• Tunnel and Underground Space
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• v.19 no.6
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• pp.545-557
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• 2009

In order to investigate dynamic damage mechanism of brittle materials, Split Hopkinson Pressure Bar (SHPB) have been adapted to apply different impact levels to rocks in South Korea. High resolution X-ray Computed Tomography (CT) was used to estimate the damage in tested rock samples nondestructively. The cracks which are parallel to the loading axis are visible on the contact surface with the incident bar under lower level of impact. The surface cracks disappeared with increment of impact level due to confined effect between the incident bar and sample, while axial splitting are happened near the outer surface.

• Nuclear Engineering and Technology
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• v.55 no.8
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• pp.2854-2863
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• 2023

Objective: To present a hybrid approach that incorporates a constrained beam-hardening estimator (CBHE) and deep learning (DL)-based post-refinement for metal artifact reduction in dental cone-beam computed tomography (CBCT). Methods: Constrained beam-hardening estimator (CBHE) is derived from a polychromatic X-ray attenuation model with respect to X-ray transmission length, which calculates associated parameters numerically. Deep-learning-based post-refinement with an artifact disentanglement network (ADN) is performed to mitigate the remaining dark shading regions around a metal. Artifact disentanglement network (ADN) supports an unsupervised learning approach, in which no paired CBCT images are required. The network consists of an encoder that separates artifacts and content and a decoder for the content. Additionally, ADN with data normalization replaces metal regions with values from bone or soft tissue regions. Finally, the metal regions obtained from the CBHE are blended into reconstructed images. The proposed approach is systematically assessed using a dental phantom with two types of metal objects for qualitative and quantitative comparisons. Results: The proposed hybrid scheme provides improved image quality in areas surrounding the metal while preserving native structures. Conclusion: This study may significantly improve the detection of areas of interest in many dentomaxillofacial applications.

• Journal of Institute of Control, Robotics and Systems
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• v.17 no.10
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• pp.1044-1050
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• 2011

The quality of brazing joints is one of the most important factors that have an effect on the performance of the brazing joint-based heat exchangers with the growing use in industry recently. Therefore, it is necessary to inspect the brazing joints in order to guarantee the performance of the heat exchangers. This paper presents a non-destructive method to inspect the brazing joints of the heat exchangers using X-ray. Firstly, X-ray cross-sectional images of the brazing joints are obtained by using CT (Computerized Tomography) technology. Cross-sectional image from CT is more useful to detect the inner defects than the traditional transmitted X-ray image. Secondly, the acquired images are processed by an algorithm proposed for the defect detection of brazing joint. Finally, two types of brazing joint are examined in a series of experiments to detect the defects in brazing joints. The experimental results show that the proposed algorithm is effective for defect detection of the brazing joints in heat exchangers.

• International Journal of Concrete Structures and Materials
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• v.7 no.2
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• pp.95-110
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• 2013

We report various synchrotron radiation laboratory based techniques used to characterize cement based materials in nanometer scale. High resolution X-ray transmission imaging combined with a rotational axis allows for rendering of samples in three dimensions revealing volumetric details. Scanning transmission X-ray microscope combines high spatial resolution imaging with high spectral resolution of the incident beam to reveal X-ray absorption near edge structure variations in the material nanostructure. Microdiffraction scans the surface of a sample to map its high order reflection or crystallographic variations with a micron-sized incident beam. High pressure X-ray diffraction measures compressibility of pure phase materials. Unique results of studies using the above tools are discussed-a study of pores, connectivity, and morphology of a 2,000 year old concrete using nanotomography; detection of localized and varying silicate chain depolymerization in Al-substituted tobermorite, and quantification of monosulfate distribution in tricalcium aluminate hydration using scanning transmission X-ray microscopy; detection and mapping of hydration products in high volume fly ash paste using microdiffraction; and determination of mechanical properties of various AFm phases using high pressure X-ray diffraction.

• Electronics and Telecommunications Trends
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• v.29 no.5
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• pp.96-104
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• 2014

1895년 독일 과학자 Wilhelm Roentgen 박사가 X-ray를 발견하고 미국의 Herman Carr가 MRI(Magnetic Resonance Imaging)의 기본 원리를 개발하여 발표한 이후 전자기장을 이용한 비침습적 의료영상 이미지 시스템은 놀라운 발전을 계속하여 왔다. 하지만, X-ray, CT(Computed Tomography), PET(Positron Emission Tomography)의 경우는 방사능의 사용과 조영제의 독성이라는 문제로 인하여 안전성에 대한 계속적인 문제를 야기해왔고 상대적으로 안전성이 입증된 MRI의 경우는 장비 자체 및 운용비가 일반화되기에는 고가여서 우리나라를 포함한 선진국에서도 아주 제한적으로 운영되고 있는 실정이다. 따라서, 세계적으로도 이러한 문제를 해결하기 위하여 안전하면서도 상대적으로 저렴한 비용으로 운용이 가능한 의료영상장비를 개발하기 위하여 많은 노력들이 경주되고 있어 관련 연구동향 및 산업화 동향을 소개하고자 한다.

• Journal of the Korean Institute of Telematics and Electronics
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• v.17 no.3
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• pp.26-35
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• 1980

The degradation of image due to the finite size of sensing devices has been one of the problems in all digital imaging systems. The basic study on the improvement of the spatial resolution was carried out in both spatial and frequency domains by the resolution recovery techniques which have been used in optics. Here, the techniques were applied to CT (Computerized Tomography) system, and image with finer resolution was obtained by these techniques. The basic theory is described and the results of the simulation are shown.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.80.4-80
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• 2002

Performance of the previously proposed 2D-image reconstruction method for soft tissues in x-ray computed tomography is evaluated thoroughly through numerical experiments with 4 assumed absorption rates of different symmetries under practical conditions, and the following special features are made clear: It is quite precise, especially at points where the object taking larger values; about two orders less magnitude errors than the conventional most precise method when no noise existing, without any 1D- or 2D-interpolation. In spite of its high sensitivity to the noises, it is even more precise by about 8dB than the latter, to relative pojection data noise power of 5%.

• Coupled systems mechanics
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• v.10 no.6
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• pp.545-560
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• 2021

An in situ experiment imaged via X-ray computed tomography was performed on a continuous glass fiber mat reinforced epoxy resin composite. The investigated dogbone specimen was subjected to uniaxial cyclic tension. The reconstructed scans (i.e., gray level volumes) were registered via Digital Volume Correlation. The calculated maximum principal strain fields and correlation residual maps exhibited strain localization areas within the material bulk, thus indicating damage inception and growth toward the specimen surface. Strained bands and areas of elevated correlation residuals were mainly concentrated in the narrowest gauge section of the investigated specimen, as well as on the specimen ligament edges. Gray level residuals were laid over the corresponding mesostructure to highlight and characterize damage development within the material bulk.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.3 s.96
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• pp.198-207
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• 1999

This paper presents an accurate algorithm for geometric calibration of X-ray imaging system. Calibration is a very important process for improving an imaging system performance. There has been a lot of previous works using linear camera modeling technique, where lens distortion is neglected and/or center of distortion is assumed to be known. Geometrical distortion of image intensifier, however, is very large and its center of distortion should be calculated. This paper presents a new calibration method to estimate the intensifier position and orientation, scale factor, distortion coefficient, magnification factor, and center of distortion using the least square method. We investigate the properties of the algorithm by computer simulation. Simulation results show that the parameters can be estimated accurately using the proposed algorithm.

• Transactions of Materials Processing
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• v.20 no.7
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• pp.518-523
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• 2011

The three dimensional geometries of an aluminum open cell foam before and after uniaxial compressive loading were investigated using the X-ray micro CT(computed tomography). Aluminum 6101-T6 open cell foams of 10, 20, 40 ppi (pore per inch) were considered in this work. After the serial sectioning CT images of aluminum foams were obtained from non-destructive X-ray images, the exact 3D structure were reproduced and visualized with commercial image processing program. The relative density ratio was around the 7.0 to 9.0 range, the unit cells showed anisotropic shapes having the different dimensional ratios of 1.1 to 1.3 between the rise and the transverse directions. The yield stress increased with the relative density ratio and the volumetric strain increased proportionally with compressive strain. The plateau stress in the compressive stress-strain curve was caused by the buckling of ligaments.