Direct observation of the anderson transition in hxwo3 bronzes by high-resolution x-ray photoelectron spectroscopy

We report high-resolution X-ray photoemission measurements of semiconducting and metallic hydrogen bronze H_xWO₃ as a function of the hydrogen/tungsten ratio. Complex structures in W 4f core-level spectra can be attributed to two discrete initial states in the semiconducting phase and to three states in the metallic phase. These results, and a comparison of valence and conduction band spectra with band structure calculations, are consistent with an Anderson transition at x ≈ 0.2 and conflict with percolation or Mott-type transition models.     

New depth-profiling method by angular-dependent x-ray photoelectron spectroscopy

A non-destructive method for depth profiling by X-ray photoelectron spectroscopy, based on the dependence of the analysed depth with the electron emission angle, is presented.The extraction of the concentration profile from angular distribution experiments is achieved, in the framework of a flat-layer model, by minimizing the difference between theoretical and experimental relative intensities. The applicability and limitations of the method are discussed on the basis of computer simulation results. In particular, constraints reflecting the physical properties of the system must be introduced in the numerical treatments. The depth probed is of the order of 3λ, λ being the value of the inelastic mean free path, and the depth resolution is of the order of λ/3. In tests of the method, the concentration depth profiles of the Ag-Al₂O₃ and the SiO₂-Si interfaces and of the surface region of a Cu-Ni alloy have been obtained.     

An easy method for the preparation of 4-acylisoxazoles from C(α),O-dianions of oximes

Several C(α),O-dilithiooximes of aromatic ketones were condensed with aroyl chlorides. The presumed diacyl intermediates were not isolated, and the reaction mixtures containing them were acid-cyclized to give 4-acylisoxazoles in 22–62% yield.     

Uptake of mercury by caged crayfish

An in situ caged crayfish experiment was conducted in the Wabigoon River System, Ontario, Canada to determine the relative importance of food and water pathways for mercury accumulation in crayfish. Two groups of 160 crayfish were suspended in the water column; one at an ucontaminated site, the other at a location with highly elevated total mercury and methylmercury levels in water. Crayfish at each site were divided into two groups. Crayfish were fed either sucker flesh obtained from an uncontaminated lake (low mercury diet) or walleye flesh from contaminated Clay Lake, Ontario, Canada (high mercury diet). After 10 weeks crayfish at both sites fed the high mercury diet had over 20 times mercury accumulation compared to crayfish on the low mercury diet. There was no statistical effects due to sharply elevated water concentrations of total and methylmercury on mercury bodyburdens. This indicated that food was the dominant pathway for mercury accumulation in crayfish.     

Chaotic and periodic emission of high power solid state lasers

Nonlinear, dynamical systems even with a few degrees of freedom may show chaotic or periodic behaviour, depending on the parameters of the system. Recently it was demonstrated, both experimentally and theoretically, that the temporal emission of a laser can become chaotic, if several longitudinal modes oscillate [Brunner and Paul (1983), and Abraham et al. (1982)]. The chaotic emission is caused by the nonlinear interaction of the modes and the longitudinal gain structure [Komtomtseva et al. (1982)]. In this paper it is pointed out that the transverse mode structure and the radial gain profile produced by the transversal modes, may give rise to temporal instabilities of the laser emission. If the relevant parameters of the laser oscillator — Fresnel number, resonator losses, pump rate — exceed certain critical values, the output intensity becomes unstable. The damped relaxation oscillation changes into undamped periodic oscillation or, with increasing values of the above parameters, into chaotic emission. The theory, using the nonlinear Kirchhoff-Fresnel integral equation and the rate equation approach, is confirmed by experimental results.     

Overview of DWDM/ODC Project

Abstract

This article introduces the main achievements resulting from the DWDM/ODC project. The five areas of research activity within the DWDM/ODC project cover some of the main issues of design and development of dense wavelength division multiplexing systems for transparent optical networks. These issues are: performance assessment with arbitrary optical filtering; performance of signaling formats; dispersion compensation strategies for directly and externally modulated systems in presence of nonlinear transmission-induced degradation; and the impact of noise and crosstalk in the extent of transparent optical networks. All five areas of research activity have contributed significantly to a better understanding of the limitations present in dense wavelength division multiplexing systems.     

Fusion around the barrier for 7Li+12C

Fusion cross-sections for the ⁷Li + ¹²C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy evaporation residues with energies below 3 MeV could not be separated out from the α-particles in the spectrum and hence their contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections due to the breakup of ⁷Li may not be significant for ⁷Li + ¹²C reaction at energies around the barrier.     

Strongly nonlinear convection in binary fluids: minimal model using symmetry decomposed modes

Spatially extended stationary and traveling states in the strongly nonlinear regime of convection in layers of binary fluid mixtures heated from below are described by a few-mode-model. It is derived from the proper hydrodynamic balance equations including experimentally relevant boundary conditions with a non-standard Galerkin approximation that uses numerically obtained, symmetry decomposed modes. Properties of the model are elucidated and compared with full numerical solutions of the field equations.     

X-ray photoelectron spectroscopy of thermally grown silicon dioxide films on silicon

At various stages of in situ thermal oxidation of Si(111) monocrystals, X-ray photoelectron spectroscopy (XPS or ESCA) reveals a shift in the silicon core-level binding energies which varies continuously from 2.4 to 4.2 eV. From the oxygen and silicon ESCA peak intensities, these films can be said to have the silicon dioxide composition with an excess in oxygen concentration. By correlating the silicon 2p or 2s binding-energy shifts with oxygen KLL Auger energy and oxygen 1s binding-energy shifts, it is shown that a Fermi level shift and differential extra-atomic relaxation energy in the interfacial region must be invoked, in addition to chemical structure considerations, to interpret these data.