Solution of inverse problems of radiative transport by soot particles of complex shapes

We work out a method of determining the effective parameters of soot particles from their radiation characteristics. The method is based on the measurements of the spectral transmission coefficient in the infrared region of the spectrum.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 6, pp. 921–925, December, 1985.     

Measurement of light absorption by aquatic particles: improvement of the quantitative filter technique by use of an integrating sphere approach

Determination of particulate absorption in natural waters is often made by measuring the transmittance of samples on glass-fiber filters with the so-called quantitative filter technique (QFT). The accuracy of this technique is limited due to variations in the optical properties of the sample/filter composite, and due to uncertainties in the path-length amplification induced by multiple scattering inside the filter. Some variations in the optical properties of the sample/filter composite can be compensated by additional measurements of the filter's reflectance (transmittance-reflectance method [T-R] [S. Tassan and G. M. Ferrari, Limnol. Oceanogr. 40, 1358 (1995)]). We propose a different, rarely used approach, namely to measure the filter's absorptance in the center of a large integrating sphere, to avoid problems with light losses due to scattering. A comparison with other QFTs includes a sensitivity study for different error sources and determination of path-length amplification factors for each measurement technique. Measurements with a point-source integrating-cavity absorption meter were therefore used to determine the true absorption. Filter to filter variability induced a much lower error in absorptance compared to a measured transmittance. This reduced error permits more accurate determination of the usually low absorption coefficient in the near IR spectral region. The error of the T-R method was lower than that of the transmittance measurement but slightly higher than that of an absorptance measurement. The mean path-length amplification was much higher for the absorptance measurement compared to the T-R method (4.50 versus 2.45) but was found to be largely independent of wavelength and optical density. With natural samples the path-length amplification was less variable for the absorptance measurement, reducing the overall error for absorption to less than ±14%, compared to ±25% for the T-R method.     

Estimation of scattering error in spectrophotometric measurements of light absorption by aquatic particles from three-dimensional radiative transfer simulations

We present an approach based on three-dimensional Monte Carlo radiative transfer simulations for estimating scattering error in measurements of light absorption by aquatic particles with a typical laboratory double-beam spectrophotometer. The scattering error is calculated by combining the weighting function describing the angular distribution of photon losses that are due to scattering on suspended particles with the volume scattering function of particles. We applied this method to absorption measurements made on marine phytoplankton, a diatom Thalassiosira pseudonana and a cyanobacterium Synechococcus. Assuming that the scattering phase function is described by the Henyey-Greenstein formula, we determined the backscatter probability of phytoplankton, which yields the best correction for scattering error at a light wavelength of 750 nm, where true absorption is null. The backscattering ratio estimated for both phytoplankton species is significantly higher than previously reported data based on Mie-scattering calculations for homogeneous spheres. Depending on the type of particles, the corrected absorption spectra obtained with our method may be similar or significantly different from spectra obtained with the null-point correction based on wavelength-independent scattering error.     

Light scattering and absorption by soot in the presence of sulfate aerosols

The radiative properties of aerosol-soot mixtures, both internal and external, are determined in the visible and near-infrared bands by use of exact indirect mode-matching solutions to electromagnetic-wave scattering from a sphere with an eccentric spherical inclusion and from a cluster of spheres. Spherical sulfate droplets are assumed to represent aerosol particles. Soot particles are represented by volume-equivalent carbon spheres, the size distribution of which is obtained from the number distribution of the primary carbon particles that aggregate into soot grains. The mean gram-specific absorption cross section and the mean albedo of aerosol-soot mixtures are obtained by integration of the corresponding characteristics of composite sulfate-carbon particles over the size range of carbon spheres. Enhanced absorption of light by soot in aerosol-soot mixtures, a result of lensing by sulfate droplets, is highlighted by maps of the electromagnetic field in a sulfate-carbon particle.     

Phase-plane analysis of multiplicity and thermal runaway in a hollow sphere subject to a constant internal radiative power source

In this paperwe present an analysis of the steady-state solutions of a classical equation describing thermal runaway in spherical symmetrymodified to study the hazard presented by a fractured optical fibre in a flammable atmosphere. Exothermic reaction is coupled with a radiation source that imposes a temperature gradient at the edge of an inert spherical core within the reaction zone. Reactant consumption is neglected. The governing equation is integrated directly and the steady-state profiles are examined with the Frank-Kamenetskii parameterbas the bifurcation parameter. Gross multiplicity of steady states is seen to be a feature for certain parameter values. Subsequentlya phase-plane approach is used which renders some features of the solutions more accessible. In particularthe point at which the system ceases to exhibit criticalitywhich is important from the hazard assessment point of viewis easily identified     

Phase-plane analysis of multiplicity and thermal runaway in a hollow sphere subject to a constant internal radiative power source

In this paperwe present an analysis of the steady-state solutions of a classical equation describing thermal runaway in spherical symmetrymodified to study the hazard presented by a fractured optical fibre in a flammable atmosphere. Exothermic reaction is coupled with a radiation source that imposes a temperature gradient at the edge of an inert spherical core within the reaction zone. Reactant consumption is neglected. The governing equation is integrated directly and the steady-state profiles are examined with the Frank-Kamenetskii parameterbas the bifurcation parameter. Gross multiplicity of steady states is seen to be a feature for certain parameter values. Subsequentlya phase-plane approach is used which renders some features of the solutions more accessible. In particularthe point at which the system ceases to exhibit criticalitywhich is important from the hazard assessment point of viewis easily identified     

共振瑞利散射光谱法在药物分析中的应用概述

共振瑞利散射光谱法因具有简便操作、灵敏度高的优势,已在药物研究领域得到广泛应用。本文综述了近年来共振瑞利散射光谱法在药物分析测定方面取得的成果,着重介绍在抗生素类,麻醉类、多糖类和一些新药等方面的应用。     

Concept of the equiphase sphere for light scattering by nonspherical dielectric particles

We introduce the concept of the equiphase sphere for light scattering by nonspherical dielectric particles. This concept facilitates the derivation of a simple analytical expression for the total scattering cross section of such particles. We tested this concept for spheroidal particles and obtained a bound on the minor-to-major axis ratio for the valid application of this technique. We show that this technique yields results that agree well with the rigorous numerical solution of Maxwell's equations obtained with the finite-difference time-domain method. The new technique has the potential to be extended to the study of light scattering by arbitrarily shaped convex dielectric particles.     

Characteristic time for the evolution of instability of a droplet charged to the Rayleigh limit

The nonlinear problem of the capillary oscillations of a charged droplet is solved to estimate the characteristic time for the evolution of instability of a droplet carrying critical charge. It is observed that breakup is delayed because of the hydrodynamic inertia of the droplet. Pis’ma Zh. Tekh. Fiz. 25, 41–45 (August 12, 1999)     

The application of graph theory to the limit analysis for torsion of thin-walled bars

Graph theory is employed in this paper as a means to establish the topological model of complex thin-walled cross-sections. On this basis, the upper and lower bound theorems of the plastic limit analysis are applied to the analysis of the plastic limit shear flows on the cross-section of thin-walled bars under St. Venant torsion. Corresponding mathematical programming problems are formulated and their duality is shown. After solving the linear programming problem corresponding to the lower bound theorem, the limit torsional moment of a thin-walled cross-section can be calculated according to the shear stress distribution in the limit state. The formula to calculate the limit torsional moment is given in the paper. Furthermore, the limit state of thin-walled cross-sections under St. Venant torsion is also discussed and a concept of the limit tree is introduced. A computer program has been developed by the author. Results calculated by the program for typical complex cross-sections are given in the paper.     

Hydrophilicity of soot particles formed in the combustion chamber of a jet engine

The particles of soot, formed in the combustion chamber of a jet engine under conditions typical of a cruising power mode, are capable of adsorbing a considerable amount of water vapor owing to their microcrystalline structure, microporosity, and chemically heterogeneous surface.     

Scanning holographic microscopy with resolution exceeding the Rayleigh limit of the objective by superposition of off-axis holograms

We present what we believe to be a new application of scanning holographic microscopy to superresolution. Spatial resolution exceeding the Rayleigh limit of the objective is obtained by digital coherent addition of the reconstructions of several off-axis Fresnel holograms. Superresolution by holographic superposition and synthetic aperture has a long history, which is briefly reviewed. The method is demonstrated experimentally by combining three off-axis holograms of fluorescent beads showing a transverse resolution gain of nearly a factor of 2.     

Variability of light absorption by aquatic particles in the near-infrared spectral region

We have measured the light absorption of a set of particle suspensions of varying nature (pure minerals, particulate standards, aquatic particles) using a double-beam spectrophotometer with a 15-cm-diameter integrating sphere. The sample was located inside the sphere so as to minimize the effect of light scattering by the particles. The results obtained showed highly variable absorption in the near-IR region of the wavelength spectrum. The same particle samples were deposited on glass-fiber filters, and their absorption was measured by the transmittance-reflectance method, based on a theoretical model that corrects for the effect of light scattering. The good agreement found between the results of the measurements carried out inside the sphere and by the transmittance-reflectance method confirms the validity of the scattering correction included in the above method.     

Screening of radiative heat flux by the injection of products of the destruction of asbestos plastic in hypersonic flow over a sphere

The variation of the coefficient of screening along the generatrix and the influence of the mode of flow in the boundary layer on its value are analyzed on the example of the flow of a CO₂ + N₂ mixture over a sphere of asbestos plastic.Translated from Inzhenero-Fizicheskii Zhurnal, Vol. 46, No. 2, pp. 303–308, February, 1984.     

An analytical model to study the effective stiffness of the composites with periodically distributed sphere particles

In order to analytically study the overall elastic stiffness of the composite containing periodically dispersed sphere particles, a new micro-mechanics model is developed in this paper. Three kinds of typical particle packing arrangements in the form of simple cubic lattice, body-centered cubic lattice and face-centered cubic lattice are considered and compared. The special characteristics of regular distribution are fully considered by incorporating the necessary geometrical symmetry conditions into strain Green’s function. It is found that particle arrangement obviously affects the macroscopic elastic response of such the kind of composite. Moreover, most of the predictions by the present model are in good agreement with the FEM computations. The effective Young’s modulus of BCC composite the effective shear modulus of SC composite are not in the range of the Hashin–Shtrikman bounds. The present model is also useful to verify some other numerical results mainly obtained by the unit-cell model, for instance, damage variables, matrix plasticity, etc.     

The formation of ionisation clusters by alpha particles in 'nanometric' volumes of nitrogen: experiment and calculation

Probability distributions of the size of ion clusters created in 'nanometric' cylindrical volumes of nitrogen by single 4.6 MeV alpha particles were measured and compared with those calculated by Monte Carlo simulation. The diameter of the sensitive volume had a mass per area of between 0.015 and 1.3 micrograms.cm-2 which, for a material at unit density, corresponds to a diameter of between 0.15 nm and 13 nm. These nanometre sizes were simulated experimentally in a device called Jet Counter. The measured or calculated cluster size probabilities confirmed that the formation of ionisation clusters along a 'nanometre' track can be characterised by Poisson's distribution only for very small targets. The present ionisation cluster probabilities produced in 'nanometric' volumes, 2 to 10 nm in diameter, are the first ever determined experimentally and confirmed by Monte Carlo simulation.     

Efficient finite-difference time-domain scheme for light scattering by dielectric particles: application to aerosols

We have examined the Maxwell-Garnett, inverted Maxwell-Garnett, and Bruggeman rules for evaluation of the mean permittivity involving partially empty cells at particle surface in conjunction with the finite-difference time-domain (FDTD) computation. Sensitivity studies show that the inverted Maxwell-Garnett rule is the most effective in reducing the staircasing effect. The discontinuity of permittivity at the interface of free space and the particle medium can be minimized by use of an effective permittivity at the cell edges determined by the average of the permittivity values associated with adjacent cells. The efficiency of the FDTD computational program is further improved by use of a perfectly matched layer absorbing boundary condition and the appropriate coding technique. The accuracy of the FDTD method is assessed on the basis of a comparison of the FDTD and the Mie calculations for ice spheres. This program is then applied to light scattering by convex and concave aerosol particles. Comparisons of the scattering phase function for these types of aerosol with those for spheres and spheroids show substantial differences in backscattering directions. Finally, we illustrate that the FDTD method is robust and flexible in computing the scattering properties of particles with complex morphological configurations.     

A computer study of the absorption of infrared radiation by systems of molecular clusters

The method of molecular dynamics is used to investigate the process of absorption of N₂O and CH₄ molecules by water clusters and to determine the frequency spectra of permittivity for systems consisting of clusters mixed in different ratios, namely, (H₂O)_n, (N₂O)_i(H₂O)₁₀, and (CH₄)_i(H₂O)₁₀. IR-radiation absorption spectra for these systems are calculated and analyzed; the radiation power scattered by these systems and the tangent of dielectric loss angle are determined. The inclusion of anharmonicity of phonon oscillation makes it possible to explain the origin of characteristic frequencies appearing in IR spectra of mixtures of cluster systems. The capture of molecules of greenhouse gases by an ultradisperse aqueous medium affects the ability of this medium to absorb terrestrial radiation, i.e., reduces the greenhouse effect.     

Deposition of tellurium films by decomposition of electrochemically-generated H2Te: application to radiative cooling devices

The preparation of homogenous, large area thin layers of tellurium on thin polyethylene foils is described. The tellurium was formed by room temperature decomposition of electrochemically generated H₂Te. Pre-treatment of the polyethylene substrates with KMnO₄ to give a Mn-oxide layer was found to improve the Te adhesion and homogeneity. Optical characterization of the layers was performed using UV/VIS/NIR spectroscopy. Such coatings have favorable characteristics for use as solar radiation shields in radiative cooling devices. The simplicity of generation of the very unstable H₂Te was also exploited to demonstrate formation of size-quantized CdTe nanocrystals.