• 비파괴검사학회지
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• 제34권4호
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• pp.277-282
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• 2014

최근 전통적 초음파기법이 탐상할 수 없는 잠닉손상을 평가할 수 있는 잠재적 기술로서 비선형 초음파기법들에 대한 많은 관심이 있다. 비선형 초음파기법중 하나인 공진주파수 변화를 이용하는 기법은 재료의 탄성영역에서의 이력에 근거한 기술이다. 공진주파수의 변화량이 아주 작기 때문에 정교한 공진주파수 측정장치가 필요하다. 본 연구에서는 비선형 전자기음향공진기법을 적용하였다. 비선형 전자기음향공진기법은 비접촉 EMAT 센서를 사용하기 때문에 재료의 주파수 응답에 영향을 최소화할 수 있다. 3점 굽힘 피로시험을 한 알루미늄판 시편에 횡파 EMAT으로 실험을 실시하였다. 전압을 여러 레벨로 인가하며 공진을 발생시켜 잠닉손상측정에 중요한 요인중 하나인 이력 비선형 파라미터 ${\alpha}$를 공진주파수 변화로부터 산출하였다. 비손상시편과 손상시편에서의 측정된 이력 비선형 인자의 값이 서로 차이가 남을 확인하였다.

• Structural Engineering and Mechanics
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• 제71권1호
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• pp.57-63
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• 2019

During the last two decades, much joint research regarding vibration based methods has been done, leading to developing various algorithms and techniques. These algorithms and techniques can be divided into modal methods and signal methods. Although modal methods have been widely used for health monitoring and damage detection, signal methods due to higher efficiency have received considerable attention in various fields, including aerospace, mechanical and civil engineering. Signal-based methods are derived directly from the recorded responses through signal processing algorithms to detect damage. According to different signal processing techniques, signal-based methods can be divided into three categories including time domain methods, frequency domain methods, and time-frequency domain methods. The frequency domain methods are well-known and interest in using them has increased in recent years. To determine dynamic behaviours, to identify systems and to detect damages of bridges, different methods and algorithms have been proposed by researchers. In this study, a new algorithm to detect seismic damage in the bridge's piers is suggested. To evaluate the algorithm, an analytical model of a bridge with simple spans is used. Based on the algorithm, before and after damage, the bridge is excited by a sine force, and the piers' responses are measured. The dynamic specifications of the bridge are extracted by Power Spectral Density function. In addition, the Least Square Method is used to detect damage in the bridge's piers. The results indicate that the proposed algorithm can identify the seismic damage effectively. The algorithm is output-only method and measuring the excitation force is not needed. Moreover, the proposed approach does not need numerical models.

• Steel and Composite Structures
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• 제44권2호
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• pp.241-254
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• 2022

The cables in a cable-stayed bridge are critical load-carrying parts. The potential damage to cables should be identified early to prevent disasters. In this study, an efficient deep learning model is proposed for the damage identification of cables using both a multi-layer perceptron (MLP) and a graph neural network (GNN). Datasets are first generated using the practical advanced analysis program (PAAP), which is a robust program for modeling and analyzing bridge structures with low computational costs. The model based on the MLP and GNN can capture complex nonlinear correlations between the vibration characteristics in the input data and the cable system damage in the output data. Multiple hidden layers with an activation function are used in the MLP to expand the original input vector of the limited measurement data to obtain a complete output data vector that preserves sufficient information for constructing the graph in the GNN. Using the gated recurrent unit and set2set model, the GNN maps the formed graph feature to the output cable damage through several updating times and provides the damage results to both the classification and regression outputs. The model is fine-tuned with the original input data using Adam optimization for the final objective function. A case study of an actual cable-stayed bridge was considered to evaluate the model performance. The results demonstrate that the proposed model provides high accuracy (over 90%) in classification and satisfactory correlation coefficients (over 0.98) in regression and is a robust approach to obtain effective identification results with a limited quantity of input data.

• Structural Engineering and Mechanics
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• 제46권5호
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• pp.615-627
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• 2013

One of the most common defects in reinforced concrete bridge decks is corrosion of steel reinforcing bars. This invisible defect reduces the deck stiffness and affects the bridge's serviceability. Regular monitoring of the bridge is required to detect and control this type of damage and in turn, minimize repair costs. Because the corrosion is hidden within the deck, this type of damage cannot be easily detected by visual inspection and therefore, an alternative damage detection technique is required. This research develops a non-destructive method for detecting reinforcing bar corrosion. Experimental modal analysis, as a non-destructive testing technique, and finite element (FE) model updating are used in this method. The location and size of corrosion in the reinforcing bars is predicted by creating a finite element model of bridge deck and updating the model characteristics to match the experimental results. The practicality and applicability of the proposed method were evaluated by applying the new technique to a two spans bridge for monitoring steel bar corrosion. It was shown that the proposed method can predict the location and size of reinforcing bars corrosion with reasonable accuracy.

• 반도체디스플레이기술학회지
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• 제22권4호
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• pp.48-52
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• 2023

From the past to the present, banners are consistently used as effective advertising means. In the case of Korea, there are frequent situations in which hidden advertisements are installed. As a result, such hidden advertisement materials may damage urban aesthetics and moreover, incur unnecessary manpower consumption and waste of money. The proposed method classifies the detected banners into good banner and bad banner. The classification results are based on whether the relevant banners are installed in compliance with legal guidelines. In the process, YOLO and Open Computer Vision library are used to determine from various perspectives whether banners in CCTV images comply with the guidelines. YOLO is used to detect the banner area in CCTV images, and OpenCV is used to detect the color values in the area for color comparison. If a banner is detected in the video, the proposed method calculates the location of the banner and the distance from the designated bulletin to determine whether it was installed within the designated location, and then compares whether the color used in the banner is complied with local government guidelines.

• 항공우주기술
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• 제10권1호
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• pp.183-192
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• 2011

최근 항공기의 성능향상 및 경량화 등의 필요에 의해 많은 항공기 특히 소형항공기 구조물에 있어 복합재료의 사용이 증가되고 있다. 그러나 복합재료의 복잡한 기계적 거동 특성 및 파손양상 등으로 인하여 그 사용에는 많은 제한이 따르고 있는 실정이다. 복합재에 발생하는 저속충격은 외관상 드러나지는 않기 때문에 복합재 구조물을 설계하는 데 있어 매우 중요하며, 특히 충격 후 충격손상으로 야기되는 층간 분리등은 구조물의 압축강도를 현저하게 저하시킬 수 있다. 본 연구에서는 적층복합재 구조물의 저속충격에 의한 손상거동 및 충격 후 잔류압축강도를 수치적으로 예측하였다. 예측 된 충격하중 이력곡선과 충격후의 압축 강도를 시험결과와 비교하였고 잘 일치함을 확인 할 수 있었다.

• 한국가구학회지
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• 제26권3호
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• pp.274-285
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• 2015

Wood carving has been extremely widely practiced, but survives much less well than the other main materials, being vulnerable to decay, insect damage, and fire. It therefore forms an important hidden element in the art history of many cultures. Even though wood is less durable than either steel or stone, it has been used for a long time due to its usefulness. Wood has a lot of benefits. So people have used wood for materials in houses, trains, cars, bridges, and simple utilities in their ways according to their own religions, climates, and environment they are living in. Nowadays, there are wood products that are made up for its weaknesses and this has made wood be used in variety fields. Moreover, wood has been widely selected materials for sculptures, interior, and also for architecture thanks to its colors and textures. Wood has helped our life more abundant and beautiful.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권6호
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• pp.2186-2196
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• 2014

Spam mail is one of the most general mail dysfunctions, which may cause psychological damage to internet users. As internet usage increases, the amount of spam mail has also gradually increased. Indiscriminate sending, in particular, occurs when spam mail is sent using smart phones or tablets connected to wireless networks. Spam mail consists of approximately 68% of mail traffic; however, it is believed that the true percentage of spam mail is at a much more severe level. In order to analyze and detect spam mail, we introduce a technique based on spam mail characteristics and text mining; in particular, spam mail is detected by extracting the linguistic analysis and language processing. Existing spam mail is analyzed, and hidden spam signatures are extracted using text clustering. Our proposed method utilizes a text mining system to improve the detection and error detection rates for existing spam mail and to respond to new spam mail types.

• 한국인터넷방송통신학회논문지
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• 제17권4호
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• pp.11-17
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• 2017

최근 많은 기업 및 기관에서 내부정보가 유출되는 사고가 지속적으로 발생하고 있으며, 이러한 내부정보 유출사고는 대부분 권한 있는 내부자에 의해 발행하고 있다. 본 논문에서는 은닉 마르코프 모델(HMM)을 이용하여 내부자의 정상행위에서 생성된 정보를 모델링한 후 내부자들의 비정상행위를 탐지하는 내부정보 유출 탐지 기법에 대해 제안한다. 보안시스템들의 로그를 통해 내부자들의 행위에 대한 특징을 추출하여 입력 시퀀스를 생성하고, HMM 모델에 학습하여 정상행위에 대한 모델을 생성한다. 이상행위에 대한 판정은 사용자 행위에 대한 관측열을 정상행위 모델에 적용하여 확률값을 계산하고, 이 값을 특정 임계값과 비교하여 이상행위를 탐지한다. 실험을 통해 내부자 정보유출 행위를 탐지하기 위한 최적의 HMM 매개변수를 결정하였고, 실험결과 제안한 시스템이 내부자 정보유출 행위에 대해 20%의 오탐율과 80%의 탐지율을 보여주었다.

• 철학연구
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• 제122호
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• pp.85-134
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• 2018

이 논문에서 필자는 가장 오래된 남성폭력의 기술화 버전이라 할 수 있는 디지털 성폭력에 대한 철학적 담론을 개진해보고자 한다. 첫 번째로 불법 도촬 카메라의 전방위적 공간성의 작동방식과 디지털 데이터 베이스로 전환된 새로운 시간성의 구조를 분석할 것이다. 나아가 디지털 성폭력과 사이버 성폭력 개념이 혼용되어 사용되고 있는 현재 담론지형에 개입해 들어가 볼 것이다. 두 번째로 정보통신기술의 발달과 사물 인터넷에 기반한 초연결성을 통해, 불법 도촬 카메라의 설치와 촬영이라는 물리적 공간에서의 활동이 사이버 공간이라는 디지털 매트릭스로 즉각 편입이 가능해짐으로써 여성신체이미지가 디지털 재화로 기능하는 측면을 분석할 것이다. 세 번째로 필자는 디지털 성폭력이라는 피해경험을 재언어화하기 위해, 새로운 감정구조를 고안해보고자 한다. 즉 성적 수치심이 아닌, 성적 불쾌감, 사회적 분노감이라는 다층화된 감정구조로의 이행을 통해, 피해자다움이라는 프레임에 갇힌 약자의 전형화에서 벗어나도록 한다. 새로운 감정 양식은 저항적, 도전적 신체 감응 양식의 창출을 도모함으로써 더 이상 사라져야할 자는 피해자가 아닌, 가해자들임을, 수치의 몫은 피해자가 아닌 가해자에게 부과해야하는 것임을 낱낱이 드러낼 것이다. 나아가 디지털 성폭력에 대한 대항실천은 한 개인의 문제가 아닌 공공성의 문제이자 정치적 시민권의 실행에 관한 문제로서 접근되어야한다.