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 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$^1$, D. R. Aliev$^1$, V. O. Skulkin$^1$, A. A. Vorontsova$^1$, E. A. Gerdt$^1$
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 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 AbstractMethanol 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 AbstractReviving fissured solar cells through self-healing
Reviving fissured solar cells through self-healing
L. -. Boudjemila
Solar cells are very fragile, and exposure to extreme weather conditions may cause micro-cracks, leading to a degradation in their performance. Therefore, a perovskite material combined with a self-healing polymer can form a composite with a dual continuous interwoven network. This composite undergoes healing through synergistic grain growth and solid diffusion processes at moderately elevated temperatures of 333 K. The ions can migrate to fill gaps or fissures, and their ionic mobility allows for the reorganization of the crystal structure, potentially restoring electrical connectivity. Various experimental techniques have been optimized in order to achieve better efficiency of the PSCs in atmospheric condition by varying the concentrations of the self-healing polymer incorporated into the perovskite material to find the suitable one. The I-V measurements show a reduction of loss in efficiency from 40% to only 4% of the damaged solar cell. This approach can provide potential protection against efficiency loss due to micro-fissures while also benefiting from the optoelectrical properties of the perovskite material.
Show AbstractInfluence of stimulated raman scattering on SIL efficiency
Influence of stimulated raman scattering on SIL efficiency
A. N. Golodukhina
Optical microresonators with high quality-factor are an advanced platform for carrying out actual scientific research in the field of quantum optics and photonics. Self-injection locking (SIL) effect is an example of phenomena realized on the platform of such resonators. SIL effect allows for narrowing the width of the emission line to the order of units of kHz. In this work, we studied features of self-injection locking regime in the presence of stimulated Raman scattering in the system. It was found that in the presence of Stokes optical microcomb the output emission linewidth turns out to be an order of magnitude higher than expected values.
Show AbstractPlasma waves in a two-dimensional graphene-based superlattice
Plasma waves in a two-dimensional graphene-based superlattice
S. Yu. Glazov, A. A. Kovalev
In this paper, the dependence of the plasma wave frequency on the wave vector and the density of plasma excitations in the electron gas of a two-dimensional graphene superlattice are theoretically investigated. The calculations are performed based on the quantum theory of plasma waves in the random phase approximation taking into account the umklapp processes. The plasmon frequency estimate for the currently theoretically studied superlattices based on graphene on a striped substrate yields ω ∼ 10$^13$ c$^−1$. A comparison of the plasmon dispersion laws of graphene and quantum semiconductor superlattices is performed.
Show AbstractScreening of periodically charged planes and filaments by a two-dimensional superlattice under the conditions of Stark quantization
Screening of periodically charged planes and filaments by a two-dimensional superlattice under the conditions of Stark quantization
S. Yu. Glazov, E. I. Dudareva
The effect of a constant homogeneous electric field on the penetration of a field of periodically charged planes and filaments into a two-dimensional electron gas of a two-dimensional superlattice is studied. In the presence of a constant quantizing electric field, the potential oscillates with frequencies that are multiples of the Stark frequency. In the case of a non-degenerate electron gas, the amplitude of the constant component of the potential is found.
Show AbstractString Thermodynamics and Number Theory
String Thermodynamics and Number Theory
A. V. Borisov$^1$, A. O. Shishanin$^2$
In this methodological note, we consider the thermodynamic properties of a simple system with an infinite number of degrees of freedom --- a quantum string equivalent to an infinite set of oscillators with frequencies multiples of the fundamental frequency $\omega$. We calculate the partition function, average energy, and heat capacity of the string as functions of temperature. Using the Laplace transform of the partition function, we show that the statistical weight of a string state with energy $E = N \hbar\omega $ is equal to the number of partitions $p(N)$ of a natural number $N$ into a sum of natural numbers, and we reproduce (up to a numerical coefficient) the well-known in number theory Hardy--Ramanujan asymptotic formula for $p(N)$ provided $N\gg 1$. We show that quantizing a string is also equivalent to quantizing a one-dimensional field theory describing, in particular, a superposition of standing electromagnetic waves.
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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