초음파를 이용한 시효재의 기계적 성질 변화에 관한 연구

柳孝善,鄭世喜 全北大學校 1996 論文集 Vol.41 No.-

The purpose of this paper is to investigate the applicability of the ultrasonic technique to the material degradation evaluation and to suggest the correlationship between the ultrasonic characteristics and material degradation. The small punch test using miniaturized small specimen(10×10×0.5^tmm) is adopted for the degradation evaluation of aged material which have similar microstructure like to degraded Cr-Mo steel in service condition. From the test results, it could be known that the ultrasonic attenuation coeffcient(α) characteristics increased according as the material degradation(ΔDBTT_sp)increased. Finally, it can be suggested that the ultrasonic technique using attenuation property is a useful test method to evaluate the degree of material degradation.

Cr-Mo강 시효재의 취화손상 평가를 위한 전기화학적 분극시험에 관한 연구

유효선 韓國非破壞檢査學會 1999 한국비파괴검사학회지 Vol.19 No.6

에너지 변환설비와 관련된 기계구조물의 내열재료는 350℃∼550℃의 온도범위에서 장시간 사용되는데 이때 조직의 결정입계에는 불순물 원소(P, Sn, Sb 등)의 편석과 탄화물의 석출 등으로 인하여 재료의 취화 현상이 발생되고, 그로 인해 입계강도의 저하가 초래된다. 따라서 노후화된 고온설비의 안전성 및 효율적인 운전조건을 확보하고, 취성파괴 방지를 위해서는 취화손상의 정량적 평가는 매우 중요하다. 그러나 가동중인 고온설비에서 파괴시험을 위한 대량의 시험편채취가 거의 불가능한 경우가 대부분이므로 비파괴적인 시험방법이 요구된다. 본 연구에서는 인공시효열처리된 2.25Cr-1Mo강의 비파괴적인 취화손상도 평가를 위해 적정 부식환경하에서 전기화학적 분극시험 방법에 의한 최적의 평가인자를 조사하였다. 또한 전기화학 시험결과들은 준비파괴시험인 SP시험에 의한 취화도 평가결과와 비교되었다. It has been well recognized that a long term service at elevated temperature of 350℃∼550℃ induces embrittlement damage due to carbide precipitation and/or P, Sb and Sn segregation at grain boundaries and thereby deteriorates the grain boundary strength of heat resisting components in the energy-related plants. Therefore, it is very important to assess quantitatively the extent of embrittlement damage of heat resisting components to secure the reliable and efficient service condition and to prevent brittle failure in service. However, because fracture tests are limited in size and number of specimen obtained from the structural components, nondestructive test method is required. In this study, the optimum electrochemical parameters are investigated and discussed to evaluate nondestructive embrittlement damage for aged 2.25Cr-1Mo steels by means of electrochemical polarization test method(ECPTM) in proper corrosive environment. In addition, the electrochemical test results are compared with embrittlement degree evaluated by semi-nondestructive SP test.

다결정 니켈표면과 산소 기체와의 상호 작용

안운선,이순보,부진효,박유용 성균관대학교 기초과학연구소 1986 論文集 Vol.37 No.2

The interaction of the gaseous oxygen molecule with polycrystalline nickel surface has been studied by the XPS through the wide range above the room temperature. For relatively lower oxygen exposure, only an O(1s) peak was observed at 530.2 eV, which is associated with the dissociative adsorption. On the other hand, with increasing oxygen exposures, two peaks was appeared at 529.7eV and 531.3eV. These peaks are attributed to nickel oxide and Ni_2O_3, respectively. The latter oxide is ascribed due to the excess adsorption over the NiO stoichiometry. However at high temperatures above 423K, the dissociative adsorption and oxidation was found to take place simultaneously. As a whole, through these XPS study it is found that the interaction of the oxygen with the polycrystalline nickel surface commences through three steps: the fast dissociative adsorption following slow initiation process, rapid oxidation corresponding to the epitaxial NiO formation, and finally the bulk oxide formation.

파종시기가 다른 일미찰의 등숙 중 호화 특성 비교

김미정, 박효진, 이유영, 김선림, 김정태, 우관식, 권영업, 정일민 忠北大學校 農業科學硏究所 2014 農業科學硏究 Vol.30 No.2

This study was conducted to investigate the pasting properties of waxy corn ‘Ilmichal’ during ripening with different sowing date. Starch content of Ilmichal was increased as matured (p<0.05). Analysis of pasting properties with waxy corn starch using a rapid visco analyser (RVA) showed linear changes in peak viscosity, trough viscosity, final viscosity, breakdown and consistency according to ripening. There were significantly positive correlation between starch content of Ilmichal and peak viscosity (0.39*), trough viscosity (0.58***), final viscosity (0.58***), and consistency (0.57**). Differential scanning calorimerty (DSC). The enthalpy of gelatinization was increased as ripening. But onset and peak temperature were decreased. There were significantly positive correlation between starch content of Ilmichal and onset temperature (0.44*), peak temperature (0.38*), and completion temperature (0.59***), on the other hand, crude protein content presented significantly negative correlation between completion temperature (-0.41*).

HT-60강 용접부의 SCC 및 AE신호특성에 관한 연구

나의균,유효선,김훈 한국비파괴검사학회 2001 한국비파괴검사학회지 Vol.21 No.1

인공해수에서 HT-60강 용접부의 응력부식균열(SCC)과 음향방출(AE)신호특성을 알아보기 위하여 SCC와 AE실험을 동시에 실시하였으며, 양 실험결과를 상호 비교ㆍ분석하였다. 모재의 경우, -0.8V에서 보다 긴 파단수명을 보였고, 용해기구 등으로 인하여 -0.8V에 비해 -0.5V에서 AE가 많이 발생하였다. 그러나 시험편에 가해진 전위 값에 관계없이 최대하중 이후의 영역에서 AE 발생과 큰 진폭의 범위(40~100dB)를 나타내었으며 최대하중 이후에도 AE 발생이 활발하였다. 또한, 보다 크고 많은 균열이 파단면에 형성되었음을 SEM관찰을 통하여 관찰할 수 있었으며, 이들 결과로부터 용접부는 인공해수에서 SCC현상이 가장 심하게 일어나고 있음을 확인할 수 있었다. 후열처리는 용접부의 연화를 초래하였고, 용접재에 비해 부식환경에 대한 민감도를 떨어뜨리는 효과를 가져왔다. In order to characterize the microscopic fracture behaviour of the weldment during stress corrosion cracking(SCC) phenomena, SCC and acoustic emission(AE) tests were carried out simultaneously and the correlation between mechanical parameters obtained from SCC and AE tests was investigated. In the case of base metal, much more AE events were produced at -0.5V than at -0.8V because of the dissolution mechanism before the maximum load. Regardless of the applied voltages to the specimens, however, AE events decreased after the maximum load. In the case of weldment, lots of AE events with larger amplitude range(40~100dB) were produced because of the singularities of weld HAZ in comparison to the base metal and post-weld heat-treated (PWHT) specimens. Numerous and larger cracks for the weldment were observed on the fractured surfaces by SEM examination. From these results, it was concluded that SCC for the weldment appeared most severely in synthetic seawater. Weld HAZ was softened by PWHT which also contributed to the reduced susceptibility to corrosive environment in comparison to weldment.

Ranitidine, Sucralfate, Bismuth Subcitrate 복합제의 흰쥐 위궤양에 대한 치료효과

조태순,조광재,주일로,이선미,유영효 成均館大學校 科學技術硏究所 1994 論文集 Vol.45 No.1

Gastric ulcer disease results when there is an imbalance between aggressive factors(acid secretion) and protective factors(mucosal defence). H_2-receptor antagonists are the most frequently used agents for treatment of gastric ulcer disease. However, use of these products should be determined by potential for adverse effects, drug interactions and cost. Ranitidine, H_2 - receptor antagonist, competitively block the H_Z-receptor on the parietal cell, causing inhibition of gastric acid secretion. Sucralfate and bismuth subcitrate coat ulcer craters and then enhance mucosal defence. Bismuth subcitrate also causes detachment of Helicobacter pylori from the gastric epithelium with subsequent lysis of the bacteria. To estimate effects of the mixture of ranitidine 20mg/kg, bismuth subcitrate 40mg/kg and sucralfate 120mg/kg on aspirin - HCl induced gastric ulcer in rats, gastric ulceration, pH, gastric secretion, free and total acidity, pepsin activity, gastric mucosal hemorrhage were investigated. Results obtained were as follow : 1) The mixture showed remarkable suppression of gastric ulceration, pH, gastric secretion, free and total acidity, pepsin activity, gastric mucosal hemorrhage compared with ranitidine alone. 2) With elapse of time, the mixture showed more increasing inhibitory effects on gastric ulceration, pH, gastric secretion, pepsin activity, gastric mucosal hemorrhage than sucralfate and bismuth subcitrate.

Clinical Practice Guidelines for Managing Frailty in Community-Dwelling Korean Elderly Adults in Primary Care Settings

Hyo-Sun You,Yu-Jin Kwon,Sun Young Kim,Yang Hyun Kim,Ye-Seul Kim,Yonghwan Kim,노용균,Byoungjin Park,Young-Kyu Park,Chang-Hae Park,Joung Sik Son,Jinyoung Shin,Hyun-Young Shin,Bumjo Oh,이재우,Jae-YongShim,Chan 대한가정의학회 2021 Korean Journal of Family Medicine Vol.42 No.6

Aging has become a global problem, and the interest in healthy aging is growing. Healthy aging involves a focus on the maintenance of the function and well-being of elderly adults, rather than a specific disease. Thus, the management of frailty, which is an accumulated decline in function, is important for healthy aging. The adaptation method was used to develop clinical practice guidelines on frailty management that are applicable in primary care settings. The guidelines were developed in three phases: preparation (organization of committees and establishment of the scope of develop-ment), literature screening and evaluation (selection of the clinical practice guidelines to be adapted and evaluation of the guidelines using the Korean Appraisal of Guidelines for Research and Evaluation II tool), and confirmation of recom-mendations (three rounds of Delphi consensus and internal and external reviews). A total of 16 recommendations (five recommendations for diagnosis and assessment, 11 recommendations for intervention of frailty) were made through the guideline development process. These clinical practice guidelines provide overall guidance on the identification, evalua-tion, intervention, and monitoring of frailty, making them applicable in primary care settings. As aging and “healthy ag-ing” become more and more important, these guidelines are also expected to increase in clinical usefulness.

A Study on Ultrasonic Test for Evaluation of Spot Weldability in Automotive Materials

Hyo Sun Yu,Byung Guk Ahn 대한기계학회 1999 KSME International Journal Vol.13 No.11

Cryogenic Fracture Toughness Evaluation for Austenitic Stainless Steels by Means of Unloading Compliance Method

Yu, Hyo-Sun,Kwon, Il-Hyun The Korean Society of Mechanical Engineers 2001 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.15 No.1

Most research to date concerning the cryogenic toughness of austenitic stainless steels has concentrated on the base metal and weld metal in weldments. The most severe problem faced on the conventional austenitic stainless steel is the thermal aging degradation such as sensitization and carbide induced embrittlement. In this paper, we investigate the cryogenic toughness degradation which can be occurred for austenitic stainless in welding. The test materials are austenitic stainless JN1, JJ1 and JK2 steels, which are materials recently developed for use in nuclear fusion apparatus at cryogenic temperature. The small punch(SP) test was conducted to detect similar isothermally aging condition with material degradation occurred in service welding. The single-specimen unloading compliance method was used to determine toughness degradation caused by thermal aging for austenitic stainless steels. In addition, we have investigated size effect on fracture toughness by using 20% side-grooved 0.5TCT specimens.

The comparison of three treatment strategies for Lamivudine-resistant chronic hepatitis B: Lamivudine and adefovir combination therapy, entecavir monotherapy, and adefovir monotherapy (초)

( Eun Sun Jang ),( Jung Hwan Yoon ),( Jeong Hoon Lee ),( Su Jong Yu ),( Eun Ju Cho ),( Hyo Joon Yang ),( Min Sun Kwak ),( Chang Hoon Lee ),( Yoon Jun Kim ),( Chung Yong Kim ),( Hyo Suk Lee ) 대한간학회 2010 Clinical and Molecular Hepatology(대한간학회지) Vol.16 No.3(S)