• 한국해양공학회지
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• 제37권6호
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• pp.256-265
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• 2023

Many numerical methods have been developed since 1961, but unresolved issues remain. This study developed a numerical method to address these issues and determine the coefficients and properties of rotational waves with a shear current in a finite water depth. The number of unknown constants was reduced significantly by introducing a wavelength-independent coordinate system. The reference depth was calculated independently using the shooting method. Therefore, there was no need for partial derivatives with respect to the wavelength and the reference depth, which simplified the numerical formulation. This method had less than half of the unknown constants of the other method because Newton's method only determines the coefficients. The breaking limit was calculated for verification, and the result agreed with the Miche formula. The water particle velocities were calculated, and the results were consistent with the experimental data. Dispersion relations were calculated, and the results are consistent with other numerical findings. The convergence of this method was examined. Although the required series order was reduced significantly, the total error was smaller, with a faster convergence speed.

• Nuclear Engineering and Technology
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• 제22권2호
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• pp.108-115
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• 1990

0.5~l.2-MeV 양성자빔에 대한 X-선 발생단면적의 측정을 Cu와 Au에 대해 수행하였다. 이 실험에서는 SNU 1.5-MV 탄뎀 반데그라프 가속기에서 얻은 양성자빔을 표적에 입사시켰다. 여기서 방출된 X-선과 후방산란된 양성자는 Si(Li) X-선 검출기와 SSB(Silicone Surface Barrier) 하전입자 검출기를 이용해 동시 측정하였다. 그리하여 측정된 X-선 발생단면적은 다른 실험치들 및 PWBA(Plane Wave Born Approximation)와 ECPSSR(Perturbed Stationary State corrected Energy loss, Coulomb deflection, Relativistic effects)인 이론치들과 비교하였다. 1.0-MeV근처의 양성자에너지에 대해 측정치는 PWBA 값보다는 ECPSSR(D.D. Cohen et al., 1985) 값에 더 잘 일치함을 보였다. 특히, Au의 측정치는 1.2-MeV 양성자빔에 대해 9.69$\pm$0.39 bams이었고, ECPSSR 이론치와는 5% 이내로 일치했으며, 0.5~l.2-MeV 양성자에 대한 실험치는 대부분의 다른 실험치들과 30% 이내로 일치했다.

• Journal of Radiation Protection and Research
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• 제18권2호
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• pp.17-25
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• 1993

액체섬광 계수기에 대한 $^3H,\;^{14}C,\;^{36}Cl$의 베타선 스펙트럼의 시뮬레이션을 Monte Carlo 법으로 수행하였다. 베타선의 손실에너지는 'continuous slowing down approximation(CSDA)' 모형으로부터 구하였다. 순 베타방출 핵종이 균일하게 용해되어 있는 섬광용액은 $1.25cm{\times}3.5cm$의 원통형 geome try로 가정하였다. $^{14}C,\;^{36}Cl$에 대한 계산결과는 계수효율의 경우 실험 값과 2%의 범위 내에서 잘 일치하였으나 $^3H$에 대해서는 상당한 편차를 나타내었다. 이는 저 에너지 베타선에 대한 섬광용액 자체의 quenching 효과에 기인하는 것으로 판단된다.

• 지능정보연구
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• 제25권4호
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• pp.53-65
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• 2019

영상 기반의 보안 시스템의 증가함에 따라 각 용도마다 다른 다양한 객체들에 대한 처리들이 중요해지고 있다. 객체 추적은 객체 인식, 검출과 같은 작업들과 함께 필수적인 작업으로 다뤄진다. 이 객체 추적을 달성하기 위해서 다양한 머신러닝이 적용될 수 있다. 성공적인 분류기로써 전체 에러율 최소화(total-error-rate minimization) 기반의 방법론이 사용될 수 있다. 이 전체 에러율 최소화 기반의 방법론은 오프라인 학습을 기반으로 하고 있다. 객체 추적은 실시간으로 처리하며 갱신해야하는 것이 필수적이므로 온라인 학습(online learning)을 기반으로 하는 것이 적합하다. 온라인 전체 에러율 최소화 방법론이 개발되었지만 점근적으로 재가중되는(approximately reweighted) 작업이 포함되어 에러를 누적시킬 수 있다는 단점이 있다. 본 논문에서는 정확하게 재가중되는(exactly reweighted) 방법론을 제안하면서 온라인 전체 에러율 최소화가 달성되었다. 이 제안된 온라인 학습 방법론을 객체 추적에 적용하여 총 8개의 데이터베이스에서 다른 추적 방법론들 보다 좋은 성능이 달성되었다.

• Nuclear Engineering and Technology
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• 제48권2호
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• pp.482-494
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• 2016

The Feshbache-Kermane-Koonin (FKK) multi-step direct (MSD) theory of pre-equilibrium reactions has been used to compute the single-step cross-sections for some (p,${\alpha}$) reactions using the knock-on and pick-up reaction mechanisms at two incident proton energies. For the knock-on mechanism, the reaction was assumed to have taken place by the direct ejection of a preformed alpha cluster in a shell-model state of the target. But the reaction was assumed to have taken place by the pick-up of a preformed triton cluster (also bound in a shell-model state of the target core) by the incident proton for the pick-up mechanism. The Yukawa forms of potential were used for the proton-alpha (for the knock-on process) and proton-triton (for the pick-up process) interaction and several parameter sets for the proton and alpha-particle optical potentials. The calculated cross-sections for both mechanisms gave satisfactory fits to the experimental data. Furthermore, it has been shown that some combinations of the calculated distorted wave Born approximation cross-sections for the two reaction mechanisms in the FKK MSD theory are able to give better fits to the experimental data, especially in terms of range of agreement. In addition, the theory has been observed to be valid over a wider range of energy.

• 한국군사과학기술학회지
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• 제2권1호
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• pp.30-37
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• 1999

흙으로 침투하는 전파의 투과도와 흙에 의한 신호감쇄량을 계산하였다 대상 복합매질을 이층구조로 모델링한 후, 적분형태로 주어진 전계 표현식을 보였다. 불균일 복합매질에서는 체적산란이 일어나며, 이의 영향이 감안된 전파특성을 분석하기 위하여 반복법인 본(Born) 근사법을 사용하였다. 또한 불균일 복합매질이 가진 랜덤성의 정도는 분산과 상관길이에 의해 정해지도록 하였다. 흙에 함유된 수분량, 흙 입자의 반경, 온도 및 주파수를 변수로 하는 투과도 및 신호감쇄량 식을 제안하였다. 제안된 식으로부터 이들 변수에 따른 투과도 및 신호감쇄량의 변화를 보였다. 분석 결과, 수분이 함유된 경우에는 신호감쇄량의 변동폭이 온도에 따라서 크게 달라짐을 보게 되었고, 그 변동치는 일반적인 예상치를 훨씬 초과하였으며 그 물리적 이유를 설명하였다.

• ETRI Journal
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• 제18권4호
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• pp.315-338
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• 1997

We extend our previous theoretical analysis of electronic and optical properties of p-type quantum well structures based on the two heavy- and light-hole system to include all the three valence bands. These theories are then used to clarify the origin of the normal incidence absorption and photo current at photon wavelengths of 2 - 3 ${\mu}m$, which was observed in addition to the absorption around 8 ${\mu}m$ by a recent experimental investigation with heavily doped p-type GaAs/AlGaAs multi-quantum well (MQW) structures. In the theoretical analysis, the Hartree and exchange-correlation many-body interactions are taken into account within one-particle local density approximation, and it is shown that normal incidence absorption occurs in two wavelength regions over the transition energy range higher than barrier height for p-type GaAs/AlGaAs superlattices with well doping of $2{\times}10^{19}\;cm^{-3}$; one region has broad absorption peaks with coefficients of about 5000 $cm^{-1}$ around 8 ${\mu}m$, and the other has two rather sharp peaks at 2.7 ${\mu}m$ and 3.4 ${\mu}m$ with 1800 $cm^{-1}$ and 1300 $cm^{-1}$, respectively. The result indicates that the theory explains the experimental observation well, as the theoretical and experimental results are in close agreement in general absorption features.

• 상하수도학회지
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• 제22권3호
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• pp.389-396
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• 2008

The hybrid model can be used to predict the initial near field mixing and the far field transport of the buoyant jets, which are discharged from the submerged wastewater ocean outfall. In the near field, the jet integral model can be used for single port diffusers while the ${\sigma}$ transformed particle tracking model was used in the far field. In this study, the experimental study was performed to verify the developed hybrid model in the previous research. The developed hybrid model properly predict the surface and vertical concentration distribution of the single buoyant jets with various effluent and ambient conditions. The hybrid model can also simulate the surface concentration distribution of the rosette diffuser except for the parallel diffuser with the higher densimetric Froude number due to the assumption that dynamic effects of the effluent plumes are negligible in the far field. The application of the hybrid model to rosette diffusers can predict the concentration near the diffuser more accurately when the line-plume approximation is used.

• 한국해안해양공학회지
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• 제4권4호
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• pp.187-200
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• 1992

Taylor 정리를 이용하여 평균위치에서의 Eulerian유속으로부터 수립자의 시간에 따른 Lagrangian 운동궤적을 결정하는 방법이 제안되었다. 이 방법을 Stokes 유한진폭파이론에 적용하여 고차 파성분을 포함하는 수립자의 운동궤적과 질양이동속도를 결정하였다. Stokes 5차파이론의 적용 결과, 평균위치에서의 Eulerian 유속으로부터 결정한 수립자의 운동궤적은 자유수면 부근을 제외하고는 5차파이론에 의한 순간속도에 의해 계산된 값과 매우 좋은 일치를 보여주었다. Stokes 5차파 이론에 의한 질양이동속도는 종전의 2차파이론에 의한 질양이동속도보다 전수심에서 작은 값을 보여준다.

• 한국항만학회지
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• 제14권4호
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• pp.451-461
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• 2000

The design and maintenance of navigation channel and water facilities of an harbor which is located at the mouth of river or at the estuary area are difficult due to the complexity of estuarial water and sediment circulation. Effects of deepening navigable waterways, of changing coastline configurations, or of discharging dredged material to the open sea are necessary to be investigated and predicted in terms of water quality and possible physical changes to the coastal environment. A borad analysis of the transport mechanism in the estuary area was made in terms of sediment property, falling velocity, concentration and flow characteristics. In order to simulate the transport processes, a two-dimensional finite element model is developed, which includes erosion, transport and deposition mechanism of suspended sediments. Galerkin’s weighted residual method is used to solve the transient convection-diffusion equation. The fluid domain is subdivided into a series of triangular elements in which a quadratic approximation is made for suspended sediment concentration. Model could deal with a continuous aggregation by stipulating the settling velocity of the flocs in each element. The model provides suspended sediment concentration, bed shear stress, erosion versus deposition rate and bed profile at the given time step.