Radiophysics and Quantum Electronics最新文献

We consider the problem of nonstationary strains of an infinite anisotropic Timoshenko plate on an elastic-inertial foundation. A monoclinic symmetry type of an elastic medium, which is characterized by one plane of symmetry, is adopted as a model of anisotropy. Analytical methods are used to construct new fundamental solutions for the nonstationary normal displacement and deflection angles. The Laplace and Fourier integral transforms are used to find fundamental solutions, which serve as the basis for obtaining the integral relations for studies of nonstationary bending waves in a plate under the influence of sets of lumped and distributed loads. An example of the calculations is presented.

We use a discrete–continuum approach to study geometrically nonlinear bending waves in a massin-mass metamaterial chain. The nonlinear equations of motion are derived, both in the form of coupled differential–difference equations and in the form of partial differential equations in the continuum limit. The possible existence of an analytical solution of continuum equations in the form of a solitary strain wave is examined.

We consider aeroelastic oscillations of a rigid channel wall having an elastic suspension with hardening cubic nonlinearity and interacting with a pulsating layer of a viscous gas in the channel. The study is based on the reduction of the coupled boundary value problem of mathematical physics with the equations of viscous gas dynamics and the equation of rigid wall dynamics included as well as the corresponding boundary conditions to the Duffing oscillator equation. Initially, the aeroelastic oscillation problem is formulated for the channel wall under consideration and analyzed asymptotically by the perturbation method. As a result, the equations for the dynamics of a viscous compressible gas are linearized and then solved iteratively. The gas reaction force on the rigid wall is determined, and an equation is obtained for the aeroelastic oscillations of the channel wall; this equation is a generalized Duffing oscillator equation. Based on solving this equation by the harmonic balance method, we determine and study the nonlinear aeroelastic response of the channel wall as well as its phase response. It is shown that the allowance for compressibility of the viscous gas leads to an increase in the values of resonance frequencies and the wall oscillation amplitudes, as well as to an additional phase shift of the disturbing force, which is determined by the given profile of the pressure pulsation at the channel ends.

We present a review of some fundamental results in the theory of dynamical systems, which have led to the discovery of dynamical chaos and its three forms, namely, two classical forms, such as conservative chaos and dissipative chaos, as well as the completely new third form, the so-called mixed dynamics in which the sets of attractors and repellers have non-empty intersection. The major part of the work is devoted to homoclinic Poincaré trajectories, i.e., doubly asymptotic trajectories to saddle periodic ones, as the main elements of dynamical chaos. Using simple examples, we show the appearance of such trajectories during periodic perturbations of two-dimensional conservative systems. As is known, the homoclinic trajectories were discovered by Poincaré. In this work, we discuss the problem (the planar circular restricted three-body problem) solving which this discovery was made. Some interesting facts concerning its history are given in the appendix.

We perform dispersion analysis of the Weibel-type electron instability in collisionless bi-Maxwellian plasma with an external magnetic field aligned with the anisotropy axis, which corresponds to the highest temperature. The range of the wave numbers of unstable modes, their growth rates, maximum growth rates, and the corresponding optimal wave number as a function of the density and anisotropy of the plasma and the external magnetic field are found for ordinary mode perturbations with the wave vector and the vector of the electric field being perpendicular and parallel to the external field, respectively. The external magnetic field, which suppresses the instability of these modes, and the r.m.s. generated magnetic field, which saturates it at the nonlinear stage, are also estimated.

We use the methods of supercontinuum generation and nonlinear parametric transformations to develop a laser system that forms femtosecond pulses with a duration of several field oscillations and a central wavelength of 910 nm, which are synchronized with the seed radiation of the pump laser. The duration of femtosecond pulses was 20 fs at a repetition rate of 1 kHz and a pulse energy higher than 5 μJ. For further amplification to an energy higher than 40 mJ, a pump laser has been developed, and the main parameters of the parametric amplifier have been calculated. The developed laser system will be used as the starting part of the PEARL petawatt parametric laser system.

We perform spectral studies of the vibrational phenomena which are caused by imperfection of the optical and mechanical units used in the technological process of applying an antireflection coating to the surfaces of large-scale optical elements. The ways of minimizing the negative effect of the revealed vibrational factors are indicated. In particular, it is shown that a decrease in the amplitudes of the low-frequency spectral components of the motion velocity of the treated elements due to the proposed modification of the optical and mechanical units allows one to create more uniform antireflection coatings. The spectrum of the laser-beam displacements spectrum in the near and far fields is also studied experimentally for various mechanical impacts on the optical and mechanical parts of a fiber laser system. It is established that the vibrations are nonlinear and, at certain impact frequencies, the laser beam in the far field oscillates at frequencies that are multiples of the impact frequency.

Being one of the most mysterious particles of the Standard Model, neutrinos have opened up new opportunities for astrophysical research. The high penetrating power of neutrinos provides insight into stellar interior and makes it possible to study the mechanisms of the origin of ultra-high energy cosmic rays. When a star explodes, a neutrino flare informs us about this event several hours earlier than electromagnetic radiation. Neutrino also plays a crucial role in cosmology, being the second most abundant known particle in the Universe. In the radiation-dominated epoch, neutrinos together with photons, determine the dynamics of the expansion of the Universe. Later, becoming nonrelativistic, the neutrinos increase the contribution Ω_m of nonrelativistic matter, which previously consisted of cold dark matter and baryonic matter. Since neutrinos affect the course of the evolution of the Universe, this fact should be taken into account when determining cosmological parameters. Recently, in addition to relic neutrinos from the Big Bang, antineutrinos of primordial nucleosynthesis have been theoretically predicted. Their detection could be additional evidence for baryon asymmetry of the Universe.

Current results from a number of independent experiments indicate the possibility of the existence of a light sterile neutrino (m_ν ~ 1–3 eV). The presence of such a neutrino is in poor agreement with the predictions of the Standard Cosmological Model, but these contradictions can be removed by its extension, for example, by the existence of a nonzero lepton asymmetry ξ_ν ~ 10⁻² of the Universe. Nowadays, there are little doubts about the existence of cosmological neutrinos, but unfortunately it is not yet possible to detect them directly due to the extremely small cross section of their interaction at low energies. However, if this can be done in the future, we will obtain direct information about the first seconds, minutes, and hours of the evolution of the Universe after the Big Bang. A review of key aspects related to the influence of cosmological neutrinos on the evolution of the Universe at different stages from the early Universe (primordial nucleosynthesis and primordial recombination) to present days is given.

We consider the current status of the binary neutron star stripping model to explain short gamma-ray bursts. After the historical joint detection of the gravitational wave event GW170817 and accompanying gamma-ray burst GRB170817A, the production of short gamma-ray bursts in the neutron star coalescence has been reliably confirmed. Many properties of GRB170817A that turned out to be peculiar compared to other short gamma-ray bursts are naturally explained in the stripping model proposed in our works in 1984. We emphasize the role of D. K. Nadyozhin (1937–2020), who quantitatively predicted the GRB and kilonova properties back in 1990. We also discuss problems that need to be solved in the context of this model, especially in simulations using the smoothed-particle hydrodynamics method.

We compare two methods of millimeter radio interferometry with and without frequency conversion using as an example experimental measurements of the transverse deformation magnitude of a metal rod under dynamic load. We reveal a good agreement between the results, demonstrating a possibility of measuring the surface deviations within times of about 1 μs with micron precision.