Vol 64, No 7 (2019)

Transmission spectra of a single crystal and artificial and natural ceramics of fluorite have been obtained in the transparency regions of the material in the THz and mid-IR ranges at room temperature. The reflectance spectra have been measured in the high-absorption region. The optical characteristics of the single crystal and optical ceramics differ only slightly.

The smallness parameter determining the possibility of application of the n-vicinity method for calculating the free energy of a spin system has been found. The types of spin systems for which approximation of the n-vicinity method is valid have been determined. It is shown that this method is adequate for studying the properties of spin systems, in which the effective number of nearest neighbors is more than \(\frac{{16}}{3}\).

The results of investigations of the flow behind cylindrical flow bodies in a flat-type hydrodynamic generator with the degree of flow overlap by the bodies S_t/S₀ = 10–80%, the numbers Re = (0.5–5) × 10⁵, the input pressure P_in = 0.2–1.0 MPa, and the output pressure P_out = 0.1–0.8 MPa. It was obtained that two different types of flow can be implemented behind the flow bodies with the same pressure drop: with a developed cavitation zone in which there is an extensive reduced-pressure region and without it but with the formation of vortex structures in the presence of the origins of cavitation bubbles in them. At a certain value of input to output pressures, which are constant for each value of the degree of flow overlap, at frequencies of 0.5–5 kHz powerful pressure peaks of the resonant type arise with an amplitude exceeding 2–2.5 times the highest value of the input pressure.

Flow past a yawed plate in the strong interaction mode is considered in the case when the pressure at its trailing edge varies along the transverse coordinate instead of being constant. It is shown that the form of the expansion of the stream functions in the vicinity of the leading edge significantly changes in the case of the appearance of large transverse gradients of induced pressure, and the third term of the expansions should be taken into account.

The extreme amplitude and frequency properties of oscillations of a thin (symmetric with respect to both axes) elongated flat body of elliptical form are studied in the neighborhood of an interface of stably stratified ideal liquids. The numerical and analytical solving procedures were developed for a self-consistent boundary value problem on an asymptotically longtime interval, which leads to their significant radiation decay and evolution in oscillation frequency. Similar characteristics found earlier by the authors for floats of other forms are compared, and the significant quantitative and qualitative differences are established.

Ice formation in an unsaturated soil is investigated in the presence of a pressure gradient and capillary forces. It is shown that the problem of determining the amount of ice formed is reduced in the linear approximation to solution of the inhomogeneous diffusion equation for water saturation. A self-similar solution is obtained for the problem in the one-dimensional approximation. It was found that the pressure drop on the cooling wall causes water flow to the crystallization front and leads to an increase in the volume of ice formed.