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We consider the short-wave diffraction of a cylindrical wave by a contour whose curvature has a Hölder type discontinuity at a point. The incidence is nontangential at the point of singularity. In the framework of the Kirchhoff method, we find an asymptotic description for the outgoing wavefield inside the transition zone at both small and moderate distances. Analysis of ray formulas allows us to characterize applicability areas of the expressions obtained. [ABSTRACT FROM AUTHOR]

In this study, we report observations of propagating radial carpet beams (RCBs) through a turbulent atmosphere at ground level with a 120 m path length. RCBs are a class of nondiffracting, accelerating, self-healing, and self-amplifying beams, and generated in the diffraction of a plane wave from amplitude/phase radial gratings having different spoke numbers. Observations were made at different times of the day. The intensity profile of an RCB becomes complicated when the number of grating spokes used to generate the beam is large, and includes high intensity spots, called main intensity spots (MISs), which are symmetrically placed at the central area around the beam axis and whose number is equal to (twice) the number of spokes of the amplitude (phase) grating used to generate the beam. With the aid of a telescope and a CCD camera, successive frames of the intensity pattern of the RCBs having different levels of structural complexity are recorded at the end of the path. For the data recorded at different times of the day, we calculate the variance of displacements of MISs along the radial direction. We observe that displacements of the MISs increase with increasing mean temperature of the air; on the other hand, as the complexity of the beam intensity pattern increases, the displacements of the MISs decrease. In order to compare the resilience of different RCBs and a well-known structured beam against atmospheric turbulence, we investigate deformation of the intensity profiles of a Laguerre–Gaussian (LG) beam having a topological charge 20 and different RCBs at the end of the path. It is shown that under the same turbulence condition, highly complex RCBs are more resilient to the destructive effects of the atmospheric turbulence. In particular, for the RCBs generated with gratings having 30 spokes and more, the number of MISs of the received intensity patterns is changed by less than 1% even when the turbulence strength is high. But for the LG beam, its intensity ring is clearly broken in different places, which makes it impossible to follow its maximum intensity in the radial direction [ABSTRACT FROM AUTHOR]

SUMMARY: Atmospheric pressure changes on Earth's surface can deform the solid Earth. Sorrells derived analytical formulae for displacement in a homogeneous, elastic half-space, generated by a moving surface pressure source with speed $c$. Ben-Menahem and Singh derived formulae when an atmospheric P wave impinges on Earth's surface. For a P wave with an incident angle close to the grazing angle, which essentially meant a slow apparent velocity $c_a$ in comparison to P- ($\alpha ^{\prime }$) and S-wave velocities ($\beta ^{\prime }$) in the Earth ($c_a \ll \beta ^{\prime } \lt \alpha ^{\prime }$), they showed that their formulae for solid-Earth deformations become identical with Sorrells' formulae if $c_a$ is replaced by $c$. But this agreement was only for the asymptotic cases ($c_a \ll \beta ^{\prime }$). The first point of this paper is that the agreement of the two solutions extends to non-asymptotic cases, or when $c_a /\beta ^{\prime }$ is not small. The second point is that the angle of incidence in Ben-Menahem and Singh's problem does not have to be the grazing angle. As long as the incident angle exceeds the critical angle of refraction from the P wave in the atmosphere to the S wave in the solid Earth, the formulae for Ben-Menahem and Singh's solution become identical to Sorrell's formulae. The third point is that this solution has two different domains depending on the speed $c$ (or $c_a$) on the surface. When $c/\beta ^{\prime }$ is small, deformations consist of the evanescent waves. When $c$ approaches Rayleigh-wave phase velocity, the driven oscillation in the solid Earth turns into a free oscillation due to resonance and dominates the wavefield. The non-asymptotic analytical solutions may be useful for the initial modelling of seismic deformations by fast-moving sources, such as those generated by shock waves from meteoroids and volcanic eruptions because the condition $c / \beta ^{\prime } \ll 1$ may be violated for such fast-moving sources. [ABSTRACT FROM AUTHOR]

In this paper we consider flexural-gravity waves propagating in a layer of water of constant depth limited by a vertical wall simulating a straight coastline. The water surface is covered with an elastic ice sheet of constant thickness. The ice sheet is split by one or two straight cracks parallel to the coastline, simulating the structure of land-fast ice with a refrozen lead. Analytical solutions of hydrodynamic equations describing the interaction of flexural-gravity waves with the ice sheet and cracks have been constructed and studied. In this paper, the amplification of the amplitude of incident waves between the shoreline and cracks was described depending on the incident angle of the wave coming from offshore. The constructed solutions allow the existence of edge waves propagating along the coastline and attenuated offshore. The energy of edge waves is trapped between the coastline and ice cracks. The application of the constructed solutions to describe wave phenomena observed in the land-fast ice of the Arctic shelf of Alaska is discussed. [ABSTRACT FROM AUTHOR]

Summary Unmanned aerial vehicle operations are quickly gaining ground due to rapid global market penetration. While on one hand, novel technologies that bridge communication networks to aviation industry are yet to be explored, on the other hand, their development requires highly scalable systems to enable beyond visual line‐of‐sight missions. This requirement imposes a big bottleneck in terms of computation complexity. This paper presents a method for fast computation of multiple diffraction of radio waves over knife‐edge obstacles based on the Deygout technique and some offline computation steps, including a ground profile analysis. We prove that this algorithm is equivalent to the original Deygout algorithm for all non‐line‐of‐sight points, show heuristics confirming that it is mostly applicable in the line‐of‐sight case. The computational and memory complexity of our algorithm is approximately O(N)$$ \mathcal{O}\left(\sqrt{N}\right) $$, compared to O(N)$$ \mathcal{O}(N) $$ for the original Deygout algorithm. Finally we discuss how to apply the approach to the Epstein‐Peterson technique and the Giovanelli technique, and how to use it to compute clutter‐loss. [ABSTRACT FROM AUTHOR]

In this work, I used the Sine–Cosine approach to examine a few conformable fractional partial nonlinear differential equations and discovered a wide range of generalized solitary and periodic solutions with unique physical features. The answers include symmetric periodic soliton solution, bright soliton, water wave soliton and diffraction peak like soliton solutions. The generalization, significance, and mathematical formulation of the equations are my main concerns. The importance of considering and using these equations stems from the complexity of nonlinear physical models from a dynamical point of view. Finally, by taking into consideration the fractional operator with conformable derivative, I provide the fundamental solution to the conformable nonlinear new Hamiltonian amplitude equation and the conformable Heisenberg ferromagnetic spin chain model. The solutions to the former are crucial to understanding nonlinear wave propagation of nonlinear optics and quantum optics, among other topics. Since the latter's answers explain the non-linear properties of magnets, they are essential to understanding contemporary magnet theory. [ABSTRACT FROM AUTHOR]

Diffraction is a fundamental phenomenon that occurs when blast or shock waves pass over sudden discontinuous surfaces. It generates a complex flow field consisting of diffracted waves, expansion waves, slipstream, contact surface, and an unstable shear layer, in addition to emitting acoustic waves. In this study, we investigated the diffraction of a blast wave passing over a series of grooved structures with different aspect ratios and geometrical shapes (rectangular, circular, and triangular) using high-speed shadowgraph images. The blast wave Mach number considered in our investigation is 1.34. The grooves feature leading-edge geometrical variations such as rectangular, circular arc, and wedge shapes positioned at various lateral locations from the exit of the shock tube. The aspect ratios of the rectangular grooves vary from 0.33, 0.5, and 0.67. The circular and triangular grooves have an aspect ratio of 0.33. The trajectories and velocities of the primary vortex are calculated by tracking the location of the vortex in the shadowgraph images. Our observations revealed that a large portion of the incident blast wave is abducted inside the groove as the aspect ratio increases in rectangular grooves, resulting in better attenuation of the blast wave. The grooves, which have circular shapes, produced weaker diffraction, which resulted in delayed and weak primary vortex. The triangular grooves produced the strongest primary vortex and have the highest attenuation characteristics among other grooves. The strength and trajectory of the primary vortex formed over the grooves strongly depend on the aspect ratio and the curvature of the leading edge for a given Mach number. Vortices generated from rectangular and triangular grooves exhibit considerable strength and longevity. [ABSTRACT FROM AUTHOR]

In this study, we are analyzing the effect of the Hilbert Transform (HT) on diffraction of a plane wave by an oscillating half-plane. Both the incident wave and oscillating half-plane have different oscillating frequencies. After the necessary mathematical computations for several types of time-dependent oscillating functions, it is verified graphically that the HT induces a shift of 90 ∘ , which can be observed from the flipping effect in the magnitude of the sinusoidal components occurring in their respective diffracted fields. Graphical illustrations presenting the effects of the HT are presented and discussed. [ABSTRACT FROM AUTHOR]

Passive parity-time (PT) symmetric metamaterials as a fundamental carrier to investigate non-Hermitian systems have attracted significant interest, but previous studies have rarely focused on the diffraction properties of the PT system, especially the diffraction effect in the metasurfaces with phase gradient modulation. Here, by merging two concepts of phase gradient and PT symmetry together, we design and study a non-Hermitian acoustic gradient metasurface (i.e., metagrating). We show that the PT symmetry breaks spatially the symmetry of reflected wave diffraction in the acoustic metagrating, making it an asymmetric mirror. In particular, at the PT-ensured exceptional point, for incident waves from one side, such metagrating behaves as a phase gradient metasurface, in which high-efficiency retroreflection governed generalized Snell's law occurs. For an incident wave from the opposite direction, such a metagrating is a common grating, whose diffraction in the reflection follows the common diffraction equation. Our work builds a bridge connecting the phase gradient and passive PT symmetric system, enriching the methods for wavefront manipulation and exhibiting potential applications in the design of multifunctional acoustic devices. [ABSTRACT FROM AUTHOR]

We present a near-field diffraction model for spin waves in perpendicularly magnetized films applicable in any geometries of excitation fields. This model relies on Kalinikos–Slavin formalism to express the dynamic susceptibility tensor in k-space and calculate the diffraction patterns via inverse 2D-Fourier transform of the response functions. We show an excellent quantitative agreement between our model and MuMax3 micro-magnetic simulations on two different geometries of antennas. Our method benchmarks spin wave diffraction in perpendicularly magnetized films and is readily applicable for future designs of magnon beamforming and interferometric devices. [ABSTRACT FROM AUTHOR]

Spin waves are proposed as information carriers for next-generation computing devices because of their low power consumption. Moreover, their wave-like nature allows for novel computing paradigms. Conventional methods to detect propagating spin waves are based either on electrical induction, limiting the downscaling and efficiency complicating eventual implementation, or on light scattering, where the minimum detectable spin-wave wavelength is set by the wavelength of the laser unless near-field techniques are used. In this article, we demonstrate the magneto-optical detection of spin waves beyond the diffraction limit using a metallic grating that selectively absorbs laser light. Specifically, we demonstrate the detection of propagating spin waves with a wavelength of 700 nm in 20 nm thick Ni 80 Fe 20 strips using a diffraction-limited laser spot with a diameter of 10 μ m. Additionally, we show that this grating is selective to the wavelength of the spin wave, providing phase-sensitive, wavevector-selective spin-wave detection in the time domain, thus providing a complementary approach to existing techniques such as Brillouin light scattering. This should open up new avenues toward the integration of the burgeoning fields of photonics and magnonics and aid in the optical detection of spin waves in the short-wavelength exchange regime for fundamental research. [ABSTRACT FROM AUTHOR]

To study the influence of pits on shock wave propagation and the propagation of shock waves within pits, numerical simulations were used to calculate the distribution of overpressure peak values at the bottom and rear of the pits at 5 depths and 5 explosion center distances. The results indicate that diffraction occurs when the explosion shock wave passes through the edge of the crater; The peak overpressure of the shock wave at the bottom of the pit exhibits a "spoon shaped" distribution, and the peak overpressure on the right side is significantly higher than that on the left side; There are two distinct boundary regions for the overpressure of the shock wave behind the crater due to the influence of the crater; The distance between the explosion centers has little effect on the distribution trend of the overpressure peak of the shock wave at the bottom and rear of the pit, mainly affecting the magnitude of the overpressure peak. The research results provide theoretical support for the analysis of the propagation law of explosion shock waves and guidance for the design of protective engineering structures, with significant engineering application value. [ABSTRACT FROM AUTHOR]

As escalating environmental pressures threaten the world's beaches, understanding the driving factors influencing their geomorphological changes is of critical global importance. This study focuses on the morphological changes of Sigeng beach adjacent to Changhua River Mouth in Hainan Island, China through decadal monitoring of shoreline and profile topography and tries to illuminate the natural and anthropogenic factors that drove geomorphological changes. The results showed that Sigeng beach undergone significant changes between 2008 and 2024, with notable accretion at the northernmost and southernmost and general erosion at other sections. The shoreline change rates ranged between -18.4 m/yr and 13.0 m/yr, with the average rate of -1.9 m/yr, indicating overall erosion. The net longshore sediment transport (LST) rates along Sigeng beach was estimated through the combination of the cross-shore (profile) and longshore (shoreline) changes. The overall direction of net LST along the beach were southward, except for the northern section where the direction was northward due to the diffraction of NE waves by the long sand spit at the northernmost. The net LST rates at each profile varied from 0.8×104 m³/yr to 3.5×104 m³/yr. The main factors controlling Sigeng beach evolution, including seasonal wave action and reduction in fluvial sediment load, followed by sand spit and coastal structures, typhoon events, aeolian transport, and sea level rise, were discussed. Subsequently, adaptive protection measures, including beach nourishment, accompanied with groin system or multiple detached breakwaters were proposed to combat with beach erosion. The analysis presented in this study is helpful to understand the morphodynamics and to predict the future change of beaches. [ABSTRACT FROM AUTHOR]

It has been shown that the acousto-optic Raman-Nath diffraction on the acoustic wave, which bears an acoustic vortex, is accompanied by the appearance of the diffraction maxima that bear an optical vortex. The charge of the vortices that appears as a result of the diffraction corresponds to the order of diffraction if the incident optical beam is the Gaussian beam and the charge of the acoustic vortex is equal to unity. When the incident optical vortex beam takes part in this process, the charge of the diffracted optical vortices is shifted on the charge value of the incident optical beam. As a result of the analysis, we obtained the relation for the charge of vortices of diffraction maxima. It has been found that the described effect can be used for controlled demultiplexing. [ABSTRACT FROM AUTHOR]

It has been shown for the first time that the electric field can enhance the acousto-optic (AO) figure of merit due to the induced ellipticity of eigenwaves through the electro-gyration effect. As a result of the analysis, we have revealed that for the isotropic types of interaction, the increasing of the strength of the electric field results in the broadening of the full width at half maximum (FWHM) of the peak of the AO figure of merit, while almost does not affect the maximal value of this peak. The FWHM of the peak of the AO figure of merit tends to saturation with increasing electric field strength. For anisotropic types of diffraction, the peak of the AO figure of merit is not observed, but with increasing the electric field strength, the surface of the AO figure of merit is expanded. [ABSTRACT FROM AUTHOR]

Using the method of fundamental components for the problem of diffraction of a TE-polarized wave on a half-plane with two-sided impedance boundary conditions a heuristic solution is obtained that approximately describes the scattered field. The verification and adjustment of heuristic formulas using a rigorous solution by the Wiener–Hopf method are carried out. A physical interpretation of the rigorous solution based on the obtained heuristic relations is proposed. [ABSTRACT FROM AUTHOR]

The present study analyzes diffraction and radiation phenomena of oblique waves interacting with a heaving floating membrane in the presence of a thick porous bed. Following the linear water wave theory, the physical problem is framed mathematically. The significance of the article resides in the following: (1) progressive wave analysis (water and membrane-covered region), (2) solving the boundary value problem (BVP) using the matched eigenfunction expansion method for diffraction and radiation problems, and (3) numerical illustration of various hydrodynamic coefficients for different membrane and porous bed parameters. Bragg scattering with varying frequency is observed for smaller values of membrane tension. Also, the present study demonstrates that the number of oscillations experienced by the reflection coefficient increases proportionally with the length of the membrane. Furthermore, cut-off membrane properties exist at a given frequency for which the zero minimum of wave force is obtained. Also, the porous bed's thickness impacts wave reflection and membrane deflection significantly. Thus, we found that the maximum reflection is observed for a fully permeable bed; however, it decreases with a decrease in the porosity of the porous medium because of its dissipative nature. Conversely, the added mass and damping coefficient increases with increased membrane length. The collective numerical observations for both diffraction and radiation provide insight into resonance phenomena, the role of membrane properties, and the intricate relationship between wave characteristics and membrane properties. The findings from this study could assist geologists and marine engineers in designing and managing ports and harbor infrastructure. [ABSTRACT FROM AUTHOR]

The diffraction of plane surface and flexural-gravity waves during their normal incidence at the edge of a floating elastic semi-infinite plate in fluid of finite depth in the presence of a current with velocity shear is studied. The explicit analytical solution to this problem is constructed using the Wiener–Hopf technique. Simple exact formulas for the reflection and transmission coefficients and the energy relations are obtained. The results of numerical calculations using the obtained formulas are presented. [ABSTRACT FROM AUTHOR]

A study has been conducted to analyse the impact of an ice sheet on the flexural-gravity wave force acting on a neutrally buoyant, spherical object immersed in a sea in accordance with the linear wave hypothesis. The bottom of the sea is presumed to be protected by a surface composed of some sort of flexibility, and the top is enclosed by an ice sheet. The solution to a diffraction problem is established using the multipole method. The estimated vertical and horizontal flexural-gravity wave forces are visualized in relation to different immersion depths of the spherical body, depths of the fluid and various flexural rigidities of the ice plate and the flexible seabed. The approach adopted here is likely to be of immense significance in the construction of various spherical gadgets like a seabed pressure detector device for tsunami recognition or communication in crisis for a submarine in earthquake zones. [ABSTRACT FROM AUTHOR]

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In the interaction of water waves with marine structures, the interplay between wave diffraction and drag-induced dissipation is seldom, if ever, considered. In particular, linear hydrodynamic models, and extensions thereof through the addition of a quadratic force term, do not represent the change in amplitude of the waves diffracted and radiated to the far field, which should result from local energy dissipation in the vicinity of the structure. In this work, a series of wave flume experiments is carried out, whereby waves of increasing amplitude impinge upon a vertical barrier, extending partway through the flume width. As the wave amplitude increases, the effect of drag - which is known to increase quadratically with the flow velocity - is enhanced, thus allowing the examination of the far-field effect of drag-induced dissipation, in terms of wave reflection and transmission. A potential flow model is proposed, with a simple quadratic pressure drop condition through a virtual porous surface, located on the sides of the barrier (where dissipation occurs). Experimental results confirm that drag-induced dissipation has a marked effect on the diffracted flow, i.e. on wave reflection and transmission, which is appropriately captured in the proposed model. Conversely, when diffraction becomes dominant as the barrier width becomes comparable to the incoming wavelength, the diffracted flow must be accounted for in predicting drag-induced forces and dissipation. [ABSTRACT FROM AUTHOR]

Extending the scope of the self-imaging phenomenon, traditionally associated with linear optics, to the domain of magnonics, this study presents the experimental demonstration and numerical analysis of spin-wave (SW) self-imaging in an in-plane magnetized yttrium iron garnet film. We explore this phenomenon using a setup in which a plane SW passes through a diffraction grating, and the resulting interference pattern is detected using Brillouin light scattering. We have varied the frequencies of the source dynamic magnetic field to discern the influence of the anisotropic dispersion relation and the caustic effect on the analyzed phenomenon. We found that at low frequencies and diffraction fields, the caustics determine the interference pattern. However, at large distances from the grating, when the waves of high diffraction order and number of slits contribute to the interference pattern, the self-imaging phenomenon and Talbot-like patterns are formed. This methodological approach not only sheds light on the behavior of SW interference under different conditions but also enhances our understanding of the SW self-imaging process in both isotropic and anisotropic media. [ABSTRACT FROM AUTHOR]

Seismic-wave scattering is observed, to variable degrees, on Earth, its moon and Mars. Current scattering models and data processing typically rely on two end-member phenomena: weak, single- or multiple-scattering events (ballistic) on the one hand, or intense scattering such that the wavefield retains no path information or bearing on its origin (diffuse).This study explores the existence of scattering behaviour intermediate between these end-members, as well as the properties of heterogeneous media that facilitate a transition between them. We apply multiscale entropy and frequency-correlation analysis to seismic coda, and observe a distinct transitional behaviour is present within a part of the investigated parameter space. Analysis of terrestrial, lunar and Martian seismograms further demonstrate the applicability of these new methods across a wide range of scattering behaviours, while also highlighting their shortcomings. Results from the planetary data indicate partially non-diffuse behaviour and low complexity within specific bandwidths of lunar wavefields, potentially contradicting the current paradigm that lunar wavefields are diffuse, and require continued study. Furthermore, Martian seismograms are shown to possess greater statistical entropy than lunar seismograms and diffuse energy properties, yet still display distinct phase arrivals, suggesting substantial scattering and transitional scattering behaviour on Mars. The robust, comparative nature of multiscale entropy and frequency-correlation analysis, applied to idealised simulation as well as three separate planetary bodies, provides a promising framework for future exploration of scattered wavefields across ballistic, transitional and diffuse regimes, that complements existing methods. [ABSTRACT FROM AUTHOR]

This study presents the development of a continuous wave diffraction radiation oscillator utilizing a sheet electron beam. The oscillator comprises a slow-wave system formed by double-comb gratings, an open resonant cavity consisting of a spherically curved mirror and a cylindrically curved mirror, and a sheet electron beam generated by a diode gun. A permanent magnetic focusing system stabilizes the transmission of the sheet electron beam within the slow-wave system. Through a combination of mechanical and electronic tuning, the oscillator generates stable signal output in the T E M 00 q mode. The oscillator's frequency tuning range spans from 87 to 97 GHz, achieving a maximum output power of 13.5 W. [ABSTRACT FROM AUTHOR]

Heuristic solutions are provided to evaluate the diffraction by uniaxial chiral screens that are isolated or arranged in planar junctions. The optical axial direction of the chiral medium is perpendicular to the screen surfaces. Plane waves at skew incidence with respect to the discontinuity of the structure are considered and the proposed solutions are built in accordance with the uniform geometrical theory of diffraction by using the reflection and transmission matrices at the shadow boundaries for the reflected and incident/transmitted electric fields. Note that the importance of this research work relies on the absence of exact and approximate analytical solutions for the considered problems. Renowned commercial software is customized and expended to validate the results. [ABSTRACT FROM AUTHOR]

Terahertz (THz) waves have demonstrated immense potential for various applications in multiple fields. To enable the development of compact THz applications, it is crucial to integrate THz emission and wavefront manipulation into a single device. This study proposes and experiments with a nonlinear binary THz emitter that utilizes a patterned indium-tin-oxide (ITO) film. By precisely controlling the displacements and area sizes of the composed ITO patches, we are able to fully and independently manipulate the phase and amplitude of the locally emitted THz wave at the +1st-order diffraction, so as to the corresponding wavefront. Our innovative approach provides a promising path toward miniaturized and functioning THz devices and systems. [ABSTRACT FROM AUTHOR]

In the context of hydrogen-based energy storage systems, the safeguarding against spontaneous ignition during high-pressure hydrogen release is of paramount importance. This study delves into the thermal safety and management technologies pertinent to such systems by numerically investigating the effects of pipeline geometry on the risk of spontaneous ignition. Employing Large Eddy Simulation (LES) coupled with detailed chemical kinetics and a linear eddy model, the research assesses the impact of different pipe angles and burst pressures on ignition behavior. The simulations are validated against experimental data, ensuring the veracity of the findings. The results demonstrate a significant interplay between the ignition propensity and both the geometrical configuration of the pipeline and the pressure of hydrogen release. Notably, the emergence and interaction of transverse waves in pipe bends are revealed to amplify mixing processes, generating vortices that elevate the temperature and promote a conducive environment for chemical reactions leading to stable flame propagation. The ignition is shown to occur predominantly near the stoichiometric mixture ratio, suggesting a narrow ignition region. These insights are vital for enhancing the safety protocols and thermal management strategies of hydrogen-based energy storage systems, paving the way for safer and more efficient energy solutions. [ABSTRACT FROM AUTHOR]

A hardware and software complex for estimating the dispersion distortion bandwidth and fading coherence bandwidth in a satellite (transionospheric) radio channel based on the results of GPS-monitoring of the ionosphere are theoretical substantiated and developed. The basis for solving this problem is development of a structural–physical model of the radio channel, which makes it possible to simultaneously take into account the phase dispersion of the wave and diffraction on small-scale inhomogeneities of the ionosphere. Analytical dependences of the dispersion distortion bandwidth and coherence of frequency-selective fading on the mean value and small-scale fluctuations of the total electron content of the ionosphere are obtained. It is shown that under conditions of ionospheric disturbances, the fading coherence bandwidth can be much smaller than the dispersion band. In accordance with the obtained dependences, a structure is developed for building a hardware and software complex for estimating the dispersion and coherence bandwidths of a satellite radio channel based on improvement of the method for GPS monitoring of the total electron content of the ionosphere with small-scale inhomogeneities. [ABSTRACT FROM AUTHOR]

A model of oblique wave diffraction by multiple arbitrary porous barriers in infinitely deep water is proposed to study the role of the porous breakwater in mitigating wave effects and dissipating wave energy. The Havelock's expansion of water wave potential along with suitable matching conditions and the single term Galerkin approximation method are used to handle the mathematical boundary value problem. The role of the arbitrary porous barrier is studied by analyzing the reflection coefficient, dissipated energy, and wave forces on the barriers. Significant changes are found in wave reflection and forces due to the consideration of porous barriers as compared to rigid barriers in the fluid region. As the separation length between the vertical barriers increases, the reflection coefficient becomes oscillatory as a function of the wavenumber, which is due to multiple reflections by the barriers. It is seen that the wave load reduces significantly with an increase in the number of barriers. It is also found that more energy is dissipated if the permeability of the barriers is increased. The correctness of the present method is confirmed by comparing the results available in the literature. [ABSTRACT FROM AUTHOR]

This paper studies the hydrodynamic performance of vertical cylindrical absorbers in front of a vertical wall. All the absorbers are independent of each other and restricted to only the heave motion. Based on a linear potential flow theory, an analytical solution is developed for the problems of wave diffraction and radiation by absorbers. In the solving procedure, the hydrodynamic problem is first transformed into an equivalent problem in an open water domain using the image principle. The number of absorbers in the equivalent problem is twice that in the real problem, and the plane layout is symmetric about the original vertical wall. The velocity potential of the fluid domain is obtained using the method of variable separation, and the unknown expansion coefficients in the velocity potential are determined by the matched boundary conditions. The heave excitation force, added mass, radiation damping, motion response, and energy capture width of the absorbers are calculated. Case studies are presented to show the effects of the wall reflection and hydrodynamic interaction on the energy extraction performance of the wave energy converter (WEC) system. Subsequently, the WEC performance under the action of irregular waves is analyzed by considering an incident wave spectrum, and the mean annual absorbed power of the device is estimated by considering the wave data statistics at the actual sites. The results indicate that when the wave motion resonates with the absorber motion, the energy extraction performance of the absorbers is significantly improved. The performance of the absorbers can be effectively improved when the structures are close to the antinodes of a standing wave field. By designing a reasonable plane layout, the hydrodynamic interaction can play a constructive role in the performance of the WEC system. [ABSTRACT FROM AUTHOR]

In this paper, diffraction of scalar waves by a screen with a circular aperture is explored, considering the incidence of either a collimated beam or a focused wave, a historical review of the development of the theory is presented, and the introduction of the Fresnel approximation is described. For diffraction by a focused wave, the general case is considered for both high numerical aperture and for finite values of the Fresnel number. One aim is to develop a theory based on the use of dimensionless optical coordinates that can help to determined the general behaviour and trends of different system parameters. An important phenomenon, the focal shift effect, is discussed as well. Explicit expressions are provided for focal shift and the peak intensity for different numerical apertures and Fresnel numbers. This is one application where the Rayleigh–Sommerfeld diffraction integrals provide inaccurate results. [ABSTRACT FROM AUTHOR]

The method of manufacturing and the results of studies of a lens corrector that converts a spherical diverging front into a plane one and is intended for studying flat surfaces as part of an interferometer with a diffraction comparison wave is described. A feature of the corrector is the use of an aspherical convex surface with a maximum deviation of ~200 μm from the nearest sphere. The first experimental results are presented, indicating the prospects for using ion-beam processing to improve the quality of the wavefront. After the procedure of ion-beam processing, the aberrations over the entire aperture of the corrector decreased by more than 4 times and amounted to the parameter of the height difference PV = 207 nm (~λ/3) and (RMS) = 19.2 nm (~λ/33). On an area with a diameter of 80%, the aberrations fell to the nanometer level: PV = 65 nm (~λ/10) and RMS = 8.3 nm (~λ/76). [ABSTRACT FROM AUTHOR]

In recent years, manipulations of amplitudes and phases of circularly polarized (CP) waves using metasurfaces have attracted significant attention. However, most of the current works are limited to operating in reflection or transmission space, and the amplitude manipulations are mainly achieved through polarization conversion or resistive loss, which will inevitably lead to cross‐polarization pollution and energy waste. Here, a transmission–reflection‐integrated metasurface that can manipulate the amplitudes and phases of the CP waves simultaneously in full space, which can not only realize arbitrary amplitude allocation of transmitted and reflected CP waves but also independently manipulate their phase responses is proposed. As proofs of concept, two integrated metasurfaces are designed and demonstrated, including a CP reflectarray antenna with simultaneously low side‐lobe level and low cross‐polarization level, and a meta‐grating that can arbitrarily control the intensity of transmitted diffraction wave while focusing the reflected wave. Both simulated and measured results agree very well with the theoretical predictions, demonstrating the powerful ability of the proposed metasurface to control the CP waves in full space, which is promising to be applied in future satellite communications, photonic meta‐devices, and so on. [ABSTRACT FROM AUTHOR]

Motion of a multi-unit wind-tracing floating offshore wind turbine (FOWT) to combined wave–current and wind is obtained in the frequency-domain. The linear diffraction wave theory with a Green function for small current speeds and the blade-element momentum method are used for the hydrodynamic and aerodynamic analysis, respectively. A finite-element method is coupled with the hydrodynamic and aerodynamic equations to obtain the elastic responses of the FOWT to the environmental loads. The wind-tracing FOWT consists of three 5 MW wind turbines installed at the corners of an equilateral triangular platform. The platform is connected to the seabed through a turret-bearing mooring system, allowing the structure to rotate and face the dominant wind direction; hence, the multi-unit FOWT is called the wind-tracing FOWT. In this study, rigid-body responses of the wind-tracing FOWT to waves and wind are compared with those to combined wave, current, and wind loads for several current speeds and various wave heading angles. For a chosen current speed and wave heading angle, hydro- and aeroelastic responses of the wind-tracing FOWT to combined waves, current, and wind are obtained and compared with those of the rigid structure. Discussion is provided on the effect of the wave–current interaction on the motion and elastic responses of the wind-tracing FOWT. The numerical results show that under the rated wind speed, the motion of the wind-tracing FOWT is mainly governed by the wave-induced hydrodynamic forces and moments and the presence of current results in larger elastic motion of the FOWT to the environmental loads. [ABSTRACT FROM AUTHOR]

To accurately simulate wave-structure interaction based on fully nonlinear potential flow theory, a three-dimensional (3 D) high-order immersed-boundary adaptive harmonic polynomial cell (IB-AHPC) method is proposed. Both the free surface and body surface are immersed in background octree cells that are adaptively refined near the boundaries of interest, thereby dramatically reducing computational costs without loss of accuracy. We also propose an easy-to-implement IB strategy to deal with possible instabilities in the time-domain solution arising from the intersection of Dirichlet–Neumann boundaries. For a linearized problem of wave-wall interaction, a matrix-based stability analysis is performed, providing mathematical support for the robustness of the proposed IB strategy. In contrast to the two-dimensional HPC method, compressed cells are found to offer superior stability compared to stretched cells in the vertical direction, while equal mesh aspect ratio in the horizontal plane is superior. Cubic octree cells are, however, still preferred in practice. The free surface is primarily described by a set of massless background wave markers; however, to address the challenges of IB methods in tracking the free surface evolution near the structure, additional body-fitted wave markers are introduced close to the waterline. The information exchange between these two sets of wave markers is realized by radial basis function (RBF) interpolation. While standard RBF schemes have grid-size-dependent filtering performance, we propose a normalized RBF scheme, which is then optimized in terms of the number of neighboring nodes, a smoothing coefficient and the basis functions. Excellent accuracy properties of the proposed 3 D IB-AHPC method are demonstrated by studying fully nonlinear wave propagation. The method is further applied to study relevant fully nonlinear wave-structure interaction problems, including sloshing in 3 D rectangular tanks and wave diffraction of a bottom-mounted cylinder in regular waves. Satisfactory agreement is demonstrated with existing experimental and numerical results, suggesting that the proposed 3 D IB-AHPC method is a promising potential-flow method in marine hydrodynamics. [ABSTRACT FROM AUTHOR]

In this work, the results of modelling the diffraction of a plane wave by the structures of type dielectric grating/dielectric layer/metal substrate are presented. The strongest field enhancement is achieved for TE polarization under of waveguide mode resonance. In addition, the reflection coefficient is zero under such resonance conditions. Waveguide mode resonance can be realized in a wide range of wavelengths by changing the grating parameters. The spectral characteristics of three types of periodic structures were modelled. The first and second structures contain a dielectric layer, while the third one does not. The waveguide mode resonance and, accordingly, zero reflection coefficient can be obtained with carefully selected structure parameters. Resonant values of the grating thicknesses and periods were determined. Numerical modelling was done with Rigorous Coupled Wavelength Analysis. The thicknesses different from the resonant ones significantly affect the reflection coefficient from the periodic structure, as was established. Absolute permissible deviation values of the thicknesses of the gratings and dielectric layers from the calculated resonance values were estimated. The waveguide mode resonance is sensitive to the incident wavelength on the periodic structure. The reflection coefficient and the field distribution along the grating period were calculated. Studied structures can be effectively used as substrates for SERS-type devices due to field enhancement and zero reflection coefficient under waveguide resonance. The strongest field on the grating surface is observed for the structure without a dielectric layer, namely, dielectric grating deposited on the metal substrate. In addition, the benefits of such periodic structures include lower manufacturing costs. [ABSTRACT FROM AUTHOR]

The Maldives face the threat of tsunamis from a multitude of sources. However, the limited availability of critical data, such as bathymetry (a recurrent problem for many island nations), has meant that the impact of these threats has not been studied at an island scale. Conducting studies of tsunami propagation at the island scale but across multiple atolls is also a challenging task due to the large domain and high resolution required for modelling. Here we use a high-resolution bathymetry dataset of the Maldives archipelago, as well as corresponding high numerical model resolution, to carry out a scenario-based tsunami hazard assessment for the entire Maldives archipelago to investigate the potential impact of plausible far-field tsunamis across the Indian Ocean at the nearshore island scales across the atolls. The results indicate that the bathymetry of the atolls, which are characterized by very steep boundaries offshore, is extremely efficient in absorbing and redirecting incoming tsunami waves. Results also highlight the importance that local effects have in modulating tsunami amplitude nearshore, including the location of the atoll in question, the location of a given island within the atoll, and the distance of that island to the reef, as well as a variety of other factors. We also find that the refraction and diffraction of tsunami waves within individual atolls contribute to the maximum tsunami amplitude patterns observed across the islands in the atolls. The findings from this study contribute to a better understanding of tsunamis across complex atoll systems and will help decision and policy makers in the Maldives assess the potential impact of tsunamis across individual islands. An online tool is provided which presents users with a simple interface, allowing the wider community to browse the simulation results presented here and assess the potential impact of tsunamis at the local scale. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to address the diffraction of non-stationary perturbations with axisymmetric boundaries in a moment elastic framework. Method: The proposed solution utilizes the Cosserat pseudocontinuum as a model, which represents one of the asymmetric hypotheses of elasticity. The hypothesis posits that a spherical cavity inside an infinite Cosserat pseudocontinuum is subject to either a plane wave or a spherical wave for expansion–compression. The relationship between the non-zero components of the displacement vector and the rotating field is constructed inside a spheroid interrelate system. This system describes the motion of the medium with the extraction taking place at the center of the cavity. In the first stages of existence, the medium exhibits a lack of further disruptions. The initial boundary conditions are represented in terms of dimensionless quantities. Results: The solution is determined using the expansion of the functions into Legendre and Gegenbauer polynomial series, as well as applying the Laplace transform at each time. The issue at hand is resolved within the domain of Laplace transforms. In the context of linear estimation, the parameters of the original series are obtained by using the Laurent series to analyze images in the vicinity of the period of origin. The findings indicate that the outcomes previously documented in the context of the classical elastic environment align with the solutions obtained via the use of limit techniques. Conclusion: To facilitate the progress of modern science and technology, it is important to possess a precise comprehension of the deformative processes shown by not only conventional materials, but also those possessing complicated structures. This encompasses materials in which the deformation of the medium may be characterized not only by displacement, but also by rotation. The academic literature generally uses the name "Cosserat medium" to denote the medium characterized by the aforementioned description. Within scholarly discourse, this theory is often referred to as moment, asymmetric, and microstructural elasticity theory. Research has been conducted on the phenomena occurring in pseudo-continuum Cosserat, specifically focusing on the diffraction of waves inside a two-dimensional context, namely by a spherical cavity. [ABSTRACT FROM AUTHOR]

Recently, Rim (Ocean Engng 239:711, 2021; J Ocean Engng Mar Energy 9:41-51, 2023) suggested an exact DtN artificial boundary condition to study the three-dimensional wave diffraction by stationary bodies. This paper is concerned with three-dimensional linear interaction between a submerged oscillating body with arbitrary shape and the regular water wave with finite depth. An exact Dirichlet-to-Neumann (DtN) boundary condition on a virtual cylindrical surface is derived, where the virtual surface is chosen so as to enclose the body and extract an interior subdomain with finite volume from the horizontally unbounded water domain. The DtN boundary condition is then applied to solve the interaction between the body and the linear wave in the interior subdomain by using boundary integral equation. Based on verification of the present model for a submerged vertical cylinder, the model is extended to the case of a submerged chamfer box with fillet radius in order to study 6-DoF oscillatory motion of the body under the free surface wave. [ABSTRACT FROM AUTHOR]

This paper introduces a method for high-resolution lattice image reconstruction and dislocation analysis based on diffraction extinction. The approach primarily involves locating extinction spots in the Fourier transform spectrum (reciprocal space) and constructing corresponding diffraction wave functions. By the coherent combination of diffraction and transmission waves, the lattice image of the extinction planes is reconstructed. This lattice image is then used for dislocation localization, enabling the observation and analysis of crystal planes that exhibit electron diffraction extinction effects and atomic jump arrangements during high-resolution transmission electron microscopy (HRTEM) characterization. Furthermore, due to the method's effectiveness in localizing dislocations, it offers a unique advantage when analyzing high-resolution images with relatively poor quality. The feasibility of this method is theoretically demonstrated in this paper. Additionally, the method was successfully applied to observed edge dislocations, such as 1 / 6 [ 21 1 − ] , 1 / 6 [ 2 − 1 1 − ] , and 1 / 2 [ 0 1 − 1 ] , which are not easily observable in conventional HRTEM characterization processes, in electro-deposited Cu thin films. The Burgers vectors were determined. Moreover, this paper also attempted to observe screw dislocations that are challenging to observe in high-resolution transmission electron microscopy. By shifting a pair of diffraction extinction spots and superimposing the reconstructed images before and after the shift, screw dislocations with a Burgers vector of 1 / 2 [ 01 1 − ] were successfully observed in electro-deposited Cu thin films. [ABSTRACT FROM AUTHOR]

The bottom of the lower mantle is a key region for material circulation and energy exchange within the Earth, with extremely high heterogeneity and complex dynamics processes. Although tomography models have revealed the large-scale velocity structure at the bottom of the lower mantle, the nature of the small-scale lateral heterogeneity structure remains controversial due to resolution limitations. The scattering observations of PKP precursors have been widely used to constrain the small-scale structures at the bottom of the lower mantle due to their special sampling paths and arrival time characteristics. This study cross-validates the presence of scatterers at the bottom of the lower mantle in the northern Bay of Bengal and the northern Gulf of Mexico through migration and array analysis of PKP precursors sampled from seismic arrays in the Sichuan–Yunnan and adjacent areas in China. The forward modelling of the envelope of PKP precursors using the Monte Carlo seismic phonon method reveals that their P -wave velocity perturbations are 0.3 and 0.55 per cent in each area, respectively. Based on the distribution range of the small-scale scatterers, we infer that the northern Bay of Bengal scatterer lies within 200 km above the core–mantle boundary, whereas the thickness of the scattering layer in the northern Gulf of Mexico is approximately 250 km. We propose that the small-scale lateral heterogeneities observed in both regions originate from subducted slabs and may have been transitioned into post-perovskite. [ABSTRACT FROM AUTHOR]

As a non-invasive therapy to promote the effect of the thrombolytic agent in the acute phase of cerebral infarction, transcranial irradiation by ultrasonic waves at the site of the occlusion has been validated and is expected to achieve clinical application. Such irradiation may, however, cause damage to the brain by interference of reflected waves within the skull. In order to avoid such a phenomenon, we proposed a transcranial acoustic lens formed by optimizing the arrangement of point-like scatterers. The optimum arrangement of scatterers was determined so that the sound field vanishes within the skull except at the focus(es) and becomes higher at the focus(es) than in the surrounding regions. The ultrasonic waves are strongly scattered by air bubbles in the water-like medium, so we attempted to install a crossbar switch in the medium covering the head and constructed an acoustic lens by producing an instantaneously adaptive air bubble array. This lens can focus an incident plane wave to the diffraction limit in the direction perpendicular to the incident direction, while the peak width in the propagation direction is more than five times higher. In this work, in order to practically improve it, we propose to arrange a point-like scatterer so as to partially cover the head and further increase the number of layers. The shape of the skull is modeled based on CT data, and more realistic parameters are employed than in a previous paper [T. Ueta, J. Appl. Phys. 132, 144504 (2022)]. [ABSTRACT FROM AUTHOR]

The core‐mantle boundary (CMB) marks the most dramatic changes in physical properties within the Earth, and plays a critical role in the understanding of the Earth's dynamics. PmKP waves are seismic phases that reflect (m − 1) times under the CMB and are useful for studying the complex CMB structure. We present an automated workflow for detecting PmKP phases using multi‐station records from global seismic stations. We employ a novel sampling method to extract PmKP waveforms into a 2‐D matrix. Two deep neural networks are then utilized for initial phase detections and subsequent slowness validations. Numerous PmKPab (3 ≤ m ≤ 7) and their CMB diffracted signals were identified for deep earthquakes (magnitude >6) occurred from 2000 to 2020, including diffracted P7KPab waves with diffraction lengths of nearly 20°. Our approach significantly improves the efficiency of PmKP phase identification and holds the capability to detect other weak core phases, such as PKiKP. Plain Language Summary: Seismic waves provide invaluable information about the Earth's core when sampling the core‐mantle boundary (CMB) complex structures. However, adequate sampling of this region remains a challenge due to the uneven distribution of earthquakes and seismic stations. PmKP is a seismic phase that reflects multiple times (m − 1) within the CMB, and even though it has been considered elusive, it offers an opportunity to overcome the sampling limitation caused by the earthquake‐station distribution and enhance the CMB seismic coverage. Here, we propose a new automated approach to detect unprecedent high reverberations of PmKP. Our method utilizes a combination of two deep neural networks to analyze seismic records from stations distributed globally. By applying this approach to seismic records between 2000 and 2020, we successfully detected up to six underside reflections of PmKP phases and their CMB diffracted waves. Our method enhances the efficiency of identifying PmKP phases and has the potential to be applied to other core seismic phases. Key Points: We propose a workflow based on neural networks to detect rarely observed core seismic phases and their diffractionsOur method successfully detects PmKP up to six underside reflections on the core‐mantle boundary (CMB), increasing the seismic sampling of the CMBThe new workflow can be used for future automated identification of other rare or weak seismic phases [ABSTRACT FROM AUTHOR]

In this paper, a triple-layer grating beam splitter with three-port output is designed. Through the combination of rigorous coupled-wave analysis (RCWA) and simulated annealing algorithms (SAA), the calculation and optimization of each parameter of the grating is carried out to make the diffraction efficiency of the grating meet the conditions. At the incident wavelength of 800 nm, the diffraction efficiencies of 0th order and ±1st order under TE polarization are 31.6% and 31.4%, respectively. The diffraction efficiencies of 0th order and ±1st order under TM polarization are 32.7% and 32.5%, respectively. It can be seen that not only the total diffraction efficiency under TE polarization and TM polarization exceeds 90%, but also the uniformity of diffraction efficiency at each order exceeds 99%. Finally, the influence of grating parameters and incident wave characteristics on diffraction efficiency is discussed. [ABSTRACT FROM AUTHOR]

We address the challenge of acoustic simulations in three-dimensional (3D) virtual rooms with parametric source positions, which have applications in virtual/augmented reality, game audio, and spatial computing. The wave equation can fully describe wave phenomena such as diffraction and interference. However, conventional numerical discretization methods are computationally expensive when simulating hundreds of source and receiver positions, making simulations with parametric source positions impractical. To overcome this limitation, we propose using deep operator networks to approximate linear wave-equation operators. This enables the rapid prediction of sound propagation in realistic 3D acoustic scenes with parametric source positions, achieving millisecond-scale computations. By learning a compact surrogate model, we avoid the offline calculation and storage of impulse responses for all relevant source/listener pairs. Our experiments, including various complex scene geometries, show good agreement with reference solutions, with root mean squared errors ranging from 0.02 to 0.10 Pa. Notably, our method signifies a paradigm shift as—to our knowledge—no prior machine learning approach has achieved precise predictions of complete wave fields within realistic domains. [ABSTRACT FROM AUTHOR]