• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.648-654
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• 2007

This paper presents the result of a comparison study to evaluate the performance of several semi-active control algorithms for use with large-scale MR damper applied to a building structure under seismic excitation using real-time hybrid test method. Recently, a variety of semi-active control algorithm studies are developed and generally evaluated the performance by using numerical analysis. In this paper real-time hybrid test method was applied to performance evaluating of semi-active control algorithms including a clipped optimal algorithm and the modulated homogeneous friction algorithm.

• 한국미생물·생명공학회지
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• 제23권2호
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• pp.209-213
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• 1995

During the screening of inhibitors of melanin biosynthesis from microbial secondary metabolites, a fungal strain MR-93 which was capable of producing high level of an inhibitor was selected from plant leaf. Based on taxonomic studies, the fungus could be classified as a strain of Trichoderma sp.. The active compound (MR-93D) was purified from the culture broth by Diaion HP-20 column chromatography, ethylacetate extraction, Sephadex LH-20 column chromatography and HPLC. The inhibitor was identified as 4-hydroxy-8-isocyano-l-oxaspiro[4-4]cyclonon-8-en-2- one by spectroscopic methods of UV, $^{1}$H-NMR, ESIMS and IR. MR-93D showed a strong tyrosinase inhibitory activity with 0.03 $\mu$g/m of IC$_{50}$ value. It also inhibited melanin biosynthesis with 35 mm inhibition zone at 30 $\mu$g/paper disc in Streptomyces bikiniensis, a bacterium used as an indicator organism in this work.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 가을 학술발표회 논문집
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• pp.34-40
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• 2004

In this paper, peliminary design procedure of magnetorheological (MR) dampers is developed for controlling the building response induced by seismic excitation. Hysteretic biviscous model which is simple and can describe the hysteretic characteristics of MR damper is used for parametric studies. The capacity of MR damper is determined as a portion of not the building weight but the lateral restoring force. A method is proposed for the optimal placement and number of MR dampers, and its effectiveness is verified by comparing it with the simplified search algorithm. Numerical results indicate that the capacity, number and the placement can be reasonably determined using the proposed design procedure.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2006년도 학술발표회 논문집
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• pp.453-460
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• 2006

Stay cables, such as used in cable-stayed bridges, are prone to vibration due to their low inherent damping characteristics. Recently some studies have shown that active and semiactive control system using MR damper can potentially achieve both higher performance levels than passive control system and adaptability with few of the detractions. However, a control system including a power supply, controller, and sensors is required to maximize the performance of the MR damper and this complicated control system is not effective to most of large civil structures. This paper proposes a smart complex damping system which consists of toggle system and MR dampers by introducing electromagnetic induction(EMI) system as an external power source to MR damper. The performance of the proposed damping device has been compared with that of the passive-type control systems employing a MR damper, a linear viscous damper, and EMI system.

• Korean Journal of Radiology
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• 제2권4호
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• pp.239-242
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• 2001

Nonketotic hyperglycinemia (NKH) is a rare metabolic brain disease caused by deficient activity of the glycine cleveage system. Localized proton MR spectroscopy (echo-time 166 msec), performed in an infant with the typical clinical and biochemical features of neonatal NKH, showed a markedly increased peak intensity at 3.55 ppm, which was assigned to glycine. Serial proton MR spectrosocpic studies indicated that glycine/choline and glycine/total creatine ratios correlated closely with the patient's clinical course. Proton MR spectroscopy was useful for the non-invasive detection and monitoring of cerebral glycine levels in this infant with NKH.

• 대한자기공명의과학회:학술대회논문집
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• 대한자기공명의과학회 2003년도 제8차 학술대회 초록집
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• pp.37-37
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• 2003

To assess the merits and demerits of postcontrast fat-suppressed (FS) brain MR imaging in children in the evaluation of various enhancing lesions, compared with postcontrast conventional or Magnetization Transfer (MT) imaging. 대상 및 방법： We reviewed patients with enhancing lesion on brain MR imaging who underwent both FS imaging and one of conventional or MT imaging as a postcontrast T1-weighted brain MR imaging. Inclusion criteria of our study were as follows： MR studies should be peformed within one-year interval and showed no significant interval change of imaging findings. Thirty-four patients (21 male, 13 female; mean age, 8 years) with 43 enhancing lesions (19 intra-axial, 19 extra-axial, and 5 orbital location) were included in this study, Twenty-one pairs of FS and conventional imaging, and 15 pairs of FS and MT imaging were available. Two radiologists visually assessed the lesion conspicuity and the presence of flow or susceptibility artifacts in a total of 36 pairs of MR imaging by consensus. For 21 measurable lesions (19 pairs of FS and conventional imaging, 5 pairs of FS and MR imaging), contrast ratio between the lesion and the normal brain( ［SIlesion-SIwater］/[SInormal brain-SIwater]) were calculated and compared.

• Journal of Korean Neurosurgical Society
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• 제47권3호
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• pp.203-209
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• 2010

Objective : The purpose of study was to evaluate the feasibility of brain magnetic resonance (MR) images of the rat obtained using a 1.5T MR machine in several blood-brain barrier (BBB) experiments. Methods : Male Sprague-Dawley rats were used. MR images were obtained using a clinical 1.5T MR machine. A microcatheter was introduced via the femoral artery to the carotid artery. Normal saline (group 1, n = 4), clotted autologous blood (group 2, n = 4), triolein emulsion (group 3, n = 4), and oleic acid emulsion (group 4, n = 4) were infused into the carotid artery through a microcatheter. Conventional and diffusion-weighted images, the apparent coefficient map, perfusion-weighted images, and contrast-enhanced MR images were obtained. Brain tissue was obtained and triphenyltetrazolium chloride (TTC) staining was performed in group 2. Fluorescein isothiocyanate (FITC)-labeled dextran images and endothelial barrier antigen (EBA) studies were performed in group 4. Results : The MR images in group 1 were of good quality. The MR images in group 2 revealed typical findings of acute cerebral infarction. Perfusion defects were noted on the perfusion-weighted images. The MR images in group 3 showed vasogenic edema and contrast enhancement, representing vascular damage. The rats in group 4 had vasogenic edema on the MR images and leakage of dextran on the FITC-labeled dextran image, representing increased vascular permeability. The immune reaction was decreased on the EBA study. Conclusion : Clinical 1.5T MR images using a rat depicted many informative results in the present study. These results can be used in further researches of the BBB using combined clinical MR machines and immunohistochemical examinations.

• Design & Manufacturing
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• 제13권3호
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• pp.12-18
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• 2019

Fluid jet polishing is a method of jetting a fluid to polish a concave or free-form surface. However, the fluid jet method is difficult to form a stable polishing spot because of the lack of concentration. In order to solve this problem, MR fluid jet polishing system using an abrasive mixed with an MR fluid whose viscosity changes according to the intensity of a magnetic field is under study. MR fluid jet polishing is not easy to formulate for precise optimal conditions and material removal due to numerous fluid compositions and process conditions. Therefore, in this paper, quantitative data on the factors that have significant influence on the machining conditions are presented using various simulations and the correlation studies are conducted. In order to verify applicability of the fabricated MR fluid jet polishing system by nozzle diameter, the flow pattern and velocity distribution of MR fluid and polishing slurry of MR fluid jet polishing were analyzed by flow analysis and shear stress due to magnetic field changes was analyzed. The MR fluid of the MR fluid jet polishing and the flow pattern and velocity distribution of the polishing slurry were analyzed according to the nozzle diameter and the effects of nozzle diameter on the polishing effect were discussed. The analysis showed that the maximum shear stress was 0.45 mm at the diameter of 0.5 mm, 0.73 mm at 1.0 mm, and 1.24 mm at 1.5 mm. The cross-sectional shape is symmetrical and smooth W-shape is generated, which is consistent with typical fluid spray polishing result. Therefore, it was confirmed that the high-quality surface polishing process can be stably performed using the developed system.

• Investigative Magnetic Resonance Imaging
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• 제10권1호
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• pp.8-15
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• 2006

목적 : 저산소성 뇌손상의 자기공명영상(MR) 소견을 유병기간 및 예후와 연관 지어 알아보고자 하였다. 대상 및 방법 : 임상적으로 저산소성 뇌손상으로 진단된 환자 18명의 19예의 MR을 대상으로 분석하였다. MR은 저산소증 발생 후 1일에서 20일(평균 8.6일)사이에 시행되었으며, 대상환자의 T1 및 T2 강조영상에서 비정상 고신호강도 병변의 위치, 뇌부종의 동반 유무 및 시간경과와 예후에 따른 병변의 양상을 분석하였다. 결과 : 전체 19예의 MR영상에서, T2 강조영상에서의 고신호강도 병변은 기저핵(15예, 78.9%), 뇌피질(13예, 68.4%), 뇌백질(9예, 47.4%), 시상(6예, 31.6%), 소뇌(4예, 21.1%), 뇌간(1예, 5.3%)의 순으로 관찰되었다. 뇌피질의 병변은 모든 경우 심부회색질에도 이상소견을 동반 하였으며 양측성, 미만성의 병변을 보였고, 뇌피질 대부분 또는 두정 후두엽에 국한되어 나타났다. 뇌피질 및 심부회색질의 T2 강조영상에서의 고신호는 급성기(6일이내)부터 아급성기(6일이후)에 걸쳐 1예를 제외한 전 예에서 다양한 정도로 있었다. 뇌간이나 소뇌의 침범은 비교적 드물었고 모두 뇌피질의 병변이 동반되어 관찰되었다. 뇌백질의 병변도 대부분 아급성기에 뇌피질과 심부회색질의 병변이 있을 때 발생했지만 양측성 분수경계역 뇌경색의 소견으로 단독 침범한 경우도 1예 있었다. T1 강조영상에서의 고신호강도 병변은 뇌피질 및 심부회색질에 주로 아급성기에 관찰되었으나, 급성기에도 일부 관찰되었다. 뇌부종은 11예에서 급성기, 아급성기에 걸쳐 관찰되었다. 의식이 회복된 환자의 MR에서 뇌피질의 침범이나 뇌부종의 빈도가 적었다. 결론 : 저산소성 뇌손상의 MR소견은 다양하지만, 거의 대부분 뇌피질과 심부 뇌회색질을 침범하는 양측성 미만성의 병변으로 나타났다. 뇌백질의 병변은 아급성기 이후에 주로 나타나나 급성기의 혹은 단독의 병변으로도 나타날 수 있다. 뇌피질의 침범정도가 경미하거나 뇌부종이 미약한 경우 예후가 좋았다.

• Journal of Korean Neurosurgical Society
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• 제43권6호
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• pp.275-280
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• 2008

Objective : In order to assess the incidence of thromboembolic events and their clinical presentations, the present study prospectively examined routine brain magnetic resonance images (MRI) taken within 48 hours after a coil embolization of cerebral aneurysms. Methods : From January 2006 to January 2008, 163 cases of coil embolization of cerebral aneurysm were performed along with routine brain MRI, including diffusion-weighted magnetic resonance (DW-MR) imaging, within 48 hours after the embolization of the aneurysm to detect the silent thromboembolic events regardless of any neurological changes. If any neurological changes were observed, an immediate brain MRI follow-up was performed. High-signal-intensity lesions in the DW-MR images were considered as acute thromboembolic events and the number and locations of the lesions were also recorded. Results : Among the 163 coil embolization cases, 98(60.1%) showed high-signal intensities in the DW-MR imaging follow-up, 66 cases (67.0%) involved the eloquent area and only 6cases (6.0%) showed focal neurological symptoms correlated to the DW-MR findings. The incidence of DW-MR lesions was higher in older patients (${\geq}60$ yrs) when compared to younger patients (<60 yrs) (p=0.002, odd's ratio=1.043). The older patients also showed a higher incidence of abnormal DW-MR signals in aneurysm-unrelated lesions (p=0.0003, odd's ratio=5.078). Conclusion : The incidence of symptomatic thromboembolic attacks after coil embolization of the cerebral aneurysm was found to be lower than that reported in previous studies. While DW-MR imaging revealed a higher number of thromboembolic events, most of these were clinically silent and transient and showed favorable clinical outcomes. However, the incidence of DW-MR abnormalities was higher in older patients, along with unpredictable thromboembolic events on DW-MR images. Thus, in order to provide adequate and timely treatment and to minimize neurological sequelae, a routine DW-MR follow-up after coil embolization of cerebral aneurysms might be helpful, especially in older patients.