The eutectic Si microstructure in .%Si alloy was changed from large flakes to fine lamellar when the Sc amount in the alloy reached 0.2 wt.%. 0.8wt.%Sc was optimal in terms of attaining the best modification effect. Study on the distribution of the modifiers and measurement of the surface tension of Al-8.5wt.%Si alloy melt with added Sr, Na, and Sc modifiers, respectively, reveals that Sc modifies eutectic Si by a decrease of surface tension, while Sr and Na modify eutectic Si mainly by an impurity-induced twinning mechanism. Al-8.5wt.%Si-0.4wt.%Sc alloy displayed approximately 50 and 70 % increases in tensile strength and elongation, respectively, over .%Si alloy in the cast state. It also presented approximately 65 and 70 % increases in tensile strength and elongation, respectively, over .%Si alloy at a ppt heat-treated state at 200 o C for 3 h.

Background: Ever since the Korean Red Cross adopted HCV NAT for blood donor screening in 2005, HCV NAT reactive donors have been identified every year. The identification of the clinical features for these HCV NAT reactive donors may be helpful for the treatment and prevention of HCV infection. Methods: We analyzed HCV NAT reactive samples to examine the distribution of HCV RNA genotypes and the quantitative values of 128 and 47 HCV NAT reactive samples in 2007 and 2017, respectively. Results: The dominant genotype of the HCV NAT reactive donors was 1b showing 50.0% (64/128) in 2007 and 44.7% (21/47) in 2017. The genotype 2a was the second most dominant at 40.6% (52/128) in 2007 and 40.4% (19/47) in 2017. The mean titers of HCV RNA were 3.17×106 IU/mL in 2007 and 2.61×106 IU/mL in 2017. More than 90% of the donors showed a range of more than 1,000 IU/mL for the HCV RNA titer. There was no difference of quantitative values in the different genotypes. Conclusion: In this study, the distribution of HCV RNA genotypes in Korean blood donors showed a similar pattern compared to that of the general population. There was no correlation between the quantitative values and genotypes in the HCV NAT reactive blood donors, and there was no significant variation in the distribution of HCV RNA genotypes of the HCV NAT reactive donors between 2007 and 2017. Yet it is thought that the characteristics of HCV NAT reactive samples in other years have to be analyzed to achieve more significant results.

Flexural behavior of printed circuit boards (PCB) is well known for the major failure mechanism under board level or product level mobile phone drop tests. This behavior induces high peeling stress between PCB and IC package. This stress causes failure including both solder joint crack and pad cratering, which leads to malfunction such as phone dead or power off. Therefore, for a more reliable mobile phone design, it is important to accurately predict behavior of the PCB. In the past, isotropic or orthogonal linear elastic model have been used for simulating PCB in finite element analysis. Also, since PCB consists of multiple layers with woven glass fiber epoxy resin composite (FR-4) and copper foils, a multilayered PCB model was developed in order to consider material properties that change along the different plies. In this paper, the isotropic elastoplastic model was employed in order to efficiently predict behavior of PCB. Tensile and flexural test of PCB were conducted initially to evaluate mechanical characteristics and obtain representative material properties. Then, simulation of flexural test was performed to develop the finite element modeling. Finally, a drop test of mobile phone adopted with PCB bare board, which did not include IC packages, was examined. Also, the strain gage was used for measuring strain of PCB. This result was compared with drop simulation results of mobile phone, which used finite element modeling suggested. In conclusion, from an industry standpoint, finite element modeling of PCB using isotropic elasoplastic model was useful and efficient.

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