Effect of prestrain on hydrogen diffusion and trapping in structural steel

Park, Cheolho,Kang, Namhyun,Kim, Myunghyun,Liu, Stephen Elsevier 2019 Materials letters Vol.235 No.-

<P><B>Abstract</B></P> <P>Hydrogen permeation tests were electrochemically performed to measure hydrogen diffusion and trapping in EH 36 steel. Permeation transients were measured through charging and decaying cycles, for specimens prestrained to varying degrees (0–20%). With increasing prestrain, the effective hydrogen diffusivity (<I>D<SUB>eff</SUB> </I>) decreased, while the total/reversible hydrogen content (<I>C<SUB>o</SUB> </I> and <I>C<SUB>r</SUB>, respectively</I>) increased. The immobile dislocation of the 20%-prestrained specimens decreased <I>D<SUB>eff</SUB> </I> by approximately ten times and increased <I>C<SUB>o</SUB> </I> and <I>C<SUB>r</SUB> </I> by approximately three times. The amount of irreversibly trapped hydrogen (<I>C<SUB>irr</SUB> </I>) remained approximately the same, regardless of the prestrain. The dislocations delay the motion of hydrogen and contain more reversible hydrogen.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hydrogen permeation tests successfully measured the hydrogen diffusivity and concentration. </LI> <LI> As the prestrain increased from 0 to 20%, the effective hydrogen diffusivity decreased. </LI> <LI> Total and reversible hydrogen concentrations increased with the prestrain. </LI> <LI> Irreversible hydrogen showed mostly the same value regardless of prestrain. </LI> <LI> The dislocations delay the motion of hydrogen and contain more reversible hydrogen. </LI> </UL> </P>

Effect of diffusible hydrogen and weld metal microstructure on cold crack susceptibility of high strength weldment

Cheolho Park(박철호),Wanchuck woo(우완측),Namhyun Kang(강남현) 대한용접·접합학회 2019 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2019 No.11

Effect of Prestrain on Hydrogen Embrittlement Susceptibility of EH 36 Steels Using In Situ Slow‑Strain‑Rate Testing

Cheolho Park,Namhyun Kang,Stephen Liu,Juseung Lee,Eunjoon Chun,Sun‑Joon Yoo 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.3

Hydrogen can provide pure and clean energy; however, to use it as an energy source, facilities such as hydrogen carriersand recharging stations need to be constructed. Structural steels are affected by hydrogen embrittlement (HE), and theirsusceptibility to this needs to be investigated prior to their use in construction. Most structural steels are normally fabricatedusing thermomechanical controlled processing, which produces a large dislocation density to increase strength. This studyinvestigated the prestrain effect on HE susceptibility of EH 36 steels using thermal desorption spectroscopy (TDS) andin situ slow-strain-rate testing. Hydrogen was electrochemically charged into specimens, and the reversible hydrogen contentand that relating to trap sites were measured using TDS. With an increase in prestrain, there was increase in the diffusiblehydrogen content; furthermore, with hydrogen charging, there was a drastic reduction in total elongation with an increasein prestrain. In addition, there was an increase in HE susceptibility with an increase in prestrain compared to when an aircondition was employed. Specifically, there was an abrupt increase in HE sensitivity at a prestrain value between 10 and15%; strain hardening was more dominant below a prestrain value of 10%; and HE was more dominant above a prestrainvalue of 15% for EH 36 steels.

Whole cigarette smoke condensates induce ferroptosis in human bronchial epithelial cells

Park, Eun-Jung,Park, Yoo-Jin,Lee, Sang Jin,Lee, Kyuhong,Yoon, Cheolho Elsevier 2019 Toxicology letters Vol.303 No.-

<P><B>Abstract</B></P> <P>Cigarette smoke is responsible for many fatal pulmonary diseases, however, the toxic mechanism is still unclear. In this study, we first confirmed that whole cigarette smoke condensates (WCSC) contain hydrophilic elements, lipophilic and gaseous components. Then, we treated BEAS-2B cells, a normal human bronchial epithelial cell line, at dosages of 0.25, 0.5, and 1% for 24 h and explored the toxic mechanism. Cell viability decreased in a dose-dependent manner, and fission and fusion of mitochondria, damage of endoplasmic reticulume (ER) structures, and formation of autophagosome-like vacuoles were found in cells treated with 1% WCSC. Mitochondrial and ER volumes, lysosomal fluorescence intensity, LDH release, and intracellular ROS levels notably decreased at the highest doses compared with the control, whereas intracellular calcium ion and NO levels were significantly elevated accompanying G2/M phase arrest. Expression of an iron-binding nuclear protein-related gene (pirin) was the most up-regulated in the WCSC-treated cells with enhanced expression of antioxidant-related genes, whereas expression of carbonic anhydrase IX gene, a marker of tumor hypoxia, was the most down-regulated. Additionally, levels of apoptosis (BAX, Apaf-1, and cleavage of caspase-3 and PARP), autophagy (p62 and LC3B-II), ER stress (PERK, IRE-1a, Bip, and CHOP), antioxidant (SOD-1 and SOD-2), and MAPkinase activation (p-ERK, p-p38, and p-JNK)-related proteins were clearly enhanced following exposure to WCSC, whereas expression of several mitochondrial dynamics-related proteins was reduced with dose. Interestingly, expression of ferritin protein (light chain) was dramatically enhanced near the ER along with that of p62 protein. More importantly, the hypoxia inducible factor-1 pathway and ferroptosis were proposed among the 20 terms in KEGG pathway analysis, and secretion of IL-6 and IL-8, which are involved in hypoxia-induced inflammation, were clearly elevated with dose. Taken together, we suggest that WCSC may induce ferroptosis in bronchial epithelial cells via ER stress and disturbed homeostasis in mitochondrial dynamics caused by induction of hypoxia conditions.</P>

Effect of grain size on the resistance to hydrogen embrittlement of API 2W Grade 60 steels using in situ slow-strain-rate testing

Park, Cheolho,Kang, Namhyun,Liu, Stephen Elsevier 2017 Corrosion science Vol.128 No.-

<P><B>Abstract</B></P> <P>This study investigated the grain size effect on the resistance to hydrogen embrittlement (HE) of API 2W Grade 60 steels using in situ slow-strain-rate testing. Hydrogen was electrochemically charged into specimens and the hydrogen content evolved from diffusible hydrogen-trap sites was measured by thermal desorption spectrometry (TDS). The fine-grained (14μm) steel showed superior HE resistance despite exhibiting higher total hydrogen content than the coarse-grained (35μm) steel. Decreasing grain size resulted in a larger grain boundary area, thereby better reducing the normalized amount of diffusible hydrogen trapped per unit length of grain boundary.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hydrogen embrittlement resistance increased with grain size refinement. </LI> <LI> Quasi cleavage fracture decreased displacement significantly with increasing grain size. </LI> <LI> The amounts of hydrogen desorbed from lattice sites and grain boundaries increased with decreasing grain size. </LI> <LI> Fine-grained steel exhibited the lowest normalized hydrogen content in a unit grain boundary. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Microstructural Tuning of Si/TiFeSi₂ Nanocomposite as Lithium Storage Materials by Mechanical Deformation

Park, Hyeong-Il,Sohn, Myungbeom,Choi, Jeong-Hee,Park, Cheolho,Kim, Jae-Hun,Kim, Hansu Elsevier 2016 ELECTROCHIMICA ACTA Vol.210 No.-

<P><B>Abstract</B></P> <P>Melt-spun Si based alloy materials have gained much attention as high capacity anode materials for lithium-ion batteries because of their high capacity and relatively low production cost. However, their long-term cycle performance should be further improved for the commercial success. Herein, it is demonstrated that the electrochemical performances of Si/TiFeSi<SUB>2</SUB> active-inactive nanocomposite anode material could be further improved by the microstructural modification using its mechanical deformation. With the help of high-energy mechanical milling, the microstructural tuned Si/TiFeSi<SUB>2</SUB> nanocomposite material showed a reversible capacity of more than 1000mAhg<SUP>−1</SUP> with stable capacity retention up to 100 cycles. <I>Ex situ</I> X-ray diffraction analysis coupled with potentiostatic intermittent titration technique revealed that refining the sizes of the active Si and inactive TiFeSi<SUB>2</SUB> limited the lithiation of Si phase to Li<SUB>21</SUB>Si<SUB>8</SUB> and this suppressed lithiation led to less volume changes of the electrodes and the improvement of the mechanical integrity of Si/TiFeSi<SUB>2</SUB> nanocomposite material.</P>

중국 CSI 300 주가지수에 대한 MACD 거래전략의 수익성

박철호(Cheolho Park) 중앙대학교 한국전자무역연구소 2023 전자무역연구 Vol.21 No.1

연구목적: 본 연구의 목적은 2012-2021년 기간의 중국 CSI 300 주가지수에 대해 MACD 거래전략의 수익성을 분석하는 것이다. MACD(moving average convergence- divergence)는 기술적 지표의 일종으로 여러 금융시장에서 가격 예측을 위한 기술적 분석(technical analysis)에 흔히 사용된다. 기술적 분석은 가격의 추세나 패턴을 이용하여 미래 가격 움직임을 예측하는 방법이며, 실무에서는 펀드운용자들이나 투자자들에 의해 널리 활용되고 있다. 학술적으로 기술적 분석은 약형(weak-form) 효율적 시장가설을 검증하는 수단으로 사용되고 있다. 논문구성/논리: 수익성 측정을 위해 MACD를 구성하는 4가지 파라미터 조합으로부터 18,221개의 방대한 거래규칙을 생성하고, 순수익률과 샤프비율 기준 하에서 이들의 거래성과를 매입보유전략의 성과와 비교한다. 먼저, 10년의 전체 기간과 각 5년의 두 하위기간에서 가장 우수한 MACD 거래전략이 매입보유전략보다 더 좋은 거래성과를 내는지 살펴본다. 다음으로, 투자자들이 실제로 활용할만한 분석방법으로 과거 일정 기간의 자료에 MACD 거래규칙들을 최적화하고, 각 기간에서 가장 우수한 성과를 보인 거래규칙을 다음 1년 동안의 거래에 적용하여 그 성과를 측정한다. 결과: 각 성과기준 하에서 전체 및 하위 분석기간 동안 MACD 거래전략은 매입보유전략에 비해 훨씬 높은 성과를 거둔 것으로 나타났다. 전체 분석기간에서 MACD 거래전략의 연평균 순수익률과 샤프비율은 각각 13.75%와 0.556이었으며, 이는 매입보유전략의 상응하는 성과인 7.45% 및 0.283과 비교된다. 특히, 첫 번째 하위기간인 2012-2016년 기간에서 MACD 거래전략은 매입보유전략보다 3배 이상 높은 순수익률(연 23.14%)과 4배가량 높은 샤프비율(0.853)을 기록하였다. 최적화 방법을 사용한 표본 외 분석에서도 과거 1년 간의 자료에 최적화된 MACD 거래규칙들은 2021년을 제외한 나머지 9년의 기간에서 모두 양(+)의 순수익률을 거두었으며, 연평균 순수익률과 사프비율은 각각 9.57%와 0.372로 매입보유전략보다 각각 연평균 2.12%, 0.089 높은 것이다. 독창성/가치: 본 논문은 국내 문헌으로서는 처음으로 대표적 추세추종 지표인 MACD를 중국 주식시장을 대표하는 CSI 300 주가지수에 적용하여 그 효과성을 분석하였다는 데 의의가 있다. 방법론적으로, 본 논문은 18,000여 개가 넘는 거래규칙들을 다양한 기간에 걸쳐 최적화하고, 이를 통해 얻는 최적 거래규칙을 이후의 분석기간에 적용하여 그 수익성 여부을 살펴보았다. 국내에서도 중국 주식시장과 관련된 다수의 수익증권과 상장지수펀드(ETF)가 활발히 거래되고 있다는 점에서 본 논문의 연구결과는 실무적으로도 시사하는 바가 크다. Purpose: This study analyzed the profitability of the MACD trading strategy for the Chinese CSI 300 stock index from 2012 to 2021. MACD is a technical indicator commonly used in technical analysis for price prediction in various financial markets. Technical analysis is a method of predicting future price movements using price trends or patterns and is widely used by fund managers and investors. Academically, technical analysis is used as a means of testing the weak-form efficient market hypothesis. Composition/Logic: To measure profitability, 18,221 trading rules were created from the four parameter combinations that make up the MACD, and their performance was compared with that of the buy-and-hold (B&H) strategy under the criteria of the net return and Sharpe ratio. First, we determined whether the best MACD strategy outperformed the B&H strategy over the full 10-yr period and each of the two five-yr sub-periods. Next, MACD trading rules were optimized for the data of a certain period in the past, and the trading rules that showed the best performance in each period were applied to transactions for the next year to measure their performance. Findings: Over the full sample period, the average annual net return and Sharpe ratio of the MACD trading strategy were 13.75% and 0.556, respectively, compared to the corresponding performance of the B&H strategy of 7.45% and 0.283. In the first sub-period, from 2012 to 2016, the MACD trading strategy recorded a net return that was three times higher than that of the B&H strategy and a sharpe ratio that was four times higher than that of the B&H strategy. Even in the out-of-sample analysis using the optimization method, the MACD trading rules optimized for the previous year achieved positive net returns in all nine years except for 2021 and outperformed the B&H strategy. Originality/Value: This study is significant in that it analyzed the effectiveness of the MACD for the first time in Korean literature by applying it to the Chinese CSI 300 stock index. Methodologically, we optimized more than 18,000 trading rules over several in-sample periods and applied the optimal rules to the subsequent period to see whether they were profitable. The findings in this study have great practical implications in that a number of beneficiary certificates and exchange-traded funds related to the Chinese stock market are also actively traded in Korea.

상장리츠의 수익, 위험, 그리고 재무적 특성: 2010~2015

박철호 ( Park Cheolho ),이재우 ( Lee Jaewoo ) 한국부동산분석학회 2016 不動産學硏究 Vol.22 No.3

This article examines the risk-return characteristics of Real Estate Investment Trusts (REITs) listed on the Korea Exchange (KRX) from 2010 to 2014, a period of stagnant growth in the real estate and equity markets. Two indexes composed of publicly traded REITs have slightly higher returns, risk and Sharpe ratios relative to the KOSPI200 equity index but lower returns, higher risk and lower Sharpe ratios relative to the KRW Cash government bond index. The REITs also have weak positive correlations with the equity index but weak negative correlations with the government bond index, illustrating their diversification potential within the framework of a mixed-asset portfolio. We employ the Sharpe-Lintner CAPM, the Fama-French three-factor model and the Carhart four factor model to measure REITs` exposure to systematic risk factors and evaluate their risk adjusted performance. Overall, the market premium alone appears to have statistically significant effects on the excess returns of REITs. Self-managed REITs with more volatile prices and lower dividend yields tend to have higher beta coefficients. Finally, we look into correlations between REITs` financial metrics and their systematic and unsystematic risks. Results show that the interest coverage ratio, market capitalization and dividend yield have moderate to strong negative correlations with unsystematic risks whereas the interest coverage ratio and market capitalization have moderate negative correlations with the beta coefficient. This finding underscores the importance of factors such as business profitability and stability when managing or investing in REITs.

Al-Si 도금된 1.5 GPa 급 핫스탬핑 강의 수소확산

박철호(Cheolho Park),강남현(Namhyun Kang) 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.11

자동차의 경량화를 위해 요구되는 철강의 강도가 높아지면서 수소 지연 파괴가 드러나고 있다. 수소취성 감수성은 철강의 강도에 따라 증가하며, 특히 약 1,000MPa 이상인 고강도 강의 경우 일정 시간이 지나면 수소취성에 의한 균열이 발생하여 갑자기 절단되는 지연파괴(delayed fracture)가 일어난다. 특히 차량 구조부 고강도 강에 수소취성이 발생한 상태에서 충돌이 발생하는 경우 심각한 사고가 될 수 있다. 수소취성 가능성을 예측하고자, 도금유무에 따른 수소확산 거동을 측정하였으며, 핫스탬핑 전과 후의 미세조직의 변화 및 수소확산거동 차이를 확인하였다.

대리모계약에 대한 유효성 논란과 법리분석

박철호(Park, CheolHo) 한양법학회 2009 漢陽法學 Vol.28 No.-

Today the advancement of life scientific technique contributed it solves a sterility effectively. It does so, it is this possibility of the artificial pregnancy such as the Artificial Insemination, the in vitro fertilization-embryo transfer, the gamete intrafalopian transfer etc. The birth of the child who leads the surrogate mother became accomplished. But the surrogate mother contract appears and the problems which forecast it cannot entirely before are proposed, There is to surrogate mother contract, the surrogate mother and the client where becomes the mother legally changes. The problem of many law will be able to occur. Each nations are taking the position which differs each other in about permission and prohibition of surrogate mother system. However the surrogate mother occurs from all countries, the nation which permits a surrogate mother contract or the nation which forbids a surrogate mother contract. Our country is not legal provision to about the surrogate mother contract. It does to entrust in interpretation of civil law. The legal interpretation as a matter of surrogate mother contract violates in the 103 provision of civil law. And so, the multiple position as invalidity thought a surrogate mother contract. But forbidding a surrogate mother contract restricts the desire of race preservation. Also the surrogate mother contract is contracted majority actually. The illegal behavior is promoted is containing a problem consequently. This Article is composed 6 part. The first and last part are introduction and conclusion. The second part is a meaning and background of surrogate mother contract. The third part is a argument in about effect of surrogate mother contract. The forth part is a juridical relation of surrogate mother contract. The fifth part is a our country legislation trend in about surrogate mother contract.