• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.7
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• pp.486-491
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• 2008

The performance of a microturbine CHP system equipped with an absorption chiller was analyzed by modeling it. The microturbine with recuperator was simulated with the Brayton cycle model. The mass flow rate and available heat energy of the exhaust gas from the microturbine were simulated. These results were utilized as input values for the generator of the absorption chiller. The absorption chiller is a single-effect air cooled type with a solution heat exchanger. The heat input into the generator was proportional to the heat transfer rate and the UA values of the heat exchangers of the absorption chiller. Furthermore, the COP of the absorption chiller increased with respect to an increase of the heat input into the generator, under the sufficient evaporator capacity condition. When the capacity of the CHP system increased from 30 to 60 kW, the mass flow rate of the LiBr for the absorption chiller doubled, and the UA values for evaporator and condenser increased by factors of x3.9 and x3.4, respectively, under the same COP condition.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.7
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• pp.341-349
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• 2017

Formation and transportation of $CO_2$-hydrate slurry was conducted by circulating saturated water with $CO_2$ through a double-tube type heat exchanger which was cooled down by brine. The inner diameter and circulation length of the heat exchanger were 1 inch and 20 m, respectively. Water in tank was supersaturated by injected $CO_2$ and the operation pressure was maintained at 3,000 to 4,000 kPa with fluid-temperature of less than $9^{\circ}C$. $CO_2$ hydrate mass fraction was calculated based on density of $CO_2$-hydrate slurry mixture. Results showed that the $CO_2$-hydrate slurry could be circulated without blockage for 1 hr. Circulation status of the $CO_2$-hydrate slurry was also visualized.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.11
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• pp.733-738
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• 2008

Due to environmental concerns $CO_2$ has been reintroduced as a potential candidate to replace HFCs in refrigeration systems. Oils are always required in a vapor-compression cycle, and thus it is necessary to precisely estimate the thermodynamic mixture properties of $CO_2$-lubricant oil. In the present study, the density and the viscosity of the mixture was calculated by the Redlich and Kwong type EoS and the modified Peng and Robinson type viscosity EoS, respectively. The viscosity model was based on the similarity between P-v-T and T-$\mu$-P relationships. The predicted results were compared with the experimental data of Pens ado et al. whose test conditions were 100$\sim$650 bar of pressure and 303 K$\sim$353 K of temperature with the $CO_2$-POEs mixtures under 92.2 wt.% and 83.3 wt.% of $CO_2$ concentration. The mean deviations of the mixture density were 7.93% and 8.32% for 92.2 wt.% and 83.3 wt.% of $CO_2$ concentration, respectively. Concerning the viscosity, the mean deviations were 4% and 10% for 92.2 wt.% and 83.3 wt.% of $CO_2$ concentration under the Pensado et al.'s test conditions.

• Archives of design research
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• v.17 no.4
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• pp.89-96
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• 2004

The public has only a superficial understanding of the computer games, in spite of it's psychological effects and social results. Therefore, in this study, one finds out the serious approach which leads the computer games to recognize its future in terms of new media. Stand-point from Freud to french post-structuralist, it helps the introduction to understand the computer games as a kind of contents in which we are able to observe psychological process. As a result, there are studies about the structure of the dream, the desire, and the language which allow to mention 'parmakon' ; 'difference' between self and object, it provokes the psychological dynamism and so on, the playing the game remains a real trace and change, at the level not only of our psyche but also of our body.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.9
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• pp.52-57
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• 2019

The key technology of the fourth industrial revolution is artificial intelligence and machine learning. In this study, FMEA was performed on fuel pumps used as key items in most systems to identify major failure components, and artificial neural networks were built using big data. The main failure mode of the fuel pump identified by the test was coil damage due to overheating. Based on the artificial neural network built, machine learning was conducted to predict the failure and the mean error rate was 4.9% when the number of hidden nodes in the artificial neural network was three and the temperature increased to $140^{\circ}C$ rapidly.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.8
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• pp.311-315
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• 2016

The efficiency of manure treatment was investigated in terms of the pH, BOD, COD, SS, T-N and TP with a variation in the injection amount of PAC, polymer and ozone. The wastewater flow rate to the AOF is of $7.4m^3/hr$ with a reaction time of 30 minutes. The amount of PAC and polymer changed by 30, 35, 40 ml/min, and 30, 40, 50 ml/min, respectively. The amount of ozone injected varied from 110, 125, and $150kg-O_3/hr$. The optimum manure treatment performance was found for a PAC of 35 ml/min for the COD and SS, with polymer of 30 ml/min, and ozone injection of $150kg-O^3/hr$. A substantially optimum dose for each PAC, polymer, and ozone was also found to exist.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.6
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• pp.529-535
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• 2005

This study experimentally examines the air-side performance of spiral finned tube heat exchangers. The effects of fin spacing, fin height, and tube alignment were investigated. Reduction of fin spacing decreased the Colburn j factor. However, the effect of fin height on the Colburn j factor was negligible. An increase of tube row decreased the Nusselt number for both staggered and in-line tube alignments. However, the decrease of the Nusselt number for the in-line tube alignment was much more significant than that of the staggered tube alignment. The average Nusselt number of the staggered tube alignment was larger than that of the in-line tube alignment by $10\%$ when the Reynolds number ranged from 300 to 1700. An empirical correlation of the Nusselt number was developed by using geometric parameters of heat exchanger and correction factors. The correction factor considered the effects of tube alignment and number of tube rows on the heat transfer. The proposed correlation yielded a mean deviation of $4\%$ from the present data.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2019.04a
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• pp.49-49
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• 2019

본 연구는 대한민국 매실나무 열매의 특성평가를 위하여 청매실의 무게를 대, 중, 소로 구분하여 발효액의 수율, 당도, 산도 및 당산비를 조사하였고, 청매실과 황매실의 발효액 특성을 비교하였다. 발효액의 수율은 82~132%의 범위로 매우 넓었으며, 대 > 중 > 소의 순으로 적은 경향을 보였다. 당도는 55.4~59.1%의 범위이었으며, 무게에 따른 차이는 나타나지 않았다. 산도는 1.73~2.71%의 범위이었으며, 무게에 따른 차이는 나타나지 않았다. 당산비는 20.6~31.3의 범위로 매우 크게 나타나 자원의 다양한 특성이 존재함을 나타내었으며, 무게에 따른 차이는 나타나지 않았다. 무게에 따른 발효액 수율, 당도, 산도 및 당산비는 처리간 차이를 나타내지 않았으나 전체적인 자원간에는 큰 차이를 나타내어 다양하였다. 발효액의 변이계수는 당산비 > 산도 > 당도 > 수율의 순이었다. 청매실과 황매실의 발효액은 수율의 경우 황매실이 높았고, 당도와 산도는 청매실이 높았으며, 당산비는 차이가 없었다.

• Korean Medical Education Review
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• v.23 no.1
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• pp.11-22
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• 2021

This review of the literature explored the experiences and effects of peer-assisted learning in basic medical education. Peer-assisted learning is most commonly utilized to teach clinical skills (including technical skills) and medical knowledge (76.4%). It has also been used, albeit less frequently, to facilitate small-group discussions including problem-based learning, to promote students' personal and professional development, to provide mentoring for career development and adaptation to school, to give tutoring to at-risk students, and to implement work-based learning in clinical settings. Near-peer learning is a common type. The use of active learning techniques and digital technology has been increasingly reported. Students' leadership had frequently been described. Student tutor training, programs for teaching skills, institutional support, and assessments have been conducted for effective peer-assisted learning. There is considerable positive evidence that peer-assisted learning is effective in teaching simple clinical skills and medical knowledge for tutees. However, its effects on complex skills and knowledge, small-group discussions, personal and professional development, peer mentoring, and work-based learning have rarely been studied. Additionally, little evidence exists regarding whether peer-assisted learning is effective for student tutors. Further research is needed to develop peer-assisted learning programs and to investigate their learning effects on student tutors, small-group discussion facilitation, personal and professional development, peer mentoring, and peer-led work-based learning in the clinical setting in South Korea. Formal programs and system advancement for a student-led learning culture is needed for effective peer-assisted learning.

• Journal of Korean society of Dental Hygiene
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• v.22 no.4
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• pp.249-257
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• 2022

Objectives: This study aimed to investigate the effect of the oral health status on risk factors for obstructive sleep apnea (OSA) using data from the 2019 National Health and Nutrition Examination Survey. Methods: Of a total of 2,422 persons, 1,295 and 1,127 were categorized into the control group (CG) and OSA risk group (OSARG), respectively. The effect of the oral health status on OSA risk factors was presented in Model 1 by performing a complex sample linear regression analysis. Results: Our findings showed that OSA risk factors decreased by 0.075 points when there were no speaking problems with demographic characteristics adjusted. In addition, when systemic diseases were adjusted for, OSA risk factors decreased to 0.074 points (p<0.05). Conclusions: Therefore, in order to reduce oral problems that affect OSA risk factors, dentists and dental hygienists should seek accurate recognition of OSA and effective oral care methods.