Combined Effects Of Anisotropy Research Articles

Compact leak-integrate-fire neuron with auto-reset functionality based on a single spin–orbit torque magnetic tunnel junction device

Leaky-integrate-fire (LIF) neurons are core components to construct a spiking neural network. The emulation of LIF neurons has been implemented in spintronic devices, but typically suffers from challenges, such as relatively complex design and the requirement of additional operations for resetting. In this Letter, we propose a compact LIF neuron device realized within a single spin–orbit torque (SOT) magnetic tunnel junction device. Distinct from standard memory devices, the input SOT current for the integrating process is applied in a manner such that the magnetization cannot cross the hard plane. Consequently, the device can automatically reset to its original state by the combined effects of anisotropy and damping, which play a vital role during the leaky process as well. We verify the proposal in three types of SOT devices by micromagnetic simulations, and the power consumption is estimated as 0.1 pJ/spike. The auto-reset process is further captured by our single-shot dynamic experiments. With the state-of-the-art SOT technology, our work provides a concise and plausible scheme to mimic LIF neurons, which is of practical interest for neuromorphic computing.

Bearing capacity of conical footings on clays considering combined effects of anisotropy and non-homogeneity

ABSTRACT A spudcan is one of the foundation systems widely used to support the load transferred from a jack-up platform for most offshore drilling operations. The spudcan is an axisymmetric footing with a conical shape. The study on the stability effects of anisotropic and non-homogeneous clays on the bearing capacity of this kind of footings is yet to be found in the current literature. This paper presents novel plastic solutions of the bearing capacity factor for conical footings on clays with linearly increasing anisotropic shear strength. The finite element limit analysis is employed to perform the bearing capacity solutions based on three dimensionless parameters including the cone apex angle, the strength gradient ratio, and the ratio between the undrained shear strength ratio obtained from the triaxial compression test and triaxial extension test. The proposed equations in this study provide a reliable solution to improve the current design standard for conical footings in anisotropic and non-homogeneous clays.

Eddy Current Loss in Grain-Oriented Steel Laminations Due to Normal Leakage Flux

Leakage flux penetrating laminated iron cores in power transformers and large generators induces eddy current and local loss. Due to the strong magnetic anisotropy of the lamination structure, the penetrating flux tends to saturate the lamination in its plane, even when the incident stray flux density is low. Therefore, the combined effect of anisotropy and nonlinearity has a great impact on the eddy current distribution and the associated power losses. Moreover, the incident normal flux often interacts with the main flux, where the phase angle between the two fluxes may play a significant role. A measurement device is developed to emulate the actual leakage flux in a steel lamination and the power losses are measured at the flux densities of various magnitudes and phases. The measurement results are compared and interpreted by the results obtained from a finite-element analysis, where the homogenization approach for material modeling is implemented, taking the combined effect of magnetic anisotropy and the saturation into account.

Anisotropic mechanical behaviour of calendered nonwoven fabrics: Strain-rate dependency

Calendered nonwovens, formed by polymeric fibres, are three-phase heterogeneous materials, comprising a fibrous matrix, bond-areas and interface regions. As a result, two main factors of anisotropy can be identified. The first one is ascribable to a random fibrous microstructure, with the second one related to orientation of a bond pattern. This paper focuses on the first type of anisotropy in thin and thick nonwovens under uniaxial tensile loading. Individual and combined effects of anisotropy and strain rate were studied by conducting uniaxial tensile tests in various loading directions (0°, 30°, 45°, 60° and 90° with regard to the main fabric’s direction) and strain rate (0.01, 0.1 and 0.5 s−1). Fabrics exhibited an initial linear elastic response, followed by nonlinear strain hardening up to necking and final softening. The studied allowed assessment of the extent the effects of loading direction (anisotropy), planar density and strain rate on the mechanical response of the calendered fabrics. The evidence supported the conclusion that anisotropy is the most crucial factor, also delineating the balance between the fabric’s load-bearing capacity and extension level along various directions. The strain rate produced a marked effect on the fibre’s response, with increased stress at higher strain rate while this effect in the fabric was small. The results demonstrated the differences of the mechanical behaviour of fabrics from that of their constituent fibres.

Geomechanical behaviors of shale after water absorption considering the combined effect of anisotropy and hydration

Geomechanical behaviors of shale in many geotechnical engineering areas, such as shale gas extraction, tunnel excavation, slope engineering, are highly influenced by anisotropy and hydration. In this work, a number of ϕ25 mm × 50 mm shale specimens were prepared with three levels of moisture contents and seven bedding plane orientations (β, in degrees) relative to the axial direction. A series of compression tests for these specimens was then conducted under four different confining pressures to investigate their geomechanical behaviors considering the combined effect of anisotropy and hydration. The results demonstrate the following points. 1) During the water absorption process, the shale specimens swell and suffer damage, which are primarily observed along the bedding plane. 2) The curve of compressive strength (peak deviatoric stress) vs. β is “U-shaped,” with the lowest value at β = 30°. The apparent elastic modulus decreases with the increase in β and then remains nearly unchanged when β > 45°. As β increases, the strains at peak stress and average apparent Poisson's ratio increase first and then decrease when β > 30°. 3) The plastic deformation stage and residual stress stage, which negatively relate to the elastic-brittle properties of shale, become more obvious with increasing moisture content, and the specimen for which β is closer to 30° exhibits a more significant change of that. 4) With increasing moisture content, the compressive strength and axial strain at peak stress decrease, apparent elastic modulus decreases nonlinearly, and average apparent Poisson's ratio increases approximately linearly. 5) The effect of anisotropy on the compressive strength decreases with increasing confining pressure and this weakened effect by confining pressure becomes less with increasing moisture content. 6) With the increase in β, the effect of water absorption on the compressive strength first strengthens a little and then weakens when β > 30° or 45°, and this change with β becomes more significant under higher confining pressure. 7) The effect of confining pressure on the compressive strength strengthens a little when β < 30° and then weakens with the increase in β, and this change with β weakens with increasing moisture content. 8) The anisotropy of shale could be the major controlling factor for geomechanical behaviors, and water absorption along the bedding plane can enhance the effect of anisotropy. The results can not only guide the design and construction of geotechnical engineering structures related to shale, but can also be used as a reference for geological research on the deformation and failure of shale formations affected by water intrusion and geological stresses.

Plastic deformation of high-purity a-titanium: model development and validation using the Taylor cylinder impact test

Results of an experimental study on the quasi-static and high-rate plastic deformation due to impact of a high-purity, polycrystalline, a-titanium material are presented. To quantify the plastic anisotropy and tension-compression asymmetry of the material, first monotonic uniaxial compression and tension tests were carried out at room temperature under quasi-static conditions. It was found that the material is transversely isotropic and displays strong strength differential effects. To characterize the material's strain rate sensitivity, Split Hopkinson Pressure Bar tests in tension and compression were also conducted. Taylor impact tests were performed for impact velocity of 196 m/s. Plastic deformation extended to 64% of the length of the deformed specimen, with little radial spreading. To model simultaneously the observed anisotropy, strain-rate sensitivity, and tension-compression asymmetry of the material, a three-dimensional constitutive model was developed. Key in the formulation is a macroscopic yield function [1] that incorporates the specificities of the plastic flow, namely the combined effects of anisotropy and tension-compression asymmetry. Comparison between model predictions and data show the capabilities of the model to describe with accuracy the plastic behavior of the a-Ti material for both quasi-static and dynamic loadings, in particular, a very good agreement was obtained between the simulated and experimental post-test Taylor specimen geometries.

Effects of Anisotropy of Preferential flow on the Hydrology and Stability of Landslides

Infiltration is one of the most important landslides triggering mechanisms and it is controlled by the hydraulic characteristics of the soil, which depend on degree of saturation, existence of preferential flow paths and anisotropy. In order to account for preferential flow that can have place in macro-pores and fissures, it is common to represent the soil matrix by means of the superimposition of two different domains: a soil matrix domain, which mainly accounts for the flow in the porous matrix, and preferential flow domain representing the flow through macro-pores and fissures. There have been recent investigations on the influences of preferential flow on slope stability; however, the combined effects of anisotropy and preferential flow on infiltration processes and on rainfall induced landslide mechanisms have not been studied yet, at our knowledge. Aiming at better understanding the effects that anisotropy combined with preferential flow has on the infiltration process, we investigated the stability of a hillslope using a numerical modelling approach. Results indicate that anisotropy affects the slope stability and its failure area.

Impact of varying irradiance on vegetation indices and chlorophyll fluorescence derived from spectroscopy data

Imaging spectroscopy (IS) provides an efficient tool to assess vegetation status and functioning at ecologically relevant scales. Reliable extraction of vegetation information from spatial and spectral high resolution spectroscopy data requires accurate retrieval schemes to account for the complex radiative transfer in the coupled vegetation-atmosphere system. Particularly the coupling of the atmosphere and vegetation considering combined effects of anisotropy, absorption and scattering typically relies on many assumptions, rendering estimates of direct (Edir) and diffuse (Edif) surface irradiance error prone. This impacts the reliability of retrieved vegetation properties.In this study we discuss and quantify the retrieval sensitivity of vegetation information using high resolution IS data to inaccurate assumptions of direct and diffuse surface irradiance. We use observations and simulations and focus on the two vegetation indices normalized difference vegetation index (NDVI) and the photochemical reflectance index (PRI), and on sun-induced chlorophyll fluorescence (Fs). Our results indicate that, even if the irradiance field (E) is exactly known, reflectance based vegetation indices show an inherent variation of 9% (NDVI) and 12% (PRI) respectively. These variations are caused by complex interactions of surface irradiance and reflectance anisotropy. The emitted Fs signal was found to be almost unaffected by those variations, if the retrieval considers surface anisotropy. Further, estimation of vegetation properties is subject to large uncertainties if instantaneous E fields are unknown. In that case, they range up to 13% for the NDVI, up to 32% for the PRI, and up to 58% for Fs. We conclude that retrieval sensitivities of vegetation indices and Fs to illumination effects must be carefully considered in data interpretation and suggest using coupled surface-atmosphere models to exploit the full information content of IS data.

Plastic deformation of high-purity α-titanium: Model development and validation using the Taylor cylinder impact test

In this paper, results of an experimental study on the quasi-static and high-rate plastic deformation due to impact of a high-purity, polycrystalline, α-titanium material are presented. It was found that the material is transversely isotropic and displays strong strength differential effects. Split Hopkinson Pressure Bar tests in tension and compression and Taylor impact tests were conducted. For an impact velocity of 196m/s, plastic deformation extended to 64% of the length of the deformed specimen, with little radial spreading. A three-dimensional constitutive model was developed. Key in the formulation was the use of a macroscopic yield function that incorporates the specificities of the plastic flow, namely the combined effects of anisotropy and tension–compression asymmetry. Comparison between model predictions and data show the capabilities of the model to describe with accuracy the plastic behavior of the α-titanium material for both quasi-static and high-rate loadings. In particular, the three-dimensional simulations of the Taylor impact test show a very good agreement with data, both the post-test major and minor side profiles and impact interface footprints are very well described.

Crystal structures and superconductivity of bismuth high temperature superconductors (Review)

In this review, a correlation between crystal structures and superconducting characteristics of high temperature bismuth superconductors (Bi HTSCs) is analyzed. The most well known works on refining of Bi-HTSC crystal structures are considered. The combined effect of anisotropy, caused by the layer character of the structures, and thermal fluctuations on superconducting characteristics of these compounds is discussed. The basic statements of the model of Bi2Sr2CaCu2O8+δ disproportionately modulated structures are considered.

Extended UH Model: Three-Dimensional Unified Hardening Model for Anisotropic Clays

AbstractExtended UH model is a three-dimensional elastoplastic constitutive model that builds on a modification of the UH model with a unified hardening parameter, to account for the effect of anisotropy and the influence of K0 consolidation on the stress-strain-strength behavior of clays. The combined effects of anisotropy and stress magnitude are considered through the minimum value of angles (α) made by the spatially mobilized planes (SMPs) and soil depositional plane. The original transformed stress tensor is revised by incorporating the anisotropic peak stress ratio Mα, which is defined as a function of α, with the stress tensor σij. The comparison with test results on San Francisco Bay Mud demonstrates the capability of the proposed anisotropic criterion. The UH model is extended to account for the combined effects of inherent anisotropy and K0 conditions on the stress-strain-strength response of anisotropic clays by incorporating the revised transformed stress tensor σij˜, the potential strength ra...

Stimulated light scattering in smectic A liquid crystals

Abstract The non-linear interaction of arbitrary polarized light with smectic layer deformations in smectic A liquids (SA) is considered. It is shown that the combined effect of anisotropy, fluidity and a characteristic kind of deformation cause a number of specific non-linear optical phenomena. Two-wave mixing in SA transforms into a partly degenerate four-wave mixing (FWM) when the polarization and the direction of propagation of the coupled electromagnetic (EM) waves are arbitrary. The interference of the EM waves gives rise to a dynamic grating of layer deformations without a change of mass density of SA. In the resonant case a propagating mode of a second sound (SS) is excited. The non-linear phenomena are analysed by solving the self-consistent system of the Maxwell equations for the non-linear anisotropic inhomogeneous medium and the hydrodynamic equations of SA in the external EM field. The explicit expressions of the EM and SS waves amplitudes are obtained. It is shown that the coupled fundamenta...

Vector wavefields for weakly attenuating anisotropic media by the ray method

The ray method is used to compute high‐frequency seismic vector wavefields in weakly attenuating layered anisotropic structures. The attenuating effects are introduced by substituting the real elastic parameters for perfectly elastic media by complex frequency dependent elastic parameters with small imaginary parts. The imaginary parts are formally considered to be of the order of [Formula: see text] for [Formula: see text]. Under this assumption, it is possible to work with real rays, only the eikonal is complex. The approximate computations based on this algorithm are only a few percent slower than those for perfectly elastic anisotropic media. The range of applicability of the weak attenuation concept is investigated by comparison of ray computations with results of the reflectivity method for an isotropic, constant gradient model. The study indicates that the region of applicability of the weak attenuation concept may be broader than expected. The combined effects of anisotropy and attenuation on the propagation of seismic waves in a three‐dimensional model of the uppermost crust with an anisotropic attenuating layer are then studied. The anisotropy as well as the attenuation are supposed to be caused by aligned partially liquid‐filled cracks. Hudson’s formulas to compute complex effective elastic parameters are used. Frequency responses and VSP synthetic seismograms for different degrees of viscosity of the liquid, and, thus, different degree of attenuation, show the effects of attenuation on the propagating waves. Nine‐component VSP vector wavefields are computed for two different source‐borehole directions along the strike of the cracks and 45 degrees off the strike of the cracks. The seismograms for the attenuating model are compared with seismograms for the corresponding perfectly elastic model.

Monolayer properties of mixed chlorophyll a-digalactosyldiacylglycerol at the nitrogen–water interface

Surface pressure, surface potential, and ellipsometric–area isotherms have been measured to investigate the properties of chlorophyll a – digalactosyldiacylglycerol monolayers at the nitrogen – water interface. The surface pressure – area isotherms of the mixed film show a pronounced negative deviation with respect to ideality, whereas the surface potential isotherms follow the additivity law for mixed films. As the mole fraction of Chl a increases from 0.1 to 0.5, each of the corresponding ellipsometric isotherm is shifted towards more negative values in the liquid expanded region. As the mole fraction is increased above 0.5, the ellipsometric δΔ values become more positive, with this trend continuing throughout the 0.5 to 0.9 mole fraction range. The combined effects of anisotropy in both the refractive indices and the absorption coefficient can explain the turnover observed in the ellipsometric δΔ isotherms as the mole fraction of Chl a becomes larger than 0.5.Hydrophilic interactions have been ruled out on the basis of the agreement with the additivity law, which is observed for surface potentials of the mixed monolayers. The observed deviation exhibited in the π–A isotherms is interpreted in terms of the intermolecular cavity effect. Key words: chlorophyll a, digalactosyldiacylglycerol, mixed monolayer, ellipsometry.

Polarisation of dielectronic recombination satellite lines

The polarisation of line radiation emitted during dielectronic recombination is investigated theoretically. By taking into account interference effects due to overlapping levels, formulae have been derived for the linear polarisation of these lines (usually called dielectronic satellites). Special attention is given to recombination of He-like systems which play an important role in hot plasmas. As an illustration, for n=4, results are reported for Li-like 1s2nl-1s2pnl satellites which contribute to the observed intensity of the He-like 1s2-1s2p parent line. The interference effects increase the polarisation up to a factor of two as n to infinity . Expressions are also given for the polarisation of well isolated Li-like satellite lines excited by an arbitrary axially symmetric electron angular distribution. Detectable (>or=10%) polarisation of j and k satellites may be expected in a low-density plasma provided the dominant thermal electrons contribute by less than about 70% of the total emission of these satellites. Finally, the combined effects of anisotropy and power-law energy distribution of a suprathermal electron tail on the intensity ratio j/w are examined. It is concluded that to neglect the presence of a small percentage of these suprathermal electrons in a thermal plasma may lead to strong overestimates of the plasma temperature.

Generalized model of the mechanics of thin-walled structures made of composite materials

1. A kinematic hypothesis which generalizes the broken line hypothesis was used to construct a variant of the theory of multilayered anisotropic shells with allowance for local effects, making it possible to study the actual law of distribution of components of the stress and strain tensors through the thickness of the layers. 2. The combined effect of anisotropy and geometric nonlinearity on the stress state of cross-reinforced shells was studied. It was found that failure to allow for anisotropy leads to serious errors in the design of composite shells with a small number of layers. 3. It was established that in the short edge-effect region near the ends of the shell, the tangential forces are distributed through the thickness of the layers in accordance with a law which is nonlinear.

Effect of Anisotropy and Stratification on Pressure Transient Analysis of Wells with Restricted Flow Entry

Effect of Anisotropy and Stratification on Pressure Transient Analysis of Wells with Pressure Transient Analysis of Wells with Restricted Flow Entry A numerical model, devised to study here the effect of anisotropy and stratification on pressure transient analysis of wells with restricted flow entry, utilizes a more realistic boundary condition than do the usual ones appearing in the literature. Nonetheless, the results from both types of models can be correlated. Introduction The effects of anisotropy and stratification on flow behavior and production performance of oil and gas wells have been studied by numerous authors. Lefkovits et al. studied the performance of totally penetrated, stratified bounded reservoirs with no penetrated, stratified bounded reservoirs with no crossflow. Others have studied a similar problem, but with crossflow; Russell and Prats have summarized the findings of these papers. Muskat studied the steady-state behavior of liquid flow for a partially penetrating well in an anisotropic system and penetrating well in an anisotropic system and concluded that the productivity weakly depended on the directional permeability ratios (k(z)/k(r) greater than 0.1). Nisle used the classical method of point source solution to the diffusivity equation to study the effect of partial penetration on pressure buildup of oil wells in an isotropic system. He found that the theoretical pressure buildup curves consisted of two straight pressure buildup curves consisted of two straight lines, the one at early buildup times having a slope proportional to the flow capacity of the open interval proportional to the flow capacity of the open interval (l-d)k(r) and the other having a slope proportional to the flow capacity of the entire formation hk(r). Later Brons and Marting supplemented the findings of Nisle and concluded that partial penetration gave rise to a pseudo damage, which reflected itself as a skin factor in pressure buildup calculations. Using the pseudo skin, they calculated the impairment of pseudo skin, they calculated the impairment of productivity of the production wells, which agreed well productivity of the production wells, which agreed well with the results of Muskat. Pizzi et al., using an electrical analog of a stratified system, concluded that a high pseudo damage resulted if the reservoir was partially penetrated. Harris" studied the optimum spacing and arrangement of perforations in cased holes. Hantush derived an expression for pressure distribution in an unbounded reservoir with restricted flow entry. Seth extended Hantush's work to a bounded reservoir. Odeh has studied a similar problem for steady-state conditions. problem for steady-state conditions. The purpose of this work was to investigate:the combined effects of anisotropy, stratification with crossflow, and restricted flow entry on pressure transient analysis of flow and buildup tests,the feasibility of calculating the horizontal permeabilities of intercommunicating stratified systems, andthe pressure interference tests in such systems. Theory The partial differential equation governing the isothermal flow of homogeneous fluids of constant compressibility is given by Eq. 1: ..............................(1) where The initial and the boundary conditions are: 1. The reservoir potential Phi is initially constant, say Phi i. JPT P. 639