Time-frequency analysis of transient dispersive waves: A comparative study

The goal in this work is to investigate the effectiveness of time-frequency representations for analysing dispersive waves by comparing the performance of three different methods. In particular, the smoothed pseudo-Wigner distribution, the continuous wavelet transform and the Hilbert-Huang transform are compared and evaluated in terms of their ability to analyse dispersive elastic waves. The waves under consideration are transient flexural ones generated by an impact in a beam. In view of the results of the comparative study, the advantages and shortcomings of each method are presented and discussed.     

A lateral differential confocal microscopy for accurate detection and localization of edge contours

Common path noise and disturbance in light source and ambient lighting affect detection accuracy of edge contours greatly in optical microscopy. In order to solve this problem, a lateral differential confocal microscopy is proposed based on principle of lateral difference and confocal microscopy. The approach proposed uses confocal dual-receiving light path arrangement and real-time heterodyne subtraction of two signals with lateral offsets by a differential detector to improve the system′s accuracy and detection sensitivity. Theoretical analyses have been presented. In addition, a simple prototype system has been built based on theoretical analyses. Related experiments have been performed under laboratory conditions. Different from former image processing methods, common path noise and additive disturbance in light source and ambient lighting are eliminated before they are recorded. Theoretical analyses and experimental results indicate a more accurate and sensitive result.     

On the Kudryashov-Sinelshchikov equation for waves in bubbly liquids

A nonlinear evolution equation for wave propagation in bubbly liquids, taking into account viscosity and heat transfer, has been derived by Kudryashov and Sinelshchikov. In the case of no dissipation the authors have provided analytical solutions representing undistorted waves. These results are cast into a simpler form and studied in more detail. In addition to the wave profiles the corresponding phase curves are presented. Depending on some parameter the solutions represent solitary or periodic waves. Some of the periodic waves exhibit peaks or cusps. From the periodic waves a new type of “meandering” solutions is constructed.     

Diffraction and radiation of flexural waves by a circular aperture loaded along the edge

An inhomogeneous wave exponentially decaying in all directions may exist near the edge of a circular aperture if the mass and the moment of inertia are appropriately chosen (i.e., their values coincide with the critical ones) [1]. In this case, the solution to the diffraction problem is not unique. This paper inquires into the feasibility of the solution to the wave diffraction and radiation problem in the case of critical loading. The solution is constructed according to the procedure suggested in [2]. It is shown that the diffraction problem always has a solution while the radiation problem may have no solution. The effects related to the critical mass and the critical moment of inertia do not manifest themselves in the far field.     

On the spectra of periodic waves for infinite-dimensional Hamiltonian systems

We consider the problem of determining the spectrum for the linearization of an infinite-dimensional Hamiltonian system about a spatially periodic traveling wave. By using a Bloch-wave decomposition, we recast the problem as determining the point spectra for a family of operators J_γL_γ, where J_γ is skew-symmetric with bounded inverse and L_γ is symmetric with compact inverse. Our main result relates the number of unstable eigenvalues of the operator J_γL_γ to the number of negative eigenvalues of the symmetric operator L_γ. The compactness of the resolvent operators allows us to greatly simplify the proofs, as compared to those where similar results are obtained for linearizations about localized waves. The theoretical results are general, and apply to a larger class of problems than those considered herein. The theory is applied to a study of the spectra associated with periodic and quasi-periodic solutions to the nonlinear Schrödinger equation, as well as periodic solutions to the generalized Korteweg-de Vries equation with power nonlinearity.     

The performance and design of ultrasonic vibration system for flexural mode

The matrix method for analyzing flexural vibration system is outlined. The displacement, stress and velocity gain of ultrasonic flexural vibration systems are investigated by transfer matrix method. A design method is given for flexural transducer and vibration system.     

Heterogeneous platform-aware workload feature recognition for edge intelligence

With the advent of the Internet of Everything, the combination of AI (Artificial Intelligence) and edge computing has become a new research hotspot, and edge intelligence has emerged, which enables network edge devices to analyze data through AI algorithms. Since the edge computing environment is more complex and variable than cloud computing, there are many issues in building edge intelligence, such as lack of quantitative evaluation criteria, heterogeneous computing platforms, complex network topologies, and changing user requirements. To analyze the performance of edge intelligence workloads running on heterogeneous hardware platform, we target machine learning workloads in edge intelligence and analyze the impact of algorithm model complexity, edge data characteristics and heterogeneous platform differences in edge intelligence in terms of relative performance. By analyzing the machine learning workload in edge intelligence, we find that the inference time and memory usage of a model can be predicted based on the amount of computation and number of parameters of the model. Moreover, image complexity, edge data network features, and batch size all affect the performance of edge intelligence workloads. Furthermore, the upper limit of model performance on the same computing platform is limited by hardware resources. And finally, the model performance of a platform depends on its own computing power and bandwidth.     

Design theory and experiment of acousto-optical tunable filter by use of flexural waves applied to thin optical fiber

Spectral response of acoustically induced microbending through thin optical fiber is discussed from mode-coupling of core and cladding modes. The thin fiber is analyzed in three-layered structure (core-cladding-air) to gain insights into acousto-optic modulation. We explained the dependence of core and/or cladding diameters on acoustic source parameters from numerical calculations. According to the calculations, we successfully fabricated all-optical tunable filter using this thin fiber that yields an efficient mode-coupling at flexural wave frequencies less than 1MHz. To increase the acousto-optic effect, we used a specially designed thin optical fiber (80 μm of cladding diameter) in the section where flexural wave is produced, and spliced both ends of the thin fiber to the tapered 125 μm fibers. The frequency and voltage tuning of fabricated filter is also confirmed by changing the driven frequency and applied voltage of the PZT, respectively. This result suggests a possibility of fiber-optic device application as all-optical tunable filter at 1.55 μm.     

On the properties of electromagnetic waves propagating inside moving dielectric media

The properties of electromagnetic waves propagating inside isotropic or uniaxial dielectric media moving in an arbitrary direction are analysed. The scalar products of electromagnetic field vectors inside these moving media are investigated in the kEB system from Maxwell's equations and Lorentz-covariant constitutive relations. Several important equations are derived. They are useful in discussing problems such as the energy density and radiation pressure, which are of interest in theoretical studies and many application subjects.     

Non-axisymmetric flexural vibrations of free-edge circular silicon wafers

Non-axisymmetric flexural vibrations of circular silicon (111) wafers are investigated. The modes with azimuthal index 2?k?30$2?k?30$ are electrostatically excited and monitored by a capacitive sensor. The splitting of the mode frequencies associated with imperfection of the wafer is observed. The measured loss factors for the modes with 6?k?26$6?k?26$ are close to those calculated according to the thermoelastic damping theory, while clamping losses likely dominate for k?6$k?6$, and surface losses at the level of inverse Q  -factor Q⁻¹≈4×10⁻⁶$Q^{-1}\approx 4\times {10}^{-6}$ prevail for the modes with large k. The modes demonstrate nonlinear behavior of mainly geometrical origin at large amplitudes.     

Symmetric waves are traveling waves for a shallow water equation modeling surface waves of moderate amplitude

Following a general principle introduced by Ehrnström, Holden and Raynaud in 2009, we prove that for an equation modeling the free surface evolution of moderate amplitude waves in shallow water, all symmetric waves are traveling waves.     

On the viscous and inviscid stability of magnetohydrodynamic shock waves

We study the viscous and inviscid stability of shock waves in barotropic and full magnetohydrodynamics. We show that there are magnetohydrodynamic shock waves that are one-dimensionally stable as viscous shock profiles while they are multidimensionally strongly unstable as planar shock discontinuities.     

Making structured metals transparent for ultrabroadband electromagnetic waves and acoustic waves

In this review, we present our recent work on making structured metals transparent for broadband electromagnetic waves and acoustic waves via excitation of surface waves. First, we theoretically show that one-dimensional metallic gratings can become transparent and completely antireflective for extremely broadband electromagnetic waves by relying on surface plasmons or spoof surface plasmons. Second, we experimentally demonstrate that metallic gratings with narrow slits are highly transparent for broadband terahertz waves at oblique incidence and high transmission efficiency is insensitive to the metal thickness. Further, we significantly develop oblique metal gratings transparent for broadband electromagnetic waves (including optical waves and terahertz ones) under normal incidence. In the third, we find the principles of broadband transparency for structured metals can be extended from one-dimensional metallic gratings to two-dimensional cases. Moreover, similar phenomena are found in sonic artificially metallic structures, which present the transparency for broadband acoustic waves. These investigations provide guidelines to develop many novel materials and devices, such as transparent conducting panels, antireflective solar cells, and other broadband metamaterials and stealth technologies.     

也论电磁波的预言及其发现过程

文章根据麦克斯韦的著作和赫兹的《综合文集》、《电波》和《回忆、书信和日记》以及相关文献，对麦克斯韦预言电磁波的问题和赫兹实验发现电磁波的过程进行了仔细考察，指出麦克斯韦没有明确预言电磁波的存在，麦克斯韦的理论不是赫兹电磁学实验研究的直接指导思想．文章认为亥姆霍兹为普鲁士科学院所提出的1879年悬赏课题对赫兹发现电磁波起到了直接的引导作用，而电磁波的发现则主要归因于赫兹精湛的实验技能和敏锐的观察力．     

The limiting behavior of smooth periodic waves for the Degasperis-Procesi equation

We study the limiting behavior of smooth periodic waves for the Degasperis-Procesi equation as the parameters trend to some special values. Using an improved qualitative method, the existence of smooth periodic waves is considered. For some limiting values of parameters of smooth periodic waves, one obtains peaked solitary waves.     

On a possible way to detect de Broglie's waves

According to de Broglie an atomic system results from the association of a localized object and an extended ondulatory phenomenon interacting through the quantum potential. A natural developement of this picture implies the existence of new effects in the superposition of incoherent waves, for example in neutron interferometric experiments.1. Permanent address: Departamento de Fisica, Facultade de Ciencias de Lisboa, Rua Ernesto Vasconcelos, Ed. C1, 1700 Lisboa, Portugal.     

On the parallel shock waves in collisionless plasma with heat fluxes

A class of shock wave solutions is discussed for collisionless anisotropic plasma with heat fluxes. For the strictly parallel one-dimensional motions of a plasma the system of equations is written in divergent form and both linear and shock wave solutions are considered. Jump expressions for the parallel shocks are obtained in analytical form as functions of the shock upstream parameters.     

Lump waves,solitary waves and interaction phenomena to the (2 + 1)-dimensional Konopelchenko–Dubrovsky equation

In this paper, we investigated the $(2+1)$-dimensional Konopelchenko–Dubrovsky equation. The lump waves, solitary waves as well as interaction between lump waves and solitary waves are presented based on the Hirota bilinear form of this equation. It is worth noting that the rational solutions are obtained by taking a long wave limit, and we also discussed the lump solutions and rogue wave solutions. Moreover, all these solutions are presented via 3-dimensional plots and density plots with choosing some special parameters to show the dynamic graphs.