• Journal of Korea Foundry Society
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• 제40권3호
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• pp.61-65
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• 2020

Rheo-diecasting with stirring has been used in many material industries. As the 4th Industrial Revolution approaches the world, eco-friendly high-strength and light-weight materials become more important. Casting methods have been studied and used for aluminum-alloy automobile parts. This study carried out the effect analysis of the micro-structure and mechanical properties, such as yield/ultimate tensile strength, elongation, and hardness, of A356 using the 6-pole EMS (electro-magnetic stirring) casting process with a high electromagnetic force. As a result, the hardness and elongation of the A356 after T6 heat-treatment show a significant improvement, respectively, by 20% and 50%.

• Solar Energy
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• 제18권1호
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• pp.69-79
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• 1998

This paper is concerned about the performance of HCFC22 alternative refrigerants used in heat pumps and industrial chillers. A water-to-water breadboard heat pump with counter-current heat exchangers and a hermetic compressor was built to carry out the experiments with various refrigerants. For each test, more than 40 temperatures, 4 pressures, power input, mass flow rates of the heat transfer fluids were measured. Refrigerants tested were HCFC22, R290(Propane), an azeotrope of 45%Propane/55%R134a mixture, and a nonazeotropic mixture of Calor 50. All tests were conducted under ARI test A condition. It is found that the COP and capacity of propane were 18% and 2.5% higher than those of HCFC22 while the COP and capacity of 45%Propane/55%R134a mixture were 3.5% and 5.3% higher than those of HCFC22 respectively. Also the COP and capacity of Calor 50 were 17% and 7.8% higher than those of HCFC22. Compressor discharge temperatures of alternative refrigerants were roughly $35^{\circ}C$ lower than that of HCFC22 indicating that these refrigerants are good from the view point of compressor reliability. The charging amounts for the alternative refrigerants were reduced by 40-60% as compared to that of HCFC22. Overall, it can be said that hydrocarbon containing alternative refrigerants are excellent in thermodynamic performance but should be used with considerable care due to their flammability.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제25권2호
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• pp.171-179
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• 2001

Experimental study has been carried out on the characteristics of pressure drop and heat transfer of brazed plate heat exchangers using R-22. Data are presented for the following range of variables: the mass flux (40∼90kg/$m^2$s), chevron angle ($20^{\circ}$, $35^{\circ}$, $45^{\circ}$) and inlet pressure of the refrigerant (1.4 and 1.6MPa). For both subcooled and two-phase flow, as chevron angle increases, pressure drop and heat transfer coefficient decrease. Condensation heat transfer coefficient and pressure drop were compared with the previously proposed correlations. Among therm, Traviss correlation agreed with experimental results within -40%∼-84% for heat transfer coefficient and -59%∼62% for pressure drop.

• Asian-Australasian Journal of Animal Sciences
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• 제18권4호
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• pp.580-583
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• 2005

We have evaluated the application of spectroscopy using an insertion-type fiber-optic probe and a sensor at wavelengths from 400 to 1,100 nm to the measurement of milk fat content on dairy farms. The internal reflectance ratios of 183 milk samples were determined with a fiber-optic spectrophotometer at 5$^{\circ}C$, 20$^{\circ}C$ and 40$^{\circ}C$. Partial least squares (PLS) regression was used to develop calibration models for the milk fat. The best accuracy of determination was found for an equation that was obtained using smoothed internal reflectance data and three PLS factors at 20$^{\circ}C$. The correlation coefficients between predicted and reference milk fat at 5$^{\circ}C$, 20$^{\circ}C$ and 40$^{\circ}C$ were r=0.753, r=0.796 and r=0.783, respectively. The predictive explained variances ($Q^2$) of the final model, moreover, were more than 0.550 at all temperatures, and the regression coefficients of determination ($R^2$) were more than 0.6 (60%). Our results indicate that milk has different internal reflectance measured in the range of visible and near infrared wavelengths (400 to 1,100 nm), depending on its fat content.

• Journal of Korean Clinical Health Science
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• 제5권4호
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• pp.1026-1031
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• 2017

Purpose. This study was to investigate the relationships among mobile internet addiction, sleep quality, anxiety, and interpersonal relationship in university students. Method. A descriptive study design was used. Between 10 and 31 March 2016, 213 subjects completed a questionnaire consisting of questions on mobile internet addiction, anxiety, sleep quality, and interpersonal relationship. The data were analyzed using descriptive statistics, One way-ANOVA, and Pearson's correlation coefficient SPSS/WIN 21.0 programs. Results. Among mobile internet addiction there were significant differences between gender (t=3.40, p<.001), grade (F= 2.31, p<.001), majority field (F=5.34, p=.005), and take exercise (t=3.50, p<.001). This study has shown that mobile internet addiction were associated with sleep quality (r=-.40, p<.001) and anxiety (r=.14, p=.037). In addition, a correlation has been found significant between anxiety, and sleep quality (r=.48, p<.001), and sleep quality has associated with interpersonal relationship (r=-.46, p<.001). Conclusion. In this study, we revealed the observed a meaningful significant correlation between mobile internet addiction, sleep quality and anxiety. Therefore, it is important to emphasize control of mobile internet addiction for university students. The results of this study can be used as a basis on which to develop a mobile internet addiction intervention program.

• Journal of the Korean institute of surface engineering
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• 제40권3호
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• pp.138-143
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• 2007

The effects of texturing and anti-reflection coating on the reflection properties of multi-crystalline silicon solar cell have been investigated. The chemical solutions of alkaline and acidic etching solutions were used for texturing at the surface of multi-crystalline Si wafer. Experiments were performed with various temperature and time conditions in order to determine the optimized etching condition. Alkaline etching solution was found inadequate to the texturing of multi-crystalline Si due to its high reflectance of about 25%. The reflectance of Si wafer texturing with acidic etching solution showed a very low reflectance about 10%, which was attributed to the formation of homogeneous. Also, deposition of ITO anti-reflection coating reduced the reflectance of multi-crystalline si etched with acidic solution($HF+HNO_3$) to 2.6%.

• Structural Engineering and Mechanics
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• 제12권3호
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• pp.249-266
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• 2001

Current seismic design provisions allow structures to deform into inelastic range during design level earthquakes since the chance to meet such event is quite rare. For this purpose, design base shear is defined in current seismic design provisions as the value of elastic seismic shear force divided by strength reduction factor, R (${\geq}1$). Strength reduction factor generally consists of four different factors, which can account for ductility capacity, overstrength, damping, and redundancy inherent in structures respectively. In this study, R factor is assumed to account for only the ductility rather than overstrength, damping, and redundancy. The R factor considering ductility is called "ductility factor" ($R_{\mu}$). This study proposes ductility factor with correction factor, C, which can account for dynamic P-${\Delta}$ effect. Correction factor, C is established as the functional form since it requires computational efforts and time for calculating this factor. From the statistical study using the results of nonlinear dynamic analysis for 40 earthquake ground motions (EQGM) it is shown that the dependence of C factor on structural period is weak, whereas C factor is strongly dependant on the change of ductility ratio and stability coefficient. To propose the functional form of C factor statistical study is carried out using 79,920 nonlinear dynamic analysis results for different combination of parameters and 40 EQGM.

• Wind and Structures
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• 제22권5호
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• pp.573-594
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• 2016

Simultaneous pressure measurements on 2D square prisms with various corner modifications were performed in uniform flow with low turbulence level, and the testing Reynolds numbers varied from $1.0{\times}10^5$ to $4.8{\times}10^5$. Experimental models were a square prism, three chamfered-corner square prisms (B/D=5%, 10%, and 15%, where B is the chamfered corner dimension and D is the cross-sectional dimension), and six rounded-corner square prisms (R/D =5%, 10%, 15%, 20%, 30%, and 40%, where R is the corner radius). Experimental results of drag coefficients, wind pressure distributions, power spectra of aerodynamic force coefficients, and Strouhal numbers are presented. Ten models are divided into various categories according to the variations of mean drag coefficients with Reynolds number. The mean drag coefficients of models with $B/D{\leq}15%$ and $R/D{\leq}15%$ are unaffected by the Reynolds number. On the contrary, the mean drag coefficients of models with R/D=20%, 30%, and 40% are obviously dependent on Reynolds number. Wind pressure distributions around each model are analyzed according to the categorized results.The influence mechanisms of corner modifications on the aerodynamic characteristics of the square prism are revealed from the perspective of flow around the model, which can be obtained by analyzing the local pressures acting on the model surface.

• Korean Journal of Soil Science and Fertilizer
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• 제50권5호
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• pp.489-496
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• 2017

This study was conducted to test the applicability of hydroxy radical reactor system, which applied advanced oxidation processes, to sterilize pathogenic bacteria for nutrient solution recycling in closed hydroponics. Removal efficiency was tested on 25 L of nutrient solution maxed with 10 mL culture solution of bacteria, E. coli, and R. solanacearum in a pilot tank. The testing conditions included various levels of hydroxy radicals resulting from air flow rates of 40, 80, and $120L\;min^{-1}$, and 12 hours processing time. The removal of bacteria, E. coli, and R. solanacearum by hydroxy radical in nutrient solution was significantly increased with an increase in the flow rate of the air from $40L\;min^{-1}$ to $120L\;min^{-1}$. The optimum removal efficiency was achieved at an air flow rate of $120L\;min^{-1}$ for 2 hours treatment. There were no significant differences in removal efficiency among bacteria, E. coli, and R. solanacearum for tested level and time of hydroxy radical. These results verified the efficiency of hydroxy radical in removing the pathogenic bacteria and the applicability of hydroxy radical reactor system in the field.

• Journal of Aerospace System Engineering
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• 제11권6호
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• pp.76-83
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• 2017

The MIL-STD-1553 standard has been used for over 40 years as a data bus technology for high-reliability mobile systems. However, 1 Mbps transmission speed is absolutely insufficient to implement sensor data convergence, which is an essential requirement of modern aerospace systems. In this paper, we analyze the hierarchical structure of the MIL-STD-1553B version specification and describe several methods to increase the transmission speed without losing the advantages of the existing MIL-STD-1553 bus. In addition, we analyzed the R & D cases of the high-speed MIL-STD-1553 technology, which have been conducted in leading aerospace countries.