Magnetohydrodynamic instability in annular linear induction pump: Part I. Experiment and numerical analysis

The present paper describes an experimental and analytical study of the magnetohydrodynamic instability arising in an annular linear induction pump. In the experiment, the instability was investigated in detail using an electromagnetic pump of flow rate 7 m³/min. The experimental results show that the instability occurs when the magnetic Reynolds number is larger than unity and the instability becomes more intensive as the slip increases. The instability is characterized by low frequency pressure pulsation, non-uniform magnetic field along the azimuth, wide-frequency vibration of the pump and pipe, fluctuation of winding voltage and current. The numerical analysis reveals that when the magnetic Reynolds number is larger than unity, an azimuthal non-uniformity of the applied magnetic field or of the sodium inlet velocity brings about sodium vortices and hence a low frequency pressure pulsation occurs. In addition, the non-uniformity causes a decrease of the developed pressure and sometimes a dip on the P–Q curve.     

Fabrication and use of a nanoscale Hall probe for measurements of the magnetic field induced by MFM tips

Extraordinary Hall effect probes with 160?nm × 160?nm working area were fabricated using photo-?and electron-beam lithographic procedures with the aim of direct measurements of MFM cantilever tip magnetic properties. The magnetic field sensitivity of the probes was 35?Ω?T(-1). Magnetic induction of the MFM cantilever tips coated by Co and SmCo films was measured with the probes. It was shown that the resolution of the probes was of the order of 10?nm.     

Spectroscopy of SiSiOx type samples prepared by oxygen implantation and processing under high pressure

The hydrostatic pressure-induced effect on the massive creation of “new” defects in CzSi with oxygen-related defects introduced by implantation of oxygen (at E?200 keV and doses D?1×10¹⁸ cm⁻²) and subsequent processing at up to 1500 K, is investigated in this work. The diamond anvil cell method (DAC) allows to carry out in situ investigations of structure, phase transitions and properties at high pressures (HP). Such a device was used for obtaining experimental absorption spectra of SiSiO_x sample in the DAC at hydrostatic pressure up to 20 GPa.     

Electronic states spectroscopy of Hydroxyapatite ceramics

Photoluminescence, surface photovoltage spectroscopy and high-resolution characterization methods (Atomic Force Microscopy, Scanning Electron Microscopy, X-ray spectroscopy and DC conductivity) are applied to nanostructured Hydroxyapatite (HAp) bioceramics and allowed to study electron (hole) energy states spectra of the HAp and distinguish bulk and surface localized levels. The measured trap spectra show strong sensitivity to preliminary heat treatment of the ceramics. It is assumed that found deep electron (hole) charged states are responsible for high bioactivity of the HAp nanoceramics.     

Open circuit potential shifts of activated carbon in aqueous solutions during chemical and adsorption interactions

Interaction of certain inorganic and organic compounds with activated carbon and the effect of such interaction on open circuit potential of activated carbon were studied. Open circuit potential shifts were observed for an overwhelming majority of the substances and brands of activated carbons investigated. Both negative and positive potential shifts were observed. It was shown that open circuit potential shifts for organic substances depend on degree of coverage of the activated carbon surface. Whereas adsorption of investigated organic compound on activated carbon led to positive potential shifts, desorption of adsorbates from the activated carbon surface led to potential shifts in the opposite direction. Furthermore, time dependencies of open circuit potential shifts were similar for different carbon brands. The magnitude of the shifts depended on the adsorbate, adsorption activity of the adsorbent, and the steric configuration of potential-determinative pores and adsorbate molecules.     

Application of potassium chloride to a Chernobyl-contaminated lake: modelling the dynamics of radiocaesium in an aquatic ecosystem and decontamination of fish

This study tests a whole-lake experiment to reduce the bioaccumulation of radiocaesium (137Cs) in fish in lakes contaminated by the Chernobyl accident. In many lakes in the Chernobyl contaminated areas, radiocaesium activity concentrations in fish are still significantly higher (up to 100 times in some species) than acceptable limits for human consumption. Estimates of the long-term rate of decline of 137Cs in fish in these regions, in the absence of countermeasures, show that radioactivity in fish in some lakes may remain above acceptable consumption limits for a further 50-100 years from the present date. In February 1998 we applied 15 t of potassium chloride to Lake Svyatoe, Kostiukovichy. The addition of potassium chloride fertilizer to the lake resulted in a decrease in activity concentration of 137Cs to approximately 40% of pre-countermeasure values in a number of different fish species. In contrast to Lake Svyatoe, 137Cs activity concentrations in fish from four control lakes showed no systematic decrease over the study period. Simplified models for transfers of 137Cs in lakes successfully 'blind' predicted the changes in 137Cs in water and fish resulting from this major alteration of the potassium concentration of the lake. The experiment represents the first test of a predictive model for the dynamics of radiocaesium in response to a major perturbation in potassium (its major competitor ion) in a whole lake ecosystem.     

Features of low-temperature oxidation of hydrogen in the medium of nitrogen,carbon dioxide,and water vapor at elevated pressures

The article discusses novel research results on combustion features of high-density Н₂/О₂ mixtures (ρ_H2 = 0.70–1.89 mol/dm³, ρ_O2 = 0.32–0.81 mol/dm³) diluted with nitrogen, carbon dioxide, or water vapor (from 46 to 76% mol.) at the uniform heating (1 K/min) of tubular reactor. Based on time dependencies of temperature increment in the reaction mixtures caused by the heat release during oxidation of H₂, it is found that the self-ignition temperature of Н₂/О₂/N₂ and Н₂/О₂/H₂O mixtures is by ≈ 30 K lower than that of the Н₂/О₂/СО₂ mixture. Unlike combustion of H₂ in the N₂ medium, in the CO₂ and H₂O media a chain-thermal explosion is observed at a certain concentration of reagents. The influencing mechanisms of diluents on the H₂ oxidation dynamics, as well as the contribution of homogeneous and heterogeneous reactions in the heat release are revealed. It is established that high heat capacity of H₂/O₂/CO₂ mixture, chemical interaction between its components, and presence of CO₂ molecules adsorbed on the reactor inner surface, are the factors determining the H₂ oxidation dynamics in CO₂ medium. At oxidation of H₂ in the H₂O medium, the process takes place against the background of water evaporation and, as a consequence, is characterized by increased heat capacity and thermal conductivity of the H₂/O₂/H₂O reaction mixture.