Oxygen States in Oxides with a Perovskite Structure and Their Catalytic Activity in Complete Oxidation Reactions: System La1 – x Ca x FeO3 – y (x = 0–1)

Oxygen states in the La_{1 – x} Ca _x FeO_{3 – y} perovskites prepared using different procedures are studied by temperature-programmed reduction (TPR). Results are compared to data on the catalytic activity in the oxidation of methane and carbon monoxide. The activity of the samples in the CO and CH₄ oxidation over a wide temperature range (200–600°C) is shown to correlate with the amount of reactive surface and subsurface oxygen removable during TPR below 420°C. These oxygen states in the samples of the La_{1 – x} Ca _x FeO_{3 – y} series can be associated with the domain or intergrain boundaries. No correlation is found between the amount of lattice oxygen removable during TPR and the activity of the La_{1 – x} Ca _x FeO_{3 – y} samples in the complete oxidation of methane at temperatures of 450–600°C. It is suggested that catalytic complete oxidation is determined by the most reactive surface and subsurface oxygen states located at the interphase boundaries, whereas the lattice oxygen does not participate in these reactions.     

A spherical-wave source based on a probe for a near-field microscope

A new type of a spherical-wave source for precise interferometry based on a fiber probe for a nearfield microscope is proposed. Data on distortions of generated wavefronts are reported. For the optical numerical aperture NA = 0.24, the root-mean-square distortions do not exceed λ/2000.     

Study of a dc magnetron discharge by using a movable grid anode

A method is proposed for determining the density of the ionizing electron component in a dc magnetron discharge in the region where the magnetic field is strong and highly nonuniform. The method is based on the analysis of the measured dependence of the discharge current on the distance between the cathode and the grid anode. The method was used to study the parameters of a magnetron discharge in a process magnetron operating in the regime with a narrow discharge region localized close to the cathode surface.     

Properties of Josephson junctions in the inhomogeneous magnetic field of a system of ferromagnetic particles

The effect of a system of ferromagnetic particles on the field-dependent critical current of a Josephson junction is experimentally studied for junctions of different geometries. For edge junctions, the effect of commensurability between the periodic magnetic field of the particles and the Josephson vortex lattice is observed. The effect manifests itself in additional maxima of the field-dependent critical current. For overlap junctions, giant (greater than sixfold) variations of the maximum critical current are observed depending on the magnetic state of the particles. The changes in the “Fraunhofer” pattern of the overlaped Josephson junctions are attributed to the formation of Abrikosov vortices due to the effect of uniformly magnetized particles. The effects revealed in the experiments can be used to analyze the inhomogeneous magnetic field of a system of submicron particles and to control the transport properties of Josephson junctions.     

Effect of resonance charge exchange between argon ions on the effective sputtering rate in a magnetron discharge

The sputtering rates of various materials in a magnetron ion sputterer are compared. The effective sputtering yields obtained when argon is used as a working gas are given. The difference between the sputtering yields found in this work and those obtained with monoenergetic ion beams is shown to be associated with resonance charge exchange between argon ions and neutral argon gas.     

Optimization and Comparing a Different Various of Head Part of a Moderator of “Central” Direction for IBR-2 Reactor

The performance of the upstream moderator for neutron beams 1, 4, 5, 6, and 9 extracted from the IBR-2 reactor is simulated towards selecting its optimum configuration. For different moderator options, gain factors with respect to the existing comb-shaped water moderator are computed. Taking into account the technological issues in manufacturing a combined moderator, the scheme with optimal physical characteristics is selected.     

Structural features and the lattice oxygen reactivity of low-temperature lanthanum manganites doped with different cations

Summary Dispersed samples of LaMnO₃prepared viathe Pechini route and annealed at 500°C were doped with cations of a different charge and size (Ce, Fe, Bi, Sr+Bi). The effects of doping on the structural features (XRD, IR) and reducibility (H₂TPR) of these samples were considered.     

q 2-convolution and itsq 2-Fourier transform

The functions on the lattice generated by the integer degrees ofq ² are considered, 0<q<1. Theq ²-shift operator is defined. The multiplicators and theq ²-convolutors are defined in the functional spaces which are dual with respect to theq ²-Fourier transform. Theq ²-analog of convolution of twoq ²-distributions is constructed. Theq ²-analog of an arbitrary order derivative is introduced. Presented at the 9th Colloquium “Quantum Groups and Integrable Systems”, Prague, 22–24 June 2000. The author was supported in part by the Russian Foundation for Fundamental Research (grant no. 0001-00143) and the NIOKR MPS RF     

Magnetoresistance and noncollinear structures of multilayer ferromagnetic nanoparticles

The distribution of the magnetization over multilayer particles, including three ferromagnetic layers separated by insulating spacers, is studied experimentally and theoretically. Experimental data on the magnetic state of these particles are obtained by measuring their magnetoresistance. For the case of zero applied field, it is shown that a multilayer particle with easy-plane magnetic anisotropy is a noncollinear helical state.