Search

The article "On the Existence of a Wave Front in the Cauchy Problem for the Gurtin–Pipkin Equation" published in Mathematical Notes discusses the existence of a front of oscillation propagation in the one-dimensional Gurtin–Pipkin Equation. The authors prove that a solution to this problem is a compactly supported function for each fixed final time if the initial function is compactly supported. The study is important for understanding thermal processes and the propagation of sound waves in various materials, and the research was supported by the Ministry of Science and Higher Education of the Russian Federation. [Extracted from the article]

The problem of boundary controllability is considered for a wide class of models. This class can be conventionally called naive mechanics. It is proved that, for all naive mechanics models except for three exceptional cases, there is no controllability to rest. All these three cases are classical examples of equations two of which require additional study of the controllability property. [ABSTRACT FROM AUTHOR]

The problem of distributed controllability for the Gurtin–Pipkin equation with a kernel represented by some series of decreasing exponential functions is considered, while certain conditions are imposed on the coefficients and exponents. It is proved that this system cannot be brought to rest even if the control action is applied to the entire region. [ABSTRACT FROM AUTHOR]

It has been experimentally shown that a low-power vacuum pinch discharge with laser ignition can emit a beam of abnormally accelerated electrons with maximum energies per unit charge almost an order of magnitude higher than the voltage across the discharge gap. It has been found that the intensity of the X-ray radiation generated when the beam is applied to the target significantly decreases with an increase in the laser pulse energy. The maximum energy of X-ray quanta is inversely proportional to the mass of the cathode substance ablated by laser radiation during discharge ignition. Possible mechanisms of the electron-beam generation process have been discussed. [ABSTRACT FROM AUTHOR]

The problem of the exact bounded control of transverse vibrations of a thin plate is considered. Control actions are applied to the boundary of the plate, which fills a certain bounded domain on the plane. The purpose of the control is to completely stop oscillations in a finite time period. [ABSTRACT FROM AUTHOR]

The boundary controllability of oscillations of a plane membrane is studied. The magnitude of the control is bounded. The controllability problem of driving the membrane to rest is considered. The method of proof proposed in this paper can be applied to any dimension but only the two-dimensional case is considered for simplicity. [ABSTRACT FROM AUTHOR]

The satellite ionosondes in highly elliptical orbits are proposed to be used for the task of continuous monitoring of the Arctic ionosphere. The monitoring scheme with the ionosonde location aboard the Arktika-M satellites is presented. The calculations of the vertical topside and transionospheric sounding using the SIMP1 ionospheric model are performed, which show the feasibility of continuous monitoring. [ABSTRACT FROM AUTHOR]

The isolation of phenanthrene from coking tar by recrystallization from a selective solvent is considered. Optimal production conditions are identified. Purified phenanthrene is obtained by recrystallization from white spirit in three stages. The oxidative processing of the purified phenanthrene is described. Applications of the oxidation products are noted. On that basis, small-scale production of more than ten products is possible. [ABSTRACT FROM AUTHOR]

An Erratum to this paper has been published: https://doi.org/10.3103/S0025654423330014 [ABSTRACT FROM AUTHOR]

Consideration was given to the problem of precise control of a system obeying the equation of string with integral “memory.” This system was proved to be reducible to the quiescent state in a finite time with the use of a distributed action bound in magnitude. The time to stop oscillations was also estimated. [ABSTRACT FROM AUTHOR]

The results of using a stationary setup for detecting and identifying explosives using the tagged neutron method (or associated particle imaging (API) method) have been presented. The source of 14.1-MeV tagged neutron beams is an ING-27 portable neutron generator made by VNIIA (Moscow). It contains an embedded 64-pixel silicon α detector with double-sided strip readout developed by the Joint Institute for Nuclear Research (JINR). The setup was tested for the identification of more than 30 explosives. [ABSTRACT FROM AUTHOR]

The article examines the use of boundary forces in controlling vibrations of a rectangular plate. It analyzes the problem of driving a plate to an equilibrium point without significant constraint imposed on the control function, and offers a proof for the existence of the boundary control which is responsible for driving a string to a stable point. Moreover, it is noted that the solutions of the problem involve the consideration of the Sobolev space consisting a set of differential functions, a Lipschitz boundary and eigenfunctions.

We consider the distributed control problem for the wave equation with memory, where the kernel is the sum of decreasing exponential functions and the control is bounded in modulus. We prove that the oscillations of the system can be brought to the state of rest in a finite time. [ABSTRACT FROM AUTHOR]

Ion acceleration in a high-current cathode plasma jet of a low-voltage vacuum spark discharge has been studied. It is established that an increase in the discharge current amplitude leads to a growth in both the density and velocity of the ion flux emitted from the discharge gap. The dependence of the ion velocity on the discharge current amplitude in the range below 10 kA is well described by a simple hydrodynamic model of the current-carrying jet with allowance for plasma compression by the intrinsic magnetic field of the discharge current. For discharge current amplitudes exceeding 10 kA, the ion velocity ceases to grow and exhibits a considerable scatter of values measured in different shots. [ABSTRACT FROM AUTHOR]

The contributions of fast and slow ion components to the average mass transfer rate in the cathode plasma jet of a low-inductance vacuum spark have been determined using time-of-flight measurements. The total mechanical momentum of the cathode plasma jet has been found using the ballistic pendulum technique. The coefficient γ of ion erosion of a cathode material was evaluated in the range of discharge current amplitudes 3–13 kA and the discharge current buildup rates 4 × 109–1.5 × 1010 A/s. The γ value exhibits small variations in the indicated range of discharge parameters and is close to the values known for vacuum arcs. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

The dynamics of fast (a current rise time of ≤1011 A/s) laser-induced vacuum discharges with moderate amplitudes of the current (≤10 kA) and voltage (≤20 kV), as well as medium storage energy (20 J), is studied. It is shown experimentally that the initial conditions specified by the energy and duration of laser radiation are a decisive factor governing the discharge dynamics. Two types of beam–plasma instabilities separated in space and time are discovered, and their occurrence conditions are analyzed. The first type of instability, observed early in the discharge, is associated with pinch structures at the front of the cathode jet expanding into a vacuum. The second type arises either at the peak or at the trailing edge of the current pulse and is accompanied by generation of hard (with an energy of ≥100 keV) bremsstrahlung from the anode region. The increase of the hard component energy over the current source potential is attributed to breaking due to plasma erosion. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

The results of experiments devoted to the study of spectral, spatial, and time characteristics of a spectrally bright point x-ray source based on a vacuum diode with a laser-plasma cathode and a titanium needle anode with a photon energy approximately equal to 4.5 keV are presented. The experimental results revealed a considerable difference between the electron emission from laser plasma in a strong electric field and the explosive electron emission and demonstrated the effectiveness of laser plasma as an electron source. The optimization of the laser radiation power density, the accelerating voltage, and the interelectrode spacing made it possible to create a point x-ray source whose spectral brightness exceeds available sources in the class of small-size pulse x-ray instruments (tubes with explosive cathodes). It has been proved experimentally that the maximum contrast of the characteristic lines of the anode material is attained in the case of an optimal choice of accelerating voltage. The x-ray source has the following parameters: (1) spectral brightness of the K-lines of titanium of the order of 10[sup 21] photons/cm² s sr keV; (2) emitting region size of 250 µm; and (3) laser pulse duration less than 20 ns. [ABSTRACT FROM AUTHOR]

We present the results of experimental investigation of a planar vacuum diode with field- and laser-controlled ferroelectric cathode based on prepolarized ceramics of the TsTS-23 (TsTS-19) grade. The diode current passes when the spontaneous polarization vector is oriented both toward the anode and in the opposite direction. It is established that an increase in the laser power density on the ceramic surface leads to a decrease in the diode current pulse duration. The maximum currents achieved in a field-controlled diode exceed the Langmuir current values by two to three orders of magnitude. The current pulse characteristics are determined by the mutual orientation of the polarization vector and the control electric field. [ABSTRACT FROM AUTHOR]