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The propagation of waves in shallow waters is affected by the bottom topography unlike deep water waves of the coastal environment. Due to the interaction of the wave with bed topography, the wave transformation processes occur. Refraction, diffraction, shoaling, and breaking are the wave transformation processes that occur in the coastal environment. The significant wave height over rugged topography is a standardized statistics to denote the characteristic height of the random waves in a sea state. Therefore, the objective of the present study is to predict the significant wave height over rugged topography. The SWAN standalone and SWAN DHH platform are used to predict significant wave height over rugged topography in Mehamn harbour, Norway. The SWAN model results are almost similar to the lab data of Vold and Lothe (2009) for all the 22 scenarios at all the output locations. Further, the four cases reported by Taehun (2011) and lab data from Vold and Lothe (2009) for that four cases are compared with the SWAN model results. It is observed that the SWAN model results are much closer to the lab data of Vold and Lothe (2009).

Since the invention of the laser in the 60s, one of the most fundamental communication channels has been the free-space optical channel. For this type of channel, a number of effects generally need to be considered, including diffraction, refraction, atmospheric extinction, pointing errors and, most importantly, turbulence. Because of all these adverse features, the free-space optical (FSO) channel is more difficult to study than a stable fiber-based link. For the same reasons, only recently it has been possible to establish the ultimate performances achievable in quantum communications via free-space channels, together with practical rates for continuous variable (CV) quantum key distribution (QKD). Differently from previous literature, mainly focused on the regime of weak turbulence, this work considers the FSO channel in the more challenging regime of moderate-to-strong turbulence, where effects of beam widening and breaking are more important than beam wandering. This regime may occur in long-distance free-space links on the ground, in uplink to high-altitude platform systems (HAPS) and, more interestingly, in downlink from near-horizon satellites. In such a regime we rigorously investigate ultimate limits for quantum communications and show that composable keys can be extracted using CV-QKD., 13 pages

Accurate measurement of temperature and velocity fields in combustion and flow diagnostic plays an important role in analyzing the heat transfer mechanism and ensuring the safe operation of equipment. In the present work, considering the refraction effect of sound waves, temperature and velocity fields are reconstructed simultaneously based on the nonlinear acoustic tomography (NAT) by using the covariance matrix adaptation evolution strategy (CMA-ES) algorithm. In the forward problem, the fast two-point ray-tracing algorithm is introduced to track curved sound waves more efficiently. Due to the sparse measurement signals caused by the limited space and curved acoustic paths, Tikhonov regularization is introduced as the constraint of smoothing prior information to reduce the ill-posedness of the problem. The influence of velocity regularization parameter and temperature regularization parameter on simultaneously visualizing the temperature and corresponding velocity fields are investigated, respectively. Then the selection strategies of these two regularization parameters are given, which are proved to have high selection efficiency. On this basis, inhomogeneous temperature and velocity fields are reconstructed simultaneously by using the CMA-ES algorithm, simulated annealing, and genetic algorithms. By solving the inverse problem of the NAT, which is highly nonlinear and ill-posed, the feasibility and effectiveness of CMA-ES algorithm in the simultaneous reconstruction of velocity and temperature fields are confirmed. The proposed method for visualizing the temperature and velocity fields will supply key feedback for the combustion process control.

Background: Skin tattoos are a common decoration, but profound scientific study whether the presence of a skin tattoo alters the acoustic response from superficial tissue, and therefore from underlying tissue, was previously lacking. Any image aberrations caused by tattoo presence may have been thought negligible, yet empirically found artifacts in brightness-mode images of tattooed skin suggest otherwise. This study investigated the nature of these artifacts theoretically and experimentally in extremely simplified cases of perfectly flat and homogenous layered media and in tattooed pork. Methods: Theory was derived for computing the acoustic response from horizontally and vertically layered media containing a thin inked layer. Experiments were performed in vitro. Artificial and pork skin were tattooed, attached to phantom material, and sonicated with a 13–6-MHz probe. The speed of sound of these materials was determined, and the perceived refraction angles was measured. Results: The measured speeds of sound of tattooed materials were higher than those of their uninked counterparts. The presence of tattoo ink was found to have increased the linear acoustic attenuation by 1 dB/cm. This value is negligible for typical tattoos of only few millimeters. The perceived critical refraction angles of adjacent materials could be detected, and their corresponding speeds of sound were quantified. These coincided with values derived from theory. Conclusion: The ratio of speeds of sound of adjacent materials was shown to create distinct highlights in brightness-mode images. The artifacts observed in in vitro and in vivo brightness-mode scans were explained from near-vertical transitions between areas of different sound speed. This is the first study correlating so-called critical refraction highlighting with speed-of-sound information. In addition, it was found that phantom material is a room-temperature acoustic alternative for experiments on live human skin. In summary, the presence of superficial tattoos has a small but quantifiable effect on the acoustic response from deeper tissues.

A wave resource characterisation is presented for the French Basque coastal region, with a specific focus on Bayonne nearshore area. The study is derived from a 10-year hindcast computation performed with a very high-resolution coastal implementation of a SWAN model. After a detailed validation of the model in intermediate and shallow water, the spatial, temporal, and spectral distributions of the local nearshore wave energy climate are characterized. Refraction over a local submarine canyon splits the coastal domain into two main regions with different general characteristics. In the southern Basque region, the spatial fluctuations of the wave resource increase drastically in shallow water. Variability nearshore was shown to be significantly higher than over the deeper part of the shelf. Noticeable hot-spots are found in the nearshore area around Bayonne, where the local wave resource substantially exceeds the outer shelf incident energy flux. Seasonal to hourly temporal fluctuations are also characterized at different nearshore locations and found to be very pronounced. The major wave resource variations found at reduced space-time scales highlight the strong influence of local small-scale bathymetry features in the Basque nearshore region.

Refraction networking is a promising censorship circumvention technique in which a participating router along the path to an innocuous destination deflects traffic to a covert site that is otherwise blocked by the censor. However, refraction networking faces major practical challenges due to performance issues and various attacks (e.g., routing-around-the-decoy and fingerprinting). Given that many sites are now hosted in the cloud, data centers offer an advantageous setting to implement refraction networking due to the physical proximity and similarity of hosted sites. We propose REDACT, a novel class of refraction networking solutions where the decoy router is a border router of a multi-tenant data center and the decoy and covert sites are tenants within the same data center. We highlight one specific example REDACT protocol, which leverages TLS session resumption to address the performance and implementation challenges in prior refraction networking protocols. REDACT also offers scope for other designs with different realistic use cases and assumptions.

There is controversy in ophthalmic research as to whether vitamin D deficiency is an independent factor in the progression of myopia.

Neutrino-neutrino refraction dominates the flavor evolution in core-collapse supernovae, neutron-star mergers, and the early universe. Ordinary neutrino flavor conversion develops on timescales determined by the vacuum oscillation frequency. However, when the neutrino density is large enough, collective flavor conversion may arise because of pairwise neutrino scattering. Pairwise conversion is deemed to be fast as it is expected to occur on timescales that depend on the neutrino-neutrino interaction energy (i.e., on the neutrino number density) and is regulated by the angular distributions of electron neutrinos and antineutrinos. The enigmatic phenomenon of fast pairwise conversion has been overlooked for a long time. However, because of the fast conversion rate, pairwise conversion may possibly occur in the proximity of the neutrino decoupling region with yet to be understood implications for the hydrodynamics of astrophysical sources and the synthesis of the heavy elements. We review the physics of this fascinating phenomenon and its implications for neutrino-dense sources., Comment: 25 pages, including 7 figures; to appear in Annual Review of Nuclear and Particle Science, vol. 71. Preprint matching the version accepted for publication

A hydrogeologic conceptualization is critical to understand, manage, protect, and sustain groundwater resources, particularly in regions where data are sparse and accessibility is difficult. We used airborne electromagnetics (AEM), shallow seismic reflection and refraction, and downhole nuclear magnetic resonance (NMR) logs to improve our understanding of an arid groundwater system influenced by palaeovalleys. We found that there is a limited connection between the palaeovalley and fractured bedrock aquifers because they are separated by a spatially variable layer of saprolite, which is the layer of chemically altered rock on top of the fractured bedrock. The AEM data provided an estimate of the top of the saprolite but failed to effectively image the bottom. In contrast, the seismic data provided an estimate of the bottom of the saprolite but failed to image the top. This geophysical combination of electrical and seismic data allowed us to map saprolite thickness in detail along a 1.7 km long transect that runs perpendicular the main trunk of a well-defined palaeovalley. These data indicate that the palaeovalley is lined with a heterogeneous layer of saprolite (approximately 3–120 m thick) that is thickest near its edges. Despite the observed variability, only a small percentage of the fractured bedrock aquifer (8%–17%) appears to be in contact with the palaeovalley aquifer. Furthermore, the lack of an elastic boundary at the top of saprolite suggests that the porosity of the saprolite is similar to the palaeovalley sediments — an observation that is supported by the downhole NMR-derived water contents. The electrical change at the top of saprolite is caused by a combination of a decrease in total dissolved solids of the groundwater in the saprolite and a change in pore structure associated weathering in situ versus transported weathered materials. The presence of saprolite, which commonly behaves as an aquitard, may limit the groundwater exchange between the palaeovalley and bedrock aquifers, with implications for the regional groundwater resource potential.

An operational method is proposed for calculating the refraction of decameter radio waves in a randomly-inhomogeneous upper atmosphere. The method is based on the numerical-analytical solution of stochastic equations of geometric optics. An integral expression is obtained for the dispersion of the refraction angle of a radio wave on the atmospheric path using the approximation of the perturbation method. For a quick calculation of the statistical moment of the refraction angle, the integral expression is reduced to an ordinary first-order differential equation. Joint numerical solution of the unperturbed ray equations and the equations for the statistical moment allows an operational estimate of beam width of radio waves arriving at the observation point. The results of numerical calculations of the standard deviations of the refraction angles of radio waves on paths of various lengths are presented.

Conditions under which a quantum particle can be described using classical quantities are studied. We investigate the wavefunction of a quantum particle submitted to a potential field for which all quantum effects vanish, even if Planck's constant is non-negligible. This problem is equivalent to the problem of the motion of a particle in a refringent medium. The indices of refraction of such media are found. In these media, quantum particles have classical momenta, while their wave properties are described by the wave-optics equation with a characteristic length equal to the de Broglie wavelength ƛ. In the 1D case, the particle cannot be found in the region near the origin, since the index of refraction tends to infinity there. For the 3D case with central symmetry, the wave properties are determined by a function that has a resonance of width about 2 ƛ. Experimental verification of theoretical predictions is discussed.

SUMMARY Accurate picking of head-wave arrival times is an important component of first-arrival traveltime tomography. Far-offset traces in particular have low signal-to-noise ratio (SNR), but picking on these traces is necessary in order to obtain velocity information at depth. Furthermore, there is often an insufficient number of far-offset traces for obtaining reliable models at depth. We present here an extrapolation method for increasing the number of first arrivals beyond the maximum recorded offset, thereby extending the supervirtual refraction interferometry (SVI) method. We refer to the method as extrapolated SVI (ESVI). It is a novel attempt to extrapolate first arrivals using a fully data-driven method. We first test the methodology on synthetic data sets, and we then apply ESVI to two published real data sets over the Pärvie fault system in northern Sweden. These data sets were acquired along the same profile at different times with different acquisition parameters and noise levels. The results show that ESVI enhances the SNR of head waves when the noise level is high. That is the same as the conventional SVI. ESVI also increases the number of pickable first arrivals by extrapolating head waves past the original maximum offset of each shot. We also show that the significant increase in first-arrival traveltime picks is beneficial for improving resolution and penetration depth in the tomographic imaging and, consequently, better revealing the subsurface velocity distribution. The tomographic images show higher velocities in the hanging walls of the main Pärvie fault and another subsidiary fault, as interpreted relative to migrated images from previous seismic reflection processing.

Uphole and surface seismic refraction surveys were carried out in parts of the Niger Delta, Nigeria, to delineate weathering thickness and velocity associated with aweathered layer. A total of twelve uphole and surface seismic refraction surveyswere shot, computed and analyzed. The velocity of the uphole seismic refraction ranged from 344.8 to 680.3 m/s with a thickness of 5.45 to 13.35 m. Surface seismic refraction ranged from 326.6 to 670.2 m/s and 4.30 to 12.0 m, respectively. The average velocity and thickness ranged from 559.6 to 548.0 m/s and 9.43 to 8.63m with differences of 11.6 m/s and 0.83 m respectively. The VW/VS ratios ranged from 0.955 to 1.059. This indicates that the uphole velocity is higher than the surface refraction velocity leading to low VW/VS values. This is a direct experimental proof of a low velocity zone, confirming the weathered nature of the area. The results of both refraction methods are reliable; the differences in surface refraction values are due to shot point offsets. Based on these findings, it is recommended that shots for seismic surveys should be located above 15.0 m in the area to delineate the effects associated with weathered layers to ensure that will be competent to withstand engineering structures.

Integrated geophysical surveys using ground penetrating radar (GPR), seismic and electrical resistivity tomography, are carried out to characterize the subsidence, combining with engineering examples in the Glauber's salt mining area in the northwestern region of Gansu Province, China. Because some of the dissolved ore bodies in the Glauber's salt mining area are accompanied by the top and floor, the geophysical response of the floor strata has different physical properties. It is theoretically feasible to use resistivity imaging, GPR and seismic methods to detect. However, it is very necessary to choose an effective geophysical method through experimentation. the limitations of electrical resistivity tomography method and GPR are discussed: in actual work, if the electrical difference between the target body and the surrounding rock is not large enough, the conventional electrical resistivity tomography method cannot be used for fine detection; due to factors such as human noise from the mine's annex, the GPR electromagnetic wave reflection method cannot carry out effective work. Seismic refraction tomography processing is discussed and it was found that the interpretation results of refraction wave tomography can better distinguish the strata in the sub-survey area, which has an excellent effect on the delineation of the range of dissolution and collapse in Glauber's salt mine. Theory and engineering examples prove that seismic refraction wave tomography technology has good applicability in the detection of underground dissolution areas in Glauber's salt mines.

First-arrival traveltime tomography (FATT) is used to delineate shallow velocity structures to identify static effects in oil exploration as well as to characterize the near surface for geotechnical purposes. Because FATT is generally used for land seismic data processing, it becomes necessary to consider irregular topography especially when performing wave-based tomography. However, the standard Cartesian finite-difference method cannot properly handle irregular topography. Hence, the embedded boundary method (EBM) is incorporated into the frequency-domain damped-wave equation to correctly describe irregular topography. The developed modeling algorithm is used to calculate first-arrival traveltimes and to perform FATT. The EBM-based modeling algorithm accurately describes the irregular surfaces of numerical velocity models on a regular mesh by exploiting the mirror image principle. The accuracy of the EBM-based traveltime calculation is validated by using two homogeneous velocity models with dipping and complex surfaces. The validation results demonstrate that our algorithm is unaffected by the staircase approximation. FATT is then applied to synthetic and real data to demonstrate the applicability of the developed algorithm to velocity models with complex topography. For the real data example, the inverted velocity model is used to apply static corrections. The processing results demonstrate an improvement in the continuity of seismic events, thus confirming the accuracy of the developed FATT method.

The belowground architecture of the critical zone (CZ) consists of soil and rock in various stages of weathering and wetness that acts as a medium for biological growth, mediates chemical reactions, and controls partitioning of hydrologic fluxes. Hydrogeophysical imaging provides unique insights into the geometries and properties of earth materials that are present in the CZ and beyond the reach of direct observation beside sparse wellbores. An improved understanding of CZ architecture can be achieved by leveraging the geophysical measurements of the subsurface. Creating categorical models of the CZ is valuable for driving hydrologic models and comparing belowground architectures between different sites to interpret weathering processes. The CZ architecture is revealed through a novel comparison of hillslopes by applying facies classification in the elastic-electric domain driven by surface-based hydrogeophysical measurements. Three pairs of hillslopes grouped according to common geologic substrates — granite, volcanic extrusive, and glacially altered — are classified by five different hydrofacies classes to reveal the relative wetness and weathering states. The hydrofacies classifications are robust to the choice of initial mean values used in the classification and noncontemporaneous timing of geophysical data acquisition. These results will lead to improved interdisciplinary models of CZ processes at various scales and to an increased ability to predict the hydrologic timing and partitioning. Beyond the hillslope scale, this enhanced capability to compare CZ architecture can also be exploited at the catchment scale with implications for improved understanding of the link between rock weathering, hydrochemical fluxes, and landscape morphology.

Of the many topics generally taught in undergraduate or graduate optics courses, the propagation of light through crystals with electrical anisotropy is one of the most difficult topics for students and for teachers who do not work in this field. In particular, the mathematics and equations are complex vectorial equations, and this complicates the visualization of the implications of the theory. Also, the standard textbooks and papers on the subject have led to some misconceptions on this problem by presenting results only for specific cases of the theory in graphical form. For example, it is a general belief that after refraction of an incident wave on the crystal, the polarization state of the two waves propagating inside the crystal, given by their displacement vectors D, are always orthogonal to each other. However, this is not the case, as explained and illustrated for uniaxial crystals by Aleman-Castaneda and Rosete-Aguilar [J. Opt. Soc. Am. A 33(4), 677–682 (2016)]. The purpose of this paper is to help students and teachers visualize the solution to Maxwell's equations in electrical anisotropic crystals. An algorithm has been written in mathematica so the reader can use it to visualize the normal surface in uniaxial and biaxial crystals. This algorithm can be used as the basis of computational projects for students to better understand the equations involved, or as a visualization tool for teachers in class.

The reflection and refraction phenomenon of propagation of waves in couple stress micropolar thermoviscous elastic solid media with independent viscoelastic and micropolar properties have been studied. The structure of the model has been taken such that the plane interface is divides the given media into two half spaces in perfect contact. Here, we find that there are five waves, one of them is propagating independently while others are set of two coupled waves travelling with different speeds. Energy ratios, reflection and refraction coefficients relative to numerous reflected and refracted waves have been investigated when set of two coupled longitudinal waves and set of two coupled transverse waves strike at the interface through the solid medium. The inequality of energy ratios, refraction coefficients and reflection coefficients are evaluated numerically and presented graphically under three theories of thermoelasticity, namely, Green-Lindsay theory (GL), Lord-Shulman theory (LS), Coupled theory (CT) versus angular frequency and angle of incidence.

Results of an experimental research of horizontal refraction into the propagation of acoustic signals in a coastal wedge are presented. When there are surface seawaves, the acoustic signal is found to be modulated in intensity and time of arrival. When signals reflect from both the bottom and the surface of the sea under the same conditions, the signal from a distant transmitter has additional directionality. It is shown that under certain condition the signal having the same type of arrival can be split spatially.

Our investigations are aimed to calculate the physical and geomechanical characteristics needed to assess the geotechnical suitability of the subsurface at Ataqa industrial zone, Suez, Egypt for constructing some industerial facilities. To accomplish our target, four seismic profiles are conducted using the refraction technique to estimate the primary seismic wave velocity as well as four profiles using the method of "Multichannel Analysis of Surface Waves" for estimating the velocity of shear waves. The stage of processing and interpretation are performed through using the "SeisImager/2D" Software. The results clarify the existence of two layers to a depth of 18 m. The top layer ranges in thickness between 2 and 4m and has a primary wave velocity ranging between 924 and 1247 m/s and a shear wave velocity ranging between 530 and 745 m/s. On the other hand, the second layer possesses an average primary velocity ranging between 1277 and 1573 m/s and a shear wave velocity ranging between 684 and 853 m/s. The measured velocities are utilized to calculate many physical and geomechanical properties of the earth materials comprising the two layers in our study area. The integration between all these parameters proves the suitability of both layers for erecting the proposed constructions.

Discrete deep targets are a significant challenge for most surface-based geophysical techniques, even when considering high property contrasts. In general, surface-based geophysical methods lose lateral and vertical resolution with depth as a result of the limited acquisition geometry and increased signal attenuation. The former can be overcome through use of cross-borehole methods, but lateral localization is still needed for optimal borehole placement. As such, a relatively small, deep void located near the maximum depth of investigation (DOI) is very unlikely to be detected. Yet, secondary features associated with these voids can be exploited for enhanced detection performance. When voids are located below the groundwater table, a significant amount of dewatering and pumping is required to make them a functional passageway. This dewatering not only removes water from the void space but also the surrounding formation, resulting in a much larger, if more diffuse, secondary target: an induced groundwater table gradient. Many geophysical sensing methods are sensitive to subsurface moisture content. We have implemented a 2D joint-petrophysical mixing model (JPM), using inverted electrical resistivity tomography (ERT) and inverted seismic refraction models to sense changes in the groundwater table gradient. Our results are validated using the depth to bedrock, groundwater-surface water information, ground-penetrating radar, and time-domain reflectometry methods. Our initial proof of concept is applied to a shallow area with a significant soil moisture gradient, through different surface soil types and bedrock. The 2D JPM results are used to generate an estimate of air, moisture, and matrix percent fractions in the investigation area, providing a clear delineation of the groundwater surface and associated gradient. This refined hydraulic gradient estimate can then be used to laterally locate a void at or below the DOI of ERT and seismic refraction.

Currents in the Baltic Sea are generally weak, but during strong winds they can grow high enough to affect the surface wave propagation and evolution. To evaluate the significance of wave-current interactions in the Baltic Sea, we conducted a study using the wave model WAM, comparing a run without surface currents to one with current forcing from a NEMO hydrodynamical model simulation. The overall changes to the wave field caused by currents were quite small. Changes of over 10 cm in significant wave height (SWH) or 1 s in the peak period (Tp) occurred only in some areas and typically less than 3% of the time. Current refraction changed the SWH annual mean by up to 2 cm, but changes up to 60 cm were seen in the maximum values. Tp had occasionally large changes due to shifts in the peak energy in two-peaked swell and wind-sea spectra. Including currents typically led to a stronger changes in swell energy compared to the changes in wind sea energy. A comparison with a wave buoy in the Gulf of Finland showed that this change in the swell energy improved the accuracy of the simulation in this narrow gulf. Current-induced refraction was most prominent near the coastal areas, where current speed occasionally exceeded 0.3 m/s. In general, SWH decreased in the coastal areas with strong currents and slightly increased in adjacent open sea areas. The current effects were most frequent in the Gulf of Finland, the Western Gotland Basin and the Åland Sea.

A wide-angle seismic reflection / refraction survey along a ~ 600 km long transect through the Junggar basin from Emin to Qitai allows to receive several images near N-S trending blind faults, which are located at the lower part of the upper crust, the middle crust and the lower crust within the basin and cut up the Moho. These faults, with high seismic velocity and without obvious dislocation, are considered as “extensional faults” formed by north-south compression and east-west extension. These deeply rooted faults provide channels via which basic to ultra-basic materials from upper mantle migrate into the crust and mix up with the crustal material causing thin thickness, high seismic velocity, high density and high magnetic intensity after cooling in the crust of the basin.

To deal with the high-resistance fault identification problem in multi-terminal VSC-HVDC, this paper proposes a high fault-resistance tolerable traveling wave protection. First, the non-unified characteristic of traveling wave front between internal and external faults is revealed, which makes the high-resistance fault identification difficult. Then, the traveling wave propagation regarding the reflection and refraction process at the remote end is investigated for the difference, and the distinctive current reduction phenomenon during the interval of two incident traveling waves under internal fault with resistance is discovered. Moreover, the current reduction phenomenon would become more significant with the increase of fault resistance. Based on this phenomenon, the high fault-resistance tolerable traveling wave protection is proposed, which could identify the high-resistance fault accurately with single-end measurement and is insensitive to fault resistance. The feasibility and robustness of the proposed protection are validated in a four-terminal VSC-HVDC.

Impact-induced mixing between bolide and target is fundamental to the geochemical evolution of a growing planet, yet aside from local mixing due to jetting – associated with large angles of incidence between impacting surfaces – mixing during planetary impacts is poorly understood. Here we describe a dynamic instability of the surface between impacting materials, showing that a region of mixing grows between two media having even minimal initial topography. This additional cause of impact-induced mixing is related to Richtmyer-Meshkov instability (RMI), and results from pressure perturbations amplified by shock-wave refraction through the corrugated interface between impactor and target. However, unlike RMI, this new impact-induced instability appears even if the bodies are made of the same material. Hydrocode simulations illustrate the growth of this mixing zone for planetary impacts, and predict results suitable for experimental validation in the laboratory. This form of impact mixing may be relevant to the formation of stony-iron and other meteorites., The authors describe a dynamic surface instability between impacting materials, showing that a region of mixing grows between two media. The study implies that this can explain mixed compositions and textures in certain meteorites.

In this work, we describe the propagation of waves in media containing localized rapidly changing inhomogeneities (for example, narrow underwater ridges or pycnoclines in ocean, layers with drastically changing optical or acoustic density, etc.). DOI 10.1134/S1061920821020011

An analysis of the focusing of an acoustic wave in a cylindrical channel filled with a pure liquid and a bubble liquid, separated by a spherical surface, as a result of its refraction at this interface is given. The influence of the frequency of an acoustic wave propagating in such a liquid–gas mixture as well as the radius of the bubbles and their volume content in it on the distance of focusing of this wave in the mixture was investigated. The conditions under which the focal distance of the acoustic lens formed in a liquid–gas mixture takes a maximum and a minimum values and an acoustic wave propagating in this mixture is focused or scattered in it were determined.

We modelled the two major layer of Earth's ionosphere, the F-layer and the D-layer, by a simplified spatial model with temporal variance to study the chromatic ionospheric effects on global 21-cm observations. From the analyses, we found that the magnitude of the ionospheric disruptions due to ionospheric refraction and absorption can be greater than the expected global 21-cm signal, and the variation of its magnitude can differ, depending on the ionospheric conditions. Within the parameter space adopted in the model, the shape of the global 21-cm signal is distorted after propagating through the ionosphere, while its amplitude is weakened. It is observed that the ionospheric effects do not cancel out over time, and thus should be accounted for in the foreground calibration at each timestep to account for the chromaticity introduced by the ionosphere., Comment: 11 pages, 13 figures, 4 tables

A brief review of the main microwave diagnostics methods of inhomogeneous plasma based on the refraction of microwaves is given. These methods make it possible to determine the plasma density distribution, the magnetic field distribution, the electron collision frequency, and the electron temperature profile. In addition, the determination of the average density of the peripheral plasma layers and the local inhomogeneities of the rotating plasma are also possible. The effect of refraction on the accuracy of determining the plasma parameters by using microwave methods for plasma diagnostics is considered.

The article highlights the study of the problem of the formation of value orientations of education in the educational process. The authors tried to determine the modern values of upbringing and to reveal the teacher’s readiness to refract the existing stereotypes of upbringing values to the real needs of a modern child. The article reveals the results of sociological and pedagogical research, which allows the authors to correlate the real needs, demands of modern children, the specifics of the existing subculture and what significant adults are oriented towards, who determine the content, approaches in the upbringing and education of children. The results of studying the ideas and requests of not only children, but also parents and teachers are highlighted.The research methodology is based on the key ideas of the competence-based and subjective approach. The main methods of studying the stated problems are: analysis, interpretation and systematization of theoretical and experimental data. The analysis of the studied patterns was carried out from the standpoint of interdisciplinarity, pedagogical and social phenomena were considered as holistic, which made it possible to develop an approach to methodological support of teachers in the organization of significant and valuable educational events for preschoolers. In the context of the research, labour actions are identified that are most characteristic of teachers in the implementation of the event-based approach. The potential of labor actions that are not included in the repertoire of specialists has been studied, the motivation for this has been determined. The obtained results of the study made it possible to identify and describe the options for relevant technological tracks in educational approaches, to determine the specifics of the organization of educational events in a preschool institution, to draw practical conclusions that allow us to design subsequent directions for study. Keywords: upbringing stereotypes, upbringing values, value attitude, children’s subculture, children’s needs

Eyes health is the most important thing in getting visual information to do daily activities. But visual disturbance or refraction disorders, experienced by many people and it cannot be ignored because they can disturb activities. Each people need to know about those kinds of refraction disorders. That way, it is expected that people can anticipate the symptoms of this refraction disorder. Knowledge of refraction disorder such as myopia, hypermetropy, and astigmatism is important for all people, especially for people who are steeped in the field of optical refraction. The purpose of this research is to know about refraction disorders knowledge of the first grade optition refraction students. The method that used in this research is descriptive quantitative, which the data from research sample is analyzed corresponding to statistic method that being used. While the instrument is questionnaire in the form of closed questions. The population is 54 regular university students majoring in optical refraction. Result of the research shows that 38% students in a good category, 44 % students are enough and the rest 18 % are in the poor category. Based on the result of the research, a solution is needed to improve students knowledge about optical refraction disorder.

Проблеме рефракции света в атмосфере посвящено много научных работ, где отмечается: «учёт атмос- ферных влияний на результаты геодезических измерений является сложнейшей физической пробле- мой, решение которой крайне затруднено...». Практически все классические метод определения реф- ракции основаны на теории рефракции, созданной Ньютоном для статически устойчивой атмосферы. В действительности атмосфера находится всегда в турбулентном движении и поэтому её оптические свойства всё время изменяются. Наиболее перспективное направление в решении проблемы рефрак- ции — использование турбулентных методов, которые учитывают динамику атмосферы.

This paper is concerned with the study of new turbulent method technique for the determining of vertical refraction when total stations are used. Required measurement accuracy of vertical refraction by conventional methods is extremely difficult due to rapid random changes in the angle of refraction. Geodetic observations are recommended to performing only during periods of indifferent temperature stratification, while the refraction is close to zero and practically unvaried. However, this period is extremely short and its boundaries are not defined, so the inefficiency of all known methods for determining refraction must be attention. The complete liberation of geodetic observations from the influence of turbulent and fluctuation processes in the atmosphere is possible only by directly measuring the angle of refraction at the time of observation. The creation of electronic total stations with automatic guidance to the target allows to successfully solving the problem of determining refraction by a turbulent method. The aim of this work is to study the new method for determining refraction in a turbulent atmosphere. The measurements are performed with a Trimble total station. The obtained results confirm that the accuracy for determining refraction is ~2″, which almost corresponds to the instrumental accuracy of the device used.

Water-cooling wall tube leakage accident is an important factor affecting the safe and economic operation of power station boilers. In this article, the acoustic method is applied to locate the leakage from a simulated water-cooling wall tube, and several key technologies are studied in order to identify the precise location of leakage source. Sound wave propagation path in ‘nonuniform temperature field is obtained to overcome the shortcoming that the traditional location technology always assumed that sound waves propagate along the straight line. Considering the refraction effect of sound waves, the reconstruction method based on radial basis function approximation with polynomial reproduction (RBF-PR) is used to reconstruct the temperature field. A generalized cross correlation with second correlation is applied to estimate the time delay of arrival (TDOA). According to the temperature field measured by acoustic method and the propagate time of sound waves, the location fingerprint method including the statistical correlation characteristics between the coordinate of fingerprint points and TDOA are constructed. Radial basis function artificial neural network (RBF ANN) is used to estimate the coordinate of leakage point. Numerical simulations and experimental study are implemented to evaluate the effectiveness of the proposed location system. An acoustic location test platform is constructed to study the location accuracy in different working conditions. The results indicate that considering the refraction effect, the reconstruction performance of temperature field is superior than that without the refraction effect, and acoustic method with RBF ANN algorithm can gain the leakage location with high accuracy and good antinoise ability in the above high-quality reconstructed nonuniform temperature distribution.

In paper the problem of the reflection and refraction of a plane harmonic sound wave by a homogeneous isotropic elastic plate with an continuously inhomogeneous anisotropic elastic coating is considered. It is assumed that the plate is adjoin to ideal fluids. The propagation of small perturbations in a ideal fluid in the case of steady state oscillations is described by Helmholtz’s equation. The propagation of elastic waves in a uniform isotropic elastic plate is described by scalar and vector Helmholtz’s equations for longitudinal and transverse waves. Oscillations of an inhomogeneous anisotropic elastic coating are described by general motion equations of the continuous medium. The boundary-value problem for the system of ordinary second order differential equations is constructed for determination of the displacement field in inhomogeneous anisotropic coating. An analytical description of the reflected and transmitted through the plate acoustic fields is obtained. Particular cases when the material of an inhomogeneous coating is transversely isotropic and isotropic are considered. The results of numerical calculations of dependence of reflection coefficient of a homogeneous isotropic plate with a transversely isotropic coating from the incidence angle of plane wave are presented.

In this article, we review the topic of Huygens’ metasurfaces with an emphasis on existing and emerging applications at microwave frequencies. Huygens’ metasurfaces have demonstrated unprecedented capabilities of controlling electromagnetic wavefronts by means of electric and magnetic dipole moments arranged in a thin sheet. We present the fundamental principles of Huygens’ metasurfaces based on the boundary conditions governing their operation. Then, we discuss the aspect of practical realization of Huygens’ metasurfaces and the different types of constituent subwavelength scatterers (unit cells). Moreover, we summarize recent developments in several areas related to metasurfaces, such as perfect anomalous refraction, polarization control, antenna beamforming and reconfigurable metasurfaces. Lastly, we provide a brief outlook on emerging metasurface-based microwave technologies that are expected to further grow in the future.

Models of the coupled nonlinear Schrodinger equations submit various critical physical phenomena with a typical equation for optical fibres with linear refraction. In this article, we will presuppose the Compact Finite Difference method with Runge-Kutta of order 4 (explicit) method, which is sixth-order and fourth-order in space and time respectively, to solve coupled nonlinear Schrodinger equations. Many methods used to solve coupled nonlinear Schrodinger equations are second order in time and need to use extra-technique to rise up to fourth-order as Richardson Extrapolation technique. The scheme obtained is immediately fourth-order in one step. This approach is a conditionally stable method. The conserved quantities and the exact single soliton solution indicate the competence and accuracy of the article’s suggestion schemes. Furthermore, the article discusses the two solitons interaction dynamics.

The stress-strain state at the interface between elastic media, which represents a contact layer characterized by the size and a set of physical-mechanical parameters, is investigated. The interface is described using the models of stratified and block media, within which the problem of a plane wave propagating through the interface is considered. The analytical expressions for the interface reflection and refraction coefficients are obtained, which allow determining the deformations at the interface and the strain distribution in the contact layer. The respective relationships for the dependence of deformation on the layer thickness at different elastic parameters of the contacting media and the interface are calculated. The regularities of deformation at the interface, described by the models of layered and block media, are analyzed. The areas of equivalent applications of these models are determined for the analysis of deformations at the interface and their distribution in the contact layer.

This essay presents an alternate theory for the mechanism of electromagnetic refraction and diffraction interference patterns and provides arguments in support of new concepts for these phenomena. These concepts are predicated on the idea that free-space appears to be composed of an energy field with characteristics of an elastic medium that the author termed “spatial energy field” or SEF. It is proposed that the geometric volume of space requires conservation, and this is achieved via stretching or compression of space while exhibiting elastic and wavelike qualities. The SEF, representing spacetime, has specific properties that appear to lead to the emergence of electromagnetic refraction and diffraction. It is proposed that the conservation of spatial volume affects the outcome of particle refraction and diffraction interference patterns. A mechanism for refraction is explained by higher density spacetime (SEF) near atomic nuclei reducing the apparent velocity of transmitted photons. For diffraction, momentum guiding “pilot waves” of spacetime (SEF) is presented as the mechanism for production and redirection of minima and maxima interference patterns of particles.

Fast-moving synoptic-scale atmospheric disturbances produce large-scale near-inertial waves in the ocean mixed layer. In this paper, we analyze the distortion of such waves by smaller-scale barotropic eddies, with a focus on the evolution of the horizontal wavevector k under the effects of straining and refraction. The model is initialized with a horizontally uniform (k = 0) surface-confined near-inertial wave, which then evolves according to the phase-averaged model of Young and Ben Jelloul. A steady barotropic vortex dipole is first considered. Shear bands appear in the jet region as wave energy propagates downward and toward the anticyclone. When measured at a fixed location, both horizontal and vertical wavenumbers grow linearly with the time t elapsed since generation such that their ratio, the slope of wave bands, is time independent. Analogy with passive scalar dynamics suggests that straining should result in the exponential growth of |k|. Here instead, straining is ineffective, not only at the jet center, but also in its confluent and diffluent regions. Low modes rapidly escape below the anticyclonic core such that weakly dispersive high modes dominate in the surface layer. In the weakly dispersive limit, k = −t∇ζ(x, y, t)/2 provided that (i) the eddy vertical vorticity ζ evolves according to the barotropic quasigeostrophic equation and (ii) k = 0 initially. In steady flows, straining is ineffective because k is always perpendicular to the flow. In unsteady flows, straining modifies the vorticity gradient and hence k, and may account for significant wave–eddy energy transfers.

The paper deals with some problems when applying a correction to reduce the effect of vertical refraction in precise leveling observation. An example for calculating the refraction correction for one first order leveling line with length of 109 km in Bulgaria is given. Comparison between the obtained errors before and after applying refraction correction has been made. The results show that is important to measure the temperatures simultaneously with the leveling by aspiration thermometer with an accuracy of ±0.1 °C. It is recommended to make experimental research and to adopt appropriate for Bulgaria model for taking into account the influence of vertical refraction.

Surface gravity waves play a major role in the exchange of momentum, heat, energy, and gases between the ocean and the atmosphere. The interaction between currents and waves can lead to variations in the wave direction, frequency, and amplitude. In the present work, we use an ensemble of synthetic currents to force the wave model WAVEWATCH III and assess the relative impact of current divergence and vorticity in modifying several properties of the waves, including direction, period, directional spreading, and significant wave height Hs. We find that the spatial variability of Hs is highly sensitive to the nature of the underlying current and that refraction is the main mechanism leading to gradients of Hs. The results obtained using synthetic currents were used to interpret the response of surface waves to realistic currents by running an additional set of simulations using the llc4320 MITgcm output in the California Current region. Our findings suggest that wave parameters could be used to detect and characterize strong gradients in the velocity field, which is particularly relevant for the Surface Water and Ocean Topography (SWOT) satellite as well as several proposed satellite missions.