Anisotropic Orientation Research Articles

Modelling interactions of cationic dimers in He droplets: microsolvation trends in HenK2+ clusters.

We report the results of a detailed theoretical investigation of small K2+-doped He clusters. The structural characteristics and stabilities of such cations are determined from ab initio electronic structure calculations at the MRCI+Q level of theory. The underlying interactions show a multireference character and such effects are analyzed. The interaction potentials are constructed employing an interpolation technique within the inverse problem theory method, while the nuclear quantum effects are computed for the trimers, their spatial arrangements are discussed, and information was extracted on the orientational anisotropy of the forces. We found that energetically the most stable conformer corresponds to linear arrangements that are taking place under large amplitude vibrations, with high zero-point energy. We have further looked into the behavior of higher-order species with various He atoms surrounding the cationic dopant. By using a sum of potentials approach and an evolutionary programming method, we analyzed the structural stability of clusters with up to six He atoms in comparison with interactions energies obtained from MRCI+Q quantum chemistry computations. Structures containing Hen motifs that characterize pure rare gas clusters, appear for the larger K2+-doped He clusters, showing selective growth during the microsolvation process of the alkali-dimer cation surrounded by He atoms. Such results indicate the existence of local solvation microstructures in these aggregates, where the cationic impurity could get trapped for a short time, contributing to the slow ionic mobility observed experimentally in ultra-cold He-droplets.

Bone elasticity and ultrasound velocity are affected by subtle changes in the organic matrix.

The mechanical competence of bone can be studied through the measurement of the components of its material elasticity, a property which can vary both in magnitude and in dependence upon orientation (anisotropy). While it is known that the elasticity is largely determined by the mineral constituents of the bone matrix, it is nonetheless clear that it must be also dependent upon the remaining constituents of bone material. In this work, the influence of organic components on the elasticity is explored by altering specific constituents of the bone matrix to varying degrees. This study addresses two questions: first, are the resulting changes in elasticity strongly or weakly dependent upon direction, and second, are they substantially dependent upon the nature and magnitude of the induced matrix alteration? To answer these questions, we performed different chemical manipulations of the bone matrix and measured the changes in elasticity and velocity using the technique of ultrasound critical angle reflectometry. Altering the properties of the organic matrix resulted in substantial and complex changes in the elasticity of bone. The observed changes were strongly dependent upon direction, could not be explained by changes in density alone, and varied strongly with the specific chemical treatment of the matrix. Immersion in urea selectively affected protein components of the organic matrix and resulted in reversible changes in velocity and elasticity, while removal of collagen caused anisotropic decreases and removal of all organic matter caused a collapse of all components of the elasticity. In conclusion, this study confirms that the organic matrix exerts a profound influence on the elasticity and indicates that the measurement of elastic properties at multiple directions is necessary in the assessment of bone mechanical competence.

Enhanced mechanical and anisotropic thermal conductive properties of polyimide nanocomposite films reinforced with hexagonal boron nitride nanosheets

AbstractTo attain thermally conductive but electrically insulating polymer films, in this study, polyimide (PI) nanocomposite films with 1–30 wt% functionalized hexagonal boron nitride nanosheets (BNNSs) were fabricated via solution casting and following imidization. The microstructures, mechanical and thermal conductive properties of PI/BNNS nanocomposite films were examined by taking account of the relative content, anisotropic orientation, and interfacial interaction of BNNS and PI matrix. The scanning electron microscopy, X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and X‐ray diffractometry data revealed that BNNSs with hydroxy and amino functional groups have specific molecular interactions with PI matrix and they form stacked aggregates in the nanocomposite films with high BNNS loadings of 10–30 wt%. The tensile mechanical strength/modulus, thermal degradation temperatures, and thermal conductivity of the nanocomposite films were found to be significantly enhanced with increasing the BNNS loadings. For the nanocomposite films with 1–30 wt% BNNS loadings, the in‐plane thermal conductivity was measured to be 1.82–2.38 W/mK, which were much higher than the out‐of‐plane values of 0.35–1.14 W/mK. The significant anisotropic thermal conductivity of the nanocomposite films was found to be owing to the synergistic anisotropic orientation effects of both BNNS and PI matrix. It is noticeable that the in‐plane and out‐of‐plane thermal conductivity values of the nanocomposite film with 30 wt% BNNS were ~1.31 and ~3.35 times higher than those of neat PI film, respectively.

Анизотропия отрицательного магнетосопротивления в эапитаксиальных слоях GaMnAs

Anisotropy of magnetotransport properties of GaMnAs epitaxial layers in ferromagnetic state has been investigated as a function of temperature. The anisotropy of negative magnetoresistance that is not related to uniaxial anisotropy and hard axis orientation has been observed. This anisotropy may be result of arising of spatially oriented structures in the GaMnAs layer during its growth.

Anisotropic optical properties of single Si2Te3 nanoplates

We report a combined experimental and computational study of the optical properties of individual silicon telluride (Si2Te3) nanoplates. The p-type semiconductor Si2Te3 has a unique layered crystal structure with hexagonal closed-packed Te sublattices and Si–Si dimers occupying octahedral intercalation sites. The orientation of the silicon dimers leads to unique optical and electronic properties. Two-dimensional Si2Te3 nanoplates with thicknesses of hundreds of nanometers and lateral sizes of tens of micrometers are synthesized by a chemical vapor deposition technique. At temperatures below 150 K, the Si2Te3 nanoplates exhibit a direct band structure with a band gap energy of 2.394 eV at 7 K and an estimated free exciton binding energy of 150 meV. Polarized reflection measurements at different temperatures show anisotropy in the absorption coefficient due to an anisotropic orientation of the silicon dimers, which is in excellent agreement with theoretical calculations of the dielectric functions. Polarized Raman measurements of single Si2Te3 nanoplates at different temperatures reveal various vibrational modes, which agree with density functional perturbation theory calculations. The unique structural and optical properties of nanostructured Si2Te3 hold great potential applications in optoelectronics and chemical sensing.

Evolution of Coordination Number of Methane Hydrate Bearing Sediments during Quasi-static Shearing

Quasi-static shearing of methane hydrate bearing sediments (MHBS) was investigated by performing numerical tests using distinct element method (DEM) so as to comprehensively understand mechanical properties of MHBS. Stress-strain response and dilation behaviour of numerical tests were presented and compared with that of physical experiments. And then an examination of the evolution of coordination number (CN) during shearing was also presented, as well as its relation to anisotropy of contact orientations. The research results led us to conclude that (i) DEM can effectively capture the main characteristics of strength and deformation of MHBS; (ii) Distribution of CN shows obvious heterogeneity which is closely associated with shear bands; (iii) The average CN has a strong correlation with total number of contacts, and could be further interpreted from the point of view of anisotropy of contact orientations;

Tumor Habitat-derived Radiomic Features at Pretreatment MRI That Are Prognostic for Progression-free Survival in Glioblastoma Are Associated with Key Morphologic Attributes at Histopathologic Examination: A Feasibility Study.

To identify radiomic features extracted from the tumor habitat on routine MR images that are prognostic for progression-free survival (PFS) and to assess their morphologic basis with corresponding histopathologic attributes in glioblastoma (GBM). In this retrospective study, 156 pretreatment GBM MR images (gadolinium-enhanced T1-weighted, T2-weighted, and fluid-attenuated inversion recovery [FLAIR] images) were curated. Of these 156 images, 122 were used for training (90 from The Cancer Imaging Archive and 32 from the Cleveland Clinic, acquired between December 1, 2011, and May 1, 2018) and 34 were used for validation. The validation set was obtained from the Ivy Glioblastoma Atlas Project database, for which the percentage extent of 11 histologic attributes was available on corresponding histopathologic specimens of the resected tumor. Following expert annotations of the tumor habitat (necrotic core, enhancing tumor, and FLAIR-hyperintense subcompartments), 1008 radiomic descriptors (eg, Haralick texture features, Laws energy features, co-occurrence of local anisotropic gradient orientations [CoLIAGe]) were extracted from the three MRI sequences. The top radiomic features were obtained from each subcompartment in the training set on the basis of their ability to risk-stratify patients according to PFS. These features were then concatenated to create a radiomics risk score (RRS). The RRS was independently validated on a holdout set. In addition, correlations (P < .05) of RRS features were computed, with the percentage extent of the 11 histopathologic attributes, using Spearman correlation analysis. RRS yielded a concordance index of 0.80 on the validation set and constituted radiomic features, including Laws (capture edges, waves, ripple patterns) and CoLIAGe (capture disease heterogeneity) from enhancing tumor and FLAIR hyperintensity. These radiomic features were correlated with histopathologic attributes associated with disease aggressiveness in GBM, particularly tumor infiltration (P = .0044) and hyperplastic blood vessels (P = .0005). Preliminary findings demonstrated significant associations of prognostic radiomic features with disease-specific histologic attributes, with implications for risk-stratifying patients with GBM for personalized treatment decisions. Supplemental material is available for this article. © RSNA, 2020.

Particle size dependent anisotropic thermoelectric properties of N-type Bi2(Te,Se)3 alloys on hot deformation

The anisotropy of thermoelectric properties and microstructures in Bi2Te2.7Se0.3 fabricated by repressing (hot deformation) is investigated. The initial particle and grain size decreased with high-energy ball milling time, which affected the degree of grain orientation during the hot deformation process. To achieve high-performance thermoelectric properties, the anisotropic TE properties are optimized with the control of the degree of grain orientation, carrier concentration and temperature-dependent transport properties. By optimizing synthesis processes, we achieved a highly anisotropic figure of merit (ZT), with peak ZT values of 0.7 and 1.05 at 423 K, in the out of plane and in-plane directions, respectively. The in-plane ZT of the hot deformation sample was enhanced by 24% compared with that of the as-pressed sample (ZT = 0.85) due to reduced electrical resistivity and thermal conductivity, which was attributed to the significant anisotropy in grain orientation.

No Association Between Structural Properties of Corpus Callosum and Handedness: Evidence from the Constrained Spherical Deconvolution Approach

Handedness is the most prominent trait of functional asymmetry in humans, associated with lateralized cognitive functions and considered in relation to mental disorders. However, the neuroanatomical correlates of handedness are still unclear. It has been hypothesized that the structural properties of sub-regions of the corpus callosum (CC) are linked to handedness. Nevertheless, tractography studies of the relation between directly measured structural properties of CC subregions and handedness are lacking. The Constrained Spherical Deconvolution (CSD) approach enables full reconstruction of the sub-regions of the CC. The current study aimed to investigate the relation between the structural properties of the CC, such as volume and the CSD metric, referred to as hindrance modulated orientational anisotropy (HMOA), and handedness. Handedness was considered in two dimensions: direction (right-handed, ambidextrous, left-handed) and degree (the absolute values of Handedness quotient). We found no association between 1) volume or HMOA as a proxy of microstructural properties, namely the axonal diameter and fiber dispersion, of each sub-region and 2) either the direction or the degree of handedness. These findings suggest the absence of a direct relation between sub-regions of the CC and handedness, demonstrating the necessity of future tractography studies.

Mind-Craft: Exploring the Effect of Digital Visual Experience on Changes to Orientation Sensitivity in Visual Contour Perception.

Visual perception depends fundamentally on statistical regularities in the environment to make sense of the world. One such regularity is the orientation anisotropy typical of natural scenes; most natural scenes contain slightly more canonical (horizontal and vertical) information than oblique information. This property is likely a primary cause of the oblique effect in which subjects experience greater perceptual fluency with horizontally and vertically oriented content than oblique. Recent changes in the visual environment, including the "carpentered" content in urban scenes and the framed, caricatured content in digital screen media presentations, may have altered the typical (natural) level of orientation anisotropy. The current work evaluated whether digital visual experience, or visual experience with framed digital content, has the potential to alter the magnitude of the oblique effect in visual perception. Experiment 1 successfully established a novel eye-tracking method capable of indexing the visual oblique effect quickly and reliably and demonstrated the oblique effect. Experiment 2 used this method and found that one session of exposure to a specific video game altered visual orientation perception. Taken together, these results indicate that exposure to the realistic, but caricatured scene statistics of digital screen media, can alter visual contour perception in one session.

Stitching nanosheets of covalent organic frameworks to build aligned nanopores in nanofiltration membranes for precise ion separations

Embedding nanofillers into polyamide (PA) matrices is considered as a simple yet effective strategy for boosting the performances of thin-film nanocomposite (TFN) nanofiltration (NF) membranes. However, the NF performances are usually compromised by the inadequate interface compatibility between nanofillers and PA matrices as well as the anisotropic orientation of nanofillers. Herein, we propose a distinctive fabrication strategy for TFN membranes featuring excellent compatibility and highly-aligned microstructures. The reactive covalent organic framework (COF) nanosheets are chemically stitched at oil-water interfaces to form continuous nanofilms, and the PA matrices are then in-situ formed to encapsulate them, giving the TFN membranes. The stitched nanofilms contain two types of perpendicularly oriented pores: intrinsic apertures in COF nanosheets, and gaps among adjacent nanosheets. Together with the abundant reactive sites, the stitched nanofilms not only mediate the controllable synthesis of PA matrices, but also are covalently fused into the matrices. The aligned pores of the stitched nanosheets are capable of sieving salt ions, endowing TFN membranes with high separation precision and fast water permeation. This work demonstrates a strategy to control the orientation of COF nanosheets, which is highly desired in diverse fields not limited to membrane separation.

Stability of Poiseuille flow in an anisotropic porous layer with oblique principal axes: More accurate solution

AbstractThe stability of fluid flow in an anisotropic porous medium of Brinkman type is investigated. Anisotropy in the permeability is considered such that its longitudinal principal axis is oriented arbitrarily with the horizontal, while transversely it is isotropic. A fourth‐order eigenvalue problem obtained by performing a linear stability analysis is solved numerically using the Chebyshev collocation and the compound matrix methods. The critical Reynolds number and the critical wave number are computed for different values of porous parameter, orientation angle of the principal axis and the mechanical anisotropy parameter. The porous and the mechanical anisotropy parameters disclose contrasting contributions to the stability of fluid flow. The orientation angle instills either stabilizing or destabilizing effects on the fluid flow depending on the value of anisotropy parameter. Besides, the streamlines of the perturbation modes are presented for various values of orientation angle and anisotropy parameter. For the Darcy case, a simple analytical method is employed and established that the flow is stable for all infinitesimal perturbations.

Improving strain in single crystal by composition-gradients design

Domain switching is one of the essential contributions for strain in ferroelectric materials. In this work, we utilize anisotropic composition gradients (CGs) to induce anisotropic orientation of both defects and spontaneous dipoles, aiming to enhance the contribution of domain switching on strain in KTa1–xNbxO3 single crystal. In this way, a remarkable improvement (over 60%) of strain is obtained in KTa0.58Nb0.42O3 single crystal along the smallest CG direction, achieving a large unipolar strain, i.e. 0.29%, at low driving electric field 10 kV cm–1. It is attributed to the preferred orientation of both defects and spontaneous dipoles along the largest CG directions, then improving the contribution of domain switching on strain along the smallest CG direction. Particularly, owing to the existence of Ein as recoverable forces caused by both flexoelectric fields and defects pinning effect, KTN show nearly zero remnant strain (srem) along with the small CG directions, corresponding to the double P-E loops. Moreover, the V–PFM images confirm that CGs can influence the microdomain structures. Thus, designing special anisotropic CGs materials is expected to be a novel method to improve the strain properties and a potential way to flexibly design next-generation anisotropic piezoelectric materials.

Constraining Ice Shelf Anisotropy Using Shear Wave Splitting Measurements from Active‐Source Borehole Seismics

Observations of ice shelf anisotropy on borehole seismic data are presented. Hot‐water‐drilledboreholes were made by the Aotearoa New Zealand Ross Ice Shelf Programme through a grounding‐line proximal site at Windless Bight and the central Ross Ice Shelf site HWD‐2. The boreholes were used to freeze seismometers into the ice at different depths. Seismic observations of shear wave splitting were made on the borehole seismometers using active sources deployed at the surface. These shear wave splitting data were used to constrain anisotropic ice crystallographic preferred orientations (CPO) within the ice column. Forward models of seismic properties from different CPO geometries are compared to the observations and a best fitting CPO model is found to explain the seismic anisotropy at HWD‐2. This model consists of a vertical girdle of ice c axes that constitute 80% of the CPO in combination with tight horizontal clusters, which contribute 20% of ice c axes. The origin of the modeled CPO is discussed with regard to calculated strain rates at the site and found to be indicative of the current shear kinematics with vertical shear plane and horizontal shear direction. At HWD‐2 the 370 m thick ice shelf is calculated to consist of at least 197 m of anisotropic ice.

Why Cervical Vertebrae Do Not Fracture – A Biomechanical Approach Using Loading Tests on Human Vertebrae of A 79-Year-Old Body Donor.

Abstract Purpose: Bone structure alters with increasing age. Material and structural properties are both important for bone strength. Despite having an ageing society, there is a paucity of data from elderly subjects in terms of these parameters. The aim of the present study was to conduct comparative examinations of the structure and material properties of the cervical spine (CS), the thoracic spine (TS) and the lumbar spine (LS), in order to identify both structural and biomechanical differences between the segments of the spine. Methods: We examined central bone cylinders of vertebral bodies C1 to L5 from a 79-year-old body donor in regards to their bone volume fraction (BVF), trabecular thickness (Tb.Th.), separation (Tb.Sp.), trabecular orientation (SMI) and degree of anisotropy (DA). Samples were obtained from all vertebrae with a Jamshidi needle®, and were prepared with a damp cloth in an Eppendorf reaction vessel (1.5 ml). The investigations were performed with a micro-CT device (SKYSCAN 1172, RJL Micro &amp; Analytic GmbH, Germany). Existing deformities and fractures were registered with quantitative computed tomography (QCT). The load tests of the vertebral bodies C1 to L5 were performed on a servo-hydraulic testing machine (MTS 858, MTS Systems Cooperation, Eden Prairie, USA). Results: Regarding BVF (p=0.003), Tb.Th. (p=0.041) and SMI (p=0.012) statistically significant differences were found in the different spinal column sections. The force per area was significantly higher in the CS than in the TS and LS (CS vs. TS, p=0.022; CS vs. LS, p&lt;0.001; TS vs. LS, p=0.012). Conclusion: Due to their unique microarchitecture cervical vertebrae are less prone to fractures than thoracic and lumbar vertebrae. Among the reasons are the higher BVF and Tb.Th. of the cervical vertebrae compared to other vertebrae. Furthermore, the SMI of the CS has more plates than rods. Thus, the CS is characterized by specific features, whose causes must be determined in further investigations.

Composite magmatic/magnetic fabrics evidences late AMS in syn-tectonic dikes in the Monteiro-Sumé plutonic-volcanic complex (NE Brazil)

Interpretations of flow fabrics in dikes using anisotropy of magnetic susceptibility (AMS) are based on the orientation of the magnetic fabric recorded next to the dike walls. However, uncertainties remain when AMS is sensitive to parameters such as grain size and composition of the magnetic carriers and deformation of the magma. We study subvolcanic andesite to dacite dikes associated with granite plutons that intrude the basement rocks. The dikes have magnetic susceptibilities mostly between 10−3 and 10−2 SI carried by Fe–Ti oxides. AMS shows fabrics that would be consistent with a lateral movement of the magma. However, the anisotropy of anhysteretic remanence (AAR) and silicate shape preferred orientation (SPO) indicate that the melt moved upward based on the steeply plunging lineations detected by AAR and SPO. Furthermore, the obliquity of the AAR foliations in the dike margins indicates a component of transtension resolved in the dike walls. As there is no evidence for internal deformation of titanomagnetite, AMS would record its late growth in the tectonic extension direction. The magnetic subfabric concealed by late AMS therefore documents an earlier tectonic episode and evidence the limits of using just AMS directions to constrain the emplacement of syntectonic magmas.

Optimizing diffusion MRI acquisition efficiency of rodent brain using simultaneous multislice EPI.

Diffusion tensor imaging (DTI) of the brain provides essential information on the white matter integrity and structural connectivity. However, it suffers from a low signal-to-noise ratio (SNR) and requires a long scan time to achieve high spatial and/or diffusion resolution and wide brain coverage. With recent advances in parallel and simultaneous multislice (multiband) imaging, the SNR efficiency has been improved by reducing the repetition time (TR ). However, due to the limited number of RF coil channels available on preclinical MRI scanners, simultaneous multislice acquisition has not been practical. In this study, we demonstrate the ability of multiband DTI to acquire high-resolution data of the mouse brain with 84 slices covering the whole brain in 0.2 mm isotropic resolution without a coil array at 9.4 T. Hadamard-encoding four-band pulses were used to acquire four slices simultaneously, with the reduction in the TR maximizing the SNR efficiency. To overcome shot-to-shot phase variations, Hadamard decoding with a self-calibrated phase was developed. Compared with single-band DTI acquired with the same scan time, the multiband DTI leads to significantly increased SNR by 40% in the white matter. This SNR gain resulted in reduced variations in fractional anisotropy, mean diffusivity, and eigenvector orientation. Furthermore, the cerebrospinal fluid signal was attenuated, leading to reduced free-water contamination. Without the need for a high-density coil array or parallel imaging, this technique enables highly efficient preclinical DTI that will facilitate connectome studies.

Effect of HIP treatment on the microstructure and mechanical properties of a Ni-based superalloy fabricated by selective laser melted method

Selective laser melting (SLM) is one of the most emerging additive manufacturing (AM) method through the melting of metal powder to manufacture the full density parts, which will lead to an orientation microstructure and anisotropy mechanical properties. Thus, corresponding post-processing treatments, such as solution treatment (ST) and hot isostatic pressing (HIP), were subjected to the specimens before tests. The effect of the HIP on the microstructure and mechanical properties of SLM Inconel 625 was investigated through uniaxial tension tests at room and elevated temperature. The fracture mechanism was systematically characterized and analyzed using scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). It was found that the microstructure after the HIP process is composed of equiaxed austenite, and the annealing twins are reduced. The tensile test results reveal that the HIP has a significant impact on the plastic behavior of the alloy at high-temperature, and is the main reason for the greatly improved elongation, compared to the ST process.

Molecular Orientation Depth Profiles in Organic Glasses Using Polarized Resonant Soft X-ray Reflectivity

Molecular orientation anisotropy can be critical in functional organic thin films. For instance, it is known that molecular orientation can affect the performance of organic electronic devices such...

Electronic and transport properties of anisotropic semiconductor quantum wires

Within the effective-mass approximation, we theoretically investigated the electronic and transport properties of 2D semiconductor quantum wires (QWs) with anisotropic effective masses and different orientations with respect to the anisotropic axis. The energy levels in the absence and presence of an external magnetic field are analytically calculated, showing: (i) a strong dependence on the spacing of energy levels related to the alignment QW angle and the anisotropy axis; and (ii) for non-null magnetic field, the quantum Hall edge states are significantly affected by the edge orientation. Moreover, by means of the split-operator technique, we analyzed the time evolution of wavepackets in straight and V-shaped anisotropic QWs and compared the transmission probabilities with those of isotropic systems. In the anisotropic case we found damped oscillations in the average values of velocity in both x and y directions for a symmetric Gaussian wavepacket propagating along a straight wide QW, with the oscillation being more evident as the non-collinearity between the group velocity and momentum vectors increases.