Amplitude Modulation Of Waves Research Articles

EMIC wave spatial and coherence scales as determined from multipoint Van Allen Probe measurements

AbstractElectromagnetic ion cyclotron (EMIC) waves can provide a strong source of energetic electron pitch angle scattering. These waves are often quite localized, thus their spatial extent can have a large effect on their overall scattering efficiency. Using measurements from the dual Van Allen Probes, we examine four EMIC wave events observed simultaneously on the two probes at varying spacecraft separations. Correlation of both the wave amplitude and phase observed at both spacecraft is examined to estimate the active region and coherence scales of the waves. We find well‐correlated wave amplitude and amplitude modulation across distances spanning hundreds to thousands of kilometers. Phase coherence persisting 30–60 s is observable during close conjunction events but is lost as spacecraft separations exceed ~1 Earth Radii.

Neural timing signal for precise tactile timing judgments.

The brain can precisely encode the temporal relationship between tactile inputs. While behavioural studies have demonstrated precise interfinger temporal judgments, the underlying neural mechanism remains unknown. Computationally, two kinds of neural responses can act as the information source. One is the phase-locked response to the phase of relatively slow inputs, and the other is the response to the amplitude change of relatively fast inputs. To isolate the contributions of these components, we measured performance of a synchrony judgment task for sine wave and amplitude-modulation (AM) wave stimuli. The sine wave stimulus was a low-frequency sinusoid, with the phase shifted in the asynchronous stimulus. The AM wave stimulus was a low-frequency sinusoidal AM of a 250-Hz carrier, with only the envelope shifted in the asynchronous stimulus. In the experiment, three stimulus pairs, two synchronous ones and one asynchronous one, were sequentially presented to neighboring fingers, and participants were asked to report which one was the asynchronous pair. We found that the asynchrony of AM waves could be detected as precisely as single impulse pair, with the threshold asynchrony being ∼20 ms. On the other hand, the asynchrony of sine waves could not be detected at all in the range from 5 to 30 Hz. Our results suggest that the timing signal for tactile judgments is provided not by the stimulus phase information but by the envelope of the response of the high-frequency-sensitive Pacini channel (PC), although they do not exclude a possible contribution of the envelope of non-PCs.

Amplitude modulation of ion-acoustic waves in magnetized electron-positron-ion plasma with q-nonextensive electrons and positrons

Using a standard reductive perturbation technique, a nonlinear Schrödinger equation has been derived that describes the nonlinear evolution of ion-acoustic waves in magnetized electron-positron-ion plasma with electrons and positrons following q-nonextensive distribution. It is shown that excitation of both bright and dark envelope solitary structures is possible in the model plasma under consideration. The conditions for the excitation and structure of these envelope solitary waves are shown to depend sensitively on the strength of the external magnetic field, obliqueness of wave propagation relative to the external magnetic field, and other plasma parameters such as the q-nonextensivity of plasma species, positron concentration, and electron-positron temperature ratio.

Stability of relativistic electron trapping by strong whistler or electromagnetic ion cyclotron waves

In the present paper, we investigate the trapping of relativistic electrons by intense whistler-mode waves or electromagnetic ion cyclotron waves in the Earth's radiation belts. We consider the non-resonant impact of additional, lower amplitude magnetic field fluctuations on the stability of electron trapping. We show that such additional non-resonant fluctuations can break the adiabatic invariant corresponding to trapped electron oscillations in the effective wave potential. This destruction results in a diffusive escape of electrons from the trapped regime of motion and thus can lead to a significant reduction of the efficiency of electron acceleration. We demonstrate that when energetic electrons are trapped by intense parallel or very oblique whistler-mode waves, non-resonant magnetic field fluctuations in the whistler-mode frequency range with moderate amplitudes around 3−15 pT (much less intense than the primary waves) can totally disrupt the trapped motion. However, the trapping of relativistic electrons by electromagnetic ion cyclotron waves is noticeably more stable. We also discuss how the proposed approach can be used to estimate the effects of wave amplitude modulations on the motion of trapped particles.

Photo-Doped Active Electrically Controlled Terahertz Modulator

We demonstrate an electric-controlled terahertz (THz) modulator which can be used to realize amplitude modulation of terahertz waves with slight photo-doping. The THz pulse transmission was efficiently modulated by electrically controlling the monolayer silicon-based device. The modulation depth reached 100% almost when the applied voltage was 7 V at an external laser intensity of 0.6 W/cm2. The saturation voltage reduced with the increase of the photo-excited intensity. In a THz continuous wave (CW) system, a significant fall in both THz transmission and reflection was also observed with the increase of applied voltage. This reduction in the THz transmission and reflection was induced by the absorption for electron injection. The results show that a high-efficiency and high modulation depth broadband electric-controlled terahertz modulator in a pure Si structure has been realized.

Experimental research on unstable movements of sandbars under wave actions

This study is motivated by recognition of complex sandbar evolution patterns under wave actions inside the surf zone. A series of physical model experiments were conducted in a wave flume to investigate sandbar migration under various wave conditions, including wave groups, regular waves, and random waves. It was observed that under certain wave conditions sandbars move alternately shoreward and seaward rather than continuously in the same direction. The measurements show that the unstable movement of sandbars is closely related to the amplitude modulation of waves. Smaller amplitude modulation tends to produce more intense unstable bar movements. Data analysis further shows that the sandbar migration does not seem to be a passive response of the sea bed to wave forcing, but is most likely caused by the feedback interaction between waves and bed topography.

Modulation of Electron-Acoustic Waves in a Plasma with Vortex Electron Distribution

Abstract In the present work, employing a one-dimensional model of a plasma composed of a cold electron fluid, hot electrons obeying a trapped/vortex-like distribution and stationary ions, we study the amplitude modulation of electron-acoustic waves by use of the conventional reductive perturbation method. Employing the field equations with fractional power type of nonlinearity, we obtained the nonlinear Schrödinger equation as the evolution equation of the same order of nonlinearity. Seeking a harmonic wave solution with progressive wave amplitude to the evolution equation it is found that the NLS equation with fractional power assumes envelope type of solitary waves.

Amplitude modulation of water waves governed by Boussinesq’s equation

This paper derives the equations of amplitude modulation of shallow water waves from the scalar Boussinesq’s (BSQ) equation by using the variational-asymptotic method. Two asymptotic solutions describing the amplitude modulation of trains of solitons and of positons are obtained. The comparison with the exact solutions of BSQ equation shows quite excellent agreement.

Modulational instability of ion-acoustic waves in fully relativistic two-component plasma

Nonlinear amplitude modulation of ion-acoustic waves (IAWs) in a fully relativistic unmagnetized two-fluid plasma has been theoretically studied by using complete set of fully relativistic dynamic equations. To describe the nonlinear evolution of the wave envelope a nonlinear Schrödinger (NLS) equation is derived by using standard multiple scale perturbation technique. Using this equation it is shown that the wave becomes modulationally unstable as the wavenumber exceeds certain critical value. This critical wavenumber is found to decrease with increase in relativistic effect. The instability growth rate has also been calculated numerically for different values of plasma drift velocity. The growth rate is shown to decrease with increase in the relativistic effect.

High speed electrically-controlled terahertz modulator

We have developed an electrically-controlled terahertz modulator which can be used to realize amplitude modulation of terahertz waves at an extremely high speed. The terahertz modulator is made on GaAs-based high electron mobility transistors (HEMTs) array on which numerous split-ring resonators (SRRs) are formed. The device exhibits the capability of dynamical response to incident terahertz waves under a fast time-varying voltage. Our measurement results reveal that an ultrafast modulation speed over 11MHz under an applied AC gate voltage can be achieved. With the resistance and the capacitance of HEMTs further optimized, it was demonstrated that the HEMT/SRR-based modulator may operate at an even higher modulation frequency.

Research on the Seismic Performance of Brick-Concrete Structural Buildings in Indonesian Rural Areas

By investigating on rural housing construction in Djetis county, a region of Java Island Banjul, Indonesia, modeling according to their different weight of roofs and other factories, and combining with 3D seismic wave that was gotten by American EL Centro-seismic wave amplitude modulation to analyze by the finite element, it is shown that the larger quality of roof and the greater the displacement of itself each part, the bigger influence of structure and the easier causes damage. Maximal displacement produced by out-of-plane is larger than maximal displacement produced by in the plane, so the out-of-plain damage is the main cause of structure damage. In addition, based on the finite element analysis, precaution against earthquake measures of limiting to widen the top roof truss girder cross section and setting continuous wall between coupling beam are presented.

Modulation of electrostatic Langmuir waves in quantum electron-hole semiconductor plasmas

Amplitude modulation of electrostatic Langmuir waves in a quantum electron–hole semiconductor plasma is considered in the quantum magnetohydrodynamic regime. The important ingredients of this study are the inclusion of the particle degeneracy pressure, exchange-correlation potential, and the quantum diffraction effects via the Bohm potential. A nonlinear Schrödinger equation (NLSE) is developed for the evolution of the amplitude of the electrostatic wave by employing the standard reductive perturbation technique. The dynamics of the wave in the slow space-time scales is governed by the NLSE. Typical values of the parameters for GaAs, GaSb, and GaN semiconductors are considered in analyzing the nonlinear dispersion of the electrostatic wave. Detail analysis of the nature of the modulation, here modulation instability, in the long-wavelength regime is presented. For some parameter ranges of the semiconductor plasmas, and at the long-wavelength regime, it is found that the electrostatic wave is modulationally unstable. Effects of the exchange-correlation potential and the Bohm potential are also studied. It is found that the exchange-correlation potential has profound effects compared to the Bohm potential in the amplitude modulation of the electrostatic wave.

Modulation instability and dissipative rogue waves in ion-beam plasma: Roles of ionization, recombination, and electron attachment

The amplitude modulation of ion-acoustic waves is investigated in an unmagnetized plasma containing positive ions, negative ions, and electrons obeying a kappa-type distribution that is penetrated by a positive ion beam. By considering dissipative mechanisms, including ionization, negative-positive ion recombination, and electron attachment, we introduce a comprehensive model for the plasma with the effects of sources and sinks. Via reductive perturbation theory, the modified nonlinear Schrödinger equation with a dissipative term is derived to govern the dynamics of the modulated waves. The effect of the plasma parameters on the modulation instability criterion for the modified nonlinear Schrödinger equation is numerically investigated in detail. Within the unstable region, first- and second-order dissipative ion-acoustic rogue waves are present. The effect of the plasma parameters on the characteristics of the dissipative rogue waves is also discussed.

Modulated amplitude waves with non-trivial phase in quasi-1D inhomogeneous Bose–Einstein condensates

Abstract We consider a 1D nonlinear Schrodinger equation (NLSE) which describes the mean field dynamics of an elongated Bose–Einstein condensate and prove the existence of modulated amplitude waves with non-trivial phase and minimal spatial period tending to infinite. The proof combines the theory of local continuation of non-degenerate periodic solutions with a property of the Ermakov–Pinney equation.

Effect of ion temperature on modulational instability and envelope solitons of ion acoustic waves in nonthermal electron–positron–ion plasmas

The modulational instability and envelope solitons of ion acoustic waves in an unmagnetized nonthermal electron–positron–ion (epi) plasma are investigated. The ions are taken to be dynamic and warm while electrons and positrons are assumed to be inertialess and hot which follow the kappa (or Generalized Lorentzian) distribution. The Krylov–Bogoliubov–Mitropolsky method is used to derive the nonlinear Schrödinger equation for nonlinear amplitude modulation of ion acoustic waves in nonthermal epi plasmas with warm ions. The dispersive and nonlinear coefficients are obtained for ion acoustic waves in nonthermal epi plasmas which depend on spectral indices of kappa distributed electrons and positrons, ion temperature and positron density. The modulationally stable and unstable regions are studied for a wide range of wave numbers and it is found that the finite ion temperature, positron density and spectral indices of kappa distributed electrons and positrons play a significant role in the formation of bright and dark envelope solitons in nonthermal epi plasmas with adiabatically heated ions. Our findings are applicable to explain some aspects of nonlinear propagation of envelope solitons in astrophysical plasma situations such as neutron stars or pulsars where nonthermal epi plasmas with warm ions can exist (Arons J 2009 Astrophys. Space Sci. Library 357 373, Blasi P and Amato E 2011 Astrophys. Space Sci. Proc. pp 623–41, Asif and Saeed 2011 Plasma Phys. Control. Fusion 53 095006).

Amplitude modulation of waves governed by Korteweg–de Vries equation

Using the variational-asymptotic method we develop the theory of amplitude modulation of waves governed by Korteweg–de Vries (KdV) equation. Two asymptotic solutions describing the amplitude modulation of trains of solitons and of positons are obtained. The comparison with the exact solutions of KdV equation shows quite excellent agreement.

Modulation of the Convectively Coupled Kelvin Waves over South America and the Tropical Atlantic Ocean in Association with the Madden–Julian Oscillation

Abstract In this study, evidence of the strong modulation of the convectively coupled Kelvin wave (CCKW) activity by the Madden–Julian oscillation (MJO) is presented, with a particular focus over the South America and tropical Atlantic region. The MJO impacts on CCKWs over this region, as noted in anomalous fields of rainfall as well as vertical profiles of wind, moisture, and temperature, are primarily through the modulation of Kelvin wave amplitude, with secondary effects on vertical structure, and little impact on wavenumber. CCKW activity is enhanced during MJO phases 8, 1, and 2 and damped during MJO phases 4, 5, and 6. Further analyses reveal that the strong modulation of the MJO on the CCKW activity could be largely through two factors: namely, the vertical zonal wind shear and the lower- to middle-tropospheric specific humidity. The CCKW activity tends to be enhanced during MJO phases when the easterly vertical wind shear and positive low- to midtroposphere moisture anomalies are present and vice versa. These two physical processes associated with the MJO are found to have positively (negatively) reinforcing influences on the CCKW activity in phase 1 (4 and 5), while counteracting influences in phases 2, 3, 6, 7, and 8, leading to the observed MJO cycle of the CCKW activity anomalies in the study region. The results presented in this study may have important implications for extended-range prediction of tropical wave activity and might suggest possible roles of the upstream CCKWs in the initiation of the MJO in the western Indian Ocean.

Birth–death process of local structures in defect turbulence described by the one-dimensional complex Ginzburg–Landau equation

Abstract Defect turbulence described by the one-dimensional complex Ginzburg–Landau equation is investigated and analyzed via a birth–death process of the local structures composed of defects, holes, and modulated amplitude waves (MAWs). All the number statistics of each local structure, in its stationary state, are subjected to Poisson statistics. In addition, the probability density functions of interarrival times of defects, lifetimes of holes, and MAWs show the existence of long-memory and some characteristic time scales caused by zigzag motions of oscillating traveling holes. The corresponding stochastic process for these observations is fully described by a non-Markovian master equation.

High-Contrast Terahertz Wave Modulation by Gated Graphene Enhanced by Extraordinary Transmission through Ring Apertures

Gate-controllable transmission of terahertz (THz) radiation makes graphene a promising material for making high-speed THz wave modulators. However, to date, graphene-based THz modulators have exhibited only small on/off ratios due to small THz absorption in single-layer graphene. Here we demonstrate a ∼50% amplitude modulation of THz waves with gated single-layer graphene by the use of extraordinary transmission through metallic ring apertures placed right above the graphene layer. The extraordinary transmission induced ∼7 times near-filed enhancement of THz absorption in graphene. These results promise complementary metal-oxide-semiconductor compatible THz modulators with tailored operation frequencies, large on/off ratios, and high speeds, ideal for applications in THz communications, imaging, and sensing.

A good approximation of modulated amplitude waves in Bose–Einstein condensates

In this paper, we present a perturbation method that utilizes Hamiltonian perturbation theory and averaging to analyze spatio-temporal structures in Gross–Pitaevskii equations and thereby investigate the dynamics of modulated amplitude waves (MAWs) in quasi-one-dimensional Bose–Einstein condensates with mean-field interactions. A good approximation for MAWs is obtained. We also explore dynamics of BECs with the nonresonant external potentials and scatter lengths varying periodically in detail using Hamiltonian perturbation theory and numerical simulations.