HF Band Research Articles

Review on HF Band Vehicular Antenna with NVIS Communication

Antennas play a fundamental role in modern communication systems by facilitating signal transmission and reception across various frequency bands. Each antenna is designed for specific applications based on its operating frequency range. Whether deployed for Car-to-Car Communication or military operations, antennas serve critical functions, with information security being paramount in military contexts. Vehicular antennas typically operate within the L Band, approximately 1 to 2 GHz, relying on satellites for signal communication. However, traditional transmission through the ionosphere faces limitations, notably the skip zone, where signal reception is hindered, leading to communication failures. To address this limitation, Near Vertical Incident Skywave (NVIS) communication has been developed. NVIS utilizes antennas with very high (> 75°) radiation angles and low HF frequencies to overcome skip zone challenges. Despite existing research efforts, achieving high radiation efficiency remains a challenge, often due to improper antenna angle settings. Additionally, previous studies have overlooked the importance of narrow beam focusing, crucial for long-range communication and direction finding. This paper aims to enhance antenna performance parameters such as efficiency and gain through the adoption of specific techniques. By optimizing antenna design and configuration, we aim to improve performance for ionospheric communication, particularly in military applications involving data and voice transmission.

Алгоритм количественной оценки кардиореспираторной синхронизации для характеристики функционального состояния и межсистемных взаимодействий у спортсменов

Introduction. The rhythm of the heart (heart rate, HR) is closely related to the rhythm of breathing. The phenomenon of respiratory sinus arrhythmia (an increase in heart rate during inhalation and a decrease during exhalation) is well known. Cardiorespiratory interactions and synchronization of these two signals are evaluated differently in the literature. The purpose of this work was to propose and test an approach to assess cardiorespiratory synchronization – the calculation of the cross-correlation coefficient between heart rate and respiration curve, for a more objective characterization of an athlete’s bodily states. Methods. A photoplethysmogram and respiration were recorded in 45 healthy athletes (18-25 years old) in three situations: rest, paced breathing at 6 times per minute (resonant frequency) and the performance of a sensorimotor task (tapping with the rhythmic metronome sounds and then reproducing a given rhythm from memory). For the HR and respiration curves, filtering and smoothing algorithms using the Savitsky-Goley method were applied sequentially, and then the cross-correlation coefficient between the two curves was calculated. The spectral parameters of heart rate variability (LF and HF) were also obtained, since during spontaneous breathing its contribution to the HR is reflected in HF band, and when breathing at a resonant frequency, a peak occurs at a frequency of 0.1 Hz in the LF band. Results. The cross-correlation coefficient, as well as the peak of HR spectral power at 0.1 Hz, increases significantly when breathing at a resonant frequency. The relationship between these indicators is most accurately described not by a linear, but by a logarithmic dependence. When performing a sensorimotor task, the so-called respiratory waves in the heart rhythm spectrum (HF) do not change from rest to tapping by a metronome and then to holding the rhythm by memory. At the same time, the cross-correlation coefficient demonstrates significant changes between these situations. In addition, a significant correlation was found between the change in the cross-correlation coefficient and the stability of rhythm maintenance (from memory): an increase in the cardiorespiratory synchronization leads to a decrease in motor rhythm stability. Conclusion. Assessment of cardiorespiratory synchronization due to the peculiarities of both signals (changes in heart rate and respiratory phases) requires preliminary preparation of data arrays: filtering and smoothing the stepped curve of heart rate dynamics. The calculation of the cross-correlation coefficient can be used to assess cardiorespiratory synchronization in real time and is likely to be applicable in short time fragments to assess emotional reactions and other short-term fluctuations in psychophysiological conditions, where the classical method of assessing changes in heart rhythm in the frequency or time domains is not applicable.

Spectral Power Distribution of Heart Rate Variability in Contiguous Short-Term Intervals.

Heart rate variability (HRV) is determined by the variation of consecutive cardiac electrical excitations, usually from RR intervals of an EKG. The sequence of intervals is a time series that yields three HRV parameter categories: time domain, frequency domain, and nonlinear. Parameter estimates are based on widely different EKG sample times: short-term (~5-10 minutes), longer (24 hours), and ultra-short (<5 minutes). Five-minute intervals are useful to evaluate intervention effects that change HRV in a single session by comparing pre-to-post values. This approach relies on knowing the minimal detectible change (MDC) that indicates a real change in clinical and research studies. The specific aims of this pilot study were to (1) evaluate HRV power and its spectral distribution among contiguous five-minute intervals, (2) compare the power distribution in a five-minute interval with a full 45-minute assessment, and (3) provide data to aid estimation of the MDC between pre- and post-interventions during a single session. Methods: Twelve self-reported healthy young adults participated after signing an approved consent. Participation required subjects who had no history of cardiovascular disease or were taking vasoactive substances. Persons with diabetes were not eligible. While subjects were supine, EKG leads were placed, and EKG was recorded for 45 minutes at 1000 samples/sec. The 45 minutes were divided into nine five-minute contiguous intervals, and the spectral density in each was determined. Total power and spectral percentages within each interval were assessed in the very low (VLF, 0.003-0.04 Hz), low (LF, 0.04-0.15 Hz), and high (HF, 0.15-0.4 Hz) frequency bands. These were compared among intervals and to the full 45-minute sample. The MDC was determined by comparing powers in five-minute intervals separated by 10 minutes. The standard error of the measurement (SEME) for each pair was calculated from the square root of the mean square error (√MSE). MSE was based on a two-factor analysis of variance, and MDC was 2×√2×SEME. Differences in total power and spectral power distribution among intervals were not statistically significant. The total mean power±SD was 4561±1434 ms². The maximum difference in total power was 7.85%. The mean power for the VLF, LF, and HF bands wasrespectively1713±1736 ms², 1574±1072 ms², and 1257±1016 ms². The maximum percentage difference in spectral power across all intervals for VLF, LF, and HF wasrespectively3.75%, 8.5%, and 7.4%. The percentage of power in the VLF, LF, and HF bands wasrespectively37.9%, 36.1%, and 25.9%. The ratios of spectral to total power for VLF, LF, and HF bands were respectively 0.80±0.07, 1.20±0.11, and 1.22±0.10. MDC percentage values were 21.0±4.9% for the HF band, 25.7±1.4% for the LF band, and 30.4±5.5% for the VLF band. Results offer initial estimates of variations in HRV power in the VLF, LF, and HF bands in contiguous five-minute intervals and estimates of the minimum detectible "real" changes between intervals separated by 10 minutes. The pattern of variation and data are useful in experimental planning in which HRV spectral power changes are assessed subsequent to a short-duration intervention during a single session. MDC values (21.0% in the HF band to 30.4% in the VLF band) provide initial estimates useful for estimating the number of participants needed to evaluate the impact of an intervention on spectral components of HRV.

Effects of Exercise Training on Heart Rate Variability in Healthy Adults: A Systematic Review and Meta-analysis of Randomized Controlled Trials.

This meta-analysis was conducted to investigate the effects of exercise training on heart rate variability (HRV) parameters associated with the autonomic nervous system (ANS) activity. Randomized controlled trials (RCTs) involving healthy adults (aged ≥ 18 years) were included. We searched PubMed, Scopus, Web of Science, and EBSCO databases to identify relevant studies. A random-effects meta-analysis was performed using the standardized mean difference (SMD) and 95% confidence interval (CI). Sixteen RCTs with a total of 623participants were selected for the final analysis. The analysis showed that exercise training improved the standard deviation of normal-to-normal intervals (SDNN) (SMD: 0.58 (0.16, 1.00); p = 0.007), the root mean square of successive differences in heart period series (RMSSD) (SMD: 0.84 (0.36, 1.31); p = 0.0005), and the absolute power of high-frequency band (HF) (SMD: 0.89 (0.27, 1.51); p = 0.005) parameters compared to the control group. Analysis of the moderator variables showed that the effect of exercise on HRV indices may be influenced by sex, age, and type of exercise used, specifically in HF band, absolute power of low-frequency band (LF), and LF/HF ratio parameters. Despite the limited number of existing RCTs related to the subject, the results suggest that exercise training enhances HRV parameters associated with vagal-related activity (RMSSD and HF) and both sympathetic and parasympathetic activities (SDNN). This study overcomes the lack of meta-analyses on the effects of exercise training on autonomic modulation among healthy adults and may bridge the gap in understanding the potential physiological underpinnings of the acknowledged positive health benefits of exercise.

Verification of effect of interference between multiple scatterers on the evaluation of backscattering coefficient

Backscatter coefficient analysis methods for biological tissues have been clinically applied but assume a homogeneous scattering medium. In addition, there are few examples of actual measurement studies in the HF band, and the consistency with theory has not been sufficiently confirmed. In this paper, the effect of correlations among scatterer positions on backscattering was investigated by performing experiments on inhomogeneous media having two types of scattering source with different structural and acoustic properties. In the echo data of phantoms containing two types of scatterer acquired by multiple sensors, the power and frequency dependence of the backscatter coefficient were different from theoretical calculations due to the interference effects of each scatterer. The effect of interference between the two types of scatterer was confirmed to be particularly strong for echoes acquired by the sensor at high intensity and HF, or for a higher number density of strong scatterers.

Evaluation of Electrocardiogram Parameters and Heart Rate Variability During Blood Pressure Elevation by Phenylephrine in Cirrhotic Rats.

Cirrhotic cardiomyopathy is a myocardial disease that may go undetected in the early stages due to peripheral vasodilatation. The aim of the study was to evaluate the electrocardiogram (ECG) and heart rate variability (HRV) after raising blood pressure by phenylephrine injection in rats with liver cirrhosis. Twenty male Sprague-Dawley rats were divided into the Sham and common bile duct ligation (CBDL) groups. After 44days, animals were anesthetized and the right femoral artery and vein catheterized. After a steady-state period, a bolus injection of phenylephrine (PHE, 10μg/μl/IV, baroreflex maneuver) was followed by a slow injection of PHE (100μg/ml/5min/IV, sustained maneuver). Rapid and slow injections of PHE resulted in a greater increase in mean arterial pressure (MAP) and a weaker bradycardia response in the CBDL group than in the Sham group. ECG analysis showed increased QT, QTc, JT, and T peak to T end in the CBDL group, which remained unchanged after PHE injection. On the other hand, the parasympathetic indices of the HF band and RMSSD, and the sympathetic index of the LF band after PHE injection were lower in the CBDL group than in the Sham group.ECG data indicated prolonged ventricular depolarization and repolarization, independent of blood pressure levels in cirrhosis. On the other hand, after PHE injection, the parasympathetic and sympathetic components of HRV decreased, regardless of the duration of elevated blood pressure. We suggest that HRV analysis can provide a useful approach to assess cardiac dysfunction associated with elevated blood pressure in cirrhosis.

The influence of the method of excitation of a near ground four-arm spiral HF band antenna on its characteristics

Abstract. Four-arm spiral antennas with internal excitation are common and are part of many radio communication, navigation and location systems (including the HF band). There are known objections in the design of these antennas, which complicate their operation and lead to a decrease in efficiency, associated with the choice of the method of excitation of radiators. The aim of the article is investigation of the influence of the method of excitation of a near ground four-arm spiral HF band antenna on its characteristics (both separate and as part of other antenna-feeder devices) and formulating recommendations for simplifying operation and increasing efficiency. In article four methods of excitation of a near ground four-arm antenna were analyzed, considered as part of an antenna system consisting of an aperiodic antenna and a termination load for its radiators in the form of a near ground four-arm spiral antenna. The influence of the method of excitation of both the antenna system as a whole and a separately near ground four-arm spiral antenna on their characteristics has been studied. The analysis of the methods of excitation of a near ground four-arm spiral HF band antenna presented in the article and the recommendations formulated for the development of HF band antenna-feeder devices allow us to design and upgrade both near ground and aperiodic antennas of radio centers with increased efficiency and simplify their operation.

Acute Cardiorespiratory Coupling Impairment in Worsening Sleep Apnea-Related Intermittent Hypoxemia.

Hypoxic load is one of the main characteristics of obstructive sleep apnea (OSA) contributing to sympathetic overdrive and weakened cardiorespiratory coupling (CRC). Whether this association changes with increasing hypoxic load has remained obscure. Therefore, we aimed to study our hypothesis that increasing hypoxic load acutely decreases the CRC. We retrospectively analyzed the electrocardiography and nasal pressure signals in 5-min segment pairs (n = 36 926) recorded during clinical polysomnographies of 603 patients with suspected OSA. The segment pairs were pooled into five groups based on the hypoxic load severity described with the the total integrated area under the blood oxygen saturation curve during desaturations. In these severity groups, we determined the frequency-domain heart rate variability (HRV) parameters, the HRV and respiratory high-frequency (HF, 0.15-0.4 Hz) peaks, and the difference between those peaks. We also computed the spectral HF coherence between HRV and respiration in the HF band. The ratio of low-frequency (LF, 0.04-0.15 Hz) to HF power increased from 1.047 to 1.805 (p < 0.001); the difference between the HRV and respiratory HF peaks increased from 0.001 Hz to 0.039 Hz (p < 0.001); and the spectral coherence between HRV and respiration in the HF band decreased from 0.813 to 0.689 (p < 0.001) as the hypoxic load increased. The vagal modulation decreases and CRC weakens significantly with increasing hypoxic load. Thus, the hypoxic load could be utilized more thoroughly in contemporary OSA diagnostics to better assess the severity of OSA-related cardiac stress.

Impact of CPAP Therapy on the Autonomic Nervous System.

Obstructive sleep apnea (OSA) is a significant risk factor for cardiovascular disease (CVD) with increasing prevalence. An important mechanism of CVD development is a dysregulation of the autonomic nervous system (ANS). This prospective and controlled cohort study aimed to investigate ANS function in OSA including the response to long-term continuous positive airway pressure (CPAP) therapy by analyzing 24 h Holter electrocardiogram and 24 h Holter ambulatory blood pressure recording parameters. The study enrolled 57 patients who were newly diagnosed with severe OSA. After 6 months of CPAP therapy, 37 patients had a good therapy adherence (usage of CPAP device >4 h per night), and their data were analyzed. The difference in nocturnal diastolic blood pressure values before and after CPAP therapy reached statistical significance (76 (68-84) vs. 74 (63-80) mmHg, p = 0.0439). Lower nocturnal values after CPAP therapy of SDNN (101.5 vs. 95 ms, p = 0.0492) and RMSSD (29.5 vs. 26 ms, p = 0.0193) were found. An increase in diurnal spectral power (1742 vs. 2112 ms2, p = 0.0282) and a decrease in nocturnal spectral power (3256 vs. 2124 ms2, p = 0.0097), nocturnal VLF band (2493 vs. 1485.4 ms2, p = 0.0176), nocturnal LF band (638.7 vs. 473 ms2, p = 0.0097), and nocturnal HF band (234.9 vs. 135.7 ms2, p = 0.0319) was found. The results showed an imbalance of the ANS with a sympathetic predominance, especially during the night hours and in those with arterial hypertension. The impact of CPAP therapy on the improvement in ANS parameters was more pronounced at night, in men, and those with arterial hypertension.

Simulation of Spatial Polarization Characteristics of a Triorthogonal Antenna Element for the Tasks of HF Band Bearing

Introduction. Achieving improved accuracy and sensitivity of the direction finding of radio signals represents a relevant research direction in the field of modern HF radio monitoring. HF radio waves propagate through ionospheric layers, which distorts the polarization parameters of the passing electromagnetic wave (EMW). One possible approach to improve the accuracy and sensitivity of the direction finding of HF radio signals consists in the use of an antenna element capable of accepting both components of the electromagnetic field in the antenna array.Aim. A comparative analysis of the proposed triorthogonal antenna element with existing solutions for the tasks of HF band bearing.Materials and methods. Antenna elements and their spatial polarization characteristics were simulated in the MATLAB environment using the Phased Array toolbox.Results. The spatial polarization characteristics of the triorthogonal antenna under study were constructed and compared with an asymmetric vertical vibrator and a biorthogonal antenna. The comparison showed that at small elevation angles, the triorthogonal antenna ensures an energy gain of up to 4.5 dB compared to a biorthogonal antenna and an asymmetric vertical vibrator. At elevation angles of 30…60° and over 60°, the increase in the quality of a signal received by the triorthogonal antenna element reaches 3 dB and 2 dB, respectively.Conclusion. According to the obtained spatial polarization characteristics, the triorthogonal antenna under study can be part of a large-base antenna array of the HF band. The use of this antenna will increase the accuracy and sensitivity of direction finding by means of matching the antenna element with the EMW polarization

Methods of reducing antenna bandwidth requirements for envelope elimination and restoration transmitter

The task of radio transmitting path efficiency increasing is relevant both for stationary high-power applications and for autonomous low-power devices. The highest efficiency can be achieved in switching operating modes (classes D, E, F). For the amplification of modern spectrally efficient broadcast and telecommunication signals with variable amplitude, for example, with OFDM, the use of switching operating modes is possible only with the use of "synthetic" amplification methods. The most promising for application can be considered Envelope Elimination and Restoration (EER) method, which is successfully used in the field of high-power broadcasting in the LF, MF and HF bands, and is the object of a large number of studies aimed at expanding its scope. Transmitting devices of radio communication and broadcasting systems in some cases are forced to work with an electrically short antenna. However, when operating with OFDM signals to a narrow-band load, high-efficiency EER transmitters require matching with an antenna circuit with an SWR of at least 1.05 in the signal frequency band. Thus, the task of antenna bandwidth requirements reducing for EER transmitter is relevant. To solve it, a simulation model was previously developed and verified to study the operation of EER switching RF power amplifiers for a narrow-band load. With its help, the dependence of output signal distortion level on the envelope path LPF parameters was studied. This article proposes and analyzes hardware circuit solutions aimed at reducing the transmitter sensitivity to antenna bandwidth. The analysis of hardware methods for reducing the EER transmitter sensitivity to the resonant antenna SWR (passband) showed the following: 1. The damping circuit, together with a double-sided loaded envelope path LPF, allows you to reduce antenna SWR requirements to a maximum value of 1.22, while the allowable antenna bandwidth can be reduced to five signal bands. 2. The high-pass filter diplexer proposed in this paper, together with a double-sided loaded envelope path LPF, makes it possible to reduce antenna SWR requirements to a maximum value of 1.47, and the allowable antenna bandwidth can be reduced to 2.5 signal bands. The disadvantages of this method include the need, depending on the antenna used, for individual design and manufacture of high-pass filter diplexers installed in the low-frequency path of each amplifying cell of the transmitter. To expand the range of antennas used, it is possible to switch capacitors of the high-pass filter diplexer from a set of 2 ... 3 pieces. Data on the production of transmitters with the proposed HPF diplexer has not been found to date. 3. Multi-phase PWM when using a 2nd order unilaterally loaded low-pass filter and installing 2nd harmonic rejectors of the operating frequency in the cells of the RF path allows you to work on antennas with a bandwidth of up to half the signal bandwidth. Restrictions on the antenna bandwidth and its SWR are imposed only by the uneven antenna frequency response in the transmitted signal band. The disadvantages of this method include the need to install narrow-band rejectors that block the power supply circuit of each RF cell in terms of the 2nd harmonic, which makes such a transmitter a custom product for a fixed operating frequency. 4. The most promising solution should be considered the use of a high-pass filter diplexer, which allows relatively simple means to expand the permissible SWR of a narrow-band antenna in the signal band from the initial value of 1.05 to 1.47.

Comparative Analysis of Disorders of Heart Rhythm Regulation Mechanisms Induced in Newborn Rats by Nickel Chloride and the Acetylcholinesterase Inhibitor Physostigmine (Eserine)

A comparative analysis of heart rate variability (HRV) indices after injection of the acetylcholinesterase inhibitor (AChE) physostigmine (¾ LD50) and the T-type calcium channel blocker (T-VDCC) Ni2+ (ED100) into animals was performed in experiments on 3-day-old newborn rats. Both drugs cause phenomenologically similar pathological heart rhythm with significant bradycardia complexes (PHRBC). Analysis of HRV indices showed that the disturbance of heart rhythm regulation mechanisms in NiCl2 poisoning of rats and in cholinoreactive structure activation caused by AChE inhibition develop according to a similar pattern. In both cases there is a decrease in the total power of the spectrum and the absolute power values of the LF (predominantly sympathetic) and HF (parasympathetic influences) bands. Significant decrease in the level of nerve influences leads to the fact that the dominant role in the regulation of heart rhythm begins to play neurohumoral factors (VLF-band). It was found that under conditions of premedication with H- or M-cholinolytics, when rats do not develop cardiac rhythm disturbances, the initial decrease in the severity of neurohumoral and subsequent increase in sympathetic and, to a lesser extent, parasympathetic influences is common. In this case, vagosympathetic balance is not decisive. In case the influence of neurohumoral factors increases after premedication, then later there is a decrease in the proportion of nerve influences and the occurrence of PHRBC. The obtained data suggest that in newborn rats both direct blockade of T-VDCC and changes in ICaT current mediated through M3-subtype muscarinic cholinoreceptors lead to disruption of pacing and development of PHRBC.

Effects of Preoperative Sarcopenia-Related Parameters on Cardiac Autonomic Function in Women with Obesity Following Bariatric Surgery: A One-Year Prospective Study.

Investigate changes in blood pressure (BP) and heart rate variability (HRV) in women with and without sarcopenia-related parameters who underwent bariatric surgery (BS) during a one-year follow-up. Women were separated into obesity (OB, n = 20) and women with obesity displaying sarcopenia-related parameters (SOP, n = 14) and evaluated before BS and 3, 6, and 12 months after BS. SOP was defined as low handgrip strength (HS) and/or low appendicular skeletal mass adjusted for weight (ASM/wt × 100, %) in the lowest quartile of the sample. ASM/wt × 100, % and HS were significantly lower in SOP than OB over a one-year follow-up of BS (p < 0.05). There was a reduction in diastolic BP, heart rate (HR), SDHR, LF, and the LF/HF ratio (p < 0.05) and an increase in the HF band in both groups during the follow-up period (p < 0.05). SOP women had reduced root mean square differences of successive RR intervals (RMSSD) and HF band and an increased LF band and SD2/SD1 ratio compared to the OB group during the one-year follow-up (p < 0.05). ASM/wt × 100, % was negatively associated with the LF band (r = -0.24, p = 0.00) and positively associated with the HF band (r = 0.22, p = 0.01). Conversely, HS had no association with LF (r = -0.14, p = 0.09) and HF (r = 0.11, p = 0.19). ASM/wt × 100, % and HS were negatively associated with the LF/HF ratio (p < 0.05). Women who underwent BS had an improved HRV over a one-year follow-up. However, the improvement in HRV variables was less pronounced in women with low muscle mass and/or HS during the follow-up period.

Collective excitations of the Chern-insulator states in commensurate double moiré superlattices of twisted bilayer graphene on hexagonal boron nitride

We study the collective excitation modes of the Chern insulator states in magic-angle twisted bilayer graphene aligned with hexagonal boron nitride (TBG/BN) at odd integer fillings ($\nu$) of the flat bands. For the $1 \times 1$ commensurate double moir\'{e} superlattices in TBG/BN at three twist angles ($\theta'$) between BN and graphene, self-consistent Hartree-Fock calculations show that the electron-electron interaction and the broken $C_{2z}$ symmetry lead to the Chern-insulator ground states with valley-spin flavor polarized HF bands at odd $\nu$. In the active-band approximation, the HF bands in the same flavor of TBG/BN are much more separated than those of the pristine TBG with TBG/BN having a larger intra-flavor band gap so that the energies of the lowest intra-flavor exciton modes of TBG/BN computed within the time-dependent HF method are much higher than those of TBG and reach about 20 meV, and the exciton wavefunctions of TBG/BN become less localized than those of TBG. The inter-flavor valley-wave modes in TBG/BN have excitation energies higher than 2.5 meV which is also much larger than that of TBG, while the spin-wave modes all have zero excitation gap. In contrast to TBG with particle-hole symmetric excitation modes for positive and negative $\nu$, the excitation spectrums and gaps of TBG/BN at positive $\nu$ are rather different from those at negative $\nu$. The quantitative behavior of the excitation spectrum of TBG/BN also varies with $\theta'$. Full HF calculations demonstrate that more HF bands besides the two central bands can have rather large contributions from the single-particle flat-band states, then the lowest exciton modes that determine the optical properties of the Chern insulator states in TBG/BN are generally the ones between the remote and flat-like bands, while the valley-wave modes have similar energies as those in the active-band approximation.

An Evaluation Method of Ship-Tracking Algorithms for High-Frequency Surface Wave Radar considering High Maneuvers Generated by the MMG Model

Thelong-distance coverage of high-frequency surface wave radar (HFSWR) has promoted it as an enormous means for ship monitoring on the country’s maritime territory. Since it is a primaryradar, noncooperative targets can also be detected. However, this radar also has a shortcoming of low spatial and temporal resolutions due to the narrow available bandwidth in the HF band. This limitation can reduce the performance of ship detection and tracking, especially for highly maneuvering ships. This paper proposes a new method to assess the tracking algorithm for a high-maneuvering ship. The absence of a high-maneuvering plot in the AIS data and existing analytical models are replaced by the MMG model run on MANSIM software. The linear, turning, and zigzag motions are generated and used to evaluate the tracking algorithms. The Monte Carlo simulation was conducted regarding the degradation of spatial resolution in the higher radial range. The tracking performance was analyzed by calculating the RMSE of four parameters, i.e., absolute position, radial range, bearing angle, and speed. For a trial case, four tracking algorithms were evaluated, i.e., Kalman filter (KF), extended Kalman filter (EKF), unscented Kalman filter (UKF), and particle filter (PF). The evaluation results showed that the EKF tracker had a minor error for the linear track with RMSE of absolute position, radial range, bearing angle, and speed being 1.368 km, 0.526 km, 1.550°, and 0.005 m/s, respectively. Otherwise, the UKF performed slightly better than EKF for the high maneuver targets. The RMSE of absolute position, radial range, bearing angle, and speed were 1.649 km, 0.639 km, 1.919°, and 0.165 m/s, respectively. The results also ensure the applicability of the MMG model to evaluate the tracking algorithm’s performance in HFSWR.

Model-based spectral causality of cardiovascular variability interactions during head-down tilt

Objective. Cardiovascular control mechanisms are commonly studied during baroreceptor unloading induced by head-up tilt. Conversely, the effect of a baroreceptor loading induced by head-down tilt (HDT) is less studied especially when the stimulus is of moderate intensity and using model-based spectral causality markers. Thus, this study computes model-based causality markers in the frequency domain derived via causal squared coherence and Geweke spectral causality approach from heart period (HP) and systolic arterial pressure (SAP) variability series. Approach. We recorded HP and SAP variability series in 12 healthy men (age: from 41 to 71 yrs, median: 57 yrs) during HDT at −25°. The approaches are compared by considering two different bivariate model structures, namely the autoregressive and dynamic adjustment models. Markers are computed in traditional frequency bands utilized in cardiovascular control analysis, namely the low frequency (LF, from 0.04 to 0.15 Hz) and high frequency (HF, from 0.15 to 0.4 Hz) bands. Main results. We found that: (i) the two spectral causality metrics are deterministically related but spectral causality markers exhibit different discriminative ability; (ii) HDT reduces the involvement of the baroreflex in regulating HP-SAP variability interactions in the LF band, while leaving unmodified the action of mechanical feedforward mechanisms in both LF and HF bands; (iii) this conclusion does not depend on the model structure. Significance. We conclude that HDT can be utilized to reduce the impact of baroreflex and to study the contribution of regulatory mechanisms different from baroreflex to the complexity of cardiovascular control in humans.

Respiration-entrained brain oscillations in healthy fMRI participants with high anxiety

Brain-body interactions can be studied by using directed coupling measurements of fMRI oscillations in the low (0.1–0.2 Hz) and high frequency bands (HF; 0.2–0.4 Hz). Recently, a preponderance of oscillations in the information flow between the brainstem and the prefrontal cortex at around 0.15/0.16 Hz was shown. The goal of this study was to investigate the information flow between BOLD-, respiratory-, and heart beat-to-beat interval (RRI) signals in the HF band in healthy subjects with high anxiety during fMRI examinations. A multivariate autoregressive model was concurrently applied to the BOLD signals from the middle frontal gyrus (MFG), precentral gyrus and the brainstem, as well as to respiratory and RRI signals. Causal coupling between all signals was determined using the Directed Transfer Function (DTF). We found a salience of fast respiratory waves with a period of 3.1 s (corresponding to ~ 0.32 Hz) and a highly significant (p < 0.001) top-down information-flow from BOLD oscillations in the MFG to the brainstem. Additionally, there was a significant (p < 0.01) information flow from RRI to respiratory oscillations. We speculate that brain oscillations around 0.32 Hz, triggered by nasal breathing, are projected downwards to the brainstem. Particularly interesting is the driving force of cardiac to respiratory waves with a ratio of 1:1 or 1:2. These results support the binary hierarchy model with preferred respiratory frequencies at 0.32 Hz and 0.16 Hz.

Sexual dimorphism in relationships between of plasma uric acid and some psycho-neuro-endocrine parameters

Background. Earlier we found that effects of plasma nitrogenous metabolites as urea, creatinine, and bilirubin on neuro-endocrine parameters, as well as anxiety, are significantly different in men and women of different ages. The purpose of this study is to analyze the relationships between the plasma uric acid level and some psycho-neuro-endocrine parameters in the same cohort. Materials and Methods. The object of observation were almost healthy volunteers: 31 males (24÷69 y) and 30 females, from among them 18 postmenopausal (48÷76 y) and 12 of reproductive age (30÷45 y). In basal conditions we determined plasma levels of uric acid and adaptation hormones, estimated the severity of the trait and reactive anxiety, recorded the ongoing HRV and EEG. After 4 or 7 days, repeated testing was performed. Results. By uric acid regression models with stepwise exclusion, it was found that in men plasma uric acid downregulates the PSD of β-rhythm in P4 and δ-rhythm in others 4 loci, but upregulates the Asymmetry of δ-rhythm, variability of α-rhythm, PSD of θ-rhythm in P3 and O1 loci, Entropy of EEG in T4 as well as Testosterone plasma level. The measure of determination is 54,5%. In postmenopausal women, uricemia downregulates the Amplitude of β-rhythm and its PSD in 8 loci as well as sympathetic tone, but upregulates the PSD of HF and VLF bands HRV, Testosterone plasma level, PSD of θ-rhythm in F3 and O2 loci as well as the Laterality of δ-rhythm. The degree of determination of neuro-endocrine parameters is 94,4%. In women of reproductive age uricemia upregulates the Asymmetry and Amplitude of β-rhythm and its PSD in 6 loci, the Amplitude and Laterality of θ-rhythm and its PSD in F8 locus, as well as the PSD of α-rhythm in F8 locus. The degree of positive determination of EEGs parameters is 95,5%. Conclusion. Plasma uric acid has a modulating effect on neuro-endocrine parameters, but this effect is significantly different in men and women of different ages, which is due, apparently, to the influence of sex hormones on the expression of adenosine receptors in neurons.

Models of HF Interference over Cyprus

Interference from other users, due to the long-distance propagation of HF signals, causes spectral congestion, which is considered a primary detrimental effect on HF (3–30 MHz) communication systems. More than a year of HF electric field measurements from a calibrated monopole HF antenna collected by a dedicated measurement system installed in Cyprus have been used to compare neural networks and non-linear regression for the development of single-allocation congestion models in the HF spectrum. These models can be used to advise operators on typical interference spectral congestion levels and assist in the planning and management of frequency usage by assessing the interference level to alleviate spectral congestion in the HF band over Cyprus. The performance of these alternative modeling approaches is discussed in the context of their ability to successfully capture the diurnal variability of HF interference at a certain incident field strength threshold.

From Molecular to Functional Effects of Different Environmental Lead Exposure Paradigms.

Simple SummaryOur comparative study brings new insights regarding the effects of environmental lead exposure on the cardiorespiratory and nervous systems. We show how various kinds of exposure can lead to different toxicities, with various degrees of nefarious effects. The developmental period is of utmost importance to the toxicity of environmental lead; however, we found that the duration of exposure is the prime reason for stronger effects, even though the dual effect of intermittent exposure causes greater molecular neuronal alterations. Lead is a heavy metal whose widespread use has resulted in environmental contamination and significant health problems, particularly if the exposure occurs during developmental stages. It is a cumulative toxicant that affects multiple systems of the body, including the cardiovascular and nervous systems. Chronic lead exposure has been defined as a cause of behavioral changes, inflammation, hypertension, and autonomic dysfunction. However, different environmental lead exposure paradigms can occur, and the different effects of these have not been described in a broad comparative study. In the present study, rats of both sexes were exposed to water containing lead acetate (0.2% w/v), from the fetal period until adulthood. Developmental Pb-exposed (DevPb) pups were exposed to lead until 12 weeks of age (n = 13); intermittent Pb exposure (IntPb) pups drank leaded water until 12 weeks of age, tap water until 20 weeks, and leaded water for a second time from 20 to 28 weeks of age (n = 14); and the permanent (PerPb) exposure group were exposed to lead until 28 weeks of age (n = 14). A control group (without exposure, Ctrl), matched in age and sex was used. After exposure protocols, at 28 weeks of age, behavioral tests were performed for assessment of anxiety (elevated plus maze test), locomotor activity (open-field test), and memory (novel object recognition test). Metabolic parameters were evaluated for 24 h, and the acute experiment was carried out. Blood pressure (BP), electrocardiogram, and heart (HR) and respiratory (RF) rates were recorded. Baroreflex gain, chemoreflex sensitivity, and sympathovagal balance were calculated. Immunohistochemistry protocol for NeuN, Syn, Iba-1, and GFAP staining was performed. All Pb-exposed groups showed hypertension, concomitant with a decrease in baroreflex gain and chemoreceptor hypersensitivity, without significant changes in HR and RF. Long-term memory impairment associated with reactive astrogliosis and microgliosis in the dentate gyrus of the hippocampus, indicating the presence of neuroinflammation, was also observed. However, these alterations seemed to reverse after lead abstinence for a certain period (DevPb) and were enhanced when a second exposure occurred (IntPb), along with a synaptic loss. These results suggest that the duration of Pb exposure is more relevant than the timing of exposure, since the PerPb group presented more pronounced effects and a significant increase in the LF and HF bands and anxiety levels. In summary, this is the first study with the characterization and comparison of physiological, autonomic, behavioral, and molecular changes caused by different low-level environmental lead exposures, from the fetal period to adulthood, where the duration of exposure was the main factor for stronger adverse effects. These kinds of studies are of immense importance, showing the importance of the surrounding environment in health from childhood until adulthood, leading to the creation of new policies for toxicant usage control.