Evaluation of Polyphenols in Wine by Voltammetric Techniques with Screen Printed Carbon Electrodes

The electrochemical oxidation processes that occur during a voltammetric assay in wine samples lead to the formation of species that obstructs the surface and reduce their active area. This effect is critical for screen printed carbon electrodes (SPCE) and leads to abnormal low values of the total polyphenols content of wines, ca. 72 % lower than those obtained with glassy carbon electrodes. This effect was examined using 10 red and Port wine samples. Mechanical polishing and electrochemical‐based treatments for the removal of this fouling layer were tested. The best results were obtained by electrochemical activation in at a constant potential of 1.2 V during 100 s Na₂CO₃ saturated solution, and by polishing. The success of some of these treatments brings an added value to SPCE, as it opens the possibility of their reuse in the wine analysis. This outcome is particularly relevant for quality control where a huge number of analysis is performed and the reduction of cost may dictates the choice of the analytical method.     

Pd–H and Ni–H phase diagrams using cluster variation method and Monte Carlo simulation

This work focuses on interstitial solid solutions of hydrogen in the face-centred cubic (fcc) host lattice of palladium and nickel, using a first-principles based approach. Cluster Variation Method (CVM) and Monte Carlo simulation algorithms were especially designed, allowing a coupled use of both techniques, to study hydrogen–vacancy interactions inside an fcc metallic host lattice. First-principles calculations provided the H–Vac interaction energies by structure inversion method. The phase diagrams and thermodynamic properties were computed using only theoretical inputs. The mechanisms leading to the formation of the miscibility gaps observed for both Pd–H and Ni–H systems and the hydrogen ordering on palladium interstitial lattice were reproduced without any empirical term.     

Assessment of the Nd/U ratio for the quantification of neodymium in UO2

The secondary ion energy spectrum of uranium depends on the experimental conditions, which is a problem for the application of a relative sensitivity factor (RSF) procedure for the measurement of the Nd concentration in UO₂. This is interpreted as due to the dependence of the sputtering and ionisation yields of uranium on the oxidation state of the surface. Three experimental procedures are being tested to cope with this difficulty.     

Modeling and simulation of cell populations interaction

Regenerative medicine and cell therapy provide great hopes for the use of adult and stem cells. The latter are far less present in tissue than the former and must be expanded using cell culture. Stem cells culture requires the conservation of their proliferation and self-renewal capabilities. Still, the complex interaction between cell populations, for example in primary cell cultures, are not well-known and may account for part of the variability of such cultures. In order to represent and understand the evolution of cultured stem cells, we present here a mathematical model of cell proliferation and differentiation. Based on the formalism of cellular automata, this model simulates the evolution of several cell classes (which may represent either different levels of differentiation or different cell types) in an environment modeling the growth medium. We model the cell cycle as on the one hand a quiescence phase during which a cell rests, and on the other hand a division phase during which the cell starts the division process. In order to represent cell–cell interaction, the transition probability between those phases depends on the local composition of the growth medium depending itself on neighboring cells. An interaction between cellular populations is represented by a quantitative parameter which has a direct impact on cellular proliferation. Differentiation results in a change of the cell class and depends on the biological model studied : it may result from an asymmetric division or be a consequence of the local composition of the growth medium. This mathematical model aims at a better understanding of the interactions between cell populations in a culture. By defining constraints on the potential or the type of the cells at the end of a culture, it will then be possible to find optimal experimental conditions for cell production.     

Optical losses and absorption cross-section of silicon nanocrystals

 Si-rich silicon oxide and SiO₂ (SRSO)/SiO₂ multilayer (ML) samples were grown by reactive magnetron sputtering and then annealed at high temperature to induce the formation of Si-nc with mean size of 3-4 nm and density of about 3.5×10¹⁸ cm⁻³ as deduced from high resolution TEM micrographs. Refractive index and thickness have been determined by m-line measurements, which have shown a birefringence of about 1.5% due to the ML structure. Rib-loaded waveguides have been fabricated to measure propagation losses in the visible-infrared range. The analysis of the different contributions to optical losses such as Mie scattering and scattering due to waveguide roughness has allowed us to isolate the contribution due to the absorption losses and thus to extract the absorption cross-section at different wavelengths. Values of about 3.5×10⁻¹⁸ cm² have been found at 830 nm, increasing with decreasing of the wavelength.     

Diastereoselective diallylation of various butane-2,3-diacetals by allylsilane

Five butane-2,3-diacetals obtained from the reaction of 1,2-diols and methanol with biacetyl have been treated with allylsilane in the presence of titanium tetrachloride to afford bis-allyldioxanes as single diastereoisomers.