• 한국지구과학회지
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• 제25권3호
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• pp.142-151
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• 2004

This study was designed to determine whether visitor behavior at science museums differs across various exhibit styles and between Family and Non Family groups. Eight exhibits in the natural history sections of the national science museum located in Daejeon were identified to have distinctive characteristics and styles. At each selected exhibit, visitor behavior was observed for an hour. An average of eighty people stopped by each exhibit. Descriptive analyses of visitors behaviors showed that: 1) families spent more time than non-family visitors; 2) families paid more attention to exhibits, for instance, they talked and commented about the exhibits; 3) exhibit characteristics related to holding power and attention span; 4) families more frequently visited exhibits related to school curriculum rather than ones that looked attractive, fun or novel. Visitors did not play with sensory simulation types of exhibits as much as expected. This implicates that exhibit style does not guarantee long visitors holding time and attracting power. Non-significant results are explained in terms of environmental and exhibit-related factors. Several potential factors including visitor factors, setting factors, and exhibit factors are discussed and explored with topics proposed for future study.

• 한국기계가공학회지
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• 제16권6호
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• pp.109-116
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• 2017

In this study, the optimization of the overall dimensions of an automobile bumper was investigated through CAE and experiment using the Six Sigma method and design of experiment (DOE) method, respectively. Injection pressure, injection speed, injection time, cooling time, holding time, injection temperature, and holding pressure were selected as the vital parameters affecting the overall width of product through analysis of trivial many using CAE. The optimal values were determined using the DOE method, and we analyzed the improvement by applying the optimal conditions to the production process. As a result, the mean value of the overall width was close to the target value, with a deviation of 0.05mm, and the processability and I-MR control were remarkably improved. Finally, the dimension pass rate of the product improved by 20%.

• 한국주조공학회지
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• 제28권3호
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• pp.129-135
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• 2008

The reheating stage of electromagnetically stirred Al billet is a critical factor in the thixoforming process. When reheated to the solid-liquid state, the microstructure evolves to a more globular and more homogeneous structure by a coarsening mechanism, the kinetics depending on the initial microstructure. Microstructural evolution has been characterized by conventional parameters (mean size of particle and shape factor) as a function of holding time in the solid-liquid state. The aim of this study is to report experimental results concerning microstructural evolution in the solid-liquid state of electromagnetically stirred Al billet. The material was elaborated in the form of continuously cast bars solidified with electromagnetic stirring to degenerate the dendritic structure. The choice of the reheating conditions is determined by a dendritic ripening and coalescence mechanism, involving variations of both the shape and size of the particles. The reheating time has to be long enough to allow a minimum degree of spheroidizing, but has to be limited as much as possible in order to avoid excessive ripening. The optimum microstructure was obtained at the reheating temperature of near $584^{\circ}C$ and the holding time of 5 min. The only means of combining high productivity with good casting quality was to use feedstock billets whose microstructure showed rapid transformation characteristics.

• 한국인터넷방송통신학회논문지
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• 제21권2호
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• pp.169-175
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• 2021

로트 크기 문제(LSP)는 다항시간으로 최적 해를 찾을 수 있는 알고리즘이 알려져 있지 않은 NP-완전의 난제이다. LSP에 대해 다항시간으로 해를 구할 수 있는 W-W 알고리즘이 알려져 있지만, 이 알고리즘은 너무나 복잡하여 이해와 적용에 어려움이 있어 S-M의 휴리스틱 근사 알고리즘이 제안되었다. 본 논문에서는 LSP의 근사 해가 아닌 최적 해를 찾을 수 있는 간단한 공식을 가진 O(n)의 선형 복잡도 알고리즘을 제안하였다. 제안된 알고리즘은 t시점에서의 로트 크기(생산량) Xt∗은 비축 비가 절차 비를 초과하지 않는 t+k 시점을 결정하여 [t,t+k] 구간의 요구량 합으로 단순히 결정하였다. 제안된 알고리즘을 다양한 실험 데이터에 적용한 결과 모든 데이터에 대해 최적 해를 찾았다.

• 한국초전도ㆍ저온공학회논문지
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• 제11권3호
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• pp.20-25
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• 2009

The quench detection system of the KSTAR (Korea Superconducting Tokamak Advanced Research) primarily uses the resistive voltage measurement due to a quench. This method is to detect the resistive voltage generated by a quench, which is continuously maintained above the preset voltage threshold for a given holding time. As the KSTAR PF (Poloidal Field) coils are operated in the pulse current mode, the large inductive voltages are generated. Therefore the voltage threshold and the quench holding time should be determined by considering both the inductive voltages measured during the operation, and the maximum conductor temperature rise through the quench analysis. In this paper, the compensation methods for minimizing the inductive voltages are presented for the KSTAR PF coils. The quench hot spot analysis of the PF coils was carried out by the analytical and numerical methods for determining the proper values of the quench voltage threshold and the allowable quench protection delay time.

• 대한산업공학회지
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• 제31권4호
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• pp.289-296
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• 2005

This study aims to measure maximum holding times(MHTs) of symmetric and asymmetric whole body postures, and to compare three representative observational methods including OWAS, RULA, REBA, based on the MHTs. An experiment was conducted for obtaining the MHTs, in which hand position was used as experimental variable, and the MHT and subjective discomfort rating as dependent variables. The hand position was defined by the percentage of the shoulder height(%SH), the percentage of the arm reach(%AR) and rotation angle(R). The results showed that three independent variables of %SH, %AR and R significantly affected on the MHTs at ${\alpha}$=0.01, and that the MHTs were negatively linearly related to the discomfort scores of Borg CR10. It was also revealed that OWAS and REBA were less sensitive to postural stress than RULA. In addition, OWAS and REBA underestimated postural load of given postures compared to RULA. Therefore, it is recommended that among the three observational methods investigated in this study, RULA be used for a more precise evaluation of postural load.

• 열처리공학회지
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• 제33권5호
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• pp.232-238
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• 2020

Heating experiments using the 7075 aluminum alloy in the state of billet and extrudate have been performed to investigate the pertinent ranges of working temperatures and holding times for the application to the various automobile parts. The 7075 specimens from raw billet of 152 mm in diameter and 400 mm in length prior to extrusion were used for heating with a holding time of 10 minutes at temperatures between 380℃ and 550℃. Then, an extrusion process using the billet has been fulfilled at 380℃ with extrusion speed of 0.8 mm/min to get an plate-type extrudate of 75 mm in width and 4.2 mm in thickness. The samples from the extrudate were subjected to heating experiments at temperatures between 380℃ and 440℃ with holding times such as 10 min, 30 min, 60 min and 120 min at each heating temperature. The microstructures were investigated on the optical and EBSD micrographs. The hardness measurement and the tensile test have been performed to investigate the effect of the heat treatment on the mechanical property. The results showed for the 7075 extrusion process that the safe heating of billet can be performed below 450℃ and the extrusion can be done safely up to 400℃.

• 한국보건간호학회지
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• 제21권1호
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• pp.25-36
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• 2007

Purpose: This study evaluated a smoking education program in middle schools in Busan. School nurses and health teachers performing additional job development with a variety of human resources on smoking education for adolescents were investigated. Method: The subjects were obtained from 133 middle schools located in Busan, and data were collected from January 10, 2005 to February 19, 2005. The data was analyzed using the descriptive statistics, multiple response and t-test on SPSS 12.0 for Windows. Results: Schools that had school nurses undertook 67% of all smoking education programs. However, 78.3% of smoking education programs were undertaken in schools that used health teachers holding an additional job, those who had other jobs, and teachers in charge of school discipline. The health teachers holding an additional job reported that they had difficulty with smoking education due to a 'lack of professionalism' (t=-2.776, p=.006). In addition, the school nurses reported that 'they had insufficient time for non-smoking education' (t=2.440, p=.016). Conclusion: The results of this study show that school nurses should be in charge of the smoking education programs developed in the middle schools in Busan.

• 한국세라믹학회지
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• 제56권4호
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• pp.394-398
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• 2019

In this paper, the joining characteristics of GDC-LSM ceramics with Crofer 22 APU metal alloys was investigated at different brazing temperatures and holding times by reactive air brazing. Brazing was performed using Ag-10 wt% CuO filler, at three different temperatures (1000, 1050, and 1100℃ for 30 minutes) as well as for three different holding times (10, 30, and 60 minutes at 1050℃). The interfacial microstructures were examined by scanning electron microscopy and the joining strengths were assessed by measuring shear strengths at room temperature. The results show that with increasing brazing temperature and holding time, joint microstructure changed obviously and shear strength was decreased. Shear strength varied from a maximum of 100±6 MPa to a minimum of 18±5 MPa, depending on the brazing conditions. These changes were attributed to an increase in the thickness of the oxide layer at the filler/metal alloy interface.

• 대한금속재료학회지
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• 제50권9호
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• pp.653-657
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• 2012

In this study, a molybdenum disilicide ($MoSi_2$) coating process was investigated by hydrogen reduction and Si-pack cementation. At first, the metallic Mo coating was carried out by hydrogen reduction of $MoO_3$ powder at $750^{\circ}C$ for various holding times (1, 2, 3 h) in hydrogen atmosphere. A $4.3{\mu}m$ thick metallic molybdenum thin film was formed at 3 h. $MoSi_2$ was obtained by Si-pack cementation on molybdenum thin film through hydrogen reduction processing. It was carried out using $Si:Al_2O_3:NH_4Cl=5:92:3$ (wt%) packs at $900^{\circ}C$ for various holding times (30, 60, 90 min) in Ar atmosphere. When the holding time was 90 min, a $MoSi_2$ layer was coated successfully and a $15.4{\mu}m$ thickness was observed.