| 1. |
- Nosikov, Igor A, et al.
(författare)
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Generalized Force Approach to Point-to-Point Ionospheric Ray Tracing and Systematic Identification of High and Low Rays
- 2020
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Ingår i: IEEE Transactions on Antennas and Propagation. - : IEEE. - 0018-926X .- 1558-2221. ; 68:1, s. 455-467
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Tidskriftsartikel (refereegranskat)abstract
- A variant of the direct optimization method for point-to-point ionospheric ray tracing is presented. The method is well suited for applications where the launch direction of the radio wave ray is unknown, but the position of the receiver is specified instead. Iterative transformation of a candidate path to the sought-for ray is guided by a generalized force, where the definition of the force depends on the ray type. For high rays, the negative gradient of the optical path functional is used. For low rays, the transformation of the gradient is applied, converting the neighborhood of a saddle point to that of a local minimum. Knowledge about the character of the rays is used to establish a scheme for systematic identification of all relevant rays between the given points, without the need to provide an accurate initial estimate for each solution. Various applications of the method to isotropic ionosphere demonstrate its ability to resolve complex ray configurations including 3-D propagation and multi-path propagation where rays are close in the launch direction. Results of the application of the method to ray tracing between Khabarovsk and Tory show good quantitative agreement with the measured oblique ionograms.
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| 2. |
- Nosikov, I A, et al.
(författare)
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Simulations of the Minimum Frequencies of Ionospheric Modes for Radio Communication Forecast
- 2021
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Ingår i: Radiophysics and Quantum Electronics. - : Springer. - 0033-8443 .- 1573-9120. ; 64:8-9, s. 605-617
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Tidskriftsartikel (refereegranskat)abstract
- We apply two promising approaches, namely, the shooting method based on global optimization and the generalized force method, to the problem of point-to-point ionospheric ray tracing where the ionospheric modes tend to the minimum frequency. In most cases, both methods are capable of finding all rays connecting the given transmitter and receiver. However, the generalized force approach is more stable in locating highly divergent high rays. Application of the methods to a long-range single-hop radio channel demonstrates their potential for expanding the simulated frequency range, refining the model ionograms in the ranges of the minimum frequency of reflection from ionospheric layers, and significantly improving the overall forecast of the lowest usable frequency. The results of numerical simulations were also compared with the experimental data. Joint application of the presented methods provides valuable means for solving applied problems of radio communication forecast.
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| 3. |
- Mikhailova, VB, et al.
(författare)
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Functional Analysis of SCN5A Genetic Variants Associated with Brugada Syndrome
- 2022
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Ingår i: Cardiology. - : S. Karger AG. - 1421-9751 .- 0008-6312. ; 147:1, s. 35-46
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Tidskriftsartikel (refereegranskat)abstract
- <b><i>Background:</i></b> Brugada syndrome (BrS) is a rare inherited cardiac arrhythmia with increased risk of sudden cardiac death. Mutations in gene <i>SCN5A</i>, which encodes the α-subunit of cardiac voltage-gated sodium channel Na<sub>V</sub>1.5, have been identified in over 20% of patients with BrS. However, only a small fraction of Na<sub>V</sub>1.5 variants, which are associated with BrS, are characterized in electrophysiological experiments. <b><i>Results:</i></b> Here we explored variants V281A and L1582P, which were found in our patients with BrS, and variants F543L and K1419E, which are reportedly associated with BrS. Heterologous expression of the variants in CHO-K1 cells and the Western blot analysis demonstrated that each variant appeared at the cell surface. We further measured sodium current in the whole-cell voltage clamp configuration. Variant F543L produced robust sodium current with a hyperpolarizing shift in the voltage dependence of steady-state fast inactivation. Other variants did not produce detectable sodium currents, indicating a complete loss of function. In a recent cryoEM structure of the hNa<sub>V</sub>1.5 channel, residues V281, K1419, and L1582 are in close contacts with residues whose mutations are reportedly associated with BrS, indicating functional importance of respective contacts. <b><i>Conclusions:</i></b> Our results support the notion that loss of function of Na<sub>V</sub>1.5 or decrease of the channel activity is involved in the pathogenesis of BrS.
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