The numerical solution by a computer of the system of magnetohydrodynamics equations in the one-dimensional approximation serves as the basis for studying the non-linear stage of the instability due to local Joule-overheating of zones with large values of magnetic field gradients in the active regions of the Sun. We have demonstrated the formation of a system of current layers responsible for efficient transformation of magnetic energy into Joule heat and kinetic energy of the macroscopic motion. The specific features of quasi-stationary skinning of magnetic field with gravitation have been noted.
The potential models of the unipolar sunspot magnetic field are calculated on the basis of magnetographic measurements of the magnetic field made in the three spectral lines of different intensities, H c~, Ca 1 26103 and Fe 1 2 4808. The computed distributions of the magnetic field vector are compared with actual distributions observed at these three levels. It is shown that the electric current density in the spot reaches values up to 105 CGSE in the volume contained between formation depths of two pairs of lines, Fe 1 24808-Cai 2 6103 and Fe 1 24808 -Hc~. Therefore, the magnetic field of the spot deviates strongly from a potential configuration. To the contrary, at higher levels, in the semi-infinite volume restricted at the bottom by the hydrogen Hc~-line, the field appears to be quite close to a potential one.
We report on the experimental studies of the interaction of electromagnetic radiation with borosilicate crown glass K108 in the ultrawide frequency range from 0.002 to 1500 THz. Four different types of spectrometers are used to measure the reflectivity and/or transmittance spectra. Spectral dependences of the complex dielectric permittivity, refractive index and extinction coefficient are extracted from the measured spectra. The optical properties of the borosilicate crown glass in the microwave spectral range (2–23 GHz) are investigated for the first time. There are three bands of anomalous dispersion in the spectral curve of the real part of the dielectric permittivity. Each band of the anomalous dispersion corresponds to an absorption band, which is clearly seen in the spectrum of the imaginary part of the dielectric permittivity. The wide low-frequency absorption band is attributed to the Boson peak. Two other examined absorption bands represent sharp peaks and are associated with the Si–O–Si bending and Si–O stretching vibration modes. The results of the study can be useful in the development of optics based on the borosilicate crown glass.
In this work, the shielding properties of mesh structures with various cell sizes on a K108 glass substrate are studied. The transmission spectra of the samples were obtained in a frequency range from 1 GHz to 1620 THz. A comparison of the experimental transmission spectra with those obtained using several theoretical models, and a numerical calculation were carried out. The most optimal theoretical model used to describe the shielding properties of a mesh structure in the frequency range upper-bounded by a resonant frequency is the one-mode calculation model. Anti-reflection coatings were used to increase the transmission coefficient of the structures in the visible and near-IR spectral ranges. These mesh structures can be used to shield optoelectronic devices such as a video camera or a laser rangefinder from microwaves.
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