Moscow University Physics Bulletin最新文献

Abstract

In this study, to create a carbon dots-based multimodal nanosensor of metal ions, a new approach to solving the inverse problem of fluorescence spectroscopy is presented. The problem is to simultaneously determine the concentration of heavy metal ions Cr({}^{3+}), Ni({}^{2+}), Cu({}^{2+}), and nitrate anions NO({}^{-}_{3}) in water by carbon dots (CDs) fluorescence spectra. A method of spectral data augmentation is proposed. It is based on the generation of excitation-emission matrices of CDs fluorescence from the noise vector using variational autoencoders and further determination of ion concentration corresponding to the generated matrices with convolutional neural networks. Implementing the proposed approach allowed reducing the mean absolute error in determining the concentration of ions by 60(%) for Cr({}^{3+}), by 41(%) for Ni({}^{2+}), by 62(%) for Cu({}^{2+}), and by 48(%) for NO({}^{-}_{3}).

The reaction ({}^{12}textrm{C}(t,p)^{14}textrm{C}) is used to study the neutron periphery of the ({}^{14}textrm{C}(g.s.)) nucleus. The experimental differential cross section of the reaction is compared with the theoretical one, taking into account the mechanisms of dineutron stripping and successive neutron transfer. The good agreement between the calculated cross section and the experimental one made it possible to determine the dineutron periphery configuration in the ground state of the ({}^{14})C nucleus. It has been shown that the dineutron periphery in ({}^{14})C represents a ‘‘skin’’ on the surface of the nucleus. The one-neutron cigar-shaped configuration, associated with the mechanism of independent neutron transfer, is quite extended.

In this paper, we propose a method of taking charge symmetry breaking (CSB) in hypernuclei and neutron stars into account within the framework of the Hartree–Fock approach with Skyrme interaction. The parameters of the contribution of (Lambda N)-Skyrme force leading to CSB are derived from the corresponding parameters of the hyperon-nucleon interaction in the meson exchange models. Based on the obtained parameters, the effect of charge symmetry breaking on the hyperon binding energy in carbon hypernuclei is analyzed. The effect of charge symmetry breaking on the characteristics of neutron stars, such as their maximum mass and radii, is considered for the first time.

Through numerical modelling techniques, data were obtained on how underwater slopes influence the dynamics of a thermal bar and the related circulations during the water body’s autumn cooling. Different geometries of the bottom topography were analyzed, aligning with configurations such as ‘‘gentle slope,’’ ‘‘stepped profile,’’ ‘‘trench,’’ and ‘‘steep slope.’’ It was determined that in the autumn, the flow structure, the formation timeframes, and the thermal bar propagation speed are significantly influenced by the morphological features of the lake bottom.

In the present work, Pro-Gly glyproline and its biologically active complexes with heparin and with the antithrombin-heparin protein complex have been studied using molecular modelling methods. This molecule is used as a drug and exhibits antithrombotic, anticoagulant immunomodulatory, antiulcer, and antidiabetic effects. The conformational profiles of the dipeptide were studied within the molecular mechanics framework, the geometry and energy of intra- and interresidual interactions were estimated for the most stable states of the investigated dipeptide. A comparative analysis of the extended and folded structures of this molecule optimized by the DFT/B3LYP/6-31 (+) G(d,p) method was carried out, the frontier molecular orbitals were calculated, the surface of the molecular electrostatic potential was studied, the effective charges on the atoms were determined, and the dipole moment and polarizability values were calculated. Molecular docking revealed that the folded structure of Pro-Gly glyproline showed a higher affinity value for both heparin and the antithrombin-heparin protein complex. A model of the pharmacophore of the Pro-Gly molecule for its interaction with a specific receptor was proposed. The obtained data form the basis for the development of effective analogs of glyprolines in the complex with heparin, which are more specific concerning their putative target—antithrombin.

In the study, the Cauchy problem for a singularly perturbed first-order ordinary differential equation is considered, with, generally speaking, a nonlinear right-hand side that depends not only on the desired function but also on this same function taken with a time delay. The problem under consideration is singularly perturbed due to the presence of a small parameter in front of the time derivative. For such problems, solutions that possess a large gradient in the vicinity of the initial time moment and in the vicinity of the moment equal to the delay time are typical. The aim of the work is to construct an asymptotic approximation and to prove the existence of a smooth solution to the problem.

Using the methods of the catastrophe theory, which take into account the symmetry of the thermodynamic system, phenomenological models of phase transitions in proper and pseudoproper ferroelastics have been constructed for interacting order parameters, one of which is fully symmetric, invariant with respect to all symmetry transformations of the crystal. A classification of models based on the number of control parameters, which depend on external thermodynamic conditions, has been carried out. A phase diagram of one of the models has been constructed, and the theoretical temperature dependence of the heat capacity has been calculated. The comparison of theoretical and experimental data showed satisfactory qualitative agreement.

Within the framework of one-loop quantum gravity, we consider the vacuum polarization effect of the minimally-coupled massive scalar field near the infinitely-thin straight cosmic string. It is shown that the massive-field relative contribution to the renormalized vacuum mean of the energy density becomes negligible at a distance of several Compton lengths.

The possibility of separating quark and gluon jets in heavy ion collisions, both in the presence of the jet quenching effect and in its absence, has been investigated. Using machine learning methods, a technique has been developed to recover the fraction of quark and gluon jets, using variables characterizing the shape, multiplicity, and charge of the jet. The potential of using these variables to study the characteristics of the dense medium that arises during high-energy ion collisions has been demonstrated.

The features of propagation in free space of light beams with a dislocation structure of the wavefront are considered. The stability to the influence of diffraction of small-scale dislocation systems providing spatial superresolution is analyzed. Based on a comparison of the characteristics of various dislocation formations, a conclusion is made about the greatest structural stability of systems with special type screw dislocations. Such dislocations can be obtained by azimuthal rotation of edge dislocations characterized by a sharp phase jump of light oscillations along the singular line. The obtained results will find application in optimizing the characteristics of optical devices with ultrahigh spatial resolution, as well as in developing software for the operation of spatial light modulators forming beams with a specified amplitude-phase profile.