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Formability Enhancement of Al-Mg Sheet by Using Hydro-Mechanical Forming
Kwon, Yong Nam,Kim, Sang Woo,Lee, Young Seon Trans Tech Publications, Ltd. 2014 Key Engineering Materials Vol.622 No.-
<P>Hydro-mechanical forming of Al sheet was investigated in the present study in order to fabricate automotive part having a complicated shape using Al 5052 alloy with a conventional formability which has been known to be quite lower compared to deep drawing steels. We have designed the hydro-mechanical forming in which Al sheet was drawn to a kind of preform step following gas blow forming for final accurate geometry. In order to judge a formability enhancement of Al sheet in terms of forming process, model geometry came from a practical automotive part which had quite depth with complicated curvatures, which was proven that a single sheet forming could not gave a successful part. Experimentally, we succeeded to make the model part with accurate dimension. The optimum forming conditions for respective forming steps were considered most important technical features of this hydro-mechanical. Also, the effort to avoid detrimental microstructure evolutions was given and discussed for a practical application.</P>
Nam, Taek-kyun,Park, Seung-won,Park, Yong-sook,Kwon, Jeong-taik,Min, Byung-kook,Hwang, Sung-nam The Korean Neurosurgical Society 2015 Journal of Korean neurosurgical society Vol.46 No.6
Objective : This study investigates the role of a burr hole and calvarial bone marrow-derived stem cells (BMSCs) in a transient ischemic brain injury model in the rat and postulates a possible mechanism for the efficacy of multiple cranial burr hole (MCBH) surgery in moyamoya disease (MMD). Methods : Twenty Sprague-Dawley rats (250 g, male) were divided into four groups : normal control group (n=5), burr hole group (n=5), ischemia group (n=5), and ischemia+burr hole group (n=5). Focal ischemia was induced by the transient middle cerebral artery occlusion (MCAO). At one week after the ischemic injury, a 2 mm-sized cranial burr hole with small cortical incision was made on the ipsilateral (left) parietal area. Bromodeoxyuridine (BrdU, 50 mg/kg) was injected intraperitoneally, 2 times a day for 6 days after the burr hole trephination. At one week after the burr hole trephination, brains were harvested. Immunohistochemical stainings for BrdU, CD34, VEGF, and Doublecortin and Nestin were done. Results : In the ischemia+burr hole group, BrdU (+), CD34 (+), and Doublecortin (+) cells were found in the cortical incision site below the burr hole. A number of cells with Nestin (+) or VEGF (+) were found in the cerebral parenchyma around the cortical incision site. In the other groups, BrdU (+), CD34 (+), Doublecortin (+), and Nestin (+) cells were not detected in the corresponding area. These findings suggest that BrdU (+) and CD34 (+) cells are bone marrow-derived stem cells, which may be derived from the calvarial bone marrow through the burr hole. The existence of CD34 (+) and VEGF (+) cells indicates increased angiogenesis, while the existence of Doublecortin (+), Nestin (+) cells indicates increased neurogenesis. Conclusion : Based on these findings, the BMSCs through burr holes seem to play an important role for the therapeutic effect of the MCBH surgery in MMD.
Change of heating value, pH and FT-IR spectra of charcoal at different carbonization temperatures
Sung Min Kwon,Jae Hyuk Jang,Seung Hwan Lee,Sang Bum Park,Nam Hun Kim 한국목재공학회 2013 목재공학 Vol.41 No.5
To understand transition characteristics from wood to charcoal, Quercus variabilis wood was carbonized at 200, 250, 300, 340, 540 and 740°C, respectively. Heating value, pH and surface property by FT-IR spectroscopy of the carbonized charcoal were investigated. Heating value and pH increased with increasing carbonization temperature from 4500 cal/g and 4.3 of the control wood to 8,000 cal/g and 9 of the charcoal carbonized at 740°C, respectively. From FT-IR spectroscopy, the peaks from O-H, C-H and C-O stretching disappeared during carbonization at 540 and 740°C. Aromatic skeletal vibration at near 1,506~1,593 cm -1 was repidly increased until 540°C. These results suggest that the chemical and physical characteristics of wood components in cell wall can be easily changed by increasing carbonization temperature and the carbonization seem to be incomplete at temperature below 540°C.