Anisotropic Orientation Research Articles

Enhanced M2 Polarization of Oriented Macrophages on the P(VDF-TrFE) Film by Coupling with Electrical Stimulation.

Electrical stimulation (ES) has been considered a promising strategy in regulating intracellular communication, membrane depolarization, ion transport, etc. Meanwhile, cell topography, such as the alignment and elongation in anisotropic orientation, also plays a critical role in triggering mechanotransduction as well as the cellular fate. However, coupling of ES and cell orientation to regulate the polarization of macrophages is yet to be explored. In this work, we intended to explore the polarization of macrophages on a poly(vinylidene fluoride-trifluoroethylene [P(VDF-TrFE)] film with intrinsic microstripe roughness, which was covered on indium tin oxide planar microelectrodes. We found that mouse bone marrow-derived macrophages (BMDMs) cultured on a P(VDF-TrFE) film exhibited an elongated morphology aligned with the microstripe crystal whisker, but their polarization behavior was not affected. However, the elongated cells were susceptible to ES and upregulated their M2 polarization, as verified by the related expression of phenotype markers, cytokines, and genes, while not affecting M1 polarization. This is due to the increased expression of the M2 polarization receptor interleukin-4Rα on the surface of elongated BMDMs, while the M1 polarization receptor toll-like receptor 4 was not affected. Thus, M2 polarization was singularly enhanced after activation of polarization by ES. The combination of surface morphology and ES to promote M2 single polarization in this work provides a new perspective for regulating macrophage polarization in the field of immunotherapy.

T 2 orientation anisotropy mapping of articular cartilage using qMRI

Objective. To provide orientation-independent MR parameters potentially sensitive to articular cartilage degeneration by measuring isotropic and anisotropic components of T 2 relaxation, as well as 3D fiber orientation angle and anisotropy via multi-orientation MR scans. Approach. Seven bovine osteochondral plugs were scanned with a high angular resolution of thirty-seven orientations spanning 180° at 9.4 T. The obtained data was fitted to the magic angle model of anisotropic T 2 relaxation to produce pixel-wise maps of the parameters of interest. Quantitative Polarized Light Microscopy (qPLM) was used as a reference method for the anisotropy and fiber orientation. Main results. The number of scanned orientations was found to be sufficient for estimating both fiber orientation and anisotropy maps. The relaxation anisotropy maps demonstrated a high correspondence with qPLM reference measurements of the collagen anisotropy of the samples. The scans also enabled calculating orientation-independent T 2 maps. Little spatial variation was observed in the isotropic component of T 2 while the anisotropic component was much faster in the deep radial zone of cartilage. The estimated fiber orientation spanned the expected 0°–90° in samples that had a sufficiently thick superficial layer. The orientation-independent magnetic resonance imaging (MRI) measures can potentially reflect the true properties of articular cartilage more precisely and robustly. Significance. The methods presented in this study will likely improve the specificity of cartilage qMRI by allowing the assessment of the physical properties such as orientation and anisotropy of collagen fibers in articular cartilage.

DEM study of an “avatar” railway ballast with real particle shape, fabric and contact mechanics

In this paper we show DEM simulations of static and cyclic large triaxial tests on a sample of railway ballast. The sample is reconstructed from X-Ray tomography images of an untested laboratory sample, recovered by impregnation with an epoxy resin. Measurements of both shape and fabric are carried out; the sample shows a high anisotropy of particle orientations due to the preparation procedure and a high shape heterogeneity. A DEM model is then generated using clumps to model single particles, preserving the shape of each particle and the fabric of the sample. Results of static and cyclic simulations are shown and compared with previous simulations on numerically generated samples, showing the importance of an accurate representation of the whole range of particle shapes, as well as confirming the effect of particle anisotropy on the mechanical response.Graphical

How Ions Break Local Symmetry: Simulations of Polarized Transient Hole Burning for Different Models of the Hydrated Electron in Contact Pairs with Na+

The hydrated electron (eaq-) is known via polarized transient hole-burning (pTHB) experiments to have a homogeneously broadened absorption spectrum. Here, we explore via quantum simulation how the pTHB spectroscopy of different eaq- models changes in the presence of electrolytes. The idea is that cation-eaq- pairing can break the local symmetry and, thus, induce persistent inhomogeneity. We find that a "hard" cavity model shows a modest increase in the pTHB recovery time in the presence of salt, while a "soft" cavity model remains homogeneously broadened independent of the salt concentration. We also explore the orientational anisotropy of a fully ab initio density functional theory-based model of the eaq-, which is strongly inhomogeneously broadened without salt and which becomes significantly more inhomogeneously broadened in the presence of salt. The results provide a direct prediction for experiments that can distinguish between different models and, thus, help pin down the hydration structure and dynamics of the eaq-.

Physics of molecular deformation mechanism in 6H-SiC

Even though there have been several studies in literature of 6H SiC, a proper physics based understanding of the molecular deformation mechanisms of the material under different loading conditions is still lacking. Experimentally, the brittle nature of the material leads to difficulties associated with in-situ determination of molecular deformation mechanisms of the material under an applied load; whereas, the complex material structure along with the bonding environment prevents proper computational identification of different types of inelasticity mechanisms within the material. Molecular dynamics study (on successful verification of the interatomic potential with experimental results) of pristine single crystals of 6H SiC have been used to probe the physics of molecular deformation mechanisms of the material along with its inherent orientational anisotropy. The study elucidates the experimentally observed mechanisms of defect nucleation and evolution through a detailed analysis of radial distribution functions, x-ray diffraction as well as phonon vibrational studies of the single crystal. Studies have been presented at room temperature, initial high temperature and different types of confinement effects of the material (including hydrostatic and different biaxial loading cases). The confinement resulted in an increase in stress and stiffness whereas increase in initial temperature resulted in a decrease compared to uniaxial stress loading conditions at room temperature.

Machine Learning Full NMR Chemical Shift Tensors of Silicon Oxides with Equivariant Graph Neural Networks.

The nuclear magnetic resonance (NMR) chemical shift tensor is a highly sensitive probe of the electronic structure of an atom and furthermore its local structure. Recently, machine learning has been applied to NMR in the prediction of isotropic chemical shifts from a structure. Current machine learning models, however, often ignore the full chemical shift tensor for the easier-to-predict isotropic chemical shift, effectively ignoring a multitude of structural information available in the NMR chemical shift tensor. Here we use an equivariant graph neural network (GNN) to predict full 29Si chemical shift tensors in silicate materials. The equivariant GNN model predicts full tensors to a mean absolute error of 1.05 ppm and is able to accurately determine the magnitude, anisotropy, and tensor orientation in a diverse set of silicon oxide local structures. When compared with other models, the equivariant GNN model outperforms the state-of-the-art machine learning models by 53%. The equivariant GNN model also outperforms historic analytical models by 57% for isotropic chemical shift and 91% for anisotropy. The software is available as a simple-to-use open-source repository, allowing similar models to be created and trained with ease.

On rate dependence and anisotropy in phase field modeling of polycrystalline fracture

A phase field theory of fracture incorporating rate dependence (i.e., kinetic viscosity) and anisotropic elasticity is implemented to study strength and failure modes in polycrystalline materials. After presentation of the constitutive framework, a new analytical solution is derived for one-dimensional (1D) homogeneous loading at constant strain rate, wherein crack viscosity is enabled. The three-dimensional (3D) theory is implemented in a finite element (FE) context, with static and dynamic solutions verified up to peak loading for homogeneous microstructures. Extensive simulations of heterogeneous polycrystalline microstructures follow, where baseline material properties correspond to either boron carbide (B4C) or titanium diboride (TiB2). Results quantify effects of loading rate, elastic anisotropy, cleavage energy anisotropy, and grain boundary surface energy on tensile strength. Notable are effects of strong basal texture, which influences average strength via both elastic anisotropy and basal cleavage plane orientation. Effects of loading rate are naturally more prominent for materials that fail mostly intergranularly rather than transgranularly, in agreement with experimental observations.

Artificial single skyrmion and biskyrmion states achieved in magnetic nanodot pairs by micromagnetic simulation

Using the shape anisotropy and magnetic field orientation changes, we realized the chirality and polarity controllable artificial skyrmion through the micromagnetic simulation software OOMMF. Combining the CoPt film with perpendicular magnetic anisotropy, and our self-designed Co nanodot pairs structure carrying magnetic vortex with controlled chirality and polarity, skyrmion states could be achieved by adding the external magnetic field. Single skyrmion state can be formed when 200 mT in-plane magnetic field is introduced; while the magnetic field intensity is reduced to 140 mT, double skyrmions state can be formed. The detail forming process of skyrmion is studied by studying the key nodes in the saturation magnetization and demagnetization process. It is also found that the polarity of skyrmion is stable even under the action of the 0.6 T out-of-plane magnetic field. By comparing the influence of Co disk thickness on the formation of skyrmion, it is found that 45 ∼ 60 nm Co disk thickness is suitable for forming stable skyrmion.

Crustal azimuthal anisotropy in the lateral collision zone of the SE margin of the Tibetan Plateau and its tectonic implications

SUMMARYResolving the detail of crustal deformation of the seismically and technically active Sichuan-Yunnan block located in the southeast margin of the Tibetan Plateau is crucial for understanding the lateral extrusion of the Tibetan Plateau. Using seismic data from two regional seismograph stations of the China Earthquake Networks Center and twenty recently deployed broad-band temporary stations from the MCD Array (Middle ChuanDian block seismic array), we constrained crustal thickness and seismic anisotropy at the west boundary of the Sichuan-Yunnan block, near the east Himalayan syntaxis by receiver function techniques including CCP stacking and sinusoidal moveout of PmS conversions. Crustal thickness varies significantly across major faults inside the block which increases by >20 km from west to east. East of the Chenghai Fault, a clear positive phase lies above the Moho and is interpreted to be caused by the magma intrusion related to a late Permian Emeishan large igneous province (ELIP). The crustal anisotropy shows strong zoning features and clockwise rotation with respect to due north. To the west of the Lijiang-Xiaojinhe and the Honghe Faults, anisotropic fast orientations are near NS, indicating strong crustal deformation and movement of southward crustal flow along the Nujiang-Lancangjiang Fault; to the east of this fault, anisotropic fast orientations are near NE. The variation of the anisotropic fast orientations indicates that the southeastward crustal flow from the Tibetan Plateau may be prevented by fast velocity anomalies beneath the ELIP. These observations provided new evidence for strong crustal deformation along the tectonic boundary in the southeastern Tibetan Plateau with the expansion of the Tibetan Plateau.

Comparative study of weld‐line strength for unfilled and glass‐filled thermoplastic polyamide‐6 materials

AbstractThe injection molding process is widely accepted for the processing of engineering thermoplastics due to the ease of manufacturing complex designs. Weld‐line is a defect occurring in injection molded parts when two flow fronts join each other. At weld‐line locations, parts exhibit lower mechanical strength mainly due to inadequate intermolecular diffusion and fiber orientation anisotropy. The present work is aimed at investigating and comparing weld‐line strength for unfilled and glass‐filled polyamide‐6 materials. To achieve this, polyamide‐6 unfilled, 30% glass‐filled, and 50% glass‐filled materials are used to manufacture plaques. The special‐purpose mold is designed to obtain plaques with and without weld‐lines with help of Moldflow simulations. The specimens for tensile tests are then cut from molded plaques and experimental testing is conducted to evaluate tensile properties. Fractured surfaces of specimens are examined using a scanning electron microscope. The results demonstrated a significant drop in tensile strength and modulus for glass‐filled material weld‐line specimens when compared to specimens of no weld‐line. However, for unfilled specimens, tensile strength and modulus are almost the same for samples with and without weld‐line. A reduction in tensile strength of 13%, 49%, and 57% is observed for unfilled, 30% glass‐filled, and 50% glass‐filled polyamide‐6 material respectively.

Geometric control of myosin II orientation during axis elongation.

The actomyosin cytoskeleton is a crucial driver of morphogenesis. Yet how the behavior of large-scale cytoskeletal patterns in deforming tissues emerges from the interplay of geometry, genetics, and mechanics remains incompletely understood. Convergent extension in Drosophila melanogaster embryos provides the opportunity to establish a quantitative understanding of the dynamics of anisotropic non-muscle myosin II. Cell-scale analysis of protein localization in fixed embryos suggests that gene expression patterns govern myosin anisotropy via complex rules. However, technical limitations have impeded quantitative and dynamic studies of this process at the whole embryo level, leaving the role of geometry open. Here, we combine in toto live imaging with quantitative analysis of molecular dynamics to characterize the distribution of myosin anisotropy and the corresponding genetic patterning. We found pair rule gene expression continuously deformed, flowing with the tissue frame. In contrast, myosin anisotropy orientation remained approximately static and was only weakly deflected from the stationary dorsal-ventral axis of the embryo. We propose that myosin is recruited by a geometrically defined static source, potentially related to the embryo-scale epithelial tension, and account for transient deflections by cytoskeletal turnover and junction reorientation by flow. With only one parameter, this model quantitatively accounts for the time course of myosin anisotropy orientation in wild-type, twist, and even-skipped embryos, as well as embryos with perturbed egg geometry. Geometric patterning of the cytoskeleton suggests a simple physical strategy to ensure a robust flow and formation of shape.

Instability of a thin film of chemotactic active suspension

In this paper, we analyse the instability of a thin-film suspension of micro-swimmers subjected to an attractant gradient. The imposed attractant gradient introduces a preferential swimming direction for the swimmers, resulting in an anisotropic orientation field. By modelling the swimmers as force dipoles, the study by Kasyap & Koch (Phys. Rev. Lett., vol. 108, issue 3, 2012, 038101, J. Fluid Mech., vol. 741, 2014, pp. 619–657) found an instability arising from the coupling between the active stress associated with an anisotropic orientation field and perturbations to the swimmer density field. In this work we begin by presenting a stability analysis that calculates the modification of this instability in the presence of an interface. We then detail the presence of a new mode of instability that arises solely from the deformation of the interface mediated by the active stress in the suspension. The resulting hydrodynamic instabilities in the system are observed to be sensitive to the direction of the attractant gradient relative to the interface. Furthermore, we show that the coupling between the two modes involving a jump in interfacial viscous stresses and normal stress differences within the suspension allows for an instability to manifest in a suspension of chemotactic pullers, previously thought to be unconditionally stable. We then use a long-wave theory to write down a set of nonlinear equations governing the film evolution. The numerical solution of the system using the long-wave theory aids in explaining the mechanism associated with the instability in addition to validating the predictions from the linear stability theory.

Anisotropic elastic recovery behavior of AlN ceramic during nanoindentation and scratching

The anisotropy of the grain orientation of aluminium nitride (AlN) ceramics leads to great differences in elastic recovery of grains which makes it difficult to achieve high machining accuracy. In this study, the anisotropic elastic recovery behavior of AlN ceramic was investigated by nanoindentation and scratch experiments. The results show that as the main Euler angle the grain increases, the elastic recovery rate of the indentation decreases from 39% to 31%, and the elastic recovery of scratch decreases from 47% to 39%. However, there is a local peak in the elastic recovery rate when the main Euler angle is 75° during scratching. Through the analysis of the Schmid factor, it is found that the ease of activating the sliding system of a grain has a great impact on the elastic recovery rate of scratches. Through further analysis, the elastic recovery rate of grains is mainly affected by the combined action of the base slip system and the prismatic slip system during scratching. The prediction models of the elastic recovery rate during nanoindentation and scratching were established and the prediction results are consistent with the experimental results, indicating the reliability of the prediction model.

Levels of orientation bias differ across digital content categories: Implications for visual perception.

With the continued growth of digital device use, a greater portion of the visual world experienced daily by many people has shifted towards digital environments. The "oblique effect" denotes a bias for horizontal and vertical (canonical) contours over oblique contours, which is derived from a disproportionate exposure to canonical content. Carpentered environments have been shown to possess proportionally more canonical than oblique contours, leading to perceptual bias in those who live in "built" environments. Likewise, there is potential for orientation sensitivity to be shaped by frequent exposure to digital content. The potential influence of digital content on the oblique effect was investigated by measuring the degree of orientation anisotropy from a range of digital scenes using Fourier analysis. Content from popular cartoons, video games, and social communication websites was compared to real-life nature, suburban, and urban scenes. Findings suggest that digital content varies widely in orientation anisotropy, but pixelated video games and social communication websites were found to exhibit a degree of orientation anisotropy substantially exceeding that observed in all measured categories of real-world environments. Therefore, the potential may exist for digital content to induce an even greater shift in orientation bias than has been observed in previous research. This potential, and implications of such a shift, is discussed.

Optimal alignment for maximizing the uniaxial modulus of 2D anisotropic random nanofiber networks

ABSTRACT Nanofiber networks are effective structural forms to utilize the excellent nanoscale properties of nanofibers in macro scale. Properly tuning the anisotropic degree of fiber orientation distribution can maximize the macroscopic mechanical properties of random nanofiber networks in a specific direction. However, the reinforcing mechanism of the anisotropic orientation distribution to the elastic behavior has not been fully understood. In this paper, the effect of anisotropic orientation distribution of nanofibers on the elastic behavior of network is studied based on the modulus-density scaling relation and stiffness thresholds. The uniaxial modulus of network is determined by both the orientation angle of each fiber and interconnectivity of the random fiber network. With the increase of anisotropic degree, the contribution of fiber orientation angle to the network modulus of the preferential direction increases and gradually tends to a constant, while the interconnectivity of the networks decreases, which may reduce the loadability of network. Therefore, at a given network density, the uniaxial modulus along the preferential direction first increases to a maximum value and then decreases with the increase of the anisotropic degree. Furthermore, an expression to predict the optimal anisotropic degrees corresponding to the maximum uniaxial moduli at different network densities is established.

Self-oriented anisotropic structure of G-hydrogels as a delicate balance between attractive and repulsive forces.

Guanine (G) hydrogels are very attractive materials made by the supramolecular organization of G-derivatives in water. In this paper, hydrogels composed of guanosine 5'-monophosphate (GMP) and guanosine (Gua), that make long, flexible and knotted G-quadruplexes, were investigated by small- and wide-angle X-ray scattering (SAXS and WAXS) to comprehend the origin of their unique orientational properties. The SAXS intensity, analysed at a fixed scattering vector modulus Q as a function of polar angle, allowed us to derive the Maier-Saupe orientation parameter m. The strong dependence of m on hydrogel composition and temperature demonstrated that the preferred orientation is controlled by the quadruplex surface charge and flexibility. Indeed, a possible correlation between the orientation parameter m and the quadruplex-to-quadruplex lateral interactions was explored. Results confirmed that the balance between attractive and repulsive interactions plays a main role in the orientational anisotropy: quadruplex clusters lose their orientational properties when attractive interactions decrease. The key role of the number of negative charges per unit length of the G-quadruplex filaments was confirmed by Atomic Force Microscopy (AFM) observations. Indeed, directionality histograms showed that in the presence of a large amount of Gua, G-quadruplexes follow preferential orientations other than those related to the strong interactions with the K+ pattern on the mica surface. The fact that lateral quadruplex-to-quadruplex interactions, even in the presence of external (opposing) forces, can tune the hydrogel alignment in a given preferred direction provides novel possibilities for scaffold/3D printing applications.

Coupled aerothermal-mechanical analysis in single crystal double wall transpiration cooled gas turbine blades with a large film hole density

• Double wall transpiration cooling protects turbine blades against high heat flux. • A high film hole density can benefit both the aerothermal and mechanical response. • The wall spacing influences the cooling effectiveness and aerothermal response. • The wall thickness ratio influences thermal stresses and the mechanical response. • Stresses tend to apply along secondary crystallographic directions around features. The ambition for increasing gas turbine efficiency beyond current levels through the elevation of gas temperatures demands substantial progress in turbine blade cooling technology. Double wall transpiration cooling (DWTC) is an emerging technology which offers enhanced thermal protection at only modest coolant flows, thanks to a combination of impingement jets and densely packed arrays of film cooling holes. This paper presents a coupled aerothermal-mechanical investigation of a transpiration cooled double wall turbine blade design, by employing Computational Fluid Dynamics (CFD), heat transfer theory as well as stress analysis based on plate theory and Finite Element (FE) analysis. In comparison to previously explored systems with modest outer wall porosity, a system with high porosity is found to display enhanced cooling effectiveness and to reduce the temperature difference across the two walls that drives thermal stresses. This difference can be decreased further by reducing the wall spacing, H , or the inner-outer wall thickness ratio, t c / t h , at the cost of higher overall metal temperatures. A lower bound for H should be used to avoid undesirable poor coolant flow distribution and hot gas ingestion effects, whereas the t c / t h ratio does not impose any aerothermal constraints. Thermal stresses associated with a fixed temperature field are invariant with H but they vary drastically with t c / t h . From a design perspective, the above suggest that H is primarily determined by aerothermal requirements, whereas t c / t h by the mechanical performance. The single crystal orientation and elastic anisotropy of Nickel alloys are shown to have a profound impact on the stress concentration around cooling holes, with secondary crystallographic directions, such as 〈 110 〉 and 〈 111 〉 , playing a prominent role in the local stress state. Our study provides a framework for optimising the aerothermal and mechanical performance in a range of high temperature components and highlights key areas where more elaborate analysis is needed.

Identifying the acidic or basic behavior of surface water: a QM/MM-MD study.

Controversies on the water surface were theoretically addressed with the help of large scale quantum mechanical molecular dynamics (QMMD) simulations on water surface model systems with and without excess hydroniums and hydroxides. It was revealed that the thermodynamic surface structures of these ions strongly depend on their location and dipole orientation. Fast hydronium diffusion by proton transfer establishes a wider kinetic depth distribution (∼6 Å) than that predicted by its thermodynamic affinity for the water surface, while slow hydroxide is shallowly trapped below the outermost molecular layer (3-4 Å). In addition, the anisotropic orientation of surface water dipole can generate a substantial magnitude of surface potential, which extends to a depth of a few molecular layers. With these distinctively different surface properties of two ions and water molecules, the seemingly contradictory observations of acidic and negatively charged water surfaces may be successfully explained. That is, the negative surface charge of neutral water mostly stems from intrinsic water properties such as water dipole orientation and electron density spillage at the surface, rather than surface OH- ions. The enhanced acidity of the water surface can be attributed in large part to the kinetic depth profile of ion density in addition to static thermodynamic origin. Furthermore, the different depth profiles of the two ions may differently affect the surface-sensitive spectroscopic observations.

Confinement-induced nonlocality and casimir force in transdimensional systems.

We study within the framework of the Lifshitz theory the long-range Casimir force for in-plane isotropic and anisotropic free-standing transdimensional material slabs. In the former case, we show that the confinement-induced nonlocality not only weakens the attraction of ultrathin slabs but also changes the distance dependence of the material-dependent correction to the Casimir force to go as contrary to the ∼1/l dependence of that of the local Lifshitz force. In the latter case, we use closely packed array of parallel aligned single-wall carbon nanotubes in a dielectric layer of finite thickness to demonstrate strong orientational anisotropy and crossover behavior for the inter-slab attractive force in addition to its reduction with decreasing slab thickness. We give physical insight as to why such a pair of ultrathin slabs prefers to stick together in the perpendicularly oriented manner, rather than in the parallel relative orientation as one would customarily expect.

Accumulation and ordering of P3HT oligomers at the liquid-vapor interface with implications for thin-film morphology.

The morphology of semiconducting polymer thin films is known to have a profound effect on their opto-electronic properties. Although considerable efforts have been made to control and understand the processes which influence the structures of these systems, it remains largely unclear what physical factors determine the arrangement of polymer chains in spin-cast films. Here, we investigate the role that the liquid-vapor interfaces in chlorobenzene solutions of poly(3-hexylthiophene) [P3HT] play in the conformational geometries adopted by the polymers. Using all-atom molecular dynamics (MD), and supported by toy-model simulations, we demonstrate that, with increasing concentration, P3HT oligomers in solution exhibit a strong propensity for the liquid-vapor interface. Due to the differential solubility of the backbone and side chains of the oligomers, in the vicinity of this interface, hexyl chains and the thiophene rings, have a clear orientational preference with respect to the liquid surface. At high concentrations, we additionally establish a substantial degree of inter-oligomer alignment and thiophene ring stacking near the interface. Our results broadly concur with the limited existing experimental evidence and we suggest that the interfacial structure can act as a template for film structure. We argue that the differences in solvent affinity of the side chain and backbone moieties are the driving force for the anisotropic orientations of the polymers near the interface. This finer grained description contrasts with the usual monolithic characterization of polymer units. Since this phenomenon can be controlled by concurrent chemical design and the choice of solvents, this work establishes a fabrication principle which may be useful to develop more highly functional polymer films.