Kind Of Anisotropy Research Articles

Anisotropic magnetoexcitons in two-dimensional transition metal trichalcogenide semiconductors

Direct and indirect excitons in Rydberg states in transition metal trichalcogenide (TMTC) monolayers, bilayers, and van der Waals (vdW) heterostructures in an external magnetic field are studied within the framework of the effective mass approximation. Binding energies of magnetoexcitons are calculated using the Rytova-Keldysh potential for direct magnetoexcitons and both the Rytova-Keldysh and Coulomb potentials for indirect magnetoexcitons. We report the magnetic field energy contribution to the binding energies and diamagnetic coefficients for magnetoexcitons that depend strongly on the effective mass anisotropy of electrons and holes. The comparative study of TMTCs and phosphorene is given. In ${\mathrm{TiS}}_{3}$, ${\mathrm{TiSe}}_{3}$, and ${\mathrm{ZrSe}}_{3}$ the excitonic binding energies and diamagnetic coefficients demonstrate the same kind of anisotropy as in phosphorene. In contrast, ${\mathrm{ZrS}}_{3}$ has the opposite anisotropy to phosphorene. The tunability of the binding energy of direct and indirect magnetoexcitons by the external magnetic field and the possibility to control the binding energy of magnetoexcitons in vdW heterostructures by manipulation of numbers of hBN monolayers are shown.

Anisotropy affects brittleness and stress-strain in ZrC

The topology structures are investigated for Zener and Every anisotropy, universal elastic anisotropy, stress-strain, and brittleness in ZrC based on Bond matrix model and tensor theory. Although the mathematical expressions of these three kinds of anisotropy are different, they give the same results, that is, the anisotropy is along the directions of [100], [110] and [111] respectively. The study of the brittleness of ZrC shows that there is a one-to-one relationship between anisotropy and brittleness. The cause of this phenomenon can be explained from the 3-D spatial structure of its negative Cauchy pressure. The investigations mainly focus on the topological structures of stress - strain in ZrC induced by point force. The results indicate that the orientation of stress-strain is not only consistent with the direction of the anisotropy of the crystal, but also with the symmetry of the crystal.

Flux-Pinning Properties of BaHfO3-Doped EuBCO-Coated Conductors Fabricated by Hot-Wall PLD

REBa2Cu3Ox (REBCO, RE = rare earth) coated conductors (CCs) are promising as superconducting wires for high-field magnets because of their high in-field critical current density (Jc) performance and high tensile tolerance. Fujikura, Ltd., has been developing BaHfO3 (BHO)-doped EuBa2Cu3Ox (EuBCO, Eu = Europium) CCs using a hot-wall-type pulsed-laser deposition (PLD) in order to further improve the in-field performance. Although a high deposition rate in the PLD process is necessary for mass production, it has been found that the in-field performance greatly differ depending on the deposition rate. In this study, flux pinning properties of BHO-doped EuBCO CCs fabricated with different deposition rates by the hot-wall PLD on IBAD substrates were investigated in detail. From the scaling characteristics of the flux-pinning force density (Fp) curve, the BHO precipitates in a fast deposition rate REBCO film appeared to behave like random pinning centers, which was almost consistent with a result of transmission electron microscope observation. On the other hand, from a decrease of anisotropy in the magnetic field angle dependence of Jc, it was also confirmed that BHO precipitates were not completely random pinning centers, that is, it has some kind of anisotropy. Considering the critical current value per production time, it was also found that the fast deposition rate is advantageous since the REBCO layer could be thicker.

Phase field modeling of brittle fracture in materials with anisotropic fracture resistance

AbstractMaterials which reveal a directionality in terms of the fracture resistance motivate the integration of anisotropic behavior within approaches for crack growth simulations. Within a variational phase field model for fracture, this kind of anisotropy is included by the enhancement of the non‐local part of the crack energy functional. Results of a numerical crack path simulation are presented and discussed to illustrate the properties of the applied model.

Flexible Linearly Polarized Photodetectors Based on All‐Inorganic Perovskite CsPbI3 Nanowires

AbstractPolarization‐sensitive photodetection has drawn a great deal of research interests, which takes advantage of anisotropy from the lattice structure or the morphology of active material. However, no photodetectors combined these two kinds of anisotropy together for linearly polarized photodetection. Here, a photodetector based on cesium lead iodide (β‐CsPbI3) nanowire array with anisotropic crystal structure is demonstrated. Owing to the crystal structure and morphology anisotropy of the β‐CsPbI3 nanowires, the device exhibited high sensitivity to linearly polarized light with a photocurrent anisotropy ratio of 2.68 and 2.17 on rigid and flexible substrates, respectively, which was much higher than existing linearly polarized photodetectors. In addition, the photocurrent anisotropy ratio of the device on flexible substrate only dropped by 5% after 500 bending cycles, indicating excellent flexibility and folding endurance of flexible CsPbI3 device. The application of anisotropic CsPbI3 nanowires in polarization‐sensitive photodetection might provide new functionalities in novel optoelectronic applications.

2D Nonlayered Selenium Nanosheets: Facile Synthesis, Photoluminescence, and Ultrafast Photonics

AbstractInvestigations into 2D nanomaterials are of considerable significance from both an academic and industrial point of view. The present work addresses, for the first time, the fabrication of 2D nonlayered ultrathin selenium through a facile liquid‐phase exfoliation method. The results reveal that the as‐prepared 2D Se nanosheets are 40–120 nm in lateral dimension and 3–6 nm in thickness. The nanosheets exhibit a trigonal crystalline phase similar to their bulk counterpart, indicating the conservation of the crystalline features during the exfoliation procedure. The successful preparation of 2D Se nanosheets from nonlayered bulk Se can be ascribed to two kinds of anisotropy: (1) that of crystalline bulk Se with chain‐like structures, where strong intrachain SeSe covalent bonds coexist with weak interchain van der Waals forces, and (2) that of probe sonication in the vertical direction. The results also show that the 2D Se nanosheets possess a size‐dependent band gap (E g), strong photoluminescence effect and robust, chemical stability under ambient conditions. Furthermore, a 2D Se‐nanosheet‐based optical modulation device is demonstrated that allows for excellent ultrashort pulse generation of an optical communication band. It is therefore anticipated that 2D Se nanosheets may find significant applications in both photoluminescence and ultrafast photonics.

INFLUENCE OF ANISOTROPY AND MAGNETIC FIELD ON THERMAL ENTANGLEMENT IN HEISENBERG MODEL AND THERMODYNAMIC ANALYSIS OF MODEL

The thermal entanglement in a two-qubit anisotropic Heisenberg XXZ system, also XYZ system, with Dzyaloshinskii-Moriya (DM) couplings in an inhomogenous magnetic field, was studied. The effects of these two kinds of anisotropies on the thermal entanglement have been studied in detail in the concept for concurrence, the measure of entanglement. The analytical expressions of concurrence are obtained for this model. It is found that the DM interaction can enhance thermal entanglement and can be efficiently controlled by the DM interaction parameter and ehchange interaction Jx, Jy and Jz. When D is large enough, the entanglement can exist for larger temperatures and strong magnetic field. We also analysed thermodynamic properties of Heisenberg model and the most important results were shown in the paper.

On correction of translational misalignments between section planes in 3D EBSD

Three-dimensional electron backscatter diffraction allows obtaining the 3D image of a material from the stack of 2D sections. This is achieved by repeated application of two different beams; electron beam for electron backscatter diffraction mapping of the surface and focused ion beam for removing a thin layer of material from the surface. In most of these systems with two beams, the experiment requires stage movements for correct positioning of the sample to the respective beams. However, imperfections in this positioning are difficult to avoid, which yield small translational misalignments between the sections in the output data. In this work, we deal with an important task of correcting these misalignments between the sections such that the 3D image is recovered properly. On a simple example, we demonstrate that commonly used methods fail in case there is a structural anisotropy in the material under consideration. We propose an improved alignment algorithm which can neglect this behaviour with the use of external support information on a systematic trend in the translational misalignments. Efficiency of the algorithm is proven on a number of simulated data with different kinds of anisotropy. Application to a real data sample of a fine grained aluminium alloy is also given. The algorithm is available in an open-source library.

INFLUENCE OF ANISOTROPY AND MAGNETIC FIELD ON THERMAL ENTANGLEMENT IN HEISENBERG MODEL AND THERMODYNAMIC ANALYSIS OF MODEL

The thermal entanglement in a two-qubit anisotropic Heisenberg XXZ system, also XYZ system, with Dzyaloshinskii-Moriya (DM) couplings in an inhomogenous magnetic field, was studied. The effects of these two kinds of anisotropies on the thermal entanglement have been studied in detail in the concept for concurrence, the measure of entanglement. The analytical expressions of concurrence are obtained for this model. It is found that the DM interaction can enhance thermal entanglement and can be efficiently controlled by the DM interaction parameter and ehchange interaction Jx, Jy and Jz. When D is large enough, the entanglement can exist for larger temperatures and strong magnetic field. We also analysed thermodynamic properties of Heisenberg model and the most important results were shown in the paper.

Superparamagnetic effect in the rotatable anisotropy of nanoparticles and films

The exchange bias effect in nano-objects is modelled by adding to the magnetic energy two terms allowing for two kinds of anisotropy, viz. a fixed-axis and a rotatable one. The signature of the second contribution is an isotropic shift HRA of the ferromagnetic resonance field. The temperature dependence of HRA that is due to the superparamagnetic theory is obtained in the framework of kinetic theory. Our analysis predicts that the temperature behaviors of HRA are qualitatively different depending on the possible symmetry type of the rotatable anisotropy energy term: unidirectional or uniaxial.

On the robustness of ILU smoothers on triangular grids

In this work, incomplete factorization techniques are used as smoothers within a geometric multigrid algorithm on triangular grids. A local Fourier analysis is proposed to study the smoothing properties of these methods, as well as the asymptotic convergence of the whole multigrid procedure. With this purpose, two- and three-grid local Fourier analysis are performed. Several two-dimensional diffusion problems, including different kinds of anisotropy are considered to demonstrate the robustness of this type of methods.

New route toward nanosized crystalline metal borides with tuneable stoichiometry and variable morphologies.

Herein we highlight for the first time the ability to tune the stoichiometry of metal boride nanocrystals through nanoparticle synthesis in thermally stable inorganic molten salts. Two metal-boron systems are chosen as case studies: boron-poor nickel borides and boron-rich yttrium borides. We show that NiB, Ni4B3, Ni2B, Ni3B, and YB6 particles can be obtained as crystalline phases with good selectivity. Anisotropic crystallization is observed in two cases: the first boron-rich YB4 nanorods are reported, while boron-poor NiB nanoparticles show a peculiar crystal habit, as they are obtained as spheres with uniaxial defects related to the crystal structure. Crystallization mechanisms are proposed to account for the appearance of these two kinds of anisotropy at the nanoscale.

Environment-induced anisotropy and sensitivity of the radical pair mechanism in the avian compass.

Several experiments over the years have shown that the earth's magnetic field is essential for orientation in birds' migration. The most promising explanation for this orientation is the photo-stimulated radical pair (RP) mechanism. In order to define a reference frame for the orientation task radicals must have an intrinsic anisotropy. We show that this kind of anisotropy and consequently the entanglement in the model are not necessary for the proper functioning of the compass. Classically correlated initial conditions for the RP, subjected to a fast decoherence process, are able to provide the anisotropy required. Even a dephasing environment can provide the necessary frame for the compass to work and also implies fast decay of any quantum correlation in the system without damaging the orientation ability. This fact significantly expands the range of applicability of the RP mechanism providing more elements for experimental search.

Thermal Effects in Anisotropic Porous Elastic Rods

This research is concerned with the thermoelastic deformation of a porous anisotropic right cylinder subjected to a thermal field independent of the axial coordinate. The case of a material with a plane of elastic symmetry which contains the axis of cylinder is considered. The solution of the problem is expressed in terms of solutions of some generalized plane strain problems. It is shown that the temperature field produces extension, torsion, and a plane strain. For this kind of anisotropy, an infinitesimal twist produces a variation of volume fraction field. The method is used to study the deformation of an inhomogeneous circular cylinder.

Isotropic and nondispersive planar fed Luneburg lens from Hamiltonian transformation optics

A modified Luneburg lens based on Hamiltonian optical transformation with planar feeds is proposed in this Letter. The lens, made of conventional all-dielectric materials, does not have any kind of anisotropy. Therefore, in theory, its bandwidth of operation has no upper frequency limitations in contrast with recent designs utilizing metamaterials. Results for wide-angle radiation and broadband operation are presented.

Nonlinear electron-magnetohydrodynamic simulations of three dimensional current shear instability

This paper deals with detailed nonlinear electron-magnetohydrodynamic simulations of a three dimensional current shear driven instability in slab geometry. The simulations show the development of the instability in the current shear layer in the linear regime leading to the generation of electromagnetic turbulence in the nonlinear regime. The electromagnetic turbulence is first generated in the unstable shear layer and then spreads into the stable regions. The turbulence spectrum shows a new kind of anisotropy in which power transfer towards shorter scales occurs preferentially in the direction perpendicular to the electron flow. Results of the present three dimensional simulations of the current shear instability are compared with those of our earlier two dimensional simulations of sausage instability. It is found that the flattening of the mean velocity profile and thus reduction in the electron current due to generation of electromagnetic turbulence in the three dimensional case is more effective as compared to that in the two dimensional case.

Anisotropic shrinkage of mineral and organic soils and its impact on soil hydraulic properties

The shrinkage behavior of soils does not only affect the aggregate formation but also it alters pore size distribution and pore functions like water and gas permeability. In order to quantify this shrinkage effect both with respect to the intensity and orientation (isotropy or anisotropy) undisturbed organic and mineral soil samples (sedge peat, peat-clay, half-bog and glacial clay) in Northern Germany were analyzed. In addition to the registration of the vertical volume change during drying by means of height change measurements assuming shrinkage isotropy, digital photography and image analysis were used to consider horizontal shrinkage components including crack formation in order to calculate the 3 dimensional shrinkage geometry (=kind of anisotropy).The organic substrates show the highest shrinkage potential according to the COLE (coefficient of linear extensibility) with values between 0.26 and 0.43. Maximum volume decreases from saturation to complete desiccation of up to 66vol.% (peat-clay) were calculated. In contrast to the mineral soils, the investigated sedge peat did not exhibit residual or zero shrinkage. Moreover, the soil volume decrease during desiccation partly even exceeded the water loss in case of the organic substrates (sedge peat, peat-clay) which can be attributed to mineralization.Shrinkage-dependent volume changes at initial desiccation were determined to be almost exclusively vertical (geometry factor rs=1). During further drying, however, shrinkage led to isotropy (rs=3) followed by a slight dominance of the horizontal shrinkage component. These results are true not only for shrinking mineral, but also for the tested organic soils.These results underline that a general assumption of a rigid pore system is hardly true. Moreover, the exclusive measurement of the shrinkage-induced soil height changes assuming shrinkage isotropy leads to a distinct overestimation of the actual shrinkage particularly at initial desiccation. Although the calculated COLE values were quite close to each other the actual shrinkage behavior differed depending on the kind of substrate and degree of initial structure.Thus, the consequences of the shrinkage pattern led to large differences of the moisture retention characteristics of the studied mineral and organic soils particularly at more negative matric potential values. Furthermore, the changes of the pore continuity due to shrinkage are intensely altered too and affect water flux modeling results.

The characteristic state

Simulations of cyclic biaxial tests on samples composed of 2D irregular polygonal particles were performed to investigate the properties of the characteristic state, transition state between contraction and dilation. Two aspect ratios of 2D angular particules and different states of initial fabric are considered. The stress ratio at characteristic state is found to be much more sensitive to initial anisotropy than to density changes. Fabric is the kind of anisotropy that seems to influence the most the characteristic state. Constant amplitude cycling does not erase the influence of the initial anisotropy of fabric which was not expected. Then, in the framework of usual soil modelling where the material is supposed to be in an initially isotropic state, the usual models for the characteristic state are only valid for constant cyclic strain amplitude loadings where the mean anisotropy throughout the cycles remains low. Des simulations d’essais biaxiaux cycliques ont été entreprises sur des échantillons constitués de particules polygonales irrégulières afin d’étudier les propriétés obtenues à l’état caractéristique, transition entre un comportement contractant et dilatant. Deux rapports d’allongement des particules sont étudiés tout comme différents états initiaux de structures. Le rapport de contraintes à l’état caractéristique est trouvé beaucoup plus sensible à l’anisotropie initiale qu’aux variations de densité. Seule l’anisotropie, dite de structure, semble agir sur cet état. Des cycles à déformations d’amplitude constante n’effacent pas l’influence de cette anisotropie initiale, ce qui n’était pas attendu. Aussi, dans un contexte classique où le matériau est initialement à l’état isotrope, les modèles décrivant l’état caractéristique ne sont-ils valides que pour des chargements cycliques symétriques où l’anisotropie moyenne reste faible.

Spatially fractional-order viscoelasticity, non-locality, and a new kind of anisotropy

A class of non-local viscoelastic equations of motion including equations of fractional order with respect to the spatial variables is studied. It is shown that space-fractional equations of motion of an order strictly less than 2 allow for a new kind of anisotropy, associated with azimuthal dependence of non-local interactions between stress and strain at different material points. Constitutive equations of such viscoelastic media are determined. Relaxation effects are additionally accounted for by replacing second-order time derivatives by lower-order fractional derivatives. Explicit fundamental solutions of the Cauchy problem for scalar equations with isotropic and anisotropic non-locality are constructed. For some particular choices of the parameters, numerical solutions are constructed.

Spontaneous exchange-bias in Fe/Mn thin multilayers

Fe/Mn multilayers were grown by means of a molecular beam epitaxy system onto quartz substrates changing the thickness of the elemental layers. A spontaneous unidirectional anisotropy develops for thickness of Fe or Mn layer of about 35 Å. Since the samples were no subjected to field cooling treatments during or after the growth, this kind of anisotropy can be explained considering besides the exchange coupling at the Fe/Mn interface, the structural disorder due to dislocations and defects. In effect, the appearance and strength of the exchange-bias field are depending on the surface roughness of the samples and are significantly enhanced by the formation of a structure constituted by islands showing a snake-like morphology. The fitting of the angular dependence of the exchange-bias field indicates that the associated anisotropy is due to the superposition of two contributions, the principal one with unidirectional symmetry and the other showing uniaxial characteristics.