Methanol emission at 84.5 GHz in infrared dark clouds
Methanol emission at 84.5 GHz in infrared dark clouds
P. S. Sozinova, N. N. Shakhvorostova
We report observations of methanol emission at 84-GHz toward 32 infrared dark cloud (IRDC) sources at various evolutionary stages. Data were obtained using the 20-meter radiotelescope located in Onsala, Sweden, during 2019-2020. Among these 32 sources, the 5$_{-1}$---4$_{0} E$ methanol emission was detected in 24. These objects do not overlap with any previously observed 84-GHz sources, making all our detections novel. Based on our findings, five sources were identified in which emission of class I methanol masers was observed. Additionally, we compare the 84-GHz observations with previous 44-GHz measurements toward the same sources, revealing a correlation between emission at both frequencies and notable similarities in their spectral profiles.
Show AbstractNumerical modeling of vapor-liquid equilibria of ternary mixtures of hydrocarbons and carbon dioxide
Numerical modeling of vapor-liquid equilibria of ternary mixtures of hydrocarbons and carbon dioxide
D. V. Selezneva
In the oil and gas industry, carbon dioxide injection into the reservoir is considered a promising method for enhancing oil recovery: when dissolved in hydrocarbons, the viscosity of oil decreases and a swelling process occurs, which improves the efficiency of displacement. At certain values of pressure and temperature, a three-phase equilibrium can form in the system - two liquid phases (enriched in carbon dioxide and enriched in hydrocarbons) and a gas phase, which seriously complicates the use of classical iterative algorithms for calculating phase equilibria with stability tests. In this paper, the method of direct minimization of the Gibbs free energy at fixed values of pressure and temperature was used to determine the boundaries of the regions of two-phase and three-phase equilibrium; in addition, the viscosities of each phase were calculated using the Lorenz-Bray-Clark model, which made it possible to quantitatively estimate the decrease in the viscosity of the oil phase.
Show AbstractEstimation of Curium effect on neutron-physical characteristics of BN and VVER reactors under the homogeneous distribution
Estimation of Curium effect on neutron-physical characteristics of BN and VVER reactors under the homogeneous distribution
V. V. Hramkov, D. R. Aliev, V. O. Skulkin, A. A. Vorontsova, E. A. Gerdt, P. M. Aleksandrovich
The research aim is investigation of the curium affection on neutron-physical and thermophysical characteristics of VVER-1200 and BN-600. The fuel assemblies neutron-physical and thermophysical models have been created for the calculations to be made. Curium was added to the common fuel homogeneously in the proportions from 0,1 to 20 % as CmO2 oxide. Characteristics considered are: neutron multiplication factor, neutron spectrum, temperature distribution. A stronger effect on the reactivity is observed of the VVER-1200 model – Keff decreases by 3,85%. The maximum decrease of BN-600 neutron multiplication factor is 3%. Adding curium increases the neutron flux density of VVER-1200. Also curium does a considerable positive effect on the fast reactor’s reactivity, that creates a possibility of using Cm as a fuel. The maximum fuel temperature decreases by 500 grad, when curium is added.
Show AbstractOn 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 AbstractThe method of "Large particles" in mathematical modeling of Kelvin–Helmholtz instability in air
The method of "Large particles" in mathematical modeling of Kelvin–Helmholtz instability in air
S. I. Kosyakov$^{1,2}$, S. N. Kulichkov$^{1,2}$, M. N. Zakirov$^1$
The application of the well–known "Large particles" method in mathematical modeling of the simplest type of shear flows - a two-dimensional unsteady plane mixing layer is considered. The results of direct numerical simulation of the Kelvin-Helmholtz instability development at the interface of two layers of air of different densities moving with a tangential velocity shift in a field of strong external acceleration are described. The reliability of the calculation results is confirmed by comparing them with analytical calculations, with the results of numerical solution of a similar problem, as well as with experimental data. Based on the results of calculations, a new functional dependence of the increase in the width of the mixing layer on time, external acceleration, the difference in the densities of the air layers and the velocity difference at the contact boundary is obtained. This dependence is obtained for large values of acceleration values, velocity differences, and density at the gap. It will be useful for predicting the expansion of mixing zones in various currents with a tangential velocity gap, which are ubiquitous both in technology and in the atmosphere – for example, at the initial section of the jet, at the initial stage of mixing in a cylindrical vortex, with the development of wavy clouds or instability of a clear sky in the atmosphere.
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 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 AbstractInvestigation of the features of Bose-Einstein condensation of unitary polaritons in crystalline and photonic-crystalline media
Investigation of the features of Bose-Einstein condensation of unitary polaritons in crystalline and photonic-crystalline media
V. V. Volkova, D. A. Gavrilovets, A. D. Kotova, M. A. Kulagina, V. V. Filatov
Unitary (transparently associated, transparent) polaritons are quanta of the electromagnetic field in matter for which interaction with the phonon subsystem leads to an effective refractive index equal to unity ("unitary", hence the name). The material medium for such light quanta is optically identical to a vacuum, which makes transparent polaritons extremely interesting both for controlled illumination of optical media and for modeling nonlinear vacuum optical processes in matter (such as, for example, γ→a). In this paper, the possibilities of condensation of transparently associated polaritons in periodic material media (crystalline and photonic crystalline) are investigated and the characteristic features for crystalline and photonic crystalline cases are clarified. It has been established that condensation of transparently associated polaritons in the visible region of the spectrum is impossible in ordinary (non-photonic) crystals, however, in photonic crystals, on the contrary, it can be realized at any required wavelength. The results obtained are interesting for obtaining tunable coherent optical generation based on the parametric optical process γγ → a(φ',φ")→γ'y', in which an intermediate (axion-like) bipolariton a is synthesized and destroyed, and the frequency of useful radiation γ'"is tuned" by auxiliary phonons φ' and φ".
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 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.
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