• 대한디지털의료영상학회논문지
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• 제3권1호
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• pp.42-50
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• 1997

• International Journal of Aeronautical and Space Sciences
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• 제14권3호
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• pp.282-295
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• 2013

In order to communicate with a ground station, the tracking profile design problem for a directional antenna system is considered. Because the motions of the gimbal angles in the antenna system affect the image quality, the main object is to minimize the motion of the gimbal angles during the satellite's imaging phase. For this goal, parameter optimization problems in the imaging and maneuver phases are formulated separately in the body-frame, and solved sequentially. Also, several mechanical constraints, such as the limitation of the gimbal angle and rate, are considered in the problems. The tracking profiles of the gimbal angles in the maneuver phases are designed with N-th order polynomials, to continuously connect the tracking profiles between two imaging phases. The results confirm that if the vector trace of the desired antenna-pointing vector is within the antenna's beam-width angle, motions of the gimbal angles are not required in the corresponding imaging phase. Also, through numerical examples, it is shown that motion of the gimbal angles in the imaging phase can be minimized by the proposed design process.

• 한국레이저가공학회지
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• 제10권1호
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• pp.11-17
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• 2007

We presented the proper laser processing conditions for the capillary line marking, which could be applied for the fabrication of injection needles. With changing the parameters such as lamp current, duty cycle and beam amplification factor of beam expander, we evaluated the processing performance considering amount of dross, processing efficiency and processed linewidth in the sample. We could carry out the proper line marking at the condition of 70% lamp current, duty cycle of 7-10% and 6-times amplification of beam diameter. To perform efficient line processing, the utilization of duty cycle of 12% at 80% lamp current was also preferred.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제27권2호
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• pp.109-122
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• 2023

In this study, we consider the application of the bifocusing method (BFM) for identifying the locations and shapes of small anomalies from scattering parameter data when the exact values of background permittivity and conductivity are unknown. To this end, an imaging function using numerical focusing operator is introduced and its mathematical structure is revealed by establishing a relationship with an infinite series of Bessel functions, antenna arrangements, and anomaly properties. On the basis of the revealed structure, we demonstrate why inaccurate location and size of anomalies were retrieved via the BFM. Some simulation results are illustrated using synthetic data polluted by random noise to support the theoretical result.

• 한국음향학회지
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• 제9권2호
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• pp.73-81
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• 1990

• 한국광학회지
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• 제4권1호
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• pp.28-35
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• 1993

수차가 정확히 알려지지 않은 결상계에 있어서, exit pupil에 인위적인 위상의 random fluctuation을 도입하고 북스펙트럼 스펙클 영상법(bispectral speckle imaging)을 이용하므로서 수차의 효과를 극소화하여 거의 회절한계의 영상을 얻을 수 있다. Defocus, 구면수차, 코마수차, 비점수차가 각각 1파장씩 있을 때, 주어진 사용영상수(50개)에 대해서 Gaussian random phase model의 correlation length가 어느 정도일 때 최적의 결과를 얻을 수 있는지를 점 물체에 대해 컴퓨터 시뮬레이션을 시행하므로서 연구하였다. 평가기준으로서는 복원된 점물체에 대한 point spread function의 FWHM, normalized peak intensity, MTF 그리고 visual inspection을 채용하였는데, exit pupil 위에서 Fried parameter ${\Upsilon}_0$ 범위에 대한 수차의 차의 rms값 $\sigma$가 구면수차에 대해서는 0.27~0.53 파장일 때, defocus와 비점수차에 대해서는 0.24~0.36 파장일 때, 좋은 결과를 주는 것으로 나타났고, 코마수차의 경우에는 좋은 결과를 얻을 수 없었다.

• 대한원격탐사학회지
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• 제16권2호
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• pp.157-175
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• 2000

A synthetic aperture radar (SAR) system is able to provide all-weather, day-and- night superior imaging capability of the earth surface, and thus is extremely useful in surveillance for both civil and military applications. In this paper, the X-band high resolution spaceborne SAR system design is demonstrated with the key design performance for a given mission and system requirements characterized by the small satellite system. The SAR multi-mode imaging technique is presented with a critical parameter assessment, and the standard mode results are analyzed in terms of the image quality performances. In line with the system requirement X-band SAR payload and ground reception/processing subsystems are designed and the major design results are presented with the key performance characteristics. This small satellite SAR system shows the wide range of imaging capability with high resolution, and proves to be an effective surveillance systems in the light weight, high performance and cost-effective points of view.

• Investigative Magnetic Resonance Imaging
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• 제25권4호
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• pp.300-312
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• 2021

Compressed sensing (CS) has been investigated in magnetic resonance (MR) parametric mapping to reduce scan time. However, the relatively long reconstruction time restricts its widespread applications in the clinic. Recently, deep learning-based methods have shown great potential in accelerating reconstruction time and improving imaging quality in fast MR imaging, although their adaptation to parametric mapping is still in an early stage. In this paper, we proposed a novel deep learning-based framework DEMO for fast and robust MR parametric mapping. Different from current deep learning-based methods, DEMO trains the network in an unsupervised way, which is more practical given that it is difficult to acquire large fully sampled training data of parametric-weighted images. Specifically, a CS-based loss function is used in DEMO to avoid the necessity of using fully sampled k-space data as the label, thus making it an unsupervised learning approach. DEMO reconstructs parametric weighted images and generates a parametric map simultaneously by unrolling an interaction approach in conventional fast MR parametric mapping, which enables multi-tasking learning. Experimental results showed promising performance of the proposed DEMO framework in quantitative MR T1ρ mapping.

• 응용통계연구
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• 제24권1호
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• pp.177-183
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• 2011

Hidden Markov random eld(HMRF) is one of the most common model for image segmentation which is an important preprocessing in many imaging devices. The HMRF has unknown hyper-parameters on Markov random field to be estimated in segmenting testing images. However, in practice, due to computational complexity, it is often assumed to be a fixed constant. In this paper, we numerically show that the segmentation results very depending on the fixed hyper-parameter, and, if the parameter is misspecified, they further depend on the choice of the class-labelling algorithm. In contrast, the HMRF with estimated hyper-parameter provides consistent segmentation results regardless of the choice of class labelling and the estimation method. Thus, we recommend practitioners estimate the hyper-parameter even though it is computationally complex.

• 비파괴검사학회지
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• 제36권2호
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• pp.112-120
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• 2016

The nonlinearity parameter is frequently measured as a sensitive indicator in damaged material characterization or tissue harmonic imaging. Several previous studies have employed the plane wave solution, and ignored the effects of beam diffraction when measuring the non-linearity parameter ${\beta}$. This paper presents a multi-Gaussian beam approach to explicitly derive diffraction corrections for fundamental and second harmonics under quasilinear and paraxial approximation. Their effects on the nonlinearity parameter estimation demonstrate complicated dependence of ${\beta}$ on the transmitter-receiver geometries, frequency, and propagation distance. The diffraction effects on the non-linearity parameter estimation are important even in the nearfield region. Experiments are performed to show that improved ${\beta}$ values can be obtained by considering the diffraction effects.