共查询到20条相似文献,搜索用时 46 毫秒
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V. K. Volosyuk S. S. Zhyla V. F. Kravchenko A. V. Morozov V. I. Pustovoit P. Hunziker 《Doklady Physics》2016,61(12):590-595
A new method for coherent superbroadband sounding of a semitransparent substance with the aim to construct a three-dimensional image of its inner structure is proposed and justified. The method is based on irradiating the studied medium with a plane ray, spectral analysis by the two-dimensional Fresnel–Fourier transform, interferometric comparison of spatial spectra of scattered and reference signals, and holographic construction of a series of two-dimensional images of the medium followed by tomographic reconstruction of its three-dimensional image. The stochastic image model has been justified in a coherent approach for the first time both in the region of high frequencies and after the transfer of the radiation spectrum to the lowfrequency range of spatial frequencies to the surface of the radiation recorder. The spectral correlation characteristics of the speckle structure of the reconstructed image have been studied. Calculations and investigations of the spread function of the structure implementing the proposed method have been carried out. 相似文献
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The stochastic solution of the monoenergetic radiative transfer equation in a finite slab random medium with pure-triplet anisotropic scattering is considered. The random medium is assumed to consist of two randomly mixed immiscible fluids labelled by 1 and 2. The extinction function, the scattering kernel, and the internal source of radiation are treated as discrete random variables, which obey the same statistics. The theoretical model used here for stochastic media transport assumes Markovian processes and exponential chord length statistics. The boundaries of the medium under consideration are considered to have specular and diffuse reflectivities with an internal source of radiation inside the medium. The ensemble-average partial heat fluxes are obtained in terms of the average albedos of the corresponding source-free problem, whose solution is obtained by using the Pomraning-Eddington approximation. Numerical results are calculated for the average forward and backward partial heat fluxes for different values of the single scattering albedo with variation of the parameters that characterize the random medium. Compared to the results obtained by Adams et al. in the case of isotropic scattering based on the Monte Carlo technique, it can be demonstrated that we have good comparable data. 相似文献
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M.M.R. Williams 《Journal of Quantitative Spectroscopy & Radiative Transfer》2008,109(10):1778-1790
A new approach has been developed to deal with stochastic transport problems in three-dimensional media. It is assumed that the medium consists of randomly distributed lumps of material embedded in a background matrix and in each lump the properties may vary randomly with time. The coefficients for scattering and absorption are represented mathematically by members of a random characteristic set function, which depend on space and time. Different physical situations can be described by different forms and combinations of these set functions. In order to effect a solution of the resulting stochastic transport equation, which may be for photons or neutrons, we make the, a priori, assumption that the functional form for the solution of the transport equation, i.e. the stochastic flux, can be represented by the same mathematical form as the scattering and absorption coefficients (or cross sections), i.e. we introduce a stochastic ansatz. This procedure leads to a set of deterministic equations from which the mean and variance of the flux in space and time can be obtained. For the case of a two-phase medium, either two or four coupled integro-differential equations are obtained for the deterministic functions that arise (depending on the problem) and expressions are given for the mean and variance of the angular flux. There is a close relationship between these equations and those from the Levermore-Pomraning (LP) theory, but the new equations offer an opportunity to deal with more general forms of stochastic processes and combine simultaneously time and space fluctuations. The stochastic characteristics of the medium are defined by the correlation functions which appear in the equations and, by making plausible assumptions about the functional form of these autocorrelation functions, different physical situations can be simulated, according to the structure of the medium. The main contribution of the present work is to include space and time fluctuations simultaneously as a pseudo-dichotomic Markov process. 相似文献
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《Waves in Random and Complex Media》2013,23(2):219-240
The stochastic solution of the monoenergetic radiative transfer equation in a finite slab random medium with pure-triplet anisotropic scattering is considered. The random medium is assumed to consist of two randomly mixed immiscible fluids labelled by 1 and 2. The extinction function, the scattering kernel, and the internal source of radiation are treated as discrete random variables, which obey the same statistics. The theoretical model used here for stochastic media transport assumes Markovian processes and exponential chord length statistics. The boundaries of the medium under consideration are considered to have specular and diffuse reflectivities with an internal source of radiation inside the medium. The ensemble-average partial heat fluxes are obtained in terms of the average albedos of the corresponding source-free problem, whose solution is obtained by using the Pomraning–Eddington approximation. Numerical results are calculated for the average forward and backward partial heat fluxes for different values of the single scattering albedo with variation of the parameters that characterize the random medium. Compared to the results obtained by Adams et al. in the case of isotropic scattering based on the Monte Carlo technique, it can be demonstrated that we have good comparable data. 相似文献
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John V. Martonchik David J. Diner 《Journal of Quantitative Spectroscopy & Radiative Transfer》1985,34(2):133-148
The three-dimensional equation of transfer for a scattering medium with planar geometry is solved by using a spatial Fourier transform and extending matrix-operator techniques developed previously for the one-dimensional equation. Doubling and adding algorithms were derived by means of an interaction principle for computing the fourier-transformed radiation field. The resulting expressions fully describe the radiative transfer process in a scattering medium, inhomogeneous in the x-, y- and z-directions, illuminated from above by an arbitrarily general intensity field and bounded from below by a surface with completely general reflection properties. 相似文献
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S. A. Tereshchenko 《Technical Physics》2017,62(9):1293-1299
The reconstruction of the spatial distribution of radiation sources in a proportional scattering medium has been considered. An exact solution of the inverse tomographic problem has been obtained by analytically solving the radiation transport equation for arbitrary distributions of radiation sources and extinction coefficient and exact boundary conditions. The type and scale of distortions associated with radiation scattering in tomographic reconstructions have been demonstrated. 相似文献
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The interaction between coherent monochromatic radiation and scattering medium results in a speckle phenomenon. The purpose of this paper is to present a stochastic approach to characterizing speckle patterns, using the differential equation that formalizes Brownian motion. This stochastic approach is based on a differential method for the approximation of diffusion. This method is validated by the characterization of solutions of latex balls of various concentrations. 相似文献
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The refocusing of a high-power femtosecond laser pulse after filamentation in a layer of atmospheric aerosol has been numerically
investigated. It is shown that the presence of an on-path cloud of aerosol particles in the atmosphere results in the decrement
of the filament energy, and the process of pulse refocusing becomes stochastic after the aerosol layer due to the competition
between the influence of perturbations induced by aerosol scattering and filtration of radiation spatial modes. 相似文献
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D.W. Mueller Jr.A.L. Crosbie 《Journal of Quantitative Spectroscopy & Radiative Transfer》2002,75(1):93-120
Three-dimensional vector radiative transfer in a semi-infinite medium exposed to spatially varying, polarized radiation is studied. The problem is to determine the generalized reflection matrix for a multiple scattering medium characterized by a 4×4 scattering matrix. A double integral transform is used to convert the three-dimensional vector radiative transfer equation to a one-dimensional form, and a modified Ambarzumian's method is then applied to derive a nonlinear integral equation for the generalized reflection matrix. The spatially varying backscattered radiation for an arbitrarily polarized incident beam can be found from the generalized reflection matrix. For Rayleigh scattering and normal incidence and emergence, the generalized reflection matrix is shown to have five non-zero elements. Benchmark results for these five elements are presented and compared to asymptotic results. When the incident radiation is polarized, the vector approach used in this study correctly predicts three-dimensional behavior, while the scalar approach does not. When the incident radiation is unpolarized, both the vector and scalar approaches predict a two-dimensional distribution of the intensity, but the error in the scalar prediction can be as high as 20%. 相似文献
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The time-dependent radiation transfer in a semi-infinite stochastic medium of binary Markovian mixture with Rayleigh scattering is presented. A formalism, developed to treat radiation transfer in statistical mixtures, is used to obtain the ensemble-averaged solution. The average reflectivity, radiant energy and net flux are computed for specular-reflecting boundary. For the sake of comparison, we use two different weight functions in our calculations. 相似文献
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《Waves in Random and Complex Media》2013,23(1):31-42
Radiation transfer through a volcanic aerosol medium has been studied. The radiation transfer properties of the medium as scattering, absorption and extinction coefficients are calculated using the Mie scattering theory. Average coefficients over the size parameter and the radiation wavelength are calculated. The radiation heat fluxes for volcanic eruption ash medium are calculated using the Variational Pomraning–Eddington approximation and compared with those obtained from the Galerkin method. The comparison showed very good agreement. 相似文献
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Within the framework of a small-angle iteration method the propagation of radiation in a three-dimensionally inhomogenous
stochastic scattering medium is considered. The results of the analysis show a significant dependence of the average light
field on the statistical structure of scattering parameters of the medium.
Deceased.
Institute of Applied Optics, National Academy of Sciences of Belarus, 11, Belynitskii-Birulya Str., Mogilev, 212793. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 234–240, March–April, 1999. 相似文献
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An expression for signal intensity fluctuations in optical coherent tomography has been obtained for the first time in the framework of the theory of the multiple scattering of low-coherent optical radiation in a random medium. The contribution of the multiple scattering of low-coherent radiation backscattered from a randomly inhomogeneous layer, as well as the speckles of the interference component in optical coherent tomography, has been calculated. 相似文献
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S. V. Blazhevich I. V. Kolosova A. V. Noskov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2012,6(2):348-355
A theory concerning the coherent X-ray radiation of relativistic electrons crossing an artificial periodic medium in Laue
scattering geometry has been constructed. Expressions describing the spectralangular characteristics of radiation in the Bragg
scattering direction have been obtained and studied. Radiation is considered in analogy with that in the crystal medium as
a result of the coherent summation of the contributions of two radiation mechanisms, in particular, parametric X-ray radiation
(PXR) and diffracted transition radiation (DTR). It is shown that the DTR yield from a layered target can exceed the particle
radiation yield in a single-crystal radiator by one order or more under similar conditions. 相似文献
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S.A. El-Wakil A. Elhanbaly 《Journal of Quantitative Spectroscopy & Radiative Transfer》2005,93(4):521-530
The properties of radiation through an aerosol medium have been achieved. This has been done by employing Mie scattering theory to calculate the radiation transfer scattering parameters in the form of extinction, absorption and scattering efficiencies. The equation of radiative transfer for the heat flux through a plane parallel atmosphere of aerosol has been solved. The aerosol size distributions are found in practical systems. Average efficiencies over size distribution for spherical particles of complex refractive index are calculated. Therefore, the radiative properties of stratospheric aerosols have been done. The obtained results found to be in a good agreement with the previous work. 相似文献
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《Journal of Quantitative Spectroscopy & Radiative Transfer》1994,52(6):791-808
The integral form of three-dimensional radiative transfer equation for an absorbing, emitting, and linear-anisotropic scattering medium with space-dependent properties is formulated. A product-integration method is subsequently applied to develop a numerical scheme for solving the corresponding integral transfer equations in a two-dimensional, axisymmetric and nonhomogeneous medium subjected to externally incident radiation or bounded by emitting and diffusely-reflecting walls. The numerical solutions for cases of constant, continuous, and stepwise variations of scattering albedo are presented to illustrate its accuracy and flexibility, and validated by comparing with results available in the literature. 相似文献
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A one-dimensional quantum model for nuclear resonant scattering using synchrotron radiation has been developed. This model
gives a clear physical interpretation of the most prominent features of the coherent forward scattering process namely, the
“speed-up” and “dynamical beat” effects. The form of the solution, for the time-dependent forward scattered intensity of the
resonant radiation from the resonant medium after synchrotron radiation excitation, is a finite series. This unique solution
can be interpreted in terms of a summation over all multiple forward scattering paths the radiation takes in reaching the
detector. The resonant medium is represented by a linear chain of N effective resonant nuclei. The analysis starts from a coupled set of quantum mechanical equations for the relevant amplitudes
in frequency space. Transformation to the time domain gives an analytical expression for the forward scattered intensity.
The contribution of every order of the multiple scattering processes from the N effective nuclei appears naturally. The expression gives a clear physical understanding of all relevant aspects of resonant
forward nuclear scattering. Furthermore, the present formalism allows the consideration of incoherent processes. This permits
the study of processes in which there is gamma emission with recoil or emission of internal-conversion electrons.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献