Line Defects Research Articles

Family behavior and Dirac bands in armchair nanoribbons with 4–8 defect lines

Bottom-up synthesis from molecular precursors is a powerful route for the creation of novel synthetic carbon-based low-dimensional materials, such as planar carbon lattices. The wealth of conceivable precursor molecules introduces a significant number of degrees-of-freedom for the design of materials with defined physical properties. In this context, a priori knowledge of the electronic, vibrational and optical properties provided by modern ab initio simulation methods can act as a valuable guide for the design of novel synthetic carbon-based building blocks. Using density functional theory, we performed simulations of the electronic properties of armchair-edged graphene nanoribbons (AGNR) with a bisecting 4–8 ring defect line. We show that the electronic structures of the defective nanoribbons of increasing width can be classified into three distinct families of semiconductors, similar to the case of pristine AGNR. In contrast to the latter, we find that every third nanoribbon is a zero-gap semiconductor with Dirac-type crossing of linear bands at the Fermi energy. By employing tight-binding models including interactions up to third-nearest neighbors, we show that the family behavior, the formation of direct and indirect band gaps and of linear band crossings in the defective nanoribbons is rooted in the electronic properties of the individual nanoribbon halves on either side of the defect lines, and can be effectively through introduction of additional ‘interhalf’ coupling terms.

Contact effects on electron transport along disordered borophene nanoribbons with line defects

Contact effects on electron transport along disordered borophene nanoribbons with line defects

Enriching surface-ordered defects on WO3 for photocatalytic CO2-to-CH4 conversion by water

Defect engineering has been widely applied in semiconductors to improve photocatalytic properties by altering the surface structures. This study is about the transformation of inactive WO3 nanosheets to a highly effective CO2-to-CH4 conversion photocatalyst by introducing surface-ordered defects in abundance. The nonstoichiometric WO3-x samples were examined by using aberration-corrected electron microscopy. Results unveil abundant surface-ordered terminations derived from the periodic {013} stacking faults with a defect density of 20.2%. The {002} surface-ordered line defects are the active sites for fixation CO2, transforming the inactive WO3 nanosheets into a highly active catalyst (CH4: O2 = 8.2: 16.7 μmol h-1). We believe that the formation of the W-O-C-W-O species is a critical step in the catalytic pathways. This work provides an atomic-level comprehension of the structural defects of catalysts for activating small molecules.

Residual stress and subsurface damage in sapphire ultra-precision grinding

This study conducted experiments on ultra-precision grinding of sapphire using various strategies. It evaluated surface and subsurface characteristics across multiple dimensions, including morphology, scale, mechanical properties, residual stresses, lattice distortions, in-service properties, and chemical components. The research aimed to explore the intrinsic relationship between these behaviours. The findings revealed that both semi-finish grinding and ultra-precision grinding achieved ductile and low-roughness surfaces, with surface hardness enhancement near the grinding surface. Additionally, Raman spectra wave shifts were able to distinguish residual stresses at different grinding strategies, with larger stresses observed in ultra-precision grinding compared to semi-finish grinding and rough grinding. Furthermore, dense etching dislocation pits were observed on the ultra-precision grinding surface, responding to the scale of residual stress. The presence of larger subsurface cracks in semi-finish grinding and rough grinding was found to contribute to the release of residual stress. Moreover, ultra-precision grinding significantly reduced subsurface damage compared to rough grinding, with a reduction from 23.8 μm to 4.3 μm. Photothermal absorption during rough grinding was noted to be over 10 times higher than in ultra-precision grinding. Transmission electron microscopy (TEM) analysis revealed that subsurface damage included microcrack-induced line defects and uniform plastic deformation areas. This damage involved lattice aberrations, dislocations, stacking faults, and thin amorphous layers. The hardness and modulus of the subsurface damage layer were observed to decrease. Additionally, Raman spectra wave shifts were able to distinguish the subsurface damage layer in ultra-precision grinding. Energy-dispersive X-ray spectroscopy (EDS) analysis showed no change in the chemical components of the subsurface damage layer. Furthermore, a model was proposed to evaluate subsurface damage based on residual stress, and the mechanism of residual stress inducing damage in ultra-precision grinding was further analysed.

Fusion category symmetry. Part I. Anomaly in-flow and gapped phases

We study generalized discrete symmetries of quantum field theories in 1+1D generated by topological defect lines with no inverse. In particular, we describe ’t Hooft anomalies and classify gapped phases stabilized by these symmetries, including new 1+1D topological phases. The algebra of these operators is not a group but rather is described by their fusion ring and crossing relations, captured algebraically as a fusion category. Such data defines a Turaev-Viro/Levin-Wen model in 2+1D, while a 1+1D system with this fusion category acting as a global symmetry defines a boundary condition. This is akin to gauging a discrete global symmetry at the boundary of Dijkgraaf-Witten theory. We describe how to “ungauge” the fusion category symmetry in these boundary conditions and separate the symmetry-preserving phases from the symmetry-breaking ones. For Tambara-Yamagami categories and their generalizations, which are associated with Kramers-Wannier-like self-dualities under orbifolding, we develop gauge theoretic techniques which simplify the analysis. We include some examples of CFTs with fusion category symmetry derived from Kramers-Wannier-like dualities as an appetizer for the Part II companion paper.

Synergistic influence of dislocations and helium cluster on hydrogen atom in tungsten

Dislocations are common line defects in the preparation and irradiation processes of tungsten (W), and they can serve as trapping sites for hydrogen (H) and helium (He) atoms. Existing studies have indicated that dislocations preferentially capture He atoms to form dislocation-He cluster structures. The focus of this study was on the effects of this new structure on the trapped and diffusion behavior of H atoms using molecular dynamics (MD) method. The study considered the number of He atoms from 1 to 150, and they were classified as small He cluster and large He cluster. By calculating the binding energy, the study revealed that the capture strength is positively correlated with the He clusters’ size. However, it is negatively correlated with the distance from the dislocation core and the captured H atoms’ number. This study output the stable configurations to analyze the growth patterns of He cluster in dislocations, and it was observed that the interstitial atoms caused by trap mutation preferentially aggregate into dislocation loops due to the dislocation core structure. Moreover, the study investigated the diffusion behavior of H atoms around the dislocation-He cluster structure at 600 K within 1 ns. The hydrogen atoms tend to migrate towards the He cluster and distribute around it uniformly. The distribution range narrows with the helium cluster's size, and the distribution pattern depends on the dislocations’ type. This demonstrated the formation of dislocation-He cluster structure, promoting the increased H retention.

Research on Ultraviolet Characteristic Parameters of DC-Positive Polarity Corona Discharge on Conductors

The detection of corona-related defects in transmission lines has been included in the work of transmission line defect detection. Ultraviolet detection technology has gradually been widely applied in the field of corona discharge detection. However, the current research on the application of ultraviolet detection technology in transmission lines is relatively simple and mainly limited to using changes in the photon count to determine whether corona discharge has occurred. To address this, this study used a mini corona cage to simulate transmission lines and measured the changes in the photon count, spot area, and corona current in the corona inception process of different types of smooth, stainless-steel conductors. This study also investigated the variations in the photon count and spot area depending on conductor corona intensity, ultraviolet imager gain, and observation distance. The results show that the photon count and spot area can, to some extent, reflect the intensity of corona discharge. Both the photon count and spot area exhibited quadratic relationships with the voltage. As the observation distance increased, both the photon count and spot area showed exponential decay. The photon count exhibited a trend of initially increasing, then decreasing, and finally increasing again with the increase of gain, while the spot area showed exponential growth with increasing gain. The photon count and spot area can complement each other to identify and characterize the intensity of corona discharge.

Superspin chains solutions from 4D Chern-Simons theory

As a generalisation of the correspondence linking 2D integrable systems with 4D Chern-Simons (CS) gauge theory, superspin chains are realized by means of crossing electric and magnetic super line defects in the 4D CS with super gauge symmetry. The oscillator realization of Lax operators solving the RLL relations of integrability is obtained in the gauge theory by extending the notion of Levi decomposition to Lie superalgebras. Based on particular 3-gradings of Lie superalgebras, we obtain graded oscillator Lax matrices for superspin chains with internal symmetries given by A(m − 1 | n − 1), B(m | n), C(n) and D(m | n).

Abstract LB185: High resolution telomere measurements in human cancer and aging using long-read nanopore sequencing

Abstract Telomere length is an important biomarker of cellular replicative potential and aging, but existing measurement methods are limited in resolution and accuracy. During human carcinogenesis, telomeres shorten profoundly in the earliest stages that precede tumor invasion. Telomere shortening can either halt cancer progression by inducing senescence and cell death or can promote cancer development by destabilizing chromosomes and generating chromosomal rearrangements. Stabilization of telomeres, typically by the upregulation of telomerase, is required for progression of nearly all human cancers. Here, we deploy digital telomere measurement by nanopore sequencing to understand how distributions of human telomere length change during aging and following carcinogenesis. We measure telomere attrition and de novo elongation with unprecedented resolution in genetically defined populations of human stem cells, in cells from the peripheral blood of healthy individuals and patients with genetic defects in telomere maintenance, cancer patients, and cancer cell lines. We find that human aging is accompanied by a progressive loss of long telomeres and an accumulation of shorter telomeres in white blood cells. In patients with inherited defects in telomere maintenance, the accumulation of short telomeres is more pronounced and correlates with phenotypic severity. We apply machine learning to train a binary classification model that distinguishes healthy individuals from those with telomere biology disorders. Next, we investigated the telomere lengths of a cohort of twenty colorectal tumors with patient-matched healthy colonic epithelia and found that two-thirds of colorectal tumors have telomere length distributions significantly shorter than the surrounding normal tissue. Finally, we explore the utility of telomere length distributions in cancer cell lines as clinically actionable disease biomarkers. This sequencing and bioinformatic pipeline will advance our understanding of telomere maintenance mechanisms and the use of telomere length as a clinical biomarker of aging and disease. Citation Format: Santiago Sanchez, Jessica Gu, Anudeep Golla, William Shomali, Annika Martin, Dirk Hockemeyer, Sharon Savage, Steven Artandi. High resolution telomere measurements in human cancer and aging using long-read nanopore sequencing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB185.

Cathodoluminescence investigations of dark-line defects in platelet-based InGaN nano-LED structures

We have investigated the optical properties of heterostructured InGaN platelets aiming at red emission, intended for use as nano-scaled light-emitting diodes. The focus is on the presence of non-radiative emission in the form of dark line defects. We have performed the study using hyperspectral cathodoluminescence imaging. The platelets were grown on a template consisting of InGaN pyramids, flattened by chemical mechanical polishing. These templates are defect free, whereas the dark line defects are introduced in the lower barrier and tend to propagate through all the subsequent layers, as revealed by the imaging of different layers in the structure. We conclude that the dark line defects are caused by stacking mismatch boundaries introduced by multiple seeding and step bunching at the edges of the as-polished, dome shaped templates. To avoid these defects, we suggest that the starting material must be flat rather than dome shaped.

Phase-field simulation of the effect of grain boundary on fission gas migration in UO2 fuel

Grain boundaries are widely recognized as line defect sinks. During reactor operation, vacancies and fission gas atoms within UO2 fuel grains migrate to the grain boundaries, forming bubbles at these locations. In order to better understand the effect of grain boundaries on the migration of fission gas atoms, this study employed a phase-field model to simulate the nucleation and growth process of fission gas bubbles within the UO2 fuel grains and in the vicinity of grain boundaries. This study also investigated the degree to which grain boundaries affect fission gas atoms under different temperature conditions. The results indicated that in models containing grain boundaries, the nucleation of fission gas bubbles occurred earlier, as compared to models without grain boundaries. A noticeable bubble denuded zone was also observed adjacent to grain boundary interfaces. Furthermore, with increasing temperature, the bubble denuded zone becomes thicker. The effects of irradiation, vacancy diffusion, Ostwald ripening, as well as grain boundary trapping were discussed.

Transmission line defect detection based on feature fusion

Transmission lines are the lifeblood of the power system, and regular line inspections are required to ensure the operation of transmission lines. However, due to the special high-voltage environment of transmission lines, the pictures collected by UAVs are characterized by many background interferences and small defect samples, and it is difficult to directly detect line inspection methods based on deep learning. For this reason, this paper proposes a high and low-dimensional fusion framework, which divides the target detection task into four modules, and greatly reduces the technical volume of the model while retaining the high-dimensional features through the collaboration between modules. This paper also introduces the window attention mechanism based on YOLOv7, which allows the model to focus on local information and improve the model’s detection ability on small targets and also introduces the Wise-IOU loss to improve the model’s prediction accuracy and inference time. Experiments prove that the method in this paper can significantly improve the accuracy of model prediction while meeting the speed requirements of industrial scenarios.

Anomalies of generalized symmetries from solitonic defects

We propose the general idea that ’t Hooft anomalies of generalized global symmetries can be understood in terms of the properties of solitonic defects, which generically are non-topological defects. The defining property of such defects is that they act as sources for background fields of generalized symmetries. ’t Hooft anomalies arise when solitonic defects are charged under these generalized symmetries. We illustrate this idea for several kinds of anomalies in various spacetime dimensions. A systematic exploration is performed in 3d for 0-form, 1-form, and 2-group symmetries, whose ’t Hooft anomalies are related to two special types of solitonic defects, namely vortex line defects and monopole operators. This analysis is supplemented with detailed computations of such anomalies in a large class of 3d gauge theories. Central to this computation is the determination of the gauge and 0-form charges of a variety of monopole operators: these involve standard gauge monopole operators, but also fractional gauge monopole operators, as well as monopole operators for 0-form symmetries. The charges of these monopole operators mainly receive contributions from Chern-Simons terms and fermions in the matter content. Along the way, we interpret the vanishing of the global gauge and ABJ anomalies, which are anomalies not captured by local anomaly polynomials, as the requirement that gauge monopole operators and mixed monopole operators for 0-form and gauge symmetries have non-fractional integer charges.

Fault Detection, Classification and Localization Along the Power Grid Line Using Optimized Machine Learning Algorithms

Distributed energy generation increases the need for smart grid monitoring, protection, and control. Localization, classification, and fault detection are essential for addressing any problems immediately and resuming the smart grid as soon as possible. Simultaneously, the capacity to swiftly identify smart grid issues utilizing sensor data and easily accessible frequency and voltage data from PMU devices is a prerequisite of this task. Therefore, this paper proposes new methods using fuzzy logic and adaptive fuzzy neural networks as well as machine learning and meta-heuristic algorithms. First, line voltage is used by a fuzzy thresholding method to estimate when a transmission line defect would develop in less than 1.2 clock cycles. Next, features taken from frequency signals in the real-time interval are utilized to classify the type of error using machine learning systems (decision tree algorithm and random forest algorithm) optimized with wild horse meta-heuristic algorithm. To locate the precise problem location, we finally use a neural fuzzy inference system that is capable of adapting to new data. We employ a simulated power transmission system in MATLAB to test our proposed solutions. Mean square error (MSE) and confusion matrix are used to assess the efficiency of a classifier or detector. For the decision tree algorithm method, the detector attained an acceptable MSE of 2.34e−4 and accuracy of 98.1%, and for the random forest algorithm method, an acceptable MSE of 3.54e−6 and accuracy of 100%. Furthermore, the placement error was less than 153.6 m in any direction along the line.

Gauging non-invertible symmetries: topological interfaces and generalized orbifold groupoid in 2d QFT

Gauging is a powerful operation on symmetries in quantum field theory (QFT), as it connects distinct theories and also reveals hidden structures in a given theory. We initiate a systematic investigation of gauging discrete generalized symmetries in two-dimensional QFT. Such symmetries are described by topological defect lines (TDLs) which obey fusion rules that are non-invertible in general. Despite this seemingly exotic feature, all well-known properties in gauging invertible symmetries carry over to this general setting, which greatly enhances both the scope and the power of gauging. This is established by formulating generalized gauging in terms of topological interfaces between QFTs, which explains the physical picture for the mathematical concept of algebra objects and associated module categories over fusion categories that encapsulate the algebraic properties of generalized symmetries and their gaugings. This perspective also provides simple physical derivations of well-known mathematical theorems in category theory from basic axiomatic properties of QFT in the presence of such interfaces. We discuss a bootstrap-type analysis to classify such topological interfaces and thus the possible generalized gaugings and demonstrate the procedure in concrete examples of fusion categories. Moreover we present a number of examples to illustrate generalized gauging and its properties in concrete conformal field theories (CFTs). In particular, we identify the generalized orbifold groupoid that captures the structure of fusion between topological interfaces (equivalently sequential gaugings) as well as a plethora of new self-dualities in CFTs under generalized gaugings.

Two-dimensional line defect lattice solitons in nonlinear fractional Schrödinger equation

The existence, stability, and propagation dynamics of two-dimensional line defect lattice solitons (LDLSs) in a photorefractive crystal with focusing saturable nonlinearity under fractional diffraction effect are numerically investigated. It is shown that, the LDLSs stability domain narrows with increasing Lévy index in the semi-infinite bandgap either in the negative or positive defect lattice. While in the first bandgap, LDLSs are stable for the negative defect lattice and unstable for the positive defect lattice. Additionally, linear stability analysis indicates that the stability and power of LDLSs depend strongly on the Lévy index, defect depth, and propagation constant in different bandgaps. For LDLSs in the semi-infinite bandgap, the stability can be improved by decreasing either the Lévy index or the negative defect depth.

Topological dualities via tensor networks

The ground state of the toric code, that of the two-dimensional class D superconductor, and the partition sum of the two-dimensional Ising model are dual to each other. This duality is remarkable in as much as it connects systems commonly associated to different areas of physics—that of long-range entangled topological order, (topological) band insulators, and classical statistical mechanics, respectively. Connecting fermionic and bosonic systems, the duality construction is intrinsically nonlocal, a complication that has been addressed in a plethora of different approaches, including dimensional reduction to one dimension, conformal field theory methods, and operator algebra. In this paper, we propose a unified approach to this duality, whose main protagonist is a tensor network (TN) assuming the role of an intermediate translator. Introducing a fourth node into the net of dualities offers several advantages: the formulation is integrative in that all links of the duality are treated on an equal footing, (unlike in field theoretical approaches) it is formulated with lattice precision, a feature that becomes key in the mapping of correlation functions, and their possible numerical implementation. Finally, the passage from bosons to fermions is formulated entirely within the two-dimensional TN framework where it assumes an intuitive and technically convenient form. We illustrate the predictive potential of the formalism by exploring the fate of phase transitions, point and line defects, topological boundary modes, and other structures under the mapping between system classes. Having condensed-matter readerships in mind, we introduce the construction pedagogically in a manner assuming only minimal familiarity with the concept of TNs. Published by the American Physical Society 2024

Spontaneous Line Defect‐Induced Co4Te7 Superlattices on SrTiO3(001) Featuring Flat Bands

Abstract1D structures/patterns (e.g., line defect arrays, 1D Moiré patterns) embedded in 2D materials provide fascinating platforms for exploring versatile intriguing phenomena, for example, 1D Luttinger liquids and charge density waves (CDWs). Despite persistent efforts, incorporating periodic 1D patterns into 2D materials remains an ongoing pursuit. Herein, the direct preparation of monolayer 1D‐defect‐induced Co4Te7 superlattices (with periodic Te defect lines in the upper Te layer in 1T‐CoTe2) is reported, on lattice‐matched SrTiO3(001) (STO(001)) substrates via molecular beam epitaxy (MBE). Utilizing on‐site scanning tunneling microscopy/spectroscopy (STM/STS) combined with density functional theory (DFT) calculations, the detailed atomic structure of monolayer Co4Te7 is identified, and its formation mechanisms from the synergistic effects of the Co/Te precursor ratio and adlayer‐substrate interfacial coupling are uncovered. The potential flat‐band feature of the monolayer Co4Te7 is also unveiled. This work should hereby offer valuable insights into the engineering of periodic 1D‐defect patterns in 2D materials, as well as the atomic‐scale structure and electronic property characterizations, thus paving ways for their intriguing property investigations.

Excitations of bubbling geometries for line defects

The half-Bogomolny-Prasad-Sommerfield (BPS) Wilson line operators in the irreducible representations labeled by the Young diagrams for N=4 U(N) super Yang-Mills theory have gravity dual descriptions. When the number k of boxes of the diagram grows as k∼N2, the bubbling geometries emerge. We evaluate the spectra of quantum fluctuations on the particular bubbling geometry involving the largest degeneracy from the large N and large k limit of the supersymmetric indices decorated by the Wilson lines. The spectra of excitations over multiparticle 1/8- and 1/2-BPS states agree with the numbers of conjugacy classes of general linear group over finite fields while degeneracies of single particle BPS states are given by the general necklace polynomial. The bubbling geometry exhibits a new class of asymptotic degeneracy of states. Published by the American Physical Society 2024

Bootstrapping smooth conformal defects in Chern-Simons-matter theories

The expectation value of a smooth conformal line defect in a CFT is a conformal invariant functional of its path in space-time. For example, in large N holographic theories, these fundamental observables are dual to the open-string partition function in AdS. In this paper, we develop a bootstrap method for studying them and apply it to conformal line defects in Chern-Simons matter theories. In these cases, the line bootstrap is based on three minimal assumptions — conformal invariance of the line defect, large N factorization, and the spectrum of the two lowest-lying operators at the end of the line. On the basis of these assumptions, we solve the one-dimensional CFT on the line and systematically compute the defect expectation value in an expansion around the straight line. We find that the conformal symmetry of a straight defect is insufficient to fix the answer. Instead, imposing the conformal symmetry of the defect along an arbitrary curved line leads to a functional bootstrap constraint. The solution to this constraint is found to be unique.