Browsing by Subject "T-MATRIX"

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  • Herranen, J.; Markkanen, J.; Muinonen, K. (2017)
    We establish a theoretical framework for solving the equations of motion for an arbitrarily shaped, inhomogeneous dust particle in the presence of radiation pressure. The repeated scattering problem involved is solved using a state-of-the-art volume integral equation-based T-matrix method. A Fortran implementation of the framework is used to solve the explicit time evolution of a homogeneous irregular sample geometry. The results are shown to be consistent with rigid body dynamics, between integrators, and comparable with predictions from an alignment efficiency potential map. Also, we demonstrate the explicit effect of single-particle dynamics to observed polarization using the obtained orientational results.
  • Frattin, E.; Munoz, O.; Moreno, F.; Nava, J.; Escobar-Cerezo, J.; Gomez Martin, J. C.; Guirado, D.; Cellino, A.; Coll, P.; Raulin, F.; Bertini, I.; Cremonese, G.; Lazzarin, M.; Naletto, G.; La Forgia, F. (2019)
    We present experimental phase function and degree of linear polarization curves for seven samples of cometary dust analogues namely: ground pieces of Allende, DaG521, FRO95002, and FRO99040 meteorites, Mg-rich olivine and pyroxene, and a sample of organic tholins. The experimental curves have been obtained at the IAA Cosmic Dust Laboratory at a wavelength of 520 nm covering a phase angle range from 3 degrees to 175 degrees. We also provide values of the backscattering enhancement for our cometary analogue samples. The final goal of this work is to compare our experimental curves with observational data of comets and asteroids to better constrain the nature of cometary and asteroidal dust grains. All measured phase functions present the typical behaviour for mu m-sized cosmic dust grains. Direct comparison with data provided by the OSIRIS/Rosetta camera for comet 67P/Churyumov-Gerasimenko reveals significant differences and supports the idea of a coma dominated by big chunks, larger than one micrometer. The polarization curves are qualitatively similar to ground-based observations of comets and asteroids. The position of the inversion polarization angle seems to be dependent on the composition of the grains. We find opposite dependence of the maximum of the polarization curve for grains sizes in the Rayleigh-resonance and geometric optics domains, respectively.
  • Xu, Guanglang (2020)
    Fast, accurate, and stable computation of the Clebsch-Gordan (C-G) coefficients is always desirable, for example, in light scattering simulations, the translation of the multipole fields, quantum physics and chemistry. Current recursive methods for computing the C-G coefficients are often unstable for large quantum numbers due to numerical overflow or underflow. In this paper, we present an improved method, called the sign-exponent recurrence, for the recursive computation of C-G coefficients. The result shows that the proposed method can significantly improve the stability of the computation without losing its efficiency, producing accurate values for the C-G coefficients even with very large quantum numbers. (C) 2020 The Author. Published by Elsevier Ltd.
  • Väisänen, Timo; Markkanen, Johannes; Penttilä, Antti; Muinonen, Karri (2019)
    We present a numerical method for solving electromagnetic scattering by dense discrete random media entitled radiative transfer with reciprocal transactions ((RT2)-T-2). The (RT2)-T-2 is a combination of the Monte Carlo radiative-transfer, coherent-backscattering, and superposition T-matrix methods. The applicability of the radiative transfer is extended to dense random media by incorporating incoherent volume elements containing multiple particles. We analyze the (RT2)-T-2 by comparing the results with the asymptotically exact superposition T-matrix method, and show that the (RT2)-T-2 removes the caveats of radiative-transfer methods by comparing it to the RT-CB. We study various implementation choices that result in an accurate and efficient numerical algorithm. In particular, we focus on the properties of the incoherent volume elements and their effects on the final solution.