338 research outputs found
Multiple scattering of polarized light in disordered media exhibiting short-range structural correlations
We develop a model based on a multiple scattering theory to describe the
diffusion of polarized light in disordered media exhibiting short-range
structural correlations. Starting from exact expressions of the average field
and the field spatial correlation function, we derive a radiative transfer
equation for the polarization-resolved specific intensity that is valid for
weak disorder and we solve it analytically in the diffusion limit. A
decomposition of the specific intensity in terms of polarization eigenmodes
reveals how structural correlations, represented via the standard anisotropic
scattering parameter , affect the diffusion of polarized light. More
specifically, we find that propagation through each polarization eigenchannel
is described by its own transport mean free path that depends on in a
specific and non-trivial way
Transport in quenched disorder: light diffusion in strongly heterogeneous turbid media
We present a theoretical and experimental study of light transport in
disordered media with strongly heterogeneous distribution of scatterers formed
via non-scattering regions. Step correlations induced by quenched disorder are
found to prevent diffusivity from diverging with increasing heterogeneity
scale, contrary to expectations from annealed models. Spectral diffusivity is
measured for a porous ceramic where nanopores act as scatterers and macropores
render their distribution heterogeneous. Results agree well with Monte Carlo
simulations and a proposed analytical model.Comment: 12 pages, 9 figures (significant amount of supplemental information
Weak localization of light in superdiffusive random systems
L\'evy flights constitute a broad class of random walks that occur in many
fields of research, from animal foraging in biology, to economy to geophysics.
The recent advent of L\'evy glasses allows to study L\'evy flights in
controlled way using light waves. This raises several questions about the
influence of superdiffusion on optical interference effects like weak and
strong localization. Super diffusive structures have the extraordinary property
that all points are connected via direct jumps, meaning that finite-size
effects become an essential part of the physical problem. Here we report on the
experimental observation of weak localization in L\'evy glasses and compare
results with recently developed optical transport theory in the superdiffusive
regime. Experimental results are in good agreement with theory and allow to
unveil how light propagates inside a finite-size superdiffusive system
A unified censored normal regression model for qPCR differential gene expression analysis
Reverse transcription quantitative polymerase chain reaction (RT-qPCR) is considered as the gold standard for accurate, sensitive, and fast measurement of gene expression. Prior to downstream statistical analysis, RT-qPCR fluorescence amplification curves are summarized into one single value, the quantification cycle (Cq). When RT-qPCR does not reach the limit of detection, the Cq is labeled as undetermined . Current state of the art qPCR data analysis pipelines acknowledge the importance of normalization for removing non-biological sample to sample variation in the Cq values. However, their strategies for handling undetermined Cq values are very ad hoc. We show that popular methods for handling undetermined values can have a severe impact on the downstream differential expression analysis. They introduce a considerable bias and suffer from a lower precision. We propose a novel method that unites preprocessing and differential expression analysis in a single statistical model that provides a rigorous way for handling undetermined Cq values. We compare our method with existing approaches in a simulation study and on published microRNA and mRNA gene expression datasets. We show that our method outperforms traditional RT-qPCR differential expression analysis pipelines in the presence of undetermined values, both in terms of accuracy and precision
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