Vanadium oxidation as a result of cw CO2 laser irradiation in atmospheric air

New results are reported concerning the vanadium oxidation by cw CO₂ laser irradiation in air at atmospheric pressure. Particular emphasis is paid both to the initial stage and the development of the oxidation process under the action of the laser radiation. Some aspects are finally discussed concerning the quantitative theoretical interpretation of the experimentally recorded data.     

Fast convolutions meet Montgomery

Arithmetic in large ring and field extensions is an important problem of symbolic computation, and it consists essentially of the combination of one multiplication and one division in the underlying ring. Methods are known for replacing one division by two short multiplications in the underlying ring, which can be performed essentially by using convolutions.

However, while using school-book multiplication, modular multiplication may be grouped into operations (where denotes the number of operations of one multiplication in the underlying ring), the short multiplication problem is an important obstruction to convolution. It raises the costs in that case to . In this paper we give a method for understanding and bypassing this problem, thus reducing the costs of ring arithmetic to roughly when also using fast convolutions. The algorithms have been implemented with results which fit well the theoretical prediction and which shall be presented in a separate paper.

     

Physical Measures for Multivalued Inverse Iterates Near Hyperbolic Repellors

We study new invariant probability measures, describing the distribution of multivalued inverse iterates (i.e. of different local inverse iterates) for a non-invertible smooth function f which is hyperbolic, but not necessarily expanding on a repellor Λ. The methods for the higher dimensional non-expanding and non-invertible case are different than the ones for diffeomorphisms, due to the lack of a nice unstable foliation (local unstable manifolds depend on prehistories and may intersect each other, both in Λ and outside Λ), and the fact that Markov partitions may not exist on Λ. We obtain that for Lebesgue almost all points z in a neighbourhood V of Λ, the normalized averages of Dirac measures on the consecutive preimage sets of z converge weakly to an equilibrium measure μ ⁻ on Λ; this implies that μ ⁻ is a physical measure for the local inverse iterates of f. It turns out that μ ⁻ is an inverse SRB measure in the sense that it is the only invariant measure satisfying a Pesin type formula for the negative Lyapunov exponents. Also we show that μ ⁻ has absolutely continuous conditional measures on local stable manifolds, by using the above convergence of measures. We prove then that f:(Λ,ℬ(Λ),μ ⁻)→(Λ,ℬ(Λ),μ ⁻) cannot be one-sided Bernoulli, although it is an exact endomorphism of Lebesgue spaces. Several classes of examples of hyperbolic non-invertible and non-expanding repellors, with their inverse SRB measures, are given in the end.     

Gamma-ray production in the 170Er(p,n)170Tm nuclear reaction

For the first time discrete gamma-rays following the nuclear reaction ¹⁷⁰Er(p,n)¹⁷⁰Tm with enriched target were measured with a high resolution GeHP spectrometer. Protons delivered by the Bucharest FN Tandem Van de Graaff accelerator bombarded a thin self-supporting film of enriched erbium. Measured γ-ray energies (E_γ), their relative intensities (I_γ) and corresponding excitation functions for the beam energy range 2.0–3.6 MeV are reported in the present work. The measured excitation functions were fairly well reproduced by compound nucleus calculations based on the Hauser-Feshbach formalism.     

Microstructure and mechanical characteristics of hydroxyapatite coatings on Ti/TiN/Si substrates synthesized by pulsed laser deposition

We synthesized by pulsed laser deposition a bilayer of Ti/TiN on Si(100) wafers which was coated in a next step with hydroxyapatite (samples labelled HA-1). Some of the structures were further thermally treated in a water vapour jet (samples labelled HA-2). In SEM, the HA surface looked rough, with micronic droplets. TEM and SAED investigations revealed a compact organization of HA crystals in the case of the HA-1 sample, while two regions (one compact and one porous) were identified for the HA-2 sample, with triclinic HA crystals within the 500 nm range. In XTEM, at the Si/TiN border, a 2–3 nm SiO₂ layer was visible, whereas at the TiN/Ti border there was a smooth transition from fcc (111) TiN to hcp (100) Ti. The HA crystals were elongated normal to the surface. According to Berkovich indentation qualitative analyses, the sample HA-1 was more homogeneous and harder but brittle. Scratch tests confirmed quantitatively that HA-1 was more resistant and adherent than HA-2 films. In the first case, the big droplets only were removed by the indenter, while the HA-2 films were delaminated on large areas as a result of wedge spallation failure.     

Optimization of Cr8O21 targets for Pulsed Laser Deposition

This work describes the preparation of Cr₈O₂₁ pellets with optimised mass density to be used as targets for Pulsed Laser Deposition (PLD) of chromium dioxide thin films. Cr₈O₂₁ is synthesised by thermal decomposition of CrO₃, at 270 °C. An attempt to reduce the grain size of the Cr₈O₂₁ powder to the nanometer scale has been made in order to increase the density of the pressed and sintered pellets serving as targets. The morphology of those starting fine powders as well as of targets (before and after laser ablation) and the corresponding thin films were characterized and studied using X‐ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Raman spectroscopy. The composition of the films is a mixture of crystallised Cr₂O₃ and amorphous CrO₂. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Enhancement of Mobile Phase Velocity in TLC by Means of an External Alternating Electric Field

JPC – Journal of Planar Chromatography – Modern TLC - In normal TLC practice, migration of the mobile phase through the layer is controlled by capillary forces. Under these conditions...     

Study of the compounds formed on damaged ZnSe windows by multi-pulse microsecond pulsed TEA-CO2 laser irradiation in air

We report on experimental data of chemical compounds formed in the damaged area at the surface of certain optical ZnSe windows subjected to multi-pulse microsecond pulsed TEA-CO₂ laser irradiation in air. The results are analysed from the viewpoint of implication of the oxidation process activated under the action of CO₂-laser power in plasma initiation and evolution of surface damage process.