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181.
The variation of the fundamental edge E0 of the pseudo-binary alloy system Zn1?xMgxTe is studied by wavelength modulated reflectivity at 300 K in the range : 0<x<0.41. The experimental bowing parameter c = 0.6 ± 0.05 eV is evaluated from the evolution with x of three structures in the spectra obtained in the vincinity of E0. It is much greater than the one we calculate with Hill's formula c = 0.067 eV. This suggests a superposition of electron-hole interaction effect on the band to band process at room temperature. 相似文献
182.
We consider the mass heterogeneity in a gas of polydisperse hard particles as a key to optimizing a dynamical property: the kinetic relaxation rate. Using the framework of the Boltzmann equation, we study the long time approach of a perturbed velocity distribution toward the equilibrium Maxwellian solution. We work out the cases of discrete as well as continuous distributions of masses, as found in dilute fluids of mesoscopic particles such as granular matter and colloids. On the basis of analytical and numerical evidence, we formulate a dynamical equipartition principle that leads to the result that no such continuous dispersion in fact minimizes the relaxation time, as the global optimum is characterized by a finite number of species. This optimal mixture is found to depend on the dimension $d$ of space, ranging from five species for $d=1$ to a single one for $d\ge 4$ . The role of the collisional kernel is also discussed, and extensions to dissipative systems are shown to be possible. 相似文献
183.
Lux F Mignot A Mowat P Louis C Dufort S Bernhard C Denat F Boschetti F Brunet C Antoine R Dugourd P Laurent S Vander Elst L Muller R Sancey L Josserand V Coll JL Stupar V Barbier E Rémy C Broisat A Ghezzi C Le Duc G Roux S Perriat P Tillement O 《Angewandte Chemie (International ed. in English)》2011,50(51):12299-12303
184.
Almeida Rui M. Du Xin Min Barbier Denis Orignac Xavier 《Journal of Sol-Gel Science and Technology》1999,14(2):209-216
Erbium doped silica-titania planar waveguides, co-doped with ytterbium and aluminum, have been prepared by sol-gel processing, using multilayer spin-coating deposition on silicon or silica glass substrates. The Er3+ doping level varied between 0 and 2 at.%, while Yb3+ varied from 0 to 3 at.%. Aluminum was incorporated up to 15 at.% Al and it was found to have no significant effect on the refractive index of the silica-titania (80 : 20 mol%) matrix. The Er3+ fluorescence emission was flat within ±0.5 dB, between 1520 and 1560 nm. The corresponding 4I13/2 metastable level lifetime was found to decrease from 6.1 to 3.5 ms, as the Er concentration increased from 0.1 to 0.5 at.%, for films co-doped with 0.5 at.% Yb and 10 at.% Al and the fluorescence decay was essentially single exponential below a Er quenching concentration of 0.5 at.% (1.1 × 1020 ions/cm3). The lifetime appears to be limited by Er-Er interactions at higher rare-earth ion concentrations and by residual OH species in the sol-gel derived waveguides. Vacuum heat treatment at a temperature near 570°C was somewhat effective in increasing the Er fluorescence lifetime, whereas reactive atmosphere processing in CCl4 or Cl2 at a similar temperature appeared to be less effective. 相似文献
185.
Isabelle Dchamps-Olivier Jean-Pierre Barbier Michel Aplincourt Nicolas Oget Franoise Chuburu Henri Handel 《Helvetica chimica acta》1999,82(5):790-795
The acid-base behavior of cyclenphosphine sulfide (cyclenPS) is appreciably different from that of cyclamphosphine sulfide (cyclamPS). The cyclenPS shows five acid functionalities compared to four for cyclamPS. The fifth acidic group in cyclenPS corresponds to the formation of a stable amidure in aqueous solution (pK=12.3). This behavior is due to the strong transannular N→P interaction. The deprotonation sequences were established by 31P-NMR and confirmed by modelling of cyclenPS. 相似文献
186.
Anionic or neutral allylic samarium or neodymium species catalyse the polymerization of styrene (catalyst/styrene ratio = 1:1000) without addition of a cocatalyst. Random syndiotactic‐rich material is obtained from tetra‐allyl‐lanthanides, whereas neutral trisallyl‐lanthanides or anionic ansa‐bis(cyclopentadienyl)bisallyl‐lanthanides afford isotactic‐rich polystyrene. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
187.
Denise Barbier‐Baudry Aicha Bouazza Claire Hlne Brachais Alain Dormond Marc Visseaux 《Macromolecular rapid communications》2000,21(5):213-217
Lanthanides (samarium and ytterbium) tris and monobenzimidinates are efficient for the polymerization of ε‐caprolactone, the systems remaining active after consumption of the monomer. Nevertheless it is not a living polymerization because the benzimidinates are recovered. Evidence for support of the proposed catalytic cycle was obtained by NMR studies. 相似文献
188.