• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.1
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• pp.32-38
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• 2009

In this paper, cycle performance analysis for cooling capacity, compression work and COP of R744($CO_2$) transcritical vapor compression refrigeration system is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include superheating degree, outlet temperature of gas cooler and evaporating temperature in the R744 vapor compression cycle. The main results were summarized as follows : The cooling capacity of R744 increases with superheating degree, but decreases with the increasing evaporating temperature and outlet temperature of gas cooler. The compression work increases with superheating degree and cooling pressure of R744, but decreases with the increasing evaporating temperature. And, The COP increases with outlet temperature and evaporating temperature of R744 gas cooler, but decreases with the increasing superheating degree. Therefore, superheating degree, outlet temperature and evaporating temperature of R744 vapor compression refrigeration system have an effect on the cooling capacity, compression work and COP of this system. With a thorough grasp of these effect, it is necessary to design the compression refrigeration cycle using R744.

• Journal of the korean academy of Pediatric Dentistry
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• v.27 no.1
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• pp.24-31
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• 2000

The purpose of study was to compare the laser fluorescence detection by Diagnodent(KaVo, Germany), visual inspection using dental explorers, and conventional dental radiography as diagnostic tests for dental caries. One hundred and three human premolars and molars which had no caries or fissure caries were tested by the three methods. Diagnodent scores increased as the scores of the other two tests increased(P<0.01) There were significant relationships between visual inspection scores and Diagnodent scores(Pearson 0.676, Spearman 0.694) and between radiography scores and Diagnodent scores(Pearson 0.623, Spearman 0.658) (P<0.01, all). Diagnodent test proved to have high sensitivity and low specificity and more studies are necessary to present the diagnostic criteria for progressive caries stages.

• Communications of Mathematical Education
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• v.27 no.4
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• pp.369-379
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• 2013

In this paper, we analyzed the freshmen's achievements on general mathematics their GPA based on 'basic mathematics diagonal test score' among college entrance types in natural science or engineering. Also, we studied the achievements of students who were not passed the 'Basic Mathematics Diagonal Test (BMDT)' and had to take supplementary lessons to improve their mathematics abilities four times a week during the first semester of academic year 2012 in Mokpo National University. We found the followings; first, freshmen were accepted by the university through the regular admission have a higher level of academic achievement compared other type admission. Second, freshmen's academic achievement in the first semester has significant meaningful effect on their academic achievement in the second semester. Finally, there are correlations between achievements of general mathematics and a curriculum of freshmen who were passed test after taking supplementary lessons.

• The Journal of the Convergence on Culture Technology
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• v.6 no.2
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• pp.77-84
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• 2020

This study was to identify the relationship among self-resilience, emotion expressiveness, achievement motivation, and problem-solving ability of nursing students and provide data to increase problem-solving ability for nursing students based on the results. This research involved 229 nursing students in B city. The analyzed by the t-test, ANOVA, Pearson's correlation coefficient using SPSS/WIN 22.0. In results of the study, there were significant differences in problem-solving ability with respect to grade (F=4.021, p=.008), academic level (F=3.791, p=.024), satisfaction of major(F=11.140, p<.001), Accomplishment (F=8.000, p<.001), interpersonal relationship(F=16.944, p<.001). There were positive correlation between problem-solving ability and self-resilience(r=-.532, p<.001), between problem-solving ability and emotion expressiveness(r=.365, p<.001), between problem-solving ability and achievement motivation (r=.694, p<.001). Through this research requires the fellow study to determine the factors affecting problem-solving ability of nursing students.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.4
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• pp.173-179
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• 2013

Middle-sized $CO_2$ water heater having compressor power of 7.45 kW was designed, and its performances were experimentally tested. Besides, optimum design of the $CO_2$ water heater was conducted by cycle simulation. When ambient temperature of $7^{\circ}C$ and hot water outlet temperature of $80^{\circ}C$ the $CO_2$ water heater showed the COP of 3.2. As hot water temperature increased the COP is getting decreased due to significant increase of compressor power consumption compared to increasing rate of heating capacity. When ambient temperature increased from $-3^{\circ}C$ to $12^{\circ}C$ the COP increased by 30%. The optimum components design of a gas cooler, an internal heat exchanger, and an evaporator were conducted, and the experimental correlation between amount of EEV opening and ambient temperature, and hot water temperature was suggested.

• Journal of Digital Convergence
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• v.19 no.11
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• pp.279-285
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• 2021

This study attempted to provide basic data for educational programs to improve career preparation behaviors by identifying the effects of nursing students' self-esteem and empathy on career preparation behaviors. Nursing Students and the 150 people who underwent descriptive research targets, data collection period was done by November 30, 2019 from IRB approval. The data were analyzed correlations between variables were analyzed using Pearson's correlation coefficient, and stepwise multiple regression analysis was used to determine the factors that affect the clinical performance of the Nursing Students (SPSS 23 version). As a result of the study, empathy ability was positively correlated with gender (r=.179, p=.029), self-esteem was negatively correlated with academic performance (r=-.231, p=.005), career preparation behavior showed a positive correlation with the number of practice hospitals(r=.178, p=.030). As the empathy ability of nursing students improved (β=.19, p=.020), career preparation behavior increased. Through this, the study is meaningful in that it suggested the need and direction to maintain a positive attitude toward career preparation behaviors of nursing students. suggest.

• Journal of Advanced Marine Engineering and Technology
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• v.18 no.4
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• pp.53-61
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• 1994

An experimental study on heat pump cycle systematizing characteristics for non-azeotropic refrigerant mixtures of R-22+R-114 was reported. Data were obtained under steady state condition at the ranges of parameters, 550- 2, 170kcal/h, 670-2, 990kcal/h, 24-71kg/h, and 0-1, for as cooling capacity, heating capacity, mass 25, 50, 75, and 100 per cent of R-22 by weight fraction for R-22+R-114 mixtures. The results shown that the C.O.P of the 50wt% of R-22 mixture was considerably larger than for pure R-22 and other weight fraction of R-22 mixtures, but the compression power of the 25wt% of R-22 was lower than that of the pure R-22 and the other weight fraction of R-22 mixtures. The hightest value of cooling capacity was obtained at the conditions of evaporating temperature 5.deg.C and R-22 50wt% mixture. In general, with an increase in the R-22 weight fraction for fixed values of the other parameter, the cooling capacity increased at first, obtained a maximum, and then decreasd. This verified the importance of accurate weight fractions od refrigerant mixtures in the heat pump cycle.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.6
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• pp.683-694
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• 1998

The application of hydrocarbon refrigerants in a hermetic reciprocating compressor for refrigerator is investigated. The selected refrigerants are isobutane(R600a), propane(R290), R12, binary mixture of R600a/R290, and OS-21CII. Both theoretical and experimental investigations have been performed for the selected refrigerants. The test results of hydrocarbon refrigerants have been compared to the traditional refrigerant(R12). The results show that hydrocarbon refrigerants(HC-Blend, OS-21C II) are very good alternatives in the refrigeration system for R12.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.3
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• pp.166-176
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• 2003

Experiments have been conducted in order to make comparisons of a alternative refrigerant (R-410A) cycle characteristic with an existing refrigerant (R-22) cycle characteristic in terms of cooling capacity and coefficient of performance (COP). The parameters examined in the present work include air flow rate, indoor/outdoor air temperatures, and indoor relative humidity. These two refrigeration cycles share all components except compressor, accumulator, oil separator, and piping connecting them. The measurements were made using an air-enthalpy calorimeter. The experimental results show that the R-410A cycle has many advantages over indoor conditions while the R-22 cycle has better performance over outdoor conditions.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.05a
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• pp.95-99
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• 2001

As a way to use energy effectively, the present study is aimed at investigating the performance characteristics of a Single Effect LiBr/Water Absorption Refrigerator using a low temperature driving heat-source. It was carried out by changing the driving heat-source temperature, the cold water outlet temperature(the refrigeration load), the cooling water inlet temperature, and the weak solution flow rate and this study compares the performance characteristics of refrigerator against the existence and non-existence of the Recirculation of the Weak solution which is used as a method to improve the performance of refrigerator. In case of Recirculation of the weak solution, more improved the Refrigeration Capacity and COP was obtained, and these effects became more larger in the high temperature of driving heat-source and large quantity of solution.