Amplitude Modulation Of Waves Research Articles

Large-scale magnetic field oscillations and their effects on modulating energetic electron precipitation

In this study, we present simultaneous multi-point observations of magnetospheric oscillations on a time scale of tens of minutes (forced-breathing mode) and modulated whistler-mode chorus waves, associated with concurrent energetic electron precipitation observed through enhanced BARREL X-rays. Similar fluctuations are observed in X-ray signatures and the compressional component of magnetic oscillations, spanning from ∼9 to 12 h in MLT and 5 to 11 in L shell. Such magnetospheric oscillations covering an extensive region in the pre-noon sector have been suggested to play a potential role in precipitating energetic electrons by either wave scattering or loss cone modulation, showing a high correlation with the enhancement in X-rays. In this event, the correlation coefficients between chorus waves (smoothed over 8 min), ambient magnetic field oscillations and X-rays are high. We perform an in-depth quasi-linear modeling analysis to evaluate the role of magnetic field oscillations in modulating energetic electron precipitation in the Earth’s magnetosphere through modulating whistler-mode chorus wave amplitude, resonance condition between chorus waves and electrons, as well as loss cone size. Model results further show that the modulation of chorus wave amplitude plays a dominant role in modulating the electron precipitation. However, the effect of the modulation in the resonant energy between chorus waves and energetic electrons due to the background magnetic field oscillations cannot be neglected. The bounce loss cone modulation, affected by the magnetic oscillations, has little influence on the electron precipitation modulation. Our results show that the low frequency magnetospheric oscillations could play a significant role in modulating the electron precipitation through modulating chorus wave intensity and the resonant energy between chorus waves and electron.

Amplitude modulation and surface wave generation in a complex plasma monolayer.

The response of a two-dimensional plasma crystal to an externally imposed initial perturbation has been explored using molecular dynamics (MD) simulations. A two-dimensional (2D) monolayer of micron-sized charged particles (dust) is formed in the plasma environment under certain conditions. The particles interacting via Yukawa pair potential are confined in the vertical (z[over ̂]) direction by an external parabolic confinement potential, which mimics the combined effect of gravity and the sheath electric field typically present in laboratory dusty plasma experiments. An external perturbation is introduced in the medium by displacing a small central region of particles in the vertical direction. The displaced particles start to oscillate in the vertical direction, and their dynamics get modulated through a parametric decay process generating beats. It has also been shown that the same motion is excited in the dynamics of unperturbed particles. A simple theoretical model is provided to understand the origin of the beat motions of particles. Additionally, in our simulations, concentric circular wavefronts propagating radially outward are observed on the surface of the monolayer. The physical mechanism and parametric dependence of the observed phenomena are discussed in detail. This research sheds light on the medium's ability to exhibit macroscopic softness, a pivotal characteristic of soft matter, while sustaining surface wave modes. Our findings are also relevant to other strongly coupled systems, such as colloids and classical one-component plasmas.

Evaluation Method of Noise Electromagnetic Radiation Interference Effect

In order to evaluate the viability of frequency equipment in complex electromagnetic environment, the electromagnetic radiation effect evaluation model of random noise is established based on the analysis of the blocking effect mechanism of frequency equipment. Through MATLAB calculation, the corresponding relationship table between the ratio of the critical interference field strength effective value of single frequency continuous wave and sinusoidal amplitude modulation wave and the key parameters of the model is given, and the prediction method of noise electromagnetic interference of frequency equipment is proposed. Taking a Beidou navigation receiver as the test object, the accuracy of the noise electromagnetic radiation blocking effect model is verified by single frequency continuous wave, random noise and narrowband noise electromagnetic radiation blocking effect test, and the maximum error is only 1.51 dB, which indicates that the model and prediction method proposed in this article can accurately evaluate and predict the electromagnetic radiation interference of random noise.

Predicting acoustic emissions of ultrasound-driven lipid-coated microbubbles

Lipid-coated microbubbles excited by ultrasound are utilized in an increasing number of diagnostic and therapeutic medical applications, in which the acoustic waves emitted by the oscillating or collapsing bubbles are the main protagonist. The emitted acoustic waves cause bioeffects, enable contrast enhancement for ultrasonic imaging, and serve as a reference to monitor cavitation activity in situ. However, quantifying the acoustic waves emitted by cavitation bubbles turns out to be difficult: the small and extremely transient phenomenon is challenging to measure in experiments with sufficient accuracy and state-of-the-art computational methods are limited in their ability to predict acoustic emissions reliably. In this contribution, we present our recent work on predicting acoustic emissions of microbubbles based on Rayleigh–Plesset models and, more generally, reduced-order models. Using the nonlinear Westervelt equation including the motion of the bubble wall and the background medium as a result of the bubble oscillations, we investigate the amplitude and frequency modulation (e.g., due to nonlinear Doppler effects, thermoviscous attenuation or geometric distortion) of acoustic waves emitted by lipid-coated microbubbles. Additionally, we explore the capabilities of a reduced-order modeling approach that drastically simplifies the computational complexity of simulating these acoustic emissions.

Simulation data of "On whistler wave amplitude modulation associated with pulsating aurora"

Simulation data of "On whistler wave amplitude modulation associated with pulsating aurora"

Nonplanar dust acoustic waves in a four-component dusty plasma with double spectral distributed electrons: modulational instability and rogue waves

A theoretical investigation of nonplanar (cylindrical and spherical) amplitude modulation of dust acoustic waves (DAWs) in a four component dusty plasma including positive and negative dusts, Maxwellian ions and double spectral electron distribution (DSED) is carried out. The focusing modified nonlinear Schrödinger equation (MNLSE) is derived using the derivative expansion perturbation technique (DEPT). The limit of DSED to Maxwell distribution is discussed. The effects of the two spectral indices, and , on the modulational instability (MI) growth rate are examined and it is deduced that increasing the value of and raises the MI growth rate. Additionally, the structure of the first and second-order dust acoustic (DA) rogue waves in the modulational unstable region is analyzed. The influences of both of and on the rogue wave amplitude (energy) are investigated. We found that increasing the value of enhances the rogue wave amplitude while the opposite behavior is found by increasing values. The findings of the present study are useful to interpret some physical phenomena in various plasma situations that found in space regions, such as Titan (the largest moon) of Saturn, auroral region and asteroid zones, where the effectiveness of non-Maxwellian particles such as DSED is existed.

Discrete localized excitations for discrete conformable fractional cubic–quintic Ginzburg–Landau model possessing the non-local quintic term

Considering conformable fractional derivative to modify the Jacobian elliptic function method, rich exact solutions of discrete conformable fractional complex cubic–quintic Ginzburg–Landau model possessing non-local quintic term are derived. Solutions with alternating phases have different properties from their continuous analogs. The effects of filter and linear dissipation parameters on explosion excitation and wave amplitude modulation are studied.

Amplitude-modulated electron-acoustic waves with bipolar ions and kappa-distributed positrons and warm electrons

In this paper, we have meticulously studied the amplitude modulation of electron-acoustic waves and the formation and properties of envelope solitons in a five-component complex plasma containing statistically kappa-distributed warm and cold electrons, kappa-distributed positrons and Boltzmann-distributed positive and negative ions. The picture considered here is very similar to solar atmosphere and planetary environments. The parametric dependence of modulational instability on kappa index, positron and electron densities, ion and reciprocal of positron temperatures has been studied in detail and the findings obtained here will be beneficial for further astrophysical investigations.

The fundamental ultrasonic edge wave mode: Propagation characteristics and potential for distant damage detection

Engineering structures are often composed of thin elements containing features such as free edges, welds, ribs, and holes, which makes distant safety inspections based on guided waves difficult due to wave scattering. However, these features can themselves generate so-called ‘feature-guided’ waves, which can potentially be utilised for damage detection. One such example are flexural wedge waves, which have been investigated extensively both theoretically and experimentally in the past. Another example is edge waves. These waves, which are a natural analogue of Rayleigh waves propagating in a finite thickness plate, have received relatively little attention, specifically with respect to their possible use in distant damage inspections and Structural Health Monitoring systems. The current paper is aimed to address this gap, and it is focused on the investigation of the fundamental mode of edge waves (ES0), which is the most promising for practical applications. The features of the transient ES0 mode are investigated experimentally and numerically, and compared with previous theoretical studies. It was demonstrated that the ES0 mode can be effectively excited with the wedge excitation method, and distant damage detection with this wave mode at low frequency-thickness values (FTV < 5) is readily achievable. In particular, in a laboratory environment the ES0 mode propagated several meters with almost no decay. However, at higher frequency-thickness values, a wave amplitude modulation, significant energy decay and strong coupling between the ES0 and S0 wave modes were observed. These phenomena may restrict the defect resolution as well as the range of damage inspections based on the fundamental edge wave mode.

Soliton dynamics based on exact solutions of conformable fractional discrete complex cubic Ginzburg–Landau equation

The Jacobian elliptic function expansion method is modified by considering conformable fractional derivative and applying a lot of relations among Jacobian elliptic functions. This modified method is applied to derive the discrete fractional soliton solutions of conformable fractional discrete complex cubic Ginzburg–Landau equation, including Jacobian elliptic function solutions and some special soliton and triangular function solutions. The singularity like tan and sec solutions ‘between sites’ can be avoided in the lattice. Based on these analytical solutions, the influence of the linear dissipation and filter parameters on wave amplitude modulations and optical explosive excitations is studied.

Nonlinear modulation of quantum electron acoustic waves in a Thomas–Fermi plasma with effects of exchange-correlation

The amplitude modulation of electron acoustic waves (EAWs) is investigated in an unmagnetized four-component quantum plasma containing dynamic cold electron fluid, Thomas–Fermi distributed hot electrons and positrons and immobile ions in presence of exchange-correlation potentials. For this purpose, basic set of quantum hydrodynamic equations is reduced to a nonlinear Schrodinger equation (NLSE) adopting a reductive perturbation technique. The regions of the stable and unstable wave packets are obtained precisely in terms of the intrinsic plasma parameters. It is shown that the NLSE leads to the modulational instability (MI) of EAWs, and the formation of EA rogue waves, which are due to the effects of nonlinearity and dispersion in the propagation of EAWs. The effects of relevant plasma parameters on the MI criterion are numerically investigated. It is also found that the modulated EAW packets can propagate in the form of bright envelope solitons as well as dark envelope solitons. Within the modulational instability region, the dependence of first- and second-order EA rogue wave profiles on the system parameters is discussed.

Phase Decoherence Within Intense Chorus Wave Packets Constrains the Efficiency of Nonlinear Resonant Electron Acceleration

AbstractElectron resonant interaction with whistler mode waves is traditionally considered as one of the main drivers of radiation belt dynamics. The two main theoretical concepts available for its description are quasi‐linear theory of electron scattering by low‐amplitude waves and nonlinear theory of electron resonant trapping and phase bunching by intense waves. Both concepts successfully describe some aspects of wave‐particle interactions but predict significantly different timescales of relativistic electron acceleration. In this study, we investigate effects that can reduce the efficiency of nonlinear interactions and bridge the gap between the predictions of these two types of models. We examine the effects of random wave phase and frequency variations observed inside whistler mode wave packets on nonlinear interactions. Our results show that phase coherence and frequency fluctuations should be taken into account to accurately model electron nonlinear resonant acceleration and that, along with wave amplitude modulation, they may reduce acceleration rates to realistic, moderate levels.

Wave amplitude modulation in fan loops as observed by AIA/SDO

Aims. We perform a detailed analysis to understand the evolution and dynamics of propagating intensity disturbances observed in a fan loop system. Methods. We performed multiwavelength time-distance analysis of a fan loop system anchored in an isolated sunspot region (AR 12553). The active region was observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. We measured the phase speeds of the propagating intensity disturbances by employing cross-correlation analysis, and by obtaining the slopes in xt-plots. We obtained original and detrended light curves at different heights of the time-distance maps and characterised them by performing Fourier and wavelet analysis, respectively. Results. The time-distance maps reveal clear propagation of intensity oscillations in all the coronal extreme ultraviolet (EUV) channels except AIA 94 and 335 Å. We determine the nature of the intensity disturbances as slow magneto-acoustic waves by measuring their phase speeds. The time-distance maps, as well as the detrended light curves, show an increase and decrease in the amplitude of propagating 3 min oscillations over time. The amplitude variations appear most prominently in AIA 171 Å, though other EUV channels also show such signatures. The Fourier power spectrum yields the presence of significant powers with several nearby frequencies in the range of 2–3 min (5–8 mHz), along with many other smaller peaks between 2–4 min. Wavelet analysis shows an increase and decrease of oscillating power around 3 min simultaneous to the amplitude variations. We obtain the modulation period to be in the range of 20–30 min. Conclusions. Our results provide the viability of occurrence of phenomenon like “Beat” among the nearby frequencies giving rise to the observed amplitude modulation. However, we cannot at this stage rule out the possibility that the modulation may be driven by variability in an underlying unknown source.

Dissipative ion-acoustic solitons in ion-beam plasma obeying a κ -distribution

The amplitude modulation of ion-acoustic waves is investigated in a plasma system consisting of ions and electrons obeying κ-distribution. Taking into account the dissipative mechanisms that consist of the ionization and applying a reductive perturbation technique, a one-parameter dissipative nonlinear Schrödinger (DNLS) equation of electrostatic potential governing the dynamics of these modulated ion-acoustic waves is derived and expressed in terms of the system parameters only. The modulational instability and its dependence on the system’s physical parameters is presented. Within the unstable region, the dynamics of dissipative ion-acoustic bright solitons propagating on a non-vanishing continuous wave background is analyzed analytically with the help of an approximative soliton solutions of the DNLS equation of the system. The effect of the plasma parameters on the dynamics of dissipative bright solitons is also presented. We find that the ion to electron temperature ratio (σ = Ti/Te) plays an important role in our analytical investigation.

Respiratory rate extraction based on plethysmographic wave analysis

Respiratory rate (RR) is one of the vital parameters of a person’s health. In certain conditions such as patients with respiratory problems or heart who are in the treatment room, respiratory rate monitoring is carried out continuously. In health care centers such as hospitals, RR measurements use a bed side monitor. However, this device is not yet widely available in small scale health services such as Community Health Centers (Puskesmas) because this device is expensive. One alternative for RR extraction is through plethysmographic wave analysis measured using a photopletismograph (PPG) device. This is based on the hypothesis that breathing affects the dynamics of PPG wave amplitude modulation so that by extracting this information we can know the respiratory rate. PPG devices are widely available in small health services because of their low prices. Meanwhile, PPG is only used to measure heart rate and oxygen saturation. In this study, a method for extracting RR information is proposed by analyzing PPG waves. Two methods, namely empirical mode decomposition (EMD) and variational mode decomposition (VMD), are applied to obtain respiratory oscillation information. The aim is to get the most optimum method for RR extraction. The performance test of the two proposed methods was carried out through time-frequency domain transformation using Fast Fourier Transform. The method used in this study is expected to be applied to conventional PPG devices.

Modulation of ion sound excitations in electron–ion plasmas with double spectral index distribution function

AbstractTheoretical investigation of amplitude modulation of ion sound waves is presented here for an electron–ion plasma where the electrons are dictated by the double spectral index (r, q) distribution function. Using the standard reductive perturbative technique, a non‐linear Schrödinger (NLS) equation is derived that describes the evolution of modulated ion sound envelope excitations. Stability analysis of the NLS equation shows that the ion sound waves remain stable for the flat‐topped and kappa‐like distributions, but they can become unstable for the spiky electron velocity distribution. It is shown that changing the electron population in regions of low and high phase space density regions results in remarkable features that have no equivalent in ion sound waves with Boltzmannian electrons. Different types of localized ion sound excitations are plotted for the different shapes of the distribution functions controlled by the double spectral indices, and the underlying physics is discussed in detail. The present investigation may be beneficial to understand ion sound excitations in space plasmas where the distribution functions of the shapes presented here are frequently encountered by the satellite missions.

Nonlinear Interactions Between Radiation Belt Electrons and Chorus Waves: Dependence on Wave Amplitude Modulation

AbstractWe use test particle simulations to model the interaction between radiation belt electrons and whistler mode chorus waves by focusing on wave amplitude modulations. We quantify the pitch angle and energy changes due to phase trapping and phase bunching (including both advection and scattering) for electrons with various initial energies and pitch angles. Three nonlinear regimes are identified in a broad range of pitch angle‐energy space systematically, each indicating different nonlinear effects. Our simulation results show that wave amplitude modulations can extend the nonlinear regimes, while significantly reducing electron acceleration by phase trapping. By including amplitude modulations, the “advective” changes in pitch angle and energy caused by phase bunching are reduced, while the “diffusive” scattering due to phase bunching is enhanced. Our study demonstrates the importance of wave amplitude modulations in nonlinear effects and suggests that they need to be properly incorporated into future theoretical and numerical studies.

Electron acoustic envelope solitons in non-Maxwellian plasmas

The NASA Van Allen Probes spacecraft has recently observed broadband electrostatic turbulence in the inner magnetosphere which has been conjectured to be produced by large amplitude electrostatic solitary waves of generally two types [D.M. Malaspina, J.R. Wygant, R.E. Ergun, G.D. Reeves, R.M. Skoug, B.A. Larsen, J. Geophys. Res.: Space Phys. 120, 4246 (2015); C.S. Dillard, I.Y. Vasko, F.S. Mozer, O.V. Agapitov, J.W. Bonnell, Phys. Plasmas 25, 022905, (2018)]. The solitary waves with highly asymmetric bipolar parallel electric field have been recently shown to correspond to the electron-acoustic plasma mode (existing due to two-temperature electron population) [C.S. Dillard, I.Y. Vasko, F.S. Mozer, O.V. Agapitov, J.W. Bonnell, Phys. Plasmas 25, 022905, (2018)]. These findings along with the observations of non-Maxwellian electrons in terrestrial magnetosheath and planetary magnetospheres [W. Masood, S.J. Schwartz, M. Maksimovic, A.N. Fazakerley, Ann. Geophys. 24, 1725 (2006); W. Masood, S.J. Schwartz, J. Geophys. Res. 113, A01216 (2008); M.N.S. Qureshi, W. Nasir, W. Masood, P.H. Yoon, H.A. Shah, S.J. Schwartz, J. Geophys. Res.: Space Phys. 119, 10059 (2014); M.N.S. Qureshi, W. Nasir, R. Bruno, W. Masood, MNRAS 488, 954 (2019)] have prompted us to theoretically investigate the problem of amplitude modulation of the electron acoustic waves (EAWs) in plasmas whose ingredients are stationary ions, inertial cold electrons and warm (r,q) distributed inertialess electrons. The nonlinear Schrodinger equation (NLSE) that governs the modulational instability (MI) of the EAWs has been derived using the standard reductive perturbation technique (RPT). The presence of the warm (r,q) distributed electrons has been shown to influence the existence conditions of MI of the EAWs and both the indices have been found to cause a decrease in the growth rate of MI. A detailed comparison has also been drawn between double spectral index (r,q), kappa and Maxwellian distribution functions and the differences are highlighted. Additionally, the nondimensional parameter α=nc0/ne0 which is the equilibrium density ratio of the cold to hot electron component, has been shown to play an important role in the formation of envelope solitary excitations.

Theoretical Analysis of Parameter Optimization for Lower-Ionosphere Excitation ELF/VLF Waves Based on Chirp-BOK Modulated Heating

To improve the anti-interference for ELF/VLF communication based on modulated heating lower-ionosphere, chirp spread spectrum technology with strong anti-interference is combined with square wave amplitude modulation, a novel method of chirp-BOK modulated heating lower-ionosphere is proposed in this paper. On this basis, to improve the radiation efficiency of ELF/VLF, the effects of heating parameters (effective radiation power, pump frequency, polarization mode, modulation frequency, duty cycle, and bandwidth) on the radiation efficiency of ELF/VLF were analyzed. The results show that the radiation amplitude of ELF/VLF increases with the increase of effective radiation power, while the radiation efficiency increases first and then decreases; the X-mode is better than the O-mode; the radiation intensity of ELF/VLF decreases with the increase of pump wave frequency from 4MHz to 10MHz; the ELF/VLF equivalent dipole moments increase with the rise of modulation frequency from 500Hz to 5kHz; with the change of duty cycle from 10% to 90%, the dipole moments first increase and then decrease, and the optimal range of duty cycle is 40% to 70%; with the increase of bandwidth, the dipole moments are unchanged. Furthermore, the ELF/VLF dipole moments of square wave amplitude modulated heating ionosphere is unchanged before and after the chirp spread spectrum.

On the physical mechanisms of the two-way coupling between a surface wave field and a circulation consisting of a roll and streak

The governing equations of a surface wave field and a coexisting roll–streak circulation typical of Langmuir circulations or submesoscale frontal circulations are derived to better describe their two-way interactions. The gradients and vertical velocities of the roll–streak circulation induce wave refraction, amplitude modulation and higher-order waves. These changes then produce wave–wave nonlinear forces and divergence of the wave-induced mass transport, both of which in turn affect the circulation. To accurately represent these processes, both a wave theory and a wave-averaged theory are developed without relying on any extrapolation, any spatiotemporal mapping or an approximation that treats the wave-induced mass divergence as being concentrated at the surface. This wave theory finds seven types of current-induced higher-order wave motions. It also determines the wave dynamics such as the governing equation of the wave action density valid in the presence of the complex circulation. The evolution of the wave action density is clearly affected by the upwelling or downwelling. The new wave-averaged theory presents the governing equations of the wave-averaged circulation which satisfies the wave-averaged mass conservation. This circulation is different from the circulation considered to satisfy the mass conservation in the Craik–Leibovich theory, and the difference becomes critical when the wave field evolves due to refraction. In this case, compared to the Craik–Leibovich theory, long waves are more important and also the rolls are more weakly forced.