• 비파괴검사학회지
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• 제25권6호
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• pp.467-474
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• 2005

The expanded multi-Gaussian beam model has recently been developed that can calculate the radiation beam field from a single, rectangular transducer with great computational efficiency. In this study, this model is adopted to calculate the radiation beam field for a phased array transducer with various time delays to achieve steering and/or focusing. The calculation beam fields are compared to those obtained by well known Rayleigh-Sommerfeld integral that provides the exact solution in order to explore the validity of the expanded multi-Gaussian beam model And then, this study proposes a complete ultrasonic measurement model including the expanded beam model, far-field scattering model and system efficiency, Using the proposed model, phased array ultrasonic testing signals for a flat-bottomed hole with/without focusing were performed.

• 천문학회보
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• 제42권1호
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• pp.33.2-33.2
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• 2017

Symbiotic stars and quasars show strong far UV resonance doublets including O VI 1032 and 1038, which are known to be major coolants of astrophysical plasma with high temperature T > $10^5K$. We investigate the transfer of $H{\alpha}$ and $Ly{\beta}$ in an emission nebula of temperature T ~ $10^5$, where n=2 population is significant. Line photons of $H{\alpha}$ and $Ly{\beta}$ are transferred in the medium through spatial and frequency diffusion altering their identity according to the branching ratios. We adopt a Monte Carlo technique to describe the transfer of $H{\alpha}$ and $Ly{\beta}$ in an emission nebula with a uniform density and a simple geometrical figure. We find that the temperature of the emission nebula is the major controlling parameter to produce a nonnegligible flux of $Ly{\beta}$. In particular, when T exceeds $10^5K$ the number flux ratio may reach ~ 25% with line center optical depth of a few. We discuss the formation of broad $H{\alpha}$ wings from Raman scattering of $Ly{\beta}$ emergent from a hot emission nebula.

• 복식
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• 제58권2호
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• pp.120-133
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• 2008

The purpose of this study is to analysis types of light and to find the characteristics of light in contemporary fashion design. In a scientific context, light is electromagnetic radiation of a wavelength that has the characteristics of straightness, reflection, refraction, scattering and diffraction. But in philosophical speculations, light has been used as a metaphor of 'being', 'to-be' or 'enlightenment.' And through the ages, people have tried to represent and apply the light into plastic art like painting and architecture. The types of light in fashion design was categorized as those; reflective light from the surface of clothing which is the result of interaction between illumination and material, representative light as the pattern of light or light effect such as sun or its rays and optical or psychedelic patterns, luminescent light from light emitting material like phosphorescence or LED which combines into fashion design, projective light from a medium to reveal virtual patterns on the surface or a fashion design itself using holography. These lights in fashion design can be considered as reflection of emphasis of sexuality, longing for fantasy and mystique, visualization of interaction and communication and groping for the play.

• Ocean and Polar Research
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• 제37권4호
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• pp.333-340
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• 2015

The contrast (fish body to medium ratio) of density and sound speed were measured to estimate acoustic scattering from small juvenile cod (Gadus macrocephalus) with the Kirchhoff-Ray Mode backscatter model. The density contrast was measured by the density-bottle method and the sound speed contrast was estimated by the time of flight method. The results revealed that the measured density contrasts of juvenile cod varied between 1.003 and 1.029 (mean = 1.014, S.D. = 0.01). On the other hand, sound speed contrasts varied between 1.039 and 1.041 (mean = 1.041, S.D. = 0.001). The relationship between averaged target strength (TS) and total length (TL) established by the model were <$TS_{38kHz}$> = 20log(TL) - 68.8 and <$TS_{38kHz}$> = 20log(TL) - 69.4, respectively.

• 한국전자파학회논문지
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• 제14권8호
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• pp.803-808
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• 2003

손실 반공간에 두 개의 원통형 파이프가 묻혀 있는 경우 파이프와 주변 매질의 특성을 반복 기법 최적화 역산란을 적용하여 구했다. 산란 전계는 경계요소법을 이용하여 계산하였으며 파이프의 크기, 위치, 내부매질의 비유전을, 도전을, 주변 매질의 비유전을, 도전을 등의 파라미터는 측정 산란 전계로부터 유전 알고리즘과 Levenberg-Marquardt 알고리즘의 혼합 알고리즘을 이용하여 역으로 계산하였다. 두 파이프가 거의 근접해 있는 경우도 역산란이 가능함을 보였다. 산란 전계의 측정오차에 의한 illposednes 는 파수 영역에서 지수 함수적으로 감쇄하는 감쇄모드를 제거하여 안정화시켰다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 1999년도 제17회 학술발표회 논문개요집
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• pp.179-179
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• 1999

Cu3AU(100) 단결정은 fcc 구조를 가지고 있으며 (100)면은 Cu와 Au가 1:1로 존재하고 가운데(200)면은 Cu만 존재한다. 따라서 Au 층은 (100)면에서만 존재하여 각 Au층은 서로 0.5nm 떨어져 있다. 이와 같은 Cu3Au(100) 단결정을 MEIS(Medium Energy Ion Scattering Spectroscopy) 실험 장비를 사용하여 0.35nm 떨어져 있는 Single unit cell의 윗면과 아래면, 즉 첫 층의 Au와 셋째층의 Au의 층분리를 통해서, 온도 변화에 따른 Cu3Au(100) 단결정의 표면 물리적 현상인 surface induced disorder을 밝혀내고자 한다. 우선 두 Au층의 분리 시도는 수소이온을 이용한 실험 조건에서는 extremely glancing exit angle 등 극한의 산란조거에서도 성공하지 못하였다. 깊이 분해능을 정해주는 electronic energy loss를 극대화하기 위해 수소이온이 아닌 질소 이온을 사용하여 energy spectra를 측정해 본 결과 아래 그림에서와 같이 표면 Au 층과 표면 셋째 Au층을 구분할 수 있었다. <110>으로 align된 조건에서는 셋째층의 Au 원자들이 완전히 shadow cone 내부에 존재하여 관측되지 않지만 9.75$^{\circ}$ tilt 한 경우 셋째층의 Au 원자들이 shadow cone 바깥으로 나오게 되어 그림에서와 같이 첫째 층과 셋째 층이 확실히 분리되어 측정되었다. 이를 바탕을 Cu3Au(100)의 온도변화에 다른 order disorder and segregation 현상을 측정하였다. ordered Cu3Au(100)은 28$0^{\circ}C$ 근처에서 surface층이 먼저 disordered상으로 바뀌는 surface induced disorder 현상이 일어나고 bulk transition 온도 39$0^{\circ}C$ 이하에서 R.T으로 온도를 낮추면 본래의 ordered 구조로 되돌아간다. 하지만 bulk transition 온도를 지나면 order-disorder transition이 비가역적이고 segregation 현상이 일어난다.

• 대한수학회논문집
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• 제16권3호
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• pp.445-458
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• 2001

The shape and the distribution of material construction of the scatterer may be obtained from its scattered fields by the iterative inversion in the spectral domain. The illposedness, the resolution, and the uniqueness of the inversion are the key problems in the inversion and inter-related. The illposedness is shown to be caused by the evanescent modes which carries and amplifies exponentially the measurement errors in the back-propagation of the measured scattered fields. By filtering out all the evanescent modes in the cost functional defined as the squared difference between the measured and the calculated spatial spectrum of the scattered fields from the iteratively chosen medium parameters of the scatterer, one may regularize the illposedness of the inversion in the expense of the resolution. There exist many local minima of the cost functional for the inversion of the large and the high-contrast scatterer and the hybrid algorithm combining the genetic algorithm and the Levenberg-Marquardt algorithm is shown to find efficiently its global minimum. The resolution of reconstruction obtained by keeping all the propating modes and filtering out the evanescent modes for the regularization becomes 0.5 wavelength. The super resolution may be obtained by keeping the evanescent modes when the measurement error and instance, respectively, are small and near.

• 한국기계가공학회지
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• 제18권11호
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• pp.18-23
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• 2019

The oil immersion method can be used to create objective lenses with long working distances without sacrificing the focusing resolution for laser processing. In this study, a space in which air or oil can be filled was formed in the middle of a lens for analyzing the optical properties of a liquid-oil immersion lens. As the refractive media, air and oils of different refractive index values (1.2 and 1.5, respectively) were used. A simulation was conducted in the ZEMAX software environment using the ray-tracing technique, and the performance of the oil immersion lens was verified by determining its image distortion and focal length (FL) in each medium. In the case of air, the calculated FL was 0.813 mm, whereas the imaged FLs were 1.594 mm and 8.126 mm when the refraction indices were 1.2 and 1.5, respectively. The FL of an oil immersion lens could be increased considerably. In terms of image distortion, the oil immersion lens exhibited little distortion at the center in all cases, but different degrees of image distortion were observed at different points away from the center depending on the refraction index degree.

• Nuclear Engineering and Technology
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• 제53권3호
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• pp.732-740
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• 2021

Scattering resonance of medium mass nuclides leads complex spectrum in the fast reactor, which requires thousands of energy groups in the spectrum calculation. When the broad-group cross sections are collapsed, reaction rate cannot be completely conserved. To eliminate the error from energy collapsing, the Super-homogenization method in energy collapsing (ESPH) was employed in the fast reactor code SARAX. An ESPH factor was derived based on the ESPH-corrected SN transport equation. By applying the factor in problems with reflective boundary condition, both the effective multiplication factor and reaction rate were conserved. The fixed-source iteration was used to ensure the stability of ESPH iteration. However, in the energy collapsing process of SARAX, the vacuum boundary condition was adopted, which was necessary for fast reactors with strong heterogeneity. To further reduce the error caused by leakage, an additional conservation factor was proposed to correct the neutron current in energy collapsing. To evaluate the performance of ESPH with conservation factor, numerical benchmarks of fast reactors were calculated. The results of broad-group calculation agreed well with the direct full-core Monte-Carlo calculation, including the effective multiplication factor, radial power distribution, total control rod worth and sodium void worth.

• 대한방사성의약품학회지
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• 제9권1호
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• pp.35-41
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• 2023

Photodynamic therapy (PDT), in which a photosensitizer (PS), light, and molecular oxygen are essential components, is a non-invasive and highly effective cancer therapeutic method. However, PDT suffers from the penetration limit of light caused by attenuation and scattering of light through tissues constraining its use to skin and endoscopically accessible cancers. Cerenkov luminescence (CL) is defined as the light illuminated when charged particles move in a dielectric medium at a velocity greater than the phase velocity of light. It is known that medical radioisotopes in preclinical and clinical settings have enough energy to generate CL, and lately, CL has been exploited as an excitation source for PDT without external light illumination. This review introduces state of the art studies of radioisotope-based PDT for cancer, in which radioisotopes are utilized as a light source.