Bulletin of the Russian Academy of Sciences: Physics最新文献

It is known that the width modes in a nanometer-thick ferrite-based magnonic crystal can split into two types: fundamental and additional. The authors study the effect the ridge-to-groove width ratio has on the energy interaction between modes, their dispersion characteristics, and the formation of band gaps. Universal ridge/groove parameters are established for engineering thin magnonic crystals with desired properties.

Radiation from a relativistic gyrotron is studied experimentally in the range of 25–29 GHz at a megawatt output power level. Radiation is recorded in the ranges of 126.3 and 146.2 GHz at the fifth cyclotron harmonic. Based on estimates of the signal from the detector, the power of radiation at the fifth harmonic of the gyrofrequency is determined indirectly and found to be –20 dB, relative to the level at the first harmonic.

An analytical model was developed to describe optical diffraction by multiplexed chirped multilayer inhomogeneous diffraction structures formed in polymer-dispersed liquid crystals. Numerical simulation revealed patterns of broadening angular selectivity and reducing diffraction efficiency in the studied structures with a change in the grating period. Control of the type of angular selectivity and the level of diffraction efficiency by applying an external electric field, taking into account the polarization state of the readout radiation, was also demonstrated.

A theory of the interaction between a cnoidal electromagnetic wave and the electron subsystem of a Dirac crystal is constructed within the Floquet formalism. The Floquet spectrum of an electron in the high-frequency electric field of a cnoidal profile is calculated. The possibilities of dynamically induced band valleys and the formation of an energy gap at the Dirac point are investigated.

The authors study the effect a constant electric field has on the propagation of a monochromatic laser beam in an array of carbon nanotubes. Maxwell’s equations are used in an approximation of slowly varying amplitudes and phases to obtain an effective equation for the intensity of the field, which is solved numerically using the Besse scheme. The dependence of the beam’s shape on the magnitude of the constant field is studied as well.

It is theoretically shown that a layered structure possessing a reflection zero allows the optical computation of the second-order mixed derivative of the profile of a linearly polarized incident beam with respect to spatial coordinates. The derivative is computed at normal incidence in the cross-polarized component of the reflected beam. The presented design and numerical simulations results of a layered structure demonstrate that high-quality computation of the second-order mixed derivative is possible, and such a structure can be used for optical detection of corners and edges in an image.

The authors model a pulsed relativistic W-band gyrotron powered by a helical electron beam with an energy of 500 keV and a current of 200 A. A system of self-consistent averaged equations is used to determine the optimum geometry of the space of electron–wave interaction. Modes of generation with an output power of approximately 40 MW are obtained. Large-particle 3D modeling confirms the possibility of achieving single-mode generation with high efficiency.

The authors propose a way of diagnosing pulmonary hypertension through machine learning-based analysis of phonocardiograms. The technique offers a cost-effective and non-invasive solution that allows it to be used in primary healthcare. It is particularly valuable for regions with limited access to specialized clinics and highly qualified cardiologists.

The results of tomographic reconstruction of shear-wave velocity inhomogeneities in the lithosphere and upper asthenosphere near the Hawaiian archipelago are presented. The initial data used are surface-wave propagation times estimated from microseismic noise correlations recorded by a network of ocean bottom seismic stations. The obtained reconstruction results agree with the expected parameter distribution in the region of the Hawaiian hotspot.

A theoretical study is performed of a microwave receiver constructed using radio-photonic components to determine the angle of arrival of a spherical wave front reflected from a distant object. A way for arranging receivers on a linear antenna array is proposed to reduce the error in determining the angle of arrival of a signal with a spherical wave front.