Moscow University Physics Bulletin最新文献

A novel method of microprobing scattering media for studying their three-dimensional structure using femtosecond light pulses, propagated to the object and returned back via a bundle of single-mode fibers, is considered. The second harmonic, generated by frequency summation of the backscattered and reference signals, is detected in the process. A number of algorithms for reconstructing the spatial distribution of the attenuation coefficient and their combination have been investigated through computer modeling.

The paper presents the fundamental principles of photometric investigation of exoplanet candidates through the analysis of archival wide-field images obtained with the robotic telescopes of the MASTER Global Network of Lomonosov Moscow State University. An algorithm has been developed and applied for studying transit exoplanet candidates that does not interfere with the primary objectives of the MASTER network—the detection of optical counterparts of high-energy astrophysical sources and the study of processes occurring in them on various time scales. A number of candidates in the field of the microquasar V404 Cyg have been examined. For the candidate TOI-3570.01, a light curve during the transit of the presumed exoplanet has been obtained, consistent with the calculated ephemerides.

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.