• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.1
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• pp.59-69
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• 2021

Recently, large-scale offshore and coastal structures have been constructed owing to the increasing interest in eco-friendly energy development. To achieve this, precise simulations of waves are necessary to ensure the safe operations of marine structures. Several experiments are required in the field to understand the offshore wave; however, in terms of scale, it is difficult to control variables, and the cost is significant. In this study, numerical waves under various wave conditions are produced using a piston-type wavemaker, and the produced wave profiles are verified by comparing with the results from a numerical wave tank (NWT) modeled using the smoothed particle hydrodynamics (SPH) method and theoretical equations. To minimize the effect by the reflected wave, a mass-weighted damping zone is set at the right end of the NWT, and therefore, stable and uniform waves are simulated. The waves are generated using the linear and Stokes wave theories, and it is observed that the numerical wave profiles calculated by the Stokes wave theory yield high accuracy. When the relative depth is smaller than two, the results show good agreement irrespective of the wave steepness. However, when the relative depth and wave steepness are larger than 2 and 0.04, respectively, the errors are negligible if the measurement position is close to the excitation plate. However, the error is 10% or larger if the measurement position is away from the excitation location. Applicable target wave ranges are confirmed through various case studies.

• Journal of the Korean Geotechnical Society
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• v.25 no.9
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• pp.45-55
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• 2009

The quality of railroad trackbed fills has been controlled by field measurements of density and bearing resistance of plate-load tests. The control measures are compatible with the design procedures whose design parameter is $k_{30}$ for both ordinary-speed railways and high-speed railways. However, one of fatal flaws of the design procedures is that there are no simple laboratory measurement procedures for the design parameters ($k_{30}$ or, $E_{v2}$ and $E_{v2}/E_{v1}$) in design stage. To overcome the defect, the compressional wave velocity was adopted as a control measure, in parallel with the advent of the new design procedure, and its measurement technique was proposed in the preliminary investigation. The key concept of the quality control procedure is that the target value for field compaction control is the compressional wave velocity determined at optimum moisture content using modified compaction test, and direct-arrival method is used for the field measurements during construction, which is simple and reliable enough for practice engineers to access. This direct-arrival method is well-suited for such a shallow and homogeneous fill lift in terms of applicability and cost effectiveness. The sensitivity of direct-arrival test results according to the compaction quality was demonstrated at a test site, and it was concluded that compressional wave velocity can be effectively used as quality control measure. The experimental background far the companion study (Park et al., 2009) was established through field and laboratory measurements of the compressional wave velocity.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.31 no.2
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• pp.159-164
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• 2013

It is well known that a single moving camera video is capable of extracting the 3-dimensional position of an object. With this in mind, current research performed image-based monitoring to establish a floating structure model using a camcorder system. Following this, the present study extracted frame images from digital camcorder video clips and matched the interest points to obtain relative 3D coordinates for both regular and irregular wave conditions. Then, the researchers evaluated the transformation accuracy of the modified SURF-based matching and image-based displacement estimation of the floating structure model in regular wave condition. For the regular wave condition, the wave generator's setting value was 3.0 sec and the cycle of the image-based displacement result was 2.993 sec. Taking into account mechanical error, these values can be considered as very similar. In terms of visual inspection, the researchers observed the shape of a regular wave in the 3-dimensional and 1-dimensional figures through the projection on X Y Z axis. In conclusion, it was possible to calculate the displacement of a floating structure module in near real-time using an average digital camcorder with 30fps video.

• Journal of the Institute of Convergence Signal Processing
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• v.13 no.3
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• pp.119-129
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• 2012

In the medical field, the hardening of tissues is one of important informations used in diagnosis or understanding progress of disease, a quantitative measuring method of hardening is important for objective diagnosis. It has been proposed MRE(Magnetic Resonance Elastography) method that measures an index of hardening, viscoelastic properties in a noninvasive. Because the S/N ratio of MRE images go down when measuring viscoelastic properties from local wavelength and local damping factor of a propagating wave in MRE method, methods using multiple phase MRE images have been examined to decrease the effect of noise. We propose a method measuring viscoelastic properties after Fitting a function for multiple phase MRE images in this research. This proposed method has a advantage to set up arbitrarily the variation rate of a space direction of viscoelastic properties or the spatial resolution of measuring values according to changing of the noise included in images, though it applies viscoelastic wave for multiple phase MRE images. We confirmed the effectiveness of a proposed method by experiment using simulation images and experiment using silicone-gel phantom.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2009.11a
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• pp.3-6
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• 2009

최근 차량통신 환경에서의 위성/지상파 DMB 등 차량통신에 대한 관심이 증대되고, 전 세계적으로 기술개발이 활발하게 진행되고 있다. 그러나 좁고 긴 도로 내에 차량이 수시로 들락거려 일정한 통신 구심점을 찾는 것이 쉽지 않고, 빠르게 이동하는 차량의 특성으로 채널 특성이 좋지않 으며, 차량통신을 위한 인프라가 충분히 설치되지 않을 경우 V2I 통신의 어려움 등이 문제점으로 지적될 수 있다. 본 논문에서는 차량통신 네트워크의 효율적 운용을 위한 적응적 클러스터링(Clustering) 기법을 제안하도록 한다. 제안된 적응적 클러스터링 방법에서는 차량의 속도, 위치, 차량 간 거리에 의하여 수시로 클러스터가 적응적으로 재구성된다. 이를 위해 효율적인 클러스터해드 설정이 이루어지며, 차량통신 인프라, 클러스터해드를 중심으로 통신이 이루어진다. 제안된 기법은 제한된 인프라에서도 이중 홉 통신 및 적응적 클러스터 재구성을 통하여 차량의 네트워크 연결성을 높인다. 컴퓨터 모의실험을 통하여 적응적 클러스터링 방법의 성능을 알아보도록 한다. 모의실험을 통하여 빠른 속도로 움직이는 차량의 네트워크 접근성을 확인하고, 차량 밀도 및 인프라 간 거리에 따른 성능변화를 확인한다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2017.11a
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• pp.28-31
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• 2017

지상파 방송 3사(KBS/MBC/SBS) 수도권 본방송 파라미터와 동일하게 설정한 제주테크노파크 100W 실험국에서 ATSC 3.0 신호를 발사한 뒤, 제주시내 일대를 이동하면서 양시청 여부는 물론 실측값을 수집하였다. 결론적으로, 현재 전송파라미터 구성으로 송수신 정합에 이상 없이, 기술적인 관점에서 수도권 모바일HD 본방송이 가능함을 검증하였고, 커버리지 산출에 필수적인 물리계층 성능 지표인 ESR5에 대한 기준값, 즉 변조오류율(MER) 기준으로 11.3dB, 수신 신호 세기(Level) 기준으로 -85.0dBm 정도임을 도출하였다.

• Journal of Digital Convergence
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• v.11 no.3
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• pp.337-344
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• 2013

This research has been conducted to determine the effect that the visually handicapped's participation in an aerobic exercise program has on cardiorespiratory function and arterial pulse wave. The subjects of this research were 20 people who have a 1st degree visual impairment. They recognized the purpose of this research and agreed to take part in it. After receiving agreements from their guardians, we divided them into an exercise group of 10 and a comparison group of 10 at random. The exercise group conducted a 50-70%HRmax treadmill exercise for 60 minutes a day, five times a week, for 12 weeks, including warm up and warm down exercises. We then conducted a two-way repeated ANOVA, which regards the period of exercise and the two groups as independent variables. The follow-up verification for exercise periods according to each group was carried out with a paired t-test. The statistical significance level was p<.05. The following are the results of this research. First, the weight and body fat of the experiment group after exercise show a meaningful reduction compared to before the exercise program (p<.05).Second, the VO2max, HRmax, and VEmax of the experiment group after exercise show a meaningful increase compared to before the exercise program (p<.05). Third, the arterial pulse wave of the experiment group after exercise display a meaningful increase compared to before the exercise program (p<.05). Fourth, the systolic blood pressure of the experiment group after exercise does not show a meaningful reduction compared to before the exercise program (p>.05). These results prove that the visually handicapped's participation in an aerobic exercise program is effective in the improvement of their cardiorespiratory function, bloodstream circulation function and blood vessel function.

• Journal of Gifted/Talented Education
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• v.23 no.5
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• pp.817-833
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• 2013

The study aims to analyze Thomas Young's problem solving processes of analogical reasoning during the formation of the interference theory of light, and to draw its implications for secondary science education, particularly for enhancing creativity in science. The research method employed in the study was literature review of the papers which Young himself had written about sound wave and property of light. His thinking processes and specific features in his thought that were obtained through analysis of his papers about light are as follows: Young reconsidered Newton's experiments and observations, and reinterpreted Newton's results in the new viewpoints. Through this analysis, Young discovered that Newton's interpretation about his own experiments and observations was faulty in a certain point of view and new interpretation is necessary. Based on the data, it is hypothesized that colors observed on thin plates and colors appeared repeatedly on Newton's ring are appeared because of the effect of light interference. Young used analogical reasoning during the process of inference of similarity between sound and light. And he formulated an hypothesis on the interference of light through using abductive reasoning from interference of water wave, and proved the hypothesis by constructing an creative experimental device, which is called a critical experiment. It is implicated that the analogical reasoning and experimental devices for explaining the light interference which Young created and used can be utilized for school science education enhancing creativity in science.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.4
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• pp.259-269
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• 1999

Elastic wave velocity measurement technique such as impact-echo method and ultrasonic pulse velocity method has been successfully used to evaluate the moduli and strength of concrete. However, estimation results obtained by the NDT methods do not agree well with real things because longitudinal wave velocity is influenced by various factors. In this paper, among several factors influencing P-wave velocity, the influence of moisture content in concrete was investigated through the experiment. Test results show that longitudinal wave velocity is significantly affected by the moisture content of concrete, i.e., the lower moisture content. the lower velocity. Moisture content influences rod-wave velocity measured by impact-echo method stronger than ultrasonic pulse velocity measured by transmission method. During drying process with ages. the difference of increasing rate between longitudinal wave velocity and compressive strength of concrete is gradually increased. Therefore, to establish more accurate relationship between longitudinal wave velocity and strength, the difference of the increasing rate should be considered.

• The KIPS Transactions:PartB
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• v.9B no.5
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• pp.673-680
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• 2002

This paper proposes a method for detecting edge using an evolutionary programming and a momentum back-propagation algorithm. The evolutionary programming does not perform crossover operation as to consider reduction of capability of algorithm and calculation cost, but uses selection operator and mutation operator. The momentum back-propagation algorithm uses assistant to weight of learning step when weight is changed at learning step. Because learning rate o is settled as less in last back-propagation algorithm the momentum back-propagation algorithm discard the problem that learning is slow as relative reduction because change rate of weight at each learning step. The method using EP-MBP is batter than GA-BP method in both learning time and detection rate and showed the decreasing learning time and effective edge detection, in consequence.