Effects of Laser and Tungsten Arc Welding Processes on the Thermal Softening and Mechanical Properties of Almag6 Aluminum Alloy

Yeonho Kwak,Tae Hoon Kang,Seung Hwan Lee,Minjung Kang 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.24 No.4

The adoption of aluminum in the mobile industry is driving development of aluminum alloys. Among the additive elements of aluminum alloy, magnesium is a crucial component commonly included in various commercial aluminum alloys. Because of its ability to enhance solid solution strengthening and work hardening, many researchers are investigating methods to increase the magnesium content in aluminum applications. Almag6 contains more than 6 wt% of magnesium and exhibits excellent structural properties; it possesses higher yield and tensile strengths than the commercial 5XXX series of aluminum materials. However, work-hardening alloys are vulnerable to welding heat. In this study, laser and tungsten arc welding processes were performed to study the effect of welding heat on the mechanical and microstructure properties of Almag6. It was found that the mechanical strength and hardness of the welds reduced significantly. Similar to other work-hardening aluminum alloys, the lowest hardness was measured in the fusion zone with a strength of over 200 MPa. Relatively low breaking strengths were measured in the tungsten arc welding specimens owing to grain coarsening in the welds.

저온진공건조 공정에 제습제 적용을 위한 타당성 연구

심연호(Yeonho Sim),강지수(Jisu Kang),변시예(Siye Byun),장영수(Young Soo Chang),강병하(Byung Ha Kang) 대한설비공학회 2016 설비공학 논문집 Vol.28 No.5

This study was conducted to improve the performance of low-temperature vacuum dryer by applying desiccant to cold trap. Performance evaluation was carried out using several desiccants. The amounts of absorption and diffusivity were measured based on analytic model. Results of desiccant performance evaluation revealed that silica-gel had the most excellent performance for conditions of low-temperature vacuum drying process. Silica-gel was applied to cold trap for evaluating the drying performance. The experiment results showed that the drying time was extended as the thickness of sample was increased due to increased heat and mass transfer resistance of drying sample. In addition, as heating plate temperature was increased, drying time was decreased due to increased evaporation pressure of drying sample. Furthermore, drying time with desiccant was decreased approximately 20% than that without desiccant.

Free-Standing Ion-Conductive Gels Based on Polymerizable Imidazolium Ionic Liquids

Kang, Tae Hui,Chae, Hyunho,Ahn, Yeonho,Kim, Dukjoon,Lee, Minjae,Yi, Gi-Ra American Chemical Society 2019 Langmuir Vol.35 No.50

<P>A free-standing ion-conductive gel is formed by spontaneous self-assembly of the amphiphilic ionic liquid 1-tetradecyl-3-methylimidazolium chloride (C<SUB>14</SUB>MIm·Cl) and the cross-linkable monomer 6-hexanediol diacrylate (HDODA) in a mixed solvent of 1-octene, 1-butanol, and water. The ionic conductivity of this ion gel is 24 mS cm<SUP>-1</SUP> at 33 °C. To enhance the mechanical strength of the ion gels, the acrylate ionic liquid 1-(2-acryloyloxyundecyl)-3-methylimidazolium bromide (A-C<SUB>11</SUB>MIm·Br) was added, leading to significant morphological changes of the HDODA phase from spherical, ellipsoid, angular platelets to interconnected with increasing addition of the acrylate ionic liquid and consequent enhancement in the mechanical strength of the resulting ion gels. Small angle X-ray scattering data reveal that the ion gels are composed of bicontinuous phase. The formation of the anisotropic HDODA structures upon introduction of the acrylate ionic liquid was accompanied by a change of the bicontinuous phase to be undulated, which increased the ionic path through the formed film, resulting in reduced ionic conductivity. Such coaxial structured gels may be a promising route for developing highly ion-conductive as well as mechanically stable solid electrolyte systems.</P> [FIG OMISSION]</BR>

Design and Analysis of Collimator in Spectrophotometer for Transmission Spectroscopy of Exoplanets

Yeonho Choi,Kang-Min Kim,Chan Park,Jeong-Gyun Jang,Inwoo Han,Byeong-Cheol Lee,Bi-Ho Jang,Jong-Ung Lee,Eui-Jeong Jeong,Myeong-Gu Park 한국천문학회 2020 天文學會報 Vol.45 No.1

DCM 공법으로 개량된 연약지반의 측방유동을 받는 교대 말뚝기초의 거동 분석에 관한 연구

최연호 ( Yeonho Choi ),강경호 ( Gyeongho Kang ) 대한지질공학회 2020 지질공학 Vol.30 No.2

연약지반 상에 도로성토를 시공할 경우 연약지반에는 편재하중이 작용하게 되어 연약지반의 측방유동이나 활동파괴가 종종 발생하게 된다. 본 연구에서는 연약지반에 설치되는 교대말둑기초의 안정성과 말뚝의 거동특성을 파악하는 것이다. 지반의 측방유동으로 인하여 말뚝에 작용하는 수평하중에 대한 기존연구자들의 연구내용을 파악하고 유한요소해석을 수행하여 교대말뚝기초의 거동특성과 보강효과를 확인하여 측방유동을 받는 교대말뚝기초의 거동을 연구하였다. 압밀도 분석 결과, 압밀 단계에 따라 연약지반 강도증가율에 의해 연약지반의 강도정수인 점착력은 약 1.1~1.8배 증가하였다. 측방유동 검토 결과, 허용수평변위 기준은 3.8 cm를 사용하는 것이 경제적으로나 시공적인 면에서 타당한 것으로 판단되나, 구조물의 중요도 및 지반의 불확실성 등을 고려하여 시공 시 계측을 실시하고 그에 따른 측방유동에 대한 철저한 안전관리가 이루어져야 할 것으로 판단된다. Sand dam is a successful water harvesting method in mountainous areas with ephemeral rivers. The success is dependent on several factors including material type, hydrogeology, slope, riverbed thickness, groundwater recharge, and streamflow. In this study, the effect of a sand dam on the groundwater level in the Chuncheon area, South Korea was assessed using the MODFLOW model. Using the model, multiple scenarios were tested to understand the groundwater head before and after the construction of the sand dam. The effect of groundwater abstraction before and after sand dam construction and the sand material type were also assessed. The results show, the groundwater level increases substantially after the application of a sand dam. The comparison of model outputs, simulated groundwater head before and after sand dam application with and without pumping well, shows a clear difference in the head. The material type has also an effect on the groundwater head. As the conductivity of the material increases, the head showed a significant rise.

Plasmon resonance energy transfer (PRET)-based molecular imaging of cytochrome c in living cells.

Choi, Yeonho,Kang, Taewook,Lee, Luke P American Chemical Society 2009 NANO LETTERS Vol.9 No.1

<P>We describe the development of innovative plasmon resonance energy transfer (PRET)-based molecular imaging of biomolecules in living cells. Our strategy of in vivo PRET imaging relies on the resonant plasmonic energy transfer from a gold nanoplasmonic probe to conjugated target molecules, which creates 'quantized quenching dips' within the Rayleigh scattering spectrum of the probe. The positions of these quantized quenching dips exactly match with the absorption peaks of the target molecule since we intentionally design nanoantennas (i.e., nanoplasmonic probes) to overlap the electronic dipoles of the molecule and the plasmonic resonance dipole of nanoantennas. Such the quenching dips allow quantitative and long-term dynamic imaging of the target molecule without the drawbacks of photobleaching and blinking inherent to fluorescent markers, which cannot provide chemical fingerprints. Compared with other imaging methods, our PRET spectroscopic imaging method allows us to generate nanoscale specific wavelengths of local light sources in living systems via nanoantennas and transmit back the nanospectroscopic imaging data of biochemical activities in living cells. As a first demonstration of in vivo PRET imaging, we performed a visualization of the dynamics of intracellular cytochrome c in HepG2 cells under ethanol-induced apoptosis.</P>

마이크로스트립 가변필터의 설계 및 제작

신연호(Yeonho Shin),고범준(Bumjun Ko),김석휘(Seokhwi Kim),강상기(Sanggee Kang) 한국통신학회 2013 한국통신학회 학술대회논문집 Vol.2013 No.11

용두교 Spliced PSC 거더 인상을 위한 Strongbacks 가설 공법

신연호(Yeonho Shin),이강민(Kang-Min Lee),김인열(In-Yeol Kim),한상민(Sang-Min Han) 한국콘크리트학회 2021 콘크리트학회지 Vol.33 No.6

Selective and sensitive detection of metal ions by plasmonic resonance energy transfer-based nanospectroscopy

Choi, Yeonho,Park, Younggeun,Kang, Taewook,Lee, Luke P. Springer Science and Business Media LLC 2009 Nature nanotechnology Vol.4 No.11

<P>Highly selective and sensitive optical methods for the detection of metal ions have had a substantial impact on molecular biology, environmental monitoring and other areas of research. Here we demonstrate a new method for detecting metal ions that is based on selective plasmonic resonance energy transfer (PRET) between conjugated metal-ligand complexes and a single gold nanoplasmonic probe. In addition to offering high spatial resolution due to the small size of the probe, our method is 100 to 1,000 times more sensitive than organic reporter-based methods. Moreover, it can achieve high selectivity owing to the selective formation of Cu(2+) complexes and selective resonant quenching of the gold nanoplasmonic probe by the conjugated complexes. We expect that PRET-based metal ion sensing could have applications in cellular imaging, systems biology and environmental monitoring.</P>

Additional amplifications of SERS <i>via</i> an optofluidic CD-based platform

Choi, Dukhyun,Kang, Taewook,Cho, Hansang,Choi, Yeonho,Lee, Luke P. Royal Society of Chemistry 2009 Lab on a chip Vol.9 No.2

<P>In this paper, signal amplifications of surface-enhanced Raman scattering (SERS) are realized by an optofluidic compact disc (CD)-based preconcentration method for effective label-free environmental and biomolecular detections. The preconcentration of target molecules is accomplished through the accumulation of adsorbed molecules on SERS-active sites by repeating a ‘filling–drying’ cycle of the assay solution in the optofluidic CD platform. After 30 cycles, the clear and high SERS signal of rhodamine 6G of 1 nM is readily detected. In addition to the preconcentration-based signal amplification by the optofluidic SERS system on the CD platform, we introduce a controlled precipitation of gold nanoparticles by CuSO<SUB>4</SUB> for SERS substrates. This method provides high-throughput, high-sensitive and large-area uniform SERS substrates on the optofluidic CD platform. The uniform SERS signals from different positions in spots of 3 mm<SUP>2</SUP> on the different CDs gives us confidence in the reliability and stability of our SERS substrates.</P> <P>Graphic Abstract</P><P>We present optofluidic SERS on a compact disk (CD) platform which is designed to preconcentrate the molecule of interest <I>via</I> simply repeating ‘filling–drying’ cycles of molecular solutions for SERS signal amplification. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b812067f'> </P>