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Correlation Between Constituent Phase and Weld Metal Properties in Ni-Reduced Duplex Stainless Steel
Youngchai Lee,Jae Hee Lee,Joonoh Moon,Tae‑Ho Lee,Changhee Lee 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.8
The intrinsic properties of austenite and ferrite on the mechanical properties and corrosion resistance of the duplex stainlesssteel weld metals was studied by substituting Ni with Mn, N, and Mn + N. The properties of the weldments fabricated throughgas tungsten arc welding (GTAW) were evaluated using tensile test, Vickers hardness, and potentiodynamic polarizationtests. The mechanical properties and corrosion resistance of the constituent phases were measured using nanoindentationand electron probe microanalysis, respectively. The austenite and ferrite phase fractions of the weld metal were maintainedat approximately 50:50, and no harmful phases degraded the properties. Excessive Mn decreased the corrosion resistance; alarge difference in corrosion resistance between austenite and ferrite also decreased the overall corrosion resistance. In thefiller metal in which Ni was replaced with only Mn or N, the austenite became harder than ferrite, as a result cracks initiatedinside the austenite. The tensile test showed that austenite, which became a relatively hard phase compared to ferrite accordingto the chemical composition, increased the yield strength and decreased the elongation of the weld metal.
Park, Jong-Moo,Cho, Yong-Jin,Lee, Kyung Bok,Park, Tai Hwan,Lee, Soo Joo,Han, Moon-Ku,Ko, Youngchai,Lee, Jun,Cha, Jae-Kwan,Lee, Byung-Chul,Yu, Kyung-Ho,Oh, Mi-Sun,Lee, Ji Sung,Lee, Juneyoung,Bae, Hee-J Elsevier 2014 Journal of stroke and cerebrovascular diseases Vol.23 No.10
<P><B>Background</B></P> <P>This study aimed to estimate the population-attributable risks (PARs) of 9 major risk factors for stroke in Korea through a case–control study and to test the feasibility and validity of internet-based control recruitment.</P> <P><B>Methods</B></P> <P>From April 2008 to September 2009, controls were enrolled via internet after providing consent for participation through a web-based survey. The cases included patients who were admitted to the participating centers due to acute stroke or transient ischemic attack within 7 days of onset during the study period. Each control was age- and sex-matched with 2 cases. Adjusted odd ratios, age-standardized prevalence, and PARs were estimated for the 9 major risk factors using the prevalence of risk factors in the control group and the age and sex characteristics from Korea's national census data.</P> <P><B>Results</B></P> <P>In total, 1041 controls were matched to 2082 stroke cases. Because of a shortage of elderly controls in the internet-based recruitment, 248 controls were recruited off-line. The PARs were 23.44%, 10.95%, 51.32%, and 6.35% for hypertension, diabetes, smoking, and stroke history, respectively. Hypercholesterolemia, atrial fibrillation, obesity, coronary heart disease, and a family history of stroke were not associated with stroke. Comparison with education and religion of the control group with that mentioned in the national census data showed a notable difference.</P> <P><B>Conclusions</B></P> <P>The study results imply that internet-based control recruitment for a case–control study requires careful selection of risk factors with high self-awareness and effective strategies to facilitate the recruitment of elderly participants.</P>
Impact of Guidelines on Clinical Practice : Intravenous Heparin Use for Acute Ischemic Stroke
Chung, Jong-Won,Kim, Beom Joon,Han, Moon-Ku,Ko, Youngchai,Lee, SooJoo,Kang, Kyusik,Park, Jong-Moo,Park, Sang-Soon,Park, Tai Hwan,Cho, Yong-Jin,Hong, Keun-Sik,Lee, Kyung Bok,Lee, Jun,Ryu, Wi-Sun,Kim, D Ovid Technologies Wolters Kluwer -American Heart A 2016 Stroke Vol.47 No.6
<P>Background and Purpose-Since its introduction, controversy has existed about the administration of intravenous heparin for the treatment of acute ischemic stroke. We studied trends in the intravenous heparin use during a 6-year time period and the potential influence of clinical guidelines in national language on intravenous heparin administration in Korea. Methods-On the basis of a prospective nationwide multicenter stroke registry, we collected data on patients with acute ischemic stroke who arrived within 7 days of symptom onset during the time period 2008 to 2013. We studied patient demographics, prestroke medical history, stroke characteristics, and stroke treatment. Data from a total of 23 425 patients from 12 university hospitals or regional stroke centers were analyzed. Results-The administration of intravenous heparin steadily decreased throughout the study period: 9.7% in 2008, 10.9% in 2009, 9.4% in 2010, 6.0% in 2011, 4.7% in 2012, and 4.3% in 2013 (P for trend < 0.001). The reduced intravenous heparin use was associated with moderate stroke severity, atrial fibrillation, and stroke of cardioembolic, other-, and undetermined etiology. In a multivariable logistic model, increase of 1 calendar year (odds ratio, 0.89; 95% confidence interval, 0.84-0.95; P < 0.001) and release of clinical practice guidelines in Korean (odd ratio, 0.74; 95% confidence interval, 0.59-0.91; P < 0.01) were independent factors associated with reduction in the frequency of intravenous heparin use. Conclusions-Use of intravenous heparin for acute ischemic stroke treatment has decreased in Korea, and this change may be attributable to the spread and successful implementation of regional clinical practice guidelines.</P>
Air Pollution Is Associated With Ischemic Stroke via Cardiogenic Embolism
Chung, Jong-Won,Bang, Oh Young,Ahn, Kangmo,Park, Sang-Soon,Park, Tai Hwan,Kim, Jae Guk,Ko, Youngchai,Lee, SooJoo,Lee, Kyung Bok,Lee, Jun,Kang, Kyusik,Park, Jong-Moo,Cho, Yong-Jin,Hong, Keun-Sik,Nah, H Ovid Technologies Wolters Kluwer -American Heart A 2017 Stroke Vol.48 No.1
<P>Conclusions-Our findings suggest that the short-term exposure to air pollutants is associated with cardioembolic stroke, and greater care should be taken for those susceptible to cerebral embolism during peak pollution periods. Public and environmental health policies to reduce air pollution could help slow down global increasing trends of cardioembolic stroke.</P>
Ko, Youngchai,Kim, Wook-Joo,Jang, Myung Suk,Yang, Mi Hwa,Park, Jung Hyun,Choi, Sang Il,Chun, Eun Ju,Lee, Soo Joo,Han, Moon-Ku,Bae, Hee-Joon Ovid Technologies Wolters Kluwer -American Heart A 2012 Stroke Vol.43 No.3
<P>Multidetector-row CT (MDCT) is emerging as a new tool for diagnosing aortic atherothrombotic disease (AAD). We elucidated whether MDCT-detected AAD is associated with an increased risk of early ischemic lesion recurrence on diffusion-weighted MRI after ischemic stroke.</P>
잣나무 침엽의 엽록소 함량의 경사면, 수관 부위, 방위의 차이에 따른 엽령별 변화
주영특,김영채,이찬호 경희대학교 환경연구소 1995 環境硏究 論文集 Vol.6 No.-
This study was carried out to examine the variation of chlorophyll contents in the needle of Pinus koraiensis by the difference of micro-environments. The sample needles were collected by the slope divided with lower, middle and upper slopes, tree crown with lower and upper parts, direction with northern and southern, forest edge and surpressed tree. Chlorophyll contents of current, 1 year old, 2 years old and 3 years old needle were measured. Total chlorophyll(a+b) contents of the needle in middle slope was the highest followed by upper and lower slope. In the total chlorophyll(a+b) contents by the needle age, the 1 year old needle showed the highest value and the current year old needles were the lowest. Total chlorophyll(a+b) contents of the needle in lower part of tree crown was higher than in upper part. The needle in northern direction had more chlorophyll than in southern. It was appeared that the chlorophyll contents in the needle of Pinus koraiensis were varied by the difference of micro-environment.
Gitae Park,Kwangjoong Kim,Youngchai Lee,Sangho Uhm,Changhee Lee 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.5
The kinetics of low-temperature tempering in a dissimilar resistance spot weldment between medium Mn transformationinducedplasticity (MT) steel and dual-phase (DP) steel were investigated to interpret the change of failure mode after apaint-baking process. After the isothermal heat treatments with various soaking conditions, the Johnson–Mehl–Avrami (JMA)model describing nucleation and growth kinetics was adopted. The results indicated that the tempering kinetics parameterswere different for each area of the welds. Especially in the coarse-grained heat-affected zone (CGHAZ) in the MT steel,carbon diffusion from martensite to austenite acts as a tempering mechanism at an earlier stage of tempering. Thereafter,the tempering mechanism changes to epsilon carbide precipitation and coarsening. In comparison, the change was relativelyslow or absent in the DP steel CGHAZ and fusion zone because of its lower kinetics parameters. Based on the results ofthis study, ways to improve the cross-tension strength of entire welds in automotive applications of MT steel are discussed.