Lagrangian Dispersion in Gaussian Self-Similar Velocity Ensembles

We analyze the Lagrangian flow in a family of simple Gaussian scale-invariant velocity ensembles that exhibit both spatial roughness and temporal correlations. We argue that the behavior of the Lagrangian dispersion of pairs of fluid particles in such models is determined by the scale dependence of the ratio between the correlation time of velocity differences and the eddy turnover time. For a non-trivial scale dependence, the asymptotic regimes of the dispersion at small and large scales are described by the models with either rapidly decorrelating or frozen velocities. In contrast to the decorrelated case, known as the Kraichnan model and exhibiting Lagrangian flows with deterministic or stochastic trajectories, fast separating or trapped together, the frozen model is poorly understood. We examine the pair dispersion behavior in its simplest, one-dimensional version, reinforcing analytic arguments by numerical analysis. The collected information about the pair dispersion statistics in the limiting models allows to partially predict the extent of different phases of the Lagrangian flow in the model with time-correlated velocities.     

FT-IR spectroscopy and chemometrics as a useful approach for determining chemical-physical properties of gasoline, by minimizing analytical times and sample handling

Since recently Mid-Infrared Spectroscopy is being used in the petrol industry for determining important chemical-physical properties of gasoline. This technique enables to achieve results similar to those obtainable with standard methods at shorter times, lower costs and safer sample handling. This can be obtained by employing multivariate regression models in the framework of a chemometric analytical approach. In the present work some gasoline properties including density, Reid vapor pressure, Research Octane Number, aromatic hydrocarbons content and fraction recovered at 70 degrees C were determined with standard methods (ISO, CEN, ASTM) on 93 samples of unleaded gasoline produced in an oil refinery. The same samples were also analyzed by FT-IR spectrophotometry, recording absorptions of seven characteristic bands. The obtained values of chemical-physical and spectroscopic properties were used to develop and validate a multivariate regression model. This established an experimental correlation between these two sets of variables derived from the same gasoline samples. The model was able to correctly predict the chemical physical properties of a set of unknown gasoline samples produced in the same refinery starting from the spectroscopic ones.     

The effect of redox state on the local structural environment of iron in silicate glasses: a combined XAFS spectroscopy, molecular dynamics, and bond valence study

A series of 27 silicate glasses of various compositions containing 0.2-2 at.% iron were synthesized at various oxygen fugacity values. The glasses were examined using X-ray absorption fine structure (XANES) spectroscopy at the Fe K-edge in order to determine iron oxidation state and first-neighbor coordination number. Spectral information extracted from the pre-edge region and principal component analysis (PCA) of the XANES region, together with a spectral inversion, were used to derive the end-member spectral components for Fe(II) and Fe(III). Linear trends in the pre-edge features were observed for most compositional series of the glasses examined as a function of Fe(II)/Fe(III) content. These linear trends are believed to be due to the similarity of average coordination numbers for both Fe(II) and Fe(III) end-members in each series. This result is consistent with model simulations of the XANES region and molecular dynamics (MD) simulations for the two end-member compositions which also show that Fe(II) and Fe(III) have similar average coordination numbers. These simulations also suggest the presence of five-coordinated Fe(III) in the melt phase. Based on a bond valence analysis of these MD simulations, a simple model is proposed to help predict the speciation of iron in oxide and silicate glasses and melts.     

Influence of a mean shear on the spectrum of passive scalar fluctuations

The form of the spectrum of passive scalar fluctuations in the inertial–convective range is investigated. In the presence of a mean shear, there exists a critical wave number k_c. At wave numbers greater than k_c, the mean shear does not influence the spectrum of scalar fluctuations and the Obukhov–Corrsin prediction holds. At wave numbers smaller than k_c, the mean shear dominates and the spectrum is less steep. These predictions are based on the study of Lagrangian dynamics of fluid particles and account for the experimental observations. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study of organic sulphur compounds (DMS,DMSP and CS2) in lagoon ecosystems: the case of the Venice lagoon

This study of the origin and fate of dimethyl sulphide (DMS) in a particular and complex lagoon ecosystem such as that of the Venice lagoon focuses on the temporal evolutions of DMS concentrations in surface water together with those of dimethylsulphoniopropionate (DMSP), carbon disulphide (CS2), nutrients (nitrate, nitrite, ammonium, phosphate, silicate), sulphate, chlorophyll a, chlorinity, water temperature and phytoplankton (composition and density). Measurements were made from 3 March 1997 to 23 July 1998 at three stations in the central part of the Venice lagoon. The temporal trends of DMS concentration showed an absolute maximum concentration in winter (65 nmol S/l, 19/2/1998, Stn. 1; 119 nmol S/l, 19/2/1998, Stn. 2; 29 nmol S/l, 17/2/1998, Stn. 3) and two relative maxima in the spring-summer period. The spring-summer secondary maxima of DMS concentration were related to the maxima of DMSP and chlorophyll a concentrations and consequently to phytoplanktonic abundance while the winter DMS maximum showed no relation to DMSP or to chlorophyll a suggesting that the production and the fate of DMS could be different for the two periods. According to previous studies the CS2 concentration increased in the spring, achieved its maximum in summer, decreased in autumn and fell to its minimum in winter.     

On 3+1 Anti-de Sitter and de Sitter Lie Bialgebras with Dimensionful Deformation Parameters

We analyze among all possible quantum deformations of the 3+1 (anti)de Sitter algebras, so(3,2) and so(4,1), which have two specific non-deformed or primitive commuting operators: the time translation/energy generator and a rotation. We prove that under these conditions there are only two families of two-parametric (anti)de Sitter Lie bialgebras. All the deformation parameters appearing in the bialgebras are dimensionful ones and they may be related to the Planck length. Some properties conveyed by the corresponding quantum deformations (zero-curvature and non-relativistic limits, space isotropy, . . . ) are studied and their dual (first-order) non-commutative spacetimes are also presented.     

Mie scattering of a partially coherent beam

The scattering of a partially coherent electromagnetic beam by a dielectric sphere is described. Two methods are presented: a coherent mode representation and a spherical harmonics expansion. In the case of a distant blackbody source, the coherent modes are plane waves and the scattered intensity is obtained by a convolution of the classical Mie results over the source surface.     

Muscari comosum L. Bulb Extracts Modulate Oxidative Stress and Redox Signaling in HepG2 Cells

Muscari comosum L. bulbs are commonly used as food in South Italy and also in folk medicine. By evaluating in vitro antioxidant activity and biological activities of their aqueous and methanol extracts, we shed light on the potential role, including both the nutraceutical and health benefits, of this plant. Total polyphenol content (TPC) and total flavonoid content (TFC) were evaluated by the Folin–Ciocalteu method and by the aluminum chloride method, respectively. Antioxidant activity was investigated by three in vitro assays and relative antioxidant capacity index (RACI) was calculated to compare results obtained by different tests. The extracts were tested to evaluate their possible involvement in redox homeostasis, using the human hepatoma (HepG2) cell line used as model. The extracts exhibited concentration/solvent dependent radical scavenging activity, as well as dysregulation of some genes involved in redox pathways by promoting Nrf2, SOD-2, GPX1, ABCC6 and ABCG2 expression. NMR metabolomics analysis suggests that HepG2 cells treated with Muscari comosum extracts experience changes in some metabolites involved in various metabolic pathways.     

A mechanistic study on the amidation of esters mediated by sodium formamide

Kinetic and computational studies on the amidation of esters with mixtures of formamide and sodium methoxide are described. Rate studies are consistent with a fast deprotonation of formamide followed by two reversible acyl transfers affected by solvent participation. MP2 calculations suggest that the first acyl transfer between the ester and sodium formamide is rate-determining. The transition structures leading to the formation and collapse of the first tetrahedral intermediate are calculated to be isoenergetic.