Scattering-absorbing Medium Research Articles

On the property of ”statistical identity” of solutions to some classical problems of the radiative transfer theory

A probabilistic interpretation of the classical solution of the diffuse reflection problem (DRP) of radiation from a semi-infinite homogeneous scattering-absorbing medium on the language of random events in the simple case of monochromatic and isotropic scattering is constructed. A certain property of the so-called ”statistical identity” is specially defined. By using these two circumstances, it is possible to construct a simple symbolic scheme for the direct transformation of the solution mentioned above in the particular case of DRP into solutions to more general cases of DRP, which taking into account the anisotropy and incoherence of scattering, as well as the temporal dependence of the task on the act of absorption. Moreover, some generalization of the primary scheme makes it possible to directly obtain solutions of the DRP also for nonhomogeneous media and for general case of time dependence (on absorption acts and free flights between them) for the quanta diffusion process. At the same time, both the well-known results of the DRP decisions and some new ones were obtained.

Dynamic blood flow phantom with negative and positive photoacoustic contrasts.

In vivo photoacoustic (PA) flow cytometry (PAFC) has great clinical potential for early, noninvasive diagnosis of cancer, infections (e.g., malaria and bacteremia), sickle anemia, and cardiovascular disorders, including stroke prevention through detection of circulating white clots with negative PA contrast. For clinical applications, this diagnostic platform still requires optimization and calibration. We have already demonstrated that this need can be partially addressed by in vivo examination of large mouse blood vessels, which are similar to human vessels used. Here, we present an alternative method for PAFC optimization that utilizes novel, clinically relevant phantoms resembling pigmented skin, tissue, vessels, and flowing blood. This phantom consists of a scattering-absorbing medium with a melanin layer and plastic tube with flowing beads to model light-absorbing red blood cells (RBCs) and circulating tumor cells (CTCs), as well as transparent beads to model white blood cells and clots. Using a laser diode, we demonstrated the extraordinary ability of PAFC to dynamically detect fast-moving mimic CTCs with positive PA contrast and white clots with negative PA contrast in an RBC background. Time-resolved detection of the delayed PA signals from blood vessels demonstrated complete suppression of the PA background from the modeled pigmented skin. This novel, medically relevant, dynamic blood flow phantom can be used to calibrate and maintain PAFC parameters for routine clinical applications.

Analytical solution of the simple nonlinear radiative transfer problem

Exploring the "Principle of invariance" and the method of "Linear images", the simple nonlinear conservative problem of radiative transfer is analyzed. The solutions of nonlinear reection-transmission and internal field problems of one dimensional scattering-absorbing medium of finite optical thickness are obtained, whereas both boundaries of medium illuminated by powerful radiation beams. Using two different approaches - a direct and inverse problem, the analytical solution of the internal field problem is derived.

102 MUSCL法を用いた散乱吸収媒体における反射率と透過率の数値解析的予測

102 MUSCL法を用いた散乱吸収媒体における反射率と透過率の数値解析的予測

104 拡散照射下における散乱吸収媒体の反射率と透過率

104 拡散照射下における散乱吸収媒体の反射率と透過率

Transient Prediction of Radiation Response in a 3-D Scattering-Absorbing Medium Subjected to a Collimated Short Square Pulse Train

Transient radiative transfer characteristics in a three-dimensional scattering-absorbing medium subjected to collimated irradiation of a short pulse train were investigated. A basic problem in which a cube is exposed to collimated irradiation of a single unit step square pulse was solved via the transient discrete-ordinates method, and Duhamel's superposition theorem was used to construct the responses of various pulse trains. The effects of optical thickness, scattering albedo, pulse width, and pulse train interval between two successive pulses on the temporal profiles of divergence of radiative heat flux, reflectance, and transmittance were scrutinized.

Rational approximation formula for Chandrasekhar’s H-function for isotropic scattering

We first establish a simple procedure to obtain with 11-figure accuracy the values of Chandrasekhar's H-function for isotropic scattering using a closed-form integral representation and the Gauss-Legendre quadrature. Based on the numerical values of the function produced by this method for various values of the single scattering albedo and the cosine of the azimuth angle of the direction of radiation emergent from or incident upon a semi-infinite scattering-absorbing medium, we propose a rational approximation formula, which allows us to reproduce the correct values of the H-function within a relative error of 2.1/100000 without recourse to any iterative procedure or root-finding process.

Conversion and conservation of light energy in a photosynthetic microbial mat ecosystem

Here we present, to the best of our knowledge, the first balanced light energy budget for a benthic microbial mat ecosystem, and show how the budget and the spatial distribution of the local photosynthetic efficiencies within the euphotic zone depend on the absorbed irradiance (J(abs)). Our approach uses microscale measurements of the rates of heat dissipation, gross photosynthesis and light absorption in the system, and a model describing light propagation and conversion in a scattering-absorbing medium. The energy budget was dominated by heat dissipation on the expense of photosynthesis: in light-limiting conditions, 95.5% of the absorbed light energy dissipated as heat and 4.5% was channeled into photosynthesis. This energy disproportionation changed in favor of heat dissipation at increasing irradiance, with >99% of the absorbed light energy being dissipated as heat and <1% used by photosynthesis at J(abs)>700 micromol photon m(-2) s(-1) (>150 J m(-2) s(-1)). Maximum photosynthetic efficiencies varied with depth in the euphotic zone between 0.014-0.047 O(2) per photon. Owing to steep light gradients, photosynthetic efficiencies varied differently with increasing irradiances at different depths in the euphotic zone; for example, at J(abs)>700 micromol photon m(-2) s(-1), they reached around 10% of the maximum values at depths 0-0.3 mm and progressively increased toward 100% below 0.3 mm. This study provides the base for addressing, in much more detail, the photobiology of densely populated photosynthetic systems with intense absorption and scattering. Furthermore, our analysis has promising applications in other areas of photosynthesis research, such as plant biology and biotechnology.

Development and comparison of models for light-pulse transport through scattering–absorbing media

We examine the transport of short light pulses through scattering-absorbing media through different approximate mathematical models. It is demonstrated that the predicted optical signal characteristics are significantly influenced by the various models considered, such as P(N) expansion, two-flux, and discrete ordinates. The effective propagation speed of the scattered radiation, the predicted magnitudes of the transmitted and backscattered fluxes, and the temporal shape and spread of the optical signals are functions of the models used to represent the intensity distributions. A computationally intensive direct numerical integration scheme that does not utilize approximations is also implemented for comparison. Results of some of the models asymptotically approach those of direct numerical simulation if the order of approximation is increased. In this study therefore we identify the importance of model selection in analyzing short-pulse laser applications such as optical tomography and remote sensing and highlight the parameters, such as wave speed, that must be examined before a model is adopted for analysis.