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We suggest a novel approach to predict and clarify the transformation of an arbitrarily polarized wave into two circularly polarized ones, based on the peculiar features of their transmission and reflection from a stack with regularly arranged gyrotropic layers. In spite of the fact that in the Faraday geometry gyrotropic media possess four electromagnetic eigenmodes, we have managed to modify the problem to be analytically resolved within the conventional transfer-matrix method. As a result, we have obtained and analyzed the dispersion relation, as well as the transmission and reflection coefficients, which are applicable for any elliptic polarization of a wave irradiating a gyrotropic superlattice with finite number of unit cells. It is shown that there exists a wide range of wave frequency and magneto-optical parameter (proportional to external dc magnetic field) inside of which the wave of given circular polarization is perfectly transmitted, while the wave with the opposite circular polarization is completely reflected. Thus, under certain conditions, the incident plane wave (taken as an appropriate example) splits up into the transmitted and reflected circular waves with mutually inverse rotations. We indicate conditions when a relatively small variation of the magnetization can reverse the polarizations mentioned above.

The depletion of a quasi-two-dimensional (quasi-2D) dipolar Bose condensed gas in the presence of both contact and long-range 1/r interactions is investigated in the framework of Hartree–Fock–Bogoliubov (HFB) approximation. When the characteristic wavelength of a mode is much larger than the trap size, the dipole-dipole (DD) interaction can be treated as a contact interaction and in the low momentum limit the long-range nature of the 1/r interaction has the dominant contribution and leads to the nonlinear (nonphononic) dispersion relation. We will show that quantum depletion is temperature independent and is determined by the contact, DD and longrange 1/r coupling constants (ɛdd = gd/g and C). The the quantum depletion is affected by long-range 1/r interaction and at large momentum limits the momentum dependence of quantum depletion unaffected by 1/r interaction.The depletion of a quasi-two-dimensional (quasi-2D) dipolar Bose condensed gas in the presence of both contact and long-range 1/r interactions is investigated in the framework of Hartree–Fock–Bogoliubov (HFB) approximation. When the characteristic wavelength of a mode is much larger than the trap size, the dipole-dipole (DD) interaction can be treated as a contact interaction and in the low momentum limit the long-range nature of the 1/r interaction has the dominant contribution and leads to the nonlinear (nonphononic) dispersion relation. We will show that quantum depletion is temperature independent and is determined by the contact, DD and longrange 1/r coupling constants (ɛdd = gd/g and C). The the quantum depletion is affected by long-range 1/r interaction and at large momentum limits the momentum dependence of quantum depletion unaffected by 1/r interaction.

We consider a family of the discrete Schrodinger operators Hλμ, in the d (d ≥ 3)-dimensional lattice with a wide class of dispersion relation and a potential constructed by a combination of the Kronecker delta function and the shift operator, depending on two parameters. The exstence of eigenvalues, threshold eigenvalues and threshold resonances and their dependence on the parameters of the operator and dimension of the lattice are explicitly derived.

The analytical investigation of the effect of collisions on the Jeans instability in dusty plasma is carried out to observe the effect of the simultaneous presence of polarization force and charge gradient force on the dust particles. The dispersion relation, the instability growth rate and the graphical analysis shows that the combined effect of the charge gradient force, dust polarization force and collisions moves the system towards stabilization.

Gravitational instability of magnetized, electrically and thermally conducting, strongly coupled fluid with radiative effects is investigated using the modified generalized hydrodynamic (GH) model. A general dispersion relation is derived with the help of linearized perturbation equations using the normal mode analysis method and it is discussed for longitudinal mode of propagation. In longitudinal mode of propagation, we find that Alfven mode is uncoupled with the gravitating mode. The fundamental Jeans criterion of gravitational instability is determined which depends up on thermal conductivity, radiative heat-loss function, shear viscosity and bulk viscosity while it is independent of magnetic field. The strongly coupled effect changes the Jeans criterion of gravitational instability. Mathematical computations have been executed to see the impact of different constraints on the growth rate of the Jeans instability.

In this paper a finite difference scheme for the one-dimensional double dispersion equation is constructed and studied. The scheme is based on the representation of this equation as a generalized Hamiltonian system. After applying the partitioned Runge-Kutta method with 3-stage Lobatto IIIA and IIIB coefficients, we get a discrete finite difference scheme with approximation error O(h2 + τ4). This scheme is symplectic, i.e. it preserves the symplectic structure of the solution on the discrete level.Numerical experiments are provided for quadratic nonlinearity. Two problems are considered: propagation of a single solitary wave and interaction of two waves traveling toward each other. The numerical results show the convergence of the discrete solution to the exact one with O(h2 + τ4) error.

A local study of linear electrostatic modes, applicable to the dynamics perpendicular to the magnetic field in a plasma with crossed electric and magnetic fields, is presented. The analysis is based on a two-fluid model that takes into account the finite-electron-gyroradius effects through a rigorous gyroviscosity tensor and includes a dissipative friction force in the electron momentum equation. A comprehensive dispersion relation, valid for arbitrary electron temperature, is derived, which describes properly all the relevant waves for wavelengths longer than the electron Larmor radius. For a homogeneous and dissipationless plasma, such a fluid dispersion relation agrees with the long-wavelength limit of the kinetic electron–cyclotron-drift instability dispersion relation that extends the results to arbitrary short wavelengths. The general fluid dispersion relation covers different parametric regimes that depend on the relative ion-to-electron drift velocity and on the presence of equilibrium inhomogeneities and/or dissipation. Depending on such conditions, its roots yield as follows: two-stream instabilities, driven solely by the relative drift between species; drift-gradient instabilities, driven by the combination of the relative drift and equilibrium gradients; and drift-dissipative instabilities, driven by the combination of the relative drift and friction. Instability thresholds are determined and some distinctive unstable modes are described analytically. This research was funded mainly by the Comunidad de Madrid (Spain), under PROMETEO-CM project, with Grant No. Y2018/NMT-4750. Enrique Bello-Benítez is supported by Spain's Ministerio de Ciencia, Innovación y Universidades, under Grant No. FPU18/03686. Jesús Ramos and Eduardo Ahedo acknowledge support by the ESPEOS project, funded by the Agencia Estatal de Investigación (Spain's National Research and Development Plan), under Grant No. PID2019-108034 RB-I00/AEI/10.13039/501100011033.

Electron cyclotron (EC) waves are studied in the Saturn’s magnetosphere. The method use of kinetic approach has been adopted toevaluate the dispersion relation, growth rate of the waves. We show the wave frequency is near the gyro frequency of the electron cyclotron wave they are right hand circularly polarized. The present study of the investigation is to examine the effect of parallel electric field (EII) in view of the observations in Saturn magnetosphere has been applied by Cassini. It is observed that the effect of increasing the Saturn’s radii (Rs) with parallel electric field is to decrease the growth/damping rate of the EC waves. The results are interpreted for the space plasma parameters appropriate to the Cassini of the Saturn’s magnetosphere plasma.

Electromagnetic ion cyclotron waves have been studied for relativistic ring distribution in the presence of parallel AC electric field by using the method of characteristic solutions and kinetic approach. The dispersion relation and the growth rate has been derived and calculated for magnetosphere of Saturn. The effect of AC frequency on the Doppler shifting frequency has been discussed. The new results have been explained for a ring distribution function rather than the bi-Maxwellian or loss cone distribution function. The effective parameters for the generation of EMIC waves are not only the temperature anisotropy but also the relativistic factor, AC field frequency, ratio of cold to warm particles number density which has been discussed in result and discussion section.

The extended first integral method is used to study the complete propagation characteristics of nonlinear surface plasmon polaritons in a multilayer slab waveguide. The method has an advantage of simultaneously obtaining dispersion relation as well as field profile of the propagating mode in the guiding structure. The dispersion characteristics have been found to depend on the input field intensity. Soliton - like nature for the electric field in the focussing nonlinear medium has been found to enhance the propagation length of the wave propagating through the waveguide.

The present study deals the wave characteristics for flexural gravity wave in the presence of porous bottom. The problem is modelled using the thin elastic plate theory and the wave past permeable bottom based on Sollitt and Cross model. Using the separation of variable method along with the boundary conditions, a complex dispersion relation is derived. Further, the effectiveness of various structural parameters and permeable bed are investigated by computing the results for group and phase velocity. This model would be useful in constructing finite flexible structure as a breakwater in the presence of a porous bed to defend harbours, bays and coasts from surface wave attacks.

This work presents a comparative study of homogeneous and inhomogeneous plasmas for the effect of different plasma parameters on the phase velocity of dust acoustic wave. For the inhomogeneous plasma the growth rate of the dust acoustic wave is intensely studied and the role of components of plasma i.e. inertialess isothermal electrons, inertialess ions at two temperature and massive dust grains with heavy charge is observed on the phase velocity. The general dispersion relation is the guiding factor for the detailed study of dust acoustic wave which is obtained using normal mode analysis.

Electromagnetic ion cyclotron (EMIC) waves with temperature anisotropy were studied in Saturn’s non-uniform magnetic layer. After the kinetic method, after injecting a cold plasma beam into the Saturn system, the growth rate of the EMIC wave was theoretically studied. An expression of the dispersion relation is drawn by using the method of the characteristic solution. Therefore, in this paper, a ring distribution is used instead of the usual Maxwellian distribution. The focus of this study is on the oblique propagation of EMIC waves, whose temperature anisotropy, ion energy density, and propagation angle vary with the direction of the magnetic field. The study found that these parameters support the growth rate of EMIC waves in the Saturn magnetosphere. Numerical analysis also shows that as the number density of cold plasma and the number of thermal plasmas increase, the growth rate of EMIC waves also increases. These results apply to the application of space plasma environments and magnetospheric systems for detailed comparison of planetary studies.

Low temperature anistropic thermoelectric power factor (PF) of single layer black phosphorus is investigated. Charge carriers assumed to be scattered by in-plane and out-of-plane phonons via deformation potential coupling. Theoretical investigations (PF) including anisotropic electronic dispersion relation show single in-plane phonon scattering process is dominant over the range of temperature and carrier concentrations considered. Numerical calculations of PF showcase role and relative importance of in-plane and out-of-plane phonon scattering mechanisms operative in the system.

Kinetic Alfven wave has been studied in superthermal plasma in both cases (warm and cold electron limit) in plasma sheet boundary layer. The effect of velocity distribution function (VDF) that exhibit a power law dependence on the high- energy tail and known as superthermal or kappa distribution, have been found to provide a better fitting to the VDF measured by several spacecraft in the plasma environment and is the key subject of this paper. Kinetic effects of electrons and ions are included to study kinetic Alfven wave because both are important in the transition region. In this work we introduce a mathematical formalism that provide expressions for dispersion relations for oblique propagating kinetic Alfven waves resulting from a kappa VDF. The effect of kappa index and thermal corrections on the dispersion relations of KAW is discussed. The method may be suitable to deal with the PSBL, where particle acceleration is also important along with wave emissions.

The encounter between Voyager and Saturn’s environment reveals the presence of electromagnetic ion cyclotron waves (EMIC) in the magnetosphere of Saturn. Cassini provides evidence of dynamic particle injection in Saturn’s internal magnetosphere. Previous theoretical studies have suggested that EMIC waves may explain the loss of relativistic electron populations. However, recent observations indicate that although the EMIC wave is responsible for the significant loss of super-relativistic electrons, the relativistic electron population is almost unaffected. In this paper, we study the effects of EMIC waves and relativistic particles on these waves in the plasma, which propagate obliquely relative to Saturn’s magnetic field. The particles are assumed to be trapped and follow ring distribution function. Using the kinetic approach, the expressions of dispersion relation and growth rate are derived. Various parameters affecting the growth of EMIC waves has been studied. The effect of drift velocity has also been studied in this case.

We present an analytical study on propagation characteristics of longitudinal electro-kinetic (LEK) waves in III-nitride semiconductor viz. GaN. The implanted ions in GaN agglomerate to form colloids. These ion colloids (ICs) are continuously bombarded by all the plasma particles and stick on them, but they acquire a net negative charge due to relatively higher mobility of electrons. To examine the influence of charged ICs on the plasma modes, we have derived a linear dispersion relation for LEK wave in ICs laden GaN semiconductor plasma. We have restricted our analysis tolow frequency regime of LEK wave where ICs can also participate in the perturbation. The dispersion relation leads to four modes of LEK waves, which are analytically investigated in zincblende (ZB) and wurtzite (WZ) structures of GaN. It is found that the presence of charged ICs significantly modifies the LEK modes. The present analysis reveals that the amplification of these modes can be optimized by fine tuning the applied electric field and wave number of the modes.

In this paper, a comprehensive analytical study on propagation of longitudinal electro-kinetic (LEK) modes and novel properties introduced due to the presence of negatively charged nano-sized ion colloids (ICs) of implanted ions is carried out. By employing multi-fluid balance equations, a compact dispersion relation has been derived for the two cases: the phase velocity of the LEK mode is less than or more than the carrier thermal speed, which are termed as slow and fast LEK modes, respectively. The charged ICs not only interact with the plasma particles but also changes the balance of charge of later in the medium through sticking processes of carriers onto the former. The dispersion relation reveals that the plasma and the charged ICs present in the GaN crystal support four LEK modes. We have carried out numerical analysis for dispersion and growth characteristics as a function of magnetic field and compared them for wurtzite and zincblende structures of GaN. The present analysis establishes that the presence of ICs together with transverse magnetic field strongly modifies the existing modes and also gives rise to new novel modes.

Modification in dispersion characteristics of space charge wave in a semiconductor plasma medium due to presence of nanoparticle cluster has been reported. This study has been conducted using classical hydrodynamic model of infinite plasma. The obtained dispersion relation has been analyzed to study convective nature of two possible propagating space charge modes. This study resulted in a strong modification in dispersion characteristics of space charge wave in an n-type semiconductor plasma medium embedded with a nanoparticle cluster/assembly. This modification is through a non-dimensional parameter ‘l’; characteristic of nanoparticle cluster, which is a function of nanoparticle density N and radius r. It is hoped that, reported study in the considered media will make it very suitable for the use as a probe for solid state diagnostics.

The quantum mechanical effects has wide applications in quantum plasma echoes, quantum plasma instabilities and microelectronics devices. Quantum effects may become important when the electron number density of the order of 1030 m−3 andsmall temperatures of a few thousand Kelvin. A dusty plasma is a three-component plasma consisting of electrons, ions, and a solid grains. We use the quantum hydrodynamic model to derive the plasma dispersion equation to study the growth rate of electron drift waves in quantum dusty plasmas. The growth shows depends on the electron temperature, electron density, electron drift velocity and wave number, ions and dust mass. The results may be useful to understand the physics of dense astrophysical objects. Different approximations are tried to solve the dispersion equation.

We present a theoretical study of nonlinear localized electromagnetic modes in a plate of a layered superconductor. Despite the symmetry of the system, the plate is assumed to be in a homogenous dielectric environment, with superconducting layers lying perpendicular to the plate surface and the modes propagating across the layers. Due to the nonlinearity of the Josephson plasma, the plate can contain localized modes that are symmetric, antisymmetric and nonsymmetric with respect to the magnetic field. It is shown that under certain conditions the dispersion of the localized modes can be anomalous whereas the group velocity vanishes. By virtue of the nonlinearity, the dispersion relations contain the amplitude of the localized mode. This opens the possibility of observing the stopping of mode light in a plate of a layered superconductor.We present a theoretical study of nonlinear localized electromagnetic modes in a plate of a layered superconductor. Despite the symmetry of the system, the plate is assumed to be in a homogenous dielectric environment, with superconducting layers lying perpendicular to the plate surface and the modes propagating across the layers. Due to the nonlinearity of the Josephson plasma, the plate can contain localized modes that are symmetric, antisymmetric and nonsymmetric with respect to the magnetic field. It is shown that under certain conditions the dispersion of the localized modes can be anomalous whereas the group velocity vanishes. By virtue of the nonlinearity, the dispersion relations contain the amplitude of the localized mode. This opens the possibility of observing the stopping of mode light in a plate of a layered superconductor.

This paper investigates the stability of planar liquid sheets surrounded by another immiscible liquid. A relation between the temporal growth rate and the wavenumber is derived using the classical stability theory. In the limit of dominant viscous stresses, the dispersion relation yields negative values for the growth rate of instability across the entire range of wavenumbers. The low capillary Reynolds number regime, or equivalently the large Ohnesorge-number limit, shows that such planar liquids in liquid systems are stable regardless of the viscosity mismatch between the two liquids for both sinuous and varicose perturbations.

The formation of density corrugation due to zonal flow, so-called zonal staircase, is investigated theoretically, based on the wave-kinetic framework. The wave-kinetic simulation is performed, considering the profile corrugation and the turbulence trapping mechanism, where the profile corrugation changes the growth rate and the dispersion relation of turbulence. The zonal density is generated by the modulation of particle transport. We obtain the analytical expression for the zonal density, which determines the staircase height. It is found that the amplitude normalized by the ambient density can be comparable to the zonal flow normalized by the diamagnetic drift velocity. The key effect that determines the turbulence profile is found to be the phenomenon of turbulence trapping by zonal flow, while the profile corrugation due to zonal density has weaker effects. Thus, turbulence is localized where the flow curvature is negative, which leads to a flattening of the density profile through the enhancement of particle transport. This fact clearly shows that the effect of turbulence trapping dominates the density gradient dependence of the local linear instability.

Spin waves in micrometer-sized, patterned Y-shaped Permalloy structures were studied using micro-focus Brillouin light scattering (BLS) with a magnetic field applied in-plane. For in-plane magnetized thin films and microstrips, the dispersion relations depend on the angle of the magnetization with respect to the microstrip axis. BLS measurements show that spin waves generated in the two arms that form the top of the Y structure can be channeled into a longer magnetic microstrip that forms the base when the applied field is oriented perpendicular to the long axis of the base. In this configuration, the base supports surface spin waves. A comparison of the BLS data with micromagnetic simulations reveals that low- k spin waves generated by a microstrip antenna in the arms are converted to higher- k spin waves in the base, which may be useful for nanomagnonic applications.

The dynamic properties of the Hall thruster breathing mode are investigated experimentally. Non-invasive time-resolved laser diagnostics are combined with a quasi-one-dimensional non-Maxwellian modeling technique to yield the high-speed evolution of a variety of plasma properties over the course of a breathing oscillation. The fluctuations of both ion and neutral densities are quantified in terms of amplitude and dispersion and are interpreted in the context of a simplified dispersion relation. It is found that the oscillations associated with the breathing mode are likely ion and neutral waves propagating with phase velocities commensurate with the local species drift speed. Further, the amplitudes of the waves are shown to decay with distance from the anode. This effect can be explained largely by the influence of the expansion of the background plasma and neutral gas. This monotonic decay combined with the downstream propagating nature of the waves suggests that these oscillations are influenced by conditions upstream of the acceleration and ionization regions. By comparing the presence of these waves to inferred electron temperature fluctuations, the hypothesis that the breathing mode is governed by a process in which the modulation of the neutral density near the anode sheath or the anode itself is coupled to a downstream ionization instability is qualitatively explored. The possibility of these waves relating to cyclical recombination of ions at the anode is also discussed.

We achieved substantially low thermal conductivity by introducing some crystal disorder into complex material BaSi2 films on Si substrates for realization of a high-performance thermoelectric material. The BaSi2 films/Si exhibited a low thermal conductivity of 0.96 W m−1 K−1 without nanostructuring, which is less than about two-thirds value of bulk BaSi2 and is the lowest among ecofriendly silicide materials. This substantially low thermal conductivity was brought by both the use of complex material with intrinsically low phonon group velocity and the introduction of point defects as the crystal disorder. The first-principles calculations revealed that the point defect modulates the phonon dispersion relation lowering longitudinal acoustic phonon group velocity. However, the transverse acoustic phonon group velocity was increased at the same time, resulting in a negligible change in average acoustic phonon group velocity. This indicated that the crystal disorder effect related to point defects in this system is enhancement of phonon scattering, not lowering phonon group velocity. The BaSi2 films/Si with point defects exhibited a higher thermoelectric power factor (2.9 μW cm−1 K−2) than bulk BaSi2. These results highlight that complex material BaSi2 film/Si with point defects, having substantially low thermal conductivity, is a candidate as a thermoelectric power generator material in the sensor network.

We report observation of the dust ionization waves (DIWs) excited by an external oscillating electric field on the Plasma Kristall-4 facility under microgravity conditions. It is shown that at the smallest excitation amplitude, the waves are linear, and the dispersion relation can be deduced from the experimental data. The microparticle oscillations are represented as a superposition of two longitudinal waves propagating in the opposite directions. In the investigated range of excitation frequency, the wavenumber is not directly proportional to the frequency, and the phase velocity is almost proportional to the frequency. We propose an interpretation of DIW assuming that the microparticle effect on the recombination rate rather than the microparticle subsystem compressibility is responsible for the wave propagation. The calculated phase velocity of DIW is compatible with the experimental one.

The methods to study capillary waves have been reviewed together with the emerging practical applications of theirs and new theoretical developments in the field. The focus is on monochromatic ripples of frequency in the range 0.1–10 kHz. A capillary wave apparatus has been constructed that combines several recent advances on the technique. It is based on the profilometry of waves decaying with distance, with a high-speed video camera detecting the light refracted by the surface. A code to process the images has been developed, which executes a regression analysis to determine the characteristics of the wave. High precision and accuracy have been achieved: standard deviation from the mean of ±0.5% for the wavelength and ±7% for the decay length; mean deviations from the theoretical values ±0.2% for the wavelength and ±5% for the decay length. An analytic approximation for the dispersion relation has been used to determine the Gibbs elasticity of a surfactant monolayer from the data for decay length vs frequency. The elasticity of an octanol monolayer has been determined with precision of ±1 mN/m, in excellent agreement with the theoretical value. Surface tension can be measured from the wavelength data with precision of ±0.3 mN/m. It has been demonstrated that the effect of the surface elasticity on the wavelength is significant, and accurate wavelength data can actually be used to determine the elasticity if the surface tension is known.

We study the linear stability of a collisional drift wave in an ultracold neutral plasma (UNP) with the aim of investigating the effect of strong coupling effects on its propagation characteristics. The dispersion relation obtained using the generalized hydrodynamic model for the ultracold ion dynamics is solved analytically in various limits for the real frequency and growth rate of the mode. It is found that strong coupling-induced viscous effects lead to a weakening of the growth rate and an enhancement in the real frequency of the mode. The impact is particularly pronounced in the “kinetic” regime, i.e., when the ion–ion correlation time is much larger than the wave period. In the regime where the density gradient is weak, we find that collisional effects can destabilize the transverse shear waves and longitudinal waves. We discuss the relevance and potential application of our results in future experimental and numerical simulation studies of UNPs.

A theoretical study of high-frequency electron waves in the plasma of a Hall-type discharge with crossed electric and magnetic fields is presented. The analysis of dispersion relations for a homogeneous weakly collisional plasma with the electron velocity distribution function obtained in the relaxation approximation is performed. It is shown that the nonequilibrium character of the electron distribution function can lead to kinetic instability of cyclotron waves. This instability occurs when the thermal velocity of electrons is comparable with the drift velocity in crossed fields. In the quasilinear approximation, a compact form of the diffusion coefficient of the distribution function in the velocity space is obtained, describing unstable modes' evolution and saturation. The analytical solutions are compared with the results of numerical simulation by the particle-in-cell method.

The great challenge with biological membrane systems is the wide range of scales involved, from nanometers and picoseconds for individual lipids, to the micrometers and beyond millisecond for cellular signalling processes. While solvent-free coarse-grained membrane models are convenient for large-scale simulations, and promising to provide insight into slow processes involving membranes, these models usually have unrealistic kinetics. One major obstacle is the lack of an equally convenient way of introducing hydrodynamic coupling without significantly increasing the computational cost of the model. To address this, we introduce a framework based on anisotropic Langevin dynamics, for which major in-plane and out-of-plane hydrodynamic effects are modeled via friction and diffusion tensors from analytical or semi-analytical solutions to Stokes hydrodynamic equations. Using this framework, we obtain accurate dispersion relations for planar membrane patches, both free-standing and in the vicinity of a wall. We also briefly discuss how non-equilibrium dynamics is affected by hydrodynamic interactions., Submitted to The Journal of Chemical Physics

The contactless manipulation of microparticles and cells by using acoustic forces is important in many applications. However, multi-band acoustophoresis has been rarely investigated in the literature. In this Letter, we propose a microscale acoustofluidic system that has multiple orders of available Lamb modes for the acoustic trapping of microparticles at various frequencies. In our device, standing Lamb waves (SLWs) of specific orders can be selectively excited in a 300-μm-thick piezoelectric lithium-niobate (LiNbO3) crystal plate by a pair of interdigitated transducers (IDTs) at the corresponding frequency. We demonstrate the acoustophoretic trapping and patterning of 7-μm particles in a single acoustofluidic device with multiple available actuating frequencies. The approach to the proposed design and the working mechanisms are explained by using thin plate and a full-wave models that solve the dispersion relations and coupling fields of the piezoelectric SLW acoustofluidic system, respectively. Furthermore, we experimentally show that the stable and tight trapping of particles in the chamber can be achieved independently along two mutually orthogonal directions. This provides the essential ground for planar manipulations of microparticles and cells based on the proposed device. The results here can trigger more innovative designs and applications of acoustofluidic devices for microparticle manipulation and microfluidic mixing, with multi-frequency channels and a wide span of different actuating frequencies in one system.

Hyperbolic phonon polaritons (HPhPs) enable strong confinements, low losses, and intrinsic beam steering capabilities determined by the refractive index anisotropy—providing opportunities from hyperlensing to flat optics and other applications. Here, two scanning-probe techniques, photothermal induced resonance (PTIR) and scattering-type scanning near-field optical microscopy (s-SNOM), are used to map infrared (6.4–7.4 µm) HPhPs in large (up to 120 × 250 µm2) near-monoisotopic (>99% 10B) hexagonal boron nitride (hBN) flakes. Wide (≈40 µm) PTIR and s-SNOM scans on such large flakes avoid interference from polaritons launched from different asperities (edges, folds, surface defects, etc.) and together with Fourier analyses (0.05 µm−1 resolution) enable precise measurements of HPhP lifetimes (up to ≈4.2 ps) and propagation lengths (up to ≈25 and ≈17 µm for the first- and second-order branches, respectively). With respect to naturally abundant hBN, we report an eightfold improved, record-high (for hBN) propagating figure of merit (i.e., with both high confinement and long lifetime) in ≈99% 10B hBN, achieving, finally, theoretically predicted values. We show that wide near-field scans critically enable accurate estimates of the polaritons’ lifetimes and propagation lengths and that the incidence angle of light, with respect to both the sample plane and the flake edge, needs to be considered to extract correctly the dispersion relation from the near-field polaritons maps. Overall, the measurements and data analyses employed here elucidate details pertaining to polaritons’ propagation in isotopically enriched hBN and pave the way for developing high-performance HPhP-based devices.

Publisher Copyright: © 2021 Author(s). Recently, a new approach to gyrokinetics, invariant under electromagnetic gauge transformations, was developed. The gyrocenter equations of motion are now expressed in terms of the perturbed fields instead of the potentials, in a form suitable for numerical simulations and analytic studies. In this paper, we verify that the long-wavelength limit, i.e., the drift-kinetic limit of the new gyrokinetic theory, is in line with existing work, providing a solid foundation for simulations. We compute the dispersion relation of the new drift-kinetic theory in slab geometry and find agreement with a long-wavelength limit of the full Vlasov-Maxwell model. Published under an exclusive license by AIP Publishing.

The Kelvin–Helmholtz (K–H) instability in a magnetized nonuniform velocity sheared dusty plasma is investigated accounting for the effects of dust polarization force due to inhomogeneity in background plasma number densities. A three-component fluid model for dusty plasma is formulated considering Boltzmann electron/ion fluids and flowing magnetized dust fluids whose dynamics are affected due to the presence of dust polarization force. A dispersion relation for the K–H instability is derived by applying normal mode analysis on the linearized perturbation equations of the system. It is found that the polarization parameter dependent dust acoustic mode significantly modifies the dispersion relation of the K–H instability. The critical shear required to excite the K–H instability (S > Scrit) decreases with an increase in the dust polarization parameter and dust cyclotron frequency. The growth rate of the K–H instability is observed to be suppressed due to the presence of the dust polarization parameter. The results have been discussed for experimental magnetized dusty plasmas, which shows that under considered parametric limits, one cannot ignore the presence of dust polarization force on the excitation of the K–H instability in dusty plasmas. The astrophysical consequences are also discussed in Saturn’s E-ring in the limiting case of varying dust grain size.

When the boundary conditions of the source and drain are asymmetric, the plasma waves may become unstable in the channel of a field effect transistor (FET). We use the quantum magnetohydrodynamic model to study the influence of the quantum Bohm potential, Fermi statistical pressure, and electron spin effects on the stability of THz plasma waves propagating perpendicular to the magnetic field in the FET. A dispersion equation governing the THz plasma oscillation is obtained. Numerical results have shown that the presence of spin effects has enlarged the instable range of β, enhanced the instability increment, and made the frequency of THz plasma waves larger. The research shows that nanometer FETs with spin effects have advantages in realizing practical terahertz radiation.

We perform a statistical study of 3-s ultra-low frequency (ULF) waves using Magnetospheric Multiscale observations in the Earth's foreshock region. The average phase velocity in the plasma rest frame is determined to be anti-sunward, and the intrinsic polarization is right-handed. We further examine the linear instability conditions based on the drift-bi-Maxwellian distribution functions according to the observed plasma conditions. The resulting instability is a solution to the common dispersion equation of the ion/ion right-hand non-resonant and left-hand resonant instabilities. The predicted wave propagation is also predominantly anti-sunward. The cyclotron resonant conditions of the solar wind and backstreaming beam ions are evaluated, and we find that, in some cases, the anti-sunward propagating waves can be resonant with beam ions, which was overlooked in previous studies. The study suggests that the dispersion equation provides the 3-s ULF waves a fundamental explanation that unifies a rich variety of resonant conditions.

Considering the anisotropy of wurtzite semiconductors, the interface optical phonons in double-channel AlGaN/GaN heterostructures are investigated by using a dielectric continuous model and transfer matrix method. Also, the ternary mixed crystal effect and size effect on the dispersion relations and electrostatic potentials of phonons are analyzed in detail. The results show that there are six branches of interface phonon modes in a double-channel heterostructure. For some values of Al composition, however, the phonon mode with the highest frequency may not exist, especially when the thicknesses of materials and the wave vectors of phonons are small. The ternary mixed crystal effect and size effect not only influence the values of phonon frequency and electrostatic potential, but also change the vibration mode of interface phonons. This suggests that the interface phonon vibrations can be controlled to reduce their adverse effects by changing the Al composition of AlGaN and the thickness of each layer in a double-channel heterostructure.

Thin films can become unstable when attractive van der Waals forces overcome the stabilizing effects of surface tension and viscous forces. In many applications, the effect of the surrounding bulk fluid cannot be neglected when considering a thin film subject to perturbations. In this work, we examine the two limits of potential flow and Stokes flow in the surrounding bulks to derive dispersion relations in each limit. We show that the effect of the surrounding bulks cannot be ignored for many film–bulk fluid pairings and film thicknesses and present conditions for the validity of each regime. In particular, the potential-flow regime exists when van der Waals forces are sufficiently strong, while the Stokes-flow regime exists when the bulk dynamic viscosity is sufficiently large. Due to the nature of the dispersion relation in the Stokes-flow limit, several distinct scenarios are identified in the corresponding stability diagram, each involving the interplay of different forces. For example, a novel instability regime involving capillary–viscous interactions is identified for large film thicknesses. Finally, by enlisting multiple realistic fluid pairings and film thicknesses wherein such instabilities can occur, we demonstrate the practical relevance of our theoretical findings. This work enables the extension of thin film stability theory to the analysis of antibubbles, splashing molten metals and ionic liquids, Mesler entrainment of microbubbles in breaking waves, and emulsion stability.

Perpendicular, magnetized, collisionless shocks in hydrogen and neon plasmas are studied with 2D particle-in-cell simulations for parameters accessible to experiments on OMEGA EP [Maywar et al., J. Phys.: Conf. Ser. 112, 032007 (2008)]. The simulations are performed with realistic ion-electron mass ratios by which the relative importance of different micro-instabilities can be accurately captured. The dispersion relation of the modified two-stream instability (MTSI), the main dissipation mechanism for these shocks, is used to find suitable parameters for upcoming experiments. Simulations show that magnetized collisionless shocks can be readily formed within a few tenths of an ion gyro-period in both hydrogen and neon gases, with a background magnetic field of 50 T, achievable using the magneto-inertial fusion electrical discharge system [Barnak et al., Rev. Sci. Instrum. 89, 033501 (2018)]. A portion of the ions are reflected to the upstream region and accelerated in both shock normal and tangential directions, indicating the formation of a supercritical shock. Shock front reformation is seen in longer time 1D simulations. The results show that the formation time and width of these shocks are determined by MTSI.

A closed-form integral representation of the electromagnetic dispersion relation for plasma waves propagating perpendicular to a magnetic field is derived. Growth rates and oscillation frequencies are calculated for several cases of the Dory–Guest–Harris instability and compared with those calculated from the usual electrostatic version of the dispersion relation. The comparisons show that the electromagnetic treatment more accurately identifies unstable configurations in plasmas with high beta, where the electrostatic dispersion relation predicts stability. Continuum kinetic simulations using the Washington approximate Riemann plasma framework confirm the theoretical calculations. The electromagnetic extension of the Dory–Guest–Harris instability provides a new benchmark problem for testing continuum kinetic simulations using the Vlasov–Maxwell plasma model, including for other numerical treatments such as particle-in-cell methods.

The fluid dispersion relation of the dust acoustic wave in a plasma, which consists of electrons, an ion flow, and a dust fluid, is investigated. The dispersion relation has a form similar to that of the conventional one of the ion acoustic wave. It can be transformed into a form that includes the energy exchange factor between the ion flow and dust fluid. The dust acoustic wave can be controlled by varying the ion flow velocity. Varying the ion flow velocity is equivalent to varying the energy exchange factor. In the region where the energy exchange factor is negative, the dust acoustic wave does not propagate and the net energy of the dust fluid is expected to be transferred to the ion flow. In contrast, in the regions where the exchange factor is positive, the dust acoustic wave propagates.

We study Alfven eigenmodes (AEs) in the TJ-II heliac in hydrogen plasmas heated by hydrogen co-field neutral beam injector. Taking advantage of the unique TJ-II flexibility in a varying plasma current, we have observed strong variation of the AE frequency from fAE ∼ 30 to ∼220 kHz for selected modes. An advanced heavy-ion beam probe diagnostic determines the spatial location and internal amplitudes of the modes. The modes satisfy a local AE dispersion relation including the geodesic acoustic frequency that represents the lowest frequency of the mode. Linear MHD modeling with STELLGAP and FAR3D codes shows that the calculated temporal evolution of the mode frequency reproduces the observed maxima and minima at the same time intervals with a similar frequency range, and the radial profile peaks near the outer edge of the observed one.

Recent studies have suggested that Weyl semimetals were the promising materials to verify Kirchhoff’s law for nonreciprocal materials in experiment. Nevertheless, existing designs based on Weyl semimetals could not achieve perfect nonreciprocal radiation around a wavelength of 10 µm at small angles. Therefore, it is of significant importance to design structures that can realize perfect nonreciprocal radiation at a shorter wavelength and smaller angle. Here, by using attenuated total reflection, we demonstrate that perfect nonreciprocal radiation can be realized at a wavelength of 10 µm at an angle of 30°. The difference between directional emissivity and absorptivity is as large as 0.99, which is the best result until now, as far as we know. The perfect nonreciprocal radiation is attributed to the nonreciprocal guided resonances in the Weyl semimetal film, which is confirmed by the distribution of magnetic field and dispersion relation. Such a design is promising in verifying Kirchhoff’s law for nonreciprocal materials in experiment.

Spin waves (SWs) in magnetic nanotubes have shown interesting nonreciprocal properties in their dispersion relation, group velocity, frequency linewidth, and attenuation lengths. The reported chiral effects are similar to those induced by the Dzyaloshinskii–Moriya interaction but originating from the dipole–dipole interaction. Here, we show that the isotropic-exchange interaction can also induce chiral effects in the SW transport; the so-called Berry phase of SWs. We demonstrate that with the application of magnetic fields, the nonreciprocity of the different SW modes can be tuned between the fully dipolar governed and the fully exchange governed cases, as they are directly related to the underlying equilibrium state. In the helical state, due to the combined action of the two effects, every single sign combination of the azimuthal and axial wave vectors leads to different dispersions, allowing for a very sophisticated tuning of the SW transport. A disentanglement of the dipole–dipole and exchange contributions so far was not reported for the SW transport in nanotubes. Furthermore, we propose a device based on coplanar waveguides that would allow to selectively measure the exchange or dipole induced SW nonreciprocities. In the context of magnonic applications, our results might encourage further developments in the emerging field of 3D magnonic devices using curved magnetic membranes.

Martensitic transformations in the body-centered cubic β-phase (Im 3 ¯m) of zirconium are studied using first-principles calculations, group-theoretical methods, and symmetry analysis. Phonon dispersion relations in the β-phase calculated within the harmonic approximation predicted an unstable phonon at wave vector 2 π a [ 1 2 , 1 2 , 0 ](N) and a soft phonon at wave vector 2 π a [ 2 3 , 2 3 , 2 3 ]( Λ). The symmetry of the unstable phonon is the same as the symmetry of the N 4 − irreducible representation, and the symmetry of the soft phonon is the same as the symmetry of the Λ 1 irreducible representation. Martensitic transformations are simulated considering two steps. Frozen phonon calculations are used to determine the first step, i.e., the transformation of the β-phase to an intermediate phase due to phonon motion. Structure relaxation is used to determine the second step, i.e., the transformation of the intermediate phase to the final phase. The unstable N 4 − phonon transforms the β-phase into an intermediate orthorhombic phase (Cmcm), which further transforms to a hexagonal close packed α-phase ( P 6 3/mmc) after structure relaxation. The soft Λ 1 phonon transforms the β-phase into an intermediate trigonal phase (P 3 ¯m1), which further transforms to a hexagonal close packed ω-phase (P6/mmm) after structure relaxation. The intermediate phase space group (Cmcm/P 3 ¯m1) is a common subgroup of the parent phase ( β) space group and the final phase ( α / ω) space group. Therefore, the martensitic transformations in zirconium are reconstructive transformations of the second kind. Symmetry characterization of the martensitic transformations is also presented.

Within the quasi-optical approach, we investigate the propagation of azimuthally symmetric TM waves in periodically corrugated cylindrical waveguides and their excitation by relativistic electron beams. Presenting the field as two, forward and backward, quasi-optical wavebeams coupled at the shallow corrugation, we obtain a dispersion equation for normal waves and thus a criterion of existence of the surface wave. For a finite-length corrugation section, the spectrum of axial evanescent eigenmodes is estimated; the spatial structure and the quality factor of the fundamental mode are found at an eigenfrequency close to the Bragg frequency. A self-consistent system of equations describing the interaction of electromagnetic waves with a rectilinear electron beam injected into the system is derived. Based on this model, we recognize two oscillation regimes, namely, the π-mode excitation regime and the regime of backward surface wave oscillator. We demonstrate the viability of practical implementation of relativistic surface wave oscillators with a power level of up to 140 MW in the sub-millimeter wavelength band.

This study presents the results of 2D particle-in-cell (PIC) simulations of the electron temperature anisotropy driven whistler instability for plasmas in which the electron species is modeled by a bi-kappa velocity distribution. These simulations utilize our previously developed method to generate the initial multi-dimensional kappa velocity distributions. The use of multi-dimensional kappa loadings in PIC simulations provides insights into the non-linear regime of wave evolution in plasmas having non-equilibrium velocity distributions. Three cases are considered, corresponding to κ e = 2 , 3, and ∞ (Maxwellian case). Owing to the use of a large value of electron anisotropy required for reasonable simulation run times, the Maxwellian electron run has the fastest growth rate, reaching saturation earliest. The κ e = 2 case exhibits the slowest growth rate. Spectral analysis of the fluctuating fields reveals considerable wave intensity at frequencies and wavenumbers that satisfy the linear whistler wave dispersion relation. In the runs with kappa distributions, the regions of most intense fluctuations comprise frequencies and wavenumbers that agree only qualitatively with linear whistler wave theory. The results suggest that after saturation, there is some degree of Landau damping of the oblique whistler modes, which returns energy to the electron species. The rate of damping of the oblique modes is highest in the Maxwellian case and lowest for κ e = 2. Evidence of significant superthermal acceleration of electrons in the direction parallel to the ambient magnetic field is also observed. Thus, the power-law index of the electron distribution is reduced by the anisotropic whistler turbulence produced.