• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.674-677
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• 2010

본 논문에서는 지반에 매립된 파이프에서 전파되는 유도초음파의 종파 모드 특성을 분석하였다. 지상 배관과는 달리 매립 배관에서는 주변 매질로 유도초음파의 누설이 발생할 수 있으며, 이로 인하여 유도초음파의 감쇠가 상대적으로 커질 수 있다. 따라서 본 연구에서는 유도초음파의 여러 특성들 중 종파 모드의 감쇠 특성을 중점적으로 분석하였다. 감쇠에 영향을 미치는 지반의 파동 특성(밀도, 체적종파속도, 체적횡파속도)을 결정하기 위하여 포화도와 다짐을 고려하였다. 포화도가 증가할수록 지반의 체적종파속도와 체적횡파속도는 감소하며, 다짐된 지반은 밀도와 체적종파속도, 체적횡파속도를 증가시킨다. 이와 같은 조건으로 결정된 지반의 파동 특성치와 배관의 물성치를 바탕으로 유도초음파 종파 모드의 감쇠 곡선을 계산하고, 특성을 분석하였다. 결과적으로 포화도가 증가할수록 종파 모드의 감쇠는 감소하는 경향을 나타내었고, 다짐이 증가할 경우 감쇠는 전반적으로 증가하는 경향을 나타냄을 알 수 있었다.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.4
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• pp.266-272
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• 2016

This paper presents the investigation of the propagation behavior of bulk longitudinal waves generated by an ultrafast laser system in thin films. A train of femtosecond laser pulses was focused onto the surface of a 150-nm thick metallic (chromium or aluminum) film on a silicon substrate to excite elastic waves, and the change in thermoreflectance at the spot was monitored to detect the arrival of echoes from the film/substrate interface. The experimental results show that the film material characteristics such as the wave velocity and Young's modulus can be evaluated through curve-fitting in numerical solutions. The material properties of nanoscale thin films are difficult to measure using conventional techniques. Therefore, this research provides an effective method for the nondestructive characterization of nanomaterials.

• (The)Study of the Eastern Classic
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• no.59
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• pp.325-357
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• 2015

Max Weber claimed that the clans as a self-sufficient community in traditional China had limited market development. His statement can be applied to the lineage groups of $Chos{\breve{o}}n$ dynasty, however, it also could be criticized as an example of oversimplifying clans. Starting from this question, in this article, I examined the lineage movement of the P'ap'yong Yun's Nojongp'a branch. Through this research, I tried to investigate the reality of the lineage group communities of $Chos{\breve{o}}n$. My issues are following. First, the Nojongp'a clan promoted the solidarity movement of their lineage in the name of practicing human morality, which belonged to their family learning. Second, the Nojongp'a clan made preparations for their own 'righteous rice fields and grains', through which they tried to establish the base structure for the clan activities. This, however, had its own limitations in aiding the starved suffering from famines and did not last long. Third, the lineage could not function as a community for living that was actively involved in the reproduction of life, and was not an exclusive self-sufficient community, either.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.5
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• pp.536-542
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• 2011

Dissimilar metal welds in nuclear power plant are known as very susceptible to PWSCC flaws, and periodically inspected by the qualified inspector and qualified procedure during in-service inspection period. According to field survey data, the majority of their DMWs are located on tapered nozzle or adjacent to a tapered component. These types of configurations restrict examination access and also limit examination volume coverage. Additionally, circumferential scan for axially oriented flaw is very difficult to detect located on tapered surface because the transducer can't receive flaw response from reflector for miss-orientation. To overcome this miss-orientation, it is necessary adapt skewed ultrasonic transducer accomodate tapered surface. The skewed refracted longitudinal ultrasonic transducer designed by modeling and manufactured from the modelling result for axial flaw detection. Experimental results showed that the skewed refracted longitudinal ultrasonic transducer get higher flaw response than non-skewed refracted longitudinal ultrasonic transducer.