• 천문학회보
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• 제44권1호
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• pp.50.1-50.1
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• 2019

In coronagraph images, it is often observed that two successive CMEs merge into one another and form complex structures. This phenomenon, so called CME cannibalism caused by the differences in ejecting times and propagating velocities, can significantly degrade forecast capability of space weather, especially if it occur near the Earth. Regarding this, we attempt to analyze the cases that two CMEs are expecting to meet around 1 AU based on their arrival times. For this, we select 13 CME-CME pairs detected by ACE, Wind and/or STEREO-A/B. We find that 8 CME-CME pairs show a shock structure, which means they already met and became one structure. Meanwhile 5 pairs clearly show magnetic holes between two respective shock structures. Based on detailed investigation for each pair and statistical analysis for all events, we can get clues for following questions: 1) How does the solar wind structure change when they are merging? 2) Are there any systematic characteristics of merging process according to the CME properties? 3) Is the merging process associated with the occurrence of energetic storm particles? 4) What causes errors in calculating CME arrival times? Our results and discussions can be helpful to understand energetic phenomena not only close to the Sun but also near the Earth.

• The Journal of Asian Finance, Economics and Business
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• 제9권1호
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• pp.177-187
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• 2022

Theoretical literature agrees on the interaction between financial instability and economic activity but explains it's dynamic in two points of view: one is that the transmission mechanism occurs in one unique regime and the other reckons a shift of regime leads to the alteration of the transmission mechanism. This study aims to find evidence of the multi-regime transmission for ASEAN developing countries. The author employs the technique of Threshold vector auto regression using the financial stress index standing for financial instability. Monthly data is collected, covering a period long enough with many episodes of high stress in recent decades. There are two conclusions: (1) A financial shock has a negative and stronger impact on economic activity during a high-stress period than it does during a low-stress period; (2) the response of economic activity to a negative financial shock during high-stress periods is stronger than it is during normal times. The findings point to the importance of the financial stress index as an additional early warning indicator for the real economy sector, as well as the positive effect that a reduction in financial stress may have on economic activity, implying the importance of "unconventional" monetary policy in times of high financial stress.

• Journal of Industrial and Engineering Chemistry
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• 제67권
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• pp.347-357
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• 2018

Steady shear response of a magnetorheological fluid (MRF) system containing porous mono-disperse magnetite ($Fe_3O_4$) spheres synthesized by solvothermal method is demonstrated. In applied magnetic field the interaction between the spherical particles leads to form strong columnar structures enhancing the yield strength and viscosity of the MRFs. The yield strengths of the MRFs also scale up with the concentration of magnetic particles in the fluid. Considering magnetic dipolar interaction between the particles the magneto-mechanical response of the MRFs is explained. Unlike metallic iron particles, the low-density corrosion resistant soft-ferrimagnetic $Fe_3O_4$ spherical particles make our studied MRF system efficient and reliable for shock-mitigation/vibration-isolation applications.

• 한국추진공학회지
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• 제14권6호
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• pp.38-44
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• 2010

과팽창 상태의 로켓 노즐에서 발생하는 충격파 경계층 간섭 형태는 엔진 시동 및 정지과정 중 예기치 않은 횡력을 수반한다. 본 연구에서는 비정상 노즐 구동 압력비 변화가 유동장의 천이형태 및 횡력 특성에 어떠한 영향을 미치는지 조사하기 위하여 수치해석적 연구를 수행하였다. 비정상, 축대칭, 압축성 N-S 방정식을 유한 체적법으로 이산화 하였으며, 난류모델은 SST k-${\omega}$을 적용하였다. 엔진 정지 및 시동과정을 모사하기 위하여, NPR은 2~10의 범위에서 계산 하였다. 본 연구의 결과로 박리 유동과 히스테리시스 현상은 구동 압력비에 크게 의존하며, 또한 압력비 변동 시간이 횡력 특성에 지대한 영향을 미칠 수 있음을 알았다.

• Earthquakes and Structures
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• 제18권4호
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• pp.467-480
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• 2020

Concrete rectangular liquid storage tanks are widely used, but there are many cases of damage in previous earthquakes. Nonlinear fluid-structure interaction (FSI) is considered, Mooney-Rivlin material is used for rubber bearing, nonlinear contact is used for sliding bearing, numerical calculation models of no-isolation, rubber isolation, sliding isolation and hybrid isolation concrete rectangular liquid storage tanks are established; dynamic responses of different structures are compared to verify the effectiveness of isolation methods; and influences of earthquake amplitude, bidirectional earthquake and far-field long-period earthquake on dynamic responses are investigated. Results show that for liquid sloshing wave height, rubber isolation cause amplification effect, while sliding isolation and hybrid isolation have reduction effect; displacement of rubber isolation structure is much larger than that of sliding isolation with limiting-devices and hybrid isolation structure; when PGA is larger, wall cracking probability of no-isolation structure becomes larger, and probability of liquid sloshing wave height and structure displacement of rubber isolation structure exceeds the limit is also larger; under bidirectional earthquake, occurrence probabilities that liquid sloshing wave height and structure displacement of rubber isolation structure exceed the limit will be increased; besides, far-field long-period earthquake mainly influences structure displacement and liquid sloshing wave height. On the whole, control effect of sliding isolation is the best, followed by hybrid isolation, and rubber isolation is the worst.

• 한국항공우주학회지
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• 제40권5호
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• pp.375-384
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• 2012

본 연구에서는 초음속 비행체에 나타나는 유동 특성 해석을 위해 1988 Wilcox $\mathcal{k}-{\omega}$ 모델과 2008 Wilcox 모델의 수치 결과를 비교하였다. 충격파 - 경계층 간섭 현상과 램프 주입기 혼합 문제에 대하여 실험결과와 비교, 검토하였다. 또한, 표면 마찰 측정의 기초가 되는 평판 흐름과 전단 층 성장에 대한 상관 관계식도 비교, 분석 하였다. 램프 주입기 케이스에서 최대 주입 질량비는 1988 Wilcox 모델을 이용하였을 때 보다 신뢰성 있는 해석 결과를 예측할 수 있었다. 그러나 충격파 - 경계층 간섭 케이스에 대해서는 2008 Wilcox 모델을 적용하였을 때 더 정확한 해석 결과가 도출됨을 확인하였다.

• Bulletin of the Korean Chemical Society
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• 제29권9호
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• pp.1717-1722
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• 2008

The 70 kDa heat-shock protein (Hsp70) involved in various cellular functions, such as protein folding, translocation and degradation, regulates apoptosis in cancer cells. Recently, it has been reported that the green tea flavonoid (−)-epigallocatechin 3-gallate (EGCG) induces apoptosis in numerous cancer cell lines and could inhibit the anti-apoptotic effect of human Hsp70 ATPase domain (hATPase). In the present study, docking model between EGCG and hATPase was determined using automated docking study. Epi-gallo moiety in EGCG participated in hydrogen bonds with side chain of K71 and T204, and has metal chelating interaction with hATPase. Hydroxyl group of catechin moiety also participated in metal chelating hydrogen bond. Gallate moiety had two hydrogen bondings with side chains of E268 and K271, and hydrophobic interaction with Y15. Based on this docking model, we determined two pharmacophore maps consisted of six or seven features, including three or four hydrogen bonding acceptors, two hydrogen bonding donors, and one lipophilic. We searched a flavonoid database including 23 naturally occurring flavonoids and 10 polyphenolic flavonoids with two maps, and myricetin and GC were hit by map I. Three hydroxyl groups of B-ring in myricetin and gallo moiety of GC formed important hydrogen bonds with hATPase. 7-OH of A-ring in myricetin and OH group of catechin moiety in GC are hydrogen bond donors similar to gallate moiety in EGCG. From these results, it can be proposed that myricetin and GC can be potent inhibitors of hATPase. This study will be helpful to understand the mechanism of inhibition of hATPase by EGCG and give insights to develop potent inhibitors of hATPase.

• 국제지역연구
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• 제14권1호
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• pp.55-76
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• 2010

본 연구는 1995년 1월 04부터 2009년 8월 30일까지 일본의 주식시장과 외환시장의 일별자료를 이용하여 두 시장의 수익률, 변동성 및 상관관계를 분석하였다. 특히, 전체 분석대상 기간을 아시아 금융위기 이전시기, 아시아 금융위기 시기, 그 이후부터 서브프라임 사태에 의한 금융위기 발발이전 시기 그리고 서브프라임사태에 의한 금융위기시기로 각각 구분하여 비교분석하였으며, 실증모형은 이변량(Bivariate) GJR-GARCH(1,1)을 가정하여 추정하였다. 실증분석의 주요한 결과는 다음과 같다. 첫째, 각 시기별로 수익률의 평균방정식과 분산방정식의 추정결과가 상당히 다르게 나타났으며 둘째, 금융위기 시기에 주식시장의 시장비효율성이 증가하고 과거의 예측하지 못한 변동성 충격에 시장이 훨씬 민감하게 반응하며, 특히 나쁜 뉴스에 의한 변동성 충격에 훨씬 많은 영향을 받는 것으로 나타났다. 셋째, 금융위기의 시기 중에서도 변동성 충격, 비대칭성 등의 측면에서 보면 아시아 금융위기 보다는 최근에 발생한 전 세계적 금융위기의 기간에 보다 뚜렷하게 나타났다. 넷째, 전체적으로 두시장의 상관관계는 대체로 정의 관계가 있는 것으로 나타났으며 이는 일본경제가 상대적으로 금융투자처로서의 매력보다는 일본 경제 전체에 실물부문의 중요성이 상대적으로 높기 때문에 나타난 현상으로 보인다. 특히 최근의 서브프라임 사태에 의한 전세계적 금융위기 기간 동안 두시장의 정의 상관관계는 더욱 심화되는 것으로 나타났다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1494-1498
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• 2007

Impulsive shooting noise is basically complex phenomenon which contains the linear and non-linear characteristics. For those reasons, numerical analysis of impulsive shooting noise has the difficulties in control of the numerical stability and accuracy on the simulation. In this research, Wave-number Extended Finite Volume Scheme (WEFVS) is applied to the numerical analysis of impulsive shooting noise. In the muzzle blast flow simulation, the generation of the precursor wave and the induced vortex ring are observed. Consequently, blast wave. vortex ring interaction and vortex ring. bow shock wave interaction are evaluated on the shooting process using the accurate and stable scheme. The sound generation in the interactions can be explained by the vorticity transport theorem. The shear layer is evolved behind the projectiles due to the jet flow. In these computations, the impulsive shooting noise is generated by the complex interaction with shooting process and is propagated to the far-field boundary. The impulsive shooting noise generation can be observed by the applications of WEFVS and analyzed by the physical phenomena.

• 소성∙가공
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• 제25권1호
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• pp.49-55
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• 2016

Electrohydraulic forming (EHF) is a high-speed forming process that uses an electric arc discharge in water. Shock waves resulting from the electric arc discharge are propagated to the blank through water and the blank moves toward the die. Advantages of EHF include improved formability due to the high-speed process and reduction of the bouncing effect. In the current study, a numerical simulation of EHF was developed using LS-DYNA. In the simulation, the model for the electric arc was assumed as an adiabatic gas expansion and an Arbitrary Lagrange-Eulerian (ALE) multi material formulation was used to describe the interaction between the electric arc and the water. In order to model the Fluid-Structure Interaction (FSI), a coupling mechanism was used. The blank of Al 1100-O was simulated using shell elements. The results of the simulation showed that the blank was deformed due to the pressure propagation of water and the bouncing effect did not affect the formability of blank.