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1.
Park Sangwon Nam Hyunbin Na Youngsang Kim Hyoungseop Moon Younghoon Kang Namhyun 《Metals and Materials International》2020,26(5):641-649
Metals and Materials International - This study investigated the influence of the initial grain size on the plastic deformation and tunnel defects that occurred from friction stir welding of... 相似文献
2.
Song HS Bang WG Chung N Cho YS Kim YS Cho MH 《Environmental science & technology》2003,37(16):3531-3536
Ambient urban particulate matter (PM) contains various transition metals. When the PM is inhaled into the lung, not all but some part of metals from the particles might be mobilized to participate in a reaction that can damage various biomolecules, such as DNA and proteins. The dust particle size as well as organic acids may influence the metal mobilization. Thus, the mobilization of the metal from two standard reference materials (SRM; NIST, USA) and urban PM (PM2.5 and PM10) collected in the Seoul area was measured in the presence of artificial or biological chelator with or without reductant. The degree of the mobilization was higher with the artificial or biological chelator than the control with saline. In some cases, a reductant increased the mobilization as much as about 5 times the control without the reductant. Especially, the mobilization of Fe was greatly influenced by the presence of reductants. In general, the degree of the mobilization of the transition metal was higher with PM2.5 than with PM10. Therefore, it is expected that, considering the previously known toxicities of the transition metals, PM2.5 is more damaging to various biomolecules than PM10. The results also suggest that not the total amount but the mobilizable fraction of the metal in the ambient PM should be considered with regard to the toxicity of the urban particulate matter. 相似文献
3.
Reaction properties and interfacial intermetallics for Sn−xAg−0.5Cu solders as a function of Ag content 总被引:1,自引:0,他引:1
Jong-Hyun Lee A-Mi Yu Jeong-Han Kim Mok-Soon Kim Namhyun Kang 《Metals and Materials International》2008,14(5):649-654
Wetting and interfacial reactions were investigated for Sn−xAg−0.5Cu alloys, in which the Ag content had a variation from
x=1.0 to x=4.0. Differential scanning calorimetry (DSC) was used to investigate the range of the melting temperature and the
solidification temperature by measuring the endothermic and the exothermic heat flow, respectively. Low Ag contents increased
the melting temperature ranges and deteriorated the wetting properties such as zero cross time and wetting force measured
at two seconds. The extent of undercooling increased and the thickness of intermetallic compounds (IMC) decreased as the Ag
content decreased. As the Ag content decreased, the initial IMC thickness decreased due to the large undercooling and, during
the solid aging at 170°C, the IMC growth slightly decelerated because of the small diffusion coefficient. For the application
of good drop shock reliability, Sn−Ag−Cu solder of low Ag content should be beneficial due to the restraint of the IMC growth
(Cu6Sn5 and Cu3Sn) and of the coarse plate-like IMC (Ag3Sn). 相似文献
4.
Reliability of flip-chip bonded RFID die using anisotropic conductive paste hybrid material 总被引:1,自引:0,他引:1
A reliability of flip-chip bonded die as a function of anisotropic conductive paste (ACP) hybrid materials, bonding conditions, and antenna pattern materials was investigated during the assembly of radio frequency identification(RFID) inlay. The optimization condition for flip-chip bonding was determined from the behavior of bonding strength. Under the optimized condition, the shear strength for the antenna printed with paste-type Ag ink was larger than that for Cu antenna. Furthermore, an identification distance was varied from the antenna materials. Comparing with the Ag antenna pattern, the as-bonded die on Cu antenna showed a larger distance of identification. However, the long-term reliability of inlay using the Cu antenna was decreased significantly as a function of aging time at room temperature because of the bended shape of Cu antenna formed during the flip-chip bonding process. 相似文献
5.
Hajun Dang Sung-Gyu Park Yixuan Wu Namhyun Choi Jun-Yeong Yang Seunghun Lee Sang-Woo Joo Lingxin Chen Jaebum Choo 《Advanced functional materials》2021,31(49):2105703
Electromagnetic enhancement effects through localized surface plasmon resonance considerably amplify the intensity of incident light when molecules are positioned in the vicinity of miniscule nanogaps. The aggregation of plasmonic nanoparticles synthesized using bottom-up methods has been extensively used to generate hot spots in solutions. These methods assist in obtaining non-periodic plasmonic signals, because the realization of uniform nanogaps through particle aggregation is difficult. Nanostructured substrates with gaps of 20–100 nm have also been fabricated using the top-down approach. However, the fabrication of smaller nanogap templates using these methods is difficult owing to high costs and low throughput. Therefore, a nanodimple array internalized with AuNPs is developed in this study to mitigate the challenges encountered in the bottom-up and top-down approaches. Precise nanogaps are generated by regularly internalizing AuNPs in the cavities of nanodimples through DNA hybridization. Simulations of the electric field distribution indicate that the incorporation of 80 nm-sized AuNPs into a curved nanodimpled Au substrate generate high-density volumetric hot spots within a detection volume, and result in a high plasmonic enhancement factor of 8.25 × 107. The tremendous potential of the proposed plasmonic platform as an SERS-based biomedical diagnostic device is also verified. 相似文献
6.
7.
Changhoon Lee Byunggu Kim Namhyun Kim 《Journal of Mechanical Science and Technology》2000,14(8):900-911
A simple Lagrangian pdf model is proposed with a new numerical algorithm for application in wall-bounded turbulent flows.
To investigate the performance of the Lagrangian model, we minimize model’s dependence on empirical constants by selecting
the simplest model for turbulent dissipation rate. The effect of viscosity is also included by adding a Brownian random walk
calculate the position of a particle. For the no-slip condition at the wall and correct near-wall behavior of velocity, we
develop a new boundary treatment for the particles that strike the wall. By applying the model to a fully developed turbulent
channel flow at low Reynolds number, we investigate the model’s performance through comparison with direct numerical simulation
result. 相似文献
8.
Changhoon Lee Namhyun Kim John Kim 《Journal of Mechanical Science and Technology》2001,15(11):1572-1579
We investigate the possibility of application of the Goore Scheme to turbulence control for drag reduction. In Part I, we examine the performance of the original Goore Scheme by applying it to a simple one-dimensional problem. For the application of the scheme to turbulence control, we extend the scheme’s capability so that it can treat multi-dimensional problems and examine its validity theoretically. The convergence of the extended scheme with a dynamic memory is faster by an order of magnitude than the original scheme. In Part II, we apply the proposed scheme to reduce drag for turbulent channel flows through direct numerical simulation. 相似文献
9.
Yool Byun Sangwon Lee Seong-Moon Seo Jong-taek Yeom Seung Eon Kim Namhyun Kang Jaekeun Hong 《Metals and Materials International》2018,24(6):1213-1220
The effects of Cr and Fe addition on the mechanical properties of Ti–6Al–4V alloys prepared by direct energy deposition were investigated. As the Cr and Fe concentrations were increased from 0 to 2 mass%, the tensile strength increased because of the fine-grained equiaxed prior β phase and martensite. An excellent combination of strength and ductility was obtained in these alloys. When the Cr and Fe concentrations were increased to 4 mass%, extremely fine-grained martensitic structures with poor ductility were obtained. In addition, Fe-added Ti–6Al–4V resulted in a partially melted Ti–6Al–4V powder because of the large difference between the melting temperatures of the Fe eutectic phase (Ti–33Fe) and the Ti–6Al–4V powder, which induced the formation of a thick liquid layer surrounding Ti–6Al–4V. The ductility of Fe-added Ti–6Al–4V was thus poorer than that of Cr-added Ti–6Al–4V. 相似文献
10.
Kinetics of Cr/Mo-rich precipitates formation for 25Cr-6.9Ni-3.8Mo-0.3N super duplex stainless steel
Sang-Ho Byun Namhyun Kang Tae-Ho Lee Sang-Kon Ahn Hae Woo Lee Woong-Seong Chang Kyung-Mox Cho 《Metals and Materials International》2012,18(2):201-207
The amount and composition of Cr-rich (σ) and Mo-rich (χ) precipitates in super duplex stainless steels was analyzed. An isothermal
heat treatment was conducted at temperatures ranging from 700 °C to 1000 °C for up to 10 days. A time-temperature transformation
(TTT) diagram was constructed for the mixture of σ and χ phases. The mixture of the σ and χ phases exhibited the fastest rate
of formation at approximately 900 °C. Minor phases, such as Cr2N, M23C6, and M7C3, were also detected using a transmission electron microscopy (TEM). Also, a continuous cooling transformation (CCT) diagram
was constructed for the mixture of σ and χ phases using the Johnson-Mehl-Avrami equation. Compared with the known CCT diagram
of the σ phase, this study revealed faster kinetics with an order of magnitude difference and a new CCT diagram was also developed
for a mixture of σ and χ phases. The calculated fraction of σ and χ phases obtained at a cooling speed of 0.5 °C/s was in
good agreement with the experimental data. 相似文献