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121.
A method is suggested to determine experimentally whether the state of a spin system is oriented or non-oriented by measuring
the angular distribution,I and the circular polarization asymmetry,A
c of the photons emitted by the system. These also provide enough data to determine the density matrix completely. 相似文献
122.
B.X. Li Y.P. Lu L.H. Liu H.P. Tan 《Journal of Quantitative Spectroscopy & Radiative Transfer》2005,92(1):51-59
For the purpose of energy conservation and uniform heating of object surface, a gas-fired porous radiant burner with a bundle of reflecting tubes is developed. A physical model is developed to simulate the directional radiative behavior of this heating device, in which the Monte Carlo method based on the concept of radiation distribution factor is used to compute the directional radiative behavior. The effects of relating parameters on the directional behavior of radiative heating and the heating efficiency are analyzed. With the increase of the length-to-radius ratio of tube, the radiation heating efficiency decreases, but the radiation energy incident on the object surface is more collimated. The radiation heating efficiency increases with the specular reflectivity. With the increase in length of tube segment with specular reflective surface, the radiation heating efficiency increases, but the extent of concentration and collimation of radiative energy decreases. For real design of the heating device, some trade-offs are needed to balance the radiation heating efficiency and the uniformity of radiative heating of object surface. 相似文献
123.
In this paper, an optimal control problem for glass cooling processes is studied. We model glass cooling using the SP1 approximations to the radiative heat transfer equations. The control variable is the temperature at the boundary of the domain. This results in a boundary control problem for a parabolic/elliptic system which is treated by a constrained optimization approach. We consider several cost functionals of tracking‐type and formally derive the first‐order optimality system. Several numerical methods based on the adjoint variables are investigated. We present results of numerical simulations illustrating the feasibility and performance of the different approaches. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
124.
125.
D. Benredjem V. Bommier H. Guennou C. Möller A. Sureau 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(1):83-87
In order to solve the radiative-transfer equation for polarized beams propagating in plasmas a matrix approach is applied.
The solution is the four-components Stokes vector, and the effect of the medium on the state of the radiation is represented
by an amplification operator. Our approach is applied to the neon-like germanium 23.6 nm line, when a right-circularly polarized
beam is injected into an amplifying plasma. The conditions governing the recovery of the initial polarization state are investigated
over the entire spectrum of the output.
Received: 10 October 1997 / Revised: 12 January 1998 / Accepted: 27 January 1998 相似文献
126.
127.
Kamal M. Katika 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,98(2):220-237
This paper presents the modified method of characteristics for simulating multidimensional transient radiative transfer in emitting, absorbing and scattering media. The method is based on the method of characteristics that follows photons along their pathlines. It makes use of a fixed set of points, and unlike the conventional method of characteristics, it follows the photons backward in space. Test problems involving diffuse irradiation in 1-D and 3-D participating media and collimated irradiation in 1-D participating media were considered. The results show good agreement with analytical and numerical solutions reported in literature. The scheme is fast and was able to capture the sharp discontinuities associated with the propagation of a radiation front in transient radiation transport. 相似文献
128.
Approximate but accurate solutions for a class of integral equations, such as those that arise in radiative transfer, are obtained with two-step method proposed. The first term of a Taylor series expansion is used to obtain a first-order approximation, followed by collocation with the first approximation as a trial function. This technique appears to be particularly attractive for non-uniform temperature distributions, for which direct numerical integration may be subject to instability, or require an excessive amount of computation, and for which other approximate methods may require numerous terms or an excessive amount of computation. Illustrative calculations for representative thermal problems indicate that the accuracy of the method depends critically on the location and number of collocation points and suggestions are provided for these choices 相似文献
129.
X-ray tomographic determination of the chemical composition and structure of an inhomogeneous medium
V. G. Nazarov 《Computational Mathematics and Mathematical Physics》2007,47(8):1358-1367
The chemical composition of an inhomogeneous body consisting of several homogeneous parts is determined by x-ray tomography. At the first stage, an indicator of inhomogeneities is used to determine the internal structure of the body. Next, under certain additional assumptions about the properties of the parts, a method is proposed for partial or complete determination of the chemical composition of each part as based on the results of the previous stage. Mathematically, the problem is reduced to solving the radiative transfer equation and systems of linear algebraic equations. Numerical experiments are performed via computer simulation. The numerical results are illustrated by graphs and tomograms. 相似文献
130.
G. A. Mikhailov N. V. Tracheva S. A. Ukhinov 《Computational Mathematics and Mathematical Physics》2007,47(7):1213-1223
The parameters of time asymptotics of the polarized radiation intensity are estimated. Precision Monte Carlo estimates of these parameters are derived for finite medium layers by iterating the resolvent of the corresponding transfer operator with a given scattering matrix and by evaluating parametric time derivatives. The computations are performed for two versions of the problem: with a Rayleigh scattering matrix and an aerosol scattering matrix. It is shown that the asymptotics of the radiation intensity are affected by polarization, except for the spatially homogeneous problem, for which the results are obtained analytically. 相似文献