Features of photon diffusion in a dispersed medium

Energy transfer by thermal radiation in a dispersed medium with a variable refractive index is discussed. This transfer can be described by a surprisingly simple diffusion equation. The process is naturally to interpret as the photon diffusion. The diffusion equation is free from strict conditions of applicability of the radiation transfer equation, which are usually not satisfied in disperse media with densely packed inhomogeneities. Quantum constraints on the value of the photon diffusion coefficient are derived. These restrictions turn out to be similar to the conditions for the applicability of geometric optics. The lower limit of the thermal conductivity coefficient is obtained, which is easier to verify in the experiment. An independent derivation of this limitation is given from considerations of symmetry and dimension.

An extrapolation method for projection data fltration in pulsed X-ray tomography

This paper deals with an inverse problem that consists of an attenuation coefficient identification for the non-stationary radiation transfer equation. To solve the problem, we propose a method that uses several pulses of radiation to extrapolate ideal projection data corresponding to a non-scattering medium. Numerical experiments on the Shepp-Logan phantom show that the method proposed improves the reconstruction quality.

Численное моделирование миграции фотонов в однородных и неоднородных цилиндрических фантомах

The specific features of photon diffusion of low-coherence pulsed irradiation in phantoms of soft biological tissues (blood-saturated tissues of the brain, breast, etc.) are described. The results of photon migration simulation using the Diffusion Approximation to the Radiation Transfer Equation (RTE) are compared with ones of the Monte Carlo simulations. It has been confirmed that the Photon Density Normalized Maximum (PDNM) moves towards the center of the investigated object in case of relatively uniform and strongly scattering media. In the presence of inhomogeneities, type of the PDNM motion changes drastically. Presence of an absorbing inhomogeneity in the medium directs trajectory of the PDNM motion of towards the point symmetric to the inhomogeneity relative to the geometric center of the investigated object. In case of scattering the PDNM moves toward the direction of the center of the scattering inhomogeneity.

Polarization of Radiation by the Aerosol-Gas Component of the Atmosphere for Lidar Wavelengths

The report presents an original algorithm for solving the radiation transfer equation based on the Monte Carlo method for problems of atmospheric laser sensing, taking into account the polarization of radiation. A number of test calculations were performed to analyze the data of the polarization scanning lidar of the V.E. Zuev Institute of Atmospheric Optics SB RAS. It is shown that the proposed algorithm, taking into account the polarization, makes it possible to reduce the discrepancy in interpreting lidar data in comparison with the algorithm without taking into account polarization.

REVIEW OF APPROACHES TO DESCRIPTION OF LIGHT SCATTERING IN BIOLOGICAL TISSUE

The article discusses various approaches to modeling the processes of light scattering in biological tissues. The analytical radiation transfer equation, the Tversky approach, the Bethe–Salpeter equation, and the ladder approximation are considered. For cases of single scattering, the Kubelka–Munk approach, the diffusion approximation, and the small perturbation method are presented. The mathematical principles of the considered methods are disclosed in the paper and the limits of applicability in solving the radiation transfer equation are analyzed.

Mathematical Model of Heat Exchange and Approximate Methods of Solution of Radiation Transfer Equation in the Melting Furnace Tank

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Analysis on the Applicability of Diffusion Approximation for the Radiative Transfer Equation with Compton Scattering

This paper deals with a diffusion approximation for the radiation transfer equation which takes into account Сompton scattering on electrons. An analytical and a numerical examples are used to compare the solution of radiation transfer equation with its diffusion approximation.