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공정 변수에 따른 전열관 U-Bending 소성가공의 형상 특성 연구
곽옥규(Ok-gyu Kwak),김원석(Won-seok Kim),구태완(Tae-wan Ku) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.5
Recently, the need for research in high quality Heat-transfer Tubes of Steam Generators(Alloy690) for life extension of APR1400 equipment is increasing. The U-ending cold working of Heat-transfer Tubes have a great influence on final product quality of steam generators as Pilgering(or Drawing) and Heat treatment p rocess have. There are permissible ovality, minimum wall thickness, tolerance of bending radius, residual stress as quality valuation factors. But, most producers of alloy690 Tubes, they are depending upon their own working experience(skill), so it is not existing for quality improvement to quantitative form control factors of U-bending cold working. Accordingly, through this study, we tried to verify of Analysis methodology as modification and ‘spring back’ condition, and reduce experimentation range, use in base data for U-bending cold working of Alloy690 Heat-transfer Tubes, and analyze the interrelation between quality valuation factors and from control factors of U-bending cold working.
Z-scan 방법에 의한 비정질 As₂S₃ 박막의 비선형 굴절률 측정
김성규(Seong Gyu Kim),이영락(Yeung Lak Lee),곽종훈(Chong Hoon Kwak),최옥식(Ok Shik Choe),이윤우(Yun Woo Lee),송재봉(Jae Bong Song),서호형(Ho Hyung Suh),이일항(El-Hang Lee) 한국광학회 1998 한국광학회지 Vol.9 No.5
비선형 Kerr 매질을 통과하는 Gaussian 빔에 대해 aberration-free approximation과 Huygens-Fresnel 회절 이론을 적용하여 Z-scan 투과율에 대한 해석해를 유도하였다. 비정질 As₂S₃ 박막에 대해 Z-scan 실험을 수행하였으며 이론과 비교하여 잘 일치함을 알았다. 633㎚ 파장에서 측정된 비선형 굴절률 γ의 크기와 기호는 +8.65×10^(-6)㎠/W이며, 또한 먼 영역(far-field)에서 빔 세기분포를 측정하여 자기 집광(self-focusing) 효과를 가시적으로 확인하였다. We present a theoretical analysis of Gaussian beam propagation in nonlinear Kerr media by using aberration-free approximation and Huygens-Fresnel diffraction integral and obtain a simple analytic formular for Z-scan characteristics. Z-scan experiments are carried out on amorphous As₂S₃ thin film and compared with the theory developed, showing good agreement. The sign and the value of γ have been measured at 633 ㎚ to be +8.65×10^(-6)㎠/W. We also measured the far-field intensity profiles, which confirm again self-focusing effect.
용매열처리에 따른 PEDOT:PSS 암모니아 가스 감지막 특성 변화
노왕규 ( Wang Gyu Noh ),염세혁 ( Se-hyuk Yeom ),이왕훈 ( Wanghoon Lee ),신한재 ( Han Jae Shin ),계지원 ( Ji Won Kye ),곽기섭 ( Giseop Kwak ),김세현 ( Se Hyun Kim ),류시옥 ( Si Ok Ryu ),한동철 ( Dong Cheul Han ) 한국센서학회 2017 센서학회지 Vol.26 No.2
Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been extensively studied as the active material in ammonia gas sensor because of its fast response time, high conductivity and environmental stability. It is well known that a post annealing process for organic devices based on PEDOT:PSS significantly increases the device performance. In this study, we propose the solvent annealing of PEDOT:PSS and investigated its effects. As a results, post solvent annealing on PEDOT:PSS lead to the surface chemical and physical properties change. These changes result in improved conductivity of the PEDOT:PSS. In additional, ammonia sensitivity of solvent annealed PEDOT:PSS become higher than pristine polymer film. The enhancement is mainly caused by the depletion of gas barrier PSS and structural re-forming PEDOT networks. We believe that the post solvent annealing is a promising method to achieve highly sensitivity PEDOT:PSS films for applications in efficient, low-cost and flexible ammonia gas sensor.
Investigation of Properties of CaO Added Wrought Mg-Zn-Y and Mg-Y-Zn Alloys
Lim, Hyun Kyu,Kwak, Tae Yang,Yang, Won Seok,Yoo, Young Gyu,Kim, Dae Guen,Yoon, Young Ok,Kim, Shae K. Trans Tech Publications, Ltd. 2014 Materials science forum Vol.783 No.-
<P>In this study, the effect of CaO as alloying element on Mg-Zn-Y and Mg-Y-Zn alloys were investigated to develop wrought magnesium alloys available for aeronautic components. The evaluation for the effect of CaO addition in these alloy systems was performed by the processing map development, the tensile test, and the ignition temperature measurement. The addition of CaO changed the hot workability and improved the ignition resistance of both Mg-Zn-Y and Mg-Y-Zn alloys. Although the mechanical properties of CaO added Mg-Zn-Y alloy were lower than those of Mg-Zn-Y alloy, the CaO addition in Mg-Y-Zn alloy enhanced the ductility of the alloy. The effect of metallic Ca addition in these alloy systems were investigated to be compared with the CaO addition.</P>
구태완,Jin-Hyun Cha,Yu-Beom Kim,Ok-Gyu Kwak,Won-Seok Kim,강범수 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.10
Steam generator is one of enormous heat exchangers that use heat energy derived from a reactor of nuclear power plant for generating steam. The steam obtained is drained into a turbine, and plays an important role for power generation. The heat transfer tubes of each steam generator used in a pressurized water reactor (PWR) are composed of about 8,000 ~ 13,000 U-shaped tubes. These tubes act as the structural material and the thermal boundary. Furthermore, these tubes account for about 70% of the cooling surface area, transmitting thermal energy between the high-temperature (about 320°C), high-pressure (about 157 Kgf/cm2) primary coolant derived from the reactor and the secondary coolant, which is at about 220°C and 60 Kgf/cm2, from the secondary system. These heat transfer tubes used in the steam generator within the PWR were fabricated from seamless tubes of stainless steel (SUS304L), Alloy 600 and Alloy690. In this study, numerical and experimental investigations are carried out on the U-bending process for fabricating heat transfer tubes from long straight SUS304L tubes. In the numerical simulation, 3-dimensional finite element analysis is performed using ABAQUS Explicit/Implicit. In detail, process parameters such as the angular speed, U-bending period, and bending angle taking into account elastic recovery after cold U-bending are considered. Additionally, experimental investigations are conducted to verify the suitability of the predicted U-shaped geometries in terms of the ovality and wall thickness of the U-shaped heat transfer tubes.
Cho, Hee Kyung,Kim, So-Yeon,Choi, Mi Jung,Baek, Seung Ok,Kwak, Sang Gyu,Ahn, Sang Ho The Korean Neurosurgical Society 2016 Journal of Korean neurosurgical society Vol.59 No.2
Objective : Lumbar disc herniation can induce sciatica by mechanical compression and/or chemical irritation. The aim of this study was to compare the effects of GCSB-5 (Shinbaro$^{(R)}$) and NSAIDs on pain-related behavior and on the expressions of microglia, astrocytes, CGRP, TRPV1, IL-6, and CX3CL1 in a rat model of lumbar disc herniation. Methods : 112 male Sprague-Dawley rats underwent implantation of nucleus pulposus to a dorsal root ganglion (DRG). Rats were divided into five groups as follows; a saline group (the vehicle control group) (n=27), a 10 mg/kg aceclofenac group (the aceclofenac group) (n=22), and 100, 300 or 600 mg/kg GCSB-5 groups (the GCSB-5 100, 300, or 600 groups) (n=21 for each group). Rats were tested for mechanical allodynia at 3 days after surgery and at 1 day, 3 days, 7 days, 14 days, 21 days, 28 days, 35 days, 42 days, 49 days, and 56 days after treatment commencement. Immunohistochemical staining of microglia (Iba1), astrocytes (GFAP), CGRP, and TRPV1, and PCR for IL-6 and CX3CL1 were performed on spinal dorsal horns and DRGs at 56 days after medication commencement. Results : After 56 days of GCSB-5 300 administration, mechanical withdrawal thresholds were significantly increased (p<0.05), and immunohistochemical expressions of Iba1, GFAP, CGRP, and TRPV1 were reduced than other groups, but this difference was not statistically significant. Conclusion : These results indicate GCSB-5 reduces mechanical allodynia and downregulates neuroglial activity and the expressions of CGRP and TRPV1 in the spinal segments of a rat model of lumbar disc herniation.
( Eun Soo Kim ),( Yoo Jin Lee ),( Byung Ik Jang ),( Kyeong Ok Kim ),( Eun Young Kim ),( Hyun Seok Lee ),( Seong Woo Jeon ),( Sang Gyu Kwak ) 대한내과학회 2018 The Korean Journal of Internal Medicine Vol.33 No.5
Background/Aims: E-health technologies have been implemented for the management of Crohn’s disease (CD). We aimed to identify differences between patient activities at home and at routine clinic visits using a web-based self-reporting CD symptom diary (CDSD) and to determine the impact of this disparity on clinical outcomes. Methods: Patients with CD from three tertiary hospitals were invited to assess their symptoms at least once a week using CDSD. We identified patients who showed disparities in disease activity (high activity at home but normal at the next hospital visit) and evaluated clinical outcomes of these patients such as unscheduled visits due to flares using Kaplan-Meier analyses. Results: One hundred and forty-three patients recorded their symptoms weekly for at least 3 consecutive months and were included. Forty-eight patients (33.6%) showed disparate disease activities between at home and at the next outpatient clinic visit. The cumulative risk of unscheduled visits was significantly higher in this disparity group than in the concordant group (p = 0.001). Disparity in activity (p = 0.003), and anti-tumor necrosis factor use (p = 0.002) were independent risk factors of unscheduled visits due to disease flares. Conclusions: Disparity in disease activity is considerable in CD patients and is related to the risk of unscheduled hospital visit.