Technical Physics最新文献

A theoretical analysis is made of the formation of longitudinal and transverse emittance of beams of charged particles in photoguns under the influence of repulsive forces of Coulomb fields. In numerical calculations, the characteristics of bunches of charged particles with uniform and Gaussian charge density distributions are compared. The efficiency of the proposed numerical-analytical model is compared with calculations using the Astra program. The obtained numerical and analytical results can be useful in the design of photoinjectors to select the optimal parameters that determine the main characteristics of photoguns.

In this paper we present the study of the features of epitaxial growth highly stressed superlattices based on highly stressed thin InGaAs/InAlAs layers on InP substrates by the molecular beam epitaxy. It was shown that the growth rates of the InGaAs and InAlAs bulk layers lattice-matched to InP substrates do not allow us to precisely determine the growth rates of thin highly stressed In_0.36Al_0.64As/In_0.67Ga_0.33As strain compensated superlattices and the error is about 10 percent. The effect is related to the difference in the growth temperatures of InGaAs and InAlAs bulk layers, which affects the intensity of indium evaporation from the growth surface.

The possibility and effectiveness of using an automated zenith telescope to determine selenodetic rotation parameters by computer simulation of observations using a telescope installed on the lunar surface are considered, in particular, modeling of star tracks at an automated zenith telescope and the possibilities of astrophysical research, development of a space observations program.

The paper presents the results of a study of the chemical composition of myocardial tissues and striated muscles at the cellular level using a combination of X-ray fluorescence microscopy and Raman microspectrosopy. The distribution of inorganic materials (Na, Si, Ca, etc.) was measured with the help of X-ray fluorescence imaging and microanalysis workstations at ELETTRA synchrotron (Italy). Methods of infrared Raman spectromicroscopy were applied for the identification of organic compounds (lipids, amides, and polysaccharides). All experiments were carried out with unstained paraffin-embedded histological sections. The research was related to the study of sodium deposits in muscle tissues.

Various approaches to the optical diagnostics of evolving polymer foams formed as a result of a decrease in the external pressure according to a given scenario in the “polymer-supercritical fluid” systems are considered. Formed polymer foams are considered as a material platform for the creation of scaffolds for biomedical applications. Diagnostics of the current state of the foam was carried out by statistical analysis of the spatiotemporal fluctuations of the probe laser radiation, multiple scattered in the volume of the evolving foam, or by analyzing the fluorescent response during foaming of the “polymer-fluorophore” mixture, pumped by laser radiation in the absorption band of the fluorophore. A relationship has been established between the average lifetime of dynamic speckles in scattered laser light and a generalized parameter characterizing the foam expansion dynamics. It was also found that the waveguide effect in the walls of the formed pores has a significant influence on the fluorescent response of the evolving foam, leading to an increase in the characteristic dwell time of fluorescence radiation in the walls and, accordingly, to an increase in the contribution of the induced component to the fluorescent response.

On the basis of diffraction transformations of wave fields, a mathematical model of a speckle interferometer of transverse displacements of a scattering object has been developed and numerical modeling of speckle-modulated interference patterns and signals at the output of the interferometer has been performed. Numerical calculations of the spatial distribution of complex amplitudes of wave fields in an interferometer were used for modeling when the displaced scattering surface was illuminated by two obliquely incident laser Gaussian beams. A statistical numerical experiment was performed to determine the measurement error of the scattering surface displacement caused by the change of realizations of interfering speckle fields. The simulation results are in good agreement with the results of experimental studies of transverse displacements in the range up to 600 micrometers.

In this work, we study the evolution of an extremely short pulse in a dielectric crystal with carbon nanotubes containing an impurity with random parameters (energy level, electron hybridization energy). The dependence of the spatial characteristics of the pulse on the impurity parameters and the number of photons taken into account in the model is analyzed.

Based on gas-dynamic methods, numerical modeling of the nonlinear dynamics of sound waves in a vibrationally excited nonequilibrium gas was carried out and the main stages of the evolution of acoustic instability were studied. It is shown that in numerical models the linear regime with an exponential growth law of the amplitude of disturbances is in good agreement with the linear analysis of stability, and at the nonlinear stage of development of acoustic instability, a system of shock waves is formed. The effects of nonlinear saturation of the intensity of shock waves, caused by the stabilization of acoustic instability, are demonstrated.

Experiments have been carried out to study the transient radiation-induced absorption in the active core of a double-clad ytterbium fiber and the response of a laser based on it under the exposure of pulsed X-rays. It has been found that the time of loss of laser performance (downtime) under pulsed irradiation increases with an increase in the absorbed of radiation and a decrease in the laser pump power and reaches values of ∼1 ms. An analysis of the experimental results shows that the laser response to the X-rays pulse exposure is determined by radiation-induced losses in the active fiber core. An experimental-calculated method for estimating the radiation reaction of a laser, based on the results of studies of the active fiber, is proposed.

The main factors resulting in conductor failure under the action of a strong pulsed magnetic field are analyzed. The theoretical model describes the geometry of a cylindrical thick-walled solenoid and considers magnetic field diffusion, ohmic heating of the material and mechanical stresses arising in it. The magnetic field amplitude at which induced stresses in the material reach the von Mises yield criterion is used as the B_th threshold field separating the areas of safe (non-destructive) and dangerous fields. In the case of an initially uniform material, the maximum heating temperature corresponding to this limit, which predetermines the thermomechanical stress, has been derived analytically. In the general case, based on the analysis of the calculated threshold field, the influence of various parameters (magnetic pulse characteristics, elastic moduli of the material, etc.) on the conductor resistance in the pulsed magnetic field is studied and ways of increasing the threshold field are proposed, in particular, by using different spatial profiles of the initial resistivity. It is shown that in comparison with a uniform material, a modified layer with increased resistivity formed on the surface allows to significantly increase the amplitude of the magnetic pulse withstood by the material without fracture.