• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.12
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• pp.1667-1675
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• 2001

Numerical simulations are carried out for the liquid encapsulant Czochralski(LEC) by imposing a magnetic field. The use of a magnetic field to the crystal growth is to suppress melt convection and to improve the homogeneity of the crystal. In the present numerical investigation, we focus on the range of 0-0.3Tesla strength for the axial and cusped magnetic field and the effect of the magnetic field on the melt-crystal interface, flow field and temperature distribution which are the major factors to determine the quality of the single crystal are of particular interest. For both axial and cusped magnetic field, increase of the magnetic field strength causes a more convex interface to the crystal. In general, the flow is weakened by the application of magnetic field so that the shape of the melt-crystal interface and the transport phenomena are affected by the change of the flow and temperature field.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.8
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• pp.1010-1013
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• 2012

This paper demonstrates the use of the convex optimization to localize the transverse magnetic $B_1^+$ field in regions of interest for recently proposed multi-sectioned alternating impedance coils and the traditional transmission line coil. An approach based on different axial slices to identical RF coils except upper stripline structure is investigated. Electromagnetic simulation results are compared for RF coils and discussed in detail at 7.0 T.

• Proceedings of the KSMRM Conference
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• 2002.11a
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• pp.78-78
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• 2002

Purpose： The purpose of this study is to describe a distributed circuit approach to high frequency volume coil design illustrated with specific coils built accordingly and results obtained from animal studies at 3.0 tesla. Method： All experiments were conducted on 3T MRI system (Medinus Co., Ltd. Korea). The tuned TEM resonator measures 15cm outer diameter. by 10cm inside diameter by 30cm in length. The inside diameter and length were determined by animals body or head size (eg. rats or small dogs, etc.) while the outer diameter was chosen for compactness with some sacrifice of the optimal coil Q predicted for a larger cavity. A spin echo sequence with a TR/TE/flip angle=500/12.4ms/$75^{\circ}$was used to check image qualities with phantom. The breed of rat which used for animal images was Sprague-dawley(SD) and was anesthetic using ketamin hydrochloride 75mg/kg.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.05a
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• pp.11-11
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• 2009

종래의 산업폐수 처리기술로는 중금속 함유 폐수에 수용성의 금속염을 첨가하여 가성소다 혹은 소석회를 이용하여 pH를 조정하고 고분자 응집제를 첨가하여 금속의 수산화물을 생성시켜 이를 부상 혹은 침전시켜 Sludge화하여 제거하는 방법이 주로 사용되고 있다. 그 외 질소, 인, 유기물이 함유된 폐수의 경우에는 Biological Oxidation Techniques, 활성탄 흡착방식이 주로 채택되고 있다.[1-3] 이러한 폐수처리기술은 화학약품 사용량이 과다하고 이는 Sludge 생성량을 증대하고 2차 폐수처리가 필요로 하는 경우가 많고, 처리장이 면적이 넓어야 하고 대용량의 Sludge 제거창치가 필요하여 고비용의 처리공정으로 문제점을 가지고 있다.[2-3] 이에 본 연구에서는 이러한 기존 기술의 문제점을 보완할 수 있고 기존 기술로는 완벽하게 처리하기 곤란한 악성 폐수들에 대한 새로운 고도처리기술로 초전도 마그네트를 이용한 고구배 자기분리기술에 대한 기초연구를 하였다. 본 연구에서 사용한 고구배 자기분리 시스템은 무헬륨 전도냉각방식으로 자기분리를 위해 사용한 필터는 SUS 430 재질의 메쉬 형태로 제작하여 실험하였다. 또한, 자기분리 처리를 위한 전처리 공정으로는 응집제를 첨가하여 자기분리 효율을 높이고자 하였다. 자기분리 처리대상수로는 포항제철에 압연 강판에 사용되는 냉각수를 대상으로 자기분리 처리에 대한 효과를 실험하였다. 또한, 자기분리에 대한 특성을 평가하기 위해 강자성의 $Fe_3O_4$ 미세자성분말을 첨가하여 처리수내의 들어있는 유기물질에 대해 자기분리 자장 및 유속에 대한 처리효율을 미치는 영향을 조사하였다. 자기분리 처리는 1~6 Tesla에서 자기필터는 디스크 형태로 다층으로 연속적으로 적층하였으며, 처리유속은 1~4 l/min으로 하였다. 고농도인 처리폐수를 자가분리 인가 자장에 따라 처리하여 고농도에서는 70%, 저농도에서는 98 %까지 처리되었다. 또한, 자기분리용 필터는 SUS 430 재질의 mesh 망을 사용하였으며 인가자장 및 유속변화에 대한 실험 결과 탁도 및 농도는 필터 크기의 영향은 거의 차이가 없었으며 단지 인가자장 및 유속에 따라서 지수적으로 감소하였다. 자기분리된 용액 내 $Fe_3O_4$ 입도 분석 결과 자기분리 이전에 분포하던 $10\sim20\;{\mu}m$의 입자는 거의 제거되었으며 2 ${\mu}m$ 이하의 입자들은 실험 횟수에 따라 점점 직경이 작은 쪽으로 분포가 좁아졌으며, 마그네타이트의 자화율을 분석한 결과 약 0.8 Tesla에서 포화 되었으며 처리수의 탁도 및 농도가 자장에 따라 감소하는 것으 알 수 있었다.

• Investigative Magnetic Resonance Imaging
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• v.19 no.1
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• pp.31-36
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• 2015

Purpose: To compare the depiction of brain metastases on contrast-enhanced images with 7.0 tesla (T) and at 1.5T MRI. Materials and Methods: Four consecutive patients with brain metastases were scanned on 7.0T whole-body scanner and 1.5T MRI. A 3D T1-weighted gradient echo sequence (3D T1-GRE) at 1.5T (voxel size = $0.9{\times}0.9{\times}1.5mm^3$ after double-dose, gadoterate meglumine, Gd-DOTA) was compared to a 7.0T 3D T1-GRE sequence (voxel size = $0.4{\times}0.4{\times}0.8mm^3$, single-dose Gd-DOTA) in four patients after a 5 minute delay. The number of contrast-enhancing metastases in MPRAGE images was compared in each patient by two radiologists in consensus. We measured contrast ratio of enhancing brain metastases and white matter in 1.5T and 7.0T. Results: In all four patients 7.0T 3D T1-GRE images after single-dose Gd-DOTA and 1.5T after double-dose Gd-DOTA depicted 11 brain metastases equally. In the quantitative analysis of contrast ratios of enhancing brain metastases and white matter, the 1.5T 3D T1-GRE after double-dose showed an increased contrast ratio compared to 7.0T 3D T1-GRE after single-dose ($0.961{\pm}0.571$ versus $0.885{\pm}0.494$; n = 11 metastases). But this difference was not statistically significant (P = 0.711). Conclusion: Our preliminary results indicate that 7.0T single-dose Gd-enhanced images were not different to 1.5T double-dose Gd-enhanced images for the detection of brain metastases.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.27 no.5
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• pp.488-491
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• 2005

A 3-year-old female, 5kg, Shih-tzu developed an acute onset of depression, disorientation, hypersalivation, nystagmus after falling down 2 meter height place. In plain skull radiography, there was fracture line in the frontal and parietal bones and next day magnetic resonance imaging examination was performed. Magnetic resonance imaging of the brain was performed with 3.0 Tesla unit. Under general anesthesia, the dog was placed in prone with its head positioned in a birdcage coil. Transverse, sagittal and coronal fast spin echo images of the brain were obtained with the following pulse sequences: T1 weighted images (TR = 560 ms and TE = 18.6 ms) and T2 weighted images (TR = 3500 ms and TE = 80 ms). Magnetic resonance imaging showed epidural hematoma in the left frontal area resulting in compression of the adjacent brain parenchyma. Left lateral ventricle was compressed secondarily and the longitudinal fissure shifted to the right, representing mass effect. The lesion was iso-to slightly hyperintense on T1 weighted image and iso-slightly hypointense signal on T2 weighted image. At necropsy, there was a skull fracture and epidural hematoma in the left frontal area. Magnetic resonance imaging of epidural hematoma is reviewed.

• The Journal of the Korea Contents Association
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• v.9 no.12
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• pp.683-690
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• 2009

The purpose of this study is to evaluate the usefulness of high-b-values diffusion weighted magnetic resonance imaging for the preoperative detection of focal rectum cancers. 60patients with diffusion weighted imaging were evaluated for the presence of rectal cancers. Forty were male and twenty were female, and their ages ranged from 38 to 71 (mean, 56) years. Used equipment was 1.5Tesla MRI((GE, General Electric Medical System, Excite HD). Examination protocols were used the fast spin echo T2, T1 weighted imaging. All examination protocols were performed by the same location with diffusion weighted imaging for accuracy detection. The b-values used in DWI were 250, 500, 750, 1000. 1500, 2000$(s/mm^2)$. The rectum, bladder to tumor contrast-to-noise ratio (CNR) of MR images were quantitativlely analyzed using GE software Functool tool, four experienced radiologists and three radiotechnologists qualitatively evaluated image quality in terms of image artifacts, lesion conspicuity and rectal wall. These data were analysed by using ANOVA and Freedman test with each b-value(p<0.05). Contrast to noise ratio of rectum, bladder and tumor in b-value 1000 were 27.21, 24.44, respectively(p<0.05) and aADC value was $0.73\times10^{-3}$. As a qualitative analysis, the conspicuity and discrimination from the rectal wall of lesions were high results as $4.0\pm0.14$, $4.4\pm0.16$ on b-value 1000(p<0.05), image artifacts were high results as $4.8\pm0.25$ on b-value 2000(p<0.05). In conclusion, DWI was provided useful information with depicting the pre-operative detection of rectal cancers, High-b-value 1000 image was the most excellent DWI value.

• Korean Journal of Veterinary Research
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• v.51 no.3
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• pp.227-231
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• 2011

This study was undertaken to assess the lateral ventricle, which was some portion of brain and related to congenital anomalies, from 1, 2, 4, and 8 months of age in healthy micropigs. They were induced general anesthesia and performed magnetic resonance imaging (MRI) with a 0.3 Tesla magnet. Each age group was evaluated by three subjects such as lateral ventricular volume, ventricular volume ratio and asymmetry. T1 weighted transverse images were acquired for calculation of lateral ventricular and corresponding brain parenchyma areas. The ratio of bilateral ventricle areas used to analyze the asymmetry. The mean ventricular volumes of each month were $676.74{\pm}25.58mm^3$ (1 month-old), $630.64{\pm}143.84mm^3$ (2 month-old), $992.12{\pm}106.03mm^3$ (4 month-old) and $1172.62{\pm}237.57mm^3$ (8 month-old), respectively. The ventricular volume ratio was the smallest at 2 month-old and re-increased from that age. The ratio was significantly different between 2 month-old and other age groups (p < 0.05). The value of bilateral area ratio showed within 1.5 in all experimental animals. Consequently the lateral ventricle showed a positive correlation with aging and symmetric shapes in both sides. The developmental pattern of the lateral ventricle provides basic data in micropigs as an experimental animal model for physiological and neurosurgical approach.

• Geomechanics and Engineering
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• v.20 no.3
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• pp.191-205
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• 2020

Soil shear strength parameters play a remarkable role in designing geotechnical structures such as retaining wall and dam. This study puts an effort to propose two accurate and practical predictive models of soil shear strength parameters via hybrid artificial neural network (ANN)-based models namely genetic algorithm (GA)-ANN and particle swarm optimization (PSO)-ANN. To reach the aim of this study, a series of consolidated undrained Triaxial tests were conducted to survey inherent strength increase due to addition of polypropylene fibers to sandy soil. Fiber material with different lengths and percentages were considered to be mixed with sandy soil to evaluate cohesion (as one of shear strength parameter) values. The obtained results from laboratory tests showed that fiber percentage, fiber length, deviator stress and pore water pressure have a significant impact on cohesion values and due to that, these parameters were selected as model inputs. Many GA-ANN and PSO-ANN models were constructed based on the most effective parameters of these models. Based on the simulation results and the computed indices' values, it is observed that the developed GA-ANN model with training and testing coefficient of determination values of 0.957 and 0.950, respectively, performs better than the proposed PSO-ANN model giving coefficient of determination values of 0.938 and 0.943 for training and testing sets, respectively. Therefore, GA-ANN can provide a new applicable model to effectively predict cohesion of fiber-reinforced sandy soil.

• Journal of Korean Neurosurgical Society
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• v.41 no.6
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• pp.371-376
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• 2007

Objective : The aim of this study was to investigate the usefulness of diffusion-weighted imaging [DWI] and apparent diffusion coefficiency [ADC] in distinguishing brain abscesses from cystic or necrotic brain tumors, which are difficult to be differentiated by conventional magnetic resonance imaging techniques. Methods : Seven patients with brain abscesses and ten patients with cystic brain tumors were studied from September 2003 to October 2005. Abscess, subdural empyema and ventriculitis were categorized to the abscess group and cystic or necrotic brain gliomas or metastatic brain tumors into the tumor group. Preoperative magnetic resonance images were performed in all patients and diffusion-weighted images and apparent diffusion coefficiency values of lesions were calculated directly from software of 1.5 tesla MRI [General Electrics, USA]. The ratio of the ADC of the lesion to contralateral regional ADC was also measured [relative ADC, rADC]. Results : The average ADC value of pyogenic abscesses group was $0.82+/-0.14{\times}10^{-3}\;[mean+/-S.D.]\;mm^2/s$ and mean rADC was 0.75. Cystic or necrotic areas had high ADC values [$2.49+/-0.79{\times}10^{-3}\;mm^2/s$, mean rADC=2.14]. ADC and rADC values of abscesses group showed about three times lower values than those of cystic or necrotic tumor group. Conclusion : This study results based on numerical comparison of signal intensities and quantitative analysis to distinguish between brain abscess and cystic or necrotic tumor, DWI and ADC mapping are thought to be very useful diagnostic tools.