Triangular Defects Research Articles

Skyrmion soliton motion on periodic substrates by atomistic and particle based simulations

Abstract We compare the dynamical behavior of magnetic skyrmions interacting with square and triangular defect arrays just above commensuration using both atomistic and particle-based models. Under applied drives, the initial motion is a kink traveling through the pinned skyrmion lattice. For the square defect array, both models agree well and show a regime in which the soliton motion is locked along 45°. The atomistic model also produces locking of a soliton along 30°, which is absent in the particle-based model. For the triangular defect array, the atomistic model exhibits 30° soliton motion over a wide region of external current values. In contrast, the particle-based model gives 45° soliton motion over a small range of external driving force values. The difference arises because the nondeforming particle model facilitates meandering skyrmion orbits while the deformable atomistic model enables stronger skyrmion-skyrmion interactions that reduce the meandering. Our results indicate that soliton motion through pinned skyrmion lattices on a periodic substrate is a robust effect.

Skew scattering and ratchet effect in photonic graphene

This paper is devoted to a comprehensive theoretical study of asymmetric (skew) scattering in photonic graphene, with the main focus on its realization with semiconductor microcavity exciton-polaritons. As an important consequence of the skew scattering, we prove the appearance of the ratchet effect in this system. Triangular defects in the form of missing micropillars in a regular honeycomb lattice are considered to be ones that break the spatial inversion symmetry, thus providing the possibility of the ratchet effect. By means of the numerical solution of the effective Schrödinger equation, we provide microscopical insight into the process of skew scattering and determine indicatrices, cross sections, and asymmetry parameters. In a system with multiple coherently oriented triangular defects, a macroscopic ratchet effect occurs as a unidirectional flux upon noiselike initial conditions. Our study broadens the concept of ratchet phenomena in the field of photonics and optics of exciton-polaritons. Published by the American Physical Society 2024

3D‐printing continuous plant fiber/polylactic acid composites with lightweight and high strength

AbstractContinuous plant yarn‐reinforced polylactic acid (PLA) composites were produced through in situ 3D printing, focusing on how plant fiber attributes influence the crystallization, mechanical, and rheological properties of the printed composites. The aim of this study was to assess the viability of plant fibers as substitutes for synthetic ones in engineering additive manufacturing. Plant fibers promoted the crystallization of PLA due to their shear induction and nucleation agent induction effects. The inherent triangular void defect during printing decreased with increasing plant fiber‐volume fraction. Rheological analysis revealed a transition to more elastic behavior post‐fiber addition, indicating solid‐like properties. The tensile strength of flax fiber‐yarn/PLA composite (volume fraction of 50.79%) was 342.37% higher than that of pure PLA, with a 22.2% lower density than pure PLA. Flax fiber demonstrated a superior reinforcement effect than carbon fiber in compressive strength for 3D printed honeycomb sheets with lower energy consumption and footprint. Optimizing fiber characteristics holds promise for high‐performance 3D‐printed natural fiber composites, particularly in vehicle applications.Highlights Plant fiber/polylactic acid (PLA) composites were in situ printed with a volume fraction of 50.79%. Plant fibers promoted the crystallization of PLA during the printing process. The tensile strength of flax fiber/PLA increased by 342.3% with a 22.2% lower density than PLA. Flax fiber showed a better reinforcement than carbon fiber in a compressive test of printed honeycomb.

Phase field modelling of elastic-plastic fatigue fracture of oil and gas pipeline

This paper established a fatigue fracture phase-field model (PFM) to evaluate fatigue damage evolution and crack propagation in oil and gas pipeline. To address inaccuracies in damage evolution, a threshold of the elastic-plastic fracture energy was introduced in the proposed PFM. Using the finite element method, the PFM was applied to simulate fatigue crack growth. Results from compact tension (CT) specimen of the X56 gas pipeline steel demonstrated that the da/dN-ΔK curve from the current PFM, accounting for plasticity, aligned more closely with experimental results than the elastic PFM. The fatigue crack propagation and fatigue life of the X80 gas pipeline with different defects of the same depth were also analyzed. The results indicated that triangular defects significantly impacted the fatigue life of the X80 gas pipeline. Finally, a model of X60 pipeline with various initial defects was developed to validate the effectiveness of the proposed PFM for full-scale pipeline fatigue fracture by comparing it to experimental a-N curves. The simulation results indicated that the distance and angle between two initial defects in the pipeline significantly influenced the propagation of fatigue cracks and the pipeline’s service life. These findings of this paper can serve as a reference for estimating the service life of gas and oil pipelines.

Atomic-scale characterization of defects in oxygen plasma-treated graphene by scanning tunneling microscopy

Defects in graphene are important nanoscale pathways for metal atoms to enter the interface between epitaxial graphene and SiC in order to form stable ultrathin metal layers with new exotic physical properties. However, the atomic-scale details of defects that mainly govern the intercalation process remain modest. In this work, we present the first atomic investigation of point defects generated by oxygen plasma treatment on epitaxial graphene grown on SiC using low-temperature scanning tunneling microscopy, corroborated by density functional theory calculations. We found a broad spectrum of point defects that varies in size, shape, and symmetry and is dominated by triangular species. Tunneling spectroscopy identified defect-induced states in the vicinity of the Fermi level that significantly perturb the graphene electronic properties at the defect site. Based on the well-defined defect symmetry, we simulated the local density of states of the triangular defects and their corresponding scanning tunneling microscopy images which further helped us to identify the exact atomic configurations of monovacancy defects. The combination of atomic-scale scanning tunneling microscopy experiments and reliable density functional theory simulations provides ultimate microscopic details and opens a new way to identify the atomic configurations of defects in oxygen plasma-treated graphene. Our work might shed light on precise control of defect engineering in graphene for metal intercalation by controlling the defect types based on a deep understanding of each configuration.

In-situ automated fiber placement gap defects filled by fused granular fabrication

This paper presents an investigation into the effect of Fused Granular Fabrication gap filling on the composition and mechanical performance of in-situ consolidation Automated Fiber Placement-manufactured laminates. Two laminates with staggered triangular gap defects were manufactured using in-situ consolidation Automated Fiber Placement. In the first laminate, the defects remained unmodified whereas in the second laminate Fused Granular Fabrication was used to fill the gap defects to mitigate out-of-plane waviness in subsequent plies and large pores which can initiate cracks. The process was successfully demonstrated. Fused Granular Fabrication layer thickness was however hard to adjust to match consolidated ply thickness of the AFP process due to the slightly uneven surface of the AFP substrate resulting in out-of-plane undulations. Compressive strength remained at the same level for both, reference and gap specimens. Tensile strength decreased 11 % and 23 % for gap defects and filled gap defects, respectively. Further work is required to utilize the full potential of the process combination.

Two-dimensional silicon-based dielectric column photonic crystal point defect microcavity Neural network modelling

In order to solve the problem that it is difficult to predict the microcavity photonic energy bands of point defects in two-dimensional silicon-based dielectric column photonic crystals, this paper proposes a method to predict the microcavity photonic energy bands of point defects in two-dimensional silicon-based photonic crystals by using an artificial neural network model. In this paper, the energy band structure of triangular lattice point defects at different radii is calculated using MPB, and a neural network model is established based on this data and the accuracy of the established model is verified.

The differences between carotid web and carotid web with plaque: based on multimodal ultrasonic and clinical characteristics.

This study aimed to examine the clinical and multimodal ultrasonic characteristics differences between carotid web (CW) and CW with plaque as well as the potential risk factors for stroke caused by CW. We retrospectively enrolled patients diagnosed with CW by CTA or high-resolution MRI (HRMRI) and simultaneously underwent contrast enhanced ultrasound (CEUS) and superb microvascular imaging examinations from January 2015 to October 2022. The CW angle was measured using computer-aided software. The variations between CW and CW with plaque were evaluated, and univariable and multivariable logistic regressions were utilized to identify possible risk predictors for stroke caused by CW. Two hundred ninety-nine patients with an average age of 60.85 (± 8.77) years were included. Sex, age, history of smoking, alcohol, hypertension, diabetes mellitus, homocysteine level, and treatment, as well as web length and thickness, luminal stenosis, location wall, number, CW angle, and CEUS enhancement, were quite different among CW and CW with plaque patients (p < 0.05). The logistic regression analysis showed that web length was an independent predictor of luminal stenosis in CW patients. For patients with CW and plaque, plaque and web thickness, as well as plaque enhancement, were associated with stenosis. Furthermore, luminal stenosis and plaque length were risk factors for symptoms. The multimodal ultrasonic and clinical manifestations of CW and CW with plaque are quite different. Web length is an independent risk factor for carotid artery stenosis in CW patients, whereas luminal stenosis and plaque length were risk factors for symptoms in CW with plaque patients. Exploring the similarities and differences between the carotid web and the carotid web with plaque, based on the stereo-geometric spatial position relationship and hemodynamic changes, may provide further insights into the underlying mechanisms of stroke occurrence caused by the carotid web. 1. Multimodal ultrasonic and clinical manifestations of carotid web and carotid web with plaque are substantially different. 2. A thin triangular endoluminal defect is identified as a typical feature of the web on superb microvascular imaging, and two kinds of typical ultrasonic features of CW with plaque are also identified. 3. Web length is an independent risk factor for carotid stenosis in carotid web patients, whereas luminal stenosis and plaque length are risk factors for symptoms in patients with CW and plaque.

Influence of Different Hydrocarbons on Chemical Vapor Deposition Growth and Surface Morphological Defects in 4H‐SiC Epitaxial Layers

Controlled epitaxial growth of 4H‐SiC is essential for advancing both power electronics and quantum technologies. This study explores how different carbon sources—methane and propane—affect the surface morphology of these epitaxial layers. By varying C/Si ratios and using the two mentioned hydrocarbons as the carbon source in chloride‐based epitaxial growth of 4H‐SiC layers, it is unveiled that methane results in an exceptionally smooth surface. However, it pronounces surface irregularities such as short step bunching and dislocation‐related etch pits. Moreover, methane amplifies the overgrowth of triangular defects with the 4H polytype. In contrast, the introduction of propane causes a step‐bunched surface together with inclined line‐like surface morphological defects. Notably, a majority of the triangular defects exhibit a pure 3C character without an overgrown 4H polytype. It is shown that these outcomes could be attributed to different sticking coefficients and diffusivity of the molecular species resulting from different carbon sources on the 4H‐SiC surface during the epitaxial growth. This research also uncovers the underlying origins and mechanisms responsible for various surface morphological defects.

Synthesis of porous single-crystal diamond with boron doping under high temperature and high pressure

In this paper, porous single-crystal diamond with boron doping were synthesized by adding TiB2 to the Fe–Ni–C system at a pressure of 5.6 GPa and a temperature of 1360 °C. The boron and nitrogen impurities were investigated in depth along with the surface defects of the diamonds. The results indicate that when the TiB2 content was within the range of 0–10 wt%, an increase in the doping concentration of TiB2 can lead to a decrease in the nitrogen content and an increase in the boron content in the diamond, causing the crystal color to transition from yellow to pale yellow, pale yellow-blue, and black. When the TiB2 content was within the range of 20–40 wt%, several triangular concave porous structures appeared on the crystal surface. With an increase in the TiB2 addition, the side length of these triangular pits decreased from 2.85 μm to 1.09 μm, while their depth decreased from 590 nm to 50 nm. The roughness of the crystal surface measured by Rq demonstrated values up to 145.302 nm. The results indicate that the size, depth, and density of the triangular defects can be adjusted by the amount of additive TiB2. Our findings provide insights into the surface regulation and functionalization of boron-doped diamond single crystals.

Defect imaging and identification in asphalt materials using coplanar capacitance sensors with single-pair electrodes

Coplanar capacitance imaging technology (CCIT) is a non-destructive method with intuitive and accurate identification. This paper aims to realize defect identification in asphalt materials based on the CCIT using coplanar single-pair electrode capacitance sensor (CSCS). Firstly, the Linear Back Projection (LBP) algorithm, the Landweber algorithm, and the Kalman-Filter (KF) algorithm, are compared and evaluated. Then, the principal component analysis (PCA) method is utilized to fuse the reconstructed images. In addition, the OTSU method, the iterative threshold (IT) method, and the genetic algorithm (OA) method, is compared and utilized to quantify the defective region. Finally, this investigation analyzes the reconstructed and segmented images of defects in asphalt materials. It is concluded that the KL algorithm is the most suitable algorithm to reconstruct the defective images. The PCA method improve the quality of the reconstructed defective images. The defective region is determined by the OTSU method, which is the most approximate imaging segment method. It is found that the CCIT can detect the invisible defect depth in asphalt materials. The different defect mediums in various asphalt materials can be identified by the CCIT. The segmented defective region error in asphalt materials is less than 13%, demonstrating that the CCIT is effective for the identification of defect shape details in asphalt materials. The segmented imaging precision of square defects in asphalt materials is the highest; circular defects are the next lowest; and triangular defects are the lowest. The outcomes of this research can assist engineers in realizing intuitive and high-accuracy identification of various invisible defects in shallow asphalt layers in bridge deck asphalt pavement utilizing the CCIT.

Postcesarean disasters – Isthmocele, ventrofixed uterus, and cesarean scar pregnancy: A case series

Abstract Isthmocele is a niche defect in the area of previous cesarean scar. It is any indention representing myometrial discontinuity or a triangular anechoic defect in the anterior uterine wall, with the base communicating to the uterine cavity at the site of the previous cesarean section (CS) scar. Ventrofixed uterus is an adhesion between anterior surface of uterus and anterior abdominal wall secondary to Caesarean section. Cesarean scar pregnancy (CSP) pregnancy at a scar site is trouble either causing scar rupture or placenta accreta syndrome. Here are the seven cases of having a problem of isthmocele or ventrofixed uterus or both. All these cases had previous CS done at peripheral hospitals. The intension of this case series is to study preoperative symptoms, clinical and investigation findings, intraoperative presentation, and challenges with postoperative recovery in cases of previous CS-related problems. All these cases presented with us post-CS either lower abdominal pain, intermenstrual spotting, menorrhagia, or secondary infertility, and one had emergency abdominal pain with pregnancy. On hysteroscopy, a large niche at CS scar with trenches was detected in five cases, and on laparoscopy, ventrofixed uterus in five cases, and four cases have both. One has multiple fibroids, one has associated ventrofixed ovarian endometrioma. One case has ruptured CSP. After corrective hysterolaparoscopy surgery, all patients recovered well. Hysterolaparoscopic corrective surgery is a real need and challenge in cases of symptomatic ventrofixed uterus and isthmocele. The incidence and prevalence of isthmocele are greater than most gynecologists realize. It is imperative to understand the etiology and adopt preventive measures during CS to reduce its incidence and also to reduce the incidence of CSP.

DEFECTED GROUND SQUARE PATCH EDGE TRUNCATED POLARIZATION RECONFIGURABLE ANTENNA

In this paper, a polarization reconfigurable antenna is reported. The proposed antenna operates in linear and circular polarization. Linear polarization is obtained using a square patch antenna and circular polarization is realized by truncating the diagonal corners of the square patch. Wideband circular polarization is obtained using two triangular defects to the ground plane beneath the truncated edge. To implement polarization reconfigurability, two pin diodes are placed on the truncated edges. These pin diodes electronically transform the proposed structure into square or truncated square patches resulting in linear or circular polarizations respectively. The proposed antenna operates in the 4.75 to 3 GHz band with circular polarization and the 4.75 to 1 GHz band with linear polarization. The antenna exhibits a higher peak gain of 7.7 dBi due to a low-loss foam substrate with the main lobe at 0&amp;deg;. A prototype of the antenna is developed and tested.

A new local flap technique for closing long-axis skin defects: the cyclist flap procedure.

Local flaps are commonly used during the treatment of skin tissue defects. Although there are many available procedures for the closure of triangular, circular and rhomboid-shaped defects, long-axis elliptical skin defects lack treatment options. To address this problem, a new local flap design called the cyclist flap procedure (CFP) was developed, so called because it resembles the silhouette of a person riding a bicycle. The CFP was performed in 29 patients aged 9-81 years in 2021-2022. The defects were localised in the sacral region (1), upper extremities (3), lower extremities (3), and head and neck regions (22). Closures of skin defects due to pressure ulcers (one patient) and after tumour excision (28 patients) were performed, and the patients were followed up for 12-20 months. Only minor complications were observed in two patients. During follow-ups, no secondary surgery was required due to dog-ear, trapdoor, recurrence or revision. Furthermore, the aesthetic results related to the skin lines and scar size were acceptable. The CFP is a new, easy-to-apply and advantageous procedure for the closure of long-axis elliptical and oval skin tissue defects.

A peridynamic model for rail crack initiation with cavity defect

Cavity defects can aggravate the rail crack initiation. To study their effect on rail fatigue crack initiation behaviour, a peridynamic model of rail crack initiation considering the characteristics of the cavity defect was proposed. First, based on the low-cycle fatigue test data, the bond failure criterion of the rail material was derived and verified to characterize the fatigue damage performance. Then, mathematical expressions for circular, triangular and rectangular defect characteristics were proposed, establishing a prefabricated method for rail cavity defects. Based on the ordinary state-based peridynamic fatigue theory, a rail crack initiation model with the cavity defect was constructed. Finally, the behaviour of rail crack initiation with the cavity defect was analysed.

Multiple-Layer Triangular Defects in 4H-SiC Homoepitaxial Films Grown by Chemical Vapor Deposition

In this study, a special triangular defect (TD) was identified on 4H-SiC epitaxial wafers. The morphology and composition characteristics of these special TDs were revealed by Raman, atomic force microscope (AFM), and scanning electron microscope (SEM). Compared to ordinary triangular defects, this defect protruded from the epitaxial layer and exhibited a laminated shape. The study also discussed the effects of several factors, such as C/Si ratio and growth time, on the triangular defects. Through analysis of these results, we developed methods to suppress the triangular defects. This research provides new insights into the morphology, structure, and composition of this serious destructive defect and is helpful for improving the performance of SiC epitaxial wafers.

Electronic properties of graphene with triangular defects in a superhoneycomb arrangement: A first-principles study

We study the electronic properties of graphene with triangular defects in the superhoneycomb arrangement by performing first-principles calculations within the framework of density functional theory. First, we investigate the band gaps using spin-unpolarized calculations. Interestingly, we find that the system-size dependence of the band gap value is unique and different from the previously known scaling law, which explains the band gap behaviors of various graphene materials with defects. In particular, the defect size dependence of the band gap value shows a different tendency, and thus, we obtain the universal scaling law with respect to the size of the defect and periodicity. We can estimate the band gap values of larger systems using this law without significant computational cost. In addition, we find that the system usually possesses a direct band gap, indicating that it is a promising material for optoelectronics applications. Further, we perform spin-polarized calculations to study stable magnetic states. We find that the ferromagnetic or the antiferromagnetic states are stable when the defect is large. From the analysis of N\'eel temperature, we also find that the spin-polarized system at 0 K exhibits spin polarization at room temperature when the distance between the defects is rather short. In addition, the band gap value of the spin-polarized system converges to a nonzero value. These findings indicate that further research on graphene with defects is highly significant and necessary for controlling the electronic properties of graphene-based materials.

A controllable spin flip and filter in zigzag graphene nanoribbons with triangular defect

Based on the recursive Green-function method together with Landauer-Büttiker formalism, we theoretically study the controllable spin-dependent electron transport properties by using zigzag graphene nanoribbons (ZGNRs) with triangular nanoconstrictions in the presence of the ferromagnetic strips and spatial modulation of Rashba spin-orbit coupling (RSOC). In this structure, the peaks of spin-flip and spin-conserved conductance can be modulated by the strength of RSOC and exchange magnetic field. The distribution of the local density of states (LDOS) around triangular nanoconstrictions is predicted. The spin filtering effect of ZGNRs with triangular and rectangular nanoconstrictions are compared by spin conductance from left (L) to right (R) lead and R to L lead, respectively. The results might be useful in designing a bidirectional spin converter and spin filter with the modulation of the multi-parameter.

Structural investigation of triangular defects in 4H-SiC epitaxial layers as nucleation source for bar shaped stacking faults (BSSFs)

The formation of recombination-induced bar shaped stacking faults (BSSFs) during forward voltage operation of SiC devices, can lead to increased voltage drop and enhanced device degradation. In this study, a triangular epitaxial defect is identified as a nucleation source for the growth of BSSF in forward-biased 4H-SiC p-n diode test structures. We performed low and high voltage current emission microscopy measurements in order to detect the position of BSSFs in the active area of the device and in-depth structural analysis to locate their nucleation source. It was found that basal plane dislocations that converted into threading screw dislocations, close to the surface of the epitaxial layer and included in the triangular defect, act as nucleation source for the BSSFs. Those BSSFs expand from the top towards the bottom of the epitaxial layer, which is a newly reported expansion mechanism compared to the already reported BSSFs growing from the substrate/epitaxial layer interface towards the epitaxial layer surface.

Evolution of the Growth Mode and Its Consequences during Bulk Crystallization of GaN.

A detailed analysis of morphology of gallium nitride crystal growth obtained by ammonothermal and halide vapor phase epitaxy methods was carried out. The work was conducted to determine the source of triangular planar defects visible in X-ray topography as areas with locally different lattice parameters. It is shown that the occurrence of these defects is related to growth hillocks. Particular attention was paid to analyzing the manner and consequences of merging hillocks. In the course of the study, the nature of the mentioned defects and the cause of their formation were determined. It was established that the appearance of the defects depends on the angle formed between the steps located on the sides of two adjacent hillocks. A universal growth model is presented to explain the cause of heterogeneity during the merging of growth hillocks.