• Smart Structures and Systems
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• 제1권2호
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• pp.185-215
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• 2005

Advanced signal processing techniques have been long introduced and widely used in structural health monitoring (SHM) and nondestructive evaluation (NDE). In our research, we applied several signal processing approaches for our embedded ultrasonic structural radar (EUSR) system to obtain improved damage detection results. The EUSR algorithm was developed to detect defects within a large area of a thin-plate specimen using a piezoelectric wafer active sensor (PWAS) array. In the EUSR, the discrete wavelet transform (DWT) was first applied for signal de-noising. Secondly, after constructing the EUSR data, the short-time Fourier transform (STFT) and continuous wavelet transform (CWT) were used for the time-frequency analysis. Then the results were compared thereafter. We eventually chose continuous wavelet transform to filter out from the original signal the component with the excitation signal's frequency. Third, cross correlation method and Hilbert transform were applied to A-scan signals to extract the time of flight (TOF) of the wave packets from the crack. Finally, the Hilbert transform was again applied to the EUSR data to extract the envelopes for final inspection result visualization. The EUSR system was implemented in LabVIEW. Several laboratory experiments have been conducted and have verified that, with the advanced signal processing approaches, the EUSR has enhanced damage detection ability.

• Advances in aircraft and spacecraft science
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• 제1권4호
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• pp.409-425
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• 2014

Converging flows of a gas and a liquid at a microchannel cross junction, under proper conditions, can result in the formation of periodic, dispersed microslugs. This microslug formation phenomenon has been proposed as the basis for a fuel injection system in a novel, 'discrete' monopropellant microthruster designed for use in next-generation miniaturized satellites. Previous experimental studies demonstrated the ability to generate fuel slugs with characteristics commensurate with the intended application during steady-state operation. In this work, numerical and experimental techniques are used to study the effect of valve actuation on slug characteristics, and the results are used to compare with equivalent steady-state slugs. Computational simulations of a valve with a 1 ms valve-actuation cycle show that as the ratio of the response time of the valve to the fully open time is increased, transient effects can increase slug length by up to 17%. The simulations also demonstrate that the effect of the valve is largely independent of surface tension coefficient, which is the thermophysical parameter most responsible for slug formation characteristics. Flow visualization experiments performed using a miniature valve with a 20 ms response time showed less than a 1% change in the length of slugs formed during the actuation cycle. The results of this study indicate that impulse bit and thrust calculations can discount transient effects for slower valves, but as valve technology improves transient effects may become more significant.

• 대한안전경영과학회지
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• 제13권1호
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• pp.183-188
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• 2011

Management of maintenance parts in the aircraft have difficulty because of high cost of part, necessity of separate managements, and very many kinds of parts. The serial number of parts was used in maintenance process and then the results was depended on worker's ability. Also the workers used printed work order and manual at every time in maintenance processes. In this study, we analyzed the maintenance process and the information that occurs in the material warehouse and hangar for large airline company to solve the problems about inventory and visualization. Based on above analysis we developed the maintenance process with integrated by information technologies such as QR code and tablet PC. We expect the reduced errors resulting from visually checking and decreased work hours and maintenance cost and will finally develop the smart work.

• 한국건설관리학회논문집
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• 제5권5호
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• pp.151-162
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• 2004

Current methods for construction site modeling employ large, expensive laser range scanners that produce dense range point clouds of a scene from different perspectives. Days of skilled interpretation and of automatic segmentation may be required to convert the clouds to a finished CAD model. The dynamic nature of the construction environment requires that a real-time local area modeling system be capable of handling a rapidly changing and uncertain work environment. However, in practice, large, simple, and reasonably accurate embodying volumes are adequate feedback to an operator who, for instance, is attempting to place materials in the midst of obstacles with an occluded view. For real-time obstacle avoidance and automated equipment control functions, such volumes also facilitate computational tractability. In this research, a human operator's ability to quickly evaluate and associate objects in a scene is exploited. The operator directs a laser range finder mounted on a pan and tilt unit to collect range points on objects throughout the workspace. These groups of points form sparse range point clouds. These sparse clouds are then used to create geometric primitives for visualization and modeling purposes. Experimental results indicate that these models can be created rapidly and with sufficient accuracy for automated obstacle avoidance and equipment control functions.

• Journal of Information Processing Systems
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• 제16권3호
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• pp.688-698
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• 2020

Point clouds have ability to express the spatial entities, however, the point clouds redundancy always involves some uncertainties in computer recognition and model construction. Therefore, point clouds thinning is an indispensable step in point clouds model reconstruction and other applications. To overcome the shortcomings of complex classification index and long time consuming in existing point clouds thinning algorithms, this paper proposes a point clouds fast thinning algorithm. Specifically, the two-dimensional index is established in plane linear array (x, y) for the scanned point clouds, and the thresholds of adjacent point distance difference and height difference are employed to further delete or retain the selected sample point. Sequentially, the index of sample point is traversed forwardly and backwardly until the process of point clouds thinning is completed. The results suggest that the proposed new algorithm can be applied to different targets when the thresholds are built in advance. Besides, the new method also performs superiority in time consuming, modelling accuracy and feature retention by comparing with octree thinning algorithm.

• 인터넷정보학회논문지
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• 제25권3호
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• pp.9-18
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• 2024

Digital therapy has emerged as a novel treatment modality, propelled by advancements in information and communication technology. In the last five years, there has been a substantial surge in research publications addressing digital therapeutics (DTx) interventions, signaling a sustained upward trajectory in this field. The dynamic nature of computer science, marked by continuous innovation and development, underscores the need for agile adaptation to rapid changes. Consequently, computer science education is compelled to offer students insights into the latest trends. This research endeavors to contribute to the evolving landscape by developing textbooks that impart knowledge about DTx, an integration of information technology. The study focuses on the application of these textbooks to elementary and middle school students in South Korea. The instructional materials have been carefully organized to enable students to learn about the principle of Attention Deficit Hyperactivity Disorder (ADHD) DTx at the elementary level and the DTx that can prevent and address the digital drama at the middle school level. Based on the application of the textbook, students who received instruction using the textbook showed statistically significant improvements in all subcategories of creative problem-solving ability, including idea modification, visualization, task focus, analogy, idea generation, and elaboration (p<.01). Additionally, there were statistically significant changes in students' self-efficacy before and after using the textbook, with negative efficacy decreasing, and positive efficacy and social efficacy increasing (p<.001).

• 한국수학교육학회지시리즈E:수학교육논문집
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• 제20권1호
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• pp.117-145
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• 2006

수학 영재들은 타고난 수학적 소질과 적성, 지적인 능력과 창의성을 바탕으로 참신한 과제에 대한 도전적이고 창조적인 호기심을 가지고 있다. 영재아들의 창의적인 사고력을 길러주기 위해서는 다양한 방법으로 문제 해결에 접근하게 하고 전략적 시도를 할 수 있도록 만들어주어야 한다. 이런 관점에서 볼 때 개방적이고 비정형적인 문제를 영재 교육프로그램의 과제로 선정하는 것은 바람직하다 할 수 있다. 본 논문에서는 다양한 유형의 개방형 문제를 구안하고, 이를 토대로 영재 학급에서 학습 활동을 전개한 후, 문제해결 과정에서 영재아들의 수학적 사고 능력의 특성과 문제 해결 전략 사례를 분석하여, 개방형 과제를 활용한 초등학교 영재 수업에 관한 시사점을 얻고자 하였다.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2006년도 공동학술대회 논문집
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• pp.201-206
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• 2006

지구과학은 지구와 지구시스템을 기술(description)하던 기존의 역할에서 벗어나, 진화하는 지구 시스템 안에서 일어나는 프로세스의 모델링(process modeling), 시뮬레이션(simulation) 그리고 이러한 현상들을 구상화(visualization)하는 방향으로 그 접근 방법이 서서히 그러나 매우 역동적으로 변화하고 있다. 하지만 이러한 모델링 및 시뮬레이션은 현대의 컴퓨터 기술의 발달에도 불구하고 그 수행이 쉽지는 않다. 그 이유로는 지구의 현상들은 그 현상의 기초원인이 되는 물리적 화학적 프로세스들이 비선형적이며, 서로 다른 프로세스들이 상호 연동되어 발생하고, 시간에 따라 변화를 보이기 때문이다. 더구나 이러한 복잡한 프로세스들이 암석의 공극구조라는 매우 복잡한 구조 안에 일어날 때, 그 현상의 모델링 및 시뮬레이션은 그 어려움이 더욱 커지게 된다.따라서 이러한 지구시스템의 여러 가지 프로세스들에 대한 효과적인 모델링 및 시뮬레이션을 위해선 지구의 기본 구성단위인 암석의 구조, 즉 복잡한 공극구조의 이해 및 그 형태를 효과적으로 컴퓨터상에서 수치적으로 기술하는 방법의 개발이 선행되어야 한다. 본 발표에서는 이러한 공극스케일의 모델링을 위한 격자볼츠만 방법, 유한요소법을 이용한 수치방법과 그 결과와, 지구의 여러가지 비선형적이고 시간종속적인 프로세서의 모델링에의 응용가능성에 대한 내용을 제시한다.

• Imaging Science in Dentistry
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• 제49권4호
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• pp.265-272
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• 2019

Purpose: To compare the diagnostic accuracy of cone-beam computed tomography (CBCT) with that of parallel(PPA) and oblique projected periapical(OPA) radiography for the detection of different types of peri-implant bone defects. Materials and Methods: Forty implants inserted into bovine rib blocks were used. Thirty had standardized bone defects(10 each of angular, fenestration, and dehiscence defects), and 10 were defect-free controls. CBCT, PPA, and OPA images of the samples were acquired. The images were evaluated twice by each of 2 blinded observers regarding the presence or absence and the type of the defects. The area under the receiver operating characteristic curve (AUC), sensitivity, and specificity were determined for each radiographic technique. The 3 modalities were compared using the Fisher exact and chi-square tests, with P<0.05 considered as statistical significance. Results: High inter-examiner reliability was observed for the 3 techniques. Angular defects were detected with high sensitivity and specificity by all 3 modalities. CBCT and OPA showed similar AUC and sensitivity in the detection of fenestration defects. In the identification of dehiscence defects, CBCT showed the highest sensitivity, followed by OPA and PPA, respectively. CBCT and OPA had a significantly greater ability than PPA to detect fenestration and dehiscence defects(P<0.05). Conclusion: The application of OPA radiography in addition to routine PPA imaging as a radiographic follow-up method for dental implantation greatly enhances the visualization of fenestration and dehiscence defects. CBCT properly depicted all defect types studied, but it involves a relatively high dose of radiation and cost.

• 한국문헌정보학회지
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• 제40권2호
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• pp.333-355
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• 2006

이 연구에서는 지적 구조 분석을 위해서 계량서지적 자료를 시각적으로 표현하는 다양한 네트워크 형성 방식에 대해서 사례와 함께 각각의 특성을 살펴보았다. 기준값 절단 방식, 최근접이웃 그래프, 최소비용 신장트리, 패스파인더 네트워크의 네 가지 네트워크 형성 방식 중에서 전체 구조와 세부 구조의 표현 능력이 모두 뛰어난 패스파인더 네트워크 알고리즘이 최근 가장 활발히 응용되고 있다. 최근접이웃 그래프는 아직까지 계량서지적 분석에 응용된 사례는 없으나 간단한 알고리즘과 클러스터링 능력 등과 같은 지적 구조 규명에 도움이 될 수 있는 몇 가지 장점을 갖추고 있는 것으로 확인되었다. 다차원척도나 군집분석과 달리 네트워크를 이용한 시각화에서는 입력자료의 전처리에 따라서 생성된 지적 구조의 차이가 큰 것으로 나타났다. 이 연구에서 고찰한 여러 네트워크 형성 방식을 적절히 활용함으로써 국내의 지적 구조 규명 연구를 활성화할 수 있을 것이라 기대된다.