Spectral and energy characteristics of acoustic emission in the laser radiation breakdown of water

Results from experimental investigations of acoustic emission from the optical breakdown zone in liquid formed by laser radiation at a wavelength of 532 nm are presented. The linear dependence of the acoustic pressure on the laser pulse energy is revealed. It is shown that the effect of an additional source of sound at a frequency of 37 kHz enhances the acoustic emission from the optical breakdown zone.     

Specific features of the acoustic emission upon the optical breakdown in liquid induced by the radiation of Nd:YAG laser

The acoustic emission from the zone of the optical breakdown in liquid is experimentally studied. The spectral characteristics and energy of the acoustic wave that is generated in liquid due to expansion of the plasma formation initiated by the optical breakdown at a wavelength of 532 nm are analyzed. Two spectral peaks that characterize the acoustic emission and the low-frequency shift of the low-frequency peak owing to an increase in the laser pulse energy are demonstrated. In general, the linear dependence of the acoustic pressure on the laser pulse energy is observed. The acoustic data can be used to reconstruct function R(t) that is in agreement with dependences R(t) resulting from the optical data. This circumstance is important for the study of breakdown in opaque media.     

Evolution of the magnetic field in plasma in a neighborhood of zero points

We consider a mathematical model of magnetic reconnection in a neighborhood of singular points in the framework of 3D magnetohydrodynamics. In the case of linear dependence of the magnetic field and the velocity on coordinates, we present self-similar solutions of the system of MHD equations. For an arbitrary initial magnetic configuration, we state a mixed problem, which is solved numerically. We describe a semi-implicit algorithm for the solution of the difference problem and present the results of several numerical experiments.     

Fast ignition by intense laser-accelerated proton beams

The concept of fast ignition with inertial confinement fusion (ICF) is a way to reduce the energy required for ignition and burn and to maximize the gain produced by a single implosion. Based on recent experimental findings at the PETAWATT laser at Lawrence Livermore National Laboratory, an intense proton beam to achieve fast ignition is proposed. It is produced by direct laser acceleration and focused onto the pellet from the rear side of an irradiated target and can be integrated into a hohlraum for indirect drive ICF.     

Acceleration of the convergence of the method of homogeneous solutions in three-dimensional problems of the theory of plates

A method is proposed for the regularization of the calculation process in investigations of homogeneous solutions of three-dimensional problems of elasticity theory by the method of homogeneous solutions. A qualitative investigation is performed of a three-dimensional compression—tension problem with mixed boundary conditions. Questions are examined of the a priori finding of limit values of the unknowns in an infinite system of equations, of the behavior of the coefficients and the series convergence on the boundary as a function of properties of the functions.Donetsk. Translated from Teoreticheskaya i Prikladnaya Mekhanika, No. 21, pp. 9–13, 1990.     

Peculiarities of boiling of emulsions with a low-boiling dispersed phase

The results of an investigation of heat transfer from thin wires to emulsions whose dispersed phase is low-boiling in comparison with its dispersion medium are presented. A peculiarity of heat transfer with such emulsions is observed in the bubble boiling regime when only droplets of the emulsion dispersed phase are boiling. Theoretical and experimental investigations of the activation mechanism of boiling centers have been performed. The critical volume V ₀ of the emulsion, with chain nucleation taking place when this volume is exceeded, has been determined. A model of chain activation of low-temperature boiling centers has been developed. The model has been qualitatively confirmed by the experimental data obtained.     

Preparation of High-Purity Silicon Tetrafluoride by Thermal Dissociation of Na2SiF6

The possibility of preparing high-purity silicon tetrafluoride by the thermal dissociation of pure grade Na₂SiF₆ was studied. The impurity composition of the product was studied by IR and atomic emission spectroscopy and by mass spectrometry.     

On rational approximation of convex functions with a given modulus of continuity

Доказывается, что для наименьших равномер ных рациональных уклоне нийR _n(f) выпуклой на [0,1] функции с модулем непрерывно сти, не превосходящемω(δ), сп раведлива оценка $$R_n (f) \leqq c\frac{{\ln ^2 n}}{{n^2 }}\mathop {\max }\limits_{e^{ - n} \leqq \theta< 1} \left\{ {\omega (\theta )\ln \frac{1}{\theta }} \right\},$$ гдес — абсолютная по стоянная.