On the development of Kelvin-Helmholtz instability in the front region of an intense nonlinear acoustic wave in the atmosphere
On the development of Kelvin-Helmholtz instability in the front region of an intense nonlinear acoustic wave in the atmosphere
S. I. Kosyakov$^{1,2}$, S. N. Kulichkov$^{1,2}$, M. Z. Nafisovich$^1$
Currently, a significant effect of the expansion of the front region of intense nonlinear acoustic waves created in the atmosphere by pulsed point sources of various nature has not been fully explained – the recorded width of the front region is several orders of magnitude larger than it follows from theoretical concepts. To explain such a significant effect, a hypothesis has been put forward about the possibility of developing Kelvin-Helmholtz instability inside the front region of the wave with a shear flow caused by a mass velocity gradient in the front region itself. The paper substantiates the proposed hypothesis. For this purpose, direct (without using any semi-empirical models) numerical simulation of the Kelvin-Helmholtz instability inside a physically infinitesimal volume of air in the front region of an intense nonlinear acoustic wave is performed. The homogeneous plane motion of compressed air in a wave is considered. It is shown for the first time that the development of Kelvin-Helmholtz instability at different distances from the source should have geometric similarity due to the fact that the process develops in an ideal environment. It does not matter whether the width of the front area increases as the wave moves away from the source or it increases due to an increase in its energy.
Show AbstractBroadband superluminescent diodes based on quantum wells
Broadband superluminescent diodes based on quantum wells
A. A. Mikheeva$^1$, A. A. Turkin, A. A. Marmalyuk
Today, amplified spontaneous emission (superluminescence) is an important effect both in injection lasers and in superluminescent diodes. In the latter, this phenomenon allows achieving the widest emission spectrum of the device at a sufficiently high output power, which is an undeniable advantage for a wide class of practical applications. Due to the relevance of the problem of creating broadband superluminescent diodes (SLDs), it seems promising to analyze the best way to broaden the spectrum of these devices depending on the design of their active region. To do this, it is necessary to carry out theoretical modeling of optical gain in various designs of SLD active regions, as well as to study the behavior of the spontaneous radiative recombination rate with increasing wavelength in these structures. When constructing the gain spectrum, it is possible to draw a conclusion about which optical transitions in the quantum well make the greatest contribution to the gain at a certain injection current. The analysis of such important effects allows to construct the calculated spectra of the SLD output power and to calculate the width of each spectrum at half-height at different injection currents. In addition, in order to understand which of the active media designs allows to create an effective broadband superluminescent diode, it is necessary to analyze the magnitude of the spectral dip between the maxima in the corresponding emission spectrum. The work shows that the broadest SLD with a small spectral dip can be created on the basis of one quantum well, in which two optical transitions are involved in the emission process.
Show AbstractFreeze-Thaw Cycle-Induced Degradation Mechanisms in Photovoltaic Modules in Cold Climates
Freeze-Thaw Cycle-Induced Degradation Mechanisms in Photovoltaic Modules in Cold Climates
Yu. -. Deng, V. V. Davydov
The modern development of renewable energy has led to the widespread adoption of photovoltaic (PV) systems. Despite traditional views, PV technologies show significant potential in cold climate regions, including vast areas of Russia, where the annual energy yield can be economically viable. However, the operation of PV modules in such harsh conditions faces a complex set of specific impacts, the most critical of which are the repeatedly occurring freeze-thaw cycles of moisture. These cyclic thermal and mechanical stresses accelerate the degradation of materials and components, causing delamination, corrosion, and microcracks, which critically affect the performance and longevity of the systems. This article is dedicated to a detailed study of the degradation mechanisms of PV modules caused by freeze-thaw cycles, using the climate of St. Petersburg as an example. Based on field observations and literature analysis, the key degradation processes affecting the reliability of PV systems in this climate zone have been identified and analyzed. The goal of the work is to deepen the understanding of degradation specifics in cold climates to develop methods for enhancing the reliability of PV modules.
Show AbstractMEMS-switch with enhanced capacitive ratio for advanced electronic systems
MEMS-switch with enhanced capacitive ratio for advanced electronic systems
M. O. Morozov$^{1,2}$, I. V. Uvarov$^2$
MEMS switches have great potential for use in advanced radar and communication systems, but their practical implementation is limited by several factors. The capacitance ratio in the closed and open state is usually several units, which does not meet the desired specifications. By adding an intermediate electrode on top of the dielectric layer, the capacitance ratio can be significantly increased. In this study, the capacitive and radio-frequency characteristics of a switch with an intermediate electrode are calculated.
Show AbstractDevelopment of an algorithm for constructing a wheel profile and detecting surface defects during wheel-rail interaction
Development of an algorithm for constructing a wheel profile and detecting surface defects during wheel-rail interaction
K. G. Arinushkina$^{1,3}$, P. I. Tsomaev$^{2,3}$, V. V. Davydov$^{1,2}$, I. Yu. Saveliev$^3$
The global growth of rail transportation contributes to economic development, but at the same time increases the safety requirements for rolling stock. Wheelset defects, which are the cause of most accidents, remain a key risk factor. To detect them in a timely manner, a comprehensive analysis of the wheel surface is required, including image collection, restoration of damaged areas and accurate measurement of geometric parameters. Optical systems are used for timely detection of defects, which allow for real-time monitoring of the surface. However, the effectiveness of such systems largely depends on the algorithms used to calculate and evaluate the parameters. The presented paper considers the relevance of developing an improved data processing algorithm for monitoring the main parameters of the wheels in order to improve the accuracy of diagnosing rolling surface defects.
Show AbstractNew method for overcoming the Standard Quantum Limit of sensitivity in optomechanical detectors of weak forces
New method for overcoming the Standard Quantum Limit of sensitivity in optomechanical detectors of weak forces
L. A. Barinov$^{1,2}$
It is shown that the laser gravitational wave detector scheme proposed in [Barinov L. A., Khalili F. Ya. // Phys. Rev. D. 2025, https://doi.org/10.1103/7mn7-qm31], which combines the advantages of a quantum speedmeter and tunable optical rigidity, can be adapted for tabletop-scale optomechanical sensors of weak forces. A numerical analysis is performed, and analytical expressions are obtained for the spectral density of quantum noise under parameters typical for modern optomechanical systems with sub-gram-scale mirrors.
Show AbstractExcited states of triply heavy tetraquarks
Excited states of triply heavy tetraquarks
V. O. Galkin$^1$, E. M. Savchenko$^{1,2}$
Masses of ground and radially and orbitally excited states of triply heavy tetraquarks with a pair of open and hidden heavy flavors (charm, bottom) were calculated within the relativistic quark model, based on the quasipotential approach and QCD. A tetraquark is considered as a bound state of a diquark with an antidiquark. Diquarks are treated as color--triplet states. Calculations take into account all relativistic effects (spin--independent and spin--dependent) and finite size of diquarks. Obtained results are compared with the strong fall--apart decay thresholds into a pair of heavy and heavy--light mesons. Tetraquark states that are most promising candidates for experimental searches are identified.
Show AbstractRare Semileptonic $\Xi^-_b$ baryon Decays
Rare Semileptonic $\Xi^-_b$ baryon Decays
V. O. Galkin$^1$, A. O. Nemtyrev$^2$
In recent decades, significant experimental progress has been achieved in studying decays of hadrons containing heavy quarks. In particular, the branching fractions of the exclusive semileptonic and rare decays of both charm and bottom mesons and baryons were measured. In this paper, we present the results of a study of the rare decay of $\Xi_{b}^-\rightarrow\Xi^-l^+l^-$. The form factors parameterizing the weak current matrix elements between baryonic states are calculated within the framework of the relativistic quark model based on the quasipotential approach and quantum chromodynamics. The calculation of the differential and total decay widths, as well as the asymmetries and polarization characteristics of the decays, is carried out on the basis of the helicity formalism. The calculations were performed both with the account of the long-range contributions of charmonium vector resonances to the Wilson coefficients and without their account. Predictions for decay widths for 3 generations of leptons have been obtained.
Show AbstractProblems of temperature control in laser metalworking using a thermal imager
Problems of temperature control in laser metalworking using a thermal imager
A. A. Gajna$^1$, A. A. Mozhaiko$^2$
The paper investigated the accuracy of temperature measurements during laser hardening of structural steel using a thermal imager operating in the mid-infrared range (8-14 microns). Experiments were conducted on installations equipped with fiber lasers, LENS 750 and ЛС-10. Several factors have been identified that affect the accuracy of measurements. These include the reflection of laser radiation, the camera resolution, incorrectly adjusted emission coefficients, and the interaction between laser radiation and air during discharge. In order to improve the accuracy, several methods have been proposed. These methods include the use of optical filters, optimization of the observation distance, and correction of emission coefficients. The study's results indicated the need for comprehensive calibration of the system in order to ensure accurate surface temperature measurement.
Show AbstractFeatures of propagation of beams of coherent phase-modulated radiation
Features of propagation of beams of coherent phase-modulated radiation
M. M. Leshcheva, A. A. Abashkina, A. A. Sharkov, O. M. Vokhnik
The transformation of intensity distributions occurring as a phase-modulated laser beam propagates is experimentally investigated. The influence of the depth of sinusoidal phase modulation on the transformation of the phase distribution into the intensity distribution occurring at a distance equal to a quarter of the Talbot length is revealed. Periodic self-reproduction of the radiation intensity distributions, the phase of which is modulated according to a periodic fractal law, is registered. The features of the Talbot effect caused by the use of a phase transparency based on the Weierstrass function are revealed.
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