• Journal of Korea Water Resources Association
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• v.38 no.6 s.155
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• pp.429-438
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• 2005

In this study, a couple of ordinary differential equations which can describe random waves are derived from the Boussinesq equations. Incident random waves are generated by using the TMA(TEXEL storm, MARSEN, ARSLOE) shallow-water spectrum. The governing equations are integrated with the 4-th order Runge-Kutta method. By using newly derived wave equations, nonlinear energy interaction of propagating waves in constant depth is studied. The characteristics of random waves propagate over a sinusoidally varying topography lying on a sloping beach are also investigated numerically. Transmission and reflection of random waves are considerably affected by nonlinearity.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.258-258
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• 2010

레이저 유기 형광법은 비침투적인 방법으로 플라즈마를 진단할 수 있는 장점이 있다. 특히 헬륨 플라즈마 내에서 전기장이 존재하는 경우에 헬륨의 에너지 준위가 분리되는 STARK 효과를 이용하여 기판 부근에 발생한 쉬스 내의 전기장을 측정할 수 있다[1]. 그러나 플라즈마의 생성을 위한 RF 소스와 레이저 간의 위상이 동기화 되지 않는 경우엔, 그 결과 값의 보정이 필요하다. 외부의 전기장이 시변하는 경우에 각각의 위상에서 헬륨의 여기종이 느끼는 전기장의 세기는 다르다. 따라서 레이저가 어떤 타이밍에 입사되는 가에 따라 신호의 분리되는 정도가 달라지는데, 레이저와 외부 전기장의 위상을 동기화하지 않은 경우에는 관측된 신호는 각각의 위상에서 여러 가지로 분리된 신호가 더해진 합의 형태로 나타난다. 이는 외부에서 인가된 전기장의 가장 큰 값을 나타낸다고 알려져 있었다[2]. 그러나 레이저 유도 형광 신호는 넓게 분산을 가지므로 이는 보정되어야 한다. 본 연구에서는 각각의 위상에서 출력되는 형광 신호를 구하고 시간의 영역에서 1주기 동안 적분하여 실제로 관측될 레이저 유도 형광신호의 보정치를 계산하였다. 이를 실험적으로 검증하기 위해서 유도 결합 플라즈마 반응 챔버 내에서 플라즈마를 방전시킨 후에, 레이저 유도 형광법을 사용하여 기판 위에 생성된 쉬스 내의 전기장을 측정하였다. 그리고, 랑뮤어 프루브를 이용하여 벌크 플라즈마 내의 플라즈마 전압을 구하고, 이를 적분 상수로 삼아 쉬스 내의 전위 분포를 구하였다. 또한 기판에 인가되는 전압을 직접 측정하여 위에서 구한 전위 분포치와 보정을 한 후의 전위 분포치를 비교, 검토하여 보정치를 검증하였다.

• Journal of the Korean Society for Heat Treatment
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• v.18 no.4
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• pp.229-234
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• 2005

Effect of incident ion beam energy on microstructure and adhesion behavior of TiN thin films were studied. Without ion beam assist, TiN film showed (111) growth mode which was thought to have the lowest deformation energy. As the ion beam assist energy increased, TiN film growth mode was changed from (111) to (200) mode. On the Si(100) substrate the critical incident energy for growth mode change was 100 eV/atom, however the critical assist energy was 121 eV/atom on the STD61 substrate. Grain size of TiN films increased with the assist ion beam energy. Finally, adhesion strength of TiN films bombarded above the critical ion assist energy showed 4~5 times higher values than that with lower bombard ion energy.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.255-255
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• 2015

지진해일은 주기가 긴 파랑으로 방파제나 방호구조물에 의한 에너지 감소가 작은 특성이 있다. 또한, 범람구역의 구조물 밀집도 및 지형적 요인에 따라 범람영역, 침수심, 파력 등이 상이하게 나타나므로 유체흐름의 입체적 변화양상을 고려하여야 한다. 본 수리모형실험은 임원항을 대상으로 구조물에 작용하는 지진해일의 파력특성을 3차원수리모형실험을 통해 검토하고, 파력산정계수(${\alpha}$)를 제시한다. 3차원 수리모형실험은 1983년 동해 중부 지진해일 발생 시 국내에서 가장 큰 피해를 입은 임원항을 대상으로 배후부지의 구조물과 인근 해안의 지형을 1/100으로 재현하여 실험에 임하였다. 입사파랑은 고립파(solitary wave)로 재현하였으며, 천수(shoaling)에 의한 파고변화를 측정하고 그에 따른 배후부지의 침수심, 구조물에 작용하는 파력을 측정하였다. 분석된 파력 산정계수(${\alpha}$)는 임원항 인근 해역 및 배후부지의 방재대책 수립을 위한 기초자료로 활용될 것으로 판단된다.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.1
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• pp.98-106
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• 2018

With the advancement in technology, miniaturization, integration, and weight reduction of satellite components have become possible. In this regard, existing medium and large satellites have been replaced by small satellites. As the demand for small satellites increases, the need for micro-thrusters has emerged for precise attitude and position control. A laser ablation micro-thruster, which generates thrust by using ablation jets that offer a wide range of thrusts and low-impulse thrusts, is considered as an alternative for micro-thrusters in small satellites. The objective of the present study is to introduce configurations of the laser ablation micro-thruster and its research trend.

• Korean Journal of Optics and Photonics
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• v.3 no.1
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• pp.43-49
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• 1992

A microwave free electron laser which consists of Marx generator, vacuum diode, bifilar helical wiggler, and guide solenoid was designed and constructed. The analysis of the magnetic field distributions of the bifilar helical wiggler and computer simulation of electron trajectories with the perpendicular effect of space charges led to the conclusion that the magnetic field distributions are suitable for the electron beam injection. Output frequency in a single $TE_{11}$

• Progress in Medical Physics
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• v.21 no.1
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• pp.86-92
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• 2010

The purpose of this study was to measure curvature contour skin dose using radiochromic film and TLD for a conventional open field. We also attempted to quantify the degradation of skin sparing associated with use of immobilization devices for high energy photon beams and to calculate the skin dose with a help of Monte Carlo (MC) simulation. To simulate head-and-neck and shoulder treatment, a cylindrical solid water phantom 11 cm in diameter was irradiated with 6 MV x-rays using $40{\times}40\;cm^2$ field at 100 cm source axis distance (SAD) to the center of the phantom. Aquaplastic mesh mask was placed on the surface of the cylindrical phantom that mimicked relevant clinical situations. The skin dose profile was obtained by taking measurements from $0^{\circ}$ to $360^{\circ}$ around the circumference of the cylindrical phantom. The skin doses obtained from radiochromic film were found to be 47% of the maximum dose of $D_{max}$ at the $0^{\circ}$ beam entry position and 61% at the $90^{\circ}$ oblique beam position without the mask. Using the mask (1.5 mm), the skin dose received was 59% at $0^{\circ}$ incidence and 78% at $80^{\circ}$ incidence. Skin dose results were also gathered using thin thermoluminescent dosimeters (TLD). With the mask, the skin dose was 66% at $0^{\circ}$ incidence and 80% at $80^{\circ}$ incidence. This method with the mask revealed the similar pattern as film measurement. For the treatments of the head-and-neck and shoulder regions in which immobilization mask was used, skin doses at around tangential angle were nearly the same as the prescription dose. When a sloping skin contour is encountered, skin doses may be abated using thinner and more perforated immoblization devices which should still maintain immoblization.

• The Korean Journal of Nuclear Medicine Technology
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• v.15 no.1
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• pp.29-33
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• 2011

Background and Purpose: Uniformity is the one of the important quality control features with respect to gamma cameras. To maintain adequate uniformity, we must acquire suitable flood table (=flood map) data because the flood table effects energy, and the type or dose of input radiation. Therefore, in this study we evaluated the difference in uniformity when uniformity does not match between the type of input radiation and the flood table data or collimator type. Subjects and Methods: For input radiation, we prepared 370 MBq of $^{57}Co$, $^{99m}Tc$, and $^{201}Tl$. Using SKYLight (Philips) and Infinia gamma cameras (GE), we acquired nine uniformity data that were corrected by technetium, cobalt flood table and did not corrected image for the three sources. Additionally, we acquired two uniformity images with a collimator that were corrected by intrinsic and extrinsic flood tables. Using this data, we evaluated and compared the uniformity values. Results: In the case of the SKYLight gamma camera, the uniformities of the images that matched between the input radiation and flood table with respect to $^{99m}Tc$ and $^{57}Co$ were better than the unmatched uniformity (3.96% vs. 5.69% ; 4.9% vs. 5.91%). However, because there was no thallium flood table, the uniformities of images at Tl were significantly incorrect (7.49%, 7.03%). The uniformities of the Infinia gamma camera had the same pattern as the SKYLight gamma camera (3.7% vs. 4.5%). Moreover, the uniformity of the $^{99m}Tc$ image acquired with a collimator and corrected by an extrinsic flood table was better than the intrinsic flood table (3.96% vs. 6.28%). Conclusion: Correcting an image by a suitable flood table can help achieve better uniformity for a gamma camera. Therefore, we have to acquire images with suitable uniformity correction, and update the flood table periodically. Whenever we acquire a nuclear medicine image, we always have to check the appropriate flood table according to the acquired condition.

• Journal of the Korean Vacuum Society
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• v.17 no.2
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• pp.160-164
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• 2008

The Characterization of $MgB_2$ Thin Film by Slow Positron Annihilation Spectroscopy Enhance signal-to-noise ratio, slow positron coincidence Doppler Broadening method has been applied to study of characteristics of $MgB_2$ superconductor film, which were performed at 30 K and 50 K sample temperature near Tc of it. In this investigation the numerical analysis of the Doppler spectra was employed to the determination of the shape parameter, S, defined as the ratio between the amount of counts in a central portion of the spectrum and the total counts of whole spectrum. The S-parameter values were increased then decreased while the positron implantation energies were increasing, that indicated the diffusion into the samples. The S-parameters of the anisotropic 1 ${\mu}m$ $MgB_2$ thin film which were implanted by positrons at 10 keV are 0.567 at 30 K and 0.570 at 50 K. It is believed that the positrons annihilate with normal-electrons instead of super-electrons in the $MgB_2$ superconductor.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.5
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• pp.345-357
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• 2011

Recently, as part of diversifying energy sources and earth environmental issues, technology development of new renewable energy using wave energy is actively promoted and commercialized around Europe and Japan etc. In particular, OWC(Oscillating Water Column) wave power generation system using air flow induced by vertical movement of the water surface by waves in an air-chamber within caisson is known as the most efficient wave energy absorption device and therefore, is one of the wave power generation apparatus the closest to commercialization. This study examines air flow velocity, which operates turbine(Wells turbine) directly in oscillating water column type wave power generation structure from two-and three-dimensional numerical experiments and discusses optimal shape of oscillating water column type wave power generation structure by estimating the maximum flow rate of air according to change in shape. The three-dimensional numerical wave flume was applied in interpretation for this study which is the model for the immiscible two-phase flow based on the Navier-Stokes Equation. From this, it turned out that size of optimal shape appears differently according to the incident wave period and air flow is maximized at the period where minimum reflection ratio occurs.