Infrared ellipsometry study of the oxidation mechanisms of hydrogenated amorphous silicon

A detailed study of the oxidation of plasma deposited amorphous silicon (a-Si : H) using infrared phase modulated ellipsometry (IRPME) is presented. a-Si : H is found to be resistant against air oxidation confirming previous measurements. A 5–6 Å thick oxide layer at the surface of a-Si : H is observed after a few months of exposure to air. The extreme sensitivity of IRPME is emphasized. In particular Si-O-Si and (O_n)Si-H stretching vibrations are identified at the film surface at the submonolayer level. The oxidation mechanisms are discussed. The weak reactivity of a-Si : H with atmosphere is correlated with the presence of a hydrogen rich thin layer at the top surface.     

Oxidation of olefins with alkanesulfoperacids

Alkanesulfonic peracids RSO₄H effectively oxidize olefins to the corresponding epoxides. The kinetics and mechanism of this reaction are studied. It was shown that both the monomer and dimer form of the peracid act as oxidizing agents. The dependence of the weight constant of the reaction of monomer RSO₄H with substituted acyclic olefins on the structure of the latter is described by the Taft equation. A linear correlation is established between log k₂ and the inductive constants of the substituents on the oxygen atom in the peracid.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 333–337, February, 1991.     

Simulation of pumping beams self focusing and defocusing in NH3 Raman laser

High power IR pumping beams self focusing and defocusing in NH₃ Raman laser is investigated by numerical methods on the basis of the solution of nonlinear quasioptical equations. The analysis of self focusing have been done for a wide range of parameters of radiation and of active medium. Spatial evolution of the beam configuration have been investigated for different regimes of nonlinear diffraction. Developed model enables to allow exactly for the spectroscopic features of active molecules and may be applied to the analysis of the properties of powerful optically pumped FIR lasers.     

用峰面积判据改善Delsuc法预测的谱

基于Prony算法的Delsuc谱预测是目前NMR LPSVD(Linear Prediction SingularValue Decomposition)法中比较实用的方法。但在高噪声的条件下,时有失峰和假峰出现且要事先知道谱的峰数。本文通过跟踪迭代过程发现Delsuc法的判别因子r_(mis) 很难选定。如果它太小会失峰,而过大又会出现假峰。同时,由于噪声的影响,弱信号的采样点之间的相关性比强信号小,从而在迭代过程中会增加数值不稳定性。文中引入峰面积判据来改善Delsuc法,经模拟与实验均证明结果有效。     

Cylindrical solitons in a Gödel Universe and their stability

Exact cylindrically symmetric solutions are obtained for a class of interacting scalar and vector fields in a rotating Godel Universe. We select those with the properties of solitons with smooth decrease of the fields to asymptotics and those with sharp boundaries (droplets). It is shown that only some of the droplets are stable with respect to perturbations that preserve cylindrical symmetry.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 24–27, May, 1991.     

Optical properties of F.I.R. metallic grids: Reflection phase shift measurements

Utilization of metallic grids stacks for F.I.R filters needs a good knowledge of optical properties of each grid. We study here an experimental method in order to determine the wave's change of phase by reflection on a wire grid. We use a Perot-Fabry interferometer constituted by these grids.     

Excitation of middle-IR range hollow metallic waveguides

The results of the efficiency of low-mode excitation of a parallel-plate hollow metallic waveguides (HMW) as a function of beam and waveguide parameters are represented. Coupling of two waveguides is also discussed.     

Buckling of laminated plates - A simple finite element based on higher-order theory

A four-noded rectangular element with seven degrees of freedom at each node is developed for buckling analysis of laminated plate structures having any number of layers with a constant thickness of individual layers. The displacement model is so chosen that it can explain adequately the parabolic distribution of transverse shear stresses and the non-linearity of in-plane displacements across the thickness. A geometrical stiffness matrix is developed using in-plane stresses. A wide range of plates from thick to thin are examined under uniaxial loading conditions. The results are compared with the existing analytical and numerical solutions. The present formulations confirm its applicability for buckling analysis of a wide range of plates.     

Differential determination of arsenic(III) and total arsenic using flow injection on-line separation and preconcentration for graphite furnace atomic absorption spectrometry

Arsenic(III) can be quantitatively extracted using sodium diethyldithiocarbamate (NaDDTC) as the complexing agent and C18 reversed phase packing as the column material for solid phase extraction. Arsenic(V) must be reduced to its trivalent oxidation state prior to extraction. A mixture of sodium sulphite, hydrochloric acid, sodium thiosulphate and potassium iodide was found to be optimum for on-line reduction. When the sorbent extraction is carried out without and with the addition of the reduction mixture, arsenic(III) and total arsenic can be determined sequentially by graphite furnace atomic absorption spectrometry with detection limits (3 σ) of 0.32 ng for As(III) and 0.43 ng for total arsenic. A 7.6-fold enhancement in peak area compared to direct injection of 40 μl samples was obtained after 60 s preconcentration. Results obtained for sea water standard reference materials, using aqueous standards for calibration, agree well with certified values. A precision of 5.5% RSD was obtained for total arsenic in a sea water sample (1.65 As). Results obtained for synthetic mixtures of trivalent and pentavalent arsenic agreed well with expected values.