Wave Branch Research Articles

Measuring the dispersion relations of spin wave bands using time-of-flight spectroscopy

We develop a generic all-inductive procedure to measure the band structure of spin waves in a magnetic thin stripe. In contrast to existing techniques, our method works even if several spin wave branches coexist in the investigated frequency interval, provided that the branches possess sufficiently different group velocities. We first measure the microwave scattering matrix of a network composed of distant antennas inductively coupled to the spin wave bath of the magnetic film. After a mathematical transformation to the time domain to get the transmission impulse response, the different spin wave branches are viewed as wave packets that reach successively the receiving antenna after different travel times. In analogy with time-of-flight spectroscopy, the wave packets are then separated by time gating. The time-gated responses are used to recalculate the contribution of each spin wave branch to the frequency domain scattering matrix. The dispersion relation of each branch stems from the absolute phase of the time-gated transmission parameter. The spin-wave wave vector can be determined unambiguously if the results for several propagation distances are combined, so as to get the dispersion relations.

Ultrathin Coding Metasurface for Underwater Wave Focusing, Branching and Self-Bending Generation with One Single Actuator

A novel metasurface is proposed that aims to generate underwater acoustic waves with various functions by only one actuator. Each metasurface unit consists of an air cavity sandwiched on one side by a vibration plate and connecting rubber supports. By properly selecting the ratio of the plate to unit lengths, a phase shift of π can be attained to constitute a binary coding metasurface. Three demonstrations, including focusing, branching and self-bending waves, are chosen to validate the functionality of the design. The design is also shown to work over a wide frequency range through changing the ratio. In addition, the design is extremely compact, with the thickness only about 1/100 of the target wavelength. Compared with commonly used phased array transducers that are utilized to generate underwater acoustic waves, this design offers has the advantage of needing only a single actuator as opposed to needing a lumped electrical control system.

Slow light mediated by mode topological transitions in hyperbolic waveguides.

We show that slow light in hyperbolic waveguides is linked to topological transitions in the dispersion diagram as the film thickness changes. The effect appears in symmetric planar structures with type II films, whose optical axis (OA) lies parallel to the waveguide interfaces. The transitions are mediated by elliptical mode branches that coalesce along the OA with anomalously ordered hyperbolic mode branches, resulting in a saddle point. When the thickness of the film increases further, the merged branch starts a transition to hyperbolic normally ordered modes propagating orthogonally to the OA. In this process, the saddle point transforms into a branch point featuring slow light for a broad range of thicknesses, and a new branch of ghost waves appears.

Structure-preserving electromagnetic–kinetic simulations of lower hybrid-wave injection and current drive

In this article, we present a first-principles electromagnetic–kinetic simulation of the slow-wave branch of the lower hybrid waves (LHWs) in electron–deuterium plasmas with real ion–electron mass ratios. Several models of two-dimensional slab configuration containing a grill antenna are constructed using different plasma parameters. Based on our recently developed fully kinetic charge-conservative electromagnetic non-canonical symplectic particle-in-cell method, we studied the coupling, propagation, absorption and current driving effect of LHWs in hot plasmas. The results for the coupling coefficient of the grill antenna, accessibility condition, and electron Landau damping rate show good agreement with theory and previous simulation. The long-term non-linear energy and current deposition of propagating LHWs are also presented, which show a decrement of heating and current-driving efficiency compared with the linear theoretical prediction. The collision effect between electrons and ions is shown to be important for actually driving the current. The relation between the density of the current generated and the amplitude of the LHW is given, which shows a qualitative agreement with the 1D theoretical prediction.

Surface Waves in a Collisional Quark-Gluon Plasma

Surface waves propagating in the semi-bounded collisional hot QCD medium (quark-gluon plasma) are considered. To investigate the effect of collisions as damping and non-ideality factor, the longitudinal and transverse dielectric functions of the quark-gluon plasma are used within the Bhatnagar-Gross-Krook (BGK) approach. The results were obtained both analytically and numerically in the long wavelength limit. First of all, collisions lead to smaller values of surface wave frequency and their stronger damping. Secondly, the results show that non-ideality leads to the appearance of a new branch of surface waves compared to the collisionless case. The relevance of the surface excitations (waves) for the QGP realized in experiments is discussed.

To the Interchange Instability Criterion in the Magnetosphere in the Presence of Velocity Shear

AbstractIn this paper, we address the issue of interchange instability excitation criterion in the magnetospheric plasma in the presence of the velocity shear using a magnetohydrodynamic approach. We conducted our analysis for the arbitrary β plasma configuration using a WKB approximation for wavelengths, λ, much smaller than the characteristic plasma inhomogeneity scale, L, and found two branches of waves. These two wave branches can exist due to the plasma velocity shear and one branch can be unstable for arbitrary angles between the plasma entropy parameter and magnetic flux tube volume gradients. The implications of these results for magnetospheric physics as well as comparison of our results with corresponding analysis of other authors are discussed.

Symmetry-breaking waves and space-time modulation mechanisms in two-dimensional plane Poiseuille flow

Two distinct scenarios of spatial modulation in two-dimensional plane Poiseuille flow have been studied. The first one is based on the identification of a new family of asymmetric Tollmien-Schlichting waves (TSW) breaking the reflectional symmetry about the channel midplane. The second follows the fate of a branch of time-periodic space-modulated waves that exclusively bridge upper-branch TSW-trains of different number of replicas by means of a codimension-2 bifurcation point. These modulated waves may therefore play a relevant role in the strange saddle governing domain-filling turbulent dynamics at high Reynolds numbers.

Trapped solitary waves over an uneven bottom

Steady two-dimensional surface waves on an ideal irrotational fluid over a complex multi-bumped topography are studied analytically in the case when the far upstream flow is slightly supercritical. Fully nonlinear equations are formulated via the von Mises variables that parametrize the bundle of streamlines in the flow over obstacles. For a given small-height topography, we construct approximate two-parametric solution sets which approach the branches of solitary waves as the typical height of the obstacle vanishes.

Chiral Magnonics: Reprogrammable Nanoscale Spin Wave Networks Based on Chiral Domain Walls.

SummarySpin waves offer promising perspectives as information carriers for future computational architectures beyond conventional complementary metal-oxide-semiconductor (CMOS) technology, owing to their benefits for device minimizations and low-ohmic losses. Although plenty of magnonic devices have been proposed previously, scalable nanoscale networks based on spin waves are still missing. Here, we demonstrate a reprogrammable two-dimensional spin wave network by combining the chiral exchange spin waves and chiral domain walls. The spin-wave network can be extended to two dimensions and offers unprecedented control of exchange spin waves. Each cell in the network can excite, transmit, and detect spin waves independently in the chiral domain wall, and spin-wave logics are also demonstrated. Our results open up perspectives for integrating spin waves into future logic and computing circuits and networks.

Fano Resonance of an Elastic Waveguide with an Island Structure

In a solid cylinder, the frequencies of the mode branches of elastic waves decrease as the diameter of a cylinder increases. This feature can be used to control the mode conversion in an elastic wa...

Longitudinal Protection Scheme of HVDC Line Based On the Characteristics of Branch Current

For the traditional high-voltage direct current (HVDC) lines with poor protection rapidity and low resistance to high resistance, This paper puts forward a kind of based on HVDC line reactance flat wave branch current changes of the longitudinal protection scheme. This scheme takes advantage of the fact that the specific harmonic component of the flat-wave reactance branch current is short-circuited by the equivalent dc filter bank when it is internal fault. The characteristics of no such harmonic component flow on the branch can be used as the basis to identify internal fault and external fault. In other words, when it is internal fault, the component of the flat-wave reactance branch is close to 0; The component of the flat wave reactance branch is much larger than 0 when it is external fault. Simulation results show that HVDC longitudinal protection scheme based on branch current characteristics can quickly and accurately identify fault types in various situations and has a strong ability to withstand transition resistance.

Tracking the Suhl instability versus angle and frequency for the backward volume mode in an yttrium iron garnet film

Using parametric excitation, we have studied the minimum frequency associated with the backward volume (BV) spin wave branch in a thin film of the ferrimagnetic material yttrium iron garnet (YIG) for the magnetic field lying in plane and parallel to the wave vector as well as for out-of-plane field angles. We find that there is a drastic change in the efficiency of parametric excitation between two different pumping frequency regimes.

Flexural Wave Propagation in Mass Chain-Filled Carbon Nanotubes.

The propagation characteristics of terahertz (THz) flexural waves in mass chain-filled single-walled carbon nanotubes (MCSCs) are studied using a continuum mechanics approach and molecular dynamics (MD) simulations, where each single-walled carbon nanotube (SWCNT) is modeled as a nonlocal Timoshenko beam based on the nonlocal strain gradient theory. The effect of the surrounding elastic medium and the van der Waals (vdW) interactions between the mass chain and the SWCNT on the wave propagation is quantitatively considered in governing equations, respectively. The analytical expressions of two flexural wave branches and the bandgap between the two branches are derived. When combining our MD simulations of the carbon-atom chain-filled SWCNT, the wave within the bandgap disperses rapidly, and the mass chain has a significant influence on the phase velocity of the flexural wave. The present theoretical solution has a high accuracy in a wide frequency range up to the THz region. In particular, the surrounding elastic medium of the MCSCs remarkably affects the phase velocity for low frequencies, but not for high frequencies. The present study indicates that the wave propagation of a SWCNT could be modulated by changing the filled mass chain and the surrounding elastic medium.

Value of Fragmented QRS Complex on 12-lead ECG as A Valuable Marker of Myocardial Damage of CAD Patients

Background: Presence of Fragmented QRS (fQRS) on a 12-lead Electrocardiogram (ECG) was associated with various cardiac diseases. This phenomenon could represent as an electrical disruption of conduction system following myocardial damage due to coronary artery disease (CAD). We aimed to investigate the value of fQRS to detect the myocardial scar as detected by SPECT Myocardial Perfusion Imaging (MPI).
 Methods: A cross-sectional study of patients with clinical diagnosis of CAD who underwent Cardiac SPECT. The fQRS defined as morphologies of QRS wave (<120 ms), which included an additional R wave (R’), notching in the nadir of S wave, or >1 R’ (fragmentation) in 2 contiguous leads, corresponding to a major coronary artery territory. Pathological Q wave, paced rhythm, typical right or left bundle branch block pattern with QRS duration of ≥ 120 ms were excluded. MPI was interpreted by visual analysis and semi-quantitative scores on 17-segment assessment according to standard nomenclature.
 Results: Total of 72 patients (49 males, mean age 54.7 ± 9.8 years). fQRS was found in 46 patients (64%). The frequency of myocardial scar was significantly higher in patients with fQRS (89% vs. 15%, p<0.05). Sensitivity, specificity, positive and negative predictive value of fQRS for any of myocardial scar as detected by SPECT analysis were 91%, 81%, 89%, and 84%, respectively. From regional scar analysis, fQRS has sensitivity and specificity of 87% and 90% for anterior wall, 76% and 80% for inferior wall, 73% and 79% for lateral wall. LVEF was significantly lower in patients with fQRS (36.9±2.1 vs. 53.2±2.2, p< 0.05).
 Conclusion: The fragmented QRS could serve as a novel ECG marker to detect and localize the myocardial damage in CAD patients. Regional fQRS patterns denote the presence of regional myocardial scar and are a valuable diagnostic marker of CAD with good sensitivity and specificity.
 Keywords: fragmented QRS, SPECT

On Accounting for the Microrotation of Particles of an Elastic Medium According to Cosserat’s Simplified Theory During Electroelastic Wave Propagation in a 6mm Class Piezoelectric Crystal

The article reveals how the micro polarity of a material influences the propagation of a one-dimensional electroelastic wave along different sections of a 6mm class piezoelectric crystal. It is shown that micro polarity leads to dispersion of a one-dimensional electroelastic wave and prohibits the propagation of high-frequency elastic shear waves. In the case of a normally incident electromagnetic wave on the surface of a piezoelectric half-space along the direction of the polarization axis of the piezoelectric crystal, three branches of electroelastic waves localized near the surface appear in the half-space. The frequency range of the existence of these waves is found from the dispersion equation. The behavior of the wave characteristics and frequency zones is numerically studied as a function of the micro polarity of the piezoelectric crystal.

On the geometric origin of spurious waves in finite-volume discretizations of shallow water equations on triangular meshes

Computational wave branches are common to linearized shallow water equations discretized on triangular meshes. It is demonstrated that for standard finite-volume discretizations these branches can be traced back to the structure of the unit cell of triangular lattice, which includes two triangles with a common edge. Only subsets of similarly oriented triangles or edges possess the translational symmetry of unit cell. As a consequence, discrete degrees of freedom placed on triangles or edges are geometrically different, creating an internal structure inside unit cells. It implies a possibility of oscillations inside unit cells seen as computational branches in the framework of linearized shallow water equations, or as grid-scale noise generally.Adding dissipative operators based on smallest stencils to discretized equations is needed to control these oscillations in solutions. A review of several finite-volume discretization is presented with focus on computational branches and dissipative operators.

Growth Rates of the Electrostatic Waves in Radio Zebra Models

Abstract Zebras were observed not only in the solar radio emission but also in radio emissions of Jupiter and the Crab Nebula pulsar. In their models, growth rates of the electrostatic waves play an important role. Considering the plasma composed from the thermal background plasma and hot and rare component with the Dory–Guest–Harris distribution, we compute the growth rates γ and dispersion branches of the electrostatic waves in the ω − k ⊥ domain. We show complexity of the electrostatic wave branches in the upper-hybrid band. In order to compare the results, which we obtained using the kinetic theory and particle-in-cell (PIC) simulations, we define and compute the integrated growth rate Γ, where the “characteristic width” of dispersion branches was considered. We found a very good agreement between the integrated growth rates and those from PIC simulations. For maximal and minimal Γ we showed locations of dispersion branches in the ω − k ⊥ domain. We found that Γ has a maximum when the dispersion branches not only cross the region with high growth rates γ, but when the dispersion branches in this region are sufficiently long and wide. We also mentioned the effects of changes in the background plasma and hot component temperatures.

Axially moving materials with granular microstructure

The mechanics of axially moving media is significant because of their broad engineering applications. In many engineering applications, it is beneficial to understand the dynamical material response from a microstructural viewpoint. Here we focus upon wave propagation in axially moving materials with granular microstructure. To this end, the granular micromechanics approach is utilized since the resulting continuum model is known to predict wave dispersion. To consider axially moving materials, this approach is enhanced to account for the axial velocity using an Eulerian description of the system accounting for convective terms in the material derivatives and utilizing variational approach. The dispersive behavior of axially moving 1D materials are then derived and compared with the dispersive behavior of non-moving materials. In the absence of microstructure, the axially moving material model simplifies to published literature and shows non-dispersive non-symmetric forward and backward waves. In the case of axially moving materials with granular microstructure, the model predicts dispersive non-symmetric waves. In this case, there are two acoustic and two optical wave branches. Axial velocity leads to narrowing and widening in the frequency band gaps in the forward and backward waves, respectively. Negative group velocity is also observed in certain wavenumber ranges. Clearly, the stopbands created by the axial velocity and the non-symmetric dispersive behavior studied here should be considered in engineering designs for vibration control when the axially moving material possesses granular microstructure. The results presented here can also be used to help obtain parameters needed for axially moving granular metamaterials to be designed for particular applications.

Internal gravity and infrasound waves during a hurricane in Moscow On May 29, 2017

The results of recording of internal gravity waves (IGWs) and infrasound waves from the warm and cold fronts associated with the atmospheric storm passing through Moscow on May 29, 2017 are presented. The waves were recorded by a network of 4 microbarographs IFA–MGU–MSR–ZNS located in Moscow and Moscow region, and compared with the data of measurements of the parameters of infrasound waves at infrasound station IS43 in Dubna. We study the temporal changes in the characteristics of IGWs and infrasound waves (coherence, direction of propagation,phase velocities, characteristic periods and frequency spectra) with the passage of warm and cold fronts through the network. The transition from the gravity to the acoustic dispersive branch of acoustic-gravity waves due to an increase in frequency and the temporal modulation of the phase velocity of infrasound waves caused by IGWs are also studied. The measurement data for PM10 aerosol concentrations and NO2 gas concentrations at various locations in Moscow during a passage of atmospheric storm are presented. The possibility of detecting wave precursors of atmospheric storms simultaneously in variations of atmospheric pressure, wind velocity and aerosol concentrations is studied.

Solitary waves in boundary layer induced by a travelling wave with increasing amplitude

The stability of solitary waves in an incompressible boundary layer, induced by a driving wave on the wall, is studied in order to investigate the generation and development of solitary waves. The nonlinear waves in the boundary layers, excited by a travelling wave with an increasing amplitude, rather than a standing wave, are described by forced Benjamin–Ono equation. In the study, pseudo-spectral method is used to approach to the solution of the governing equation. The results show that there are several wave energy wave branches and energy jumps to higher branch via violent oscillation. The wave pattern remains similar at every branch but the number of spike increases by one with every wave oscillation. In order to study the stability of the nonlinear waves, the perturbed wave equation is derived and a complex oscillator system is obtained from the linear perturbed wave equation. The stability analysis shows that the original wave loses its stability and wave energy begins to oscillate, and a new spike-like wave is born, when imaginary part of eigenvalue reaches to zero. Indeed, spile-like solitary waves can be induced by a travelling wave during the wave energy oscillations in boundary layers.