Base-promoted in situ generation of methyl acrylate from dimethyl 3, 3'-dithiodipropionate. Application To N-alkylation of heterocycles

In basic medium, dimethyl 3,3'-dithiopropionate generates methyl acrylate, which serves in situ as a source of propionate moiety. This property was applied to the alkylation of indoles and other nitrogen heterocycles leading to a series of 3-(heteroaryl-substituted) propionates. A mechanistic rationale for the generation of acrylate is presented along with supportive experimental data.     

Mesure de la duree de vie de niveaux d'energie d'ions par transfert de coherence dans une collision de penning: Application aux niveaux 4f 2F72 et 2F52 de Mg+

Metastable 2³S₁ He atoms are optically oriented and their orientation is transferred to metallic ions produced by Penning collisions $\text{[He (2}{}^3\text{S}{}_1\text{)}\text{+ M →}\text{He (}{}^1\text{S}{}_0\text{)}\text{+ M}{}^{\mathrm{+}}\text{+}\text{e}$. If r.f. transitions are induced in the 2³S₁ He level, the circularly polarized light emitted by the ions in a direction perpendicular to the static magnetic field is modulated at the r.f. frequency. The variation of the modulation amplitude with frequency depends on the lifetime of the level of the excited ion.We describe an experimental apparatus with which we measure the modulation amplitude from 1 MHz to 110 MHz. In this way the lifetime of the 4f²F_{$\text{7}\text{2}$} and ²F_{$\text{5}\text{2}$} Mg⁺ levels has been determined.     

Optical pumping measurement of the hyperfine structure of cadmium ion ground state

The 5²S_{$\text{1}\text{2}$} ground state of Cd⁺ ions has been oriented by Schearer's technique. The hyperfine structure constant for this level has been determined as ¦A¦ = 14700 ± 700 MHz for the odd isotopes 111 and 113.     

2-Groupe des classes positives d'un corps de nombres et noyau sauvage de la K-théorie

We compute the 2-rank of the wild kernel WK₂(F) of a number field by constructing a 2-class group ad hoc. The main result generalizes in the more intricate case the canonical isomorphism established for odd primes under the assumption in a previous article (cf. (Acta. Arith. 67 (1994) 335; Math. Z. 238 (2001) 335)). It involves a criterium of triviality for the 2-part of the wild kernel of Galois number fields and, in the particular case of quadratic fields, it leads to a logarithmic interpretation of the diophantine conditions obtained by other authors.     

Concentration of sodium ion as the determining factor for the association of dansyl amino acids with the teicoplanin molecule in reversed-phase liquid chromatography

The mechanism of the binding of D,L dansyl amino acids to teicoplanin was investigated. Na+ was used as an indicator of the interactions between the solutes and teicoplanin. The number (n) of sodium ions, Na+, excluded from the solute-teicoplanin interface when analyte transfer occurred was determined. A thermodynamic study and enthalpy-entropy compensation were performed to further explore the interaction mechanism. From these results, it was shown that teicoplanin was balanced between 2 conformational states characterized by distinct enantioselective properties. This approach indicates that liquid chromatography (LC) is a useful tool to extract physicochemical and molecular information from retention data. Thus, LC can be used as a complementary technique with the conventional techniques of molecular interaction analysis.     

Determination of vanadium in serum by pre-irradiation and post-irradiation chemistry and neutron activation analysis

Vanadium in serum was investigated by pre-irradiation chemistry neutron activation analysis employing anion exchange chromatography and post-irradiation neutron activation employing solvent extraction techniques. From a comparison of these techniques it is concluded that vanadium is present in human serum in the sub-ppb range.     

Set-valued average value at risk and its computation

New versions of the set-valued average value at risk for multivariate risks are introduced by generalizing the well-known certainty equivalent representation to the set-valued case. The first ’regulator’ version is independent from any market model whereas the second version, called the market extension, takes trading opportunities into account. Essential properties of both versions are proven and an algorithmic approach is provided which admits to compute the values of both versions over finite probability spaces. Several examples illustrate various features of the theoretical constructions.     

Dynamical screening and ionic conductivity in water from ab initio simulations

We present a method to calculate ionic conductivities of complex fluids from ab initio simulations. This is achieved by combining density functional theory molecular dynamics simulations with polarization theory. Conductivities are then obtained via a Green-Kubo formula using time-dependent effective charges of electronically screened ions. The method is applied to two different phases of warm dense water. We observe large fluctuations in the effective charges; protons can transport effective charges greater than +e for ultrashort time scales. Furthermore, we compare our results with a simpler model of ionic conductivity in water that is based on diffusion coefficients. Our approach can be directly applied to study ionic conductivities of electronically insulating materials of arbitrary composition, e.g., complex molecular mixtures under such extreme conditions that occur deep inside giant planets.     

A Two-Dimensional Network Model to Simulate Permeability Decrease Under Hydrodynamic Effect of Particle Release and Capture

A model was developed to simulate permeability decrease induced by hydrodynamic effects when injecting a fluid in a reservoir with respect to particle release and capture mechanisms and the parameters of the fluid–rock system. The kinetics of particle release and capture were integrated after computing the initial permeability of the porous medium with a square lattice of a two–dimensional network model. The rate of particle release is related to the difference between a microscopic velocity of the fluid and a critical velocity. The permeability decrease shows a direct link to the reduction of pore throat radii by three mechanisms of particle capture: straining and particle accumulation through direct interception or diffusion. Comparison between the simulations and the experimental results shows that the model reproduces the physics of the permeability decrease phenomenon, although the values are overestimated. The difference between the two sets of results can be explained by the fact that the simulations are realized at constant pressure whereas the experiments are realized at constant flow rate, and that re–entrainment of the trapped particles was not taken into account in the model.