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A S Kovalev

Publications and source records attributed to A S Kovalev.

11 recordsLinked to original sources
PubMed2002

Solitary Rayleigh waves in the presence of surface nonlinearities.

The propagation of Rayleigh waves is investigated in a solid substrate of linear material covered by a film consisting of a material with large nonlinear elastic moduli. For this system, a nonlinear evolution equation is derived that may be regarded as a special case in a wider class of evolution equations with a specific type of nonlocal nonlinearity. Periodic pulse train solutions are computed. For a certain member of the class of nonlinear evolution equations, several families of solitary wave solutions and their associated periodic stationary wave solutions are derived analytically.

Journal Article↗
PubMed1999

Bifurcation picture for gap solitons in nonlinear modulated systems.

We investigate the problem of nonlinear wave propagation in periodic media. Four different classes of periodic nonlinear media are taken into consideration: a nonlinear diatomic elastic chain, modulated nonlinear optical media, a diatomic easy-axis ferromagnetic chain, and an easy-plane antiferromagnet in an external magnetic field. The main result of our work is a qualitative analysis of all kinds of small amplitude soliton excitations with frequencies lying in the gap and near the gap of the linear wave spectrum. We also study the evolution of the system phase portrait and the bifurcation picture of the soliton solutions under changes of the medium parameters.

Journal Article↗
PubMedDate not supplied

[Control of effective doses in x-ray studies].

Developing the controlling techniques for dose loads in patients has led to the introduction of methods for evaluating the new dosimetric value an effective dose. When it is determined, regular refinement of calculating multiples causes errors as hundredths of a percent. Therefore, in addition to tabulated techniques of evaluating the effective dose and direct measurement of the dose absorbed per radiation area, one can determine midpoint exposure of an X-ray feeding device and use a translating program implemented in the Indor-C indicating device designed by the authors. In going from 60 kW to 120 kW, changes in the superficial dose by 15-50%, the absorbed dose by 10-45%, the 5-cm depth dose by 3-5 times can be neglected.

Adolescent↗
PubMedDate not supplied

[Device-aided determination of an effective dose in x-ray studies].

The paper proposes how to determine an effective radiation dose for patients undergone X-ray examinations, which includes the estimation of the size of a field while measuring the superficial dose and the assessment of an experiment protocol by taking into account the X-ray receiver used to measure exposure.

Adult↗
PubMedDate not supplied

[Meteoropathic reactions in patients with circulatory system diseases: their prevalence, the characteristics of their manifestation and their correction].

Presented in the paper are topical aspects of prevalence, specificities of manifestation, and correction of meteoropathologic reactions (MR) in disorders of the circulatory system. A total of 1260 patients were examined. Of these, 518 had hypertensive disease (HD), 198 were coronary (IHD) patients, 544 had HD concurrent with IHD. Based on the standardized questionnaire and results of clinical and instrumental studies meteorosensitivity was assessed, with meteorogramme having been taken into account. To correct MR aero- and balneoprocedures were used together with speleotherapy and physical training. High meteorologic factors sensitivity was ascertained in 67 percent of patients. MR frequency was found out to be related to overstrain, failure to stick to the daily time-table, bad habits, constitutional specificities, low physical activity. Depending on the features of manifestation three degrees of severity have come to be recognized in MR. A complex of measures designed to correct MR is submitted. The use of the above complex allowed the MR frequency to be reduced, their severity to be alleviated.

Cardiovascular Diseases↗