Excimer laser-induced crystallization of CdSe thin films

We have investigated ArF (λ=193 nm) excimer laser-induced crystallization of amorphous CdSe semiconductor thin films. The crystallization has been monitored by a related photoluminescence emission in the free-exciton and defect-band transition regions. For different irradiation conditions, we have observed formation of nanorods, up to 2 μm long, as well as the formation of arrays of CdSe nanobeads with a narrow size distribution and characteristic dimensions corresponding to λ/2 and λ/8. The successful crystallization has also been confirmed by confocal Raman spectroscopy.     

Local vibration of an elastic plate and zero-group velocity Lamb modes

Elastic plates or cylinders can support guided modes with zero group velocity (ZGV) at a nonzero value of the wave number. Using laser-based ultrasonic techniques, we experimentally investigate some fascinating properties of these ZGV modes: resonance and ringing effects, backward wave propagation, interference between backward and forward modes. Then, the conditions required for the existence of ZGV Lamb modes in isotropic plates are discussed. It is shown that these modes appear in a range of Poisson's ratio about the value for which the cutoff frequency curves of modes belonging to the same family intercept, i.e., for a bulk wave velocity ratio equal to a rational number. An interpretation of this phenomenon in terms of a strong repulsion between a pair of modes having a different parity in the vicinity of the cutoff frequencies is given. Experiments performed with materials of various Poisson's ratio demonstrate that the resonance spectrum of an unloaded elastic plate, locally excited by a laser pulse, is dominated by the ZGV Lamb modes.     

Core-electron relaxation energy in small metallic particles

A general calculation method for screening in a finite electron gas proposed by Cini, is applied to study of core-hole relaxation energy in small metallic particles. In order to obtain quantitative results, a pseudopotential theory is developed for the core-hole perturbation which provides excellent agreement with the generally accepted excited-atom model in the bulk limit. The transition and noble metals treated by means of a semi-empirical extension of the method. The present calculation method of extra-atomic relaxation energies, involving an electron gas approximation for the conduction electrons allows straightforward applications of the method of Cini in the case of a finite-spherical metal particle. The relaxation energy is found to give an important contribution to core-hole binding energy shifts in small particles.     

Anisotropy of the turbidity of a nematic liquid crystal

The absorption coefficient of a nematic liquid present an important anisotropy. The measurement of this coefficient in three simple geometries allows the determination of the three Frank elastic constants on the same sample. We give the results obtained for MBBA at room temperature.     

α- Addition des amines sur les glycosyl isonitriles.

α-Addition reactions of glycosyl isonitriles with primary and secondary amines allowed to prepare substituted glycosyl formamidines representing good precursors in the synthesis of nucleosides.     

A Chemical Study of Burley Tobacco Flavour (Nicotiana tabacum L.). II. Medium-Volatile,free Acidic Constituents (b.p. ∼84–114°/0.001 Torr)

The acidic part of a fraction b.p. 84–114°/0.001 Torr from Burley Tobacco condensate was investigated. Among the 22 compounds identified, 9 appeared to be new tobacco flavour components. This result increased to 208, the total number of Burley tobacco constituents so far isolated and identified in this laboratory.     

Spectral hole burning measurement thulium-doped fiber amplifiers

An accurate technique was implemented to measure spectral hole burning in rare-earth amplifiers at room temperature, showing that thulium-doped fiber amplifiers exhibit hole depths four times lower than those of C -band erbium-doped fiber amplifiers.     

UVB-activated psoralen reduces luminal narrowing after balloon dilation because of inhibition of constrictive remodeling

In this study we have explored the potential of PUVB (8-MOP + UVB) therapy for the reduction of luminal narrowing after arterial injury. In 15 rabbits, balloon dilation of iliac arteries was performed. In 20 arteries, dilation was combined with the delivery of pulsed ultraviolet light B (UVB) irradiation with 10 arteries being previously subjected to sensitizer infusion. Changes in vessel diameter, proliferation and extracellular matrix protein content at 6 weeks were evaluated by means of angiography and histomorphometry-immunohistochemistry. We found that PUVB, applied at the time of dilation, induced reduction in late loss (LL) at 6 weeks (percutaneous transluminal angioplasty vs UVB vs PUVB: 0.64 +/- 0.15 mm vs 0.61 +/- 0.05 mm vs 0.29 +/- 0.05 mm; p = 0.018). The same holds true for constrictive remodeling (0.53 +/- 0.15 mm vs 0.45 +/- 0.06 mm vs 0.15 +/- 0.05 mm; p = 0.016). In the irradiation groups, LL was independent of acute gain (AG), as opposed to the control. Collagen content increased significantly after PUVB in media and adventitia, without increased cellular proliferation in all vessel layers. Thus, PUVB at the time of dilation reduced luminal narrowing at follow-up without effecting proliferation. This effect was independent of AG and was associated with increased collagen content in media and adventitia.     

Kinetic of catalytic sucrose esterification in aqueous media

The process of sucrose esterification in the presence of a homogeneous catalyst was developed directing the reaction to the production of weakly substituted esters. Esterification of sucrose was processed with octanoyl chloride in a discontinuous reactor, in presence of 4-dimethylaminopyridine as catalyst. The process was operated in a time interval ranging from 0 to 80 min, at temperatures from 288 to 303 K, pH=10 and at atmospheric pressure. The following conversion levels were obtained: octanoyl chloride 11-84%, primary monoester production of 9-67%, secondary monoesters of 1.3-17%. Activation energies ranging from 158 l to 300 kJ/mol characterized the stages of the process, among them the stage of formation of the DMAP/RCOCl complex (162.43 kJ/mol). The increase in primary monoesters yield due to the temperature rise, leads to an increase in the rate of the direct reaction as well as in the speed of secondary monoester conversion to primary monoesters, quantifying a selectivity in primary isomers in the following positions sequence: 6> 1" > 6".