$0.5 $\mu$m sizes at 1200$^{\circ}C$ grew to 0.2$\sim$2 $\mu$m and their size distribution became broader at 1300$^{\circ}C$.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.2098-2100
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• 2000

We propose pulsed $CO_2$ laser below 30W by the AC(60Hz) switching control of leakage transformer primary which has some advantage of cost and size compared to a typical pulsed power supply. Pulse repetition rate is adjusted from 5Hz to 60Hz to control laser output. In this laser, a low voltage open loop control for high voltage discharge circuit is employed to avoid the HV sampling or switching and high voltage leakage transformer is used to convert rectified low voltage pulse to high voltage one. A ZCS(Zero Cross Switch) circuit and a PIC one-chip microprocessor are used to control gate signal of SCR precisely. The pulse repetition rate is limited by 60Hz due to the frequency of AC line and a high leakage inductance. The maximum laser output was obtained about 23W at pulse repetition rate of 60Hz, total gas mixture of $CO_{2}/N_{2}$/He = 1/9/15, SCR gate trigger angle 90$^{\circ}$, and total pressure of 18Torr.

• Journal of the Korean Magnetics Society
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• v.2 no.2
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• pp.91-98
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• 1992

In a $Co_{67}Fe_{4.5}Nb_{2}Si_{10}B_{15}$ amorphous alloy ribbon the effect to two-step annealing on the soft magnetic properties has been studied. By two-step annealing method which the second annealing at low temperature of $310^{\circ}C$ for 2 hours is undertaken after the primary annealing at high temperature above $480^{\circ}C$ for 20 minutes at the vacuum state, the coercive force and the squareness are not changed nearly but the initial permeability at d.c. and the effective permeability at a.c. are remark-ably increased compared with the one-step annealing. The maxima of the initial permeability and the effective permeability at 1 kHz after the two-step annealing are 290,000 and 41,000, respectively, which are 30% higher than those of the one-step annealing. The change of magnetic properties with annealing temperature is discussed in terms of the residual stress, the domain size, the cluster and the crystalline phase.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.4
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• pp.265-271
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• 2014

304L stainless steel sheets are used as a primary barrier for the insulation of membrane-type liquefied natural gas(LNG) carrier cargo containment system. 304L stainless steel is a transformation-induced-plasticity(TRIP) steel that exhibits complex material behavior, because it undergoes phase transformation during plastic deformation. Since the TRIP behavior is very important mechanical characteristics in a low-temperature environment, significant amounts of data are available in the literature. In the present study, a uniaxial tensile test for 304L stainless steel was performed to investigate nonlinear mechanical characteristics. In addition, a viscoplastic model and damage model is proposed to predict material fractures under arbitrary loads. The verification was conducted not only by a material-based comparative study involving experimental investigations, but also by a structural application to the LNG membrane of a Mark-III-type cargo containment system.

• The Korean Journal of Zoology
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• v.32 no.2
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• pp.153-162
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• 1989

Expedments were perfonned to examine the role of cAMP-dependent protein kinase (PK-A) and diacylglycerol-dependent protein kinase (PK-C) during the meiodc resumption and the first mitotic cell cycle of mouse embryogenesis. Mejoric GV oocytes and one-cell embryos derived from in vitro fertilization were cultured in vitro, and morphological changes in response to activators of PK-A and PK-C were examined. Treatments with a membrane-permeable cAMP analog, dbcAMP (0.1 mg/mi), phosphodiesterase inhibitor, IBMX (0.1 mM), biologically active phorbol ester, WA (10 nglmi), or a synthetic diacylglycerol, sn-diC8 inhibited resumption of melosis. Combination of PK-A and PK-C activator brought about furiher inhibition. On the contrary, dbcAMP (0.1 mg/mi), IBMX (0.2 mM), WA (10 nglml), and sn-diC8 (0.5 mM) did not inhibit pronucleus membrane breakdown (PNBD) when added S or G2 phase of cell cycle. However, activators of PK-C inhibited cleavage of one-cefl embryos. This result indicates that the action mechanism of PK-A and PK-C on dissolution of nuclear membrane in primary meiotic arrest oocytes may be different from that of mitotic one-cell embryos.

• Education of Primary School Mathematics
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• v.18 no.2
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• pp.77-89
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• 2015

In this study, an 'Independent Study Checklist' for gifted mathematics students was developed and applied. The characteristics shown in the results after the 'Independent Study Checklist' was applied to mathematics gifted students were analysed. The checklist was divided into six phases of the independent study process and included checking contents at each stage. Observations, student interviews and results of the process of 'Independent Study' were collected and analysed to understand the characteristics of students' outcomes. The results from the application of the 'Independent Study Checklist' suggest the followings. First, the 'Independent Study Checklist' took the role of a self-check list to identify the process of the 'Independent Study'. Second, the check points of the 'Independent Study Checklist' presented the view of discussion to gifted students. Third, the 'Independent Study Checklist' was used as teaching material for teachers of gifted students. Fourth, 'Independent Study Checklist' was optionally used according student's study topics and method. Fifth, the checklist at each phase was continuously used during the whole process of 'Independent Study'. The teachers' interest and encouragement took the role of facilitating students' study process.

• Molecules and Cells
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• v.40 no.8
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• pp.587-597
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• 2017

MicroRNAs (miRNAs) are essential small RNA molecules that regulate the expression of target mRNAs in plants and animals. Here, we aimed to identify miRNAs and their putative targets in Hibiscus syriacus, the national flower of South Korea. We employed high-throughput sequencing of small RNAs obtained from four different tissues (i.e., leaf, root, flower, and ovary) and identified 33 conserved and 30 novel miRNA families, many of which showed differential tissuespecific expressions. In addition, we computationally predicted novel targets of miRNAs and validated some of them using 5' rapid amplification of cDNA ends analysis. One of the validated novel targets of miR477 was a terpene synthase, the primary gene involved in the formation of disease-resistant terpene metabolites such as sterols and phytoalexins. In addition, a predicted target of conserved miRNAs, miR396, is SHORT VEGETATIVE PHASE, which is involved in flower initiation and is duplicated in H. syriacus. Collectively, this study provides the first reliable draft of the H. syriacus miRNA transcriptome that should constitute a basis for understanding the biological roles of miRNAs in H. syriacus.