• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.158-159
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• 2000

광원의 근처에만 존재하는 근접장(Near-field)이 먼장(Far-field)과는 매우 다른 특성을 보인다는 것은 널리 알려진 사실이다. 일반적으로 먼장은 횡파(transverse wave)이며 광원에서 멀어질수록 1/r의 함수로 그 세기가 감소하는데 반하여, 근접장은 시간의존항을 제외하고는 정적인 분포를 보이고(static), 종파(logitudinal wave)성분이 오히려 크며 광원의 미세구조에 직접 관련되어 있다. 이러한 근접장이 근접장 주사 광학현미경(Near-field Scanning Optical Microscopy)의 발전으로 인해 실험적으로 연구되기 시작하면서 여러 가지 예기치 못한 현상들이 발견되고 있다. 그중 하나로서, 원편광된 빛(Circularly polarized light)을 내는 광원의 근접장을 측정한 실험에서 광원에 접근할수록 원편광이 사라지는 현상이 실험적으로 보고된바 있다.$^{(1)}$ 본 발표에서는 Bethe의 모델과 다중극 장(Multipole field)의 근접장을 분석하여 고전전자기론 내에서 근접장의 각 운동량에 대해 논의한다. (중략)

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.969-974
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• 2004

Although guided-waves are very efficient for long-range nondestructive damage inspection, it is not easy to extract meaningful pulses of small magnitude out of noisy signals. The ultimate goal of this research is to develop an efficient signal processing technique for the current guided-wave technology. The specific contribution of this investigation towards achieving this goal, a two-stage Gabor pulse-based matching pursuit algorithm is proposed : rough approximations with a set for predetermined parameters characterizing the Gabor pulse and fine adjustments of the parameters by optimization. The parameters estimated from the measured signal are then used to assess not only the location but also the size of a crack existing in a rod. To validate the effectiveness of the proposed method, the longitudinal wave-based damage detection in rods is considered. To estimate the crack size, Love's theory for the dispersion of longitudinal waves is employed.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.103-106
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• 2000

Nondestructive tests are useful method in rapidly evaluating the condition of existing concrete structures. An objective of this work is to investigate the factors influencing the longitudinal wave velocity-strength relationship, such as w/c ratio, curing temperature, curing condition. Test results show that a change in the w/c ratio ranging from 0.46 to 0.88 and in the curing temperature from 1$0^{\circ}C$ to 3$0^{\circ}C$ did not alter the velocity-strength relationship. however, curing methods had significant effects on the velocity-strength relationship. Therefore, the estimation of compressive strength until 28 day can be accomplished by only a nonlinear equation with consideration of curing condition.

• Journal of the Korea Concrete Institute
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• v.12 no.6
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• pp.67-74
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• 2000

The usage of nondestructive testing on early-aged concrete leads to enhacned safty and allows effective scheduling of construction, thus making it possible to maximize the time and cost efficiencies. In this study, a reliable nondestructive strength evaluation method for early-aged concrete using the longitudinal wave velocity is proposed. Compression tests were performed to examine factors influencing the velocity-strength relationship of concrete, such as water-cement (w/c) ratio, fine aggregate ratio, curing temperature, and curing condition. The test results show that a change in the w/c ratio and curing temperature has minor effect on the velocity-strength relationship/ However, curing condition significantly influences the velocity-strength relationship of early-aged concrete. Moreover, the longitudinal wave velocity increases with decreasing fine aggregate ratio. It is concluded from this study that the strength evaluation of early-age concrete can be achieved by a nonlinear equation which considers the effects of curing condition and fine aggregate ratio.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.208-213
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• 2002

A new method is presented for the isolation of resonances from scattered waves for elastic wave resonance scattering problems. The resonance scattering function consisting purely of resonance information is defined. Elastic wave resonance scattering from a water-filled cylindrical cavity imbedded in an aluminum matrix is numerically analyzed. The classical resonance scattering theory and the new method compute different magnitudes and phases of the resonances from each partial wave, and therefore. their total resonance spectra are quite different. The exact $\pi$ - radians phase shifts through the resonance and anti-resonance frequencies show that the proposed method properly extracts the vibrational resonance information of the scatterer compared to resonance scattering theory.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.336-341
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• 2004

This research investigates the feasibility of ultrasonic microscope for nondestructive assessment of thermal degradation in artificially aged commercial Co-base superalloy, FSX414. This alloy has been used for high temperature structure applications such as stationary gas turbine blade and nozzle chamber in fossil plant. Microstructural change was found that the fine carbides became coarser and spheroidized in matrix as aging time increased. The leaky surface acoustic wave velocity gradually decreases by a maximum of 4.7% with increasing aging time up to 4,000hours. However, the longitudinal wave velocity has a little change. Also, it has a good correlation between leaky surface acoustic wave velocity and Vickers hardness. Consequently, LSAW can be used to examine the degree of degradation in thermally aged Co-base superalloy.

• Journal of Biomedical Engineering Research
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• v.20 no.1
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• pp.91-97
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• 1999

We propose a new method for measuring the frequency characteristics of phase velocity along a bone for bending vibration modes to diagnose its mechanical characteristics. By introducing a simple model of a distributed-constant-network, the phase velocity is determined for each frequency from the spatial distribution of velocity along a radius bone surface which is measured by the ultrasonic Doppler method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.615-618
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• 2004

For successful guided-wave damage inspection, the appropriate signal processing of measured wave signals is very important. The objective of this paper is to introduce an efficient signal processing technique especially suitable for the guided-waves used for damage detection. The key idea of this technique is to model guided-waves by chirp functions of special form considering the dispersion phenomenon. To determine the parameter of the chirp functions simulating guided-waves, the matching pursuit algorithm is employed. The damage information in waveguides can be extracted by pulse-characterizing parameters. The effectiveness of present method is checked with the longitudinal wave-based damage inspection.

• Journal of Korean Foot and Ankle Society
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• v.27 no.3
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• pp.99-102
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• 2023

Acute rupture of the tibialis anterior tendon is rare, but the diagnosis is often delayed when it occurs. Acute rupture of the tibialis anterior tendon is often caused by minor trauma or it occurs spontaneously. Therefore, the diagnosis is more likely to be delayed. Among ruptures of the tibialis anterior tendon, longitudinal ruptures are less common and difficult to diagnose. Thus far, there are no reports of ruptures of the tibialis anterior tendon caused by direct trauma in Korea. This paper reports a case of chronic longitudinal tear of the tibialis anterior tendon caused by trauma in a 50-year-old male patient with no specific history of the disease, along with a review of the relevant literature.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.6 no.2
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• pp.81-92
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• 2001

According to analyses of high-resolution seismic profiles (air gun, sparker, and SBP) and a deep-drill core(YSDP 105) in the mid-eastern Yellow Sea, stratigraphic and geoacoustic models have been established and seismo-acoustic modeling has been fulfilled using ray tracing of finite element method. Stratigraphic model reflects seismo-, litho-, and chrono-stratigraphic sequences formed under a significant influence of Quaternary glacio-eustatic sea-level fluctuations. Each sequence consists of terrestrial to very-shallow-marine coarse-grained lowstand systems tract and tidal fine-grained transgressive to highstand systems tract. Based on mean grain-size data (121 samples) of the drill core, bulk density and P-wave velocity of depositional units have been inferred and extrapolated down to a depth of the recovery using the Hamilton's regression equations. As goo-acoustic parameters, the 121 pairs of bulk density and P-wave velocity have been averaged on each unit of the stratigraphic model. As a result of computer ray-tracing simulation of the subsurface strata, we have found that there are complex ray paths and many acoustic-shadow zones owing to the presence of irregular layer boundaries and low-velocity layers.