1,676 research outputs found
Statistical outliers in random laser emission
We provide theoretical and experimental evidence of statistical outliers in
random laser emission that are not accounted for by the, now established,
power-law tailed (L\'evy) distribution. Such outliers manifest themselves as
single, large isolated spikes over an otherwise smooth background. A
statistical test convincingly shows that their probability is larger than the
one extrapolated from lower-intensity events. To compare with experimental
data, we introduced the anomaly parameter that allows for an identification of
such rare events from experimental spectral measurements and that agrees as
well with the simulations of our Monte Carlo model. A possible interpretation
in terms of Black Swans or Dragon Kings, large events having a different
generation mechanism from their peers, is discussed
The use of India ink in tissue-simulating phantoms
The optical properties of India ink, an absorber often used in preparation of tissue simulating phantoms, have been investigated at visible and near infrared wavelengths. The extinction coefficient has been obtained from measurements of collimated transmittance and from spectrophotometric measurements, the absorption coefficient from multidistance measurements of fluence rate in a diffusive infinite medium with small concentrations of added ink. Measurements have been carried out on samples of India ink from five different brands, and for some brands also from different batches. As also reported in previously published papers the results we have obtained showed large inter-brand and inter-batch variations for both the absorption and the extinction coefficient. On the contrary, our results showed small variations for the ratio between the absorption and the extinction coefficient. The albedo is therefore similar for all samples: The values averaged over all samples investigated were 0.161, 0.115, and 0.115 at λ = 632.8, 751, and 833 nm respectively, with maximum deviations of 0.044, 0.019, and 0.035. These results indicate that, using the values we have obtained for the albedo, it should be possible to obtain with uncertainty smaller than about 4% the absorption coefficient of a sample of unknown ink from simple measurements of extinction coefficient. A similar accuracy is not easily obtained with the complicated procedures necessary for measurements of absorption coefficient
Invariance property in inhomogeneous scattering media with refractive-index mismatch
The mean path length invariance property is a very important property of
scattering media illuminated by an isotropic and homogeneous radiation. Here we
investigate the case of inhomogeneous media with refractive index mismatch
between the external environment and also among their subdomains. The
invariance property remains valid by the introduction of a correction,
dependent on the refractive index, of the mean path length value. It is a
consequence of the stationary solution of the radiative transfer equation in a
medium subjected to an isotropic and homogeneous radiance. The theoretical
results are in agreement with the reported results for numerical simulations
for both the three-dimensional and the two-dimensional media
Invariance properties of exact solutions of the radiative transfer equation
Abstract In this work, special invariance properties of a class of exact solutions of the radiative transfer equation (RTE) pertaining to a uniform Lambertian illumination of any non-absorbing homogeneous and inhomogeneous volume are presented and discussed. This class of solutions of the RTE traces a reference ground under which light propagation can be studied in a special simplified regime. Despite the difficulties to obtain general solutions of the radiative transfer equation, the condition of Lambertian illumination determines a unique regime of photon transport where quite easy and simple invariant solutions can be obtained in all generality for homogeneous and inhomogeneous geometries. These solutions are invariant both with respect to the geometry (size and shape of the volume) and with respect to the scattering properties, i.e. scattering coefficient, scattering function and homogeneity of the considered domain. Another evident advantage of these solutions is that they are exact solutions known with arbitrary precision and can thus be used as reference standard for photon migration studies
Crude Oil Bioremediation: From Bacteria to Microalgae
Crude oil is one of the major pollutants present. Its extraction and processing generate processing waters contaminated by hydrocarbons which are harmful to both human health and the flora and fauna that come into contact with it. Hydrocarbon contamination can involve soil and water, and several technologies are used for recovery. The most used techniques for the recovery of spilt oil involve chemical-physical methods that can remove most of the pollutants. Among these, must consider the bioremediation by microorganisms, mostly bacterial capable of degrading many of the toxic compounds contained within the petroleum. Microalgae participate in bioremediation indirectly, supporting the growth of degrading bacteria, and directly acting on contaminants. Their direct contribution is based on the activation of various mechanisms ranging from the production of enzymes capable of degrading hydrocarbons, such as lipoxygenases, to the attack through the liberation of free radicals. The following review analyzed all the works published in the last ten years concerning the ability of microalgae to remove hydrocarbons, intending to identify in these microorganisms an alternative technology to the use of bacteria. The advantages of using microalgae concern not only their ability to remove toxic compounds and release oxygen into the atmosphere but their biomass could then be used in a circular economy process to produce biofuels
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