High Frequency Waves Research Articles

The effect of TENS on sleep: A pilot study

BackgroundInsomnia is the second most common neuropsychiatric disorder, but the current treatments are not very effective. There is therefore an urgent need to develop better treatments. Transcutaneous electrical nerve stimulation (TENS) may be a promising means of treating insomnia. ObjectiveThis work aims to explore whether and how TENS modulate sleep and the effect of stimulation waveforms on sleep. MethodsForty-five healthy subjects participated in this study. Electroencephalography (EEG) data were recorded before and after four mode low-frequency (1 Hz) TENS with different waveforms, which were formed by superimposing sine waves of different high frequencies (60–210 Hz) and low frequencies (1–6 Hz). The four waveform modes are formed by combining sine waves of varying frequencies. Mode 1 (M1) consists of a combination of high frequencies (60–110 Hz) and low frequencies (1–6 Hz). Mode 2 (M2) is made up of high frequencies (60–210 Hz) and low frequencies (1–6 Hz). Mode 3 (M3) consists of high frequencies (110–160 Hz) and low frequencies (1–6 Hz), while mode 4 (M4) is composed of high frequencies (160–210 Hz) and low frequencies (1–6 Hz). For M1, M3 and M4, the high frequency portions of the stimulus waveforms account for 50%, while for M2, the high frequency portion of the waveform accounts for 65%. For each mode, the current intensities ranged from 4 mA to 7 mA, with values for each participant adjusted according to individual tolerance. During stimulation, the subjects were stimulated at the greater occipital nerve by the four mode TENS. ResultsM1, M3, and M4 slowed down the frequency of neural activity, broadened the distribution of theta waves, and caused a decrease in activity in wakefulness-related regions and an increase in activity in sleep-related regions. However, M2 has the opposite modulation effect. ConclusionThese results indicated that low-frequency TENS (1 Hz) may facilitate sleep in a waveform-specific manner. Our findings provide new insights into the mechanisms of sleep modulation by TENS and the design of effective insomnia treatments.

Approximation of High-Frequency Wave Propagation in Dispersive Media

Approximation of High-Frequency Wave Propagation in Dispersive Media

Modeling and Theoretical Analysis of Zero-Flowrate-Switching Control Method for a Dynamic Load System to Reduce Switching Power Loss of Control Valves

Valve switching is one of the most important power losses in digital hydraulics. In this paper, a dynamic Zero-Flowrate-Switching (ZFS) control method is developed for hydraulic/pneumatic systems. The proposed control strategy is to actively reduce the flowrate passing through the valve to zero before switching off the valve. To realize it, an accessory line, in which a RLC oscillator is applied to generate a sinusoidal flowrate, is allocated parallel to the main control line for flowrate regulation. The pressure, with high frequency and small amplitude wave outputs from a regular piston pump, is used to drive the RLC oscillator. To evaluate the performance of this strategy, mathematical models for switching power loss and pressure pulses are developed and characteristic analysis is conducted. The results show that the energy loss of the system when applying the dynamic ZFS controller is reduced to 16% compared to that of a normal hydraulic system without a dynamic ZFS controller; moreover, pressure pulses in a dynamic ZFS system are much more minor than those in a Hard-Switching system.

Measurements of Wave‐Induced Attenuation in Saturated Metapelite and the Band‐Limitation of Low‐Frequency Earthquakes

AbstractThe most common explanation for the depletion of high frequency waves that defines low‐frequency earthquakes (LFEs) and very low‐frequency earthquakes (VLFEs) is that fault rupture and slip are slower than typical earthquakes. However, it is difficult to rule out the possibility that the high frequency waves are produced during slip, but attenuated near the LFE source. One reason this hypothesis has been poorly tested is that there are no measurements of attenuation on the relevant rocks. We present the results of forced oscillation experiments that measure the frequency‐dependent attenuation of a chlorite‐rich metapelitic schist, a lithology found along the subduction plate boundary where LFEs and VLFEs have been documented. Experiments were run on dry and water‐saturated schist at effective pressures of 2–10 MPa and at frequencies of 2 × 10−5–30 Hz. We find that pore fluids and low effective pressure result in the attenuation of high frequencies. The frequency‐dependent attenuation is consistent with the concomitant operation of two wave‐induced fluid flow mechanisms, squirt flow, and patchy saturation. When the effects of these mechanisms are extrapolated to geologic conditions using rock physics models, our results predict that attenuation is capable of completely diminishing the frequencies depleted in LFEs and VLFEs. Therefore, LFEs and VLFEs may not necessarily record slow fault slip, but possibly the presence of high fluid pressure.

Interaction of the high frequency waves in the vicinity of the ionospheric window

It is well-known that an ordinary high frequency electromagnetic (EM) wave radiated into the ionosphere at the Spitze angle is totally transformed at the reflection height (z0) into the Z-mode. This mode, in turn, penetrates deeper into the ionosphere and it is reflected at some height (zref) usually significantly higher than the O-mode reflection height. This result is reconsidered in the present paper. It is argued that the wave appearing as a continuation of the propagating upward quasi-electrostatic wave changes the direction of motion along the vertical axis slightly above z0 and takes the form of the down-going wave. This wave is excited in the vicinity of the height z0 due to the phase resonance with the up-going O-mode wave which transforms into the Z-mode propagating upward. Thus, the ionospheric window is not totally transparent for the O-mode radiated at the Spitze angle. The up-going O-mode wave loses some part of its energy due to excitation of the down-going EM wave. This wave, in turn, propagates to the ground as the O-mode wave.

High-frequency Decayless Waves with Significant Energy in Solar Orbiter/EUI Observations

High-frequency wave phenomena present a great deal of interest as one of the possible candidates to contribute to the energy input required to heat the corona as a part of the alternating current heating theory. However, the resolution of imaging instruments up until the Solar Orbiter has made it impossible to resolve the necessary time and spatial scales. The present paper reports on high-frequency transverse motions in a small loop located in a quiet-Sun region of the corona. The oscillations were observed with the High Resolution Imager in the Extreme Ultraviolet telescope (17.4 nm) of the Extreme Ultraviolet Imager instrument on board the Solar Orbiter. We detect two transverse oscillations in short loops with lengths of 4.5 and 11 Mm. The shorter loop displays an oscillation with a 14 s period and the longer a 30 s period. Despite the high resolution, no definitive identification as propagating or standing waves is possible. The velocity amplitudes are found to be equal to 72 and 125 km s−1, respectively, for the shorter and longer loops. Based on that, we also estimated the values of the energy flux contained in the loops—the energy flux of the 14 s oscillation is 1.9 kW m−2 and that of the 30 s oscillation is 6.5 kW m−2. While these oscillations have been observed in the quiet Sun, their energy fluxes are of the same order as the energy input required to heat the active solar corona. Numerical simulations were performed in order to reproduce the observed oscillations. The correspondence of the numerical results to the observations provides support to the estimates of energy content for the observations. Such high energy densities have not yet been observed in decayless coronal waves, and this is promising for coronal heating models based on wave damping.

Stem stiffness functionality in a submerged canopy patch under oscillatory flow

Seagrass canopies are coastal ecosystems that are able to modify the abiotic environment through their architectural structure. They have different structural parameters, such as plant stem stiffness, patch length and canopy density, all of which determine their overall functionality in modifying the seafloor hydrodynamics within coastal areas. To determine the interaction between hydrodynamics and the canopy structure, a set of laboratory experiments were carried out with both rigid and flexible stems for different canopy densities, patch lengths and wave frequencies. In the upper part of the canopy, flexible plants move with the flow without generating drag or producing turbulent kinetic energy, while rigid plants generate drag and produce turbulent kinetic energy. In the inner canopy layer, both types of plants behave like rigid stems and produce turbulent kinetic energy. A non-dimensional model based on the turbulent kinetic energy, the wave velocity and the plant characteristics is presented to describe the behaviour of flexible and rigid plants under an oscillating flow. Flexible plants behave in a stiffer manner under high wave frequencies than under low wave frequencies, thus making their behaviour closer to that of rigid plant stems. This difference between both canopy structures can explain their distribution in the environment, with rigid canopies being more extended in more sheltered regions while flexible plants are characteristic of more exposed regions with high flow energy.

Predicting Path Loss of an Indoor Environment Using Artificial Intelligence in the 28-GHz Band

The propagation of signal and its strength in an indoor area have become crucial in the era of fifth-generation (5G) and beyond-5G communication systems, which use high bandwidth. High millimeter wave (mmWave) frequencies present a high signal loss and low signal strength, particularly during signal propagation in indoor areas. It is considerably difficult to design indoor wireless communication systems through deterministic modeling owing to the complex nature of the construction materials and environmental changes caused by human interactions. This study presents a methodology of data-driven techniques that will be applied to predict path loss using artificial intelligence. The proposed methodology enables the prediction of signal loss in an indoor environment with an accuracy of 97.4%.

Time reversal of surface plasmons

<p style='text-indent:20px;'>We study in this work the so-called "instantaneous time mirrors" in the context of surface plasmons. The latter are associated with high frequency waves at the surface of a conducting sheet. Instantaneous time mirrors were introduced in [<xref ref-type="bibr" rid="b3">3</xref>], with the idea that singular perturbations in the time variable in a wave-type equation create a time-reversed focusing wave. We consider the time-dependent three-dimensional Maxwell's equations, coupled to Drude's model for the description of the surface current. The time mirror is modeled by a sudden, strong, change in the Drude weight of the electrons on the sheet. Our goal is to characterize the time-reversed wave, in particular to quantify the quality of refocusing. We establish that the latter depends on the distance of the source to the sheet, and on some physical parameters such as the relaxation time of the electrons. We also show that, in addition to the plasmonic wave, the time mirror generates a free propagating wave that offers, contrary to the surface wave, some resolution in the direction orthogonal to the sheet. Blurring effects due to non-instantaneous mirrors are finally investigated.</p>

Application of the scattering matrix method for investigating the propagation characteristics of terahertz waves in magnetized dusty plasma

A scattering matrix method is applied to investigate propagation characteristics of oblique incident terahertz waves into magnetized dusty plasmas. The numerical results agree well with those given by the Wenzell–Kramer–Brillouin method. Three different electron density distributions are taken into account, and both the right- and left-hand circularly polarized (RCP and LCP) waves are analyzed. Transmission properties of terahertz (THz) waves with different physical parameters, such as external magnetic, dust particle density, and dust particle radius, are discussed systematically. There exists a transmissivity peak at the lower-frequency band for RCP waves when an external magnetic field is presented. The value of the peak nearly keeps invariant, and its location moves toward the higher-frequency direction if the magnetic field enhances. Increasing the dust particle density or radius can make the value of a transmissivity peak larger. The transmissivity of higher-frequency RCP THz waves decreases if the external magnetic field increases. However, for LCP waves, there is no transmissivity peak. It increases monotonously as the frequency of a THz wave increases. Different from the RCP waves, enhancing the external magnetic field is better for the LCP waves to penetrate the dusty plasma. Our results may provide some theoretical basis for alleviating the problem of “blackout.”

Theory, design and characterization of metamaterial absorbers: a formal assessment

Metamaterial (MTM) absorbers and their design have been of prime interest in view of their capability to absorb electromagnetic waves of high frequencies. Different types of MTM absorbers have been reported in the last two decades. Keeping this in view an attempt was made to review the progress of MTM absorbers in terms of the theory behind them, designing and construction. This paper reviewed the basic theory and design regulations of a perfect MTM absorber at high, narrow and broad band frequencies. Also we reviewed tunable frequency and coherent absorbers. This exercise was done to focus on recent developments in metamaterial absorbers and present the tested results in a more precise way

Effect of hyperoxic inhalations for athletes of different sports, including those who had COVID-19, when training in the middle altitude

To identify hyperoxic inhalations on the functional state of the cardiorespiratory system of athletes of different sports, who have previously had COVID-19, when training in the middle altitude. The study included 64 elite athletes during the preparatory period. The studies were conducted in Kislovodsk in the middle altitude (1240 meters) on the Maloe Sedlo mountain, in the conditions of training camps. We studied the parameters of heart rate variability and functional state of cardiovascular and respiratory systems. Hyperoxic inhalations were performed with the JAY-10 oxygen concentrator (LONGFIAN SCITECH CO., LTD., China). The oxygen concentration in the mixture was 93±3%, capacity - 5 l/min, exposure time - 20 min. Athletes specializing in sports with predominantly anaerobic lactate and mixed mechanism of energy supply, respectively experiencing hypoxia in the process of their athletic activity during training can experience hypoxia at rest as well. The state of hypoxia during exercise in the middle altitude in such athletes is shown in heart rate variability indices (high values of heart rate and stress index, low power of high frequency waves), low saturation, increased oxygen uptake from the blood microcirculation system. The use of oxygen therapy in athletes promotes positive dynamics of the functional state, consisting in a reduced stress of regulatory mechanisms, strengthened tone of the parasympathetic nervous system in the heart rate regulation, increased economization of the central hemodynamics' parameters, improved functions of the external respiratory system. Application of hyperoxic inhalations during intense exercise in the middle altitude has a favorable effect on the functional state of the cardiorespiratory system in all the studied sports, especially in athletes who have previously had COVID-19.

A noise-based high-resolution time-reversal method for acoustic defect localization in water pipes.

Pressurized water supply pipeline systems (PWSPS) are quintessential to human development and sustenance, but suffer a multitude of unresolved defects (i.e., leaks, blockages, etc.) due to aging and inaccessibility. In this paper, the ubiquitous high-frequency background noise in PWSPS is harnessed to introduce a high-resolution, passive defect detection technique. The relation between the acoustic Green's and cross correlation functions for a pressurized water pipe is derived for the case of high frequency waves, i.e., acoustic wavelengths smaller than the pipe diameter. This relation is subsequently used to formulate a time-reversal technique for localizing anomalies such as small variations in pipe wall impedance and through-wall defects (i.e., leaks). It is shown that the derived relationship between the cross correlation and acoustic Green's functions enables very accurate defect detection and localization by measuring the background noise at two locations along a pipe. This is an important result given that (i) there is limited access to buried PWSPS to conduct high-frequency active defect detection, and (ii) traditional methods to actively probe pipes (e.g., valve maneuverer) are low-resolution (tens to hundreds of meters) and often result in pipe overloading and fatigue.

First-Principles Study of Structure and Optical Properties of Perovskite PbTiO3 under Pressure

The effects of pressure on electronic and optical properties of PbTiO3 (PTO) are studied by using first-principles calculation. Cubic paraelectric PTO (CP-PTO) is the most stable and has the strongest deformation resistance. The band gap of pre-perovskite PTO (PP-PTO) is 1.26 eV, and it has the smallest band gap at 30 GPa among the three phases. With pressure rising, the delocalization of O-2p and Ti-3d orbitals for the three phases gradually increases, which manifests that the absorption peaks and reflectivity peaks of CP-PTO and tetragonal ferroelectric PbTiO3 (TP-PTO) shift to the direction of high frequency wave. The absorption peak and reflection peak of PP-PTO are transparent to light when pressure up to 20 GPa.

Sources and Pathways of Intraseasonal Meridional Kinetic Energy in the Equatorial Atlantic Ocean

Abstract In the equatorial Atlantic Ocean, meridional velocity variability exhibits a pronounced peak on intraseasonal time scales whereas zonal velocity dominantly varies on seasonal to interannual time scales. We focus on the intraseasonal meridional velocity variability away from the near-surface layer, its source regions, and its pathways into the deep ocean. This deep intraseasonal velocity variability plays a key role in equatorial dynamics as it is an important energy source for the deep equatorial circulation. The results are based on the output of a high-resolution ocean model revealing intraseasonal energy levels along the equator at all depths that are in good agreement with shipboard and moored velocity data. Spectral analyses reveal a pronounced signal of intraseasonal Yanai waves with westward phase velocities and zonal wavelengths longer than 450 km. Different sources and characteristics of these Yanai waves are identified: near the surface between 40° and 10°W, low-baroclinic-mode Yanai waves with periods of around 30 days are excited. These waves have a strong seasonal cycle with a maximum in August. High-frequency Yanai waves (10–20-day period) are excited at the surface east of 10°W. In the region between the North Brazil Current and the Equatorial Undercurrent, high-baroclinic-mode Yanai waves with periods between 30 and 40 days are generated. Yanai waves with longer periods (40–80 days) are shed from the deep western boundary current. The Yanai wave energy is carried along beams eastward and downward, thus explaining differences in strength, structure, and periodicity of the meridional intraseasonal variability in the equatorial Atlantic Ocean. Significance Statement Past studies show that intraseasonal meridional kinetic energy is important for the deep equatorial circulation (DEC). However, numerical studies use intraseasonal variability with varying characteristics to investigate the formation and maintenance of the DEC. This is partly because of sparse observations at depth that are limited to single locations. This study investigates intraseasonal meridional kinetic energy in the equatorial Atlantic in a high-resolution ocean model that is tested against available shipboard and moored observations. We analyze the spatial and temporal distribution and the baroclinic structure of intraseasonal variability. Using the model, we identify different sources and pathways of intraseasonal energy in the deep equatorial Atlantic. We offer groundwork for further studies on the formation and maintenance of the DEC.

The Association of High COVID-19 Cases and Mortality with Anomalous High Surface Ozone Concentration in Moscow City in Summer 2021

Aim: to compare statistical data on the frequency of COVID-19 and deaths from it with the ozone content in the surface atmosphere of Moscow in the summer of 2021.Materials and methods. We used data on the frequency of daily COVID-19 cases and mortality from COVID-19 in Moscow in 2020–2021 published by Rospotrebnadzor. Data on the ozone content in the surface layer of the atmosphere were obtained by an automatic monitoring station using a chemiluminescent analyzer.Results. The waves of high frequency of COVID-19 cases and mortality from COVID-19 in Moscow in the summer of 2021 were compared with abnormally high concentrations of ozone in the surface atmosphere of the megalopolis. Variations of these parameters were found to be markedly correlated. The coefficients of correlation of the COVID-19 cases and mortality with the concentration of ground-level ozone were 0,59 (p < 0.01) and 0.60 (p < 0.01), respectively.Conclusion. The observed noticeable relationship may be due to the combined pathological effect of high concentrations of ozone and the SARS-CoV-2 on the respiratory and circulatory organs, which can lead to both easier transmission of infection and a more severe course of the disease with increased mortality.

Dynamic tensile failure of a V-shaped canyon induced by vertically travelling SV waves

Seismic-induced slope instability is a threat to transportation infrastructures in V-shaped canyons. The seismic-induced tensile cracks are commonly observed in the upper part of slopes and promote the seismic-induced slope instability. It is necessary to reveal the mechanism of tensile cracking in the upper part of a slope during an earthquake. The boundary integral equation method is employed to calculate the stresses induced by the self-weight and the vertically travelling SV wave. The stress development process shows that the self-weight induced stress plays an essential role in the development of tensile stress. Besides, the diffracted Rayleigh wave travelling along the ground surface is the major contributor to the generation of tensile stresses on the ground surface near the canyon. The effects of parameters, such as excitation frequency, canyon depth and slope inclination, on stress development are discussed. Parametric analyses indicate that the ground surface near a steeper slope more likely suffers tensile cracking. Higher-frequency waves prioritize producing the tensile cracks on the ground surface near a canyon. The steep slope of a deeper canyon allows the seismic waves within a wider frequency range to induce the tensile cracks on the ground surface near a canyon in priority.

Broadband Whistler Waves and Differential Electron Fluxes in the Equatorial Region of the Magnetosphere behind the Plasmapause during Substorm Injections

This paper considers the whistler waves in the frequency band from 3 to 30 kHz observed on the Van Allen Probe-B satellite on March 17, 2019, when the satellite was on L-shells from 2.8 to 5.4. The upper frequency in the emission spectrum followed the course of the electron gyrofrequency {{f}_{{ce}}} and was lower than it by 1–5 kHz. The emission spectrum often had two spectral maxima (above and below fce/2); the maximum at frequencies above fce/2 could be either more or less intense. High-frequency whistler waves at frequencies > fce/2 were observed simultaneously with an increase in low-energy electron fluxes with energies more than 102 eV, which had transverse anisotropy. To explain the observed spectrum, we used simultaneous satellite measurements of the cold plasma density and differential fluxes of energetic electrons in the energy range from 0.015 to 250 keV in a wide range of pitch angles to determine the electron distribution function and calculate local linear growth rate as a function of frequency f and wave normal angle theta . The calculations were performed for three cyclotron resonances (n = 1, 0, –1) that make the largest contributions to the wave growth rate. The calculations showed the presence of a pronounced maximum at frequencies (0.8–0.9) fce. The energy range and pitch angles of electrons with a maximum contribution to wave excitation at these frequencies were estimated.

On the Cauchy Problem for the Hall and Electron Magnetohydrodynamic Equations Without Resistivity I: Illposedness Near Degenerate Stationary Solutions

In this article, we prove various illposedness results for the Cauchy problem for the incompressible Hall- and electron-magnetohydrodynamic (MHD) equations without resistivity. These PDEs are fluid descriptions of plasmas, where the effect of collisions is neglected (no resistivity), while the motion of the electrons relative to the ions (Hall current term) is taken into account. The Hall current term endows the magnetic field equation with a quasilinear dispersive character, which is key to our mechanism for illposedness. Perhaps the most striking conclusion of this article is that the Cauchy problems for the Hall-MHD (either viscous or inviscid) and the electron-MHD equations, under one translational symmetry, are ill-posed near the trivial solution in any sufficiently high regularity Sobolev space $$H^{s}$$ and even in any Gevrey spaces. This result holds despite obvious wellposedness of the linearized equations near the trivial solution, as well as conservation of the nonlinear energy, by which the $$L^{2}$$ norm (energy) of the solution stays constant in time. The core illposedness (or instability) mechanism is degeneration of certain high frequency wave packet solutions to the linearization around a class of linearly degenerate stationary solutions of these equations, which are essentially dispersive equations with degenerate principal symbols. The method developed in this work is sharp and robust, in that we also prove nonlinear $$H^{s}$$ -illposedness (for s arbitrarily high) in the presence of fractional dissipation of any order less than 1, matching the previously known wellposedness results. The results in this article are complemented by a companion work, where we provide geometric conditions on the initial magnetic field that ensure wellposedness(!) of the Cauchy problems for the incompressible Hall and electron-MHD equations. In particular, in stark contrast to the results here, it is shown in the companion work that the nonlinear Cauchy problems are well-posed near any nonzero constant magnetic field.

High-Frequency and Spectrum-Clean Shear-Horizontal Acoustic Wave Resonators with AlN Overlay.

By bonding the sub-wavelength-thick lithium niobate (LiNbO3) layer to high-phase-velocity (vp) substrates, such as Si, the shear-horizontal (SH) modes no longer couple with the bulk modes leaking into substrates. As the propagation loss is no longer the major concern for these types of nonleaky SH wave devices, the YX-LiNbO3 with a low rotation angle providing ultra-large coupling coefficient (keff2) can be used. In addition, by overlaying a high-velocity layer such as AlN on top of LiNbO3/Si, the vp of the SH wave can be significantly enhanced at a small cost of keff2. By a careful design of the stack, both the wide-band spurious (Lamb wave) and near-band spurious (Rayleigh wave) are suppressed successfully. This paper focuses on the design of layered substrate not only to optimize its resonance characteristics—series frequency (fs), quality factor (Q), keff2, and temperature coefficient of frequency (TCF)—but also for eliminating the out-of-band spurious responses. The optimized substrate design demonstrates the minimal propagation loss, high fs of 3 GHz, large keff2 of 14.4% and a spurious-free response at 0–6 GHz. These novel nonleaky SH wave devices can potentially enable the low loss and wideband processing functions, which is promising for the 5G/6G radio frequency (RF) communication systems.