• Smart Structures and Systems
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• 제32권4호
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• pp.253-266
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• 2023

The time-reversal method is employed to improve the ability of pipeline defect detection, and a new approach of identifying the pipeline defect depth is proposed in this research. When the L(0,2) mode ultrasonic guided wave excited through a lead zirconate titinate (PZT) transduce array propagates along the pipeline with a defect, it will interact with the defect and be partially converted to flexural F(n, m) modes and longitudinal L(0,1) mode. Using a receiving PZT array attached axisymmetrically around the pipeline, the L(0,2) reflection signal as well as the mode conversion signals at the defect are obtained. An appropriate rectangle window is used to intercept the L(0,2) reflection signal and the mode conversion signals from the obtained direct detection signals. The intercepted signals are time reversed and re-excited in the pipeline again, result in the guided wave energy focusing on the pipeline defect, the L(0,2) reflection and the L(0,1) mode conversion signals being enhanced to a higher level, especially for the small defect in the early crack stage. Besides the L(0,2) reflection signal, the L(0,1) mode conversion signal also contains useful pipeline defect information. It is possible to identify the pipeline defect depth by monitoring the variation trend of L(0,2) and L(0,1) reflection coefficients. The finite element method (FEM) simulation and experiment results are given in the paper, the enhancement of pipeline defect reflection signals by time-reversal method is obvious, and the way to identify pipeline defect depth is demonstrated to be effective.

• Journal of Magnetics
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• 제17권4호
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• pp.275-279
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• 2012

The linear actuator has the inherent drawback of air gap variation because its linear motion is usually guided by the springs, which destabilizes the dynamic performance. In order to design the linear actuator to be insensitive to air gap, this paper describes the robust design of the air compressor driving linear actuator using Taguchi method. The orthogonal arrays are constructed with selected control factors and noise factor for minimum experiment. The control factors are thickness of inner magnet, height of upper yoke, thickness of outer magnet and thickness of lower yoke while noise factor is airgap. The finite element analysis using commercial electromagnetic analysis program "MAXWELL" are performed instead of experiment. ANOVA are performed to investigate the effects of design factors. In result, the optimal robust linear actuator which is insensitive to air gap variation is designed.

• 한국초등과학교육학회지:초등과학교육
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• 제18권2호
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• pp.35-46
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• 1999

The most of elementary school science textbook contents are composed of observation and experiment activities. When students study natural phenomena, observation and experiment are st rongly emphasized to improve understanding of scientific concepts and inquiry abilities. The purpose of this study is deep understanding about experimental science classes. This ethnographic study is conducted by observations of experimental science classes in natural setting and interviews of teachers, students of the 5th grade. The conclusions of this study are as follows: First, the general process of the elementary science experimental classes is 'identifying learning purposes -1 planning experiments -1 predicting the results -1 experimenting-t summarizing the results.' The experiments are conducted by group activities and the teachers conceived that the me st difficult step considered by students is 'planning experiments'. Second, students like hands-on activities, but they feel difficulty on less guided experiments. Students perform results oriented-activities. Third, in group activities, students prefer to work with the same gender or collaborative peers.

• Transactions on Electrical and Electronic Materials
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• 제14권4호
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• pp.187-192
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• 2013

Because of the importance of small target detection in infrared images, many studies have been carried out in this area. Using a Kalman filter and mean shift algorithm, this study proposes an algorithm to track multiple small moving targets even in cases of target disappearance and appearance in serial infrared images in an environment with many noises. Difference images, which highlight the background images estimated with a background estimation filter from the original images, have a relatively very bright value, which becomes a candidate target area. Multiple target tracking consists of a Kalman filter section (target position prediction) and candidate target classification section (target selection). The system removes error detection from the detection results of candidate targets in still images and associates targets in serial images. The final target detection locations were revised with the mean shift algorithm to have comparatively low tracking location errors and allow for continuous tracking with standard model updating. In the experiment with actual marine infrared serial images, the proposed system was compared with the Kalman filter method and mean shift algorithm. As a result, the proposed system recorded the lowest tracking location errors and ensured stable tracking with no tracking location diffusion.

• 비파괴검사학회지
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• 제28권5호
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• pp.416-420
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• 2008

전자기음향변환기 분야에서는 나선형 RF 코일이 솔레노이드 코일보다 훨씬 널리 사용되고 있다. 그러나 실린더 구조물의 원거리 초음파검사용 자왜 스트립 도파변환기 분야에서는 솔레노이드 코일이 주로 사용되어왔다. 이는 아마도 낮은 주파수의(즉, 치수가 큰) 나선형 코일의 제작의 어려움에 기인하는 것 같다. 본 논문에서는 FFC(flexible flat cable)로 나선형 코일 자왜 스트립 도파변환기를 제작하는 방법을 기술한다. 기존의 솔레노이드 코일 변환기와의 비교실험을 통하여 나선형 코일 변환기가 훨씬 우수한 성능(감도, 신호-대-잡음 비, 도파방향조정능력)을 갖는다는 것을 실증한다.

• 한국항만학회지
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• 제14권2호
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• pp.187-197
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• 2000

In this paper, an adaptive mechanism based on immune algorithm is designed and it is applied to the driving control of the autonomous guided vehicle(AGV). When the immune algorithm is applied to the PID controller, there exists the case that the plant is damaged by the abrupt change of PID parameters since the parameters are adjusted almost randomly. To solve this problem, a neural network used to model the plant and the parameter tuning of the model is performed by the immune algorithm. After the PID parameters are determined through this off-line manner, these parameters are then applied to the plant for the on-line control using immune adaptive algorithm. Moreover, even though the neural network model may not be accurate enough initially, the weighting parameters are adjusted more accurately through the on-line fine tuning. The experiment for the control of steering and speed of AGV is performed. The results show that the proposed controller provides better performances than other conventional controllers.

• 로봇학회논문지
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• 제5권2호
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• pp.120-126
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• 2010

This paper presents to study the path tracking method of AGV(autonomous guided vehicle) which has a laser guidance system. An existing automatic guided vehicles(AGVs) which were able to drive on wired line only had a automatic guidance system. However, the automatic guidance systems that those used had the high cost of installation and maintenance, and the difficulty of system change according to variation of working environment. To solve such problems, we make the laser guidance system which is consisted of a laser navigation and gyro, encoder. That is robust against noise, and flexible according to working environment through sensor fusion. The laser guidance system can do a perfect autonomous driving. However, the commercialization of perfect autonomous driving system is difficult, because the perfect autonomous driving system must recognize the whole environment of working space. Hence, this paper studied the path tracking of AGV using laser guidance system without wired line. The path tracking method is consisted of virtual path generation method and driving control method. To experiment, we use the fork-type AGV which is made by ourselves, and do a path tracking experiments repeatedly on same experimental environment. In result, we verified that proposed system is efficient and stable for actual fork-type AGV.

• Journal of Periodontal and Implant Science
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• 제26권3호
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• pp.771-778
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• 1996

The assessment of alveolar bone changes on dental radiographs to indicate progression of periodontal diseases or healing response to therapy is routine procedure. However, the diagnostic accuracy in detecting small alveolar bone changes is very limited. Recently, guided bone regeneration therapy is popular, but the quantification of new bone is somewhat difficult with conventional evaluation method. To quantificate the amount of new bone, various evaluating methods have been introduced including histomorphometry, radiomorphometry, biochemical analysis, X-ray probe microanalysis, scanning electron microscope backscatter method. In this study, guided bone regeneration using resorbable membrane with & without PDGF-BB is quatificated through histomorphmetry to evaluate the efficacy of histomorphometric analysis. 4 beagle dogs and 8 Sprague-Dawley rats were selected as experimental animals. In beagle dog experiment, $4{\times}4mm$ Class II defects were created in maxillary both second premolars, and biodegradable membrane containing PDGF-BB(experimental group) were covered over one defect, and same membrane without PDGF-BB(control group) were covered over the other defect. At 2 weeks, 5 weeks after surgery, each beagle dogs were sacrificed, and the tissues were treated by undecalcified fixation. In Sprague-Dawley rat experiment, 5mm round defect were created in temporal bone, the same membranes were covered on the defects. At 1 week, 2 weeks after surgery, each rats were sacrificed, and undecalcified fixation were taken. After grinding tissue specimen, we analyse them histomorphometrically using image analysis system. In beagle dog 2 weeks specimens, new bone formation area were $0.03123mm^2$ in experimental group,and $0.03012mm^2$ in control group. At 5 weeks specimens, $0.15324mm^2$ in experimental group, and $0.09123mm^2$ in control group. In Sprague-Dawley rat specimens, new bone fomation area were $0.20448mm^2$ in 1 week experimental group, $0.03604mm^2$ in 1 week control group. At 2 weeks specimens, $0.46349mm^2$ in experimental group, $0.17741mm^2$ in control group. The results indicated that histomorphometric analysis of new bone formation using image analysis system is very effective quantification method to evaluate the efficacy of treatment modalities.

• Journal of Periodontal and Implant Science
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• 제33권4호
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• pp.673-691
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• 2003

The current interest in periodontal tissue regeneration has lead to research in bone graft, root surface treatments, guided-tissue regeneration, and the administration of growth factors as possible means of regenerating lost periodontal tissue. Several studies have shown that a strong correlation between platelet-rich plasma and the stimulation of remodeling and remineralization of grafted bone exists, resulting in a possible increase of 15-30% in the density of bone trabeculae. The purpose of this study was to study the histopathological correlation between the use of platelet-rich plasma and a bone xenograft used in conjunction with a non-resorbable guided-tissue membrane, e-PTFE, compared to a control group with regards to bone regeneration at the implant fixture site. Implant fixtures were inserted and graft materials placed into the left femur of in the experimental group, while the control group received only implant fixtures. In the first experimental group, platelet-rich plasma and BBP xenograft were placed at the implant fixture site, and the second experimental group had platelet-rich plasma, BBP xenograft, and the e-PTFE membrane placed at the fixture site. The degree of bone regeneration adjacent to the implant fixture was observed and compared histopathologically at 2 , 4, and 8 weeks after implant fixture insertion. The results of the experiment are as follows: 1. The rate of osseointegration to the fixture threads was found to be greater in the first experimental group compared to the control group. 2. The histopathological findings of the second experimental group showed rapid resorption of BBP with subsequent new bone formation replacing the resorbed BBP. 3. The second experimental group showed new bone formation in the area adjacent to the fixture threads beginning two weeks after fixture implantation, with continued bone remodeling in the areas mesial and distal to the fixture. 4. Significant new bone formation and bone remodeling was observed in both experimental groups near the implant fixture sites. 5. The rate of osseointegration at the fixture threads was greater in the second experimental group compared to the first group, and the formation of new bone and trabeculae around the fixture site occurred after the fourth week in the second experimental group. The results of the experiment suggest that a greater degree of new bone formation and osseointegration can occur at the implant fixture site by utilizing platelet-rich plasma and bone xenografts, and that these effects can be accelerated and enhanced by concurrent use of a non-resorbable guided tissue membrane.

• 한국건축시공학회지
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• 제13권6호
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• pp.579-584
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• 2013

유사시 군 지휘시설에서는 시설 외부로부터의 수자원 및 에너지자원 공급이 차단 혹은 제한된다. 따라서 방호시설 내부에는 작전기간 중 필요한 충분한 양의 수자원 및 에너지자원을 확보하고 있어야 한다. 하지만, 전쟁양상의 변화는 시설내부에서 최소 2주 이상의 작전지속성을 요구하고 있다. 이러한 요구로 인하여 유사시에도 시설 외부로부터 내부로의 수자원 및 에너지자원 공급이 불가피하게 되었다. 이에 본 연구에서는 유전체 자체의 EMP 차폐 성능에 착안하여, 작전지속성 보장을 위한 충분한 급수/급유가 가능한 도파관 설치를 위하여 도파관 직경 및 유전체 종류에 따른 EMP 방호성능을 실험적으로 분석하였다. 실험을 통해 다중 도파관을 통해 효과적인 EMP 차폐와 동시에 군 지휘시설 내부로의 안정적인 급수/급유가 가능함을 확인할 수 있었다.