Radial Shear Research Articles

Rotational radial shear in the low solar photosphere

Context. Radial differential rotation is an important physical ingredient in stellar dynamo theory. In the case of the Sun, heliosismology techniques have revealed the existence of a near-surface shear layer covering 15–20% of the upper convection zone. It was recently shown that the rotation velocity gradient is not uniform in this layer and that it displays a steep increase in a shallow layer near the surface. Aims. We report the detection of a rotation velocity depth-gradient in the low photosphere that is not accessible to heliosismology techniques. Methods. We applied differential interferometric methods to spectroscopic data obtained with the solar telescope THEMIS, which is equipped with an efficient adaptative optics system. The detection was based on the measurement of a systematic east-west shift between images of the solar granulation at different depths in the FeI 630.15 nm at the center of the solar disk. The same technique was applied to obtain the depth-difference between the images from their perspective shift when they are observed away from the disk center. Both THEMIS and HINODE/SOT data were used for the height-difference measurement, giving similar results. Results. At the center of the solar disk, we measured a systematic retrograde shift of the photospheric granular structures on the east-west axis and with no shift in the north-south direction. The retrograde shift increases linearly with height. We interpret these findings as a signature of a steep decrease in the angular velocity in the low photosphere. Conclusions. The rotational radial shear in the low solar photosphere is likely related to the dynamics of the subsurface shear layer. Its measurement yields a valuable constraint on the numerical simulations of the solar upper convection zone.

Thermodynamics, structural and transport properties of liquid para-Hydrogen: The Feynman–Hibbs molecular dynamics approach

In this study, we use molecular dynamics (MD) simulation to predict the thermodynamics, structural, and transport characteristics of liquid para-hydrogen (para-H[Formula: see text] over a wide temperature range. The Feynman–Hibbs (FH) technique employs Lennard-Jones pair potentials (LJ) which are enhanced by quantum modifications to describe molecular interactions. Results retain the FH’s structural, thermodynamics and transport properties, and the classical LJ models (the radial distribution function, total energy, pressure, potential energy, enthalpy, diffusion coefficient, and shear viscosity). The datasets included in the paper were also considered, along with the experimental data collected, where possible. This work shows that for liquid para-H2, FH approach integrated to classical MD simulation, including quantum corrections yields an excellent accordance with the experimental findings. The FH potential improves concordance with the shear viscosity and diffusion coefficient values, as demonstrated by the results. With greater accuracy to experimental data, the FH Molecular Dynamics approach (FHMD) predicts such values.

The two roles of the SPH Kernel and dissipation on accretion disc modelling in semi-detached Low-Mass Close Binaries

This study addresses two aspects of the SPH technique. The first aspect regards the 3D (2D) numerical integration. The second aspect deals with the necessary damping for handling inviscid flow discontinuities. Accretion discs in Low-Mass Close Binaries (LMCBs) are a context pushing the limit of SPH codes since turbulence, shocks, and shear flows coexist. Thus, an LMCB with high mass-transfer from the inner Lagrangian point is considered. This choice is made for an in-depth understanding of the numerical and physical aspects related to pressure forces computed through SPH Kernel spatial gradients in high-speed collisional flows. In this regard, gas compressibility also plays a role. Firstly, we pay attention to the algebraic term 4πr2 coming from the cubic differential d3r and affecting any 3D SPH integration. This is made through a comparison of physically inviscid SPH structures referring to the same LMCB and mass-transfer conditions. Then, a reformulation of the non-viscous damping is also considered by adopting a Lagrangian-free physical formulation. Inviscid accretion discs should develop a steady toroidal structure because radial transport mechanisms should be excluded by missing any radial shear flow damping. Therefore, thinner discs, also including a steady toroidal ring, identify that SPH inviscid modelling free of any incorrect pressure gradient excess among thick disc structures. This task is simplified since initial conditions deliberately favour thick discs. The physically viscous hydrodynamics of the disc is also addressed by adopting a Prandtl-like turbulent kinematic viscosity coefficient in the Navier–Stokes equations, distinguishing the roles of the bulk and shear viscosities.

Linear and non-linear properties of the Goldreich–Schubert–Fricke instability in stellar interiors with arbitrary local radial and latitudinal differential rotation

ABSTRACT We investigate the linear and non-linear properties of the Goldreich–Schubert–Fricke (GSF) instability in stellar radiative zones with arbitrary local (radial and latitudinal) differential rotation. This instability may lead to turbulence that contributes to the redistribution of angular momentum and chemical composition in stars. In our local Boussinesq model, we investigate varying the orientation of the shear with respect to the ‘effective gravity’, which we describe using the angle ϕ. We first perform an axisymmetric linear analysis to explore the effects of varying ϕ on the local stability of arbitrary differential rotations. We then explore the non-linear hydrodynamical evolution in three dimensions using a modified shearing box. The model exhibits both diffusive GSF instability and a non-diffusive instability that occurs when the Solberg-Høiland criteria are violated. We observe the non-linear development of strong zonal jets (‘layering’ in the angular momentum) with a preferred orientation in both cases, which can considerably enhance turbulent transport. By varying ϕ, we find instability with mixed radial and latitudinal shears transports angular momentum more efficiently (particularly if adiabatically unstable) than cases with purely radial shear (ϕ = 0). By exploring the dependence on box size, we find the transport properties of the GSF instability to be largely insensitive to this, implying we can meaningfully extrapolate our results to stars. However, there is no preferred length-scale for adiabatic instability, which therefore exhibits strong box-size dependence. These instabilities may contribute to the missing angular momentum transport required in red giant and subgiant stars and drive turbulence in the solar tachocline.

Investigation of the flow patterns and mixing efficiency in a stirred tank through particle image velocimetry

BackgroundFluid mixing is a complex process that can be significantly influenced by the impeller type and its geometry. Therefore, the selection of an appropriate impeller for effective mixing is crucial. MethodsA stirred tank setup incorporating various combinations of a lab-manufactured propulsion impeller, propeller boss cap fin (PBCF), and bottom impeller was proposed and experimentally investigated using particle image velocimetry (PIV). Significant findingsThe installation of the PBCF onto the propulsion impeller led to an increase in the radial velocity component and shear rate, along with an enhancement in the flow circulation. Combining the bottom impeller with the propulsion impeller resulted in improved axial recirculation of the fluid. In all experiments involving the bottom impeller, the locations with the highest shear rate and maximum radial velocity components coincided, indicating the dominance of the radial velocity component in determining the shear rate. The mixing efficiency was found to be the highest for the propulsion impeller combined with the PBCF, followed by the propulsion impeller alone and the combination of all three impellers. The use of the bottom impeller alone yielded the lowest mixing efficiency. Additionally, the installation of the propulsion impeller improved the mixing efficiency while causing only a marginal increase in power consumption.

Numerical simulation of workpiece temperature field during radial shear rolling of biomedical Co-Cr-Mo alloy

This paper describes the analysis of temperature field of workpiece during radial shear rolling (RSR) of biomedical Co-28Cr-6Mo alloy. In the process of hot metal forming, the temperature distribution in the deformation zone has a significant influence on the quality and properties of the final product. In some cases, the deformation within a narrow temperature range is required to provide the desired properties. To obtain data on change in temperature, the computer simulation of RSR was carried out using finite element method. According to simulation results, the temperature distribution of bar depending on the variable process parameters such as temperature of workpiece, rotary velocity of rolls, elongation ratio, diameter of workpiece, and temperature of tool was evaluated. It was determined that the most significant parameters influencing on the distribution of the temperature field are the workpiece heating temperature and the rolling speed. The RSR process makes it possible to effectively manage the distribution of temperature field due to selecting technological parameters and, thereby, control the formation of the alloy structure. The data obtained can be useful for developing the modes of RSR of Co–Cr–Mo alloy.

Joint inversion of formation radial shear-velocity profiles by dipole acoustic logging while drilling

Formation properties near a borehole are frequently altered by mechanical damage from drilling, leading to variations of formation elastic velocities in the radial direction. Inversions of radial shear profiles are necessary for a real-time evaluation of the drilling conditions. In this study, we investigate acoustic wave propagation in a logging-while-drilling (LWD) model excited by a dipole transducer in cylindrically layered media. It is revealed that the dispersion characteristics of the dipole waves of the LWD are sensitive to the radial formation velocity variation. Accordingly, we develop a joint inversion method that evaluates radial shear-velocity profiles using the dipole modes of the first and second orders. The propagation of these two modes is strongly influenced by formation alterations, but the inversion results obtained using a single dipole mode indicate ambiguity caused by the nonuniqueness problem. Through our joint inversion, the additional second-order dipole wave can effectively help address the nonuniqueness issue in dipole acoustic logging, although its dispersion features differ in fast and slow formations. It is validated that the joint inversion has considerably improved convergence and accuracy in evaluating the thickness and shear velocity of the altered zone, compared with the estimation by a single acoustic mode. Furthermore, we develop numerical results based on synthetic logging data to demonstrate the feasibility of this inversion in a continuously varying profile, regardless of whether the formation surrounding the borehole is fast or slow. Even when strong drilling noises of low frequencies are added to the receiver signal arrays, the means of joint inversion can remain stable, and the shear-velocity profiles can be evaluated with good precision.

Three-Dimensional Ultrasound Elastography Detects Age-Related Increase in Anterior Peripapillary Sclera and Optic Nerve Head Compression During IOP Elevation.

High-frequency ultrasound elastography offers a tool to resolve the complex and heterogeneous deformation through the full thickness of the optic nerve head (ONH) and peripapillary sclera (PPS). Using this tool, we quantified the three-dimensional deformation of the ONH and PPS in human donor eyes and evaluated age-associated changes. The ONH and PPS in 15 human donor globes were imaged with a 50-MHz ultrasound probe while increasing intraocular pressure (IOP) from 15 to 30 mmHg. Tissue displacements were obtained using correlation-based ultrasound speckle tracking. Three-dimensional spherical strains (radial, circumferential, meridional, and respective shear strains) were calculated for the ONH and PPS volumes segmented from three-dimensional ultrasound images. Age-related trends of different strains in each region of interest were explored. The dominant form of IOP-induced deformation in the ONH and PPS was radial compression. High-magnitude localized out-of-plane shear strains were also observed in both regions. Most strains were concentrated in the anterior one-half of the ONH and PPS. The magnitude of radial and volumetric strains increased with age in the anterior ONH and anterior PPS, indicating greater radial compression and volume loss during IOP elevation in older age. The age-associated increase of radial compression, the predominant form of IOP-induced deformation in anterior ONH and PPS, may underlie age-associated glaucoma risk. High-frequency ultrasound elastography offers a useful tool to quantify all types of deformation comprehensively in all regions of ONH and PPS, which may improve our understanding of the biomechanical factors contributing to glaucoma risk.

Recording of incoherent vector holograms using elements of the spatial cross-spectral density matrix

We present an approach to record incoherent vector holograms using a highly stable field-based interferometer employing radial shearing. The vector holograms are recorded as the elements of the 2 × 2 cross-spectral density (CSD) matrix and reconstruction of the object encoded into these holograms is demonstrated by digitally propagating the elements of the CSD matrix. The CSD matrix contains its elements in the form of a complex spatial coherence function and is connected with an incoherent vector source by the vectorial van Cittert-Zernike theorem. The experimental measurement of the two-dimensional distributions of the complex elements of the CSD matrix is realized by a Sagnac radial shearing interferometer with a phase-shifting approach. The five-step phase-shifting technique is used to measure the fringe visibility and corresponding phase which give the complex elements of the CSD matrix. Recording of incoherent vector holograms is demonstrated from the experimentally recovered elements of the CSD matrix and results are presented for two different incoherent sources, namely polarized and unpolarized. The complex nature of the CSD matrix elements helps in the digital reconstruction and focusing of the incoherent source.

Impact of edge biasing on the cross-field transport and power spectra

The impact of positive and negative edge biasing on the interchange plasma turbulence in the edge and scrape-off layer (SOL) regions of a tokamak is assessed by comparing numerical simulation results with and without any biasing. The concomitant modifications in the radial transport and power spectra are also analyzed. It is found that a positive bias shifts the peak of the ky-spectra toward a lower ky value in the edge region, but no such shift takes place in the SOL region. A negative bias produces a negligible shift. The heat and particle fluxes in the edge region are seen to increase with the radial electric field shear in the region where a flow reversal takes place. Elsewhere, the fluxes decrease with an increase in the shear. The heat and particle loads per unit time on the limiter/divertor material plates decrease with the biasing voltages in comparison to those w/o biasing, but the load intensities increase. It is found that the blob fraction decreases with the radial electric field shear, but at lower radial positions around the biasing region, it increases from −16 to +64 V.

Structure and strength of Al-Mn-Cu-Zr-Cr-Fe ALTEC alloy after radial-shear rolling

The phase composition and structure of as-cast and deformed Al-1.53Cu-1.66Mn-0.38Zr-0.15Cr-0.15Fe (wt.%) were investigated. The radial shear rolling was used for the deformation of the alloy. The structure of as-cast alloy consists of aluminum solid solution, eutectic Al6(FeMn) and Al2Cu, as well as Al7Cr and Al20Cu2Mn3 dispersive particles. It is assumed that radial shear rolling results in the refinement and partial dissolution of Al20Cu2Mn3 dispersoids. Along with this, significant grain refinement was established after deformation. The average grain-subgrain size in the alloy after deformation is 1.6 μm. After deformation the alloy has the yield stress of 83 MPa and ultimate strength of 216 MPa. The elongation to failure of the deformed alloy is 25 %. Owing to the partial deformation induced dissolution of the aluminides and supersaturated solid solution formation, there is a potential for strengthening upon heat treatment of the alloy and improvement of its thermal resistance.

Evidence of a Quasiperiodic Global-scale Oscillation in the Near-surface Shear Layer of the Sun

We present evidence of hitherto undiscovered global-scale oscillations in the near-surface shear layer of the Sun. These oscillations are seen as large-scale variations of radial shear in both the zonal and meridional flows relative to their mean values. The variations cover all or most of a visible hemisphere, and reverse with a timescale on the order of a solar rotation. A large annual variation in the meridional shear anomaly is understandable in terms of the tilt of the rotation axis, but the rapid oscillations of the shear anomalies in both zonal and the meridional directions appear to be modulated in a more complex, not-quite-annual way, although the latter are also strongly modulated by the projected rotational axis angle. Small-scale anomalies in the neighborhood of active regions lend support to their solar origin and physical interpretation. These results were obtained by analyzing ring-diagram fits of low-order modes in high-resolution Doppler data from the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory.

The performance of equilibrium radial electric field shear on microturbulence with different magnetic shears in tokamak plasmas

Global gyrokinetic particle simulations show that equilibrium radial electric field (E r ) shear reduces the linear growth rate, ion heat conductivity, and nonlinear turbulence amplitude for both the ion temperature gradient (ITG) and kinetic ballooning mode (KBM) microturbulence by tilting the poloidal mode structure. The increase in the magnetic shear enhances the stabilizing performance of the E r shear on linear growth rate for the ITG case but has no effect on that for the KBM case. The radial correlation length of the ITG turbulence is decreased by increasing the magnetic shear in a weak ion diamagnetic flow shear condition with low β, leading to a reduction in the effective E × B shearing rate, which weakens the suppression performance of the E r shear on the ITG turbulence amplitude. In contrast, under a larger ion diamagnetic shear flow for higher β, an increase in magnetic shear strengthens the suppression performance of the E r shear on the KBM turbulence amplitude due to an increase in the effective shearing rate by increasing the radial correlation length of the turbulence.

Mean flow and Convective instability analysis of the BEK and related rotating boundary layer flows subject to a uniform static magnetic field

This study examines the convective instability of the hydromagnetic Bödewadt, Ekman, and von Kármán (BEK) rotating system under the low magnetic Reynolds number approximation. The computations for the mean flow are carried out for different magnetic parameters using MATLAB for several flows of the BEK family. The equations for the linear instability are derived and then solved through the Chebyshev-spectral method for both Type-I (Inviscid) and Type-II (viscous) modes. It is observed that the Rossby number, the Reynolds number, and the magnetic parameter characterize the stability of the hydromagnetic BEK flows. The Reynolds number is based on the dimensionless radial location at the disk while the Rossby number is the ratio of the difference between the angular speeds of fluid and disk and the angular speed of the disk. The magnetic number is the ratio of magnetic field strength and the system rotation rate. The analysis reveals a stabilizing effect of the magnetic parameter on the Type-I modes for Rossby numbers in the range [−1,1]. Further, the Type-II modes disappear upon elevating the magnetic parameter in the aforementioned range of the Rossby number. The growth rates, |αi|, also diminish upon increasing the magnetic parameter. The computations for mean flow reveal that the radial wall shear stress diminishes upon elevating the strength of the applied magnetic field. However, a reverse trend is noted for the azimuthal wall shear stress which indicates an increase in the torque on the disk with enhancing the intensity of the magnetic field.

The Effect of Radial-Shear Rolling Deformation Processing on the Structure and Properties of Zr-2.5Nb Alloy.

The rheological properties of the Zr-2.5Nb alloy by the strain rate range of 0.5-15 s-1 and by the temperature range of 20-770 °C was studied. The dilatometric method for phase states temperature ranges was experimentally determined. A material properties database for computer FEM simulation regards the indicated temperature-velocity ranges were created. Using this database and DEFORM-3D FEM-softpack, the radial shear rolling complex process numerical simulation was carried out. The contributed conditions for the ultrafine-grained state alloy structure refinement were determined. Based on the simulation results, a full-scale experiment of Zr-2.5Nb rod rolling a on a radial-shear rolling mill RSP-14/40 was carried out. It takes in seven passes from a diameter of 37-20 mm with a total diameter reduction ε = 85%. According to this case simulation data, the total equivalent strain in the most processed peripheral zone 27.5 mm/mm was reached. Due to the complex vortex metal flow, the equivalent strain over the section distribution was uneven with a gradient reducing towards the axial zone. This fact should have a deep effect on the structure change. Changes and structure gradient by sample section EBSD mapping with 2 mm resolution were studied. The microhardness section gradient by the HV 0.5 method was also studied. The axial and central zones of the sample by the TEM method were studied. The rod section structure has an expressed gradient from the formed equiaxed ultrafine-grained (UFG) structure on a few outer millimeters of the peripheral section to the elongated rolling texture in the center of the bar. The work shows the possibility of processing with the gradient structure obtaining and enhanced properties for the Zr-2.5Nb alloy, and a database for this alloy FEM numerical simulations are also presents.

Rearrangement of GO nanosheets with inner and outer forces under high-speed spin for supercapacitor

The self-standing graphene membranes are considered as ideal electrode materials for supercapacitors. However, maintaining highly regularized and uniform graphene membranes with satisfied electrochemical performance is still a challenge. Herein, with the chelation of metal cation and the radial shear force introduced by high-speed spinning, the uniform interlayer channels and shrunken cracks between adjacent nanosheets can be achieved in the metal-intercalated graphene oxide (GO) membranes, thus realizing regularization both in normal and radial direction. With the promotion in electron transfer and electrolyte penetration, the iron cross-linked GO membrane with spin coating for 40 cycles exhibits a high specific capacitance (427 F g−1 at 1 A g−1) and rate capability (42.6% capacitance retention from 1 to 40 A g−1), as well as excellent cyclic capability (90.5% capacitance retention after 20,000 cycles). Particularly, a 21% increasement in capacitance can be achieved after high-speed spinning treatment. Moreover, the spin regularization strategy can be extended to GO membranes cross-linked by various multi-valence metal cations, the electrochemical performance of metal-cation cross-linked GO membrane electrodes after high-speed spinning treatment can also be improved obviously. Therefore, this paper provides a novel method to fabricate highly ordered GO membranes with promising electrochemical performance, which presents an immense potential application in membrane materials applied in energy storage, separation and catalysis.

Single-shot isotropic differential interference contrast microscopy

Differential interference contrast (DIC) microscopy allows high-contrast, low-phototoxicity, and label-free imaging of transparent biological objects, and has been applied in the field of cellular morphology, cell segmentation, particle tracking, optical measurement and others. Commercial DIC microscopy based on Nomarski or Wollaston prism resorts to the interference of two polarized waves with a lateral differential offset (shear) and axial phase shift (bias). However, the shear generated by these prisms is limited to the rectilinear direction, unfortunately resulting in anisotropic contrast imaging. Here we propose an ultracompact metasurface-assisted isotropic DIC (i-DIC) microscopy based on a grand original pattern of radial shear interferometry, that converts the rectilinear shear into rotationally symmetric along radial direction, enabling single-shot isotropic imaging capabilities. The i-DIC presents a complementary fusion of typical meta-optics, traditional microscopes and integrated optical system, and showcases the promising and synergetic advancements in edge detection, particle motion tracking, and label-free cellular imaging.

Strain and Strain Rate Tensor Mapping of Medial Gastrocnemius at Submaximal Isometric Contraction and Three Ankle Angles.

The aim of this study is to analyze the muscle kinematics of the medial gastrocnemius (MG) during submaximal isometric contractions and to explore the relationship between deformation and force generated at plantarflexed (PF), neutral (N) and dorsiflexed (DF) ankle angles. Strain and Strain Rate (SR) tensors were calculated from velocity-encoded magnetic resonance phase-contrast images in six young men acquired during 25% and 50% Maximum Voluntary Contraction (MVC). Strain and SR indices as well as force normalized values were statistically analyzed using two-way repeated measures ANOVA for differences with force level and ankle angle. An exploratory analysis of differences between absolute values of longitudinal compressive strain (Eλ1) and radial expansion strains (Eλ2) and maximum shear strain (Emax) based on paired t-test was also performed for each ankle angle. Compressive strains/SRs were significantly lower at 25%MVC. Normalized strains/SR were significantly different between %MVC and ankle angles with lowest values for DF. Absolute values of Eλ2 and Emax were significantly higher than Eλ1 for DF suggesting higher deformation asymmetry and higher shear strain, respectively. In addition to the known optimum muscle fiber length, the study identified two potential new causes of increased force generation at dorsiflexion ankle angle, higher fiber cross-section deformation asymmetry and higher shear strains.

Effect of radial-shear rolling on particle’s morphology and mechanical properties of AA7075 alloy

Effect of radial shear rolling on the morphology of intermetallic particles, and the mechanical properties of 7075 alloy at different processing temperatures and heat treatment after deformation was investigated. The results were consistent with data on metallographic investigation of phase particle shape, counts, and distribution. It was found that the formation, quantitative distribution, and circularity of particles at the surface and in the centre of the bar depended on the processing temperature and temperature gradient between surface and centre and were defined with a scheme of stresses in the deformation zone. The values of strength properties for all bars obtained by RSR depended on the processing regimes, while plasticity (elongation to failure δ = 14%–20%) increased with the growth of processing temperature. Article highlights Radial shear rolling makes it possible to obtain aluminium alloy bars with a gradient structure and a combination of high strength and ductility. The influence of the RSR method is reflected in the nature of the distribution of dispersive particles in the matrix of alloy. Mechanical properties of bars subjected to the RSR method depend on the initial processing regimes, while the level of plasticity increases with the growth of processing temperature.

Taylor-Couette flow for astrophysical purposes.

A concise review is given of astrophysically motivated experimental and theoretical research on Taylor-Couette flow. The flows of interest rotate differentially with the inner cylinder faster than the outer, but are linearly stable against Rayleigh's inviscid centrifugal instability. At shear Reynolds numbers as large as [Formula: see text], hydrodynamic flows of this type (quasi-Keplerian) appear to be nonlinearly stable: no turbulence is seen that cannot be attributed to interaction with the axial boundaries, rather than the radial shear itself. Direct numerical simulations agree, although they cannot yet reach such high Reynolds numbers. This result indicates that accretion-disc turbulence is not purely hydrodynamic in origin, at least insofar as it is driven by radial shear. Theory, however, predicts linear magnetohydrodynamic (MHD) instabilities in astrophysical discs: in particular, the standard magnetorotational instability (SMRI). MHD Taylor-Couette experiments aimed at SMRI are challenged by the low magnetic Prandtl numbers of liquid metals. High fluid Reynolds numbers and careful control of the axial boundaries are required. The quest for laboratory SMRI has been rewarded with the discovery of some interesting inductionless cousins of SMRI, and with the recently reported success in demonstrating SMRI itself using conducting axial boundaries. Some outstanding questions and near-future prospects are discussed, especially in connection with astrophysics. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (Part 2)'.