Edge Orientation Research Articles

Antiferromagnetic second-order topological insulator with fractional mass-kink

Generally, the topological corner state in two-dimensional (2D) second-order topological insulator (SOTI) is equivalent to the well-known domain wall state, which is originated from the mass-inversion between two adjacent edges with phase shift of π. In this work, go beyond this conventional physical picture, we report a fractional mass-kink induced 2D SOTI in monolayer FeSe with canted checkerboard antiferromagnetic (AFM) order by analytic model and first-principles calculations. The canted spin associated in-plane Zeeman field can gap out the quantum spin Hall edge state of FeSe, forming a fractional mass-kink with phase shift of π/2 at the rectangular corner, and generating an in-gap topological corner state with fractional charge of e/4. Moreover, the topological corner state is robust to a finite perturbation, existing in both naturally and non-naturally cleaved corners, regardless of the edge orientation. Our results not only demonstrate a material system to realize the unique 2D AFM SOTI, but also pave a way to design the higher-order topological states from fractional mass-kink with arbitrary phase shift.

The resting-state causal human connectome is characterized by hub connectivity of executive and attentional networks

We demonstrate a data-driven approach for calculating a “causal connectome” of directed connectivity from resting-state fMRI data using a greedy adjacency search and pairwise non-Gaussian edge orientations. We used this approach to construct n = 442 causal connectomes. These connectomes were very sparse in comparison to typical Pearson correlation-based graphs (roughly 2.25% edge density) yet were fully connected in nearly all cases. Prominent highly connected hubs of the causal connectome were situated in attentional (dorsal attention) and executive (frontoparietal and cingulo-opercular) networks. These hub networks had distinctly different connectivity profiles: attentional networks shared incoming connections with sensory regions and outgoing connections with higher cognitive networks, while executive networks primarily connected to other higher cognitive networks and had a high degree of bidirected connectivity. Virtual lesion analyses accentuated these findings, demonstrating that attentional and executive hub networks are points of critical vulnerability in the human causal connectome. These data highlight the central role of attention and executive control networks in the human cortical connectome and set the stage for future applications of data-driven causal connectivity analysis in psychiatry.

Effect of Build Orientation on Load Capacity of 3D Printed Parts

Fused Deposition Modeling (FDM) is one of the most commonly used 3D printing technologies for creating complex parts from a Computer Aided Design (CAD) model. It is observed that mechanical strength of 3D printed polylactic acid (PLA) parts are affected by various parameters associated with part, process, material and operating conditions. One of the key parameters that influences tensile and flexural strength of 3D printed PLA parts is build orientation. Researchers have investigated the effect of a limited number of build orientations on tensile strength. Moreover, less work has been reported which studies the effect of build orientation on flexural strength. None of the studies modeled tensile load and bending load as a function of thickness and compared tensile loading capacity with flexural loading for different orientations. Therefore, an attempt is made to include a greater number of build orientations that occur during 3D printing of complex PLA parts. Build orientations considered in this study are flat, flat-support, edge, edge-45, upright and upright-45 with three thicknesses i.e., 1.2 mm, 2.0 mm and 2.8 mm. Tensile and flexural tests are performed as per American Society for Testing and Materials (ASTM) standards. Experimental results show that six orientations form two groups i.e., strong orientation group and weak orientation group. PLA appears stronger in tensile loading than bending. Edge orientation is strongest during tensile as well as bending loading whereas upright orientation is weakest in tensile loading and upright-45 orientation is weakest in bending. Force trends, it can be concluded that thickness can be minimized where build orientation belongs to the strong orientation group. Similarly, thickness can be increased where build orientation belongs to the weak orientation group.

PSL: An Algorithm for Partial Bayesian Network Structure Learning

Learning partial Bayesian network (BN) structure is an interesting and challenging problem. In this challenge, it is computationally expensive to use global BN structure learning algorithms, while only one part of a BN structure is interesting, local BN structure learning algorithms are not a favourable solution either due to the issue of false edge orientation. To address the problem, this article first presents a detailed analysis of the false edge orientation issue with local BN structure learning algorithms and then proposes PSL, an efficient and accurate P artial BN S tructure L earning (PSL) algorithm. Specifically, PSL divides V-structures in a Markov blanket (MB) into two types: Type-C V-structures and Type-NC V-structures, then it starts from the given node of interest and recursively finds both types of V-structures in the MB of the current node until all edges in the partial BN structure are oriented. To further improve the efficiency of PSL, the PSL-FS algorithm is designed by incorporating F eature S election (FS) into PSL. Extensive experiments with six benchmark BNs validate the efficiency and accuracy of the proposed algorithms.

Zigzag dice lattice ribbons: Distinct edge morphologies and structure-spectrum correspondences

Ribbons of two-dimensional lattices have properties depending sensitively on the morphology of the two edges. For regular ribbons with two parallel straight edges, the atomic chains terminating the two edges may have more than one choice for a general edge orientation. We enumerate the possible choices for zigzag dice lattice ribbons, which are regular ribbons of the dice lattice with edges parallel to a zigzag direction, and explore the relation between the edge morphologies and their electronic spectra. A formula is introduced to count the number of distinct edge termination morphologies for the regular ribbons, which gives 18 distinct edge termination morphologies for the zigzag dice lattice ribbons. For the pure dice model, because the equivalence of the two rim sublattices, the numerical spectra of the zigzag ribbons show qualitative degeneracies among the different edge termination morphologies. For the symmetrically biased dice model, we see a one-to-one correspondence between the 18 edge termination morphologies and their electronic spectra, when both the zero-energy flat bands and the dispersive or nonzero-energy in-gap states are considered. We analytically study several interesting features in the electronic spectra, including the number and wave functions of the zero-energy flat bands, and the analytical spectrum of unique in-gap states. The in-gap states of the zigzag dice lattice ribbons both exhibit interesting similarities and show salient differences when compared to the spectra of the zigzag ribbons of the honeycomb lattice.

Morphological Edge Detection on CT Images

In this paper, a novel mathematical morphology edge detection algorithm is proposed to detect lungs CT medical image edge. It is a better method for edge information detecting and noise filtering than differential operation, which is sensitive to noise. And it is a better compromise method between noise smoothing and edge orientation, but the computation is more complex than general morphological edge detection algorithms

Fast Identification of the Crystallographic Orientation of Violet Phosphorus Nanoflakes with Preferred In‐Plane Cleavage Edge Orientation

AbstractSemiconducting layered violet phosphorus, the most stable phosphorus allotrope, has recently been successfully produced with large single crystal sizes and high yields. A promising anisotropy is expected by the reduced symmetry of violet phosphorus in various properties. The in‐plane crystallographic anisotropy and cleavage edge orientation are especially important to the exfoliated 2D structures for their electronic, photonic, magnetic, and mechanic applications. However, the anisotropy of violet phosphorus has not been studied. Here, a fast and nondestructive way is reported to identify the crystallographic orientation of 2D violet phosphorus nanoflakes by a single polarized Raman spectrum. The 2D violet phosphorus nanoflakes have been found to have preferred in‐plane cleavage edges along ‐[P2][P8][P2][P9]‐ tubular strands with <1, 1, 0> edge alignment. The b‐axis (a‐axis) direction has been demonstrated to be easily identified that forms an angle of 45° or 135° from the cleavage edge by the intensity of Ag mode, especially the appearance or disappearance of 491 cm–1, under parallel configuration using polarized Raman scattering. A simple and fast method has been developed to identify the crystallographic orientation of violet phosphorus nanoflakes by a single Raman spectrum to obtain the corresponding a‐axis and b‐axis.

Placing Arrows in Directed Graph Layouts: Algorithms and Experiments

AbstractWe study how to place arrow heads in directed graph drawings aiming at minimizing their overlaps and avoiding intersections between arrow heads and edges. The objective is to support users to correctly and quickly recognize edge orientations, i.e. to deduce unambiguously the edge orientations. Our contribution is two‐fold: (i) We present exact and heuristic algorithms for this arrow placement problem, along with an extensive experimental analysis of these techniques; and (ii) we report on a user study aimed to understand the impact of different arrow placement strategies on performing global and local analysis tasks on directed graph layouts.

Multispectral Image Matching Method Based on Histogram of Maximum Gradient and Edge Orientation

Motivated by the problem of nonlinear intensity changes in multispectral image matching, this letter introduces a robust and efficient image-matching method. The proposed method consists of three steps. First, control-point candidates are identified that are widely distributed in the areas of effective main structure. Then, a novel feature descriptor called the histogram of maximum gradient and edge orientation (HGEO) is proposed for the purpose of multispectral image matching. Finally, a bilateral matching process is carried out to perform the matching process and remove mismatches. The proposed method is successfully applied for matching various multispectral remote sensing images, and experiments are performed with typical datasets that are widely applied in tests of multispectral image matching. According to some popular feature descriptors, the test results demonstrate that the proposed HGEO achieves better matching performance than do many currently used methods.

Translational surface coupling along a line with non-conforming meshes

In the modelling of large-scale metal structures, comprising plated components intersecting along weld lines, the meshing efficiency and flexibility are limited by the requirements of nodal alignment and compliance of element size, shape and edge orientation throughout the domain. Such limitations necessitate the use of complex transitional meshes in intersection regions and result in highly complex global mesh configurations. This paper presents an original and systematic methodology for surface coupling along an arbitrary 1D interface, which is applicable to any type of 2D and 3D FEs, and which provides a systematic framework for: (i) geometric modelling of weld lines; (ii) coupling of regions with different levels of discretisation detail or element types within a system; and (iii) domain partitioning problems involving computationally heterogeneous partitions. The strategy is based upon a novel coupling element formulation, which uses the fundamental principles of the mortar method and an augmented Lagrangian Multiplier optimisation approach. Particular consideration is given to an element formulation that enforces rigid translational coupling, which has been implemented for employment with co-rotational Reissner-Mindlin shell elements. Various numerical examples are presented to demonstrate the accuracy, versatility and substantial computational benefits of the developed methodology for modelling large-scale metal structural systems.

Simple shapes guide visual attention based on their global outline or global orientation contingent on search goals.

It is still unclear which features of a two-dimensional shape (e.g., triangle, square) can efficiently guide visual attention. Possible guiding features are edge orientations (single oriented shape edges; e.g., verticals during search for squares), global outlines (combination of the target edges; e.g., squares), or global orientations (specific orientations of global outlines; e.g., squares but not diamonds). Using a contingent-capture protocol, we found evidence for task-dependent guidance by the global shape outline and the global shape orientation. First, if participants searched for a shape (an equilateral triangle) independent of its pointing direction, cues with the same global shape outline as the target captured attention, even without sharing any edge orientations with the target. Second, however, if a shape's specific pointing direction was task-relevant, attentional guidance changed to the specific orientation of the global shape. Our results show that the global shape outline and the global shape orientation can both guide visual attention, contingent on the nature of the shape and the current search goals. We discuss differences between shapes (equilateral triangles and isosceles trapezoids) considering models of shape perception and conclude with a critical review of the contingent-capture protocol as a complementary method to visual search protocols. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Training image selection for development of subsurface geological cross-section by conditional simulations

Delineation of a subsurface geological cross-section can be accomplished by conditional simulations, which can effectively combine prior geological knowledge as training images with site-specific measurements for spatial interpolation. Valuable prior geological knowledge may be concisely represented by a single training image, and the evaluation and optimal selection of a representative training image is crucial for a successful application of conditional simulation methods. In this study, a data-driven method based on edge orientation detection is proposed for selection of the optimal training image. The stratigraphic soil boundaries of all candidate training images (CTIs) and site-specific measurements are scanned by an edge detector. The derived edge orientations are quantified and compared between CTIs and site-specific measurements. Among all CTIs, the CTI that has the minimal difference of edge orientation distribution with respect to the site-specific measurements is selected as the optimal one. The proposed method is validated using both an illustrative example and a real case. It is demonstrated that edge orientation successfully differentiates soil stratigraphic patterns between different training images, and the derived edge orientation distribution can be used as a quantitative indicator for selection of the optimal training image.

Chemical Etching of Screw Dislocated Transition Metal Dichalcogenides.

Chemical etching can create novel structures inaccessible by growth and provide complementary understanding on the growth mechanisms of complex nanostructures. Screw dislocation-driven growth influences the layer stackings of transition metal dichalcogenides (MX2) resulting in complex spiral morphologies. Herein, we experimentally and theoretically study the etching of screw dislocated WS2 and WSe2 nanostructures using H2O2 etchant. The kinetic Wulff constructions and Monte Carlo simulations establish the etching principles of single MX2 layers. Atomic force microscopy characterization reveals diverse etching morphology evolution behaviors around the dislocation cores and along the exterior edges, including triangular, hexagonal, or truncated hexagonal holes and smooth or rough edges. These behaviors are influenced by the edge orientations, layer stackings, and the strain of screw dislocations. Ab initio calculation and kinetic Monte Carlo simulations support the experimental observations and provide further mechanistic insights. This knowledge can help one to understand more complex structures created by screw dislocations through etching.

AN EFFICIENT METHOD FOR HAND GESTURE RECOGNITION USING ROBUST FEATURES VECTOR

Integration of technology for the Fourth Industrial Revolution (IR 4.0) has increased the need for efficient methods for developing dynamic human computer interfaces and virtual environments. In this context, hand gesture recognition can play a vital role to serve as a natural mode of interactive human machine interaction. Unfixed brightness, complex backgrounds, color constraints, dependency on hand shape, rotation, and scale variance are the challenging issues which have an impact on robust performance for the existing methods as per outlined in previous researches. This research presents an efficient method for hand gesture recognition by constructing a robust features vector. The proposed method is performed in two phases, where in the first phase the features vector is constructed by selecting interest points at distinctive locations using a blob detector based on Hessian matrix approximation. After detecting the area of the hand from the features vector, edge detection is applied in the isolated hand followed by edge orientation computation. After this, templates are generated using one and two dimensional mapping to compare candidate and prototype images using adaptive threshold. The proposed research performed extensive experimentation, where a recognition accuracy rate of 98.33% was achieved by it, which is higher as compared to previous research results. Experimental results reveal the effectiveness of the proposed methodology in real time.

Vibrational properties of graphene quantum dots: Effects of confinement, geometrical structure, and edge orientation

We perform ab initio density functional theory calculations to study the lattice vibrations of graphene quantum dots (GQDs) with triangular, quadrate, and hexagonal shapes in lateral confinement of 1 to 3 nm and terminated in both zigzag and armchair orientations. We see the vibrational properties of GQD transform from molecular type into bulk-like type with increasing dot size and the features of the vibrational density of state also highly depend on the symmetry of the GQD. We find that the out-of-plane vibrated standing waves induced by lateral confinement instead of the in-plane vibrations dominate the lattice vibrations of small GQDs. By projecting the vibrational eigenvectors of GQDs on those of single-layer graphene, we see the mixture of the out-of-plane and in-plane vibrational characters in GQDs as the result of the strong lateral confinement. We identify coherent acoustic phonon modes in GQDs and find that the size dependence of coherent acoustic phonon frequency increases with increasing the isotropy of nanostructures. Moreover, different confinement effects on lattice vibrations along zigzag and armchair edge orientations are identified from ab initio calculations. We describe the Raman intensity of GQDs and observe a blue shift of the G-mode position in GQDs comparing to that of the single-layer graphene. Combining the bond length distribution at the edge of GQDs with the positive Gr\"uneisen parameters, we link such blue shift to the surface effect of GQDs.

Investigation and modelling of edge corrosion of e‐coated galvanized steel with respect to the spatial edge orientation

AbstractThe effect of the spatial orientation of e‐coated hot dip galvanized test sheets on edge corrosion is investigated. Therefore paint delamination from corrosion sample edges at different steps in time of samples at different angles relative to the horizontal during a corrosion test is analysed. Two general relations are found: Horizontally oriented edges exhibit significantly increased coating delamination compared with vertically oriented edges. This is due to increased exposure to the electrolyte, resulting from the pinning of electrolyte droplets along the upper edge. With increasing angular displacement relative to the ground, electrolyte exposure and edge delamination decrease. The edges of the upward‐facing specimen side showed a higher delamination width compared with the downward‐facing side at the same angle. These results are supported by electrochemical impedance spectroscopy and a wetting test. Ultimately, a semi‐empirical model to numerically predict the edge delamination over time, incorporating electrochemical impedance spectroscopy and polarization curves, is presented.

An atomistic investigation of dislocation velocity in body-centered cubic FeCrAl alloys

Edge, screw, and mixed dislocation velocities in FeCrAl body-centered cubic alloy were investigated by classical molecular dynamics simulation at several temperatures for the 〈111〉{110} type slip system. For screw orientation, the dislocation velocity as a function of applied shear stress was found to be zero up to a threshold stress, beyond which the velocity increases with applied shear stress. For edge and mixed orientations, the dislocation velocity as a function of applied shear stress was found to have four regimes: zero value below a threshold stress, slow glide regime just above the threshold stress, a linear regime, and a final nonlinear regime past a certain velocity with a relatively lower slope. Two main features of the dislocation velocity were observed in FeCrAl alloys. First is that the rate of increase of the velocity with the applied shear stress decreases with chromium concentration and aluminum concentration, and that the dependence of the dislocation velocity on the angle between direction of the Burgers vector and the dislocation line direction shows a sinusoidal-like behavior.

Hall and bend resistance of a phosphorene Hall bar

The dependence of the Hall and bend resistances on a perpendicular magnetic field and on vacancy defects in a four-terminal phosphorene single layer Hall bar is investigated. A tight-binding model in combination with the Landauer-B\"uttiker formalism is used to calculate the energy spectrum, the lead-to-lead transmissions, and the Hall and bend resistances of the system. It is shown that the terminals with zigzag edge orientation are responsible for the absence of quantized plateaus in the Hall resistance and peaks in the longitudinal resistance. A negative bend resistance in the ballistic regime is found due to the presence of high- and low-energy transport modes in the armchair and zigzag terminals, respectively. The system density of states, with single vacancy defects, shows that the presence of in-gap states is proportional to the number of vacancies. Quantized plateaus in the Hall resistance are only formed in a sufficiently clean system. The effects of different kinds of vacancies where the plateaus are destroyed and a diffusive regime appears in the bend resistance are investigated.

Computing inductive vertex orderings

Inductive vertex orderings or edge orientations of graphs, such as inductive k-independence and k-simpliciality orderings, and k-perfect orientation, arise naturally in geometric intersection graphs and have been systematically studied in Ye and Borodin (2012) [4] and Kammer and Tholey (2014) [5]. In general, those orderings and orientations are hard to compute, even approximately. In this note, we show that an inductive k-independence ordering can be computed in k-simplicial graphs, and a k-approximation (that is, a solution with approximation ratio at most k) to the optimal inductive independence ordering can be computed in k-perfectly orientable graphs. As a result, we obtain a k-approximation (2k-approximation) algorithm for maximum weight independent sets in k-simplicial (k-perfectly orientable, respectively) graphs that runs in polynomial time independent of k without prior knowledge of the ordering.

Structured discrete shape approximation: Theoretical complexity and practical algorithm

We consider the problem of approximating a two-dimensional shape contour (or curve segment) using discrete assembly systems, which allow to build geometric structures based on limited sets of node and edge types subject to edge length and orientation restrictions. We show that already deciding feasibility of such approximation problems is NP-hard, and remains intractable even for very simple setups. We then devise an algorithmic framework that combines shape sampling with exact cardinality minimization to obtain good approximations using few components. As a particular application and showcase example, we discuss approximating shape contours using the classical Zometool construction kit and provide promising computational results, demonstrating that our algorithm is capable of obtaining good shape representations within reasonable time, in spite of the problem's general intractability. We conclude the paper with an outlook on possible extensions of the developed methodology, in particular regarding 3D shape approximation tasks.