Differential non-destructive image current detection in a fourier transform quadrupole ion trap

Dual-detector differential non-destructive Fourier transform detection in a quadrupole ion trap is shown to improve signal intensity and reduce noise compared with spectra recorded using a single detector. A larger area detector in each end-cap electrode is machined to fit its hyperbolic shape and so minimize field imperfections on the z-axis. Argon, acetophenone and bromobenzene spectra were recorded to allow a comparison between single- and dual-detector (differential) modes of detection and to demonstrate the improvement achieved with differential detection. Copyright 1999 John Wiley & Sons, Ltd.     

Pseudo-steady-state solutions for solidification in a wedge

Polubarinova-Kochina's analytical differential equation methodis used to determine the pseudo-steady-state solution to problemsinvolving the freezing (solidification) of wedges of liquidwhich are initially at their fusion temperature. In particular,we consider four distinct problems for wedges which are: freezingwith the same constant boundary temperature, freezing with thesame constant boundary heat fluxes, freezing with distinct constantboundary temperatures and freezing with distinct constant fluxesat the boundaries. For the last two problems, a Heun's differentialequation with an unknown singularity is derived, which in bothcases admits a particularly elegant simple solution for thespecial case when the wedge angle is . The moving boundariesobtained are shown pictorially.     

Reduction selective de composes carbonyles par catalyse heterogene a la surface des sels

The reduction of carbonyl compounds carried out with ethoxyhydrogenosilanes and alkali metal fluorides as catalyst and without solvent is highly selective. The reactivity order is aldehyde > ketone > ester. The reduction of aldehydes is possible in the presence of ketones, and of ketones in the presence of esters. The keto-group in a keto-ester can be selectively reduced. The high selectivity of this system is due to three factors: hydrogenosilane reactivity (EtO)₂SiMeH<(EtO)₃SiH), nature of the salt (KF<CsF) and temperature. Chlorides, amides, anhydrides and ethylenic, bromo, nitro groups are not reduced. This enables the selective reduction of the carbonyl group in bifunction compounds.     

Acidity in aqueous mixed solvent systems—III : Influence of the organic solvent molecular structure on the acidity of aquo-organic mixtures (acidity function,water structure,hydrophilic and hydrophobic effects)

The acidity functions Ho and H_R have been determined for different aqueous organic mixtures (diols, carbohydrates) at constant acid concentration. We have checked, with a reaction involving a slow proton transfer, that Ho and H_R vary in direct proportion to the acidity of the systems.The results are interpreted in terms of the variations of the proton activity which is dependent on the modifications of the water structure by the organic cosolvent.