Inherent Anisotropy Research Articles

Influence of soil inherent anisotropy on behavior of crushed sand-steel interfaces

This paper presents the results of an extensive series of direct shear tests covering a broad spectrum of bedding plane inclination angles with respect to the shearing plane to study the outcome of inherent anisotropy on the mechanical behavior of sand-steel interfaces. As a part of the research, it is shown that the peak friction and the maximum dilation angles of the tested inherently anisotropic sand are highly influenced by the bedding plane inclination angle. However, for smooth, intermediate, rough, and very rough sand-steel interfaces, the test results indicate that the variation in peak friction angle with the bedding plane inclination angle is meaningfully less than that for the same sand. Moreover, it is observed that the extrema of peak friction and maximum dilation angles in sand-steel interface tests are attained at bedding plane inclination angles that are significantly different from those obtained from direct shear tests on sand samples.

Phase-field simulation of tip splitting in dendritic growth of Fe-C alloy

Two types of dendrite tip splitting including dendrite orientation transition and twinned-like dendrites in Fe-C alloys were investigated by phase-field method. In equiaxed growth, the possible dendrite growth directions and the effect of supersaturation on tip splitting were discussed; the dendrite orientation transition was observed, and it was found that the orientation regions of anisotropy parameters were reduced from three to two with increasing the supersaturation, which was due to the effect of interfacial anisotropy controlled by the solute in front of S/L interface changing with the increase of supersaturation. In directional solidification, it was found that the twinned-like dendrites were formed with the fixed anisotropy couples and no seaweed dendrites were observed; these were concluded from the results of competition between process anisotropy and inherent anisotropy. The formation process of twinned-like dendrite was investigated by tip splitting phenomenon, which was related to the changes of dendrite tips growth velocity. Then, the critical speed of tips splitting and solute concentration of twinned-like dendrites were investigated, and a new type of microsegregation in Fe-C alloys was proposed to supplement the dendrite growth theories.

CHRR: coordinate hit-and-run with rounding for uniform sampling of constraint-based models.

SummaryIn constraint-based metabolic modelling, physical and biochemical constraints define a polyhedral convex set of feasible flux vectors. Uniform sampling of this set provides an unbiased characterization of the metabolic capabilities of a biochemical network. However, reliable uniform sampling of genome-scale biochemical networks is challenging due to their high dimensionality and inherent anisotropy. Here, we present an implementation of a new sampling algorithm, coordinate hit-and-run with rounding (CHRR). This algorithm is based on the provably efficient hit-and-run random walk and crucially uses a preprocessing step to round the anisotropic flux set. CHRR provably converges to a uniform stationary sampling distribution. We apply it to metabolic networks of increasing dimensionality. We show that it converges several times faster than a popular artificial centering hit-and-run algorithm, enabling reliable and tractable sampling of genome-scale biochemical networks.Availability and Implementation https://github.com/opencobra/cobratoolbox.Supplementary information Supplementary data are available at Bioinformatics online.

Strong Localization of Anionic Electrons at Interlayer for Electrical and Magnetic Anisotropy in Two-Dimensional Y2C Electride.

We have synthesized a single crystalline Y2C electride of centimeter-scale by floating-zone method and successfully characterized its anisotropic electrical and magnetic properties. In-plane resistivity upturn at low temperature together with anisotropic behavior of negative magnetoresistance is ascribed to the stronger suppression of spin fluctuation along in-plane than that along the c-axis, verifying the existence of magnetic moments preferred for the c-axis. A superior magnetic moment along the c-axis to that along the in-plane direction strongly demonstrates the anisotropic magnetism of Y2C electride containing a magnetically easy axis. It is clarified from the theoretical calculations that the anisotropic nature of the Y2C electride originates from strongly localized anionic electrons with an inherent magnetic anisotropy in the interlayer spaces.

Natural extracted aerogels with inherent anisotropy and their 3D printing assisted biomedical applications.

Exemplified with jackfruit and sugarcane, natural extracted aerogels with inherent structural anisotropy were investigated for the first time. With the help of nano-modification, the dual liquid/current directing capability of the Ag decorated jackfruit aerogel was discovered. This interesting material was then applied as the core component of a 3D printed wearable device for intelligent wound management. The as-prepared ultra-light (<10 g) wearable device could provide drainage diversion, wound warning and triple antibacterial treatment in a continuous and automatic manner.

A DEM study of oedometric compression of model granular materials Initial state influence, stress ratio, elasticity, irreversibility.

A DEM simulation study of spherical beads with elastic-frictional contacts in oedometric compression is carried out for a wide variety of initial states, differing in solid fraction Φ, coordination number z (independent of Φ in dense systems) and inherent anisotropy. Stress ratio K 0 = σ2 /σ1 , along with z , Φ and force and fabric anisotropies are monitored in compressions in which axial stress σ1 varies by more than 3 orders of magnitude. K 0 tends to remain constant if the material was already one-dimensionally compressed in the assembling stage. Otherwise, it decreases steadily over the investigated stress range. K 0 relates to force and fabric anisotropy parameters by a simple formula. Elastic moduli may express the response to very small stress increments about the transversely isotropic equilibrated states, although oedometric compression proves an essentially anelastic process, mainly due to friction mobilization. Despite apparent nearly reversible increases of axial strain ϵ 1 (or density Φ), especially in dense samples, internal state evolutions are strongly irreversible, as evidenced by changes in z and K 0 . Fabric changes are reflected by anisotropic elastic moduli.

Two-Dimensional Material-Based Mode Confinement Engineering in Electro-Optic Modulators

The ability to modulate light using 2-dimensional (2D) materials is fundamentally challenged by their small optical cross-section leading to miniscule modal confinements in diffraction-limited photonics despite intrinsically high electro-optic absorption modulation (EAM) potential given by their strong exciton binding energies. However the inherent polarization anisotropy in 2D materials and device tradeoffs lead to additional requirements with respect to electric field directions and modal confinement. A detailed relationship between modal confinement factor and obtainable modulation strength including definitions on bounding limits are outstanding. Here, we show that the modal confinement factor is a key parameter determining both the modulation strength and the modulator extinction ratio-to-insertion loss metric. We show that the modal confinement and hence the modulation strength of a single-layer modulated 2D material in a plasmonically confined mode is able to improve by more than 10× compared to diffraction-limited modes. Combined with the strong-index modulation of graphene, the modulation strength can be more than 2-orders of magnitude higher compared to Silicon-based EAMs. Furthermore, modal confinement was found to be synergistic with performance optimization via enhanced light-matter-interactions. These results show that there is room for scaling 2D-material EAMs with respect to modal engineering toward realizing synergistic designs leading to high-performance modulators.

Two-Coordinate Co(II) Imido Complexes as Outstanding Single-Molecule Magnets

The pursuit of single-molecule magnets (SMMs) with better performance urges new molecular design that can endow SMMs larger magnetic anisotropy. Here we report that two-coordinate cobalt imido complexes featuring highly covalent Co═N cores exhibit slow relaxation of magnetization under zero direct-current field with a high effective relaxation barrier up to 413 cm-1, a new record for transition metal based SMMs. Two theoretical models were carried out to investigate the anisotropy of these complexes: single-ion model and Co-N coupling model. The former indicates that the pseudo linear ligand field helps to preserve the first-order orbital momentum, while the latter suggests that the strong ferromagnetic interaction between Co and N makes the [CoN]+ fragment a pseudo single paramagnetic ion, and that the excellent performance of these cobalt imido SMMs is attributed to the inherent large magnetic anisotropy of the [CoN]+ core with |MJ = ± 7/2⟩ ground Kramers doublet.

Evaluation of monitoring methods for electron beam melting powder bed fusion additive manufacturing technology

In-process process sensing and monitoring is being incorporated across additive manufacturing technologies due to the need for part qualification. Implementation of additively manufactured end-use parts has been hindered by the inherent process variability and anisotropy that adversely affect part performance. Process monitoring methods have the potential to ensure fabrication integrity is achieved and part isotropy is maintained across the entirety of a part. This manuscript compares two methods (pyrometer and infrared thermography) that have the potential to monitor layerwise surfaces of a powder bed fusion process. Measurement of surface temperatures during fabrication can be useful for parameter development of novel materials, prediction of resulting microstructural architectures, and ultimately as feedback used in a closed-loop control system to allow full spatial and temporal control of melting and microstructure. A multi-wavelength pyrometer was externally mounted atop an electron beam melting (EBM) additive manufacturing system to observe and record surface temperatures during the fabrication process. The multi-wavelength pyrometer used in this study was a non-contact device that was emissivity independent and capable of taking fixed spot sized measurements. An infrared camera was also installed atop an EBM system to monitor the fabrication surface and was used to measure temperature variations across the entire build area. Although the IR camera produces spatial measurements of an entire part, temperature data is emissivity dependent. Parts with variations in processing were fabricated and monitored using each instrument. Thermal variations between parts were identified with each instrument and related to microstructure. The advantages and disadvantages of each monitoring device were documented and are discussed in this manuscript.

Formulation of Anisotropic Strength Criteria for Cohesionless Granular Materials

AbstractGranular materials deposited under gravity usually exhibit inherent fabric anisotropy, which leads to profoundly varying strength under different loading directions in regard to the bedding...

Ultra‐broadband nanophotonic beamsplitter using an anisotropic sub‐wavelength metamaterial

AbstractNanophotonic beamsplitters are fundamental building blocks in integrated optics, with applications ranging from high speed telecom receivers to biological sensors and quantum splitters. While high‐performance multiport beamsplitters have been demonstrated in several material platforms using multimode interference couplers, their operation bandwidth remains fundamentally limited. Here, we leverage the inherent anisotropy and dispersion of a sub‐wavelength structured photonic metamaterial to demonstrate ultra‐broadband integrated beamsplitting. Our device, which is three times more compact than its conventional counterpart, can achieve high‐performance operation over an unprecedented 500 nm design bandwidth exceeding all optical communication bands combined, and making it one of the most broadband silicon photonics components reported to date. Our demonstration paves the way toward nanophotonic waveguide components with ultra‐broadband operation for next generation integrated photonic systems. image

Equilibrium crystal phases of triblock Janus colloids

Triblock Janus colloids, which are colloidal spheres decorated with attractive patches at each pole, have recently generated significant interest as potential building blocks for functional materials. Their inherent anisotropy is known to induce self-assembly into open structures at moderate temperatures and pressures, where they are stabilized over close-packed crystals by entropic effects. We present a numerical investigation of the equilibrium phases of triblock Janus particles with many different patch geometries in three dimensions, using Monte Carlo simulations combined with free energy calculations. In all cases, we find that the free energy difference between crystal polymorphs is less than 0.2 kBT per particle. By varying the patch fraction and interaction range, we show that large patches stabilize the formation of structures with four bonds per patch over those with three. This transition occurs abruptly above a patch fraction of 0.30 and has a strong dependence on the interaction range. Furthermore, we find that a short interaction range favors four bonds per patch, with longer range increasingly stabilizing structures with only three bonds per patch. By quantifying the effect of patch geometry on the stability of the equilibrium crystal structures, we provide insights into the fundamental design rules for constructing complex colloidal crystals.

Effects of inherent fabric anisotropy and intermediate principal stress on constitutive behavior of uncemented and cemented sands

Sand response changes with intensity of cementation bonds between sand grains, magnitude of intermediate principal stress and with fabric anisotropy. First a critical state bounding surface plasticity model is presented in this paper. In this constitutive model, the loading surface always passes through the current stress state regardless of location or position of the stress path. Second to simulate hollow cylinder tests which represent different modes of shearing including triaxial compression and triaxial extension, the fabric anisotropy and b-parameter are incorporated in the model. Simultaneous integration of cohesion, non-associated flow rule, fabric anisotropy, kinematic hardening, critical state and state parameter makes the proposed model unique compared to previous proposed bounding surface models. Comparison of model outcomes and hollow cylinder experimental tests shows great predictive capability of the proposed model. Sensitivity analysis also suggests that triaxial compression and triaxial extension are respectively strongest and weakest modes of shearing.

Intermixing and Formation of Cu-Rich Secondary Phases at Sputtered CdS/CuInGaSe2Heterojunctions

The Cu migration behavior in PVD-CdS/PVD-Cu(In,Ga)Se2 (CIGS) heterojunctions is investigated by high-resolution electron microscopy (HREM) and energy dispersive X-ray spectroscopy (EDS). Incorporation of Cu into the CdS forms Cu-rich domains but has no effect on epitaxy of the CdS. Epitaxy is commonly observed in the CdS studied. Secondary ion mass spectroscopy depth profiles confirm the presence of Cu in the CdS. In some cases, Cd is completely replaced by Cu, resulting in a Cu–S binary compound epitaxially grown on the CIGS and fully coherent with the surrounding CdS. This is most likely to be cubic Cu2S, based on lattice spacing measurements from HREM images and EDS elemental quantification. In addition, we find that the buffer layer crystal structure influences the extent of Ga depletion at the CIGS surface, which is more pronounced adjacent to zinc-blende CdS than wurtzite CdS. Density functional theory calculations reveal that Cu clustering and different Ga depletion widths can be attributed to the inherent anisotropy of wurtzite CdS and differences in CIGS point-defect migration barriers. Understanding the influence of these effects on device properties is a critical step in developing more efficient CdS/CIGS-based photovoltaics.

Multiscale Simulations of Anisotropic Grain Growth Using Wavelet Based Multiresolution Analysis

The present work serves to document the development and findings associated with a wavelet-based multiscale simulation analysis for anisotropic grain growth of a two-dimensional polycrystalline material. In particular, lattice-based Monte Carlo and atomically-based Molecular Dynamics simulations are used to compute the grain boundary energies over their respective spatial domains. Serial coupling is performed utilizing an orthonormal set of Haar wavelet transforms embedded within a corresponding multiresolution analysis. For the Monte Carlo approach, anisotropies in grain boundary energies, caused by differences in grain orientation (texturing), are examined using two distinct methods, while the molecular dynamics simulations, offering inherent anisotropy, are conducted assuming the interatomic Lennard Jones potential. Among other findings, under the present context, the results confirm the viability of the wavelet-based multiresolution analysis (MRA) method for use as a potential coupling agent, and provide substantiation for its use with other applications. The results further offer quantitative comparisons between isotropic and anisotropic modeling results, and demonstrate their range of applicability.

The comparison of modelling inherent and evolving anisotropy on the behaviour of a full-scale embankment

The behaviour of a full-scale embankment constructed on a soft soil deposit has been studied using two different anisotropic elasto-plastic constitutive models, namely S-CLAY1 and Sekiguchi–Ohta (SO) inviscid, in order to investigate the influence of modelling (initial) inherent and evolving anisotropy on boundary value level simulations. The initial inherent anisotropy which is generally modelled by a rotated yield surface can also influence the model prediction capability. A Finnish test embankment known as Murro embankment was chosen for finite-element analysis using the two advanced soil models. The predictions of each model were studied and compared with measured field data. For the purpose of model comparison, the influence of evolution of anisotropy was further investigated by using only the inherent anisotropy feature of S-CLAY1 model, by setting the values of rational hardening parameters to zero. Overall, the S-CLAY1 model predictions are in good agreement with the measured data, which is due to the incorporation of a rotational hardening law (evolution of anisotropy) into the model in addition to the consideration of inherent anisotropy. However, the SO inviscid model predictions are less comparable with the measured data due to the consideration of only the inherent anisotropy into the model. The results clearly demonstrate the importance of including soil’s evolving anisotropy in the analysis and how the inherent anisotropy is modelled (i.e. the shape of yield surface).

Tool materials influence on surface roughness and oversize in machining glass fiber reinforced polypropylene (GFR-PP) composites

ABSTRACTGlass fiber reinforced Polypropylene (GFR-PP) is used in manufacturing industries like bicycles, auto bodies, aircraft, and civil applications due to superior properties. Machining of fiber-reinforced plastics is problematic especially when drilling due to their inherent in-homogeneity, anisotropy and limited plastic deformation. Drilling is often required to facilitate the assembly of the parts to get the final products. Surface quality in drilled composites is an essential design characteristic in many situations, such as accurate fits, aesthetic requirements, etc. The present work deals with detailed investigation on the influence of tool materials and machining parameters during drilling of GFR-PP composite material. The study mainly focused on machined surface quality such as surface roughness of the drilled hole and dimensional inaccuracies such as oversize of the hole. The better dimensional and surface quality of drilled hole is observed from solid carbide drill with a spindle speed of 2500 rpm and a feed rate of 0.05 mm/rev. Regression model is developed using experimental data for estimating the surface roughness and oversize. The developed model has high R-sq value which shows the strong relationship between the model and the response variables. The effect of drilling process parameters and associated interactions are discussed in detail.

Correcting motion in multiplanar cardiac magnetic resonance images.

BackgroundMisalignment in cardiac magnetic resonance (CMR) images can adversely affect three-dimensional left ventricle modelling and downstream quantitative analysis. Currently, there are two types of approaches for dealing with realignment and motion distortion problems, one image based and the other geometry based. Image-based approaches are limited by the inherent non-homogeneity and anisotropy of CMR images. Geometry-based approaches rely on idealized models and over-simplified assumptions. This study was motivated by the need for a robust and effective approach for correcting motion related distortions due to misalignment in CMR images.MethodsA cine cardiac magnetic resonance image sequence was acquired using our routine clinical imaging protocol. The left ventricular endocardium was delineated manually with software assistance on all long and short-axis images. Long and short-axis contours were projected onto a patient-based coordinate system and then realigned using iterative registration. The realigned contour points were used to reconstruct the shape of the left ventricle for quantitative validation.ResultsThe method was tested on five myocardial infarction patients whose images showed substantial misalignment. Realignment time was about 16 seconds per case, using a 2.5 GHz CPU desktop with obvious elimination of the distortion in the reconstructed model. Using the long-axis contour as a reference in evaluating the reconstructed models, it was apparent that the models with realigned contours had better accuracy than the non-realigned ones.ConclusionThis study presents a novel, geometry-based method for correcting motion distortions in CMR images. The method incorporates (1) manual delineation, (2) registration based on a generalized, iterative closest point algorithm, and (3) reconstruction of the shape of the left ventricle for quantitative validation. The effectiveness of our approach is corroborated both visually and by quantitative assessment. We envision the use of our method in current clinical practice as a means of improving accuracy in the evaluation of cardiac function.

Anisotropic properties of directed energy deposition (DED)-processed Ti–6Al–4V

Directed energy deposited (DED) Ti–6Al–4V components and prototypes are quickly growing in prevalence in aerospace and biomedical industries for their increased strength and fast processing time. However, one of the remaining challenges in DED processes, particularly laser engineered net shaping (LENS), is the characterization of the inherent anisotropy in material properties. Anisotropy in microstructure, porosity and mechanical behavior arises due to unique material thermal histories during processing. Understanding anisotropy in additive manufacturing can lead to refined process parameters, characterization methods, material and thermal modeling as well as improved mechanical properties. This paper investigates the anisotropic mechanical properties, specifically ultimate tensile strength, of LENS-processed Ti–6Al–4V and how these properties depend on geometry and direction of build processing. Mechanical properties were found to be most desirable when the tensile orientation is orthogonal to the build direction and parallel to the scan direction as well as closer to the center of a fully dense component. This study investigates microstructure through X-ray diffraction, fractography and porosity shape and connectivity analysis. Models that predict mechanical behavior based on processing details are in development. There is potential to achieve desirable mechanical properties through melt pool and thermal controls for high-strength and energy efficient materials by predicting mechanical properties from process parameters.

Three-dimensional morphology and palaeobiology of the trace fossil Dactyloidites jordii nov. isp. from the Carboniferous of England

The diverse ichnological assemblage from the outcrops near Howick (Northumberland, United Kingdom) is exceptionally well-preserved. Among these Carboniferous ichnotaxa is a new ichnospecies of Dactyloidites. Specimens were collected and processed using high-resolution serial grinding and photography to produce an accurate and precise three-dimensional model of these new burrows in full colour. The model produced in association with petrographic thin sections and field observations is used as the basis for comparison between Dactyloidites jordii nov. isp. and other ichnospecies of Dactyloidites. The current taxonomic status of the ichnogenus is examined and reviewed. D. jordii nov. isp. is a broadly bisymmetrical, stellate to palmate burrow composed of numerous long, narrow rays that exhibit three orders of branching arranged into tiered galleries radiating from a central shaft. The trace maker is suggested to be a vermiform organism with an adaptive burrowing strategy that facilitates alteration of its burrow construction to accommodate suboptimal sediment conditions. The adaptive nature of trace-making organisms and the inherent anisotropy of many burrowed media highlight the need for ichnologists to provide a type series rather than a single holotype, in order to capture the inherent range of common burrow morphologies.