Investigations of alkali doped Fe2O3--V2O5 catalysts by transmission and conversion electron Mössbauer spectroscopy

Fe₂O₃--V₂O₅ catalysts doped with Cs₂SO₄ (molar ratio: V:Fe:Cs=1:0.74:0.06) were found to be a rather inhomogeneous mixture of various crystalline and amorphous iron vanadate phases. After calcination in air the catalyst was divided into three different parts which were analyzed separately revealing the formation of FeVO₄ in the top and bottom fraction of the crucible and Fe₂V₄O₁₃ in the middle fraction. As compared to the well crystallized FeVO₄ reference sample, the quadrupole splittings of FeVO₄ in the Cs-doped catalysts were larger pointing to more distorted iron sites which were assumed to be responsible for high catalytic selectivities. In contrast, the quadrupole splittings of FeVO₄ in the less selective K- and Rb-doped Fe₂O₃--V₂O₅ catalysts were smaller. Additional components in the bottom fraction were also α-Fe₂O₃ and Fe_1-xS. As indicated by the CEMS spectra the latter is located preferentially on the surface of the catalyst particles. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of relaxation on the profile of a nonlinear acoustic pulse

The influence of transverse relaxation on a nonlinear acoustic wave generated in the presence of the acoustic self-induced transparency (SIT) phenomenon is investigated. An explicit analytical equation for the profile of the nonlinear acoustic wave is derived by a perturbation theory developed on the basis of the inverse scattering problem. This equation provides a possible means for investigating experimentally the profile of an acoustic SIT pulse with allowance for relaxation effects, so that these results can be used to construct new types of acoustoelectronic devices. Zh. Tekh. Fiz. 68, 130–131 (May 1998)     

Modifications of the Wolfe Line Search Rules to Satisfy Second-Order Optimally Conditions in Unconstrained Optimization

The line search method incorporating the Wolfe conditions is modified to ensure that a descent algorithm terminates in a finite number of steps at an approximate stationary point where the second-order conditions of optimality are satisfied. A simple procedure based on conjugate directions is proposed to determine directions of negative curvature.     

Determination of aqueous plutonium oxidation states by solvent extraction

The reliability of two solvent extraction techniques for the determination of Pu oxidation states in solution was tested with low-ionic-strength solutions and with high-Na and high-Mg brines that contained Pu concentrations sufficient for spectrophotometric analysis. One procedure only differentiates between reduced Pu [Pu(III) and Pu(IV)] and oxidized Pu [Pu(V) and Pu(VI)], whereas the second procedure was designed to differentiate between Pu(IV), Pu(V), and Pu(VI) in solution. Both procedures successfully differentiated between oxidized and reduced Pu in both dilute solutions and brines when tested with samples that contained only the Pu(IV), Pu(V), or Pu(VI) oxidation states. However, when the second solvent extraction procedure, which differentiates between Pu(V) and Pu(VI), was employed for solutions that did not contain a strong oxidant to maintain the Pu(VI) oxidation state, significant quantities of Pu(VI) were reduced to Pu(V) during extraction, indicating that accurate quantification of Pu(V) and Pu(VI) is not possible with this procedure.Work supported by the U. S. Department of Energy under Contract DE-ACO6-76RLO 1830.     

Two-dimensional antiferromagnet in an external staggered field

We calculate the temperature-dependent energy gap in the magnetic excitations spectrum of the two-dimensional antiferromagnet in the presence of a staggered magnetic field, using the nonlinear sigma model.     

1.2 Anorganische analyse

Ohne Zusammenfassung     

On a new class of function systems of Faber-Schauder type

In this paper, we introduce a new class of function systems generalizing the classical Faber-Schauder system. Under the condition that the generating sequence is bounded, we show that systems of such a class constitute bases in the space of continuous functions and prove some properties of series expansions of functions in these systems.