• Journal of the Korean Chemical Society
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• v.35 no.4
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• pp.355-361
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• 1991

The separative preconcentration of trace mercury[Hg(II)] in a water sample was studied by a coprecipitation flotation technique. The trace Hg(II) was precipitated together with Ce(OH)$_3$ by adding 3.0 ml of 0.1M Ce$^{3+}$ solution to 1,000 ml of water sample and adjusting pH to 11.0 with 1.0M NaOH solution. The hydrophobic precipitate[Ce(OH)$_3$-Hg(OH)$_2$], which was formed by adding 2.0 ml of 0.1${\%}$ ethanolic sodium oleate solution, were floated on the surface with an aid of tiny nitrogen gas bubbles. The floated materials were quatitatively collected in a suction flask and dissolved with 5.0 ml of 2.0M HNO$_3$. The solution was marked to 25.00 ml with a deionized water. The content of Hg(II) was determined by cold vapor atomic absorption spectrophotometry. Any interferences of concomitants such as Ag$^+$, Br$^-$, I$^- $, etc. were not observed on the whole procedure. The analytical result showed that Hg(II) found in the wastewater of Seochang Campus, Korea University was 1.98 ng/ml with the relative standard deviation of 3.6${\%}$. And recoveries of Hg(II) in the wastewater into which 1.0 ng/ml and 2.0 ng/ml were added were 95${\%}$ and 91${\%}$, respectively. From such results, this procedure could be concluded to be tolerably accurate and reproducible for the determination of trace mercury in a water sample.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.4
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• pp.293-301
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• 2017

A Sub-kWe small-scale experimental test loop was manufactured to investigate characteristics of the supercritical carbon dioxide power cycle. A high-speed turbo-generator was also designed and manufactured. The designed rotational speed of this turbo-generator was 200,000 rpm. Because of the low expansion ratio through the turbine and low mass flowrate, the rotational speed of the turbo-generator was high. Therefore, it was difficult to select the rotating parts and design the turbine wheel, axial force balance and rotor dynamics in the lab-scale experimental test loop. Using only one channel of the nozzle, the partial admission method was adapted to reduce the rotational speed of the rotor. This was the world's first approach to the supercritical carbon dioxide turbo-generator. A cold-run test using nitrogen gas under an atmospheric condition was conducted to observe the effect of the partial admission nozzle on the rotor dynamics. The vibration level of the rotor was obtained using a gap sensor, and the results showed that the effect of the partial admission nozzle on the rotor dynamics was allowable.

• Food Science of Animal Resources
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• v.30 no.2
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• pp.313-320
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• 2010

The purpose of this study was to evaluate the freshness of chicken meat during 19 d of storage at $4^{\circ}C$ using a portable electronic nose. The portable system consisted of six different metal oxide sensors and a moisture sensor. Determination of volatile compounds with gas chromatography-mass spectrometry, total bacterial count (TBC), and 2-thiobarbituric acid reactive substances (TBARS) monitored the quality change of the samples. These results were compared with the results measured by the electronic nose system. TBC and TBARS measurements could be separated into five groups and seven groups, respectively, among ten groups. According to principal component analysis and linear discriminant analysis with the signals of the portable electronic nose, the sample groups could be clearly separated into eight groups and nine groups, respectively, among ten groups. The portable electronic nose demonstrated potential for evaluating freshness of stored chicken.

• Journal of Energy Engineering
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• v.15 no.4 s.48
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• pp.277-283
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• 2006

In this study, butane 100% was used as fuel to verify the real fuel effect such as vapor pressure variation due to temperature change. A MPI fuel injection system for V-6 engine, which has reverse 'L' type cross section to minimize the possibility of liquid phase injection, was composed and one bank was operated under sequential injection scheme. Flow rate were measured according to injection duration, interval, and pressure. Also occurring of liquid phase injection was monitored with varying vaporizer and fuel rail temperature. The result shows that basic characteristics of injection is a relatively difference between air and LPG injection. Under cold start condition, however, the occurrence of liquid injection becomes more severe as the pressure increases, and sufficiently high temperature both in vaporizer and fuel rail is very important to insure gaseous injection. In addition, the temperature of vaporizer plays more important role in keeping LPG vapor state and the reverse 'L' type cross section of the rail is available to prevent liquid injection.

• Journal of the Korean Applied Science and Technology
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• v.34 no.4
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• pp.1085-1093
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• 2017

Plasticizers are materials added to give softness and elasticity to plastics having rigid properties to give soft properties as products, and they are mainly added to high molecular materials to give flexibility to improve workability and to improve cold resistance, resistance to volatility and electrical properties. It is used for the purpose. Most plasticizers are inert liquids, similar in function to solvents but with high molecular weight and no volatility. In addition, when dissolved in petrochemical products, only the plasticizer is separated by the matrix effect with other compounds, and qualitative and quantitative analysis. In this study, qualitative and quantitative analysis of DOA and DOP, which are representative components of petrochemical products, were conducted using MD-GC/MS and developed an optimal plasticizer analysis method.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.4
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• pp.463-470
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• 1998

To improve muscle quality and prolong freshness of sashimi, the effects of freezing-thawing condition on physicochemical and rheological properties of plaice muscle were investigated. Muscle tested were frozen with quick freezing (liquid nitrogen gas) or slow freezing ($-15^{\circ}C$ air). Transition time of zone of ice crystal formation was within 10 minute for quick freezing and 110 minute for slow freezing. Time required for thawing to $0^{\circ}C$ in muscle temperature by various thawing methods was shortest with $25^{\circ}C$ tap water, followed by $15^{\circ}C$ tap water, $10^{\circ}C$ tap water, $25^{\circ}C$ air, $5^{\circ}C$ tap water and $0^{\circ}C$ cold water. Breaking strength of muscle was higher in quickly frozen sample than in slowly frozen sample. According to sashimi term, changes in breaking strength of muscle did not show any difference in quickly frozen sample, while showed significant difference in slowly frozen sample. The remaining content of ATP was not effected by freezing speed, and ATP content was apt to higher in quickly thawed sample than in slowly thawed sample. IMP was the majority of ATP and it's related compounds of sample after freezing and thawing. Collagen matrix was weakened markedly in slowly frozen sample than in quickly frozen sample.

• Journal of the Korean Society of Food Science and Nutrition
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• v.36 no.1
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• pp.131-135
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• 2007

Various Phellinus species (Hymenochaetaceae) including P. linteus, P. baumii, P. pini, and P. igniarius of domestic and foreign products, were examined by gas chromatography to validate their composition of crude polysaccharides. The crude polysaccharide fraction, which is known to be one of the physiologically active fractions, were prepared by a cold ethanol precipitation method and the yield of the crude polysaccharide fractions of P. linteus, P. baumii, P. pini, and P. igniarius were 15.0%, 5.1%, 6.3% and 5.7%, respectively. The total monosaccharide amount of the crude polysaccharide fraction of P. linteus was 148.713 mg/g (dry weight of mushroom) while those of P. baumii, P. pini and P. igniarius were 29.022 mg/g, 29.222 mg/g and 1.546 mg/g, respectively. Although the major monosaccharide of all Phellinus mushrooms was glucose, there were remarkable differences in the absolute quantity of each monosaccharide. P. linteus included plenty of monosaccharides except mannose and ribose in comparison with P. baumii and P. pini. The absolute quantities of monosaccharides of P. baumii and P. pini were nearly similar except arabinose. The total monosaccharides of P. igniarius were minimal, but the portions of galactose and mannose in P. igniarius were greater than in the other species.

• Food Science and Preservation
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• v.12 no.4
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• pp.361-366
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• 2005

An electronic nose equipped with metal oxide sensor(MOS) was used for investigating the quality of reconstitute orange juice added different recoverable oil(cold pressed valencia oil) contents during 21 days of storage at $4^{\circ}C$. Quality changes in orange juice was described in terms of the sensitivity(${\Delta}R_{gas}/R_{air}$) of the sensors. Principal component analysis(PCA) was carried out using data obtained from twelve metal oxide sensors. The flavor of orange juice contained with the different recoverable oil contents($0.01\%{\sim}0.05\%$) was separated in PCA plot, in which the first principal component score was correlated with the content of recoverable oil. As storage periods prolonged, no significantly different sensitivity score of orange juice was observed in electronic nose. The content of recoverable oil in orange juice was reduced rapidly within 14 days, and then the decreasing ratio was slow on the next 7 days during storage at $4^{\circ}C$. The sensory score for overall and orange flavor of orange juice added $0.03\%$ recoverable oil was decreased during the 14 days and then rapidly dropped next 7 days of storage at $4^{\circ}C$.

• Journal of Wetlands Research
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• v.24 no.4
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• pp.288-300
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• 2022

As industrialization and urbanization progress extensively, climate change is intensifying due to greenhouse gas emissions. In Korea, the average temperature increased, and the annual precipitation also increased due to climate change. In addition, the meaning of the solar term, which expresses seasons according to the movement of the sun, is also being overshadowed. Therefore, this study investigated the seasonal changes and solar-term changes of average temperature and precipitation observed in the past as well as simulated for future RCP climate change scenarios for five major regions (Capital Region, Gyeongsang, Chungcheong, Jeolla, and Gangwon). For the seasonal length, the length of summer became longer, the length of winter became shorter nationwide, and the precipitation in summer generally increased compared to the past. In the Chungcheong area, under the RCP 8.5 scenario, the length of summer increased by 46%, precipitation increased by 16.2%, and the length of winter decreased by 31.8% compared to the past. For the solar term, the temperature rose in all seasons. In the Chungcheong area, under the RCP 8.5 scenario, the temperature of major heat increased by 15.5%, and the temperature of major cold increased by 75.7% compared to the past. The overall results showed that the hydrological characteristics of the season and solar term were identified by region, which can be used as basic data to prepare policies to respond to climate change.

• Journal of Mushroom
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• v.18 no.4
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• pp.339-343
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• 2020

This study aimed to optimize total nitrogen (TN) content in the medium and the growth temperature to improve the shelf life of Pleurotus eryngii Keneutari No. 2. We investigated the growth characteristics and changes in the O2/CO2 content in polypropylene film and performed sensory evaluations during cold storage under 1.5%, 1.8%, 2.1%, and 2.4% TN and at temperatures of 9℃, 12℃, and 15℃. The diameter and weight of the fruit bodies tended to increase with increasing nitrogen content, regardless of the growth temperature, and the highest weight per bottle (149.5 g) was obtained at 12℃ and 2.4% TN. Regardless of the nitrogen content, leaf color deepened with decreasing temperature. The gas concentration in the film, which changes depending on storage time, was maintained for the longest period at 9℃ and 2.1% TN. The sensory evaluation revealed no difference between the different nitrogen conditions tested, and the odor, discoloration, and decay were similar at 15℃ and 9℃ until day 28 of storage.