Poincaré inequalities and quasiconformal structure on the boundary of some hyperbolic buildings

In this paper we shall show that the boundary of the hyperbolic building considered by M. Bourdon admits Poincaré type inequalities. Then by using Heinonen-Koskela's work, we shall prove Loewner capacity estimates for some families of curves of and the fact that every quasiconformal homeomorphism is quasisymmetric. Therefore by these results, the answer to questions 19 and 20 of Heinonen and Semmes (Thirty-three YES or NO questions about mappings, measures and metrics, Conform Geom. Dyn. 1 (1997), 1-12) is NO.

     

Growth of anthracene thin films by matrix-assisted pulsed-laser evaporation

Thin films of anthracene (C₁₄H₁₀) have been grown by matrix-assisted pulsed-laser evaporation. Frozen solutions of 2 wt% anthracene (solute) in ortho-xylene or in chloroform were used as targets and were irradiated by a frequency-quadrupled Nd:YAG laser (266 nm). The deposited films were studied by the complementary use of infrared absorption and photoluminescence emission. The vibrational bands and fluorescence emission of bulk anthracene were clearly identified in the films. This means that the organic molecules were not modified by photochemical reactions during the laser irradiations, despite the strong absorption of anthracene at 266 nm. Among the growth parameters, the laser fluence was found to be critical in order to avoid the fragmentation of the anthracene molecules. The results show that matrix-assisted pulsed-laser evaporation is suitable for growing thin films of organic materials even if they absorb at the irradiating wavelength. PACS 81.15.Fg; 78.55.Kz; 33.20.Ea; 71.20.Rv     

Rigidity of quasi-isometries for some hyperbolic buildings

For a family of negatively-curved buildings, we show that any quasi-isometry lies within bounded distance from an isometry. Received: February 2, 2000.     

Droplet Sizing by Mie Scattering Interferometry in a Spark Ignition Engine

A theoretical explanation is given of a technique based on Mie scattering interferometry (MSI), obtained by defocusing of the collecting optics, to size droplets. The originality of this study is the development of a droplet sizing method by planar laser light scattering for the case of a scattering angle range close to 90°. The feasibility of this method and its limitations are fully described. The dependence on intensity levels and refractive index variations can be neglected. After discussion of some practical details about particle size, imaging and camera constraints, the results obtained in the combustion chamber of a spark ignition (SI) engine, near the spark plug, prior to ignition and for different injection timings are described and discussed. It can be concluded that the implementation of the MSI method in this experimental set-up has been realized successfully to provide droplet distributions in an SI engine. To allow the easier use of the technique, image processing software will be developed in the Matlab environment.     

Vibrational properties of hydrogen in compound semiconductors

Hydrogen introduced in compound semiconductors generally forms complexes with atoms of the crystal. They result from the interaction of hydrogen with some dopants, residual impurities and defects. It is shown here how vibrational spectroscopy can inform on the chemical nature of the complexes and on their structure, which can explain some electrical effects. From the experimental data, a kind of classification of the complexes, depending on the binding and location of the H atom, is established. Spectroscopy under uniaxial stress allows to determine the symmetry of the complexes and the relation with theoretical models is discussed. From the stress-induced dichroism one can derive reorientation energies related to the lattice distortion induced by the complex. An overview of the complexes in proton-implanted materials is presented and we finally try to summarize some of the questions not yet answered on the interaction between hydrogen and bulk compound semiconductors.     

New results on the Zeeman effect of phosphorus in silicon

We report variational calculations of the quadratic Zeeman effect of phosphorus impurity in silicon, which are compared to our experimental data for B⊥E and B⊥E. It is shown that a small variation of the ratio γ of the transverse and effective masses can lead to a good agreement between theory and experiment for the 2p₀ line. The shift of the central component of the 2p_± line has been found to depend on the polarization of the incident radiation and this fact has not yet been explained. It is also shown that the shift observed for the line ascribed previously to a 1s(A₁)→3d₀ transition can be consistent with this attribution, giving experimental evidence of its electronic nature.     

Effective mass-like states of the deep acceptor level of Au and Pt in silicon

In this note we report the absorption spectra associated with the acceptor level of Au and Pt in silicon. The structures observed are experimental evidence of effective mass-like states related with these centres. A symmetry lower than T_d is suggested for both centres.