Polycrystalline hydroxyapatites Ca(10-x)REE(x)(PO(4))(6)(OH)(2-x)O(x) were synthesized and studied by X-ray powder diffraction, infrared absorption, diffuse-reflectance spectroscopy, and thermogravimetry. The solubility limits x(max) of rare earth elements (REE) in Ca hydroxyapatites decreases with an increasing REE atomic number from x(max) = 2.00 for La, Pr, and Nd to x(max) = 0.20 for Yb at 1100 °C. Refinements of X-ray diffraction patterns by the Rietveld method show that REE atoms substitute for Ca preferentially at the Ca(2) sites of the apatite structure. The substitution decreases the Ca(2)-O(4) atomic distances in the calcium coordination polyhedra and increases the Ca(2)-O(1,2,3) distances. This observation shows that interatomic distances depend not only on radii of the ions involved in the substitution but also on their charges.

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Digital skills are essential for a technologized society. For younger generations, it has become almost necessary to have such skills. This study focuses on a valid and reliable measurement tool to determine the digital skills of university students. The research was carried out with the participation of a total of 463 university students. Exploratory factor analysis and confirmatory factor analysis were conducted to investigate the validity and reliability of the digital skills survey. Consequently, research on the validity and reliability of the digital skills survey in the Russian environment was conducted. 25 items and six factors (access to and management of digital content, digital empathy, use of digital means, digital safety, communication of digital content, creation of digital content) were identified after the analysis. Future research should employ the adapted survey to assess the level of students’ digital skills. In addition, the survey’s validity may be analyzed in the context of other cultures.

Microbiological conversion of biosphere renewable resources to produce useful products, in particular biofuels, is currently one of the pressing problems of biotechnology. To establish a microbiological production of biobutanol at an industrial scale, strains with high-yield solvent production on plant biomass as a cheap substrate are needed. This paper summarizes the main outcomes of the authors’ original research focused on a) obtaining new butanol-producing strains of Clostridium genus, b) testing different sources of non-food raw material as a substrate for fermentation. A comparison of different methods of biomass pretreatment and their efficiency for the accumulation of butanol in the liquid medium is also reported. In particular, the efficiency of butanol production by C. acetobutylicum strains isolated or mutagenized by the authors on a) ground green rapeseed, switchgrass, sweet sorghum, soybean, wheat biomass; b) components of switchgrass after thermobaric hydrolysis and c) paper mill sludge from the pulp as substrates is reported. This paper also highlights the progress made concerning substrate pre-treatment and optimization of cultivation conditions to increase butanol production. Finally, future directions to optimize the different biotechnological steps leading to butanol production are discussed.

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