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.     

Joint redundancy and maintenance optimization for multistate series–parallel systems

This paper formulates the joint redundancy and replacement schedule optimization problem generalized to multistate system, where the system and its components have a range of performance levels. Multistate system reliability is defined as the ability to maintain a specified performance level. The system elements are chosen from a list of available products on the market and the number of such elements is determined for each system component. Each element is characterized by its capacity, reliability and cost. The reliability of a system element is characterized by its lifetime distribution with the hazard rate, which increases with time. It is specified as the expected number of failures during different time intervals. The optimal system structure and the number of element replacements during the study period are defined as those which provide the desired level of system reliability with minimal sum of costs of capital investments, maintenance and unsupplied demand caused by failures. A universal generating function technique is applied to evaluate the multistate system reliability. A genetic algorithm is used as an optimization technique. Examples of determination of the optimal system structure and replacement schedule are provided.     

Insights into Mechanisms of Damage Recognition and Catalysis by APE1-like Enzymes

Apurinic/apyrimidinic (AP) endonucleases are the key DNA repair enzymes in the base excision repair (BER) pathway, and are responsible for hydrolyzing phosphodiester bonds on the 5′ side of an AP site. The enzymes can recognize not only AP sites but also some types of damaged bases, such as 1,N⁶-ethenoadenosine, α-adenosine, and 5,6-dihydrouridine. Here, to elucidate the mechanism underlying such a broad substrate specificity as that of AP endonucleases, we performed a computational study of four homologous APE1-like endonucleases: insect (Drosophila melanogaster) Rrp1, amphibian (Xenopus laevis) APE1 (xAPE1), fish (Danio rerio) APE1 (zAPE1), and human APE1 (hAPE1). The contact between the amino acid residues of the active site of each homologous APE1-like enzyme and the set of damaged DNA substrates was analyzed. A comparison of molecular dynamic simulation data with the known catalytic efficiency of these enzymes allowed us to gain a deep insight into the differences in the efficiency of the cleavage of various damaged nucleotides. The obtained data support that the amino acid residues within the “damage recognition” loop containing residues Asn222–Ala230 significantly affect the catalytic-complex formation. Moreover, every damaged nucleotide has its unique position and a specific set of interactions with the amino acid residues of the active site.