Angle Anisotropy Research Articles

Magnetospheric Multiscale Observation of Quasiperiodic EMIC Waves Associated With Enhanced Solar Wind Pressure

AbstractWe present a Magnetospheric Multiscale mission observation of quasiperiodic electromagnetic ion cyclotron (EMIC) variations on 24 December 2015 corresponding to magnetic field depressions as well as proton pitch angle anisotropy enhancements. Proton dynamic pressure obtained by WIND indicates that the solar wind was periodically compressing the magnetosphere with a period ∼7.5 min, which is consistent with the EMIC modulation period observed by the Magnetospheric Multiscale. Numerical calculations demonstrate that the EMIC modulation period is comparable with the magnetic field line resonance period, suggesting that quasiperiodic solar wind enhancement compressing the magnetosphere and propagating as the fast mode can lead to the magnetic field line oscillation and hence the presence of quasiperiodic magnetic compressions and discrete proton anisotropy elements, which provides optimal conditions for modulating the EMIC instability. Current results provide a complete chain of self‐consistent observational evidences to illustrate the process connecting solar wind variations to EMIC wave amplitude modulation in the magnetosphere.

Evaluating the use of Beer's law for estimating light interception in canopy architectures with varying heterogeneity and anisotropy

Light interception in plant canopies is most commonly estimated using a simple one-dimensional turbid medium model (i.e., Beer's law). Inherent in this class of models are assumptions that vegetation is uniformly distributed in space (homogeneous) and in many cases that vegetation orientation is uniformly distributed (isotropic). It is known that these assumptions are violated in a wide range of canopies, as real canopies commonly have heterogeneity at multiple scales and almost always have highly anisotropic leaf angle distributions. However, it is not quantitatively known under what conditions these assumptions become problematic given the difficulty of robustly evaluating model results for a range of canopy architectures. In this study, assumptions of vegetation homogeneity and isotropy were evaluated under clear sky conditions for a range of virtually-generated crop canopies with the aid of a detailed three-dimensional, leaf-resolving radiation model. Results showed that Beer's law consistently over predicted light interception for all canopy configurations. For canopies where the plant spacing was comparable to the plant height, Beer's law performed poorly, and over predicted daily intercepted sunlight by up to ∼115%. For vegetation with a highly anisotropic leaf inclination distribution but a relatively isotropic leaf azimuth distribution, the assumption of canopy isotropy (i.e., G = 0.5) resulted in relatively small errors. However, if leaf elevation and azimuth were both highly anisotropic, the assumption of canopy isotropy could introduce significant errors depending on the orientation of the azimuthal anisotropy with respect to the sun's path.

Critical current density in anisotropic superconductors containing columnar defects

In order to reveal the influence of the tilt angle of columnar defects on angular dependence of critical current density the Monte Carlo simulation of vortex system in three-dimensional layered high-temperature superconductor (HTSC) was performed. For simulations, the three-dimensional model of layered HTSC generalized for the case of tilted magnetic field was used. The angular dependencies of the critical current were calculated at different splay angle of columnar defects and different anisotropy of HTSC. It was shown that simulation results correspond qualitatively to the experimental results for REBCO coated conductors.

Biophysical parameter assessment of winter crops using polarimetric variables—entropy (H), anisotropy (A), and alpha (α)

The study brings out the potential of SAR polarimetric time series data for the study of crop biophysical parameter assessment of major winter field crops in India. We examined the entropy-alpha-anisotropy approach in radar polarimetric C-band data and related the polarimetric parameters to the biomass to understand the interaction of microwave signal with the major winter crops across dominant biomass ranges in India. The crop phenology response in terms of the changes in polarimetric parameters like entropy (H), anisotropy (A), and alpha (α) angle and their derived parameters has been studied for dominant winter field crops like wheat, mustard, and gram with variation in their variables like biomass. A trend is established emerging from this study which shows that entropy, alpha, and anisotropy for agricultural areas are closely related to the growth rate of the crops and their phenological stages. This paper outlines a methodology for using RADARSAT-2 full-polarimetric data for vegetation (winter crops) monitoring using the abovementioned standard polarimetric parameters for understanding crop vigor and phenology. The polarimetric parameters were observed to be more dynamic in wheat (H 0.45 to 0.8) than in mustard (H 0.6 to 0.85) in December to February data though late sown crop of mustard showed a higher range with respect to their biomass.

Crack development in transversely isotropic sandstone discs subjected to Brazilian tests observed using digital image correlation

Digital image correlation (DIC) is used to investigate crack initiation and propagation in discs of transversely isotropic Hawkesbury sandstone subjected to the Brazilian test. To verify DIC's validity and precision a simple calibration method is presented. It involves adjusting the size and spacing of subsets of pixels within images of a specimen's surface from which local deformations and strains are quantified, achieving agreement between strains measured by DIC and gauges attached to the surface. Using DIC the tensile and shear strain fields, crack opening displacements (CODs) and displacement vectors are determined at all stages of loading. The development of the fracture process zone is also identified prior to a major crack initiation. Also, a range of load contact configurations is considered, including the loads being applied via flat rigid platens and across finite strips with widths controlled by small (3 mm wide) and big (5 mm wide) wooden cushions placed between the load applicators and discs. It is observed that, for 0° and 90° anisotropy angles (representing layering normal to and parallel to diameters connecting load contacts) and for both the flat platen and small wooden cushion, cracks initiate far from the disc centres. Also, for the 45° anisotropy angle and all load configurations, cracks initiate at the disc centres. Furthermore, when the loads are applied via big wooden cushions, cracks initiate at the disc centres regardless of the anisotropy angle. Also, specimens loaded via big wood cushions exhibited the largest COD while the specimens loaded via small wood cushions exhibited the smallest. Also, specimens loaded via flat platens failed at smaller loads compared to those using wooden cushions. This study confirms transverse isotropy has strong effect on crack development. It also demonstrates important parameters including time and location of initiation, as well as COD, may be determined using DIC.

Whistler Waves Driven by Field‐Aligned Streaming Electrons in the Near‐Earth Magnetotail Reconnection

AbstractWe analyze Magnetospheric Multiscale Mission observations of whistler waves and associated electron field‐aligned crescent distribution in the vicinity of the magnetotail near‐Earth X‐line. The whistler waves propagate outward from the X‐line in the neutral sheet. The associated field‐aligned streaming electrons exhibit a crescent‐like shape, with an inverse slope (df/d|v|||>0) at 1–5 keV. The parallel phase velocity of the waves is in the range (1–5 keV) of the inverse slope of the field‐aligned crescents in the velocity space. We demonstrate that the observed whistler waves are driven by the electron field‐aligned crescents through Landau resonance. The cyclotron resonance is at the high‐energy tail with negligible free energy of pitch angle anisotropy in these events.

Measurement of the anisotropic elastic properties of shale: uncertainty analysis and water effect

The static anisotropic elastic properties of shales can be measured by performing uniaxial compression on core specimens with bedding planes of different inclination angles (or anisotropy angles). However, these measurements differ when different numbers of specimens are tested, mainly because of the heterogeneity of shales. This study aimed to quantify the uncertainties of the anisotropic elastic properties of a shale when testing different numbers of specimens with distinct anisotropic angles. Three sets of room-dried core samples were prepared, and each set consisted of seven specimens with incremental anisotropic angles of 15°. Uniaxial compression measurements were used to determine the anisotropic elastic properties for a given number (2–7) of specimens in each set. The results indicated that the uncertainties of the determined anisotropic elastic properties decreased monotonically as the number of measurements was increased. The results also suggested that at least five specimens with different anisotropic angles should be tested in order to obtain accurate elastic properties (uncertainty <10%). An additional set of wet specimens of the same shale were also tested and analyzed. It was found that water absorption significantly decreased Young’s moduli, increased Poisson’s ratios, and had a limited effect on the shear modulus. The wet specimens also displayed a slightly stronger anisotropic ratio of the elastic moduli compared to the room-dried specimens. Finally, the alteration of the anisotropic elastic properties of shales upon water absorption was tentatively related to the mineralogy and microstructure heterogeneity. The findings of this study have major implications for many geoengineering operations where the anisotropic elastic properties of shales must be considered.

Controllable anisotropic properties of wet-laid hydroentangled nonwovens

For nonwovens, fiber orientation distribution is an important structural characteristic that directly influences the anisotropic properties of the materials. Different Vslurry/Vbelt ratios were adopted to fabricate nonwovens during the wet-laid process. The results indicated that fiber orientation distribution of nonwovens can be regulated by adopting different Vslurry/Vbelt ratios owing to the web-forming principle of wet-laid techniques. Mechanical tests showed that both wet and dry tensile strength of nonwovens in different angle directions present anisotropy under different Vslurry/Vbelt ratio parameters. A liquid spreading distribution experiment proved that liquid spreading length and area of nonwovens could be manipulated using different Vslurry/Vbelt ratios in the fabrication process. Therefore, specific anisotropic properties of wet-laid hydroentangled nonwovens can be realized by controlling the process parameters for particular end-use applications.

Analysis of the strength and break state of anisotropic coal in indirect tensile test

The article is to perform the results of the indirect tensile test with two combination samples of dim coal (peat) which has the anisotropic angle of α = 00 and α = 900. The results showed that the tensile strength in both cases above was anisotropy. However, the case of α = 900 has the anisotropic angle larger than the case of α = 00, or in another word, the featured anisotropic tensile strength depends on the angle which was created by bedding and loading direction.

Experimental Investigation of Fracture Propagation Behavior Induced by Hydraulic Fracturing in Anisotropic Shale Cores

Hydraulic fracturing is a key technology for the development of unconventional resources such as shale gas. Due to the existence of numerous bedding planes, shale reservoirs can be considered typical anisotropic materials. In anisotropic shale reservoirs, the complex hydraulic fracture network (HFN) formed by the interaction of hydraulic fracture (HF) and bedding plane (BP) is the key to fracturing treatment. In this paper, considering the anisotropic angle, stress state and injection rate, a series of hydraulic fracturing experiments were conducted to investigate the effect of anisotropic characteristics of shale reservoirs on HFN formation. The results showed that the breakdown pressure increased first and then decreased when the anisotropic angle changed at 0°–90°, while the circumferential displacement had the opposite trend with a small difference. When θ = 0°, fracturing efficiency of shale specimens was much higher than that under other operating conditions. When θ ≤ 15°, the bedding-plane mode is ubiquitous in all shale reservoirs. While θ ranged from 30°–45°, a comprehensive propagation pattern of bedding-plane and crossing is presented. When θ ≥ 60°, the HFN pattern changes from comprehensive mode to crossing mode. The propagation pattern obtained from physical experiments were verified by theoretical analysis. The closure proportion of the circumferential displacement was the highest when the propagation pattern was the bedding-plane mode (θ ≤ 15°), following by crossing. The closure proportion was minimum only when the bedding-plane and crossing mode were simultaneously presented in the HFN. The results can provide some basic data for the design in hydraulic fracturing of tight oil/gas reservoirs.

Excitation of Highly Oblique Lower Band and Upper Band Chorus by a Loss Cone Feature and Temperature Anisotropy Distribution

AbstractRecent studies have indicated that highly oblique lower band chorus could be excited by temperature anisotropy with a low‐energy electron plateau. Here we present another excitation mechanism of highly oblique lower and upper band chorus by using the simultaneous observations and numerical modeling. During 23:00–24:00 UT on 3 July 2016, Van Allen probe A observed chorus with the wave normal angle close to the resonance cone both in the lower and upper bands around L = 5.0 and MLT = 3. Enhanced flux and pitch angle anisotropy of energetic electrons were observed in the same spatial region. Calculations of chorus growth rates show that highly oblique chorus waves can be excited by the energetic electrons with a loss cone feature and distinct temperature anisotropy, particularly more efficient in the presence of a low‐energy plateau. The temperature anisotropy for the oblique upper band is higher than that for the lower band.

Edge directionality properties in complex spherical networks.

Spatially embedded networks have attracted increasing attention in the past decade. In this context, network characteristics have been introduced which explicitly take spatial information into account. Among others, edge directionality properties have recently gained particular interest. In this work, we investigate the applicability of mean edge direction, anisotropy, and local mean angle as geometric characteristics in complex spherical networks. By studying these measures, both analytically and numerically, we demonstrate the existence of a systematic bias in spatial networks where individual nodes represent different shares on a spherical surface, and we describe a strategy for correcting for this effect. Moreover, we illustrate the application of the mentioned edge directionality properties to different examples of real-world spatial networks in spherical geometry (with or without the geometric correction depending on each specific case), including functional climate networks, transportation, and trade networks. In climate networks, our approach highlights relevant patterns, such as large-scale circulation cells, the El Niño-Southern Oscillation, and the Atlantic Niño. In an air transportation network, we are able to characterize distinct air transportation zones, while we confirm the important role of the European Union for the global economy by identifying convergent edge directionality patterns in the world trade network.

Intercomparison of the POES/MEPED Loss Cone Electron Fluxes With the CMIP6 Parametrization

AbstractQuantitative measurements of medium energy electron (MEE) precipitation (&gt;40 keV) are a key to understand the total effect of particle precipitation on the atmosphere. The Medium Energy Proton and Electron Detector (MEPED) instrument on board the NOAA/Polar Orbiting Environmental Satellites (POES) has two sets of electron telescopes pointing ~0° and ~90° to the local vertical. Pitch angle anisotropy, which varies with particle energy, location, and geomagnetic activity, makes the 0° detector measurements a lower estimate of the flux of precipitating electrons. In the solar forcing recommended for Coupled Model Intercomparison Project (CMIP) 6 (v3.2) MEE precipitation is parameterized by Ap based on 0° detector measurements hence providing a general underestimate of the flux level. In order to assess the accuracy of the Ap model, we compare the modeled electron fluxes with estimates of the loss cone fluxes using both detectors in combination with electron pitch angle distributions from theory of wave‐particle interactions. The Ap model falls short in respect to reproducing the flux level and variability associated with strong geomagnetic storms (Ap &gt; 40) as well as the duration of corotating interaction region storms causing a systematic bias within a solar cycle. As the Ap‐parameterized fluxes reach a plateau for Ap &gt; 40, the model's ability to reflect the flux level of previous solar cycles associated with generally higher Ap values is questioned. The objective of this comparison is to understand the potential uncertainty in the energetic particle precipitation applying the CMIP6 particle energy input in order to assess its subsequent impact on the atmosphere.

Modeling anisotropic shape evolution during Czochralski growth of oxide single crystals

We present a technique for modeling three-dimensional (3D) anisotropic crystal shape evolution in meniscus defined growth systems. In particular we apply this model to a simplified low gradient Czochralski growth process used to grow bismuth–germanium–oxide–like crystals. Our Lattice Boltzmann Model (LBM) based approach involves a two-dimensional unstructured mesh (embedded within the 3D LBM grid) which accurately tracks the crystal/melt and melt/gas interfaces while accounting for anisotropic interface attachment kinetics as well as capillarity, involving the enforcement of either isotropic or anisotropic growth angles (GA) at the crystal/melt/gas triple phase line (GA-TPL). The robustness of the algorithm is demonstrated by a series of tests involving mesh refinement, comparisons with results from an older study and an evaluation of the impact on accuracy of a time-saving artificial pull-rate speedup scheme described within the manuscript. Physically significant results (which do not involve diameter control) include a demonstration of the impact of changes in kinetic parameters on resultant ingot shapes, calculations showing how (for conditions considered here) the diameter of the growing crystal decreases with increasing isotropic growth angle values, and growth simulations demonstrating how anisotropic growth angles can impact the shape of the evolving ingot. The dependence of crystal diameter on isotropic growth angle values is reproduced in a local sense in the case of anisotropic growth angles. A specific point on the GA-TPL will tend to extend inwards or outwards (respectively exhibiting a decreased or increased local radial position value) when the growth angle value is locally (and respectively) increased or decreased. As a result, considering crystals whose non-circular cross-sectional shapes are due to kinetic anisotropy as a baseline, growth angle anisotropy acts to either decrease or increase shape anisotropy when the extended (rough) parts of the GA-TPL respectively support large or small local growth angle values as compared to reduced-radius (faceted) parts of the GA-TPL. It should finally be mentioned that our results, concerning the sensitivity of the (local or average) radial position value of the GA-TPL to the growth angle, are consistent with other computational results exhibited in the literature (concerning solidifying semiconductor drops and floating zone growth of oxides).

Paper-Based Magneto-Resistive Sensor: Modeling, Fabrication, Characterization, and Application.

In this work, we developed and fabricated a paper-based anisotropic magneto-resistive sensor using a sputtered permalloy (NiFe) thin film. To interpret the characteristics of the sensor, we proposed a computational model to capture the influence of the stochastic fiber network of the paper surface and to explain the physics behind the empirically observed difference in paper-based anisotropic magneto-resistance (AMR). Using the model, we verified two main empirical observations: (1) The stochastic fiber network of the paper substrate induces a shift of in the AMR response of the paper-based NiFe thin film compared to a NiFe film on a smooth surface as long as the fibrous topography has not become buried. (2) The ratio of magnitudes of AMR peaks at different anisotropy angles and the inverted AMR peak at the -anisotropy angle are explained through the superposition of the responses of NiFe inheriting the fibrous topography and smoother NiFe on buried fibrous topographies. As for the sensitivity and reproducibility of the sensor signal, we obtained a maximum AMR peak of , min-max sensitivity range of , average asymmetry of peak location of within two consecutive magnetic loading cycles, and a deviation of 250–850 of peak location across several anisotropy angles at a base resistance of ∼100 . Last, we demonstrated the usability of the sensor in two educational application examples: a textbook clicker and interactive braille flashcards.

High-Fidelity Sensitivity Analysis of Modal Properties of Mistuned Bladed Disks Regarding Material Anisotropy

A new method has been developed for sensitivity calculations of modal characteristics of bladed disks made of anisotropic materials. The method allows the determination of the sensitivity of the natural frequencies and mode shapes of mistuned bladed disks with respect to anisotropy angles that define the crystal orientation of the monocrystalline blades using full-scale finite element models. An enhanced method is proposed to provide high accuracy for the sensitivity analysis of mode shapes. An approach has also been developed for transforming the modal sensitivities to coordinate systems (CS) used in industry for description of the blade anisotropy orientations. The capabilities of the developed methods are demonstrated on examples of a single blade and a mistuned realistic bladed disk finite element models. The modal sensitivity of mistuned bladed disks to anisotropic material orientation is thoroughly studied.

Effect of rock anisotropy on wellbore stresses and hydraulic fracture propagation

Using a newly developed 2D numerical model based on the displacement discontinuity method (DDM) and the fictitious stress method (FSM), hydraulic fracture propagation near and away from a horizontal wellbore in anisotropic mudstones is studied. In addition to elastic anisotropy, the effect of fracture toughness anisotropy on hydraulic fracture propagation is included and fluid flow in fractures is fully coupled with rock deformation. Simulations show wellbore failure pressure, fracture trajectory, and near wellbore fracture apertures are significantly affected by elastic and fracture toughness anisotropy. A simple plane strain analytical solution might indicate that near wellbore fracture opening is enhanced in vertically transversely isotropic (VTI) rock. However, near wellbore fracture turning in a rock with high fracture toughness anisotropy results in severe constriction of fracture apertures. This effect becomes more severe with increase in fracture toughness anisotropy and perforation misalignment angle. Simulations of multiple hydraulic fractures from horizontal wellbores suggest that fracture lengths and apertures are affected by their orientation with respect to the directions of elastic symmetry. The spatial extent of the induced normal stresses perpendicular to the fracture surface increases when the fracture is aligned with the direction of least Young's modulus. The larger spatial extent of induced stresses in anisotropic rock leads to early termination of the fractures emanating from the inner perforation clusters, resulting in fracture networks with dominant outer fractures. In the presence of fracture toughness anisotropy, the fractures deviate towards the plane of least fracture toughness under low differential stress conditions.

A Study on the Static and Seismic Earth Pressure Problems in Anisotropic Granular Media

The limit load in stability problems in soils is often influenced by the inherent anisotropy. Accordingly, it can be more or less misestimated if an anisotropic soil is simply assumed as being isotropic. In this research, the static and seismic active and passive earth pressures of vertical retaining walls in anisotropic sands are investigated by the use of the lower bound limit analysis method in conjunction with the finite elements and linear programming optimization technique. In this regard, the effect of friction angle anisotropy on the limit pressure was considered. To do so, an iterative procedure was made to incorporate the effect of soil anisotropy. In the proposed iterative procedure, the friction angle was incrementally updated after each iteration. After sufficient iterations, a converged solution and a consistent field of friction angle is achieved which satisfy the convergence criteria of the direction of the major principal stresses and the limit load, as well as a stable stress field. It is worth mentioning that the pseudo-static approach was considered in order to apply the seismic condition. The results were compared with those found in the literature and some design charts were developed. Findings indicate that the passive earth pressure coefficient is much more influenced by the degree of anisotropy than the active earth pressure coefficient.

High resolution in-vivo DT-CMR using an interleaved variable density spiral STEAM sequence.

Diffusion tensor cardiovascular magnetic resonance (DT-CMR) has a limited spatial resolution. The purpose of this study was to demonstrate high-resolution DT-CMR using a segmented variable density spiral sequence with correction for motion, off-resonance, and T2*-related blurring. A single-shot stimulated echo acquisition mode (STEAM) echo-planar-imaging (EPI) DT-CMR sequence at 2.8 × 2.8 × 8 mm3 and 1.8 × 1.8 × 8 mm3 was compared to a single-shot spiral at 2.8 × 2.8 × 8 mm3 and an interleaved spiral sequence at 1.8 × 1.8 × 8 mm3 resolution in 10 healthy volunteers at peak systole and diastasis. Motion-induced phase was corrected using the densely sampled central k-space data of the spirals. STEAM field maps and T2* measures were obtained using a pair of stimulated echoes each with a double spiral readout, the first used to correct the motion-induced phase of the second. The high-resolution spiral sequence produced similar DT-CMR results and quality measures to the standard-resolution sequence in both cardiac phases. Residual differences in fractional anisotropy and helix angle gradient between the resolutions could be attributed to spatial resolution and/or signal-to-noise ratio. Data quality increased after both motion-induced phase correction and off-resonance correction, and sharpness increased after T2* correction. The high-resolution EPI sequence failed to provide sufficient data quality for DT-CMR reconstruction. In this study, an in vivo DT-CMR acquisition at 1.8 × 1.8 mm2 in-plane resolution was demonstrated using a segmented spiral STEAM sequence. Motion-induced phase and off-resonance corrections are essential for high-resolution spiral DT-CMR. Segmented variable density spiral STEAM was found to be the optimal method for acquiring high-resolution DT-CMR data.

An Event on Simultaneous Amplification of Exohiss and Chorus Waves Associated With Electron Density Enhancements

AbstractWhistler mode exohiss are the structureless hiss waves observed outside the plasmapause with featured equatorward Poynting flux. An event of the amplification of exohiss as well as chorus waves was recorded by Van Allen Probes during the recovery phase of a weak geomagnetic storm. Amplitudes of both types of the waves showed a significant increase at the regions of electron density enhancements. It is found that the electrons resonant with exohiss and chorus showed moderate pitch angle anisotropies. The ratio of the number of electrons resonating with exohiss to total electron number presented in‐phase correlation with density variations, which suggests that exohiss can be amplified due to electron density enhancement in terms of cyclotron instability. The calculation of linear growth rates further supports above conclusion. We suggest that exohiss waves have potential to become more significant due to the background plasma fluctuation.