On the possibility of the realization of combustion and detonation waves in a system of nuclear isomers

The possible regimes of the propagation of a self-sustained fluorescence wave of long-lived nuclear isomers, which is initiated by transitions to the nearest short-lived level owing to the absorption of X-ray photons and inelastic collisions of electrons in a plasma, have been analyzed. It has been found that, when the energy exchange between the nuclear subsystem and plasma is due to absorption and emission of photons, the fluorescence wave can propagate in the fast (with a near-light velocity) deflagration regime induced by the radiative heat transfer mechanism. When the energy exchange between the subsystems is nonradiative, the (slower) detonation regime becomes significant. The implementation of each of the two regimes requires certain conditions on the characteristics of the system.     

Preservation and control of the proton and deuteron polarizations in the proposed electron-ion collider at Jefferson Lab

We propose a scheme of preserving the proton and deuteron beam polarizations during acceleration and storage in the proposed electron-ion collider at Jefferson Lab. This scheme allows one to provide both the longitudinal and transverse polarization orientations of the proton and deuteron beams at the interaction points of the figure-8 ion collider ring. We discuss questions of matching the polarization direction at all stages of the beam transport including the pre-booster, large booster and ion collider ring.     

Structural and phase transformations in C/Si multilayers during annealing

The structural evolution of a C/Si periodical multilayers is studied by small-angle X-ray diffraction and cross-section transmission electron microscopy. Mixed zones 0.6–0.65 nm thick with different densities are detected at the C/Si and Si/C interfaces in the initial state. The effect of annealing on the thickness, the density, and the phase composition of the layers and the mixed zones is investigated in the temperature range 300–1050°C. Two stages of changing the multilayer composition period upon heating are found. The period increases as the temperature increases up to 700°C and then decreases. The fracture of the composition begins in the silicon layers, where pores and cubic 3C-SiC nanocrystals form at 900°C. The fracture of the layered structure of the composition is completed at T > 1000°C.     

Sliced linear zone plates for hard X-ray radiation

Linear zone plates for hard (E > 10 keV) X rays are considered. The technology of the plates includes cutting magnetron-sputtered W₅Si₃/Si multilayer coatings. The results of numerical computation suggest that this pair of materials provides a high efficiency in the first and second diffraction orders. It is found experimentally that good multilayer structures consisting of several hundreds of layers can be synthesized on silicon and glass substrates. It is shown that they can be cut by ion etching the multilayer coating through a mask.     

Elucidating the Role of Oxygen Species in Oxidative Coupling of Methane over Supported MnOx−Na2WO4-containing Catalysts

The present study of oxidative coupling of methane (OCM) over MnO_x−Na₂WO₄/support catalysts demonstrated that the selectivity to C₂H₆ and C₂H₄ (C₂-hydrocarbons) is affected by the kind of support, co-fed water, and the kind of oxidant (O₂ vs. N₂O). In addition to previous studies with MnO_x−Na₂WO₄/SiO₂, an enhancing water effect was obtained using catalysts based on TiO₂- or ZrO₂-containing supports. However, a negative effect on methane conversion was established for SiO₂−Al₂O₃-supported catalysts. Temporal analysis of products with isotopic tracers suggests that the ability of MnO_x−Na₂WO₄ to generate diatomic adsorbed oxygen species depends on the kind of support and is the key property for the water effect. The strength of the water effect on the activity decreases with an increase in the surface area of working catalysts. The kind of support also affects products selectivity due to its influence on the mobility/releasability of lattice oxygen in supported MnO_x−Na₂WO₄. Among the prepared catalysts, MnO_x−Na₂WO₄/TiO₂ was found to be promising for H₂O-assisted OCM. The use of N₂O instead of O₂ further increases the selectivity to C₂-hydrocarbons to 84 % at 6.8 % CH₄ conversion due to the formation of predominantly monoatomic oxygen species from N₂O that selectively convert CH₄ into C₂H₆.     

Structure and optical properties of multilayer X-ray mirrors for long wave part (3.1–4.4 nm) of “water window”

Structure and optical properties (at λ - 0.154 nm and λ - 3.16 nm) of W Ti, W TiN, W Sc, and Cr Sc multilayer X-ray mirrors for long wave part of “water window”' wavelength range (3.1–4.4 nm) were studied by methods of X-ray diffractometry and cross-sectional electron microscopy. The reflectivities at λ - 0.154 nm are increased going from W TiN, Cr Sc, W Ti to W Sc multilayers. Cr Sc mirrors have highest reflectivity and resolution at λ - 3.16 nm. Influence of the ambient atmosphere on optical properties of multilayer mirrors is shown.     

Controlling Metal-Oxide Reducibility for Efficient C−H Bond Activation in Hydrocarbons

Knowing the structure of catalytically active species/phases and providing methods for their purposeful generation are two prerequisites for the design of catalysts with desired performance. Herein, we introduce a simple method for precise preparation of supported/bulk catalysts. It utilizes the ability of metal oxides to dissolve and to simultaneously precipitate during their treatment in an aqueous ammonia solution. Applying this method for a conventional VO_x−Al₂O₃ catalyst, the concentration of coordinatively unsaturated Al sites was tuned simply by changing the pH value of the solution. These sites affect the strength of V−O−Al bonds of isolated VO_x species and thus the reducibility of the latter. This method is also applicable for controlling the reducibility of bulk catalysts as demonstrated for a CeO₂−ZrO₂−Al₂O₃ system. The application potential of the developed catalysts was confirmed in the oxidative dehydrogenation of ethylbenzene to styrene with CO₂ and in the non-oxidative propane dehydrogenation to propene. Our approach is extendable to the preparation of any metal oxide catalysts dissolvable in an ammonia solution.