Space-frequency correlation of classical waves in disordered media: high-frequency and small scale asymptotics

Two-frequency radiative transfer (2f-RT) theory is developed for geometrical optics in random media. The space-frequency correlation is described by the two-frequency Wigner distribution (2f-WD) which satisfies a closed form equation, the two-frequency Wigner-Moyal equation. In the RT regime it is proved rigorously that 2f-WD satisfies a Fokker-Planck-like equation with complex-valued coefficients. By dimensional analysis 2f-RT equation yields the scaling behavior of three physical parameters: the spatial spread, the coherence length and the coherence bandwidth. The sub-transport-mean-free-path behavior is obtained in a closed form by analytically solving a paraxial 2f-RT equation

Anisotropic multiple scattering in diffuse media

The multiple scattering of scalar waves in diffusive media is investigated by means of the radiative transfer equation. This approach amounts to a resummation of the ladder diagrams of the Born series; it does not rely on the diffusion approximation. Quantitative predictions are obtained, concerning various observables pertaining to optically thick slabs, such as the mean angle-resolved reflected and transmitted intensities, and the shape of the enhanced backscattering cone. Special emphasis is put on the dependence of these quantities on the anisotropy of the cross-section of the individual scatterers, and on the internal reflections due to the optical index mismatch at the boundaries of the sample. The regime of very anisotropic scattering, where the transport mean free path $\ell^*$ is much larger than the scattering mean free path $\ell$, is studied in full detail. For the first time the relevant Schwarzschild-Milne equation is solved exactly in the absence of internal reflections, and asymptotically in the regime of a large index mismatch. An unexpected outcome concerns the angular width of the enhanced backscattering cone, which is predicted to scale as $\Delta\theta\sim\lambda/\sqrt{\ell\ell^*}$, in contrast with the generally accepted $\lambda/\ell^*$ law, derived within the diffusion approximation.Comment: 53 pages TEX, including 2 tables. The 4 figures are sent at reques

Phase transitions, hysteresis, and hyperbolicity for self-organized alignment dynamics

International audienceWe provide a complete and rigorous description of phase transitions for kinetic models of self-propelled particles interacting through alignment. These models exhibit a competition between alignment and noise. Both the alignment frequency and noise intensity depend on a measure of the local alignment. We show that, in the spatially homogeneous case, the phase transition features (number and nature of equilibria, stability, convergence rate, phase diagram, hysteresis) are totally encoded in how the ratio between the alignment and noise intensities depend on the local alignment. In the spatially inhomogeneous case, we derive the macroscopic models associated to the stable equilibria and classify their hyperbolicity according to the same function

Evaluation of phenolic contents and antioxidant activity of various solvent extracts of Sonchus asper (L.) Hill

<p>Abstract</p> <p>Background</p> <p><it>Sonchus asper </it>(SA) is traditionally used for the treatment of various ailments associated with liver, lungs and kidneys. This study was aimed to investigate the therapeutic potential of nonpolar (hexane, SAHE; ethyl acetate, SAEE and chloroform, SACE) and polar (methanol, SAME) crude extracts of the whole plant.</p> <p>Methods</p> <p>To achieve these goals, several parameters including free-radical (DPPH^•, ABTS^•+, H₂O₂and ^•OH) scavenging, iron chelating activity, scavenging of superoxide radicals, total flavonoids and total phenolic content (TPC) were examined.</p> <p>Results</p> <p>The SA extracts presented a remarkable capacity to scavenge all the tested reactive species with IC₅₀values being found at the μg ⁄ ml level. The SAME was shown to have the highest TPCs while lowest IC₅₀values for the DPPH^•, ABTS^•+radical scavenging capacities and iron chelating scavenging efficiency, moreover, SAME had best activities in scavenging of superoxide radicals and hydrogen peroxide as well as potently scavenged the hydroxyl radicals.</p> <p>Conclusion</p> <p>These results suggest the potential of <it>S. asper </it>as a medicine against free-radical-associated oxidative damage.</p

Antioxidant, Anti-inflammatory and Cytotoxicity of Phaleria macrocarpa (Boerl.) Scheff Fruit

<p>Abstract</p> <p>Background</p> <p><it>Phaleria macrocarpa </it>(Scheff.) Boerl (Thymelaceae) originates from Papua Island, Indonesia and grows in tropical areas. The different parts of the fruit of <it>P. macrocarpa </it>were evaluated for antioxidant, anti-inflammatory, and cytotoxic activities.</p> <p>Methods</p> <p><it>Phaleria macrocarpa </it>fruit were divided into pericarp, mesocarp and seed. All parts of the fruit were reflux extracted with methanol. The antioxidant activity of the extracts were characterized in various <it>in vitro </it>model systems such as FTC, TBA, DPPH radical, reducing power and NO radical. Anti-inflammatory assays were done by using NO production by macrophage RAW 264.7 cell lines induced by LPS/IFN-γ and cytotoxic activities were determined by using several cancer cell lines and one normal cell line</p> <p>Results</p> <p>The results showed that different parts (pericarp, mesocarp, and seed) of <it>Phaleria macrocarpa </it>fruit contain various amount of total phenolic (59.2 ± 0.04, 60.5 ± 0.17, 47.7 ± 1.04 mg gallic acid equivalent/g DW) and flavonoid compounds (161.3 ± 1.58, 131.7 ± 1.66, 35.9 ± 2.47 mg rutin equivalent/g DW). Pericarp and mesocarp showed high antioxidant activities by using DPPH (71.97%, 62.41%), ferric reducing antioxidant power (92.35%, 78.78%) and NO scavenging activity (65.68%, 53.45%). Ferric thiocyanate and thiobarbituric acid tests showed appreciable antioxidant activity in the percentage hydroperoxides inhibitory activity from pericarp and mesocarp in the last day of the assay. Similarly, the pericarp and mesocarp inhibited inducible nitric oxide synthesis with values of 63.4 ± 1.4% and 69.5 ± 1.4% in macrophage RAW 264.7 cell lines induced by LPS/IFN-γ indicating their notable anti-inflammatory potential. Cytotoxic activities against HT-29, MCF-7, HeLa and Chang cell lines were observed in all parts.</p> <p>Conclusions</p> <p>These results indicated the possible application of <it>P. macrocarpa </it>fruit as a source of bioactive compounds, potent as an antioxidant, anti inflammatory and cytotoxic agents.</p

An Essential Difference between the Flavonoids MonoHER and Quercetin in Their Interplay with the Endogenous Antioxidant Network

Antioxidants can scavenge highly reactive radicals. As a result the antioxidants are converted into oxidation products that might cause damage to vital cellular components. To prevent this damage, the human body possesses an intricate network of antioxidants that pass over the reactivity from one antioxidant to another in a controlled way. The aim of the present study was to investigate how the semi-synthetic flavonoid 7-mono-O-(β-hydroxyethyl)-rutoside (monoHER), a potential protective agent against doxorubicin-induced cardiotoxicity, fits into this antioxidant network. This position was compared with that of the well-known flavonoid quercetin. The present study shows that the oxidation products of both monoHER and quercetin are reactive towards thiol groups of both GSH and proteins. However, in human blood plasma, oxidized quercetin easily reacts with protein thiols, whereas oxidized monoHER does not react with plasma protein thiols. Our results indicate that this can be explained by the presence of ascorbate in plasma; ascorbate is able to reduce oxidized monoHER to the parent compound monoHER before oxidized monoHER can react with thiols. This is a major difference with oxidized quercetin that preferentially reacts with thiols rather than ascorbate. The difference in selectivity between monoHER and quercetin originates from an intrinsic difference in the chemical nature of their oxidation products, which was corroborated by molecular quantum chemical calculations. These findings point towards an essential difference between structurally closely related flavonoids in their interplay with the endogenous antioxidant network. The advantage of monoHER is that it can safely channel the reactivity of radicals into the antioxidant network where the reactivity is completely neutralized

Multiple Rayleigh Scattering of Electromagnetic Waves

Multiple scattering of polarized electromagnetic waves in diffusive media is investigated by means of radiative transfer theory. This approach amounts to summing the ladder diagrams for the diffuse reflected or transmitted intensity, or the cyclical ones for the cone of enhanced backscattering. The method becomes exact in several situations of interest, such as a thick-slab experiment (slab thickness $L\gg$ mean free path $\ell\gg$ wavelength $\lambda$). The present study is restricted to Rayleigh scattering. It incorporates in a natural way the dependence on the incident and detected polarizations, and takes full account of the internal reflections at the boundaries of the sample, due to the possible mismatch between the mean optical index $n$ of the medium and that $n_1$ of the surroundings. This work does not rely on the diffusion approximation. It therefore correctly describes radiation in the skin layers, where a crossover takes place between free and diffusive propagation, and vice-versa. Quantities of interest, such as the polarization-dependent, angle-resolved mean diffuse intensity in reflection and in transmission, and the shape of the cone of enhanced backscattering, are predicted in terms of solutions to Schwarzschild-Milne equations. The latter are obtained analytically, both in the absence of internal reflections ($n=n_1$), and in the regime of a large index mismatch ($n/n_1\ll 1 {\rm or} \gg 1$)