Carré d’unn-vecteur dans unE n

A _n being an-vector of a vectorial spaceE _n we calculate (A _n)² which is equal to 1 or −1.      

Théorie excitonique des constantes de couplage nucléaires dans les molécules organiques

Sans résumé     

Detection of air pollutants with a tunable CO2 laser

Following a method described by Kreuzeret al., we have et up an improved spectroscopic system to detect trace pollutants in ambient air. A CO₂ laser is tuned to various transitions coincident with absorption lines or bands of pollutant gases. The laser beam is amplitude modulated at the resonant frequency of an acoustical cavity which serves as sample chamber. The pressure waves detected by sensitive microphones placed inside the cavity yield a signal proportional to the energy taken up by the absorbing gases. So far sensitivity limits of a few ppb have been achieved for some typical pollutants, together with high rejection ratios against interference among these gases and against water and CO₂.     

The analysis of linear probing sort by the use of a new mathematical transform

A variant of the distribution sort approach which makes use of extra storage to sort a list of n elements in an average of about probes into a table is presented. An accurate analysis of this technique is made by introducing a transform from a Poisson approximation to the exact (finite) distribution. This analysis also leads to the solution of an interesting parking problem.     

Structural investigation of LaAlO3 up to 63 GPa

We report a high-pressure synchrotron x-ray diffraction on a LaAlO(3) single crystal. The transition from rhombohedral to cubic at 14.8 GPa is confirmed by the loss of the superstructure reflections, whose intensity shows a linear pressure dependence, characteristic of a second-order transition. The crystal remains cubic up to 63 GPa, the highest pressure reached, which provides a confirmation over a very large pressure range of the general rules for the evolution of distortions of perovskites under pressure. We report the parameters of the Birch-Murnaghan equations of state in the low- and high-pressure phases and discuss the evolution of the bulk modulus.     

Determination of polycyclic aromatic hydrocarbon metabolites in milk by a quick,easy, cheap,effective, rugged and safe extraction and capillary electrophoresis

We describe the first application of a quick, easy, cheap, effective, rugged and safe extraction technique to the CZE analysis of monohydroxylated metabolites of polycyclic aromatic hydrocarbons in milk. Complete resolution of 2‐hydroxyfluorenene, 1‐hydroxynaphthalene, 2‐hydroxynaphthalene, 3‐hydroxyphenanthrene, and 9‐hydroxyphenanthrene was accomplished in 4 min of electrophoretic run. Limits of detection at the parts‐per‐billion were obtained with a single solvent (acetonitrile) for metabolite extraction and sample stacking. The small sample volume (1.2 mL) and the conservative usage of chemicals provided a simple and rapid procedure for the simultaneous extraction of numerous samples. Adding 4 min of electrophoretic run per sample, it should be possible to screen ten samples in approximately 1 h of analysis time. The nanoliter extract volume required for sample injection allows for further chromatographic usage and confirmation of positive samples. The unique electrophoretic pattern of the studied metabolites demonstrates the potential for the unambiguous determination of positional isomers with very similar chromatographic behaviors and undistinguishable mass fragmentation patterns.     

Dynamic Activation of Ga Sites by Pt Dopant in Low-Temperature Liquid-Metal Catalysts

Liquid GaPt catalysts with Pt concentrations as low as 1×10⁻⁴ atomic % have recently been identified as highly active for the oxidation of methanol and pyrogallol under mild reaction conditions. However, almost nothing is known about how liquid state catalysts support these significant improvements in activity. Here, ab initio molecular dynamics simulations are employed to examine GaPt catalysts in isolation and interacting with adsorbates. We find that persistent geometric features can exist in the liquid state, given the correct environment. We postulate that the Pt dopant may not be limited to direct involvement in catalysis of reactions, but rather that its presence can also enable Ga atoms to become catalytically active.