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Surface wrinkle defect of carbon steel in the hot bar rolling process
Kwon, Hyuck-Cheol,Lee, Ho-Won,Kim, Hak-Young,Im, Yong-Taek,Park, Hae-Doo,Lee, Duk-Lak Elsevier 2009 Journal of materials processing technology Vol.209 No.9
<P><B>Abstract</B></P><P>It is well known that surface defect is a common problem encountered in the multi-stage hot bar rolling process of carbon steel. In this study, the phenomenon was investigated by simulating the process by the finite element technique to identify the location where the surface defect might occur and checking the surface qualities obtained from the compression tests at various temperatures and strain rates to clarify the important parameter governing the possible surface defect formation. Also, the surface temperature was measured by employing pyrometer to support the experimental observation. The levels of temperature and specific deformation energy obtained from finite element simulations depending on the roll groove geometry were compared with the experimental observation to better understand the formation of the surface defect in the hot rolled bar. Based on this study, the surface defect might be formed by dissipating the excessive deformation energy accumulated by generating the new surface at the lower level of temperature where recrystallization cannot occur. According to this work, the comparison of the specific deformation energy level for determining the instability of the hot working process might be interesting for further investigation.</P>
피부에서 경추 경막외강까지의 거리와 예측인자에 대한 연구
임윤희,권택민,이상석,우승훈,홍기혁 인제대학교 2000 仁濟醫學 Vol.21 No.2
Background: It is important that we know the depth of cervical epidural space beneath skin as the use of cervical epidural block to treatment of chronic pain in the head, neck, and upper extremities, We studied the distance from skin to cervical epidural space (DSES) in adult patients. Method and Materials: Data were gathered from 110 patients who visited pain clinic to have cervical epidural block for the relief of cervical and upper extremity pain. All block were performed using hanging drop method at C6-7 intervertebral space. Results: Mean DSES was 5.12 ± 0.68cm at C6-7 intervertebral space. DSES has not correlated with body weight, height. neck circumference and ponderal index (PI).
Process design for refinement and homogenization of microstructure in bar rolling
Kwon, Hyuck-Chul,Im, Yong-Taek Elsevier 2005 Journal of materials processing technology Vol.167 No.2
<P><B>Abstract</B></P><P>Depending on process design of the bar rolling process, the final microstructure distribution varies. In this final distribution two perspectives should be taken into account: homogenization and refinement. Most of the studies carried out so far are focused on minimization of the grain size but the uniformity of the grain size is also important because the locally coarse grain sizes significantly deteriorate the overall performance of the rolled bar. In this study two criteria are proposed as a measure of the refinement and homogenization of the austenite grain size (AGS) distribution. The effect of process parameters on these two parameters was investigated to determine the major controlling parameter for better process design of round-oval-round pass sequence in the bar rolling under the isothermal and non-isothermal conditions. The investigation revealed that the temperature was the most important controlling parameter and the decrease of initial processing temperature was effective not only in the grain refinement but also in the grain homogenization.</P>
Green tea consumption and risk of stomach cancer: A meta-analysis of epidemiologic studies
Myung, Seung Kwon,Bae, Woo Kyung,Oh, Seung Min,Kim, Yeol,Ju, Woong,Sung, Joohon,Lee, Yeon Ji,Ko, Jeong Ah,Song, Jong Im,Choi, Hyuck Jae Wiley Subscription Services, Inc., A Wiley Company 2009 International journal of cancer: Journal internati Vol.124 No.3
<P>This meta-analysis investigated the quantitative association between the consumption of green tea and the risk of stomach cancer in epidemiologic studies using crude data and adjusted data. We searched MEDLINE, EMBASE and the Cochrane Review in August 2007. All the articles searched were independently reviewed and selected by 3 evaluators according to predetermined criteria. A total of 13 epidemiologic studies were included. When all the case–control and cohort studies were pooled, the relative risks (RR) of stomach cancer for the highest level of green tea consumption when compared with the lowest level of consumption were shown to be 1.10 (95% confidence interval (CI), 0.92–1.32) using the crude data and 0.82 (95% CI, 0.70–0.96) using the adjusted data. In the meta-analyses of case–control studies, no significant association was seen between green tea consumption and stomach cancer using the crude data (RR, 0.79; 95% CI, 0.58–1.07), but green tea was shown to have a preventive effect on stomach cancer using the adjusted data (RR, 0.73; 95% CI, 0.64–0.83). In the meta-analyses of the recent cohort studies, the highest green tea consumption was shown to significantly increase stomach cancer risk using the crude data (RR, 1.59; 95% CI, 1.16–2.18), but no significant association between them was seen when using the adjusted data (RR, 1.04; 95% CI, 0.93–1.17). Unlike the case–control studies, no preventive effect on stomach cancer was seen for the highest green tea consumption in the meta-analysis of the recent cohort studies. Further clinical trials are needed. © 2008 Wiley-Liss, Inc.</P>
Heo, Jin Hyuck,Lee, Seung-Chul,Jung, Su-Kyo,Kwon, O-Pil,Im, Sang Hyuk The Royal Society of Chemistry 2017 Journal of materials chemistry. A, Materials for e Vol.5 No.39
<▼1><P>Highly efficient and thermally stable inverted MAPbI3 and FAPbI3−xBr<I>x</I> perovskite planar solar cells are demonstrated by using a <I>N</I>,<I>N</I>′-bis(phenylmethyl)naphthalene-1,4,5,8-tetracarboxylicdiimide (NDI-PM)-based electron transporting material (ETM) instead of a conventional PCBM-based ETM.</P></▼1><▼2><P>Highly efficient and thermally stable inverted CH3NH3PbI3 (MAPbI3) and HC(NH2)2PbI3−xBrx (FAPbI3−xBrx) perovskite planar solar cells are demonstrated by using a <I>N</I>,<I>N</I>′-bis(phenylmethyl)naphthalene-1,4,5,8-tetracarboxylic diimide (NDI-PM)-based electron transporting material (ETM) instead of a conventional fullerene-based phenyl-C61-butyric acid methyl ester (PCBM) ETM. The MAPbI3 and FAPbI3−xBrx devices with the NDI-PM-based ETM exhibit 18.4% and 19.6% power conversion efficiency under an illumination of 1 Sun (100 mW cm<SUP>−2</SUP>), respectively, which are comparable to the efficiency of PCBM ETM-based ones (18.9% and 20.0%). The improved thermal stability of NDI-based perovskite solar cells is attributed to much stronger hydrogen bonds in the NDI-PM molecular crystals than the PCBM crystals.</P></▼2>