• Title/Summary/Keyword: 확산근사

Search Result 99, Processing Time 0.022 seconds

A Study on Diffusion Approximations to Neutron Transport Boundary Conditions (중성자 수송경계조건의 확산근사에 대한 연구)

  • Noh, Taewan
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
    • /
    • v.16 no.2
    • /
    • pp.203-209
    • /
    • 2018
  • To correctly predict the neutron behavior based on diffusion calculations, it is necessary to adopt well-specified boundary conditions using suitable diffusion approximations to transport boundary conditions. Boundary conditions such as the zero net-current, the Marshak, the Mark, the zero scalar flux, and the Albedo condition have been used extensively in diffusion theory to approximate the reflective and vacuum conditions in transport theory. In this paper, we derive and analyze these conditions to prove their mathematical validity and to understand their physical implications, as well as their relationships with one another. To show the validity of these diffusion boundary conditions, we solve a sample problem. The results show that solutions of the diffusion equation with these well-formulated boundary conditions are very close to the solution of the transport equation with transport boundary conditions.

Representation of translucent materials using hybrid-P3 approximation (Hybrid-P3 근사화 기법을 이용한 반투명 재질의 효과적인 표현 기법)

  • Lee, Seung-Joo;Kim, Hoi-Min;Ko, Kwang-Hee;Lee, Kwan H.
    • Proceedings of the Korea Information Processing Society Conference
    • /
    • 2010.04a
    • /
    • pp.534-537
    • /
    • 2010
  • 반투명 재질의 효과적인 표현을 위해서 일반적으로 사용되는 빛의 확산 모델은 일반적 확산 모델(Standard Diffusion model: SDA)이다. 그러나 일반적 확산 모델은 흡수 변수 (absorption coefficient) ${\sigma}_a$가 감소한 산란 변수(reduced scattering coefficient) ${\sigma}_s$ 보다 상대적으로 큰 재질에 대해서는 부정확한 한계를 가지고 있다. 이러한 한계를 극복하기 위하여 다양한 모델이 제시되었다. $P_N$ 근사화 이론은 이러한 일반적 확산 모델이 가지고 있는 한계를 잘 극복한다. 우리는 일반적 확산 모델을 기반으로 하고 $P_3$ 근사화 이론의 변수들을 이용하는 hybrid-P3 근사화 방법을 이용하여 흡수 변수가 감소한 산란 변수보다 상대적으로 큰 재질을 그래픽 공간 상에서 효과적으로 표현하는 방법을 제시한다. 또한 그 재질의 광학적 특성을 추정하기 위하여 우리가 제안하는 모델에 적합한 측정장비를 개발하다.

An Approximation Method for the Estimation of Exposed dose due to Gamma - rays from Radioactive Materials dispersed to the Atmoshere (대기로 확산된 방사성물질로부터 방출되는 감마선에 의한 피폭선량을 계산하기 위한 근사화 방법)

  • Kim, T.W.;Park, C.M.;Ro, S.G.
    • Journal of Radiation Protection and Research
    • /
    • v.15 no.2
    • /
    • pp.51-56
    • /
    • 1990
  • The dispersing model of radioactive plume in the atmosphere was assumed to form finite ellipseshaped volumes rather than a single plume and gamma absorbed doses from the plume were computed using the proposed model. The results obtained were compared with those computed by the Gaussian plume and the circular approximation models. The results computed by the proposed ellipse-shaped approximation model were close to those by the Gaussian plume model. and more accurate than those by the circular approximation model. The computing time for the proposed approximation model was one fortieth of that for the Gaussian plume model.

  • PDF

Likelihood Approximation of Diffusion Models through Approximating Brownian Bridge (브라운다리 근사를 통한 확산모형의 우도 근사법)

  • Lee, Eun-kyung;Sim, Songyong;Lee, Yoon Dong
    • The Korean Journal of Applied Statistics
    • /
    • v.28 no.5
    • /
    • pp.895-906
    • /
    • 2015
  • Diffusion is a mathematical tool to explain the fluctuation of financial assets and the movement of particles in a micro time scale. There are ongoing statistical trials to develop an estimation method for diffusion models based on likelihood. When we estimate diffusion models by applying the maximum likelihood estimation method on data observed at discrete time points, we need to know the transition density of the diffusion. In order to approximate the transition densities of diffusion models, we suggests the method to approximate the path integral of the random process with normal random variables, and compare the numerical properties of the method with other approximation methods.

Approximated Model and Chaining Pattern of Hash Functions (해쉬 함수의 근사적 모델과 연쇄패턴)

  • Lee Sun-Young
    • Journal of Internet Computing and Services
    • /
    • v.7 no.1
    • /
    • pp.39-47
    • /
    • 2006
  • The evaluation of MDx family hash functions such as MD5 is difficult because the design background or a generalized model is unknown. In this paper, an approximated model is proposed to generalize hash functions. The diffusion of a input difference is tested by an approximated model for MD5. The results show that MD5 does not provide perfect diffusion, so MD5 is weak against some attacks. We propose a multiple chaining pattern which provides perfect diffusion in approximated model of hash function without extra calculation or memory. And We show the probability of differential characteristics of our proposal.

  • PDF

A Brief Review of a Term Saddlepoint Approximation Method for Estimating Diffusion Processes (단일항 안장점근사법에 의한 확산모형의 추정)

  • Lee, Eun-Kyung;Lee, Yoon-Dong;Choi, Young-Soo
    • Communications for Statistical Applications and Methods
    • /
    • v.17 no.3
    • /
    • pp.367-376
    • /
    • 2010
  • Recently various methods were suggested and reviewed for estimating diffusion processes. Out of suggested estimation method, we mainly concerns on the estimation method using saddlepoint approximation method, and we suggest a term saddlepoint approximation(ASP) method which is the simplest saddlepoint approximation method. We will show that ASP method provides fast estimator as much as Euler approximation method(EAM) in computing, and the estimator also has good statistical properties comparable to the maximum likelihood estimator(MLE). By simulation study we compare the properties of ASP estimator with MLE and EAM, for Ornstein-Uhlenbeck diffusion processes.

Performacne Analysis of DS/SS DPSK Communication Systems over Fading Dispersive Channels (페이딩 디스퍼시브 채널에서 DS/SS DPSK 통신 시스템의 성능 분석)

  • 김기준;강병권;황금찬
    • The Journal of Korean Institute of Communications and Information Sciences
    • /
    • v.18 no.7
    • /
    • pp.959-969
    • /
    • 1993
  • In this paper, the performance of DS/SS DPSK communications is analysed over fading dispersive channels considering the spreads of the channel in time and in frequency. The two spreads mentioned above are represented with multipath spread and Doppler spread, respectively. The bit error probabilities of DS/SS DPSK systems are derived in terms of channel and system parameters, and an approximation method is presented for computational efficiency. And the numerical results are given for various chip numbers in Rayleigh and Rician fading channels using the approximation method.

  • PDF

A NEW NUMERICAL APPROXIMATION OF DIFFUSION FLUX IN UNSTRUCTURED CELL-CENTERED METHOD (비정렬 셀 중심 방법에서 확산플럭스의 새로운 수치근사방법)

  • Myoung H.K.
    • Journal of computational fluids engineering
    • /
    • v.11 no.1 s.32
    • /
    • pp.8-15
    • /
    • 2006
  • The existing approximations of diffusion flux in unstructured cell-centered finite volume methods are examined in detail with each other and clarified to have indefinite expressions in several respects. A new numerical approximation of diffusion flux at cell face center is then proposed, which is second-order accurate even on irregular grids and may be easily implemented in CFD code using cell-centered finite volume method with unstructured grids composed of arbitrary convex polyhedral shape.

Long-Term Prediction of Radionuclide Leaching from Waste Matrix by Finite-Slab Approximation Method (유한 격판 근사 방법에 의한 고화체로부터의 방사성 핵종의 용출율 장기 예측)

  • Doh, Jeong-Yeul;Lee, Kun-Jai
    • Nuclear Engineering and Technology
    • /
    • v.20 no.3
    • /
    • pp.197-202
    • /
    • 1988
  • A finite slab approximation method was developed to predict the long-term teachability. It is based on the assumption that the diffusional characteristics of radionuclides in a waste matrix are not dependent on matrix geometry but dependent on volume to surface ratio V/S) and diffusion coefficient. Consequently it can be expressed as the solution of the equations obtained from a finite slab with an equal V/S ratio (imaginary diffusion length). The calculational results by the finite slab approximation method have been compared with the results obtained for finite cylinder and sphere with corresponding diffusional analysis. The results of this simple model have showed a good agreement and presented a general applicability for the long-term prediction of the radionuclide leaching behavior.

  • PDF

Error Probability of a DS/SSMA system with Hard-Limiting Correlators (부호상관기를 쓰는 DS/SSMA 계통의 오류확률)

  • 윤진선;송익호;박성일
    • The Journal of the Acoustical Society of Korea
    • /
    • v.12 no.2E
    • /
    • pp.27-32
    • /
    • 1993
  • 이 논문에서는 충격성 잡음이 있는 비선택적 라이시안 페이딩 채널에서 부호 상관 수신기를 쓴 DS/SSMA 계통의 성능을 분석하였다. 이 계통의 평균 이진 오류 확률을 확산 수열이 짧을 때에는 정확한 계산으로, 확산 수열이 길 때에는 근사적인 방법으로 얻었다.

  • PDF