197Au Mössbauer study of a gold-doped YBa2Cu3O7-σ high-temperature superconductor

A high temperature superconductor with the composition YBa₂Cu_2.9Au_0.1O_7– was studied by Mössbauer spectroscopy with the 77 keV gamma rays of¹⁹⁷Au, by X-ray diffraction, and by magnetization measurements. The main component in the Mössbauer spectrum, a quadrupole doublet with an isomer shift of +3.29 mm/s with respect to metallic gold and a quadrupole splitting of 3.61 mm/s, can be attributed to Au³⁺ in a square planar oxygen coordination, as is expected for gold replacing Cu(1). A further, weak doublet becomes dominant upon reduction of the specimen, and has an isomer shift of +3.46 mm/s and a quadrupole splitting of 7.12 mm/s. This component may be Au⁺ or Au³⁺ in an unusual coordination. Only a small fraction of the gold was found to be metallic in both the oxidized and the reduced state.     

Vibrational excitation effects on silane reactivity in its reaction with bromine atoms

A rate increase of SiH₃Br formation in SiH₄ photobromination under irradiation by a cw CO₂ laser is reported. At low SiH₄ pressures (1–2 Pa) the radiation effect is shown to be isotope-selective.

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SiH₃Br CO₂ SiH₄. , SiH₄ (1–2 ) .

     

Effect of vibrational excitation on the reactivity of methyl fluoride with bromine atoms

The influence of non-equilibrium vibrational excitation of CH₃F molecules on the rate of their reaction with bromine atoms has been investigated. A three-fold increace in the reaction rate has been registered at CH₃F and Br₂ pressures of 0.07 Torr and at 100°C. The increase is shown not to be associated with equilibrium thermal heating.

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CH₃F . CH₃F Br₂ 0,07 100°C. , .

     

Data acquisition system for the Baikal-GVD neutrino telescope

The objective of the Baikal-GVD project is the construction of a km³-scale neutrino telescope in Lake Baikal. The Gigaton Volume Detector consists of a large three-dimensional array of photo-multiplier tubes. The first GVD-cluster has been deployed and commissioned in April 2015. The data acquisition system (DAQ) of the detector takes care of the digitization of the photo-multiplier tube signals, data transmission, filtering and storage. The design and the implementation of the data acquisition system are described.     

Preface

In situ observations have shown that underground storage of hydrogen behaves like a natural chemical reactor and generates methane. The mechanism of this generation is the metabolic activity of methanogenic bacteria which consume hydrogen and carbon dioxide and transform them into methane and water. The coupled mathematical model of the reactive transport and population dynamics in a storage is suggested in this paper which also takes into account the fact that the population growth rate depends on the structure of the bacterium colony. The suggested system of equations is reduced to the Turing reaction-diffusion model which proves the appearance of non-attenuating self-oscillations in time which are uniform in space. These solutions are unstable and, once perturbed, generate regular spatial stationary waves which correspond to the alternations of zones which are rich in CH₄ or CO₂. This result predicts the effect of a natural in situ separation of gases, which was observed in practice. If the diffusivity of bacteria is neglected with respect to the effective diffusivity of the injected gas, then only large-scale spatial waves arise. A low but non-zero bacterium diffusivity causes the appearance of additional small-scale linear oscillations whose period is the intrinsic parameter of the process and is proportional to the bacteria–gas diffusivity ratio. The analysis is completed with numerical simulations of 2D problems and analytical solutions of 1D problems obtained using the technique of two-scale asymptotic expansion. The estimations for the parameters of the model were obtained.     

Underground Storage of Hydrogen: In Situ Self-Organisation and Methane Generation

In situ observations have shown that underground storage of hydrogen behaves like a natural chemical reactor and generates methane. The mechanism of this generation is the metabolic activity of methanogenic bacteria which consume hydrogen and carbon dioxide and transform them into methane and water. The coupled mathematical model of the reactive transport and population dynamics in a storage is suggested in this paper which also takes into account the fact that the population growth rate depends on the structure of the bacterium colony. The suggested system of equations is reduced to the Turing reaction-diffusion model which proves the appearance of non-attenuating self-oscillations in time which are uniform in space. These solutions are unstable and, once perturbed, generate regular spatial stationary waves which correspond to the alternations of zones which are rich in CH₄ or CO₂. This result predicts the effect of a natural in situ separation of gases, which was observed in practice. If the diffusivity of bacteria is neglected with respect to the effective diffusivity of the injected gas, then only large-scale spatial waves arise. A low but non-zero bacterium diffusivity causes the appearance of additional small-scale linear oscillations whose period is the intrinsic parameter of the process and is proportional to the bacteria–gas diffusivity ratio. The analysis is completed with numerical simulations of 2D problems and analytical solutions of 1D problems obtained using the technique of two-scale asymptotic expansion. The estimations for the parameters of the model were obtained.     

Modeling of mixing during injection of an agent into oil reservoirs with development of fractal structures

A mathematical model of phase mixing in a subsurface reservoir during gas injection into an oil deposit with the objective of reducing the oil viscosity or modifying the phase state is investigated. The gas intrusion into the reservoir causes the development of fractal fields. To determine the mixing timet _*, it is proposed to divide the process into three stages, those of convective and diffusive mixing and the phase transition stage.The characteristic diffusive mixing time is orders of magnitude greater than the characteristic times of the other stages. This makes it possible to consider the stages as independent and use a successive alternation scheme. The convective mixing stage was described by the models of diffusion-limited aggregation or of invasion percolation with delayed action. For the stage of diffusive mixing, the problem of diffusion from a fractal was solved without account for phase transition. Relations for the characteristic times of total and partial mixing of the oil and gas were derived. It is shown that in some cases these times are of the order of several decades and are comparable with the oil field development duration.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 5, pp. 187–189, September–October, 1995.     

Impact of Pore Clogging by Bacteria on Underground Hydrogen Storage

The idea of underground storage of hydrogen exists today in several forms. One of the most promising methods is the option of underground methanation, which consists of injecting H₂ and CO₂ into an underground porous reservoir (aquifer) and converting them into methane by means of methanogenic bacteria that initiate the methanation reaction. However, due to their activities, the high accumulation of bacteria in the pore walls causes pore-clogging (microbial-induced clogging); one of the main problems that can become an obstacle to the implementation of this idea. In this paper, we develop a conceptual model of bio-clogging, which consists of several stages of attachment to pore walls, detachment from the walls and pore plugging by the biomass growth. This model was built into the numerical model of multicomponent two-phase flow. The effect of bio-clogging on gas movement in the storage was analyzed numerically. It has been found that bio-clogging reduces vertical rise of hydrogen and results in more uniform radial gas penetration into the reservoir.