• Korean Chemical Engineering Research
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• v.40 no.6
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• pp.676-680
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• 2002

The specific gravity meter is the instrument used to measure the density of fluids under the reference conditions and it can be widely used in industrial areas, especially in massive flow rate natural gas industry. This study has been carried out in an attempt to improve measurement accuracy of natural gas flow rate calculation, providing the adequate installation and proper operation conditions of specific gravity meter. The test results are 1) the density measurement errors in case of using methane and standard gas as calibration gases are smaller than using methane and nitrogen gas, 2) the periodical calibration to maintain accurate density measurements is essential, and 3) the specific gravity meter is sensitive to changes of environmental conditions, especially environmental temperature surrounding the specific gravity meter.

• Journal of the Korean Chemical Society
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• v.46 no.2
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• pp.169-176
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• 2002

In this study, the chemistry achievement of the Korean 8th grade students in the Third Inter-national Mathematics and Science Study-Repeat(TIMSS-R), which was administered internationally in 1999,was analyzed. By the 6th national curriculum, 31 chemistry problems were selected from the categories of 'classification of matter', 'structure of matter', 'chemical reactivity and transformations', 'physical properties and physical changes of matter', 'heat and temperature', 'subatomic particles', 'pollution', 'scientific method',and 'scientific measurements' among the total 143 problems. Based on the analysis of the percentage of cor-rectness on each problem, the weak and strong points of the 6th curriculum were discussed. The implications for the development of national curriculum and textbook are suggested.

• Journal of the korean academy of Pediatric Dentistry
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• v.33 no.1
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• pp.77-84
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• 2006

Since the long-term exposure of mutans streptococci to xylitol is known to select for xylitol-resistant $(X^R)$ natural mutants, the occurrence and survival of such $(X^R)$ strains were performed in batch culture methods. The aim of the study was to compare the differentiation and quantification of mRNA expression of the gtf genes of $X^R\;and\;X^S$ mutans streptococci. Using a real-time reverse-transcription polymerase chain reaction, the expression of each gtf was determined. In $X^R$ strains, the relative levels of transcription of gtfB and gtfC were decreased while that of gtfD was increased, suggesting the presence of independent promoters. It also suggested that mutation related to production of glucosyltransferase occurred under the exposure of xylitol could explain the caries-preventive mechanisms of xylitol.

• Polymer(Korea)
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• v.37 no.1
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• pp.74-79
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• 2013

Polyvinylidene fluoride (PVDF) and its copolymer with hexafluoropropylene (HFP) were successfully prepared from free radical solution polymerizations using diisopropyl peroxidicarbonate (DIPPDC) in the presence of 1,1,2-trichlorotrifluoroethane (R-113). The reactivity ratios of VDF and HFP were estimated as$r_{VDF}=2.06{\pm}0.03$ and $r_{HFP}{\approx}0$. This result indicates that HFP cannot undergo self propagation. The weight-average molecular weight and molecular weight distribution of copolymers were found to decrease with increasing HFP content. The melting temperature of copolymers linearly decreased with the increase of HFP content because of the introduction of HFP. Moreover, no melting peak was observed for the copolymers with high HFP content. The glass transition temperature of copolymers gradually increased with the increase of HFP content due to the restricted flexibility of the polymer chains.

• KSBB Journal
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• v.21 no.2
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• pp.118-122
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• 2006

In this report, we describe that the use of GroEL/GroES-enriched S30 extract remarkably enhances the solubility and enzymatic activity of cell-free synthesized rPA, which requires the correct formation of 9 disulfide bonds for its biological activity. We found that the stable maintenance of redox potential is necessary, but not sufficient for the optimal expression of active rPA. In a control reaction without using additional molecular chaperones, most of the rPA molecules were aggregated almost instantly after their expression and thus failed to exhibit the enzymatic activity. However, by the use of GroEL/GroES-enriched extract, combined with IAM-treatment, approximately $30{\mu}g/ml$ of active rPA was expressed in the cell-free synthesis reaction. This result not only demonstrates the efficient production of complex proteins, but also shows the control and flexibility offered by the cell-free protein synthesis system.

• Knowledge Management Research
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• v.23 no.3
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• pp.285-311
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• 2022

In this study, based on the S-O-R framework, how individual's stimuli (i.e., video characteristics, YouTuber characteristics, real-time broadcasting characteristics of YouTube channel) form organisms (i.e., perceived usefulness, perceived pleasure, social presence), leading to viewers' responses (i.e., continuous watching intention, paid sponsorship intention) on real-time YouTube channels. For this purpose, a research model and hypotheses were constructed, and 369 questionnaire data collected from users of real-time broadcasting channel services on the YouTube platform were analyzed. Result findings confirmed that some video/YouTuber/real-time broadcasting characteristics significantly affect viewers' perceived usefulness/perceived pleasure/social presence, and further influence continuous watching/paid sponsorship intentions. Theoretical and practical implications of the findings are discussed in conclusion.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.1
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• pp.207-217
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• 1992

In this study, isolated and cultured nitrogen fixed microbes were seeded in the three-phase fluidized bed in which gas, solid and liquid were contacted directly. Input velocity was varied from 8.12 cm/hr to 16.32 cm/hr. And upflow gas pressure was fixed to 80 psi. Return ratios were from 0.2 to 0.6 with the each experimental condition. According to these condition, movement of media, growth of biofilm and removal efficiency were measured. As the results, in case of briquette ash, biofilm was developed to $170{\mu}m$ when velocity was 8.12 cm/hr and return ratio was 0.6. In this condition, COD removal efficiency was 97% and $NH_4$-N removal efficiency was 83%. At the same condition, biofilm thickness of glass bead was $17.59{\mu}m$ and its COD and $NH_4$-N removal efficiency was 83% and 72%. Nitrogen fixed microbes have following characters: it formed dark-brownish sludge, excellent adhesive force, easy solid-liquid separation and low oxygen uptake ratio, but sensitive to DO concentration. Not only it endured shock loading, but required short time to steady state.

• The Journal of Engineering Geology
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• v.17 no.1 s.50
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• pp.143-150
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• 2007

AMD (Acid mine drainage) from disused mines is one or the most significant pollutant problems to make harmful effect to human health. We demonstrated the mechanism of resolution and adsorption reaction for arsenic, manganese and zink from the soil and mine tailings which were located in the vicinity of a disused mine in Kyoungnam area. The resolution experiments were carried with a column test f3r 45 days continuously. Metal chemical forms in water were changed with the condition of solution pH and ORP (oxidation-reduction potential). Metal chemical forms affected on the reaction of resolution and adsorption of metals in water environments. Even though the sampling was carried in very closed location, there was significant different results of pollution level and ORP changes in terms of column operations. Hence It was important to note the pH and ORP in AMD to evaluate a risk assessment and a soil management using monitoring metals. When we operate AMD management with the mechanism of resolution and adsorption it can be achieved better economic solution.

• Applied Biological Chemistry
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• v.29 no.2
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• pp.116-121
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• 1986

869 wheat lines were selected and analyzed for protein and lysine composition. Also, high protein-high lysine wheat were evaluated by stability parameter to determine varietal response to environments. Protein content had highly significant positive correlation coefficient of $0.902^{**}$ with lysine content but negatively correlated with lysine per protein content. Bezostaya and Lancota with low regression coefficient provided relatively low response to environment in protein content, while CI 13449 and Centurk with high regression coefficients (1.0) had a relatively high response. High heritability has been formed for protein $(h^2=0.809)$ and lysine content $(h^2=0.647)$.

• Journal of the Korea Organic Resources Recycling Association
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• v.15 no.4
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• pp.131-137
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• 2007

In this study, the biodegradation test on lignocellulose under sulfate reducing conditions was carried out. In particular, the interaction between cellulose and lignin was investigated with various g-cellulose/g-lignin (C/L) ratios: 42.15, 4.59, 2.51, 1.14 and 0.7. It was shown that the rate of cellulose degradation decreased in proportion to the lignin content. Assuming first order degradation kinetics, the consequences of competitive inhibition were graphically shown for different C/L ratios. The relation between cellulose reduction rate and C/L ratio was expressed by logarithm function with a determination coefficient of 0.97. Lignocellulose reduction rate was also described as a logarithm function of C/L ratio showing a inhibition effect by lignin. In the mean time, the rate of lignin decomposition was higher at C/L ratio of 2.51 and 1.14 compared with C/L ratios of 4.59 and 0.7, indicating that excessive extra carbon source is not appropriate for lignin biodegradation.