Obtention d'alkoxy-2 cyano-3 2H chromènes

2-Alkoxy-3-cyano-2H-chromenes were prepared by the action of an alcohol on 2-morpholino-3-cyano-2H-chromenes in the presence of hydrochloric acid.     

Structure and microstructure of the metastable B phase (NiAl10O16): I. Preparation and structural study by X-ray diffraction

The B phase of composition NiAl₁₀O₁₆ is one of the metastable phases found in the Al₂O₃NiO system. Twinned crystals of B were prepared by annealing samples at 1150°C. Indexing the crystal diffraction patterns with 12 twin variants was done. A structural model belonging to the space group $\text{P2}{}_1\text{b}$ is proposed. The B phase has a periodic antiphase boundary (PAPB) structure based on the (100) spinel planes with an antiphase vector R = $\text{1}\text{4}\text{[1}\text{1}\text{0]}$. Moreover this structure is slightly modified by introducing periodic steps on PAPB planes. These steps give rise to a particular order of cation vacancies.     

Vibrational signature of charge solvation vs salt bridge isomers of sodiated amino acids in the gas phase

The vibrational spectra of the gaseous sodium complexes of glycine (Gly-Na(+)) and proline (Pro-Na(+)) have been recorded in the spectral range 1150-2000 cm(-1). The complexes were formed by matrix-assisted laser desorption-ionization, introduced in the cell of a Fourier transform ion cyclotron resonance mass spectrometer, and their infrared spectra were recorded using photons of variable energy emitted by a free electron laser. Photon absorption was probed by the diminished intensity of the parent ion, due to its infrared-induced dissociation into bare sodium cation and the free amino acid and the appearance of Na(+). The observed absorption bands are assigned using ab initio computations of the IR spectra of the lowest energy isomers in each case. They provide the first experimental evidence that the salt bridge isomer is formed in the case of Pro-Na(+). In contrast, charge solvation by chelation of Na(+) between nitrogen and the carbonyl oxygen seems to be most favorable for Gly-Na(+), but a mixture of isomers cannot be ruled out in this case.     

Experimental and numerical study of air-coupled surface waves generated above strips of finite impedance

A series of laboratory experiments are described in which air coupled surface waves are generated from a point source in the frequency range between 800 and 1700 Hz above a surface composed of a lattice of small cavities. Since the sound pressure near the lattice of cavities can be greater than if the surface was rigid, passive amplification is obtained. Moreover, directional receivers can be designed by restricting the lattice of cavities to a strip of finite width. These directional receivers are shown to provide more amplification than would be obtained with a semi-infinite lattice of cavities. Theoretical calculations using a boundary element method predict gains of up to 6 dB, relative to the pressure on a rigid plane when the strip width is of the order of 1 wavelength. The strips are further modified by changing their shape or by adding reflectors to further enhance the amplification. Gains of 12 dB have been measured and predictions show that gains of 20 dB are theoretically possible.     

Fresnel phase matching: a universal phase matching scheme

We present new theoretical concepts for Fresnel phase matching. A guided wave approach is described, which allows us to intrinsically take into account all the physical processes involved. To cite this article: M. Raybaut et al., C. R. Physique 8 (2007).