Biomedical subjects

Kari Lumme

Publications and source records attributed to Kari Lumme.

3 recordsLinked to original sources

PubMed2006

Light-scattering efficiency of starch acetate pigments as a function of size and packing density.

We study theoretically the light-scattering efficiency of paper coatings made of starch acetate pigments. For the light-scattering code we use a discrete dipole approximation method. The coating layer is assumed to consists of roughly equal-sized spherical pigments packed either at a packing density of 50% (large cylindrical slabs) or at 37% or 57% (large spheres). Because the scanning electron microscope images of starch acetate samples show either a particulate or a porous structure, we model the coatings in two complementary ways. The material can be either inside the constituent spheres (particulate case) or outside of those (cheeselike, porous medium). For the packing of our spheres we use either a simulated annealing or a dropping code. We can estimate, among other things, that the ideal sphere diameter is in the range 0.25-0.4 microm.

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PubMed2005

Multiple scattering by the iterative Foldy-Lax scheme.

The Foldy-Lax multiple-scattering equations in matrix form were examined for their suitability for solving the phase function and degree of linear polarization of clusters of particles as a complementary approach to the superposition T-matrix scheme. The constituent particles used for verification against the latter method were spheres with size parameters close to unity, with their aggregation governed by generalized Brownian motion. The number of constituents can be enlarged beyond the limitations of the benchmark method by a relatively small sacrifice in accuracy, but increasing constituent size and introducing nonsphericity easily result in numerical noise and overwhelming computational effort unless a large amount of the accuracy is going to be traded off.

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PubMed2003

Coherence, power laws, and the negative polarization surge.

We develop a second-order ray-tracing model that includes the constructive interference of reciprocal rays and Fresnel reflections from an inverse gamma-type distribution function of path length to predict the negative polarization branch seen in some astronomical bodies. We expect that such a path-length distribution might resemble the path lengths undertaken by rays incident upon some astronomical bodies. The resulting negative polarization is largely wavelength independent and depends primarily on the power law in the path-length distribution, which coincides with some observations.

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