Properties Of Waves Research Articles

Connection Between Chorus Wave Amplitude and Background Magnetic Field Inhomogeneity: A Parametric Study

AbstractWhistler mode chorus waves frequently appear as discrete, repetitive, and quasi‐monochromatic emissions with frequency chirping. With different wave amplitude and frequency chirping rate, chorus waves have been observed not only in the magnetosphere of the Earth but also in the magnetospheres of other planets, such as Saturn and Jupiter. Motivated by understanding different properties of chorus waves at these planets using the recently proposed “Trap‐Release‐Amplify” (TaRA) model, we perform a parametric study using Particle‐In‐Cell simulations by varying background magnetic field inhomogeneity and the corresponding threshold hot electron number density. We show the consistency between simulation results and theoretical predictions for threshold hot electron number density, chorus chirping rate, and wave amplitude. Our results suggest the significant role of the background magnetic field inhomogeneity in affecting chorus wave properties, including its amplitude at different planets as predicted by the TaRA model.

Hydrodynamic Performance of an Array of Stratified Pile Rock Breakwaters Placed on Elevated Seabed

Abstract The present study outlines the hydrodynamic performance of stratified pile-rock breakwaters (SPRBs) in series using the analytical calculation under the framework of linearized potential flow theory. The rubble mounds are separated into two porous layers (surface and bottom layers) and tightly packed within the space available between the seaside and leeside vertical piles. The SPRB is installed on the elevated bed, and it is considered as a bottom rigid layer. The newly proposed breakwater is titled as stratified pile-rock breakwater and vertical piles are suggested to minimize the unwanted displacements of rubble mounds from frequent failures due to the incident wave stroke. The analytical model is developed based on the method of matched eigenfunction expansions (MMEEs) along with suitable boundary conditions to assess the hydrodynamic performance of the SPRB. The study results are compared with the literature based on experimental and analytical methods for specific conditions. The wave reflection, transmission, and energy damping by a series of SPRBs are reported for changes in incident wave properties and breakwater physical properties. The effect of layer porosity, angle of contact, free spacing, and number of breakwaters on the hydrodynamic coefficients is reported. The study suggested that a pair of SPRBs having 80% and 40% porosities for surface and bottom layers, with clear spacing, varied within 1 ≤ w/h1 ≤ 2, and the angle of contact varied within 30 deg ≤ θ ≤ 45 deg to achieve a 90% wave-damping when the relative wavenumber is k10h1 = 1.

“Cumulative effect” of second harmonic Lamb waves in a lossy plate

The second harmonic Lamb waves have high sensitivity to microstructural defects in materials and are therefore promising for incipient damage detection and monitoring of thin-walled structures. Existing studies have shown that the second harmonic Lamb waves can be cumulative with increasing propagation distance under the internal resonance conditions, which is conducive to nonlinear wave measurements in view of structural health monitoring. However, when propagating in a lossy structure with damping, the cumulative properties of the second harmonic Lamb waves are affected by energy dissipation and thus need to be re-examined. In this paper, a method for predicting the cumulative characteristics of second harmonic Lamb waves in damped plates is proposed. Instead of using material damping parameters which are difficult to obtain in practice, the proposed method relies on the attenuation patterns of Lamb waves at fundamental and double frequencies while taking into account the influence of the wave beam divergence. The proposed methodology is validated by finite element simulations and experiments. The results show that the cumulative second harmonic Lamb waves in the damped plate tend to increase and then decrease, and a “sweet” zone of relatively large amplitude can be predicted using the proposed method. The elucidation of the cumulative characteristics of the second harmonic Lamb waves provides guidance for effective system design for structural damage detection and monitoring applications.

A highly accurate indirect boundary integral equation solution for three dimensional elastic scattering problem

In this paper, we propose a numerical formula for three dimensional elastic wave scattering problem. Different from the classical boundary integral equation method, the three dimensional elastic scattering problem is transformed into a coupled boundary value problem including a scalar Helmholtz equation and a vector Helmholtz equation by the decomposition of the displacement. The coupled boundary value problem can be solved by the boundary integral equations based on the Helmholtz equation. A denseness result is given to support this algorithm. A comparative study with the classical method of fundamental solutions getting from the boundary integral equation method is given to check the accuracy with different types of boundary conditions. From the numerical results, the present method can give more accurate results than the classical method of fundamental solutions method.

Localized excitation and fractal structures of a (2 + 1)-dimensional Longwater wave equation

Localized excitation and fractal structures of a (2 + 1)-dimensional Longwater wave equation

Efficient estimation of directional wave buoy spectra using a reformulated Maximum Shannon Entropy Method: Analysis and comparisons for coastal wave datasets

Directional spectra are a fundamental property of waves, determining how they interact with structures and the wider marine environment. Directional spectra can be estimated (although not directly measured) by wave buoys, the ubiquitous source of in-situ wave and seastate data. The most accurate standard method for estimating the directional spectrum is the Maximum Shannon Entropy Method (MEM-II). However, in practice, speed and numerical convergence issues force engineers to routinely rely on the simpler, but less representative methods such as the Maximum Burg Entropy Method (MEM-I) or one-parameter reconstructions.By reformulating the underlying equations, we have developed a new algorithm (and associated Matlab tool) to accurately and easily generate MEM-II reconstructions, capable of producing a month’s worth of half-hourly spectra in ten minutes. A year’s worth of directional data for six UK coastal locations was analysed using this method. Spectra were compared with those from the simpler cos2s and MEM-I methods, which were seen to produce misleading results for real sea data, including large systematic errors in spectral width. The MEM-II reconstruction also offered insights into directional bimodality for both wind seas and swells.

A novel holographic framework preserving reflection positivity in dSd spacetime

This manuscript introduces a novel holographic correspondence in d-dimensional de Sitter (dSd) spacetime, connecting bulk dSd scalar unitary irreducible representations (UIRs) with their counterparts at the dSd boundary I±, all while preserving reflection positivity. The proposed approach, with potential applicability to diverse dSd UIRs, is rooted in the geometry of the complex dSd spacetime and leverages the inherent properties of the (global) dSd plane waves, as defined within their designated tube domains.

Multi-scale ultrasonic imaging of sub-surface concrete defects

This paper introduces a new method for creating the ultrasonic image of concrete that utilizes both linear and nonlinear wave properties in a single measurement. Linear ultrasonic imaging relies on wave velocity. The resolution of linear ultrasonics for various inclusion sizes and inclusion-to-base material ratios is numerically and experimentally studied. The nonlinear ultrasonic testing (NLUT) image is based on the acoustic nonlinearity coefficient, calculated using inputs of the first and second harmonic amplitudes, wave number, and the distance between the transmitter and receiver. The ultrasonic waveform is decomposed into its harmonics using wavelet transform. Their wave velocities, wave numbers, and amplitudes are extracted to calculate the linear wave velocity and the acoustic nonlinearity coefficient. Four calibration samples with different inclusions are tested to evaluate the effectiveness of combining two imaging methods: pure concrete, concrete with small foam inserts simulating air inclusions, and two concrete samples with larger foam inclusions. The angle dependence of acoustic nonlinearity coefficient is shown. The results show that constructing both linear and nonlinear ultrasonic imaging is necessary when the defect’s properties are unknown.

SLOW ELECTROMAGNETIC WAVES IN PLANAR THREE-COMPONENT WAVEGUIDE STRUCTURE WITH MU-NEGATIVE METAMATERIAL

This work is devoted to study of the dispersive properties of the slow electromagnetic waves that propagate along the planar waveguide structure that consists of semi-bounded plasma region, metamaterial slab and semibounded region of ordinary dielectric. It is studied the case when all media are homogeneous and isotropic. The dispersion properties, the phase and group velocities, as well as the electromagnetic field spatial structure of the eigen TE modes are studied in the frequency range where the metamaterial possess negative permeability.

Subnanosecond microlaser pumped fan-out grating design MgO:PPLN optical parametric generator continuously tunable from near- to mid-infrared

An in-depth analysis and description of, to the best of our knowledge, the first subnanosecond pulse duration optical parametric generator (OPG) based on a fan-out grating design MgO-doped periodically-poled lithium niobate (MgO:PPLN) crystal is presented. Pumped by high energy subnanosecond pulse duration Q-switched Nd:YAG microlaser pulses, our OPG provides high output energies ranging from tens to hundreds of μJ with up to 45% conversion efficiency and enables fast and precise wavelength tuning across the near-to-mid infrared spectral regions (1414–4303 nm) just by laterally displacing the fan-out crystal without the need for temperature tuning. Limits of operation of the device were found in terms of the laser-induced damage threshold (LIDT) of the fan-out MgO:PPLN crystal. The OPG was fully characterized in terms of spectral, energy, and spatial properties of the signal wave, and analyzed experimentally and theoretically for the feasibility of producing broadband infrared output through non-collinear quasi-phase-matching and conversion of the fan-out grating structure into a chirped one.

Vectorial characterization of surface wave via one-dimensional photonic-atomic structure

Quantitative assessment of polarization properties of waves opens up the way for effective exploitation of them in many amazing applications. Tamm surface waves (TSW) that propagate on the interface of periodic dielectric media are proposed for many applications in numerous reports. The polarization state of TSW is not simply intuitive and would not be extracted from reflection spectra. Here considering orientation sensitive nature of the interaction between polarized electromagnetic wave and atom, we try to quantitatively characterize the polarization state of TSWs, excited on the surface of the 1D photonic crystal. To do this we performed direct contact between TSW and rubidium atomic gas by fabrication of a one-dimensional photonic crystal-atomic vapor cell and applied a moderate external magnetic field to create geometrical meaning and a sense of directionality to dark lines in reflection intensity. Our experimental results indicate that transition lines in the reflection spectrum of our hybrid system modify dependent on the orientation of the applied magnetic field and the transverse spin of TSW. We have used these changes to redefine the geometry of Voigt and Faraday for evanescent waves, especially Tamm surface waves. In the end, we performed simple mathematical operations on absorption spectra and extract the ratio of longitudinal and transverse electric field components of the polarization vector of TSW equal to 25\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\frac{2}{5}$$\\end{document}.

Датчики уровня жидкости и анализа термодинамических процессов при ее замерзании на объемных акустических волнах

A fundamental property of longitudinal bulk acoustic waves (BAW) is their inability to propagate in a gaseous medium due to strong absorption in the MHz range and, on the contrary, their ability to propagate in liquids. Based on this property, a liquid level sensor based on BAW is proposed. For these purposes, for the first time, it was used not to measure changes in the velocity and attenuation of waves, but to change the time of their propagation from the emitter to the receiver. It is shown that this acoustic parameter is ideal for such measurements, since it weakly depends on temperature, but depends on the aggregate state of the propagation medium. A technique has been developed for non-contact research of exo-, endo- and isothermal processes accompanying liquid-ice and ice-liquid phase transitions. With its help, the isothermal nature of the water-ice phase transition under normal conditions was experimentally demonstrated.

Constrained nonlinear amplitude-variation-with-offset inversion for reservoir dynamic changes estimation from time-lapse seismic data

We develop a novel elastic amplitude-variation-with-offset (AVO) inversion process to estimate the fluid saturation and effective pressure or variations in these properties from time-lapse seismic data sets. These changes occur in oil and gas reservoirs caused by fluid injection or hydrocarbon production that leads to changes in the elastic wave properties, reflectivity, and seismic response. Our method is based on a seismic forward model that consists of a linearized AVO equation and a rock-physics model. The AVO equation links the elastic wave properties to seismic reflection amplitudes, whereas the rock-physics model maps the saturation and pressure into seismic velocities and density. The inversion approach relies on the gradient descent technique to estimate the unknown variables by searching for the minimum of the least-squares misfit between the observed and modeled data. The first-order gradient equations of the least-squares data misfit function with respect to effective pressure and water saturation are derived by using the adjoint-state method and the chain rule. The optimization method used to minimize the misfit function and obtain the best optimal solution is a limited-memory quasi-Newton algorithm. This inversion process allows us to incorporate prior constraints by using the logistic function to map the model variables to a bounded range. To achieve a stable solution to ill-posed inversion problems, optimal regularization weights are applied. The application of the developed workflow on 1D synthetic and real well-log data from the Edvard Grieg oil field simulating various saturation-pressure conditions during production demonstrates the validity of the approach with different noise levels. The inversion is then applied to a 2D synthetic data set modeled from the reservoir model of the Smeaheia field, a potential site for a large-scale offshore CO2 storage field located in the North Sea. Our results illustrate that our inversion method efficiently and accurately estimates reservoir saturation and pressure variations.

Pole-skipping of gravitational waves in the backgrounds of four-dimensional massive black holes

Pole-skipping is a property of gravitational waves dictated by their behaviour at horizons of black holes. It stems from the inability to unambiguously impose ingoing boundary conditions at the horizon at an infinite discrete set of Fourier modes. The phenomenon has been best understood, when such a description exists, in terms of dual holographic (AdS/CFT) correlation functions that take the value of ‘0/0’ at these special points. In this work, we investigate details of pole-skipping purely from the point of view of classical gravity in 4d massive black hole geometries with flat, spherical and hyperbolic horizons, and with an arbitrary cosmological constant. We show that pole-skipping points naturally fall into two categories: the algebraically special points and a set of pole-skipping points that is common to the even and odd channels of perturbations. Our analysis utilises and generalises (to arbitrary maximally symmetric horizon topology and cosmological constant) the ‘integrable’ structure of the Darboux transformations, which relate the master field equations that describe the evolution of gravitational perturbations in the two channels. Finally, we provide new insights into a number of special cases: spherical black holes, asymptotically Anti-de Sitter black branes and pole-skipping at the cosmological horizon in de Sitter space.

A novel analysis of Cole–Hopf transformations in different dimensions, solitons, and rogue waves for a (2 + 1)-dimensional shallow water wave equation of ion-acoustic waves in plasmas

This work investigates a (2 + 1)-dimensional shallow water wave equation of ion-acoustic waves in plasma physics. It comprehensively analyzes Cole–Hopf transformations concerning dimensions x, y, and t and obtains the dispersion for a phase variable of this equation. We show that the soliton solutions are independent of the different logarithmic transformations for the investigated equation. We also explore the linear equations in the auxiliary function f present in Cole–Hopf transformations. We study this equation's first- and second-order rogue waves using a generalized N-rogue wave expression from the N-soliton Hirota technique. We generate the rogue waves by applying a symbolic technique with β and γ as center parameters. We create rogue wave solutions for first- and second-order using direct computation for appropriate choices of several constants in the equation and center parameters. We obtain a trilinear equation by transforming variables ξ and y via logarithmic transformation for u in the function F. We harness the computational power of the symbolic tool Mathematica to demonstrate the graphics of the soliton and center-controlled rogue wave solutions with suitable choices of parameters. The outcomes of this study transcend the confines of plasma physics, shedding light on the interaction dynamics of ion-acoustic solitons in three-dimensional space. The equation's implications resonate across diverse scientific domains, encompassing classical shallow water theory, fluid dynamics, optical fibers, nonlinear dynamics, and many other nonlinear fields.

Intriguing Plasma Composition Pattern in a Solar Active Region: A Result of Nonresonant Alfvén Waves?

The plasma composition of the solar corona is different from that of the solar photosphere. Elements that have a low first ionization potential (FIP) are preferentially transported to the corona and therefore show enhanced abundances in the corona compared to the photosphere. The level of enhancement is measured using the FIP bias parameter. In this work, we use data from the EUV Imaging Spectrometer on Hinode to study the plasma composition in an active region following an episode of significant new flux emergence into the preexisting magnetic environment of the active region. We use two FIP bias diagnostics: Si x 258.375 Å/S x 264.233 Å (temperature of approximately 1.5 MK) and Ca xiv 193.874 Å/Ar xiv 194.396 Å (temperature of approximately 4 MK). We observe slightly higher FIP bias values with the Ca/Ar diagnostic than Si/S in the newly emerging loops, and this pattern is much stronger in the preexisting loops (those that had been formed before the flux emergence). This result can be interpreted in the context of the ponderomotive force model, which proposes that the plasma fractionation is generally driven by Alfvén waves. Model simulations predict this difference between diagnostics using simple assumptions about the wave properties, particularly that the fractionation is driven by resonant/nonresonant waves in the emerging/preexisting loops. We propose that this results in the different fractionation patterns observed in these two sets of loops.

Statistical Properties of Lower Hybrid Waves Within Foreshock Transient Boundaries

AbstractLower hybrid waves (LHWs) are plasma waves commonly observed within the foreshock transient environment. Using Magnetospheric Multiscale in situ measurements, we present a statistical analysis of LHWs regarding their spatial distribution, wave properties, occurrence rate, and potential impact on plasmas at the density boundaries of foreshock transients. LHWs are mostly localized at the low‐density side of the boundaries, with a typical wave electric field below 2 mV/m. The occurrence rate of LHWs decreases as the density gradient length scale (Ln) normalized to the ion gyroradius (ρi) increases and the plasma beta (β) increases. This dependence of the wave occurrence is consistent with the linear growth rate of LHWs. The occurrence rate of LHWs exhibits a preference for conditions characterized by Ln/ρi < 3 and β < 3. In the case of a strong gradient (Ln/ρi ≲ 0.5), the occurrence rate exceeds 0.2. These findings provide valuable statistical evidence shedding light on the average behavior of LHWs within foreshock transients.

Quantum computing perspective for electromagnetic wave propagation in cold magnetized plasmas

Electromagnetic waves are an inherent part of all plasmas—laboratory fusion plasmas or astrophysical plasmas. The conventional methods for studying properties of electromagnetic waves rely on discretization of Maxwell equations suitable for implementing on classical, present day, computers. The traditional methodology is not efficient for quantum computing implementation—a future computational source offering a tantalizing possibility of enormous speed up and a significant reduction in computational cost. This paper addresses two topics relevant to implementing Maxwell equations on a quantum computer. The first is on formulating a quantum Schrödinger representation of Maxwell equations for wave propagation in a cold, inhomogeneous, and magnetized plasma. This representation admits unitary, energy preserving, evolution and conveniently lends itself to appropriate discretization for a quantum computer. Riding on the coattails of these results, the second topic is on developing a sequence of unitary operators which form the basis for a qubit lattice algorithm (QLA). The QLA, suitable for quantum computers, can be implemented and tested on existing classical computers for accuracy as well as scaling of computational time with the number of available processors. In order to illustrate the QLA for Maxwell equations, results are presented from a time evolving, full wave simulation of propagation and scattering of an electromagnetic wave packet by non-dispersive dielectric medium localized in space.

The quality of visual entrainment correlates with forward traveling wave properties in human cortex

AbstractBackgroundFlickering light stimulation has been shown to entrain the brain’s oscillatory activity at the input frequency and synchronize different cortical regions in that frequency (Herrmann et al., 2001; Lahijanian et al., 2021). Brain entrainment at gamma frequency has been proposed and shown promising results as a non‐pharmaceutical therapeutic approach for Alzheimer’s disease (Cimenser et al., 2021). Studying the effects of such stimulation on the brain’s neural activity can help explain the mechanisms that underlie the reported improvements. It is known that neural oscillations form traveling waves across the brain during various cognitive functions (Bhattacharya et al., 2022). In this study, we use different flickering light frequencies as entrainment input and investigate the spatiotemporal pattern of neural activity modulated by visual entrainment which appears as a traveling wave across the posterior‐frontal pathway.MethodEEG data recorded from young healthy adults were analyzed during multi‐trial flickering light stimulation at 10, 15, 20, 22, and 30Hz frequencies. In order to analyze the quality of posterior‐frontal waves, the spatiotemporal phase pattern was measured over the head midline. The wave quality was defined as the consistency of the spatiotemporal phase pattern during consecutive time intervals, and the quality of entrainment was defined as the intensity of the power spectral density at the input frequency.ResultDuring the resting state, different wave patterns traveling across the frontoparietal link are canceled out. However, visual stimulation invigorates the forward wave from the sensory (posterior – visual) region to the upstream area (frontal lobe) at the target frequency compared to the baseline. Meanwhile, in contrast to the forward wave, traveling wave in the backward direction does not show noticeable presence at the stimulation frequency. Furthermore, as the entrainment quality increases, the wave pattern consistency is improved for all stimulating frequencies (Figs. 1, 2).ConclusionThe forward wave induced during non‐invasive visual stimulation represents long‐range activity along the posterior‐frontal pathway known to be activated during sensory processing and inference. The observed correlation between the wave’s quality and the quality of entrainment at the target frequency points to the mechanism underlying the therapeutic effects of gamma entrainment.

Boundary effects on dispersion relations of ion-acoustic wave and physical properties of overlapping soliton in a plasma waveguide

Taking into account the cylindrical boundary, a theoretical investigation has been made for the low frequency electrostatic waves in an electron-positron-ion plasma waveguide. The dispersion relation of ion-acoustic (IA) wave is obtained, and a predication for the linear interaction phenomenon of small-amplitude cylindrical IA solitons is presented. It is shown that the cylindrical boundary has significant effects on the dispersion property of IA waves, and the frequency for short wave is significantly modified by the plasma parameters. It has also been noted that cylindrical IA solitons add up linearly when they overlap and penetrate through each other, the maximum amplitude of the overlapping soliton is nearly the sum of the individual soliton amplitude, indicating an apparent linear interaction. Furthermore, the relationships between phase delay and kinetic energy of colliding solitons for an axisymetric cylindrical geometry are derived and discussed in detail. The work presented would be useful to enrich the solitons interaction theory in astrophysical and laboratorial plasma situations.