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김하성(Hasung Kim),김민수(Minsoo Kim),이형일(Hyungyil Lee),김낙수(Naksoo Kim),김동철(Dongchoul Kim) 대한기계학회 2013 大韓機械學會論文集A Vol.37 No.7
본 연구에서는, 핵연료 지지격자 딤플 굴곡부에 성형결함을 줄이고자, 1차 스탬핑 금형이 추가된 2-step 스탬핑모델을 제시한다. 우선 순수굽힘 변형률과의 비교로, 딤플 굴곡부 변형률의 특성을 조사한다. 이어 2 차원 1-step 기준 스탬핑 유한요소모델을 정하고 이에 상응하는 최대변형률을 구한다. 1차 스탬핑 금형의 설계변수들을 각각 변화시켜 변형률에 대한 목적함수를 구하고, 반응표면법을 이용해 1차 스탬핑 금형의 최적 변수값을 선정한다. 다음으로 이를 3차원 모델에 적용해 2-step 스탬핑 모델의 향상된 성형성을 확인한다. In this study, a 2-step stamping model with an additional 1st stamping tool is proposed to reduce stamping flaws in the curved parts of a dimple in a nuclear fuel spacer grid. First, the strains of curved part of dimple are characterized via a comparison with strain solutions in pure bending. A reference 2D finite element (FE) model of 1-step stamping is then established, and the corresponding maximum strain is obtained. By varying the values of design variables of the 1st stamping tool in the 2-step stamping model, FE solutions are obtained to express the strain as a function of process variables, which provides the optimum values of process variables. Finally, applying these optimum values to a 3D FE model, we demonstrate the enhanced formability of the proposed 2-step stamping model.
김하성(Hasung Kim),김민수(Minsoo Kim),이형일(Hyungyil Lee),김낙수(Naksoo Kim),김동철(Dongchoul Kim) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
In this study, a 2-step stamping model with additional 1st stamping tool is proposed to reduce stamping flaws in the curved parts of dimple in nuclear fuel spacer grid. A reference 2D FE model of 1-step stamping is then established, and corresponding maximum strain is obtained. By varying the values of process variables of 1st stamping tool in 2-step stamping model, FE solutions are obtained to express the strain as a function of process variables, which provides the optimum values of process variables. Finally, applying these optimum values to a 3D FE model, we show the enhanced formability of the proposed 2-step stamping model.
Min Jae Cha,William D Kim,Hoyoun Won,Jaeeun Joo,Hasung Kim,In-Cheol Kim,Jin Young Kim,Seonhwa Lee,Iksung Cho 대한심장학회 2022 Korean Circulation Journal Vol.52 No.11
Background and Objectives: Real-world trends in the utility and type of gatekeeping studies in invasive coronary angiography (ICA) requires further investigation. Methods: We identified outpatients who underwent noninvasive cardiac tests or directly ICA for suspected coronary artery disease (CAD) from the nationwide Korea Health Insurance Review and Assessment Service-National Patient Sample database between 2012 and 2018. Results: Among 71,401 patients, the percentage of patients who were evaluated for suspected CAD was 34.7% for treadmill test (TMT), 4.2% for single-photon emission computed tomography (SPECT), 24.2% for coronary computed tomography angiography (CCTA), 1.6% for multiple gatekeepers, and 32.3% for directly ICA without noninvasive studies. The proportion of CCTA as a gatekeeper showed linear increase, (18.6% in 2012 and 28.8% in 2018; p<0.001), while those of TMT, SPECT, and direct ICA have decreased (p<0.001, p=0.03, and p<0.001, respectively). The overall incidence of downstream ICA after gatekeeper was 13.8% (6,662/48,346), and SPECT showed higher ICA rate in pairwise comparison with TMT and CCTA (p<0.001). Patients who performed gatekeepers before ICA showed higher rate of subsequent PCI (34.7% vs. 32.3%; p<0.001) and CABG (3.5% vs. 1.0%; p<0.001), compared to those who directly underwent ICA, and CCTA was associated with higher revascularization rate after ICA in pairwise comparison with TMT and SPECT (p<0.001). Conclusions: Nationwide database demonstrated that CCTA is utilized increasingly as a gatekeeper for ICA and is associated with high revascularization rate after ICA in outpatients with suspected CAD.
Renormalization of spin excitations in hexagonal HoMnO3 by magnon-phonon coupling
Kim, Taehun,Leiner, Jonathan C.,Park, Kisoo,Oh, Joosung,Sim, Hasung,Iida, Kazuki,Kamazawa, Kazuya,Park, Je-Geun American Physical Society 2018 Physical review. B Vol.97 No.20
<P>Hexagonal HoMnO3, a two-dimensional Heisenberg antiferromagnet, has been studied via inelastic neutron scattering. A simple Heisenberg model with a single-ion anisotropy describes most features of the spin-wave dispersion curves. However, there is shown to be a renormalization of the magnon energies located at around 11 meV. Since both the magnon-magnon interaction and magnon-phonon coupling can affect the renormalization in a noncollinear magnet, we have accounted for both of these couplings by using a Heisenberg XXZ model with 1 /S expansions [ 1 ] and the Einstein site phonon model [13], respectively. This quantitative analysis leads to the conclusion that the renormalization effect primarily originates from the magnon-phonon coupling, while the spontaneous magnon decay due to the magnon-magnon interaction is suppressed by strong two-ion anisotropy.</P>
Financing through Stock Market in Emerging Economy : Do They Lead to Real Investments?
Hasung Jang,Woojin Kim,YoungKyung Ko 한국재무학회 2009 한국재무학회 학술대회 Vol.2009 No.11
This paper evaluates the principal role of a stock market in efficiently allocating resources in an emerging economy. Using a sample of 900 follow-on primary common stock offerings made by Korean publicly traded firms during 2000 to 2007, we find that half of the proceeds are raised through private placements made to creditor banks through debt-equity swaps. Moreover, more than a third of the proceeds raised through public offerings are used to increase equity investments in other (affiliated) firms. We also find that equity issuing firms are generally in bad financial conditions and more likely to get delisted subsequent to the issue especially during the earlier part of the sample period. These findings suggest that the key role of new equities in these markets may be to recapitalize the existing investments or to reshape the overall control structure of a business group in response to external government regulations rather than to finance new real investments.
New Equity Issues in Emerging Economy : Investment Financing or Recapitalization?
Hasung Jang,Woojin Kim,YoungKyung Ko 한국재무학회 2009 한국재무학회 학술대회 Vol.2009 No.08
This paper evaluates the principal role of a stock market in allocating resources in an emerging economy by testing whether new equities are issued to finance new investments or to recapitalize existing investments. Using a sample of 900 follow-on primary common stock offerings made by Korean publicly traded firms during 2000 to 2007, we find that half of the proceeds are raised through private placements made to creditor banks through debt-equity swaps. We also find that equity issuing firms are generally in bad financial conditions, more likely to replace existing debt with the proceeds raised and get delisted subsequent to the issue regardless of the offer type, except for rights offerings which account for only a small fraction. These findings are hard to reconcile with the traditional theories of capital structure, and suggest that the key role of new equities may be to recapitalize the existing investments or facilitate changes in control rather than finance new investments.