• 대한전기학회논문지
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• 제39권9호
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• pp.934-943
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• 1990

There are no turn-on losses in the series Resonant Converter which operates above the resonance frequency, and the commutation stress on the switched component is low. For a given Series Resonant Converter with specified load resistance, the output voltage is a function of the operation frequency. This paper describes the static and dynamic characteristic analysis of the Series Resonant DC to DC Converter, which is operating above the resonant frequency, with frequency control. For the analysis method, state plane technique is adopted, and the circuit operation is defined from normalized switching frequency, Fsn. Under this condition, circuit performance is analyzed ideally. The validity of the proposed analysis is verified by comparing with experimental results, the stability of the converter is confirmed against small variations around the operating point by conventional frequency domain analysis, and the stress quantity added to switch component is shown.

• Journal of electromagnetic engineering and science
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• 제5권2호
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• pp.92-96
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• 2005

This paper presents a novel microwave oscillator incorporating a simple microstrip ring type resonant cell as its terminating resonance component. Reduced chip size, higher dc-ac power efficiency, superior harmonic characteristics can be achieved from the introduction of a compact microstrip ring resonator cell. The oscillator provides a second harmonic suppression of 26.51 dB and the output power of 2.046 dBm at 2.11 GHz.

• International Journal of Safety
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• 제5권1호
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• pp.1-4
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• 2006

The safety performance of the current collection system is evaluated by conducting a test run in which accelerometer and load cell signals are analyzed. It has been found that the current collection performance is strongly influenced by the train speed, with the major frequency components arising from the train traversing the span spacing and the 8.5 Hz component originating from the panhead resonance. The train acceleration is found to have significant influence on the span passing frequency but negligible effect on the resonant response.

• IEIE Transactions on Smart Processing and Computing
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• 제4권5호
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• pp.311-317
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• 2015

The aim of this study is to develop a 3D registration algorithm for positron emission tomography/computed tomography (PET/CT) and magnetic resonance (MR) images acquired from independent PET/CT and MR imaging systems. Combined PET/CT images provide anatomic and functional information, and MR images have high resolution for soft tissue. With the registration technique, the strengths of each modality image can be combined to achieve higher performance in diagnosis and radiotherapy planning. The proposed method consists of two stages: normalized mutual information (NMI)-based global matching and independent component analysis (ICA)-based refinement. In global matching, the field of view of the CT and MR images are adjusted to the same size in the preprocessing step. Then, the target image is geometrically transformed, and the similarities between the two images are measured with NMI. The optimization step updates the transformation parameters to efficiently find the best matched parameter set. In the refinement stage, ICA planes from the windowed image slices are extracted and the similarity between the images is measured to determine the transformation parameters of the control points. B-spline. based freeform deformation is performed for the geometric transformation. The results show good agreement between PET/CT and MR images.

• Journal of Korean Neurosurgical Society
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• 제54권6호
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• pp.518-520
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• 2013

Ossified lipoma or osteolipoma are rarely reported. It is defined as a histologic variant of lipoma that has undergone osseous metaplasia. Osteolipoma presents with a dominant osseous component within a lipoma. We report a case of a histologically confirmed osteolipoma on the nuchal ligament independent of bone. The patient was a 51-year-old female who presented with a 5-year history of a painless, progressively enlarging mass on the posterior neck. Computed tomography and magnetic resonance imaging showed a circumscribed mass compatible with fat between the C2 and C6 spinous processes with a large calcified irregular component. The mass with dual components was totally removed under general anesthesia and no recurrence was observed after 6 months of follow-up. We also reviewed the clinicopathologic features of previously reported osteolipomas in the literature and suggest that although osteolipoma is a rare variant of lipoma, it should be considered in the differential diagnosis when a lipoma of the posterior neck mixed with a bony component is encountered.

• 한국소음진동공학회논문집
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• 제16권4호
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• pp.420-427
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• 2006

In this study, wind loads transmitted to a transmission tower from transmission lines are mitigated using rotational viscoelastic dampers. First, the wind load characteristics in a transmission tower is investigated considering the effect of the transmission lines through stochastic analysis. The assemblage of the transmission line and insulator are modeled as a double pendulum system connected to the SDOF model of the tower. From the result of the stochastic analysis, the background component of the overturing moment caused by the wind loads acting on the transmission lines are found to have considerable portion in the total overturning moment. Based on this observation result, a strategy Installing rotational viscoelastic damper (VED) between tower arm and transmission line is proposed for the mitigation of the transmission line reactions, which play a role as dynamic loads on a transmission tower. For the purpose of verification, time history analysis is conducted for different wind velocities and VED parameters. The analysis result shows that the rotational VED is effective for the mitigation of the background component rather than the resonance component of the transmission line reactions and achieves the reduction ratio of 50% even for higher wind speed.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2011년도 한국컴퓨터종합학술대회논문집 Vol.38 No.1(C)
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• pp.191-194
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• 2011

문서를 이루는 단어들의 빈도수가 지수법칙(power law)를 따른다는 지프의 법칩(Zipf's law)이 있다. 이러한 단어분포를 고려하여 문서의 토픽을 찾아내는 기계학습법이 디리쉴레 프로세스(Dirichlet process) 이다. 이를 발전시켜서 데이터의 잠재 요인(latent factor)들을 베이즈 확률모델에 기반한 샘플링 바탕으로 찾는 방법이 인디언 뷔페 과정(Indian buffet process) 이다. 우리는 25가지의 특징(feature)들에 대한 점수(rating)들이 볼드(blood oxygen dependent level) 신호와 함께 주어지는 PBAIC 2007 데이터에 주성분 분석법(principal component analysis)를 적용했다. PBAIC 2007 데이터는 비디오 게임을 수행하며 기능적뇌영상(functional magnetic resonance imaging, fMRI) 촬영을 하여 얻어진 공개데이터이다. 우리의 연구에서는 주성분 분석법을 이용하여 10개의 독립 성분(independent component)들을 찾았다. 그리고 1.75초 마다 촬영된 BOLD 신호와 10개의 고유벡터(eigenvector)들간의 내적을 취하여 가중치(weight)를 구하였다. 성분들의 가중치를 낮은 순서로 정렬함으로써 각 시간마다 주도적으로 영향을 미치는 성분들을 알아낼 수 있었다.

• 한국산학기술학회논문지
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• 제11권12호
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• pp.4891-4895
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• 2010

본 자기공명영상장치(MRI: Magnetic Resonance Imaging)의 구성 요소인 RF Coil의 성능은 영상의 신호대 잡음비(Signal to Noise Ratio)를 결정하는 장치이다. RF Coil의 성능은 민감도(Sensitivity)와 라디오주파수 필드 균질성(RF Field Uniformity)으로 나타내고, RF Coil에 의해 유기되는 라디오 주파수 자기장(B1 Field)의 세기는 RF Coil의 구조 및 배열에 따라 공간적으로 달라진다. MRI 신호의 크기는 RF Coil이 만들어내는 자기장의 세기에 의해 결정되기 때문에 RF Coil에 의해 형성되는 공간상의 B1 Field의 분포를 확인할 수 있어야 한다. 본 논문에서는 다채널 RF Coil 설계에 있어서 가장 기본이 되는 형태의 RF Coil 구조와 이의 B1 Field 분포를 Matlab을 이용하여 모의실험을 통해 확인 하였다. Matlab을 이용하여 계산된 기본 구조의 RF 코일이 형성하는 B1 Field 분포는 다채널 RF 코일 설계시 매우 유용하게 사용될 수 있을 것이다.

• Journal of Korean Neurosurgical Society
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• 제29권8호
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• pp.1063-1068
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• 2000

Objectives : To determine the contribution of cranial magnetic resonance angiography(MRA) for the evaluation of patients with ischemic cerebrovascular accident. Methods : Magnetic resonance image(MRI) and MRA studies performed on 34 patients with ischemic stroke were retrospectively reviewed with the clinical records. Results : There were 9 transient ischemic attacks and 25 completed strokes in our series. Twenty-three of 34 MRA examinations(68%) were positive for stenosis or occlusion. The distribution of stenotic or occlusive vascular lesions were correlated with the location of infarction in 22 of the 23 positive cases(96%). MRA provided additional information not obtained from the MRI in 19 cases(56%). Conclusions : Vascular lesions demonstrated on intracranial MRA show a high correlation with infarct distribution. MRA provided information adjunctive to conventional MRI in a majority of cases. We conclude that MRA is an important noninvasive component of the complete evaluation of ischemic stroke.

• Investigative Magnetic Resonance Imaging
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• 제19권4호
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• pp.231-236
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• 2015

A 17-year-old girl presented with complaints of headache and decreasing vision of one month's duration, without any history of fever, weight loss, or any evidence of an immuno-compromised state. Her neurological examination was normal, except for papilledema. Laboratory investigations were within normal limits, except for a slightly increased Erythrocyte Sedimentation Rate (ESR). Non-contrast computerized tomography of her head revealed complex mass in left frontal lobe with a concentric, slightly hyperdense, thickened wall, and moderate perilesional edema with mass effect. Differential diagnoses considered in this case were pilocytic astrocytoma, metastasis and abscess. Magnetic resonance imaging (MRI) obtained in 3.0 Tesla (3.0T) scanner revealed a lobulated outline cystic mass in the left frontal lobe with two concentric layers of T2 hypointense wall, with T2 hyperintensity between the concentric ring. Moderate perilesional edema and mass effect were seen. Post gadolinium study showed a markedly enhancing irregular wall with some enhancing nodular solid component. No restricted diffusion was seen in this mass in diffusion weighted imaging (DWI). Magnetic resonance spectroscopy (MRS) showed increased lactate and lipid peaks in the central part of this mass, although some areas at the wall and perilesional T2 hyperintensity showed an increased choline peak without significant decrease in N-acetylaspartate (NAA) level. Arterial spin labelling (ASL) and dynamic susceptibility contrast (DSC) enhanced perfusion study showed decrease in relative cerebral blood volume at this region. These features in MRI were suggestive of brain abscess. The patient underwent craniotomy with excision of a grayish nodular lesion. Abundant acid fast bacilli (AFB) in acid fast staining, and epithelioid cell granulomas, caseation necrosis and Langhans giant cells in histopathology, were conclusive of tubercular abscess. Tubercular brain abscess is a rare manifestation that simulates malignancy and cause diagnostic dilemma. MRI along with MRS and magnetic resonance perfusion studies, are powerful tools to differentiate lesions in such equivocal cases.