Photochemically generated carotenoid radicals on Nafion film and silica gel: an EPR and ENDOR study

Carotenoid cation radicals have been observed at 120 K, by EPR and proton ENDOR measurements, to be formed upon 77 K photolysis of thin films of Nafion or silica gel coated with the carotenoids, β-carotene and canthaxanthin. The powder ENDOR spectra consist of resolvable lines due to couplings larger than 2.8 MHz but smaller than 17 MHz assigned to the methyl protons of the carotenoid cation radical and to an -proton of the planar polyene chain.     

绝缘层上半导体多晶膜激光再结晶临界条件

从理论的角度分析了绝缘衬底对其上面半导体多晶膜激光熔化再结晶过程的影响, 发现低导热的绝缘层使产生固一液相变的临界激光功率有明显的降低.用喇曼光谱测量了激光再结晶SOI层中的应力. 应力的出现是多晶膜内曾经发生过固一液相的佐证.从这一思想出发, 对LPCVD方法制备的大量SOI 样品进行激光再结晶临界条件的研究, 证明了忽略绝缘层低热导影响的模型不能解释实验结果, 而经过修正的公式则可以较好地拟合实验结果, 关键词：     

Temporal characteristics of picosecond stimulated Raman scattering in oxide crystals

The temporal characteristics of stimulated Raman scattering (SRS) under 22-ps laser excitation were studied in eight oxide crystals with a T ₂ optical-phonon dephasing time variable by up to two orders of magnitude. The measured SRS pulse width was shortened from 13.8 ps for Ba(NO₃)₂ (T ₂ = 26.5 ps) to 4 ps for the LiNbO₃ (T ₂ = 0.38 ps) crystal. The dependence of SRS pulse width on the dephasing time was analyzed in the framework of the known SRS theory.     

Temperature distribution in the bright spot of the optical discharge in an optical fiber

2D simulation of the optical discharge propagation in an optical fiber is performed. In contrast to the previous works, the temperature dependences of the transfer coefficient are taken into account for the bright-spot plasma. The results are compared with the recently published measurements of the spatial distribution of the bright-spot radiation intensity. Good agreement is obtained for the discharge propagation velocity and the dependence of the bright-spot size on the laser power.     

Characterization of phospho-olivines as materials for Li-ion cell cathodes

Solid State Reaction was employed to prepare phospho-olivines LiMPO₄ (where M=Fe, Co) as pure phase and LiNiPO₄ in presence of foreign phases, as cathodic materials for lithiumions batteries. The relationship between structural, morphological and electrochemical properties were investigated in the case of LiFePO₄. Structural investigation has been carried out by means of X-ray powder diffraction (XRPD) and Rietveld refinement. The influence on the morphology of annealing temperature, different flowing gas mixture and addition of ascorbic acid during the synthesis, has been analysed via scanning electron microscopy. The electrochemical cycling performances on LiFePO₄ showed to be positively affected by the modifications of the experimental conditions. Cyclic voltammetry showed a good reversibility during insertion-extraction mechanism, in particular in presence of additives. LiCoPO₄ and LiNiPO₄ are interesting as high voltage cathode materials for Li-ion batteries and have been taken into account, but their electrochemical operating conditions are still to be optimised. In the case of LiNiPO₄ it is very difficult to obtain, by solid state synthesis, suitable purity powders, having a grain size small enough to exploit it usefully as cathodic material for Li-ion cells. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16 – 22, 2000.     

Continuum Approaches in the Mechanics of Curved Composites and Associated Problems for Structural Members

A review is made of studies on the mechanics of curved composites carried out using continuum approaches. The relevant theory, problem formulations, and solution methods are considered and some typical results on the influence of structural distortion on the mechanical behavior of composites are analyzed. Subjects for near-term studies are proposed     

One-Parameter Fixed-Point Theory and Gradient Flows of Closed 1-Forms

We use the one-parameter fixed-point theory of Geoghegan and Nicas to get information about the closed orbit structure of transverse gradient flows of closed 1-forms on a closed manifold M. We define a noncommutative zeta function in an object related to the first Hochschild homology group of the Novikov ring associated to the 1-form and relate it to the torsion of a natural chain homotopy equivalence between the Novikov complex and a completed simplicial chain complex of the universal cover of M.