Long-term investigation of erosion behaviors on metal surfaces by impingement of liquid droplet with high-speed

최덕현,김경훈,김형준 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.3

Understanding wall-thinning erosion of pipelines in nuclear or steam power plants is critically important for predicting and preventinghuman and material accidents. Wall thinning of pipelines in power plants occurs mainly by flow acceleration corrosion (FAC), cavitationerosion (C/E), and liquid droplet impingement erosion (LIE). Wall thinning by FAC and C/E has been well-investigated; however, LIE inplant industries has rarely been studied due to the experimental difficulty of setting up a long injection of highly pressurized air. We designeda long-term experimental system for LIE and investigated the behavior of LIE for three kinds of materials (A106B, SS400,A6061). The main control parameter was the air-water ratio (α), which was defined as the volumetric ratio of water to air (0.79, 1.00,1.72). To clearly understand LIE, the spraying velocity (v) of liquid droplets was controlled larger than 160 m/s and the experiments wereperformed for 15 days. The surface morphology and hardness of the materials were examined every five days. Since the spraying velocityof liquid droplets and their contact area (Ac) on specimens were changed according to the air-water ratio, we analyzed the behavior ofLIE for the materials using the impulse (I), which was defined as I = (α × v) / Ac. Finally, the prediction equations (the erosion rate) forthe LIE of the materials were determined for the air-water ratios.

Applying Multiple Fuzzy Majority of Alternatives for Aggregating Incomplete Preference Judgments in

최덕현 韓國交通大學校 2013 한국교통대학교 논문집 Vol.48 No.-

With the goal to makes the best decision they can, based on all the information they have, as quickly as possible, with the right level of participation and commitment, many organizations employ groups in decision-making. In this study, the extended group decision-making method of the procedure presented by Choi et al.’s1 is presented. Contrary to prior work, the different dominating degrees are calculated for each alternative based on the different fuzzy majority concepts of each decision-maker, considered individually.

전공별 교과목 현황 분석 방법에 관한 연구

최덕현 忠州大學校 2008 한국교통대학교 논문집 Vol.43 No.-

For assuring professional competence of its graduates, educational programs in universities should develop curriculum that has adequate educational elements. This paper suggests a method for analyzing the situation of curriculum design and its application to the context of engineering education programs in a national university in Korea.

안전공학전공 대입전형 간 GPA와 이탈률 비교 연구

최덕현 한국교통대학교 2017 한국교통대학교 논문집 Vol.52 No.-

Recently, various admission systems have been tested as an attempt to reform university admission system. To scrutinize the influence of admission systems on GPA and defection rate, this study conducted statistical tests with 289 students data in safety engineering major. With this purpose, the types of admission system were categorized into regular admission, nonscheduled general admission, admission officer system, and special admission. The results of analysis of variance and cross-tabulation analysis showed that there is significant relationship between admission types and GPA. However, the relationship between admission types and defection rate is not significant in the context of safety engineering major. It seems that the students admitted through admission officer system show pros of low defection rate and cons of non-improvment in GPA.

A Dichotomous Approach for Trust in Social Networking Service

최덕현 한국자료분석학회 2012 Journal of the Korean Data Analysis Society Vol.14 No.5

With the prevalence of social networking service (SNS), there are growing concerns over users giving out too much personal information and the possible leaks and improper use of it. For on-going use of SNS, trust in service provider has been proposed as a serious issue in this field. However, considering the main purpose of SNS use is to build and develop interpersonal relationship, the benevolence/integrity of other users can be more critical determinant for service use continuance. To reflect the property of SNS context, this study proposed a dichotomous approach for trust constructs, in which trust in service provider and trust in other users were examined simultaneously. For an empirical exploration, 268 samples were collected from the users of a social networking site. The results of a multiple regression analysis confirmed that continuance intention in SNS context is influenced by trust in other users rather than by trust in service provider. The results of this exploratory study might be useful for future research on trust construct in SNS context.

급성 Vitamin A 중독으로 인한 간세포의 미세형태학적 변화에 대한 연구

최덕현,방희연,서인수,조태환 慶北大學校 醫科大學 1985 慶北醫大誌 Vol.26 No.1

Vit.A 중독의 간상해 기전을 알아보기 위해 체중 20gm 내외의 생쥐에 vit.A 5,000IU 씩을 매일 근육내에 5일간 주사한 후 간에 야기된 변화를 광학 및 전자현미경으로 검색하였던 바 다음과 같은 소견을 얻을 수 있었다. 광학현미경학적으로는 동양혈관 주변에서 Ito세포의 증식을 볼 수 있었다. 간세포는 별다른 변화를 볼 수 없었으며, Kupffer세포가 두드러져 보였다. 전자현미경적으로 간세포는 SER의 증식, RER의 층상구조의 파괴, 불규칙한 모양을 한 mitochondria의 출현 및 cristae 배열의 불규칙화, 그리고 myelin figure의 출현 등을 볼 수 있었다. Ito세포는 증식하였으며, 이들 세포는 지방적으로 충만되어 있고 어떤 세포는 세포체가 파괴된 것도 보였다. Kupper세포는 지방적을 포함하여 괴사된 Ito세포를 탐식하고 있었다. 동양혈관강 및 Disse강은 국소적으로 이들 괴사세포체, 지방적, 비후된 Kupffer세포 및 증식한 Ito세포로 폐쇄되어 있었으며, 이렇게 양강이 폐쇄된 지역에서 간세포의 변성성 변화가 더 심한 편이었였다. 이상의 성적으로 보아 과량의 vit.A에 의한 간손상은 일차적으로 동양혈관 및 Disse강의 폐쇄때문에 야기된 산소결핍 때문이며, 이들 강의 폐쇄는 증식한 Ito세포 및 이들의 파괴 때문인 것으로 사료된다. 파괴된 세포체를 탐식함으로써 비후된 Kupffer세포 역시 이들 강의 폐쇄에 일익을 담당할 것으로 사료된다. 이와 같이 간세포 손상이 산소결핍에 의한 이차적인 것이라고 해석되지만 myelin figure형성은 vit.A 자체의 직접 작용인 것도 배제할 수 없다. The authors studied the ultrastructural changes of the liver after intramuscular injections of large doses of vitamin A to investigate the mechanism of the hepatotoxicity of hypervitaminosis A. Mice were daily injected by 5,000 IU of vitamin A for 5 days. The results obtained were summarized as follow: Light microscopically, proliferation of Ito cells was noted on the perisinusoidal spaces. Liver cells were intact, but Kupffer cells were more prominent. Electron microscopically, the livers cells showed proliferation of smooth-surfaced endoplasmic reticulum, destruction of lamellar structure of rough-surfaced ER, appearance of irregular shaped mitochondria with irregularity in arrangement of cristae and appearance of myelin figures. Proliferated Ito cells showed increased number of fat droplets with destruction of the cell bodies in certain areas. Kupffer cells phagocytized necrotic Ito cells including their fat droplets. Sinusoidal lumina and Disse spaces were partially obstructed by these necrotic cell debris, fat droplets, enlarged Kupffer cells and proliferated Ito cells, in which areas degenerative changes of the liver cells were more prominent. It is suggested that primary hepatotoxicity of the large amounts of vitamin A is exerted by anoxia resulted from obliteration of the sinusoidal lumina and Disse spaces, due to proliferating Ito cells with destruction of them. Enlargement of Kupffer cells due to phagocytosis of the destructed Ito cells also participates in obliteration of sinusoidal lumina and Disse spaces. Although liver cell changes are secondary due to anoxia, myelin figure formation within the liver cells seems to be direct effects of vitamin A itself.

산업경영공학전공 대입전형 간 GPA와 이탈률 비교 연구

최덕현 한국교통대학교 2016 한국교통대학교 논문집 Vol.51 No.-

In recent years, a variety of admission systems has been tested as an attempt to reform university admission system. To scrutinize the influence of admission systems on GPA and defection rate, this study conducted statistical tests with 279 students data in industrial and management engineering major. With this purpose, the types of admission system were categorized into regular admission, nonscheduled general admission, admission officer system, and special admission. The results of analysis of variance and cross-tabulation analysis showed that there are no significant relationship between admission types and GPA as well as defection rate in the context of industrial and management engineering major. Though not significant, it seems that the students admitted through admission officer system show pros of low defection rate and cons of non-improvment in GPA

A Multi-Dimensional Approach for Understanding Perceived Usefulness in Social Networking Service Context

최덕현 한국자료분석학회 2014 Journal of the Korean Data Analysis Society Vol.16 No.5

With the proliferation of social networking service (SNS), people can experience variety of services such as making posts, viewing others’ posts, sharing interesting contents, replying to others, and playing web games. Taking into account the characteristics of SNS and the roles of its users, we can consider SNS platforms as multi-purpose artifacts. Reflecting this property, this study proposes a multi-dimensional approach for perceived usefulness constructs. Following the previous study on uses and gratification theory, perceived usefulness for utilitarian purposes (i.e., coordination and immediate access) and perceived usefulness for hedonic purposes (i.e., affection and leisure) were examined simultaneously. With an empirical analysis using 259 samples, it was confirmed that the constructs of perceived usefulness can be discriminated into four different dimensions according to those specified purposes. The result of multiple regression analysis showed the differences in the impact of each dimension of perceived usefulness on continuance intention. The results of this exploratory study can be useful for future research on the technology adoption and usability test within SNS context.

Nonalcoholic Fatty Liver Disease and Abdominal Fat Accumulation According to Vitamin D Status in Patients with Type 2 Diabetes

최덕현,정찬희,목지오,김철희,강성구,김보연 대한비만학회 2018 The Korean journal of obesity Vol.27 No.1

Background: Vitamin D deficiency is known to increase the incidence of metabolic syndrome. Nonalcoholic fatty liver disease is a common metabolic disease in patients with type 2 diabetes. This study evaluated nonalcoholic fatty liver disease and abdominal fat accumulation according to 25-hydroxyvitamin D status in patients with type 2 diabetes. Methods: The study comprised 302 patients with type 2 diabetes. Patients were divided into three groups based upon their 25-hydroxyvitamin D status: vitamin D deficient group (<10 ng/mL), vitamin D insufficient group (≥10 to <20 ng/mL) and vitamin D sufficient group (≥20 ng/mL). Patient clinical and laboratory markers were evaluated retrospectively. Results: Visceral fat thickness was significantly higher in the vitamin D deficient group. There were no differences in glycemic control, body mass index, and subcutaneous fat thickness correlated with 25-hydroxyvitamin D status. The prevalence of nonalcoholic fatty liver disease was significantly higher in the vitamin D deficient group compared to the vitamin D sufficient and vitamin D insufficient groups. In multivariate logistic analysis, after adjustment for age, sex, body mass index, glycated hemoglobin and homeostasis model assessment of insulin resistance, patients with type 2 diabetes in the vitamin D sufficient group showed significantly lower odds ratio for nonalcoholic fatty liver disease than those within the vitamin D deficient group. Conclusion: In type 2 diabetes, the vitamin D deficient group showed thicker visceral fat thickness and higher nonalcoholic fatty liver disease prevalence.

경영학전공 대입전형 간 GPA와 이탈률 비교 연구

최덕현 한국교통대학교 2018 한국교통대학교 논문집 Vol.53 No.-

Nowadays, a variety of admission systems have been applied as an attempt to improve university admission system. In this study, for the purpose of scrutinizing the influence of admission systems on GPA and defection rate within business administration major context, statistical tests was conducted with 231 students data. For this study, the types of admission system were categorized into four types (regular admission, nonscheduled general admission, admission officer system, and special admission). The results of analysis of variance and cross-tabulation analysis showed that there is no significant relationship between admission types and GPA. The relationship between admission types and defection rate was not significant in the context of business administration major. Thus, it seems that the customized follow-up services for each admission types are not required for business administration major. In addition, it seems that there are not any urgent necessities for admission systems changes.