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그래핀의 나노스케일 마찰 및 표면 특성에 대한 연구동향
윤민아(Min-Ah Yoon),김광섭(Kwang-Seop Kim),조대현(Dae-Hyun Cho) 한국트라이볼로지학회 2021 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.37 No.5
Since the discovery of single-layer graphene, exploiting graphene’s excellent physical/chemical properties in tribology systems has been a topic of interest in academia over the last few decades. There is no doubt that understanding the underlying friction mechanism of graphite should precede this. Even now, new properties of graphene are being reported in academia, and based on this, studies exploring the origins of graphene’s surface properties and friction characteristics in a wide range of scales are also being performed. From the perspective of lubrication engineering, graphene research can be largely divided into studies that 1) reveal its basic friction mechanism at the nanoscale and 2) explore its application in macroscale sliding systems. At the nanoscale, the basic friction mechanism of graphene is mainly due to its atomic thickness. In this paper, the various research on the nanoscale friction and surface characteristics of graphene is reviewed. Graphene surface properties, such as wettability and surface energy and the basic friction mechanisms of graphene attributed to adhesion, electronphonon scattering, bending stiffness, and the underlying substrate, are summarized. Further, we provide the research outcomes on the superlubricity of graphene. Finally, the potential application and challenges of the superlubricity of graphene are highlighted. Through this, we intend to provide summarized information to researchers interested in the tribological properties of graphene and help set the direction of future research.
경북지역 발달장애아동의 식행동과 영양소 섭취량에 관한 연구
윤민아(Yoon Min-A),최영선(Choi Young-Sun) 韓國營養學會 2012 Journal of Nutrition and Health Vol.45 No.1
This study investigated dietary behavior and nutrient intake in children with developmental disorders as compared with non-disabled children and assessed the relationship between dietary behavior and nutrient intake. The survey was conducted on 118 students (4th and 5th grade) of four special education schools and 244 students of an elementary school (control group). The survey was carried out using a questionnaire and an interview. Of the disabled children, children with a mental disorder comprised 72.9% and those with emotional disorders including autism comprised 26.3%. The average percentages of height and weight to standards for age were significantly lower in the disabled female children as compared with the non-disabled female children. Scores for table utensil handling skills, eating behavior, and an unbalanced diet were lower in the disabled children compared with those in the non-disabled children. Dietary behavior scores were not significantly different by either gender or age in the disabled children. Mean energy intake was less than the estimated energy requirement in both groups. Nutrients taken at less than the recommended intake level were calcium, iron, vitamin A, and folate in both groups. Food behavior score at mealtime, personal hygiene score at mealtime, and an unbalanced diet score were significantly correlated with iron and vitamin A intake in disabled male children. Personal hygiene score at mealtime was significantly correlated with calcium, iron, and vitamin A intake, and unbalanced diet score was significantly correlated with iron and vitamin A intake in disabled female children. Although the nutritional status of disabled children with developmental disorders was appropriate in general, improvement in their dietary behaviors through education and practice would allow them to eat balanced diets with essential nutrients.
비열등성 임상시험에서 독립인 두 비율 차 검정에 대한 비교 연구
윤민,곽민정,Yoon, Min,Kwak, Min-Jung 한국통계학회 2010 응용통계연구 Vol.23 No.6
두 비율비교 비열등성 임상시험(non-inferiority trial)에서의 검정은 두 비율간에 차이가 없다는 영가설에 근거한 정규근사 산출식이 흔히 사용 된다. 본 연구에서는 두 비율차이가 영이 아니라는 가설에서 유도된 Miettinen과 Nurminen이 제안한 우도 스코어검정(likelihood score test)과 Farrington과 Manning의 검정 그리고 비대칭도(skewness)을 보정한 Gart와 Nam이 제안한 검정방법을 소개하고 모의실험을 통하여 제 1종 오류와 검정력을 비교하여 비열등성 임상시험에서 검정방법의 결정에 가이드라인을 제시하고자 한다. Normal approximation methods under the null hypothesis of no difference are frequently used to test the two independent proportions in non-inferiority trials. However, these tests are not appropriate under the null hypothesis of non-zero difference. We review the likelihood score methods proposed by Miettinen and Nurminen, Farrington and Manning, and Gart and Nam and compare the performance of these tests. The simulation study shows that the likelihood score tests under the null hypothesis of non-zero difference have better performance at a Type I error and power than usual normal approximation methods.
윤민,최영수,이윤동,Yoon, Min,Choi, Young-Soo,Lee, Yoon-Dong 한국통계학회 2008 응용통계연구 Vol.21 No.5
확산모형은 금융현상을 모형화하기 위한 방법으로 자주 사용된다. 특히 최근에 제안된 다양한 확산모형들은 정교한 추론방법을 필요로 하게 되고, 이러한 필요성에 따라 정밀도가 높은 여러 가지 추론 방법에 대한 연구가 진행되고 있다. 본 논문에서는 확률편미분방정식에 의하여 표현되는 확산과정의 추론을 위하여 사용되는 여러 가지 방법 중 우도추론법에 대하여 살펴보게 된다. 다양한 우도추론법 중에서도, 근사적 우도추론법의 일종인 추세계수 국소선형근사법을 중심으로 그 수리적 성질을 검토한다. Modeling financial phenomena with diffusion processes is a commonly used methodology in the area of modern finance. Recently, various types of diffusion models have been suggested to explain the specific financial processes, and their related inference methodology have been also developed. In particular, likelihood methods for the efficient and accurate inference have been explored in various ways. In this paper, we review the mathematical properties of an approximated likelihood method, which is obtained by linearizing the drift coefficient of a diffusion process.