Simulation and analysis of neutron energy spectra from irradiation channels of the IBR-2 reactor

With the purpose of perfecting neutron activation analysis calculation methods, neutron energy spectra for three irradiation channels were modeled and analyzed. On the basis of the results obtained, the renormalization factors were obtained for resonance integrals of the real resonance neutron spectrum from one of the irradiation channels.     

L0 trigger unit prototype for BM@N setup

The BM@N facility is a fixed target experiment based on heavy ion beams of the Nuclotron-M accelerator. The aim of the BM@N is to study nucleus – nucleus collisions at energies up to 4.5 GeV per nucleon. A level 0 trigger processor unit (Trigger L0 unit, T0U) for the BM@N deuterons and carbon ions at Run’2015 has been developed. The T0U is used to generate a BM@N zero level trigger and a TOF detector precise start.T0U generates trigger signal based on beam line and target area detector signals. This module also provides both control and monitoring of the detector front-end electronics power supplies. This article presents a concept, characteristics and test results of the T0U module during the Run 2015.     

On exact dimensional splitting for a multidimensional scalar quasilinear hyperbolic conservation law

A dimensional splitting scheme is applied to a multidimensional scalar homogeneous quasilinear hyperbolic equation (conservation law). It is proved that the splitting error is zero. The proof is presented for the above partial differential equation in an arbitrary number of dimensions. A numerical example is given that illustrates the proved accuracy of the splitting scheme. In the example, the grid convergence of split (locally one-dimensional) compact and bicompact difference schemes and unsplit bicompact schemes combined with high-order accurate time-stepping schemes (namely, Runge–Kutta methods of order 3, 4, and 5) is analyzed. The errors of the numerical solutions produced by these schemes are compared. It is shown that the orders of convergence of the split schemes remain high, which agrees with the conclusion that the splitting error is zero.     

Approximation of the erosion zone profile in planar magnetrons with a disk cathode

We have proposed a universal approximation of the normalized erosion zone profile of planar magnetrons with a disk cathode by a composite function that includes the probability density function for the minimal distribution of extremal values for the region from the center of the disk cathode to the maximum of the erosion zone and the survival Weibull distribution function (from the maximum to the outer boundary of the sputtering zone). The accuracy of the approximation has been verified for six magnetrons differing in the cathode size or in the design of the magnetic systems. In all cases, good agreement has been observed between the approximation and experimentally measured values. The results reported here can be used to analyze processes that occur on the cathode during sputtering and to refine the calculations of coating profiles.     

Anisotropic piezoeffect in microelectromechanical systems based on epitaxial Al<Subscript>0.5</Subscript>Ga<Subscript>0.5</Subscript>As/AlAs heterostructures

A microelectromechanical system is created that has the form of a cantilever-fitted microbar with a cross-sectional area of several square micrometers. The system is formed by applying epitaxial AlGaAs layers on the GaAs(001) surface and selective chemical etching of the AlAs layer lying under the bar. Two micro-cantilevers that are made on the same GaAs(001) wafer and directed along the [110] and [1$ \bar 1 $ \bar 1 0] orthogonal diagonal axes are studied. The static and dynamic characteristics of the systems are studied by white light optical interferometry. The deflection of the bars as a function of the applied voltage is measured in the static mode. An opposite shift of orthogonal microcantilevers on which the same voltage is applied is considered as direct evidence of the efficiency of a piezoeffect-based microengine. The calculated parameters of the micro-electromechanical system, the sensitivity and eigenfrequency, are in good agreement with the measurements.     

Uniqueness of a high-order accurate bicompact scheme for quasilinear hyperbolic equations

The possibility of constructing new third- and fourth-order accurate differential-difference bicompact schemes is explored. The schemes are constructed for the one-dimensional quasilinear advection equation on a symmetric three-point spatial stencil. It is proved that this family of schemes consists of a single fourth-order accurate bicompact scheme. The result is extended to the case of an asymmetric three-point stencil.     

Interaction of platinum and molybdophosphoric heteropoly acid under conditions of catalyst preparation for benzene oxidation to phenol with an O2-H2 gas mixture

The transformations of platinum and a heteropoly acid (HPA) in binary systems prepared from H₂PtCl₆ or H₂PtCl₄ and H₃PMo₁₂O₄₀ were studied using IR and UV-VIS spectroscopy, elemental analysis, XPS, EXAFS, TPR, and HREM. The calcination of platinum chloride with the HPA to 450°C resulted in the formation of a platinum salt of the HPA along with decomposition products (mixture I). The reduction of calcined samples containing Pt: HPA = 1: 1 with hydrogen at 300°C (mixture II) followed by exposure to air resulted in the regeneration of the HPA structure. The resulting solid samples of Pt _1?n ⁰ Pt _n ^II Cl_mO_xH_y) (H_3+p PMo _12?p ^VI Mo _p ^V O₄₀) (III) contained platinum and molybdenum in both oxidized and reduced states. The following association species were isolated from mixtures I and II by dissolving in water: [Pt _n ^II PMo₁₂O₄₀] (I _s) (n = 0.3?0.8) and [Pt _n ⁰ PMo ₁₂ ^red O₄₀] (II _s) (n ≈ 1). Under exposure to air, the solutions of I _s were stable (pH ～2), whereas Pt^met was released from II _s. After the drying of I _s, the solid association species (Pt _n ^II Cl_mO_xH_y). (H₃PMo₁₂O₄₀), where n = 0.3?0.8, m = 0.2?1, and x = 3?0, (I _solid) were obtained. The I _solid/SiO₂ supported samples were prepared by impregnating SiO₂ with a solution of I _s and drying at 100°C. Platinum metal particles of size ～20 Å and a mixed-valence association species of platinum with the HPA were observed after the reduction of I _solid/SiO₂ with hydrogen at 100–250°C. These samples were active in the gas-phase oxidation of benzene to phenol at 180°C with the use of an O₂-H₂-N₂ mixture.     

Minimal dissipation hybrid bicompact schemes for hyperbolic equations

New monotonicity-preserving hybrid schemes are proposed for multidimensional hyperbolic equations. They are convex combinations of high-order accurate central bicompact schemes and upwind schemes of first-order accuracy in time and space. The weighting coefficients in these combinations depend on the local difference between the solutions produced by the high- and low-order accurate schemes at the current space-time point. The bicompact schemes are third-order accurate in time, while having the fourth order of accuracy and the first difference order in space. At every time level, they can be solved by marching in each spatial variable without using spatial splitting. The upwind schemes have minimal dissipation among all monotone schemes constructed on a minimum space-time stencil. The hybrid schemes constructed has been successfully tested as applied to a number of two-dimensional gas dynamics benchmark problems.     

Cathodic materials for intermediate-temperature solid oxide fuel cells based on praseodymium nickelates-cobaltites

A unique combination of methods (TPD of O₂, thermogravimetry, isotopic heteroexchange of oxygen in different modes) was used to carry out detailed studies of oxygen mobility and reactivity in mixed praseodymium nickelates-cobaltites (PrNi_{1 ? x} Co _x O_{3 + δ}) and their composites with doped cerium dioxide (Ce_0.9Y_0.1O_{2 ? δ}) as promising cathodic materials stable towards the effect of CO₂ in the intermediate-temperature region. It is shown that in the case of composites of PrNi_{1 ? x} Co _x O_3+δ-Ce_0.9Y_0.1O_{2 ? δ} synthesized using the Pechini method and ultrasonic treatment, stabilization of the disordered cubic perovskite phase due to redistribution of cations between the phases provides high oxygen mobility. Preliminary results on tests of cathodic materials of this type supported on planar NiO/YSZ anodes (H.C. Starck) with a thin layer of YSZ electrolyte and a buffer Ce_0.9Y_0.1O_{2 ? δ} layer showed that power density of up to 0.4 W/cm² was reached in the region of medium (600–700°C) temperatures, which was close to typical values for fuel cells of this type with cathodes based on strontium-doped perovskites and their composites with electrolytes.