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Narrowband (Δf ≲ 0.1fcp), high‐frequency (0.9fcp ≲ f < fcp) electromagnetic ion cyclotron (EMIC) waves, or HFEMIC waves for short, are a relatively new type of EMIC waves, where fcp is the proton cyclotron frequency. Here, we investigate the instability threshold conditions and the nonlinear evolution of HFEMIC waves at parallel propagation. First, linear theory analysis is extended to a regime relevant to HFEMIC waves (parallel proton beta β‖p < 0.01). The instability threshold follows a similar anisotropy‐β‖p relation and requires a large value of anisotropy (T⊥p/T‖p ≳ 10) for wave growth. As a result of decreasing group velocity, the convective growth rate at a fixed threshold exhibits a similar inverse relation with β‖p. Heavy ions affect the instability only weakly, primarily through the introduction of stop bands. Second, we carry out one‐dimensional hybrid simulations in a parabolic background magnetic field, with initial parameters constrained by observation. Despite the narrow source region (within about ±3° latitude), HFEMIC waves can grow well above the thermal noise level due in large part to a small group velocity of HFEMIC waves. The saturation level is well within the range of observational amplitudes, and the quasilinear process primarily determines the wave evolution. Finally, we demonstrate that the present results compare favorably to the recent statistical results, thereby supporting anisotropic low‐energy protons as free energy source for HFEMIC waves. Key Points: Instability threshold analysis of EMIC waves with parameters constrained by observations is extended to the high‐frequency regimeWave saturation in 1D hybrid simulations initialized with realistic parameters compares favorably to EMIC amplitude of observationsPresent results show qualitative agreement with observational data, supporting anisotropic low‐energy protons as free energy source [ABSTRACT FROM AUTHOR]

We observe maxon-like dispersion of ultrasonic guided waves in elastic metamaterials consisting of a rectangular beam and an array of cylindrical resonators. The pillars act as asymmetric resonators that induce a strong modal hybridization. We experimentally observe the strongly localized maxon mode with zero group velocity. Our study also demonstrates a unique feature of the maxon with a down-shifting peak frequency in space. To reveal the fundamental mechanism, we conduct comprehensive numerical studies on all frieze group symmetries and key geometric parameters. [ABSTRACT FROM AUTHOR]

In this paper, we present the higher-order nonlinear Schrödinger equation (NLSE) with third order dispersion (3OD), fourth-order dispersion (4OD), and cubic-quintic nonlinearity (CQNL) terms that define the propagation of ultrashort pulses. Two analytical methods, which are the new Kudryashov's method and the unified Riccati equation expansion method, are implemented to extract the analytical soliton solutions of the presented equation for the first time. Thus, bright, dark, and singular soliton solutions are acquired. To illustrate the physical behavior of some of the obtained solutions, 3D, 2D, and contour graphs are depicted. In particular, to understand the effects of the group velocity dispersion, 3OD, 4OD, CQNLs, self-steepening coefficient terms, and group velocity term of the traveling wave transformation on the soliton dynamics of the proposed equation, 2D plots for different values of coefficients are represented. The obtained results provide us with the knowledge that the presented model can be examined from a physical perspective. It can be concluded that the used methods are effective approaches to derive the analytical solutions for the NLSE. [ABSTRACT FROM AUTHOR]

Phonon polaritons (PHPs) in freestanding and supported multilayers of hexagonal boron nitride are systematically studied using a macroscopic optical-phonon model. The PHP properties such as confinement, group velocity, propagation quality factor (PQF), and wavelength scaling are studied. Owing to high-frequency screening, there is an upper frequency limit making the two-dimensional (2D) PHPs have a frequency band and also a maximum PQF occurs near the center frequency. The substrate's dielectric response should be included to accurately calculate the PHP properties. While the simple electrostatic approximation (ESA) is valid for PHPs with frequencies ω above ω 0 (e.g., ω > 1.03 ω 0 for the 30-layers; ω 0 is the Γ point optical-phonon frequency), it fails to describe the PHP properties near ω 0 and the effect of retardation should be included for a proper description. The PHP wavelength vs layer thickness near ω 0 deviates significantly from a linear scaling law given by the ESA due to strong coupling of photons and longitudinal optical phonons. The calculated PHP dispersion and scaling are compared with experimental data of a number of spectroscopic studies and found to be in good agreement for most of the results. While the frequency of incident light should be near the center frequency to maximize the PQF, the PHP wavelength, confinement, and propagation length can be engineered by varying the multilayer thickness and its dielectric environment. [ABSTRACT FROM AUTHOR]

Nonlinear phenomena are crucial for magnon-based information processing, but the nonlinear interaction between two spin-wave signals requires their spatiotemporal overlap, which can be challenging for directional processing devices. Our study focuses on a gallium-substituted yttrium iron garnet film, which exhibits an exchange-dominated dispersion relation and, thus, provides a particularly broad range of group velocities compared to pure YIG. Using time- and space-resolved Brillouin light scattering spectroscopy, we demonstrate the excitation of time-separated spin-wave pulses at different frequencies from the same source, where the delayed pulse catches up with the previously excited pulse and outruns it due to its higher group velocity. By varying the excitation power of the faster pulse, the outcome can be finely tuned from a linear superposition to a nonlinear interaction of both pulses, resulting in a full attenuation of the slower pulse. Therefore, our findings demonstrate the all-magnonic erasing process of a propagating magnonic signal, which enables the realization of complex temporal logic operations with potential application, e.g., in inhibitory neuromorphic functionalities. [ABSTRACT FROM AUTHOR]

Acoustoelasticity, a characteristic of material anharmonicity, gives rise to a link between wave propagation velocity and the stress state in materials. Ultrasonic techniques to monitor this coupling, particularly with high sensitivity and in a noncontact manner, can have widespread application both in the quantification of applied and residual stress and in the characterization of nonlinear material behavior through measurement of higher order elastic constants. Here, we use a laser ultrasonic technique to excite and detect zero group velocity (ZGV) Lamb wave resonances in aluminum plates under uniaxial loading. A laser line source is used to excite these resonances at different orientations with respect to the applied load, and the signals are detected using an interferometer. The effects of stress and source orientation on ZGV resonance frequencies are validated using the theory of acoustoelastic Lamb wave propagation. In addition, a model-based inversion technique is used to extract Murnaghan's third-order elastic constants from measurements of the stress dependence of the first two ZGV modes generated parallel and perpendicular to the applied load. Laser generation and detection of ZGV resonances is shown to be an effective and powerful approach for the noncontact and nondestructive acoustoelastic characterization of elastic waveguides. [ABSTRACT FROM AUTHOR]

Superradiance, a phenomenon of multiple facets, normally occurs in classical/quantum physics under extreme conditions. Here, we present its manifestation in spin waves under a practical condition. We show that an interface between a current-free ferromagnetic region and a current-flow ferromagnetic region can be a spin wave supermirror whose reflection coefficient is larger than 1. The super-reflection is the consequence of current-induced spectrum inversion where phase and group velocities of spin waves are in the opposite directions. An incident spin wave activates a backward propagating refractive wave inside the current-flow region. The refractive spin wave re-enters the current-free region to constructively interfere with the reflective wave. It appears that the current-flow region coherently emits reflective waves, leading to a super-reflection. The process resembles superradiance of a spinning black hole through the Hawking radiation process or Dicke superradiance of cavity photons inside population inverted media. [ABSTRACT FROM AUTHOR]

We have studied Rayleigh wave group velocities beneath the Aegean region of Türkiye using ambient noise tomography. Noise data were gathered from 43 broadband seismic stations belonging to three permanent broad-band arrays. The cross-correlation method was used to estimate empirical Green's functions. Group velocities of the fundamental mode Rayleigh waves were determined using multiple filter technique. We measured dispersion for each station pair in a period range of 2-12 s and computed maps of group velocity distribution using the fast marching surface tomography method. The group velocity maps correlate well with the geological and tectonic features of the region, displaying low velocities for the Quaternary alluvial basins, moderate velocities for Cretaceous rocks, and high velocities for the regions where gneiss and granitoid rocks outcrop. Low velocity anomalies may be associated with the grabens and horsts formed by faulting and to deep mantle flow. We detect potential offshore geothermal zones in Izmir and Candarli Bay. The information from broad-band networks improves the resolution of crustal surface wave velocity structures, particularly for shallow depths. This improvement will support the assessment of seismic hazard, as the shallow layers of the crust contribute significantly to seismic activity. [ABSTRACT FROM AUTHOR]

Magnonics has long been hailed as a promising technology poised to overcome the heat dissipation challenges in traditional electronic devices. With the escalating integration level of magnon devices, the demand arises for lower external field excitation conditions, coupled with enhanced coherence and frequency-selective excitation characteristics. In this proposal, we suggest introducing a localized perpendicular magnetic anisotropy nanofilm stack into the spin-wave transmission channel to finely regulate the propagation characteristics of spin waves. This adjustment can be achieved by altering the width and period of the stack in both horizontal and vertical dimensions. Additionally, the optimal transmission characteristics of spin waves are achieved at low frequencies (1–1.67 GHz) and in the presence of small magnetic fields (0–20 mT). Frequency-selective spin waves with triggering stability can effectively prevent signal folding resulting from changes in microwave power within the range of −30 to 0 dBm. At 1.08 GHz, the group velocity of frequency-selective spin waves can be increased by up to 2.86 times. This innovative method of regulating spin waves presents a potential alternative pathway for the development of future magnonic circuits. [ABSTRACT FROM AUTHOR]

Acoustic hyperbolic metamaterials are artificial materials with hyperbolic dispersion characteristics and strong anisotropy. Their negative refractive properties are the theoretical basis for studying the implementation of high-resolution focused superlenses. In response to the problem that the recognition of far-field noise sources is limited by the resolution of 0. 5 times wavelength acoustic Rayleigh diffraction recognition, combined with the excellent control effect of acoustic metamaterials on sound waves, a hyperbolic metamaterial that can achieve sub wavelength super-resolution imaging is introduced, and its negative refractive characteristics are used to design an acoustic hyperbolic structure for working at a frequency of 2 271. 5 Hz. The dispersion and negative refraction characteristics of the hyperbolic structure of this configuration were analyzed, and the results show that, the group velocity direction of sound waves propagating in this hyperbolic metamaterial is perpendicular to the wave vector and follows the normal direction of the dispersion curve. The research in this paper provides some design references for realizing arbitrary regulation of sound wave and elastic wave, as well as focusing, locating, identifying and amplifying noise sources. [ABSTRACT FROM AUTHOR]

This paper presents a study of global Rayleigh wave attenuation and group velocity at a period of around 20 s using data from the International Seismological Centre (ISC) bulletin. Rayleigh waves at this period are sensitive to the crustal structure beneath continents and the uppermost mantle beneath oceans. Tomographic imaging reveals strong continental-ocean contrasts due to this. Oceanic group velocities are high but vary with seafloor depth, while oceanic attenuation shows mid-ocean ridges. Subduction zone regions display high attenuation but little velocity reduction, indicating scattering attenuation. Low attenuation regions are associated with the Earth's major cratonic regions, but there are no associated velocity changes. This implies that intrinsic attenuation is low and scattering dominates. Cratonic crustal scatterers have been annealed. A new surface wave magnitude scale is constructed that is valid from near-source to near-antipode distances. [ABSTRACT FROM AUTHOR]

The corrosion of reinforced concrete (RC) is one of the most serious durability problems in civil engineering structures, and the corrosion detection of internal reinforcements is an important basis for structural durability assessment. In this paper, the appropriate frequency required to cause excitation signals in the specimen is first analyzed by means of frequency dispersion curves. Subsequently, the effectiveness of five damage indexes (DIs) is discussed using random corrosion in finite elements. Finally, guided ultrasonic wave (GUW) tests are conducted on reinforcement and RC specimens at different corrosion degrees, and the test results are verified using a theoretical corrosion model. The results show that the larger the covered thickness is at the same frequency, the higher the modal order of the GUW in the frequency dispersion curve is, and the smaller the group velocity is. The SAD is the most sensitive to the corrosion state of the reinforcement compared with the other DIs, and it shows a linear increasing trend with the increase in the corrosion degree of the reinforcement. The SAD values of the RC specimens showed a three-stage change with the increase in the corrosion time, and the time until the appearance of corrosion cracks was increased with the increase in the covered thickness. It can be seen that increasing the covered thickness is an effective method to delay the time until the appearance of corrosion cracks in RC specimens. [ABSTRACT FROM AUTHOR]

The high‐entropy concept, extensively studied in alloys and ceramics, has produced intriguing results, but its use in thermoelectric materials is still in its infancy. This study introduces a pioneering high‐entropy half‐Heusler (hH) alloy, ZrTiNiFeSnSb, synthesized via arc melting and heat treatment. Phonon scattering from multiple elements significantly reduces the lattice thermal conductivity of the alloy, which decreases to a minimum of 3.5 Wm−1 K−1 (700 K) in this material. The experimental thermal data matches the density functional theory calculations for phonon dispersion, phonon group velocity, and Grüneisen parameters. This demonstrates that crystal distortion induced anharmonicity slows the alloy's phonon heat transport, which is suitable for thermoelectric applications. Notably possessing elevated electrical conductivity and a moderate Seebeck coefficient, this high‐entropy hH alloy emerges as a promising thermoelectric material for energy harvesting. [ABSTRACT FROM AUTHOR]

The Λ cold dark matter (ΛCDM) standard cosmological model is in severe tension with several cosmological observations. Foremost is the Hubble tension, which exceeds 5σ confidence. Galaxy number counts show the Keenan–Barger–Cowie (KBC) supervoid, a significant underdensity out to 300 Mpc that cannot be reconciled with ΛCDM cosmology. Haslbauer et al. previously showed that a high local Hubble constant arises naturally due to gravitationally driven outflows from the observed KBC supervoid. The main prediction of this model is that peculiar velocities are typically much larger than expected in the ΛCDM framework. This agrees with the recent discovery by Watkins et al. that galaxies in the CosmicFlows-4 catalogue have significantly faster bulk flows than expected in the ΛCDM model on scales of |$100-250 \, h^{-1}$| Mpc. The rising bulk flow curve is unexpected in standard cosmology, causing 4.8σ tension at |$200 \, h^{-1}$| Mpc. In this work, we determine what the semi-analytic void model of Haslbauer et al. predicts for the bulk flows on these scales. We find qualitative agreement with the observations, especially if our vantage point is chosen to match the observed bulk flow on a scale of |$50 \, h^{-1}$| Mpc. This represents a highly non-trivial success of a previously published model that was not constrained by bulk flow measurements, but which was shown to solve the Hubble tension and explain the KBC void consistently with the peculiar velocity of the Local Group. Our results suggest that several cosmological tensions can be simultaneously resolved if structure grows more efficiently than in the ΛCDM paradigm on scales of tens to hundreds of Mpc. [ABSTRACT FROM AUTHOR]

Second harmonic generation (SHG) in glass optical fibers calls for creating a second order susceptibility in the fiber glass and for achieving phase matching between the pump and the second harmonic signal. The latter is very challenging when using ultrashort pulses, given that the group velocities of the pump and the second harmonic should also be matched. We have shown in previous work that it is possible to achieve simultaneous modal phase matching (MPM) and group velocity matching (GVM) when the pump and the second harmonic are propagating in the LP01 and LP02 modes, respectively, in high GeO2-content double-clad optical fibers. However, simultaneous MPM and GVM can only be obtained in optical fibers with dedicated designs and within very tight geometrical tolerances. In this paper, we show that instead of considering the matching of phase and group velocities separately, we can consider a more general or "effective" phase matching approach, in which we consider all the dispersion terms up to the second order in the expressions of the propagation constants of the pump and second harmonic signals. This allows introducing the pulse duration as a controllable parameter that helps to enforce the said effective phase matching in fibers with designs that deviate by as much as 10% from the target, while providing for temporal walk-off lengths in excess of several centimeters. The impact of this finding goes beyond SHG only and can be applied to other ultrashort laser pulse-based nonlinear optical processes in fibers and waveguides. [ABSTRACT FROM AUTHOR]

The miniaturization and higher power density of modern electronics pose a significant challenge in thermal management. A key focus in addressing this challenge revolves around the advancement of thermal interfaces within microchip packaging, aiming to enhance thermal energy dissipation and optimization of performance. Copper nanowires are extensively employed in the chip industry as interconnects for signal transmission and thermal management purposes. Investigating the impact of reduced cross-section on the thermal transport properties of nanowires is crucial. In this study, the thermal conductivity of copper and silicon nanowires is studied with variations in the length of the nanowires. The simulation is conducted with the Equilibrium Molecular Dynamics (EMD) process. The cross-section of the nanowire is kept fixed (10 × 10 nm) and with the increase in length, its thermal conductivity is studied. At room temperature for a 50 nm length, the lattice thermal conductivity value is 1.68 and 0.037 W m − 1 K − 1 for silicon and copper nanowires, respectively. We further studied the phonon scattering, mean free path, and group velocity of silicon and copper lattices. Our study may help to design more thermally efficient microchips and innovate new cooling methods of microelectronics. [ABSTRACT FROM AUTHOR]

We have studied dispersion of surface plasmon polaritons (SPPs) in the Kretschmann geometry (prism/Ag/dye-doped polymer) in weak, intermediate, and ultra-strong exciton–plasmon coupling regimes. The dispersion curves obtained in the reflection experiment were in good agreement with the simple model predictions at small concentrations of dye (Rhodamine 590, Rh590) in the polymer (Poly(methyl methacrylate), PMMA). At the same time, highly unusual multi-segment "staircase-like" dispersion curves were observed at extra-large dye concentrations, also in agreement with the simple theoretical model predicting large, small, and negative group velocities featured by different polariton branches. In a separate experiment, we measured angular dependent emission of Rh590 dye and obtained the dispersion curves consisting of two branches, one nearly resembling the SPP dispersion found in reflection and the second one almost horizontal. The results of our study pave the road to unparalleled fundamental science and future applications of weak and strong light—matter interactions. [ABSTRACT FROM AUTHOR]

Green's function plays an important role in the relationship of a future strong earthquake epicenter to the average earthquake potential score. In the frame of the latter, the fractal dimension of the unified scaling law for earthquakes naturally arises. Here it is also shown to be a cornerstone for the development of a new ambient noise tomography methodology, which is applied for example to the west coast of Central Greece. In particular, we show that a fast and reliable 3D shear velocity model extraction is possible without the need for a large amount of data, great-circle propagation assumptions, or the intermediate step of inverting for group velocity maps. The tomography results are consistent with previous studies conducted in the neighboring region. [ABSTRACT FROM AUTHOR]

Due to the electron deficiency of boron, two-dimensional boron systems and its derivatives have a great diversity of configurations, such as the hydrogenated borophene, providing a promising platform to realize different electronic and thermal functions. In this work, using first-principles calculations combined with phonon Boltzmann transport equation, we study the lattice thermal conductivity ( κ L ) of two hydrogenated borophene structures with different B–H bond configurations. We find that the κ L of hydrogenated borophene can be doubled, when the B–H bond is replaced by the bridged B–H–B bond. Benefit from the electron deficiency of boron, the bridged B–H–B bond can provide electrons to the borophene layer, generating stronger B–B covalent bonds. This configuration further results in the blue-shift of phonon modes as well as the bunching effect for acoustic branches, which simultaneously increase the phonon group velocity and suppress the phonon–phonon scatterings, consequently enhancing the thermal conductivity. Our work offers an effective approach to optimize lattice thermal conductivity of two-dimensional materials via structure engineering, without varying the material content. [ABSTRACT FROM AUTHOR]

In this paper, the Surface Plasmon Polariton (SPP) dispersion relation in the TM polarization for the plane interface between a homogeneous dielectric medium (with constant εd) and a gradedpermittivity (i.e. nonhomogeneous) plasmonic medium (with dielectric function εp(z)) is obtained where ‘z’ is normal coordinate to the interface. For small variation of εp(z) it is revealed that the dispersion relation is related to the derivative of εp(z) at the interface and when εp becomes constant or when its derivative at the interface is zero the well-known dispersion relation for homogeneous plasmonic medium is obtained. For the case where εp(z) depends linearly on z, the dispersion relation is obtained. It is seen that two branches appear. The upper branch has a free-space-like behavior at small wavenumbers. Inclusion of frequency dependence in the εp(z) through Drude model, reveals that the upper branch has negative-value group velocity at intermediate wavenumbers. The results show that non-homogeneity of the plasmonic medium offers a good tunability to control dispersion relation and SPP group velocity. [ABSTRACT FROM AUTHOR]

Longitudinal wave propagation in axially graded nanotubes was explored. The effect of shear deformation and lateral inertia on nanorods was considered using the nonlocal Raylegh–Bishop rod theory. As a novel approach, a nonlocal parameter was assumed in the graded formulation. The higher order Haar wavelet method was utilized for solving the governing equation of motion. The effects of material grading power-law index and nonlocal parameters on the longitudinal wave response of axially graded nanorods were investigated. Phase and group velocity variations of the axially graded nanorod were obtained. The present study may be useful in the modeling of advanced functional composite nanowires. [ABSTRACT FROM AUTHOR]

Recently, the 2D van der Waals (vdW) layered MA2Z4 series has attracted a lot of attention. Among these 2D materials, MoSi2P4 and WSi2P4 monolayers each demonstrate strong environmental stability, a moderate band gap, and considerable carrier mobility. The lattice thermal transport properties in MoSi2P4 and WSi2P4 monolayer structures have been investigated using first-principles calculations. Due to the gap present in the phonon energy band structure of the WSi2P4 monolayer within the middle frequency range, the specific heat capacity, phonon group velocity, and phonon relaxation time of the WSi2P4 monolayer structure are smaller than those of the MoSi2P4 monolayer structure. This makes the lattice thermal conductivity of the WSi2P4 monolayer lower than that of the MoSi2P4 monolayer. The MoSi2P4 structure has a lattice thermal conductivity of 28 W/mK at 300 K. The WSi2P4 structure has a lattice thermal conductivity of 14.5 W/mK in the x -direction and 15 W/mK in the y -direction. The results suggest that the MoSi2P4 and WSi2P4 monolayers can be potentially used as nanoelectronics devices for thermal transport applications. [ABSTRACT FROM AUTHOR]

This study reports a modified Haldane model that supports transitions between valley and Chern topological phases in photonic crystals. Berry curvatures of this system can be flexibly diffused, converged, or flipped by endowing different model parameters, thus exhibiting exotic topological interface/edge behaviors, such as topological bound states with ideally zero dispersion. Importantly, the coexistence of chiral and antichiral edge states preserved simultaneously by valley and Chern topological phases is achieved by splicing together two kinds of topological structures as an entirety. It further employs a honeycomb lattice comprising gyromagnetic and ceramic cylinders at microwave frequencies, where inversion and time‐reversal symmetries can be flexibly manipulated. Topological interface transport is demonstrated, including two opposite signs of group velocities jointly protected by topologically distinct regimes. These results bridge the gap between valley and Chern topological physics and shed light on developing reconfigurable integrated device applications for classical (quantum) information processing and photonic computing. [ABSTRACT FROM AUTHOR]

To understand how coastal precipitation is controlled by the low-level background wind, we performed comprehensive analysis using the 17-yr observations of the TRMM PR over the entire region of the tropics. We classified the data according to the direction (onshore or offshore) and strength of the cross-shore wind. Under weak winds, the contribution of the diurnal cycle to total precipitation is large, indicating that thermally forced precipitation with a symmetrical propagation pattern with opposite sign across the coastline is dominant. As the background wind strengthens, the contribution of the diurnal cycle reduces owing to the predominance of mechanical forcing; however, the effect of the diurnal cycle remains nonnegligible with an asymmetrical propagation pattern across the coastline. Using the linear theory of the sea–land-breeze circulation, we demonstrated that the difference in propagation is attributable to gravity waves excited by the land–ocean surface heating difference. Under weak winds, symmetrical diurnal phase propagation is caused by the two symmetrical modes of landward and seaward gravity waves. Under stronger background winds, in addition to the Doppler-shifted landward and seaward modes, waves propagating toward the upwind side in the flow-relative frame but with slow group velocity are advected to the downwind near the coastline, forming another mode that moves slowly in the downwind direction. The superposition of the three modes leads to asymmetrical propagation of precipitation with varying phase speed depending on the distance from the coastline. [ABSTRACT FROM AUTHOR]

We consider random wave coupling along a flat boundary in dimension three, where the coupling is between surface and body modes and is induced by scattering by a randomly heterogeneous medium. In an appropriate scaling regime we obtain a system of radiative transfer equations which are satisfied by the mean Wigner transform of the mode amplitudes. We provide a rigorous probabilistic framework for describing solutions to this system using that it has the form of a Kolmogorov equation for some Markov process. We then prove statistical stability of the smoothed Wigner transform under the Gaussian approximation. We conclude with analyzing the nonlinear inverse problem for the radiative transfer equations and establish the unique recovery of phase and group velocities as well as power spectral information for the medium fluctuations from the observed smoothed Wigner transform. The mentioned statistical stability is essential in monitoring applications where the realization of the random medium may change. [ABSTRACT FROM AUTHOR]

The current work focuses on investigating how various external and structural factors can affect the electronic structure and optical properties of a GaAs/Ga1−xAlxAs quantum ring. Specifically, we have studied the effects of spin–orbit interaction (SOI), pressure, temperature, and dimensions on the energy levels, dipole transition matrix elements (DTMEs), susceptibilities, optical absorption coefficients (OACs), refractive index changes (RICs), and group velocity of the quantum ring. These results show that the ground state energy of the system increases with the concentration of aluminum, while increasing temperature and ring size leads to a decrease in DTMEs due to a decrease in wave function overlap. We have also found that the presence of Rashba SOI, pressure, temperature, as well as the ring’s size dominate the electronic structure and subsequently affect the OACs and RICs of the system. A significant enhancement of the OACs can be witnessed when the Rashba coefficient and ring size are enlarged. Furthermore, the results represent a red shift with enhanced Rashba coefficient and relaxation time, whereas the growing ring size results in a blue shift in Optical sensitivities. Finally, we have analyzed the dependence of the group velocity of probe light pulses on the ring's size, photon frequency, and incident optical intensity. Our findings suggest that by controlling these parameters appropriately, it may be possible to achieve effective control of light speed, which could have interesting applications in electro-optical quantum communication networks. Overall, this work sheds light on the potential applications of these findings in the design and construction of spin-based devices and may offer new avenues for further research in this field. [ABSTRACT FROM AUTHOR]

In this study, the first derivatives of this equation with respect to temperature (thermo-optic coefficients) and wavelength (spectral dispersion) were derived in the MATLAB software, and a special code was written to solve the equations and found for temperatures that range from 100 to 750 K and wavelength range from 1.2 to 14 μm. The results of the computation were compared with previously published data, and showed a good agreement. Once that was done, the values of phase velocity and group velocity that depend on refractive index and spectral dispersion in the medium were found. The phase velocity and group velocity were plotted in three dimensions to show the overall change over different values of wavelengths and temperature. [ABSTRACT FROM AUTHOR]

Wave processes propagating in a medium of collisional and viscous quark-gluon plasma (QGP) are comprehensively analyzed in the paper. To investigate various optical properties of the medium, the longitudinal and transverse dielectric functions of the quark-gluon plasma are taken to study. The calculations of perturbations in these dielectric functions facilitate the derivation of dispersion relations for wave propagation within such media. Through extensive further analysis, the phase and group velocities were calculated for the considered models. The resulting graphs for phase and group velocity distinctly illustrate the dissipative properties inherent in the medium, revealing how these properties influence the propagation speed of both the wave phase and the wave packet of environmental disturbances. This article provides an in-depth analysis of the obtained results, discussing the possible behavior of waves across different models of quark-gluon plasma media. The study concludes by highlighting the achievements and contributions of this research, emphasizing its importance in advancing the understanding of wave dynamics in such extreme states of matter. [ABSTRACT FROM AUTHOR]

We investigate the interaction between an anticyclonic eddy (AE) and semidiurnal internal tide (SIT) on the continental slope of the northeastern South China Sea (SCS), using a high spatiotemporal resolution numerical model. Two key findings are as follows: first, the AE promotes energy conversion from low-mode to higher-mode SIT. Additionally, production terms indicate that energy is also transferred from the SIT field to the eddy field at an average rate of 3.0 mW m -2 (accounting for 7 % of the incoming energy flux of SIT when integrated over the eddy diameter). Second, the AE can modify the spatial distribution of tidal-induced dissipation by refracting, scattering, and reflecting low-mode SIT. The phase and group velocities of the SIT are significantly influenced by the eddy field, resulting in a northward or southward shift in the internal tidal rays. These findings deepen our understanding of the complex interactions between AE and SIT, as well as their impacts on energy conversion, wave propagation, and coastal processes. [ABSTRACT FROM AUTHOR]

A numerical model of wave packets on the surface of the reservoir was built with slowly changing depth, concentrated in the vicinity of moving points along space-time rays with group velocity (such wave packets are called quasiphotons). At the bottom, profile of the reservoir was taken as the bottom profile of the Gulf of Finland in the coastal zone of the Sestroretsk approach fairway. [ABSTRACT FROM AUTHOR]

In this work, internal gravity waves are considered that propagate in a stratified medium of finite depth with variable background shear flows. In the linear formulation, using the Fourier method, the author constructed the Green function of the corresponding equation of internal gravity waves. The asymptotic of the Green function in the far zone expressed through the square of the Airy function is studied. It is shown that, for real distributions of buoyancy frequency and shear flow vector, the wave zone is bounded by two closed curves: head and rear fronts. In the case when the components of shear velocity vector less vary over the vertical, the head wave front is a circle expanding with a maximum group velocity of the separate wave mode without flows and shifted by the flow with a velocity equal to the average value of the shear velocity vector taken with some weight. [ABSTRACT FROM AUTHOR]

This work proposes a noise-reduction structure that integrates phase-modulating metasurface (PMM) with acoustic liners (ALs) to enhance the narrow band absorption performance of a duct with relatively small length-diameter ratio. The PMM manipulates the wavefront by introducing different transmission phase shifts based on an array of Helmholtz resonators, so that the spinning wave within the duct can be generated. Compared with the plane wave, the generated spinning wave has a lower group velocity, which results in a greater traveling distance over the ALs in the duct. The optimization design is performed to determine the final structural parameters of the PMM, which is based on the predictions of the amplitude and phase shift of the acoustic wave at the outlet of the PMM using the theory of passive phased array. With the manipulation of the PMM, the incident plane wave is modulated into a spinning wave, and then enters into the acoustic liner duct (ALD), whose structural parameters are optimized by maximizing the transmission loss using the mode-matching technique. Finally, the noise-reduction performance of this combined structure is evaluated by numerical simulations in the presence of grazing flow. The results demonstrate that, compared with the traditional ALD, the proposed structure exhibits a significant increase in transmission loss within the considered frequency band, especially near the peak frequency of the narrow band noise. [ABSTRACT FROM AUTHOR]

Quantum technology has the potential to revolutionize sensors and the Internet of Things (IoT). Efficient and secure data transfer among sensors and IoT devices is a major challenge. To address this, the manuscript presents coherent manipulation of the scattering cross section and its sensitivity based on subluminal propagation and rotary photon drag, using an atomic medium with two levels coupled with a cavity. The group index of the proposed atomic medium is measured in the range of - 0.1 ≤ n g ≤ 150 and group velocity in the range of 2 × 10 6 m / s ≤ v g ≤ ± 2 × 10 9 m/s. The maximum delay time is reported to t g = 0.3 μ s and rotary photon drag to θ d = ± 5 micro radian. This effect of photon drag is used in sensing, energy harvesting, and optical switching in IoT. The scattering cross-section of 0.1 × 10 21 m 2 is reported. The scattering cross-section impacts the efficiency and reliability of quantum-based communication for IoT. The maximum cross-sectional sensitivity is measured to S σ = 0.4 × 10 - 19 m 2 / n r . The cross-sectional sensitivity potentially impacts secure communication and highly precise detection in sensors and IoT. [ABSTRACT FROM AUTHOR]

The lattice dynamics of face-centered square and edge-centered square lattice structures is classically examined using the harmonic approximation between atoms. The dynamical matrices and dispersion relations for the two lattice structures are derived. The eigenfrequencies are presented numerically. At long wavelengths, the acoustic branches and corresponding group and phase velocities are obtained. [ABSTRACT FROM AUTHOR]

We study the acoustically driven spin wave resonance (ADSWR) in a Ni film sputtered on a 128° Y-cut lithium niobate (LiNbO3) substrate under the condition that the beam steering effect exists due to the surface acoustic waves (SAWs) transmitted along several selected crystal orientations. SAW devices with that effect exhibit significantly different ADSWR spectra from devices without it. By using the magnetoelastic coupling theory and finite element simulation associated with SAW, we find that the beam steering effect of magnetoacoustic waves has an important influence on the acoustic attenuation. The relationship between its group velocity direction and the magnetization vector can be used to define the magnetoacoustic wave mode. The mode affects acoustic attenuation magnitude, which can break the fourfold symmetry. Increasing its power flow angle will significantly increase the maximum acoustic attenuation caused by magnon–phonon coupling. [ABSTRACT FROM AUTHOR]

The treatment of Maxwell equations show that propagating wave of packets in fiber-optic cables is dispersive, propagating in groups, such that group velocity along certain curves in the frequency-phase velocity diagrams vanishes. It is suggested that stalling of wave groups is responsible, for bursting propagation observed in experimental measurements, causing some delay in transmission. The dispersion equations developed here, are different from those given in texts that are based on "weakly guiding approximation". The queue of such data packets arriving at a router station is found to have a "raised tail" distribution unlike that of Poisson arrivals. For accounting the property, a Mittag–Leffler function distribution (MLFD) of probability is used following a modification of that for a Poisson process, the tail raising is shown to cause delay in transmission, and its estimate is analysed based on the theory. [ABSTRACT FROM AUTHOR]

The article presents the results of studies of internal waves in the shelf zone of the Black Sea in the water area near the mouth of the Kodor River, conducted in June 2021. Spatial surveys were carried out with the Rio Grande 600 kHz ADCP, which revealed the main characteristics of currents and the presence of internal waves generated by river inflow into the sea. Internal waves were recorded on two transects oriented along the normal to the coastline and extending to depths of 100 m. The observed waves had the features of nonlinear waves, were located on the near-surface thermocline, and had heights of up to 3–6 m. Also, short-period internal waves in the form of a wave train with an apparent period of about 3.5 min were recorded by a thermistor chain in the coastal zone of the sea. The dispersion curves and eigenfunctions of internal waves were calculated by numerically solving the internal wave equation, taking into account the velocity shift in the sea. Theoretical data are compared with experimental data. The significant influence of river inflow on the parameters of the generated internal waves moving with the flow was revealed. The experimentally observed decrease in wave periods and increase in their group and phase velocities were confirmed. [ABSTRACT FROM AUTHOR]

Periodically patterned conductor surfaces can transmit electromagnetic modes similar to surface plasmon polaritons, which are called spoof surface plasmon polaritons (SSPPs). In this paper, noncoplanar dentate complementary structure units are proposed. In this case, the fundamental SSPP is split into two modes, of which the mode in the high‐frequency side exhibits negative group velocity (NGV) near the cutoff frequency. The dispersion characteristics of NGV modes can be controlled by manipulating the symmetry of the complementary structure. It is confirmed that the actual transmission wave in the SSPP waveguide is the superposition result of the two split‐mode wave components. [ABSTRACT FROM AUTHOR]

Six profiling floats measured water-mass properties (T, S), horizontal velocities (u, υ), and microstructure thermal-variance dissipation rates χT in the upper ∼1 km of the Iceland and Irminger Basins in the eastern subpolar North Atlantic from June 2019 to April 2021. The floats drifted into slope boundary currents to travel counterclockwise around the basins. Pairs of velocity profiles half an inertial period apart were collected every 7–14 days. These half-inertial-period pairs are separated into subinertial eddy (sum) and inertial/semidiurnal (difference) motions. Eddy flow speeds are ∼O(0.1) m s−1 in the upper 400 m, diminishing to ∼O(0.01) m s−1 by ∼800-m depth. In late summer through early spring, near-inertial motions are energized in the surface layer and permanent pycnocline to at least 800-m depth almost simultaneously (within the 14-day temporal resolution), suggesting rapid transformation of large-horizontal-scale surface-layer inertial oscillations into near-inertial internal waves with high vertical group velocities through interactions with eddy vorticity gradients (effective β). During the same period, internal-wave vertical shear variance was 2–5 times canonical midlatitude magnitudes and dominantly clockwise-with-depth (downward energy propagation). In late spring and early summer, shear levels are comparable to canonical midlatitude values and dominantly counterclockwise-with-depth (upward energy propagation), particularly over major topographic ridges. Turbulent diapycnal diffusivities K ∼ O(10−4) m2 s−1 are an order of magnitude larger than canonical midlatitude values. Depth-averaged (10–1000 m) diffusivities exhibit factor-of-3 month-by-month variability with minima in early August. [ABSTRACT FROM AUTHOR]

A methodology is proposed for high-precision local measurement of the group velocity of longitudinal waves in solid samples with millimeter thickness. Achievement of the required accuracy involves laser thermo-optical excitation of submicrosecond ultrasonic video pulses and ultrawideband piezoelectric recording of acoustic signals reflected from the test sample. Plane-parallel samples made of duralumin, quartz, and steel with a thickness of 2–6 mm are studied. To achieve the required accuracy in measuring the group velocity of ultrasound, the signal shape is mathematically processed with compensation for diffraction of the ultrasonic beam as it propagates through the sample. The possibility of ensuring the uncertainty in measuring the group velocity of ultrasound in the 1–15 MHz frequency range at a level of 0.1% in samples with millimeter thickness is demonstrated. [ABSTRACT FROM AUTHOR]

Recently, PbSnSe2 alloy was found to exhibit a large hysteresis effect on transport properties, demonstrating its significant potential for thermoelectric applications. Using ab initio approaches, we studied the carrier transport properties of PbSnSe2 crystal, which is a special case of the alloy with the shortest‐range order. A peak power factor of 134.2 μW cm−1 K−2 was found along the cross‐plane direction in the n‐type PbSnSe2 at a doping concentration of 7 × 1020 cm−3 at 700 K. This high power factor originates from delocalized p electrons between intra‐plane Pb–Se pairs and between cross‐plane Sn–Se pairs that can build up transport channels for conducting electrons, leading to a high electrical conductivity of 5.9 × 105 S m−1. Introducing Pb atoms into Pnma phase SnSe can decrease the phonon group velocities and enhance the phonon–phonon scatterings, leading to a low thermal conductivity of 0.53 W m−1 K−1 at 700 K along the cross‐plane direction. The calculated peak ZT of ~3 along the cross‐plane direction at an n‐type doping concentration of around 5 × 1019 cm−3, which represents a theoretical upper limit for an idealized PbSnSe2 crystal. This work interprets the origins of three‐dimensional charge and two‐dimensional phonon transport behavior in PbSnSe2 and demonstrates that such crystals are promising high‐performance thermoelectric semiconductors. [ABSTRACT FROM AUTHOR]

Abstract The Radon and Hilbert transform and their applications to convectively coupled waves (CCWs) are reviewed. The Hilbert Transform is used to compute the wave envelope, whereas the Radon transform is used to estimate the phase and group velocities of CCWs. Together, they provide an objective method to understand CCW propagation. Results reveal phase speeds and group velocities for fast waves (mixed Rossby‐gravity, westward and eastward inertio‐gravity, and Kelvin) that are consistent with previous studies and with Matsuno's equatorial wave dispersion curves. However, slowly‐propagating tropical depression‐like systems and equatorial Rossby waves exhibit wave envelopes that propagate faster than the individual wave crests, which is not predicted by dry shallow water theory.

We theoretically propose a hybrid nanomechanical resonator (NR) system, where a doubly clamped suspended NR with an embedded quantum dot driven by two-tone fields is coupled to another NR via the Coulomb interaction, and we investigate the absorption spectra of the probe field under different exciton-pump field detuning. In the condition of pump on-resonance, the absorption spectrum gives a method to determine the coupling strength of the two NRs. In the pump off resonance, the absorption spectra exhibit double-Fano resonance, which is determined by the interaction of the two NRs, the frequencies of the two NRs, as well as the pump detuning. Furthermore, the double-Fano resonances are accompanied by the rapid normal phase dispersion, which indicates the slow- and fast-light effect. The results show that the group velocity index is tunable by the interaction of the two NRs, the detuning, and the different resonator frequencies, which can achieve the conversion from fast light to slow light. [ABSTRACT FROM AUTHOR]

With the concept of topological order of electronic states in crystals being proposed, the pursuit of topological phases in various systems has become an important subject of modern physical science. The existence of antisymmetric Dzyaloshinskii–Moriya interaction caused by spin–orbit coupling in magnetic systems leads to the non-reciprocal propagation of magnons, which is a key factor to realize the magnonic analog of an electronic topological insulator (TI). Here, a two-dimensional magnetic skyrmion crystal (SkX) is introduced as a platform for realizing magnonic TI. It is numerically demonstrated that nonchiral and chiral edge states could exist in different magnonic bandgaps. The nonchiral edge magnons can propagate to both directions simultaneously along the boundary of the SkX with different wavelengths and group velocities. By contrast, chiral edge magnons are topologically protected, resulting in the unidirectional propagation along the boundaries and the robustness against defects or disorders. Furthermore, the chirality and the presence of edge magnons can be manipulated by the polarity of skyrmions and the width of the second magnonic bandgap via the magnetic field. Our findings could provide a skyrmionic paradigm for investigating topological magnonics and even quantum magnonics. [ABSTRACT FROM AUTHOR]