• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2007년도 특별 심포지엄 논문집
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• pp.31-42
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• 2007

Dc resistivity monitoring has been increasingly used in order to understand the changes of subsurface conditions in terms of conductivity. The commonly adopted interpretation approach which separately inverts time-lapse data may generate inversion artifacts due to measurement error. Eventually the contaminated error amplifies the artifacts when reconstructing the difference images to quantitatively estimate the change of ground condition. In order to alleviate the problems, we defined the subsurface structure as four dimensional (4-D) space-time model and developed 4-D inversion algorithm which can calculate the reasonable subsurface structure continuously changing in time even when the material properties change during data measurements. In this paper, we discussed two case histories of resistivity monitoring to study the ground condition change when the properties of the subsurface material were artificially altered by injecting conductive materials into the ground: (1) dye tracer experiment to study the applicability of electrical resistivity tomography to monitoring of water movement in soil profile and (2) the evaluation of cement grouting performed to reinforce the ground. Through these two case histories, we demonstrated that the 4-D resistivity imaging technique is very powerful to precisely delineate the change of ground condition. Particularly owing to the 4-D inversion algorithm, we were able to reconstruct the history of the change of subsurface material property.

• Journal of Radiation Protection and Research
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• 제40권2호
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• pp.87-91
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• 2015

We have employed X-ray photoelectron spectroscopy (XPS) technique to examine the combined effects of low-energy electron (LEE) irradiation and $Fe^{3+}$ ion on DNA damage. pBR322 plasmid DNA extracted from E. coli ER2420 was used for preparing DNA-$Fe^{3+}$ sample. The C1s XPS spectra were scanned for LEE-irradiated and LEE-unirradiated samples and then curve-fitted. For the samples with LEE irradiation only or with Fe ion only, no significant changes from pure DNA samples were observed - a single effect of either $Fe^{3+}$ ion or LEE irradiation did not cause a significant damage. However, when these two components were combined, the DNA damage was increased quite significantly, compared to the sum of DNA damages caused by $Fe^{3+}$ ion and by LEE irradiation independently. This observation is consistent with our previous results [Radiat. Res. 177, 775 (2012)] which was done using gel-electrophoresis technique. Partial interpretation of the observed spectrum peaks was also attempted.

• 한국철도학회논문집
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• 제12권2호
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• pp.190-198
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• 2009

본 연구에서는 승객, 공중 및 직원의 철도 사상사고를 대상으로 위험도 평가모델을 개발하였다. 이를 위해 철도 사상사고의 위험요인을 분석하여 관련 위험사건을 정의하였고, 위험사건의 발생을 초래하는 위험요인들의 논리적 연계성을 사건발생 시나리오로 구성하여 사건발생빈도 평가모델을 고장수목(Fault Tree)을 이용하여 개발하였다. 또한 사건수목(Event Tree)을 이용하여 인명피해를 초래하는 영향인자를 사건진전 시나리오로 구성하고, 위험사건별 사고 심각도를 등가사망지수로 환산하여 계산하는 위험도 평가모델을 개발하였다. 본 연구의 결과는 비용효과 분석, 안전대책의 민감도 분석 등에 다양하게 활용될 수 있다.

• Applied Microscopy
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• 제44권4호
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• pp.138-143
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• 2014

Transmission electron microscope (TEM) is an excellent tool for studying the structure and properties of nanostructured materials. As the development of $C_s$-corrected TEM, the direct analysis of atomic structures of nanostructured materials can be performed in the high-resolution transmission electron microscopy (HRTEM). Especially, fast Fourier transform (FFT) technique in image processing is very useful way to determine the crystal structure of HRTEM images in reciprocal space. To apply FFT technique in HRTEM analysis in more reasonable and friendly manner, we made a new circular region of interest (C-ROI) FFT script and tested it for several HRTEM analysis. Consequentially, it was proved that the new FFT application shows more quantitative and clearer results than conventional FFT script by removing the streaky artifacts in FFT pattern images. Finally, it is expected that the new FFT script gives great advantages for quantitative interpretation of HRTEM images of many nanostructured materials.

• 비파괴검사학회지
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• 제22권1호
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• pp.59-64
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• 2002

CANDU형 핵연료채널 압력관(Zr-2.5%Nb)과 calandria관(Zircaloy-2)에 대한 원격장 와전류탐상의 자계분포특성을 파악하기 위하여 유한요소 해석을 수행하였다. 압력관과 칼란드리아관의 전자기장 분포와 위상각 해석을 통하여 최적 검사 주파수와 감지코일의 위치를 평가하였다. 또한 축대칭 구조물(Al-ring과 Al-block)이 공존시 파라미터해석을 통하여 원격장 와전류의 특성을 평가하였다.

• 비파괴검사학회지
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• 제30권3호
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• pp.181-193
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• 2010

The paper presents an alternative way to classical stereocorrelation. First, 2D image processing of random patterns is described. Sub-pixel displacements are determined using phase analysis. Then distortion evaluation is presented. The distortion is identified without any assumption on the lens model because of the use of a grid technique approach. Last, shape measurement and shape variation is caught by fringe projection. Analysis is based on two pin-hole assumptions for the video-projector and the camera. Then, fringe projection is coupled to in-plane displacement to give rise to 3D measurement set-up. Metrological characterization shows a resolution comparable to classical (stereo) correlation technique ($1/100^{th}$ pixel). Spatial resolution seems to be an advantage of the method, because of the use of temporal phase stepping (shape measurement, 1 pixel) and windowed Fourier transform (in plane displacements measurement, 9 pixels). Two examples are given. First one is the study of skin properties; second one is a study on leather fabric. In both cases, results are convincing, and have been exploited to give mechanical interpretation.

• 한국환경과학회지
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• 제28권1호
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• pp.125-135
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• 2019

For the purposes of enhancing usability of Numerical Weather Prediction (NWP), the quantitative precipitation prediction scheme by machine learning has been proposed. In this study, heavy rainfall was corrected for by utilizing rainfall predictors from LENS and Radar from 2017 to 2018, as well as machine learning tools LightGBM and XGBoost. The results were analyzed using Mean Absolute Error (MAE), Normalized Peak Error (NPE), and Peak Timing Error (PTE) for rainfall corrected through machine learning. Machine learning results (i.e. using LightGBM and XGBoost) showed improvements in the overall correction of rainfall and maximum rainfall compared to LENS. For example, the MAE of case 5 was found to be 24.252 using LENS, 11.564 using LightGBM, and 11.693 using XGBoost, showing excellent error improvement in machine learning results. This rainfall correction technique can provide hydrologically meaningful rainfall information such as predictions of flooding. Future research on the interpretation of various hydrologic processes using machine learning is necessary.

• Geomechanics and Engineering
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• 제36권3호
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• pp.247-258
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• 2024

Tailings are waste materials of mining operations, consisting of a mixture of clay, silt, sand with a high content of unrecoverable metals, process water, and chemical reagents. They are usually discharged as slurry into the storage area retained by dams or earth embankments. Poor knowledge of the hydro-mechanical behaviour of tailings has often resulted in a high rate of failures in which static liquefaction has been widely recognized as one of the major causes of dam collapse. Many studies have dealt with the static liquefaction of coarse soils in saturated conditions. This research provides an extension to the case of silty tailings in unsaturated conditions. The static liquefaction resistance was evaluated in terms of stress-strain behavior by means of monotonic triaxial tests. Its dependency on the preparation method, the volumetric water content, the void ratio, and the degree of saturation was studied and compared with literature data. The static liquefaction response was proved to be dependent mainly on the preparation technique and degree of saturation that, in turn, controls the excess of pore pressure whose leading role is investigated by means of the relationship between the -B Skempton parameter and the degree of saturation. A preliminary interpretation of the static liquefaction response of Stava tailings is also provided within the Critical State framework.

• Clinical Endoscopy
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• 제55권2호
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• pp.197-207
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• 2022

Background/Aims: Endoscopic visualization of the microscopic anatomy can facilitate the real-time diagnosis of pancreatobiliary disorders and provide guidance for treatment. This study aimed to review the technique, image classification, and diagnostic performance of confocal laser endomicroscopy (CLE). Methods: We conducted a systematic review of CLE in pancreatic and biliary ducts of humans, and have provided a narrative of the technique, image classification, diagnostic performance, ongoing research, and limitations. Results: Probe-based CLE differentiates malignant from benign biliary strictures (sensitivity, ≥89%; specificity, ≥61%). Needle-based CLE differentiates mucinous from non-mucinous pancreatic cysts (sensitivity, 59%; specificity, ≥94%) and identifies dysplasia. Pancreatitis may develop in 2-7% of pancreatic cyst cases. Needle-based CLE has potential applications in adenocarcinoma, neuroendocrine tumors, and pancreatitis (chronic or autoimmune). Costs, catheter lifespan, endoscopist training, and interobserver variability are challenges for routine utilization. Conclusions: CLE reveals microscopic pancreatobiliary system anatomy with adequate specificity and sensitivity. Reducing costs and simplifying image interpretation will promote utilization by advanced endoscopists.

• 지구물리
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• 제6권1호
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• pp.1-11
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• 2003

측지망 조정에는 여러 가지 기법이 있으나 가장 보편적인 것이 최소자승법이다. 지각 변위 연구 등 지구역학적 연구를 위해 GPS 자료를 처리할 때 일반적으로 두 가지 망조정 기법이 사용되는데 그 중 하나는 자유망 조정법이고 나머지 하나는 제한적망 조정법이다. 이 두가지 기법 중에서 어느 것이 더 지구역학적 목적에 적절한지 결정하기 위해 두 개의 다른 측지망 즉, "이집트의 시나이 측지망"과 "한국의 HGN 측지망"의 데이터를 사용하여 조사하였다. 사용된 두 개의 망은 서로 모양이 다를 뿐만 아니라 지진학적 활동이 다른 지역에 위치해 있다. 이 연구의 결과는 두 기법이 모두 RMS 입장에서 보면 고정밀성을 가지고 있고 큰 차이가 없을을 보인다. 그러나 좌표값 결과를 볼 때 제한적망 고정법이 자유망 조정법에 비해 더 많은 왜곡을 일으켰을 분만 아니라 측지망을 정의하는 고정점이 변하면 좌표값도 다르게 결정되었다. 이러한 왜곡은 측정점의 위치 이동량은 물론 자료처리 결과의 지구역학적 해석에 중요한 역할을 하는 변위요소들의 추정에도 영향을 미친다. 이 연구의 대상 지역에 대해 널리 알려진 지구역학 모델과 두 기법으로부터 얻어진 결과를 비교해 보면, 자유망 조정법의 결과가 이들 모델에 확실히 잘 맞는 반면 제한적망 조정법의 결과는 전혀 맞지 않는것으로 나타났다. 이런 결과를 종합해 볼 때 자유망 조정법이 지구역학적 목적에 더 부합하는 측지망 조정기법이라고 판단된다.