Calculation of the radiative properties of photosynthetic microorganisms

Abstract

a b s t r a c tA generic methodological chain for the predictive calculation of the light-scattering and absorption properties of photosynthetic microorganisms within the visible spectrum is presented here. This methodology has been developed in order to provide the radiative properties needed for the analysis of radiative transfer within photobioreactor processes, with a view to enable their optimization for large-scale sustainable production of chemicals for energy and chemistry. It gathers an electromagnetic model of lightparticle interaction along with detailed and validated protocols for the determination of input parameters: morphological and structural characteristics of the studied microorganisms as well as their photosynthetic-pigment content. The microorganisms are described as homogeneous equivalent-particles whose shape and size distribution is characterized by image analysis. The imaginary part of their refractive index is obtained thanks to a new and quite extended database of the in vivo absorption spectra of photosynthetic pigments (that is made available to the reader). The real part of the refractive index is then calculated by using the singly subtractive Kramers-Krönig approximation, for which the anchor point is determined with the Bruggeman mixing rule, based on the volume fraction of the microorganism internal-structures and their refractive indices (extracted from a database). Afterwards, the radiative properties are estimated using the Schiff approximation for spheroidal or cylindrical particles, as a first step toward the description of the complexity and diversity of the shapes encountered within the microbial world. Finally, these predictive results are confronted to experimental normal-hemispherical transmittance spectra for validation. This entire procedure is implemented for Rhodospirillum rubrum, Arthrospira platensis and Chlamydomonas reinhardtii, each representative of the main three kinds of photosynthetic microorganisms, i.e. respectively photosynthetic bacteria, cyanobacteria and eukaryotic microalgae. The obtained results are in very good agreement with the experimental measurements when the shape of the microorganisms is well described (in comparison to the standard

Quantifying bioalbedo: a new physically based model and discussion of empirical methods for characterising biological influence on ice and snow albedo

“…The water fraction (x w ) and density of cellular dry mass (ρ dm ) are assumed constant throughout the simulations presented in this paper (ρ dm = 1400 kg m −3 , x w = 0.8: Dauchet et al, 2015); however, we provide Eq. (2) to enable derivation of x w from empirical data (see Pottier et al, 2005;Kandilian et al, 2016).…”

“…(1), since k λ will become infinite when x w = 0. Equation (1) is therefore applicable for 0<x w <1, where realistic values are likely to be close to 0.8 (Dauchet et al, 2015). Information about the size of the cells is obtained using a second model that creates particle size distributions from the mean cell radius and standard deviation.…”

10 Knowledge models for the engineering and optimization of photobioreactors

“…), which has marked effects on the pigment contents or the size distribution of the cells. 10.6), often very different from spheres, the authors are currently developing a predictive method (Dauchet et al 2012b) that allows radiative properties to be computed for any given shape of rotationally symmetric randomly oriented scatterers from the anomalous diffraction approximation (Van de Hulst 1981). Solving this problem using a model of equivalent sphere for the micro-organisms is referred to as the Lorenz-Mie theory, which today is quite easy to compute (Bohren and Brought to you by | New York University Bobst Library Technical Services Authenticated Download Date | 2/6/15 2:03 AM Huffman 1983; Pottier et al 2005).…”

Addressing nonlinearities in Monte Carlo

“…Results shown in Extended Data Figure 2 are obtained for k = 2π/λ, with wavelength λ = 500nm and the scattering potential U in = −2k(m − 1), with m = 1.2 − i 4 .10 −3 (scatterer relative refractive index [20]). The shape of the scatterer is helical with length L = 50µm, pitch P = 15µm, helix diameter D = 20µm, cylinder diameter d = 3.5µm.…”