Kazan Federal University

About: Kazan Federal University is a education organization based out in Kazan’, Russia. It is known for research contribution in the topics: Population & Chemistry. The organization has 9868 authors who have published 14390 publications receiving 135726 citations. The organization is also known as: Kazan (Volga region) Federal University & Kazan State University.

On the spreading layer emission in luminous accreting neutron stars

Abstract: Emission of the neutron star surface potentially contains information about its size and thus of vital importance for high energy astrophysics. In spite of the wealth of data on the emission of luminous accreting neutron stars, the emission of their surfaces is hard to disentangle from their time averaged spectra. A recent X-ray transient source XTE J1701-462 has provided a unique dataset covering the largest ever observed luminosity range for a single source. In this paper, we extract the spectrum of the boundary layer between the inner part of the accretion disc and the neutron star surface with the help of maximally spectral model-independent method. We show compelling evidences that the energy spectrum of the boundary layer stays virtually the same over factor of 20 variations of the source luminosity. It is rather wide and cannot be described by a single temperature blackbody spectrum, probably because of the inhomogeneity of the boundary layer and a spread in the colour temperature. The observed maximum colour temperature of the boundary/spreading layer emission of kT~2.4-2.6 keV is very close to the maximum observed colour temperature in the photospheric radius expansion X-ray bursts, which is set by the limiting Eddington flux at the neutron star surface. Observed stability of the boundary layer spectrum and its maximum colour temperature strongly supports theoretical models of the boundary/spreading layers on surfaces of luminous accreting neutron stars, which assume the presence of a region emitting at the local Eddington limit. Variations in the luminosity in that case lead to changes in the size of this region, but affect less the spectral shape. Elaboration of this model will provide solid theoretical grounds for measurements of the neutron star sizes using the emission of the boundary/spreading layers of luminous accreting neutron stars.

The Interplay of manganese and nitrate in hydroxyapatite nanoparticles as revealed by pulsed EPR and DFT

Abstract: The interplay of oppositely charged substitutions in the structure of hydroxyapatite (HAp) nanopowders is investigated on the atomic level by pulsed electron paramagnetic resonance (EPR) technique and ab initio density functional theory calculations. Benefits of EPR to determine Mn2+ ions in nano-HAp samples are demonstrated. A simple approach based on the measurements of electron spin relaxation times allowed observing the strong influence of fast-relaxing Mn2+ ions on the relaxation characteristics of the nitrate ions (NO3−/NO32−) incorporated in trace amounts. Based on the results of ab initio calculations, we show the propensity of Mn2+ and NO3−/NO32− to associate within the HAp crystal lattice. This could have a direct impact on the functional properties of the material especially to resorption and ion exchange. Furthermore, such an effect can increase a propensity of undesired impurities to incorporate into the doped nanocrystals.

Biochar-carrying hydrocarbon decomposers promote degradation during theearly stage of bioremediation

Abstract: . Oil pollution is one of the most serious current environmental problems. In this study, four strategies of bioremediation of oil-polluted soil were tested in the laboratory over a period of 84 days: (A) aeration and moistening; (B) amendment with 1 % biochar (w ⁄ w) in combination with A; amendment with 1 % biochar with immobilized Pseudomonas aeruginosa (C) or Acinetobacter radioresistens (D) in combination with A. All strategies used resulted in a decrease of the hydrocarbon content, while biochar addition (B, C, D strategies) led to acceleration of decomposition in the beginning. Microbial biomass and respiration rate increased significantly at the start of bioremediation. It was demonstrated that moistening and aeration were the main factors influencing microbial biomass, while implementation of biochar and introduction of microbes were the main factors influencing microbial respiration. All four remediation strategies altered bacterial community structure and phytotoxicity. The Illumina MiSeq method revealed 391 unique operational taxonomic units (OTUs) belonging to 40 bacterial phyla and a domination of Proteobacteria in all investigated soil samples. The lowest alpha diversity was observed in the samples with introduced bacteria on the first day of remediation. Metric multidimensional scaling demonstrated that in the beginning and at the end, microbial community structures were more similar than those on the 28th day of remediation. Strategies A and B decreased phytotoxicity of remediated soil between 2.5 and 3.1 times as compared with untreated soil. C and D strategies led to additional decrease of phytotoxicity between 2.1 and 3.2 times.

Divergent mineralization of hydrophilic and hydrophobic organic substrates and their priming effect in soils depending on their preferential utilization by bacteria and fungi

Abstract: Hydrophilic and hydrophobic organic compounds extracted from 13C-labelled maize residues were incubated with soils to evaluate their mineralization and priming effect (PE) caused by their utilization by microbial groups. Two soils with contrasting soil properties were collected from well-drained upland and water-logged paddy. Mineralization of the 13C-labelled fractions and their PE were quantified by monitoring the CO2 efflux and 13C enrichment during a 40-day incubation. The composition of main microbial groups (bacteria and fungi) involved in the utilization of 13C-labelled fractions was determined based on phospholipid fatty acids (PLFAs) analysis. At the initial stage (6–24 h), hydrophilic fraction had faster mineralization rate (3.6–70 times) and induced 1.5–10 times stronger PE (positive in upland soil and negative in paddy soil) than those of hydrophobic fraction. The 13C-PLFAs data showed that the incorporation of hydrophilic fraction into bacteria was 11.4–16.4 times greater than that into fungi, whereas the hydrophobic fraction incorporated into fungi was 1.0–1.5 times larger than that into bacteria at day 2. This indicated greater contributions of r-strategists (fast-growing bacteria) for the uptake of hydrophilic fraction versus K-strategists (slow-growing fungi) for hydrophobic fraction. Compared with K-strategists, the r-strategists possessed a much faster metabolism and thus triggered stronger apparent PE by accelerating microbial biomass turnover, resulting in higher mineralization and stronger PE for the hydrophilic than hydrophobic fraction. The slower and less mineralization of both fractions in paddy than in upland soils is due to the suppression of microbial activity and substrate utilization under flooding. At the end of 40-day incubation, the cumulative mineralization of hydrophilic and hydrophobic fractions was similar. Consequnently, microbial mechanisms underlying the utilization of organic compounds with contrasting solubility (hydrophilic or hydrophobic) are crucial for evaluating the stabilization and destabilization (e.g., priming) processes of soil organic matter.