Surface waves in thermocapillary flow–revisited

The European Physical Journal Special Topics - Following theoretical predictions [1,2] thermocapillary layers can exhibit instabilities called “hydrothermal waves” (HTWs) and...     

Bloch–Floquet waves and controlled stop bands in periodic thermo-elastic structures

An algorithm for controlling the stop bands for elastic Bloch–Floquet waves within a periodic structure is proposed. Explicit asymptotic estimates of frequencies of translational and rotational standing waves, together with the numerical estimates of the stop band frequencies, are given. Thermal pre-stress is introduced and used to control the position of the stop bands on the dispersion diagram.     

Surface versus volume emissions in photon–hadron correlations

High-p _T photon–hadron correlations are studied within the next-to-leading order (NLO) perturbative QCD parton model with modified parton-jet fragmentation functions due to jet quenching in high-energy A+A collisions. In central A+A collisions, the away-side hadrons with large z _T=p _T ^h /p _T ^γ are controlled mainly by the surface emission of the gamma-jet events, while a small z _T region will be volume emission bias. In other words, gamma jets for a small-z _T region probe the dense matter deeper than those gamma jets for a large-z _T region, so the small-z _T gamma jets are found to be slightly more sensitive to the properties of the dense matter than the large-z _T gamma jets.     

Dynamics evolution of shock waves in laser–material interaction

In this work, the dynamics and internal structure of shock waves in picosecond laser–material interaction are explored at the atomistic level. The pressure of the shock wave, its propagation, and interaction zone thickness between the plume and ambience are evaluated to study the effect of the laser absorption depth, ambient pressure, and laser fluence. Sound agreement is observed between the MD simulation and theoretical prediction of shock wave propagation and mass velocity. Due to the strong constraint from the compressed ambient gas, it is observed that the ablated plume could stop moving forward and mix with the ambient gas, or move backward to the target surface, leading to surface redeposition. Under smaller laser absorption depth, lower ambient pressure, or higher laser fluence, the shock wave will propagate faster and have a thicker interaction zone between the target and ambient gas.     

Combustion waves in composite solid material of shell–core type

In this article, an asymptotic and numerical analysis of combustion wave propagation in shell–core composite solid energetic material is undertaken based on the diffusional–thermal model with an overall Arrhenius reaction step. Flame speed and structure are found for a broad range of parameter values. Two different regimes of flame propagation are identified. In the weak recuperation regime, the temperatures of the shell and core are monotonic functions of the coordinates, and they differ only slightly in the reaction zone of the flame. In the strong recuperation regime, the temperature of the shell is significantly higher than that of the core and has a sharp peak in the reaction zone with the maximum value exceeding the adiabatic flame temperature for pure energetic material. It is found that the highest level of flame acceleration in the composite material can be attained in the strong recuperation regime. The competition of these flame propagation regimes may lead to the coexistence of multiple combustion waves travelling with different velocities. The stability is investigated of combustion waves in the practically important strong recuperation regime.     

Propagation of SH waves in layered functionally gradient piezoelectric–piezomagnetic structures

Abstract

The propagation of SH waves is studied in two bonded semi-infinite material, one piezoelectric and the other piezomagnetic. Both materials are functionally gradient materials. The material properties of the two materials vary in two directions, one parallel to the interface and the other perpendicular to the interface. The dispersion relations are obtained in explicit forms for different forms of the non-homogeneities. The effects of gradient variation about material constants on the frequency of SH waves and on the wave numbers are shown graphically.     

Nonlinear ion-acoustic structures in a nonextensive electron–positron–ion–dust plasma: Modulational instability and rogue waves

The nonlinear propagation of planar and nonplanar (cylindrical and spherical) ion-acoustic waves in an unmagnetized electron–positron–ion–dust plasma with two-electron temperature distributions is investigated in the context of the nonextensive statistics. Using the reductive perturbation method, a modified nonlinear Schrödinger equation is derived for the potential wave amplitude. The effects of plasma parameters on the modulational instability of ion-acoustic waves are discussed in detail for planar as well as for cylindrical and spherical geometries. In addition, for the planar case, we analyze how the plasma parameters influence the nonlinear structures of the first- and second-order ion-acoustic rogue waves within the modulational instability region. The present results may be helpful in providing a good fit between the theoretical analysis and real applications in future spatial observations and laboratory plasma experiments.     

Surface waves at the interface between tunable LC–MTMs and nonlinear media

The surface wave propagation at the interface between tunable metamaterials (MTMs) and nonlinear media is investigated. Tunable MTMs have a refractive index which can be tuned to negative?Czero?Cpositive values. The nonlinear media are assumed to have a Kerr-like refractive index. The dispersion equation is analytically derived and solved numerically. Results display the different behaviors of the propagating waves as the refractive index is tuned.     

Coupled spin waves in magnetic waveguides induced by elastic deformations in YIG–piezoelectric structures

The numerical simulation and Brillouin spectroscopy measurement have demonstrated the possibility of controlling the properties of coupled spin waves propagating in a transversely limited layered YIG–piezoelectric structure. It has been shown that an electric field applied to the piezoelectric layer induces an inhomogeneous distribution of an internal magnetic field in the ferromagnetic layer, which results in the formation of waveguide channels for spin magnetostatic waves. In this case, the properties of coupled spin waves can be efficiently controlled by varying the magnetization angle of the structure. The results demonstrate the possibility of integration of straintronics and magnonics to fabricate electric- and magnetic-field-controlled power splitters, multiplexers, and microwave couplers.     

Refraction of active waves in reaction—diffusion media

The refraction of active waves is analyzed for a stable—metastable reaction—diffusion system consisting of two regions with different diffusion coefficients. The equations governing the evolution of wavefronts are derived by means of an asymptotic perturbation method for boundary layers. These equations describe non-stationary refraction near the steady state regime. It is shown that the dynamics of wavefronts separates into that in the region near the boundary and that far from the boundary.     

Spin waves in periodic magnetic structures—magnonic crystals

Propagation of spin waves (SWs) through a periodic multilayered magnetic structure is analyzed. It is assumed that the structure consists of ferromagnetic layers having the same thickness but different magnetizations. The wave spectrum obtained contains forbidden zones (stop bands) in which wave propagation is prohibited. Introduction into the structure of the ferromagnetic layer with a different thickness breaks the structural symmetry and leads to a localization of the SW mode with the frequency lying in the stop band. Reflection of the wave by the structure of the finite length and transmission of the wave through the structure are also investigated. Numerical calculations of the wave dispersion and the transmission coefficients for symmetrical periodic structures as well as the structures with a defect are presented. Drawing an analogy from photonic crystals known in optics, such magnetic structures can be called one-dimensional (1-D) magnonic crystals (MCs). The possibilities of existence of the 2-D MCs are also discussed.     

Band structures of elastic waves in two-dimensional eight-fold solid–solid quasi-periodic phononic crystals

Combined with the supercell method,band structures of the anti-plane and in-plane modes of two-dimensional(2D)eight-fold solid–solid quasi-periodic phononic crystals(QPNCs) are calculated by using the finite element method.The influences of the supercell on the band structure and the wave localization phenomenon are discussed based on the modal distributions.The reason for the appearance of unphysical bands is analyzed.The influence of the incidence angle on the transmission spectrum is also discussed.     

Near equilibrium dynamics and one-dimensional spatial–temporal structures of polar active liquid crystals

We systematically explore near equilibrium, flow-driven, and flow-activity coupled dynamics of polar active liquid crystals using a continuum model. Firstly, we re-derive the hydrodynamic model to ensure the thermodynamic laws are obeyed and elastic stresses and forces are consistently accounted. We then carry out a linear stability analysis about constant steady states to study near equilibrium dynamics around the steady states, revealing long-wave instability inherent in this model system and how active parameters in the model affect the instability. We then study model predictions for onedimensional(1D) spatial–temporal structures of active liquid crystals in a channel subject to physical boundary conditions.We discuss the model prediction in two selected regimes, one is the viscous stress dominated regime, also known as the flow-driven regime, while the other is the full regime, in which all active mechanisms are included. In the viscous stress dominated regime, the polarity vector is driven by the prescribed flow field. Dynamics depend sensitively on the physical boundary condition and the type of the driven flow field. Bulk-dominated temporal periodic states and spatially homogeneous states are possible under weak anchoring conditions while spatially inhomogeneous states exist under strong anchoring conditions. In the full model, flow-orientation interaction generates a host of planar as well as out-of-plane spatial–temporal structures related to the spontaneous flows due to the molecular self-propelled motion. These results provide contact with the recent literature on active nematic suspensions. In addition, symmetry breaking patterns emerge as the additional active viscous stress due to the polarity vector is included in the force balance. The inertia effect is found to limit the long-time survival of spatial structures to those with small wave numbers, i.e., an asymptotic coarsening to long wave structures. A rich set of mechanisms for generating and limiting the flow structures as well as the spatial–temporal structures predicted by the model are displayed.     

Reaction–diffusion waves in biology

The theory of reaction–diffusion waves begins in the 1930s with the works in population dynamics, combustion theory and chemical kinetics. At the present time, it is a well developed area of research which includes qualitative properties of travelling waves for the scalar reaction–diffusion equation and for system of equations, complex nonlinear dynamics, numerous applications in physics, chemistry, biology, medicine. This paper reviews biological applications of reaction–diffusion waves.     

Solitons and cnoidal waves of the Klein–Gordon–Zakharov equation in plasmas

This paper studies the Klein?CGordon?CZakharov equation with power-law nonlinearity. This is a coupled nonlinear evolution equation. The solutions for this equation are obtained by the travelling wave hypothesis method, (G??/G) method and the mapping method.     

Acoustic waves in (001) InN–AlN and InN–GaN superlattices

We study the acoustic waves of (001) InN–AlN and InN–GaN superlattices. We obtain the dispersion curves for various symmetric and general orientations of the wavevector parallel to the interfaces. The results reveal the impact of the elastic anisotropy due to the zinc-blende structure of the constituent materials. It is found that for certain material parameters and orientations, the dispersion curves exhibit wide gaps with potential for the existence of surface localized waves.     

Surface Anchoring and Director Distribution in a Grandjean–Cano Wedge

Theoretical calculations of the director distribution in a Grandjean–Cano wedge in relation to the anchoring strength and mutual orientation of the easy axes at the wedge surfaces are performed for various model surface anchoring potentials. Comparison of the theory and experiment allows one to propose the socalled model D-potential, quadratic in angle of director deviation from the easy axes, as the best one in fitting the experiment in the angular range of performed measurements. To satisfy general requirements on the wedge surface, a modified D-potential is proposed. The optimal conditions of the experiment aimed at restoring the potential in the whole range of its definition (in particular, nonparallel orientation of the easy axes at the wedge surfaces) are formulated.     

Shear Bloch waves and coupled phonon–polariton in periodic piezoelectric waveguides

Coupled electro-elastic SH waves propagating in a periodic piezoelectric finite-width waveguide are considered in the framework of the full system of Maxwell’s electrodynamic equations. We investigate Bloch–Floquet waves under homogeneous or alternating boundary conditions for the elastic and electromagnetic fields along the guide walls. Zero frequency stop bands, trapped modes as well as some anomalous features due to piezoelectricity are identified. For mixed boundary conditions, by modulating the ratio of the length of the unit cell to the width of the waveguide, the minimum widths of the stop bands can be moved to the middle of the Brillouin zone. The dispersion equation has been investigated also for phonon–polariton band gaps. It is shown that for waveguides at acoustic frequencies, acousto-optic coupling gives rise to polariton behavior at wavelengths much larger than the length of the unit cell but at optical frequencies polariton resonance occurs at wavelengths comparable with the period of the waveguide.