Anisotropic Orientation Research Articles

Interfacial engineering manipulation of magnetic anisotropy evolution via orbital reconstruction in low-dimensional manganite superlattices

Control of magnetic anisotropy in low-dimensional systems is of paramount importance in terms of their fundamental and technological perspectives. La0.7Sr0.3MnO3 (LSMO) is a ferromagnetic half-metal with a high Curie temperature and many efforts have been made to control its magnetic anisotropy. However, the relationship between the evolution of the magnetic anisotropy orientation and the electronic structure of low-dimensional LSMO still remains poorly understood. Here, the high-quality superlattices comprised of LSMO and SrMnO3 (SMO) layers are synthesized with a compatible structure at the atomic scale. Their magnetic anisotropy is gradually varied from planar to perpendicular by increasing the SMO thickness, and the special fourfold magnetic anisotropy is also observed at the intermediate superlattice thickness. The evolution of the magnetic anisotropy in these systems is confirmed by the electronic transport and magnetic measurements. Moreover, X-ray linear dichroism measurements and first-principles calculations reveal the interfacial orbital reconstruction with the in-plane to out-of-plane magnetic reorientation transition. Therefore, a new microscopic method for magnetic anisotropy manipulation is developed in the present study, enabling discovery of novel phenomena as well as control of the magnetic properties.

Depth-dependent crustal azimuthal anisotropy in the Salton Trough, southern California

We present new crustal models of azimuthally anisotropic P-wave velocity, isotropic P-wave velocity (Vp), isotropic S-wave velocity (Vs) and Vp/Vs ratio for the Salton Trough. High Vp/Vs ratio is revealed at depths of 2–8 km along the San Andreas Fault, implying the possible presence of fluids. High Vp and high Vp/Vs ratio (>1.8) structures of the mid-lower crust beneath the Salton Trough possibly reflect the underplated gabbroic rocks as a result of the extension-induced partial melting of the upwelling asthenospheric materials. The fast velocity directions (FVDs) generally correlate with the direction of the maximum horizontal compressive stress except that fault-parallel FVDs are found at main fault traces. However, the FVDs in the Salton Trough show complex features. The northern Slaton Trough basin (the northern Salton Sea basin and Coachella Valley basin) is dominated by NW-SE FVDs, which are possibly due to the active compression happening there. E-W oriented FVDs predominate the upper crust of the southern Salton Trough basin (the southern Salton Sea basin and Imperial Valley basin), possibly due to faulting and/or block rotation. As the depth increases (12–18 km), the FVDs to the south of the Salton Sea have an overall rotation and gradually become NW-SE. The depth-dependent variation of anisotropy orientation may be attributed to a large band of underlying heat source that probably causes a change of stress field by imposing thermal stress on overlying rocks. In all, our velocity models suggest that faults in the Salton Trough may bear a high risk of mechanical failures due to the complexities of stress distribution and geological structures as well as the presence of a large volume of fluids and heat.

On the validation of mixed-mode I/II crack growth theories for anisotropic rocks

We evaluate the accuracy of three well-known fracture growth theories to predict crack trajectories in anisotropic rocks through comparison with new experimental data. The results of 99 fracture toughness tests on the metamorphic Grimsel Granite under four different ratios of mixed-mode I/II loadings are reported. For each ratio, the influence of the anisotropy orientation on the direction of fracture growth is also analyzed. Our results show that for certain loading configurations, the anisotropy offsets the loading influence in determining the direction of crack growth, whereas in other configurations, these factors reinforce each other. To evaluate the accuracy of the fracture growth theories, we compare the experiment results for the kink angle and the effective fracture toughness with the predictions of the maximum tangential stress (MTS), the maximum energy release rate (MERR), and the maximum strain energy density (MSED) criteria. The criteria are first assessed in their classical forms employed in the literature. It is demonstrated that the energy-based criteria in their classical formulation cannot yield good predictions. We then present modified forms of the ERR and SED functions in which the tensile and shear components are decomposed. These modified forms give significantly better predictions of fracture growth paths. The evaluation of the three criteria illustrates that the modified MSED criterion is the least accurate model even in the modified form, while the results predicted by MTS and modified MERR are well matched with the experimental results.

Numerical simulation of filtration processes in the flow-induced deformation of fibrous porous media by a three-dimensional two-way fluid–structure interaction scheme

This study develops a numerical scheme to simulate three-dimensional two-way fluid–structure interaction (twFSI) problems capable of handling multiple simultaneous collision/contact (MSC) of a large number of flexible fibers. Our previous work of the twFSI scheme coupling the lattice Boltzmann method (LBM) as a fluid solver and the Cosserat rod model (CRM) as a structure solver is extended. To stably and efficiently calculate the collision/contact behaviors of numerous flexible fibers, the second-order extrapolation refilling method and the constrained-based collision model are implemented. The developed scheme (MSC-twFSI) is successfully validated in the experimental benchmark of flexible fiber collision/contact behaviors induced by airflows in a wind tunnel. The MSC-twFSI scheme is then applied to simulate the fluid flows through deformable nonwoven fabric geometry. In filtration processes through layers of fibrous materials such as face mask applications, the fluid flow induces a pressure distribution on individual fibers, resulting in deformation of each fiber and hence the overall fibrous porous structure is deformed. Therefore, we investigate the effect of the flow-induced deformation of fibrous porous media on the critical parameters of the filtration efficiency. They (porosity, compression ratio and permeability of the fibrous materials) are the key factors for designing filtration products. Fluid flows through deformable nonwoven fabrics, whose geometrical structures are close to realistic ones produced by the spunbonded lay-down process, are discussed under the actual air filtration environment of coughing. It is then found that (i) between the deformable and non-deformable fiber conditions, the maximum prediction difference for the permeability is 20.7%, (ii) the permeability difference comes from the anisotropic orientation of the fibers along the flow direction, and (iii) the effect of the flow-induced deformation approaches asymptotically ignorable below the porosity of around 0.83.

Large-Scale Synthesis of Metal Additively-Manufactured Microstructures Using Markov Random Fields

A data-driven framework is developed and examined for creating spatially-varying crystallographic textures over component-scale Computer-Aided Design (CAD) models. Here, a set of three orthogonal 2D micrographs of an Additively-Manufactured (AM) specimen are first obtained experimentally through Electron Backscatter Diffraction (EBSD) and subsequently converted to a 3D representative unit cell using the Markov Random Field (MRF) technique. Features such as grain size, crystallographic orientation, and grain boundary misorientation distributions are used to validate the reconstructed 3D microstructure against input experimental EBSD images. The variations of microstructural features during a powder-based additive manufacturing process are subsequently modeled by merging patches from the 3D snapshot of AM microstructural unit cell in a part-scale geometry using a tensor-based optimization process. The optimization algorithm repeatedly pastes microstructural elements from the reconstructed MRF unit cell onto the geometrical CAD domain until it is entirely covered. Here, through a simple Graphical User Interface (GUI), the user specifies a tensor field over the volumetric CAD model, defining the local control over grain-scale, anisotropy, and crystal growth orientation. This new approach provides a workflow for reconstructing global maps of AM microstructures in real-time by embedding site-specific images based on known AM microstructural patterns seen in experimental characterization techniques. The numerical results are helpful specifically for the visualization of process–microstructure relationships in metal additive manufacturing techniques.

Zenith-angle resolved polarized Raman spectroscopy of graphene

Angle resolved polarized Raman (ARPR) spectroscopy has been widely used to study basic properties of two-dimensional materials (2DMs), such as underlying symmetry, mode assignment, crystallographic orientation and optical anisotropy. The substrate effect has never been uncovered in ARPR spectroscopy. In this work, we investigated zenith-angle resolved polarized Raman (ZRPR) spectra of the G mode of graphene (1LG) deposited on different substrates as well as graphite under in-plane and out-of-plane configurations. In contrast to the independent behavior in normal incidence geometry, the G mode intensity exhibits obvious zenith-angle dependence. In particular, this polarization behavior is sensitive to the underlying substrates underneath 1LG. The ZRPR intensity of the G mode can be well understood by a model considering both Raman selection rule and zenith-angle resolved interference effect. This work enriches the understanding of polarized Raman spectroscopy of 2DMs and the approach can be applicable to other 2DMs, especially in-plane anisotropic 2DMs.

Relationship between the Drift of Medium-Scale Irregularities and the Orientation of Transverse Anisotropy of Small-Scale Irregularities in the F Region of the Midlatitude Ionosphere

Relationship between the Drift of Medium-Scale Irregularities and the Orientation of Transverse Anisotropy of Small-Scale Irregularities in the F Region of the Midlatitude Ionosphere

Uncertainties of GRACE‐Based Terrestrial Water Storage Anomalies for Arbitrary Averaging Regions

AbstractThe application of terrestrial water storage (TWS) data observed with GRACE and GRACE‐FO often requires realistic uncertainties. For gridded TWS data, this requires the knowledge of the covariances, which can be derived from the formal, i.e., formally estimated in the parameter estimation, variance‐covariance matrix provided together with the Stokes coefficients. However, the propagation of monthly variance‐covariance matrices to TWS data is computationally expensive, so we apply a spatial covariance model for TWS data. The covariance model provides non‐homogeneous (location depending), non‐stationary (time depending), and anisotropic (orientation depending) covariances between any two given points. Further, the model accommodates wave‐like behavior of East‐West‐directed covariances, which residuals of GRACE striping errors can cause. The main application of such spatial covariances is the estimation of uncertainties for mean TWS time series for arbitrary regions such as river basins. Alternatively, regional uncertainties can be derived from the above mentioned formal variance‐covariance matrices of the Stokes coefficients. This study compares modeled basin uncertainties for GFZ RL06 and ITSG‐Grace2018 TWS data with the formal basin uncertainties from the ITSG‐Grace 2018 solution. The modeled and formal uncertainties fit both in the spatial and temporal domain. We further evaluate the modeled uncertainties by comparison to empirical uncertainties over arid regions. Here, again the appropriateness of the modeled uncertainties is shown. The results, namely the TWS uncertainties for global river basins, are available via the GravIS portal. Further, we provide a Python toolbox, which allows computing uncertainties and covariance matrices.

Fast Identification of the Crystallographic Orientation of Violet Phosphorus Nanoflakes with Preferred In‐Plane Cleavage Edge Orientation

AbstractSemiconducting layered violet phosphorus, the most stable phosphorus allotrope, has recently been successfully produced with large single crystal sizes and high yields. A promising anisotropy is expected by the reduced symmetry of violet phosphorus in various properties. The in‐plane crystallographic anisotropy and cleavage edge orientation are especially important to the exfoliated 2D structures for their electronic, photonic, magnetic, and mechanic applications. However, the anisotropy of violet phosphorus has not been studied. Here, a fast and nondestructive way is reported to identify the crystallographic orientation of 2D violet phosphorus nanoflakes by a single polarized Raman spectrum. The 2D violet phosphorus nanoflakes have been found to have preferred in‐plane cleavage edges along ‐[P2][P8][P2][P9]‐ tubular strands with <1, 1, 0> edge alignment. The b‐axis (a‐axis) direction has been demonstrated to be easily identified that forms an angle of 45° or 135° from the cleavage edge by the intensity of Ag mode, especially the appearance or disappearance of 491 cm–1, under parallel configuration using polarized Raman scattering. A simple and fast method has been developed to identify the crystallographic orientation of violet phosphorus nanoflakes by a single Raman spectrum to obtain the corresponding a‐axis and b‐axis.

Hydrogel-Based Fiber Biofabrication Techniques for Skeletal Muscle Tissue Engineering.

The functional capabilities of skeletal muscle are strongly correlated with its well-arranged microstructure, consisting of parallelly aligned myotubes. In case of extensive muscle loss, the endogenous regenerative capacity is hindered by scar tissue formation, which compromises the native muscle structure, ultimately leading to severe functional impairment. To address such an issue, skeletal muscle tissue engineering (SMTE) attempts to fabricate in vitro bioartificial muscle tissue constructs to assist and accelerate the regeneration process. Due to its dynamic nature, SMTE strategies must employ suitable biomaterials (combined with muscle progenitors) and proper 3D architectures. In light of this, 3D fiber-based strategies are gaining increasing interest for the generation of hydrogel microfibers as advanced skeletal muscle constructs. Indeed, hydrogels possess exceptional biomimetic properties, while the fiber-shaped morphology allows for the creation of geometrical cues to guarantee proper myoblast alignment. In this review, we summarize commonly used hydrogels in SMTE and their main properties, and we discuss the first efforts to engineer hydrogels to guide myoblast anisotropic orientation. Then, we focus on presenting the main hydrogel fiber-based techniques for SMTE, including molding, electrospinning, 3D bioprinting, extrusion, and microfluidic spinning. Furthermore, we describe the effect of external stimulation (i.e., mechanical and electrical) on such constructs and the application of hydrogel fiber-based methods on recapitulating complex skeletal muscle tissue interfaces. Finally, we discuss the future developments in the application of hydrogel microfibers for SMTE.

A machine learning approach to determine the elastic properties of printed fiber-reinforced polymers

This work focuses on the simultaneous determination of the elastic constants and the fiber orientation state for a short fiber-reinforced polymer composite by performing a minimum of experimental tests. We introduce a methodology that enables the inverse determination of fiber orientation state and the in-situ polymer properties by performing tensile tests at the composite coupon level. We demonstrate the approach for the extrusion deposition additive manufacturing (EDAM) process to illustrate one application of the methodology, but the development is such that it can be applied to short fiber-reinforced polymer (SFRP) systems processed via other methods. Currently, developing composites additive manufacturing digital twins require extensive material characterization. In particular, the mechanical characterization of the orthotropic elastic properties of a composite involves extensive sample preparation and testing, therefore the elasticity tensor is generally populated using a micromechanics model. This, however, requires measuring the fiber orientation state in addition to knowing the constituent material properties. Experimentally measuring the fiber orientation state can be tedious and time consuming. Further, optical methods are limited to resolving the orientation of cylindrical fibers or cluster of non-cylindrical fibers, and computed tomography (CT) methods scan regions of volume that are much smaller than a full printed bead. Therefore, we propose a methodology, accelerated by machine learning, to identify the anisotropic mechanical properties and fiber orientation state at the same time. Early results show that inference of the fiber orientation and composite properties is possible with as few as three tensile tests. Our results show that a combination of the choice of the micromechanics model and reliable set of experiments can yield the nine elastic constants, as well as, the fiber orientation state.

Laser Assisted Bioprinting of laminin on biodegradable PLGA substrates: Effect on neural stem cell adhesion and differentiation

Laser Assisted Bioprinting (LAB) is recognized to be an enabling and versatile microfabrication technology for regenerative medicine and artificial tissue engineering. Current bioprinting concentrates on a layer-by-layer approach to print cells in consecutive stacks or nets, to recreate specialized tissue functions with a top-down approach. This synthering of proximal cells however reduces the long range correlation of tissue parenchyma and stroma given by natural development, as result of cells mobility and signaling. In this work, laminin, one of the main components of brain extracellular matrix is deposited by LAB on a biodegradable scaffold made of poly(lactic-co-glycolic acid) (PLGA), providing chemical cues for the adhesion and differentiation of neural stem cells NE-4C induced by retinoic acid. Surface roughness and LAB induced aggregates promote the initial adhesion of neuronal stem cells to the PLGA substrate and influence the formation of clusters and interconnection between them. The amount of laminin delivered inside the spot area may be controlled down to sub-monolayer coverage and a positive correlation between the laminin spots and soma of trafficking cells is demonstrated, also by computational modelling. Anisotropic orientation of neurite outgrowth is induced upon differentiation, up to 70% of processes protruding from stem cell clusters. The comparative analysis shows that the topological cue plays a major role in enhabling cluster formation on the scaffold, but the bioprinted laminin spots appear to be regulating the strength of connection between them, opening the way to control the functional morphology of artificial neural tissue constructs.

Spin-Dependent Visible Dyakonov Surface Waves in a Thin Hyperbolic Metamaterial Film.

A Dyakonov surface wave offers a promising way of guiding light in two dimensions with almost no loss but also additional freedom of modulation through the anisotropy at the interface. Here we experimentally demonstrated a spin-dependent Dyakonov surface wave mode propagating in a hyperbolic metamaterial film at a visible frequency. Due to the strong anisotropy of the hyperbolic metamaterial, a Dyakonov type mode shows a large allowed angle band and transverse spin with its direction determined by the orientations of the hyperbolic anisotropy and surface normal, based on which we experimentally observed the photonic spin Hall effect of the surface wave mode. This work enables a new generation of two-dimensional photonic circuits with spin-dependent excitation/detection and modulation devices at the subwavelength level.

Size dependent creep deformation of elastically constrained compliant metallic joints

The present study proposes a novel method to predict the size dependent creep behavior of bi-material joints formed by constraining a creep compliant metal, such as Sn, having varied thickness ranging from 1.4 mm to 170 µm, between stiff elastic substrates, such as Cu. A dramatic reduction in the secondary or minimum creep rate was observed with decrease in joint thickness. Finite element (FE) analysis using continuum formulations attributed this strengthening to the geometric constraints imposed by Cu, which increases the triaxiality in the joints and hence reduces the effective stress. While FE results were in close agreement with experiment in thick joints, it significantly overpredicted the creep rate of miniature joints. Further, orientation imaging revealed that microstructure varied with length scale, from bulk Sn with multiple grains to miniature joints having a few grains. The additional strengthening was captured using dislocation-based crystal plasticity (CP) creep modeling of Sn-Cu joints by incorporating this microstructural length scale, in addition to the geometric constraints. CP simulations revealed that orientation anisotropy of Sn and the constraints imposed by substrates on dislocation motion lead to higher strength in the miniature joints. Using the insights from FE and CP modeling a unified length scale sensitive model, incorporating both geometric or continuum and microstructural factors, was developed that can accurately predict the creep response of the joints of macro and meso length scale.

Evaluation of the Microstructural Characteristics of Bone Surrounding Anchor Screws Placed under a Horizontal Load by Exploring the Orientation of Biological Apatite Crystals and Collagen Fiber Anisotropy

The objective of this study was to carry out quantitative evaluations of the microstructural characteristics of bone surrounding anchor screws placed under a horizontal load and the microstructural characteristics of bone on the compressed and non-compressed sides of anchor screws by investigating the orientation of biological apatite (BAp) crystals and collagen fiber anisotropy. Anchor screws were implanted in the femurs of adult rats. They were divided into those placed under a horizontal load (horizontal loading group, n = 4), those not placed under a horizontal load (unloaded group, n = 4), and a sham group of rats that did not undergo femoral anchor screw implantation. In addition to histological observations, BAp crystal orientation and collagen fiber anisotropy were also analyzed. Osteocytes adjacent to anchor screws on the compressed side in the horizontal loading group were rounder in shape than those in normal femurs, the unloaded group, and on the non-compressed side in the horizontal loading group. Collagen fibers showed anisotropy on the non-compressed side in the horizontal loading group. BAp crystals also showed a uniaxial preferential orientation in the direction of traction on the compressed side in the horizontal loading group. These results demonstrated that the osteogenesis of bone around anchor screws placed under a sustained horizontal load gave this bone structural characteristics that differed in some respects from those of normal bone. They also showed that this bone acquired micro/nanostructural characteristics adapted to its new mechanical environment.

On the Origin of Seismic Anisotropy in the Shallow Crust of the Northern Volcanic Zone, Iceland

AbstractThe Icelandic crust is a product of its unique tectonic setting, where the interaction of an ascending mantle plume and the Mid‐Atlantic Ridge has caused elevated mantle melting, with the melt accreted and cooled in the crust to form an oceanic plateau. We investigate the strength and orientation of seismic anisotropy in the upper crust of the Northern Volcanic Zone using local earthquake shear‐wave splitting, with a view to understanding how the contemporary stress field may influence sub‐wavelength structure and processes. This is achieved using a data set comprising 50,000 earthquakes located in the top 10 km of the crust, recorded by up to 70 stations over a 9 year period. We find that anisotropy is largely confined to the top 3–4 km of the crust, with an average delay time of 0.10 ± 0.05 s, and an average orientation of the fast axis of anisotropy of N014°E ± 27°, which is perpendicular to the spreading direction of the Eurasian and North American plates (N106°E). These results are consistent with the presence of rift‐parallel cracks that gradually close with depth, the preferential opening of which is controlled by the regional stress field. Lateral variations in the strength of shear wave anisotropy (SWA) reveal that regions with the highest concentrations of earthquakes have the highest SWA values (∼10%), which reflects the presence of significant brittle deformation. Disruption of the orientation of the fast axis of anisotropy around Askja volcano can be related to local stress changes caused by underlying magmatic processes.

On the Similarity Between the Orientation of the Cross-Field Anisotropy of Small-Scale Irregularities and the Direction of the Plasma Drift in the Ionosphere Over Moscow

On the Similarity Between the Orientation of the Cross-Field Anisotropy of Small-Scale Irregularities and the Direction of the Plasma Drift in the Ionosphere Over Moscow

Preferential Orientation and Mechanical Properties Anisotropy of Wire and Arc Additive Manufactured Duplex Stainless Steel

Preferential Orientation and Mechanical Properties Anisotropy of Wire and Arc Additive Manufactured Duplex Stainless Steel

Crustal Structure Beneath the Northern Appalachians and the Eastern Grenville Province

AbstractSoutheastern Canada and the northeastern USA include terranes that were tectonized since the Archean, making this region an excellent place to investigate the evolution of continental crust. Our study area covers the Archean southeastern Superior Province, the Proterozoic eastern Grenville, and the Phanerozoic northern Appalachians comprising terranes with either Peri‐Laurentian or Peri‐Gondwanan heritage. Adopting a Rayleigh wave ambient noise tomography method, we used noise data recorded between 2013 and 2015, and obtained high resolution anisotropic tomographic images of the crust enabling us to discuss tectonic implications. The azimuthal anisotropy orientations follow a dominant NE‐SW trend across the study area, but some localized changes of anisotropy direction in the Bay of Fundy and across the Appalachian front are observed. The crust beneath the older Superior and Grenville provinces is generally fast, whereas the Appalachians include strong slow anomalies, especially at upper crustal depths, where they represent thick sedimentary basins beneath the St. Lawrence valley, the Gulf of St. Lawrence, and the Bay of Fundy. We suggest that the boundary between the Peri‐Laurentian and the Peri‐Gondwanan terranes at depth is marked by a Moho‐offset feature observable in our models. A generally similar crustal seismic signature for the two youngest easternmost tectonic domains suggest that they were never separated by a wide ocean basin. Our results provide important evidence for evolution of the continental crust during and after accretionary/collisional episodes in the study area.

Characterization of Anisotropic Mechanical Properties of X70 Spiral Welded Steel Pipes

Abstract Anisotropic tensile and compressive properties of base metals and girth welds of two API X70 spiral welded pipes have been investigated in this study. Spiral welded pipes exhibit different characteristics of anisotropy from UOE pipes, as the anisotropic property is determined by the thermo-mechanical rolling process of plates and coils produced for pipes. Spiral pipe steels have the lowest strengths in the pipe's transverse direction, contrary to UOE pipes with high strengths in the transverse direction. Yield strengths measured from tensile and compressive tests and their anisotropic characteristics are comparable, although tensile yield strengths are somewhat greater. The results of compressive tests also indicate an anisotropy in the pipe's through-thickness orientation as well as in the longitudinal orientation; yield strengths are highest in the through-thickness direction for both base metals and girth welds of the two pipes.