Mikhail S. Mikhailov

This paper shows the importance of such a parameter as the linearity of the modulation characteristic of the generator of the probing signal of linear-frequency modulation (LFM) of the georadar. The error in determining the depth of the desired underground object, arising due to the nonlinearity of this characteristic, may turn out to be unacceptably large. The paper considers a technique for calculating the error and gives an example of calculating the nonlinearity of the modulation characteristic and the maximum allowable frequency deviation from the linear law in the frequency tuning range of a voltage controlled oscillator (VCO)

Варианты хирургического лечения пациентов с сочетанной патологией коронарных и каротидных артерий

The draft clinical guidelines were developed by the team of the scientific group for the treatment of wounds and wound process of the Reaviz Medical University, taking into account modern scientific data, practical experience and original research. The data on the formulation of the diagnosis in diabetic foot syndrome, the existing classification of ulcers and wounds, the survey plan, basic and additional therapy, local treatment of ulcers and wounds are presented.

The paper proposes to calculate the electromagnetic field along a path with simple geometric dielectric obstacles based on the parabolic equation method. The forest environment model is defined as discrete volumetric diffusers. The article compares statistical samples with the location of trees in space according to different distribution laws. For statistical samples with the same tree parameters at different frequencies, the mathematical expectation, variance and fluctuations of the values of the power flux density were calculated. Laborious calculations were performed using parallelization technology on GPUs. It was revealed that various patterns of trees in space do not strongly affect the resulting field. And the calculation of the electromagnetic field on the GPU is four or more times faster than on the central processor. The proposed forest environment model allows much more accurate calculation of the field near the forest border.

When researching the mechanisms of propagation of radio waves inside the forest, there are two main approaches. The first is a mathematical description of the forest as a continuum or a system of layers with averaged dielectric permittivity, the second is the representation of a forest in the form of randomly located individual trees as discrete diffusers. The first approach gives adequate results in the VHF range, when the forest is sufficiently dense, and its structural elements are less than the length of the electromagnetic wave. The second is convenient to use at higher frequencies, when the individual elements of the tree, the diameter of the trunks, branches, and leaves are commensurate with the wavelength, as well as in a rare forest, with a large distance between the trees, when it is difficult to average out. The article compares the results of the calculation of the attenuation of the electromagnetic field using both approaches, gives the interpretation of the resulting physical mechanisms of radio wave propagation.

For the practical application of methods for assessing the propagation of radio waves in a wide range of tasks, an integrated accounting of all environmental parameters is necessary. The main influencing factors are terrain, forest vegetation and urban development. With the existing variety of approaches to the analysis and calculation of the electromagnetic field, one has to choose universal methods that provide a compromise between the convenience of specifying the model parameters and the calculation time. The article proposes to use the data of heights to build a realistic terrain with forest vegetation, an assessment of characteristic cases for small-scale relief, and demonstrates the results of calculating the models obtained using the parabolic equation method.

At the stage of tracking space debris objects, it becomes possible to obtain information on the approximate sizes of objects in terms of the average bistatic radar cross section values. We proposes a general method for estimating the size of space debris objects using the maximum likelihood function. The specific type of algorithm depends on the signal being probed.

The influence of forests and roughnesses on the propagation of radio waves is an actual topic of research stimulated by practical tasks related to the operation of various types of communication, radar, radio navigation, geodesy, and remote sensing of the earth's surface. The greatest interest at present is the study of the influence of the forest on the propagation of radio waves of the meter-centimeter range in the context of the seasonal nature of changes in attenuation and dispersion of waves in a particular geography of radio lines. Changes in the formulation of tasks within this problem are due to the development of new wavelength ranges and the emergence of qualitatively new radio engineering systems. Seasonal changes occurring in forest environments significantly affect the propagation of radio waves in forests due to changes in the dielectric constant parameter of the medium.