• Korean Journal of Materials Research
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• v.13 no.3
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• pp.137-143
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• 2003

The air gap between the metal and mold, formed by shrinkage during solidification, causes surface and subsurface cracks in the continuous casting process. Molten crack on the surface might also occur due to improper heat transfer between them. In order to compensate the air gap in mold design, the thermal contraction is an essential factor. In this study, the thermal contraction and expansion behaviors were examined from the ($\alpha$ and pearlite)/${\gamma}$ to ${\gamma}$/$\delta$ transformations in continuous casting steels by the commercial dilatometer and the self- assembled dilatometer with laser distance measurement. It was found that the thermal contraction and expansion behaviors were very dependant on the phase transformation of the ${\gamma}$/$\delta$ as well as ($\alpha$ and pearlite)/${\gamma}$. The sudden volume change from $\delta$ to ${\gamma}$ which might cause cracks in the continuous casting process, was observed on cooling just below the melting temperature by the self-assembled dilatometer.

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.80-82
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• 1996

This paper deals with the effects of the volume of thermal expansion chamber on the interrupting performance in thermal expansion type 25.8kV 25kA gas circuit breaker. Model interrupters with 5 type thermal expansion chamber were designed and manufactured. Short-circuit tests were carried out for those model interrupters with 25kA breaking current. Pressure rise in the expansion chamber were measured and compared with the calculated one which was obtained from a self-developed program in our team. The analysis on the interrupting performance of each model interrupter has been done on the base of the short-circuit test results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.10a
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• pp.223-224
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• 2006

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.39 no.2
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• pp.27-38
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• 2002

A new self-consistent mathematical model for semiconductor quantum well device was developed. The model was based on the direct solution of the Boltzmann transport equation, coupled to the Schrodinger and Poisson equations. The solution yielded the distribution function for a two-dimensional electron gas(2DEG) in quantum well devices. To solve the Boltzmann equation, it was transformed into a tractable form using a Legendre polynomial expansion. The Legendre expansion facilitated analytical evaluation of the collision integral, and allowed for a reduction of the dimensionality of the problem. The transformed Boltzmann equation was then discretized and solved using sparce matrix algebra. The overall system was solved by iteration between Poisson, Schrodinger and Boltzmann equations until convergence was attained.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.9
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• pp.24-32
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• 2020

A self-blast type gas circuit breaker has been studied in this study to improve efficiency of interrupting performance of short line fault(SLF). Hot gas flows of gas circuit breaker have been simulated to evaluate interruption performance using CFD. Design parameters such as various types of expansion chamber and nozzles are suggested by using simulation results. Simulated results and experimental ones are compared with previous (ones that of in under development and with capacitor) GCB. Modified new shape of an expansion chamber and nozzle has been suggested to improve the efficiency of gas flow and to provide guidelines for designing self-blast breaker with a higher interruption capability.

• International Journal of Advanced Culture Technology
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• v.5 no.4
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• pp.10-14
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• 2017

The tourism motivations of the senior tourists were used to analyze the effect on the tourism satisfaction. As result of the analysis, the rest motivation and knowledge expansion motivation bring positive effect except the social connectedness motivation. The senior tourist wanted to have their own time and preferred the tourism program focused on the leisure. They also seemed to have comparably high self-esteem. The self-development programs should be made and good relationship through the tourism satisfaction must be developed. The result of the study shows that the senior tourists are exhausted mentally and physically, and this fact affected a lot on the rest motivation which is one of the tourism motivations.

• Korean Business Review
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• v.9
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• pp.219-231
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• 1996

• 한국노년학
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• v.39 no.2
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• pp.241-259
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• 2019

The purpose of this study was to study the performance of volunteer work for the elderly from the perspective of self-efficacy and self-extension of the elderly, not from successful aging or productive aging. Through this, the research aims to confirm the expansion of internal growth and self-sufficiency that can occur in old age, and to provide an opportunity to re-examine one's life in old age. In order to verify the purpose of this research, questionnaires were distributed to 300 senior citizens who participated in volunteer activities at the City Hall and the District Office of Busan Metropolitan City over a period of three months from September to November 2018 and used the data from 266 questionnaires for the study, excluding the 34questionnaire answered unfaithfully. The results of the study are as follows. First, the motivation for volunteering activities (value function, social function, understanding function) of the elderly has a positive effect on self-efficacy. Second, the motivation for volunteering activities (value functions, social functions, understanding functions) have a positive effect on self-extension. Third, it has been shown that the elderly's sense of self-efficacy (self-regulation efficacy, confidence) has a positive effect on their self-extension. Fourth, it was found that self-efficacy has a mediated effect on the motivation of the elderly to participate in volunteer activities and the relationship of self-extension. This study identified the relevance of the motivation for volunteering activities of the elderly to influence their effectiveness and self-extension. In particular, the research suggests practical and policy measures for the revitalization of volunteer activities of the elderly by providing a new perspective on the welfare of the elderly by utilizing parameters of self-efficacy, a psychological and social concept for the elderly.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.39 no.1
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• pp.31-34
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• 2013

In dentistry, tissue expanders have been used to obtain sufficient soft tissue for alveolar bone augmentation in the severely atrophic ridge. Herein, we review two cases of soft tissue augmentation using a self-inflating tissue expander in patients in the Department of Oral and Maxillofacial Surgery at Ewha Womans University Mokdong Hospital for bone graft and implant operations. The results of each patient were presented using pre-operative and post-operative radiographs and clinical exams. The results of our study indicate successful bone graft and implant surgery using a self-inflating tissue expander.

• Archives of Plastic Surgery
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• v.47 no.5
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• pp.419-427
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• 2020

Background This study evaluated the Blossom system, an innovative self-filling, rate-controlled, pressure-responsive saline tissue expander (TE) system. We investigated the feasibility of utilizing this technology to facilitate implant-based and combined flap with implant-based breast reconstruction in comparison to conventional tissue expansion. Methods In this prospective, single-center, single-surgeon pilot study, participants underwent either implant-based breast reconstruction or a combination of autologous flap and implantbased breast reconstruction. Outcome measures included time to full expansion, complications, total expansion volume, and pain scores. Results Fourteen patients (TEs; n=22), were included in this study. The mean time to full expansion was 13.4 days (standard error of the mean [SEM], 1.3 days) in the combination group and 11.7 days (SEM, 1.4 days) in the implant group (P=0.78). The overall major complication rate was 4.5% (n=1). No statistically significant differences were found in the complication rate between the combination group and the implant group. The maximum patient-reported pain scores during the expansion process were low, but were significantly higher in the combination group (mean, 2.00±0.09) than in the implant group (mean, 0.29±0.25; P=0.005). Conclusions The reported average duration for conventional subcutaneous TE expansion is 79.4 days, but this pilot study using the Blossom system achieved an average expansion duration of less than 14 days in both groups. The Blossom system may accommodate single-stage breast reconstruction. The overall complication rate of this study was 4.5%, which is promising compared to the reported complication rates of two-stage breast reconstruction with TEs (20%-45%).