• Journal of Korean Neurosurgical Society
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• 제59권1호
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• pp.6-10
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• 2016

Objective : The objectives of this study was to determine the incidence and outcomes of procedural rupture (PR) during coil embolization of unruptured intracranial aneurysm (UIA) and to explore potential risk factors. Methods : This retrospective study evaluated 1038 patients treated with coil embolization between January 2001 and May 2013 in a single tertiary medical institute. PR was defined as evidence of rupture during coil embolization or post procedural imaging. The patient's medical records were reviewed including procedure description, image findings and clinical outcomes. Results : Twelve of 1038 (1.1%) patients showed PR. Points and time of rupture were parent artery rupture during stent delivery (n=2), aneurysm rupture during filling stage (n=9) and unknown (n=1). Two parent artery rupture and one aneurysm neck rupture showed poor clinical outcomes [modified Rankin Scale (mRs) >2] Nine aneurysm dome rupture cases showed favorable outcomes ($mRS{\leq}2$). Location (anterior cerebral artery) of aneurysm was associated with high procedural rupture rate (p<0.05). Conclusion : The clinical course of a patientwith procedural aneurysm rupture during filling stage seemed benign. Parent artery and aneurysm neck rupture seemed relatively urgent, serious and life threatening. Although the permanent morbidity rate was low, clinicians should pay attention to prevent PR, especially when confronting the anterior cerebral artery aneurysm.

• Advances in aircraft and spacecraft science
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• 제3권1호
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• pp.61-75
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• 2016

Climate changes brought on by human interventions have proved to be more devastating than predicted during the recent decades. Recognition of seriousness of the situation has led regulatory organisations to impose strict targets on allowable carbon dioxide emissions from automotive vehicles. As a possible solution, it has been proposed that Fibre Metal Laminate (FML) system is used to reduce the weight of future vehicles. To facilitate this investigation, FML based on steel and self-reinforced polypropylene was stamp formed into dome shapes under different blank holder forces (BHFs) at room temperature and its forming behaviour analysed. An open-die configuration was used in a hydraulic press so that a 3D photogrammetric measurement system (ARAMIS) could capture real-time surface strains. This paper presents findings on strain evolutions at different points along and at $45^{\circ}$ to fibre directions of circular FML blank, through various stages of forming. It was found initiation and rate of deformation varied with distance from the pole, that the mode of deformations range from biaxial stretching at the pole to drawing towards flange region, at decreasing magnitudes away from the pole in general. More uniform strain distribution was observed for the FML compared to that of plain steel and the most significant effects of BHF were its influence on forming depth and level of strain reached before failure.

• 설비공학논문집
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• 제20권1호
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• pp.35-41
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• 2008

The radiative heat loss from a receiver of a dish solar collector is numerically investigated. The dish solar collector considered in this paper consists of a receiver and multi-faceted mirrors. In order to investigate the performance comparison of dish solar collectors, six different mirror arrays and four different receivers are considered. A parabolic- shaped perfect mirror of which diameter is 1.40 m is considered as the reference for the mirror arrays. The other mirror arrays which consist of twelve identical parabolic-shaped mirror facets of which diameter are 0.405 m are suggested for comparison. Their reflecting areas, which are 1.545 $m^{2}$, are the same. Four different receiver shapes are a conical, a dome, a cylindrical, and a unicorn type. The radiative properties of the mirror surfaces and the receiver surfaces may vary the thermal performance of the dish solar collector so that various surface properties are considered. In order to calculate the radiative heat loss in the receiver, two kinds of methods are used. The Net Radiation Method that is based on the radiation heat balance on the surface is used to calculate the radiation heat transfer rate from the inside surface of the receiver to the environment. The Monte-Carlo Method that is the statistical approach is adopted to predict the radiation heat transfer rate from the reflector to the receiver. The collector efficiency is defined as the results of the optical efficiency and the receiver efficiency. Based on the calculation, the unicorn type has the best performance in receiver shapes and the STAR has the best performance in mirror arrays except the perfect mirror.

• 지구물리와물리탐사
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• 제8권3호
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• pp.207-217
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• 2005

이 연구에서는 배경 전기전도도 구조가 1차원 층서구조가 아닌 경우에도 적분방정식법을 이용하여 비교적 정확히 모델링 할 수 있는 근사적 방법에 대한 유도 과정을 제시하였으며, 이를 기반으로 전자탐사 수치 모델링을 구현하여 그 정확도 및 효율성에 대해 고찰하였다. 이 연구에서 제시된 방법은 통상적인 적분방정식법과 마찬가지로 1차원 층서구조에서의 Green함수를 그대로 이용할 수 있어 계산 측면에서 매우 효율적이며, 대체적으로 적분방정식을 구성하기 위한 행렬의 크기를 줄일 수 있다. 본 연구에서 개발된 근사 적분방정식 알고리듬을 간단한 수치 모델에 대하여 적용한 결과 정확도는 반응을 구하고자 하는 이상체 부근에서는 거의 차이가 없었으며, 또한 계산 시간에 대한 분석을 통해 이 모델링 알고리듬을 이용하여 역산을 수행하고자 할 때 계산 시간을 대폭 감소시킬 수 있음을 확인하였다. 본 연구에서 제안된 방법은 1차원 층서구조가 아닌 이미 알려진 공통된 구조론 갖는 여러 지질 모델에 대한 전자탐사 반응을 매우 효율적으로 구할 수 있을 것으로 판단된다.

• 한국전산구조공학회논문집
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• 제34권5호
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• pp.339-345
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• 2021

본 논문에서는 우리나라의 중저준위 방폐물 처분을 위한 사일로 형식 지하동굴의 유한요소해석을 수행하였다. 사일로의 벽체부분은 지름 25m의 원형구조이고, 높이는 35m이다. 사일로의 천장부분은 지름 30m의 돔 형식이고, 높이 17.4m의 규모이다. 사일로는 해수면으로부터 -80m에서 -130m에 위치하고 있다. 중저준위 방폐물 처분 1단계 시설로 6개의 사일로가 건설되어 운영되고 있으나, 본 연구에서는 1개의 사일로에 대해서 고려하였다. SMAP-3D 프로그램을 사용하여 2차원 축대칭 유한요소모델과 3차원 유한요소모델을 생성하였다. Generalized Hoek and Brown Model이 수치해석에 적용되었다. 다양한 측압계수(수평방향 현장응력과 수직방향 현장응력의 비)의 변화에 따른 사일로 형식 지하동굴의 유한요소해석을 수행하였으며, 수치해석결과 및 분석결과가 제시되었다.

• 한국지진공학회논문집
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• 제25권2호
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• pp.83-91
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• 2021

Seismic designs for Korean nuclear power plants (NPPs) under earthquakes' design basis are noticed due to the recent earthquake events in Korea and Japan. Japan has developed the technologies and experiences of the NPPs through theoretical research and experimental verification with extensively accumulated measurement data. This paper describes the main features of the design-time history complying with the Japanese seismic design standard. Proper seed motions in the earthquake catalog are used to generate one set of design time histories. A magnitude and epicentral distance specify the amplitude envelope function configuring the shape of the earthquake. Cumulative velocity response spectral values of the design time histories are compared and checked to the target response spectra. Spectral accelerations of the time histories and the multiple-damping target response spectra are also checked to exceed. The generated design time histories are input to the reactor building seismic analyses with fixed-base boundary conditions to calculate the seismic responses. Another set of design time histories is generated to comply with Korean seismic design procedures for NPPs and used for seismic input motions to the same reactor containment building seismic analyses. The responses at the dome apex of the building are compared and analyzed. The generated design time histories will be also applied to subsequent seismic analyses of other Korean standard NPP structures.

• Journal of Korean Neurosurgical Society
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• 제62권2호
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• pp.183-192
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• 2019

Objective : The objective of this study was to analyze patient-specific blood flow in ruptured aneurysms using obtained non-Newtonian viscosity and to observe associated hemodynamic features and morphological effects. Methods : Five patients with acute subarachnoid hemorrhage caused by ruptured posterior communicating artery aneurysms were included in the study. Patients' blood samples were measured immediately after enrollment. Computational fluid dynamics (CFD) was conducted to evaluate viscosity distributions and wall shear stress (WSS) distributions using a patient-specific geometric model and shear-thinning viscosity properties. Results : Substantial viscosity change was found at the dome of the aneurysms studied when applying non-Newtonian blood viscosity measured at peak-systole and end-diastole. The maximal WSS of the non-Newtonian model on an aneurysm at peak-systole was approximately 16% lower compared to Newtonian fluid, and most of the hemodynamic features of Newtonian flow at the aneurysms were higher, except for minimal WSS value. However, the differences between the Newtonian and non-Newtonian flow were not statistically significant. Rupture point of an aneurysm showed low WSS regardless of Newtonian or non-Newtonian CFD analyses. Conclusion : By using measured non-Newtonian viscosity and geometry on patient-specific CFD analysis, morphologic differences in hemodynamic features, such as changes in whole blood viscosity and WSS, were observed. Therefore, measured non-Newtonian viscosity might be possibly useful to obtain patient-specific hemodynamic and morphologic result.

• Journal of Korean Neurosurgical Society
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• 제62권1호
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• pp.27-34
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• 2019

Objective : Stent-assisted coil embolization of intracranial wide-necked aneurysm requires long-term postoperative antiplatelet therapy to prevent in-stent thrombosis. This study aimed to demonstrate results of temporary stent placement for coiling wide necked small intracranial aneurysms, which eliminated need for antiplatelet agents, and to discuss its feasibility and safety. Methods : Data of 156 patients who underwent stent-assisted coil embolization between 2011 and 2014 were retrospectively analyzed. Thirteen cases of temporary stent-assisted coil embolization were included, and their clinical and radiological results were evaluated. Results : The aneurysms treated were all unruptured except one case. All of them had wide neck with mean dome-to-neck ratio of 0.96 and were small-sized aneurysms with mean maximal diameter of 4.2 mm. There was no technical failure in retrieval of stent after completion of embolization of the target aneurysm. Immediate angiography revealed 11 complete and two partial embolization (one residual neck and one residual aneurysm). Two cases encountered thrombosis complication, and they were managed without neurological sequelae. The mean follow-up period was 43 months, angiographic follow-up revealed two cases with minor recurrence, and clinical outcome was good with modified Rankin scale score of 0. Conclusion : Temporary stent-assisted coil embolization of small wide-necked intracranial aneurysm using fully retrievable stent appears safe and effective. Further application and evaluation of this technique in more cases with larger size aneurysm is warranted.

• 한국전산구조공학회논문집
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• 제33권6호
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• pp.391-399
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• 2020

본 연구는 유한요소 해석모델을 이용해 아치 형상을 갖는 석션 상판의 거동을 분석하였다. 평판형 및 아치형 상판의 기본적인 구조성능에 대해 비교함으로써 아치형 상판의 이점을 설명하였다. 또한 아치형 상판의 기하 및 보강재 배치 변화에 따른 거동 변화를 비교하여 각 인자가 상판의 응력 및 변형에 미치는 영향을 조사하였다. 추가로 아치형 상판 가장자리의 경계조건 영향을 수치적으로 분석함으로써, 아치형 상판의 보강재 배치와 가물막이 벽체와의 상호거동 영향을 규명하고 이를 통해 보강형 아치형 상판의 구조설계의 기본 개념을 도출하였다. 평판형 상판과 달리 환형 보강재가 아치형 상판의 구조 거동을 확연히 개선시킬 수 있음을 확인하였으며, 방사 보강재의 역할은 상판 가장자리의 구속상태에 의존적이었다.

• Journal of Korean Neurosurgical Society
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• 제64권2호
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• pp.217-228
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• 2021

Objective : Given the high risk of rebleeding and recurrence of blood blister-like aneurysms (BBAs), we treated ruptured BBAs of the internal carotid artery (ICA) with stent-assisted coil embolization (SAC). This study aimed to evaluate the efficacy and safety of SACs. Methods : We retrospectively reviewed clinical and radiological data from eight patients with ruptured BBAs of the supraclinoid ICA. The modified Rankin Scale (mRS) was used to assess clinical outcomes, while radiological outcomes were evaluated on angiographs. For a pooled analysis, data from literature reporting the outcomes of ruptured BBAs treated with SAC were collected and analyzed in conjunction with our data. Results : In our cohort, the mean Raymond classification score was 1.57±0.53 immediately after initial endovascular treatment. There were no perioperative complications or rebleeding events during the follow-up period. The mean mRS score at patient discharge was 1.00±0.81 and improved to 0.28±0.48 by the last follow-up day. The recurrence rate was 25% with an asymptomatic presentation and successful treatment with multiple stent insertion. Pooled analysis of 76 cases of SAC revealed a complete occlusion rate immediately after treatment of 54.8%, rebleeding rate 7.94%, and recurrence rate 24.2%. Good clinical outcomes with mRS score 0-2 were observed in 89.9% by the last clinical follow-up. Total mortality rate was 7.7%. Conclusion : This treatment appears to not only minimize the hemodynamic burden on the fragile dome specific to this type of aneurysm, but also provides an opportunity for safe and effective treatment in recurrent cases.