• Publications of The Korean Astronomical Society
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• v.6 no.1
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• pp.27-37
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• 1991

두 스칼라장 $\phi_1$, $\phi_2$를 사용한 원시 검은 구멍 생성모형을 살펴보았다. $\phi_1$은 Linde의 혼돈 인플레이션장을, 그리고 $\phi_2$는 SU(5) 대통일 이론의 Higgs장을 사용하였다. 인플레이션은 $\phi_1$에 의해서 일어난다고 가정하였는데, 재가열(reheating) 온도가 $\phi_2$장의 임계온도(${\sim}1.31{\times}10^{14}GeV$)보다 높을 경우 재가열 직후에 검은 구멍이 생성됨을 알 수 있었다. 재가열 온도가 $1.48{\times}10^{14}GeV$정도 되면, 질량이 1kg쯤인 검은 구멍이 생성되는데, 현재의 지평선에 해당되는 당시의 영역 내에서 생성되었던 검은 구멍들의 총 질량이 ${\sim}10^{55}g$($\approx$현재 우주의 지평선 질량)이 되어, 그 증발과정이 우주론적으로 중요해질 수 있다.

• 기계와재료
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• v.23 no.3
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• pp.16-29
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• 2011

결정 합금 대비 비정질 합금은 높은 경도를 갖기 때문에 마모 저항성도 좋고 내부 식성 등 환경에 대한 저항성도 월등하며, 또한 과냉된 액상 상태까지 재가열하게 되면 낮은 점성도를 갖게 되므로 복잡한 3차원적인 형상을 가지는 부품을 환경에 대한 저항성, 피로 저항성, 강도 및 경도 등을 모두 고려하여 높은 정밀도를 가지고 제조하는 것이 가능하므로 우수한 물성을 갖는 구조 및 기능성 재료로의 다양한 응용이 타진되고 있다. 이러한 비정질 합금의 변형 거동에 대한 연구는 대부분 유리 천이 온도 이하에서의 전단 및 파단에 이르는 이른바 불균일 변형(Inhomogeneous Deformation) 거동에 대한 이해를 위한 실험 및 해석적 연구에 집중되어 왔다. 반면 상업화의 기반이 되는 고상 기반 2차 정형 성형은 과냉 액상 영역에서의 구조 완화 및 결정화롤 대표되는 미세 구조 제어 균일 변형(Homogeneous Deformation)에 대한 이해 없이는 불가능하므로, 이러한 관점에서 비정질 합금 특유의 점성 유동 특성을 이용한 균일 변형 응용 예시 및 미세구조 변화 연계 해석 기술의 현황을 소개하고자 한다.

• Journal of Welding and Joining
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• v.12 no.4
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• pp.151-161
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• 1994

FCAW has wide application in ship fabrication, maintenance and field erection. It has many advantages over SMAW.SAW and GMAW process. In many applications, the FCAW provides highquality weld metal. This method can reduce weld defects especially porosity and spatter. But the fatigue characteristics of those deposited metal have been rarely investigated. The purpose of this study is to investigate the cyclic stress-strain behavior and fatigue tests by the constant strain control were carried out on the rounded smooth specimen with deposited metal using the metal type flux cored wire. As the results of this study for the deposited metal welded by the metal type flux cored wire, the hardening or softening characteristics under cyclic load were investigated and cyclic stress-strain curve, strain-fatigue life curve, stress-strain function and fatigue life relation which are useful to estimate the fatigue life under the stress concentration condition were obtained.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2003.11a
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• pp.477-478
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• 2003

에너지 사용의 증대에 따라 대기중으로의 질소산화물 배출양이 증가하고 있으며, 이에 따른 산성비, 광화학 스모그등 많은 피해가 나타나고 있다. 이러한 질소산화물중 고정원에서 배출되는 질소산화물은 선택적 촉매환원법에 의해 제거가 되고 있다. 선택적 촉매 환원법에 사용되고 있는 촉매는 주로 V$_2$O$_{5}$/TiO$_2$ 계열로써 300 ~ 40$0^{\circ}C$ 영역에서 최적의 반응을 보인다(H. Bosch and F. Janssen, 1988). 그러나 촉매의 내구성 증진, 재가열에 따른 에너지 절감등의 이유로 저온에서 우수한 활성을 보이는 촉매의 개발이 필요하다. (중략)

• Composites Research
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• v.31 no.2
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• pp.63-68
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• 2018

Thermoplastic composite has been limitedly used in high performance aerospace industry due to relatively low mechanical properties even though it has various advantages. But, thermoplastic aromatic polymer composite has recently been researched and utilized much. In this study, PEEK and PPS neat resin film as representative thermoplastic aromatic polymer were processed through continuous heating, cooling and reheating cycle. Property change such as glass transition temperature and melting temperature were identified and crystallinity variation by different cooling rate were evaluated. In the first (heating) run, polymer specimens were kept for 5 minutes at higher temperature than melting point to remove previous thermal history, and crystallization reaction was controlled by adjusting cooling rate to 2, 5, 10, 20 and $40^{\circ}C/minute$ in the second (cooling) run. In the third (heating) run, specimen crystallinity were verified by measuring the melting enthalpy. The initial specimens containing high portion of amorphous structure exhibited cold crystallization and clear glass transition in the first run whereas they did not show in the third run due to the increase of crystalline structure portion. As cooling rate decreases through the second cooling run, the crystallinity of the specimen increased. PEEK polymer had 21.9~39.3% crystallinity depending on cooling rate change whereas PPS polymer showed 29.1~31.2%.

• Korean journal of food and cookery science
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• v.26 no.5
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• pp.603-616
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• 2010

Based on recent dramatic increases in foodborne outbreaks in restaurants, self-managed sanitation systems are now recommended to control contributing risk factors. This study aimed to improve sanitation management practices in restaurants and had two objectives. First, we tried to develop a self-managed sanitation check-list, including risk factors contributing to foodborne illness and Korean food hygiene regulation articles. We also tried to evaluate current sanitation management practices in restaurants according to operation and restaurant type. Thirty restaurants were evaluated by on-the-spot inspectors using an auditing tool consisting of four dimensions, seventeen categories, and forty-one items. Total compliance rate categorized by operation type significantly differed between chain restaurants and self-managed restaurants, with values of 85.5% and 51.6%, respectively. Therefore, self-managed restaurants, which showed the lowest compliance rate of below 30.0%, need more strict control to improve current unsanitary management practices, specifically relating to 'sterilization of knives, chopping boards, and wiping cloths', 'sanitation training', 'not allowing access into the kitchen to outsiders', 'handling of food or utensils on shelves at a 15 cm distance away from floor', 'prevention of cross-contamination of cooked foods or vegetables', and 'records of kitchen access or inspection'. Thus, an effective food sanitation system is essential and should be implemented to improve the existing sanitary conditions in restaurants. However, the most important factor to achieving food sanitation management objectives is food handlers' self-motivation.

• Journal of the Korean Society of Food Science and Nutrition
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• v.38 no.5
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• pp.618-625
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• 2009

The purposes of this study were to evaluate food safety knowledge and to assess home food safety performance of home-delivered meal service recipients. Two facilities providing home-delivered meal services for older adults were located in Seoul. A total of 120 service recipients were surveyed using an individual interview technique and 97 responses were used for data analysis. A statistical data analysis was completed using SPSS program (ver.14) for descriptive analysis, t-test, ANOVA, and correlation analysis. The majority of the participants were 70 years old or older and females. They perceived their health status as poor or very poor and took more than one kind of medicines. An average score of the food safety knowledge test was 11.48 based on 18 points (63.8%). The results revealed that the older adults knew the importance of hand washing but were not aware of when and how to wash hands. There was room to improve knowledge on cleaning and sanitizing fresh fruits and using wiping cloth. The knowledge score for each category was not significantly different by gender and age. The home food safety practices of the older adults was rated as 2.8 out of 4 points; the highest score was associated for proper food handling category and the lowest score was for cleaning and sanitizing. The worst performance was related to managing hand cuts and wounds (1.96). The total knowledge score and an average performance score were significantly correlated (p<0.01). Food safety education programs targeting the older adults who receive home-delivered meal services would improve the recipients' food safety knowledge and practices related to consumption of the meals at home. The programs should focus on not only improving food safety knowledge but also changing food safety practices.