Twisted Waves near a Plasma Cutoff

This work considers twisted wave propagation in inhomogeneous and unmagnetised plasma, and discusses the wave properties in the cutoff region. The qualitative differences between twisted waves described by a single Laguerre–Gauss (LG) mode, and light springs resulting from the superposition of two or more LG modes with different frequency and helicity are studied. The peculiar properties displayed by these waves in the nonuniform plasma are discussed. The pulse envelope of a light-spring shows a contraction at reflection, which resembles that of a compressed mechanical spring. The case of normal incidence is examined, and nonlinear ponderomotive effects are discussed, using theory and simulations.

Epsilon-Near-Zero Metamaterials

This Element introduces the exotic wave phenomena arising from the extremely small optical refractive index, and sheds light on the underlying mechanisms, with a primary focus on the basic concepts and fundamental wave physics. The authors reveal the exciting applications of ENZ metamaterials, which have profound impacts over a wide range of fields of science and technology. The sections are organized as follows: in Section 2, the authors demonstrate the extraordinary wave properties in ENZ metamaterials, analyzing the unique wave dynamics and the resulting effects. Section 3 is dedicated to introducing various realization methods of the ENZ metamaterials with periodic and non-periodic styles. The applications of ENZ metamaterials are discussed in Sections 4 and 5, from the perspectives of microwave engineering, optics, and quantum physics. The authors close in Section 6 by presenting an outlook on the development of ENZ metamaterials and discussing the key challenges addressed in future works.

An analysis of axisymmetric Sezawa waves in elastic solids

The wave propagation in elastic solids covered by a thin layer has received significant attention due to the existence of Sezawa waves in many applications such as medical imaging. With a Helmholtz decomposition in cylindrical coordinates and subsequent solutions with Bessel functions, it is found that the velocity of such Sezawa waves is the same as the one in Cartesian coordinates, but the displacement will be decaying along the radius with eventual conversion to plane waves. The decaying with radius exhibits a strong contrast to the uniform displacement in the Cartesian formulation, and the asymptotic approximation is accurate in the range about one wavelength away from the origin. The displacement components in the vicinity of origin are naturally given in Bessel functions which can be singular, making it more suitable to analyze waves excited by a point source with solutions from cylindrical coordinates. This is particularly important in extracting vital wave properties and reconstructing the waveform in the vicinity of source of excitation with measurement data from the outer region.

Analysis of surface acoustic wave properties in CaYAl3O7 single crystal

The success on the growth of new piezoelectric materials allows sufficiently increase the operating temperature of the surface acoustic wave (SAW) devices from 300°C to 1000°C. A new calcium yttrium aluminate (CaYAl3O7) single crystal of the tetragonal symmetry has piezoelectric properties up to the temperature of 1000°C. The paper presents a numerical study of the surface acoustic wave properties in the crystal. The SAW velocity, electromechanical coupling coefficient and power flow angle are studied for different crystal cuts of CaYAl3O7. It is shown that the maximum value of SAW coupling coefficient (0.24%) is on the Z+60°-cut and wave propagation direction along the X-axis of the crystal. For the Z-cut and wave propagation direction along the X+45°-axis of crystal, the SAW coupling coefficient is equal to 0.2%. These two cuts of the crystal are potentially useful for SAW device applications.

Acoustic Wave Properties in Footpoints of Coronal Loops in 3D MHD Simulations

Acoustic waves excited in the photosphere and below might play an integral part in the heating of the solar chromosphere and corona. However, it is yet not fully clear how much of the initially acoustic wave flux reaches the corona and in what form. We investigate the wave propagation, damping, transmission, and conversion in the lower layers of the solar atmosphere using 3D numerical MHD simulations. A model of a gravitationally stratified expanding straight coronal loop, stretching from photosphere to photosphere, is perturbed at one footpoint by an acoustic driver with a period of 370 s. For this period, acoustic cutoff regions are present below the transition region (TR). About 2% of the initial energy from the driver reaches the corona. The shape of the cutoff regions and the height of the TR show a highly dynamic behavior. Taking only the driven waves into account, the waves have a propagating nature below and above the cutoff region, but are standing and evanescent within the cutoff region. Studying the driven waves together with the background motions in the model reveals standing waves between the cutoff region and the TR. These standing waves cause an oscillation of the TR height. In addition, fast or leaky sausage body-like waves might have been excited close to the base of the loop. These waves then possibly convert to fast or leaky sausage surface-like waves at the top of the main cutoff region, followed by a conversion to slow sausage body-like waves around the TR.

Interrelation of global changes in the planet's biosphere with the expansion of viruses and the COVID-19 pandemic

Epidemics of new, previously unknown human viral diseases have been occurring with increasing frequency in recent decades. The COVID-19 pandemic caused by the SARS-CoV-2 coronavirus has demonstrated humanity's unpreparedness for new challenges and a complete lack of understanding of the causes of viral aggression. An attempt to explain the catastrophic development of the pandemic by accidental transmission of the virus from an animal to a person does not seem convincing. The explosive development of the epidemic process in large ecosystems negates the existing ideas about the contact mechanism of pathogenic virus transmission from person to person. Probably, the causes of the pandemic are related to global changes in the biosphere of the planet. According to V. I. Vernadsky's theory, the biosphere consists of three main parts: plants, animals and microorganisms, the total mass of which is a constant value. In recent decades, the rate of destruction of forests as the main resource of the plant world has considerably increased. The number of wild animals has decreased and at the same time the human population has increased. The growing disproportions led to the expansion of viruses with a new vector from animals to humans. Global insight into the role of viruses in the biosphere of the planet leads to understanding of the COVID-19 pandemic causes. There is every reason to believe that viruses have wave properties, and are able to produce a magnetic field, stable coherent resonance systems and interact without the participation of biochemical transformations. The energy of the electromagnetic field can be high enough for non-contact infection and assembly of an active biological virus inside the human body. The physical theory of viruses significantly expands the existing understanding of the role of viruses in the biosphere of the planet and the causes of new viral infections.

A Generating - Absorbing Boundary Condition Applied to Wave - Current Interactions Using the Method of Fundamental Solutions

The purpose of this work is to study the feasibility and efficiency of Generating Absorbing Boundary Conditions (GABCs), applied to wave-current interactions using the Method of Fundamental Solutions (MFS) as radial basis function, the problem is solved by collocation method. The objective is modeling wave-current interactions phenomena applied in a Numerical Wave Tank (NWT) where the flow is described within the potential theory, using a condition without resorting to the sponge layers on the boundaries. To check the feasibility and efficiency of GABCs presented in this paper, we verify accurately the numerical solutions by comparing the numerical solutions with the analytical ones. Further, we check the accuracy of numerical solutions by trying a different number of nodes. Thereafter, we evaluate the influence of different aspects of current (coplanar current, without current, and opposing current) on the wave properties. As an application, we take into account the generating-absorbing boundary conditions GABCs in a computational domain with a wavy downstream wall to confirm the efficiency of the adopted numerical boundary condition.

A Wind–Wave-Dependent Sea Spray Volume Flux Model Based on Field Experiments

Sea spray can contribute significantly to the exchanges of heat and momentum across the air–sea interface. However, while critical, sea spray physics are typically not included in operational atmospheric and oceanic models due to large uncertainties in their parameterizations. In large part, this is because of the scarcity of in-situ sea spray observations which prevent rigorous validation of existing sea spray models. Moreover, while sea spray is critically produced through the fundamental interactions between wind and waves, traditionally, sea spray models are parameterized in terms of wind properties only. In this study, we present novel in-situ observations of sea spray derived from a laser altimeter through the adoption of the Beer–Lambert law. Observations of sea spray cover a broad range of wind and wave properties and are used to develop a wind–wave-dependent sea spray volume flux model. Improved performance of the model is observed when wave properties are included, in contrast to a parameterization based on wind properties alone. The novel in-situ sea spray observations and the predictive model derived here are consistent with the classic spray model in both trend and magnitude. Our model and novel observations provide opportunities to improve the prediction of air–sea fluxes in operational weather forecasting models.

Physics of Traveling Waves in Shallow Water Environment

We present a study of the physical characteristics of traveling waves at shallow and intermediate water depths. The main subject of study is to the influence of nonlinearity on the dispersion properties of waves, their limiting heights and steepness, the shape of solitary waves, etc. A fully nonlinear Serre–Green–Naghdi-type model, a classical weakly nonlinear Boussinesq model and fifth-order Stokes wave solutions were chosen as models for comparison. The analysis showed significant, if not critical, differences in the effect of nonlinearity on the properties of traveling waves for these models. A comparison with experiments was carried out on the basis of the results of a joint Russian–Taiwanese experiment, which was carried out in 2015 at the Tainan Hydraulic Laboratory, and on available experimental data. A comparison with the experimental results confirms the applicability of a completely nonlinear model for calculating traveling waves over the entire range of applicability of the model in contrast to the Boussinesq model, which shows contradictory and unrealistic wave properties for moderate wavelengths.

Mathematical Principles of Object 3D Reconstruction by Shape-from-Focus Methods

Shape-from-Focus (SFF) methods have been developed for about twenty years. They able to obtain the shape of 3D objects from a series of partially focused images. The plane to which the microscope or camera is focused intersects the 3D object in a contour line. Due to wave properties of light and due to finite resolution of the output device, the image can be considered as sharp not only on this contour line, but also in a certain interval of height—the zone of sharpness. SSFs are able to identify these focused parts to compose a fully focused 2D image and to reconstruct a 3D profile of the surface to be observed.