Application of hydroacoustic radiators for the generation of seismic waves

To excite seismic waves with a high coherence, powerful hydroacoustic radiators placed in a natural reservoir were used. Theoretical estimates and the test data demonstrate a high efficiency of the proposed method of seismic wave excitation. The calculations are in good agreement with the results of measurements. The results of phasing the radiation with the use of two monopole sources separated by a quarter-wave distance are presented. It is shown that the use of the proposed scheme of excitation makes it possible to control the radiation pattern while obtaining a high coherence of seismic waves.     

Behavior of massless feynman integrals near singular points

Nizhnetagil' State Pedagogical Institute. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 80, No. 3, pp. 372–380, September, 1989.     

Simulation of seismic response to the action of a rain drop

The seismic response to the action of a falling rain drop on the ground is simulated in laboratory. The pulse signal from the output of accelerometers set up near points near the falling of a drop on a hard surface was experimentally recorded. The level is measured, and the spectrum of the vibration signal is analyzed. The theoretical estimates of the level and spectrum of the elastic-wave response agree with the results of experiment. The simulation results can be used to reduce the level of noise caused by precipitation, as well as to study the features of a moving droplet interacting with a hard boundary.

     

Powerful Cherenkov oscillators with 2D distributed feedback

The feasibility of using 2D distributed feedback based on 2D planar and coaxial Bragg structures for generating spatially coherent radiation from rectilinear ribbon and tubular electron beams is studied. One-section and sectional Cherenkov masers are analyzed. In the former design, a 2D Bragg structure acts as a resonator and a periodic slow-wave system simultaneously. In the latter (sectional) design, radiation is synchronized in a 2D Bragg structure that is placed at the cathode end of the interaction space and couples longitudinal and transverse (azimuthal) wave flows. The wave is amplified by the electron beam mainly in the fairly long middle section. The output (collector) part contains a standard 1D Bragg structure that partially reflects the amplified radiation toward the cathode and closes the feedback circuit. It is shown that dissipation introduced into the 2D Bragg structure of the sectional design makes it possible to increase one of the transverse sizes of the system to ∼10³ wavelengths with the energy exchange efficiency and one-frequency masing mode stability remaining the same. With such an overdimension, the millimeter-wave radiation integral power may reach a gigawatt level.     

Effect of extension on the structure and thermophysical properties of kapron (nylon 6)

The effect of extension on the structure and thermal conductivity of kapron has been investigated experimentally in the temperature range +20–130° C. The thermophysical characteristics were determined via a method based on the principle of the regular regime. The structure of the kapron was investigated by infrared spectroscopy and x-ray and microstructural analysis. The mechanical loads produced important structural changes that affected the thermophysical parameters of the kapron.Mekhanika Polimerov, Vol. 4, No. 1, pp. 180–182, 1968     

Mach reflection of weak shock waves from a rigid wall

On the basis of experimental observations and theoretical analysis of flow structure in the neighborhood of the triple point, it is shown that one should reject the condition for equality of the angle of deflection of flows passing through the Mach front and the two other fronts and replace it with some supplementary condition. The system of consistency equations in the indicated region is closed by an equation which is obtained under the assumption of the extremality of the deflection angle of a flow passing through the incident and reflected fronts. Calculations of the pressure drops behind the shock fronts agree with experimental data in this case.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 26–33, September–October, 1973.The authors thank S. A. Khristianovich for consideration of the work and advice.     

Flow structure in a flat vortex chamber

We investigate a flow in a flat vortex chamber in which the distance between the end walls is smaller than the radius of the chamber. The study was mainly performed by optical methods: a Töpler device was employed, with the Foucault knife replaced by a diaphragm. It is shown that the flow in the chamber has a complicated spatial structure. In addition to the basic helical flow, an intense “transverse” rotation of the type of Taylor-Görtler vortices occurs. In contrast to previously studied flows, where these vortices were observed near a concave surface, in the motion considered transverse vortices occur in the entire working volume of the chamber. In this case, four parallel vortex filaments are formed. The high intensity of the vortices has allowed one to visualize them by the Töpler method and by “tinting” the flow by highly disperse particles. Quantitative dependences of the dimensions of the vortex cells on the flow regime, i.e., on the pressure of gas deceleration, were obtained.     

An asymptotic method for studying nonequilibrium systems

The following is a well-known problem of statistical physics: can a dynamic system of oscillators with nonlinear coupling be described approximately by statistical laws? This problem was studied for the first time by Fermi, Ulam, and Pasta [1] for the following system of equations describing coupled oscillators:

$$\begin{gathered} x^{..} _i = x_{i + 1} - 2x_i + x_{i - 1} + \alpha [(x_{i + 1} - x_i )^2 ] - (x_i ..x_{i - 1} )^2 ], \hfill \\ (i = 1,...,N;\alpha< 1).(0.1) \hfill \\ \end{gathered} $$