Generalized Multiparticle Mie-solution Research Articles

Optical properties of chain-like atmospheric aerosol particles

Using the generalized multiparticle Mie-solution method, this study examines the optical properties of chain-like particles under different atmospheric conditions and various arrangements. The structural composition of aerosols exhibits a more pronounced impact on their extinction and absorption cross sections when the incident wavelength is below 600 nm, whereas significant changes are observed in backscattering cross sections for incident wavelengths above 600 nm. As the orientation angle between the incident wave and particle chain increases, the extinction cross sections and absorption cross sections exhibit varying degrees of decline. Furthermore, marine atmospheric aerosol chains demonstrate similar extinction cross sections to those of polluted atmospheric aerosols, and their absorption cross sections closely resemble those of clean atmospheric aerosols. In addition, for a particle chain of fixed length, the greater the disparity in particle sizes within the chain, the larger the difference between the backscattering cross section and that of the chains with equal particle sizes. This research provides theoretical support for assessing the climate effects of aerosols and inverting aerosol properties by LiDAR data.

Inhibited radiation transmittance and enhanced thermal stability of silica aerogels under very-high temperature

Silica aerogels are applied extensively in thermal insulation due to their extra-low density and thermal conductivity. However, this can be heavily undermined under high temperature, especially beyond 700–800 °C, due to not only a high transparency for radiation heat transfer, but also an instability caused by nanoparticle collapse. The present study demonstrated a solution to this problem by two steps. Firstly, the size effect of nanoparticles is explored by experimentally preparing unconventional samples composed of large-diameter particles (larger than 20 nm). The prepared sample microstructures and radiative characteristics are investigated by SEM apparatus and FTIR measurements, respectively. Additionally, based on the fractal structures reconstructed using the Diffusion-Limited Colloid Aggregation (DLCA) method, the effects of particle size on thermal stability of silica aerogels are theoretically investigated and the light shielding performance is numerically analyzed by the Generalized Multiparticle Mie-solution (GMM) method. The simulation and experimental results indicate that the enhanced size of nanoparticles can improve the radiative inhibition and thermal stability property under high temperature significantly. However, the ideal above should be refined as it brings an increasing contribution of conduction heat transfer. Thus, a novel structure of core-mantle nanoparticle is proposed to retain the excellent resistance in radiation but avoid an increased thermal conduction. The present work may pave a new direction for developing aerogels under extreme temperature conditions, compared with the widely-used opacifier addition.

Influence of fractal-like aggregation on radiative properties of Chlamydomonas reinhardtii and H2 production rate in the plate photobioreactor

Chlamydomonas reinhardtii (C. reinhardtii) is regarded as one of the best candidates for photobiological H2 production. The radiative properties of its cells are pivotal in determining photosynthetic efficiency. The generalized multiparticle Mie-solution method is employed in this study to compute the radiative properties of fractal-like C. reinhardtii cells which aggregate in random orientations. The effects of fractal dimension, monomer radius, and the number of monomers of the aggregations on the radiative properties are investigated thoroughly. By comparing the radiative properties of the fractal clusters with those of volume-equivalent spheres, it is found that the difference in the extinction and scattering cross-sections of the aggregates and of the volume-equivalent spheres is significant for the cluster with a large fractal dimension and small monomers, whereas the variation in terms of the absorbing cross-section and the single-scattering albedo is slight. Similar conclusions can be obtained with respect to the differences between the radiative properties of the aggregates and those of the spheres with a corresponding radius of gyration. Finally, the light transfer and specific H2 production rate in the plate photobioreactor are investigated using the finite volume method and the Michaelis–Menten type equation. Results demonstrate that the effective H2 production region is large for photobioreactors that contain aggregates with a large fractal dimension and small monomers. However, the difference in the effective H2 production regions in terms of varying fractal dimensions and number of monomers in the aggregates decreases gradually with the increase in the size of the monomers in the aggregates. A similar conclusion can be drawn when the intensity of the incident irradiation on the photobioreactors changes.

Using the DDA (Discrete Dipole Approximation) Method in Determining the Extinction Cross Section of Black Carbon

AbstractBC (Black Carbon), which can be found in the atmosphere, is characterized by a large value of the imaginary part of the complex refractive index and, therefore, might have an impact on the global warming effect. To study the interaction of BC with light often computer simulations are used. One of the methods, which are capable of performing light scattering simulations by any shape, is DDA (Discrete Dipole Approximation). In this work its accuracy was estimated in respect to BC structures using the latest stable version of the ADDA (vr. 1.2) algorithm. As the reference algorithm the GMM (Generalized Multiparticle Mie-Solution) code was used. The study shows that the number of volume elements (dipoles) is the main parameter that defines the quality of results. However, they can be improved by a proper polarizability expression. The most accurate, and least time consuming, simulations were observed for IGT_SO. When an aggregate consists of particles composed of ca. 750 volume elements (dipoles), the averaged relative extinction error should not exceed ca. 4.5%.

Scattering and propagation of terahertz pulses in random soot aggregate systems

Scattering and propagation of terahertz pulses in random soot aggregate systems are studied by using the generalized multi-particle Mie-solution (GMM) and the pulse propagation theory. Soot aggregates are obtained by the diffusion-limited aggregation (DLA) model. For a soot aggregate in soot aggregate systems, scattering characteristics are analyzed by using the GMM. Scattering intensities versus scattering angles are given. The effects of different positions of the aggregate on the scattering intensities, scattering cross sections, extinction cross sections, and absorption cross sections are computed and compared. Based on pulse propagation in random media, the transmission of terahertz pulses in random soot aggregate systems is determined by the two-frequency mutual coherence function. Numerical simulations and analysis are given for terahertz pulses (0.7956 THz).

Theoretical Predictions of Spectral Emissivity for Coal Ash Deposits

Coal ash inevitably forms deposits as combustion residue on the walls and heat transfer surfaces of coal-fired boilers. Ash deposits decrease the boiler efficiency, reduce the generating capacity, and cause unscheduled outages. The radiative heat transfer is the major heat transfer mechanism in utility boilers; thus, the ash deposit emissivity is critical to boiler efficiency and safety. This paper presents a radiative transfer model to predict the spectral emissivities of coal ash deposits. The model includes the effects of the microstructure, chemical composition, and temperature. Typical ash deposit microstructures are generated using diffusion-limited aggregation (DLA). The radiative properties are then calculated using the generalized multiparticle Mie-solution (GMM). The combined GMM and DLA model predicts spectral emissivity better than the original Mie theory and Tien's dependent scattering theory with the average relative difference between predicted results and experimental data decreasing from 17.8% to 9.1% for sample 1 and from 18.6% to 4.2% for sample 2. Maxwell-Garnett (MG) effective medium theory is used to calculate the ash deposit optical constants based on the chemical compositions to include the effect of chemical composition. Increasing temperatures increase the particle diameters and particle volume fractions and, thus, the spectral emissivities. The spectral emissivity ultimately remains constant and less than one. The homogeneous slab model gives the upper limit of the ash deposit spectral emissivity.

Scattering of electromagnetic radiation by three-dimensional periodic arrays of identical particles

The generalized multiparticle Mie-solution (GMM), a Lorenz-Mie-type rigorous theory for the scattering of a monochromatic plane wave by an arbitrary configuration of nonintersecting scattering bodies, has lately been revisited and further developed. A recent progress is the initiation of a special version applied to one- and two-dimensional (1D and 2D) periodic arrays (PAs) of identical particles [J. Opt. Soc. Am. A30, 1053 (2013)]. As a continuous advance, the present work extends the initiative PA-type solution from 1D and 2D to the more involved three-dimensional (3D) regular arrays. Analytical formulations applicable to the 3D PAs are derived, including the special PA-type explicit expressions for cross sections of extinction, scattering, backscattering, and radiation pressure. The specific PA-version is a complement to the general formulation and solution process of the standard GMM. In either 1D and 2D or 3D cases, the newly devised PA-approach is capable of providing expeditiously theoretical predictions of radiative scattering characteristics for periodic structures consisting of a huge number of identical unit cells, which the general approach of the GMM is unable to handle in practical calculations, owing to excessive computing time and/or computer memory requirements. To illustrate practical applications, sample numerical solutions obtained via the PA-approach are shown for 3D PAs of finite lengths that have ∼5×10(7) component particles, including structures having a rectangular opening. Also discussed is potential future work on the theory and its tests.

Scattering of electromagnetic waves by periodic particle arrays

The generalized multiparticle Mie-solution (GMM) is an extension of the well-known Mie-theory for single homogeneous spheres to the general case of an arbitrary ensemble of variously sized and shaped particles. The present work explores its specific application to periodic structures, starting from one- and two-dimensional regular arrays of identical particles. Emphasis is placed on particle arrays with a truncated periodic structure, i.e., periodic arrays (PAs) with finite overall dimensions. To predict radiative scattering characteristics of a PA with a large number of identical particles within the framework of the GMM, it is sufficient to solve interactive scattering for only one single component particle, unlike the general case where partial scattered fields must be solved for every individual constituent. The total scattering from an array as a whole is simply the convolution of the scattering from a single representative scattering center with the periodic spatial distribution of all replica constituent units, in the terminology of Fourier analysis. Implemented in practical calculations, both computing time and computer memory required by the special version of GMM formulation applicable to PAs are trivial for ordinary desktops and laptops. For illustration, the radiative scattering properties of several regular arrays of identical particles at a fixed spatial orientation are computed and analyzed. Numerical results obtained from the newly developed approach for PAs are compared with those calculated from the general GMM computer codes (that have been available online for about a decade). The two sets of numerical outputs show no significant relative deviations. However, the CPU time required by the specific approach for PAs could drop more than 10,000 times, in comparison with the general approach. In addition, an example PA is also presented, which consists of as large as 10(8) particles and the general solution process is unable to handle.

Electromagnetic scattering from uniaxial anisotropic bispheres located in a Gaussian beam

Based on the Generalized Lorenz–Mie Theory (GLMT) and generalized multiparticle Mie-solution (GMM), scattering of two interacting homogeneous uniaxial anisotropic spheres with parallel primary optical axes and arbitrary configuration from a Gaussian beam is investigated. By introducing the Fourier transformation, the electromagnetic fields in the uniaxial anisotropic spheres are expanded in terms of the spherical vector wave functions (SVWFs). The interactive scattering coefficients and the expansion coefficients of the internal fields are derived through the continuous boundary conditions on which the interaction of the bispheres is considered. The influences of the beam waist widths, beam center position, and spheres separation distance on scattering characteristics of uniaxial anisotropic bispheres located in a Gaussian beam are numerically analyzed in detail.

Scattering properties of non-spherical particles in the CO2 shortwave infrared band

Based on the T-matrix method and the generalized multiparticle Mie-solution (GMM) method combined with diffusion-limited aggregation simulator, the scattering properties of non-spherical particles and aggregates are simulated at 1.6 μm and 2.0 μm. And the effects of the equal-volume sphere radius, the complex refractive index, the particle shape and the relative humidity (RH) on the scattering characteristics parameters of non-spherical aerosol are analyzed. The results show that besides the equal-volume sphere radius and the particle shape, the RH could also lead to a large change of the scattering properties. And the relative differences in back scattering between spherical particles and non-spherical particles in different relative humidities are all larger than 18%. If the RH increases, the back scattering will increase for small-size particles, while the back scattering of large-size ones will decrease. The asymmetry factors of the smaller aggregates are 0.023 averagely greater than those of the single equal-volume non-spherical particles, which the asymmetry factors of the bigger aggregates are 0.055 averagely less than those of the single equal-volume non-spherical particles. The differences in single scattering albedo between the two wavelengths 1.6 μm and 2.0 μm are all much larger for either aggregates or single equal-volume particles, and the biggest difference reaches 0.226. This research has scientific significance for studying the aerosol multiple scattering influencing on the accuracy of CO2 satellite retrieval.

Comparison investigation of near- and far-field properties for plasmon resonance of silver nanosphere dimers

Near- and far-field plasmon resonance properties of silver nanospheres dimers are calculated and compared based on the Generalized Multiparticle Mie-solution method. Greater differences between near- and far-field plasmon resonances are found than those of silver single nanoparticle, while the dimer of strongest near-field electric field amplitude and the dimer of highest far-field extinction coefficient almost have the same geometry parameter value under the illumination with fixed wavelength and polarization.

Monte Carlo simulations of spectral albedo for artificial snowpacks composed of spherical and nonspherical particles

The optical properties of snowpacks composed of spherical and nonspherical particles artificially prepared in a cold laboratory are investigated by measuring spectral albedos. The measured spectral albedo in the spectral region lambda=0.35-2.5 microm is compared with the theoretically calculated albedo, for which a Monte Carlo radiative transfer model is employed for multiple scattering combined with the Mie theory and the ray-tracing technique for single scattering by snow particles. Since the spherical particles are a little aggregate, the effects of a cluster of the spheres on snow albedo are examined using a generalized multiparticle Mie-solution model [Appl. Opt. 34, 4573 (1995); J. Quant. Spectrosc. Radiat. Transf. 79-80, 1121 (2003)]. The snow albedo of a cluster of the spheres can be represented with that of the singe sphere slightly larger than its component of the cluster in case of small grains. The observed albedos for the spherical snow particles agree with the theoretically calculated ones for the snow grain size measured in the snow pit work. The snow albedos for the nonspherical particles, which were dendrites, are influenced by the branch width and the branch length, based on a comparison of the theoretically calculated albedo by using circular cylindrical snow particles and the observed albedo. The snow albedo in the near-infrared region depends on the branch width only when the branch length is sufficiently greater than the branch width. The comparison between the spherical and nonspherical snow particles indicates that the spectral albedo of the nonspherical particles can be represented by using an equal volume-area ratio sphere.

Radiative-scattering signatures of an ensemble of nonspherical particles

In a similar way to Mie theory of describing light scattering by a single homogeneous sphere, the generalized multiparticle Mie-solution (GMM) precisely predicts light-scattering characteristics of an ensemble of arbitrarily shaped and arbitrarily oriented nonintersecting particles. Some numerical solutions obtained from the GMM are presented to demonstrate how the scattering and polarization properties of an ensemble of particles vary with particle number, shape, orientation, and configuration. These practical examples clearly show that polarization analysis could be a powerful tool for characterization of small particles.

Orientation-averaged radiative properties of an arbitrary configuration of scatterers

We discuss both analytical and numerical methods in calculating radiative scattering parameters of a randomly oriented ensemble of particles. There exist two approaches to rigorously solving multiparticle scattering. One is the generalized multiparticle Mie-solution (GMM) and the other is cluster T-matrix approach (CTM). We show that, the same as in the case of fixed-orientation scattering, the random-orientation formulations of GMM and CTM have a remarkable contrast in capability of handling the overall dimension of an ensemble of particles in practical applications. We also show that the use of a standard scheme of numerical quadrature could be more efficient than straightforwardly taking an unweighted arithmetic average in discrete orientational averaging.