• 한국전자파학회논문지
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• 제14권5호
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• pp.458-465
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• 2003

본 논문에서는 3차원 유전체로부터의 전자기 과도 응답을 해석하기 위하여 시간 영역 전장 적분방정식을 이용한 새로운 해법을 제안한다. 이를 위하여 공간 및 시간 시험 과정으로 분리한 갤러킨 방법을 적용한다. 3차원임의 형태의 유전체 표면을 삼각형으로 분할한 다음, 공간에 대한 등가 전류의 전개 및 시험 함수로서 삼각형 벡터 함수를 사용한다. 시간 영역의 미지 계수를 라게르 함수로부터 유도된 기저함수로 근사하며, 이 함수를 시간 영역의 시험 함수로도 사용한다 제안된 방법에 의하여 계산된 등가 전류 및 원거리장의 수치 결과들을 제시한다.

• 대한방사선기술학회지:방사선기술과학
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• 제16권2호
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• pp.19-26
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• 1993

Magnetic Resonance Image represents three-dimensional diagnostic imaging technique using both nuclear magnetic resonance phenomenon and computer. Compared with computed tomography (CT), MRI have advantages harmless to patient's body, three-dimensional image with high resolution and disadvantages long data acquisition time because of long T1 relaxation time, relatively low signal to noise ratio, high cost of setting, also. As physiologic motion of tissue results in motion ghost in MRI, high 2.0Tesla make improve low signal to noise ratio. This study have aim to improve image quality with controling motion ghost of tissue. Supposing a moving pixel in constant frequency, one pixel make two ghosts which are same size and different anti-phase. So, this study will show adjust parameter on locational control of motion ghost. Author made moving phantom replaced by respiratory movement of human, researched change of motion frequency, FOV by location shift, and them decided optimal FOV (field of view). The results are as follows: 1. The frequency content of the motion determines how far the image always appear in phase-encoding direction, the morphology of the ghost image is characteristic of the direction of the motion and its amplitude. 2. Double FOV of fixed signal object for locational control of motion ghost is recommended. Decreasement of spatial resolution by increasing FOV can compensate on increasing of matrix in spite of scan time increasement.

• 천문학회보
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• 제44권1호
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• pp.52.1-52.1
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• 2019

The Helioseismic and Magnetic Imager (HMI) is the instrument of Solar Dynamics Observatory (SDO) to study the magnetic field and oscillation at the solar surface. The HMI image is not enough to analyze very small magnetic features on solar surface since it has a spatial resolution of one arcsec. Super resolution is a technique that enhances the resolution of a low resolution image. In this study, we use a method for enhancing the solar image resolution using a Deep-learning model which generates a high resolution HMI image from a low resolution HMI image (4 by 4 binning). Deep learning networks try to find the hidden equation between low resolution image and high resolution image from given input and the corresponding output image. In this study, we trained a model based on a very deep residual channel attention networks (RCAN) with HMI images in 2014 and test it with HMI images in 2015. We find that the model achieves high quality results in view of both visual and measures: 31.40 peak signal-to-noise ratio(PSNR), Correlation Coefficient (0.96), Root mean square error (RMSE) is 0.004. This result is much better than the conventional bi-cubic interpolation. We will apply this model to full-resolution SDO/HMI and GST magnetograms.

• 한국초전도ㆍ저온공학회논문지
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• 제15권2호
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• pp.16-19
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• 2013

The magneto-resistivity and electric field-current density (E-J) curves were investigated up to a magnetic field 9 T in the optimally doped $BaFe_{1.8}Co_{0.2}As_2$ single crystal with a superconducting temperature ($T_c$) of 24.6 K. The E-J Scaling behaviors below and above vortex glass transition temperature ($T_g$) were found, confirming the existence of the vortex glass phase transition. The critical exponents for the diverging spatial and time correlations at $T_g$, were obtained as v = $1.1{\pm}0.1$ and z = $4.5{\pm}0.3$, respectively. The obtained critical exponents are in good agreement with the predicted values of v ~ 1 - 2 and z > 4 within the 3D vortex glass theory.

• Progress in Superconductivity
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• 제3권2호
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• pp.159-162
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• 2002

We have detected cracks inside multi-layer metal sheets with nondestructive evaluation system consisting of SQUID gradiometer. Double D-shape coil was carefully designed with computer simulation for spatial distribution of magnetic field. It was aligned and placed in between SQUID and metal sheets in order to reduce the field effect to SQUID and to maximize eddy current in the sheets. The metal plate in bottom of the metal stack contained artificial cracks which were scanned by an X-Y scanning system. The information of crack position and size could be estimated by analysis of SQUID signal. Details of the results will be discussed .

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.189-195
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• 1999

We have studied the vortex dynamics in YBa$_2Cu_3O_7$ single crystals with columnar defects using micro Hall-probe array. The Hall-probe array technique allowed a simultaneous measurement of the time and spatial dependence of the vortex density so that more detailed information on flux dynamics could be obtained. We found that field profiles inside sample were similar to the Bean's critical state model from the magnetic hysteresis measurement. Normalized relaxation rates were maximum near the center and decreased toward the edge if applied field H$_{app}$ is greater than the penetration field H. But applied magnetic field H$_{app}$ is less than H, relaxation rates were minimum near the center and increased toward edge. We found that glassy exponent ${\mu}$ has the value of ${\sim}$ 1 whose corresponding vortex motion is half-loop excitation. However, single vortex creep, ${\mu}$ ${\sim}$ 1/7, was also found at 30 K and H$_{app}$ ${\cong}$ H'. Calculation of activation energy, U, was possible from direct analysis of the local relaxation data using the basic diffusion equation. From these results, we found that U increases logarithmically with time and U around center was lower than that at the edge.

• 한국초전도ㆍ저온공학회논문지
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• 제22권2호
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• pp.38-43
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• 2020

This paper presents comparative research on characteristics of air-cored and iron-cored high-temperature superconductor (HTS) field winding synchronous motors. The 100 kW air-cored model is designed analytically by Spatial Harmonic Method, and based on this model, the iron-cored model having the same output power is designed for comparison. Due to the substantial difference of permeability property between air and iron-core, there is a difference of magnetic field magnitude and angle with respect to the HTS tape c-axis, resulting in a different critical current of the field winding considering the anisotropic property of HTS tape. For a detailed comparison between two models, the following key motor characteristics are calculated through the Finite Element Method (FEM) simulation: 1) critical current; 2) HTS wire length; and 3) torque characteristics. From the simulation results, it can be confirmed that the critical current value of the iron-cored model increases by 33 %. Also, in the case of the superconducting wire consumption, those of the iron-cored and air-cored models are 95.3 m and 815.6 m, respectively. So the wire usage can be reduced to about 88 % by using iron core. However, in terms of torque characteristics, the torque ripple of the iron-cored model is about twice as large as that of the air-cored model, which may be a disadvantage on vibration and acoustic noise.

• 센서학회지
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• 제5권2호
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• pp.29-36
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• 1996

본 논문에서는 전기기기 및 전력설비의 운전 조작중에 발생하는 극저주파 영역(ELF)의 자장을 측정 및 분석 할 수 있는 장치로써 멀티턴 루우프형 센서를 이용한 3차원 자장측정계에 대해 기술한다. 저주파특성의 개선과 왜곡없는 공간자장성분의 측정 등 우수한 성능을 얻기 위해서, 자장측정계를 멀티턴 루우프형 센서와 증폭기, 능동성 적분기로 구성하여 3차원적으로 설계 제작하였다. 교정실험을 통하여 측정계의 고유응답특성을 산출한 결과, 주파수대역은 x, y, z 축 각각 8[Hz]에서 53[kHz] 정도이고, 응답감도는 9.54, 9.21, $10.89[mV/{\mu}T]$이다. 진동성 임펄스전류발생기를 이용한 적용실험으로써 측정계의 신뢰성을 확인하였고, 소형 전등기의 기동시에 발생하는 자장과 측정거리에 따른 정상운전중의 자장특성을 측정 분석한 결과 자장의 세기는 각각 최대 15.8, $8.61[{\mu}T]$이며, 거리가 증가할수록 급격한 감소를 보였다.

• 대한의용생체공학회:의공학회지
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• 제25권2호
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• pp.145-150
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• 2004

시각장애인의 시각보조를 위하여 공간 및 방향감각 보조시스템으로 초음파거리계 및 전자나침반을 개발하였다. 초음파거리계는 40 KHz 초음파의 반사를 이용하여 장애물까지 거리 정보를 거리에 비례하는 시간간격의 가청음 자극을 제공하며, 전자나침반은 자기저항브리지를 이용하여 지구자기장을 검출하고 자북 방향 정보를 이마주위의 진동모터를 통하여 촉각자극을 제공하도록 설계하였다. 초음파저리계의 측정범위는 0.065-3.26미터이며 전자나침반의 방향 분해능은 22.5도이다. 그리고 초음파거리계와 전자나침반을 통합한 일체형 시각보조시스템을 구현하였으며 이때 거리정보는 두부에서 진동모터의 위치로 전달하도록 하였다. 본 연구의 목표는 시각장애인의 공간 및 방향감각을 위한 실용적인 보조시스템을 구현하는 것이며, 본 보조시스템을 반복 사용함에 따라 시각장애인의 공간 및 방향감각 기능이 향상될 것으로 추측된다.

• Investigative Magnetic Resonance Imaging
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• 제23권1호
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• pp.38-45
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• 2019

Purpose: To demonstrate the high-resolution numerical simulation of the respiration-induced dynamic $B_0$ shift in the head using generalized susceptibility voxel convolution (gSVC). Materials and Methods: Previous dynamic $B_0$ simulation research has been limited to low-resolution numerical models due to the large computational demands of conventional Fourier-based $B_0$ calculation methods. Here, we show that a recently-proposed gSVC method can simulate dynamic $B_0$ maps from a realistic breathing human body model with high spatiotemporal resolution in a time-efficient manner. For a human body model, we used the Extended Cardiac And Torso (XCAT) phantom originally developed for computed tomography. The spatial resolution (voxel size) was kept isotropic and varied from 1 to 10 mm. We calculated $B_0$ maps in the brain of the model at 10 equally spaced points in a respiration cycle and analyzed the spatial gradients of each of them. The results were compared with experimental measurements in the literature. Results: The simulation predicted a maximum temporal variation of the $B_0$ shift in the brain of about 7 Hz at 7T. The magnitudes of the respiration-induced $B_0$ gradient in the x (right/left), y (anterior/posterior), and z (head/feet) directions determined by volumetric linear fitting, were < 0.01 Hz/cm, 0.18 Hz/cm, and 0.26 Hz/cm, respectively. These compared favorably with previous reports. We found that simulation voxel sizes greater than 5 mm can produce unreliable results. Conclusion: We have presented an efficient simulation framework for respiration-induced $B_0$ variation in the head. The method can be used to predict $B_0$ shifts with high spatiotemporal resolution under different breathing conditions and aid in the design of dynamic $B_0$ compensation strategies.