卷 61, 编号 5 (2018)

We perform a numerical simulation of evolution of the wind waves, which is based on solving the Euler equations for a two-dimensional potential flow and, therefore, allows for the nonlinear effects. Analysis of the obtained realizations of the surface profiles shows that the proposed direct numerical simulation allows one to reproduce the features of modulation of short surface waves. The model dependence, which describes the characteristic deviation of the spectral density from the dispersion curve on the frequency–wave number plane, is obtained. Comparison with the wave spectra measured under natural conditions is indicative of a qualitative agreement between the calculated and experimental results.

We develop the numerical method of moments for solving an integral equation that describes the distribution of the charge along a thin finite-length antenna wire in an anisotropic medium in the quasistatic approximation. It is shown that the method of moments can be used to calculate the electrodynamic characteristics of such an antenna under the conditions where the kernel of the integral equation has a singularity related to the resonance cone. The influence of the ratio between the elements of the dielectric permittivity tensor and the method of partitioning of the antenna surface on the calculation accuracy is analyzed. It is shown that the relative error of calculations of the antenna characteristics is a fairly small value of about 1% if the antenna wire is divided into ten segments.

The power dependence α(ν) ∝ ν^μ, where μ > 0 is the power exponent which is noninteger in the general case, is observed for amorphous polymers with a small absorption coefficient α in the low-frequency part of the terahertz range, which approximately corresponds to the frequencies ν from 0.1 to 2–3 THz. This dependence is fractal, which is due to the fractal structure of the polymer macromolecules. In this work, we find the power-law index at room temperature for the absorption coefficient of some amorphous polymers. This index is determined on the basis of the dynamics of transmission of a broadband picosecond terahertz pulse through the polymer sample, i.e., using the method of the pulse terahertz spectroscopy in the time-domain representation.