• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.4
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• pp.285-289
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• 2011

In this study, lead-free $(K_{0.5}Na_{0.5+X})(Nb_{0.96}Sb_{0.04})O_3+0.2mol%La_2O_3+1.2mol%$ $K_4CuNb_8O_{23}$ (X= 0~0.025) ceramics were fabricated by normal sintering method at $1060^{\circ}C$ for 5 h. Microstructures, piezoelectric and dielectric properties of specimens were investigated with special emphasis in the influence of Na excess addition. The grain size of specimen was slightly decreased with increasing Na content. In the 2 [mol%] Na excess addition of NKNS ceramics, density, electromechanical coupling factor, piezoelectric constant and electromechancal quality factor of specimen were found to reach the optimum values of 4.25 [$g/cm^3$], 0.4357, 154.43 [pC/N] and 580, respectively.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.1
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• pp.1-11
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• 2013

Additives such as glycerol, methanol, acetone, and ethanol were used to prevent $NaBO_2$ from precipitation, and their effects on hydrogen generation properties of $NaBH_4$ hydrolysis were investigated. When the concentration of additives was 5 wt%, the additives such as methanol, acetone, and ethanol could not prevent $NaBO_2$ precipitation. Although glycerol prevented $NaBO_2$ precipitation, conversion efficiency decreased to 78.0% due to its viscosity. Based on test results, hydrogen generation tests were also performed at various concentration of glycerol and methanol to investigate the concentration effects on hydrogen generation properties. As the concentration of glycerol increased from 1 wt% to 3 wt%, conversion efficiency increased owing to additive effect. When its concentration increased to 5 wt%, conversion efficiency decreased due to its viscosity. As the concentration of methanol increased from 5 wt% to 10 wt%, conversion efficiency increased owing to additive effect. When its concentration increased to 15 wt%, conversion efficiency decreased due to $NaB(OCH_3)_4$ precipitate. Although conversion efficiency decreased about 1% when 3 wt% glycerol was added, $NaBO_2$ precipitation was prevented. Consequently, addition of 3 wt% glycerol to $NaBH_4$ solution improves stability of hydrogen generation system.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.4
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• pp.190-195
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• 2009

Na-tetrasilicic fluorine mica powders were synthesized by skull melting method. The staring materials having chemical composition of $Mg_3(OH)_2Si_4O_{10}:Na_2SiF_6:SiO_2=8.3:24.8:66.9$ mol% were charged into a cold crucible of 13 cm in diameter and 14cm in height and heated by R.F. generator at working frequency of 2.84 MHz. The materials were maintained for 1hr as a molten state and cooled down in the container. In this study, the specific electric resistance of mica was estimated and the columnar and plate shaped mica were synthesized.

• Korean Journal of Materials Research
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• v.24 no.3
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• pp.123-128
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• 2014

To realize high-performance thin film solar cells, we prepared CIGS by the co-evaporation technique on both sodalime and Corning glass substrates. The structural and efficient properties were investigated by varying the thickness of the Mo:Na layer, where the total thickness of the back contact was fixed at 1${\mu}m$. As a result, when the Mo:Na thickness was 300 nm on soda-lime glass, the measured Na content was 0.28 %, the surface morphology was a plate-like compact structure, and the crystallinity by XRD showed a strong peak of (112) preferential orientation together with relatively intense (220) and (204) peaks as the secondary phases influenced crystal formation. In addition, the substrates on soda-lime glass effected the lowest surface roughness of 2.76 nm and the highest carrier density and short circuit current. Through the optimization of the Mo:Na layer, a solar conversion efficiency of 11.34% was achieved. When using the Corning glass, a rather low conversion efficiency of 9.59% was obtained. To determine the effects of the concentration of sodium and in order to develop a highefficiency solar cells, a very small amount of sodium was added to the soda lime glass substrate.

• Korean Journal of Soil Science and Fertilizer
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• v.36 no.6
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• pp.357-366
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• 2003

This study was conducted to develop n convenient and efficient granular type absorbent with high CEC from powdery zeolite, which is a waste produced while crushing the natural zeolite of Korea to get a particular particle size. The change of mineralogical characteristics during hydrothermal alternation of natural zeolite to Na-P zeolite in alkaline solution at various reaction times was determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and total elemental analysis. The columnar aggregate of Na-P Zeolite was produced by calcinating the natural zeolite-charcoal extrudates of about 3 mm diameter. In 24 hours reaction, clinoptillonite, mordenite and feldspar in natural zeolite were disappeared by 3 N NaOH treatment, while Na-P Zeolite with spherical granular structure was newly detected by XRD. As increasing reaction time, Si/Al ratio in remaining solution was deceased. The CEC of the synthesized material increased more than 2 times compared with that of natural zeolite, although the diameter of Na-P zeolite were rather increased.

• Journal of Preventive Medicine and Public Health
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• v.20 no.2 s.22
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• pp.341-351
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• 1987

For the purpose of the determination of the most proper sampling time on using spot urine which can represent the general status of electrolytes in 24 hour urine and for test of the validity of filter paper method which was developed recently in estimation of the amount of daily salt intake, the author investigated this study by different sampling time and various measuring methods in 21 healthy men and 12 women. The summarized results were as follows; 1) The mean excretion amount of urinary electrolytes were Na 3.93 g/l, K 1.47 g/l, and creatinine 1.08 g/l in male, and Na 3.83 g/l, K 1.86 g/l, and creatinine 0.99 g/l in female. 2) In using spot urine for estimation of the amount of daily salt intake, morning urine was the most approximate to that of 24 hour urine in both sexes. 3) There was validity in estimation of daily salt intake by filter paper method using spot urine instead of 24 hour urine. 4) The estimated amounts of daily salt intake in male was higher than the values in female as 16.04-16.22 g and 13.35-13.82 g respectively.

• Journal of the Korean Chemical Society
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• v.38 no.3
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• pp.254-259
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• 1994

Five new crown ethers containing methyl groups were synthesized. 2,3,4,5: 9,10,11,12-Dibenzo-8,8-dimethyl-15,18,1-trioxacycloeicosane, 2,3,4,5: 9,10,11,12-dibenzo-8,8-dimethyl-15,18,21,1-tetraoxacyclotricosane, 2,3,4,5 : 9,10,11,12-dibenzo-8,8-dimethyl-15,18,21,24,1-pentaoxacyclohexacosane, 2,3,4,5 : 9,10,11,12 : 22,23,24,25 : 29,30,31,32-tetrabenzo-8,8,28,28-tetramethyl-15,18,21,35,38,1-hexaoxacyclotetracontane and 2,3,4,5 : 9,10,11,12 : 25,26,27,28:32,33,34,35-tetrabenzo-8,8,31,31-tetramethyl-15,18,21,24,38,41,44,1-octaoxacyclohexatetracontane were synthesized by reaction of 4,4'-isopropylidenediphenol with di-, tri-and tetraethyleneglycol ditosylate in the presence of MOH(M = Na, K). Di-, tri- and tetraethyleneglycol ditosylate were synthesized by reaction of p-toluenesulfonylchloride with diethyleneglycol, triethyleneglycol and tetraethyleneglycol in the presence of NaOH.

• Nuclear Engineering and Technology
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• v.2 no.2
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• pp.67-72
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• 1970

The measurements of the fast neutron flux and its spectrum have been carried out by the threshold detectors in the central thimble of TRIGA Mark-II reactor operating at 250 KW. The following reactions have been employed for these measurements, viz : Ni$^{58}$ (n, p) Co$^{58}$ ； $Mg^{24}$ (n, p) Na$^{24}$ ； $Al^{27}$ (n, $\alpha$) Na$^{24}$ . From the activation data the fast neutron spectrum were calculated by CDC-3600 computer making use of two semi-empirical methods. It has been verified that the validity of assumption of a fission spectrum in the central thimble exists only above 1 to 2 Mev energy level. With this spectrum, a fast neutron flux in the range of 1 $\times$ 10$^{12}$ n/$\textrm{cm}^2$-sec above the energy of 2.6 Mev was observed in the central thimble of TRIGA MARK-II reactor.

• Advanced Composite Materials
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• v.18 no.3
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• pp.197-208
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• 2009

Changes occurring in jute and coir fiber composites with 2-8% concentration of a NaOH treatment for 24 h were investigated, respectively, for void content, microscopy images, mechanical properties and water absorption. The jute and coir fibers were vacuum dried before molding composite specimens. Mechanical properties indicated good adhesion between natural fibers and PP. Jute fibers, when alkali-treated with 2% concentration for 24 h, showed best improvement in tensile strength by 40% and modulus by 9%, respectively, while coir fibers, when alkali-treated with 6% concentration for 24 h, showed best improvement in tensile strengths by 62% and modulus by 17%, respectively. With 2% concentration of alkali-treatments, the elongation of jute and coir composites reached 8% and 13.5%, respectively. Moisture absorption for jute and coir composites are 50% and 60% lower than untreated fiber composites, respectively.

• Reproductive and Developmental Biology
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• v.30 no.1
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• pp.7-11
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• 2006

This study was conducted to examine the effects of hormone and sodium pyruvate on in vitro maturation of canine oocytes. Canine oocytes were collected from the ovaries of dogs and cultured in NCSU-37 medium with hormones and sodium pyruvate for 72 hr. Oocytes matured to the metaphase II (MII) stage were observed only from estradiol $17{\beta}\;(E_2)$, and the presence of gonadotropin did not improve the nuclear maturation. No oocytes were developed to the MII stage when $E_2$ was added to medium during the first 6 and 24 hrs of culture period. The presence of $E_2$ during the whole culture period enhanced the nuclear maturation to the MII stage (6.0%, P<0.05). High concentration of sodium pyruvate (2.5 mM) slightly enhanced the nuclear maturation to the metapahse I (HMI) stage, but not the MII stage. the result of the present study shows that the presence of $ E_2$ during the whole culture period of 72 hr enhances the maturation of canine oocytes to the M stage, but sodium pyruvate does not affect the nuclear maturation of the canine oocytes.