HF Waves Research Articles

Modeling E‐Region Artificial Periodic Inhomogeneity

AbstractArtificial periodic inhomogeneity or API experiments were conducted at the HAARP facility in Gakona, Alaska, in October 2022. The experiments concentrated on measuring ionospheric irregularities induced in the E‐region. The irregularities exhibited characteristics regarding their occurrence altitudes, rise and fall times, and Doppler shifts comparable to results from experiments conducted previously at HAARP and elsewhere. The irregularities also occurred in discrete altitude bands. Seeking to quantify these results, we constructed a simple, one‐dimensional fluid model which includes the effects of HF wave heating (direct and indirect) together with electron and ion cooling and thermal conduction, ion production, loss, and diffusion. Critically, the model includes a potential solver and can represent the ambipolar electric field. The model produced API irregularities in three distinct altitude bands which decayed according to the ambipolar diffusion rate.

Состояние вегетативной адаптации у пациентов с хроническим описторхозом

Aim: to assess autonomic regulation by analyzing heart rate variability in patients with chronic opisthorchiasis (CO). Patients and Methods: the study involved 31 patients with CO and 30 healthy volunteers (control group). Clinical parameters of the biliary system and autonomic nervous system were as-sessed in all participants. The Baevsky method of mathematical analysis of heart rhythm was used to study autonomic nervous system functions. Parameters characterizing the activity of various branches of the autonomic nervous system were calculated. The results obtained were processed using the original CORVEG program. Results and Discussion: frequency analysis in patients with CO revealed significant deviations of SD, AMo, and CV in the supine position and EV, MSD, Mo, and AMo in active orthostatic position, thereby illustrating an increase in the effect of the sympathetic branch and a reduction in the effect of the parasympathetic branch of the autonomic nervous system (a decrease in heart rate variability in the CO group). Values of the HF and LF waves were significantly higher in the CO group (p<0.05) in the supine position, thereby illustrating an impairment of humoral regulation and a decrease in the activity of intersystem regulation. Changes in the parameters of heart rate regulation significantly (p<0.05) showed increased sympathetic regulation at rest and orthostasis in CO. Their autonomic homeostasis shifted toward the sympathetic nervous system both at rest and during exercise. Moreover, in some patients (31%), central dysregulation was detected. Autonomic tone and autonomic reactivity in CO were also significantly (p<0.05) shifted toward sympathicotonia and hypersympathicotonia. Conclusion: in CO, deviations at all levels of autonomic regulation were detected, which manifested as increased activity of the sympathetic branch and decreased parasympathetic regulation, vasoreflex and baroreflex mechanisms, and humoral regulation. KEYWORDS: chronic opisthorchiasis, Opisthorchis felineus, autonomic nervous system, parasympathetic nervous system, sympathetic nervous system, heart rate variability, cardiointervalography. FOR CITATION: Plotnikova E.Yu., Karbysheva N.V., Nikonorova M.A., Beskhlebova O.V., Ivanova M.E., Sinkov M.A., Kanner E.V., Kanner I.D. Vegetative adaptation in patients with chronic opisthorchiasis. Russian Medical Inquiry. 2023;7(11):725–732 (in Russ.). DOI: 10.32364/2587- 6821-2023-7-11-4.

Effects of the beta-stimulating training in recovery of adaptive reserves in athletes of different sports

To identify effects of the beta-stimulating training in recovery of adaptive reserves in athletes of different sports. The study included young male athletes aged 18-22 years (n=1020), distributed according to the type of sports: group 1 - cyclic sports (n=387); group 2 - speed-strength sports (n=255); group 3 - single combat (n=31); group 4 - team sports (n=173); group 5 - complex-coordination sports (n=174). The main objective of the beta-stimulating training was to select a strategy to raise the beta rhythm level while muscles were relaxed. For each group, we identified training efficiency periods according to the lowest value of the attention index (θ/β, c.u.), then we examined distribution of brain rhythms (α, %; β, %; θ, %) according to EEG. The level of adaptive reserves was identified according to the heart rate variability (HRV) spectral analysis («VNS-Spektr», Neurosoft, Ivanovo). We identified following periods of the beta-stimulating training efficiency according to the attention index (θ/β, c.u.): group 1 - 10th session (game variant); group 2 - 5th session (graphic and game variants); group 3 - 1st and 10th sessions (game variant), 5th session (graphic variant); group 4 (game variant) - 1st, 5th and 10th sessions; group 5 (game variant) - 5th and 10th sessions. The efficiency periods in the observed groups were accompanied by the following distribution of rhythms in the EEG structure: β-rhythm - 45-60%; θ-rhythm - 20-35%, α-rhythm - 19-25%. During these periods, wave structure of the heart rhythm also changed: the activity of VLF waves increased (%); the proportion of HF waves decreased in the range of 23.3-31.59% in the groups 1, 2 and 3; the share of HF waves increased in the range of 32.3-39.8% in the group 4 at the 1st session and in the group 5 at the 10th session. The values of total power (TP, ms2) reduce at the 10th session in the groups 1, 3 and 4 and at the 5th session in the group 5. The vagosympathetic balance coefficient (LF/HF, c.u.) in the studied groups corresponds to the range of normal values; the values increased in the group 2 at the 5th session, in the groups 3 and 4 - at the 5th and 10th sessions, in the 5th group - at the 5th session. The index decreased in the groups 3 and 4 at the 1st session. The index was stable in the groups 1 and 5 at the 10th session of the training. Periods of the beta-stimulating training efficiency associated with the improvement of attention according to the lowest values of θ/β (c.u.) are accompanied by changes in the modulation of the structure of brain rhythms and the wave structure of heart rate variability, optimizing the psychophysiological state of athletes depending on the type of sport, the number of sessions completed and the session variants chosen.

Heart rate variability in cross-country skiers with different level of maximum oxygen consumption

AIM: This research aimed to study heart rate variability (HRV) in cross-country skiers with different levels of maximal oxygen consumption (VO2max).
 MATERIALS AND METHODS: HRV analysis was carried out using the Ecosan-2007 (Medical Computer Systems, Russia) complex in 52 cross-country skiers from the Komi Republic team (candidates for master of sports and master of sports of Russia). The Oxycon Pro ergospirometric system (Erich Jaeger, Germany) was used to calculate VO2max. To identify the HRV patterns in individuals with different levels of VO2max, volunteers were divided into two groups: with VO2max up to 4400 ml/min (n=27) and over 4400 ml/min (n=25). The MannWhitney U-test was used to ascertain whether the differences between groups were statistically significant. A Spearman correlation test was used to analyze the relationship between the VO2max and HRV.
 RESULTS: Athletes with different levels of VO2max showed significant differences in several HRV indicators as follows: absolute values of LF and VLF waves, the relative value of HF waves, LF/HF, and IC indices. Correlation analysis indicated the presence of a significant negative correlation between the absolute values of VO2max and MxDMn, MxRMn, LF/HF, IC, power of LF, and LF%. VLF waves. Furthermore, a positive correlation was observed between VO2max and HF%. The relative values of the VO2max/kg showed a significant negative correlation with MxRMn, TP, LF, VLF, LF/HF, and IC; and positive with HF%.
 CONCLUSION: In cross-country skiers, a significant correlation was identified between VO2max and HRV parameters. Compared to Athletes with lower VO2max, those with higher VO2max had a more efficient mode of heart rate regulation.

Features of the Effects of Serotonin and Dopamine on Changes in Heart Rate Variability in Non-Linear Rats under Conditions of Acute Stress.

Changes in indicators of heart rate variability after a single injection of serotonin (200 μg/kg) or dopamine (60 μg/kg) were analyzed in male non-linear rats at rest and during acute stress. At rest, administration of serotonin is accompanied by an increase in the role of the vasomotor center in the formation of heart rate variability; administration of dopamine causes a moderate weakening of HF waves. In both cases, no sharp shifts in the sympathetic-parasympathetic relations are seen, but a more variable rhythm is formed under the effect of serotonin. Under conditions of acute stress, the increase in HR after injection of serotonin is half as much as in the control series, a trend towards weakening of the power of VLF- and even LF-waves is observed. After dopamine injection, a sharp increase in HR and strain index and a decrease in the power of waves of all spectral ranges and the centralization index are observed at the beginning of stress, but by the 30th min, tachycardia becomes moderate, the powers of all waves are restored; HF waves dominate in the spectrum, but potentiation of VLF- and LF-waves and growth of the centralization index are not observed in contrast to the control series. In general, serotonin and dopamine exhibit stress-limiting properties and moderate activation of sympathoadrenal influences and the suprasegmental level of regulation under stress conditions, but after dopamine injection we observed increased reactivity at the beginning of stress and less variable HR. Therefore, serotonin has more pronounced stress limiting effects, which can be revealed by heart rate variability analysis.

Joule heating in the mid-latitude ionosphere by high power HF radio waves

We present an estimation of the heating rate due to Joule heating in the F region of the ionosphere as a result of its interaction with high-power HF O-mode radio waves transmitted by a ground-based antenna. We refer to experiments conducted at Platteville, Colorado in the 70’s, i.e., at a mid-latitude ionosphere, as the ionospheric conditions and experimental facility parameters are well known. Analytical expressions for the electric field of the HF wave, ionospheric electric conductivity and heating rate are inserted into the calculations. The subsequent spatial and temporal changes in electron and ion temperatures were estimated. The results show that the electron temperatures demonstrate an increase of 115% above their unperturbed values and the ion temperatures demonstrate a corresponding increase of 13%.

Real-Time Phase-Contrast MRI to Monitor Cervical Blood and Cerebrospinal Fluid Flow Beat-by-Beat Variability.

Beat-by-beat variability (BBV) rhythms are observed in both cardiovascular (CV) and intracranial (IC) compartments, yet interactions between the two are not fully understood. Real-Time Phase-Contrast (RT-PC) MRI sequence was acquired for 30 healthy volunteers at 1st cervical level on a 3T scanner. The arterial (AF), venous (VF), and cerebrospinal fluid (CSF) flow (CSFF) were computed as velocity integrals over the internal carotid artery, internal jugular vein, and CSF. AF, VF, and CSFF signals were segmented in inspiration and expiration beats, to assess the respiration influence. Systolic and diastolic BBV, and heart period series underwent autoregressive power spectral density analysis, to evaluate the low-frequency (LF, Mayer waves) and high frequency (HF, respiratory waves) components. The diastolic VF had the largest BBV. LF power was high in the diastolic AF series, poor in all CSFF series. The pulse wave analyses revealed higher mean amplitude during inspiration. Findings suggests a possible role of LF modulation of IC resistances and propagation of HF waves from VF to AF and CCSF. PC-RT-MRI could provide new insight into the interaction between CV and IC regulation and pave the way for a detailed analysis of the cerebrovascular effects of varied respiration patterns due to exercise and rehabilitation.

Wave Height and Wave Period Measurements Using Small-Aperture HF Radar

A small-aperture receiving array occupying a small area provides convenience for the layout of HF radars. However, this kind of antennas has a wide beam, which adversely affects wave measurements. To solve this problem, a method for extracting wave parameters from wide-beam radar echoes, that models current variations across the beam, is proposed in this article. The nondirectional wave spectrum is extracted from the echoes of a small-aperture HF radar and wave parameters such as the significant wave height, the peak and mean wave period are then calculated from it. Simulation is carried out to assess the performance of the method for different current velocities, radar frequencies and wind conditions. The proposed method is then applied to a 9-day data set collected by an MHF-C radar for further validation via comparisons between the radar-estimated and the buoy-measured wave parameters. Some factors that may affect the performance of wave height measurements are analyzed, such as the signal-to-noise ratio and radial current velocity. The correlation coefficient (CC) between the radar-estimated and the buoy-measured significant wave height is 0.90, and the root mean square difference (RMSD) is 0.51 m. For the mean wave period, the CC is 0.61 and the RMSD is 0.67 s. The results demonstrate that the significant wave height and the mean wave period extracted by the proposed method are consistent with the buoy-measured values and the proposed method can overcome the broadening influence of the Doppler spectrum caused by ocean currents.

Explore the Echo Characteristics of HF Radar in Artificial Disturbance Ionosphere Using Ray‐Tracing Technology

AbstractArtificial ionospheric hole created by the release of neutral gases (such as sulfur hexafluoride) has a significant impact on the propagation of radio waves. Based on the ray‐tracing method, the propagation patterns of HF radio waves in the ionospheric hole and the characteristics of its echoes are discussed in this paper. The results show that the HF waves will be deflected and bended while passing through the ionospheric hole, thus changing its original path. The sounding frequency, elevation angle, position of transmitter and receiver, and the dynamic variation of the hole all affect the reception of echoes. Generally, when the frequency is low, the echoes received on the ground mainly come from rays with low‐elevation angles, and the multi‐hop rays are more likely to occur. While with a high frequency, the received echoes are mainly contributed by high‐elevation rays. It is not conducive to the reception of the echoes if the transmitter and receiver is too far away from the hole. Single‐peak, double‐peak and multi‐peak echo signals can be found in the group path‐amplitude diagram, and the maximum group path difference can reflect the size of the ionospheric hole to some extent. Due to the dynamic evolution of the hole, the propagation of HF waves and received echoes also changes over time. The group path‐time diagrams show that the come‐back echoes mainly appear in the period of 20–100 s after release. The results of this paper have a guiding significance for the diagnosis and application of active experiments.

Multiple Phase Screen Modeling of HF Wave Field Scintillations Caused by the Irregularities in Inhomogeneous Media

AbstractHigh frequency (HF) radio waves propagating through regions of ionospheric plasma irregularities exhibit random fluctuations in both amplitude and phase referred to as scintillations, which heavily influences the detection performance of HF sky‐wave radar and hybrid sky‐surface wave radar systems. In this paper, a numerical multiple phase screen model for HF sky‐wave propagation is developed, which can simulate the HF wave field scintillations caused by the irregularities in inhomogeneous media. In this model, the random phase changes due to irregularities and the diffraction effect due to phase mixing are considered separately and computed sequentially, where the phase change is numerically calculated using a geometric optical phase delay to allow for the consideration of horizontal electron density gradients. Utilizing the proposed model, we first simulate the observations of scintillation from the direct wave of the HF hybrid sky‐surface wave radar. The statistics of simulation and measured data, including power spectrum and scintillation indices on amplitude and phase, are considered to verify the effectiveness of the proposed model. Then, we analyze the effects of traveling ionospheric disturbances (TIDs) on the intensity of scintillation. The simulation indicates that the horizontal electron density gradients due to TIDs cause the fluctuation of the amplitude scintillation index .

Peculiarities of Heart Rate Variability Changes in Random-Bred Male Rats during Transition into Anesthetic Sleep under Stimulation of Central Neurotransmitter Systems.

General anesthesia with Nembutal (40 mg/kg) dramatically decreased the power of all waves of HRV spectrum in rats, especially in LF and VLF frequency bands, but the HR and respiration rate were little changed. At this, individual spectral peaks in HF range were observed at the same frequencies (1.3-1.5 Hz), which are characteristic of the wakeful state. Preliminary stimulation of noradrenergic system with maprotiline (10 mg/kg) increased the power of HF waves and elevated the respiratory rate in narcotized rats in comparison with the control values, although it did not shift the spectral peak at 1.5 Hz in frequency axis. Preliminary stimulation of cholinergic system with galantamine (2 mg/kg) somewhat decreased the power of HF waves and respiratory rate in narcotized rats (in comparison with the control values); additionally, it shifted HF peak to 1.1-1.4 Hz. Activation of serotonergic system with 5-hydroxytryptophan (50 mg/kg) and fluoxetine (3 mg/kg) decreased the HR, the power of HF waves, and respiratory rate in narcotized rats. It also shifted the spectral peak of HF waves to 0.9-0.95 Hz. Preliminary stimulation of dopaminergic system with L-DOPA (20 ml/kg) and amantadine (20 ml/kg) increased the power of VLF waves in narcotized rats in comparison with the control values. Numerous peaks appeared in HF (1.1-1.2 Hz) and VLF frequency bands. Generally, preliminary stimulation of serotonergic or dopaminergic systems markedly affects the neural activity under following general anesthesia: first aggravates the effect of anesthesia on vital centers in CNS, whereas second weakens the effect of anesthesia at the suprasegmental level of neural control.

GLONASS Observation of Artificial Field‐Aligned Plasma Irregularities Near Magnetic Zenith During EISCAT HF Experiment

AbstractWe report on simultaneous observation of artificial plasma density irregularities near the magnetic zenith (MZ) by incoherent scatter radar and GNSS satellite in the high latitude. During an EISCAT (European Incoherent Scatter Scientific Association) HF heating experiment, a GLONASS satellite signal intersected the disturbed ionospheric volume along the local magnetic field lines. The satellite signal amplitude and phase were simultaneously perturbed when the electron temperature increased in the F region through O‐mode HF waves. The field‐aligned irregularities (FAIs) and associated density perturbations are most significantly found in the MZ direction. The growth of FAI reached the saturation level in 30 s while large‐scale electron density perturbation on the order of 0.1 TECU developed in a few minutes. The observed density perturbations agree well with recent numerical studies of FAI generation due to the thermal self‐focusing process.

Contribution estimation of singular points in solving problems of radiation of HF VHF wire antennas arbitrarily located above the earth

The radiation solving the problem features of the wire antennas placed above the earth are considered. Based on the method of integral equations, the singular points contribution in solving radiation problems of the HF VHF wire antennas arbitrarily located above the earth is researched. The contribution of singular points is estimated depending on the frequency and parameters of the earth. It is shown that in the HF and VHF waves, their contribution of singular points is significant. The radiation solving the problem features of the wire antennas placed above the earth are considered. The value of elements of the Green’s tensor function is usually expressed in the Sommerfeld’s integrals form. The aim of this work is to estimate the contribution of singular points to the value of Sommerfeld’s integrals. Based on the method of integral equations, the singular points contribution in solving radiation problems of the HF VHF wire antennas arbitrarily located above the earth is researched. The contribution of singular points is estimated depending on the frequency and parameters of the earth. It is shown that in the HF and VHF waves, their contribution of singular points is significant.

INDICATORS OF HEART RATE VARIABILITY AT REST AND DURING AN ORTHOSTATIC CHALLENGE AT DIFFERENT RANGES OF MxDMn VALUE AND THEIR CHANGE IN TRACK AND FIELD ATHLETES IN THE TRAINING PROCESS

The aim of the study is to develop the standards of HRV indexes at rest and during an orthostatic challenge, taking into account different ranges of variability of cardiac intervals (MxDMn) of track and field athletes. The other purpose is to identify the features of changes in the standards in the training process in cases of malfunctions of cardioregulatory systems, sinus node functioning and recovery process, overtraining, and decrease in athletic performance. The authors used the results of individual dynamic express-tests of heart rate variability (HRV) in track and field athletes belonging to different specific training orientations to achieve the goals of the study. Research Methods and Organization. We carried out 1740 dynamic HRV measurements at rest and during an orthostatic challenge. The studies involved 56 track and field athletes (sprinters, middle distance runners and stayers) aged 18 to 29 years, belonging to the 1st adult category, Candidates Master of Sports and Masters of Sports, in different periods of the training process. We carried out HRV measurements in the laboratory of functional research methods of the Institute of physical culture and sports at Udmurt State University, as well as at training camps in the middle mountains (Kyrgyzstan, Kislovodsk) and on the plain (Elabuga). We examined the test subjects at rest in the morning after the previous training day, using the VARICARD 2.51 device and the ISCIM6 and VARICARD MP programs (Ryazan). We recorded cardio intervals of athletes for 5 minutes in lying position and for 6 minutes in standing position. We applied HRV measurements to one or four athletes simultaneously using the ISCIM6 and VARICARD MP programs. Research results. We assigned special emphasis to the assessment of changes in the variational range of cardiointervals (MxDMn) reflecting the state of cardiac regulation and the sinus node functioning during dynamic HRV studies in the training process of each runner. We identified seven MxDMn variation ranges from <150ms to >650ms. We revealed that each MxDMn variation range corresponds to a certain prevailing type of regulation. We demonstrated that frequent shifts of the MxDMn ranges from one level to another in the training process of runners indicate instability of cardiac regulation. We elaborated standards for the variational range of cardiointervals (MxDMn), taking into account the predominance of the HF and LF power in the HRV power spectrum for runners with different specific training orientations. We found that respiratory (HF) or vasomotor waves (LF) could prevail within the same MxDMn variation ranges, which points to a different autonomic balance. We revealed that at rest, the variational range of cardiointervals (MxDMn) depends more on the state of cardiac regulation and the sinus node functioning and less on the specifics of running. We often detected paradoxical reactions to an orthostatic challenge at low or extremely high MxDMn values in the overtrained runners. We determined that runners of any specific training orientation could increase their fitness, adaptive and reserve capabilities only in the context of the optimal regulation state, stable favorable ranges of MxDMn values, and the absence of paradoxical reactions to an orthostatic challenge. The paper contains tables with standard HRV indicators for different MxDMn variation ranges and consideration of the predominance of HF and LF waves at rest and during an orthostatic challenge, as well as examples of the results of HRV analysis at rest and during an orthostatic challenge in runners with different MxDMn variation ranges in the training process. Conclusion. The research demonstrated that the use of the HRV analysis method at rest and during an orthostatic challenge, taking into account the standards of MxDMn values in the training process of track and field athletes, is aimed at obtaining the necessary information about the stability of autonomic balance, autonomic reactivity and body reserves that ensure optimal adaptation and recovery processes.

Features of autonomous regulation in young subjects with increased vestibular analyzer sensitivity

Introduction: Each person's body have adaptation during the load due to different changes in the cardiovascular system. One of the first systems that responds to any factors and is actively involved in the processes of adaptation is the autonomic nervous system. It is known that as a result of excitement of the vestibular analyzer kinetosis develops - "motion sickness", which is accompanied by nausea, dizziness, unsteadiness of gait, general weakness. In this regard, assessment of the functional state of the body and its adaptive reserves continues to be one of the most important problems of modern physiology and medicine.The purpose of the study was to evaluate the features of autonomous regulation in subjects with increased sensitivity of the vestibular analyzer.Materials and methods: 60 people between the ages of 18-19 were examined. Vestibular sensitivity was determined with a help of questionnaire. The state of the autonomic nervous system was determined by analyzing heart rate variability using a 5-minute ECG registration technique. The registration and recording was performed by the «PolySpectr +» computer program.Results and discussion: Based on the questionnaire, the students were divided into 2 groups: with proper and with increased vestibular sensitivity. In students with proper vestibular sensitivity, the LF / HF ratio of 1.06 indicates a balanced type of autonomic heart rate modulation. The analysis of spectral indices in subjects with increased vestibular sensitivity showed a lower overall power of the spectrum, which indicates less functional reserves of the organism. We set much higher HF waves, which indicates an increase in the activity of the parasympathetic system. This is also indicated by the LF / HF ratio of 0.59. When considering the rhythmograms of subjects with increased vestibular sensitivity, 64% of 1-st grade rhythmograms, 20% of 2-nd grade rhythmograms and 16.6% of 3-rd grade rhythmograms were registered. When assessing rhythmograms of the 3-rd class, it can be concluded that the level of functional reserves of subjects with increased sensitivity of the vestibular analyzer can be reduced, which may lead to a decrease in the adaptive capacity of these subjects.Conclusions: In subjects with increased vestibular sensitivity, the parasympathetic autonomic nervous system makes the greatest contribution to the regulation of cardiac rhythm.

A Ray Tracing Simulation of HF Ionospheric Radar Performance at African Equatorial Latitudes

AbstractHigh‐frequency (HF) coherent radars are widely applied for studying electrodynamic processes in the Earth's upper atmosphere and ionosphere. Super Dual Auroral Radar Network (SuperDARN) is an international network of such radars located at high‐ and middle‐latitude regions in the Northern and Southern Hemispheres. A major criterion of the HF coherent radar technique entails that the HF waves propagate orthogonal to the geomagnetic field lines (aspect angle 1°) in the ionospheric irregularity region from where backscatter originates. In this paper we present an HF ray tracing simulation of the performance of three proposed equatorial HF radar systems for the African equatorial sector. We use a number of realistic average ionospheres deduced from the International Reference Ionosphere (IRI) 2012 model and magnetic field geometries from the International Geomagnetic Reference Field (IGRF) to determine likely propagation paths and orthogonality conditions for such radar systems. The east‐west azimuth ( 25° range) has a significant likelihood of achieving a SuperDARN‐type backscatter in the African equatorial sector, mainly due to the prevailing magnetic field geometry. This analysis provides a feasibility study for developing a SuperDARN‐like radar for studying the equatorial ionosphere over the African longitude sector, for example, in determining the technical radar characteristics such as preferable operating frequencies, antenna boresight orientation, and azimuth coverage and provides a simulation of the expected localization of radar backscatter as a function of radar location and beam direction, as well as the time of day, season, and sunspot number.

Experimental Observation and Analysis of Ionosphere Echoes in the Mid-Latitude Region of China Using High-Frequency Surface Wave Radar and Ionosonde

Ionospheric clutter is a major factor affecting the performance of high-frequency surface wave radar (HFSWR). Previous studies have been mainly focused on the development of ionospheric clutter suppression methods involving delicate signal processing techniques or additional antennas. However, ionospheric clutter originates from the interaction between HF waves and the ionosphere, thus it contains the characteristics of the latter. Therefore, ionospheric clutter can be analyzed to obtain the parameters of the reflecting ionosphere, expanding the value of HFSWR. This article presents the preliminary coordinated observation and analysis results of the characteristics of the ionosphere at mid-latitudes of China using both HFSWR and ionosonde. The results demonstrate the existence of an oblique skywave propagation path (0.5 jump, 1 jump, etc.) in addition to the vertical reflection path and ionosphere-ocean mixed path. HFSWR beams were also found split into an O-trace and an X-trace after entering the ionosphere. Furthermore, range-folded ionospheric echoes are related to the short-term thickening of the F2-layer, showing strong fluctuation in the range-Doppler spectrum of HFSWR. These observed characteristics of ionospheric echoes are useful for the development of an efficient ionospheric clutter suppression algorithm for HFSWR and further investigation of the ionospheric mechanisms at mid-latitudes.

Relationship Between the Polar Electrojet Dynamics and the Amplitude of ELF/VLF Signal from the Ionospheric Source in the Modulated Ionospheric Heating Experiment

We consider the results of the experiment on the polar ionosphere heating by a high-power modulated HF wave conducted by the AARI at the EISCAT/heating facility in October 2016. The data on joint processing of the values of the equivalent polar electrojet current above the heated ionosphere region retrieved by the IMAGE network of ground-based stations and the amplitudes of a signal of the horizontal component of the magnetic field from an ionospheric source at the modulation frequency recorded in the PGI network of high-latitude stations are presented. The events with a strong positive correlation between the magnetic field amplitude variations and the polar electrojet current variations are considered. It is shown that if the direction of the current changes from eastward to northward, correlation between the current variations and magnetic field variations almost disappears at a modulation frequency of 3017 Hz. Temporal and spatial variations of the coefficient of linear regression of the amplitude of the horizontal magnetic-field component with respect to the electrojet current are analyzed. In the transition from day to night, which is accompanied by the electrojet current decrease, the regression slope increases, and it decreases with increasing distance between the heater and the observation point.

Polarization analysis of ELF/VLF waves generated by beating of two HF waves in the polar ionosphere

Modulated high frequency heating of the polar ionosphere in the presence of a polar electrojet current (PEJ) can generate extremely/very low frequency (ELF/VLF, 3 Hz–30 kHz). In order to overcome the dependence of the radiation intensity on the variable PEJ, researchers have focused on electrojet-independent approaches. One potential method is so-called “beat-wave” (BW) ELF/VLF generation invoking nonlinearity of the F-region ionospheric plasma, but this F-region source mechanism remains controversial. We perform polarization analysis of BW generated ELF/VLF waves using EISCAT heating facility near Tromsø. The results show that ELF/VLF waves can be decomposed into right- (R) and -left (L) handed circularly polarized waves with comparable strengths, and the polarization ellipse tends to be parallel to the well-known dominant background electric field, which is fully consistent with the recognized features of ELF/VLF waves generated by PEJ modulation. Hence, the results demonstrate that the BW generated current is located in the D/E region, and not the F region.

EFFECT OF HEXAMETONIUM, ATROPINE, ANAPRILINE AND THEIR COMBINATION ON THE HEART RATE VARIABILITY IN RATS

In this work, we set out to study changes in the heart rate frequency (HRF) and wave characteristics of the heart rate variability (HRV) of nonlinear male rats in pharmacological tests under a single administration of hexametonium (HM, 7 mg/kg), atropine (AT, 1 mg/kg), anapriline (ANP, 2 mg/kg), as well as under a sequential administration of HM and atropine (anapriline) in the same doses. A spectral analysis of the HRV was carried out across the following ranges: HF (0.9–3.5 Hz), LF (0.32–0.9 Hz), VLF (0.15–0.32 Hz). HM administration increased the HRF by 12–16%, simultaneously reducing the power of VLF, LF and HF by 85% (p<0.001), 60% (p<0.05) and almost 40%, respectively. This indicates the degree of participation of H-cholinergic transmission in the formation of HRV waves at the level of vegetative nodes. The blockade of M-cholinoreceptors (M-ChR) with AT sharply increased the HRF (by 30%, p<0.001) and reduced the wave power of the HRV spectrum by 95–98% (p<0.001), which confi rms the leading role of the cardiomyocyte M-ChR system in the formation of all the waves of the HRV spectrum. The injection of the β-AR blocker lowered the HRF by 25% (p<0.001) and the HRV wave power, in particular VLF, by 70% (p<0.01). A preliminary blockade of the vegetative nodes by HM somewhat weakened a drop in the power of HRV waves after AT administration, leveled the reduction of the HRF and potentiated the increase in the power of HF waves after ANP administration. The results indicate that the wave power across the entire range of the HRV spectrum is greatly determined (by 95–98%) by regulatory infl uences through the M-cholinoreceptors of the cardiomyocyte system, as well as by their interaction with infl uences through the myocardial adrenoreceptors and the ganglionic level of the autonomic nervous system. Vegetative nodes contribute to the formation of all HRV waves, in particular VLF and LF, change the degree and character of HRV changes when affecting the myocardial M-ChR and AR, which should be taken into account in experimental practice.