Azimuthal Behavior Research Articles

Insightful inspection of the nonlinear instability of an azimuthal disturbance separating two rotating magnetic liquid columns

The nonlinear stability examination of two revolving magnetized liquid columns connecting two completely submerged fluids in a permeable region is the aim of the existing paper. Two endless vertical cylinders occupied with two magnetic fluids make up the present structure. Significantly, the disturbance at the border displays an azimuthal behavior. The entire structure is activated by an azimuthal unchanging magnetic field (MF). The increasing interest in the atmospheric and oceanic dynamics is the primary motivation in exploring this problem. To relax the complication of the mathematical processes, the viscous potential theory (VPT) is established. The motion is assessed using three basic coexistent field formulations: Maxwell's formula, Brinkman's formula, and the continuity condition, in the construction of the Coriolis force and centrifugal implications. The explanations of the linearized formula of motion produce a nonlinear categorizing diffusion structure because of the implications of the nonlinear boundary conditions (BCs). The non-perturbative approach (NPA) based on the He's frequency formulation (HFF) is employed to transform the nonlinear characteristic ordinary differential equation (ODE) into a linear one. A short description of the NPA is also presented. The nonlinear ODE with real and imaginary coefficients is exposed by the stability analysis. The stability requirements are implemented using only a nonlinear analysis. As demonstrated, as an unusual state, it is exposed that ignoring the Weber number removes all complex items of the nonlinear formulation. Physically, this means the absence of the angular velocities from the physical model. For both the real and complex situations of the original equation, the stability remains unchanged. It is found that the azimuthal MF, rotating parameter, and Darcy’s numeral have a maintenance impact. On the other hand, the azimuthal wave numeral has a destabilizing one. Several polar designs are drawn to agreement the stability situations.

Effects of Directional Wave Spectra on the Modeling of Ocean Radar Backscatter at Various Azimuth Angles by a Modified Two-Scale Method

Knowledge of the ocean backscatter at various azimuth angles is critical to the radar detection of the ocean environment. In this study, the modified two-scale model (TSM), which introduces a correction term in the conventional TSM, is improved based on the empirical model, CMOD5.n. Then, the influences of different directional wave spectra on the prediction of azimuthal behavior of ocean radar backscatter are investigated by comparing the simulated results with CMOD5.n and the Advanced Scatterometer (ASCAT) measurements. The results show that the overall performance of the single spectra of D, A, E, and H18 and the composite spectra of AH18 and AEH18 in predicting ocean backscatter are different at different wind speeds and incidence angles. Generally, the AH18 spectrum has better performance at low and moderate wind speeds, while the A spectrum works better at high wind speed. Nevertheless, the wave spectra have little effect on the prediction of the azimuthal fluctuation of scattering, which is highly dependent on the directional spreading function. The relative patterns of azimuthal undulation produced by different spreading functions are rather different at different wind speeds, but similar under different incidence angles. The Gaussian spreading function generally has better performance in predicting the azimuthal fluctuation of scattering.

Hydrogenation effect on magnetic single domains of high-temperature-deposited uniform CoxPd1−x/MoS2 flakes

In this study, 6-nm CoxPd1−x alloy films were deposited on MoS2 flakes at a high temperature (HT) of 200 °C. The morphology and magnetic properties of these flakes was studied. In contrast to the nanoparticle assembly fabricated through room-temperature deposition, HT growth led to a relatively uniform coverage on MoS2 flakes with a roughness of less than 1 nm. The flat CoxPd1−x alloy films form magnetic single domains on individual MoS2 flakes. For 6-nm Co0.5Pd0.5 and Co0.35Pd0.65, the magnetic coercivity (Hc) was approximately 50 Oe. Co0.5Pd0.5/MoS2 exhibited more distinct azimuthal angle-dependent magnetic behavior than that of Co0.35Pd0.65/MoS2. The different angle-dependent Hc variation for various MoS2 flakes could be attributed to the shape and demagnetization effect at the edge. After hydrogen exposure, the Hc of Co0.5Pd0.5/MoS2 was enhanced by 30% ± 10% and the magnetic domains extended over the MoS2 flakes, which indicated that H absorption in Co0.5Pd0.5 bridges magnetic coupling across the MoS2 edge.

Nonlinear hydromagnetic instability of oscillatory rotating rigid-fluid columns

The current paper is concerned with the nonlinear stability analysis of rotating magnetic fluid columns. The rotation sources are a mixture of both uniform and oscillating behavior. The motivation behind tackling this topic is the increasing interest in atmospheric and oceanic motions. The system consists of two magnetic phase fluid that fills two infinite vertical cylinders. An azimuthal uniform magnetic field is penetrated on the system. The governing equations of motion, in terms of the Coriolis force and reduced pressure, along with Maxwell’s equation in the quasi-static approximations are considered. Consequently, the disturbance of the interface has an azimuthal behavior. The fluids are fully saturated in porous media. In light of the implication of the nonlinear boundary conditions, the solutions of the linearized equations of motion resulted in a nonlinear characteristic dispersion equation. Utilizing the homotopy perturbation technique, this equation is analyzed. A modification of the latter equation is made to seem like a nonlinear Klein–Gordon equation. The stability criteria are realized in linear as well as nonlinear approaches. A set of diagrams is graphed to illustrate the effects of several non-dimensional numbers on the stability profile in resonance as well as non-resonance cases.

Flow dynamics and azimuthal behavior of the self-excited acoustic modes in axisymmetric shallow cavities

Self-excitation of acoustic resonance in axisymmetric cavities can lead to a complex flow–acoustic coupling, which may result in severe noise generation. In this work, a large eddy simulation is performed to model the different flow–sound coupling mechanisms during the self-excitation of various excitable acoustic modes in an axisymmetric shallow cavity configuration with an aspect ratio of L/d = 1 over the lock-in region. The compressible Navier–Stokes equations are solved at a resolution sufficient to capture the flow and the acoustic dynamics. The excitation of three acoustic modes of different aerodynamic characteristics over the range of the tested flow velocities was observed. These modes are a stationary diametral mode, a spinning diametral mode, and a longitudinal mode. The initiation and separation of vortices over the cavity mouth accompanying the self-excitation of each mode involve different dynamics. If two antisymmetric series of vortical crescents separate successively at the leading edge, a stationary acoustic mode is excited. The formation of a continuously rotating helical vortex, connecting the leading edge and the trailing edge, leads to the excitation of the diametral spinning mode. The excitation of the longitudinal mode is associated with symmetric rings of vortices. Complex patterns of flow velocities and Reynolds stresses in the circumferential direction are observed for the diametral modes but not for the longitudinal mode. In all cases, the excitation of acoustic resonance requires a synchronization of the vortex separation and impingement processes, which is necessary for efficient feedback to sustain the flow–sound coupling mechanism.

The effects of azimuthal anisotropy on 3D and 4D seismic amplitude variation with offset responses

Seismic reflection amplitude variation with source-receiver offset (AVO) is an important tool in hydrocarbon exploration and reservoir monitoring, due to its sensitivity to elastic rock properties that are affected by changes in pore-fluid saturation and pressure. In most cases, 4D seismic feasibility studies and interpretation analyses assume that the earth is isotropic. This assumption can be problematic because it is becoming increasingly apparent that anisotropic rocks are quite common. Furthermore, the presence of even small amounts of anisotropy can have significant effects on AVO, and in the presence of azimuthal anisotropy the AVO will vary with azimuth. We determine that if 4D seismic surveys are acquired with different survey azimuths in the presence of azimuthal anisotropy, it is likely that 4D AVO interpretations will be significantly affected, leading to incorrect or nonphysical interpretations. This possibility is especially apparent in the context of the North West Shelf, Australia, where significant stress-induced azimuthal anisotropy is prevalent in sandstone formations that form the reservoir rocks. We model 4D AVO responses with and without azimuthal anisotropy effects for a variety of pore-fluid saturation and pressure change scenarios using average reservoir properties from the Stybarrow field, Australia. We found that azimuthal anisotropy does not affect the small reflection angles of the 4D AVO response, but it has a significant effect on larger reflection angles when comparing 4D surveys acquired at different acquisition azimuths. This azimuthal behavior leads to what we call an “apparent 4D effect” when reservoir properties do not change and a “contaminated 4D effect” when reservoir properties do change. We found real data examples in which we determine that the 4D AVO response must incorporate azimuthal anisotropy to be explained correctly. Our results further emphasize the importance of repeating survey acquisition azimuths whenever possible and/or accurately accounting for azimuthal anisotropy effects.

Azimuthal dependence of the acoustic field in a year long Canada Basin Acoustic Propagation Experiment

As in the mid-latitudes, the variability of the oceanography in the arctic ocean causes azimuthal dependent acoustic fields induced by the environmental parameters, such as the variable sound speed profile and bathymetry. Preliminary analysis of a year-long experimental data from “deep-to-shallow” and the “shallow-water” Canada Basin Acoustic Propagation Experiment (SW CANAPE) shows strong azimuthal variability of broadband signals recorded on 11 spatially distributed acoustic receiver arrays on the Chukchi shelf from September 2016 to October 2017. Particular attention is paid on geotimes pertaining to the variable sound speed profiles around the dynamic shelf-break region. Although acoustic modeling of the propagation requires a physics based ocean model for a complete modeling exercise, preliminary determination of the azimuthal behavior of broadband propagation is conducted using multiple two-dimensional Parabolic Equation (Nx2D) with the collected oceanographic data. Calculations for long-range, as well as short-range, source-receiver pairs in the SW CANAPE data show that azimuthal variabilities occur frequently and are related to the spatial and temporal characteristics of signal dispersion for different range and geotime scales. [Work supported by ONR.]

Influence of mesoporous or parasitic BiFeO3 structural state on the magnetization reversal in multiferroic BiFeO3/Ni81Fe19 polycrystalline bilayers

Coupled ferromagnetic and antiferromagnetic bilayers are an important class of materials that allow manipulating magnetic properties, including the interfacial exchange bias phenomenon. Bismuth ferrite, BiFeO3, is the most studied single-phase magnetoelectric multiferroic due to its unique ferroelectric and antiferromagnetic orderings well above room temperature. We report on a systematic experimental study regarding the direct correlation between the Bi2O3 parasitic phase concentration in the BiFeO3 and the magnetic properties of the polycrystalline heterostructure BiFeO3/Ni81Fe19 deposited via magnetron sputtering. It was found that the macroscopic exchange field, that arises from exchange bias coupling, is zero for phase-pure BiFeO3 and increases up to 18 Oe on increasing the concentration of Bi2O3. This trend is in agreement with the azimuthal behavior of the magnetization reversal. The structural characterization also indicates that phase-pure BiFeO3 has a disordered mesoporous structure. The influence of the Bi2O3 parasitic phase and mesoporous state, that is known to exist and introduce defects in the polycrystalline bilayers of BiFeO3/Ni81Fe19, on the magnetization reversal and exchange bias coupling is reported for the first time in this study.

Application of perturbation theory to a P-wave eikonal equation in orthorhombic media

The P-wave eikonal equation for orthorhombic (ORT) anisotropic media is a highly nonlinear partial differential equation requiring the solution of a sixth-order polynomial to obtain traveltimes, resulting in complex and time-consuming numerical solutions. To alleviate this complexity, we approximate the solution of this equation by applying a multiparametric perturbation approach. We also investigated the sensitivity of traveltime surfaces in ORT media with respect to three anelliptic parameters. As a result, a simple and accurate P-wave traveltime approximation valid for ORT media was derived. Two different possible anelliptic parameterizations were compared. One of the parameterizations includes anelliptic parameters defined at zero offset: [Formula: see text], [Formula: see text], and [Formula: see text]. Another parameterization includes anelliptic parameters defined for all symmetry planes: [Formula: see text], [Formula: see text], and [Formula: see text]. The azimuthal behavior of sensitivity coefficients with different parameterizations was used to analyze the crosstalk between anelliptic parameters.

Azimuthal Correlation and Collective Behavior in Nucleus–Nucleus Collisions

Azimuthal Correlation and Collective Behavior in Nucleus–Nucleus Collisions

Experimental evidence for exchange bias in polycrystalline BiFeO3/Ni81Fe19 thin films

We report on experimental evidence of exchange bias between a polycrystalline antiferromagnetic BiFeO3 and a ferromagnetic Ni81Fe19 film at room temperature. The measured 17 Oe hysteresis loop shift corresponds to an exchange energy of 11×10-3 erg/cm2 per unit area of the interface coupling the two films, which is comparable with those observed for similar epitaxially-grown systems. The azimuthal behavior of the longitudinal and transverse magnetization components revealed the presence of induced unidirectional and biquadratic anisotropies. A misalignment between unidirectional and biquadratic anisotropy axes was also observed.

Generalized (two-point) stokes-parameters representation in terms of the radial and azimuthal field components

Within the paraxial framework, a generalization of the Stokes representation is introduced in terms of the radial and azimuthal field structure of the beam cross-section. These generalized parameters depend on two spatial variables and are closely related with the cross-spectral density (CSD) matrix of the field. The propagation law of such parameters through general first-order optical systems is also given. It allows to describe, in terms of the radial and azimuthal field components, the coherence and polarization behavior of partially-polarized, partially-coherent beams.

A study of a LEIS azimuthal scan behavior: Classical dynamics simulation

A classical dynamics simulation of the low energy He + ion scattering on a Cu(100) surface was carried out for a more detailed explanation of LEIS azimuthal scans with respect to a previous work. The Thomas-Fermi–Molière screened potential was used in the calculations to describe interatomic repulsive interactions. A stopping power and thermal vibrations of target atoms were involved as well. The results of the simulations were compared with the experiment and thus the correction factors of interatomic scans found. The main features of the calculated azimuthal scans N( Φ) are discussed and the relevant parts compared. Additionally, ion blocking effects were studied by the analysis of N Φ , β distribution of ions backscattered into the whole half-space above the Cu(100) surface. This gave us a more transparent view into the low energy ion scattering processes on this periodic surface.

Improvements of Sound Localization Abilities by the Facial Ruff of the Barn Owl (Tyto alba) as Demonstrated by Virtual Ruff Removal

BackgroundWhen sound arrives at the eardrum it has already been filtered by the body, head, and outer ear. This process is mathematically described by the head-related transfer functions (HRTFs), which are characteristic for the spatial position of a sound source and for the individual ear. HRTFs in the barn owl (Tyto alba) are also shaped by the facial ruff, a specialization that alters interaural time differences (ITD), interaural intensity differences (ILD), and the frequency spectrum of the incoming sound to improve sound localization. Here we created novel stimuli to simulate the removal of the barn owl's ruff in a virtual acoustic environment, thus creating a situation similar to passive listening in other animals, and used these stimuli in behavioral tests.Methodology/Principal FindingsHRTFs were recorded from an owl before and after removal of the ruff feathers. Normal and ruff-removed conditions were created by filtering broadband noise with the HRTFs. Under normal virtual conditions, no differences in azimuthal head-turning behavior between individualized and non-individualized HRTFs were observed. The owls were able to respond differently to stimuli from the back than to stimuli from the front having the same ITD. By contrast, such a discrimination was not possible after the virtual removal of the ruff. Elevational head-turn angles were (slightly) smaller with non-individualized than with individualized HRTFs. The removal of the ruff resulted in a large decrease in elevational head-turning amplitudes.Conclusions/SignificanceThe facial ruff a) improves azimuthal sound localization by increasing the ITD range and b) improves elevational sound localization in the frontal field by introducing a shift of iso–ILD lines out of the midsagittal plane, which causes ILDs to increase with increasing stimulus elevation. The changes at the behavioral level could be related to the changes in the binaural physical parameters that occurred after the virtual removal of the ruff. These data provide new insights into the function of external hearing structures and open up the possibility to apply the results on autonomous agents, creation of virtual auditory environments for humans, or in hearing aids.

Resonant x-ray scattering study of layeredTbBaCo2O5.5

Resonant x-ray scattering (RXS) experiments have been performed at the Co $K$ edge in the ${\text{TbBaCo}}_{2}{\text{O}}_{5.5}$ sample. Linear scans in the reciprocal space along $[0k0]$ and $[h00]$ directions were carried out at different energies between 350 and 90 K. This temperature range probes the metallic, insulating, ferrimagnetic, and antiferromagnetic phases. No new reflections, either resonant or not, were detected in any phase transition. We have found strong resonances close to the absorption edge energy for $(0k0)$ reflections with $k$ odd. These resonances remain almost constant for the different phases. The cusp of the resonant scattering is either up---(0 3 0) and (0 7 0)---or down---(0 1 0) and (0 5 0)---depending on the $k$ value, and this behavior was completely explained in the frame of the crystal structure and the atomic position of the Tb and Ba atoms. The occurrence of the resonant scattering and its azimuthal behavior has been explained in terms of the anisotropy of the tensor of susceptibility (ATS reflections). RXS comes from the presence of two different environments for the Co ions, octahedra and pyramids of oxygens, ordered along the $b$ axis. No evidence for further contributions, such as an orbital ordering, has been found in these experiments in the insulating low temperature phase.

Microwave propagation in ferromagnetic semiconductors

Ferromagnetic semiconductors may exhibit gyroelectric and gyromagnetic behavior at the same time. In order to treat the Maxwell equations and the propagation in such semiconductors, the description of the two phenomena are unified in a general framework, concerning gyroelectromagnetic media. This allows one to describe the modes in waveguides with a gyroelectromagnetic core, so the high azimuthal index mode behavior may be predicted in ferromagnetic semiconductors, focusing on microwave frequency domain towards technological applications.

Photoalignment in Ultrathin Films of a Layer-by-Layer Deposited Water-Soluble Azobenzene Dye

The photoalignment of alternate layer-by-layer (LBL) deposited water-soluble azobenzene dye, direct red 80 (DR80), and polycations have been investigated. The ultrathin films were probed by polarized irradiation, UV−vis spectroscopy, and angle-dependent optical retardation measurements using a hybrid liquid crystal (LC) cell. Dye aggregates within layers were found to reorient anisotropically with polarized irradiated visible light. The selective photoisomerization process primarily enhances the E-isomer, giving high dichroism with the long axes of the azobenzene dye oriented perpendicular to the polarization vector of irradiated light (actinic light). The degree of photoalignment was dependent on the number of adsorbed layers, aggregation behavior, and type of polycation pairs in contrast to spin-coated or Langmuir−Blodgett (LB) films. Atomic force microscopy (AFM) before and after photoisomerization showed lateral expansion of the morphological features consistent with greater anisotropic ordering. These results correlated with the in-plane azimuthal LC photoalignment behavior in hybrid LC cells. Interesting trends were observed, including thickness-dependent photoalignment behavior, different irradiation stabilities, phase shift, and read−write capabilities as photoactive ultrathin films.

A physical model for the narrowing of the directional sea wave spectra in the short gravity to gravity‐capillary range

This paper gives the description of a theoretical model of the sea wave spectrum for short gravity to gravity‐capillary waves. It accounts for wind forcing, viscous damping, dissipation due to white capping, and nonlinear resonant three‐wave interactions, which are expected to be dominating over the four‐wave interactions near the gravity‐capillary transition. It is based upon the approach used by Janssen et al. [1998] for their physical omnidirectional spectral model of the sea surface. It is shown that by adding the momentum balance equation to the energy balance equation, the approach used by Janssen et al. to produce their omnidirectional sea wave spectral model may be generalized to obtain a two‐dimensional sea wave spectrum. The azimuthal behavior of the inferred sea wave spectrum is examined and shown to be consistent with spectral anisotropy of the sea wave spectrum observed at decimeter to centimeter wavelengths.

Shear zones in the Proterozoic lithosphere of the Arabian Shield and the nature of the Hales discontinuity

Seismic velocity discontinuities are commonly found within the upper 100 km of the mantle lithosphere, with great variability in their depth, lateral extent, and the polarity of velocity jump. Among the more commonly observed is the ‘80 km’ or Hales discontinuity, identified in a variety of tectonic environments, and sometimes associated with seismic anisotropy. Teleseismic receiver functions for Global Seismographic Network station RAYN on the eastern edge of the Arabian Shield contain a strong converted-phase P Hs that we believe arises from the Hales discontinuity at the depth of 70 km. On the basis of the polarization, azimuthal behavior and frequency dependence of P Hs, we characterize the Hales discontinuity as marking an upper boundary of a zone of depth-dependent anisotropy within the upper mantle. The RAYN receiver functions indicate a similar zone at the crust-mantle transition at 40 km. Forward modeling in simple one-dimensional anisotropic models indicates that the receiver functions require, assuming hexagonal anisotropy, an inclined symmetry-axis with N–S strike. In our preferred model there are two anisotropic zones bounded, respectively, by the sharp Moho and the Hales discontinuities on the top. Smooth gradients of anisotropic properties extend beneath the discontinuities. Within both zones the anisotropic symmetry axes, indicative of systematic fabric in the olivine-dominated upper mantle material, are oriented along the N–S direction (±10°), and are tilted from the vertical 50° toward the south. We propose that these regions of coherent fabric within the upper mantle represent shear zones developed during late Proterozoic continent–continent collision, when the Ar-Rayn tectonic block underwent northward ‘escape’ along the northern flank of the Najd fault system.

Birefringence parameters: Indicators of anisotropic symmetry systems

The difference in travel times between split shear waves (travel-time splitting) in anisotropic media depends on nine combinations of the density normalized elastic parameters (the birefringence parameters). These combinations are all zero in isotropic media, where there is no shear-wave splitting. The number of nonzero birefringence parameters increases with decreasing symmetry elements in the medium: from one in cubic media to nine in triclinic media. The birefringence parameters may be recovered from travel-time splitting observations. Their azimuthal behavior may then be interpreted in terms of crack orientation (strike and dip directions).