Relation between molecular electronic structure and nuclear spin-induced circular dichroism

The recently theoretically described nuclear spin-induced circular dichroism (NSCD) is a promising method for the optical detection of nuclear magnetization. NSCD involves both optical excitations of the molecule and hyperfine interactions and, thus, it offers a means to realize a spectroscopy with spatially localized, high-resolution information. To survey the factors relating the molecular and electronic structure to the NSCD signal, we theoretically investigate NSCD of twenty structures of the four most common nucleic acid bases (adenine, guanine, thymine, cytosine). The NSCD signal correlates with the spatial distribution of the excited states and couplings between them, reflecting changes in molecular structure and conformation. This constitutes a marked difference to the nuclear magnetic resonance (NMR) chemical shift, which only reflects the local molecular structure in the ground electronic state. The calculated NSCD spectra are rationalized by means of changes in the electronic density and by a sum-over-states approach, which allows to identify the contributions of the individual excited states. Two separate contributions to NSCD are identified and their physical origins and relative magnitudes are discussed. The results underline NSCD spectroscopy as a plausible tool with a power for the identification of not only different molecules, but their specific structures as well.Peer reviewe

Investigations and Non-destructive Testing in New Building Design

Mechanical rebar couplers are preferable in the advanced building construction and structural design of antiseismic elements. The paper presents destructive inspection techniques used to investigate stress fields (tensile and compressive) and deformation curves for mechanical rebar splicing. The properties of mechanical rebar splicing are investigated by the non-destructive testing digital radiography. The behavior of real connections (column-to-column, beam-to-column) is studied under static and dynamic loads. Investigation results allow the elaboration of recommendations on their application in the universal prefabricated antiseismic structural system developed at Tomsk State University of Architecture and Building, Tomsk, Russia

Shock-induced melting and crystallization in titanium irradiated by ultrashort laser pulse

Modification of titanium microstructure after propagation of a melting shock wave (SW) generated by a femtosecond laser pulse is investigated experimentally and analyzed using hydrodynamic and atomistic simulations. Scanning and transmission electron microscopy with analysis of microdiffraction is used to determine the microstructure of subsurface layers of pure titanium sample before and after modification. We found that two layers of modified titanium are formed beneath the surface. A top surface polycrystalline layer of nanoscale grains is formed from a shock-molten layer via rapid crystallization. In a deeper subsurface layer, where the shock-induced melting becomes impossible due attenuation of SW, recrystallization of plastically deformed titanium leads to grain size changes in comparison with intact titanium. Molecular dynamics simulation of single-crystal titanium reveals that the SW front continues to melt/liquefy even after its temperature drops below the melting curve $T_m(P)$. The enormous shear stress generated in a narrow SW front leads to collapse/amorphization of the crystal lattice and formation of a supercooled metastable melt. Such melt crystallizes in an unloading tail of SW until its temperature becomes higher than $T_m(P)$ due to a rapid pressure drop. Later, crystallization of the subsurface molten layer will continue after the heat leaves it. After the shear stress drops below $\sim 12$GPa within the SW front, such the cold mechanical melting ceases giving place to the shock-induced plastic deformations. The depth of modification is limited by SW attenuation to the Hugoniot elastic limit, and can reach several micrometers. The obtained results reveal the basic physical mechanisms of surface hardening of metals by ultrashort laser pulses.Comment: 15 pages, 13 figures. The work was reported at the 38 International Conference ELBRUS-2023 on March 1, 2023, and submitted to Physical Review Applie

The problems of zeolites detection and their influence on development of the productive reservoirs in the Messoyakha group of fields

It is found out that zeolites are formed in alkaline environment at diagenesis or katagenesis and reduce permeability and porosity of reservoir rocks. It is shown that zeolite content in reservoir rocks is directly related to the porosity value and can reach 13 % of the total volume of rock. It is quite difficult to detect zones of zeolitization by means of well logs. Therefore logs should be corrected for the possible content of zeolities on the base of core analysis data which provide detection of the intervals with zeolitization. The authors have determined that the process of zeolitization in Messoyakha group of fields is related to the specific stratigraphic intervals and namely with Suhodudinskaya Formation of Lower Cretaceous age. On a regional scale the zeolitized rocks occur in regional fault zones and zones with enclosing rocks undergone strong metasomatic changes. Based on the core and log data the existing depositional environment concept of producing reservoirs of Messoyakha group of fields has been revised and the most favorable conditions and periods of zeolites formation have been determined. In addition, based on the experience of development of fields with high zeolites content, the best method of near wellbore treatment, which has a direct impact on oil recovery enhance, was offered

Improvement of the well cementing technology, increasing the reliability of the annule isolation and preserving the permeability of the reservoir

The article presents measures to improve the quality of cementing the production string of high-performance wells. The relevance of the proposed technological solutions is substantiated. The results of experimental studies of the installation simulating the processes occurring during the thickening of the cement slurry under the action of gravitational forces are presented. An algorithm for creating overpressure on the wellhead during fastening of the production string is proposed. The compositions of process fluids are described, which increase the reliability of the annular space isolation and preserve the permeability of the reservoir, and provide the main data on the results of their laboratory studies. For cementing the annular space of the production string, the composition of the expanding cement slurry has been developed and the procedure for its preparation has been established. The proposed solution has low water separation and high sedimentation resistance; has adjustable rheological parameters. Cement stone is characterized by low gas permeability and high strength properties

Biological and Oxidative Degradation of Ultrathin-Fibrous Nonwovens Based on Poly(lactic Acid)/Poly(3-Hydroxybutyrate) Blends

Developing biodegradable materials based on polymer blends with a programmable self-destruction period in the environmental conditions of living systems is a promising direction in polymer chemistry. In this work, novel non-woven fibrous materials obtained by electrospinning based on the blends of poly(lactic acid) (PLA) and poly(3-hydroxybutyrate) (PHB) were developed. The kinetics of biodegradation was studied in the aquatic environment of the inoculum of soil microorganisms. Oxidative degradation was studied under the ozone gaseous medium. The changes in chemical composition and structure of the materials were studied by optical microscopy, DSC, TGA, and FTIR-spectroscopy. The disappearance of the structural bands of PHB in the IR-spectra of the blends and a significant decrease in the enthalpy of melting after 90 days of exposure in the inoculum indicated the biodegradation of PHB while PLA remained stable. It was shown that the rate of ozonation was higher for PLA and the blends with a high content of PLA. The lower density of the amorphous regions of the blends determined an increased rate of their oxidation by ozone compared to homopolymers. The optimal composition in terms of degradation kinetics is a fibrous material based on the blend of 30PLA/70PHB that can be used as an effective ecosorbent, for biopackaging, and as a highly porous covering material for agricultural purposes