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SAPH440재료의 GMA용접시 용접변수에 따른 인장 강도 특성 평가
김원섭(Won-Seop Kim),이종훈(Jong-Hun Lee),이한섭(Han-Seop Lee Seo),박상흡(Sang-Heup Park) 한국산학기술학회 2019 한국산학기술학회논문지 Vol.20 No.8
본 논문은 자동차 구조용 열간 압연 강재인 SAPH440을 GMAW 겹치기 용접을 하여 용접 변수인 용접 전류, 용접 전압, 이송 속도를 달리하여 인장 특성을 평가하였다. GMAW 공정의 접합 변수에 따라 인장 시험을 수행하기 위하여 겹치기 용접 하여 KS B ISO 9018에 따라 시험편을 제작하여 실험하였다. 각 조건에 따른 비드 외관을 관찰하였고 그에 따른 인장시험을 하여 용접성을 평가하였다. 평가 결과 용접전류가 높을수록 깊은 용입이 형성되는 것을 알 수 있었으나 인장강도 측면에서는 모재부 파단으로 인해 일정 변수 이상부터는 큰 차이는 없는 것으로 확인되었다. 용접전류 200A, 용접 전압 17V의 조건에서와 같이 전압에 비해 전류가 높으면 다량의 스패터가 발생하며 용접이 불안정하고 이로 인해 용접부 파단이 일어나는 것을 확인 하였다. 전압이 높을수록 대체로 결함이 발생 되지 않을 정도의 비드외관을 관찰할 수 있었으며 너무 높은 전압 또한 용접성에 영향을 끼치는 것을 확인하였다. 너무 낮은 전류와 전압의 조건에서는 용접이 정상적으로 되지 않아 인장강도를 측정할 수 없었다. 그러나 용접이 가능한 용접 조건에서는 전류가 증가함에 따라 전압과 이송속도가 증가하더라도 인장강도에는 큰 영향을 미치지 않았다. This study evaluated the tensile properties of SAPH440, a hot-rolled steel for automotive structural applications, based on GMAW lap welding, the welding current, the welding voltage, and the feed rate. Tensile tests were performed according to the joint parameters of the GMAW process, for which specimens were fabricated according to KS B ISO 9018 by lap welding. The bead appearance was observed in each condition, and the weldability was evaluated by the tensile test. Higher the welding current resulted in a deeper weld, but the tensile strength was not significantly different from when the parameter was fixed due to the fracture of the base material. When the current was higher than the voltage, as in the case of a welding current of 200 A and welding voltage of 17 V, a large amount of spatter is generated, the welding is unstable, and the welded part breaks. Higher the voltage resulted in the bead not causing defects in general, and it also affected the weldability. If the current and voltage were too low, the welding was not performed normally, and the tensile strength could not be measured. However, as the current increased, the increase of the voltage and the feed rate did not affect the tensile strength.
Graphene-based crack lithography for high-throughput fabrication of terahertz metamaterials
Won, Sejeong,Jung, Hyun-June,Kim, Dasom,Lee, Sang-Hun,Van Lam, Do,Kim, Hyeon-Don,Kim, Kwang-Seop,Lee, Seung-Mo,Seo, Minah,Kim, Dai-Sik,Lee, Hak-Joo,Kim, Jae-Hyun Elsevier 2020 Carbon Vol.158 No.-
<P><B>Abstract</B></P> <P>Terahertz (THz) nanoantennas have significant potential for versatile applications in THz spectroscopy because of their capability for strong electromagnetic field localization. Electron-beam lithography or focused ion beam machining is typically employed to fabricate nanoantenna structures. These nanolithography methods present limitations in the widespread utilization of THz nanoantennas because of their high cost and low productivity. In this work, we proposed graphene-based crack lithography as a high throughput fabrication method for nanoantenna structures. A double-layer graphene interface was introduced to enable independent control of the nanoantenna dimensions and provide graphene-based nanoantenna structures. We analyzed the underlying mechanism of graphene-based cracking and developed an analytical model governing the geometric parameters of the fabricated nanostructures. As a vital application of the fabricated nanoantenna structures, we demonstrated the highly sensitive detection of <SMALL>D</SMALL>-Glucose molecules. Graphene-based crack lithography can provide a cost-effective method for generating nanoantenna structures with the desired characteristics and can accelerate the development of practical applications of electromagnetic metamaterials.</P> <P><B>Graphical abstract</B></P> <P>Nanoantennas of various materials with desired terahertz resonance characteristics can be readily manufactured on a large scale using the graphene-based crack lithography.</P> <P>[DISPLAY OMISSION]</P>
서호종,김기훈,박성호,최진욱,김광석,고성만,서광섭,김홍자,김호정,허병원,김해경 중앙대학교 의과대학 의과학연구소 2001 中央醫大誌 Vol.26 No.3
Ulcerative colitis(UC)is a disease that affects the mucosal lining of the colon. Epidemiologlcal studies revealed that UC is global in distribution and the incidence has risen in recent decades. The pathogenesis of UC, remains uncertain. However, recent studies have suggested that colonic environment, most notably bacteria flora, genetic susceptibility, mucosal defects, immunologic abnormalities, altered levels of specific cytokine and inflammatory mediators,and dietary factors are implicated. The major symptoms of ulcerative colitis include diarrher, abdominal pain, and hematochezia(rectal bleeding). Ulcerative colitis also may be complicated by many local and systemic disorders as extracolonic symptoms. Erythema nodosum is one of the most frequent dermatologic complications associated with ulcerative colitis. It is an acute, painful, rective skin inflammation of unknown cause. Physicians can disgnose clinically, since there is no accepted histological diagnostic criteria. Conventational therapy is preferred to control causative disease. We authors experienced a case of suppurative erythema nodosum on both shins of ulcerative colitis patient, which was treated with high dose corticosteroids and discharged with clinical improvement of dematologic manifiestation, coincidently controlled acute exacerbation of the bowel disease. So we report this case with a brief literature review.
Association between Perceived Parenting Style and Adolescents’ Attitudes toward Suicide
Seo-Hyun Choi,Sang-Eun Lee,Chai Won Lee,Seri Maeng,Jisung Son,Won-Hyoung Kim,Jae Nam Bae,Jeong Seop Lee,Hyeyoung Kim 대한소아청소년정신의학회 2020 소아청소년정신의학 Vol.31 No.4
Objectives: Adolescent suicide, a major cause of adolescent death, is affected by various factors, including attitudes toward suicide. This study investigated the association between parenting style and adolescents’ attitudes toward suicide and the mediating role of attitude toward suicide between parenting style and suicidal ideation. Methods: We surveyed 1,071 adolescents from eight middle schools in Incheon, Korea. The survey included sociodemographic information, attitudes toward suicide, perception of parenting style, depression severity, and suicidality. Results: Students in the authoritarian parenting group had a more permissive attitude toward suicide compared with the democratic and permissive parenting groups. These students considered that suicide is justified in certain situations and that choosing suicide is an individual’s right. They also had a negative attitude toward talking about suicide or intervening in others’ suicide. This association remained statistically significant after adjusting for the impact of confounding factors that could affect attitudes toward suicide, except for suicidal processes and preparedness to prevent suicide. In the mediation analysis, we observed that some factors of the attitudes toward suicide mediated between authoritarian parenting attitudes and suicidal ideation, namely, suicide as a right, preventability, suicide as normal/common, preparedness to prevent suicide, and resignation. Conclusion: This study revealed the significant impact of parenting style on children’s attitudes toward suicide. Educating parents about the appropriate parenting attitudes–sympathetic and rational–can help prevent youth suicide.
서원섭,정해양 慶熙大學校 레이저 工學硏究所 1995 레이저공학 Vol.6 No.-
Special optical fibers with high Ge contents for fiber Btragg gratings(FBR) have been fabricated by the modified chemical vapor deposition(MCVD) technique. Ge contents of 18 mol% has been confirmed by surface analysis of a fabricated fiber preform. NA of fabricated optical fibers have adjusted to 0.12 for minimizing coupling loss to communication fibers. Propagation loss of 40 dB/Km for fabricated fibers were measured by OTDR.
Effects of PECVD SiO₂ Gate Dielectric Thickness on Recessed AlGaN/GaN MOS-HFETs
Hyun-Seop Kim,Won-Ho Jang,Su-Keun Eom,Sang-Woo Han,Hyungtak Kim,Kwang-Seok Seo,Chun-Hyung Cho,Ho-Young Cha 대한전자공학회 2018 Journal of semiconductor technology and science Vol.18 No.2
We have investigated the interface fixed charge density and the oxide bulk charge density of the metal/PECVD SiO₂/recessed GaN MOS structure. The fabricated AlGaN/GaN-on-Si recessed MOSHFETs exhibited the excellent on/off ratio characteristics. The extracted effective interface fixed charge density and effective oxide bulk charge density for the PECVD SiO₂ deposited on the recessed GaN surface were -5.94 × 10<SUP>11 </SUP>cm<SUP>-2</SUP> and -2.19 × 10<SUP>17</SUP> cm<SUP>-3</SUP>, respectively. The negative bulk charges in the SiO₂ layer were responsible for the positive shift in the threshold voltage as the SiO₂ thickness increased.