Moscow University Physics Bulletin最新文献

Using the previously developed alignment method for the Time Projection Chamber (TPC) in the MPD detector, the influence of misalignment on the reconstructed parameters of a charged particle track, such as transverse momentum and rapidity, is studied. The concept of a misalignment unit is introduced for the TPC. By simulating the TPC response to charged particles, distortions in the reconstructed track parameters depending on the magnitude of misalignment are analyzed. The influence of alignment errors on the reconstructed track parameters in the MPD TPC can be neglected. A systematic variation of the measured transverse momentum depending on the track projection width onto the readout plane is observed. This width is determined by the gas conditions and the electric field in the detector chamber. The alignment tools developed for the MPD Time Projection Chamber make it possible to estimate this width from experimental data and apply corrections to the reconstructed track parameters.

In this paper, new approaches to the investigation of gas-dynamic processes in shock tubes using modern methods of visualization and analysis are presented. Studies were conducted on the flow behind a shock wave in a rectangular channel of a shock tube with constant cross-section and in a channel with an obstacle. The experiments include the use of high-speed digital imaging, infrared thermography, particle tracing, allowing high temporal and spatial resolution analysis of the flow evolution in the shock tube. The obtained results showed that the flow in the channel of the shock tube can be used for investigations for 20–25 ms, which significantly exceeds the time ranges previously used. It is possible to carry out experiments, including studies of heat-and-mass transfer associated with the flow around the channel walls, obstacles with initiation of pulsed discharges in the flow. Results of the investigation of the evolution of flow parameters are presented. It is shown that the use of machine learning and computer vision methods, including convolutional neural networks, enables effective processing and analysis of large datasets obtained during high-speed recording.

Within the five-dimensional ADD model of space-time with compactification radius (R), we consider the classical gravitational bremsstrahlung arising from the collision of two ultrarelativistic charges. The collision is governed by the impact parameter (b) and the Lorentz factor (gamma). Using the perturbation theory, the total energy, radiated as a gravitational wave, is calculated in the leading order in (gamma), as well as the spectral-angular and polarization characteristics. The radiation is characterized by concentration within a cone of opening angle of order (1/gamma), with the dominant contribution coming from frequencies of order (gamma^{2}/b). The average number of Kaluza–Klein emission modes is estimated to be of the order of (gamma R/b).

The potential for information transmission via quantum channels with multiphoton entanglement is considered. Protocols for quantum key distribution and direct information transmission are developed, with strict consideration of the sending and receiving times of messages, which helps to counteract a wide range of attacks.

The paper considers a boundary-value problem for a singularly perturbed elliptic system of fast and slow equations, commonly referred to as a system of Tikhonov type. A distinctive feature of the problem is the presence of terms containing the squared gradient of the unknown function (KPZ nonlinearities). A boundary layer asymptotic expansion of the solution is constructed in the case of Dirichlet boundary conditions, the existence of a solution with the constructed asymptotics is proved, and its Lyapunov asymptotic stability is studied. The proof of the theorems is based on the asymptotic method of differential inequalities developed by N.N. Nefedov.

To develop highly sensitive biosensors based on field-effect transistors with a silicon nanowire channel (FET), single interactions of antibodies with prostate-specific antigen (PSA) on the surface of pure silicon modified with 5 nm gold nanoparticles were studied. A digital immunocomplex registration method using scanning electron microscopy was employed, where 25 nm gold nanoparticles served as antibody visualizing labels. A specialized algorithm was developed to calculate the nanoparticle density on the silicon surface. Various methods of chemical silicon modification using silanes (3-glycidoxypropyltrimethoxysilane (GOPS), 3-mercaptopropyltrimethoxysilane (GOPS-SH), and 3-aminopropyltriethoxysilane (APTES)), bifunctional reagents, and polyethylene glycol were applied to investigate covalent antibody immobilization. It has been shown that chemical modification methods using GOPS are characterized by a lower detection limit for prostate-specific antigen (PSA)—a biomarker of prostate tumors. Biosensor structures based on field-effect transistors with nanowire channels, whose surfaces were modified by two different methods using GOPS, were fabricated, and their pH sensitivity was studied. It has been demonstrated that the modification method using GOPS-SH is characterized by a maximum pH sensitivity of 70 mV/pH and is the most promising for the development of highly sensitive biosensors for biomarker detection.

An analysis of the molecular dynamics method for node placement in the construction of unstructured meshes is presented. A method for its improvement is considered. An energy-based approach to the problem of triangular mesh node placement on a surface is proposed, which is based on the idea of finding the minimum potential energy of a system of charges using the gradient descent method.

The results of the search for ‘‘dark’’ bosons using the iDREAM neutrino detector at the Kalinin NPP are presented. Based on data on the composition of the VVER-1000 reactor core and the fission fractions of the main fissile isotopes, the spectrum of (gamma)-radiation in the core has been calculated. Assuming that dark bosons can be produced in the reactor core via (gamma)-scattering on electrons and subsequently detected by the iDREAM detector in the inverse process, model-independent experimental constraints on the coupling constant of (pseudo)scalar dark bosons with charged leptons of the Standard Model, (g_{X}), have been established.

Using first-principles methods for calculating crystal energy, the atomic mechanism of the transformation between the BCC ((beta)) and HCP ((alpha)) phases of zirconium at low temperature has been investigated. An accurate two-parameter geometric approach has been developed to describe the lattice transformation via the Burgers mechanism. The proposed description method accounts for changes in atomic volume and the shape of the crystal lattice during the transformation. Using the proposed transformation description, potential energy surfaces of zirconium during the BCC–HCP transformation were constructed in the pressure range from 0 to 25 GPa with a step of 5 GPa. The gradient descent method was used to determine the minimum energy paths along the potential energy surfaces. Analysis of the results revealed a strong dependence of the shape of the energy surfaces and the minimum energy path on pressure. As the pressure increases to 25 GPa, the shape of the potential energy surface of zirconium undergoes a critical change, and a structure appears on the surface with an energy 10.5 meV lower than that of the HCP phase. Comparison of the calculated results obtained using the developed two-parameter transformation description method with one-parameter analogues from the literature demonstrated the inconsistency of the latter as a tool for studying atomic mechanisms of phase transitions.

Semiconducting mesoporous films with a large specific surface area are of interest for the development of gaseous medium sensors. In this study, such sensors were fabricated using a material synthesized on bulk substrates via a chemical reaction between gaseous H({}_{2})S and Mo vapour obtained by thermal evaporation. X-ray photoelectron spectroscopy confirmed that the obtained layers consist of MoS({}_{2}). Scanning electron microscopy (SEM) revealed that the films deposited on different substrates are an array of crystallites with thicknesses of a few nanometers and transversal dimensions of several hundred nanometers. The MoS({}_{2}) crystallites are predominantly oriented perpendicular to the substrate surface and are spaced by distances of several tens of nanometers. The surface electrical resistance of the mesoporous MoS({}_{2}) layers was measured as a function of water vapour and ammonia vapour concentrations in the surrounding medium. It was discovered that the electrical resistance of MoS({}_{2}) decreases with increasing relative humidity and ammonia vapour concentration. The current response profile to changes in the concentration of these components in air exhibits an exponential time dependence with two characteristic time constants. For NH({}_{3}) vapour, the characteristic rise times are 0.9 and 17 s, while the fall times are 1.2 and 29 s. In the case of H({}_{2})O vapour, the characteristic rise times are 4 and 45 s, and the fall times are 1.25 and 42 s. The mechanisms underlying the increase in electrical conductivity of MoS({}_{2}) films with increasing humidity and ammonia vapour concentration are discussed.